JP7124629B2 - Image forming apparatus and photoreceptor lifetime monitoring method - Google Patents

Description

The present invention relates to image forming apparatuses such as copiers, printers, and facsimiles that form images by electrophotography, and more particularly to technology for detecting the film thickness of an overcoat layer formed on the outermost layer of the surface of a photoreceptor.

2. Description of the Related Art In recent years, image forming apparatuses have been required to be smaller and less costly, and at the same time, to be capable of forming images at higher speeds and with higher image quality. Furthermore, a long service life is also required, and for this reason, a layer called an overcoat layer that protects the underlying photosensitive layer is formed as the outermost layer of the photoreceptor.

However, if the thickness of the overcoat layer is too thick, the peripheral portion of the latent image spreads in terms of electric charge, so the toner is also attracted to the peripheral portion during the transfer process, resulting in a thicker image and a sharper image. It has the drawback of lacking sturdiness.

Therefore, it is necessary to make the overcoat layer as thin as possible.

In order to solve the contradictory problem of thinning and longevity, at present, a hard material is used for the overcoat layer to make it difficult to scrape and thinning is attempted to solve the contradiction.

However, when the overcoat layer is made hard and thin, new problems have arisen. This is because even with a hard overcoat layer, repeated image formation over a long period of time causes the film thickness to become thin and the protective function to the underlying layer to deteriorate. Film thickness monitoring techniques cannot measure the thickness of thin overcoat layers.

For example, Japanese Laid-Open Patent Publication No. 2002-200001 discloses a technique for detecting the degree of progress of abrasion of a film of a photoreceptor. Further, Japanese Patent Application Laid-Open No. 2002-100000 focuses on the fact that the photoreceptor changes in electric sensitivity characteristics due to film scraping, and proposes a technique for detecting the degree of progress of film scraping of the photoreceptor from changes in the toner image density on the photoreceptor. Disclose.

JP 2014-016651 A JP 2015-166820 A

In the above-mentioned existing technology, for example, the change in current of the charging roller is about 500 to 1000 μA when the film thickness of the photoreceptor changes by 10 μm. , the thickness of which is several μm at most, and even if the entire film thickness is removed, the amount of change in current is less than several hundred μA, and the change is no more than a variation in measurement.

Also, even if it is attempted to monitor the film thickness from the image density, there is almost no change in density when the thickness changes by several μm, which is not practical. For this reason, film thickness monitoring is impossible with existing techniques.

Furthermore, a method of estimating the scraped amount based on the number of rotations of the photoreceptor, the number of printed sheets, the usage time, the accumulated time, etc., and setting a flag indicating the end of the service life when the specified number is reached is being studied. Because it ignores the physical properties of , cleaning members, etc., variations in installation, and changes in the state of energization from the charging member and transfer member, the flag is raised or already It is possible and impractical to have a situation where the lifetime has been exceeded but the flag has not yet been raised.

The present invention proposes a technology capable of monitoring the film thickness of a thin overcoat layer, which could not be monitored by the existing technology, based on the findings of the inventors, which will be described later.

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 electrophotography, and includes a photoreceptor having an overcoat layer containing a metal filler formed as the outermost layer. charging means for charging the photoreceptor to a first polarity; exposure means for exposing the charged photoreceptor to form an electrostatic latent image on the photoreceptor; and toner of the first polarity. a first developing bias used for developing an electrostatic latent image formed during image formation as a developing bias supplied to the developer carrier; and a service life of the photoreceptor. a bias power supply means which is used for monitoring and can be switched between a second developing bias for injecting more charge of a second polarity opposite to the first polarity into the photosensitive member than the first developing bias, and the photosensitive member; When the life of the body is monitored, the charging means and the exposure means are controlled to prohibit exposure while charging the photoreceptor, thereby forming an electrostatic latent image corresponding to a non-image on the photoreceptor. control means for executing a life monitoring mode for controlling the bias power supply means to supply the second developing bias to the developer bearing member; determining means for determining whether or not a toner image caused by uniformity has been formed on the photoreceptor; and a notification means for notifying that the film thickness has decreased below the specified film thickness.

The first developing bias and the second developing bias are obtained by superimposing an AC component on a DC component of the first polarity. The two-peak voltage may be set to a large value, or the AC component frequency may be set to a small value.

Further, the first developing bias and the second developing bias are obtained by superimposing an AC component on a DC component of the first polarity. A value obtained by dividing the time Tβ of the AC component β by one cycle is defined as the duty ratio Dh. , the absolute value Vn of the peak voltage of the AC component β of the second developing bias is the same as that of the first developing bias, and the absolute value Vm of the peak voltage of the AC component α is larger than that of the first developing bias. Furthermore, the duty ratio Dh may be larger than the first developing bias.

Further, a charging power supply means for supplying a charging voltage to the charging means is provided, and the control means controls the charging voltage of the first polarity of the photosensitive member and the first polarity of the second developing bias in the life monitoring mode. The charging voltage may be supplied from the charging power supply unit to the charging unit so that the fogging margin defined by the magnitude of the difference from the DC voltage is larger than that in normal image formation.

Further, the control means controls when the cumulative number of times of image formation reaches a first predetermined value, when the cumulative number of revolutions or cumulative operation time of the photoreceptor reaches a second predetermined value, or when the photoreceptor is new. The life monitoring mode may be executed when the elapsed time from the start reaches a third predetermined value.

Here, after the photoreceptor is brand new, the control means executes the life monitoring mode for the first time, and then executes the second execution. When reaching a smaller fourth predetermined value, when the number of rotations of the photoreceptor or the operating time from the first execution reaches a fifth predetermined value smaller than the second predetermined value, or from the first execution may be executed when the elapsed time of reaches a sixth predetermined value that is smaller than the third predetermined value.

Further, the control means has a relationship of U1>U2, where U1 is the interval from the first implementation to the second implementation of the life monitoring mode, and U2 is the interval from the second implementation to the third implementation of the life monitoring mode. The life monitoring mode may be performed for the second time and the third time so as to satisfy

Further, a transfer unit for transferring the toner image on the photoreceptor to a transfer material is further provided, and the determination unit determines whether the toner image is transferred to the transfer material after the toner image is formed on the photoreceptor by executing the life monitoring mode. It is also possible to have detecting means arranged at a position capable of detecting the toner image, and to perform the determination based on the detection result of the toner image by the detecting means.

Here, the transfer-receiving body may be an intermediate transfer body, or a sheet in which the toner image is transferred from the photoreceptor to the sheet via the intermediate transfer body.

Further, the transfer-receiving member is a sheet in a configuration in which the toner image is transferred from the photosensitive member to the sheet through an intermediate transfer member, and the transferred sheet is output from an image forming apparatus. , after the output, the scanner may read a toner image existing on the sheet placed at the reading position.

