JP2012208385A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent image failure due to thinning of a photosensitive layer of a photosensitive drum at an end of life of a process cartridge.SOLUTION: The image forming apparatus includes a CPU 414 that determines (S112) whether a process cartridge 201 comes to the end of life or not based on an exposure cumulative irradiation time stored in a nonvolatile memory 413; when determining that the process cartridge 201 does not come to the end of life (S112 N), controls (S113) LEDs 10 and 11 to perform light exposure at an exposure light quantity setting value S; and when determining that the process cartridge 201 comes to the end of life (S112 Y), controls (S114) the LEDs 10 and 11 to perform the light exposure at an exposure light quantity setting value L (>S).

Description

  The present invention relates to an image forming apparatus using an electrophotographic process.

  2. Description of the Related Art Conventionally, in order to prevent image defects such as horizontal white stripes in the DC charging method, a configuration is provided in which a charge eliminating unit that discharges (removes) a residual potential by irradiating light to the photosensitive drum before the charging process of the photosensitive drum. is there. For example, Patent Document 1 discloses a configuration in which the light holding power on the photosensitive drum is weakened by performing continuous printing, so that the amount of light from a pre-exposure lamp, which is a charge eliminating unit, is reduced according to the number of printed sheets. .

JP-A-61-83568

  However, it may be possible to perform printing so that the toner is consumed at the assumed toner consumption rate (toner consumption per transfer material) for the process cartridge, but the toner consumption is lower than the assumed toner consumption rate. When the toner is consumed at a rate, there are the following problems. That is, when the toner is consumed at a toner consumption rate lower than the assumed toner consumption rate, the assumed life of the photosensitive drum may be exceeded before the toner consumption is completed. Here, the life of the photosensitive drum is a guarantee period in which the photosensitive drum can be used. In this case, the photosensitive drum is driven beyond the life of the photosensitive drum, and the photosensitive drum is thinned by charging or charge removal, and the charge on the photosensitive drum is likely to remain partially. End up. If the static elimination of the photosensitive drum is continued in such a state, for example, a ghost image (a phenomenon in which an image formed on the previous transfer material is transferred lightly again) or a horizontal streak image (a phenomenon in which a white horizontal line enters the image) There is a possibility that a defective image is generated. As a countermeasure against this, it is conceivable to increase the thickness of the photosensitive layer of the photosensitive drum. However, in this case, the cost may increase.

  The present invention has been made under such circumstances, and an object thereof is to prevent image defects due to thinning of the photosensitive layer of the photosensitive drum at the end of the life of the process cartridge.

  In order to solve the above-described problems, the present invention has the following configuration.

  (1) An image carrier, a charging unit for charging the image carrier, a latent image forming unit for forming an electrostatic latent image on the image carrier charged by the charging unit, and the latent image formation A detachable process cartridge having a developing means for developing the electrostatic latent image formed on the image carrier by means of a developer, and a storage means for storing information, and a charge remaining on the image carrier. An image forming apparatus comprising: a pre-exposure unit that exposes the image carrier to remove the toner; and determining whether the process cartridge has reached the end of its life based on the information stored in the storage unit When it is determined that the process cartridge has not reached the end of its life, the pre-exposure means is controlled to perform exposure with the first light amount. When it is determined that the process cartridge has reached the end of its life, An image forming apparatus comprising a control means for controlling the pre-exposure means to perform the exposure in one of the light intensity is greater than the second amount.

  According to the present invention, it is possible to prevent image defects due to thinning of the photosensitive layer of the photosensitive drum at the end of the life of the process cartridge.

FIG. 1 is a configuration diagram of a main part of an image forming apparatus according to a first embodiment. The figure explaining the process cartridge vicinity of Example 1 The figure explaining the EV characteristic of a photosensitive drum, the figure which shows a light quantity control circuit, and the waveform figure of a drive signal 1 is a block diagram illustrating an image forming apparatus according to a first exemplary embodiment. Conceptual diagram illustrating toner remaining amount detection according to the first exemplary embodiment. Flowchart for explaining pre-exposure light amount setting control processing according to the first embodiment. The figure which shows the relationship between the pre-exposure accumulated irradiation time of Example 2, remaining toner amount, photosensitive layer thickness, and the amount of pre-exposure light. The figure which shows the relationship of the pre-exposure accumulated irradiation time after progress of the standard lifetime of Example 2, toner remaining amount, photosensitive layer thickness, and the amount of pre-exposure light. Flowchart for explaining pre-exposure light amount setting control processing according to the second embodiment. Flowchart for explaining control processing for pre-exposure light amount setting according to the third embodiment.

