JP4842536B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of securing satisfactory accuracy necessary for correcting (calibrating) sensitivity, and capable of shortening an image quality adjusting time, and also, capable of suppressing the consumption of toner for the image quality adjustment. <P>SOLUTION: A gradation pattern 71A with black toner (K), gradation patterns 71B, 71C and 71D with color toner (CMY) are formed in parallel in the advancing direction of a transfer belt 18, and a black toner detection (colorless gradation pattern detection) P sensor 40A and a color toner detection (colored gradation pattern detection) P sensor 40E are separately arranged and positioned so as to detect respective color patterns. The sensitivity correction (calibration) of the optical detecting means is performed based on the two-dimensional arrangement data of the output voltage of specular-reflected light and the output voltage of diffused/reflected light of the gradation patterns obtained based on the results detected by the optical detecting means (P sensors), and the sticking quality or the image density is obtained. <P>COPYRIGHT: (C)2006,JPO&amp;NCIPI

Description

  The present invention relates to a color image forming apparatus using an electrophotographic system such as a copying machine or a laser beam printer, and more particularly to an image forming apparatus that detects image density by optical detection means and controls image density.

Conventionally, in an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, a density detection toner patch is provided on an image carrier such as a photoconductor in order to always obtain a stable image density. (Tone pattern) is created, the patch density is detected by optical detection means (hereinafter also simply referred to as a sensor), and the development potential is changed based on the detection result (specifically, LD power, charging bias) , Change of development bias).
In the case of the two-component development method, image density control is performed such that the maximum target adhesion amount (adhesion amount for obtaining a target ID) becomes a target value by changing the toner density control target value in the developing device. It is carried out.

As such a density detection patch detection means, a reflection type sensor in which an LED as a light emitting element (light emitting means) and a PD (photodiode) or PTr (phototransistor) as a light receiving element (light receiving means) is generally combined. Are known.
As the sensor configuration, (A) a type that detects only specularly reflected light as shown in FIG. 2 (see JP 2001-324840 A), (B) only diffusely reflected light as shown in FIG. 3 (see Japanese Patent Laid-Open No. 5-249787, Japanese Patent No. 3155555, etc.), and (C) a type that detects both (see Japanese Patent Laid-Open No. 2001-194843, etc.) as shown in FIG. There are two types. 2, 3, and 4, reference numerals 50 </ b> A, 50 </ b> B, and 50 </ b> C denote element holders, 51 denotes an LED, 52 denotes a regular reflection light receiving element, 53 denotes a detection target surface, and 54 denotes a toner patch on the detection target surface. , 55 denotes a diffuse reflection light receiving element.

In recent years, as shown in FIG. 5, a beam splitter is provided in the light path on the light emitting side and the light receiving side (see Japanese Patent No. 2729976, Japanese Patent Laid-Open No. 10-221902, Japanese Patent Laid-Open No. 2002-72612, etc.) Has also been used a lot ((D)). In FIG. 5, 56 is an LED, 57 and 58 are beam splitters, 59 is a photodiode as a light receiving means for P wave light (regular reflection light), and 60 is a light receiving means for S wave light (diffuse reflected light). Each photodiode is shown.
A plurality of gradation patterns are continuously formed in a line on a detection target surface such as an intermediate transfer belt with different adhesion amounts.

Japanese Patent No. 2729976 JP-A-10-221902 JP 2001-194443 A JP 2001-215850 A JP 2002-72612 A JP 2004-279664 A

As many of the above-mentioned publications and patent publications relate to a color image forming apparatus, since color density fluctuations in the color image forming apparatus lead to color fluctuations, density detection is required to stabilize the image density. It is important to accurately detect the amount of the applied pattern and control the density.
Since the image density to be stabilized here is the “image density of the output image”, the conventional monochrome image forming apparatus detects the density on the photoconductor, whereas the color image forming apparatus transfers it to the paper. It is desirable to carry out on the transfer belt immediately before being applied, and the aim of the image density control is to control so that the maximum target adhesion amount becomes a target value, so that even a high adhesion amount region can be accurately detected. desirable.
However, with the conventional detection method, it is difficult to always perform stable and accurate adhesion amount detection over the entire adhesion amount.

Further, in order to accurately detect the adhesion amount, the optical detection means is based on the two-dimensional array data of the regular reflection light output voltage and the diffuse reflection light output voltage of the gradation pattern obtained as a result of detection by the optical detection means. It is effective to obtain the amount of adhesion or image density by performing sensitivity correction (calibration), and for this purpose, the larger the number of data points, the better.
However, increasing the number of data points is nothing but increasing the number of gradation patterns, which means that the image quality adjustment time becomes longer and the amount of toner consumed for image quality adjustment increases, which is not desirable. .
When trying to detect gradation patterns of all colors with one optical detection means, the number of optical detection means is only one, but since the total length of the pattern becomes long, total processing from the start to the end of image quality adjustment. Takes time and increases machine downtime.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of ensuring sufficient and sufficient accuracy for sensitivity correction (calibration), shortening image quality adjustment time, and suppressing toner consumption consumed for image quality adjustment.
In addition, the present invention can ensure the necessary and sufficient accuracy for sensitivity correction (calibration), reduce the image quality adjustment time, reduce the amount of toner consumed to adjust the image quality, and constantly apply over the entire adhesion amount. An object of the present invention is to provide an image forming apparatus capable of detecting a stable and accurate adhesion amount.

In order to achieve the above object, according to the first aspect of the present invention, the detection target surface and a plurality of gradation patterns having different adhesion amounts formed continuously on the detection target surface are provided with a light emitting element and a light receiving element. The regular reflection light output voltage and the diffuse reflection light output voltage of the gradation pattern obtained as a result of detection by the optical detection means capable of simultaneously detecting the specular reflection light and the diffuse reflection light arranged at the position facing the detection target surface In the image forming apparatus for correcting the sensitivity of the optical detection means based on the two-dimensional array data and obtaining the adhesion amount or the image density, the sensitivity correction of the optical detection means with the toner adhesion amount on the basis of the regular reflection light output and the diffuse reflection light output obtained at low coating weight range up zero to 1 layer formation, determining the minimum value of the ratio of the diffuse reflection light output and the positive reflection light output, This value is the diffuse reflection light And diffuse reflection component of the regular reflection light output by multiplying the force, by the regular reflection light component of the regular reflection light output by subtracting the diffuse reflection light component from the regular reflection light output, the regular reflection light output diffuse reflected light The component is divided into a component and a specularly reflected light component, and only the specularly reflected light component is extracted, and this is divided by the value of the specularly reflected light component when the toner adhesion amount on the background portion of the detection target surface is zero. Is converted into a normalized value as an exposure rate of the background portion, and based on the normalized value having a linear relationship with the toner adhesion amount,
Diffusion reflection light output−background portion output × normalization value in the low adhesion amount region obtained by obtaining the diffuse reflection light output value after the background portion variation correction and plotting it against the normalization value Based on the first-order linear relationship between the value and the diffuse reflection output value after the background fluctuation correction, a diffuse reflection output value after the background fluctuation correction corresponding to a certain normalized value is obtained from the slope of the straight line. Is calculated by converting the diffuse reflected light output value after the background fluctuation correction to a value uniquely determined in relation to the toner adhesion amount. The gradation pattern is divided into two columns of a chromatic color gradation pattern and an achromatic color gradation pattern formed for each of a plurality of colors, and the optical detection means is for detecting a chromatic color gradation pattern and achromatic color. Independent for gradation pattern detection Among the two optical detection means, the optical detection means for detecting a chromatic gradation pattern has a peak emission wavelength λp on the light emission side of 800 nm or more and a peak spectral sensitivity on the light reception side. By changing the pattern writing value level by the light writing unit of the gradation pattern of each color detected by the optical detecting means for detecting the chromatic color gradation pattern with the wavelength λp of 800 nm or more for each color, the sensitivity correction is performed. The plotted data values used for the calculation are distributed.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect , of the two optical detection means, the optical detection means for detecting a chromatic color gradation pattern includes regular reflection light and diffuse reflection light. The configuration is such that two outputs can be detected simultaneously, and the optical detection means for detecting the achromatic color gradation pattern has a configuration capable of detecting only the regular reflected light output .

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect , of the chromatic color gradation pattern and the achromatic color gradation pattern created in parallel in the image forming direction, The process from the start to the end of the creation is performed from the start to the end of the creation of the chromatic color gradation pattern composed of a plurality of colors .

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the plurality of image carriers and the toner images formed on the respective image carriers are sequentially used as intermediate transfer members. It is characterized by having a configuration in which a color image is obtained by transferring images to a sheet-like recording medium after transferring them in a superimposed manner .

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, a sheet-like recording medium in which toner images formed on a plurality of image carriers are carried on a transfer body. The color image is obtained by transferring the images one after another.

According to the present invention, the image quality adjustment time without causing a detection error of the light biological detection means can be shortened (process control operation time), it is possible to improve the efficiency of work time.

According to the present invention, it is possible to achieve both shortening and cost reduction image quality adjustment time.

According to the present invention, it detects a chromatic gradation pattern of multiple simultaneously and since the arithmetic processing as a single two-dimensional array data is performed, it becomes possible to reduce the number of patterns, shortening of the image quality adjustment time As a result, the amount of toner used for image quality adjustment can be reduced.

According to the present invention, it can be shortened in the image quality adjustment time.

According to the present invention , the number of gradation patterns of each color can be reduced, so that the image quality adjustment time can be shortened and the amount of toner used for image quality adjustment can be reduced.

According to the present invention , optical detection means can be arranged in parallel, gradation patterns can be written in parallel, and detection can be processed in parallel, so that the process control operation time can be shortened.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
First, before describing the configuration and functions of the present embodiment, the background of the study that has led to the realization of the present invention will be described.
[Selection of optical detection means and consideration of its function]
When considering which type of sensor is used to detect the density pattern on the transfer belt as the detection target surface, there is a drawback that even the high reflection amount region cannot be detected with the type of (A) only regular reflection light. In the case of the diffuse reflection light only type (B), if the transfer belt is black (in many cases, the transfer belt is often black because carbon is used as a resistance adjusting agent), black toner is used. Have a fatal defect that the sensor cannot be detected, and the diffuse reflected light output at the transfer belt background is almost zero, so that the sensor sensitivity cannot be calibrated.
In order to cope with such a problem, the difference between the outputs of the two light receiving sensors is obtained by using the combination type of (C) and (D) (Japanese Patent No. 3155555, Japanese Patent Laid-Open No. 2001-194843, etc.) It is considered that many methods have been proposed for detecting the amount of adhesion by taking a ratio (see JP 10-221902 A).