A photoreceptor life monitoring method according to the present invention is a photoreceptor life monitoring method in an image forming apparatus for forming an image by electrophotography on a photoreceptor having an overcoat layer containing a metal filler formed on the outermost layer. The image forming apparatus includes charging means for charging the photoreceptor to a first polarity, and exposure means for exposing the charged photoreceptor to form an electrostatic latent image on the photoreceptor. , a developer bearing member for carrying a developer containing a toner of a first polarity; It is possible to switch between a bias and a second developing bias that is used when monitoring the life of the photoreceptor and injects more charge of a second polarity opposite to the first polarity into the photoreceptor than the first developing bias. and a bias power supply means, wherein the photoreceptor life monitoring method controls the charging means and the exposure means to prohibit exposure while charging the photoreceptor when the life monitoring time of the photoreceptor comes. a control for forming an electrostatic latent image corresponding to a non-image on the photosensitive member and executing a life monitoring mode for controlling the bias power supply means to supply the second developing bias to the developer carrier; a determination step of determining whether or not a toner image is formed on the photoreceptor due to non-uniformity of the dispersed state of the metal filler by executing the life monitoring mode; and a reporting step of reporting that the thickness of the overcoat layer of the photoreceptor has decreased below the specified thickness when it is determined that the overcoat layer has not been formed.

Prior to explaining the reason why the film thickness of the thin overcoat layer can be monitored by the above configuration, knowledge obtained by the present inventor will be explained.
<<Knowledge acquired by the present inventor>>
Metal fillers are dispersed in the overcoat layer, which is the outermost surface of the photoreceptor, to give it mechanical strength. There is a mixed (dense) part in In the overcoat layer, the portion where the filler is concentrated has a lower electrical resistance value than the other portion. Even if the overcoat layer contains areas with low electrical resistance locally, in the image forming process during normal printing, i.e. charging, exposing, and developing, the potential of the developing roller in the developing section against the charged potential on the photoreceptor By adjusting the magnitude of the developing bias supplied to the developer carrier such as the developer carrier, the formed image is prevented from being affected.

In contrast to the fact that the developing bias is adjusted so as not to affect the formed image, the inventor of the present invention reversed the idea and applied a developing bias that would affect the formed image. When the overcoat layer is present, the formed image is affected due to non-uniformity in the dispersed state of the filler. It was thought that such an influence of the formed image should be eliminated.

In other words, if the formed image is affected, the overcoat layer is not so worn, and if the effect disappears, it can be determined that the photoreceptor has reached the end of its life due to wear of the overcoat layer.

Specifically, in a so-called reversal development method in which the photoreceptor and toner have the same polarity, for example, a negative polarity (first polarity), the developing bias is set to a positive polarity (second polarity) rather than the first developing bias during normal printing. The second developing bias is set to a voltage that injects a large amount of charge (polarity). This voltage is obtained by increasing the positive component of the AC voltage superimposed on the DC voltage, for example, by increasing the peak-to-peak voltage of the AC or lowering the frequency.

After uniformly charging the photoreceptor, the second developing bias is applied to the developer bearing member of the developing section while forming an electrostatic latent image corresponding to a non-image without exposure, that is, without adhering toner. is supplied, the electrostatic latent image is brought to the development position. Here, the development position refers to a position on the peripheral surface of the photoreceptor facing the developer carrier with a slight or almost no gap.

Even if the non-image electrostatic latent image reaches the development position, the toner should not adhere to the photoreceptor. The voltage is such that a large amount is injected into the photoreceptor.

For this reason, in spite of being a non-image area, the low resistance area where the electrical resistance value is lowered due to the dense filler is different from the surrounding high resistance area where the electrical resistance value is not lowered. , the potential (negative) slightly approaches 0 V due to the amount of positive charge supplied by the developing bias due to the small electrical resistance value.

In the reversal development method, the closer the potential on the photoreceptor is to 0 V, the easier it is for the toner to move from the developer carrier to the photoreceptor at the development position. That is, it becomes easier to develop with toner. Among the non-image areas on the photoreceptor, in high-resistance areas where the filler is not densely packed (properly dispersed), toner does not adhere as it should even if a large amount of positive charge is injected, resulting in localized A phenomenon occurs in which the toner adheres only to the relatively low-resistance portion as the potential decreases. For this reason, the injection of positive charge is such that toner does not adhere to the high-resistance areas where the filler is not concentrated among the non-image areas on the photoreceptor, and toner only adheres to the low-resistance areas where the filler is concentrated. A second development bias is predetermined to provide an injection amount that adheres.

However, even though toner adheres to the non-image area, the absolute value of the negative potential remains considerably high because the non-image area has not been exposed. For this reason, even if a positive charge is injected by the developing bias, the potential (absolute value) of the photoreceptor does not drop to near 0 V, and the toner adhering to the low resistance portion is not a so-called solid image, but rather number of toner particles are collected, which is the so-called fog level.

FIG. 15 is a schematic plan view of the sheet S after the toner image Tf made of the toner adhering to the low-resistance portion is transferred from the drum-type photoreceptor to the sheet S. As shown in FIG. As shown in the drawing, the toner image Tf has a density that causes fogging, and is hereinafter referred to as a fogging toner image Tf.

In the figure, the fog toner images Tf are scattered at three locations C, D, and E spaced apart in the main scanning direction. , that is, the part where the filler is dense. The interval P in the sub-scanning direction corresponds to the peripheral length of the photosensitive member.

Originally, the entire surface of the sheet S is non-image, and the fact that the fog toner image Tf is locally formed affects the originally formed image. The film thickness of the overcoat layer can be monitored by determining whether such a fog toner image Tf is formed. The fog toner image Tf can be detected by, for example, an optical sensor.

According to the findings of the present inventors, a fog toner image Tf as shown in FIG. , the fog toner image Tf is not formed, that is, the entire surface becomes a non-image area. Therefore, according to the present invention, it is possible to monitor the end of life due to wear of a thin overcoat layer that cannot be detected by existing film thickness detection techniques.

With the above configuration, it is possible to accurately monitor the film thickness of the thin overcoat layer.

1 is a diagram showing the overall configuration of a printer according to an embodiment; FIG. 3 is a diagram showing a cross-sectional configuration of a photoreceptor drum; FIG. 3 is a block diagram showing the configuration of a control unit; FIG. 3 is a block diagram showing the configuration of a developing bias power supply section; FIG. (a) is a diagram showing the waveform of the developing bias during normal printing, and (b) is a diagram showing the waveform of the developing bias in the photoreceptor life monitoring mode. 3 is a block diagram showing the configuration of a charging power supply; FIG. FIG. 3 is a schematic diagram for explaining the reason why fog toner is formed in a non-image area; FIG. 10 is a diagram showing an example of an appropriate range of Vpp for an AC component of a developing bias; FIG. 10 is a diagram showing the proper range of the duty ratio and frequency of the AC component of the developing bias; FIG. 10 is a diagram showing a modified example of the waveform of the developing bias; FIG. 10 is a diagram showing another modification of the waveform of the developing bias; 5 is a flow chart showing the details of the print operation executed by the control unit and the control of the photoreceptor life monitoring mode; 4 is a flow chart showing the contents of a subroutine for execution control of a photoreceptor life monitoring mode; 5 is a graph illustrating the relationship between the toner adhesion amount on the intermediate transfer belt and the output voltage of the detection sensor; FIG. 2 is a schematic plan view of a sheet after a toner image adhered to a low-resistance portion existing in an overcoat layer of a photoreceptor is transferred from the photoreceptor to the sheet; It is a figure which shows the modification of the arrangement|positioning location of a detection sensor.

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 "printer") as an example.
(1) Overall Configuration of Printer FIG. 1 is a diagram showing the overall configuration of a printer 1. As shown in FIG.