  The mode for carrying out the present invention will be described in detail below with reference to examples.

  The structure of Example 1 is shown in FIGS. In this embodiment, a color image forming apparatus will be described as an example of an image forming apparatus that is required to increase the speed and size of the apparatus. The color image forming apparatus is divided into various systems, for example, a well-known multiple transfer system and intermediate transfer body system. In addition, a multiple development system that forms images by superimposing color images on the surface of the photoreceptor and forming images at once, or a process station that is a plurality of different color image forming means, arranged in series, is transferred by a transfer belt. There is an in-line method for transferring a developed image to a material. Among these, the inline method is an excellent method because it is possible to increase the speed, and the number of times of image transfer is small, which is advantageous for image quality.

[Configuration and operation of image forming apparatus]
FIG. 1 shows an inline configuration. In FIG. 1, an electrostatic adsorption transfer belt (hereinafter referred to as ETB: Electrostatic Transfer Belt) 1 is stretched by each of a driving roller 6, an adsorption opposing roller 7, and tension rollers 8 and 9, and rotates in a direction indicated by an arrow. On the peripheral surface of the ETB 1, process cartridges 201 (yellow), 202 (magenta), 203 (cyan), and 204 (black) of different colors are arranged in a row. Each of the process cartridges 201 to 204 is detachable. When the toner (developer) is consumed, printing can be performed by replacing the cartridge with a new process cartridge. Photosensitive drums 211 to 241 (image carriers) in the process cartridges 201 to 204 are in contact with the transfer roller 3 via the ETB 1. Further, the suction roller 5 is disposed upstream of the process cartridges 201 to 204 and is in contact with the suction counter roller 7. Here, when the transfer material P passes through the nip portion formed by the suction roller 5 and the suction counter roller 7, a voltage is applied by the power source 16, electrostatically attracted to the ETB 1, and conveyed in the direction indicated by the arrow. Is done. Details of the process cartridges 201 to 204 will be described later.

  Here, the image forming process will be described. First, an image forming process in the process cartridges 201 to 204 will be described. The description will be given for the yellow process cartridge 201, but the same applies to the process cartridges 202 to 204 of other colors. FIG. 2A shows the configuration of the process cartridges 202 and 203. The photosensitive drum 211 is uniformly charged by a charger 212 (charging means), and an electrostatic latent image is formed by the scanning light 214 emitted from the exposure optical system 213 (latent image forming means). This electrostatic latent image is developed by the developing roller 215, and a toner image is formed on the photosensitive drum 211 (on the image carrier). Toner remaining on the photosensitive drum 211 without being transferred in the transfer process described later is scraped off by the cleaning blade 217 and stored in the remaining toner container 218.

  Next, the transfer process will be described. In the generally used reversal development method, when the photosensitive drum 211 is, for example, a negative-polarity OPC photoreceptor, negative-polarity toner is used when developing the exposed portion. Accordingly, a positive transfer voltage is applied to the transfer roller 3 from the voltage power source 4 (see FIG. 1). In the actual printing process, the following series of processes is performed in consideration of the moving speed of the ETB 1 and the distance between the transfer positions of each process cartridge. That is, the image formation with the process cartridge 201, the transfer process, and the transfer material P are conveyed at the timing when the positions of the toner images of the respective colors formed on the transfer material P coincide. By performing such a process, a full-color toner image is completed on the transfer material while the transfer material P once passes through the process cartridges 201 to 204. After the toner image is completed on the transfer material P, the transfer material P is conveyed to a fixing device (not shown), and the toner image is fixed on the transfer material P.

