KR940003119B1 - Circuit and method for adjusting automatic exposure - Google Patents

Abstract

The machine optimally senses the back ground density to regulate the exposure of paper and gets the stable image by regulating the lighting voltage automatically. The method has the adventage of saving power and preventing the error of density sensing. The method includes a paper density sensing means which senses the paper density, a level specifying means which outputs the specified paper density voltage, a reference voltage generating means which generates the reference voltage, a rectangular pulse outputting means which outputs the rectangular pulse and a CPU (50) which controls the lighting voltage according to the paper density.

Description

Automatic Exposure Control Circuit and Method of Electronic Copier

1 is a conventional exposure voltage control circuit diagram.

2 is an automatic exposure control circuit diagram according to the present invention.

3 is an operation waveform diagram of each part of FIG.

4 is a state diagram at the time of automatic exposure adjustment according to the present invention.

5 is an operation flowchart of an automatic exposure control mode according to the present invention.

* Explanation of symbols for main parts of the drawings

10: Photointerrupter 20: Back reference voltage generator

30: reference voltage generator 40: comparator

50: CPU

The present invention relates to an automatic exposure control circuit of an electronic copying machine, and more particularly, to an automatic exposure control circuit and a method for automatically adjusting the exposure amount by detecting a background density of an original.

FIG. 1 is a conventional exposure amount control circuit diagram. A photodiode 1 which is attached near a lens to receive an average amount of light in an effective area in one line and outputs a current Ip corresponding to the amount of light, and the photocurrent Ip and The output of the first amplifier AMP1 is amplified by the amplification degree formed by the combination of the first amplifier AMP1 converting the current into a voltage by the resistor R6, the resistors R3-R4, and the variable resistor Rvr. Digital data of an integrated circuit comprising a second amplifier (AMP2), a resistor (R2) and a capacitor (C1) for charging and reading the maximum value of the output of the second amplifier (AMP2) and the output of the integral circuit. It consists of an A / D converter 2 for converting the data and a CPU 3 for receiving data from the converter 2 in series or in parallel and recognizing the value at that time.

The difference between the reference white tape at the bottom of the platen sheet and the lightest part of the document is detected, and an appropriate exposure position is selected to perform autoexposure (AE). At this time, the photocurrent Ip output from the photodiode 1 is converted into a voltage (ie, V1 = Ip · R6) by the combination of the resistor R6 in the first amplifier AMP.

Since this voltage is a small value, it is amplified by the second amplifier AMP2, and the amplified voltage value V2 is as follows.

The amplification voltage V2 of the second amplifier AM2 is converted into digital data by the A / D converter 2 through an integrated circuit composed of a resistor R2 and a capacitor C1, and is serially or in parallel with the CPU ( It is input to the port of 3). The CPU 3 recognizes and judges this input value and adjusts the exposure amount according to the original background density at that time.

Thus, the conventional circuit as shown in FIG. 1 requires a lens for efficiently condensing light from the photodiode, and when the amplifier stage is mounted on the control board and the output of the photodiode is connected to the board through a wire, the output level is increased. If the noise is loaded because it is a small value, the result of amplifying the noise, rather than the output corresponding to the actual amount of reflected light, results in amplification of the AE function. Since the output is an analog signal, the CPU requires an A / D converter to recognize it. Also, if the light amount of the exposure lamp changes, accurate output from the photodiode cannot be expected.

In addition, the amplification degree has to be adjusted in accordance with the maximum amount of light incident on the photodiode. This is because if the output becomes saturated above the TTL level, the CPU cannot recognize the correct level.

It is therefore an object of the present invention to provide an automatic exposure control circuit and method for automatically adjusting the exposure amount in response to the background density of an original in an electronic copying machine.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is an automatic exposure control circuit diagram according to the present invention, and includes a reflective photo interrupt (10) consisting of a light emitting element (LED) and a light receiving element (PT1) attached to a mirror to detect a background density of a specified area of an original; A variable resistor for adjusting the current of the light emitting device (LED) in order to improve the sensitivity characteristics of the transistor (TR), the light receiving device (PT1) in accordance with the driving of the light receiving device (PT1) of the reflective photo interrupt 10. (VR1), the variable resistor (VR2) for adjusting the black level voltage (V _H ), the white reference voltage generator 20 for generating a reference voltage (V _L ) of the back level, and the data corresponding to the exposure detection density A reference pulse generator 30 for generating a reference pulse Vr for reading in multiple stages, an exposure concentration detection signal V _O and a reference voltage Vf controlled by the variable resistor VR2. Comparator 4 for inputting and converting into square wave pulses; And a CPU 50 for inputting a square wave pulse output from 0) to calculate the original density.

3 is an operation waveform diagram of each part according to the present invention, FIG. 4 is an operation state diagram at the time of automatic labor adjustment, and FIG. 5 is a flowchart of the automatic exposure operation mode according to the present invention.

Based on the above-described configuration, an embodiment of the present invention will be described in detail with reference to FIGS.

Since the light emitted from the photointerrupter 10 LED is reflected from the original surface and supplied to the light receiving element PT1, the light receiving element PT1 controls the operating point of the transistor TR according to the contrast of the original surface. . The original surface is if the black portion the original surface into the V _L is the white part is the output is a value close to the side V _H. At this time, the output voltage V _O as shown in FIG. 3a adjusted by the variable resistor VR2 is applied to the resistor R1 and the variable resistor VR2 based on the back level reference voltage applied from the back reference voltage generator 20. It is determined by the voltage distributed by and the voltage according to the operation of the transistor TR.

