JP5063312B2 - Image forming apparatus - Google Patents

Description

  In the present invention, a toner image transferred from an image carrier such as a photoconductor to the surface of an endless belt member, or a toner adhesion amount per unit area of the toner image is detected by an optical sensor, and a predetermined amount is determined based on the detection result. The present invention relates to an image forming apparatus such as a copying machine, a facsimile, or a printer that performs the above process.

  Conventionally, as an image forming apparatus such as a copying machine or a printer, an electrostatic latent image formed by exposure scanning with respect to an image carrier such as a photoreceptor is developed with toner, as described in Patent Document 1 or Patent Document 2. A toner image is known. In this type of image forming apparatus, the exposure intensity when forming an electrostatic latent image by exposure scanning on the surface of an image carrier such as a photoconductor, the development potential when developing the electrostatic latent image with toner, etc. If the image forming conditions are not suitable for the environment, the image density (toner adhesion amount per unit area) of the toner image deviates from the target value.

  The image forming apparatus described in Patent Document 1 transfers a toner image formed on the surface of a photoconductor as an image carrier to a transported recording paper while being held on the surface of a transfer belt as a belt member. Then, the following control is performed at a predetermined timing. That is, after a toner patch image, which is a toner image for detecting image density, is formed on a photoreceptor, it is transferred to the surface of a transfer belt in a state where no recording paper is held. Then, the image density of the toner patch image on the transfer belt is detected by a reflective photosensor as an optical sensor, and the image forming conditions are adjusted based on the detection result. According to this configuration, by adjusting the image forming conditions as described above, the image density can be stabilized even if the environment fluctuates.

  Note that the image forming apparatus described in Patent Document 1 forms a multicolor toner image by a so-called tandem method. In the tandem method, a toner image is formed on each of a plurality of image carriers arranged so as to be arranged along the surface of the belt member, and the toner images are held on the surface of the belt member or the surface of the belt member. In this method, the recording material is superimposed and transferred. By forming toner images of different colors on each image carrier, a multicolor toner image can be formed by superimposing the toner images.

  The image forming apparatus described in Patent Document 2 also forms a multicolor toner image by a tandem method. Specifically, toner images of different colors are formed on a plurality of photoconductors arranged along the surface of the intermediate transfer belt as a belt member, and these are superimposed on the surface of the intermediate transfer belt to be transferred in multiple colors. A toner image is obtained. Then, the relative displacement amount of each color toner image is periodically detected at a predetermined timing, and the latent image writing start timing and the like are corrected according to the detection result. Specifically, first, a toner image for detecting misregistration is formed on each photoconductor, and a pattern image for detecting misregistration is formed on the intermediate transfer belt by sequentially transferring them onto the intermediate transfer belt. . Then, based on the timing at which each color toner image in the positional deviation detection pattern image is detected by the reflective photosensor, the relative position deviation of each color toner image is detected. Next, the latent image writing start timing for each photoconductor is adjusted based on the detection result.

  In such a configuration, it is possible to suppress the occurrence of color misregistration due to the relative positional shift of each color toner image. Specifically, in a tandem image forming apparatus, when expansion or contraction due to a temperature change occurs in a lens, a mirror, or the like in an exposure scanning apparatus that plays a role of latent image formation, the latent image writing start position of each photoconductor is set. A relative shift occurs. As a result, the toner images of the respective colors are formed so as to be displaced relative to the respective photoconductors, and so-called color misregistration occurs. In Patent Document 1, a relative position shift of each color toner image is detected based on a result of detecting the above-described position shift detection pattern by a reflective photosensor, and a latent image writing timing is determined based on the result. By adjusting the above, the occurrence of color misregistration can be suppressed.

  As described above, the image forming apparatus in Patent Documents 1 and 2 detects a toner patch image on the surface of the belt member based on a change in light reflectance as an optical characteristic on the surface of the belt member, The image density is detected. In such a configuration, if the distance between the surface of the belt member and the reflection type photosensor is slightly changed due to the delicate undulation accompanying the running of the belt member, the toner patch image and the image density cannot be accurately detected. For this reason, it is desirable to make the area around the tension roller, which is unlikely to cause subtle undulations associated with traveling, of the entire area in the moving direction of the surface of the belt member, to be a test object of the reflective photosensor. Also in the image forming apparatus described in Patent Document 1, such a hung region is a test object.

Japanese Patent Laid-Open No. 2002-006568 JP 2001-0334030 A

  However, there are cases where it is difficult to obtain good detection accuracy due to a layout restriction that it is desired to use the position opposed to the above-described wrapping area as an application different from the arrangement position of the reflective photosensor. In such a case, if a dedicated tension roller for suppressing the undulation of the belt at a position facing the reflective photosensor is newly provided, the belt circumference is lengthened for this purpose. I will invite you.

  In addition, although the problem which arises when a reflection type photosensor is used as an optical sensor has been described, a similar problem can also occur when a transmission type photosensor is used.

  The present invention has been made in view of the above background, and an object of the present invention is to accurately detect the toner image on the surface of the belt member and its image density without causing an increase in the size of the apparatus. It is an object of the present invention to provide an image forming apparatus capable of performing the above.

In order to achieve the above object, an invention according to claim 1 is directed to an image carrier that carries a toner image, and an endless belt member that is endlessly moved while being stretched by a plurality of rotatable tension rollers. A transfer means for transferring the toner image carried on the image carrier to the surface of the belt member, and the toner image on the surface or the toner image based on a change in optical characteristics on the surface of the belt member. An optical sensor for detecting the toner adhesion amount per unit area, and a control means for performing a predetermined process based on a detection result by the optical sensor, and any one of the plurality of stretching rollers first position opposite from the belt front side against over turning region of the belt member with respect to, moved by a recording member or the drive means, is conveyed to record a toner image et In the image forming apparatus which temporarily enters the moving member, the that, around the rotation center of the tension roller to form the hook turning region by swinging the optical sensor, the not opposed to the seat turning area and 2 positions, the sensor moving means for moving the optical sensor between said first position is provided, based on the detection result by the optical sensor in a first position, to perform the predetermined processing, The control means is configured.
According to a second aspect of the present invention, there is provided an image carrier that carries a toner image, an endless belt member that is endlessly moved in a state of being stretched by a plurality of rotatable tension rollers, and an image on the image carrier. Transfer means for transferring the toner image carried on the surface of the belt member, and a toner image on the surface or a toner per unit area with respect to the toner image based on a change in optical characteristics on the surface of the belt member. An optical sensor for detecting the amount of adhesion, and a control means for performing a predetermined process based on a detection result of the optical sensor, and the belt member is hung on any one of the plurality of stretching rollers the first position facing the first belt region is a region of turning area from the belt front side movement, recording member is transported to record a toner image, or by the drive means In the image forming apparatus which temporarily enters the moving member, the to be crimped, by swinging the optical sensor about a rotation center of the tension roller to form the hook turning region, the belt traveling in said seat turning area a second position facing the second belt region with respect to the center direction is a region of the seat turning area on the away than the first belt region, from the belt front side, the first position sensor moving means for moving the optical sensor with the provided based on the detection result by the optical sensor in a first position, to perform the predetermined processing, that constitute the control means It is a feature.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, when the recording member or the moving member enters the first position, the optical sensor is moved from the first position to the second position. The above-mentioned sensor moving means is configured so as to be retracted.
According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the third aspect, wherein the transfer unit includes a first transfer unit that transfers a toner image carried on the image carrier onto the surface of the belt member. in addition to including, and the toner image on the surface of the belt member to a recording member at a transfer position to come into close contact with the surface of the belt member intended to include a second transfer means for transferring to the recording member, the recording infeed means for feeding toward the member to the transfer position, is disposed in the image forming apparatus main body in the housing, members which temporarily enters the first position, toward the said transfer position from said transmission write means The recording member to be fed, and the first position is a position in a feeding conveyance path for conveying the recording member from the feeding means toward the transfer position. Is.
According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the tension roller adjacent to the second transfer unit on the upstream side in the belt moving direction is used as the tension roller that forms the wrapping region. It is characterized by adopting a rack roller.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the protective member is disposed between the optical sensor and the belt member at the second position to protect the optical sensor. Is provided.
According to a seventh aspect of the present invention, in the image forming apparatus of the sixth aspect , a cleaning member that cleans the optical sensor by rubbing against the optical sensor moving from the first position toward the second position. Is fixed to the protective member .

