CN111077749B

CN111077749B - Image forming apparatus and method for monitoring photoreceptor lifetime

Info

Publication number: CN111077749B
Application number: CN201910976674.8A
Authority: CN
Inventors: 稻田保幸
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 2018-10-19
Filing date: 2019-10-15
Publication date: 2022-06-28
Anticipated expiration: 2039-10-15
Also published as: CN111077749A; JP2020064237A; JP7124629B2

Abstract

The invention provides an image forming apparatus and a method for monitoring the service life of a photoreceptor. The electrostatic latent image in the non-image area is formed on a photoreceptor, and is developed with toner of negative polarity by a developing bias Vb2 having a larger AC component Vpp' than a developing bias Vb1 in a normal state. When the resistance value of the portion of the overcoat layer where the metal filler is dense is lowered and the development bias Vb2 is applied, a larger positive charge is supplied to the photoreceptor by the voltage δ 2 having a larger positive component than that in the normal case. By supplying the positive charge, the photoreceptor potential at the portion where the resistance value is reduced is lower in absolute value than at the portion where the resistance value is high. This makes it possible to develop a fog toner image, which does not appear during normal printing, on the portion of the photoreceptor having a reduced resistance value. Since the gray tone image does not appear when the overcoat layer is worn away, the thickness of the overcoat layer can be monitored by determining whether the gray tone image appears.

Description

Image forming apparatus and method for monitoring photoreceptor lifetime

Technical Field

The present invention relates to an image forming apparatus that performs image formation by an electrophotographic method, such as a copying machine, a printer, and a facsimile machine, and more particularly to a technique for detecting the thickness of an overcoat layer formed on the outermost layer of the surface of a photoreceptor.

Background

In recent years, image forming apparatuses are required to be compact and low-cost, and image forming performance at higher speed and higher image quality is required. Further, since a long life is required, a layer for protecting the photosensitive layer as an underlayer of the overcoat layer is formed on the outermost layer of the photoreceptor.

However, when the thickness of the overcoat layer is large, the charge of the peripheral portion of the latent image is increased, and therefore, the toner is also adsorbed to the peripheral portion in the transfer step, resulting in a defect of coarsening of the image and lack of sharpness.

Therefore, the overcoat layer needs to be as thin as possible, but if it is too thin, the margin for reduction is small, and the life of the photoreceptor is shortened.

In order to solve the contradiction between the reduction in thickness and the life, a hard material is currently used as an overcoat layer, and the reduction is difficult and the reduction in thickness is achieved, thereby solving the contradiction.

However, when the overcoat layer is made hard and thin, a new problem occurs. Even if the overcoat layer is hard, the film thickness becomes thin and the protective function for the lower layer is lowered when repeated image formation is performed for a long time, and therefore, the film thickness must be monitored.

For example, patent document 1 discloses a technique for detecting the progress of film cutting of a photoreceptor. Patent document 2 focuses on the change in the sensitivity characteristic of the potential of the photoreceptor due to the film reduction, and discloses a technique for detecting the progress of the film reduction of the photoreceptor in accordance with the change in the density of the toner image on the photoreceptor.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2014-016651

Patent document 2: japanese patent laid-open publication No. 2015-166820

Disclosure of Invention

In the above-described conventional technique, for example, when the thickness of the photoreceptor changes by 10 μm, the amount of current change of the charging roller is about 500 to 1000 μ a, and the thickness of the outermost layer of the photoreceptor of high hardness currently used is not more than several μm at most, and even if the entire thickness is reduced, the amount of current change is not as large as several hundred μ a, which is merely a change in the degree of measurement variation.

Even if the film thickness is monitored according to the image density, the density hardly changes even when the thickness changes by about several μm, which is not practical. Therefore, in the conventional technique, it is impossible to monitor the film thickness.

Further, a method of estimating a reduction amount from the number of revolutions of the photoreceptor, the number of printed sheets, the use time, the accumulated time, and the like, and establishing a flag indicating the end of the life when the predetermined number is reached has been studied, but there is a possibility that the flag is established despite the fact that there is some redundancy that can be used, or the flag is not established despite the end of the life, because the deviation of physical properties or mounting of the photoreceptor, the cleaning member, and the like, or the change of the state of energization from the charging member or the transfer member is ignored, and it is not practical.

The present invention has been made based on the findings of the inventors described below, and has proposed a technique capable of monitoring the thickness of an overcoat layer of a thin film that has not been monitored by the conventional technique.

Means for solving the problems

In order to achieve the above object, an image forming apparatus according to the present invention is an image forming apparatus that performs image formation by an electrophotographic method, the image forming apparatus including: a photoreceptor having an overcoat layer containing a metal filler formed on the outermost layer; a charging mechanism for charging the photoreceptor with a 1 st polarity; an exposure mechanism that exposes the charged photoreceptor to form an electrostatic latent image on the photoreceptor; a developer carrying body that carries a developer containing a 1 st polarity toner; a bias power supply mechanism that is switchable between a 1 st developing bias for developing an electrostatic latent image formed during image formation and a 2 nd developing bias used during life monitoring of the photoreceptor, as developing biases to be supplied to the developer carrier, and injects charges of a 2 nd polarity, which is opposite to the 1 st polarity, into the photoreceptor in a larger amount than the 1 st developing bias; a control unit configured to control the charging unit and the exposure unit to charge the photoreceptor and inhibit exposure when a lifetime monitoring period of the photoreceptor is reached, thereby forming an electrostatic latent image corresponding to a non-image on the photoreceptor, and to control the bias power supply unit to execute a lifetime monitoring mode in which the 2 nd developing bias is supplied to the developer carrier; a determination unit configured to determine whether or not a toner image is formed on the photoreceptor due to non-uniformity in the dispersion state of the metal filler by executing the lifetime monitoring mode; and a broadcasting means for broadcasting that the film thickness of the overcoat layer of the photoreceptor is reduced by a predetermined film thickness if it is determined that the toner image is not formed.

Further, it may be configured such that an alternating current component is superimposed on a direct current component of the 1 st polarity in the 1 st developing bias and the 2 nd developing bias, and the peak-to-peak voltage of the alternating current component is set to a larger value or the frequency of the alternating current component is set to a smaller value in the 2 nd developing bias than in the 1 st developing bias.

Further, in the 1 st developing bias and the 2 nd developing bias, when an alternating current is superimposed on the dc component of the 1 st polarity, and a side having a peak voltage of the 2 nd polarity is defined as an alternating current component α, a side having the 1 st polarity is defined as an alternating current component β, and a value obtained by dividing a time T β of the alternating current component β by 1 cycle is defined as a duty Dh, a waveform of 1 cycle of the alternating current is defined as a voltage value of the superimposed dc component of the 1 st polarity, an absolute value Vn of a peak voltage of the alternating current component β in the 2 nd developing bias may be the same as that of the 1 st developing bias, an absolute value Vm of a peak voltage of the alternating current component α may be larger than that of the 1 st developing bias, and the duty Dh may be larger than that of the 1 st developing bias.

Further, the charging device may include a charging power supply mechanism configured to supply a charging voltage to the charging mechanism; the control means supplies a charging voltage from the charging power supply means to the charging means such that a fog margin defined by a difference between a charging voltage of the 1 st polarity of the photoreceptor and a dc voltage of the 1 st polarity of the 2 nd developing bias in the life monitoring mode is larger than that in normal image formation.

The control unit may execute the lifetime monitoring mode when the cumulative number of times of image formation reaches a 1 st predetermined value, when the cumulative number of rotations or the cumulative operation time of the photoconductor reaches a 2 nd predetermined value, or when an elapsed time from the time of a new product of the photoconductor reaches a 3 rd predetermined value.

Here, the control means may execute the 2 nd execution when the number of times of image formation from the 1 st execution reaches a 4 th predetermined value smaller than the 1 st predetermined value, when the number of rotations or operation time of the photosensitive body from the 1 st execution reaches a 5 th predetermined value smaller than the 2 nd predetermined value, or when the elapsed time from the 1 st execution reaches a 6 th predetermined value smaller than a 3 rd predetermined value after the life monitoring mode is first executed since the photosensitive body is a new product.

Further, the control means may perform the 2 nd and 3 rd executions of the life monitoring mode so as to satisfy the relationship of U1> U2, when an interval from the 1 st execution to the 2 nd execution of the life monitoring mode is denoted by U1 and an interval from the 2 nd execution to the 3 rd execution is denoted by U2.

Further, the transfer device may further include a transfer mechanism for transferring the toner image on the photoreceptor to a transfer target; the determination means has detection means disposed at a position where the toner image transferred to the transfer target after being formed on the photoreceptor by executing the life monitoring mode can be detected, and performs the determination based on a detection result of the toner image by the detection means.

Here, the transfer target may be an intermediate transfer member, or a sheet having a structure in which the toner image is transferred from the photoreceptor to the sheet via the intermediate transfer member.

