JP7797822B2 - Image forming apparatus and lubricant amount control method - Google Patents

Description

The present invention relates to an image forming apparatus and a lubricant amount control method.

Image forming devices that use the electrophotographic process generally have a cleaning blade to remove residual toner and other deposits from the surface of the photosensitive drum. They also have a mechanism for applying a lubricant to the photosensitive drum to prevent the cleaning blade from curling up.

The lubricant applied to the photosensitive member transfers to the intermediate transfer belt (intermediate transfer member) when the toner image formed on the surface of the photosensitive member is transferred to the intermediate transfer belt. However, changes in the amount of lubricant on the intermediate transfer belt affect the transferability of the image. Therefore, it is necessary to maintain a constant level of lubricant on the intermediate transfer belt.

For example, Patent Document 1 describes that when the belt load on the intermediate transfer belt is smaller than a reference value, i.e., when there is an excess of lubricant, the photosensitive element with the smallest drum load is selected and the amount of lubricant applied is reduced.

JP 2015-99259 A

Incidentally, in recent years, image forming devices have been released that add a fifth or sixth color, such as white toner or clear toner, to the standard four-color printing of yellow (Y), magenta (M), cyan (C), and black (K). The fifth and sixth colors are used as a base when printing on color paper, etc., and are not used all the time. As a result, the amount of lubricant on the intermediate transfer belt changes between normal color printing and printing with a different number of colors, causing fluctuations in transferability. This results in problems such as color variations and unevenness.

The control described in Patent Document 1 is applied only when the drum load is smaller than a reference value; if the drum load is larger than the reference value, the amount of lubricant on the intermediate transfer belt cannot be reduced, and the effect of suppressing fluctuations in transferability is insufficient.

The objective of the present invention is to provide an image forming apparatus and a lubricant amount control method that can optimize the amount of lubricant on the intermediate transfer body and suppress fluctuations in transferability.

In order to solve the above problems, the image forming apparatus of the present invention comprises:
a plurality of photoreceptors each having a lubricant supplying means for supplying a lubricant to the surface of the photoreceptor on which a toner image is formed;
an intermediate transfer member onto which a toner image formed on a surface of at least one of the plurality of photoreceptors is transferred during printing;
a control unit for controlling execution of a lubricant amount control mode for controlling the amount of lubricant on the intermediate transfer body in accordance with the number of the photosensitive bodies used during printing;
Equipped with
The lubricant amount control mode includes an operation of controlling the amount of lubricant on the intermediate transfer body by providing a difference in peripheral speed between the photosensitive body and the intermediate transfer body .

Further, the lubricant amount control method of the present invention includes the steps of:
a plurality of photoreceptors each having a lubricant supplying means for supplying a lubricant to the surface of the photoreceptor on which a toner image is formed;
an intermediate transfer member onto which a toner image formed on a surface of at least one of the plurality of photoreceptors is transferred during printing;
A method for controlling the amount of lubricant in an image forming apparatus comprising:
a control step of controlling execution of a lubricant amount control mode for controlling the amount of lubricant on the intermediate transfer body in accordance with the number of the photoconductors used during printing;
The lubricant amount control mode includes an operation of controlling the amount of lubricant on the intermediate transfer body by providing a difference in peripheral speed between the photosensitive body and the intermediate transfer body .

The present invention provides an image forming apparatus and a lubricant amount control method that can optimize the amount of lubricant on the intermediate transfer member and suppress fluctuations in transferability.

FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus. FIG. 2 is a block diagram showing a main functional configuration of the image forming apparatus. FIG. 2 is a diagram illustrating a schematic configuration of an image forming unit. FIG. 10 is a diagram illustrating an example of recording usage results for each color mode. (a) is a diagram showing a schematic diagram of the thickness of the lubricant on the intermediate transfer belt during YMCK printing, (b) is a diagram showing a schematic diagram of the thickness of the lubricant on the intermediate transfer belt during YMCK+W printing, and (c) is a diagram showing a schematic diagram of the thickness of the lubricant on the intermediate transfer belt when the peripheral speed of the photosensitive body is set to 0.75 times that of the intermediate transfer belt during YMCK+W printing. 10A and 10B are diagrams illustrating a control for transferring a lubricant to a secondary transfer belt. 3 is a flowchart showing the flow of a print control process executed by the control unit in FIG. 2 . 10 is a graph showing the change in the amount of lubricant on the intermediate transfer belt with respect to the change in the number of printed sheets when the number of photosensitive members used is 4 and the image coverage is 1%. FIG. 10 is a diagram showing the lubricant amount coefficient for each combination of the number of photoreceptors used and image coverage.

Embodiments of the present invention will be described in detail below with reference to the drawings.

[Configuration of Image Forming Apparatus]
First, the configuration of an image forming apparatus 1 according to this embodiment will be described.
The image forming apparatus 1 is an intermediate transfer type color image forming apparatus that utilizes electrophotographic process technology, and as shown in Figures 1 and 2, is configured to include an automatic document transport unit 2, a scanner unit 3, an image forming unit 4, a paper feed unit 5, a memory unit 6, an operation display unit 7, a communication unit 8, and a control unit 10.