  In these inventions, with all of the invention specific matters of claim 1, if the optical sensor is disposed at the first position facing the hanging region of the belt member with respect to the stretching roller, it does not face the hanging region. Compared with the case where it is disposed at the second position, the toner image on the surface of the belt member and the image density thereof can be detected with high accuracy by the optical sensor. However, there is a layout restriction that the optical sensor cannot be fixed to the first position because a moving member such as a recording member or an arm of a drive transmission system is temporarily entered. Therefore, in the present invention, the optical sensor is moved between the first position and the second position by the sensor moving means. Then, when the optical sensor is moved to the first position where the toner image and its image density can be accurately detected, the toner for detecting the positional deviation on the surface of the belt member based on the detection result. Predetermined processing such as detecting an image or detecting the image density of a toner image for density detection is performed. In such a configuration, at least when the recording member or the moving member enters the first position, the optical sensor is retracted from the first position to the second position, while the recording member or the moving member does not need to enter the first position. By moving the optical sensor from the second position to the first position at the timing, the optical sensor can be placed at the first position without providing a new tension roller. Therefore, it is possible to accurately detect the toner image on the surface of the belt member and its image density without increasing the size of the apparatus.

  Moreover, in what has all the invention specific matters of Claim 2, among the 1st belt area | region and 2nd belt area | region in a belt member, at least 1st belt area | region has become the winding location with respect to a stretching roller. . Since the first belt region is closer to the center in the belt movement direction in the region around the tension roller than the second belt region, undulations associated with traveling are suppressed. For this reason, the toner image on the surface of the belt member is more disposed in the first position facing the first belt region than in the second position facing the second belt region. And its image density can be detected with high accuracy. However, there is a layout restriction that the optical sensor cannot be fixed to the first position because a moving member such as a recording member or an arm of a drive transmission system is temporarily entered. Therefore, the optical sensor is moved between the first position and the second position by the sensor moving means. Thus, as in the invention according to claim 1, the toner image on the surface of the belt member and its image density can be detected with high accuracy without causing an increase in the size of the apparatus.

Before describing an embodiment in which the present invention is applied to a tandem indirect transfer type color laser printer (hereinafter simply referred to as a printer) which is an electrophotographic image forming apparatus , reference is made in understanding the present invention. A printer according to the reference embodiment will be described . It should be noted that a so-called person skilled in the art can easily make other embodiments by changing or modifying the present invention described in the claims without departing from the technical idea thereof. Accordingly, such changes and modifications are included in the scope of the claims, and the following description is an example of the best mode of the present invention and does not limit the scope of the claims.

FIG. 1 is a schematic configuration diagram illustrating a printer according to a reference embodiment.
An intermediate transfer belt 10 as an endless belt member is provided in the center of the printer 1 main body. The intermediate transfer belt 10 has a multilayer structure. For example, a sheet having a small elongation, which serves as a base layer, is made of a fluorine resin such as PVDF or a polyimide resin, and the surface thereof is covered with a coating layer having good smoothness such as a fluorine resin. As shown in FIG. 1, the intermediate transfer belt can be rotated and conveyed counterclockwise in the drawing while being wound around a stretching roller.

  In the printer 1, four tension rollers 12, 13, 14, and 15 are provided as tension rollers that stretch the intermediate transfer belt 10 while being positioned inside the loop of the intermediate transfer belt 10. Of these, the tension roller denoted by 12 in the figure is driven to rotate in the counterclockwise direction in the figure by a driving means (not shown), so that the intermediate transfer belt 10 is rotated in the counterclockwise direction in the figure. It is a driving roller that moves endlessly. Further, a tension roller denoted by reference numeral 13 in the drawing is a cleaning backup roller that backs up cleaning by the belt cleaning device 19 by sandwiching the intermediate transfer belt 10 with a belt cleaning device 19 described later. . Further, a stretching roller denoted by reference numeral 14 in the drawing is a secondary transfer nip that stretches the intermediate transfer belt 10 at a position slightly away from the inlet of the secondary transfer nip described later slightly upstream in the belt movement direction. It is an entrance roller. Further, a tension roller denoted by 15 in the figure is a tension roller that applies tension to the intermediate transfer belt 10 by being biased toward the intermediate transfer belt 10 by a biasing coil spring.

  The printer 1 includes four process units 5Y, 5M, C, and K for generating toner images of yellow, magenta, cyan, and black (hereinafter referred to as Y, M, C, and K). These use Y, M, C, and K toners of different colors as the image forming material, but the other configurations are the same and are replaced when the lifetime is reached. Taking a process unit 5Y for generating a Y toner image as an example, this includes a drum-shaped photosensitive member 1Y as a latent image carrier, a drum cleaning device 2Y, a charge eliminating device (not shown), a charging roller 4Y, and a developing device 5Y. Etc. The process unit 5Y, which is an image forming unit, is detachable from the printer main body, so that consumable parts can be replaced at a time.

  The charging roller 4Y to which a charging bias is applied by a power source (not shown) is disposed so as to be in contact with or close to the photoreceptor 1Y, and generates a discharge on its surface and the surface of the photoreceptor 1Y, thereby exposing the photoreceptor 1Y. The surface of the body 1Y is uniformly charged to the same polarity (minus in this example) as that of Y toner. The uniformly charged surface of the photoreceptor 1Y is exposed and scanned by a laser beam L emitted from an optical writing unit (not shown) as an exposure unit, and carries a Y electrostatic latent image. The Y electrostatic latent image is developed by the developing device 5Y using Y toner to become a Y toner image. Then, intermediate transfer is performed on the intermediate transfer belt 10. The drum cleaning device 2Y scrapes and removes the transfer residual Y toner remaining on the surface of the photoreceptor 1Y after the intermediate transfer process by the cleaning blade 3Y. The static eliminator neutralizes residual charges on the photoreceptor 1Y after cleaning. By this charge removal, the surface of the photoreceptor 1Y is initialized and prepared for the next image formation. In the other color process units (5M, C, K), (M, C, K) toner images are similarly formed on the photoreceptors (1M, C, K). These toner images are intermediately transferred in such a manner that they are sequentially superimposed on the Y toner image on the intermediate transfer belt 10.

In the printer according to the reference embodiment , as the charging means for uniformly charging the photoconductors 1Y, 1M, 1C, and 1K, one having the charging rollers 4Y, 4M, 4C, and 4K is used. You may use what comprises a brush roller. A scorotron charger or a corotron charger may be used as the charging means.

As a developing device for developing an electrostatic latent image, a developer using a one-component developer containing only a toner among a magnetic carrier and a toner, and a two-component developer containing both are used. However, in the printer 1 according to the reference embodiment, any developing device can be adopted.

  The process units 5Y, 5M, 5C, and 5K are arranged so as to be aligned in the horizontal direction along the lower stretched surface of the intermediate transfer belt 10 that is stretched so as to extend in the horizontal direction. Below these process units 5Y, 5M, 5C, and 5K, an optical writing unit (not shown) as a latent image writing device is disposed. The optical writing unit is configured such that the photoconductors 1Y, 1M, 1C, and 1K in the process units 5Y, M, C, and K are generated by laser light L emitted based on image information sent from an external personal computer, a scanner, or the like. Is scanned by exposure. The optical writing unit irradiates the photosensitive member through a plurality of optical lenses and mirrors while scanning the laser light L emitted from the light source with a polygon mirror rotated by a motor.

  A paper feed cassette 25, a paper feed roller 26 incorporated in the paper feed cassette 25, and the like are disposed at the lower part of the printer casing. The paper feed cassette 25 stores a plurality of recording papers P as sheet-like recording members, and a paper feed roller 26 is brought into contact with the uppermost recording paper P. When the paper feed roller 26 is driven to rotate in the counterclockwise direction in the drawing by a driving means (not shown), the uppermost recording paper P is sent out toward the paper feed conveyance path 27.

  Near the end of the paper feeding / conveying path 27, a pair of registration rollers 28 is provided as a feeding means. The registration roller pair 28 rotationally drives the two rollers to sandwich the recording paper P, but temporarily stops rotation immediately after the recording paper P is sandwiched. Then, by restarting the rotation at a predetermined timing, the recording paper P is sent out toward a secondary transfer nip described later at an appropriate timing.