The transfer target may be a sheet in which the toner image is transferred from the photoreceptor to the sheet via an intermediate transfer member, and the transferred sheet is then discharged from the image forming apparatus, and the detection means may be a scanner that reads the toner image that is placed at a reading position and that is present on the sheet after the discharge.

The present invention provides a method for monitoring the lifetime of a photoreceptor in an image forming apparatus that forms an image by an electrophotographic method on a photoreceptor having an overcoat layer containing a metal filler formed on the outermost layer, the method comprising: a charging mechanism for charging the photoreceptor with a 1 st polarity; an exposure mechanism that exposes the charged photoreceptor to form an electrostatic latent image on the photoreceptor; a developer bearing body that bears a developer containing a toner of a 1 st polarity; and a bias power supply mechanism that is switchable between a 1 st developing bias and a 2 nd developing bias as a developing bias to be supplied to the developer carrier, the 1 st developing bias being used for developing an electrostatic latent image formed at the time of image formation, the 2 nd developing bias being used at the time of monitoring the lifetime of the photosensitive body, and charges of a 2 nd polarity opposite to the 1 st polarity being injected into the photosensitive body in a larger amount than the 1 st developing bias; the photoreceptor life monitoring method performs steps comprising: a control step of controlling the charging mechanism and the exposure mechanism to charge the photoreceptor and inhibit exposure when a lifetime monitoring period of the photoreceptor is reached, thereby forming an electrostatic latent image corresponding to a non-image on the photoreceptor, and controlling the bias power supply mechanism to execute a lifetime monitoring mode in which the 2 nd developing bias is supplied to the developer carrier; a determination step of determining whether or not a toner image is formed on the photoreceptor due to non-uniformity in the dispersion state of the metal filler by executing the lifetime monitoring mode; and a broadcasting step of broadcasting that the thickness of the overcoat layer of the photoreceptor is reduced by a predetermined thickness if it is determined that the toner image is not formed.

The findings obtained by the present inventors will be described before explaining the reason why the thickness of the thin film overcoat layer can be monitored by the above-described configuration.

Findings obtained by the present inventors

In the overcoat layer as the outermost surface of the photoreceptor, a metal filler is dispersed so as to have mechanical strength, but since the dispersion state of the filler is strictly nonuniform, there is a portion where the filler is locally densely mixed (dense). In the overcoat layer, the resistance value is reduced in the dense portion of the filler than in other portions. Even if the overcoat layer partially includes a portion having a low resistance value, the magnitude of the developing bias supplied to a developer carrier such as a developing roller of a developing section with respect to the charging potential on the photoreceptor is adjusted so as not to affect the formed image in the image forming step in normal printing, that is, in charging, exposure, and development.

The present inventors have made an opposite thought with respect to the manner in which the development bias is adjusted so as not to affect the formed image, and have considered that if the development bias affecting the formed image is applied instead, the formed image is affected by the non-uniformity of the dispersion state of the filler when the overcoat layer is present, but if the overcoat layer is continued to disappear, the filler itself is not present, and the effect of the formed image is lost.

That is, if the formed image is affected, the overcoat layer is not excessively worn, and if the formed image is not affected, it can be judged that the end of the life of the photoreceptor is reached due to the wear of the overcoat layer.

Specifically, in a so-called reversal development method in which the photoreceptor and the toner have the same polarity, for example, a negative polarity (1 st polarity), the development bias is set to a 2 nd development bias at which more positive (2 nd polarity) charges are injected than the 1 st development bias at the time of normal printing. This voltage increases the positive component of the ac voltage superimposed on the dc voltage as compared with the normal voltage, and there are methods of increasing the peak-to-peak voltage of the ac voltage and reducing the frequency, for example.

After the photoreceptor is similarly charged, the photoreceptor is not exposed to light, that is, the electrostatic latent image corresponding to the non-image to which no toner is attached is formed, and the electrostatic latent image is brought to the development position in a state where the 2 nd development bias is supplied to the developer bearing member of the development section. Here, the developing position is a position of a portion of the peripheral surface of the photoreceptor that faces the developer bearing member with a slight gap or almost no gap.

Even if the electrostatic latent image of the non-image reaches the development position, the toner should not adhere to the photoreceptor, but the 2 nd development bias is a voltage at which more positive charges are injected into the photoreceptor than the 1 st development bias at the time of normal printing.

Therefore, regardless of the non-image region, it is considered that the resistance value is small in the low-resistance portion where the resistance value is reduced due to the dense filler, compared with the high-resistance portion in the periphery where the resistance value is not reduced, and the potential (negative) is slightly close to 0V by the supply amount of positive charge by the development bias.

In the reversal development method, the toner is more likely to move from the developer bearing member to the photoreceptor at the development position in a portion where the potential on the photoreceptor is closer to 0V. That is, it is easily developed by the toner. In the non-image area on the photoreceptor, even if more positive charges are injected into the high-resistance portion where the filler is not densely (properly dispersed), no toner is attached as in the conventional case, and toner is attached only to the local low-resistance portion as the potential thereof is lowered. Accordingly, the 2 nd developing bias is determined in advance so that toner is not attached to a high-resistance portion where the filler is not dense and toner is attached only to a low-resistance portion where the filler is dense, in a non-image region on the photoreceptor in the injection amount of positive charge injection.

However, even if toner adheres, the negative potential is maintained considerably high in absolute value because the non-image area is not exposed to light. Therefore, even if positive charge is injected by the developing bias, the potential (absolute value) of the photoreceptor does not decrease to the vicinity of 0V, and the toner adhering to the low-resistance portion is not a so-called solid image but a degree of aggregation of a certain number of toner particles, that is, a so-called fog degree.

Fig. 15 is a schematic plan view of the sheet S after a toner image Tf composed of toner adhering to a low-resistance portion is transferred from the drum-shaped photoconductor to the sheet S. As shown in the figure, the toner image Tf is a density of a degree of occurrence of fog, and is hereinafter referred to as a fog toner image Tf.

In the figure, the fog toner images Tf are dispersed at 3 locations C, D, E spaced apart from each other in the main scanning direction, but the portion on the photoreceptor on which the fog toner images Tf are formed is a low-resistance portion, that is, a portion where the filler is dense. The interval P in the sub-scanning direction corresponds to the circumferential length of the photoreceptor.

When the entire surface of the original sheet S is a non-image, the partially formed fog toner image Tf affects the original formed image. By determining whether or not such a gray tone image Tf is formed, the thickness of the overcoat layer can be monitored. The gray-fog pink image Tf can be detected by, for example, an optical sensor or the like.

According to the findings of the present inventors, the fog toner image Tf as shown in fig. 15 is formed in the process until the top coat layer having a high hardness in the film is reduced to a predetermined level or more, and if the top coat layer is reduced to a predetermined level or more, the fog toner image Tf is not formed thereafter, that is, a non-image region is confirmed to be formed on the entire surface. Therefore, according to the present invention, it is possible to monitor the end of life due to wear of the overcoat layer of the thin film, which cannot be detected by the conventional film thickness detection technique.

Effects of the invention

With the above configuration, the thickness of the thin film overcoat layer can be monitored with good accuracy.

Drawings

Fig. 1 is a diagram showing the overall configuration of a printer according to an embodiment.

Fig. 2 is a diagram showing a sectional structure of the photosensitive drum.

Fig. 3 is a block diagram showing the configuration of the control unit.

Fig. 4 is a block diagram showing the structure of the development bias power supply section.

Fig. 5 (a) is a diagram showing a waveform of a developing bias in a normal printing, and (b) is a diagram showing a waveform of a developing bias in a photoreceptor life monitoring mode.

Fig. 6 is a block diagram showing the configuration of the charging power supply unit.

Fig. 7 is a schematic diagram for explaining the reason why the fog toner is formed in the non-image area.

Fig. 8 is a diagram illustrating an example of an appropriate range of Vpp of the alternating current component of the developing bias.

Fig. 9 is a graph showing an appropriate range of the duty ratio and the frequency of the alternating current component of the development bias.

Fig. 10 is a diagram illustrating a modification of the waveform of the developing bias.

Fig. 11 is a diagram illustrating another modification of the waveform of the development bias.

Fig. 12 is a flowchart showing the contents of the printing operation and the control of the photoreceptor life monitoring mode performed by the control section.

Fig. 13 is a flowchart showing the content of a subroutine of the execution control of the photoconductor life monitoring mode.

Fig. 14 is a diagram illustrating a relationship between the amount of toner adhesion on the intermediate transfer belt and the output voltage of the detection sensor.

Fig. 15 is a schematic plan view of a sheet after a toner image adhering to a low-resistance portion where an overcoat layer of a photoreceptor is transferred from the photoreceptor to the sheet.

Fig. 16 is a diagram showing a modification of the arrangement position of the detection sensor.

