Image forming apparatus

Abstract

The productivity of the image forming apparatus is reduced by waiting for the start of image formation until the calculation for determining the execution of the cleaning operation is completed.SOLUTION: An image forming apparatus 101 includes a photosensitive drum 1, a charging roller 2, a developing device 3, an exposure device 4, and a transfer roller 5, and is configured to form an image based on image data. The image forming apparatus 200 further includes a charging roller cleaning necessity determination unit 330 configured to control execution of a cleaning operation for causing the developing device 3 to collect toner remaining on the photosensitive drum 1 without being transferred by the transfer roller 5. The charging roller cleaning necessity determination unit 330 sets a toner printing rate to a value at which the cleaning operation is not executed if calculation of the toner printing rate is not in time for image formation.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a cleaning operation for recovering toner that has not been transferred from a photosensitive drum and remains on the photosensitive drum. [Background technology]

[0002] In image forming devices that use toner to form images, toner remaining on a photoconductor after an image has been transferred (residual toner) may adhere to the charging member again as the photoconductor rotates. When residual toner adheres to the charging member, the photoconductor cannot be sufficiently charged by the charging member, resulting in charging defects. Specifically, this can cause uneven potential on the surface of the photoconductor (uneven potential on the photoconductor) or prevent the surface of the photoconductor from reaching a predetermined potential. If an image is formed in this state, image defects such as uneven density and black streaks (black lines appearing in the image) may occur.

[0003] Therefore, it is necessary to clean the toner adhering to the charging member. A technique using the print rate of an image formed based on image data is known as a method for determining the timing to clean the charging member (Patent Document 1). This print rate is correlated with the amount of residual toner after transfer; a higher print rate results in a larger amount of residual toner, and a lower print rate results in a smaller amount of residual toner after transfer.

[0004] The image forming apparatus described in Patent Document 1 calculates the printing rate for each of a plurality of regions in the longitudinal direction of the photosensitive drum, and estimates the amount of residual toner from the printing rate for each of the plurality of regions. Then, in this image forming apparatus, if the amount of residual toner in the plurality of regions is greater than a predetermined amount, a cleaning operation is performed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-11159 Summary of the Invention [Problem to be solved by the invention]

[0006] The time required to calculate the coverage rate or the amount of residual toner increases when, for example, the image data is large or complex. This is because the calculation of the coverage rate or the amount of residual toner is performed while converting the image data into a printable format. Therefore, when forming an image based on image data, if the calculation to determine whether to perform a cleaning operation is completed, image formation will not begin, reducing the productivity of the image forming device.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to prevent a decrease in productivity of an image forming apparatus caused by waiting to start image formation until calculation for determining whether or not to perform a cleaning operation is completed. [Means for solving the problem]

[0008] In order to solve the above problem, the image forming apparatus described in claim 1 is an image forming apparatus that forms an image on a sheet based on image data, and includes a photosensitive body, a charging means that contacts the photosensitive body and charges the photosensitive body, an exposure means that exposes the photosensitive body to light to form an electrostatic latent image on the photosensitive body charged by the charging means, a developing means that develops the electrostatic latent image on the photosensitive body using toner, a transfer means that transfers the image on the photosensitive body developed by the developing means, a determination means that determines a value related to the amount of toner that adheres to the photosensitive body by analyzing the image data, and a control means that controls the execution of a cleaning operation to have the developing means recover toner that remains on the photosensitive body without being transferred by the transfer means based on the value, and the control means is characterized in that if the analysis of the image data by the determination means is not completed within a specified time, the value is set to a predetermined value such that the cleaning operation is not executed. [Effects of the Invention]

[0009] According to the present invention, it is possible to prevent a decrease in productivity of an image forming apparatus. [Brief explanation of the drawings]

[0010] [Figure 1] Image forming system configuration diagram including an image forming apparatus [Figure 2] Schematic cross-sectional view of an image forming apparatus [Figure 3] Schematic diagram illustrating the potentials of the photosensitive drum, charging roller, and developing sleeve. [Figure 4] Schematic diagram explaining charging failure caused by toner contamination on the charging roller [Figure 5] Schematic diagram explaining charging failure caused by toner contamination on the charging roller [Figure 6] FIG. 1 is a timing chart showing the control timing of each part during the cleaning operation of the charging roller. [Figure 7] Control block diagram of an image forming apparatus [Figure 8] FIG. 10 is a diagram showing the relationship between the amount of toner applied and the fixing temperature. [Figure 9] Flowchart of control using the print rate of the image forming apparatus [Figure 10] Schematic diagram of the screen displayed on the display unit DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the technical scope of the present invention is determined by the claims and is not limited to the individual embodiments described below.

[0012] Example 1 (System Configuration) 1 is a diagram showing an example of an image forming system 1 including an image forming apparatus 101 according to a first embodiment. In FIG. 1, the image forming system 1 according to the first embodiment is configured to include the image forming apparatus 101, a print server 102, a client PC 103, and a network 104. The image forming apparatus 101, the print server 102, and the client PC 103 are communicably connected via the network 104. The image forming apparatus 101 performs image formation (image creation) processing of various input data from the print server 102, the client PC 103, or a reading device (scanner) of the image forming apparatus 101 itself, and executes processing to output a printed matter.

[0013] (Image formation operation) FIG. 2 is a monochrome laser beam printer that employs a cleanerless system and a contact charging system, which is an example of an electrophotographic image forming apparatus 101 according to the first embodiment. The image formation operation in the image forming apparatus 101 will be described with reference to FIG. 2.

