JP7254571B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus using electrophotographic technology, such as a printer, copier, facsimile machine, or multi-function machine.

2. Description of the Related Art Conventionally, there has been proposed an intermediate transfer tandem type image forming apparatus in which a plurality of image forming units having photosensitive drums, developing devices, etc. are arranged along the moving direction of an intermediate transfer belt. In this image forming apparatus, a patch toner image for density detection is formed on an intermediate transfer belt, and based on the detection result of the patch toner image by a density sensor, the amount of misalignment between colors (color misalignment amount) and density unevenness are determined. Correction is possible (Patent Document 1). The density sensor is an optical sensor capable of irradiating the surface of the intermediate transfer belt with light and detecting the reflected light of the intermediate transfer belt and the reflected light of the patch toner image with respect to the irradiated light. are spaced apart.

In the image forming apparatus configured as described above, for example, a color mode in which an image is formed using the yellow, magenta, cyan, and black image forming units, and a monochrome mode in which an image is formed using only the black image forming unit are selectively selected. It is viable. In that case, all the photosensitive drums are in contact with the intermediate transfer belt in the color mode, while only the black photosensitive drum is in contact with the intermediate transfer belt in the monochrome mode, and the other photosensitive drums are separated from the intermediate transfer belt. It is

JP-A-2007-33571

By the way, when the intermediate transfer belt deteriorates, the amount of light reflected by the optical sensor decreases compared to when the intermediate transfer belt has not deteriorated. A decrease in reflected light from the intermediate transfer belt affects the detection result of the optical sensor. Therefore, conventionally, in a state in which all the photosensitive drums are in contact with the intermediate transfer belt (color mode), an optical sensor is used so that the detection result of the optical sensor is not affected even if the reflected light from the intermediate transfer belt is reduced. It is made possible to adjust the light intensity of the irradiated light.

However, as described above, in the monochrome mode, only the black photosensitive drum is in contact with the intermediate transfer belt, and in this state the distance between the intermediate transfer belt and the optical sensor is different from that in the color mode. If the distance between the intermediate transfer belt and the optical sensor is not the same, even if the intermediate transfer belt is irradiated with the same amount of light, the intensity of the reflected light from the intermediate transfer belt detected by the optical sensor may vary. That is, even if the density of the actual patch toner image is the same, the density of the patch toner image based on the detection result of the optical sensor may differ. Despite this possibility, conventionally, the amount of light emitted by the optical sensor was adjusted while all the photosensitive drums were in contact with the intermediate transfer belt. Such image defects tended to occur.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of adjusting the amount of light emitted by an optical sensor so as not to cause image defects such as density unevenness even in monochrome mode.

An image forming apparatus according to an embodiment of the present invention includes a first image carrier and a second image carrier that each carry a toner image and rotate, a rotating intermediate transfer belt, and the intermediate transfer belt that is stretched. a plurality of stretching members, a first transfer member for transferring the toner image of the first image carrier to the intermediate transfer belt, and a second transfer member for transferring the toner image of the second image carrier to the intermediate transfer belt. moving a member, an optical sensor spaced apart from the intermediate transfer belt so as to irradiate the intermediate transfer belt with light and receive reflected light of the irradiated light, and the first transfer member; a contacting/separating mechanism for contacting/separating the intermediate transfer belt from/to the first image carrier; a first light amount adjustment mode for adjusting the amount of light to be irradiated to the sensor; and a control means capable of executing two light amount adjustment modes, wherein the control means forms an image while the first image carrier and the second image carrier are in contact with the intermediate transfer belt. at the end of the first image forming job, the first transfer member is moved to separate the intermediate transfer belt from the first image carrier, the second light amount adjustment mode is executed, and only the second image carrier is is in contact with the intermediate transfer belt, the first transfer member is moved to bring the intermediate transfer belt into contact with the first image carrier, and the second image forming job is completed. It is characterized by executing one light quantity adjustment mode .

According to the present invention, the optical sensor is irradiated with the first image carrier and the second image carrier in contact with the intermediate transfer belt, and with only the second image carrier in contact with the intermediate transfer belt. By adjusting the amount of light to be applied, it is possible to easily prevent image defects such as density unevenness from occurring.

1 is a schematic diagram showing the configuration of an image forming apparatus according to the present embodiment; FIG. 3A and 3B are perspective views showing an intermediate transfer unit, in which (a) shows a state where an intermediate transfer belt is attached, and (b) shows a state where the intermediate transfer belt is removed. 4A and 4B are schematic diagrams for explaining a concentration sensor; FIG. 4A and 4B are schematic diagrams for explaining a spacing mechanism, in which (a) is in color mode and (b) is in monochrome mode; Schematic diagram showing a separation slider. FIG. 2 is a control block diagram for explaining a control unit; 4A and 4B are graphs for explaining the light amount adjustment of the density sensor, in which (a) is a graph showing the time change of the sensor output, and (b) is a graph showing the relationship with the light amount determined based on the sensor output; 4A and 4B are schematic diagrams showing an intermediate transfer unit, in which (a) is in a color mode and (b) is in a monochrome mode; 4A and 4B are diagrams for explaining the distance between the surface of the intermediate transfer belt and the optical sensor in color mode and monochrome mode; FIG. 4 is a flowchart showing light amount adjustment processing according to the embodiment;

<Image forming apparatus>
First, an overview of the image forming apparatus of this embodiment will be described with reference to FIG. The image forming apparatus 100 shown in FIG. 1 has four color (yellow, cyan, magenta, and black) image forming units PY, PM, PC, and PK arranged opposite to an intermediate transfer belt 101 in the main body of the apparatus. This is a tandem type color image forming apparatus. In the present embodiment, an intermediate transfer belt unit 200 (see FIGS. 2A and 2B), which will be described later in detail, is removably supported by a support frame (not shown) in the apparatus main body 100a.