Description of the reference symbols

1 Printer

11Y, 11M, 11C, 11K photosensitive drum

12Y, 12M, 12C, 12K charging roller

13Y, 13M, 13C, 13K exposure part

14Y, 14M, 14C, 14K developing part

19Y, 19M, 19C, 19K developing roller

21 intermediate transfer belt

23 detection sensor

50 control part

60Y, 60M, 60C, 60K developing bias power supply unit

61 st offset output part

62 nd 2 offset output

63. 83 switching part

70 operating part

71 display unit

80Y, 80M, 80C, 80K live power supply unit

81 st charged voltage output unit

82 nd 2 nd charged voltage output part

95 outer coating

105 photoreceptor life monitoring mode execution unit

106 cumulative print sheet number storage part

111 execution time judging unit

112 life determination unit

113 judging result output unit

Sheet for S-recording

Tf fog toner image

Vo charged potential

DC voltage component of Vdc develop bias

Vpp peak-to-peak voltage

Vz fog margin

Detailed Description

Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described by taking a tandem color printer (hereinafter, simply referred to as a "printer") as an example.

(1) Integral structure of printer

Fig. 1 is a diagram showing the overall configuration of the printer 1.

As shown in the figure, the printer 1 forms an image by a known electrophotographic method, and includes: the image forming unit 10, the intermediate transfer unit 20, the paper feeding unit 30, the fixing unit 40, the control unit 50, the developing bias power supply unit 60, the operation unit 70, and the charging power supply unit 80 are connected to a network (for example, LAN), and when an instruction to execute a print job is received from an external terminal (not shown), image formation of colors including yellow (Y), magenta (M), cyan (C), and black (K) is executed based on the instruction.

The image forming section 10 includes image forming units 10Y to 10K corresponding to the colors Y to K, respectively. The image forming unit 10Y includes: a photosensitive drum 11Y as an example of an image carrier, a charging roller 12Y as a charging portion disposed around the photosensitive drum, an exposure portion 13Y, a developing portion 14Y, a primary transfer roller 15Y, a cleaner for cleaning the photosensitive drum 11Y, and the like.

As shown in fig. 2, the photosensitive drum 11Y is composed of an Organic Photoreceptor (OPC) in which an undercoat layer (UCL)92, a Charge Generation Layer (CGL)93, a Charge Transport Layer (CTL)94, and an overcoat layer (OCL)95 as a high-hardness surface layer are sequentially laminated on a metal product such as an aluminum pipe 91. For example, the total thickness of UCL92 and CGL93 is 2 μm, the thickness of CTL94 is 20 to 30 μm, and the thickness of overcoat 95 is 2 to 4 μm. The overcoat layer 95 contains and disperses a conductive metal filler obtained by surface-treating a metal working material such as titanium oxide, tin oxide, copper aluminum oxide, or the like, in order to have mechanical strength and appropriate electrical resistance. By providing the overcoat layer 95, the life of the photosensitive drum 11Y can be extended as compared with a structure not provided.

Returning to fig. 1, the charging roller 12Y uniformly charges the circumferential surface of the photosensitive drum 11Y rotating in the direction indicated by the arrow. Here, the charged polarity is negative.

The exposure section 13Y performs exposure scanning of the charged photosensitive drum 11Y with laser light, and forms an electrostatic latent image on the photosensitive drum 11Y.

The developing unit 14Y is a developing unit of a reverse developing system, and develops an electrostatic latent image on the photosensitive drum 11Y with the developer D carried on the developing roller 19Y, which is an example of a developer carrying member disposed to face the photosensitive drum 11Y at a developing position of the photosensitive drum 11Y.

Here, as the developer D, a two-component developer including a carrier having a positively charged polarity and a toner having a negatively charged polarity is used. The toner is moved onto the photosensitive drum 11Y and adheres to the electrostatic latent image on the photosensitive drum 11Y, thereby developing the electrostatic latent image, and the toner image of the Y color is visualized on the photosensitive drum 11Y. For example, a polymerized toner having a particle diameter of 7 μm or less, preferably 4.5 μm or more and 6.5 μm or less is used as the toner. Further, the toner may be pulverized.

The primary transfer roller 15Y receives a positive transfer voltage from a transfer power source, not shown, and at a transfer position on the photosensitive drum 11Y, the Y toner image on the photosensitive drum 11Y is primarily transferred to the intermediate transfer belt 21 of the intermediate transfer section 20 by electrostatic action. The other image forming units 10M to 10K have the same configuration as the image forming unit 10Y, and the

image forming units

10M, 10C, and 10K include charging

rollers

12M, 12C, and 12K, exposure portions 13M, 13C, and 13K, and

primary transfer rollers

15M, 15C, and 15K.

The intermediate transfer belt 21 is an endless belt, is stretched over a driving roller and a driven roller, and is driven by the driving force of the driving roller to travel around in the direction indicated by the arrow in the figure (belt winding direction). The intermediate transfer belt 21 is formed by, for example, dispersing carbon in polyphenylene sulfide (PPS) resin and adjusting the surface resistivity to 10⁹～10¹²Omega/□, volume resistivity of 10⁶～10¹²Omega/cm belt, and having a seamless belt shape. In addition, a material in which a conductive filler containing carbon or the like or an ionic conductive material is dispersed in a resin such as a Polycarbonate (PC) resin, a Polyimide (PI) resin, a polyurethane resin, a fluorine resin, or a nylon resin, and resistance adjustment is performed may be used.

In the

image forming units

10Y, 10M, 10C, and 10K, toner images of respective colors are formed on the photosensitive drums 11Y, 11M, 11C, and 11K, and the toner images thus formed are transferred onto the intermediate transfer belt 21, respectively. The image forming operations for the respective colors of Y to K are performed with timings shifted from the upstream side to the downstream side in the belt winding direction so that the toner images of the respective colors are transferred in superposition (primary transfer) at the same position of the running intermediate transfer belt 21.

The paper feed section 30 feeds out the recording sheets S from the paper feed cassette 1 sheet at a time together with the above-described image forming timing in the image forming section 10, and the fed-out recording sheets S are sent to the secondary transfer roller 22 along the conveyance path 35.

When the recording sheet S fed to the secondary transfer roller 22 passes through the secondary transfer position 22a between the secondary transfer roller 22 and the intermediate transfer belt 21, the toner images of the respective colors formed on the intermediate transfer belt 21 are secondarily transferred to the recording sheet S together by the electrostatic action of the secondary transfer roller 22.

The recording sheet S to which the toner images of the respective colors have been secondarily transferred is conveyed to the fixing section 40, heated and pressed when passing between the fixing roller 41 and the pressure roller 42 of the fixing section 40, and the toner on the surface is fused and fixed on the surface of the recording sheet S, and then discharged onto the discharge tray 39 by the discharge roller 38.

The charging power supply unit 80 supplies a negative charging voltage of a predetermined magnitude to the charging rollers 12Y to 12K.

The developing bias power supply portion 60 supplies developing bias voltage for development to the developing

rollers

19Y, 19M, 19C, 19K of the developing

portions

14Y, 14M, 14C, 14K, and is provided with power supply portions 60Y to 60K corresponding to the respective image forming units. The power supply units 60Y to 60K each output a voltage in which an Alternating Current (AC) component is superimposed on a Direct Current (DC) component as a developing bias voltage.

In the image forming unit 10Y, when the charging potential of the photosensitive drum 11Y is set to-Vo, the voltage of the dc component of the developing bias voltage is set to-Vdc, and the potential of the exposed portion (image forming region) in the photosensitive drum 11Y is set to-Vl, the absolute values thereof have a relationship of Vo > Vdc > Vl. Thereby, the toner of the developing roller 19Y moves to the image forming area on the photosensitive drum 11Y and is reversely developed, and a toner image is formed in the image forming area. The same is true for the other image forming units 10M to 10K.

By applying a developing bias voltage in which an alternating current component is superimposed on a direct current component to the developing rollers 19Y to 19K, a predetermined potential difference necessary for development is generated between the developing rollers 19Y to 19K and the photosensitive drums 11Y to 11K at a developing position, and toner particles of the developer D are reciprocated between the developing rollers 19Y to 19K and the photosensitive drums 11Y to 11K by the AC component, whereby the electrostatic latent images of the toner particles from the developing rollers 19Y to 19K to the photosensitive drums 11Y to 11K are easily moved, thereby improving the developability.

In a photoreceptor life monitoring mode executed at a timing different from that in normal printing (image formation), the developing bias voltage changes the AC component to a value suitable for life monitoring of the photoreceptor drums 11 to 11K. The photoreceptor life monitoring mode will be described in detail later.

A detection sensor 23 composed of a reflection-type optical sensor having a light emitting portion and a light receiving portion is disposed at a position located around the intermediate transfer belt 21, on the downstream side of the image forming unit 10K in the belt traveling direction, and on the upstream side of the secondary transfer position 22 a.

The detection sensor 23 detects the fog toner image Tf shown in fig. 15, irradiates light from the light-emitting portion to the intermediate transfer belt 21, receives the reflected light from the light-receiving portion, generates an electric signal corresponding to the amount of the reflected light, and outputs the electric signal to the control portion 50.