[0014] The image forming apparatus 101 in this embodiment is provided with a cylindrical photosensitive member serving as an image carrier, i.e., a photosensitive drum 1. A charging roller 2 serving as a charging means and a developing device 3 serving as a developing means are provided around the photosensitive drum 1. In addition, an exposure device 4 serving as an exposure means is provided between the charging roller 2 and the developing device 3 in the rotation direction of the photosensitive drum 1 in FIG. 2. A transfer roller 5 serving as a transfer means is pressed against the photosensitive drum 1.

[0015] The photosensitive drum 1 in this embodiment is a negatively charged organic photosensitive member. This photosensitive drum 1 has a photosensitive layer on a drum-shaped aluminum substrate, and is driven to rotate at a predetermined process speed in the direction indicated by the arrow in the figure (clockwise direction) by a drive motor (not shown) serving as a driving means. In this embodiment, the process speed corresponds to the peripheral speed (surface movement speed) of the photosensitive drum 1, which is 140 mm / sec, and the outer diameter of the photosensitive drum 1 is 24 mm.

[0016] The charging roller 2, which is a charging member, contacts the photosensitive drum 1 with a predetermined pressure to form a charging portion. During charging, a predetermined charging voltage (charging bias) is applied to the charging roller 2 by a charging power supply (not shown). In this embodiment, a negative DC voltage is applied as the charging voltage to the charging roller 2 during charging. As an example, the charging voltage in this embodiment is −1300 V. As a result, in this embodiment, the surface of the photosensitive drum 1 is uniformly charged to a dark potential Vd of −600 V. Here, the description will be given assuming that the contact portion between the charging roller 2 and the photosensitive drum 1 in the rotational direction of the photosensitive drum 1 is the charging portion.

[0017] In this embodiment, the exposure device 4, which is an exposure unit, is a laser scanner device that outputs laser light corresponding to image data input from an external device such as a host computer, and scans and exposes the surface of the photosensitive drum 1. This exposure forms an electrostatic latent image (electrostatic image) corresponding to the image data on the surface of the photosensitive drum 1. In this embodiment, the dark area potential Vd of the surface of the photosensitive drum 1, which has been uniformly charged, is exposed by the exposure device 4, and its absolute value decreases to a light area potential Vl of −100 V. Here, the position on the photosensitive drum 1 that is exposed by the exposure device 4 in the rotational direction of the photosensitive drum 1 is considered to be the exposure area (exposure position). Note that the exposure device 4 is not limited to a laser scanner device, and may be, for example, an LED array in which multiple LEDs are arranged along the longitudinal direction of the photosensitive drum 1.

[0018] In this embodiment, a contact development method is used as the development method. The developing unit 3 includes a developing roller 31 as a developer carrier, a toner supply roller 32 as developer supply means, a toner storage chamber 33 that stores toner, and a developing blade 34. The toner supplied from the toner storage chamber 33 to the developing roller 31 by the toner supply roller 32 is charged to a predetermined polarity by passing through the blade nip, which is the contact point between the developing roller 31 and the developing blade 34. The toner carried on the developing roller 31 moves from the developing roller 31 to the photosensitive drum 1 in accordance with the potential difference between the developing roller 31 and the photosensitive drum 1.

[0019] Hereinafter, the area where toner moves from the developing roller 31 to the photosensitive drum 1 in relation to the rotation direction of the photosensitive drum 1 will be referred to as the developing section. The developing roller 31 is driven to rotate counterclockwise in the drawing so that the photosensitive drum 1 and the developing roller 31 move forward. Note that the drive motor serving as the drive means (not shown) for driving the developing roller 31 may be a main motor shared with the drive means (not shown) for the photosensitive drum 1, or separate drive motors may rotate the photosensitive drum 1 and the developing roller 31, respectively.

[0020] During development, a predetermined development voltage (development bias) is applied to the development roller 31 by a development power supply (not shown) as a development voltage application means. In this embodiment, during development, a negative DC voltage is applied to the development roller 31 as the development voltage, and the development voltage is set to −380 V.

[0021] In this embodiment, toner charged with the same polarity as the charge polarity of the photosensitive drum 1 (negative in this embodiment) adheres to the exposed surface (image area), which is the image forming area on the photosensitive drum 1, where the absolute value of the potential is reduced by exposure after being uniformly charged. In this embodiment, the normal polarity, which is the charge polarity of the toner during development, is negative. Note that while this embodiment employs a one-component non-magnetic contact development method, the present invention is not limited to this embodiment and may employ a two-component non-magnetic contact development method, non-contact development method, magnetic development method, etc. Two-component non-magnetic contact development is a method in which a two-component developer comprising non-magnetic toner and magnetic carrier is used as the developer, and development is performed by bringing the developer carried on a developer carrier into contact with the photosensitive drum 1. Non-contact development is a method in which toner is sprayed onto the photosensitive drum from a developer carrier arranged opposite the photosensitive drum without contacting the photosensitive drum. The magnetic development method is a method of developing by magnetically supporting magnetic toner on a developer carrier that contains a magnet as a magnetic field generating means and is arranged opposite the photosensitive member in contact or non-contact with the photosensitive member. In this embodiment, toner with a median average particle size of 6 μm and a normal negative charge polarity is used.