A recording material conveying process of the image forming apparatus 100 will be described. The recording materials S are stored in a stack in a cassette 120, and fed one by one to a conveying path by a paper feed roller 121 in accordance with image forming timing. Also, the recording materials S stacked on a manual feed tray (not shown) or a stacking device may be fed to the transport path one by one. When the recording material S is conveyed to the registration rollers 122 arranged in the middle of the conveyance path, the registration rollers 122 perform skew correction and timing correction on the recording material S, and then the recording material S is sent to the secondary transfer portion T2. The secondary transfer portion T2 is a transfer nip formed by a secondary transfer inner roller 110 and a secondary transfer outer roller 111 facing each other. A secondary transfer inner roller 110 presses the intermediate transfer belt 101 from the inside to form a transfer portion of the toner image on the recording material S. As shown in FIG. In the secondary transfer portion T2, a secondary transfer voltage is applied to the secondary transfer outer roller 111 by a power source (not shown), and current flows between the secondary transfer outer roller 111 and the secondary transfer inner roller 110. Thus, the toner image is secondarily transferred from the intermediate transfer belt 101 to the recording material S.

A process of forming an image sent to the secondary transfer portion T2 at the same timing as the above-described process of conveying the recording material S to the secondary transfer portion T2 will be described. First, the image forming units PY to PK will be described. However, the image forming units PY to PK have almost the same configuration except that the toner colors used in the developing devices 106Y, 106M, 106C, and 106K are different from yellow, magenta, cyan, and black. Therefore, the yellow image forming station PY will be described below as a representative example, and descriptions of the other image forming stations PM, PC, and PK will be omitted.

The image forming unit PY mainly includes a photosensitive drum 103Y, a charging device 104Y, an exposure device 105Y, a developing device 106Y, a drum cleaner 108Y, and the like. The surface of the photosensitive drum 103Y rotationally driven in the direction of arrow R1 in the drawing is uniformly charged in advance by a charging device 104Y, and then an exposure device 105Y (laser scanner unit) driven based on a signal of image information. forms an electrostatic latent image. Next, the electrostatic latent image formed on the photosensitive drum 103Y is visualized through toner development using developer by the developing device 106Y. After that, a predetermined pressure and a primary transfer voltage are applied by a primary transfer roller 107Y arranged to face the image forming portion PY with the intermediate transfer belt 101 interposed therebetween. Primary transfer is performed on the top. The toner remaining on the photosensitive drum 103Y after the primary transfer is collected by the drum cleaner 108Y and reused in the next image forming process.

The endless intermediate transfer belt 101 is stretched by a tension roller 112, a secondary transfer inner roller 110, and tension rollers (also called idler rollers) 113 and 114 as tension members, and moves in the direction of arrow R2 in the figure. driven to move. In this embodiment, the inner secondary transfer roller 110 also serves as a drive roller for driving the intermediate transfer belt 101 . The image forming process of each color processed by the above image forming units PY to PK is performed at the timing of sequentially superimposing on the toner image of the color upstream in the movement direction primarily transferred onto the intermediate transfer belt 101 . As a result, a full-color toner image is finally formed on the intermediate transfer belt 101 and conveyed to the secondary transfer portion T2. Note that the toner remaining on the intermediate transfer belt 101 after passing through the secondary transfer portion T2 is removed from the intermediate transfer belt 101 by the belt cleaning device 102 .

With the conveying process and the image forming process described above, the timings of the recording material S and the full-color toner image are matched at the secondary transfer portion T2, and the toner image is secondarily transferred from the intermediate transfer belt 101 to the recording material S. After that, the recording material S is conveyed to the fixing device 130 , and the toner image is fixed on the recording material S by applying pressure and heat to the recording material S by the fixing device 130 . The recording material S on which the toner image is thus fixed is discharged onto a paper discharge tray 124 by a paper discharge roller 123 .

The primary transfer rollers 107Y to 107K, the intermediate transfer belt 101, the tension roller 112, the tension rollers 113 and 114, the inner secondary transfer roller 110, etc. are integrated as an intermediate transfer belt unit 200 (hereinafter simply referred to as a belt unit). is provided. The belt unit 200 is detachably provided in the apparatus main body 100a. That is, the intermediate transfer belt 101 and the secondary transfer inner roller 110 are likely to deteriorate with use and have a short durability life compared to others, and therefore need to be replaced. Make it removable. Although not shown, the apparatus main body 100a is provided with an opening through which the belt unit 200 can be freely inserted and removed. In the case of this embodiment, the direction of insertion of the belt unit 200 into the apparatus main body 100 a is the direction that intersects the rotation axis direction of the inner secondary transfer roller 110 .