[Process cartridge configuration]
In recent years, the diameter and interval of photosensitive drums have been reduced in order to reduce the size of color image forming apparatuses. For this reason, a space for installing a pre-exposure means for removing charges to remove charges has been limited. In this embodiment, as shown in FIG. 2, the LEDs 10 and 11 as pre-exposure means for static elimination are surrounded by a photosensitive drum 211, ETB 1, a shutter 216 of the photosensitive drum 211, and a frame 219 of the process cartridge 201. It is installed at an angle to irradiate from the side. In this embodiment, the interval between the transfer material P to be conveyed is narrow, and it is difficult to install the light guide in a space sandwiched between the frame of the process cartridge 201 and the ETB 1. For this reason, in this embodiment, the light guide is not provided, and the light from the LEDs 10 and 11 is directly irradiated onto the photosensitive drum 211. Further, the LEDs 10 and 11 are arranged so as to face the longitudinal direction of the photosensitive drum 211 (direction orthogonal to the rotation direction of the photosensitive drum 211) in order to increase the printing speed and reduce optical axis adjustment. 1 and 2, the members of the process cartridge 202 are numbered in the 220 series, the members of the process cartridge 203 in FIG. 1 are numbered in the 230 series, and the members of the process cartridge 204 are numbered in the 240 series. The code | symbol is attached | subjected.

  FIG. 2B is a view of the vicinity of the process cartridge of FIG. Here, the LEDs 10 and 11 are set in the direction of the photosensitive drum at an angle of 3 to 4 degrees with respect to the rotation axis of the photosensitive drum 211, and the luminous flux of the LEDs 10 and 11 is in the area L1 after transfer on the photosensitive drum 211. Projected. When the light from the LEDs 10 and 11 irradiates the surface of the photosensitive drum before transfer in the adjacent process cartridge 202, an image such as scattering of a line image (a phenomenon in which a fine dot-shaped image is formed around the line-shaped image). It needs to be shielded from light to cause defects. As the characteristics of the LEDs 10 and 11, it is desirable that the LED has a peak wavelength in the photosensitive wavelength range of the photosensitive drum 211, the directivity angle is narrowed, and the luminous intensity is large. As such an LED, for example, a LED having a peak wavelength of 630 nm, a directivity angle of 7 degrees, and a luminous intensity of 7000 mcd may be used. By using such an LED, it becomes possible to satisfactorily irradiate the entire area in the longitudinal direction of the photosensitive drum 211 without providing a special light collecting means.

[Relationship between the photosensitive drum potential setting and the amount of pre-charge exposure]
Here, the relationship between the potential setting of the photosensitive drum 211 and the light amount of pre-charging exposure will be described. The graph shown in FIG. 3A is an EV characteristic when the photosensitive drum used in this embodiment is charged to a charging potential: VD = −600V. FIG. 3A is a graph in which the horizontal axis represents energy (μJ / cm ² ) and the vertical axis represents the photosensitive drum potential (−V). Residual potential Vs1 of the photosensitive drum indicates a saturation potential (Vs1 in FIG. 3A) in the strong exposure portion shown in FIG. 3A, and in this region, it is almost constant regardless of the exposure intensity and the charging potential. Indicates potential. Although it is known that this residual potential: Vs1 depends on the film thickness of the photosensitive drum, the CG material, the film thickness, and the like, in this embodiment, a photosensitive drum of residual potential: Vs1 = −40V is adopted. If the light amount of the pre-charging exposure is adjusted so that the potential of the photosensitive drum becomes a residual potential: Vs1 = −40 V with respect to the photosensitive drum as described above, the correct value is obtained as the pre-charging exposure light amount. Become. The amount of light for such pre-charge exposure is represented by energy: E (μJ / cm ² ).

  In order to change the amount of light for pre-charging exposure, the current input to the LEDs 10 and 11 is changed to a pulse waveform, and the effective time for irradiating the photosensitive drum surface is adjusted. FIG. 3B shows a light amount control circuit (404, which will be described later), and FIG. 3C shows waveforms of drive signals (hereinafter referred to as LED_ON signals) in the case of different light amount setting values S and L for pre-charging exposure. When the LED_ON signal is output from the CPU 414, the transistor 502 is driven and the LEDs 10 and 11 are driven via the limiting resistors R1 and R2. When the LED_ON signal is PWM-modulated, it is smoothed by the resistor R3 and the capacitor C1, so that the CPU 414 can control the current flowing through the LED 10 and LED 11, and can adjust the light quantity of the LED 10 and 11 in proportion to this.