[0022] The transfer roller 5 serving as the transfer member can be preferably made of an elastic material such as polyurethane rubber, EPDM (ethylene propylene diene rubber), or sponge rubber made of NBR (nitrile butadiene rubber). The transfer roller 5 is pressed against the photosensitive drum 1, forming a transfer section where the photosensitive drum 1 and the transfer roller 5 are in pressure contact. During transfer, a predetermined transfer voltage (transfer bias) is applied to the transfer roller 5 by a transfer power supply (not shown) serving as a transfer voltage application means. In this embodiment, a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal polarity of the toner is applied to the transfer roller 5 as the transfer voltage. In this embodiment, the transfer voltage during transfer is, for example, +1000 V. The toner image is then electrostatically transferred from the photosensitive drum 1 to the sheet S by the action of the electric field formed between the transfer roller 5 and the photosensitive drum 1.

[0023] A sheet S stored in a cassette 6 is fed by a paper feed unit 7 in time with the toner image formed on the photosensitive drum 1 reaching the transfer section, and is conveyed to the transfer section via a pair of registration rollers 8. The toner image formed on the photosensitive drum 1 is transferred onto the sheet S by a transfer roller 5 to which a predetermined transfer voltage is applied by a transfer high-voltage power supply.

[0024] After the toner image has been transferred, the sheet S is conveyed to a fixing device 9. The fixing device 9 is a film heating type fixing device that includes a fixing film 91 incorporating a fixing heater (not shown) and a thermistor (not shown) that measures the temperature of the fixing heater, and a pressure roller 92 that presses against the fixing film 91. The toner image is fixed on the sheet S by heating and pressing it, and the sheet S passes through a pair of paper discharge rollers 12 and is discharged outside the apparatus.

[0025] Further, the transfer residual toner that has not been transferred to the sheet S and remains on the photosensitive drum 1 is removed in the following process.

[0026] The residual toner contains a mixture of positively charged toner and negatively charged toner that does not have a sufficient charge. The residual toner is charged negatively again by discharge at the charging section of the charging roller 2. The residual toner that has been charged negatively again by the charging roller 2 reaches the developing section as the photosensitive drum 1 rotates. Here, an electrostatic latent image may be formed on the surface of the photosensitive drum 1 that has reached the developing section, forming an image forming section, or a non-image forming section where no electrostatic latent image is formed. The behavior of the residual toner that has reached the developing section will be explained separately for the image forming section and non-image forming section of the photosensitive drum 1.

[0027] The residual toner adhering to the image forming portion of the photosensitive drum 1 is not transferred from the photosensitive drum 1 to the developing roller 31 in the developing portion, but moves to the transfer portion together with the developed toner from the developing roller 31, where it is transferred to the sheet S and used for image formation.

[0028] Meanwhile, the transfer residual toner adhering to the non-image forming portion of the photosensitive drum 1 is recharged to the normal negative polarity by the charging portion, and is transferred to the developing roller 31 in the developing portion due to the potential difference between the potential of the non-image forming portion of the photosensitive drum 1 and the developing voltage, and is then collected in the toner storage chamber 33. The toner collected in the toner storage chamber 33 is used again for image formation.

[0029] A pre-exposure device 13 is provided as a means for eliminating the charged potential of the photosensitive drum 1 between the transfer unit and the charging unit in the rotation direction of the photosensitive drum 1. This is to stabilize the discharge at the charging unit by leveling out the unevenness of the surface potential of the photosensitive drum 1 caused by transfer, thereby obtaining a uniform charged potential.

[0030] (Process for treating residual toner after transfer) Next, a process for treating toner that is not used in image formation, such as transfer residual toner remaining on the photosensitive drum 1 after transfer, will be described.

[0031] Residual toner remaining on the photosensitive drum 1 includes a mixture of toner charged to a positive polarity (opposite to the normal polarity of the toner) and toner charged to a negative polarity but with insufficient charge. Just before the charging section, where the charging roller 2 and photosensitive drum 1 contact, these toner particles are sufficiently charged to a negative polarity by discharge due to the potential difference created between the charging roller 2 and the photosensitive drum 1. This creates an electrostatic repulsive force with the charging roller 2, to which a negative charging voltage is applied, allowing the toner to pass through the charging section without adhering to the charging roller 2. Furthermore, some of the toner particles that were not sufficiently charged to a negative polarity by the discharge at the charging section initially adhere to the charging roller 2. However, at the charging section, the toner particles are again charged to a negative polarity due to friction between the charging roller 2 and the photosensitive drum 1 and the application of a charging voltage, and are then transferred from the charging roller 2 to the photosensitive drum 1 by the electrostatic repulsive force with the charging roller 2, to which a negative charging voltage is applied.

[0032] The residual toner on the photosensitive drum 1, which has been negatively charged in the charging section, reaches the developing section as the photosensitive drum 1 rotates, and is then processed as follows.

[0033] 3 shows the relationship between the surface potential formed on the photosensitive drum 1 in the developing unit and the developing voltage in Example 1. As shown in FIG. 3, in a non-image forming portion in the developing unit where an electrostatic latent image is not formed, the developing voltage is relatively more positive than the surface potential of the photosensitive drum 1 charged by the charging roller 2. Therefore, due to the above potential relationship, the negatively charged residual toner on the photosensitive drum 1 is transferred from the photosensitive drum 1 to the developing roller 31 and then collected in the toner storage chamber 33.