In the photoreceptor life monitoring mode, since the reflected light amount becomes smaller in a portion where the fog toner image Tf is formed on the intermediate transfer belt 21 than in a non-image area where the fog toner image Tf is not present, the output signal changes depending on whether or not the fog toner image Tf is present. In addition, as the detection sensor 23, a sensor having the same degree of performance as that of an optical sensor for patch detection used in a known stabilization processing technique can be used.

The control unit 50 executes the photoreceptor life monitoring mode, and determines whether or not the end of the life of each of the photoreceptor drums 11Y to 11K is reached based on the output signal of the detection sensor 23.

The operation unit 70 is disposed in front of the printer 1 at a position that is easy for a user to operate, and includes a key for receiving a setting input of the number of printed sheets by the user, a key for receiving a selection input of various modes, and the like, and a display unit 71 for displaying a message of a life determination result of the photosensitive drum.

(2) Structure of control unit 50

Fig. 3 is a block diagram showing the configuration of the control unit 50.

As shown in the drawing, the control unit 50 includes, as main components, a communication interface (I/F) unit 101, a CPU102, a ROM103, a RAM104, a photoreceptor life monitoring mode execution unit 105, and a cumulative print number storage unit 106, and the respective units are configured to be able to exchange signals and data with each other.

The communication I/F unit 101 is an interface for connecting to a network, here, a LAN card or a LAN board for connecting to a LAN, and receives data of a print job transmitted from an external terminal via the LAN.

The CPU102 reads a necessary program from the ROM103, and controls the image forming unit 10, the intermediate transfer unit 20, the paper feeding unit 30, the fixing unit 40, and the like based on the data of the print job received via the communication I/F unit 101 to smoothly perform the image forming operation. The RAM104 is a work area of the CPU 102.

The photoreceptor life monitoring mode execution unit 105 includes an execution time determination unit 111, a life determination unit 112, and a determination result output unit 113.

The execution time determination unit 111 determines whether or not the execution time is the execution time of the photoreceptor life monitoring mode. When it is determined that the timing is not the execution timing of the photoreceptor life monitoring mode, the normal developing bias and charging voltage are instructed to be output to the developing bias power supply unit 60 and the charging power supply unit 80 during normal printing execution.

On the other hand, if it is determined that the time is the execution time of the photoreceptor life monitoring mode, the developing bias and the charging voltage at the time of switching the developing bias power supply section 60 and the charging power supply section 80 to the photoreceptor life monitoring mode are instructed during standby or the like other than the normal printing time when the photoreceptor life monitoring mode is to be executed.

When the execution timing of the photoreceptor life monitoring mode is reached, the execution timing determination unit 111 instructs the life determination unit 112 to perform the life determination of the photoreceptor drums 11Y to 11K.

Upon receiving the command from the execution time determination unit 111, the life determination unit 112 determines the life of the photoreceptor based on the output signal of the detection sensor 23. Specifically, when the fog toner image Tf shown in fig. 15 is detected, the thickness of the overcoat layer 95 is present to some extent, and the photoreceptor does not reach the end of its life, and when the fog toner image Tf is not detected, the overcoat layer 95 is almost absent or completely disappears due to abrasion or reduction, and thus it is determined that the photoreceptor has reached the end of its life. When the overcoat layer 95 as a protective layer disappears, the charge transport layer 94 thereunder is exposed, but since the charge transport layer 94 is not so hard, it is drastically reduced, and the functional life as a photoreceptor is reached. The life determination unit 112 transmits the determination result to the determination result output unit 113.

The determination result output unit 113 displays a message indicating the contents thereof on the display unit 71 of the operation unit 70 only when it is determined that the photoreceptor has reached the end of its life, and notifies the user of the fact that the photoreceptor has reached the end of its life.

The cumulative-printed-sheet-count storage unit 106 is a nonvolatile storage unit that, when printing on 1 sheet S is completed, increments the current cumulative printed sheet count Qm by 1 and stores this information as a new cumulative printed sheet count Qm. By referring to the cumulative number of printed sheets Qm stored in the cumulative number-of-printed-sheets storage unit 106, the cumulative number of printed sheets Qm executed by the printer 1 since the time of the new product can be confirmed.

(3) Structure of developing bias power supply unit 60

Fig. 4 is a block diagram illustrating the structure of the development bias power supply section 60.

As shown in the figure, the developing bias power supply unit 60 includes: y color power supply unit 60Y, M color power supply unit 60M, C color power supply unit 60C, and K color power supply unit 60K. The Y color power supply units 60Y to K color power supply units 60K have basically the same configuration, and only the Y color power supply unit 60Y will be described here, and the description of the other power supply units 60M to 60K will be omitted.

The power supply unit 60Y for Y color includes: a 1 st offset output section 61, a 2 nd offset output section 62, and a switching section 63.

The 1 st bias output unit 61 is connected in series with a dc power supply 61a and an ac power supply 61b, and a positive terminal 61c of the dc power supply 61a is grounded to output a development bias Vb1 obtained by superimposing an ac voltage of the ac power supply 61b on a dc voltage of the dc power supply 61a as a development bias at the time of normal printing.

Fig. 5 (a) is a graph in which the waveform of the development bias Vb1 for 1 cycle is extracted and displayed, the abscissa indicates time, the ordinate indicates voltage values, and the upper side across 0v (gnd) indicates negative polarity and the lower side indicates positive polarity.

As shown in the figure, for example, the DC voltage Vdc of the developing bias Vb1 is-350V, the AC waveform is a rectangular wave, the frequency H of the AC voltage is 7kHz, and the peak-to-peak value Vpp is 1.4 kV. Here, Vo1 in the figure represents a charging potential of the photosensitive drum 11Y during normal printing, for example, -500V.

In a waveform of 1 cycle of the alternating current, when a side having a peak voltage with a positive polarity (2 nd polarity) is referred to as an alternating current component α and a side having a negative polarity (1 st polarity) is referred to as an alternating current component β with a-Vdc of the superimposed direct current voltage as a boundary, a peak voltage of the alternating current component α is Vm (700V in this case) and a peak voltage of the alternating current component β is-Vn (1050V in this case).

Note that, when the time of the alternating current component α is denoted by ta, the time of the alternating current component β is denoted by T β, and the value obtained by dividing the time T β by 1 cycle is denoted by the duty Dh, the duty Dh is 50% because T α is T β.

Returning to fig. 4, the 2 nd bias output unit 62 is connected in series with a dc power supply 62a and an ac power supply 62b, and the positive terminal 62c of the dc power supply 62a is grounded to output a development bias Vb2 obtained by superimposing the ac voltage of the ac power supply 62b on the dc voltage of the dc power supply 62a as a development bias during life monitoring.

FIG. 5(b) is a view showing the waveform of the development bias Vb2 extracted for 1 cycle.

As shown in the figure, the developing bias Vb2 and the developing bias Vb1 have the same peak-to-peak Vpp', but have the same value of-Vdc, frequency H, and duty Dh. Vpp' of the development bias Vb2 is greater than Vpp, here 1.6 kV. The peak voltage (absolute value) of the positive ac component α is Vm 'larger than Vm at the time of normal printing, and the peak voltage of the negative ac component β is-Vn' smaller than (larger in absolute value) -Vn at the time of normal printing.

The charging potential of the photoconductive drum 11Y is set to-Vo 2, for example, -550V, which is larger in absolute value than-Vo 1 in the normal state. The reason why the developing bias Vb2 during lifetime monitoring is different from the developing bias Vb1 during normal operation in this way is that the fog toner image Tf shown in fig. 15 is positively formed in a non-image area. The reason for this will be described below in the section (5) of formation of the fog toner Tf.

Returning to fig. 4, the switching unit 63 is a switch for switching the developing bias to supply any one of the 1 st bias output unit 61 and the 2 nd bias output unit 62 to the developing roller 19Y based on a control signal from the control unit 50. Here, switching is performed so that the developing bias Vb1 is supplied to the developing roller 19Y at the time of normal printing, and the developing bias Vb2 is supplied to the developing roller 19Y at the time of life monitoring.

(4) Structure of live power supply unit 80

Fig. 6 is a block diagram showing the structure of the charging power supply unit 80.

As shown in the figure, the charging power supply unit 80 includes: y color power supply section 80Y, M color power supply section 80M, C color power supply section 80C, and K color power supply section 80K. Since the Y color power supply units 80Y to K color power supply units 80K have substantially the same configuration, only the Y color power supply unit 80Y will be described here, and the description of the other power supply units 80M to 80K will be omitted.

The power supply section 80Y for Y color includes: a 1 st charging voltage output unit 81, a 2 nd charging voltage output unit 82, and a switching unit 83.

The 1 st charging voltage output unit 81 has a dc power supply 81a, and a positive terminal 81b of the dc power supply 81a is grounded, and outputs a negative charging voltage-Vo 1 ((a) in fig. 5) as a charging voltage at the time of normal printing. Vo1 is for example-500V.

