JP2008292938A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing the service life of a photoreceptor drum from getting short without causing cost rise. <P>SOLUTION: When judging that toner adheres to a toner concentration part, a laser output control part 48 calculates a delay time Δt when the adhesion of the toner to the toner concentration part can be avoided as shown in Fig.5 concerning laser beam output start timing by an optical unit 23, and starts output of the laser beam by the optical unit 23 in timing T2' that the laser beam output start timing is delayed by the delay time Δt from the predetermined timing. Thus, a laser beam radiating position on the surface of the photoreceptor drum 22 is wholly shifted to the periphery direction of the photoreceptor drum 22 by shift amount Δx decided based on the delay time Δt and the rotational speed V of the photoreceptor drum 22. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet by transferring a toner image formed on the surface of the photosensitive drum onto a sheet conveyed in synchronization with the rotation of the photosensitive drum.

  In an image forming apparatus such as a copying machine or a printer, in general, the peripheral surface of a photoconductor is discharged by a discharging operation by a charger installed in the vicinity of the peripheral surface of the photoconductor (photoconductor drum) rotating around an axis. The surface is charged, and the surface of the photoconductor subjected to the charging process is irradiated with light based on image information from the exposure device, and an electrostatic latent image is formed by the disappearance of the charged state of the portion exposed to the light. When the toner is supplied from the developing device toward the electrostatic latent image, a toner image is formed on the peripheral surface of the photosensitive member, and the toner image is transferred onto a sheet.

In the following Patent Document 1, in an image forming apparatus having this type of configuration, when toner remains on the surface of the photoconductor after the transfer, and the accumulated amount of the remaining toner increases, the residual toner is removed by a cleaning blade. A toner having a liquid lubricant on the surface of toner particles and containing 10 to 200 parts by weight of magnetic powder is used for the purpose of increasing the load acting on the surface of the photoconductor by operation and causing deterioration of the surface of the photoconductor drum. Technology has been proposed.
JP 2000-75527 A

  However, in Patent Document 1, since it is necessary to add a liquid lubricant or magnetic powder to the toner, the cost of the toner is increased accordingly.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of preventing the life of a photosensitive drum from being shortened without causing an increase in cost. .

  According to the first aspect of the present invention, the image carrier, the toner image forming unit that forms a toner image on the surface of the image carrier, and the cumulative value of the toner attached to each part on the surface of the image carrier. A storage unit that stores the updated information separately for each part, and the storage unit among the parts on the surface of the image carrier when a new toner image needs to be formed on the surface of the image carrier. A portion where the cumulative value of the toner stored in the image exceeds a threshold value for the cumulative value is extracted as a toner concentration portion, and the toner is attached to the toner concentration portion by forming the toner image to be newly executed. A determination unit that determines whether or not the toner is scheduled, and a predetermined normal formation position on the surface of the image carrier when the determination unit determines that toner is not scheduled to adhere to the toner concentration portion Tona When an instruction to form an image is output to the toner image forming unit and it is determined that the toner is to be attached to the toner concentration portion, the position where the toner image is formed on the surface of the image carrier is An image forming apparatus comprising: a change instruction unit that outputs an instruction to shift to a forming position to the toner image forming unit.

  According to the present invention, when it is determined that the toner is to adhere to the toner concentration part, the toner image formation position on the surface of the image carrier is shifted with respect to the normal formation position. Thus, it is possible to avoid the toner from adhering to the toner concentration part.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus includes a detection unit that detects a predetermined position on the surface of the image carrier as a reference position, and the determination unit includes the detection unit. The position of each part on the surface of the image carrier is grasped based on the reference position detected by the unit.

  According to this aspect of the invention, the detection unit includes a detection unit that detects a predetermined position on the surface of the image carrier as a reference position, and the determination unit uses the reference position detected by the detection unit as a reference. Since the position of each part on the surface of the image carrier is grasped, when it becomes necessary to newly form a toner image on the surface of the image carrier, the determination unit detects the reference position detected by the detection unit. Based on the above, it is possible to detect the relationship between each part on the surface of the image carrier, the cumulative value of the toner, and the toner amount to be adhered.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, a paper transport mechanism that transports the paper to a transfer position where the toner image formed on the surface of the image carrier is transferred to the paper. And a sheet conveyance control unit that adjusts the sheet conveyance speed by the sheet conveyance mechanism in accordance with the shift amount of the toner image formation position by the change instruction unit.

