JP7016648B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus such as a copier, a printer, and a facsimile machine using an electrophotographic method or an electrostatic recording method.

Conventionally, in an image forming apparatus using an electrophotographic method or the like, a toner image formed on an image carrier such as a photoconductor is transferred directly or via an intermediate transfer body to a recording material such as recording paper to form an image. Toner. Further, as an image forming apparatus capable of forming a color image, there is a tandem type image forming apparatus having a plurality of image forming portions, each having an image carrier. For example, in a tandem image forming apparatus that uses an electrophotographic method and an intermediate transfer method, a toner image formed on a photoconductor as an image carrier provided by a plurality of image forming portions is used as a transferred body. The primary transfer is sequentially performed so as to be superimposed on the intermediate transfer body of. Then, the toner image on the intermediate transfer body is secondarily transferred to a recording material such as recording paper.

In such an image forming apparatus, the toner remaining on the image carrier (transfer residual toner) after the toner image is transferred from the image carrier to the transferred object is removed from the image carrier by the cleaning means. As a cleaning means, a cleaning member that comes into contact with the image carrier is widely used, and as a cleaning member, a cleaning blade made of an elastic material such as rubber is widely used. Generally, the edge of the free end of the cleaning blade is brought into contact with the image carrier so that the free end is in the counter direction facing upstream in the moving direction of the surface of the image carrier. be.

This cleaning method has advantages such as simple configuration, low cost, and high toner removal performance. However, the coefficient of friction on the surface of an image carrier, such as a photoconductor used in an electrophotographic image forming apparatus, generally tends to increase by repeating image forming. Therefore, when the image formation is repeated, the frictional force between the image carrier and the cleaning blade increases. Then, when the frictional force between the image carrier and the cleaning blade becomes larger than a certain level due to factors such as continued image formation with a lower image ratio than expected, the output image or the device is put into operation. On the other hand, various influences are likely to occur.

For example, the load on the cleaning blade increases, the frictional force between the image carrier and the cleaning blade increases, and the contact state of the cleaning blade with the image carrier becomes unstable, which causes the following problems. May occur. That is, the cleaning blade chattering (abnormal vibration) that causes abnormal noise, toner slippage, or color shift can occur, or the cleaning blade can be rolled up in the moving direction of the surface of the image carrier to drive the image carrier. It may disappear. As described above, an abnormal image or downtime (a period during which the image cannot be output due to maintenance or the like) may occur due to the contact state of the cleaning blade with the image carrier.

Here, in Patent Document 1, a method of detecting a fluctuation in the rotation speed of the drive motor of the intermediate transfer body by using an encoder, and reducing the gain to a value that can be controlled by the control unit when a rotation abnormality of the drive motor is detected. Is disclosed.

Japanese Unexamined Patent Publication No. 2010-74887

However, the method of Patent Document 1 does not suppress the above-mentioned problem when the frictional force between the image carrier and the cleaning blade becomes large.

Further, the image forming apparatus may be configured to drive the image carriers of a plurality of image forming portions by a common drive source in order to simplify the configuration and reduce the cost. In the case of a configuration in which the drive sources for driving the image carriers of the plurality of image forming portions are shared in this way, in the method of detecting the rotation speed of the drive motor as described in Patent Document 1, which image forming portion is used. It is difficult to identify if the problem is occurring on the image carrier. Therefore, the problem must be dealt with equally in all image forming units. Even in that case, if the rotation speed of a common drive motor is detected, only the detection signal averaged for a plurality of image forming portions can be obtained, so that the sensitivity becomes dull, which causes a problem with high accuracy. It's difficult to deal with.

Therefore, an object of the present invention is to provide an image forming apparatus capable of accurately performing a process of reducing a frictional force between an image carrier and a cleaning member when necessary.

Further, another object of the present invention is a configuration in which a plurality of image carriers are driven by a common drive source, but a process for reducing the frictional force between each image carrier and the cleaning member is required with high accuracy. It is to provide an image forming apparatus that can be executed from time to time.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention comprises a rotatable first image carrier carrying a toner image, a rotatable second image carrier carrying a toner image, and the first image carrier in contact with the first image carrier. To supply toner to the first cleaning member that removes toner from the image carrier, the second cleaning member that contacts the second image carrier and removes toner from the second image carrier, and the first image carrier. A first developing means for forming a toner image on the first image carrier, and a second developing means for supplying toner to the second image carrier to form a toner image on the second image carrier. A common drive source for driving the first image carrier and the second image carrier, a first encoder for detecting the rotation speed of the first image carrier, and a rotation speed of the second image carrier are detected. Based on the detection results of the second encoder and the first encoder detected during the non-image formation period in which toner is not supplied from the first developing means to the first image carrier, the first developing means said the first. The first supply operation of supplying toner to the one image carrier and supplying the toner to the contact portion between the first image carrier and the first cleaning member is controlled, and the second image carrier is supported by the second developing means. Based on the detection result of the second encoder detected during the non-image forming period in which the toner is not supplied to the body, the toner is supplied to the second image carrier by the second developing means to support the second image carrier. The image forming apparatus is characterized by having a control means for controlling a second supply operation of supplying toner to a contact portion with the second cleaning member .

According to the present invention, the process of reducing the frictional force between the image carrier and the cleaning member can be accurately executed when necessary. Further, according to the present invention, even in a configuration in which a plurality of image carriers are driven by a common drive source, processing for reducing the frictional force between each image carrier and the cleaning member is accurately executed when necessary. can do.

It is a schematic cross-sectional view of an image forming apparatus. It is a schematic cross-sectional view of an image forming part. It is a block diagram which shows the drive composition and the control mode in Example 1. FIG. It is a schematic diagram which shows the drive composition in Example 1. FIG. It is a graph which shows the detection signal of an encoder. It is a graph which shows the result of FFT processing of the detection signal of an encoder. It is a schematic diagram which shows the toner band formed in a supply operation. It is a flowchart of the control in Example 1. FIG. It is a block diagram which shows the drive composition and the control mode in Example 2. FIG. It is a schematic diagram which shows the drive composition in Example 2. FIG. It is a flowchart of the control in Example 3. FIG.

Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

[Example 1]
1. 1. Overall Configuration and Operation of the Image Forming Device FIG. 1 is a schematic cross-sectional view of the image forming apparatus 100 of the present embodiment. The image forming apparatus 100 of this embodiment is a tandem type laser beam printer that employs an intermediate transfer method and can form a full-color image by using an electrophotographic method.

The image forming apparatus 100 has the first, second, third, and fourth image forming units SY, SM, which form images of each color of yellow, magenta, cyan, and black as a plurality of image forming units (stations), respectively. Has SC and SK. For elements having the same or corresponding functions or configurations in each image forming unit SY, SM, SC, SK, Y, M, C, K at the end of the code indicating that the element is for any color is omitted. And there is a general explanation. In addition, each element of the first, second, third, and fourth image forming units SY, SM, SC, and SK is added to the beginning of the word as "first", "second", "third", and so on. It may be distinguished by adding "fourth". FIG. 2 is a schematic cross-sectional view of the image forming unit S. In this embodiment, the image forming unit S includes a photosensitive drum 1, a charging roller 2, an exposure device 3, a developing device 4, a primary transfer roller 5, a drum cleaning device 6, and the like, which will be described later.