The 2 nd charging voltage output unit 82 has a dc power supply 82a, and a positive terminal 82b of the dc power supply 82a is grounded, and outputs a negative charging voltage-Vo 2 ((b) in fig. 5) as a charging voltage at the time of life monitoring. Vo2 is greater in absolute value than Vo1, e.g., -550V. The reason why Vo2 is larger than Vo1 in absolute value is as described later.

The switching unit 83 switches the charging voltage to be supplied to any one of the 1 st charging voltage output unit 81 and the 2 nd charging voltage output unit 82 to the charging roller 12Y based on a control signal from the control unit 50. Here, switching is performed so that-Vo 1 is supplied to the charging roller 12Y during normal printing, and-Vo 2 is supplied to the charging roller 12Y during life monitoring.

(5) Formation of fog toner Tf

Fig. 7 is a schematic diagram for explaining the reason why the fog toner Tf is formed in the non-image area, and shows in order how the surface potential of the photosensitive drum 11Y (hereinafter referred to as "photosensitive body potential") changes during charging, immediately before development, and during development in the case where the developing process is performed without exposure after the surface of the photosensitive drum 11Y (hereinafter referred to as "drum surface") is charged.

Further, 5 locations A, B, C, D, E different in the main scanning direction on the drum surface are taken, and C, D, E is indicated as an example of a portion where the local filler in the overcoat 95 is dense. Therefore, the photoconductive drum 11Y forms a gray-tone image Tf at a portion C, D, E on the drum surface while the amount of wear of the overcoat 95 reaches a predetermined value from a new product (fig. 15). Further, reference numeral 111 denotes a rotation axis of the photosensitive drum 11Y.

Immediately before the charging step and the developing step, the photoreceptor potential of the non-image region becomes-Vo, which is the same at the portion C, D, E. In the developing step, focusing on the portion D in the portion C, D, E, the photoreceptor potential of the portion D and the peripheral regions I, J (portions where the filler is not dense) on both sides in the main scanning direction of the portion D are shown on the drum surface.

In the time T α in which a positive component is supplied in 1 cycle of AC (alternating current), a charge (positive charge) of the positive component is simultaneously injected into the portion D and the region I, J by the potential difference between the photoconductor potential-Vo and the + Vmax of the AC component. It is estimated that the injection of the positive charge causes a phenomenon in which the potential of the photoreceptor changes as described below.

That is, in the portion D, the resistance value greatly decreases with respect to the peripheral region I, J due to the density of the filler, and-Vo rises to-Va (> -Vo) (decreases in absolute value). At this time, the magnitude relation of the DC component-Vdc with respect to the developing bias becomes-Va > -Vdc. This magnitude relationship causes the negative-polarity toner to generate an electric field in a direction from the developing roller 19Y toward the photosensitive drum 11Y. That is, by injecting positive charges, the portion D is brought into a state of approximate (pseudo) exposure, and appears as if a main developing process is performed on the surface.

On the other hand, since the peripheral region I, J has a high resistance, it remains at-Vo and hardly changes, and does not change from the charged state in the original non-image region.

During the remaining time T β to which the negative component is supplied among 1 cycle of AC, the photoreceptor potential of the portion D still rises to-Va, and the toner moves from the developing roller 19Y to the photoreceptor drum 11Y by the potential difference Ve from-Vmin of the AC component. This phenomenon corresponds to the main development on the surface described above, and forms a fog toner image Tf shown in fig. 15 in the portion D. The final development on the surface forms a fog toner image Tf, which is referred to as photoreceptor fog.

On the other hand, in the peripheral region I, J, since the photoreceptor potential remains at-Vo and does not change from the original non-image region, the toner does not move from the developing roller 19Y and adheres to the drum surface due to the relationship of-Vmin < -Vo < -Vdc. That is, in the region I, J, the fog toner image Tf due to the fog of the photoconductor is not formed.

Here, the values of-Vmin and-Vdc are fixed, and if-Vo is set to a value slightly larger in absolute value, the potential difference Vz between-Vdc and-Vo increases. The increase in the potential difference Vz means that the electric field in the direction from the developing roller 19Y to the photosensitive drum 11Y is weakened in the peripheral region I, J, and therefore, regardless of the unevenness in the dispersed state of the filler in the overcoat 95, it is possible to further suppress the occurrence of so-called development fog in which the toner particles move to the photosensitive body side in the region I, J due to the magnitude of the difference between-Vdc and-Vo. The potential difference Vz is referred to as a fog margin, and the larger the fog margin is, the more the development fog can be suppressed. In this sense, the generation cause of the photoreceptor fog is different from that of the developing fog.

In fig. 5 (b), the reason why the charging voltage (═ Vo2) is set to be slightly larger in absolute value than the charging voltage (═ Vo1) at the time of normal printing than δ 1 is to suppress the generation of the development fog as compared with the time of normal printing.

Although the above description has been made for the portion D, in the other portions C and E, as in the portion D, the photoreceptor potential increases (decreases in absolute value) from the original-Vo to-Va, but when the resistance value decreases differently in each portion, the larger the decrease in potential resistance value, the absolute value of-Va becomes smaller (approaches 0V), and the potential difference Ve described above increases, so that the amount of toner moving from the developing unit 14Y to the drum surface tends to increase, and the density of the fog toner image Tf tends to increase.

In addition, in the above, it is explained that the photoreceptor potential of the portion D is increased from-Vo to-Va by supplying positive charges, but such increase of the photoreceptor potential occurs only when positive charges are supplied to a portion where the resistance value is greatly reduced in the overcoat layer 95, and does not occur when negative charges are supplied. The reason for this is presumed that the photoreceptor potential is determined by the magnitude of the charging voltage or current from the charging roller 12Y to the photoreceptor drum 11Y in the charging step, and even if negative charges included in the AC component of the developing bias are supplied to the drum surface, the photoreceptor potential at that point in time does not further decrease (increase in absolute value).

As the conditions for the generation of the fog of the photoreceptor, the present inventors have experimentally derived an example of appropriate ranges of the peak-to-peak voltage Vpp', the duty Dh, and the frequency H, which are the alternating current components of the developing bias Vb2 shown in fig. 5 (b).

Fig. 8 is a graph showing an appropriate range of the peak-to-peak voltage Vpp of the developing bias Vb2, and fig. 9 is a graph showing an appropriate range of the duty Dh and the frequency H. In fig. 8, the fog level on the vertical axis indicates the degree of fog, and a level of 5 indicates no fog, and as the numerical value becomes smaller, fog is more conspicuous, that is, the amount of toner deposited per unit area becomes larger (density becomes higher), and a level of 1 indicates the most severe fog. Generally, when the level is 3 or more, there is no problem in image quality, and when the level is less than 3, it is considered that the image quality is degraded.

In the present embodiment, the lifetime of the overcoat layer 95 is determined by whether or not a gray-fog toner image Tf is formed when the electrostatic latent image corresponding to the non-image is developed, but fog is likely to occur as the gradation becomes lower, that is, fog of the photoreceptor is likely to occur not only in the portion C, D, E where the low resistance is formed due to the dense filler but also in the other high-resistance region I, J.

Accordingly, Vpp' is determined in a range of class 3 or more within a range in which no problem occurs in image quality so that photoconductor fog occurs in the low resistance portion C, D, E but not in the high resistance region I, J at the time of life monitoring. Specifically, in the case of class 3 or more, 1600V is set to Vpp' at the time of life determination in the range of Vpp where the gray-tone image Tf is likely to occur, here 1400 to 1600V.

Similarly, in fig. 9, it is understood that when the duty ratio Dh is set to 40 (black triangle dots), the frequency H is within a range of 5 to 8.5kHz and the fog level is 3 or more, but when the duty ratio Dh is set to 50 (black four-corner dots), the frequency H is within a range of about 6 to 8.5kHz and the fog level is 3 or more. Here, since the duty Dh is 50% and the frequency H is 7kHz in a normal state and the fog level is in a range of 3 or more from this figure, the same duty Dh (50) and the same rate H (7 kHz) are set in the life monitoring. Needless to say, not limited to the above values, appropriate values of the direct current component (voltage) and the alternating current component (Vpp, duty Dh, frequency H) of the developing bias Vb2 are determined in advance by experiments or the like so that the photoreceptor fog forms the fog toner image Tf only in the portion (C, D or the like) where the filler is dense and becomes low resistance when the overcoat layer 95 is present.

For example, the development bias Vb21 shown in fig. 10 can also be used. Specifically, with respect to the developing bias Vb2 shown in (b) of fig. 5, the developing bias Vb21 forms a waveform in which Vmin (peak voltage of the alternating current component β) is the same as-Vn at the time of normal printing, and in 1 cycle of alternating current, the time T β of the alternating current component β on the negative side is longer than the time T α of the alternating current component α on the positive side, and the duty Dh is increased from 50% to 60%, for example.