As shown in the figure, the printer 1 forms an image by a well-known electrophotographic method, and includes an image forming unit 10, an intermediate transfer unit 20, a paper feeding unit 30, a fixing unit 40, and a control unit. 50, a developing bias power supply unit 60, an operation unit 70, and a charging power supply unit 80, which is connected to a network (for example, a LAN) and receives a print job execution instruction from an external terminal (not shown). Upon acceptance, color image formation of 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 Y to K colors, respectively. The image forming unit 10Y includes a photosensitive drum 11Y as an example of an image bearing member, a charging roller 12Y as a charging unit disposed around the photosensitive drum 11Y, an exposure unit 13Y, a developing unit 14Y, a primary transfer roller 15Y, and a photosensitive drum. A cleaner for cleaning 11Y is provided.

As shown in FIG. 2, the photoreceptor drum 11Y is made of metal, for example, an aluminum tube 91, an undercoat layer (UCL) 92, a charge generation layer (CGL) 93, a charge transport layer (CTL) 94, and a hard surface. An overcoat layer (OCL) 95 as a layer is composed of an organic photoreceptor (OPC) laminated in this order. For example, the total thickness of UCL 92 and CGL 93 is 2 μm, the thickness of CTL 94 is 20-30 μm, and the thickness of overcoat layer 95 is 2-4 μm. In order to give the overcoat layer 95 mechanical strength and appropriate electrical resistance, it contains and disperses a conductive metal filler obtained by surface-treating a processed metal such as titanium oxide, tin oxide, or copper alumina. there is By providing the overcoat layer 95, the life of the photoreceptor drum 11Y can be extended as compared with the configuration without the overcoat layer 95. FIG.

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 charging polarity is made negative.

The exposure unit 13Y exposes and scans the charged photoreceptor drum 11Y with laser light to form an electrostatic latent image on the photoreceptor drum 11Y.

The development unit 14Y is a development unit of a reversal development method, and the developer D is carried on a development roller 19Y, which is an example of a developer carrying member, arranged to face the photoreceptor drum 11Y at the development position of the photoreceptor drum 11Y. is used to develop the electrostatic latent image on the photosensitive drum 11Y.

Here, as the developer D, a two-component developer containing a carrier having a positive charging polarity and a toner having a negative charging polarity is used. Development is performed by the toner moving to the photosensitive drum 11Y and adhering to the electrostatic latent image on the photosensitive drum 11Y, and a yellow toner image is visualized on the photosensitive drum 11Y. As the toner, for example, polymerized toner having a particle size of 7 μm or less, preferably 4.5 μm or more and 6.5 μm or less is used. Note that pulverized toner may also be used.

The primary transfer roller 15Y is supplied with a positive transfer voltage from a transfer power source (not shown), and transfers the Y-color toner image on the photoreceptor drum 11Y to the intermediate transfer portion 20 by electrostatic action at the transfer position on the photoreceptor drum 11Y. are primarily transferred onto the intermediate transfer belt 21 . 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 units 13M, 13C, and 13K, and primary transfer rollers. 15M, 15C and 15K.

The intermediate transfer belt 21 is an endless belt, stretched between a driving roller and a driven roller, and driven by the driving roller in a direction indicated by an arrow (belt winding direction). The intermediate transfer belt 21 is made of, for example, polyphenylene sulfide (PPS) resin dispersed with carbon to have a surface resistivity of 10 ⁹ to 10 ¹² Ω/□ and a volume resistivity of 10 ⁶ to 10 ¹² Ω/cm. used and has a seamless belt shape. Other resins such as polycarbonate (PC) resin, polyimide (PI) resin, urethane-based resin, fluorine-based resin, and nylon-based resin contain conductive fillers such as carbon and ionic conductive materials dispersedly to adjust the resistance. material may be used.

In the image forming units 10Y, 10M, 10C, and 10K, toner images of corresponding colors are formed on the photosensitive drums 11Y, 11M, 11C, and 11K, and the formed toner images are transferred to the intermediate transfer belt 21, respectively. transcribed above. The image forming operation of each color of Y to K is performed from the upstream side to the downstream side in the belt rotation direction so that the toner images of each color are superimposed and transferred (primary transfer) to the same position of the running intermediate transfer belt 21 . It is executed with staggered timing.

The paper feed unit 30 feeds out the recording sheets S one by one from the paper feed cassette in accordance with the above-described image forming timing in the image forming unit 10 , and performs secondary transfer on the fed out recording sheets S along the conveying path 35 . Send to roller 22 .

When the recording sheet S sent 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, each color toner image formed on the intermediate transfer belt 21 is transferred. They are secondary-transferred collectively onto the recording sheet S by the electrostatic action of the secondary transfer roller 22 .

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

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

The development bias power supply section 60 supplies a development bias voltage for development to the development rollers 19Y, 19M, 19C and 19K of the development sections 14Y, 14M, 14C and 14K. Sections 60Y to 60K are provided. Each of the power supply units 60Y to 60K outputs 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, if the charging potential of the photosensitive drum 11Y is -Vo, the voltage of the DC component of the developing bias voltage is -Vdc, and the potential of the exposed portion (image forming area) of the photosensitive drum 11Y is -Vl, Their absolute values have a relationship of Vo>Vdc>Vl. As a result, the toner on the developing roller 19Y moves to the image forming area on the photosensitive drum 11Y to perform reversal development, forming a toner image on the image forming area. The same applies to other image forming units 10M to 10K.

A developing bias voltage in which an AC component is superimposed on a DC component is applied to the developing rollers 19Y to 19K. , and the AC component reciprocates the toner particles of the developer D between the developing rollers 19Y to 19K and the photosensitive drums 11Y to 11K. Since the movement of the photosensitive drums 11Y to 11K from the photosensitive drums 11Y to 11K to the electrostatic latent image is facilitated, the developability is improved.

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

A reflective optical sensor having a light-emitting portion and a light-receiving portion is provided around the intermediate transfer belt 21, downstream of the image forming unit 10K and upstream of the secondary transfer position 22a in the belt running direction. A detection sensor 23 consisting of is arranged.

The detection sensor 23 is for detecting the fog toner image Tf shown in FIG. is generated and output to the control unit 50 .

In the photoreceptor life monitoring mode, the fog toner image Tf exists in the portion where the fog toner image Tf is formed on the intermediate transfer belt 21 because the amount of reflected light is smaller than that in the non-image region where the fog toner image Tf does not exist. The output signal changes depending on whether or not As the detection sensor 23, it is possible to use a sensor having performance comparable to that of an optical sensor for patch detection used in a known stabilization technique.

The control unit 50 executes a photoreceptor life monitoring mode, and based on the output signal of the detection sensor 23, individually determines whether each of the photoreceptor drums 11Y to 11K has reached the end of its life.

The operation unit 70 is arranged on the front surface of the printer 1 at a position that is easy for the user to operate. A display unit 71 is provided for displaying a message or the like indicating the life determination result of the photosensitive drum.
(2) Configuration of Control Unit 50 FIG. 3 is a block diagram showing the configuration of the control unit 50. As shown in FIG.

As shown in the figure, the control unit 50 includes, as main components, a communication interface (I/F) unit 101, a CPU 102, a ROM 103, a RAM 104, a photoreceptor life monitoring mode execution unit 105, and an accumulated number of prints. A storage unit 106 is provided, and each unit can exchange signals and data with each other.