[0034] Here, the back contrast (Vback), which is the potential difference between the surface potential of the photosensitive drum 1 and the development voltage in the non-image forming portion shown in FIG. 3, is preferably set as follows: In order to recover the negatively charged toner on the photosensitive drum 1 onto the development roller 31, a sufficient Vback is ensured in the development portion. It is also preferable to set Vback to a value that can prevent the toner carried on the development roller 31 from unintentionally developing on the surface of the photosensitive drum 1, i.e., prevent the generation of fog toner, which will be described later. Specifically, it is preferable to set Vback to approximately 100V to 500V.

[0035] If Vback is 100 V or less, it is not possible to sufficiently collect the negatively charged toner adhering to the surface of the photosensitive drum 1. Furthermore, the negatively charged toner on the developing roller 31 is likely to be unintentionally developed onto the photosensitive drum 1, i.e., fog toner is likely to occur.

[0036] On the other hand, if Vback is greater than 500V, Vback is too large, and discharge occurs between the developing roller 31 and the photosensitive drum 1, causing the toner on the developing roller 31 to be charged to the positive polarity. This makes it easier for fogging toner to occur from the developing roller 31 onto the photosensitive drum 1. In Example 1, the surface potential Vd of the photosensitive drum 1 was set to -600V, the developing voltage was set to -300V, and Vback was set to 300V.

[0037] 3, in the image forming section where the electrostatic latent image is formed in the developing section, a development contrast (Vcont) is formed, which is a potential relationship that develops the negatively charged toner from the developing roller 31 to the photosensitive drum 1. Therefore, the negatively charged toner on the photosensitive drum 1 is used as a toner image as it is, and in addition, a toner image is formed by developing the toner from the developing roller 31, and then the toner image moves to the transfer section and is transferred to the sheet S.

[0038] However, if there is a large amount of residual toner on the photosensitive drum 1 after transfer, the charging unit cannot sufficiently charge the residual toner on the photosensitive drum 1 to a negative polarity, which can result in the toner being positively charged adhering to the charging roller 2 and causing toner stains to accumulate on the charging roller 2.

[0039] When a large amount of toner remains on the photosensitive drum 1 after transfer, there may be a large area where a large amount of toner is applied. This may cause toner contamination to accumulate on the charging roller 2.

[0040] As shown in Figure 4, when a large amount of toner accumulates on the charging roller 2, the toner-stained areas of the charging roller 2 cause insufficient charging of the photosensitive drum 1 by the charging roller 2, resulting in a decrease in Vback. This is because the toner adhesion to the surface of the charging roller 2 increases resistance, preventing proper discharge. In particular, when Vback is less than 100 V, as mentioned above, the negatively charged residual toner on the photosensitive drum 1 in the non-image-forming area of ​​the development unit is not properly collected by the developing roller 31. Furthermore, there is a risk of fog toner on the photosensitive drum 1. Residual toner that was not developed and collected on the photosensitive drum 1 and fog toner adhere to the charging roller 2 as toner stains, further exacerbating the charging failure. Furthermore, the toner stains on the charging roller 2 reduce the amount of discharge at the charging unit, thereby reducing the absolute value of the surface potential of the photosensitive drum 1. As the amount of discharge decreases, Vback decreases, and the amount of fog toner increases. As a result, as shown in Figure 5, the photosensitive drum 1 is ultimately unable to be charged at the toner-stained areas of the charging roller 2. Furthermore, a part of the toner developed on the poorly charged portion of the photosensitive drum 1 due to toner contamination of the charging roller 2 is transferred onto the sheet S, resulting in a defective image due to toner contamination.

[0041] (Cleaning of charging roller) The image forming apparatus 101 of this embodiment is provided with a cleaning operation (cleaning operation) for the charging roller 2, which will be described below. Fig. 6 shows a timing chart of the cleaning operation in this embodiment. The cleaning operation is performed when the maximum toner amount on a page is equal to or greater than a predetermined amount and the toner coverage rate is equal to or greater than a predetermined amount. The calculation of the maximum toner amount and the toner coverage rate will be described later.

[0042] At T1, the charging voltage and developing voltage are applied, and the pre-exposure device 13 is turned on. In this embodiment, various voltages are applied before the photosensitive drum 1 is driven. In this embodiment, the charging voltage is -500 V, and the developing voltage is +200 V. The charging voltage is set to a voltage below the discharge start voltage. In this embodiment, the discharge start voltage is set to -550 V. By applying the charging voltage and developing voltage, the potential difference required for cleaning can be created between the photosensitive drum 1 and the charging roller 2, and between the photosensitive drum 1 and the developing roller 31. After the charging voltage and developing voltage have sufficiently risen, driving of the photosensitive drum 1 begins at timing T2. As a result, the charging voltage is applied, and toner expelled onto the surface of the photosensitive drum 1 due to the potential difference generated in the charging section can be efficiently collected in the developing section.

[0043] At T3 after the cleaning operation is performed, the drive of the photosensitive drum 1 is first turned off. Then, at T4, the charging voltage, developing voltage, and exposure of the pre-exposure device 13 are turned off almost simultaneously. Here, the cleaning operation of the charging roller 2 is performed from T2 to T3, and in this embodiment, the time from T2 to T3, from when the drive motor (not shown) is turned on until it is turned off, is set to one rotation of the photosensitive drum 1. During the cleaning operation, the developing roller 31 and charging roller 2 are in contact with the photosensitive drum 1. The timing of T3 and T4 may also be simultaneous.