The image forming apparatus 100 has a photosensitive drum 1 which is a drum-shaped (cylindrical) photosensitive member (electrophotographic photosensitive member) as a rotatable image carrier. In this embodiment, the photosensitive drum 1 is configured by coating OPC (organic optical semiconductor) as a photosensitive layer on the outer peripheral surface of an aluminum cylinder having an outer diameter of 30 mm, and a curable resin is used for the charge transport layer. It is used as a resin for. The photosensitive drum 1 is rotationally driven at a predetermined peripheral speed (process speed) in the direction of arrow R1 (counterclockwise) in the figure by a drive motor described later.

The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative electrode property in this embodiment) by a charging roller 2 which is a roller-type charging member (contact charging member) as a charging means. Be made to. In this embodiment, the charging roller 2 is configured by providing an elastic layer on a conductive support, and a conductive agent such as carbon black is appropriately added to the elastic layer to have a resistance value of less than 10 ¹⁰ Ω. It is adjusted to have conductivity. Further, in this embodiment, the charging roller 2 has an outer diameter of 14 mm, is pressed against the surface of the photosensitive drum 1 with a predetermined pressure, and is brought into contact with the surface of the photosensitive drum 1, and is driven to rotate as the photosensitive drum 1 rotates. do. During the charging process, a charging voltage (charging bias), which is a vibration voltage obtained by superimposing a DC voltage (DC voltage) and an AC voltage (AC voltage), is applied to the charging roller 2 by a charging power supply (high voltage power supply circuit) E1. Will be done.

The surface of the charged photosensitive drum 1 is scanned and exposed by an exposure apparatus 3 as an exposure means according to image information, and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 1. In this embodiment, the exposure apparatus 3 is a laser beam scanner that irradiates a photosensitive drum 1 with a laser beam having a wavelength of 780 nm according to image information to form an electrostatic image on the photosensitive drum 1.

The electrostatic image formed on the photosensitive drum 1 is developed (visualized) by supplying toner as a developer by the developing apparatus 4 as a developing means, and a toner image is formed on the photosensitive drum 1. In this embodiment, the developing device 4 is a two-component contact developing device that uses a two-component developing agent containing a toner (non-magnetic toner particles) and a carrier (magnetic carrier particles) as a developing agent. The developing apparatus 4 has a hollow cylindrical developing sleeve 41 made of a non-magnetic material as a developing agent carrier (developing member), and a developing container 42 for accommodating the developing agent. The developing sleeve 41 is rotatably supported by the developing container 42 facing the photosensitive drum 1. The developing sleeve 41 is rotationally driven in the direction of arrow R3 in the drawing. Inside the developing sleeve 41 (hollow portion), a magnet roller 43 as a magnetic field generating means is fixedly arranged with respect to the developing container 42. Further, the developing container 42 is provided with a developing blade 44 as a developing agent regulating member facing the developing sleeve 41.

The developing sleeve 41 carries a two-component developer containing toner and a carrier by the action of the magnetic field generated by the magnet roller 43, and conveys the developing sleeve 41 to the developing unit D which is a facing portion between the developing sleeve 41 and the photosensitive drum 1. .. The developer on the developing sleeve 41 stands up in the developing unit D due to the action of the magnetic field generated by the magnet roller 43 to form a magnetic brush. In this embodiment, the magnetic brush with the developer on the developing sleeve 41 comes into contact with the surface of the photosensitive drum 1 in the developing unit D. Further, during the development process, a development voltage (development bias), which is a vibration voltage in which a DC voltage (DC voltage) and an AC voltage (AC voltage) are superimposed, is applied to the development sleeve 41 by the development power supply E2. In this embodiment, the exposed portion on the photosensitive drum 1 whose absolute potential value is lowered by being exposed after being uniformly charged has the same polarity as the charging polarity of the photosensitive drum 1 (negative electrode property in this embodiment). ) Is charged with toner (reversal development). In this embodiment, the normal charging polarity of the toner, which is the charging polarity of the toner at the time of development, is the negative electrode property. An external additive such as silica is externally added to the toner. Further, in this embodiment, the average charge amount (charge amount per unit weight) of the toner during development is −1.0 × 10 ⁻² C / kg to −6.0 × 10 ⁻² C / kg.

An intermediate transfer belt 7 composed of an endless belt as an intermediate transfer body is arranged so as to face all the photosensitive drums 1. The intermediate transfer belt 7 is stretched over a drive roller 71, a tension roller 72, and a secondary transfer facing roller 73 as a plurality of support members (tension rollers), and is tensioned with a predetermined tension. The intermediate transfer belt 7 is rotated (circulated) in the direction of arrow R2 (clockwise) in the figure by rotationally driving the drive roller 71 by a belt drive motor (not shown). In this embodiment, the intermediate transfer belt 7 is rotationally driven so that the speed difference between the surface of the photosensitive drum 1 and the surface of the intermediate transfer belt 7 is within the range of 1 to 5%. In this embodiment, the intermediate transfer belt 7 is configured to have an endless belt-shaped substrate molded to a thickness of 100 μm using a polyimide resin. If the thickness of the intermediate transfer belt 7 is less than 50 μm, sufficient durability may not be obtained due to wear, and if the thickness exceeds 500 μm, the intermediate transfer belt 7 becomes difficult to bend appropriately on the support shaft. , Running may not be stable. Further, a conductive agent for adjusting the electric resistance value such as carbon black is added to the substrate of the intermediate transfer belt 1. In this embodiment, the intermediate transfer belt 7 has a volume resistance value of 1.0 × 10 ¹⁰ [Ω · cm] and a surface resistance value of 6.0 × 10 ¹¹ [Ω / □]. In this embodiment, a single-layer structure intermediate transfer belt is used, but a multi-layer structure intermediate transfer belt having an elastic layer may be used.

On the inner peripheral surface side of the intermediate transfer belt 7, a primary transfer roller 5 which is a roller type primary transfer member as a primary transfer means is arranged corresponding to each photosensitive drum 1. The primary transfer roller 5 is pressed toward the photosensitive drum 1 via the intermediate transfer belt 7 to form a primary transfer portion (primary transfer nip) T1 in which the photosensitive drum 1 and the intermediate transfer belt 7 come into contact with each other. In this embodiment, the primary transfer roller 5 has an outer diameter of 18 mm, is brought into contact with the inner peripheral surface of the intermediate transfer belt 7, and is driven to rotate as the intermediate transfer belt 7 rotates. The primary transfer roller 5 and the photosensitive drum 1 can be appropriately switched to a contact state or a separation state by a contact / separation mechanism as a contact / separation means (not shown). When the primary transfer roller 5 is separated from the photosensitive drum 1, the intermediate transfer belt 7 is separated from the photosensitive drum 1.

The toner image formed on the photosensitive drum 1 as described above is transferred (primary transfer) on the intermediate transfer belt 7 as a rotating object to be transferred by the action of the primary transfer roller 5 in the primary transfer unit T1. Will be done. During the primary transfer step, the primary transfer roller 5 is subjected to a primary transfer voltage (high voltage power supply circuit) E3, which is a DC voltage having a polarity opposite to the normal charging polarity of the toner (positive electrode property in this embodiment). Primary transfer bias) is applied. For example, when forming a full-color image, the yellow, magenta, cyan, and black toner images formed on the photosensitive drums 1Y, 1M, 1C, and 1K are sequentially superimposed on the intermediate transfer belt 7. Primary transcription.