[Block diagram of image forming apparatus]
FIG. 4 shows an electrical block diagram of the image forming apparatus 401 of this embodiment. Here, the yellow process cartridge 201 will be described as a representative. The toner container 20 stores toner (hatched portion in the figure). The nonvolatile memory 413 (storage means) stores ID code information for identifying the process cartridge 201. The nonvolatile memory 413 stores the following information. That is, the cumulative irradiation time (predetermined information) and pre-exposure light amount of pre-charge exposure (hereinafter simply referred to as pre-exposure) after the process cartridge 201 irradiated to the photosensitive drum 211 in the process cartridge 201 is started to be mounted. Stores the set value. Further, the nonvolatile memory 413 stores information such as the remaining amount of toner (the amount of developer) in the toner container 20 (in the developing unit). The engine controller 403 controls the image forming apparatus 401 that is an engine. The CPU 414 irradiates the pre-exposure LEDs 10 and 11 through the light amount control circuit 404 described with reference to FIG. 3B, or drives the motor 408 through the motor drive circuit 405 to rotate the photosensitive drum 211. Further, the CPU 414 detects the remaining amount of toner in the toner container 20 by the remaining toner detection circuit 406 (detection means). The LEDs 10 and 11 perform pre-exposure, and the light amount control circuit 404 irradiates the photosensitive drum 211 for discharging after cleaning.

[Toner level detection]
An outline of toner remaining amount detection will be described with reference to FIG. FIG. 5A is a schematic cross-sectional view of the toner container 20 included in the developing device (developing unit). In the figure, a toner container 20 is for containing toner, and a toner supply roller 21 is for supplying toner to the developing roller 215. The stirring sheet 23 is for sending toner to the developing roller 215, the LED 30 is a light source of a toner remaining amount detection sensor which is a light transmission type toner remaining amount detecting means, and the phototransistor 31 emits light emitted from the LED 30. It is for detection.

  The light emitted from the LED 30 passes through the detection window 24a and enters the toner container 20, passes through the detection window 24b, and reaches the phototransistor 31. When toner is present on the bottom surface of the toner container 20, the light from the LED 30 is blocked by the toner. On the other hand, when the stirring sheet 23 rotates and passes through the detection window 24 b while scooping up the toner, the light from the LED 30 is transmitted through the toner container 20, and the light reaches the phototransistor 31. Thereafter, after the toner falls to the bottom surface of the toner container 20, the light is again blocked. For example, as shown in FIG. 5B, when the remaining amount of toner is large, the toner falls on the bottom surface of the toner container 20 after the stirring sheet 23 has passed through the detection window 24b below the developing container, and the toner enters the detection window 24b. Since the time until it is covered is short, the period t1 during which light transmission (transmission) continues is short. On the other hand, when the remaining amount of toner decreases as shown in FIG. 5C, the time from when the stirring sheet 23 scoops up the toner to when the toner falls and the detection window 24b is covered with toner becomes longer. The period t2 during which light is transmitted becomes longer. Accordingly, it is possible to measure the periods t1 and t2 during which light transmission continues with respect to the period T in which the stirring sheet 23 rotates, and to detect the remaining amount of toner from the period ratio.

[Control processing of exposure light quantity before charging]
Control of the amount of pre-exposure light at the end of the life will be described based on the flowchart of FIG. The life is a usable warranty period, and the end of life is the time immediately before the end of the life. When printing is started in step (hereinafter referred to as S) 101, in S102, the CPU 414 reads a pre-exposure light amount setting value (simply referred to as a light amount setting value in the drawing) from the nonvolatile memory 413 in the attached process cartridge 201. . It is assumed that the initial value of the pre-exposure light amount setting value stored in the nonvolatile memory 413 is the light amount setting value S. In step S <b> 103, the CPU 414 drives the pre-exposure LEDs 10 and 11 with the pre-exposure light amount set via the light amount control circuit 404 according to the pre-exposure light amount setting value read from the nonvolatile memory 413, and pre-exposes on the photosensitive drum 221. Irradiate. That is, if the pre-exposure light amount setting value read from the nonvolatile memory 413 is S in S103, the CPU 414 sets the pre-exposure light amount setting value S in the light amount control circuit 404 in S104. On the other hand, if the pre-exposure light amount setting value read from the nonvolatile memory 413 is not S in S103, the CPU 414 sets the pre-exposure light amount setting value L in the light amount control circuit 404 in S105. The light quantity setting value S and the light quantity setting value L are in a relationship of the light quantity setting value S <the light quantity setting value L (see FIG. 3C). Here, the pre-exposure light amount setting value stored in the non-volatile memory 413 is the pre-exposure light amount setting value S when the pre-exposure accumulated time is less than the predetermined value by the processing of S112 to S114 described later. In the above case, the pre-exposure light amount setting value L is used.