The automatic document transport unit 2 includes a tray on which the document D is placed, a mechanism for transporting the document D, transport rollers, etc., and transports the document D to a predetermined transport path.
The scanner unit 3 is configured with an optical system including a light source and a reflecting mirror, and irradiates the document D conveyed along a predetermined conveying path or the document D placed on a platen glass with the light source, and receives the reflected light. The scanner unit 3 also converts the received reflected light into an electrical signal and outputs it to the control unit 10 as image data.

The image forming unit 4 is configured to include a yellow imaging unit Y, a magenta imaging unit M, a cyan imaging unit C, a black imaging unit K, a white imaging unit W, an intermediate transfer belt T, and a fixing unit F. In this embodiment, in addition to the four color imaging units used in normal color printing (yellow, magenta, cyan, and black), a white imaging unit is provided as an imaging unit for a fifth color (special color). However, imaging units for other colors, such as a clear (transparent) imaging unit, may also be provided. Also, a sixth color imaging unit may be provided.
Each of the image forming units YMCKW forms a toner image of yellow, magenta, cyan, black, or white on the photosensitive member 41, and the toner image of each of the YMCKW colors formed on the photosensitive member 41 is primarily transferred onto the intermediate transfer belt T.

FIG. 3 is a diagram showing the schematic configuration of each image forming unit in the image forming unit 4. Each image forming unit includes a drum-shaped photoreceptor 41 rotated in the direction A shown in FIG. 3 , a charging device 42 that uniformly charges the surface of the photoreceptor 41, an exposure device 43 that exposes the surface of the photoreceptor 41 charged by the charging device 42 to light to form an electrostatic latent image, a developing device 44 that visualizes the electrostatic latent image formed by the exposure device 43 using a developer containing toner, a primary transfer roller 45 that transfers the toner image formed on the photoreceptor 41 to an intermediate transfer belt T, and a cleaning unit 47 that removes toner from the photoreceptor 41 that has passed through the transfer area. The toner image formed on the photoreceptor 41 is then primarily transferred to the intermediate transfer belt T, which moves in the direction B shown in FIG. 3 . The toner image transferred to the intermediate transfer belt T is then transferred to paper P by a secondary transfer roller 46, and then transported to a fixing unit F where it is fixed to the paper P. The components of each of the image forming units Y, M, C, K, and W described above are elongated in the axial direction of the photoreceptor 41.
Since the image forming units YMCKW have the same configuration and operation, the following will explain a series of image forming operations performed by the image forming unit 4, taking the yellow image forming unit Y as an example.

The photoreceptor 41 is an organic photoreceptor having a photosensitive layer made of a resin containing an organic photoconductor formed on the outer peripheral surface of a drum-shaped metal substrate, and is driven to rotate in the direction A shown in Fig. 3. Examples of resins that can be used to form the photosensitive layer include polycarbonate resin, silicone resin, polystyrene resin, acrylic resin, methacrylic resin, epoxy resin, polyurethane resin, vinyl chloride resin, and melamine resin.
The photoreceptor 41 is made of a conductive tube such as an aluminum tube, and is formed with an undercoat layer (UCL), a charge generation layer (CGL), a charge transport layer (CTL), and a
The layer structure is arranged in this order: Charge Transport Layer.

The charging device 42 is, for example, a scorotron type, and uses a charger to charge the photosensitive member 41 to a constant negative potential.

The exposure device 43 exposes the non-image area of the photosensitive member 41 based on image data Dy from the control unit 10 to remove charge from the exposed area, thereby forming an electrostatic latent image in the image area of the photosensitive member 41 .
Specifically, when the surface of the photoconductor 41 is negatively charged by the charging device 42, the charge is removed by exposure by the exposure device 43, and both positive and negative charges are generated in the charge generation material (CGM) in the CGL. The positive charges (holes) pass through the CTL to reach the surface of the photoconductor 41, and the negative charges pass through the UCL to reach the element tube, thereby forming an electrostatic latent image on the surface of the photoconductor 41.

The developing device 44 includes a developing sleeve 44a disposed opposite the photoconductor 41 across a development area. A developing bias, for example, a DC voltage having the same polarity as the charging polarity of the charging device 42, i.e., a negative polarity, and an AC voltage superimposed thereon, is applied to the developing sleeve 44a, thereby supplying a developer onto the electrostatic latent image formed on the photoconductor 41 and forming a yellow toner image on the photoconductor 41. The developer includes toner and a carrier for charging the toner.
The toner is not particularly limited, and any commonly used known toner can be used. For example, a toner containing a colorant and, if necessary, a charge control agent, a release agent, etc., in a binder resin and treated with an external additive can be used. The toner particle size is not particularly limited, but is preferably about 3 to 15 μm.

The primary transfer roller 45 performs primary transfer of the yellow toner image formed on the photoreceptor 41 onto the intermediate transfer belt T. Similarly, the other image forming units M, C, K, W perform primary transfer of magenta, cyan, black, and white toner images onto the intermediate transfer belt T. As a result, toner images of each of the Y, M, C, K, and W colors are formed on the intermediate transfer belt T.