[0044] In this embodiment, the charging voltage, developing voltage, and pre-exposure device 13 are all turned on at the same timing, but the charging voltage and developing voltage need to be applied before the drive motor 110 is driven. However, the timing of exposure of the pre-exposure device 13 may be controlled. Specifically, exposure may begin when the surface of the photosensitive drum 1 that formed the developing portion while the drive of the photosensitive drum 1 is stopped reaches the opposing surface of the pre-exposure device 13, i.e., the pre-exposure portion that exposes the surface of the photosensitive drum 1. Furthermore, exposure may begin when the surface of the photosensitive drum 1 that formed the charging portion reaches the pre-exposure portion that exposes the surface of the photosensitive drum 1.

[0045] The cleaning operation is preferably performed at least as long as the charging roller 2 makes one revolution and the surface of the photosensitive drum 1 forming the charging portion reaches the developing portion during that revolution. This is because the charging roller 2 needs to be rotated long enough to clean the entire circumference and to recover the toner expelled from the charging roller 2 onto the surface of the photosensitive drum 1 in the developing portion. Of course, the cleaning operation may be longer than that. In this embodiment, the cleaning operation is performed for the length of one revolution of the photosensitive drum.

[0046] We will now explain the action of the cleaning operation of the charging roller 2. First, by setting the developing voltage to a positive polarity, it is possible to form an appropriate Vback even when poor charging of the photosensitive drum 1 occurs due to toner contamination on the charging roller 2. This makes it possible to prevent poor collection of residual toner on the photosensitive drum 1 at the developing unit and the occurrence of fogging toner due to poor charging.

[0047] In addition, by rotating the charging roller 2 and the photosensitive drum 1 while a negative charging voltage is applied, the toner adhering to the charging roller 2 is charged to a negative polarity, and can be transferred from the charging roller 2 to the photosensitive drum 1 by the electrostatic repulsion force with the charging roller 2.

[0048] Here, in order to ensure the electrostatic repulsion between the charging roller 2 and the negatively charged toner, the charging voltage must be made more negative than the surface potential of the photosensitive drum 1 at the charging portion.

[0049] However, if the charging voltage is too negative relative to the surface potential of the photosensitive drum 1, the amount of discharge between the charging roller 2 and the photosensitive drum 1 increases immediately before the charging portion between the charging roller 2 and the photosensitive drum 1. This may promote the conversion of the toner adhering to the charging roller 2 to a positive polarity, making it difficult to convert the toner adhering to the charging roller 2 to a negative polarity.

[0050] Specifically, the charging voltage during the cleaning operation is set to be more negative than the surface potential of the photosensitive drum 1 at the charging portion. Furthermore, the potential difference between the charging voltage during the cleaning operation and the surface potential of the photosensitive drum 1 at the charging portion is set to be equal to or greater than Vcont during the image formation operation. Furthermore, a charging voltage equal to or less than the discharge start voltage is applied so that the potential is equal to or less than the discharge threshold for discharge occurring between the charging roller 2 and the photosensitive drum 1. This allows both the transfer of negatively charged toner on the charging roller 2 to the photosensitive drum 1 and the negative charging of toner on the charging roller 2. Controlling the potential difference at the charging portion to be greater than Vcont, which is set to ensure developability, improves the toner discharge performance from the charging roller 2. In other words, forming a potential difference at the charging portion greater than Vcont electrically ensures that toner is transferred to the surface of the photosensitive drum 1.

[0051] In this embodiment, when the cleaning operation of the charging roller 2 is performed, the pre-exposure device 13 performs static elimination on the photosensitive drum 1, thereby erasing the history of the surface potential of the photosensitive drum 1 before the cleaning operation and setting the charging potential of the photosensitive drum 1 to approximately 0 V. This makes it easy to control the potential difference between the charging voltage and the surface potential of the photosensitive drum 1.

[0052] The negatively charged toner transferred from the charging roller 2 to the photosensitive drum 1 is then transferred to the developing roller 31 in a developing section that forms an appropriate Vback, and collected in the toner storage chamber 33, thereby removing the toner adhering to the charging roller 2.

[0053] (Control mode) FIG. 7 is a block diagram of the image forming apparatus 101 according to the first embodiment.

[0054] 7, the image forming apparatus 101 is made up of a controller 300 and a printing unit 320. The controller 300 is configured so that a CPU 301, a storage unit 302, a ROM 303, a RAM 304, a network communication control unit 305, an operation unit 306, a printer communication control unit 307, a printer communication IF 308, and an image processing unit 310 can communicate with each other. The CPU 301 reads a main program from the ROM 303 in accordance with an initial program in the ROM 303 and stores it in the RAM 304. The RAM 304 is used as a main memory for storing programs and for working purposes.

[0055] Furthermore, image processing unit 310 includes an encoding / decoding unit 311 that mainly processes image data, an image generation unit 312, and a halftone processing unit 314. Image processing unit 310 also includes a toner application amount calculation unit 315 that calculates the maximum toner application amount, and a toner coverage rate calculation unit 316 that calculates the coverage rate.

[0056] The encoding / decoding unit 311 decodes encoded image data received by the network communication control unit 305 from the client PC 103 or the like via the network interface to generate image data, and stores the image data in the RAM 304 .