<Belt unit>
The belt unit 200 is shown in FIGS. 2(a) and 2(b). 2A shows a state in which the intermediate transfer belt 101 is mounted, and FIG. 2B shows a state in which the intermediate transfer belt 101 is not mounted. In the belt unit 200, the tension roller 112, the tension rollers 113 and 114, and the inner secondary transfer roller 110 are rotatably supported at both ends in the direction of the rotation axis in such a manner that they are sandwiched between the front frame 21F and the rear frame 21R. ing. The front frame 21F is arranged on the front side of the image forming apparatus 100 shown in FIG. 1, and the rear frame 21R is arranged on the back side of the image forming apparatus 100 shown in FIG. The tension roller 112 is rotatably supported by a tension bearing 23 provided at one end of the front frame 21F and the rear frame 21R.

A drive coupling 22 is attached to one end portion of the inner secondary transfer roller 110 in the direction of the rotational axis. A drive force can be transmitted to the drive coupling 22 by being connected to an output shaft of a belt drive unit (not shown) provided in the apparatus main body 100a. The inner secondary transfer roller 110 has a conductive surface and is made of a material having a relatively high coefficient of friction, such as conductive rubber. The transfer belt 101 can be driven. In this embodiment, the drive coupling 22 is used as the drive transmission means with the apparatus main body 100a, but a gear may be used.

A tension spring 25, which is a compression spring, is arranged between the tension bearing 23 and the front frame 21F and the rear frame 21R. By contracting the tension spring 25 in the state shown in FIG. 2A, tension is applied to the intermediate transfer belt 101 via the tension roller 112 while the intermediate transfer belt 101 is mounted. The primary transfer rollers 107Y to 107K (see FIG. 1) are metal rollers made of metal having a volume resistivity of 600 Ωcm or less, for example. A primary transfer voltage for primary transfer of the toner image onto the intermediate transfer belt 101 is applied to the primary transfer rollers 107Y to 107K by corresponding power supply units HVa to HVd.

<Concentration sensor>
As shown in FIG. 1, in the image forming apparatus 100 of the present embodiment, the density sensor 141 detects the difference between the primary transfer portion T1 and the secondary transfer portion T2 of the black image forming portion PK with respect to the moving direction of the intermediate transfer belt 101. It is provided facing the outer peripheral surface of the intermediate transfer belt 101 between them. The density sensor 141 is spaced apart from the intermediate transfer belt 101 so as to irradiate the intermediate transfer belt 101 with light and receive the reflected light of the irradiated light. In this embodiment, the density sensor 141 is arranged downstream of the photosensitive drum 103K and upstream of the tension roller 114 with respect to the direction of movement of the intermediate transfer belt 101 (direction of arrow R2 in the figure). Therefore, as will be described later, it can be said that the density sensor 141 is likely to be affected by the stretched state of the intermediate transfer belt 101 that differs between the color mode and the monochrome mode.

The density sensor 141 will be described with reference to FIG. The density sensor 141 is a reflective optical sensor, and as shown in FIG. The density sensor 141 has a light emitting portion 301 such as an LED, a first light receiving portion 302 and a second light receiving portion 303 such as a photodiode, and a light amount control board 304 for controlling the amount of light emitted from the light emitting portion 301 .

The light emitting unit 301 irradiates the intermediate transfer belt 101 with light such as infrared light at an angle of 45 degrees with respect to the normal line of the intermediate transfer belt 101, for example. The first light receiving portion 302 receives specularly reflected light from the surface of the intermediate transfer belt 101 on which the patch toner image 307 is not formed and from the patch toner image 307 obtained by irradiating the light from the light emitting portion 301 . On the other hand, the second light-receiving unit 303 emits light from the light-emitting unit 301 and diffuses reflected light scattered by the surface of the intermediate transfer belt 101 on which the patch toner image 307 is not formed and the patch toner image 307 . receive light. The density sensor 141 is formed of epoxy resin, for example, in order to create a path for light emitted by the light emitting section 301 and a path for light received by the first light receiving section 302 and the second light receiving section 303 . A lens 306 is provided on the intermediate transfer belt 101 side.

Since specularly reflected light from the intermediate transfer belt 101 mainly enters the first light receiving portion 302, the amount of reflected light received by the first light receiving portion 302 decreases when the patch toner image 307 is formed on the intermediate transfer belt 101. do. On the other hand, the amount of diffusely reflected light from the surface of the intermediate transfer belt 101 and the black patch toner image 307 is smaller than that from the yellow, magenta, and cyan patch toner images 307 . As the area density of the color toner increases, the amount of diffusely reflected light increases, so the amount of light received by the second light receiving unit 303 increases. Since the output level (current value) of density sensor 141 is proportional to the amount of light received by first light receiving section 302 and second light receiving section 303 , the density of patch toner image 307 can be grasped based on the output level of density sensor 141 .