  In S <b> 106, the light amount control circuit 404 drives the LEDs 10 and 11 with the pre-exposure light amount setting value S set by the CPU 414 in S <b> 104 or the pre-exposure light amount setting value L set by the CPU 414 in S <b> 105, and emits light onto the photosensitive drum 221. Irradiate and perform pre-exposure. At this time, for example, the CPU 414 operates a timer (not shown) to measure the pre-exposure irradiation time that the LEDs 10 and 11 irradiate the photosensitive drum 221. When the CPU 414 determines that the printing is not finished in the determination of S109 described later and returns to the processing of S106, the CPU 414 performs the following processing. In other words, the CPU 414 adds the pre-exposure irradiation time measured this time to the previous pre-exposure irradiation time stored in, for example, a main body memory (not shown), and the current number of pages in one print job. The accumulated irradiation time until is stored in the memory. Then, the CPU 414 performs charging with the charging roller 102, irradiates the electrostatic latent image on the photosensitive drum 221 with the scanner unit 103, and then develops with the developing device. When performing these operations, the CPU 414 drives the motor 408 by the motor driving circuit 405 to rotate the photosensitive drum 221 and stirs the toner by the stirring sheet 23 in the toner container 20. In step S <b> 107, the CPU 414 detects the remaining amount of toner in the toner container 20 by the LED 30 and the phototransistor 31 of the remaining toner detection circuit 406 while the stirring sheet 23 is being driven. In S108, the CPU 414 writes the remaining toner amount detected by the remaining toner detection circuit 406 in S107 into the nonvolatile memory 413, and updates the previous data to the data obtained this time (memory update). In S109, the CPU 414 determines whether or not printing is finished. If printing (print job) is not finished, the processing of S106 to S109 is repeated.

  If the CPU 414 determines in S109 that printing has ended, it performs the following processing in S110. In S110, the CPU 414 adds the pre-exposure cumulative irradiation time irradiated from the LEDs 10 and 11 onto the photosensitive drum 221 in S106 in the current print job to the pre-exposure cumulative irradiation time of the previous print job stored in the nonvolatile memory 413. To do. In the drawing, the pre-exposure accumulated irradiation time is simply referred to as irradiation time. In S111, the CPU 414 stores and updates the result of addition in S110 in the nonvolatile memory 413 as a new pre-exposure cumulative irradiation time (cumulative time). As a result, the pre-exposure accumulated irradiation time from when the process cartridge 201 is newly installed in the image forming apparatus 401 to the present time is stored in the nonvolatile memory 413.

  In S112, the CPU 414 (control unit) determines whether or not the pre-exposure accumulated irradiation time updated in S111 is equal to or longer than the nominal life time of the process cartridge 201 (hereinafter referred to as standard life time). Here, it is assumed that the standard life time of the process cartridge 201 is a life time set so that 3000 sheets of LTR size can be printed at a toner consumption rate of 4%, for example. In the case of such a process cartridge 201, if the toner consumption rate is less than 4%, the toner cannot be consumed during the set standard life, so that the performance of the photosensitive drum 211 is required to exceed the life. Is done. In such a case, in the photosensitive drum at the end of its life in a low temperature and low humidity environment, the photosensitive layer is thinned and the sensitivity is lowered. Therefore, a ghost may occur unless the static elimination intensity, that is, the light quantity of the pre-exposed LEDs 10 and 11 is increased. There is. That is, when the pre-exposure cumulative irradiation time is longer than the standard life time of the process cartridge 201, the static elimination intensity must be increased. For this reason, if the CPU 414 determines in S112 that the pre-exposure accumulated irradiation time is equal to or longer than the standard life time of the process cartridge 201, it performs the process of S114. That is, in S114, the CPU 414 sets the pre-exposure light amount setting value of the LEDs 10 and 11 to L (> S) (second light amount).