Here, VR2 is for adjusting the black level voltage V _H. At this time, the reason why the signal is output between the white level (V _L ) and the black level (V _H ) is to set the range having the optimum sensitivity for accurate concentration detection. The signal adjusted by the variable resistor VR2 is output as V _{0 of} FIG. 3a according to the background concentration and is supplied to the non-inverting input terminal (+) of the comparator 40. The comparator 40 outputs a square wave signal such as Po of FIG. 3b in comparison with the voltage level of the reference voltage Vf supplied to the inverting input terminal (−). Here, the reference voltage Vf outputs a pulse in the range of V _L to V _H by the divided voltage of the resistors R5 and R6. Since the Po output from the comparator 40 is input to the port A of the CPU 50, the CPU 50 reads the input value n times for a predetermined time (t = t1 + t2). By counting the number of 1 ", it becomes possible to obtain the average concentration in the time t in n steps. That is, if the number of times of "1" read 256 times is 128, then the concentration voltage (Vs) at that time is

Becomes

At this time, the speed of reading n times from the CPU 50 and the period of the reference voltage Vf may be set the same. However, the means of movement in the sub-scanning direction should be shorter than the speed of the motor moving in one line.

In addition, the CPU 50 allows the same circuit as the port A to be applied to the port B. FIG.

The reason for this is that if only one reflective port interrupt 10 is provided, the original may be lifted, or if only the black portion exists in the portion, the image may be degraded due to the misconductivity detection. Therefore, the position of the reflective photo interrupt 10 should be placed as close to the original surface as possible without blocking the optical path.

Therefore, two reflective photo interrupts 10 are provided at a predetermined position, and the background density detection of one odd line of originals and the detection of density of even lines of another are performed as shown in FIG. To determine the correct document density.

Referring to the operation of calculating the density of the original by inputting the square wave signal output from the comparator 40 in the flowchart of FIG. 5, the CPU 50 first starts the automatic exposure (AE) operation mode in step 5a. If it is not in the AE operation mode (step 5b), the copy key) is pressed and the normal mode operation is performed.

However, if it is the AE operation mode in step (5a), it goes to the standby state until the COPY KEY is pressed in step (5c).

In step 5c, the COPY KEY is pressed and at the same time, in step 5d, the home key is moved from the home position to the start line. The reason is that detection of the part is omitted in order to prevent detection error near the tip. In step (5e), one line is advanced from the start line, and in step (5f), the first line is checked to determine whether it is the first line (5g). In the step (5g), the CPU 50 reads the original density value of the advanced one line (odd line) from the port A in step 5h in step 5h, and the value is " 1 " in step 5i. Count and remember the number of times. In step (5i), the CPU 50 reads the document density value from the port B in the step (5l) n times in step (5l) in step (5m). The number (T times) of the lines having the smallest number of 1 "is compared and converted to the voltage value corresponding thereto in step (50).

Where the voltage conversion value to be.

The reason for selecting the minimum number at this time is that the background density of the original is closer to the back level (V _L ) than the portion where the image exists, so the minimum number is considered to be close to the original background density.

In step 5P, the difference (ΔV = Vr-Vs) from the white voltage level V _L of the copier reference sheet is detected, and in step 5g, the exposure voltage and the bias voltage corresponding to this ΔV are adjusted. do. In step 5r, the process returns to the home position, and in step 5t, the copy operation corresponding to the background density of the original is performed.

Here, the first line can be arbitrarily set, but it can be limited to a portion in which an image does not exist in a normal document.

As described above, after adjusting the black level and the white level of the original in the electronic copying machine, the optimum background density is detected and the exposure voltage is automatically adjusted to obtain a stable image, and a lens for condensing light is unnecessary, and the background density is detected. Since the concentration can be detected without turning on the exposure lamp for a period of time, there is an advantage in that the density detection error due to power consumption and exposure lamp light intensity instability can be prevented.

Claims (4)

In the automatic exposure control circuit of an electronic copying machine, an original density detection means for detecting an original density, and a black level (V _H ) and a white level (V _L ) of an original density detected by the original density detection means are adjusted to be optimal. Level setting means for outputting an original density voltage set to a sensitivity level, reference voltage generating means for generating a reference voltage to read the original density in multiple stages, original density voltage set to an optimum sensitivity level in the level setting means; Controlling the exposure voltage according to the original density by inputting the square wave pulse output means for outputting the square wave pulse for discriminating the original density by comparing the reference voltage generated by the reference voltage generating means, and the square wave pulse of the square wave pulse output stage Automatic exposure control circuit, characterized in that consisting of a CPU (50). The automatic exposure control circuit according to claim 1, wherein the document density detecting means comprises two port interrupts. 3. The automatic exposure control circuit according to claim 2, wherein the two photo interrupters detect the original and even line original concentrations of odd lines, respectively. In the automatic exposure control method of the electronic multiplier, the process of reading the original density detection signal by a predetermined number (n) within a predetermined time to calculate the average concentration, and converting the average concentration calculated in the average concentration calculation process to a voltage Detecting an exposure voltage adjustment value by detecting a difference ΔV from the white voltage Vr, and returning to the home position by adjusting the exposure voltage with the exposure adjustment value detected in the exposure adjustment value detection process. Automatic exposure control method characterized in that.