The light amount control board 304 is a circuit that adjusts the voltage applied to the light emitting section 301 to control the light emission amount of the light emitting section 301 . Further, the light amount control board 304 is mounted with a light receiving circuit having an IV conversion function for voltage conversion of the current flowing according to the amount of light received by the first light receiving section 302 and the second light receiving section 303 . As the amount of light emitted from the light emitting unit 301 is changed by the light amount control board 304, the amount of reflected light from the same target irradiated with light can be varied. That is, when the amount of light emitted from the light emitting unit 301 is increased, the amount of reflected light from the surface of the intermediate transfer belt 101 and the patch toner image 307 can be increased proportionally. The light amount control board 304 can operate the light emitting unit 301 with an amount of emitted light suitable for detecting the density of the patch toner image 307 .

In order to prevent the light emitted by the light emitting unit 301 from being directly received by the first light receiving unit 302 and the second light receiving unit 303, the density sensor 141 is provided with a shield made of, for example, black resin. A member 305 is provided. A shutter 308 is provided so as to block the density sensor 141 and the intermediate transfer belt 101 . That is, the shutter 308 is moved to the position indicated by the solid line and opened when detection is performed by the density sensor 141 . On the other hand, the shutter 308 is moved in front of the density sensor 141 indicated by the dotted line and closed when the density sensor 141 does not perform detection. As a result, the light-emitting portion 301, the first light-receiving portion 302, and the second light-receiving portion 303 can be prevented from being stained with toner or the like, so that the density sensor 141 can detect the density of the patch toner image 307 appropriately. there is

<Contact and separation mechanism>
In the image forming apparatus 100 of the present embodiment, the image forming modes are a color mode in which image formation is performed using all of the image forming units PY to PK, and a monochrome mode in which image formation is performed using only the black image forming unit PK. is selectively executable. As described above, generally, in the monochrome mode, the photosensitive drums 103Y, 103M, and 103C (first image carriers) of the image forming units PY, PM, and PC, which do not form images other than black, are connected to the intermediate transfer belt 101. are separated from In this case, among the plurality of photosensitive drums 103Y to 103K, only one photosensitive drum 103K (second image bearing member) of the black image forming portion PK is brought into contact with the intermediate transfer belt 101 to form an image. To do so, the image forming apparatus 100 includes a contact/separation mechanism 50 for contacting/separating the photosensitive drums 103Y, 103M, and 103C from the intermediate transfer belt 101, as shown in FIGS. 4(a) and 4(b). It has

An example of the contact/separation mechanism 50 will be described with reference to FIGS. 4(a) to 5 while referring to FIG. As shown in FIGS. 4A and 4B, the contact/separation mechanism 50 has primary transfer bearings 29Y to 29K, a separation slider 26, a separation cam 27, and a separation shaft . The primary transfer bearings 29Y-29K rotatably support both ends of the primary transfer rollers 107Y-107K. The primary transfer bearings 29Y to 29K restrict the reciprocating motion of the intermediate transfer belt 101 in the moving direction (the direction of arrow R2 in the figure) to the front frame 21F and the rear frame 21R, respectively, but also in the direction intersecting the moving direction. It is held so that it can be raised and lowered. One end of the primary transfer bearings 29Y to 29K is connected to the other ends of primary transfer springs SPY to SPK fixed to the front frame 21F and the rear frame 21R. The primary transfer springs SPY to SPK urge the primary transfer bearings 29Y to 29K in the direction toward the intermediate transfer belt 101, respectively.

Note that the tension roller 113 arranged upstream in the moving direction of the intermediate transfer belt 101 from the primary transfer roller 107Y may have the same configuration as the primary transfer rollers 107Y to 107K. That is, the tension roller 113 is rotatably supported by a tension roller bearing 29a, and the tension roller bearing 29a is biased toward the intermediate transfer belt 101 by a tension roller spring SPa.

A spacing coupling 24 (see FIG. 2) is attached to one axial end of the spacing shaft 28 . The separation coupling 24 is connected to a driving source (not shown) to transmit the driving force. The separation shaft 28 is provided with a separation cam 27 for urging the slide biasing surfaces 26d of the separation sliders 26 provided in the front frame 21F and the rear frame 21R to cause the separation sliders 26 to slide. there is As shown in FIG. 5, the separation slider 26 has primary transfer roller elevating surfaces 26Y to 26C, a tension roller elevating surface 26a, and a slide biasing surface 26d.

When switching from the color mode shown in FIG. 4(a) to the monochrome mode shown in FIG. 4(b), the drive force of the drive source (not shown) is transmitted to the separation coupling 24 (see FIG. 2). . In conjunction with the rotation of the separation coupling 24 by this driving force, the separation cam 27 rotates in the direction of arrow R3 in FIG. 4(a). At this time, the separation coupling 24 urges the slide urging surface 26d (see FIG. 5) of the separation slider 26, so that the separation slider 26 slides in the moving direction of the intermediate transfer belt 101 (arrow R2 direction in the drawing). Moving. As the separation slider 26 slides, the projections 29Y1, 29M1 and 29C1 of the primary transfer bearings 29Y, 29M and 29C are pushed up by the primary transfer roller elevating surfaces 26Y, 26M and 26C of the separation slider 26. That is, the primary transfer bearings 29Y, 29M, and 29C move away from the intermediate transfer belt 101 . Thus, the primary transfer rollers 107Y, 107M, and 107C as first transfer members are separated from the intermediate transfer belt 101 . A primary transfer roller 107K as a second transfer member is kept in contact with the intermediate transfer belt 101 .