  On the other hand, if the CPU 414 determines in S112 that the pre-exposure accumulated irradiation time is shorter than the standard lifetime of the process cartridge 201, the CPU sets the pre-exposure light amount setting value to S (first light amount) in S113. In S115, the CPU 414 writes the pre-exposure light amount setting value (S or L) set in S113 or S114 in the nonvolatile memory 413. Thus, in the next print job, the LEDs 10 and 11 perform pre-exposure of the photosensitive drum 211 with the pre-exposure light amount setting value S or L set by the CPU 414 and stored in the nonvolatile memory 413. The pre-exposure light amount setting value L can be realized by increasing the on-duty by PWM modulation as shown in FIG. 3C with respect to the initial value S of the pre-exposure light amount setting value. As a result, although the thinning of the photosensitive layer is accelerated by increasing the amount of pre-exposure light, it is possible to maintain the image quality because the toner consumption can be completed before the image quality degradation occurs. Become.

  In this embodiment, the pre-exposure light quantity setting is set to two, S and L, but a configuration in which a plurality of pre-exposure light quantity settings are set according to the cumulative irradiation time may be used. In addition, since each process cartridge has a non-volatile memory, pre-exposure processing is performed with an optimal amount of light for each process cartridge, and even if the toner consumption rate is low, image defects are reduced and high quality images are obtained. A forming apparatus can be provided. Further, a black process cartridge with a high toner consumption rate has a configuration in which the toner capacity is larger than that of the color toner. In such a case, the photosensitive layer thickness of the photosensitive drum is different, but even in such a case, it is possible to extend the life by setting the threshold value of the pre-exposure accumulated time for setting the pre-exposure light amount setting value in the nonvolatile memory. Is possible. Note that the threshold of the pre-exposure accumulated time is set to the standard life time as an example in S112 of this embodiment.

  As described above, according to this embodiment, it is possible to prevent image defects due to the thinning of the photosensitive layer of the photosensitive drum at the end of the life of the process cartridge.

  FIG. 7 shows the pre-exposure cumulative irradiation time, the remaining amount of toner in the process cartridge 201, the photosensitive layer thickness, and the amount of pre-exposure light. As shown in FIG. 7A, when the toner consumption rate (developer consumption rate) is low (broken line), the remaining amount of toner does not become zero even after the standard life time of the photosensitive drum 211 has passed. Incidentally, the toner out is shown in the pre-exposure cumulative irradiation time when the remaining amount of toner becomes zero. For this reason, in Example 1, in order to prevent the occurrence of image deterioration, the pre-exposure light amount setting value is changed from S to L (> S) to increase the light amount. However, if the light quantity setting value is increased from S to L, the wear of the photosensitive drum 211 may be accelerated. Therefore, the life of the photosensitive drum is reached before the remaining amount of toner becomes 0 (toner out). Streaks occur. In FIG. 7B, the photosensitive layer thickness of the photosensitive drum in which the horizontal stripe is generated is indicated by a dotted line. Therefore, in this embodiment, as shown in FIG. 8, the light amount setting value is controlled from the remaining toner amount and the toner consumption rate after the standard life time has elapsed.

  FIG. 8A shows a predicted remaining toner amount of the process cartridge 201 at the toner consumption rates 1 to 3 with respect to the pre-exposure cumulative irradiation time after the pre-exposure cumulative irradiation time has passed the standard life time. FIG. 8B shows the estimated number of printable sheets predicted from the remaining amount of toner after the standard lifetime, FIG. 8C shows the photosensitive layer thickness of the photosensitive drum 211, and FIG. 8D shows the pre-exposure light quantity setting. Indicates the relationship of values. Even if the toner remaining amount is the same when the standard life time elapses, the toner consumption rate 3 having a low toner consumption rate compared to the toner consumption rate 1 having a high toner consumption rate increases the predicted number of printable sheets. Further, the higher the toner consumption rate, the larger the pre-exposure light quantity setting value is set (L3 (toner consumption rate 1)> L2 (toner consumption rate 2)> L1 (toner consumption rate 3)). Proceed quickly. However, at any toner consumption rate, the toner is out before the photosensitive layer thickness reaches the photosensitive layer thickness at which horizontal streaks occur.