On the outer peripheral surface side of the intermediate transfer belt 7, a secondary transfer roller 8 which is a roller type secondary transfer member as a secondary transfer means is arranged at a position facing the secondary transfer facing roller 73. The secondary transfer roller 8 is pressed toward the secondary transfer facing roller 73 via the intermediate transfer belt 7, and the secondary transfer portion (secondary transfer nip) in which the intermediate transfer belt 7 and the secondary transfer roller 8 come into contact with each other. Form T2. In this embodiment, the secondary transfer roller 8 has an outer diameter of 24 mm, is brought into contact with the outer peripheral surface of the intermediate transfer belt 7, and is driven to rotate as the intermediate transfer belt 7 rotates. The toner image formed on the intermediate transfer belt 7 as described above is sandwiched and conveyed between the intermediate transfer belt 7 and the secondary transfer roller 8 by the action of the secondary transfer roller 8 in the secondary transfer unit T2. It is transferred (secondary transfer) onto a recording material P such as a recording paper. During the secondary transfer step, the secondary transfer roller 8 has a DC voltage (positive electrode property in this embodiment) opposite to the normal charging polarity of the toner due to a secondary transfer power supply (high voltage power supply circuit) (not shown). A secondary transfer voltage (secondary transfer bias) is applied.

The recording material (sheet, transfer material) P is supplied to the secondary transfer unit T2 at the same timing as the toner image on the intermediate transfer belt 7 by a feeding device equipped with a paper feed roller, a transfer roller, or the like (not shown). .. Further, the recording material P to which the toner image is transferred is heated and pressurized by the fixing device 10 as a fixing means to fix (melt and fix) the toner image, and then as an image forming object (print, copy). It is discharged (output) to the outside of the main body of the image forming apparatus 100.

On the other hand, the toner remaining on the surface of the photosensitive drum 1 without being transferred to the intermediate transfer belt 7 during the primary transfer (primary transfer residual toner) is removed from the surface of the photosensitive drum 1 by the drum cleaning device 6 as a photoconductor cleaning means. Will be collected. The drum cleaning device 6 has a cleaning blade 61 as a cleaning member that comes into contact with the surface of the photosensitive drum 1 and a cleaning container 62. In this embodiment, the cleaning blade 61 is a flat plate-shaped member made of polyurethane rubber, and is supported by a sheet metal as a support member. The cleaning blade 61 is arranged so that the longitudinal direction is substantially parallel to the rotation axis direction of the photosensitive drum 1. Further, the cleaning blade 61 has an edge portion of the free end portion of the photosensitive drum 1 so that the free end portion in the lateral direction substantially orthogonal to the longitudinal direction faces the upstream side in the rotation direction of the photosensitive drum 1. It is in contact with the surface of the. Then, the drum cleaning device 6 scrapes the primary transfer residual toner from the surface of the rotating photosensitive drum 1 by the cleaning blade 61 and stores it in the cleaning container 62. Further, on the outer peripheral surface side of the intermediate transfer belt 7, a belt cleaning device 9 as an intermediate transfer body cleaning means is arranged at a position facing the drive roller 71. The toner (secondary transfer residual toner) remaining on the surface of the intermediate transfer belt 7 without being transferred to the recording material P during the secondary transfer is removed from the surface of the intermediate transfer belt 7 by the belt cleaning device 9 and recovered. Similar to the drum cleaning device 6, the belt cleaning device 9 scrapes the secondary transfer residual toner from the surface of the rotating intermediate transfer belt 7 by the cleaning blade and stores it in the cleaning container. In this embodiment, the same cleaning blade as the cleaning blade 61 of the drum cleaning device 6 was used as the cleaning blade of the belt cleaning device 7. The transfer residual toner contained in each cleaning container is sent to a collection container (not shown) by a toner transfer screw (not shown) or the like.

Here, in the present embodiment, the image forming apparatus 100 can form an image in a color mode (first mode) and a monochrome mode (second mode). In the color mode, a toner image can be formed by the first to fourth image forming units SY, SM, SC, and SK to form a full-color image. In the monochrome mode, a toner image can be formed only by the fourth image forming unit SK among the first to fourth image forming units SY, SM, SC, and SK to form a black monochromatic image. In the color mode, in all the image forming units SY, SM, SC, and SK, the primary transfer roller 5 is pressed toward the photosensitive drum 1 via the intermediate transfer belt 7, and the photosensitive drum 1 and the intermediate transfer belt 7 are pressed. Be abutted. On the other hand, in the monochrome mode, the primary transfer roller 5 is moved away from the photosensitive drum 1 and the intermediate transfer belt 7 is separated from the photosensitive drum 1 in the first to third image forming units SY, SM, and SC. Further, in the monochrome mode, in the fourth image forming unit SK, the primary transfer roller 5 is pressurized toward the photosensitive drum 1 via the intermediate transfer belt 7, and the photosensitive drum 1 and the intermediate transfer belt 7 are brought into contact with each other. To. Then, in the monochrome mode, the driving of the photosensitive drum 1 and the developing device 4 is stopped in the first to third image forming units PY, PM, and PC that are not used for image forming. This makes it possible to suppress deterioration of the photosensitive drum 1 and the developer in the image forming unit S that is not used for image forming.

2. 2. Drive Configuration of Photosensitive Drum FIG. 3 is a schematic block diagram showing a drive configuration and a control mode of the photosensitive drum 1 in this embodiment. Further, FIG. 4 is a schematic diagram showing in more detail the drive configuration of the photosensitive drum 1 in this embodiment. In this embodiment, the photosensitive drum 1 can be attached to and detached from the main body of the image forming apparatus 100 substantially alone or together with at least one of process means such as a charging means, a developing means, and a cleaning means. It is said that.

As shown in FIG. 3, in the present embodiment, the drive device 20 as the drive means is an independent drive for driving the first, second, third, and fourth photosensitive drums 1Y, 1M, 1C, and 1K, respectively. It has first, second, third, and fourth drive motors 21Y, 21M, 21C, and 21K as sources. Further, as shown in FIG. 3, the main body of the image forming apparatus 100 includes a CPU 31 as a control means, a memory (nonvolatile memory) 32 as a storage means, and drive circuits of drive motors 21Y, 21M, 21C, and 21K. A drive control unit 25 which is a driver) is provided.

As shown in FIG. 4, a drum coupling 11 as a drive receiving portion is provided at one end of the photosensitive drum 1 in the rotation axis direction (longitudinal direction). Further, the main body of the image forming apparatus 100 is provided with drive shafts 22Y, 22M, 22C, 22K rotated by the drive motors 21Y, 21M, 21C, 21K. Further, a main body coupling 23Y, 23M, 23C, 23K as a drive transmission member is provided at one end of each drive shaft 22Y, 22M, 22C, 22K in the rotation axis direction. The drum couplings 11Y, 11M, 11C, and 11K provided on the photosensitive drums 1Y, 1M, 1C, and 1K are the main body couplings 23Y, 23M, and 23C provided on the drive shafts 22Y, 22M, 22C, and 22K. , Engage with 23K. As a result, the photosensitive drums 1Y, 1M, 1C, and 1K rotate by transmitting power from the drive motors 21Y, 21M, 21C, and 21K connected to the drive shafts 22Y, 22M, 22C, and 22K.