  The intermediate transfer belt 10 disposed above the process units 5Y, M, C, and K constitutes a part of the transfer unit 9 as transfer means. In addition to the intermediate transfer belt 10 and the four tension rollers (12 to 15) described above, the transfer unit 9 includes a belt cleaning device 19 and a secondary transfer roller 21 disposed outside the loop of the intermediate transfer belt 10. Have. Further, it also has four primary transfer bias rollers 11Y, 11M, 11C, and 11K disposed inside the loop of the intermediate transfer belt 10.

  The primary transfer bias rollers 11Y, 11M, 11C, and 11K each have an intermediate transfer belt 10 that is moved endlessly between the photoreceptors 1Y, 1M, 1C, and 1K to form primary transfer nips. A primary transfer bias power supply 111 is connected to the primary transfer bias rollers 11Y, 11M, 11C, and 11K via a switch 110. The primary transfer power source 111 outputs a primary transfer bias having a polarity opposite to the charging polarity of the toner, which is supplied individually to the primary transfer biases 11Y, 11M, 11C, and 11K. By applying such primary transfer bias to the primary transfer bias rollers 11Y, 11M, 11C, and 11K, primary transfer electric fields are respectively generated in the primary transfer nips for Y, M, C, and K. It is formed. The intermediate transfer belt 10 sequentially passes through the primary transfer nips for Y, M, C, and K along with the endless movement thereof, and Y, M, and C on the photoreceptors 1Y, 1M, 1C, and 1K. , K toner images are superimposed and intermediate transferred. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the intermediate transfer belt 10.

  The driving roller 12 disposed inside the belt loop sandwiches the intermediate transfer belt 10 with the secondary transfer roller 21 disposed outside the belt loop. Thus, a secondary transfer nip is formed in which the secondary transfer roller 21 and the front surface of the intermediate transfer belt 10 abut. A secondary transfer bias having a polarity opposite to the charging polarity of the toner is applied to the secondary transfer roller 21 by a secondary transfer bias power source 120. On the other hand, the drive roller 12 is connected to ground. The four-color toner image formed on the intermediate transfer belt 10 is transferred to the recording paper P in the secondary transfer nip. Then, combined with the white color of the transfer paper P, a full color toner image is obtained.

  Untransferred toner that has not been transferred to the recording paper P adheres to the intermediate transfer belt 10 after passing through the secondary transfer nip. This is scraped off the belt surface by the belt cleaning device 19. In addition, the recording paper P on which the four-color toner images are collectively transferred at the secondary transfer nip is sent to the fixing device 30 positioned above the secondary transfer nip.

  The fixing device 30 forms a fixing nip with a fixing roller having a heat source such as a halogen lamp inside and a pressure roller that rotates while contacting the fixing roller with a predetermined pressure. The recording paper P sent into the fixing device 30 is sandwiched between the fixing nips so that the unfixed toner image carrying surface is in close contact with the fixing roller. Then, the toner in the toner image is softened by the influence of heating and pressurization, and the full color image is fixed.

  The recording paper P on which the full-color image has been fixed in the fixing device 30 exits the fixing device 30 and is then discharged out of the apparatus via the paper discharge roller pair 32.

  When image information is sent from an external personal computer or the like, the intermediate transfer belt 10 is moved endlessly while the driving roller 12 is rotationally driven by a driving motor (not shown) and the other three stretching rollers are driven to rotate. . At the same time, the photoreceptors 1Y, M, C, and K in the individual process units 5Y, M, C, and K are rotated to form Y, M, C, and K toner images on the photoreceptors, respectively. Then, the toner images are sequentially superimposed and transferred onto the endless moving intermediate transfer belt 10 to form a composite color image on the intermediate transfer belt 10.

  On the other hand, when image information is sent from a personal computer or the like, the paper feed roller 26 selectively rotates and feeds the recording paper P from the paper feed cassette 25. The recording paper P is separated one by one by a separation roller (not shown), then conveyed by the conveying roller 27 and guided to the paper feeding / conveying path 27, and then hits the registration roller 28 and stops. Then, the registration roller 28 rotates in synchronization with the composite color image on the intermediate transfer belt 10 to feed the recording paper P sheet into the above-described secondary transfer nip. The composite color image on the intermediate transfer belt 10 is secondarily transferred collectively to the recording paper P fed into the secondary transfer nip.

  The recording paper P after image transfer is fed to the fixing device 30 while being conveyed by the secondary transfer roller 21, and after the composite color image is fixed by application of heat and pressure in the fixing device 30, the recording paper P is discharged. The paper is discharged out of the apparatus by the roller pair 32 and stacked on a paper discharge tray. On the other hand, the intermediate transfer belt 10 after image transfer is prepared for re-image formation by removing residual toner remaining on the intermediate transfer belt 10 after image transfer by the belt cleaning device 19.

  FIG. 9 is a block diagram showing a part of an electric circuit in the printer. In the figure, a control unit 200 as control means includes a CPU (Central Processing Unit) 201, a ROM (Read Only Memory) 202 that stores a control program and various data, and a RAM (Random Access Memory) that temporarily stores various data. 203). The control unit 200 includes a primary transfer bias power supply 111, a secondary transfer bias power supply 120, and an optical writing unit via an I / O interface 204 for transmitting / receiving signals to / from each peripheral control unit. An optical writing control circuit 205 that is dedicated to control is connected. Further, a belt driving motor 162 that is a driving source of the driving roller (12), a scanning display unit 184 that includes a touch panel, and the like are also connected. Furthermore, the optical sensor unit 150 includes a first end photosensor 151, a center photosensor 152, a second end photosensor 153, a Y photosensor 154Y, an M photosensor 154M, a C photosensor 154C, a K photosensor 154K, and the like. Is also connected. Each of these photosensors is a reflection type photosensor that reflects light emitted from a light emitting means (not shown) on a surface to be examined and detects the reflected light by a light receiving means (not shown).

  This printer performs image forming condition adjustment processing for adjusting image forming conditions of an image forming apparatus including an optical writing unit and process units (5Y, M, C, K) of each color, etc. It is implemented at a predetermined timing. In this image forming condition adjustment process, a process control process and a positional deviation correction process which will be described later are performed. In these processes, the optical writing control circuit 205 controls the optical writing unit or the like based on a command input from the control unit 200 via the I / O interface 204, or the control unit 200 controls each process unit. And control the drive of the transfer unit. As a result, a gradation pattern image for image density detection, which will be described later, and a patch pattern image composed of a plurality of toner images for color misregistration detection are formed on the intermediate transfer belt 10.

  More specifically, in the process control process in the image forming condition adjustment process, a gradation pattern image for image density detection is formed on the intermediate transfer belt 10. As the gradation pattern images for image density detection, four gradation pattern images of Y, M, C, and K are formed. Each gradation pattern image is composed of 14 Y, M, C, and K reference toner images each having a predetermined pixel pattern. Each of the 14 Y, M, C, and K reference toner images is formed to have a different toner adhesion amount (image density).

  For example, taking a K gradation pattern image SK as an example, this is referred to as Y reference toner images SK1, SK2,... SK13, SK14 in which the toner adhesion amount gradually increases as shown in FIG. It consists of 14 K reference toner images. These K reference toner images are formed on the front surface of the belt so as to be arranged at a predetermined interval in the traveling direction of the intermediate transfer belt 10, and the toner adhesion amount per unit area with respect to these K reference toner images is determined by an optical sensor. Detected by the K photo sensor 154K of the unit 150. This detection result is sent to the RAM 203 via the I / O interface 204 as an output value Vpi (i = 1 to 14).

  In the optical sensor unit 150, the photosensors (153, 154K, C, 152, 154M, Y, 151) are arranged in a straight line in the belt width direction (the rotation axis direction of the roller). The K reference toner image described above is formed at the same position as the installation position of the K photo sensor 154K in the belt width direction of the front surface of the intermediate transfer belt 8, and is thus detected by the K photo sensor 154K. Similarly to K, for Y, M, and C, the 14 Y, M, and C reference toner images are the same as the installation positions of the Y, M, and C photosensors 154Y, M, and C in the belt width direction. And detected by the Y, M, C photosensors 154Y, M, C. Then, output values Vp 1 to 14 of Y, M, and C photosensors 154 Y, M, and C, which are detection results of the toner adhesion amounts with respect to the Y, M, and C reference toner images, are stored in the RAM 203.