The intermediate transfer belt (intermediate transfer body) T is a semiconductive endless belt suspended and rotatably supported by multiple rollers, and is driven to rotate in the direction B shown in Figure 3 as the rollers rotate. This intermediate transfer belt T is pressed against each of the opposing photosensitive bodies 41 by primary transfer rollers 45. A transfer current corresponding to the applied voltage flows through each primary transfer roller 45. As a result, each toner image developed on the surface of each photosensitive body 41 is sequentially transferred (primary transfer) to the intermediate transfer belt T by each primary transfer roller 45.

The secondary transfer roller 46 rotates while being pressed against the intermediate transfer belt T via the secondary transfer belt (secondary transfer member) 462, thereby secondarily transferring the YMCKW color toner images formed by being transferred onto the intermediate transfer belt T onto paper P transported from the paper feed trays 51-53 of the paper feed unit 5. More specifically, the secondary transfer roller 46 is positioned in contact with the secondary transfer opposing roller 461 via the secondary transfer belt 462 and the intermediate transfer belt T, and the toner image on the intermediate transfer belt T is secondarily transferred onto paper P as the paper P passes through the transfer nip formed between the secondary transfer roller 46 and the secondary transfer opposing roller 461. Note that a configuration may also be adopted in which the secondary transfer roller 46 is pressed directly against the intermediate transfer belt T, without including the secondary transfer belt 462. In this case, the secondary transfer roller 46 corresponds to the secondary transfer member of the present invention.

The toner remaining on the photosensitive member 41 without being transferred onto the intermediate transfer belt T in the transfer area is transported to the cleaning unit 47 and collected by the cleaning unit 47 .
The photosensitive member 41 from which the toner on the surface has been collected by the cleaning unit 47 is again charged by the charging device 42, and the next electrostatic latent image is formed, thus repeating the process of forming a toner image.

The cleaning unit 47 includes a blade member 47a, a recovery screw 47b located substantially below the blade member 47a, an application roller 47c located downstream of the blade member 47a in the direction of rotation of the photosensitive member 41, a lubricant rod 47d for supplying lubricant to the application roller 47c, a pressing unit 47e for pressing and holding the lubricant rod 47d against the application roller 47c, and a fixed blade 47f located downstream of the application roller 47c in the direction of rotation of the photosensitive member 41.

The blade member 47a comprises an elastic body, such as polyurethane rubber, processed into a flat plate, and is positioned so that its tip rubs against the photosensitive element 41, scraping off and removing any untransferred toner or other adhering matter remaining on the surface of the photosensitive element 41.

The recovery screw 47b rotates in one direction and transports the toner scraped off by the blade member 47a and dropped to a waste toner box (not shown).

The application roller 47c is a roll-shaped brush member positioned so that its tip can come into contact with the photoreceptor 41. Under the control of the control unit 10, the application roller 47c rotates counter-rotatingly at the point of contact with the photoreceptor 41, with its surface moving in the opposite direction to the surface of the photoreceptor 41, thereby applying (supplying) lubricant to the photoreceptor 41.

The lubricant rod 47d is made by melting, shaping, and solidifying a powdered lubricant, such as zinc stearate, made of metal soap. The lubricant rod 47d is positioned so that it can come into contact with the tip of the application roller 47c, and is scraped off from the tip as the application roller 47c rotates. The scraped off lubricant is transported directly to the photoreceptor 41 and supplied to the surface of the photoreceptor 41.

The pressing portion 47e includes, for example, a compression spring that biases the lubricant rod 47d toward the application roller 47c, and presses and holds the lubricant rod 47d against the application roller 47c.
The application roller 47c, the lubricant rod 47d, and the pressing portion 47e constitute a lubricant supplying means.

The fixed blade 47f is made of an elastic material such as polyurethane rubber processed into a flat plate, similar to the blade member 47a. The fixed blade 47f is in trailing contact with the surface of the photoreceptor 41, with its tip rubbing against the photoreceptor 41.
This fixed blade 47f is used to spread the lubricant powder supplied to the surface of the photoreceptor 41 and form a film (lubricant layer) on the surface of the photoreceptor 41. The lubricant layer formed from zinc stearate is characterized by high releasability (high contact angle with pure water) and a small coefficient of friction, which results in good transferability and cleaning properties, and also reduces wear on the photoreceptor 41, thereby extending its lifespan.

In addition, toner and other particles that remain on the intermediate transfer belt T without being transferred to the paper P are transported to a cleaning unit (cleaning member) 48 equipped with a blade member 48a that contacts the intermediate transfer belt T, and are removed and collected by the cleaning unit 48.

In the image forming unit 4, the paper P onto which the toner images of each color of YMCKW have been secondarily transferred is heated and pressed by the fixing unit F, and then the paper P is passed through a predetermined conveying path and discharged outside the machine.
The image forming unit 4 has the above configuration.

The paper feed unit 5 is equipped with multiple paper feed trays 51-53, each of which stores multiple different types of paper P. The paper feed unit 5 feeds the stored paper P to the image forming unit 4 via a specified transport path.

The storage unit 6 is composed of a hard disk drive (HDD), semiconductor memory, etc., and stores data such as program data, various setting data, and job information (job setting information and job image data) in a manner that allows it to be read and written by the control unit 10. Job setting information includes information such as the type and size of paper used in the job, whether it is single-sided or double-sided, the total number of sheets to be printed, and application settings.