Further, each drive shaft 22Y, 22M, 22C, 22K is used as a speed detecting means for detecting the rotation speed of each drive shaft 22Y, 22M, 22C, 22K (that is, each photosensitive drum 1Y, 1M, 1C, 1K). Rotary encoders (hereinafter, also referred to as "encoders") 24Y, 24M, 24C, 24K are attached. The CPU 31 issues a command to the drive control unit 25 to rotate each drive motor 21Y, 21M, 21C, 21K at a predetermined rotation speed. When the drive motors 21Y, 21M, 21C, 21K start to rotate, the rotation speeds of the photosensitive drums 1Y, 1M, 1C, and 1K change to the encoders 24Y, 24M, which are attached to the drive shafts 22Y, 22M, 22C, and 22K. Detected by 24C and 24K. The detection signals of the encoders 24Y, 24M, 24C, and 24K are fed back to the drive control unit 25, and each drive motor is rotated by the drive control unit 25 so that the photosensitive drums 1Y, 1M, 1C, and 1K rotate at a predetermined rotation speed. 21Y, 21M, 21C, 21K are controlled.

In this embodiment, the CPU 31 issues a command to the drive control unit 25 based on the program or data stored in the memory 32 to control the rotation of each photosensitive drum 1Y, 1M, 1C, 1K, and the like. The operation of each part of the image forming apparatus 100 is comprehensively controlled. The CPU 31 controls the operation of the image forming apparatus 100 so as to form an image corresponding to image data (electrical image information) input from an external device such as a personal computer or an image reading device on the recording material P and output the image. I do. Further, in this embodiment, the CPU 31 controls the supply operation as the contact state detection process and the frictional force reduction process, which will be described later.

Here, the image forming apparatus 100 executes a job (printing operation) which is a series of operations of forming and outputting an image on a single or a plurality of recording materials P, which is started by one start instruction. The job generally includes an image forming step, a front rotation step, a paper-to-paper step when forming an image on a plurality of recording materials P, and a back rotation step. The image forming step is a period during which an electrostatic image of an image actually formed and output on the recording material P is formed, a toner image is formed, and a primary transfer or a secondary transfer of the toner image is performed, and at the time of image formation (image formation). Period) means this period. More specifically, the timing at the time of image formation differs depending on the position where each of the steps of forming the electrostatic image, forming the toner image, and performing the primary transfer and the secondary transfer of the toner image is performed. The pre-rotation step is a period during which the preparatory operation before the image forming step is performed from the input of the start instruction to the actual start of forming the image. The paper-to-paper process is a period corresponding to the space between the recording material P and the recording material P when image formation is continuously performed on the plurality of recording materials P (continuous image formation). The post-rotation process is a period during which the rearranging operation (preparation operation) is performed after the image forming process. The non-image forming time (non-image forming period) is a period other than the image forming time, and is from the pre-rotation step, the paper-to-paper step, the back-rotation step, and further, when the power of the image forming apparatus 100 is turned on or from the sleep state. It includes a pre-multi-rotation process, which is a preparatory operation at the time of recovery. In this embodiment, at the time of non-image formation, the contact state detection process and the supply operation as the frictional force reduction process, which will be described later, are executed.

3. 3. Contact state detection process and friction force reduction process Next, the contact state detection process for detecting the contact state of the cleaning blade 61 with respect to the photosensitive drum 1 in this embodiment, and the friction between the photosensitive drum 1 and the cleaning blade 61. The frictional force reduction process for reducing the force will be described. In this embodiment, the contact state detection process and the frictional force reduction process in each image forming unit S are substantially the same, so here, one image forming unit S will be focused on.

5 (a) and 5 (b) show the elapsed time and the rotation speed (mm / sec) detected by the encoder 24 when the photosensitive drum 1 is rotated with the target rotation speed (peripheral speed) of 200 mm / sec. It is a graph which shows the relationship (transition of a detection signal) with. FIG. 5A shows the state in which the cleaning blade 61 is stably in contact with the photosensitive drum 1, and FIG. 5B shows the photosensitive drum 1 being rotated in a state where abnormal noise is generated due to chattering of the cleaning blade 61. It is a detection signal of the encoder 24 for 5 seconds at the time of making it. Further, in FIGS. 6 (a) and 6 (b), the detection signals of the encoder 24 shown in FIGS. 5 (a) and 5 (b) are subjected to fast Fourier transform (hereinafter, also referred to as “FFT”) processing by the CPU 31. It is a graph which shows the result of extracting the rotation speed fluctuation of a photosensitive drum 1 for each frequency. In FIGS. 6A and 6B, the horizontal axis shows the frequency, and the vertical axis shows the signal value in the velocity frequency space (corresponding to the rate (%) of the rotation speed fluctuation when the frequency is taken as a parameter).

In a state where abnormal noise is generated due to chattering of the cleaning blade 61 shown in FIG. 6 (b), a point having the largest signal strength (rotational speed fluctuation) is seen around 43 Hz (hereinafter, also referred to as “peak value”). Be done. This indicates that the contact state of the cleaning blade 61 fluctuates periodically at about 43 Hz, and the rotation speed of the photosensitive drum 1 fluctuates with the same cycle. On the other hand, when the cleaning blade 61 shown in FIG. 6A is in stable contact with the photosensitive drum, the above-mentioned remarkable peak is not observed.

In this way, whether or not the contact state of the cleaning blade 61 with the photosensitive drum 1 is stable can be determined by detecting the rotation speed of the photosensitive drum 1.

In this embodiment, when the peak value of the detection signal of the encoder 24 in the velocity frequency space after the FFT processing is equal to or higher than a preset predetermined threshold value, the contact state of the cleaning blade 61 with the photosensitive drum 1 is unstable. Judge that there are signs that it has begun to change. Then, in order to stabilize the contact state of the cleaning blade 61 with the photosensitive drum 1, a frictional force reducing process for reducing the frictional force between the photosensitive drum 1 and the cleaning blade 61 is executed. As a result, abnormal images such as toner slippage and color shift due to periodic changes in the contact state of the cleaning blade 61 with respect to the photosensitive drum 1 and the occurrence of downtime are efficiently suppressed.

Specifically, the contact state detection process for detecting the contact state of the cleaning blade 61 with the photosensitive drum 1 at the time of non-image formation is performed at a predetermined timing. Thereby, it is determined whether or not the peak value of the detection signal of the encoder 24 in the velocity frequency space after the FFT processing is 0.10 or more, which is the threshold value. Then, when it is determined that the peak value is equal to or higher than the threshold value, the frictional force reduction process is executed at the time of non-image formation. In particular, in this embodiment, as a frictional force reducing process, a toner (including a toner external additive) that functions as a lubricant is supplied to the contact portion (blade nip portion) N between the cleaning blade 61 and the photosensitive drum 1. Perform the supply operation. On the other hand, if it is determined that the peak value is less than the threshold value of 0.10, the frictional force reduction process is not executed until the timing of the next contact state detection process. As described above, in the present embodiment, the contact state detection process includes a process of detecting the rotational speed of the photosensitive drum 1 (speed detection process), a process of detecting a variation in the rotational speed of the photosensitive drum 1 (variation detection process), and the like. Includes processing to determine the contact state (judgment processing). In this embodiment, the encoder 24 constitutes a speed detection means for performing speed detection processing. Further, in this embodiment, the CPU 31 has a function of a fluctuation detection unit that performs fluctuation detection processing and a judgment processing unit that performs judgment processing. The fluctuation detection unit and the determination processing unit are realized by the CPU 31 executing a program stored in the memory 32.