However, with the conventional detection method using both of the combination types (C) and (D), it is considered difficult to always perform stable and accurate adhesion amount detection for the reasons described below.
(1) Lot variation in light emitting element output and light receiving element output is not taken into consideration. ... (Sensor variations)
(2) Temperature characteristics of light emitting element output, light receiving element output, and deterioration with time are not taken into consideration. ... (Sensor fluctuation)
(3) The influence of deterioration over time of the transfer belt that is the detection target surface is not taken into consideration. ... (Fluctuation of belt)
This point will be described in detail below.

Explanation of (1) In order to investigate how much the sensor element varies, several lots (1 lot = 197 pieces) of LED (light emitting element) and PTr (phototransistor) are measured by the following method. The variation width was evaluated.
[Light emitting element side]
The light receiving element when the light emitting element is sequentially switched and light is irradiated to a certain reference plate under the condition that the sensor head shown in FIG. Photocurrent: Measure IL and determine the magnitude of the light output.
[Light receiving element side]
The light receiving element when the light receiving element is sequentially replaced and light is irradiated to a certain reference plate under the conditions that the sensor head shown in FIG. Photocurrent: Measure IL and determine the magnitude of light reception sensitivity. The measurement results are shown in Table 1.

From Table 1, it was found that the output variation was slightly less than twice on the light emitting element side and slightly less than four times on the light receiving element side.
The size of the element variation seems to vary depending on the type of element (top view type, side view type) and manufacturer, but at least the variation at the level that requires adjustment should be no matter which element is used. It is.
This point is not mentioned at all in each of the above prior arts. It seems that this is a matter of course, but in order to accurately detect the amount of adhesion using the method described in the prior art, strict output is required at the inspection stage of the sensor (element). Adjustment is required.

Therefore, what happens when there is no adjustment will be described below based on the prediction result based on experimental data.
FIG. 6 shows the result of measuring the amount of color toner adhering to the transfer belt using the sensor shown in FIG. 4. The horizontal axis: the amount of adhesion, the vertical axis represents the specular reflection light output voltage, and the diffuse reflection light output. The voltage is plotted.
Here, even when there is element variation in each of the light emitting element, the specular reflection light receiving element, and the diffuse reflection light element, at least for the specular reflection light output, since it has the characteristic that the output is maximum at the belt background, If the LED current is adjusted so that the output at the belt background becomes a certain value (3.0 V in this case), output variations due to variations in the light emitting element and regular reflection light receiving element can be absorbed. An almost unique output characteristic can be obtained as the sensor output with respect to the quantity.

The large square mark in FIG. 6 is a point where the diffused light output after LED adjustment is plotted. If the variation of the light receiving element is doubled, the light receiving element of the diffuse reflected light output has a light receiving sensitivity of 1/2. , The diffused light output at that time is an output (Vd / 2) represented by a small square mark. Therefore, when the difference from the specularly reflected light (Vr) is taken in each case, as shown in FIG. The output relationship with the amount of adhesion is not uniquely determined. This is the same even when the ratio is taken.
In addition, as shown in FIG. 7, when the values of the two conditions coincide with each other at the point where the amount of adhesion is zero, and when these values are deviated in the high amount of adhesion region, the regular output of the specular reflection light output conventionally known is normal. Even if an operation such as a conversion process is performed, it cannot be determined uniquely.
Based on the above, the relationship between “regular reflection light output” and “diffuse reflection light output” when the amount of adhesion is converted based on the difference between “regular reflection light output” and “diffuse reflection light output” or ratio data It is necessary to always satisfy a certain relationship, and for this purpose, for example, at the sensor shipping inspection stage, it is necessary to correct variations such as strictly adjusting the relationship between the specular reflection light output and the diffuse reflection light output with respect to a certain reference plate. Become.

Even if the method described in the above prior art is adjusted after the adjustment described above, it is only necessary to take a difference or take a ratio. ), The amount of adhesion cannot be detected accurately due to fluctuation factors (sensor fluctuation, belt fluctuation).
Explanation for (3) Since the transfer belt is always in contact with the transfer paper as the sheet-like recording medium during image output, the surface of the belt becomes rough over time due to wear. In addition, when the transfer paper containing a large amount of white agent is continuously fed, the belt surface becomes white over time.
Before showing the experimental result about this, the state change factor of regular reflection light output and diffuse reflection light output is demonstrated.
The specularly reflected light output is light that is specularly reflected by the detection target surface (incident angle and reflection angle are equal), and when the detection target surface is smooth (= high specular gloss), it is shown in FIG. As described above, the irradiated light 61 is only slightly diffused on the detection target surface 53, and most of the light is specularly reflected as the regular reflection light 62. In FIG. 8, reference numeral 63 indicates the specular reflection light sensitivity, and 64 indicates the diffuse reflection light sensitivity in a distributed area.

As shown in FIG. 9, when the toner 65 as powder adheres to the detection target surface 53, since the incident light 61 is diffused by the toner 65, the specular reflection light 62 decreases, and conversely, the diffuse reflection light 66. Will increase. However, the diffuse reflected light 66 increases when the toner 65 is a color toner. When the toner 65 is a black toner, the irradiated light 61 is almost absorbed. Little increase.
That is, the output of specularly reflected light changes due to the “change in state of surface property (glossiness, surface roughness, etc.) of the object to be detected, and the diffuse reflected light output is the“ color characteristic (brightness, etc.) The output changes due to factors completely independent of each other, such as the output changing due to the “state change”.

The experimental results will be described. In the quadruple tandem direct transfer type color image forming apparatus shown in FIG. 1, assuming that the surface of the transfer belt is rough and whitened over time, “specular gloss (Gs)” and “lightness (L ^* ) A 16-tone pattern was formed on three types of transfer belts with different "", and the results were predicted when they varied over time by comparing the sensor detection output of these patterns. The conditions of the experiment are shown below.
<Transfer belt (detection target surface)>
Black belt: Specular gloss: Gs (60) = 57, Brightness: L ^* = 10
Brown belt: Specular gloss: Gs (60) = 27, Brightness: L ^* = 25
Gray belt: Specular gloss: Gs (60) = 5, Brightness: L ^* = 18
<Detection sensor (optical detection means)> Detailed specification of the sensor shown in FIG. 4 Light emitting side element: GaAs infrared light emitting diode (peak emission wavelength: λp = 950 nm), top view type Spot diameter: φ1.0 mm
Light receiving side element: Si phototransistor (peak spectral sensitivity: λp = 800 nm), top view type Spot diameter:
Regular reflection light receiving side: φ1.0mm
Diffuse reflected light receiving side: φ3.0mm
Detection distance: 5 mm (distance from the sensor top to the detection target surface)
LED current: 25 mA fixed
<Line speed>
125mm / sec
<Sampling frequency>
500 Sampling / sec (= 2 msec)
Note 1: The specular gloss value is a value measured at a measurement angle of 60 ° using a gloss meter PG-1 made by Nippon Denshoku.
Note 2: Brightness is a value measured using a spectrocolorimeter: X-Rite 938 manufactured by X-Rite, with a light source of D50 and a viewing angle of 2 °.

FIG. 10 shows the regular reflection light output characteristic with respect to the black toner adhesion amount, and FIG. 11 shows the regular reflection light output characteristic with respect to the color toner adhesion amount.
In this experiment, the sensor side input condition is fixed (LED current: If = 25 mA fixed), so in the high adhesion amount region (M / A = 0.4 mg / cm ² or more) where the influence of the belt background is not exerted. Although the specularly reflected light output (voltage) is substantially the same for the three types of belts, it is not the same in the low adhesion amount region (M / A = 0.4 mg / cm ² or less) affected by the belt background.
As can be seen from this result, when the mirror glossiness of the transfer belt decreases with time, that is, when the surface roughness deteriorates, as indicated by the arrow in the low adhesion amount region where the belt background portion where the adhesion amount is zero is exposed. It can be seen that the specular reflection light output (voltage) decreases.

[Consideration of defects in conventional technology (when using type (A) sensor)]
Based on the above experimental facts, the biggest difficulty when the amount of adhesion is detected by the sensor of type (A) that has only specular reflection output is that the adhesion amount detectable range is the gloss of the transfer belt in color adhesion amount detection. That is, it becomes narrower with time as the temperature decreases.
The reason for this is that, in the prior art, the adhesion amount detection of the color adhesion amount is performed by the following adhesion amount detection algorithm, so that the sensor output characteristic with respect to the adhesion amount is an adhesion amount greater than the inflection point (minimum value) shown in FIG. This is because cannot be detected.
<Conventional specular light output type adhesion amount conversion formula>
In FIG. 11, when the output minimum value of each belt is obtained by calculating the inflection point of the approximate curve, the maximum detectable amount of adhesion is 0.36 (57), 0.30 (27) as the belt deteriorates over time. ), 0.17 (5), and so on. Figures in parentheses indicate gloss values. The adhesion amount detectable range is the output value and the adhesion amount that is the minimum value.
As for the black toner adhesion amount detection, the maximum detectable adhesion amount can be detected with little change, although the output SN ratio is simply lowered, and the detection accuracy is slightly reduced.

Next, the horizontal axis: the diffused light output characteristic with respect to the black toner adhesion amount is shown in FIG. 12, and the horizontal axis: the diffuse reflected light output characteristic with respect to the color toner adhesion amount is shown in FIG.
Diffuse reflected light output is almost unaffected by the belt background, but the output is almost the same for the three types of belts. However, in the low adhesion amount area, which is affected by the change in brightness of the belt background, the effect of the change in brightness is low. Output does not match.
That is, it can be seen that when the transfer belt becomes white over time, the diffuse reflected light output of the transfer belt background portion increases.

[Consideration of defects in conventional technology (when using type (B) sensor)]
Due to the above experimental fact, the biggest difficulty when the amount of adhesion is detected with a sensor of type (B) that has only diffuse reflected light output. First, the temporal change in characteristics of the detection target surface is corrected. Secondly, the sensor sensitivity calibration cannot be performed on the detection target surface, particularly when the detection target surface is black, such as lightness: L ^* <20.
The reason why the sensitivity cannot be calibrated when the lightness is L ^* <20 is that the diffuse reflected light output from the background becomes almost zero.
For reference, the sensor sensitivity calibration method that the applicant has done for the conventional machine will be described. After the sensor is attached to the image forming apparatus at the factory, the sensor output for a certain white reference plate is a certain value. The LED light emission side adjustment of the sensor light emission side was performed so that it might become. However, even if it can be adjusted initially in this way, since there is no means for correcting the change in sensitivity due to the temperature characteristics of the sensor, LED degradation over time, etc., a reliable guarantee for quality over time cannot be obtained.