Similarly, as the separation slider 26 slides, the protrusion 29a1 of the tension roller bearing 29a is pushed up by the tension roller elevating surface 26a of the separation slider 26. FIG. However, the distance between the tension rollers 113 is smaller than the distance between the primary transfer rollers 107Y, 107M, and 107C (see FIG. 5). Therefore, the intermediate transfer belt 101 is kept stretched by the tension roller 113 (FIG. 4B). In this way, the primary transfer rollers 107Y, 107M, and 107C are separated from the intermediate transfer belt 101, and the tension roller 113 is moved away from the intermediate transfer belt 101 to the extent that it does not separate from the intermediate transfer belt 101. The suspension state changes. Thereby, the intermediate transfer belt 101 can be separated from the photosensitive drums 103Y, 103M, and 103C.

On the other hand, switching from the monochrome mode (FIG. 4(b)) to the color mode (FIG. 4(a)) is performed by rotating the separation cam 27 in the direction opposite to the direction of arrow R3 in FIG. 4(a). As a result, an operation that follows the procedure opposite to the separation operation described above is performed, and an approaching operation in which the primary transfer rollers 107Y, 107M, and 107C approach the intermediate transfer belt 101 is realized. Although description of the approaching operation is omitted here, all of the primary transfer rollers 107Y to 107K come into contact with the intermediate transfer belt 101 due to this approaching operation. By switching the stretched state of the intermediate transfer belt 101 from the monochrome mode to the color mode in this manner, the intermediate transfer belt 101 can come into contact with all of the photosensitive drums 103Y to 103K.

<Control part>
Further, as shown in FIG. 1 , the image forming apparatus 100 includes a control section 500 . The control unit 500 will be explained using FIG. Note that the control unit 500 applies voltages to, for example, various motors for driving the photosensitive drums 103Y to 103K and the secondary transfer inner roller 110, the primary transfer rollers 107Y to 107K, and the secondary transfer outer roller 111, in addition to those shown in the drawings. Various power sources, the fixing device 130, and the like are connected. However, since it is not the gist of the invention here, illustration and description thereof are omitted.

A control unit 500 as a control means performs various controls of the image forming apparatus 100 such as image forming operation, and has a CPU (Central Processing Unit) 501 and a memory 502, for example. A memory 502 includes a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and stores various programs and data for controlling the image forming apparatus 100 . The CPU 501 can execute an image forming job (program) stored in the memory 502 to operate the image forming apparatus 100 to form an image. In the case of this embodiment, the CPU 501 can execute the “light amount adjustment process” (see FIG. 10 described later) stored in the memory 502 . Note that the memory 502 can temporarily store arithmetic processing results and the like associated with the execution of various programs.

An operation unit 400 is connected to the control unit 500 via an input/output interface. The operation unit 400 is, for example, an external terminal such as a scanner or a personal computer, or an operation panel, which receives a user's instruction to start various programs such as an image forming job, input of various data, and the like. In the present embodiment, the user can use the operation unit 400 to specify either a color mode capable of forming a color image on the recording material S or a monochrome mode capable of forming a black monochrome image on the recording material S. is. When the operation unit 400 issues an instruction to start an image forming job in any of the above print modes, the control unit 500 performs image forming processing stored in the memory 502 based on the image data input from the operation unit 400. to run (a program); The control unit 500 controls the image forming apparatus 100 based on execution of image forming processing.

An image forming job is a series of operations based on a print signal for forming an image on the recording material S, from the start of image formation to the completion of the image forming operation. That is, after starting a preliminary operation (so-called pre-rotation) necessary for image formation, the image forming process is performed, and then a preliminary operation (so-called post-rotation) necessary for completing image formation is completed. It is a series of actions up to Specifically, it refers to the period from the time of pre-rotation (preparatory operation before image formation) after receiving a print signal to the time of post-rotation (operation after image formation), including the image formation period and the interval between sheets.

Further, the concentration sensor 141 described above is connected to the control unit 500 via an input/output interface. As described above, the density sensor 141 detects reflected light from the patch toner image formed on the intermediate transfer belt 101 and reflected light from the surface of the intermediate transfer belt 101 on which no patch toner image is formed. The control unit 500 transmits a emitted light amount signal (current value) to the light amount control board 304 (see FIG. 3) of the density sensor 141 so that the reflected light amount of the reflected light reaches a predetermined light amount level. Accordingly, the control unit 500 receives from the density sensor 141 a reflected light amount signal (current value) obtained by light irradiation, and detects the density of the patch toner image based on this. In this embodiment, the memory 502 stores a light emission signal for the color mode and a light emission signal for the monochrome mode, and the controller 500 uses the light emission signal corresponding to the selected print mode. These color mode emission light amount signal and monochrome mode emission light amount signal are stored in the memory 502 along with the execution of a "light amount adjustment process" (see FIG. 10, which will be described later).