Further, for example, the developing bias Vb22 shown in fig. 11 can be used. Specifically, regarding the developing bias Vb22, Vmax and Vmin are the same as Vm and Vn in the normal printing with respect to the developing bias Vb2 shown in (b) of fig. 5, the frequency H of the AC component is a waveform of 4.5kHz in the developing bias Vb22 with respect to 7kHz in the normal printing, for example, and the duty Dh is 50% as in the normal printing. The time Tc of the alternating current components α and β in 1 cycle is smaller in frequency H than that in normal printing, and is longer than ta and T β in normal printing.

The developing biases Vb21 and 22 shown in fig. 10 and 11 can inject more positive charges into the photoreceptor than Vb1 at the time of normal printing by the amount of δ 2 shown in fig. 10 and the amount of δ 3 shown in fig. 11 (corresponding to the increase of the positive component with respect to the time T α (broken line) at the time of normal printing).

By changing the values of Vpp, frequency H, and duty Dh with respect to the normal printing time in this manner, the amount of positive charges injected into the photoreceptor is increased as compared to the normal printing time, and thus, when the overcoat layer 95 is present, a fog toner image Tf of the photoreceptor fog can be formed in a low-resistance region (C, D, etc.) where the filler is dense, and a fog toner image Tf of the photoreceptor fog can be formed in other high-resistance regions. At least one of Vpp, frequency H, and duty Dh may be changed with respect to the normal printing time so that the fog toner image Tf of the photoreceptor fog is formed only in the low resistance portion.

(6) Control for printing operation and photoreceptor life monitoring mode

Fig. 12 is a flowchart showing the contents of the printing operation and the control of the photoreceptor life monitoring mode performed by the control section 50. This flow is executed by a main routine not shown when called at regular intervals.

As shown in the figure, it is determined whether or not the print job is started (step S1). If the print job is not started (no in step S1), the process returns.

If a decision is made that the print job is started (yes at step S1), the charging potential Vo is set to-Vo 1, and the development bias Vb is set to Vb1 (step S2). This setting is performed by the execution timing determination section 111 instructing the development bias power supply section 60 and the charging power supply section 80 to output the development bias (═ Vb1) and the charging voltage (═ Vo1) at the normal time.

The print job is executed under the condition that the charged potential Vo becomes-Vo 1 and the development bias Vb becomes Vb1 (step S3). If a decision is made that the print job is ended (yes at step S4), the routine proceeds to step S5.

In step S5, the current cumulative number of printed sheets Qm is read out from the cumulative-number-of-printed-sheets storage unit 106 and acquired. The execution timing determination unit 111 takes charge of the processing of step S5 and subsequent steps S6 and S7.

It is determined whether or not the cumulative number of prints Qm is equal to or greater than a predetermined value Qa (step S6). Here, the predetermined value Qa is, for example, 70% of the cumulative number of printed sheets in the design expected to reach the life of the photoreceptor. Specifically, if the number of sheets in design is, for example, 100 ten thousand, the predetermined value Qa reaches 70 ten thousand.

If it is determined that the cumulative number of printed sheets Qm is equal to or greater than the predetermined value Qa (yes in step S6), it is next determined whether or not the cumulative number of printed sheets Qm is a multiple of 10000 (10 k), that is, 70 ten thousand, 71 ten thousand, or 72 ten thousand … … (step S7).

If it is determined that the cumulative number of printed sheets Qm has reached a multiple of 10000 (yes in step S7), the photoreceptor life monitoring mode is executed (step S8), and the process returns.

On the other hand, if it is determined that the cumulative number of printed sheets Qm is not equal to or greater than the predetermined value Qa (no in step S6), the cumulative number of printed sheets Qm is small, and therefore the photosensitive drums 11Y to 11K are assumed not to have reached the lifetime due to the wear of the overcoat 95, and the process returns to the photoreceptor lifetime monitoring mode without any timing.

Further, it is determined that the cumulative number of printed sheets Qm is not a multiple of 10000 (no in step S7), and the process returns as it is. The reason for this is that the wear of the overcoat 95 progresses as the cumulative number of printed sheets Qm is equal to or greater than the predetermined value Qa, but the wear of the overcoat 95 progresses extremely slowly. Therefore, in the process of 1 ten thousand sheets, even if the photoreceptor life monitoring mode is repeatedly executed a plurality of times, the determination result is not changed in many cases in each time. In this way, the first photoreceptor life monitoring mode is executed when the cumulative number of printed sheets Qm from the time of the new product of the photoreceptor drum 11Y reaches the predetermined value Qa, and the photoreceptor life monitoring modes of … … at the 2 nd and 3 rd times are intermittently executed every time the number of printed sheets reaches the predetermined value (here, 1 ten thousand sheets).

Fig. 13 is a flowchart showing the contents of a subroutine of execution control of the photoreceptor life monitoring mode, and the image forming section 10 and the intermediate transfer section 20 are driven under the same conditions as those in normal printing when the photoreceptor life monitoring mode is executed.

As shown in the figure, one of the image forming units 10Y to 10K is selected (step S10). Here, the image forming unit 10Y is selected.

In the image forming unit 10Y, the charging potential is set to-Vo 2, and the rotating photoconductive drum 11Y is charged at-Vo 2[ V ] (step S11). The charging is performed by the charging timing determination unit 111 instructing the charging power supply unit 80 to output a charging voltage (═ Vo2) when the photoreceptor life monitoring mode is executed.

Next, the electrostatic latent image on the photosensitive drum 11Y (here, the electrostatic latent image corresponding to the non-image is formed without exposure after charging) is developed by the development bias Vb2 (step S12). The development is performed by the development timing determination section 111 instructing the development bias power supply section 60 to output the development bias Vb2 when the photoreceptor life monitoring mode is executed.

Thus, as shown in fig. 5 (b), the development of the electrostatic latent image corresponding to the non-image is performed in the developing unit 14Y to which the developing bias Vb2 is supplied, with respect to the photosensitive drum 11Y having the charged potential of-Vo 2. The Vpp 'of the developing bias Vb2 is larger than Vpp at the time of normal printing, and the difference δ 2 between the voltages Vm and Vm' of the positive components of AC is larger than that at the time of normal printing, and this corresponds to the amount of increase in positive charge injection, which is likely to cause generation of the photoreceptor fog.

When the overcoat layer 95 is not worn so much that the end of life is not reached, a fog toner image Tf due to fog of the photoreceptor is developed in a dense portion C, D, E (fig. 7) of the filler or the like. On the other hand, when the wear of the overcoat layer 95 is a predetermined amount or more, the fog toner image Tf due to the fog of the photoreceptor does not appear.

Next, the primary transfer voltage is supplied to the primary transfer roller 15Y under the same conditions as those in the normal printing (step S14). If the fog toner image Tf is formed on the photosensitive drum 11Y, the fog toner image Tf is primarily transferred from the photosensitive drum 11Y to the intermediate transfer belt 21 by the electrostatic action of the primary transfer roller 15Y. Of course, when the fog toner image Tf is not formed on the photosensitive drum 11Y, the fog toner image Tf is not primarily transferred onto the intermediate transfer belt 21 even if the primary transfer voltage is supplied to the primary transfer roller 15Y.

Next, a detection signal (output voltage) Vp of the detection sensor 23 disposed opposite to the intermediate transfer belt 21 is acquired as needed (step S15).

In the case where the fog toner image Tf is primarily transferred onto the intermediate transfer belt 21, the fog toner image Tf on the intermediate transfer belt 21 approaches the detection area of the detection sensor 23 by the circling travel of the intermediate transfer belt 21, and can be detected while passing through the detection area.

On the surface of the intermediate transfer belt 21, the output voltage Vp of the detection sensor 23 changes as described above between the portion where the fog toner image Tf exists and the portion where the fog toner image Tf does not exist, and therefore, it is possible to determine whether or not the fog toner image Tf exists depending on the output voltage Vp.

Fig. 14 is a graph illustrating a relationship between the amount of toner adhering to the intermediate transfer belt 21 (unit: mg) and the output voltage Vp of the detection sensor 23. The detection sensor 23 used in the present embodiment has a characteristic that the output voltage Vp becomes higher as the amount of toner adhesion becomes smaller. In the case of the detection sensor 23 using such characteristics, the output voltage Vp shows the maximum value when the gray-fog toner image Tf is not formed, that is, when the toner adhesion amount reaches 0.

Therefore, the output voltage Vp is monitored as needed, (i) when the output voltage Vp reaches a value smaller than the maximum value, it can be detected that the photoreceptor has not reached the end of its life from the formation of the gray-fog toner image Tf; (ii) when the maximum value is reached, it can be detected that the overcoat layer 95 is almost absent or is becoming absent due to abrasion or reduction from the fact that the gray-tone image Tf is not formed, and the photoreceptor reaches the end of the life.