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

The CPU 102 reads necessary programs from the ROM 103 and controls the image forming unit 10, the intermediate transfer unit 20, the paper feeding unit 30, the fixing unit 40, etc. based on the print job data received via the communication I/F unit 101. to smoothly execute the image forming operation. A RAM 104 serves as a work area for the CPU 102 .

Photoreceptor life monitoring mode execution unit 105 includes execution timing determination unit 111 , life determination unit 112 , and determination result output unit 113 .

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

On the other hand, when it is determined that it is time to execute the photoreceptor life monitoring mode, the development bias power supply unit 60 and the charging power supply unit 80 are turned on during standby other than during normal printing to execute the photoreceptor life monitoring mode. An instruction is given to switch to the developing bias and charging voltage when the photoreceptor life monitoring mode is executed.

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

Upon receiving the instruction from the execution time determination unit 111 , the life determination unit 112 determines the life of the photosensitive member based on the output signal of the detection sensor 23 . Specifically, when the fog toner image Tf shown in FIG. It is determined that the photoreceptor has reached the end of its life because the coat layer 95 is almost non-existent or has completely disappeared due to abrasion or abrasion. When the overcoat layer 95 as a protective layer is removed, the charge transport layer 94 underneath is exposed. However, the charge transport layer 94 is not so hard and is rapidly scraped off to reach the end of its functional life as a photoreceptor. become. The lifespan determination unit 112 sends the determination result to the determination result output unit 113 .

Only when it is determined that the photoreceptor has reached the end of its life, the determination result output unit 113 causes the display unit 71 of the operation unit 70 to display a message to that effect, thereby indicating that the photoreceptor has reached the end of its life. Notify users that

The cumulative number of printed sheets storage unit 106 stores the current cumulative number of printed sheets Qm incremented by 1 as a new cumulative number of printed sheets Qm each time printing of one sheet S is completed. It is a storage unit. By referring to the cumulative number of prints Qm stored in the cumulative number of prints storage unit 106, the cumulative number of prints Qm executed since the printer 1 was brand new can be confirmed.

(3) Configuration of Development Bias Power Supply Unit 60 FIG. 4 is a block diagram showing the configuration of the development bias power supply unit 60. As shown in FIG.

As shown in the figure, the development bias power supply section 60 includes a Y-color power supply section 60Y, an M-color power supply section 60M, a C-color power supply section 60C, and a K-color power supply section 60K. Since the Y-color power supply unit 60Y to K-color power supply unit 60K have basically the same configuration, 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 Y-color power source section 60 Y has a first bias output section 61 , a second bias output section 62 and a switching section 63 .

The first bias output unit 61 is formed by connecting a DC power supply 61a and an AC power supply 61b in series. A positive terminal 61c of the DC power supply 61a is grounded, and the AC voltage of the AC power supply 61b is superimposed on the DC voltage of the DC power supply 61a. The applied developing bias Vb1 is output as the developing bias for normal printing.

FIG. 5(a) is a diagram showing only one cycle of the waveform of the developing bias Vb1. The horizontal axis is time, the vertical axis is voltage value, and the upper side of 0 V (GND) is the negative polarity. The bottom side is positive polarity.

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

In the waveform of one cycle of alternating current, the side with the peak voltage having positive polarity (second polarity) with -Vdc of the superimposed DC voltage as the boundary is the alternating current component α, and the side with negative polarity (first polarity) is the AC component β, the peak voltage of the AC component α is Vm (here, 700 V), and the peak voltage of the AC component β is -Vn (here, -1050 V).

Further, when the value obtained by dividing the time Tα of the AC component α, the time Tβ of the AC component β, and the time Tβ by one period is the duty ratio Dh, here, Tα=Tβ, so the duty ratio Dh is 50%. It's becoming

Returning to FIG. 4, the second bias output section 62 is formed by connecting a DC power supply 62a and an AC power supply 62b in series, and the plus terminal 62c of the DC power supply 62a is grounded. The developing bias Vb2 superimposed with the AC voltage 62b is output as the developing bias during life monitoring.

FIG. 5B is a diagram showing the waveform of the developing bias Vb2 by extracting only one cycle.

As shown in the figure, the developing bias Vb2 differs from the developing bias Vb1 in peak-to-peak Vpp' value, but -Vdc, frequency H, and duty ratio Dh are the same. Vpp' of the developing bias Vb2 is 1.6 kV, which is larger than Vpp. The peak voltage (absolute value) of the AC component α on the positive side is Vm', which is higher than Vm during normal printing, and the peak voltage of the AC component β on the negative side is -Vn', which is normal. is smaller (larger in absolute value) than -Vn at the time of printing.

Also, the charging potential of the photosensitive drum 11Y is -Vo2, for example, -550 V, which is larger in absolute value than -Vo1 at the normal time. The reason why the developing bias Vb2 during life monitoring is different from the developing bias Vb1 during normal operation is to positively form the fog toner image Tf shown in FIG. 15 in the non-image area. The reason for this will be described in the following section (5) Formation of fogging toner Tf.

Returning to FIG. 4, the switching unit 63 determines which of the first bias output unit 61 and the second bias output unit 62 supplies the developing bias to the developing roller 19Y based on the control signal from the control unit 50. It is a switch that switches between Here, the developing bias Vb1 is supplied to the developing roller 19Y during normal printing, and the developing bias Vb2 is supplied to the developing roller 19Y during life monitoring.

(4) Configuration of Charging Power Supply Unit 80 FIG. 6 is a block diagram showing the configuration of the charging power supply unit 80. As shown in FIG.

As shown in the figure, the charging power supply section 80 includes a Y-color power supply section 80Y, an M-color power supply section 80M, a C-color power supply section 80C, and a K-color power supply section 80K. Since the Y-color power supply unit 80Y to K-color power supply unit 80K have basically 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 Y-color power supply section 80</b>Y has a first charging voltage output section 81 , a second charging voltage output section 82 , and a switching section 83 .

The first charging voltage output unit 81 has a DC power supply 81a, and the positive terminal 81b of the DC power supply 81a is grounded. Output as charged voltage. Vo1 is, for example, -500V.

The second charging voltage output unit 82 has a DC power supply 82a, and a positive terminal 82b of the DC power supply 82a is grounded. Output as voltage. Vo2 is larger than Vo1 in absolute value, eg, -550V. The reason why the absolute value of Vo2 is larger than Vo1 will be described later.

The switching unit 83 is a switch for switching which of the first charging voltage output unit 81 and the second charging voltage output unit 82 to supply the charging voltage to the charging roller 12Y based on the control signal from the control unit 50. be. Here, -Vo1 is supplied to the charging roller 12Y during normal printing, and -Vo2 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. ), the surface potential of the photoreceptor drum 11Y (hereinafter referred to as “photoreceptor potential”) changes during charging, immediately before development, and during development when the development process is performed without exposure. are shown in this order.

Five different locations A, B, C, D, and E are taken on the drum surface in the main scanning direction. showing. Therefore, during the period from when the photoreceptor drum 11Y is brand new to when the wear amount of the overcoat layer 95 reaches the specified value, the fog toner image Tf (FIG. 15) is formed on the portions C, D, and E on the drum surface. become. Reference numeral 111 denotes the rotation shaft of the photosensitive drum 11Y.