[Control processing of pre-exposure light intensity setting value]
The processing of this embodiment will be described with reference to the flowchart of FIG. Since S201 to S209 are the same processes as S101 to S109 of FIG. In addition, although only L is illustrated in S205, the CPU 414 sets one of S218 to S220 to be described later, and sets one of the pre-exposure light amount setting values L1, L2, and L3 stored in the nonvolatile memory 413 in S221. Will be set. In S210, the CPU 414 calculates the toner consumption rate from the remaining amount of toner recorded in the nonvolatile memory 413 in S208 and the cumulative number of printed sheets. Note that the information on the number of printed sheets is obtained from, for example, print job information. The cumulative number of prints is assumed to be stored, for example, in a memory on the main body (not shown), for example, and the print number of the current print job is added to the previous cumulative number of prints. calculate. Since S211 and S212 are the same processes as S110 and S111 of FIG.

  If the CPU 414 determines that the pre-exposure accumulated irradiation time added in S211 is less than the standard life time in S213, the CPU 414 sets the next pre-exposure light amount setting value to S in S214. If the CPU 414 determines in S213 that the pre-exposure accumulated irradiation time is equal to or longer than the standard lifetime, in S215, the remaining printable number of sheets is predicted from the remaining toner amount stored in S208 and the toner consumption rate calculated in S210. In S216, the CPU 414 determines whether or not the remaining number of printable sheets predicted in S215 is equal to or greater than P (constant) (see FIG. 8B).

  If the CPU 414 determines in S216 that the predicted remaining number of printable sheets is P or more, whether or not the remaining printable number of sheets is greater than or equal to Q (constant) (> P) (see FIG. 8B) in S217. Judging. If the CPU 414 determines in S217 that the predicted remaining printable number is equal to or greater than Q (Q ≦ the predicted remaining number of prints), the pre-exposure light quantity setting value is set to L1 in S218. If the CPU 414 determines in S217 that the predicted remaining printable number is less than Q (P ≦ predicted remaining print number <Q), the pre-exposure light quantity setting value is set to L2 (> L1) in S219. If the CPU 414 determines in S216 that the predicted remaining printable sheet number is less than P (predicted remaining print sheet number <P), it sets the pre-exposure light amount setting value to L3 (> L2) in S220.

  Here, the relationship regarding the predicted number of printable sheets is P <Q (see FIG. 8B), and the light amount relationship of the setting value of the pre-exposure light amount setting is S <L1 <L2 <L3. As shown in FIG. 8B, the threshold P when setting the pre-exposure light amount setting value is larger than the printable number of sheets when the toner consumption rate is 1, and smaller than the printable number of sheets when the toner consumption rate is 2. It is. The threshold value Q when setting the pre-exposure light amount setting value is larger than the printable number of sheets when the toner consumption rate is 2, and smaller than the printable number of sheets when the toner consumption rate is 3. In this embodiment, the pre-exposure light quantity setting values after the standard life time have elapsed are set to three (L1, L2, L3). However, the pre-exposure light quantity setting values are set to N (≧ 2) and the threshold value is set to (N− 1) It is good also as a structure to provide. Since the process of S221 is the same as the process of S115 of FIG. 6 described in the first embodiment, the description thereof is omitted.

  As described above, in this embodiment, when the pre-exposure cumulative irradiation time is equal to or longer than the standard life time of the process cartridge 201, the pre-exposure light amount is determined according to the estimated number of printable sheets estimated from the remaining amount of toner and the toner consumption rate. Set the setting value. Specifically, the light amount setting value of the pre-exposure light amount is increased as the predicted number of printable sheets is smaller. As a result, when the toner consumption rate is low and the estimated number of printable sheets is large, the amount of pre-exposure light can be suppressed to suppress the thinning of the photosensitive drum.

  As described above, according to this embodiment, it is possible to prevent image defects due to the thinning of the photosensitive layer of the photosensitive drum at the end of the life of the process cartridge.