  According to the present invention, since the sheet conveying speed by the sheet conveying mechanism is adjusted according to the shift amount of the toner image forming position by the change instruction unit, the toner image forming position on the surface of the image carrier is changed. Even when it is shifted with respect to the normal formation position, the position of the toner image on the paper can be made substantially the same as when the toner image is formed at the normal formation position.

  According to the present invention, it is possible to avoid the toner from adhering to the toner concentration part, and therefore it is possible to prevent or suppress the life of the photosensitive drum from being shortened by the local concentration of the toner. it can.

  Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is a side view showing the internal configuration of the multifunction machine. The multifunction device 1 has functions such as a copy function, a printer function, a scanner function, and a facsimile function. The multifunction device 1 has a main body 2, a stack tray 3 disposed on the left side of the main body 2, and a main body 2. The document reading unit 4 is disposed above the document reading unit 4 and the document feeding unit 5 is disposed above the document reading unit 4.

  An operation unit 6 is provided on the front part of the multifunction machine 1. The operation unit 6 displays a start key 7 for a user to input a print execution instruction, a numeric keypad 8 for inputting the number of copies to be printed, operation guide information for various copying operations, and the like. Display unit 9 including a liquid crystal display or the like having a touch panel function, a reset key 10 for resetting setting contents set on display unit 9, and a stop key for stopping a printing (image forming) operation being executed 11 and a function switching key 12 for switching between a copy function, a printer function, a scanner function, and a facsimile function.

  The document reading unit 4 includes a scanner unit 13 including a CCD (Charge Coupled Device) sensor and an exposure lamp, and a document table 14 and a document reading slit 15 made of a transparent member such as glass. The scanner unit 13 is configured to be movable by a drive unit (not shown). When reading a document placed on the document table 14, the scanner unit 13 is moved along the document surface at a position facing the document table 14, and the document image is displayed. The image data acquired while scanning is output to the control unit 35 (see FIG. 2). When reading the document fed by the document feeding unit 5, the document is moved to a position facing the document reading slit 15 and synchronized with the document feeding operation by the document feeding unit 5 via the document reading slit 15. The image of the original is acquired and the image data is output to the control unit 35.

  The document feeder 5 includes a document placement unit 16 for placing a document, a document discharge unit 17 for ejecting an image-read document, and a document placed on the document placement unit 16. A document transport mechanism 18 including a paper feed roller, a transport roller (not shown), and the like for feeding the paper one by one to a position facing the document reading slit 15 and discharging it to the document discharge section 17 is provided.

  Further, the document feeding unit 5 is provided so as to be rotatable with respect to the main body unit 2 so that the front side thereof can move upward. By moving the front side of the document feeder 5 upward to open the upper surface of the document table 14, the operator can place a read document, for example, a book in a spread state, on the upper surface of the document table 14. It has become.

  The main body 2 includes a plurality of paper feed cassettes 19, a paper feed roller 20 that feeds the paper from the paper feed cassette 19 one by one and transports it to the image forming unit 21, and an image on the paper transported from the paper feed cassette 19. And an image forming unit 21 for forming the image.

  The image forming unit 21 outputs a laser beam or the like based on the image data acquired by the scanner unit 13 to expose the photosensitive drum 22, and forms an electrostatic latent image on the surface of the photosensitive drum 22. A developing unit 24 that forms a toner image by attaching toner to the surface of the photosensitive drum 22 on which the electrostatic latent image is formed, and a transfer unit 25 that transfers the toner image on the photosensitive drum 22 to a sheet. A fixing device 28 including a pair of rollers 26 and 27 for fixing the toner image to the paper by heating the paper on which the toner image has been transferred, and a paper feed path in the image forming unit 21; 3 or a discharge roller pair 30 and 31 and a pair of registration rollers 50 and 51 are provided.

  Assuming that the position at which the toner image formed on the surface of the photosensitive drum 22 is transferred to the paper is the transfer position, the registration roller pair 50 and 51 is installed at a predetermined position before the transfer position, and the photosensitive drum 22 is a pair of rollers for aligning the position of the toner image formed on the surface of 22 and the position of the sheet, and for example, the sheet transport operation is stopped for a predetermined time before the transfer position in order to perform the alignment. After that, the sheet is conveyed toward the transfer position.