Further, the contact/separation mechanism 50 described above is connected to the control unit 500 via an input/output interface. The control unit 500 slides the separation slider 26 (see FIG. 4A) of the contact/separation mechanism 50 as described above, thereby separating the intermediate transfer belt 101 and the photosensitive drums 103Y to 103C according to the selected print mode. can be spaced apart or abutted.

Next, the light amount adjustment of the density sensor 141 (that is, the adjustment of the emitted light amount signal) will be described. When the amount of reflected light received by the density sensor 141 decreases due to deterioration of the intermediate transfer belt 101 or other factors, the output of the density sensor 141 decreases and the dynamic range in measuring the toner density decreases. In that case, the density sensor 141 may not be able to detect the density of the patch toner image 307 properly. Therefore, it is necessary to adjust the light amount of the density sensor 141 to return the output of the density sensor 141 to a predetermined output. Although it is publicly known, a method for adjusting the amount of light for the density sensor 141 will be described below with reference to FIGS. 7A and 7B while referring to FIG.

In adjusting the light amount of the density sensor 141, the current flowing through the light emitting portion 301 of the density sensor 141 is divided into three levels, and the light emitting portion 301 sequentially irradiates the surface of the intermediate transfer belt 101 with light for a predetermined time. FIG. 7A shows the output waveform of the density sensor 141 that is output in such a case. As shown in FIG. 7A, as a result of irradiating light while dividing the current into three stages, the output waveform of the density sensor 141 also has three levels of waveforms depending on the magnitude of the current.

Then, based on the output waveform of the density sensor 141, the output levels of 8 points (P11 to P18, P21 to P28, P31 to P38) are detected for each stage, and the average value thereof is calculated. Then, based on the calculated average levels (P1ave, P2ave, P3ave), the amount of light at which the output level of the density sensor 141 becomes the target value (the target sensor output in FIG. 7B) is determined. Specifically, as shown in FIG. 7B, the calculated average level is linearly interpolated to determine the amount of light that makes the output level of the density sensor 141 the target value. If the target output level is not reached even if the current flowing through the light-emitting portion 301 is maximized, the specular reflection output gain of the density sensor 141 is switched, and the current flowing through the light-emitting portion 301 is set in three levels again. It suffices to irradiate the light in order by dividing it.

<Effect on density sensor>
Next, the effect on the density sensor 141 due to the difference in the stretched state of the intermediate transfer belt 101 between the color mode and the monochrome mode will be described with reference to FIGS. As described above, by switching from the color mode to the monochrome mode, the stretched state of the intermediate transfer belt 101 changes from the stretched state shown in FIG. 8A to the stretched state shown in FIG. 8B. In the case of the stretched state shown in FIG. 8B, the excess length L generated in the intermediate transfer belt 101 due to the change from the stretched state shown in FIG. . However, in such a case, the tension spring 25 is in an extended state, and the biasing force of the tension spring 25 to the intermediate transfer belt 101 is reduced. As a result, the tension of the intermediate transfer belt 101 at the primary transfer portion T1 formed at the most downstream in the moving direction of the intermediate transfer belt 101 is reduced.

In this way, the tension applied to the intermediate transfer belt 101 by the primary transfer rollers 107Y to 107K differs between the color mode (FIG. 8A) and the monochrome mode (FIG. 8B). Also, a difference may occur in the amount of deformation of the tension rollers 113 and 114 . In that case, the surface position of the intermediate transfer belt 101 differs between the color mode and the monochrome mode. Specifically, since the tension applied to the intermediate transfer belt 101 is higher in the color mode than in the monochrome mode, the deformation amount of the tension roller 114 is larger. As shown in FIG. 9, the density sensor 141 is located downstream of the photosensitive drum 103K and upstream of the tension roller 114 with respect to the direction of movement of the intermediate transfer belts (101CL, 101Bk) (direction of arrow R2 in the drawing). are placed. Therefore, the surface position (solid line) of the intermediate transfer belt 101CL in the color mode is offset from the surface position (dotted line) of the intermediate transfer belt 101Bk in the monochrome mode from the Z2 direction to the Z1 direction. That is, the distance between the surface of the intermediate transfer belt 101 and the density sensor 141 (specifically, the light emitting unit 301, the first light receiving unit 302, and the second light receiving unit 303) differs between the color mode and the monochrome mode. In this case, even if the same amount of light is emitted from the density sensor 141 , the intensity of the reflected light from the intermediate transfer belt 101 may vary depending on the interval, and the output of the density sensor 141 may be affected.

Nevertheless, conventionally, in order to correct the density unevenness of a monochrome image, a toner patch image is formed on the intermediate transfer belt 101 after adjusting the light amount of the density sensor 141 in the color mode, and the density is detected by the density sensor. 141 (density correction). As described above, conventionally, the light amount of the density sensor 141 is adjusted in a state in which all the photosensitive drums 103Y to 103K are in contact with the intermediate transfer belt 101 (color mode), so density unevenness occurs in the monochrome mode. It was easy. In particular, when the primary transfer rollers 107Y to 107K are metal rollers and, as described above, the primary transfer rollers 107Y to 107C are separated from the intermediate transfer belt 101 in the monochrome mode (FIG. 4B). It was noticeable.