The operation display unit 7 is configured, for example, by a liquid crystal display (LCD) with a touch panel, and functions as a display unit 71 and an operation unit 72 .
The display unit 71 displays various operation screens, the operating status of each function, etc. in accordance with a display control signal input from the control unit 10. The display unit 71 also accepts touch operations by the user and outputs an operation signal to the control unit 10.
The operation unit 72 includes various operation keys such as a numeric keypad and a start key, and a touch panel formed on the display unit 71, and accepts various input operations by the user and outputs operation signals to the control unit 10. By operating the operation display unit 7, the user can perform settings related to image formation such as image quality settings, magnification settings, application settings, output settings, and paper settings, give paper transport instructions, and stop the device.

The communication unit 8 is composed of a communication control card such as a LAN (Local Area Network) card, and transmits and receives various data to and from external devices connected to communication networks such as a LAN or WAN (Wide Area Network). For example, the communication unit 8 receives job information from external devices.

The control unit 10 is configured with a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), etc. The CPU expands various programs stored in the ROM or memory unit 6 into the RAM, and works in cooperation with the expanded programs to comprehensively control the operation of each part of the image forming device 1, such as the automatic document transport unit 2, scanner unit 3, image forming unit 4, paper feed unit 5, memory unit 6, operation display unit 7, and communication unit 8 (see Figure 2).
For example, the control unit 10 stores job information input via the operation unit 72 and the scanner unit 3 and job information received via the communication unit 8 in the memory unit 6, and executes the printing control process (see Figure 7) described below based on the job execution instruction.

[Operation of Image Forming Apparatus]
Next, the operation of the image forming apparatus 1 will be described.
When the number of photoreceptors 41 used during printing (i.e., the number of colors) changes, the amount of lubricant that transfers from the photoreceptors 41 to the intermediate transfer belt T changes, and the amount of lubricant on the intermediate transfer belt T changes, resulting in fluctuations in transferability. For example, if W is added to normal YMCK four-color printing, the amount of lubricant that transfers from the photoreceptors 41 to the intermediate transfer belt T increases by a simple calculation to 1.25 times, and the thickness of the lubricant layer on the intermediate transfer belt T increases. A change in the thickness of the lubricant layer as a resistive layer causes changes in transferability. For example, when four-color and five-color print jobs are performed alternately, variations in the amount of lubricant on the intermediate transfer belt T during printing occur, resulting in problems such as changes in color tone or, in the worst case, unevenness.

The control unit 10 of the image forming apparatus 1 of this embodiment therefore controls the execution of a lubricant amount control mode that controls the amount of lubricant on the intermediate transfer belt T depending on the number of photoconductors 41 operating (used) during printing. Specifically, the lubricant amount control mode is executed when the number of photoconductors 41 used during printing differs from a preset reference number of photoconductors.

For example, for a user who mainly uses four-color printing in YMCK, the lubricant amount control mode is executed when the number of operations of the photosensitive drum 41 changes, based on four-color printing in YMCK (i.e., based on four photosensitive drums).
When the number of photosensitive drums is set to four as the standard, if the number of photosensitive drums is less than the standard, such as when operating in monochrome, the lubricant amount control mode is operated in the direction of increasing the amount of lubricant applied to the intermediate transfer belt T for each photosensitive drum 41, and if the number of photosensitive drums is greater than the standard, such as five or six colors, the lubricant amount control mode is operated in the direction of decreasing the amount of lubricant for each photosensitive drum 41.

The reference number of photoconductors is set, for example, by having a means for recording the usage record for each number of photoconductors 41 and using the number of photoconductors that is most frequently used as the reference number.
For example, as shown in Figures 4(a) and 4(b), the control unit 10 records the number of prints for each color mode (colors used in printing) in the memory unit 6, and sets the number of photoconductors for the color mode with the largest number of prints as the standard. For example, as shown in Figure 4(a), if the number of prints for four colors, YMCK, is the largest, the number of photoconductors is set to four. As shown in Figure 4(b), if the number of prints for YMCK+W is the largest, the number of photoconductors is set to five.

In this embodiment, as shown in Figures 4(a) and (b), usage history for each number of photoconductors 41 is obtained by recording the number of prints for each color mode. However, usage history for each number of photoconductors 41 may also be obtained using other indicators, such as the number of photoconductors 41 driven instead of color mode, or the photoconductor driving distance instead of the number of prints.

In the lubricant amount control mode, the control unit 10 selects and executes one or more of the following lubricant amount control operations (1) to (4).
(1) The amount of lubricant applied to the photoreceptor 41 is controlled.
The amount of lubricant applied to the photoreceptor 41 can be changed, for example, by controlling the angle θ of the application roller 47c during image formation. θ is the speed ratio (peripheral speed ratio) of the application roller 47c to the photoreceptor 41. By increasing θ, the amount of lubricant applied to the photoreceptor 41 can be increased, and by decreasing θ, the amount of lubricant applied to the photoreceptor 41 can be decreased.
For example, when printing with six photosensitive elements, as opposed to the standard number of four photosensitive elements, by controlling the θ of the application roller 47c of each photosensitive element 41 so that the amount of lubricant applied is 4/6 of that when printing with the standard number of photosensitive elements, the amount of lubricant on the intermediate transfer belt T can be maintained at the same level as the standard, and fluctuations in transferability can be suppressed.