  Based on these output values stored in the RAM 203 and the data table stored in the ROM 202, the control unit 200 converts each output value into a toner adhesion amount per unit area, as toner adhesion amount data. Stored in the RAM 203.

FIG. 11 is a graph in which the relationship between the potential of the photoconductor and the toner adhesion amount is plotted on the xy coordinates. In the figure, the development potential (difference between the development bias voltage at the time of gradation pattern image formation and the surface potential of the photoreceptors 1K, Y, M, and C: unit V) is assigned to the x-axis, and the unit is assigned to the y-axis. The toner adhesion amount per area (mg / cm ² ) is allocated.

  The control unit 200 selects, from the potential data and toner adhesion amount data stored in the RAM 203, a region in which the relationship (development characteristics) between the potential data and the toner adhesion amount data is a straight line for each color, These data are smoothed. The least square method is applied to the potential data and the toner adhesion amount data after the smoothing process to perform linear approximation of the developing characteristics of each developing device. Further, after obtaining the linear equation y = ax + b of the developing characteristics of each developing device for each color, the image forming conditions in each process unit (5K, Y, M, C) are adjusted based on the slope a in this linear equation. . Examples of the method for adjusting the image forming conditions include a method for adjusting the uniform charging potential of the photosensitive member and the developing bias as described in JP-A-9-211191. When the two-component development method is adopted, the control target value of the toner concentration of the two-component developer may be adjusted.

  As shown in FIG. 11, the process control process includes 14 K reference toner images SK1, SK2,... SK13, SK14 arranged at a predetermined pitch in the moving direction (sub scanning direction) of the intermediate transfer belt 10. A K gradation pattern image SK is formed. Further, 14 Y reference toner images SY1, SY2 arranged at a predetermined pitch in the sub-scanning direction (belt traveling direction) so as to be adjacent to the K gradation pattern image SK in the main scanning direction (belt width direction). ... A Y gradation pattern image SY composed of SY13 and SY14 is formed. Further, an M-th floor composed of 14 M reference toner images SM1, SM2,... SM13, SM14 arranged at a predetermined pitch in the sub-scanning direction so as to be adjacent to the Y gradation pattern image SY in the main scanning direction. A tone pattern image SM is formed. Further, the M-th floor composed of 14 C reference toner images SC1, SC2,... SC13, SC14 arranged at a predetermined pitch in the sub scanning direction so as to be adjacent to the M gradation pattern image SM in the main scanning direction. A tone pattern image SC is formed.

  In the misregistration correction process in the image forming condition adjustment process, a misregistration detection patch pattern as shown in FIG. 12 is formed near both ends and the center of the intermediate transfer belt 10 in the width direction. These three patch patterns formed near both ends and near the center are composed of four Y, M, C, and K reference toner images Sy, Sm, Sc, and Sk arranged at predetermined intervals in the sub-scanning direction. The reference toner images are formed so as to be aligned in the main scanning direction.

  In the drawing, each reference toner image in the patch pattern formed near the front end in the belt width direction is detected by the first end photosensor 151. Each reference toner image in the patch pattern formed near the center in the belt width direction is detected by the center photosensor 152. Further, each reference toner image in the patch pattern formed near the back end in the belt width direction is detected by the second end photosensor 153. If the formation timings of the reference toner images of the respective colors are appropriate, the detection intervals of the reference toner images are equal to each other, but if they are inappropriate, the formation intervals of the reference toner images of the respective colors are not equal. Also, the detection intervals are not equal. If there is no optical writing skew in the optical system, the reference toner images of the same color are detected at the same timing between the three patch patterns. However, if the skew is generated, the detection timing is different. come. The control unit 200 adjusts the optical writing start timing and the optical system for each photoconductor on the basis of the detection interval and detection timing of each color toner image in the main scanning direction and the sub-scanning direction, and determines the position of each color toner image. Reduce the deviation.

  When the above-described gradation pattern image or patch pattern is formed, the secondary transfer roller 21 shown in FIG. 1 is separated from the intermediate transfer belt 10, and the gradation pattern image or patch pattern secondary transfer roller is formed. The dislocation to 21 is avoided.

  The skew deviation is corrected by adjusting the tilt of the mirror for turning back each color laser beam in the optical writing unit by a driving mechanism (not shown). A stepping motor is used as a drive source for biasing the mirror. The positional deviation correction of each color toner image in the sub-scanning direction (belt moving direction) is performed by adjusting the optical writing start timing for each photoconductor. Further, when the magnification in the main scanning direction of each reference toner image in the Y, M, and C patch patterns is deviated from the reference color K, the clock that can change the signal frequency in very small steps. The magnification is corrected by a device such as a generator.

  As shown in FIG. 3, a gradation pattern for image density detection and a patch pattern for position shift detection may be alternately formed.

FIG. 2 is an enlarged configuration diagram illustrating the periphery of the secondary transfer nip of the printer according to the reference embodiment. As shown in FIG. 2, the optical sensor unit 150 described above is disposed below the secondary transfer nip entrance roller 14. This optical sensor unit 150 holds the above-described plurality of reflective photosensors by a bracket (not shown).

  As shown in FIG. 1, the printer 1 is provided with four driving rollers 12, a cleaning backup roller 13, a tension roller 15, and a secondary transfer nip entrance roller 15 as stretching rollers. As described above, it is desirable that the optical sensor unit 150 is disposed so as to face the belt-wrapping region of any one of these stretching rollers.

  In the drawing, for convenience, the secondary transfer nip where the driving roller 12 is located on the back side of the belt and the fixing device 30 above the belt are shown relatively apart from each other, but the distance between the two is actually a little. It is. A secondary transfer roller 21 is located on the right side of the driving roller 12 in the drawing. For these reasons, the optical sensor unit 150 cannot be opposed to the belt wrapping region with respect to the driving roller 12.

  A toner bottle (not shown) is disposed above the cleaning backup roller 13. Furthermore, a belt cleaning device 19 is disposed on the left side of the cleaning backup roller 13 in the drawing. For these reasons, the optical sensor unit 150 cannot be disposed in the belt running region with respect to the cleaning backup roller 13.

  Further, the tension roller 15 is supported so as to be able to be urged by the urging coil spring, and moves slightly as the intermediate transfer belt 10 travels, so that the belt runs around the tension roller 15. It is not preferable to dispose the optical sensor unit in the region. Instead of using the tension roller 15 as a stationary tension roller, the cleaning backup roller 13 may be used as a tension roller and moved together with the belt cleaning device 19. However, even with such a configuration, since the developing device 6Y for Y exists at a position facing the belt 15 with respect to the roller 15, the optical sensor unit 150 is not disposed at the facing position. Can not.

  Further, at the position facing the secondary transfer nip entrance roller 14, the above-described feeding conveyance path exists. There is a slight space for placing the optical sensor unit 150 on the side of the transporting path. In the printer 1, the optical sensor unit 150 is placed in that space. However, as shown in FIG. 2, the arrangement position faces the belt running area with respect to the secondary transfer nip entrance roller 14, but in the belt running area, the intermediate transfer belt 10 starts to wind around the roller. Because of the position, the belt undulates. Therefore, at the illustrated position, the optical sensor unit 150 cannot accurately detect the gradation pattern and the patch pattern. In order to perform detection with high accuracy, it is necessary to set an area in which no belt waviness occurs in the belt-wrapping area around the secondary transfer nip entrance roller 14 as a test target. Such a region is a belt region that is closer to the center in the belt movement direction indicated by a symbol La in the drawing, but the first conveyance guide plate 41 is present at a position facing the belt region. That is, in the illustrated printer, the belt is wound around the secondary transfer nip entrance roller 14 at a first position facing the first belt region that is relatively close to the center La or that includes the center La. Although the optical sensor unit 150 is desired to be disposed, the first transport guide plate 41 is present at the first position. For this reason, although it is a belt-wrapping region, it is farther from the center La than the first belt region and faces the second belt region that is a winding start region for the secondary transfer nip entrance roller 14. The optical sensor unit 150 must be disposed at two positions.