<Light intensity adjustment processing>
Therefore, in this embodiment, the density sensor 141 is designed so that the reflected light from the intermediate transfer belt 101 detected by the density sensor 141 is not affected when the same amount of light is irradiated in the monochrome mode and the color mode. The amount of light emitted by is adjustable. The light amount adjustment processing of this embodiment will be described below using FIG. 10 while referring to FIG. 6 . The light amount adjustment process of the present embodiment is started by the control unit 500 when an image forming job start instruction is input from the operation unit 400 .

As shown in FIG. 10, the control unit 500 receives a print signal transmitted from the operation unit 400 (S1). If the print mode is the monochrome mode and the intermediate transfer belt 101 and the photosensitive drums 103Y to 103C are in contact with each other, the controller 500 separates the photosensitive drums 103Y to 103C from the intermediate transfer belt 101. That is, only the black photosensitive drum 103K is brought into contact with the intermediate transfer belt 101. FIG. On the other hand, if the print mode is the full-color mode and the intermediate transfer belt 101 and the photosensitive drums 103Y to 103C are separated from each other, the intermediate transfer belt 101 is brought into contact with the photosensitive drums 103Y to 103C. That is, the intermediate transfer belt 101 is brought into contact with all the photosensitive drums 103Y to 103K.

After that, the control unit 500 determines whether or not it is time to execute the density correction mode based on the density correction information (S2). In the density correction mode, a patch toner image for density detection is formed on the intermediate transfer belt 101, and based on the detection result of the patch toner image by the density sensor 141, the deviation amount (color deviation amount) between colors and density unevenness are corrected. This is a process for correcting the Here, as the density correction information, for example, the temperature outside the machine, the temperature of the laser scanner unit (exposure device), the elapsed time from the end of the previous image forming job, and the cumulative total of image formation after execution of the previous density correction mode are recorded. The number of sheets of material S, etc. are mentioned. If it is not the timing to execute the density correction mode (No in S2), the control unit 500 jumps to the process of step S7. On the other hand, if it is time to execute the density correction mode (Yes in S2), the control unit 500 determines whether the print mode is the monochrome mode based on the print signal (S3).

If the print mode is the monochrome mode (Yes in S3), the controller 500 adjusts the light intensity of the density sensor 141 (second light intensity adjustment mode) while only the black photosensitive drum 103K is in contact with the intermediate transfer belt 101. (S4). Thereafter, the controller 500 performs density correction using the toner patch image (S6). The emitted light amount signal obtained by the light amount adjustment here is stored in the memory 502 and referred to as the emitted light amount signal for monochrome mode.

If the print mode is not the monochrome mode (No in S3), the control unit 500 adjusts the light amount of the density sensor 141 (first light amount adjustment mode) while all the photosensitive drums 103Y to 103K are in contact with the intermediate transfer belt 101. (S5). After that, the controller 500 executes the density correction mode using the toner patch image (S6). The emitted light amount signal obtained by the light amount adjustment here is stored in the memory 502 and referred to as the emitted light amount signal for the color mode. As described above, in the present embodiment, the state of contact between the intermediate transfer belt 101 and the photosensitive drums 103Y to 103K is varied according to the print mode during the pre-rotation of an image forming job or between sheets during an image forming job. Light amount adjustment of the density sensor 141 is performed. Then, after the light quantity adjustment of the density sensor 141 is performed, the density correction mode is performed.

After executing the light quantity adjustment (S4, S5) and the density correction (S6), the control unit 500 executes image formation (S7). Then, the control unit 500 determines whether or not to end the image forming job (S8). If the image forming job is not to be ended (No in S8), the control unit 500 returns to the process of step S2 and repeats the processes of S2 to S7. When the image forming job is finished (Yes in S8), the control unit 500 determines whether or not the light amount of the density sensor 141 has been adjusted during the image forming job (S9). If the light intensity of the density sensor 141 has not been adjusted during the image forming job (No in S9), the controller 500 ends the light intensity adjustment process.

On the other hand, if the light amount of the density sensor 141 is adjusted during the image forming job (Yes in S9), the control unit 500 determines whether or not the print mode of the completed image forming job is monochrome mode (S10). . If the mode is the monochrome mode (Yes in S10), the control unit 500 operates the contact/separation mechanism 50 to bring the photosensitive drums 103Y to 103C into contact with the intermediate transfer belt 101, and then adjusts the light amount of the density sensor 141 in the contact state. (First light amount adjustment mode) is performed (S11). That is, the control unit 500 changes the state in which only the black photosensitive drum 103K is in contact with the intermediate transfer belt 101 to the state in which all the photosensitive drums 103Y to 103K are in contact with the intermediate transfer belt 101. FIG. Then, the control unit 500 adjusts the light amount of the density sensor 141 in a state in which all the photosensitive drums 103Y to 103K are in contact with the intermediate transfer belt 101 (image formation possible in color mode). Here, it is not necessary to execute the density correction mode using the toner patch image after adjusting the light amount of the density sensor 141 . The emitted light amount signal obtained by the light amount adjustment here is stored in the memory 502 as the emitted light amount signal for the color mode, and is referred to in the next image forming job in the color mode.