In the present embodiment, the value th0 slightly smaller than the maximum value is set as a threshold in advance in consideration of the detection error, and it is determined that the photoreceptor has not reached the end of life when the output voltage Vp is equal to or less than the threshold th0, and it is determined that the photoreceptor has reached the end of life when the output voltage Vp > the threshold th 0.

In order to improve the detection accuracy of the fog toner image Tf by the detection sensor 23, it is desirable to use a sensor having a detection area of the sensor 23, that is, a detection field of view that is large to some extent, so that the detection can be performed even if the fog toner image Tf appears at an arbitrary position in the main scanning direction. Alternatively, the following configuration may be adopted: by arranging a plurality of sensors 23 having narrow detection fields of view in parallel along the main scanning direction, even if the gray-tone image Tf appears at an arbitrary position in the main scanning direction, it is possible to reliably detect the gray-tone image Tf by any of the sensors.

Returning to fig. 13, if it is determined that the output voltage Vp > the threshold th0 is not reached (no in step S16), the process proceeds to step S18 if the photoreceptor has not reached the end of its life. On the other hand, if it is determined that the output voltage Vp > the threshold th0 is reached (yes in step S16), the content of the end of the lifetime of the photoconductor is broadcasted, and here, a message is displayed on the display unit 71 of the operation unit 70 (step S17), and the process proceeds to step S18. The lifetime determination unit 112 performs the processing of steps S15 and S16, and the determination result output unit 113 performs the processing of step S17.

In step S18, it is determined whether or not the photoconductor life monitoring mode is executed for all the image forming units 10Y to 10K. In the case where an unexecuted image forming unit remains (no in step S18), the process returns to step S11. When it is determined that the photoreceptor life monitoring mode has been executed for all the image forming units by repeating the processing of steps S11 to S18 (yes in step S18), the process returns. This makes it possible to determine whether or not each of the 4 photosensitive drums 11Y to 11K has reached the end of the life.

As described above, in the present embodiment, since it is determined whether or not the fog toner image Tf due to the photoreceptor fog occurs due to the unevenness of the dispersion state of the metal filler in the overcoat layer 95 (there is a portion where the metal filler is locally dense), it is possible to monitor the end of life due to the overcoat layer abrasion of the thin film, which cannot be detected by the conventional film thickness detection technique.

Note that, although the timing of executing the photoreceptor life monitoring mode is set after the end of the printing operation in the above description, it may be performed as one of the image stabilization controls or the like during a period other than the printing operation (image formation), for example, during standby when the printer 1 is in the energy saving mode to wait for the printing operation, or during a period after the end of the previous print job and before the start of the next print job.

The present invention is not limited to the image forming apparatus, and may be a photoreceptor life monitoring method. Further, the program of the method may be executed by a computer. The program according to the present invention may be recorded on various computer-readable recording media such as magnetic disks such as magnetic tapes and flexible disks, optical recording media such as DVD-ROM, DVD-RAM, CD-ROM, CD-R, MO, and PD, and flash memory-based recording media, may be produced and transferred as the recording media, and may be transmitted and supplied as the program via various wired and wireless networks including the internet, broadcasting, electric communication lines, satellite communication, and the like. Note that the processing in the above-described embodiment may be performed by software or may be performed by a hardware circuit.

< modification example >

The present invention is not limited to the above-described embodiments, and can be implemented in various ways. Other possible embodiments are listed below.

(1) In the above embodiment, the configuration example in which the detection sensor 23 (detection means) detects the gray-fog toner image Tf primarily transferred to the intermediate transfer belt 21 as the transfer target has been described, but the present invention is not limited thereto. For example, it is also possible to adopt a configuration in which the gray-fog toner image Tf on the intermediate transfer belt 21 is further secondarily transferred to the sheet S as a transferred object, and the gray-fog toner image Tf on the sheet S after the secondary transfer is detected by another detection sensor.

In this modification, specifically, for example, as shown in fig. 16, a configuration may be adopted in which the detection sensor 23a is disposed at a position between the secondary transfer position 22a and the fixing section 40 along the conveyance path 35, or a configuration may be adopted in which the detection sensor 23b is disposed at a position between the fixing section 40 and the discharge roller 38. Alternatively, it is also possible to adopt a configuration in which the detection sensor 23c detects the gray-fog toner image Tf on the photosensitive drum before the gray-fog toner image Tf formed on the photosensitive drum is primarily transferred to the intermediate transfer belt 21.

Further, as shown in fig. 16, in the configuration having the known scanner 90, it is also possible to detect whether or not a gray-fog toner image Tf exists on the sheet S by reading the discharged sheet S at the reading position of the scanner 90. The local portion where the gray tone image Tf exists and the non-existing region can be distinguished with good accuracy for the entire sheet. In this configuration, the scanner 90 constitutes a detection mechanism for detecting the gray-fog toner image Tf.

The determination means includes a structure for directly detecting the gray-fog toner image Tf formed on the photosensitive drum and a structure for indirectly detecting the gray-fog toner image Tf after the transfer of the photosensitive drum, which are different from each other directly and indirectly.

(2) In the above embodiment, the first photoreceptor life monitoring mode from the time when the photoreceptor drum is new is performed when the cumulative number of printed sheets Qm indicating the cumulative number of times of image formation reaches the 1 st predetermined value Qa or more. For example, the cumulative rotational speed or cumulative operating time of the photosensitive drum from the time of the new product may reach the 2 nd predetermined value, that is, the predetermined rotational speed or operating time may be set to a value that is supposed to cause wear or reduction of the overcoat layer 95 to a certain extent. Further, it is also possible to trigger when the elapsed time from the time of the new product of the photosensitive drum reaches the 3 rd predetermined value.

Further, the photoreceptor life monitoring mode after the 2 nd time is performed when the cumulative number of printed sheets Qm reaches a multiple (4 th predetermined value) of 10000(═ 10k), but is not limited to 10 k. The value (4 th predetermined value) may be set to an appropriate value, for example, 5k or the like, depending on the device configuration, as long as the value is smaller than the 1 st predetermined value Qa which is the first execution opportunity.

The 2 nd execution of the photoreceptor life monitoring mode may be executed when the rotation speed or operation time of the photoreceptor drum from the 1 st execution reaches a 5 th predetermined value (for example, 10k) smaller than the 2 nd predetermined value (for example, 3000k) or when the elapsed time from the 1 st execution reaches a 6 th predetermined value (for example, 20 hours) smaller than the 3 rd predetermined value (for example, 500 hours). The same setting can be made after 3 rd time.

Further, the execution time of the 2 nd and subsequent times may be set so that the interval U1 from the 1 st execution to the 2 nd execution, the interval U2 from the 2 nd to the 3 rd execution, and the interval U3 from the 3 rd to the 4 th execution of the photoreceptor life monitoring mode gradually decrease (U1> U2> U3 … …). The reason for this is that since the wear of the overcoat 95 progresses as the cumulative number of printed sheets Qm increases and the layer thickness of the remaining overcoat 95 decreases, the execution interval is shortened as the lifetime approaches, and the accuracy of lifetime determination can be improved.

(3) In the above-described embodiment, the example in which the image forming apparatus according to the present invention is applied to the tandem type color printer has been described, but the present invention is not limited thereto. The present invention can be applied to an image forming apparatus that performs development using a development bias voltage including an ac component regardless of color or monochrome image formation and can change at least one of the frequency, Vpp, and duty of the ac component with respect to the frequency, Vpp, and duty of a normal printing operation in order to facilitate generation of photoreceptor fog, for example, a copier, a FAX, an MFP (multi Function Peripheral), and the like. In addition, although the charging potential is switched from-Vo 1 to-Vo 2 in the normal printing operation in order to suppress the development fog, a device configuration may be adopted in which the charging potential is not switched in the case where it is possible to determine whether or not the fog toner image Tf due to the photoreceptor fog is detected without performing this operation.

Further, although an example of the drum-shaped photoreceptor is described, the present invention is not limited to this, and can be applied to a configuration using a belt-shaped photoreceptor, for example. Further, although a configuration example in which a charging roller is used as a charging means for charging the photoreceptor has been described, the present invention is not limited thereto, and a charging electrode or the like can be used.

Further, the example of using the developing roller as the developer bearing member for bearing the developer is described, but the developing roller is not limited to a roller shape, and for example, a sleeve shape or the like can be used. The configuration example using the two-component developer containing the carrier and the toner as the developer is described, but it can also be applied to the configuration using, for example, the one-component developer containing no carrier and containing the toner. Further, an example of a configuration in which the charging polarity of the photoreceptor is negative and the charging polarity of the toner is negative has been described as a reverse development method, but the present invention is not limited thereto, and can be applied to a configuration of a reverse polarity.

In addition, the contents of the above embodiment and the above modification may be combined where possible.

The present invention can be widely applied to an image forming apparatus for forming an image on a photoreceptor having an overcoat layer.