  As described above, the recording paper is fed from the registration roller pair 28 to the feeding conveyance path formed by the first conveyance guide plate 41 and the second conveyance guide plate 40 facing each other. I'm not sending in. The recording paper is only fed in at the timing when the four-color toner image on the intermediate transfer belt 10 enters the secondary transfer nip. At such timing, the above-described gradation pattern for detecting image density and patch pattern for detecting displacement are not formed. These patterns are not for secondary transfer onto the recording paper, but for detection by the optical sensor unit 150. After the detection with the movement of the belt, the belt cleaning device 19 passes through a position facing the secondary transfer roller 21 (at this time, the secondary transfer roller 21 is separated from the belt as described above). Is removed from the belt surface.

  The present inventors paid attention to the fact that the recording paper is not fed into the feeding / conveying path when forming the gradation pattern for density detection and the pattern for detecting positional deviation as described above. When the original function is not exhibited in the feeding conveyance path, it is not necessary to exhibit the function as the feeding conveyance path. Therefore, the optical sensor unit 150 is caused to enter the first position in the feeding conveyance path at the time of pattern detection. There is no problem. Therefore, in the printer 1, the first conveyance guide plate 41 is provided with a through opening through which the optical sensor unit 150 can pass. And at the time of pattern detection, the sensor movement means which is not shown in figure which moves the optical sensor unit 150 from the 2nd position shown in FIG. 2 to the 1st position shown in FIG. 4 is provided. When the optical sensor unit 150 is moved between the first position and the second position, the optical sensor unit 150 passes through the through opening of the first transport guide plate 41. Note that the second position in FIG. 4 is the first belt region at the center La in the belt moving direction in the belt winding region with respect to the secondary transfer nip entrance roller 14 as can be seen from a comparison between FIG. 2 and FIG. (In this example, the distance is zero with respect to the center La). On the other hand, the first position shown in FIG. 2 is a position facing the second belt region located farther from the center La than the first belt region.

  The control unit 200 performs control to move the optical sensor unit 150 from the second position to the first position only when the optical sensor unit 150 detects the pattern on the intermediate transfer belt 10. In such a configuration, when recording paper as a specific member enters the first position, the optical sensor unit 150 is retracted from the first position to the second position, while the recording paper does not need to enter the first position. By moving the optical sensor unit from the second position to the first position, it is possible to place the optical sensor unit 150 in the first position without providing a new tension roller. Therefore, it is possible to accurately detect the gradation pattern and the patch pattern on the surface of the intermediate transfer belt 10 without increasing the size of the apparatus.

  FIG. 13 is an enlarged configuration diagram showing the optical sensor unit 150 and its peripheral configuration. In the figure, a protective member 102 is disposed below the secondary transfer nip entrance roller 14. When the optical sensor unit 150 is in the second position indicated by a solid line in the drawing, the protective member 102 is provided with a detection surface (light emitting surface and light incident surface) of each reflective photosensor of the optical sensor unit 150 and an intermediate transfer. It is interposed between the belt 10 and protects the detection surface. In this configuration, the toner that falls from the front surface of the intermediate transfer belt 10 toward the detection surface of each reflective photosensor of the optical sensor unit 150 at the second position is received by the protective member 102 before reaching the detection surface. As a result, the occurrence of toner contamination on the detection surface can be suppressed. In the configuration in which the detection surface of the reflection type photosensor is positioned immediately below the belt front surface at the second position as in the printer 1, the protective member 102 is provided to effectively remove the toner on the detection surface. Can be suppressed.

  A cleaning brush 103 made of a plurality of raised brushes as a cleaning member is fixed to the surface of the protective member 102 facing the reflective photosensor. Then, when the optical sensor unit 150 is moved from the first position indicated by the dotted line in the figure to the second position indicated by the solid line in the figure, the detection surface of each reflective photosensor of the optical sensor unit 150 is rubbed against the cleaning brush 103. The structure which cleans a detection surface by damaging is adopted. In such a configuration, even if toner contamination is generated on the detection surface of each reflective photosensor, the toner contamination can be removed by cleaning with the cleaning brush 103.

  In this printer, as a stretching roller that forms a belt-wrapping region at a position facing the optical sensor unit 150, a driving that is a stretching roller that stretches the intermediate transfer belt 10 at the secondary transfer nip as a transfer position. A secondary transfer nip entrance roller adjacent to the roller 12 on the upstream side in the belt moving direction is employed. In order to form an infeed conveyance path by facing the first conveyance guide plate 41 and the second conveyance guide plate 40 upstream of the secondary transfer nip in the belt movement direction, The secondary transfer nip entrance roller 14 is disposed at a position closest to the feeding conveyance path. In the present printer 1, the optical sensor unit 150 is opposed to the belt winding position with respect to the secondary transfer nip entrance roller 14 to be disposed closest to the feeding conveyance path as described above. Effective use as the first position for causing the optical sensor unit 150 to detect the pattern with high accuracy in the feeding conveyance path can be easily realized.

  In the sensor moving means, a solenoid or a motor can be exemplified as a driving source that exerts a driving force for moving the optical sensor unit 150.

Next, a printer according to an embodiment in which a characteristic configuration is added to the printer 1 according to the reference embodiment will be described. Incidentally, unless otherwise noted below, the configuration of the printer according to the embodiment is similar to the printer according to the reference embodiment.
[ Embodiment ]
In the printer according to the embodiment , the optical sensor unit 150 is swung around the rotation center of the secondary transfer nip entrance roller 14 that is a stretching roller that forms a belt-wrapping region at a position facing the optical sensor unit 150. Thus, the sensor moving means is configured. In such a configuration, the rotating shaft of the secondary transfer nip entrance roller 14 is used as a supporting means for movably supporting the bracket of the optical sensor unit 150, and the optical sensor unit 150 is supported via a bearing with respect to this rotating shaft. Can be made. Thereby, the optical sensor unit 150 can be moved between the first position and the second position without newly providing support means for movably supporting the optical sensor unit 150.

Next, printers of reference examples in which some configuration is added to the printer according to the reference embodiment will be described.
[First Reference Example ]
FIG. 5 is an enlarged configuration diagram showing the optical sensor unit 150 of the printer according to the first reference example and its peripheral configuration. In the figure, the first conveyance guide plate 41 is not provided with an opening for allowing the optical sensor unit 150 moving between the first position and the second position to pass therethrough. Instead, the first transport guide plate 41 is fixed to a bracket (not shown) of the optical sensor unit 150. As shown in FIG. 6, the sensor moving means is configured to move the first transport guide plate 41 together with the optical sensor unit 150.

As shown in FIG. 10 and FIG. 12, the optical sensor unit 150 includes a plurality of reflective photosensors arranged in the belt width direction, so that it is almost equal to the belt width of the intermediate transfer belt 10. It is the same length. When the opening for passing the optical sensor unit 150 having such a length is provided in the first transport guide plate 41 as in the printer 1 according to the reference embodiment, the length of the opening must be approximately the same as the belt width. In fact, the opening is inevitably large. Then, it becomes easy to generate a jam by hooking the recording paper being conveyed on the feeding conveyance path to the opening. On the other hand, if the first transport guide plate 41 is moved together with the optical sensor unit 150 as in the first reference example , a large opening for passing the optical sensor unit 150 is provided in the first transport guide plate 41. There is no need. Thereby, it is possible to avoid the occurrence of a jam due to the recording paper being caught in the opening of the first conveyance guide plate 41.

[ Second Reference Example ]
FIG. 7 is an enlarged configuration diagram for explaining the movement of the optical sensor unit from the second position to the first position in the printer according to the second reference example . As illustrated, in the printer according to the second reference example , the secondary transfer roller 21 as a transfer nip forming member is moved to the intermediate transfer belt 10 in conjunction with the movement of the optical sensor unit 150 from the second position to the first position. The sensor moving means is configured so as to be separated from the sensor. The sensor moving means is also configured to bring the secondary transfer roller 21 into contact with the intermediate transfer belt 10 in conjunction with the movement of the optical sensor unit 150 from the first position to the second position.