[0057] The image generation unit 312 uses the image data stored in RAM 304 to generate raster image data suitable for printing, and outputs it for each pixel as RGB data and attribute data indicating the data attributes of each pixel. The encoding / decoding unit 311 and the image generation unit 312 may be configured to handle image data read by a reading unit provided in the image forming apparatus 101 itself, rather than image data received from the client PC 103 or the like. The reading unit here may include, for example, a CCD (Charged Couple Device) or a CIS (Contact Image Sensor). A processing unit that performs predetermined image processing on the read image data may also be provided.

[0058] The toner amount calculation unit 315 calculates the maximum toner amount based on the image data. In this embodiment, for example, 3×3 pixels is used as a unit area, and the toner amount calculation unit 315 calculates the toner amount per unit area.

[0059] Image data is composed of image signal values ​​that correlate with the amount of applied toner. Each pixel is represented by an 8-bit image signal value ranging from 0 to 255. The amount of applied toner per unit area is calculated from the image signal values ​​of, for example, 9 pixels (3 x 3 pixels). A toner amount of 0 indicates that no toner has been used, and the density increases as the amount of applied toner increases. When the toner amount reaches 2295, the maximum density is reached. In the following, when the image signal value per unit area is 2295, the toner amount per unit area is said to be 100%.

[0060] Next, the applied toner amount calculation unit 315 identifies the applied toner amount per unit area for the entire page corresponding to the image data, and calculates the maximum applied toner amount per unit area on the page as the applied toner amount value.

[0061] The toner coverage rate calculation unit 316 calculates the coverage rate for each page based on the amount of toner consumed when the image on the page is a full solid image.

[0062] Specifically, the toner amount per unit area calculated by the toner amount calculation unit 315 is added up for each page, and the ratio based on the case where the image on the page is a full solid image is calculated as the printing rate.

[0063] The halftone processing unit 314 performs halftone processing on the image data. Specific configurations of the halftone processing unit 314 include screen processing and error diffusion processing. Screen processing converts the input image data to N-values ​​using a predetermined number of dither matrices. Error diffusion processing converts the input image data to N-values ​​by comparing it with a predetermined threshold, and then diffuses the difference between the input image data and the threshold to surrounding pixels that are subsequently subjected to N-value processing.

[0064] The printer communication IF 308 and the controller communication IF 325 are IFs (interfaces) for mutual communication between the controller 300 and the printing unit 320. Information exchanged between them includes image data, toner application amount values, control signals from the controller 300, etc.

[0065] The printer communication control unit 307 selects data to be transmitted from the printer communication IF 308 to the controller communication IF 325 , and executes control to transmit the data to the printing unit 320 via the printer communication IF 308 .

[0066] The printing unit 320 corresponds to the hardware configuration shown in FIG. 2. The CPU 321 controls each unit of the printing unit 320 (the image forming apparatus 101 shown in FIG. 2). The ROM 323 is a storage unit in which various programs are stored. The CPU 321 controls each unit of the printing unit 320 by reading out the programs stored in the ROM 323. The RAM 324 functions as a system work memory. The controller communication IF 325 is an interface for communicating with the controller 300.

[0067] Image forming unit 327 is configured with the charging unit, exposure unit, and development unit described in Fig. 2. Image forming unit 327 forms a toner image in accordance with image data transmitted from controller 300.

[0068] The charge roller cleaning necessity determination unit 330 determines whether cleaning of the charge roller 2 is necessary based on the toner amount value and toner coverage rate sent from the controller 300 to the printing unit 320. In this embodiment, if the toner amount value is 80% or more and the toner coverage rate is 50% or more, it determines that cleaning of the charge roller 2 is necessary, and the image forming unit 327 performs the above-mentioned cleaning operation of the charge roller 2. This allows for appropriate cleaning in situations where a wide range of areas with a high toner amount are present and the charge roller 2 is likely to become soiled by transfer residual toner.

[0069] The fixing temperature control unit 326 calculates the minimum temperature required for fixing relative to the target value of the fixing temperature according to the toner amount value transmitted from the controller 300 to the printing unit 320. The fixing temperature control unit 326 controls the temperature of the fixing unit 9 based on the target value of the fixing temperature and the minimum temperature required for fixing. Details will be described in FIG. 8.

[0070] The fixing device 9 constitutes the fixing means described in Fig. 2. The fixing device 9 applies heat to the toner image formed on the recording paper S by the image forming unit 327 to melt and fix the toner image. The operation unit 306 is made up of various keys for the user to operate the image processing device and a display unit that displays various information.

[0071] (Method for calculating fixing temperature based on toner amount) Next, a method for calculating the fixing temperature required for fixing the target page according to the specified toner amount value as a result of the calculation process by the toner amount calculation unit 315 will be described.

[0072] As mentioned above, the toner application amount value refers to the amount of toner applied per unit area on the image data. In order to fix the toner to the recording paper S without causing fixing problems, the temperature of the fixing device 9 must be set to a fixing temperature that can reliably fix the maximum toner application amount on the target page. At this time, the maximum toner application amount value differs depending on the image data to be printed, and therefore the temperature required for fixing also differs for each image data. Furthermore, the larger the maximum toner application amount value, the higher the temperature required by the fixing device 9 to fix the toner.

[0073] 8 is a diagram showing the relationship between the toner amount value in the image forming apparatus 101 according to the first embodiment and the fixing temperature required for the fixing unit 9 to fix the toner. The horizontal axis in FIG. 8 indicates the toner amount value, and the vertical axis indicates the temperature required for the fixing unit 9 to fix the toner to the recording paper S.