FIG. 14 shows the result of examining the correlation between the specular gloss and the specular reflection light output, and FIG. 15 shows the result of examining the correlation between the brightness and the diffuse reflection light output.
FIG. 14 shows the specular reflection light output when 42 types of transfer belts having different “glossiness” and “lightness” are fixed to LED current: 20 mA using the reflection type photosensor shown in FIG. Horizontal axis: plotted against 60 ° gloss.
The gloss value measured on the horizontal axis is a value measured at a measurement angle of 60 ° using a Nippon Denshoku gloss meter PG-1.
As shown in FIG. 9, since the regular reflection light output includes a diffuse reflection light component, if the results are sorted for each brightness range, the regular reflection light output voltage has a relationship that is approximately linearly proportional to the glossiness. It turns out that it is obtained.
The reason why the linear proportional relationship is obtained in this way is that the specular reflection itself is measured with respect to the specular glossiness. (Refer to JISZ8741 Specular Gloss-Measurement Method)

FIG. 15 is a graph in which the diffuse reflected light output measured at the same time is plotted with respect to the horizontal axis: the brightness of the belt. In FIG. 15, [-] means that there is no unit.
The brightness on the horizontal axis is a value measured using a spectrocolorimeter: X-Rite 938 manufactured by X-Rite Co., Ltd., with a light source: D50 and a viewing angle: 2 °.
The relationship between the two is not a linear relationship because of differences in the light source, measurement angle, etc., but since it is plotted on the same curve without being affected by the glossiness, the diffuse reflected light output is positive. It can be seen that it is independent of the reflected light output.

When the surface of the transfer belt becomes rough with time and the specular reflection light output of the belt background portion decreases, or when the diffuse reflection light output of the background portion increases due to whitening, or when these two progress simultaneously, either of these Since the relationship between “regular reflection light output” and “diffuse reflection light output” is broken, the output cannot be made the same as the initial state simply by taking the difference between the two outputs or taking the ratio.
Therefore, even if the adhesion amount conversion is performed based on this, the same result as the initial stage can never be obtained. Even if the amount of adhesion is not converted and this result is directly fed back to the density control, the result only deviates from the initial value.

Therefore, when the specular reflection light output decreases due to the belt glossiness decrease, it is conceivable to correct the LED current by increasing that amount.For example, adjustment is made so that the regular reflection light output of the belt background becomes the initial value. If this is done, at least the belt background portion is the same as the initial value, but as shown in FIG. 16, in the case of color toner, the output increases over the entire amount of adhesion.
In addition, since the output of the diffuse reflected light output voltage increases as the amount of received light increases, the resulting differential output is managed together with the initial value in the low coverage area as shown in FIG. However, since the deviation occurs in the high adhesion amount region, the same result as the initial stage cannot be obtained. This is the same even when the ratio is taken instead of the differential output.

Explanation for (2) Even if there is no change over time as described above, if the output characteristics of the light-emitting element and the light-receiving element, which are semiconductors, change due to an increase in the ambient temperature, the initial stage is similarly performed. The output result differs from the determined state.

As described above, the means for detecting the adhesion amount in the high adhesion amount region, and particularly the means for detecting the toner adhesion amount up to the high adhesion amount region on the black belt often used in the color image forming apparatus. In the method shown in the related art proposed as: (a) In order to make full use of the gradation pattern detection technique, the two outputs of the density detection sensor used for this are strictly adjusted in advance, that is, at the shipping inspection stage. It seems to be a major premise that a very strict adjustment is required. (B) There is no countermeasure against the environmental variation with time of the density detection sensor, and (c) the countermeasure with respect to the temporal variation of the detection target surface (transfer belt). Considering that there is no problem, it can be said that there are still many technical problems in the detection of gradation patterns.
In other words, on the black belt where the diffused reflected light output sensitivity cannot be adjusted, (a) output variations due to sensor lot variations, (b) aging and environmental variations of the density detection sensor, (c) detection target surface (transfer belt) (2) It is not influenced by any factor of the time-dependent fluctuations)), and a technical problem to be solved is how to always detect the toner adhesion amount in a stable high adhesion amount region.

One of the objects of the present invention is to solve the above-mentioned problems hidden in the prior art,
(1) Strict adjustment of the output relationship between “regular reflected light output” and “diffuse reflected light power” on the sensor side (hardware side) is not required, that is, it is manufactured with a greater degree of freedom at the shipping stage. Contributes to cost reduction,
(2) In spite of the presence of the above three factors, it is possible to automatically correct by the feature on the software side, and to achieve high accuracy of gradation pattern detection.
The above-described aim of the present invention is achieved by an adhesion amount conversion algorithm according to the present invention described below and an image forming apparatus using the same.
Specifically, the gradation pattern is read by a reflection type optical sensor having two outputs of “C” and “D” of “regular reflection light output” and “diffuse reflection light output”, and the regular reflection light is used. In the adhesion amount range where the adhesion amount can be detected, these two outputs are converted into values having a linear relationship with the adhesion amount, and based on the conversion value of the specular reflection light output that provides a unique relationship with the adhesion amount. In addition, by performing sensitivity correction of the diffuse reflected light output conversion value, the diffuse reflected light output is also achieved by an algorithm that converts the diffuse reflected light output to a value uniquely determined with respect to the adhesion amount.

Hereinafter, the adhesion amount conversion algorithm in the present invention will be described in detail.
First, as shown in FIG. 1, a schematic configuration of a color laser printer of a quadruple tandem direct transfer system as an image forming apparatus and a powder adhesion amount detection apparatus will be described.
The color laser printer has three paper feed trays, one manual feed tray 36, two paper feed cassettes 34 (first paper feed tray), and 34 (second paper feed tray). A transfer sheet (not shown) as a sheet-like recording medium that has been formed is separated one by one in order from the uppermost one by a paper feeding roller 37 and conveyed toward the registration roller pair 23. The transfer sheets fed from the first sheet feed tray 34 or the second sheet feed tray 34 are separated one by one from the uppermost one by the sheet feed roller 35 and are transferred to the registration roller pair 23 via the transport roller pair 39. It is conveyed toward.
The fed transfer paper is temporarily stopped by the pair of registration rollers 23, the skew is corrected, and then the leading edge of the image formed on the photosensitive drum 14Y positioned at the uppermost stream described later and the transfer paper in the transport direction. At a timing coincident with the predetermined position, the sheet is conveyed toward the transfer belt 18 by the rotation operation of the registration roller pair 23 by ON control of a registration clutch (not shown).
When the transfer paper passes through a paper suction nip composed of the transfer belt 18 and a paper suction roller 41 in contact with the transfer belt 18, the transfer paper is attracted to the transfer belt 18 by an electrostatic force by a bias applied to the paper suction roller 41. It is conveyed at a process linear velocity of 125 mm / sec.

The transfer paper adsorbed by the transfer belt 18 has toner transferred to the transfer brushes 21B, 21C, 21M, and 21Y disposed at positions facing the photosensitive drums 14B, 14C, 14M, and 14Y of the respective colors with the transfer belt 18 interposed therebetween. By applying a transfer bias (plus) opposite to the charging polarity (minus), the toner images of the respective colors formed on the photoconductor drums 14B, 14C, 14M, and 14Y are converted into yellow (Y) and magenta (M ), Cyan (C), and black (Bk).
The transfer paper that has undergone the transfer process of each color is separated from the transfer belt 18 by the downstream drive roller 19 and is conveyed to the fixing device 24. By passing through a fixing nip formed by the fixing belt 25 and the pressure roller 26 in the fixing device 24, the toner image is fixed on the transfer paper by heat and pressure. In the single-sided printing mode, the fixed transfer paper is discharged to an FD (face-down) tray 30 formed on the upper surface of the apparatus main body.
When the double-sided printing mode is selected in advance, the transfer paper that has exited the fixing device 24 is sent to a reversing unit (not shown), and the front and back sides are reversed by the unit, and then the double-sided transport unit positioned below the transfer unit It is conveyed to 33. The transfer paper is fed again from the double-sided conveyance unit 33 and conveyed to the registration roller pair 23 through the conveyance roller pair 39. Thereafter, it passes through the fixing device 24 through the same operation as in the single-sided printing mode, and is discharged to the FD tray 30.

Next, the configuration and image forming operation in the image forming unit of the color laser printer will be described in detail.
Since the image forming unit has the same configuration and operation for each color, the configuration and operation for forming a yellow image will be described as a representative.
An image forming unit 12Y having a charging roller 42Y and a cleaning unit 43Y, a developing unit 13Y, an optical writing unit 16, and the like are provided around the photosensitive drum 14Y positioned on the most upstream side in the transfer paper conveyance direction.
At the time of image formation, the photosensitive drum 14Y is driven to rotate clockwise by a main motor (not shown), is neutralized by an AC bias (DC component is zero) applied to the charging roller 42Y, and the surface potential is a reference of approximately −50v. It becomes a potential.

Next, the photosensitive drum 14Y is uniformly charged to a potential substantially equal to the DC component by applying a DC bias with an AC bias superimposed on the charging roller 42Y, and the surface potential thereof is approximately −500 v to −700 v (target charging). The potential is determined by the process control unit).
Digital image information sent from a controller unit (not shown) as a print image is converted into a binarized LD light emission signal for each color, and a cylinder lens, a polygon motor, an fθ lens, first to third mirrors, and a WTL. Exposure light 16Y is irradiated onto the photosensitive drum 14Y by an optical writing unit 16 having a lens or the like.
The drum surface potential of the irradiated portion becomes approximately −50 v, and an electrostatic latent image corresponding to the image information is formed.

The electrostatic latent image corresponding to the yellow image information on the photosensitive drum 14Y is visualized by the developing unit 13Y. By applying DC (-300 to -500 v) with an AC bias superimposed on the developing sleeve 44Y of the developing unit 13Y, toner (Q / M: -20 to -30 μC / g) is developed to form a toner image.
The formed toner images on the photosensitive drums 14B, 14C, 14M, and 14Y of the respective colors are transferred onto the transfer paper adsorbed on the transfer belt 18 by the transfer bias.

In the color laser printer according to this embodiment, in addition to the image forming mode as described above, a process control operation (hereinafter referred to as a process control operation) is performed in order to optimize the image density of each color when the power is turned on or after a predetermined number of sheets have passed. Is abbreviated).
In this process control operation, a density detection patch (hereinafter abbreviated as P pattern) as a plurality of gradation patterns for each color is formed on a transfer belt by sequentially switching between a charging bias and a developing bias at an appropriate timing. The output voltage of the P pattern is detected by a density detection sensor (hereinafter abbreviated as P sensor) 40 as an optical detection means disposed outside the transfer belt 18 in the vicinity of the driving roller 19, and the output voltage is detected according to the present invention. The adhesion amount is converted by an adhesion amount conversion algorithm (powder adhesion amount conversion method) to calculate (development Y, Vk) representing the current developing ability. Based on the calculated values, the development bias value and the toner density control target are calculated. Control to change the value.