FIG. 14 is a perspective view illustrating a link mechanism provided in the sensor moving unit of the printer according to the second reference example and a part of the transfer unit. In the figure, the secondary transfer roller 21 as a nip forming member is rotatably supported by a bearing 140 on its rotating shaft. A spacing coil spring (not shown) is fixed to the bearing 140, whereby a force is applied to the secondary transfer roller 21 in a direction away from the intermediate transfer belt 10.

  The link mechanism of the sensor moving means includes a sensor unit moving arm 170, a cam 175, a roller moving first arm 171, a roller moving second arm 172, a cam drive motor (not shown), and the like. The bracket 160 of the optical sensor unit 150 having a plurality of reflective photosensors such as the first end photosensor 151 is fixed to the sensor unit moving arm 170. The sensor unit moving arm 170 is supported by a bearing (not shown) of the printer main body so as to swing around the swing shaft 170a. When the sensor unit moving arm 170 swings about the swinging shaft 170a, the optical sensor unit 150 fixed to the sensor unit moving arm 170 moves between the first position and the second position described above. Can do. However, a biasing coil spring (not shown) is fixed to the sensor unit moving arm 170, and thereby a swinging force in a direction to move the optical sensor unit 150 from the first position to the second position is applied.

  The roller moving first arm 171 of the link mechanism is supported by a bearing (not shown) of the printer main body so as to swing about the swing shaft 171a. Then, the end side which is the outer edge of the swinging track is brought into contact with the first butting protrusion 172b or the second butting protrusion 172c of the second roller moving arm 172 according to the swinging position. .

  The roller moving second arm 172 of the link mechanism is supported by a bearing (not shown) of the printer main body so as to swing around the swing shaft 172a. Then, the side end of the arm portion is abutted against the bearing 140 of the secondary transfer roller 21.

  The cam 175 of the link mechanism is disposed between the sensor unit moving arm 170 and the roller moving first arm 171 and is in contact with both arms. In the state shown in the drawing, the cam 175 pushes the sensor unit moving arm 170 in a direction opposite to the biasing force of the biasing coil spring. Thereby, the optical sensor unit 150 is moved to the first position where accurate detection can be performed. At the same time, the cam 175 is in contact with the roller moving first arm 171 at the point where the center radius becomes the smallest, so that the roller moving first arm 171 has the end of the roller moving second arm 172 at the second end. It abuts against the abutment protrusion 172c. In this state, the roller moving second arm 172 is relatively separated from the intermediate transfer belt 10 with respect to the bearing 140 of the secondary transfer roller 21 that is biased in a direction away from the intermediate transfer belt 10 by the separation coil spring. It strikes at the position. As a result, the secondary transfer roller 21 is separated from the intermediate transfer belt 10. That is, in the state shown in the figure, the link mechanism moves the secondary transfer roller 21 away from the intermediate transfer belt 10 in conjunction with the movement of the optical sensor unit 150 to the first position.

  When the cam 150 rotates by a predetermined angle from the state shown in the figure by rotation of a cam drive motor (not shown), the sensor unit moving arm 170 is rotated clockwise around the swinging shaft 170a by the biasing of the biasing coil spring. Rotate by a predetermined angle. Then, the optical sensor unit 150 fixed to the sensor unit moving arm 170 is retracted from the first position to the second position. At the same time, the roller moving first arm 171 rotates around the swinging shaft 171a by a predetermined angle in the clockwise direction in the drawing, and the swinging end portion of the roller moving second arm 172 becomes the first abutting protrusion 172b. Hit it. Then, the roller moving second arm 17 rotates around the swing shaft 172a by a predetermined angle in the clockwise direction in the figure, and the bearing 140 of the secondary transfer roller 21 is opposed to the biasing direction of the separating coil spring. And press it toward the intermediate transfer belt 10. As a result, the secondary transfer roller 21 contacts the intermediate transfer belt 10 to form a secondary transfer nip. That is, the link mechanism of the sensor moving means causes the secondary transfer roller 21 to contact the intermediate transfer belt 10 in conjunction with retracting the optical sensor unit 150 from the first position to the second position.

  In such a configuration, the contact and separation of the secondary transfer roller 21 to avoid transferring the gradation pattern or patch pattern formed on the intermediate transfer belt 10 from the belt to the secondary transfer roller 21 at the secondary transfer nip. The operation and the movement operation of the optical sensor unit 150 are performed by one drive source (cam drive motor). Thereby, compared with the case where each operation | movement is each implemented with an individual drive source, cost reduction and simplification of a control program can be achieved.

Next, each reference specific example printer in which a further configuration is added to the printer according to the second reference example will be described. Unless otherwise specified, the configuration of the printer according to each reference specific example is the same as that of the second reference example .
[First Reference Specific Example]
In the printer according to the first reference specific example, a registration driving motor (not shown) that is a driving source for rotating the registration roller pair 28 is also used as a driving source for the optical sensor unit 150 and the secondary transfer roller 21. Yes. Specifically, the bracket of the optical sensor unit 150 is fixed to an arm (not shown) that can swing about a swing shaft, and a gear (not shown) is fixed to the swing shaft of the arm. The arm is biased in a direction to move the optical sensor unit 150 from the second position toward the first position by being biased by a biasing coil spring (not shown). As a result, at normal times, the optical sensor unit 150 is present at the first position where accurate detection can be performed. Unlike the printer according to the second reference example , the home position of the optical sensor unit 150 is the first position. The gear fixed to the swing shaft of the arm meshes with a drive transmission system for receiving a drive force from the motor shaft of the registration drive motor. When the registration driving motor is driven to rotate, the driving force causes the arm to move in the direction of moving the optical sensor unit 150 from the first position, which is the home position, to the second position about the swing axis. When the optical sensor unit 150 is moved to the position where the optical sensor unit 150 is moved to the second position, the gear fixed to the swing shaft of the arm is idled and the movement of the arm is stopped. As a result, the optical sensor unit 150 is locked at the second position.

  When the rotation of the registration drive motor is started, the recording paper starts to be sent out from the registration roller pair 28. However, before the recording paper reaches the first position in the feeding conveyance path, the optical sensor unit 150 is moved to the first position. From the first position to the second position is saved. For this reason, a collision between the recording sheet being fed into the feeding conveyance path and the optical sensor unit 150 being retracted from the first position toward the second position is avoided.

On the other hand, the bearing 140 of the secondary transfer roller 21 is fixed to an arm (not shown) that can swing about a swing shaft, and a gear (not shown) is fixed to the swing shaft of the arm. The arm is urged by a separation coil spring (not shown) to urge the secondary transfer roller 21 in a direction in which the secondary transfer roller 21 is moved from the contact position to the intermediate transfer belt 10 toward the separation position. As a result, the secondary transfer roller 21 is normally located at a separation position away from the intermediate transfer belt 10. Unlike the printer according to the second reference example , the home position of the secondary transfer roller 21 is a separated position. The gear fixed to the swing shaft of the arm meshes with a drive transmission system for receiving a drive force from the motor shaft of the registration drive motor. When the registration drive motor is driven to rotate, the driving force causes the arm to move in the direction in which the secondary transfer roller 21 is moved from the separated position, which is the home position, to the contact position with the swing shaft as the center. When the secondary transfer roller 21 contacts the intermediate transfer belt 10 and moves to a position where a secondary transfer nip is formed, the gear fixed to the swing shaft of the arm is idled and the movement of the arm stops. As a result, the secondary transfer roller 21 is locked at the contact position.

  When the registration drive motor starts to rotate, the recording paper starts to be sent out from the registration roller pair 28. However, before the recording paper enters between the secondary transfer roller 21 and the intermediate transfer belt 10, the secondary transfer is performed. The roller 21 moves to the contact position to form a secondary transfer nip.

  When the rotational drive of the registration drive motor stops, the arm supporting the bracket of the optical sensor unit 150 moves about the swing axis by the biasing force of the biasing coil spring, and the optical sensor unit 150 is moved from the second position. Move to the first position. Further, the arm supporting the bearing 140 of the secondary transfer roller 21 moves about the swing shaft by the biasing force of the separation coil spring, and moves the secondary transfer roller 21 from the contact position to the separation position. .