(2) A lubricant removal operation (refreshing operation) is performed on the intermediate transfer belt T.
In the lubricant removal operation, an image is formed on the intermediate transfer belt T from the photosensitive member 41 and rotated to send a certain amount of developer to the cleaning unit 48, and then the photosensitive member 41 and the intermediate transfer belt T are idly rotated for a certain period of time while being separated from each other. This allows the lubricant on the intermediate transfer belt T to be scraped off and removed by the cleaning unit 48 together with the developer.
The lubricant removal operation is performed, for example, by interrupting a job when a predetermined condition is met during the job. It may also be performed between jobs. By changing the amount of developer sent to the cleaning unit 48 and the idle rotation time depending on the current amount of lubricant, the reference number of photoconductors, and the number of photoconductors in use, it is possible to reduce the amount of lubricant on the intermediate transfer belt T to the same level as during reference printing, thereby suppressing fluctuations in transferability.
Increasing the amount of developer sent to the cleaning unit 48 allows a larger amount of lubricant to be removed, thereby shortening the idle rotation time. In other words, the downtime due to the lubricant removal operation can be shortened.

(3) A difference in peripheral speed is provided between the photosensitive member 41 and the intermediate transfer belt T.
Normally, during printing (image creation), the photosensitive member 41 and the intermediate transfer belt T move at the same peripheral speed, but by creating a difference in peripheral speed between the photosensitive member 41 and the intermediate transfer belt T, the amount (thickness) of lubricant on the intermediate transfer belt T can be changed.
FIG. 5( a ) is a schematic diagram showing the thickness of the lubricant on the intermediate transfer belt T during four-color printing (YMCK). FIG. 5( b ) is a schematic diagram showing the thickness of the lubricant on the intermediate transfer belt T during five-color printing (YMCK+W). FIG. 5( c ) is a schematic diagram showing the thickness of the lubricant on the intermediate transfer belt T when the peripheral speed of the photoconductor 41 is increased to 0.75 times that of the intermediate transfer belt T during YMCK+W printing. The dotted line in FIG. 5( c ) indicates the lubricant thickness in FIG. 5( b ) for comparison. As shown in FIG. 5( b ), when the number of colors (i.e., the number of operating photoconductors) increases from four to five, the amount of lubricant per unit area on the intermediate transfer belt T increases by 1.25 times, resulting in a thicker lubricant. Therefore, by increasing the peripheral speed of the photoconductor 41 to 0.75 times, the amount of lubricant per unit area on the intermediate transfer belt T becomes the same as when printing with four colors, as shown in FIG. 5( c ).
By making the peripheral speed of the photosensitive member 41 slower than the peripheral speed of the intermediate transfer belt T, it is possible to reduce the thickness of the lubricant on the intermediate transfer belt T. By making the peripheral speed of the photosensitive member 41 faster than the peripheral speed of the intermediate transfer belt T, it is possible to increase the thickness of the lubricant on the intermediate transfer belt T.
By changing the speed in accordance with the timing when the number of photosensitive bodies is changed from the standard and creating a difference in peripheral speed between the photosensitive body 41 and the intermediate transfer belt T, the thickness of the lubricant on the intermediate transfer belt T can be maintained at the same level as when printing with the standard number of photosensitive bodies, and fluctuations in transferability can be suppressed.

(4) A voltage of a polarity opposite to that of the lubricant is applied to the secondary transfer member (secondary transfer belt 462) to electrically remove the lubricant from the intermediate transfer belt T.
As shown in Figure 6, since the lubricant is positively charged, by applying a bias voltage of the opposite polarity (negative) to the secondary transfer belt 462, the lubricant can be moved to the secondary transfer belt 462 and removed from the intermediate transfer belt T.
This lubricant removal operation is performed between images when a predetermined condition is met during a job, for example, or may be performed between jobs.
The amount of lubricant removed can be controlled by adjusting the applied voltage. By adjusting the applied voltage based on the difference between the number of standard photoconductors and the number of photoconductors used for printing, the amount of lubricant on the intermediate transfer belt T can be adjusted to the same level as the standard, thereby suppressing fluctuations in transferability.
The way in which the applied voltage is adjusted may be experimentally determined in advance in accordance with changes in the number of photosensitive drums, or the amount of variation depending on the number of colors may be predicted from the measured value of the amount of lubricant during operation, the reflectance of the intermediate transfer belt T (the reflectance changes depending on the amount of lubricant), the driving torque of the intermediate transfer belt T, changes in the transferability of patches, etc., and the amount of variation may be changed as needed.