  When images are formed on both sides of a sheet, the image forming unit 21 forms an image on one side of the sheet, and then the sheet is nipped between the pair of conveying rollers 30 on the discharge tray 29 side. In this state, the conveyance roller pair 30 is reversed to switch back the sheet, and the sheet is sent to the sheet conveyance path 32 to be conveyed again to the upstream area of the image forming unit 21. The image forming unit 21 forms an image on the other surface. After that, the paper is discharged to the stack tray 3 or the discharge tray 29.

  FIG. 2 is a block diagram illustrating an electrical configuration of the multifunction machine 1. As shown in FIG. 2, the multifunction device 1 includes a document reading unit 4, an image processing unit 33, an image forming unit 21, a fixing device 28, a data memory 34, a control unit 35, an operation unit 6, a facsimile communication unit 36, a network I. / F unit 37, parallel I / F unit 38, serial I / F unit 39, and HDD (hard disk drive) 40.

  The document reading unit 4, the image processing unit 33, the data memory 34, the control unit 35, the operation unit 6, and the network I / F unit 37 realize a network scanner function for transmitting the captured image data to a pre-specified IP address. Is done. The document reading unit 4, the image processing unit 33, the image forming unit 21, the data memory 34, the control unit 35, the operation unit 6, and the facsimile communication unit 36 realize a facsimile function. Further, the image processing unit 33, the image forming unit 21, the control unit 35, the operation unit 6, the network I / F unit 37, and the parallel I / F unit 38 realize a printer function. The document reading unit 4, the image processing unit 33, the image forming unit 21, the control unit 35 and the operation unit 6 implement a copy function.

  The operation unit 6 corresponds to the operation unit 6 shown in FIG. 1 and is used by a user to perform operations related to a copy function, a printer function, a facsimile function, a scanner function, and the like. Is given to the control unit 35. The operation unit 6 includes a display unit 9 having a touch panel and the like, and an operation key unit 41 including the start key 7 and the numeric keypad 8 described above. The operation key unit 41 is used for inputting various instructions such as a copy execution start command or a facsimile transmission start command by the user, and as will be described later, the operation key unit 41 is used for the fixing device 28 from the sleep mode (during printing standby) or the like. This is used for input by the user to set the contents related to the return operation (start-up operation).

  The document reading unit 4 corresponds to the document reading unit 4 shown in FIG. 1, and optically acquires an image of a document and generates image data.

  The image processing unit 33 performs various image processing on the image data. For example, the image processing unit 33 performs predetermined correction processing such as level correction and γ correction, image data compression or expansion processing, enlargement or reduction processing, and the like on the image data obtained by the reading operation by the document reading unit 4. Various image processes (processing processes) are performed. The image processing unit 33 includes an unillustrated image memory, and stores processed image data or the like in the image memory or outputs the image data to the image forming unit 21, the facsimile communication unit 36, the network I / F unit 37, or the like. To do.

  The image forming unit 21 corresponds to the image forming unit 21 described above, and includes image data of a document read by the document reading unit 4 and an image received from an external personal computer or the like via the network I / F unit 37. An image corresponding to image data such as fax data received from an external facsimile apparatus by the data and facsimile communication unit 36 is printed on a predetermined sheet.

  The data memory 34 is a storage means for previously storing the destination name and the facsimile number of the abbreviated button registration when performing facsimile communication, and also the IP address of the transmission destination when used as a network scanner. Pre-stored.

  The control unit 35 includes a CPU (Central Processing Unit) (not shown), a RAM (Random Access Memory) and a ROM (Read Only Memory) that store programs that define the operation of the CPU, and temporarily. Peripheral devices such as a storage unit such as a RAM for storing data are included. As a result, the control unit 35 controls the entire multifunction device 1 in accordance with the instruction information received by the operation unit 6 and the like and the detection signals from the sensors provided in various parts of the multifunction device 1. More specifically, the control unit 35 functions as a scanner controller 42, a facsimile controller 43, a printer controller 44, and a copy controller 45.