  In such a configuration, the registration driving motor is also used as a driving source for the sensor moving means for moving the optical sensor unit 150, so that the registration roller pair 28 and the sensor moving means are driven by separate driving sources, respectively. Cost reduction can be achieved and the control program can be simplified. Further, the registration drive motor is also used as a drive source for the contact / separation means for bringing the secondary transfer roller 21 into and out of contact with the intermediate transfer belt 10, thereby further reducing the cost and further reducing the control program. Costs can be reduced.

[Second specific example]
FIG. 8 is an enlarged configuration diagram illustrating one end portion of the printer according to the second specific example. As shown in the figure, this printer is provided with an opening / closing cover 51 as an opening / closing door at one end of the housing. The opening / closing cover 51 can be opened and closed with respect to the casing by swinging about a swing shaft 51a provided near the lower end of the casing. When the opening / closing cover 51 is opened, the paper feeding and conveying path 27 and the feeding and conveying path are exposed to the outside, and jammed paper jammed in these conveying paths can be easily removed. The open / close cover 51 is an open / close door for exposing the recording paper jammed at the secondary transfer nip and before and after the secondary transfer nip to the outside of the housing. When the opening / closing cover 51 is opened, the jam paper removal workability can be improved by separating the registration roller pair 28 from the intermediate transfer belt 10.

  Therefore, when the opening / closing cover 51 is opened, the sensor moving unit is configured to retract the optical sensor unit 150 to the second position and to separate the secondary transfer roller 21 from the intermediate transfer belt 10. is doing. Specifically, when the recording paper is fed out from the registration roller pair 28, the optical sensor unit 150 and the secondary transfer roller 21 are present at the following positions as already described. In other words, the optical sensor unit 150 is present at the second position outside the feed conveyance path, and the secondary transfer roller 21 is present at the contact position to form a secondary transfer nip. The occurrence of jammed paper at the secondary transfer nip and before and after that mostly occurs at this time, and the secondary transfer roller 21 is in contact with the intermediate transfer belt 10. In this state, the jam handling performance is poor. Therefore, when the opening / closing cover 51 is opened in this state, the sensor moving means is configured to move the secondary transfer roller 21 to the separation position in conjunction with the opening operation. It is doing. At this time, since the optical sensor unit 150 is present at the second position outside the infeed conveyance path, the optical sensor unit 150 is locked at the second position as it is.

  At the timing when the optical sensor unit 150 is present at the first position in the feeding conveyance path and the secondary transfer roller 21 is present at the contact position, the probability of occurrence of jammed paper is small, but it is very rare. In addition, the leading edge may be clogged in the path with the trailing edge of the recording paper sandwiched between the secondary transfer nips. Further, unlike the occurrence of jammed paper, the user may consider opening the open / close cover 51 at the above-mentioned timing for reasons. In these cases, when the opening / closing cover 51 is opened, the sensor is moved so that the secondary transfer roller 21 is retracted from the contact position to the separated position and the optical sensor unit 150 is retracted from the first position to the second position. Means. By retracting the optical sensor unit 150 from the first position to the second position, it is possible to avoid a situation in which the user touches the optical sensor unit 150 existing at the first position exposed to the outside.

The linkage between the opening operation of the opening / closing cover 51 and the movement of the optical sensor unit 150 and the secondary transfer roller 21 may be realized mechanically or by control. For example, when the interlocking with the operation of the opening / closing cover 51 is realized by the control, the following may be performed. That is, in the printer according to the embodiment , the cam surface of the cam 175 moves the optical sensor unit 150 to the second position at the predetermined first rotation position of the cam 175 and contacts the secondary transfer roller 21. While moving to the position, the optical sensor unit 150 was moved to the first position at the second rotational position, and the secondary transfer roller 21 was moved to the separated position. As the cam surface, in addition to the above-described function, a cam surface is added which has a function of moving the optical sensor unit to the second position at the third rotational position and moving the secondary transfer roller 21 to the separated position. Then, a known detection sensor for detecting the opening operation of the opening / closing cover 51 is provided, and when the opening operation is detected by this detection sensor, the cam 175 may be rotated to the third rotation position described above.

  Up to now, the first belt region and the second belt region are both belt-wrapping regions, and the first belt region is closer to the center La of the belt-wrapping region than the second belt region. Although a printer has been described that employs a configuration in which the position is a position facing the first belt area and the second position is a position facing the second belt area, the following may be employed. . In other words, the first position is a position facing the belt wrapping area, while the second position is a position not facing the belt wrapping area.

  In addition, a printer having a configuration in which a toner image based on a user command such as a print command is transferred from the photosensitive member to the intermediate transfer belt 10 has been described. However, the toner image may be transferred as follows. . That is, as in the image forming apparatus described in Patent Document 1, the image is directly transferred from the photoreceptor to the belt member. Even in such a configuration, the positional deviation detection pattern is transferred to the surface of the belt member instead of the recording paper on the belt member, so that the reflective photosensor detects the positional deviation detection pattern. Is possible.

As described above, in the printer according to the reference embodiment, when the recording paper P as a specific member enters the first position, the sensor movement is performed so that the optical sensor unit 150 is retracted from the first position to the second position. Means. In such a configuration, the first position with respect to the optical sensor unit 150 is avoided while avoiding the occurrence of jammed paper due to the recording paper P being fed into the feeding conveyance path while the optical sensor unit 150 is present at the first position. Thus, it is possible to accurately detect a gradation pattern image and a patch pattern image.

In the printer according to the reference embodiment, the toner on the surface of the intermediate transfer belt 10 is a secondary transfer nip serving as a transfer position where the transfer unit 9 serving as a transfer unit closely contacts the surface of the intermediate transfer belt 10 with the recording paper P. A pair of registration rollers 28 serving as feeding means for transferring the image onto the recording paper P and feeding the recording paper P toward the secondary transfer nip at a predetermined timing is disposed in the housing of the printer main body. The specific member that enters the first position at the timing is the recording paper P that is fed from the registration roller pair 28 toward the secondary transfer nip, and the first position is that the recording paper P is fed to the registration roller pair 28. To the secondary transfer nip. In such a configuration, as the first position where the optical sensor unit 150 detects the gradation pattern and the patch pattern with high accuracy, the size of the apparatus is increased by using the feeding conveyance path through which the recording paper is fed at a predetermined timing. Can be avoided.

In the printer according to the reference embodiment, the tension roller that stretches the intermediate transfer belt 10 at the secondary transfer nip as a transfer position is used as a tension roller that forms a belt-wrapping region at a position facing the optical sensor unit 150. A secondary transfer nip entrance roller that is adjacent to the driving roller 12 that is a rack roller on the upstream side in the belt moving direction is employed. In such a configuration, the optical sensor unit 150 is opposed to the belt-wrapped portion of the secondary transfer nip entrance roller 14 so that the optical sensor unit 150 can accurately detect the pattern in the feeding and conveying path. Effective use as the first position can be easily realized.

In the printer according to the embodiment , the optical sensor unit 150 is centered on the rotation center of the secondary transfer nip entrance roller 14 that is a stretching roller that forms a belt-wrapping region at a position facing the optical sensor unit 150. The sensor moving means is configured to swing. In this configuration, as described above, the optical sensor unit 150 can be moved between the first position and the second position without newly providing support means for movably supporting the optical sensor unit 150. Can do. Furthermore, since the distance between the belt surface and the sensor detection surface is made constant regardless of the movement position of the optical sensor unit 150, even if a slight stop position deviation occurs in the optical sensor unit 150, the detection error caused by the deviation is reduced. Occurrence can be avoided.

Further, in the printer according to the reference embodiment, the protective member 102 that protects the optical sensor unit 150 is provided between the optical sensor unit 150 and the intermediate transfer belt 10 at the second position. In this configuration, the toner that falls from the front surface of the intermediate transfer belt 10 toward the detection surface of each reflective photosensor of the optical sensor unit 150 at the second position is received by the protective member 102 before reaching the detection surface. As a result, the occurrence of toner contamination on the detection surface can be suppressed. Thereby, it is possible to suppress a decrease in detection capability over time due to the progress of toner contamination.

Further, in the printer according to the reference embodiment, as a cleaning member that cleans the detection surface of each reflective photosensor by rubbing against the optical sensor unit 150 moving from the first position toward the second position. The cleaning brush 103 is fixed to the protection member 102. In such a configuration, even if toner contamination is generated on the detection surface of each reflective photosensor, the toner contamination can be removed by cleaning with the cleaning brush 103. Thereby, it is possible to avoid the deterioration of detection accuracy due to the progress of toner contamination.