The above-mentioned controls (2) and (4) require the printing operation to be stopped during the job (the job must be temporarily paused) and therefore result in downtime. Therefore, for small-lot jobs with a small number of prints, it is preferable to implement (1) or (3). On the other hand, (1) controls the amount of lubricant applied to the photoreceptor 41, so if it is implemented for a long period of time, there is a possibility that the amount of lubricant required for the photoreceptor 41 will fall below that. As for (3), since it controls the speed of the writing system, there is a possibility that it will affect the image if it is implemented for a long period of time. Therefore, for jobs with a large number of prints, it is preferable to implement (2) and (4).
Furthermore, the speed at which the amount of lubricant on the intermediate transfer belt T increases or decreases varies depending on the printing rate (image coverage) of the image to be printed.
Therefore, when the control unit 10 is instructed to start a job (start printing), it executes the print control process shown in Figure 7, determines whether or not to execute the lubricant amount control mode based on the number of photosensitive drums used during printing, and if it determines to execute it, selects and executes the lubricant amount control operation from among (1) to (4) above based on printing conditions such as the number of prints for the job and image coverage.
The print control process will be described below with reference to FIG.

First, the control unit 10 determines whether the number of photoconductors to be used in the job (that is, to be used during printing) is the reference number of photoconductors (step S1).
For example, the control unit 10 derives the number of photosensitive drums to be used in the job based on the image data of the job, and references the number of prints for each color mode stored in the memory unit 6 to obtain the number of photosensitive drums in the color mode with the highest number of prints as the standard number of photosensitive drums, and determines whether the number of photosensitive drums to be used in the job is the standard number of photosensitive drums.

When it is determined that the number of photoconductors used in the job is the reference number of photoconductors (step S1; YES), the control unit 10 executes the normal job (step S2).
In step S2, the image forming unit 4 prints on paper based on the job information. At this time, the control unit 10 rotates the photoconductors 41 at a preset reference peripheral speed. The control unit 10 also rotates the application roller 47c so that the speed ratio (peripheral speed ratio) of the application roller 47c to each photoconductor 41 being used becomes a preset speed ratio (θ).

If it is determined that the number of photoconductors to be operated in the job is not the standard number of photoconductors (step S1; NO), the control unit 10 sets the lubricant amount control mode to ON (step S3) and selects the lubricant amount control operation to be executed in the lubricant amount control mode (step S4).

In step S4, the control unit 10 selects the lubricant amount control operation to be executed in the lubricant amount control mode from among the above-mentioned controls (1) to (4), based on, for example, the relationship between the number of photosensitive drums used in the job and the number of reference photosensitive drums, the number of prints, image coverage, and other printing conditions.
For example, if the number of photosensitive elements used is less than the standard number of photosensitive elements, the amount (thickness) of lubricant on the intermediate transfer belt T will be less than the standard amount of lubricant, so control (1) or (3) is selected, which can increase the amount (thickness) of lubricant on the intermediate transfer belt T.
As mentioned above, for small lot jobs where the number of printed sheets is less than a predetermined threshold (for example, 100 sheets), (1) or (3) is selected, which will not cause downtime, and for jobs where the number of printed sheets is equal to or greater than the predetermined threshold, (2) or (4) is selected, which will cause downtime but will not affect the image even if the job is run for a long time.
Furthermore, when the image coverage is large, a large amount of lubricant is removed by the cleaning unit 48 along with the developer, and therefore, in the case of a small lot job, the effect of changes in the amount of lubricant may be negligible. Therefore, in the case of a small lot job in which the number of printed sheets is less than a predetermined threshold (for example, 100 sheets) and the image coverage is equal to or greater than the predetermined threshold (for example, 5% or greater), it is possible to select none of the controls (1) to (4) (it is also possible to select either (1) or (3)).
Here, the image coverage is the average image coverage of the images printed in the job.
For example, if the image data for a job is six A3 sheets (297 x 420 mm), the image coverage for the first sheet is 1%, the image coverage for the second to fifth sheets is 5%, the image coverage for the sixth sheet is 1%, and the paper spacing is 50 mm, then the image coverage will be 3.3%, as shown in the following (Equation 1).
(420mm×1%+420mm×5%×4+420mm×1%)/(420mm×6+50mm×6)×100 = 3.3% (Formula 1)

Next, the control unit 10 executes the job while controlling the amount of lubricant on the intermediate transfer belt T using the selected lubricant amount control operation in the lubricant amount control mode (step S5).

For example, when (1) is selected, the control unit 10 performs printing based on the job by controlling θ, which is the speed ratio (peripheral speed ratio) of the application roller 47c to each photoconductor 41 being used, based on the number of photoconductors being used (in use) and the reference number of photoconductors, so that the amount of lubricant on the intermediate transfer belt T is the same as when the reference number of photoconductors 41 are operated.

For example, when (3) is selected, the control unit 10 controls the difference in peripheral speed between the photosensitive drums 41 and the intermediate transfer belt T based on the number of photosensitive drums to be used (in use) and the reference number of photosensitive drums, so that the thickness of the lubricant on the intermediate transfer belt T is the same as when the reference number of photosensitive drums 41 are operated.

Furthermore, for example, if (2) or (4) is selected, and the amount of lubricant on the intermediate transfer belt T during the job exceeds a preset threshold value for the reference number of photosensitive elements, the control unit 10 temporarily stops the job and executes the selected lubricant removal operation of (2) or (4). When the amount of lubricant on the intermediate transfer belt T decreases to a preset reference value for the reference number of photosensitive elements, the control unit 10 stops the lubricant removal operation and resumes the job. The threshold and reference values for the amount of lubricant on the intermediate transfer belt T for each number of photosensitive elements are stored in advance in the memory unit 6.