Immediately before the charging and developing steps, the photoreceptor potential in the non-image areas is -Vo, and the same is true for portions C, D and E. In the development process, attention is paid to the portion D among the portions C, D, and E, and on the drum surface, the portion D and the peripheral regions I and J (portions where the filler is not concentrated) on both sides of the portion D in the main scanning direction are formed. It shows the photoreceptor potential.

During the time Tα during which the positive component is supplied in one cycle of AC (alternating current), the potential difference between the photoreceptor potential −Vo and the AC component +Vmax causes the charge of the positive component (positive charge) to flow between the portion D and the area D. I and J are injected simultaneously. It is presumed that the injection of this positive charge causes the following change in the photoreceptor potential.

That is, in the portion D, due to the density of the filler, the electrical resistance value is greatly reduced compared to the peripheral regions I and J, and -Vo increases to -Va (>-Vo) (absolute value down). At this time, the magnitude relationship with -Vdc, which is the DC component of the developing bias, is -Va>-Vdc. This magnitude relationship produces an electric field in a direction that directs the negative polarity toner from the developing roller 19Y toward the photosensitive drum 11Y. In other words, the injection of the positive charge brings the portion D into a state as if it were (pseudo) exposed to light, and it appears that a normal development process is being performed.

On the other hand, since the peripheral areas I and J have a high resistance, they remain -Vo and remain almost unchanged from the charged state in the original non-image areas.

During the remaining time Tβ during which the negative component is supplied in one cycle of AC, the photoreceptor potential remains raised to -Va in the portion D, and the potential difference Ve between -Vmin of the AC component causes development. Toner moves from the roller 19Y to the photosensitive drum 11Y. This phenomenon corresponds to the above apparent normal development, and the fog toner image Tf shown in FIG. The fact that the fog toner image Tf is formed by this apparently regular development is called photoreceptor fog.

On the other hand, in the peripheral areas I and J, the photoreceptor potential remains -Vo, which is the same as the original non-image area. Toner does not move and adhere. That is, in the areas I and J, the fog toner image Tf due to the fogging of the photosensitive member is not formed.

Here, if the values of -Vmin and -Vdc are fixed and -Vo is set to a slightly larger absolute value, the potential difference Vz between -Vdc and -Vo becomes larger. An increase in the potential difference Vz means a decrease in the electric field in the direction in which the negative polarity toner is directed from the developing roller 19Y toward the photosensitive drum 11Y in the peripheral regions I and J. In areas I and J, it is possible to further suppress the occurrence of so-called development fog, in which toner particles move toward the photoreceptor due to the magnitude of the difference between -Vdc and -Vo regardless of the non-uniformity of the dispersion state of the toner particles. Become. The potential difference Vz is called a fog margin, and the larger the fog margin is, the more the development fog can be suppressed. In this sense, the causes of the photoreceptor fogging and the development fogging are different.

In FIG. 5B, the charging voltage (=-Vo2) is slightly larger than the charging voltage (=-Vo1) during normal printing by an absolute value of .delta.1. This is to suppress it more than when printing.

Although the portion D has been described above, the photoreceptor potential increases (reduces in absolute value) from the original -Vo to -Va in the other portions C and E as well as the portion D, but the electric resistance If the values decrease in different ways, the greater the decrease in the potential resistance value, the smaller the absolute value of -Va (approaching 0 V), and the greater the potential difference Ve, so that the toner that moves from the developing unit 14Y to the drum surface. As the amount increases, the density of the fog toner image Tf tends to increase.

In the above description, it has been described that the photoreceptor potential in the portion D rises from -Vo to -Va by supplying a positive charge. It occurs only when a positive charge is applied to the portion where the V is greatly reduced, and not when a negative charge is applied. This is because 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 process, and the negative charge contained in the AC component of the developing bias is supplied to the drum surface. It is presumed that this is because, even if such a change is made, the action of further lowering (increasing the absolute value of) the potential of the photoreceptor at that time does not occur.

As a condition for causing the above-mentioned photoreceptor fogging, the inventor of the present application found an example of an appropriate range of the peak-to-peak voltage Vpp', which is the AC component of the developing bias Vb2, the duty ratio Dh, and the frequency H shown in FIG. was derived experimentally.

8 is a diagram showing the proper range of the peak-to-peak voltage Vpp of the developing bias Vb2, and FIG. 9 is a diagram showing the proper ranges of the duty ratio Dh and the frequency H. As shown in FIG. In FIG. 8, the fog rank on the vertical axis indicates the degree of fogging. A rank of 5 indicates no fogging, and the smaller the number, the more noticeable the occurrence of fogging. The amount of toner adhered increases (the density increases), and rank 1 indicates the worst fog state. Generally, there is no problem in image quality at rank 3 or higher, and image quality lower than rank 3 is regarded as deterioration in image quality.

In the present embodiment, the life of the overcoat layer 95 is judged based on whether or not the fog toner image Tf is formed when an electrostatic latent image corresponding to a non-image is developed. As a result, fogging is likely to occur, that is, not only the portions C, D, and E having low resistance due to the dense filler, but also the other high-resistance regions I and J are likely to have fogging on the photoreceptor.

For this reason, when monitoring the service life, fogging of the photosensitive member occurs in the low-resistance areas C, D, and E but does not occur in the high-resistance areas I and J. Vpp' is determined within a range of 3 or more. Specifically, for rank 3 or higher, 1600V was set as Vpp' at the time of life determination in the range of Vpp in which the fog toner image Tf is likely to occur, here 1400V to 1600V.

Similarly, in FIG. 9, when the duty ratio Dh is set to 40 (black triangle plot), the fog rank falls within the range of 3 or more when the frequency H is 5 to 8.5 kHz, but the duty ratio Dh is set to 50. In the case (plotted with black squares), it was found that the fog rank falls within the range of 3 or more when the frequency H is between about 6 and 8.5 kHz. Here, the normal duty ratio Dh is 50% and the frequency H is 7 kHz, and from the figure, the fog rank is in the range of 3 or more. H (=7 kHz) was set. Of course, the value is not limited to the above values, and when the overcoat layer 95 is present, the fog toner image Tf is formed only in the portions (C, D, etc.) where the resistance is low due to the density of the filler due to fogging of the photosensitive member. , appropriate values for the DC component (voltage) and AC component (Vpp, duty ratio Dh, frequency H) of the developing bias Vb2 are determined in advance through experiments or the like.

For example, the developing bias Vb21 shown in FIG. 10 can also be employed. Specifically, the developing bias Vb21 is such that Vmin (peak voltage of the AC component β) is the same as -Vn during normal printing, as opposed to the developing bias Vb2 shown in FIG. Of these waveforms, the time Tβ of the AC component β on the negative side is longer than the time Tα of the AC component α on the positive side, and the waveform has a duty ratio Dh increased from 50% to 60%, for example.

Also, for example, a developing bias Vb22 shown in FIG. 11 can be employed. Specifically, the developing bias Vb22 is such that Vmax and Vmin are the same as Vm and -Vn during normal printing with respect to the developing bias Vb2 shown in FIG. The waveform of the developing bias Vb22 is 4.5 kHz, which is smaller than that during printing, for example, 7 kHz during normal printing, and the duty ratio Dh is 50%, which is the same as during normal printing. The time Tc of the AC components α and β in one cycle is longer than Tα and Tβ during normal printing by the amount that the frequency H is smaller than during normal printing.