Further, in the printer according to the first reference example , the sensor movement is performed so that the first conveyance guide plate 41 that guides the recording paper P in the feeding conveyance path toward the secondary transfer nip is moved together with the optical sensor unit 150. Means. In this configuration, as described above, it is not necessary to provide the first conveyance guide plate 41 with a large opening for allowing the optical sensor unit 150 to pass therethrough, so that the recording paper is hooked on the opening of the first conveyance guide plate 41. It is possible to avoid the occurrence of jams.

In the printer according to the second reference example , a secondary transfer roller 21 serving as a transfer nip forming member that contacts the intermediate transfer belt 10 to form a secondary transfer nip is provided, and the second position is changed from the first position to the second position. The secondary transfer roller 21 is brought into contact with the intermediate transfer belt 10 in conjunction with the movement of the optical sensor unit 150 to the second position, while the second movement is performed in conjunction with the movement of the optical sensor unit 150 from the second position to the first position. A sensor moving unit is configured to separate the next transfer roller 21 from the intermediate transfer belt 10. In such a configuration, as described above, the contact / separation operation of the secondary transfer roller 21 and the movement operation of the optical sensor unit 150 are performed by one drive source (cam drive motor), so that each operation is performed. Compared with the case of using an individual drive source, the cost can be reduced and the control program can be simplified.

Further, in the printer according to the first reference specific example, the sensor moving unit is configured to move the optical sensor unit 150 by using the driving force of the registration roller pair 28 serving as the feeding unit. In such a configuration, the registration driving motor is also used as a driving source of the sensor moving unit that moves the optical sensor unit 150, so that the registration roller pair 28 and the sensor moving unit are respectively driven by separate driving sources. Costs can be reduced and the control program can be simplified.

Further, in the printer according to the second reference specific example, an opening / closing cover as an opening / closing door for exposing the jammed paper, which is the recording paper P jammed in the secondary transfer nip or the front and back thereof, to the outside of the printer body housing When the opening / closing cover 51 is opened, the optical sensor unit 150 is retracted to the second position and the secondary transfer roller 21 is separated from the intermediate transfer belt 10 when the opening / closing cover 51 is opened. It constitutes a moving means. In this configuration, as described above, when the opening / closing cover 51 is opened, the register roller pair 28 is separated from the intermediate transfer belt 10, so that the jam paper removal workability can be improved. Further, when the open / close cover 51 is opened, the optical sensor unit 150 is retracted to the second position, so that the user accidentally touches the optical sensor unit 150 existing at the first position exposed to the outside. The occurrence of a situation can be avoided.

1 is a schematic configuration diagram showing a printer according to a reference form. FIG. 3 is an enlarged configuration diagram illustrating an enlarged periphery of a secondary transfer nip of a printer according to a reference embodiment. The schematic diagram which shows the modification of a gradation pattern and a patch pattern. The expanded block diagram for demonstrating the movement to the 1st position from the 2nd position of an optical sensor unit. FIG. 3 is an enlarged configuration diagram illustrating an optical sensor unit of a printer according to a first reference example and a surrounding configuration thereof. FIG. 3 is an enlarged configuration diagram for explaining movement of an optical sensor unit from a second position to a first position in the printer. FIG. 9 is an enlarged configuration diagram for explaining movement of an optical sensor unit from a second position to a first position in a printer according to a second reference example . FIG. 8 is an enlarged configuration diagram illustrating one end portion of the printer according to the second reference specific example. The block diagram which shows a part of electric circuit in the printer which concerns on a reference form. FIG. 4 is a perspective view showing a gradation pattern image formed on an intermediate transfer belt of a printer according to a reference embodiment. The graph which plotted the relationship between the electric potential of a photoconductor and the toner adhesion amount to xy coordinates. FIG. 5 is a perspective view showing a patch pattern formed on an intermediate transfer belt according to a reference form. FIG. 3 is an enlarged configuration diagram illustrating an optical sensor unit of a printer according to a reference embodiment and a surrounding configuration thereof. The perspective view which shows the link mechanism with which the sensor moving means of the printer which concerns on a 2nd reference example is equipped, and a part of transfer unit.

Explanation of symbols

1: Printer 10: Intermediate transfer belt (belt member)
12: Driving roller (stretching roller)
13: Cleaning backup roller (stretching roller)
14: Secondary transfer nip entrance roller (stretching roller)
15: Tension roller (stretching roller)
21: Secondary transfer roller (nip forming member)
25: Paper feeding cassette 26: Paper feeding roller 27: Conveying roller 28: Registration roller pair (feeding means)
40: Second conveyance guide plate 41: First conveyance guide plate 51: Opening / closing cover (opening / closing door)
102: Protection member 103: Cleaning member 150: Optical sensor unit

Claims (7)

An image carrier that carries a toner image, an endless belt member that is endlessly moved while being stretched by a plurality of rotatable tension rollers, and a toner image carried on the image carrier. A transfer means for transferring to the surface of the member, and an optical sensor for detecting a toner image on the surface or a toner adhesion amount per unit area on the toner image based on a change in optical characteristics on the surface of the belt member; And a control means for performing a predetermined process based on a detection result by the optical sensor, and a belt front with respect to a region where the belt member is wound around any one of the plurality of stretching rollers. first position opposite from the side, the image forming instrumentation to temporarily enter the moving member, which is moved by the recording member, or driving means, is conveyed to record a toner image In,
By swinging the optical sensor about a rotation center of the tension roller to form the hook turning region, wherein said optical sensor between the second position not opposed to the hook turning region and the first position A sensor moving means for moving
An image forming apparatus, wherein the control unit is configured to perform the predetermined process based on a detection result by the optical sensor at the first position. An image carrier that carries a toner image, an endless belt member that is endlessly moved while being stretched by a plurality of rotatable tension rollers, and a toner image carried on the image carrier. A transfer means for transferring to the surface of the member, and an optical sensor for detecting a toner image on the surface or a toner adhesion amount per unit area on the toner image based on a change in optical characteristics on the surface of the belt member; And a control means for performing a predetermined process based on a detection result by the optical sensor, and a first area that is a region in which the belt member is wound around any one of the plurality of stretching rollers. first position opposed to the belt region from the belt front side, the moving member that is moved by the recording member, or driving means, is conveyed to record a toner image, a An image forming apparatus for time to enter,
Around the rotational center of the tension roller to form the hook turning region by swinging the optical sensor, where the relative center of the belt moving direction of the seat turning region away than the first belt region a second position facing the second belt region is a region of a said hook turning region, from the belt front side, the sensor moving means for moving the optical sensor between said first position is provided,
An image forming apparatus, wherein the control unit is configured to perform the predetermined process based on a detection result by the optical sensor at the first position. The image forming apparatus according to claim 1 or 2,
The image forming apparatus is characterized in that the sensor moving means is configured to retract the optical sensor from the first position to the second position when the recording member or the moving member enters the first position. apparatus. The image forming apparatus according to claim 3,
The transfer means, the toner image carried on the image carrier onto In addition to having a first transfer means for transferring to the surface of the belt member, a transfer position in which the recording member is in close contact with the surface of the belt member And a second transfer means for transferring the toner image on the surface of the belt member to the recording member.
The recording member infeed means for feeding toward the transfer position, is disposed in the image forming apparatus main body in the casing,
The member that temporarily enters the first position is the recording member that is fed from the feeding means toward the transfer position,
In addition, the image forming apparatus is characterized in that the first position is a position in a feeding conveyance path for conveying the recording member from the feeding means toward the transfer position. The image forming apparatus according to claim 4.
As a stretching roller that forms the above-mentioned hanging area,
An image forming apparatus characterized in that a stretch roller adjacent to the second transfer means on the upstream side in the belt moving direction is employed. The image forming apparatus according to claim 1 to 5,
An image forming apparatus comprising: a protective member that is interposed between the optical sensor and the belt member at the second position to protect the optical sensor. The image forming apparatus according to claim 6 .
An image forming apparatus, wherein a cleaning member that cleans the optical sensor by rubbing against the optical sensor moving from the first position toward the second position is fixed to the protective member .

Images