[Pre-exposure light intensity setting value control process]
The processing of the third embodiment will be described along the flowchart of FIG. In this embodiment, control of the pre-exposure light amount setting value when communication with the nonvolatile memory 413 cannot be performed (when communication is abnormal) will be described. The processing of S301, S303, S304, and S308 is the same as the processing of S101, S106, S107, and S109 in FIG. The toner remaining amount detected by the toner remaining amount detection circuit 406 in S304 cannot be stored in the nonvolatile memory 413, and is stored in a memory on the main body (not shown). In S302, the CPU 414 sets the pre-exposure light amount setting value to S as provisional. In step S305, the CPU 414 determines whether the toner consumption rate is less than a predetermined value and whether the remaining amount of toner is equal to or less than a predetermined amount. Here, the toner consumption rate is calculated by the method described in the second embodiment. That is, it is calculated from the remaining amount of toner and the number of printed sheets. However, since communication with the nonvolatile memory 413 is not possible in this embodiment, the remaining amount of toner used for calculating the toner consumption rate is the amount of toner detected in S304 and stored in the memory on the main body side. The predetermined value used as the threshold value of the toner consumption rate is 4% of the toner consumption rate assumed in advance as described in the first embodiment, for example. On the other hand, the predetermined amount used as the threshold for the remaining amount of toner is, for example, 10%. These numerical values are changed by the assumed image forming apparatus, and are not limited to the values in this embodiment.

  If the CPU 414 determines in step S305 that the toner consumption rate is less than the predetermined value and the remaining amount of toner is equal to or less than the predetermined amount, the CPU 414 determines that the photosensitive layer thickness of the photosensitive drum 221 is thin, and in step S306. The pre-exposure light quantity setting value is set to L. If the CPU 414 determines in step S305 that the toner consumption rate is less than the predetermined value and the remaining amount of toner is not less than the predetermined amount, the pre-exposure light amount setting value is set to S in step S307. Thereafter, the processes in S303 to S308 are repeated until the print job is completed. Note that when the process cartridge 201 that cannot communicate with the nonvolatile memory 413 is replaced and a new process cartridge is mounted, the memory information on the main body (not shown) is reset.

  Also in this embodiment, since the remaining amount of toner and the toner consumption rate can be obtained, the configuration of the embodiment 2 is applied when the toner consumption rate is less than a predetermined value and the remaining amount of toner is less than a predetermined amount. it can. In other words, the predicted number of printable sheets may be calculated from the remaining amount of toner and the toner consumption rate, and the pre-exposure light amount setting value may be set according to the predicted number of sheets.

  As described above, even when the CPU 414 cannot communicate with the non-volatile memory 413 and cannot obtain information from the non-volatile memory 413, by setting the pre-exposure light amount according to the remaining amount of toner and the toner consumption rate, It is possible to prevent image defects such as.

  As described above, according to this embodiment, it is possible to prevent image defects due to the thinning of the photosensitive layer of the photosensitive drum at the end of the life of the process cartridge.

10, 11 LED
201 Process cartridge 211 Photosensitive drum 413 Non-volatile memory 414 CPU

Claims (6)

An image carrier, a charging unit for charging the image carrier, a latent image forming unit for forming an electrostatic latent image on the image carrier charged by the charging unit, and the latent image forming unit A detachable process cartridge having developing means for developing the electrostatic latent image formed on the image carrier with a developer, and storage means for storing information;
Pre-exposure means for exposing the image carrier to remove charges remaining on the image carrier;
An image forming apparatus comprising:
Based on the information stored in the storage means, it is determined whether or not the process cartridge has reached the end of its life. When it is determined that the process cartridge has not reached its end of life, exposure is performed with a first light amount. Control means for controlling the pre-exposure means to control the pre-exposure means to perform exposure with a second light quantity larger than the first light quantity when it is determined that the process cartridge has reached the end of its life. An image forming apparatus.   The image forming apparatus according to claim 1, wherein the information stored in the storage unit is an accumulated time during which the pre-exposure unit exposes the image carrier. Detecting means for detecting the amount of developer in the developing means;
The control means stores the amount of developer detected by the detection means in the storage means, the amount of developer stored in the storage means, and the consumption rate of the developer calculated based on the amount of developer. The image forming apparatus according to claim 1, wherein the second light quantity is set based on the first and second light quantities. Detecting means for detecting the amount of developer in the developing means;
If the information cannot be obtained from the storage means, the control means is based on the amount of developer detected by the detection means and the consumption rate of the developer calculated based on the amount of developer. 2. The image forming apparatus according to claim 1, wherein it is determined whether or not the process cartridge has reached the end of its life.   The image forming apparatus according to claim 4, wherein the control unit sets the second light amount based on the amount of the developer and a consumption rate of the developer.   The control means predicts the number of printable transfer materials based on the amount of developer and the consumption rate of the developer, and increases the second light quantity as the predicted number of printable transfer materials decreases. The image forming apparatus according to claim 3, wherein the image forming apparatus is set to a light amount.

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