  A program for realizing the above-described functions by being read by a computer as the control unit 35 is stored in a non-volatile and large-capacity external storage device such as the HDD 40, and is appropriately transferred to the main storage device such as the RAM. By doing so, it is also possible to provide execution by the CPU. The program can be supplied through a recording medium such as a ROM or a CD-ROM, or can be supplied through a transmission medium such as a network connected to the network I / F unit 37. The transmission medium is not limited to a wired transmission medium, and may be a wireless transmission medium. The transmission medium includes not only a communication line but also a relay device that relays the communication line, for example, a communication link such as a router.

  When the program is supplied through the ROM, it can be used for execution by the CPU by mounting the ROM on which the program is recorded in the control unit 35. When the program is supplied through a CD-ROM, the CD-ROM reader is connected to, for example, the parallel I / F unit 38 and transferred to the RAM or HDD 40 for execution by the CPU. it can. When the program is supplied through a transmission medium, the program received through the network I / F unit 37 can be transferred to the RAM or the HDD 40 for execution by the CPU.

  The scanner controller 42 controls the operation of each unit used to realize the scanner function. The facsimile controller 43 controls the operation of each unit used to implement the facsimile function. The printer controller 44 controls the operation of each unit used for realizing the printer function. The copy controller controls the operation of each unit used for realizing the copy function.

  The facsimile communication unit 36 includes an encoding / decoding unit (not shown), a modulation / demodulation unit (not shown), and an NCU (Network Control Unit: not shown), and an image of a document read by the document reading unit 4. Data is transmitted to another facsimile apparatus via a telephone line or an Internet line, and image data transmitted from another facsimile apparatus is received. The encoding / decoding unit compresses / decodes image data to be transmitted and expands / decodes received image data. The modem unit modulates the compressed / decoded image data into an audio signal. Or the received signal (audio signal) is demodulated into image data. The NCU controls connection with a facsimile machine as a transmission destination via a telephone line.

  The network I / F unit 37 uses a network interface (for example, 10 / 100base-TX) or the like to control transmission / reception of various data to / from a user side server connected via the network. When one or more terminal devices (not shown) such as a personal computer are connected to the network, the network I / F unit 37 controls transmission / reception of various data to / from these terminal devices. For example, the network I / F unit 37 transmits document image data read by the document reading unit 4 to the terminal device, or receives image data sent from the terminal device for printing by the image forming unit 21. To do.

  The parallel I / F unit 38 uses a high-speed bidirectional parallel interface (for example, IEEE1284 compliant) or the like to transmit print data from an external device or the like by parallel transmission in which data is transmitted in units of a plurality of bits using a plurality of signal lines. To receive. The serial I / F unit 39 uses a serial interface (for example, RS-232C) or the like, and receives various data from an external device or the like by serial transmission that sequentially transmits data bit by bit using a single signal line. To do.

  The HDD 40 stores image data read by the document reading unit 4, image data transmitted via a network, an output format set for the image data, and the like. The image data stored in the HDD 40 is not only used by the multifunction device 1 but also confirmed by the terminal device via the network I / F unit 37 or transferred to a predetermined folder of the terminal device. Or used in the terminal device.

  In the multifunction machine 1, various functions are realized by combining the above-described functions. For example, as the scanner function, a PC transmission function, an E-mail transmission function, a FAX transmission function, or the like may be realized. Here, the PC transmission function is a function for directly transmitting image data read from a document to an arbitrary terminal device or the like via a network. The E-mail transmission function directly transmits image data read from a document as an attached file of an e-mail to, for example, an SMTP server (not shown) via a network, and further, an arbitrary external terminal device from the SMTP server via the network. This is a function for transmitting image data read from a document as an attached file of an e-mail by transmitting the e-mail to the user. The FAX transmission function is a function for directly transmitting image data read from a document to an arbitrary facsimile machine or the like via a telephone line or the like.

  The reference position detection unit 52 detects a reference position set in advance on the surface of the photosensitive drum 22, and includes, for example, a pair of light projecting and receiving devices 52a and 52b (see FIG. 4). The light projector 52 a is installed in a part of the surface of the photosensitive drum 22 that avoids the area where the toner image can be formed, and the light receiver 52 b is installed in a proper position of a member facing the photosensitive drum 22. When the light output from the projector 52a is detected by the light receiver 52b, the reference position detector 52 outputs a light reception signal generated by the light receiver 52b to the control unit 35 as a detection signal.