The timing for executing the speed detection process in the contact state detection process may be any timing as long as the photosensitive drum 1 is rotating. However, it is during the following period that the contact state of the cleaning blade 61 becomes unstable and the rotational speed fluctuation of the photosensitive drum 1 tends to be remarkable. That is, during the pre-rotation, which is the preparatory rotation before the image formation starts and the toner starts to be supplied to the photosensitive drum 1, or during the post-rotation, which is the down rotation where the image formation is completed and the toner is not supplied to the photosensitive drum 1. Is. That is, typically, fog toner is constantly supplied to the photosensitive drum 1 during image formation, and the toner external additive gradually slips through the edge portion of the cleaning blade 61 to form the photosensitive drum 1 and the cleaning blade 61. Is supplied during. Therefore, the frictional force between the photosensitive drum 1 and the cleaning blade 61 is reduced, and the contact state of the cleaning blade 61 with the photosensitive drum 1 is relatively easy to be stable. In the fog toner, toner or the like whose charging polarity is reversed to the normal polarity due to the potential difference between the charging potential of the photosensitive drum 1 and the potential of the developing sleeve 41 (DC component of the developing voltage) is on the photosensitive drum 1. It is a toner that causes "fog", which is a phenomenon that adheres to the non-image area of the toner. On the other hand, during the forward rotation or the backward rotation, the photosensitive drum 1 continues to rotate in a state where the toner is not supplied to the photosensitive drum 1, and the amount of the toner external additive that slips through the edge portion of the cleaning blade 61 is small. Therefore, the frictional force between the photosensitive drum 1 and the cleaning blade 61 becomes large, and the contact state of the cleaning blade 61 with the photosensitive drum 1 tends to become unstable. In other words, during image formation, the contact state is irrespective of whether or not the contact state of the cleaning blade 61 with the photosensitive drum 1 is likely to become unstable due to an increase in the friction coefficient of the surface of the photosensitive drum 1. Is easy to stabilize, so the accuracy of determining the corresponding contact state is likely to decrease. Therefore, it is desirable that the execution timing of the speed detection process in the contact state detection process is the timing at which the photosensitive drum 1 is rotated in a state where the toner is not supplied to the photosensitive drum 1, such as during forward rotation or backward rotation. ..

Further, the timing for executing the supply operation may be any timing as long as the photosensitive drum 1 is rotating. However, for the same reason as described above, it is desirable that the photosensitive drum 1 is rotating at a timing in which the toner is not supplied, such as during forward rotation or backward rotation.

Therefore, in this embodiment, the speed detection process in the contact state detection process is executed during the forward rotation, and the detection signal of the encoder 24 is acquired for 1 second. Then, during the image formation, the CPU 31 executes the fluctuation detection process and the determination process in the contact state detection process. That is, the detection signal of the encoder 24 is FFT processed to calculate the peak value (variation detection processing), and it is determined whether or not the peak value is 0.10 or more, which is the threshold value (determination processing). Then, when it is determined that the peak value is 0.10 or more, which is the threshold value, the supply operation is executed during the rear rotation. In this embodiment, the above-mentioned contact state detection process (speed detection process, fluctuation detection process, judgment process) is executed in parallel for each image forming unit S, and the peak value is equal to or higher than the threshold value in the contact state detection process. If there is a certain image forming unit S, the supply operation is executed only in the image forming unit S.

The reason why the supply operation is executed during the rear rotation instead of the front rotation is that it takes time to execute the supply operation during the front rotation, and the start timing of image formation may be delayed. Further, even if the supply operation is executed during the forward rotation, the image formation starts immediately after that, and the fog toner and the primary transfer residual toner start to be supplied to the blade nip N, so that the time for obtaining the effect is short. .. In this embodiment, the speed detection process in the contact state detection process is executed during the pre-rotation of each job, but the speed detection process is executed at a predetermined frequency such as once for a plurality of jobs. You may do so.

In the supply operation, as shown in FIG. 7, a band-shaped toner image (hereinafter, also referred to as “toner band”) t made of toner supplied to the blade nip portion N extending in the rotation axis direction of the photosensitive drum 1 is a photosensitive drum. 1 Form on top. In this embodiment, the toner band t is formed over the entire development width (width of the region where the toner can be supplied) of the developing device 4 in the rotation axis direction of the photosensitive drum 1. In this embodiment, the development width is substantially the same as the width of the image forming region (region in which the toner image can be formed) in the rotation axis direction of the photosensitive drum 1, and is equivalent to the length in the longitudinal direction of the cleaning blade 61. Is. In this embodiment, this toner band is formed on the photosensitive drum 1 through the steps of charging, exposure, and development in the same manner as in the case of image formation described above. Then, this toner band is passed through the primary transfer portion T1 and supplied to the blade nip portion N. In this embodiment, when the toner band passes through the primary transfer unit T1, the primary transfer roller 5 has the opposite polarity to that at the time of image formation, that is, the same polarity as the normal charging polarity of the toner (in this embodiment). Apply a DC voltage (negative polarity). As a result, the amount of toner in the toner band transferred to the intermediate transfer belt 7 is reduced, and the toner is effectively supplied to the blade nip portion N.

In this embodiment, the amount of toner on the toner band t (the weight of the toner adhering to the surface of the photosensitive drum 1 per unit area) is about 0.50 mg / cm ² . Further, the width of the toner band t in the main scanning direction (direction of the rotation axis of the photosensitive drum 1) is 320 mm, which is the same as the width of the region carrying the toner on the developing sleeve 41. Further, the length of the toner band t in the sub-scanning direction (moving direction of the surface of the photosensitive drum 1) is 30 mm. However, the amount of toner supplied to the blade nip portion N in the supply operation is not limited to that of the present embodiment. For example, it can be appropriately set according to the surface roughness of the photosensitive drum 1, the setting of the AC voltage of the charging voltage, the setting angle (contact angle) of the cleaning blade 61, the setting of the linear pressure (contact pressure), and the like.

In this embodiment, the speed detection process in the contact state detection process is executed during the front rotation, but it may be executed during the rear rotation. Further, in this embodiment, the rotation speed fluctuation of the photosensitive drum 1 is detected during the rotation of the photosensitive drum 1 in a state where the charging voltage is not applied to the charging roller 2, but the rotation speed fluctuation during image formation is detected. May be good.

4. Control procedure Next, the control procedure of the contact state detection process and the supply operation in this embodiment will be described. FIG. 8 is a flowchart showing an outline of a job control procedure including a contact state detection process and a supply operation in this embodiment. Here, a job in color mode will be described as an example.

When the image forming signal is input (S101), the CPU 31 starts the rotation of each photosensitive drum 1Y, 1M, 1C, and 1K to start the forward rotation (S102). The CPU 31 acquires the detection results of the rotation speeds of the photosensitive drums 1Y, 1M, 1C, and 1K by the encoders 24Y, 24M, 24C, and 24K during the forward rotation (S103). Next, the CPU 31 starts image formation as soon as the operation of the predetermined front rotation step is completed (S104).