[0074] In FIG. 8, for example, if the calculation result by the toner amount calculation unit 315 is 100%, the minimum temperature required for toner fixing is Temp1. Similarly, if the calculation result by the toner amount calculation unit 315 is 75%, 50%, or 25%, the minimum temperatures required for toner fixing are Temp2, Temp3, and Temp4, respectively. If the fixing temperature of the fixing device 31 is raised to a temperature at which the maximum toner amount value appearing in the image data can be fixed, the problem of poor toner fixing will not occur when toner related to the image data is fixed. Therefore, the minimum temperature required to fix the toner of the print target can be obtained from the toner amount value calculated by the toner amount calculation unit 315.

[0075] The relationship between the toner amount value and the fixing temperature in the graph shown in FIG. 8 may be stored in the storage means 302, RAM 304, etc. as lookup table data, for example, so that the toner amount calculation unit 315 can refer to it as needed.

[0076] (Action when toner amount value is not completed within the specified time) The operation when the calculation of the toner amount value is not completed within a specified time, which is a feature of this embodiment, will be described below.

[0077] The processing time required for the image processing unit 310 to decode the encoded image data received from the client PC 103 or the like is not always constant because it depends on the content of the encoded image data. Furthermore, the processing time required to calculate the amount of applied toner and the toner coverage rate also varies depending on the number of pixels per unit area. In other words, the time required to analyze image data depends on the image data. Therefore, if the time required for the image processing unit 310 to decode the image data (encoded data) and calculate the amount of applied toner and the toner coverage rate increases, the time required to determine whether charging roller cleaning is necessary and to set the temperature of the fixing device 9 also increases. If image formation is not started until it is determined whether charging roller cleaning is necessary, the productivity of the image forming apparatus 101 decreases.

[0078] 9 is a diagram showing a control flow in this embodiment. In step S1001, the CPU 301 receives encoded image data from the client PC 103 or the like via the network communication control unit 305 and writes it to the RAM 304. The encoded data received in step S1001 is encoded data consisting of one page or multiple pages. In step S1002, the image processing unit 310 acquires a specified time that is stored in advance in the RAM 304.

[0079] The aforementioned specified time is the standard time required to decode the encoded data for one page of image, calculate the toner application amount, and calculate the toner coverage rate, and is set in advance based on the target productivity (also known as printing speed) of the image forming apparatus 101. For example, if the image forming apparatus 101 can print images on 60 A4-sized sheets per minute, the printing time per sheet is one second. The CPU 301 determines the specified time to be 0.8 seconds, allowing for a margin of 0.2 seconds for the printing time. Furthermore, if the image forming apparatus 101 is controlled based on multiple printing speeds, the CPU 301 selects the specified time based on the paper type from multiple specified times corresponding to the multiple printing speeds. This is because the printing speed is determined based on the paper type. Note that the specified time is not limited to the processing time for one page, but may also be the specified time for a unit page, such as 1 / 2 page, 1 / 3 page, 2 pages, or 3 pages.

[0080] In step S1003, the image processing unit 310 starts decoding each page based on the image data (encoded data) and calculating the toner amount and toner coverage rate for each page. At this time, the image processing unit 310 uses its internal counter to measure the total time required for image processing, which includes decoding and calculating the toner amount and toner coverage rate, for each page.

[0081] In step S1004, CPU 301 determines whether processing for one page has been completed within a specified time. If the total time for one page is equal to or less than the specified time in step S1004, CPU 301 proceeds to step S1005. In step S1005, image processing unit 310 notifies fixing temperature control unit 326 and charging roller cleaning necessity determination unit 330 of the toner application amount and printing rate calculated in steps S1003 and S1004.

[0082] On the other hand, if the processing for one page is not completed within the specified time in step S1004, the CPU 301 proceeds to step S1006. In step S1006, the image processing unit 310 stops decoding and calculating the toner amount and coverage rate. The CPU 301 then notifies the fixing temperature control unit 326 that the toner amount is 100% and the toner coverage rate is 100%, and notifies the charging roller cleaning necessity determination unit 330 that the toner amount is 0% and the toner coverage rate is 0%.

[0083] In step S1007, the charge roller cleaning necessity determination unit 330 and the fixing temperature control unit 326 determine the fixing temperature and whether charge roller cleaning is necessary based on the toner amount and the coverage rate notified in step S1005 or step S1006. In step S1006, if the calculation of the toner amount is not completed within the specified time, the fixing temperature control unit 326 is notified of a toner amount of 100% and a toner coverage rate of 100%, thereby controlling the fixing temperature to a level that allows fixing of any image. Also, in step S1006, if the calculation of the toner amount is not completed within the specified time, the charge roller cleaning necessity determination unit 330 is notified of a toner amount of 0% and a toner coverage rate of 0%, thereby suppressing the execution of charge roller cleaning. If excessive charge roller cleaning can be suppressed, downtime can be suppressed, and a decrease in productivity of the image forming apparatus 101 can be suppressed.

[0084] In step S1008, if the image processing unit 310 has completed decoding of the encoded data for the last page and calculation of the toner application amount and printing rate, the CPU 301 ends the process. On the other hand, if the image processing unit 310 has not completed decoding of the encoded data for the last page and calculation of the toner application amount and printing rate, the CPU 301 proceeds to step S1003. As a result, the processes from step S1003 to step S1008 are repeated until decoding of the encoded data for all images formed based on image data and calculation of the toner application amount and printing rate are completed.