Developing biases Vb21 and 22 shown in FIGS. 10 and 11 correspond to Vb1 during normal printing by δ2 shown in FIG. 10 and δ3 shown in FIG. (corresponding to the increment of the component), a large amount of positive charge can be injected into the photoreceptor.

By changing the values of Vpp, the frequency H, and the duty ratio Dh from those during normal printing, the overcoat layer 95 is formed so that the amount of positive charge injected into the photoreceptor is greater than that during normal printing. When there is a fog toner image Tf due to fogging on the photoreceptor, the fogging toner image Tf due to the fogging on the photoreceptor is formed in the low-resistance portions (C, D, etc.) where the filler is dense, and the fogging toner image Tf due to the fogging on the photoreceptor is formed in the other high-resistance areas. can be prevented from forming. At least one of Vpp, frequency H, and duty ratio Dh can be changed from that during normal printing so that the fog toner image Tf is formed only on the low-resistance portion of the photosensitive member.

(6) Print Operation and Photoreceptor Life Monitoring Mode Control FIG. 12 is a flow chart showing the details of the print operation and photoreceptor life monitoring mode control executed by the controller 50 . This flow is executed every time it is called by a main routine (not shown) at regular intervals.

As shown in the figure, it is determined whether or not to start a print job (step S1). If the print job is not to be started ("No" in step S1), the process returns.

When it is determined that the print job has started ("Yes" in step S1), the charging potential Vo is set to -Vo1, and the developing bias Vb is set to Vb1 (step S2). This setting is performed by the execution time determining unit 111 instructing the developing bias power supply unit 60 and the charging power supply unit 80 to output the normal developing bias (=Vb1) and charging voltage (=-Vo1). will be

The print job is executed under the condition that the charging potential Vo is -Vo1 and the developing bias Vb is Vb1 (step S3). When it is determined that the print job has ended ("Yes" in step S4), the process proceeds to step S5.

In step S5, the current cumulative number of prints Qm is read from the cumulative number of prints storage unit 106 and obtained. The execution timing determination unit 111 is in charge of the processing of step S5 and subsequent steps S6 and S7.

It is determined whether or not the cumulative number of printed sheets Qm is equal to or greater than a predetermined value Qa (step S6). Here, the predetermined value Qa is, for example, 70% of the design cumulative number of printed sheets assumed to reach the life of the photoreceptor. Specifically, if the designed number of sheets is, for example, 1,000,000 sheets, the predetermined value Qa is 700,000 sheets.

If it is determined that the cumulative number of prints Qm≧predetermined value Qa ("Yes" in step S6), then the cumulative number of prints Qm is a multiple of 10000 (=10k), that is, 700,000, 710,000, 720,000. . . is determined (step S7).

When it is determined that the cumulative number of printed sheets Qm is a multiple of 10000 ("Yes" in step S7), the photosensitive member life monitoring mode is executed (step 8), 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. It is not yet time to execute the photoreceptor life monitoring mode, so the process returns.

Also, even if it is determined that the cumulative number of printed sheets Qm is not a multiple of 10000 ("No" in step S7), the process returns as it is. This is because the cumulative number of printed sheets Qm≧the predetermined value Qa, so the wear of the overcoat layer 95 progresses, but the wear of the overcoat layer 95 progresses extremely slowly. For this reason, even if the photoreceptor life monitoring mode is repeatedly executed on the way to 10,000 sheets, the determination result often does not change each time. In this way, when the cumulative number of prints Qm from when the photoreceptor drum 11Y is new reaches the predetermined value Qa, the first photoreceptor life monitoring mode is executed. 10,000 sheets), the photoreceptor life monitoring mode is intermittently executed for the second time, the third time, and so on.

FIG. 13 is a flow chart showing the details of the subroutine for controlling the execution of the photoreceptor life monitoring mode. driven by

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 -Vo2, and the rotating photosensitive drum 11Y is charged with -Vo2 [V] (step S11). This charging is performed by the execution timing determining section 111 instructing the charging power supply section 80 to output the charging voltage (=-Vo2) when the photosensitive member life monitoring mode is executed.

Next, the electrostatic latent image on the photoreceptor drum 11Y (because no exposure is performed after charging, the electrostatic latent image corresponds to a non-image) is developed with the developing bias Vb2 (step S12). ). This development is performed by the execution time determining unit 111 instructing the developing bias power supply unit 60 to output the developing bias Vb2 for the execution of the photoreceptor life monitoring mode.

As a result, as shown in FIG. 5B, an electrostatic latent image corresponding to a non-image is formed on the photosensitive drum 11Y whose charging potential is -Vo2 by the developing section 14Y to which the developing bias Vb2 is supplied. Development is performed. Vpp' of the developing bias Vb2 is larger than Vpp at the time of normal printing, and the difference δ2 between the AC positive component voltages Vm and Vm' makes fogging of the photoreceptor more likely than at the time of normal printing. It corresponds to the injection increment of charge.

When the overcoat layer 95 is not so worn and has not reached the end of its life, a fog toner image Tf due to fogging of the photoreceptor is visualized in the dense filler portions C, D, and E (FIG. 7). On the other hand, when the wear of the overcoat layer 95 reaches the specified amount or more, the fog toner image Tf due to the photoreceptor fog does not appear.

Next, a primary transfer voltage is supplied to the primary transfer roller 15Y under the same conditions as during normal printing (step S14). If the fog toner image Tf is formed on the photoreceptor drum 11Y, the fog toner image Tf is primarily transferred from the photoreceptor 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 to the intermediate transfer belt 21 even if the primary transfer voltage is supplied to the primary transfer roller 15Y. do not have.

Subsequently, the detection signal (output voltage) Vp of the detection sensor 23 arranged to face the intermediate transfer belt 21 is obtained as needed (step S15).

When the fog toner image Tf is primarily transferred to 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 and passes through the detection area as the intermediate transfer belt 21 rotates. During this time, the fog toner image Tf can be detected.

On the surface of the intermediate transfer belt 21, the output voltage Vp of the detection sensor 23 changes between the portion where the fog toner image Tf exists and the portion where it does not exist. can be judged.

FIG. 14 is a graph illustrating the relationship between the toner adhesion amount (unit: mg) on the intermediate transfer belt 21 and the output voltage Vp of the detection sensor 23. As shown in FIG. The detection sensor 23 used in this embodiment has a characteristic that the output voltage Vp increases as the toner adhesion amount decreases. When the detection sensor 23 having such characteristics is used, the output voltage Vp exhibits the maximum value when the fog toner image Tf is not formed, that is, when the toner adhesion amount becomes zero.

Therefore, the output voltage Vp is monitored at any time, and (i) when the output voltage Vp becomes only a value smaller than the maximum value, the fog toner image Tf is formed, and the photoreceptor has not reached the end of its life. , (ii) when the maximum value is reached, the fog toner image Tf is not formed, so the overcoat layer 95 is almost non-existent or non-existent due to abrasion or scraping, and the photoreceptor reaches the end of its life. can be detected.

In the present embodiment, a value th0 that is slightly smaller than the maximum value is set in advance as the threshold in consideration of detection errors. If the output voltage Vp>threshold value th0 is satisfied, it is determined that the photoreceptor has reached the end of its life.