During image formation, the CPU 31 performs FFT processing on the detection signals of the rotation speeds of the photosensitive drums 1Y, 1M, 1C, and 1K by the encoders 24Y, 24M, 24C, and 24K, and the peak value in the speed frequency space after the FFT processing. Is calculated (S105). Further, the CPU 31 compares the calculated peak value with the threshold value of 0.10 during image formation, and determines whether or not there is an image forming unit S whose peak value is equal to or greater than the threshold value (S106). Then, when the CPU 31 determines in S106 that there is an image forming unit S whose peak value is equal to or higher than the threshold value, the CPU 31 executes a supply operation only in the image forming unit S during the post-rotation after image formation (S107). ). After that, the CPU 31 ends the operation of the image forming apparatus 100 as soon as the operation of the predetermined back rotation process is completed (S108). Further, when the CPU 31 determines in S106 that there is no image forming unit S whose peak value is equal to or higher than the threshold value, the CPU 31 does not execute the supply operation in any of the image forming units S, and operates the predetermined post-rotation process. The operation of the image forming apparatus 100 is terminated as soon as the operation is completed (S108).

5. Effect In the image forming apparatus 100 of this example, a durability test was conducted in which a single color solid vertical band image of yellow, magenta, cyan, and black was repeatedly formed as a test image on an A4 size recording material P. The test was conducted in an environment with a temperature of 32.5 ° C. and a humidity of 85%. The test image has a length of 6 mm in the main scanning direction, a length of 210 mm in the sub-scanning direction, and an image ratio of 2 in the center of the image so that the amount of toner supplied to the photosensitive drum 1 at the time of image formation is small for each color. % Image. Further, the test was repeated up to 200,000 images under the condition of intermittent images of 100 images, that is, a job with 100 images formed until the total number of images formed was 200,000. This durability test was performed while confirming the peak value of the detection signal of the encoder 24 in the velocity frequency space after the FFT processing. As a result, no abnormal noise or abnormal image due to chattering of the cleaning blade 61 was generated, and a stable and good image could be maintained.

As described above, in the present embodiment, the image forming apparatus 100 has a CPU 31 capable of executing a frictional force reducing process for reducing the frictional force between the photosensitive drum 1 and the cleaning blade 61. Then, the CPU 31 executes the frictional force reduction process according to the information regarding the rotation speed fluctuation of the photosensitive drum 1 acquired based on the detection result of the encoder 24. In this embodiment, the encoder 24 is attached to the drive shaft 22 of the photosensitive drum 1. In particular, in this embodiment, the image forming apparatus 100 is provided corresponding to each of the photosensitive drums 1 of the plurality of image forming portions S, and detects the rotation speed of each of the photosensitive drums 1 of the plurality of image forming portions S. It has a plurality of encoders 24. Further, in this embodiment, the CPU 31 can execute a frictional force reducing process for reducing the frictional force between the photosensitive drum 1 and the cleaning blade 61 of the plurality of image forming portions S. At this time, the CPU 31 receives friction regarding each of the plurality of image forming units S according to the information regarding the variation in the rotation speed of each of the photosensitive drums 1 of the plurality of image forming units S acquired based on the detection results of the plurality of encoders 24. Perform force reduction processing. In this embodiment, the plurality of encoders 24 are attached to the drive shafts 22 of the photosensitive drums 1 of the plurality of image forming units S. Further, in this embodiment, the CPU 31 acquires information on the rotation speed fluctuation of the photosensitive drum 1 based on the detection result of the encoder 24 during the period when the toner is not supplied to the photosensitive drum 1.

Further, in this embodiment, the image forming apparatus 100 has a supply means for supplying a lubricant to the photosensitive drum 1. Then, as a frictional force reducing process, the CPU 31 supplies the lubricant to the photosensitive drum 1 by the supply means during the non-image forming period, and supplies the lubricant to the contact portion N between the photosensitive drum 1 and the cleaning blade 61. Change the settings. In particular, in this embodiment, the CPU 31 changes whether or not the supply operation is executed as the setting of the supply operation. Further, in the present embodiment, the CPU 31 executes the supply operation when the index value that correlates with the magnitude of the rotation speed fluctuation of the photosensitive drum 1 acquired based on the detection result of the encoder 24 is equal to or more than a predetermined threshold value. .. Further, in this embodiment, the CPU 31 performs a fast Fourier transform process on the detection result of the encoder 24 to acquire the index value. In particular, in this embodiment, the supply operation is an operation in which the toner as a lubricant is supplied to the photosensitive drum 1 by the developing device 4 as the supply means, and the toner is brought to the contact portion N by the rotation of the photosensitive drum 1. be.

As described above, according to the present embodiment, the required image forming unit S is based on the FFT processing result of the rotation speed detected for each photosensitive drum 1 by the encoder 24 provided on the drive shaft 22 of each photosensitive drum 1. Only the frictional force reduction process can be performed. As a result, the contact state of the cleaning blade 61 with the photosensitive drum 1 can be efficiently stabilized, and the occurrence of abnormal images and downtime can be efficiently suppressed. That is, according to this embodiment, the process of reducing the frictional force between the photosensitive drum 1 and the cleaning blade 61 can be accurately executed when necessary. In particular, according to this embodiment, even in a configuration in which a plurality of photosensitive drums 1 are driven by a common drive source, it is necessary to accurately perform a process of reducing the frictional force between each photosensitive drum 1 and the cleaning blade 1. Can be done at times.

[Example 2]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, in the image forming apparatus of the present embodiment, the elements having the same or corresponding functions or configurations as those of the image forming apparatus of the first embodiment are designated by the same reference numerals as those of the first embodiment, and detailed description thereof is omitted. do.

FIG. 9 is a schematic block diagram showing a drive configuration and a control mode of the photosensitive drum 1 in this embodiment. Further, FIG. 10 is a schematic diagram showing in more detail the drive configuration of the photosensitive drum 1 in this embodiment.

As shown in FIG. 9, in the present embodiment, the drive device 20 as the drive means is the first drive as a common drive source for driving the first, second, and third photosensitive drums 1Y, 1M, and 1C. It has a motor (hereinafter, also referred to as “color motor”) 21a. Further, the drive device 20 has a second drive motor (hereinafter, also referred to as “black motor”) 21b as an independent drive source for driving the fourth photosensitive drum 1K. As described above, in this embodiment, the drive sources of the first, second, and third photosensitive drums 1Y, 1M, and 1K are shared. The drum couplings 11Y, 11M, and 11C provided on the first, second, and third photosensitive drums 1Y, 1M, and 1C are the main body couplings 23Y, 23M provided on the drive shafts 22Y, 22M, and 22C. Engage with 23C. Then, the drive shafts 22Y, 22M, and 22C are connected to the color motor 21a via the gear (gear train) 26. As a result, the first, second, and third photosensitive drums 1Y, 1M, and 1C are rotated by transmitting power from the color motor 21a, respectively. The fourth photosensitive drum 1K is rotationally driven by the black motor 21b in the same manner as in the first embodiment.

Encoders 24Y, 24M, and 24C are attached to the drive shafts 22Y, 22M, and 22C of the first, second, and third photosensitive drums 1Y, 1M, and 1C, respectively, as in the first embodiment. As a result, the first, second, and third photosensitive drums 1Y, 1M, and 1C are driven by a single color motor 21a, but the rotation of the first, second, and third photosensitive drums 1Y, 1M, and 1C. The speed can be detected independently. An encoder 27K is also attached to the drive shaft 22K of the fourth photosensitive drum 1K. Thereby, the rotation speed of the fourth photosensitive drum 1K can also be independently detected.