The configuration of the P sensor is as shown in FIG. 4, and the specifications are as described above.
Here, PTr (phototransistor) is used as the light receiving element, but a light receiving element such as PD (photodiode) may be used.

The adhesion amount conversion algorithm in the present invention will be described below based on the experimental results shown in FIGS. In this algorithm, the diffused light output is converted into an adhesion amount value according to the following procedure.
(1) Sampling the regular reflection light output and diffuse reflection light output of the gradation pattern (see FIGS. 11 and 13);
(2) Extracting specularly reflected light output into [specularly reflected light component] and [diffuse reflected light component] to extract only [specularly reflected light component]
(3) Extracting [diffuse light component from toner] by removing [diffuse reflection light component from belt background] from the diffuse reflection output,
(4) An adhesion amount range in which the adhesion amount can be detected by specular reflection light using a linear relationship with the adhesion amount of two output conversion values that are independent (intersect) obtained from (2) and (3). By adjusting the sensitivity of the diffuse reflection light output conversion value so that the diffuse reflection light output conversion value of a certain regular reflection light output conversion value (or adhesion amount) becomes a certain value in the (low adhesion amount region), the adhesion amount Diffuse reflected light output (correction value) is uniquely determined for
(5) The adhesion amount conversion process is performed from the relationship between the “adhesion amount” and the “diffuse reflected light output correction value” obtained in advance.

(1) to (5) will be described below in order.
Description of (1) FIGS. 11 and 13 show “regular reflection light output voltage” in which the P pattern 70 for density detection shown in FIG. 18 formed on the transfer belt 18 is detected by the P sensor 40 shown in FIG. The “diffuse reflected light output voltage” is plotted against the color toner adhesion amount [mg / cm ² ] precisely measured by the electronic balance. In the gradation pattern 70, the toner adhesion amount increases on the upstream side in the belt moving direction.
As described above, three types of transfer belt 18 having different specular glossiness and brightness are used.

Explanation of (2) Here, when the regular reflection light output characteristic with respect to the black toner adhesion amount shown in FIG. 10 is compared with the regular reflection light output characteristic with respect to the color toner adhesion amount shown in FIG. It can be seen that the reflected light output shifts from monotonic decrease to monotonic increase at a certain adhesion amount (in this case 0.2 to 0.4 mg / cm ² ) or more, as shown in FIGS. 19 and 20. The light received by the regular reflection light receiving element 52 as regular reflection light includes, in addition to pure [regular reflection light component], [diffuse reflection light component from belt surface], [diffuse reflection light component from toner layer]. It is because it is included. In FIG. 19B, reference numeral 54 denotes a cyan solid portion.
Considering that the irradiation light from the LED 51 is evenly diffused on the detection target surface as shown in FIG. 19, the diffuse reflected light component received by the regular reflection light receiving element 52 and the diffusion entering the diffuse light receiving element 55. There should be an n-fold relationship with the reflected light.
The value of n times used here is a value determined by the optical layout such as the light receiving diameter and arrangement of the light receiving elements 52 and 55.

The actual output is output as a voltage after the reflected light entering each of the light receiving elements 52 and 55 is IV-converted in the circuit by the OP amplifier. The difference between these is also accumulated, and the α-fold relationship should be established.
If such a coefficient α can be obtained, it is considered that the specular reflection light output can be decomposed into “regular reflection component” and “diffuse reflection component”.
Here, considering how to obtain the coefficient α, the diffuse reflection component of Bk toner is so small that it is almost equal to zero. Therefore, the regular reflection light output characteristic of Bk shown in FIG. This is considered to be almost equal to the regular reflection component output characteristic from which the component is removed.
As shown in FIG. 10, the specular reflection light output characteristic of Bk toner becomes almost zero or slightly positive as the adhesion amount increases, and never becomes negative. Find the minimum value of the ratio between the specular reflection light output and the diffuse reflection light output every time, multiply the diffuse reflection light output by the minimum value of this ratio, and subtract it from the specular reflection light output. It should be possible to extract the output characteristics.

The processing flow will be described below based on the output result of the brown belt (Gs = 27, L ^* = 25) shown in FIG. In addition, the meaning of the symbol (abbreviation) in the following description is as follows.
Vsg: Output voltage of the background portion of the transfer belt 18 Vsp: Output voltage of each pattern portion Voffset: Offset voltage (output voltage when the LED 51 is off)
_reg. ... Specular reflection output (abbreviation for Regular Reflection)
_dif. ... Diffuse reflected light output (abbreviation for Diffuse Reflection, see JISZ8105 color terms)
[n] ... number of elements: array variable of n (STEP 1): data sampling: calculation of ΔVsp and ΔVsg (see FIGS. 21 and 22)
First, the difference from the offset voltage is calculated for all points [n] for both regular reflection light output and diffuse reflection light output.
This is because, in the end, it is desired to express only “the increment of the sensor output by the change of the amount of color toner attached”.

  However, in the case of using an OP amplifier in which each offset voltage value (Voffset_reg .: 0.0621V, Voffset_dif .: 0.0635V) when the LED 51 is OFF is sufficiently small to a negligible level as in this embodiment. Such difference processing is not necessary.

(STEP2): Calculation of sensitivity correction coefficient α (see FIG. 22)
ΔVsp_reg. Determined in STEP 1 [n], ΔVsp_dif. [n], ΔVsp_reg. [n] / ΔVsp_dif. [n] is calculated, and the coefficient α multiplied by the diffuse reflected light output (ΔVsp_dif. [n]) is calculated when the component decomposition of the regular reflected light output is performed in STEP3.

The reason why α is obtained from the minimum value of the ratio is that it is known in advance that the minimum value of the regular reflection component of the regular reflection light output is almost zero and is a positive value. Here, the gradation pattern has at least one, preferably three or more adhesion amount patterns in the vicinity of the adhesion amount that provides the minimum value of the ratio between the specular reflection light output and the diffuse reflection light output. . At least one or more, preferably three or more, in the vicinity of the amount of adhesion at which the minimum value of the ratio between the specular reflection light output increment and the diffuse reflection light output increment obtained from the difference from each output value when the light emitting means is off is obtained. You may make it have an adhesion amount pattern. In addition, the regular reflection light output conversion value may have at least one, preferably three or more adhesion amount patterns within an adhesion amount range in which the linear reflection relationship with the adhesion amount is linear.
(STEP3): Component decomposition of specularly reflected light (see FIG. 23)
The component decomposition of the regular reflection light output is performed by the following equation.

When the components are decomposed in this way, the regular reflection component of the regular reflection light output becomes zero in the pattern portion where the sensitivity correction coefficient α is obtained.
By this processing, as shown in FIG. 23, the regular reflected light output is decomposed into [regular reflected light component] and [diffuse reflected light component].
(STEP 4): specular reflection light output_regular reflection component normalization (see FIG. 24)
Next, in order to correct the difference in the specular reflection light output of the three types of belt background portions, the ratio of each pattern portion output to the belt background portion output is taken and converted to a normalized value from 0 to 1.

FIG. 24 shows the results of conversion into normalized values obtained by performing the same processing for all three types of belts shown in FIG.
In this way, by analyzing the components of the specularly reflected light, only the specularly reflected light component is extracted and converted into a normalized value, thereby uniquely determining the relationship between the specularly reflected light component and the amount of adhesion. Can do. This value represents the exposure rate of the belt background portion, and in the adhesion amount range from zero to one layer formation, this normalized value (= belt background exposure rate) is relative to the adhesion amount. There is a linear relationship.
If it is desired to obtain the toner adhesion amount in the low adhesion amount region from M / A} = 0 to 0.4 mg / cm ² , the relationship between the adhesion amount and the normalized value as shown in FIG. If it is experimentally obtained in advance as mathematical formulas or table data, the adhesion amount can be converted by inverse conversion or reference to the table.

Here, a comparison with the prior art will be made. In claim 4 of Japanese Patent Laid-Open No. 2001-215850, specular reflection light + (diffuse reflection light−diffuse reflection light output min) × predetermined coefficient is shown. In the embodiment in the specification, the corrected output is the first order. Although there is a description that the predetermined coefficient is “−6” so as to have a correlation, the multiplication of the predetermined coefficient in this form does not take into account the characteristic variation of the optical detection means as described above. It can be said that there is practically no point.
On the other hand, in the present embodiment, since the coefficient calculated based on the sensor output of regular reflection light and diffuse reflection light is multiplied as the predetermined coefficient, high accuracy in consideration of variation in characteristics of the optical detection means is taken into account. Detection can be performed.

Explanation for (3) Next, processing for removing [diffuse reflected light output component from the belt background portion] from [diffuse reflected light output voltage] will be described.
What is finally determined by the adhesion amount conversion algorithm in this embodiment is a unique relationship between the diffuse reflection light output and the toner adhesion amount.
However, as shown in FIG. 20, the light that enters the diffuse reflection light receiving element 55 includes diffuse reflection light (noise component) from the belt background in addition to the diffuse reflection light from the toner layer. This component needs to be removed from the output.
In FIG. 20, the ratio between the “background part output” and the “pattern part output” of the regular reflection component is uniquely determined with respect to the adhesion amount (adhesion amount detectable range: 0 to 0.4 mg / cm ² ).
In addition, in the diffuse reflection component from the toner layer, if the irradiation light to the detection target surface is constant, the relationship with the adhesion amount is uniquely determined (attachment amount detectable range: 0 to 1.0 mg / cm ² ).
As a continuation of STEP 4, the processing flow will be described based on the output result of the brown belt (Gs = 27, L ^* = 25) shown in FIG.
As shown in the results of FIG. 13, the diffuse reflected light output from the belt background portion becomes maximum at the belt background portion where the toner is not attached, and the component gradually decreases as the toner adheres.
The relationship with the amount of adhesion of the diffuse reflection light output voltage increment due to the light that directly enters the diffuse reflection light receiving element 55 from the belt background is the exposure ratio of the transfer belt 18, that is, the specular reflection component of the specular reflection light output obtained previously. In order to be proportional to the normalized value (see FIG. 24), the processing for removing [diffuse reflected light output component from the belt background portion] from [diffuse reflected light output voltage] is as follows.
(STEP 5): Background variation correction of diffuse reflected light output (see FIG. 25)

The results are shown in FIG. By performing such correction processing, the influence of the background portion of the transfer belt 18 can be eliminated. Accordingly, the [diffuse reflected light component directly reflected from the belt background portion] can be removed from the [diffuse reflected light output] in the low adhesion amount region where the regular reflected light output has sensitivity.
By performing such processing, the corrected diffuse reflection light output in the adhesion amount range from zero adhesion to one layer formation is converted to a value having a linear relationship with the adhesion amount through the origin. .