In addition, in order to improve the detection accuracy of the fog toner image Tf by the detection sensor 23, the size of the detection area of the sensor 23, that is, the detection field of view, can detect the fog toner image Tf at any position in the main scanning direction. It is desirable to use something as large as possible. Alternatively, instead of this, a plurality of sensors 23 having a narrow detection field of view are arranged side by side in the main scanning direction so that any one of the sensors can reliably detect the fogging toner image Tf regardless of its position in the main scanning direction. It can also be configured to allow

Returning to FIG. 13, if it is determined that the output voltage Vp>threshold th0 is not satisfied ("No" in step S16), it is determined that the photoreceptor has not reached the end of its life, and the process proceeds to step S18. On the other hand, when it is determined that the output voltage Vp>threshold value th0 ("Yes" in step S16), it is notified that the photosensitive member has reached the end of its life. (step S17), and proceeds to step S18. The processing of steps S15 and S16 is handled by the life determination unit 112, and the processing of step S17 is handled by the determination result output unit 113. FIG.

In step S18, it is determined whether or not the photosensitive member life monitoring mode has been executed for all the image forming units 10Y to 10K. If there are still imaging units that have not been executed ("No" in step S18), the process returns to step S11. By repeating the processing of steps S11 to S18, if it is determined that the photoreceptor life monitoring mode has been executed for all image forming units ("Yes" in step S18), the process returns. As a result, it is possible to determine whether each of the four photosensitive drums 11Y to 11K has reached the end of its life.

As described above, in the present embodiment, the fog caused by fogging on the photoreceptor caused by non-uniformity in the dispersed state of the metal filler in the overcoat layer 95 (there is a localized portion of the metal filler) Since the control is performed to determine whether or not the toner image Tf appears, it is possible to monitor the end of life due to wear of the thin overcoat layer that cannot be detected by the existing film thickness detection technology.

In the above description, the execution timing of the photoreceptor life monitoring mode is after the end of the printing operation. Alternatively, after the previous print job is finished and before the next print job is started, it may be performed as one control in the image stabilization control.

The present invention is not limited to an image forming apparatus, and may be a photoreceptor life monitoring method. Alternatively, the method may be a program executed by a computer. Further, the program according to the present invention can be, for example, a magnetic disk such as a magnetic tape or a flexible disk, an optical recording medium such as a DVD-ROM, a DVD-RAM, a CD-ROM, a CD-R, an MO, or a PD, or a flash memory type recording medium. etc., can be recorded on various computer-readable recording media, and may be produced, transferred, etc. in the form of such recording media, or in the form of programs, various wired and wireless networks including the Internet, It may be transmitted and supplied via broadcasting, electric communication lines, satellite communication, or the like. Further, the processing in the above embodiments may be performed by software, or may be performed by using hardware circuits.

<Modification>
The present invention is not limited to the above embodiments, and can be implemented in various forms. Other possible embodiments are listed below.

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

Specifically, in this modified example, for example, as shown in FIG. , the detection sensor 23b may be arranged at a position between the output roller 38 and the paper discharge roller 38. As shown in FIG. Alternatively, before the fog toner image Tf formed on the photoreceptor drum is primarily transferred to the intermediate transfer belt 21, the detection sensor 23c may detect the fog toner image Tf on the photoreceptor drum. is.

In addition, in the configuration having a known scanner 90 as shown in FIG. 16, by reading the discharged sheet S at the reading position of the scanner 90, it is detected whether or not the fog toner image Tf exists on the sheet S. You can also With respect to the entire surface of the sheet, it is possible to accurately distinguish between a local portion where the fog toner image Tf exists and a region where it does not exist. In this configuration, the scanner 90 constitutes detection means for detecting the fog toner image Tf.

There is a configuration in which the fog toner image Tf formed on the photosensitive drum is directly detected, and a configuration in which the fogged toner image Tf formed on the photosensitive drum is indirectly detected after transfer from the photosensitive drum. There is no change in determining whether or not the fog toner image Tf has been formed, and it can be said that it is included in this determining means.

(2) In the above-described embodiment, the photoreceptor life monitoring mode for the first time after the photoreceptor drum is brand new is triggered when the cumulative number of printed sheets Qm indicating the cumulative number of image formations reaches or exceeds the first predetermined value Qa. However, it is not limited to this. For example, the cumulative number of rotations or the cumulative operating time from when the photoreceptor drum is new reaches the second predetermined value, that is, the predetermined number of rotations or the cumulative operating time at which the wear or scraping of the overcoat layer 95 is assumed to have progressed to some extent. It is also possible to adopt a configuration in which execution is triggered by the event. Alternatively, the time elapsed since the photosensitive drum was new may be used as a trigger.

Furthermore, the second and subsequent photoreceptor life monitoring modes are performed each time the cumulative number of prints Qm reaches a multiple (fourth predetermined value) of 10000 (=10k), but the number is not limited to 10k. Any value (fourth predetermined value) that is smaller than the first predetermined value Qa that triggers the first execution may be used, and a suitable value, such as 5k, may be set according to the device configuration.

Further, the second execution of the photoreceptor life monitoring mode is performed at a fifth predetermined value (for example, 10k) smaller than the second predetermined value (for example, 3000k) for the rotational speed or operation time of the photoreceptor drum from the first execution. ), or when the elapsed time from the first execution reaches a sixth predetermined value (e.g., 20 hours) that is smaller than the third predetermined value (e.g., 500 hours). Also good. The same can be applied to the third and subsequent times.

Further, the interval U1 from the first to the second implementation of the photoreceptor life monitoring mode, the interval U2 from the second to the third, and the interval U3 from the third to the fourth are gradually reduced (U1 >U2>U3 . . . ). As the cumulative number of printed sheets Qm increases, the wear of the overcoat layer 95 progresses and the remaining layer thickness of the overcoat layer 95 decreases. Because you can.

(3) In the above embodiment, an example in which the image forming apparatus according to the present invention is applied to a tandem color printer has been described, but the present invention is not limited to this. Regardless of color or monochrome image formation, development is performed using a developing bias voltage containing an AC component, and at least one of the frequency, Vpp, and duty ratio of the AC component is normally set to facilitate the occurrence of fogging on the photoreceptor. It can be applied to an image forming apparatus having a variable configuration for printing, such as a copying machine, a FAX, and an MFP (Multiple Function Peripheral). In order to suppress development fogging, the charging potential is switched from -Vo1 during normal printing to -Vo2. If possible, it is possible to employ a device configuration in which the charging potential is not switched.

In addition, although the example of the drum-type photoreceptor has been described, the present invention is not limited to this, and can be applied to a configuration using a belt-like photoreceptor, for example. In addition, although the configuration example using the charging roller as the charging means for charging the photoreceptor has been described, the present invention is not limited to this, and a charging charger or the like can also be used.

Furthermore, although the example of using the developing roller as the developer carrier for carrying the developer has been described, the shape is not limited to the roller shape, and a sleeve-shaped one, for example, can also be used. Although a configuration example using a two-component developer containing a carrier and a toner as a developer has been described, a configuration using a one-component developer that does not contain a carrier but contains a toner, for example, is also applicable. Further, as the reversal development system, an example of a configuration in which the charge polarity of the photoreceptor is negative and the charge polarity of the toner is negative has been described, but the present invention is not limited to this, and a reverse polarity configuration can also be applied.

Also, the contents of the above embodiment and the above modifications may be combined as much as possible.