Claims

1. An image forming apparatus that performs image formation by an electrophotographic method, comprising:

A photoreceptor having an overcoat layer containing a metal filler formed on the outermost layer;

a charging mechanism for charging the photoreceptor with a 1 st polarity;

an exposure mechanism that exposes the charged photoreceptor to form an electrostatic latent image on the photoreceptor;

a developer bearing body that bears a developer containing a toner of a 1 st polarity;

a bias power supply mechanism capable of switching between a 1 st developing bias and a 2 nd developing bias, the 1 st developing bias being used for developing an electrostatic latent image formed during image formation, the 2 nd developing bias being used during life monitoring of the photosensitive body, and charging a charge of a 2 nd polarity, which is opposite to the 1 st polarity, into the photosensitive body in an amount larger than the 1 st developing bias;

a control unit for controlling the charging unit and the exposure unit to charge the photoreceptor and inhibit exposure when a life monitoring period of the photoreceptor is reached, thereby forming an electrostatic latent image corresponding to a non-image on the photoreceptor, and controlling the bias power supply unit to execute a life monitoring mode for supplying the 2 nd developing bias to the developer carrier;

A determination unit configured to determine whether or not a toner image is formed on the photoreceptor due to non-uniformity in the dispersion state of the metal filler by executing the lifetime monitoring mode; and

and a broadcasting means for broadcasting that the film thickness of the overcoat layer of the photoreceptor is reduced by a predetermined film thickness if it is determined that the toner image is not formed.

2. The image forming apparatus according to claim 1,

with respect to the 1 st developing bias and the 2 nd developing bias,

an alternating current component is superimposed on the direct current component of the 1 st polarity,

the peak-to-peak voltage of the alternating current component of the 2 nd developing bias is set to a larger value or the frequency of the alternating current component is set to a smaller value than that of the 1 st developing bias.

3. The image forming apparatus according to claim 1,

with respect to the 1 st developing bias and the 2 nd developing bias,

an alternating current is superimposed on the direct current component of the 1 st polarity,

in the waveform of 1 cycle of the alternating current, with the voltage value of the superimposed direct current component of the 1 st polarity as a boundary, the side of the peak voltage having the 2 nd polarity is referred to as an alternating current component alpha, the side having the 1 st polarity is referred to as an alternating current component beta, and the duty ratio Dh is referred to as a value obtained by dividing the time T beta of the alternating current component beta by 1 cycle,

In the 2 nd developing bias, an absolute value Vn of a peak voltage of the alternating current component β is the same as the 1 st developing bias, an absolute value Vm of a peak voltage of the alternating current component α is larger than the 1 st developing bias, and a duty Dh is larger than the 1 st developing bias.

4. The image forming apparatus according to claim 2, comprising:

a charging power supply mechanism for supplying a charging voltage to the charging mechanism;

the control means supplies a charging voltage from the charging power supply means to the charging means such that a fog margin defined by a difference between a charging voltage of the 1 st polarity of the photoreceptor and a dc voltage of the 1 st polarity of the 2 nd developing bias in the life monitoring mode is larger than that in normal image formation.

5. The image forming apparatus according to any one of claims 1 to 4,

the control means executes the life monitoring mode when the cumulative number of image formations reaches a 1 st predetermined value, when the cumulative number of rotations or the cumulative operating time of the photoreceptor reaches a 2 nd predetermined value, or when the elapsed time from the time of a new product of the photoreceptor reaches a 3 rd predetermined value.

6. The image forming apparatus according to claim 5,

the control means executes the 2 nd execution when the number of times of image formation from the 1 st execution reaches a 4 th predetermined value smaller than the 1 st predetermined value, when the number of times of image formation from the 1 st execution reaches a 5 th predetermined value smaller than the 2 nd predetermined value, or when the elapsed time from the 1 st execution reaches a 6 th predetermined value smaller than the 3 rd predetermined value after the photoreceptor first executes the life monitoring mode since a new product.

7. The image forming apparatus according to claim 6,

the control means performs the 2 nd and 3 rd executions of the life monitoring mode so as to satisfy the relationship of U1> U2, when an interval from the 1 st execution to the 2 nd execution of the life monitoring mode is denoted as U1 and an interval from the 2 nd execution to the 3 rd execution is denoted as U2.

8. The image forming apparatus according to any one of claims 1 to 4, further comprising:

a transfer mechanism for transferring the toner image on the photoreceptor to a transfer object;

the determination means has detection means disposed at a position where the toner image transferred to the transfer target body after being formed on the photoreceptor by executing the life monitoring mode can be detected,

The determination means performs the determination based on a detection result of the toner image by the detection means.

9. The image forming apparatus according to claim 8,

the transfer target is an intermediate transfer member, or a sheet having a structure in which the toner image is transferred from the photoreceptor to the sheet via the intermediate transfer member.

10. The image forming apparatus according to claim 8,

the transfer receiving body is a sheet having a configuration in which the toner image is transferred from the photoreceptor to the sheet via an intermediate transfer body, and the transferred sheet is then discharged from the image forming apparatus,

the detection mechanism is a scanner that reads a toner image that is placed at a reading position and is present on the sheet after the output.

11. A method for monitoring the lifetime of a photoreceptor in an image forming apparatus for performing image formation by an electrophotographic system on the photoreceptor having an overcoat layer containing a metal filler formed on the outermost layer thereof,

the image forming apparatus includes:

a charging mechanism for charging the photoreceptor with a 1 st polarity;

a developer carrying body that carries a developer containing a 1 st polarity toner; and

the photoreceptor life monitoring method performs steps including:

a control step of controlling the charging mechanism and the exposure mechanism to charge the photoreceptor and inhibit exposure when a lifetime monitoring period of the photoreceptor is reached, thereby forming an electrostatic latent image corresponding to a non-image on the photoreceptor, and controlling the bias power supply mechanism to execute a lifetime monitoring mode in which the 2 nd developing bias is supplied to the developer carrier;

a determination step of determining whether or not a toner image is formed on the photoreceptor due to non-uniformity in the dispersion state of the metal filler by executing the lifetime monitoring mode; and

And a broadcasting step of broadcasting that the film thickness of the overcoat layer of the photoreceptor is reduced by a predetermined film thickness if it is determined that the toner image is not formed.

12. The method for monitoring the lifetime of a photoreceptor according to claim 11,

as for the 1 st developing bias and the 2 nd developing bias,

13. The photoreceptor life monitoring method according to claim 11,

as for the 1 st developing bias and the 2 nd developing bias,

14. The method for monitoring the lifetime of a photoreceptor according to claim 12,

the image forming apparatus includes a charging power supply mechanism that supplies a charging voltage to the charging mechanism;

in the control step, a charging voltage is supplied from the charging power supply mechanism to the charging mechanism so that a fog margin defined by a magnitude of a difference between a charging voltage of a 1 st polarity of the photoreceptor in the life monitor mode and a dc voltage of a 1 st polarity of the 2 nd developing bias is larger than that in normal image formation.

15. The method for monitoring the lifetime of a photoreceptor according to any one of claims 11 to 14,

in the control step, the lifetime monitoring mode is executed when the cumulative number of times of image formation reaches a 1 st predetermined value, when the cumulative number of rotations or cumulative operation time of the photoconductor reaches a 2 nd predetermined value, or when an elapsed time from the time of a new product of the photoconductor reaches a 3 rd predetermined value.

16. The method for monitoring the lifetime of a photoreceptor according to claim 15,

in the control step, after the life monitoring mode is first executed since the time of the photoreceptor is a new product, the 2 nd execution is executed when the number of times of image formation from the 1 st execution reaches a 4 th predetermined value smaller than a 1 st predetermined value, when the number of rotations or operation time of the photoreceptor from the 1 st execution reaches a 5 th predetermined value smaller than a 2 nd predetermined value, or when the elapsed time from the 1 st execution reaches a 6 th predetermined value smaller than a 3 rd predetermined value.

17. The photoreceptor life monitoring method according to claim 16,

in the control step, when the interval from the 1 st execution to the 2 nd execution of the lifetime monitoring mode is denoted by U1 and the interval from the 2 nd execution to the 3 rd execution is denoted by U2, the 2 nd and 3 rd executions of the lifetime monitoring mode are performed so as to satisfy the relationship of U1> U2.

18. The method for monitoring the lifetime of the photoreceptor according to any one of claims 11 to 14, wherein the image forming apparatus further comprises:

a transfer mechanism for transferring the toner image on the photoreceptor to a transfer target; and

a detection means disposed at a position where it is possible to detect a toner image transferred to the transfer target after being formed on the photoreceptor by executing the life monitoring mode,

in the determining step, the determination is performed based on a detection result of the toner image by the detecting means.

19. The photoreceptor life monitoring method according to claim 18,

the transfer receiving body is an intermediate transfer body, or a sheet having a structure in which the toner image is transferred from the photoreceptor to the sheet through the intermediate transfer body.

20. The photoreceptor life monitoring method according to claim 18,