Here, a supplementary explanation of the diffuse reflected light will be given. Since the specularly reflected light is light reflected from the surface of the detection target surface, as shown in FIG. 24, when the detection target surface is 100% covered with toner, the output changes substantially in the adhesion amount region beyond that. The normalized conversion value becomes almost zero.
On the other hand, the diffuse reflected light is light that is reflected from the LED 51 and enters the toner layer, and thus is reflected multiple times. Therefore, as shown in FIG. 13, a high adhesion amount region in which the toner layer is covered 100% or more. However, the sensor output has a monotonically increasing characteristic.
Therefore, as shown in FIG. 26, the light reflected from the belt background portion also includes a primary component directly reflected from the belt background portion and secondary and tertiary components reflected through the toner layer. is there.
In this embodiment, only the primary component is corrected in STEP 5, but this correction alone can remove the influence of the belt background portion almost accurately only in the low adhesion amount region where sensitivity correction is performed. Since the second-order and third-order components are sufficiently smaller than the first-order components, practically sufficient accuracy can be obtained even by correcting only the first-order components.

Explanation for (4) By the above processing, in the low adhesion amount region where the specular reflection light output has sensitivity, the relationship between the toner adhesion amount and the specular reflection light can be uniquely expressed in (2) [regular reflection light component ], And in (3), the [diffuse reflected light component reflected directly from the belt background] could be removed from the diffuse reflected light. Based on these, the sensitivity of the diffuse reflected light output Make corrections.
Here, the reason for performing the sensitivity correction is to perform the following correction as described above.
(1) Correction for lot variation of light emitting element output and light receiving element output (2) Correction for temperature characteristic and aging deterioration characteristic of light emitting element output and light receiving element output The biggest point in this processing is that only one toner layer is formed. In the low adhesion amount area,
(A) The normalized value of the regular reflection light output (regular reflection component), that is, the exposure rate of the background portion of the transfer belt has a linear relationship with the toner adhesion amount.
(B) [diffuse reflection component from toner layer] has a linear relationship that passes through the origin with respect to the toner adhesion amount.
That is, the sensitivity of the diffuse reflected light output is corrected by utilizing the fact that the two corrected outputs of the specular reflected light and the diffuse reflected light are both in a linear relationship with the toner adhesion amount.
Several methods can be considered for this sensitivity correction. Here, two methods will be described as examples.

(STEP 6): Sensitivity correction of diffuse reflected light output (see FIG. 25)
<Processing formula by the first method>
As shown in FIG. 27, the diffuse reflected light output after correcting the fluctuation of the background portion is plotted against the “normalized value of regular reflected light (regular reflected component)”, and the diffuse reflected light output is obtained from the linear relationship in the low adhesion amount region. And the correction is performed so that the sensitivity becomes a predetermined target sensitivity.
Here, what is described as the sensitivity of the diffuse reflected light output is the slope of the straight line shown in FIG. 27, and the diffuse reflected light output after correction of the background portion fluctuation of a certain normalized value (here 0.3. In this case, a correction coefficient for multiplying the current inclination is calculated and corrected so as to be 1.2).
(1) The slope of the straight line is obtained by the least square method.

In this embodiment, the lower limit value of the range of x used for the calculation is 0.06, but this lower limit value is a value that can be arbitrarily determined within a range where x and y are in a linear relationship. The upper limit value is set to 1 because the normalized value is a value from 0 to 1.
(2) A sensitivity correction coefficient γ is obtained such that a certain normalized value a calculated from the sensitivity thus obtained becomes a certain value b.

(3) The diffused reflected light output after the background portion fluctuation correction obtained in STEP 5 is corrected by multiplying by this sensitivity correction coefficient γ. The reference point for performing sensitivity correction (a specular reflection light output conversion value when a diffuse reflection light output conversion value of a specular reflection light output conversion value becomes a certain value) is a specular reflection light. This is an area where the amount of adhesion can be detected.

<Processing formula by the second method>
According to the inverse conversion formula obtained from the relationship between the adhesion amount (measured value) obtained in FIG. 24 and the normalized value of the specular reflection light (specular reflection component), or by referring to the conversion table, “specular reflection light (regular reflection component) ) Normalized value ”is converted into adhesion amount (conversion value), and the diffuse reflected light output after correction of background fluctuation is plotted against this adhesion amount (conversion value), and diffused from the linear relationship in the low adhesion amount region. The sensitivity of the reflected light output is obtained, and correction is performed so that this sensitivity becomes a predetermined target sensitivity.
The difference from the first method is that the horizontal axis is changed from “normalized value of regular reflection light (regular reflection component)” to “attachment amount (conversion value)”. Here, the sensitivity of the diffuse reflected light output is the slope of the straight line shown in FIG. 28, and the diffuse reflected light output after the background portion fluctuation correction of a certain adhesion amount (conversion value) is a certain value (here, 0). The correction coefficient by which the current inclination is multiplied is calculated and corrected so as to be 1.2) when .175.
(1) The slope of the straight line is obtained by the least square method.

In the present embodiment, the upper limit value of the x range used for the calculation is 0.3, but this upper limit value is a value that can be arbitrarily determined within a range in which x and y are in a linear relationship. The lower limit value was set to 0 because the lower limit value of the adhesion amount was 0.
(2) A sensitivity correction coefficient γ is obtained such that a certain normalized value a calculated from the sensitivity thus obtained becomes a certain value b.

(3) The diffused reflected light output after the background portion fluctuation correction obtained in STEP 5 is corrected by multiplying by this sensitivity correction coefficient γ.

FIG. 29 shows the results of conversion into normalized values obtained by performing the same processing for all three types of belts.
Here, since the diffuse reflection light output voltage before correction is as shown in FIG. 13, the above processing is one of the objects of the present invention.
(1) Correction with respect to lot variation of light emitting element output and light receiving element output (2) It was confirmed that the temperature characteristic of the light emitting element output and the light receiving element output and the correction with respect to deterioration with time were sufficiently corrected.
By such processing, the diffuse reflected light output after the sensitivity correction can be uniquely expressed with respect to the toner adhesion amount. Therefore, if it is experimentally obtained in advance as an equation or table data, By referring to the conversion table, it is possible to accurately convert the adhesion amount up to the high adhesion amount region.

FIG. 30 shows the result of plotting the adhesion amount (conversion value) obtained by actually inversely transforming the normalized value against the adhesion amount measurement value by an electronic balance.
As shown in FIG. 30, it can be confirmed that the adhesion amount can be converted almost accurately up to the high adhesion amount region. Since accurate adhesion amount detection up to a high adhesion amount region becomes possible, it becomes possible to accurately control the maximum target adhesion amount in image density control, so regardless of time, environment, and sensor lot variation. , You can always get a stable image quality.

FIG. 31 shows a color produced on the transfer belt 18 of the laser color printer A shown in FIG. 1 with three sensors extracted as the upper and lower limit products and the center product of the variation among 200 prototypes of density detection sensors. A diffuse reflected light output voltage obtained by detecting a total of 30 P patterns (gradation patterns) of 10 toner colors is shown. FIG. 32 shows the diffuse reflected light conversion values according to the conversion algorithms of STEP1 to STEP6. The LED current at this time is a value when the regular reflected light output voltage of the background portion of the transfer belt 18 is adjusted to 4.0V.
As a result, by using the algorithm of the present invention, the output variation of the light receiving element due to various factors in the optical detection means as described above can be performed on the algorithm side, that is, on the software side without requiring strict adjustment on the hardware side. The wear side can automatically and accurately correct.

In the above description, the optical detection means having the light emitting means, the specular reflection light receiving element, and the diffuse reflection light receiving element shown in FIG. 4 is used. However, the optical detection means having the beam splitter shown in FIG. The same detection function can be obtained even if is used.
In the above description, the detection target surface is the transfer belt 18 as a transfer body, but each photosensitive drum may be a detection target surface. In this case, the P sensor 40 is provided to face each photosensitive drum.

In the above description, an example of a four-tandem direct transfer type color image forming apparatus has been shown. However, as shown in FIG. The same can be applied to a color image forming apparatus of the above type.
In this case, the P pattern for density detection shown in FIG. 18 is formed on the intermediate transfer belt 2 as an intermediate transfer member, and this is detected by the P sensor 40 disposed in the vicinity of the support roller 2B. That is, the intermediate transfer belt 2 is a detection target surface. The detection method and operation (e.g., handling of detected data) are the same as in the first example.

The outline of the configuration and operation of a tandem type color copier as an image forming apparatus in this example will be described below. The color copying machine 1 has an image forming unit 1A located at the center of the apparatus main body, a paper feeding unit 1B located below the image forming unit 1A, and an image reading unit 1C located above the image forming unit 1A. is doing.
An intermediate transfer belt 2 as a transfer body having a transfer surface extending in the horizontal direction is disposed in the image forming unit 1A, and an image of a color complementary to the color separation color is disposed on the upper surface of the intermediate transfer belt 2. The structure for forming is provided. That is, the photosensitive drums 3Y, 3M, 3C, and 3B as image carriers capable of carrying an image of complementary color toners (yellow, magenta, cyan, and black) are arranged along the transfer surface of the intermediate transfer belt 2. It is juxtaposed.

Each of the photosensitive drums 3Y, 3M, 3C, and 3B is composed of a drum that can rotate in the same counterclockwise direction, and around the charging device 4 is a charging unit that performs image forming processing in the rotation process. The optical writing device 5 as an exposure unit for forming an electrostatic latent image having a potential _VL based on the image information on each of the photosensitive drums 3Y, 3M, 3C, and 3B. A developing device 6 as a developing unit that develops the electrostatic latent image with toner having the same polarity as the electrostatic latent image, a transfer bias roller 7 as a primary transfer unit, an applied voltage member 15, and a cleaning device 8 are arranged. The alphabets attached to the respective symbols correspond to the colors of the toner as in the photosensitive drum 3. Each developing device 6 accommodates each color toner.
The intermediate transfer belt 2 is configured to be wound around a plurality of rollers 2A to 2C and to move in the same direction at a position facing the photosensitive drums 3Y, 3M, 3C, and 3B. A roller 2C, which is different from the rollers 2A and 2B that support the transfer surface, faces the secondary transfer device 9 with the intermediate transfer belt 2 interposed therebetween. In FIG. 33, reference numeral 10 indicates a cleaning device for the intermediate transfer belt 2.