On the other hand, if the color mode is selected instead of the monochrome mode (No in S10), the control unit 500 operates the contact/separation mechanism 50 to separate the photosensitive drums 103Y to 103C from the intermediate transfer belt 101, and then, in the separated state, the density sensor. Light amount adjustment of 141 is performed (S12). That is, the control unit 500 shifts from a state in which all the photosensitive drums 103Y to 103K are in contact with the intermediate transfer belt 101 to a state in which only the black photosensitive drum 103K is in contact with the intermediate transfer belt 101. FIG. Then, the control unit 500 adjusts the light amount of the density sensor 141 in a state in which only the black photosensitive drum 103K is brought into contact with the intermediate transfer belt 101 (a state in which image formation is possible in monochrome mode) (second light amount adjustment mode). . Here, it is not necessary to execute the density correction mode using the toner patch image after adjusting the light amount of the density sensor 141 . The emission light amount signal obtained by the light amount adjustment here is stored in the memory 502 as the emission light amount signal for monochrome mode, and is referred to in the next monochrome mode image forming job. After executing the light amount adjustment (S11, S12) of the density sensor 141 described above, the control unit 500 ends the light amount adjustment process.

As described above, according to the present embodiment, in the monochrome mode (during the second image forming job), the light amount of the density sensor 141 is adjusted while only the black photosensitive drum 103K is brought into contact with the intermediate transfer belt 101. was made to take place. In the color mode (during the first image forming job), the light amount of the density sensor 141 is adjusted while all the photosensitive drums 103Y to 103K are in contact with the intermediate transfer belt 101. FIG. That is, the light amount adjustment mode is executed in the same contact state between the intermediate transfer belt 101 and the photosensitive drums 103Y to 103K as in the image forming job. As a result, the density sensor 141 (optical sensor) controls the amount of light emitted to the intermediate transfer belt 101 so that there is no difference in the reflected light of the light emitted to the intermediate transfer belt 101 between the monochrome mode and the color mode. You will be able to adjust the amount of light. Therefore, it is possible to easily prevent image defects such as density unevenness from occurring not only in the color mode but also in the monochrome mode.

Also, when the light amount adjustment mode is executed in the color mode, the light amount adjustment mode in the monochrome mode is executed at the end of the image forming job (first image forming job). Then, when the light amount adjustment mode is executed in the monochrome mode, the light amount adjustment mode in the color mode is executed at the end of the image forming job (second image forming job). By doing so, even if an image forming job is performed in a different image forming mode from the previous image forming job, such as during pre-rotation for the next image forming job or when returning from the standby state, It is not necessary to execute the light amount adjustment mode of Therefore, efficient operation of the image forming apparatus 100 can be realized.

50 Contact and separation mechanism 100 Image forming apparatus 101 Intermediate transfer belt 103Y, 103M, 103C First image carrier (photosensitive drum) 103K Second image carrier (photosensitive drum) 107Y, 107M, 107C, 107K...Transfer member (primary transfer roller) 113, 114...Tension member (tension roller) 141...Optical sensor (density sensor) 307...Toner image for control (patch toner image) 500...Control means (control part)

Claims (3)

a first image carrier and a second image carrier, each carrying a toner image and rotating;
a rotating intermediate transfer belt;
a plurality of stretching members for stretching the intermediate transfer belt;
a first transfer member that transfers the toner image of the first image carrier to the intermediate transfer belt;
a second transfer member that transfers the toner image of the second image carrier to the intermediate transfer belt;
an optical sensor arranged at a distance from the intermediate transfer belt so as to irradiate the intermediate transfer belt with light and receive reflected light of the irradiated light;
a contact/separation mechanism for moving the first transfer member to bring the intermediate transfer belt into contact with and separate from the first image carrier;
a first light amount adjustment mode for adjusting the amount of light emitted to the optical sensor while the first image carrier and the second image carrier are in contact with the intermediate transfer belt; and the second image carrier. a control means capable of executing a second light amount adjustment mode for adjusting the amount of light emitted to the optical sensor while only the body is in contact with the intermediate transfer belt ;
The control means moves the first transfer member at the end of a first image forming job in which an image is formed while the first image carrier and the second image carrier are in contact with the intermediate transfer belt. The second image is formed by separating the intermediate transfer belt from the first image carrier, executing the second light amount adjustment mode, and forming an image in a state in which only the second image carrier is brought into contact with the intermediate transfer belt. At the end of a forming job, the first transfer member is moved to bring the intermediate transfer belt into contact with the first image carrier to execute the first light amount adjustment mode;
An image forming apparatus characterized by: The control means adjusts the amount of light emitted to the optical sensor so that the optical sensor receives the same amount of reflected light in the first light amount adjustment mode and the second light amount adjustment mode.
2. The image forming apparatus according to claim 1, wherein: The control means can execute a density correction mode for adjusting density of a toner image formed during an image forming job based on a detection result of the optical sensor when a control toner image is formed on the intermediate transfer belt. ,
When executing the density correction mode during a first image forming job for forming an image with the first image carrier and the second image carrier in contact with the intermediate transfer belt, the first light amount adjustment mode and run
executing the second light amount adjustment mode when executing the density correction mode during a second image forming job in which an image is formed while only the second image bearing member is in contact with the intermediate transfer belt;
3. The image forming apparatus according to claim 1 , wherein:

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