  Based on the detection signal output from the reference position detection unit 52, the multi-function device 1 performs a laser light output operation and a paper transport operation by the optical unit 23. Hereinafter, this point will be described later.

  The paper detection unit 53 is installed at a predetermined position on the paper conveyance path L from the paper feed cassette 19 to the image forming unit 21, and detects that the paper has been conveyed to the predetermined position. Although not shown in detail, the paper detection unit 53 includes, for example, a pair of light projectors and light receivers. The light output from the light projectors is reflected by the paper conveyed to the predetermined position, and the reflected light is reflected. When the light is received by the light receiver, a light reception signal is generated, and this light reception signal is output to the control unit 35 as a detection signal indicating that the sheet has been conveyed to the predetermined position.

  In addition to the functions as the controllers 42 to 45, the control unit 35 has functions as a toner adhesion total amount storage unit 46, a determination unit 47, a laser output control unit 48, and a paper transport control unit 49.

  The total toner adhesion amount storage unit 46 stores the total amount (total value) of toner adhered to each position on the surface of the photosensitive drum 22 in an update manner. For example, when paying attention to a certain position on the surface of the photosensitive drum 22 and assuming that the total amount of toner adhered to the current position up to the present time is “100”, the total toner adhesion amount storage unit 46 is The toner total amount “100” is stored. When a new image forming operation occurs, the toner adhesion total amount storage unit 46, when the amount of toner attached to the target position in the image forming operation is “2”, stores the total amount of toner stored in the toner total amount. It is updated and stored as “102” obtained by adding “2” to the amount of toner attached this time to “100”.

  The total toner adhesion amount storage unit 46 stores the total amount of toner adhered at each position on the surface of the photosensitive drum 22 in this manner, and creates a histogram as shown in FIG. In the histogram shown in FIG. 3, the position of each part on the surface of the photosensitive drum 22 is the main scanning direction (the rotational axis direction of the photosensitive drum 22) with the installation position of the projector 52a of the reference position detection unit 52 as the origin. And a position in the sub-scanning direction (circumferential direction of the photosensitive drum 22), and a three-dimensional coordinate system is set in which the position in the main scanning direction, the position in the sub-scanning direction, and the total amount of toner are set as dimensions. The total amount of toner in the part is represented by a bar graph. The total toner adhesion amount storage unit updates and stores such a histogram every time an image forming operation is performed. The position in the sub-scanning direction can be detected by using the elapsed time from the time when the presence of the projector 52a is detected and the rotational speed of the photosensitive drum 22.

  The determination unit 47 determines whether or not there is a portion having a large amount of toner adhesion (hereinafter referred to as toner concentration portion) on the surface of the photosensitive drum 22, and if it is determined that there is a toner concentration portion, When it is necessary to perform an image forming operation, it is determined whether or not toner is not attached to the toner concentration portion by the new image forming operation. An arrow P in FIG. 3 indicates a toner concentration part.

  The determination unit 47 first determines the presence or absence of a toner concentration site based on the histogram stored in the total toner adhesion amount storage unit 46. When the determination unit 47 determines that there is a toner concentration portion, the toner concentration portion (position) indicated by, for example, the arrow P in FIG. As a method for detecting the toner concentration part, for example, a method of detecting a part that exceeds a preset threshold for the total amount of toner adhesion as the toner concentration part is assumed as an example. Then, when a new image forming operation becomes necessary, the determination unit 47 determines whether or not toner is attached to the toner concentration portion by the image forming operation.

  Here, in the MFP 1, when the toner concentration portion does not exist, as shown in FIG. 5, after a predetermined time has elapsed from the reception timing T1 of the light reception signal output from the reference position detection unit 52, as shown in FIG. At the timing T2, output of laser light by the optical unit 23 is started. Further, the sheet is made to reach the transfer position at a timing T3 after a predetermined time has elapsed from the timing T2. The above operation is called normal operation.

  When the toner concentration portion exists, the determination unit 47 determines whether or not the toner is attached to the toner concentration portion when the optical unit 23 outputs laser light based on the normal operation described above. to decide. That is, when laser light is output to the surface of the photosensitive drum 22 based on the normal operation, as shown in FIG. 4A, the toner corresponding to the image at the position indicated by the arrow Q on the document. When the image is formed at the position indicated by the arrow R in FIG. 4B, the determination unit 47 determines whether or not the position indicated by the arrow R matches the toner concentration portion indicated by the arrow P in FIG. To do.