8 is a graph showing the change in the amount of lubricant on the intermediate transfer belt T, with the horizontal axis representing the number of printed sheets and the vertical axis representing the amount of lubricant on the intermediate transfer belt T, where an image with an image coverage of 1% is printed with four operating photoconductors, and the lubricant removal operation described in (2) above is carried out when the number of printed sheets reaches 2,000. FIG. 8 shows the case where embossed paper (Lezac 66 203 gsm) is used, which is particularly susceptible to deterioration in image quality due to the lubricant.
As shown in Figure 8, when the image coverage is 1% and the number of operating photoconductors is four, the amount of lubricant on the intermediate transfer belt T continues to increase in proportion to the number of printed sheets. With an image coverage of 1%, after printing approximately 2000 sheets, the amount of lubricant on the intermediate transfer belt T (which can be substituted, for example, by the pure water contact angle or the amount of light reflected on the belt) increases to about 1072, and if printing continues at this level, images will have transfer unevenness. Therefore, by implementing the lubricant amount control mode, the amount of lubricant on the intermediate transfer belt T can be reduced, making it possible to output printed materials with good image quality.

In order to maintain good image quality when printing, it is necessary to suppress the amount of lubricant on the intermediate transfer belt T to a predetermined threshold (400 in this embodiment) at which image quality can be guaranteed. This predetermined threshold is a value determined in advance by experiment for each number of photosensitive drums, and it is preferable to perform the lubricant amount control operation (2) or (4) above when the amount of lubricant on the intermediate transfer belt T exceeds the predetermined threshold corresponding to the reference number of photosensitive drums.
As shown in Figure 8, the rate at which the amount of lubricant on the intermediate transfer belt T increases is proportional to the number of printed sheets, but the slope of the increase varies depending on the image coverage and the number of photoconductors used. Therefore, for example, as shown in Figure 9, a lubricant amount coefficient is experimentally determined in advance for each combination of image coverage and number of photoconductors used and stored in the memory unit 6. Each time printing is performed during job execution, the control unit 10 estimates the amount of lubricant on the intermediate transfer belt T using the following equation (2). When the estimated amount of lubricant exceeds the threshold value, the control unit 10 pauses the job and performs the lubricant removal operation (2) or (4) described above, thereby reducing the amount of lubricant on the intermediate transfer belt T to a preset reference value for the reference number of photoconductors. When the lubricant removal operation is completed, the job is resumed.
Amount of lubricant on intermediate transfer belt = lubricant amount coefficient x number of prints + initial value (Equation 2)

The initial value of (Equation 2) is the amount of lubricant on the intermediate transfer belt T at the start of the job. To obtain this initial value, the control unit 10 calculates the amount of lubricant using (Equation 2) and stores it in the memory unit 6 each time printing is performed for a job. When the lubricant amount control operations (1) and (3) described above are performed, the amount of lubricant is controlled to be the amount for the reference number of photosensitive elements, so the amount of lubricant on the intermediate transfer belt T is estimated using, for example, the lubricant amount coefficient for the combination of image coverage and the reference number of photosensitive elements.

Note that the amount of lubricant on the intermediate transfer belt T may be reduced depending on the image coverage. For example, starting with four operating photoconductors with no lubricant applied, if 750 images with 1% image coverage are printed, and then 200 images with 25% image coverage are printed, the amount of lubricant on the intermediate transfer belt T will return to the amount it was before printing the 1% image coverage images.

When printing based on the job information is completed, the control unit 10 proceeds to step S6, adds the number of sheets printed in the job (number of prints) to the value stored in the memory unit 6 in association with the color mode of the job (step S6), and ends the print control process.

As described above, the control unit 10 of the image forming apparatus 1 of this embodiment controls the execution of a lubricant amount control mode that controls the amount of lubricant on the intermediate transfer belt T in accordance with the number of photoconductors 41 used during printing. For example, when the number of photoconductors used during printing differs from a preset reference number of photoconductors, the control unit 10 executes the lubricant amount control mode.
Therefore, it is possible to suppress the amount of lubricant on the intermediate transfer belt T from changing due to a change in the number of photosensitive members used during printing, and thus the fluctuation in transferability.

The control unit 10 also selects and executes one or more of the multiple lubricant amount control operations included in the lubricant amount control mode depending on printing conditions, such as the number of photosensitive drums used, image coverage, and number of copies printed. Therefore, it is possible to perform lubricant amount control operations that are appropriate for the printing conditions.

The above-described embodiment is a preferred example of the present invention, and the present invention is not limited to this.
For example, in the above embodiment, the lubricant amount control mode includes four lubricant amount control operations, and the control unit 10 selects a lubricant amount control operation based on the printing conditions, etc. However, the number of lubricant amount control operations in the lubricant amount control mode is not particularly limited. For example, only one lubricant amount control operation may be executable, or multiple lubricant amount control operations other than four may be executable.