The surface of the photosensitive drum 3Y is uniformly charged by the charging device 4Y, and an electrostatic latent image is formed on the photosensitive drum 3Y based on the image information from the image reading unit 1C. The electrostatic latent image is visualized as a toner image by a two-component (carrier and toner) developing device 6Y containing yellow toner, and the toner image is formed on the intermediate transfer belt 2 as a first transfer step. The image is attracted and transferred by the electric field generated by the voltage applied to the transfer bias roller 7Y.
The applied voltage member 15Y is provided on the upstream side of the transfer bias roller 7Y in the rotation direction of the photosensitive drum 3Y. The applied voltage member 15Y applies a voltage to the intermediate transfer belt 2 that has the same polarity as the charging polarity of the photosensitive drum 3Y and has an absolute value that is larger than the solid _VL , and before the toner image enters the transfer area, the photosensitive drum 3Y. From the toner to the intermediate transfer belt 2 is prevented, and the disturbance due to dust during the transfer of toner from the photosensitive drum 3Y to the intermediate transfer belt 2 is prevented.

The other photoconductor drums 3M, 3C, and 3B also form similar images only with different toner colors, and the toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 2 and superimposed.
The toner remaining on the photosensitive drum 3 after the transfer is removed by the cleaning device 8, and the potential of the photosensitive drum 3 is initialized by a neutralizing lamp (not shown) after the transfer to prepare for the next image forming process.
The secondary transfer device 9 includes a transfer belt 9 </ b> C that is wound around the charging drive roller 9 </ b> A and the driven roller 9 </ b> B and moves in the same direction as the intermediate transfer belt 2. By charging the transfer belt 9C with the charging drive roller 9A, it is possible to transfer a multicolor image superimposed on the intermediate transfer belt 2 or a supported single color image onto a paper 28 as a sheet-like recording medium.

The paper 28 is fed from the paper feed unit 1B to the secondary transfer position. The paper feed unit 1B has a plurality of paper feed cassettes 1B1 in which papers 28 are stacked and housed, and a paper feed roller 1B2 that separates and feeds the papers 28 contained in the paper feed cassette 1B1 one by one in order from the top. A pair of conveying rollers 1B3, a pair of registration rollers 1B4 positioned upstream of the secondary transfer position, and the like.
The paper 28 fed from the paper feed cassette 1B1 is temporarily stopped by the registration roller pair 1B4, and after correcting the oblique displacement and the like, the front end of the toner image on the intermediate transfer belt 2 and a predetermined position at the front end in the transport direction are set. Are sent to the secondary transfer position by the registration roller pair 1B4. A manual feed tray 29 is provided on the right side of the apparatus main body so that it can be turned up and down, and the paper 28 accommodated in the manual feed tray 29 joins the paper feed path from the paper feed cassette 1B1 fed by the paper feed roller 31. The paper is sent toward the registration roller pair 1B4 by the conveying path.

In the optical writing device 5, writing light is controlled by image information from the image reading unit 1C or image information output from a computer (not shown), and the photosensitive drums 3Y, 3M, 3C, and 3B correspond to the image information. Writing light is emitted to form an electrostatic latent image.
The image reading unit 1C includes an automatic document feeder 1C1, a scanner 1C2 having a contact glass 80 as a document table, and the like. The automatic document feeder 1C1 has a configuration capable of reversing the document fed on the contact glass 80, and can perform scanning on each surface of the document.
The electrostatic latent image formed on the photosensitive drum 3 formed by the optical writing device 5 is subjected to visible image processing by the developing device 6 and is primarily transferred to the intermediate transfer belt 2. When the toner images for each color are superimposed and transferred onto the intermediate transfer belt 2, they are secondarily transferred onto the paper 28 by the secondary transfer device 9. The second-transferred paper 28 is sent to the fixing device 11 where the unfixed image is fixed by heat and pressure. Residual toner on the intermediate transfer belt 2 after the secondary transfer is removed by the cleaning device 10.

  The paper 28 that has passed through the fixing device 11 is selectively guided to the conveyance path toward the paper discharge tray 27 and the reverse conveyance path RP by the conveyance path switching claw 12 provided on the downstream side of the fixing apparatus 11. When the paper is conveyed toward the paper discharge tray 27, it is discharged onto the paper discharge tray 27 by the paper discharge roller pair 32 and stacked. When guided to the reversal conveyance path RP, it is reversed by the reversing device 38 and sent again toward the registration roller pair 1B4.

With the above configuration, in the color copying machine 1, the photosensitive drum 3 that is uniformly charged is statically exposed by scanning the document placed on the contact glass 80 or by image information from the computer. An electrostatic latent image is formed, and the electrostatic latent image is subjected to visible image processing by the developing device 6, and then the toner image is primarily transferred to the intermediate transfer belt 2.
In the case of a single image, the toner image transferred to the intermediate transfer belt 2 is transferred as it is to the paper 28 fed out from the paper supply unit 1B. In the case of a multi-color image, the images are superimposed by repeating primary transfer, and then secondary transferred onto the paper 28 at once.
After the secondary transfer, the paper 28 is fixed with an unfixed image by the fixing device 11 and then discharged to the paper discharge tray 27 or reversed and sent again toward the registration roller pair 1B4 for double-sided image formation.
In this example, the detection target surface is the intermediate transfer belt 2 as a transfer body, but each photosensitive drum may be a detection target surface. In this case, the P sensor 40 is provided to face each photosensitive drum.

Further, each color toner image is formed by using one photosensitive drum and a revolver type developing device, and each toner image is transferred onto an intermediate transfer member, and then transferred onto a transfer sheet as a sheet-like recording medium. The same can be applied to the color image forming apparatus of the type. An example is shown in FIG.
In this case, a P pattern for density detection shown in FIG. 18 is formed on an intermediate transfer belt 426 as an intermediate transfer member, and this is detected by a P sensor 40 disposed in the vicinity of the drive roller 444. That is, the intermediate transfer belt 426 is a detection target surface. The detection method and operation (handling of detection data, etc.) are the same as in the first example.

The outline of the configuration of the color copying machine as the image forming apparatus in this example will be described below.
In a color copying machine, a writing optical unit 400 serving as an exposure unit converts color image data from the color scanner 200 into an optical signal and performs optical writing corresponding to a document image, on a photosensitive drum 402 serving as an image carrier. An electrostatic latent image is formed on the surface.
The writing optical unit 400 includes a laser diode 404, a polygon mirror 406, a rotation motor 408 thereof, an fθ lens 410, a reflection mirror 412, and the like.
The photosensitive drum 402 is rotated in the counterclockwise direction as indicated by an arrow, and the photosensitive drum cleaning unit 414, the charge eliminating lamp 416, the potential sensor 420, and the rotary developing device 422 are selected around the photosensitive drum 402. A developing device, a development density pattern detector 424, an intermediate transfer belt 426 as an intermediate transfer member, and the like are arranged.

The rotary developing device 422 includes a black developing unit 428, a cyan developing unit 430, a magenta developing unit 432, a yellow developing unit 434, and a rotation driving unit (not shown) that rotates each developing unit. Each developing device is a so-called two-component developing type developing device containing a mixed developer of carrier and toner, and has the same configuration as the developing device 4 shown in the above example. The conditions and specifications of the magnetic carrier are the same.
In the standby state, the rotary developing device 422 is set at the black development position. When the copying operation is started, the color scanner 200 starts reading the black image data at a predetermined timing. Based on the above, optical writing with a laser beam and formation of an electrostatic latent image (black latent image) are started.

In order to develop from the leading edge of the black latent image, before the leading edge of the latent image reaches the developing position of the black developing device 428, the developing sleeve is started to rotate and the black latent image is developed with black toner. A negative polarity toner is formed on the photosensitive drum 402.
Thereafter, the development operation of the black latent image area is continued, but when the trailing edge of the latent image passes the black development position, the rotary development is quickly performed from the development position for black to the development position for the next color. The device 422 rotates. This operation is completed at least before the leading edge of the latent image by the next image data arrives.
When the image forming cycle is started, first, the photosensitive drum 402 is rotated counterclockwise as indicated by an arrow, and the intermediate transfer belt 426 is rotated clockwise by a drive motor (not shown). As the intermediate transfer belt 426 rotates, black toner image formation, cyan toner image formation, magenta toner image formation, and yellow toner image formation are performed. Finally, black (Bk), cyan (C), and magenta (M) are formed. , Yellow (Y) in this order (primary transfer) on the intermediate transfer belt 426 to form a toner image.

The intermediate transfer belt 426 includes a primary transfer electrode roller 450 that faces the photosensitive drum 402, a drive roller 444, a secondary transfer counter roller 446 that faces the secondary transfer roller 454, and a cleaning unit that cleans the surface of the intermediate transfer belt 426. It is stretched between the supporting members of the cleaning facing roller 448A facing the surface 452, and is driven and controlled by a driving motor (not shown).
The black, cyan, magenta, and yellow toner images sequentially formed on the photosensitive drum 402 are accurately and sequentially aligned on the intermediate transfer belt 426, thereby forming a four-color superimposed belt transfer image. This belt transfer image is collectively transferred onto a sheet by a secondary transfer counter roller 446.

Each of the recording paper cassettes 458, 460, and 462 in the paper supply bank 456 contains various sizes of paper different from the size of the paper stored in the cassette 464 in the apparatus body. The designated paper is fed and conveyed in the direction of the registration roller pair 470 by the paper feed roller 466 from the size paper storage cassette. In FIG. 34, reference numeral 468 denotes a manual paper feed tray for OHP paper, thick paper, and the like.
At the time when image formation is started, the paper is fed from the paper feed port of one of the above cassettes and waits at the nip portion of the registration roller pair 470. Then, when the leading edge of the toner image on the intermediate transfer belt 426 approaches the secondary transfer counter roller 446, the registration roller pair 470 is driven so that the leading edge of the sheet exactly coincides with the leading edge of the image. Is done.

In this manner, the sheet is overlapped with the intermediate transfer belt 426 and passes under the secondary transfer counter roller 446 to which a voltage having the same polarity as the toner is applied. At this time, the toner image is transferred to the paper. Subsequently, the sheet is neutralized, peeled off from the intermediate transfer belt 426, and moved to the sheet conveying belt 472.
The sheet onto which the four-color superimposed toner images have been collectively transferred from the intermediate transfer belt 426 is conveyed to the belt fixing type fixing device 470 by the paper conveying belt 472, and the toner image is fixed by the fixing device 470 by heat and pressure. The sheet that has been fixed is discharged out of the apparatus by the discharge roller pair 480 and stacked on a tray (not shown). Thereby, a full color copy is obtained.
In this example, the detection target surface is the intermediate transfer belt 426 as a transfer body, but the photosensitive drum 402 may be the detection target surface. In this case, the P sensor 40 is provided to face the photosensitive drum 402.

In each of the above examples, the processing is based on the minimum value of the ratio between the specular reflection light output and the diffuse reflection light output, but the regular reflection light output increment obtained from the difference from each output value when the light emitting means is off and A similar detection function can be obtained as a method of processing based on the minimum value of the ratio to the diffuse reflection light output increment.
In each of the above examples, the image forming apparatus is exemplified as the powder adhesion amount detection device. However, the same detection function can be obtained by the same processing method in the field of adhesion amount detection that handles powder other than toner.