  The laser output control unit 48 controls the laser beam output operation by the optical unit 23. Specifically, the laser output control unit 48 performs the above-described normal operation when the determination unit 47 determines that the toner concentration portion does not exist or toner is not scheduled to adhere to the toner concentration portion. As described above, the output operation of the laser beam by the optical unit 23 is controlled.

  On the other hand, when it is determined that the toner is attached to the toner concentration part, the laser output control unit 48 relates to the output start timing of the laser light by the optical unit 23, as shown in FIG. A delay time Δt (for example, a delay time corresponding to one line) that can avoid toner adhesion is calculated, and a timing T2 ′ that delays the output start timing of the laser beam by the delay time Δt with respect to the predetermined timing. The output of the laser beam by the optical unit 23 is started. As a result, the irradiation position of the laser beam on the surface of the photosensitive drum 22 as a whole is shifted in the circumferential direction of the photosensitive drum 22 by a shift amount Δx determined by the delay time Δt and the rotational speed V of the photosensitive drum 22. Shifted. As a result, the toner image corresponding to the image indicated by the arrow Q in FIG. 4A is shifted in the circumferential direction by the shift amount Δx from the toner concentration portion indicated by the arrow R in FIG. 4, for example, the arrow in FIG. It is formed at a position indicated by W.

  The paper transport control unit 49 controls the operation of a motor that rotationally drives the registration roller pairs 50 and 51 installed on the paper transport path L. When the determination unit 47 determines that the toner concentration portion does not exist or the toner does not adhere to the toner concentration portion, the sheet conveyance control unit 49 performs the sheet conveyance operation according to the normal operation described above. Do.

  On the other hand, when the determination unit 47 determines that the toner is to be attached to the toner concentration portion, the sheet conveyance control unit 49 performs the sheet conveyance operation for the same time as the delay time Δt. After increasing the paper conveyance stop time due to, the operation of resuming the paper conveyance operation is performed.

  FIG. 6 is a flowchart showing image forming processing by the control unit 35. As shown in FIG. 6, when it is necessary to perform an image forming operation by a copy instruction from the operation unit 6 or reception of image data from an external device or the like, the control unit 35 indicates that the sheet has been conveyed to the predetermined position. It is determined whether or not a detection signal is received from the paper detection unit 53 (step # 1). When the detection signal is not received, the control unit 35 stands by (NO in step # 1). When the detection signal is received (YES in step # 1), the control unit 35 stops the conveyance of the sheet and performs step # 2. Proceed to processing.

  When there is no toner concentration part (NO in Step # 2), the control unit 35 executes the normal operation shown in FIG. 5 (Step # 6), whereas when the toner concentration part exists (Step # 6). When the normal operation is performed when the detection signal is output from the reference position detection unit 52 (NO in step # 3), and when the detection signal is received (YES in step # 3) In step # 4, it is determined whether or not toner is to adhere to the toner concentration portion.

  When the control unit 35 determines that the toner does not adhere to the toner concentration part (NO in step # 4), the control unit 35 executes the normal operation (step # 6), while the toner is applied to the toner concentration part. Is determined (YES in step # 4), a toner concentration avoidance operation described later is executed (step # 5). After the processing of step # 5 or # 6, the control unit 35 accumulates the amount of toner adhered to each part of the photosensitive drum 22 by the current image forming operation for each part, and after the accumulation. Is stored (the histogram) (step # 7).

  FIG. 7 is a flowchart showing the toner concentration avoidance operation shown in FIG. As shown in FIG. 7, the control unit 35 calculates the delay time Δt that can avoid toner adhesion to the toner concentration part (step # 11), and the laser unit output start timing and transfer position by the optical unit 23. The paper arrival timing is postponed (delayed) by the delay time Δt (step # 12). Then, the control unit 35 causes the toner image formed on the surface of the photosensitive drum 22 to be transferred to the paper that has reached the transfer position (step # 13).