In addition, in the above embodiment, the lubricant amount control mode is not executed for normal jobs (jobs that operate with the standard number of photoconductors), but the lubricant amount control operation (2) or (4) described above may also be executed.

In addition, in the above embodiment, the lubricant amount control operation (2) or (4) was described as being performed by temporarily pausing the job, but it may also be performed at the end of a job or when the number of photoconductors is changed.

Furthermore, because the effect of lubricant on transferability varies depending on the type of paper used for printing, the control unit 10 may change the parameters used in the lubricant amount control mode depending on the type of paper used during printing. For example, embossed paper, which has a highly irregular surface, significantly reduces transferability due to the effect of lubricant. Therefore, when printing using embossed paper, it is preferable to use parameters that reduce the amount of lubricant on the intermediate transfer belt T compared to other paper types. For example, when printing using embossed paper, in case (1), θ is reduced compared to when other paper types are used. In case (2), the amount of developer sent to the intermediate transfer belt T is increased, and the idle rotation time is increased. In case (3), the peripheral speed ratio (the ratio of the peripheral speed of the photosensitive element 41 to the peripheral speed of the intermediate transfer belt T) is reduced. In case (4), the applied voltage is increased.

In addition, the detailed configuration and operation of each device that makes up the image forming apparatus may be modified as appropriate without departing from the spirit and scope of the present invention.

REFERENCE SIGNS LIST 1 Image forming apparatus 2 Automatic document transport unit 3 Scanner unit 4 Image forming unit 41 Photosensitive member 42 Charging device 43 Exposure device 44 Developing device 45 Primary transfer roller 46 Secondary transfer roller 47 Cleaning unit 47c Application roller 47d Lubricant rod 47e Pressing unit 48 Cleaning unit 48a Blade member T Intermediate transfer belt 5 Paper feed unit 6 Memory unit 7 Operation display unit 8 Communication unit 10 Control unit

Claims (11)

a plurality of photoreceptors each having a lubricant supplying means for supplying a lubricant to the surface of the photoreceptor on which a toner image is formed;
an intermediate transfer member onto which a toner image formed on the surface of at least one of the plurality of photoreceptors is transferred during printing;
a control unit for controlling execution of a lubricant amount control mode for controlling the amount of lubricant on the intermediate transfer body in accordance with the number of the photosensitive bodies used during printing;
Equipped with
The lubricant amount control mode includes an operation of controlling the amount of lubricant on the intermediate transfer body by providing a difference in peripheral speed between the photosensitive body and the intermediate transfer body. The image forming apparatus of claim 1, wherein the control means executes the lubricant amount control mode when the number of photoconductors used during printing differs from a preset reference number of photoconductors. a storage means for storing usage records for each number of the photosensitive members;
3. The image forming apparatus according to claim 2, wherein the control means sets the number of photosensitive elements with the most usage history as a reference number of photosensitive elements, and executes the lubricant amount control mode when the number of photosensitive elements used during printing differs from the reference number of photosensitive elements. The image forming apparatus of any one of claims 1 to 3, wherein the lubricant amount control mode includes an operation of controlling the amount of lubricant supplied to the photosensitive member by the lubricant supply means. The image forming apparatus of any one of claims 1 to 4, wherein the lubricant amount control mode includes an operation in which the intermediate transfer body is rotated while the photosensitive body is spaced from the intermediate transfer body, and the lubricant on the intermediate transfer body is removed by a cleaning member that contacts the intermediate transfer body. The image forming apparatus of any one of claims 1 to 5, wherein the lubricant amount control mode includes an operation in which the secondary transfer member is pressed against the intermediate transfer member and a voltage of opposite polarity to the lubricant is applied to the secondary transfer member, thereby transferring the lubricant on the intermediate transfer member to the secondary transfer member and removing it. The image forming apparatus of any one of claims 1 to 6, wherein the control unit selects and executes one or more of the lubricant amount control operations included in the lubricant amount control mode, depending on the printing conditions during printing. The image forming apparatus of claim 5 or 6, wherein the control means estimates the amount of lubricant on the intermediate transfer body based on the number of photosensitive drums used during printing, image coverage, and the number of prints, and performs an operation to remove the lubricant when the estimated amount of lubricant exceeds a predetermined threshold. The image forming apparatus according to any one of claims 1 to 8, wherein the control means changes the parameters used in the lubricant amount control mode depending on the type of paper used during printing. The image forming apparatus of claim 9, wherein the control means uses parameters that reduce the amount of lubricant on the intermediate transfer body when the paper type is embossed paper compared to when other types of paper are used. a plurality of photoreceptors each having a lubricant supplying means for supplying a lubricant to the surface of the photoreceptor on which a toner image is formed;
an intermediate transfer member onto which a toner image formed on a surface of at least one of the plurality of photoreceptors is transferred during printing;
A method for controlling the amount of lubricant in an image forming apparatus comprising:
a control step of controlling execution of a lubricant amount control mode for controlling the amount of lubricant on the intermediate transfer body in accordance with the number of the photoconductors used during printing;
The lubricant amount control method includes an operation of controlling the amount of lubricant on the intermediate transfer body by providing a peripheral speed difference between the photosensitive body and the intermediate transfer body.