The effects obtained in the above examples will be described below.
In the prior art, as described above, the color adhesion amount detectable range is gradually narrowed due to the decrease in glossiness of the detection target surface over time, and wear deterioration of the detection target surface over time becomes the rate-determining factor of the life. However, by performing the conversion process as described above, compared with the conventional regular reflection light detection, the adhesion amount detection range is expanded, and accurate adhesion amount detection can be performed without depending on the glossiness. .
In each of the above examples, the life of the detection target surface can be extended because it does not depend on the wear deterioration of the detection target surface.
A belt with low glossiness, which is said to be difficult to detect density in the prior art, by applying the regular reflection light output conversion algorithm to the detection of the amount of adhesion with the image carrier or transfer body as the detection target surface in a color image forming apparatus. The amount of adhesion can be converted without any problem even on the surface to be detected, and the concentration control can be performed based on the converted amount of adhesion.

Further, by performing the above conversion process, the diffuse reflected light output can be converted to a value that can obtain a linear relationship with the adhesion amount in the low adhesion amount range from zero adhesion amount to powder single layer formation.
In addition, by performing the above conversion process (automatic correction function of diffused light output sensitivity), the diffused light output variation (hardware side) due to the output variation of the light emitting element and the light receiving element of the density detection sensor is converted into an adhesion amount conversion algorithm. Adjustment is possible on the sensor side (software side), so adjustment work on the sensor side (hardware side) at the time of sensor shipment inspection as previously done is unnecessary, or the adjustment range can be greatly expanded. It becomes.
By the way, in the diffuse reflection type sensor that the applicant of the present invention has mounted on the conventional machine, the output adjustment time is nearly 2 minutes per sensor, but as a result of wide tolerance range, it is less than 10 seconds. It became possible to adjust.
Thereby, the productivity in sensor manufacturing can be dramatically improved, and the cost of the sensor can be reduced, and hence the cost of the image forming apparatus can be reduced.

In addition, even with the decrease in the amount of LED light over time of the density detection sensor and the output fluctuation due to the temperature characteristics of the light emitting element and the light receiving element, an automatic correction function of the diffuse reflected light output sensitivity always performs stable adhesion amount conversion. Can do.
In the prior art, sensitivity calibration is difficult with a sensor (type (B)) having only diffuse reflected light output, and accurate sensitivity calibration and adhesion amount detection can be performed even when the detection target surface is black. .
In addition, in the past, in the case of a sensor (types (C) and (D)) using both regular reflection light output and diffuse reflection light output type, the accuracy of detecting the amount of adhesion decreases with time due to characteristic changes due to deterioration over time of the detection target surface. However, the automatic correction function of the diffuse reflected light output sensitivity allows the algorithm side (software side) to absorb changes in the characteristics of the detection target surface over time. Even if it is very low, the diffuse reflected light output can be accurately converted into an adhesion amount regardless of the glossiness, and even in the case of black, over a high adhesion amount region. As a result, the life of the detection target surface can be extended, and the running cost can be reduced.
By applying the diffuse reflected light output conversion algorithm to the detection of the amount of adhesion using the image carrier or transfer body as the detection target surface in a color image forming apparatus, the glossiness is low, which is said to be difficult to detect density in the prior art. Even if it is a belt, or even if the detection target surface is a black belt, it is possible to detect the amount of adhesion with high accuracy up to a high adhesion amount region without any problem. As a result, the solid adhesion amount that is the maximum adhesion amount target value can be detected, and stable image density control can always be performed regardless of environmental changes over time.

In addition, the life of an image carrier such as a photoconductor or a transfer belt which is a detection target surface can be extended. The detection target surface, such as a transfer belt, is generally united with the developing device, etc., and a method of batch replacement is adopted, but early batch replacement is performed because of the deterioration in detection accuracy due to deterioration of the detection target surface only over time. Therefore, the running cost can be greatly reduced in relation to other unit parts that have not reached the end of their service life.
By having at least one, preferably three or more adhesion amount patterns (the number of adhesion amount patches) in the vicinity of the adhesion amount at which the minimum value of the ratio between the specular reflection light output and the diffuse reflection light output is obtained. Therefore, it is possible to convert the amount of adhesion with higher accuracy.
Further, at least one, preferably three, in the vicinity of the amount of adhesion at which the minimum value of the ratio between the specular reflection light output increment and the diffuse reflection light output increment obtained from the difference from each output value when the light emitting means is off is obtained. By having the above adhesion amount pattern, it is possible to convert the adhesion amount with higher accuracy.
In addition, the specular reflection light output conversion value has at least one, preferably three or more adhesion amount patterns within the adhesion amount range having a linear relationship with the adhesion amount, thereby achieving higher accuracy. Adhesion amount conversion is possible.

The gist of the embodiment of the present invention will be described below.
First, the case where the above-described adhesion amount conversion algorithm is actually applied to a color image forming apparatus will be considered in detail.
In the above-described conversion algorithm, the sensitivity (sensitivity correction coefficients: α, γ) on the diffuse reflection output side of the sensor from the two-dimensional data array of specular reflection light and diffuse reflection output of each patch when the gradation pattern is detected. ) Is calculated.
Among these sensitivity corrections, the calculation of the sensitivity correction coefficient γ shown in Step 6 is particularly important. Therefore, the more data points used for this approximate calculation, the more accurately the sensitivity correction (calibration) can be performed.
However, on the other hand, increasing the number of data points within this adhesion amount range (x range 0 ≦ x ≦ 0.3 used in the calculation) is nothing but increasing the number of gradation patterns, and adjusting the image quality. This means that the time is increased and the amount of toner consumed for image quality adjustment is increased, which is not desirable.

Therefore, a method is considered that can ensure sufficient accuracy for sensitivity correction (calibration) and can shorten the image quality adjustment time.
FIG. 35 is a layout diagram when a gradation pattern of all colors of CMYK is detected by a single optical detection means (P sensor 40).
The gradation pattern 71 includes a K pattern 71A as an achromatic gradation pattern, and an M pattern 71B, C pattern 71C, and Y pattern 71D as chromatic gradation patterns, and 1 as a whole in the traveling direction of the transfer belt 18. Formed in rows.
In this way, when the gradation pattern of all colors is to be detected by one sensor, the number of sensors is only one, but since the total length of the pattern becomes long, it takes a total processing time from the start to the end of image quality adjustment. , Machine downtime will be longer.

In order to shorten the image quality adjustment time as much as possible, as shown in FIG. 36, all gradation patterns of all colors are arranged in parallel, and optical detection means (40A, 40B, 40C, 40D) are arranged for each color. The method is considered the most efficient (first embodiment).
However, in this case, that is, when a plurality of chromatic colors are detected by different sensors, an error may occur in the control density (image density, toner density) of each color by the detection error for each sensor. High nature.
In the case of chromatic color toners (CMY toners) that produce the final image color by color superposition, the error of each color is a shift in color tone (color tone) with respect to the original image. It is desirable to detect.

Here, consider each color toner to be detected and the spectral characteristics of the optical detection means for detecting the toner.
FIG. 38 shows the spectral characteristics on the light emission side of the P sensor 40 as an optical detection means, FIG. 39 shows the spectral characteristics on the light receiving element side, and FIG. 40 shows the spectral characteristic data of each color toner to be detected. .
When detection is performed using an element having peak sensitivity in the wavelength region in which the light reflection characteristics of the toner to be detected are substantially equal on the light emitting side and the light receiving side, that is, in the infrared region of 800 um or more, as the optical detection means CMY toners, which are chromatic color toners, do not distinguish between colors that are seen with so-called visible light when viewed from the optical detection means.

That is, when a plurality of chromatic color gradation patterns, that is, CMY toner gradation patterns are detected by a single sensor having a peak wavelength in infrared light, each patch detection output (regular reflection light output) of the gradation pattern is used. , Diffuse reflected light output) can be handled as one two-dimensional data array, and if these are simultaneously detected by one sensor, it is necessary for calculating the sensitivity correction coefficient γ described in Step 6 and FIGS. 27 and 28. The number of data points (the range of x used for calculation 0 ≦ x ≦ 0.3) means that there are data points for three colors.
Therefore, if three chromatic color toners are detected by one optical detection means, the number of patterns can be reduced, so that the amount of wasted toner consumed for image quality adjustment can be minimized. It becomes.

In consideration of these points, the maximum reduction in image quality adjustment time is considered, the color tone error with respect to the original due to sensitivity correction (calibration) errors is minimized, and unnecessary consumption of toner used for image quality adjustment is minimized. FIG. 37 shows a layout of gradation pattern detection according to the second embodiment of the present invention.
In this embodiment, the black toner (K) gradation pattern 71A and the color toner (CMY) gradation patterns 71B, 71C, and 71D are formed in parallel in the traveling direction of the transfer belt 18, and each of these colors is formed. Black toner detection (achromatic color gradation pattern detection) P sensor 40A and color toner detection (chromatic color gradation pattern detection) P sensor 40E are arranged at positions where the pattern can be detected. In the P sensor 40E, the peak emission wavelength λp on the light emission side is 800 μm or more, and the peak spectral sensitivity wavelength λp on the light reception side is 800 μm or more.
With this combination, the reduction in image quality adjustment time is taken into consideration as much as possible, the color tone error from the original due to sensitivity correction (calibration) errors is minimized, and wasteful consumption of toner used for image quality adjustment is minimized. It becomes possible to suppress.

  When the sensor configuration in this embodiment, that is, the optical detection means is divided into two for detecting a chromatic color gradation pattern and for detecting an achromatic color gradation pattern, almost all diffused light from the gradation pattern is obtained. For the achromatic color black toner detection means (P sensor 40A), since it is not necessary to provide a diffuse reflected light output, type A can be used, and a sensor element configuration corresponding to each light reflection characteristic and By doing so, the cost can be reduced.

In the case of the sensor configuration in the present embodiment, the purpose of shortening the image quality adjustment time can be achieved by performing parallel processing of pattern creation to detection to termination. In addition, the creation and termination of the achromatic pattern may be performed.
In FIG. 37, an achromatic color (K) gradation pattern is formed in advance with respect to a chromatic color (CMY) gradation pattern on the transfer belt 18, but this is a quadruple tandem device and is a black station. This is because the black pattern is transferred ahead of the M pattern by an inter-drum pitch on the transfer belt 18 as a result of simultaneously forming the KM pattern on the photosensitive member.