  As described above, out of each part on the surface of the photosensitive drum 22, a part to which a large amount of toner has been attached in the past (toner concentration part) is avoided to adhere to the part. Further, since the total toner adhesion amount is uneven for each part of the surface of the photosensitive drum 22, it is possible to suppress or prevent the surface of the photosensitive drum 22 from being locally deteriorated and shortening the life of the photosensitive drum 22.

  The present invention is not limited to the above embodiment, or the following modification can be adopted instead of the above embodiment.

  [1] In the above embodiment, the laser light irradiation position is shifted in the circumferential direction of the photosensitive drum 22 by the shift amount Δx when it is determined that the toner adheres to the toner concentration portion. When the body drum 22 has a sufficient length in the axial direction, the toner concentration portion is controlled by controlling the laser light output operation by the optical unit 23 so that the vertical and horizontal directions of the toner image formed in the normal operation are switched. You may make it avoid adhesion of the toner to.

  That is, in the normal operation, for example, as shown in FIGS. 8A and 8B, the horizontal direction of the original corresponds to the circumferential direction (sub-scanning direction) of the photosensitive drum 22, and the vertical direction of the original is photosensitive. When it corresponds to the axial direction (main scanning direction) of the body drum 22, when the control unit 35 determines that the toner is attached to the toner concentration portion, as shown in FIG. Laser beam output operation by the optical unit 23 so that the vertical direction corresponds to the axial direction (main scanning direction) of the photosensitive drum 22 and the horizontal direction of the document corresponds to the circumferential direction (sub-scanning direction) of the photosensitive drum 22. May be controlled.

  [2] The reference position detection unit 52 is not limited to a pair of projectors / receivers, and may include a permanent magnet and a Hall element, for example.

1 is a side view schematically showing an internal configuration of a multifunction machine as an example of an image processing apparatus according to the present invention. FIG. 3 is a block diagram illustrating an electrical configuration of the multifunction machine. 6 is a histogram showing the total amount of toner adhesion at each part on the surface of the photosensitive drum. (A) is a diagram showing an image formed on a document, and (b) is a diagram showing a toner image formed on the surface of the photosensitive drum corresponding to the image shown in (a). (A) is a time chart showing a normal image forming operation, and (b) is a time chart showing an image forming operation when toner concentration is avoided. It is a flowchart which shows the image formation process by a control part. 7 is a flowchart illustrating a toner concentration avoidance operation illustrated in FIG. 6. It is explanatory drawing of a deformation | transformation form.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multifunction machine 21 Image forming part 22 Photosensitive drum 23 Optical unit 24 Developing part 25 Transfer part 52 Reference position detection part 52a Light projector 52b Light receiver 53 Paper detection part 33 Image processing part 35 Control part 46 Total toner adhesion amount storage part 47 Determination part 48 Laser output control unit 49 Paper transport control unit 50 Registration roller pair

Claims (3)

An image carrier;
A toner image forming unit for forming a toner image on the surface of the image carrier;
A storage unit for renewably storing the cumulative value of the toner attached to each part on the surface of the image carrier for each part;
When it is necessary to newly form a toner image on the surface of the image carrier, the cumulative value of the toner stored in the storage unit among the portions on the surface of the image carrier is A determination unit that extracts a portion exceeding a threshold value as a toner concentration portion and determines whether or not toner is to be attached to the toner concentration portion by forming the toner image to be newly executed;
When the determination unit determines that the toner is not scheduled to adhere to the toner concentration portion, the toner image forming unit is instructed to form a toner image at a predetermined normal formation position on the surface of the image carrier. And when the toner image is determined to be attached to the toner concentration portion, the toner image is instructed to shift the toner image formation position on the surface of the image carrier relative to the normal formation position. An image forming apparatus comprising: a change instruction unit that outputs to a forming unit. A detection unit that detects a predetermined position on the surface of the image carrier as a reference position;
The image forming apparatus according to claim 1, wherein the determination unit grasps the position of each part on the surface of the image carrier based on the reference position detected by the detection unit. A paper transport mechanism for transporting the paper to a transfer position where the toner image formed on the surface of the image carrier is transferred to the paper;
The image forming apparatus according to claim 1, further comprising: a sheet conveyance control unit that adjusts a sheet conveyance speed by the sheet conveyance mechanism according to a shift amount of a toner image formation position by the change instruction unit.

Images