In this embodiment, the drive control unit 25 feedback-controls the first and second drive motors 21a and 21b based on the detection signals of the encoders 24Y, 24M, 24C and 24K under the control of the CPU 31. Further, the CPU 31 performs FTT processing on the detection signals of the encoders 24Y, 24M, 24C, and 24K in the same manner as in the first embodiment, and extracts the rotation speed fluctuations of the photosensitive drums 1Y, 1M, 1C, and 1K for each frequency. And calculate the peak value.

The job control procedure including the contact state detection process and the supply operation in this embodiment is the same as that in the first embodiment (FIG. 8).

In the image forming apparatus 100 of this example, the same durability test as that described for Example 1 was performed. As a result, no abnormal noise or abnormal image due to chattering of the cleaning blade 61 was generated up to 200,000 sheets, and a stable and good image could be maintained.

As described above, according to the present embodiment, the same effect as that of the first embodiment can be obtained. Further, in the present embodiment, by sharing the drive source for the plurality of photosensitive drums 1, the configuration can be simplified and the cost can be reduced.

[Example 3]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, in the image forming apparatus of the present embodiment, the elements having the same or corresponding functions or configurations as those of the image forming apparatus of the first embodiment are designated by the same reference numerals as those of the first embodiment, and detailed description thereof is omitted. do.

It should be noted that this embodiment can be applied to any of the drive configurations of Examples 1 and 2 as the drive configuration of the photosensitive drum 1.

In this embodiment, the content of the frictional force reduction processing is changed according to the peak value of the velocity frequency space calculated by FFT processing the detection signal of the encoder 24. Specifically, in this embodiment, as shown in Table 1 below, the toner supply amount to the photosensitive drum 1 in the supply operation as the frictional force reduction process is changed according to the calculated peak value. That is, in this embodiment, the sub-scanning direction of the toner band t so that the larger the peak value, which is an index value that correlates with the magnitude of the rotation speed fluctuation of the photosensitive drum 1, the larger the amount of toner supplied to the photosensitive drum 1. Change the length of. Information indicating the relationship between the peak value and the toner supply amount as shown in Table 1 is preset and stored in the memory 32. Also in this embodiment, as in the first and second embodiments, if the peak value is less than 0.10, the supply operation is not executed (the toner band t is not formed).

FIG. 11 is a flowchart showing an outline of a job control procedure including a contact state detection process and a supply operation in this embodiment. Here, a job in color mode will be described as an example. Since the processes of S201 to S205 and S209 of FIG. 11 are the same as the processes of S101 to S105 and S108 of FIG. 8 in Example 1, detailed description thereof will be omitted.

In this embodiment, the CPU 31 refers to the information shown in Table 1 stored in the memory 32 from the peak value calculated in S205 during image formation, and the toner supply amount to the photosensitive drum 1 during rear rotation. Is determined for each image forming unit S (S206). Further, the CPU 31 determines whether or not there is an image forming unit S that supplies toner during rear rotation (whether or not there is an image forming unit S having a peak value of 0.10 or more) during image formation (S207). ). Then, when the CPU 31 determines that there is an image formation for supplying toner in S207, the CPU 31 executes a supply operation for supplying the amount of toner determined in S206 during the post-rotation after image formation for the image forming unit S. (S208). After that, the CPU 31 ends the operation of the image forming apparatus 100 as soon as the operation of the predetermined back rotation process is completed (S209). Further, when the CPU 31 determines in S207 that there is no image forming unit S for supplying toner, the operation of the predetermined post-rotation process ends without executing the supply operation in any of the image forming units S. The operation of the image forming apparatus 100 is gradually terminated (S209).

In the image forming apparatus 100 of this example, the same durability test as that described for Example 1 was performed. As a result, no abnormal noise or abnormal image due to chattering of the cleaning blade 61 was generated up to 200,000 sheets, and a stable and good image could be maintained.

As described above, in this embodiment, the CPU 31 changes the supply amount of the lubricant in the supply operation as the setting of the supply operation. Further, in this embodiment, the CPU 31 has a first value as compared with the case where the index value that correlates with the magnitude of the rotation speed fluctuation of the photosensitive drum 1 acquired based on the detection result of the encoder 24 is the first value. Make sure that the supply is higher for the larger second value.

As described above, according to the present embodiment, the same effects as those of the first and second embodiments can be obtained. Further, in this embodiment, by changing the content of the frictional force reducing process according to the contact state of the cleaning blade 61 with the photosensitive drum 1, the consumption of materials, the consumption of members, or the reduction of downtime due to the supply operation can be reduced. Can be planned.

[others]
Although the present invention has been described above with reference to specific examples, the present invention is not limited to the above-mentioned examples.

In the above-described embodiment, the toner band is described as being formed on the photosensitive drum through the charging, exposure, and developing steps as in the image formation in the supply operation, but the present invention is limited thereto. It's not something. By adjusting the setting of the potential difference between the surface potential of the photosensitive drum and the potential of the developing sleeve, the toner band may be formed on the photosensitive drum without going through the exposure step or the charging step and the exposure step. For example, by rotating the developing sleeve of a developing device and applying a developing voltage without charging the photosensitive drum and performing an exposure process, toner is generated by the potential difference between the surface potential of the photosensitive drum and the potential of the developing sleeve. It can be supplied on a photosensitive drum.

In the above-described embodiment, as the frictional force reducing process, a timing for supplying toner to the photosensitive drum during the rear rotation is provided to increase the amount of toner supplied to the blade nip portion. However, the present invention is not limited to this, and as the frictional force reducing treatment, any treatment can be adopted as long as the frictional force between the photosensitive drum and the cleaning blade can be reduced. Can be done. Next, some other examples of frictional force reduction processing will be given. The frictional force reducing treatments exemplified here, including those of the above-described embodiment, may be performed in combination of two or more.

That is, as a frictional force reduction process, by changing the frequency of interrupting the timing of supplying toner to the photosensitive drum 1 between papers during job execution, the toner to the blade nip portion per unit time (number of images formed) is changed. You may increase the supply. That is, the CPU 31 can change the execution frequency of the supply operation (the number of executions per unit time (number of image formations)) as the setting of the supply operation. In this case, the CPU 31 can change the execution frequency according to an index value that correlates with the magnitude of the rotation speed fluctuation of the photosensitive drum 1 acquired based on the detection result of the encoder 24. Specifically, the execution frequency may be higher when the index value is a second value larger than the first value than when the index value is the first value.

In addition, as a frictional force reduction process, by changing the setting of the fog removal potential difference Vback, which is the difference between the DC component of the development voltage (development DC voltage) and the DC component of the charge voltage (charged DC voltage) at the time of image formation. The amount of fog toner may be increased. This potential difference corresponds to the potential difference between the charging potential of the photosensitive drum and the potential of the developing sleeve (DC component of the developing voltage). The potential difference may be changed by changing either the developed DC voltage or the charged DC voltage, or may be changed by changing both the developed DC voltage and the charged DC voltage. That is, the CPU 31 changes the setting of the potential difference between the voltage applied to the charging roller 2 for the charging process and the voltage applied to the developing sleeve 41 for supplying toner to the photosensitive drum 1 as the frictional force reducing process. can do. In this case, the CPU 31 can reduce the potential difference when the index value that correlates with the magnitude of the rotational speed fluctuation of the photosensitive drum 1 acquired based on the detection result of the encoder 24 becomes a predetermined threshold value or more. Alternatively, the CPU 31 can change the potential difference according to the index value. Specifically, the potential difference may be smaller when the index value is a second value larger than the first value than when the index value is the first value.