[0085] As explained above, a time limit (prescribed time) is set for the time required to decode the encoded data for one page of image and calculate the toner amount and printing rate, and image formation is started if the process is not completed within the prescribed time. This makes it possible to prevent a decrease in productivity of the image forming apparatus 101. Furthermore, if the process is not completed within the prescribed time, a fixing temperature is set so as not to cause fixing defects. Furthermore, if the process is not completed within the prescribed time, the execution of charging roller cleaning is suppressed, allowing printing to continue.

[0086] In this embodiment, if the calculation of the toner amount value and printing rate is not completed within the specified time, the image forming condition determination unit is notified of a predetermined value that will prevent the cleaning operation from being performed, thereby performing optimal operation. However, it is also possible to predetermine the operation to be performed if no notification is received.

[0087] Furthermore, the image forming apparatus 101 of this embodiment has been described as being configured to perform the cleaning operation of the charging roller 2 when both the toner application amount value and the printing rate satisfy the conditions, but is not limited to this configuration. The execution of the cleaning operation of the charging roller 2 may be determined based on the amount of residual toner remaining on the photosensitive drum 1. Therefore, the cleaning operation may be performed if the toner printing rate is 65% or higher, without using the toner application amount value.

[0088] In addition, in this embodiment, the toner amount and toner coverage rate have been used as examples of image data to be analyzed, but the ratio of toner presence or absence to all pixels on a page (toner coverage rate) may also be used to optimize process control.

[0089] Furthermore, the image forming apparatus 101 of this embodiment is not limited to a monochrome printer, but may also be a color printer. In the case of a color printer, the toner amount value and toner coverage rate are calculated for each color from the image signal values ​​of CMYK, and if the average value of these values ​​satisfies the conditions, the cleaning operation is performed. Also, instead of the average value, a combined value may be used.

[0090] Example 2 In the image forming system 1 described in the first embodiment, if the analysis of image data is not completed within a specified time corresponding to the printing time, values ​​appropriate for each process control are notified. This makes it possible to suppress the occurrence of problems such as poor image quality while also suppressing a decrease in productivity. However, if the calculation of the toner application amount value and the printing rate is not completed within the specified time, the fixing temperature control unit 326 is notified of a toner application amount of 100% and a toner printing rate of 100%, so that poor fixing does not occur. However, if an image with a low toner application amount is formed on a sheet, the fixing temperature may be excessively high, which may result in a decrease in image quality after fixing.

[0091] Therefore, the image forming system 1 described in this embodiment is configured so that the user can select whether to prioritize productivity or image quality, similarly to the first embodiment.

[0092] The CPU 301 displays a screen such as that shown in Fig. 10 on the operation unit 306, and when the user selects "productivity priority mode," executes the processing described in the first embodiment. On the other hand, when the user selects "image quality priority mode" on the screen of Fig. 10, the CPU 301 does not set a time limit for analyzing the image data, and performs output using optimal process control settings based on the analysis of the image data. In other words, when the image quality priority mode is selected, image formation starts after decoding of the encoded data and calculation of the toner amount and printing rate are completed. As a result, the image forming system 2 described in the second embodiment allows the user to arbitrarily select whether to prioritize productivity or image quality, and can execute processing that suits the user's preferences. [Explanation of symbols]

[0093] 1 Photosensitive drum 2 Charging roller 3 Developer 5 Transfer roller 301 CPU 310 Image Processing Unit 330 Charging roller cleaning necessity determination unit

Claims

1. An image forming apparatus that forms an image on a sheet based on image data, A photoreceptor; a charging means for contacting the photosensitive member and charging the photosensitive member; an exposure unit that exposes the photosensitive member to light in order to form an electrostatic latent image on the photosensitive member charged by the charging unit; a developing means for developing the electrostatic latent image on the photosensitive member with toner; a transfer means for transferring the image on the photoreceptor developed by the developing means; determining means for determining a value relating to the amount of toner adhering to the photoreceptor by analyzing the image data; a control unit that controls, based on the value, the execution of a cleaning operation in which the developing unit recovers the toner that has not been transferred by the transfer unit and remains on the photosensitive member, The image forming apparatus is characterized in that the control means sets the value to a predetermined value such that the cleaning operation is not performed unless the analysis of the image data by the determination means is completed within a specified time.

2. 2. The image forming apparatus according to claim 1, wherein the value is a printing rate indicating the ratio of the amount of toner adhering to the photosensitive body when an image corresponding to the image data is formed to the amount of toner adhering to the photosensitive body when an image of maximum density is formed on one page.

3. 3. The image forming apparatus according to claim 2, wherein the control means executes the cleaning operation if the printing rate is greater than a predetermined rate.

4. the determining means calculates the toner amount of an image formed on one sheet based on the image data for each of a plurality of regions on the photosensitive member, and determines a maximum toner amount from the toner amounts of the plurality of regions; 3. The image forming apparatus according to claim 2, wherein the control unit executes the cleaning operation when the printing rate is greater than a predetermined rate and the maximum amount of applied toner is greater than a predetermined amount.

5. the developing means develops an electrostatic latent image corresponding to an image formed on the sheet based on a voltage of a first polarity; 2. The image forming apparatus according to claim 1, wherein the control unit controls the developing unit based on a voltage of a second polarity different from the first polarity when the cleaning operation is performed.

Images