Next, consider further reducing the number of chromatic gradation patterns.
When the development ability control target value and the toner adhesion amount control target value of all chromatic color toners are the same, the write value levels of these gradation patterns are shown in Table 2 if the image density control is performed as intended. In this case, the data values used when calculating the sensitivity correction coefficient γ substantially overlap each other as shown in FIG.

When it is desired to obtain the sensitivity correction coefficient γ with high accuracy, the data is evenly distributed in the predetermined data section, in the present embodiment, in the range of 0 ≦ x ≦ 0.3. It is desirable that they are dispersed.
For this purpose, it is desirable that the LD writing value level when writing the gradation pattern is different for each color as shown in Table 3.

FIG. 42 shows a graph corresponding to FIG. 41 when the LD writing value level is changed for each color.
In this way, by changing the writing value level of the gradation pattern for each color, the data points used for the calculation of the sensitivity correction coefficient γ can be appropriately dispersed within the data section used for the calculation. I want.
If the data values are dispersed in this way, as shown in FIG. 42, the approximate straight line can be calculated accurately even if there are not nine data points in total for each of the three colors, thereby reducing the number of patterns. It becomes possible.
That is, the number of gradation patterns can be reduced, the image quality adjustment time can be shortened, and the amount of toner consumed for image quality adjustment can be reduced.

  As described above, since three color chromatic color toners can be processed simultaneously, the number of patterns can be reduced. However, for black toner, chromatic color gradation patterns and achromatic colors are used as they are. The number of patterns may be different depending on the gradation pattern.

If the present invention is applied to a quadruple tandem image forming apparatus, chromatic and achromatic gradation patterns can be created simultaneously. In addition, the image quality adjustment time can be shortened.
In the above embodiment, the image quality adjustment time shortening function of the present invention and the adhesion amount conversion algorithm of the present invention are implemented at the same time. However, the regular reflection light output voltage of the gradation pattern and the diffuse reflection light output voltage of 2 are used. In a general image forming apparatus that performs sensitivity correction (calibration) of the optical detection means based on the dimensional array data and obtains the adhesion amount or the image density, only the image quality adjustment time shortening function of the present invention is added. An effect corresponding to this can be obtained.

1 is a schematic front view of a color laser printer as an image forming apparatus according to an embodiment of the present invention. It is a block diagram of the optical detection means of the type which detects only regular reflection light. It is a block diagram of the optical detection means of the type which detects only diffuse reflection light. It is a block diagram of the optical detection means of the type which detects a regular reflection light and diffuse reflection light simultaneously. FIG. 5 is a configuration diagram of an optical detection means using a beam splitter, which is a type that detects specular reflection light and diffuse reflection light simultaneously. It is a graph which shows the detection result of the regular reflection light output with respect to color toner adhesion amount, and a diffuse reflection light output. 6 is a graph showing a relationship between a color toner adhesion amount and a difference between specular reflection light. It is a schematic diagram which shows the reflection state of irradiation light in case the mirror surface glossiness of a detection target surface is high. FIG. 6 is a schematic diagram illustrating a reflection state of irradiation light when toner is attached and the specular glossiness of a detection target surface is decreased. It is a graph which shows the regular reflection light output characteristic with respect to the black toner adhesion amount. It is a graph which shows the regular reflection light output characteristic with respect to the color toner adhesion amount. It is a graph which shows the diffuse reflected light output characteristic with respect to black toner adhesion amount. It is a graph which shows the diffuse reflected light output characteristic with respect to the color toner adhesion amount. It is a graph which shows the regular reflection light output characteristic with respect to the mirror surface glossiness of a detection target surface. It is a graph which shows the diffuse reflected light output characteristic with respect to the brightness of a detection target surface. It is a graph which shows the relationship between the fall of the glossiness of a detection target surface with time, and correction | amendment of a regular reflection light output. It is a graph which shows the relationship between the color toner adhesion amount and the difference of regular reflection light in the fall of the glossiness with time of a detection object surface. It is a top view which shows a gradation pattern. Indicates that the light received by the specular reflection light receiving element as specular reflection light includes a diffuse reflection light component from the detection target surface and a diffuse reflection light component from the toner layer in addition to a pure specular reflection light component. It is a schematic diagram. It is a block diagram which shows the relationship between the reflected light component which should be actually detected by the optical detection means, and the reflected light component which should be removed. It is a graph which shows the relationship between the adhesion amount at the time of data sampling, and a detection output. It is a graph which shows the relationship between the sensitivity correction coefficient multiplied by a diffuse reflection light output, the adhesion amount, and a detection output. It is a graph which shows component decomposition | disassembly of regular reflection light. It is a graph which shows normalization of the regular reflection component of a regular reflection light output. It is a graph which shows the relationship between the surface part fluctuation | variation correction amount of a diffuse reflected light output, the adhesion amount, and a detection output. It is a schematic diagram which shows that a some component exists also in the component reflected from a belt background part. It is a graph which shows the relationship between the normalization value of a regular reflection component, and the diffuse reflected light output after background part fluctuation | variation correction | amendment. It is a graph which shows the sensitivity of a diffuse reflected light output. It is a graph which shows the conversion result to a normalized value. It is a graph which shows the result of having plotted the adhesion amount obtained by carrying out reverse conversion of the normalization value with respect to the adhesion amount measurement value by an electronic balance. It is a graph which shows the relationship between the lot dispersion | variation in the optical detection means extracted from many prototypes, and the diffuse reflected light output in a gradation pattern detection. It is a graph which shows the relationship between the lot dispersion | variation of the optical detection means extracted from many prototypes, and the diffuse reflected light output after the sensitivity correction | amendment in gradation pattern detection. FIG. 2 is a schematic front view of a color image forming apparatus of a system in which the images are transferred onto a transfer sheet after being transferred onto an intermediate transfer member in a quadruple tandem configuration. 1 is a schematic front view of a color image forming apparatus of a type in which each toner image is transferred onto an intermediate transfer member by one photosensitive drum, and then transferred onto a transfer sheet at a time. FIG. 5 is a layout diagram in the case where a single optical detection unit detects a single row of gradation patterns of CMYK colors. FIG. 5 is a diagram illustrating the first embodiment, and is a layout diagram in the case where all gradation patterns of all colors are arranged in parallel and an optical detection unit is arranged for each color. It is a figure which shows 2nd Embodiment, and is a layout figure in the case of arrange | positioning an achromatic color gradation pattern and a chromatic color gradation pattern in parallel, and arrange | positioning an optical detection means for every pattern. It is a graph which shows the spectral characteristic of the light emission side of an optical detection means. It is a graph which shows the spectral characteristic of the light-receiving side of an optical detection means. It is a graph which shows the spectral characteristic data of each color toner. It is a graph which shows the sensitivity of a diffuse reflected light output. It is a graph which shows the sensitivity of a diffuse reflected light output.

Explanation of symbols

14Y, 14M, 14C, 14B Photosensitive drum as image carrier 18 Transfer belt as detection target surface 51 LED as light emitting means
52 Regular Reflected Light Receiving Element as Light Receiving Means 55 Diffuse Reflected Light Receiving Element as Light Receiving Means 70, 71 Gradation Pattern 71A Achromatic Gradation Pattern 71B, 71C, 71D Chromatic Color Gradation Pattern

Claims (5)

Regularly reflected light that has a light-emitting element and a light-receiving element and is arranged at a position facing the detection target surface, and a gradation pattern with different adhesion amounts formed on the detection target surface and a plurality of continuous detection target surfaces. Sensitivity correction of the optical detection means based on the two-dimensional array data of the regular reflection light output voltage and the diffuse reflection light output voltage of the gradation pattern obtained as a result of detection by the optical detection means capable of simultaneously detecting diffuse reflection light In an image forming apparatus that performs (calibration) and calculates an adhesion amount or an image density,
Sensitivity correction of the optical detection means is based on specular reflection light output and diffuse reflection light output obtained in a low adhesion amount region in which specular reflection light has sensitivity and toner adhesion amount is zero to one layer formation,
The minimum value of the ratio between the specular reflection light output and the diffuse reflection light output is obtained, and this value is multiplied by the diffuse reflection light output to obtain the diffuse reflection light component of the specular reflection light output. The diffuse reflection light component is obtained from the specular reflection light output. By subtracting it into a regular reflection light component of the regular reflection light output , the regular reflection light output is decomposed into a diffuse reflection light component and a regular reflection light component, and only the regular reflection light component is extracted, and this is the detection target. It is converted into a normalized value as an exposure rate of the background portion divided by the value of the specularly reflected light component when the toner adhesion amount on the surface of the surface is zero, and has a linear relationship with the toner adhesion amount. Based on the above normalized value,
Diffusion reflection light output−background portion output × normalization value in the low adhesion amount region obtained by obtaining the diffuse reflection light output value after the background portion variation correction and plotting it against the normalization value Based on the first-order linear relationship between the value and the diffuse reflection output value after the background fluctuation correction, a diffuse reflection output value after the background fluctuation correction corresponding to a certain normalized value is obtained from the slope of the straight line. Is calculated by converting the diffuse reflected light output value after the background fluctuation correction to a value uniquely determined in relation to the toner adhesion amount. ,
The gradation pattern is divided into two columns of a chromatic gradation pattern and an achromatic gradation pattern formed for each of a plurality of colors, and the optical detection means is for detecting a chromatic gradation pattern and an achromatic color scale. Independently configured and juxtaposed to the two for key pattern detection,
Of the two optical detection means described above, the optical detection means for detecting a chromatic gradation pattern has a peak emission wavelength λp on the light emission side of 800 nm or more and a peak spectral sensitivity wavelength λp on the light reception side of 800 nm or more. Yes,
The plotted data used for the calculation of the sensitivity correction by varying the pattern writing value level by the light writing unit of the gradation pattern of each color detected by the optical detection means for detecting the chromatic color gradation pattern for each color An image forming apparatus that distributes values. The image forming apparatus according to claim 1.
Of the two optical detection means, the optical detection means for detecting a chromatic color gradation pattern has a configuration capable of simultaneously detecting two outputs of regular reflection light and diffuse reflection light. An image forming apparatus characterized in that the optical detection means is configured to detect only a regular reflection light output. The image forming apparatus according to claim 1 or 2,
Of the chromatic color gradation pattern and achromatic color gradation pattern created in parallel in the image formation direction, the chromatic color gradation pattern composed of multiple colors is used from the start to the end of the creation of the achromatic color gradation pattern. An image forming apparatus, which is performed between the start and end of creation. The image forming apparatus according to any one of claims 1 to 3,
A plurality of image carriers and a toner image formed on each image carrier are sequentially transferred onto an intermediate transfer member and then transferred onto a sheet-like recording medium to obtain a color image. An image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus having a configuration for obtaining a color image by sequentially superimposing and transferring toner images formed on a plurality of image carriers on a sheet-like recording medium supported on a transfer member .

Images