INDUSTRIAL APPLICABILITY The present invention can be widely applied to image forming apparatuses that form an image on a photoreceptor having an overcoat layer.

1 Printer 11Y, 11M, 11C, 11K Photoreceptor drum 12Y, 12M, 12C, 12K Charging roller 13Y, 13M, 13C, 13K Exposure unit 14Y, 14M, 14C, 14K Development unit 19Y, 19M, 19C, 19K Development roller 21 Middle Transfer belt 23 Detection sensor 50 Control section 60Y, 60M, 60C, 60K Development bias power supply section 61 First bias output section 62 Second bias output section 63, 83 Switching section 70 Operation section 71 Display section 80Y, 80M, 80C, 80K Charging Power supply unit 81 First charging voltage output unit 82 Second charging voltage output unit 95 Overcoat layer 105 Photoreceptor life monitoring mode execution unit 106 Cumulative number of printed sheets storage unit 111 Execution timing judgment unit 112 Life judgment unit 113 Judgment result output unit S Recording Sheet for Tf Fog toner image Vo Charging potential Vdc DC voltage component of development bias Vpp Peak-to-peak voltage Vz Fog margin

Claims (11)

An image forming apparatus for forming an image by electrophotography,
a photoreceptor in which an overcoat layer containing a metal filler is formed as the outermost layer;
charging means for charging the photoreceptor to a first polarity;
an exposure unit that exposes the charged photoreceptor to form an electrostatic latent image on the photoreceptor;
a developer carrier that carries a developer containing toner of a first polarity;
As the developing bias supplied to the developer bearing member, a first developing bias used for developing an electrostatic latent image formed during image formation and a first developing bias used for monitoring the life of the photoreceptor, which are opposite in polarity to the first developing bias. a bias power supply means capable of switching between a second developing bias for injecting more charge of the second polarity into the photoreceptor than the first developing bias;
When the end of life of the photoreceptor is monitored, the charging means and the exposure means are controlled to prohibit exposure while charging the photoreceptor, thereby forming an electrostatic latent image corresponding to a non-image on the photoreceptor. control means for executing a life monitoring mode for controlling the bias power supply means to supply the second developing bias to the developer carrier;
determining means for determining whether or not a toner image is formed on the photoreceptor due to non-uniformity in the dispersed state of the metal filler by execution of the life monitoring mode;
a notification means for notifying that the thickness of the overcoat layer of the photoreceptor has decreased below a specified thickness when it is determined that the toner image has not been formed;
An image forming apparatus comprising: The first developing bias and the second developing bias are
An AC component is superimposed on a DC component of the first polarity,
The second developing bias is characterized in that the peak-to-peak voltage of the AC component is set to a value larger than that of the first developing bias, or the frequency of the AC component is set to a value smaller than that of the first developing bias. The image forming apparatus according to claim 1. The first developing bias and the second developing bias are
alternating current is superimposed on the direct current component of the first polarity,
In the waveform of one cycle of the alternating current, the side of the peak voltage having the second polarity with the voltage value of the DC component of the first polarity to be superimposed as a boundary is the alternating component α, and the side having the first polarity is the alternating component When the value obtained by dividing β and the time Tβ of the AC component β by one cycle is the duty ratio Dh,
The second developing bias has the same absolute value Vn of the peak voltage of the AC component β as that of the first developing bias, and the absolute value Vm of the peak voltage of the AC component α is larger than that of the first developing bias, and 2. The image forming apparatus according to claim 1, wherein the duty ratio Dh is larger than the first developing bias. A charging power supply means for supplying a charging voltage to the charging means,
The control means is
The fogging margin defined by the magnitude of the difference between the charging voltage of the first polarity of the photoreceptor in the life monitoring mode and the DC voltage of the first polarity of the second developing bias is larger than that during normal image formation. 4. The image forming apparatus according to claim 2, wherein a charging voltage is supplied from said charging power supply means to said charging means so as to increase the voltage. The control means is
When the cumulative number of times of image formation reaches a first predetermined value, when the cumulative number of revolutions or cumulative operating time of the photoreceptor reaches a second predetermined value, or when the photoreceptor reaches a new state, a third time elapses. 5. The image forming apparatus according to claim 1, wherein the life monitoring mode is executed when a predetermined value is reached. The control means is
After the photoreceptor is brand new, the life monitoring mode is executed first, and then the number of times of image formation since the first execution reaches a fourth predetermined value smaller than the first predetermined value. when the number of rotations of the photoreceptor or the operation time after the first execution reaches a fifth predetermined value smaller than the second predetermined value, or when the elapsed time since the first execution is the third predetermined value 6. The image forming apparatus according to claim 5, wherein the execution is triggered when a sixth predetermined value smaller than the value is reached. The control means is
When the interval from the first implementation to the second implementation of the life monitoring mode is U1, and the interval from the second implementation to the third implementation is U2, the life span is adjusted so as to satisfy the relationship U1>U2. 7. The image forming apparatus according to claim 6, wherein the second and third executions of the monitoring mode are performed. further comprising transfer means for transferring the toner image on the photoreceptor to a transfer material;
The determination means is
a detecting means disposed at a position capable of detecting a toner image formed on the photosensitive member and transferred to the transfer receiving member by executing the life monitoring mode;
The image forming apparatus according to any one of claims 1 to 7, wherein the determination is performed from a detection result of the toner image by the detection means. 9. The image according to claim 8, wherein the transfer-receiving member is an intermediate transfer member, or a sheet in which the toner image is transferred from the photosensitive member to the sheet via the intermediate transfer member. forming device. The transfer-receiving member is a sheet in a configuration in which the toner image is transferred from the photosensitive member to the sheet through an intermediate transfer member, and then the transferred sheet is output from an image forming apparatus;
9. The image forming apparatus according to claim 8, wherein said detecting means is a scanner for reading a toner image existing on said sheet placed at a reading position after said output. A photoreceptor lifetime monitoring method in an image forming apparatus for forming an image by an electrophotographic method on a photoreceptor having an overcoat layer containing a metal filler formed on the outermost surface, comprising:
The image forming apparatus is
charging means for charging the photoreceptor to a first polarity;
an exposure unit that exposes the charged photoreceptor to form an electrostatic latent image on the photoreceptor;
a developer carrier that carries a developer containing toner of a first polarity;
As the developing bias supplied to the developer bearing member, a first developing bias used for developing an electrostatic latent image formed during image formation and a first developing bias used for monitoring the life of the photoreceptor, which are opposite in polarity to the first developing bias. and a bias power supply means capable of switching between a second developing bias that injects more charge of the second polarity into the photoreceptor than the first developing bias,
The photoreceptor life monitoring method includes:
When the end of life of the photoreceptor is monitored, the charging means and the exposure means are controlled to prohibit exposure while charging the photoreceptor, thereby forming an electrostatic latent image corresponding to a non-image on the photoreceptor. a control step of executing a life monitoring mode of controlling the bias power supply means to supply the second developing bias to the developer carrier;
a determination step of determining whether or not a toner image is formed on the photoreceptor due to non-uniformity of the dispersed state of the metal filler by execution of the life monitoring mode;
a notification step of notifying that the film thickness of the overcoat layer of the photoreceptor has decreased below a specified film thickness when it is determined that the toner image has not been formed;
A photoreceptor life monitoring method, comprising:

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