Further, as a friction force reduction process, even if the increase in the friction coefficient on the surface of the photosensitive drum is suppressed by changing the setting of the AC voltage of the charge voltage at the time of image formation and changing the discharge current at the time of the charge process. good. That is, the CPU 31 can change the setting of the discharge current during the charging process as the frictional force reducing process. In this case, the CPU 31 reduces the peak-to-peak voltage as the setting when the index value that correlates with the magnitude of the rotational speed fluctuation of the photosensitive drum 1 acquired based on the detection result of the encoder 24 becomes a predetermined threshold value or more. The discharge current can be reduced. Alternatively, the CPU 31 can change the discharge current by changing the peak voltage as the setting according to the index value. Specifically, the peak-to-peak voltage is smaller in the case of the second value larger than the first value than in the case where the index value is the first value so that the discharge current is reduced. do it.

Further, as the frictional force reducing process, the amount of the primary transfer residual toner may be increased by changing the setting of the primary transfer voltage (primary transfer current) at the time of image formation. That is, the CPU 31 can change the setting of the voltage applied to the primary transfer roller 5 for transfer as the frictional force reduction process. In this case, the CPU 31 has an absolute primary transfer voltage (primary transfer current) when the index value that correlates with the magnitude of the rotational speed fluctuation of the photosensitive drum 1 acquired based on the detection result of the encoder 24 becomes a predetermined threshold value or more. The value can be reduced. Alternatively, the CPU 31 can change the absolute value of the primary transfer voltage (primary transfer current) according to the index value. Specifically, the absolute value of the primary transfer voltage (primary transfer current) becomes smaller when the index value is a second value larger than the first value than when the index value is the first value. You can do it.

In the above-mentioned embodiment, the case where the lubricant supplied to the blade nip portion in the supply operation as the frictional force reducing treatment is toner (including the toner external additive) has been described. By using toner as a lubricant, a developing means can be used as a lubricant supply means, which is advantageous in terms of simplification of configuration and cost reduction as compared with the case where a separate supply means is provided. However, the present invention is not limited to this, and for example, a supply means for supplying a lubricant such as toner or fine particles similar to the toner's external additive to the blade nip portion may be provided separately from the developing means. good.

In the above-described embodiment, the case where the drive sources of the three photosensitive drums are shared as a plurality of photosensitive drums has been illustrated, but the present invention is not limited to this, and the photosensitive drums have a common drive source. The number of drums may be two or four or more. Further, in the above-described embodiment, the photosensitive drum has been described as being removable from the device main body of the image forming apparatus, but the photosensitive drum is configured so as not to be easily attached to and detached from the device main body of the image forming apparatus. May be.

In the above-described embodiment, the image forming apparatus has been described as adopting an intermediate transfer method, but the present invention can also be applied to a direct transfer type image forming apparatus. As is well known to those skilled in the art, a tandem type image forming apparatus adopting a direct transfer method has a recording material carrier composed of an endless belt or the like instead of the intermediate transfer body in the above-described embodiment. .. Then, the toner image formed on the photosensitive drum of each image forming portion is directly transferred to the recording material supported and conveyed on the recording material carrier in the same manner as the primary transfer in the image forming apparatus of the intermediate transfer method. .. By applying the present invention to such an image forming apparatus, the same effect as that of the above-described embodiment can be obtained. The present invention can also be applied to an image forming apparatus having only one image forming portion.

Further, the photoconductor is not limited to a drum-shaped one (photosensitive drum), and may be an endless belt-shaped one (photoreceptor belt). Further, the intermediate transfer body and the recording material carrier are not limited to the endless belt-shaped body, and may be, for example, a drum-shaped body formed by stretching a film on a frame body. Further, in the case of an electrostatic recording type image forming apparatus, the image carrier may be a drum-shaped or endless belt-shaped electrostatic recording dielectric.

Further, the present invention works particularly preferably when the cleaning member is a blade-shaped member, but the cleaning member is not limited to the blade-shaped member. For example, if it is a member such as a block-shaped (pad-shaped) or sheet-shaped member that may cause a problem due to an increase in frictional force with the image carrier, the above implementation can be performed by applying the present invention. The same effect as the example can be expected.

1 Photosensitive drum 2 Charging roller 3 Exposure device 4 Developing device 5 Primary transfer roller 6 Drum cleaning device 21 Drive motor 22 Drive shaft 24 Rotary encoder 31 Control unit

Claims (6)

A rotatable first image carrier that supports the toner image, and
A rotatable second image carrier that supports the toner image and
A first cleaning member that comes into contact with the first image carrier and removes toner from the first image carrier.
A second cleaning member that comes into contact with the second image carrier and removes toner from the second image carrier.
A first developing means for supplying toner to the first image carrier to form a toner image on the first image carrier, and
A second developing means for supplying toner to the second image carrier to form a toner image on the second image carrier, and
A common drive source for driving the first image carrier and the second image carrier ,
A first encoder that detects the rotation speed of the first image carrier, and
A second encoder that detects the rotation speed of the second image carrier, and
Toner is supplied to the first image carrier by the first developing means based on the detection result of the first encoder detected during the non-image forming period in which the toner is not supplied from the first developing means to the first image carrier. To control the first supply operation of supplying toner to the contact portion between the first image carrier and the first cleaning member, and the toner is not supplied from the second developing means to the second image carrier. Based on the detection result of the second encoder detected during the non-image formation period, toner is supplied to the second image carrier by the second developing means to supply the second image carrier and the second cleaning member. A control means for controlling the second supply operation of supplying toner to the contact portion of the
An image forming apparatus characterized by having . The first aspect of claim 1 is characterized in that the first encoder is attached to a drive shaft of the first image carrier , and the second encoder is attached to the drive shaft of the second image carrier. The image forming apparatus according to the description. The control means is the presence / absence of each execution of the first supply operation and the second supply operation, the amount of toner supplied in each of the first supply operation and the second supply operation, or the first supply operation and the said . The image forming apparatus according to claim 1 or 2, wherein the execution frequency of each of the second supply operations is changed. When the control means changes the presence or absence of each execution of the first supply operation and the second supply operation, the first is acquired based on the detection results of the first encoder and the second encoder . When the index value correlating with the magnitude of the rotation speed fluctuation of each of the image carrier and the second image carrier is equal to or greater than a predetermined threshold value, the first supply operation and the second supply operation are executed, respectively . When changing the amount of toner supplied in each of the first supply operation and the second supply operation, the index value correlates with the magnitude of the rotation speed fluctuation of each of the first image carrier and the second image carrier. The supply amount of each of the second value larger than the first value is larger than that of the first value, and each of the first supply operation and the second supply operation is performed. When changing the execution frequency of, the first value is higher than the first value, which correlates with the magnitude of the rotation speed fluctuation of each of the first image carrier and the second image carrier. The image forming apparatus according to claim 3, wherein each execution frequency is increased in the case of a second value larger than the value of. The image forming apparatus according to claim 4, wherein the control means obtains the index value by performing a fast Fourier transform process on the detection result. The control means is the non-image forming period of the preparation period for rotating the first image carrier and the second image carrier before the start of image formation, or the first image carrier and the said after the start of image formation. One of claims 1 to 5, wherein the detection results of the first encoder and the second encoder are acquired during the non-image formation period of the preparation period before stopping the second image carrier . The image forming apparatus according to item 1.

Images