JP5574234B2 - Image forming apparatus - Google Patents

Description

  The present invention detects the toner image on the surface of the image carrier or the amount of toner adhering to the toner image based on the result of detecting the specularly reflected light on the surface of the image carrier by a reflection type optical sensor. The present invention relates to an image forming apparatus.

  Conventionally, as this type of image forming apparatus, the one described in Patent Document 1 is known. This image forming apparatus performs image forming condition adjustment processing at a predetermined timing immediately after the power is turned on or every time a predetermined number of prints are performed. In the image forming condition adjustment processing, first, a predetermined reference toner image is formed on the surface of the intermediate transfer belt as an image carrier. Then, the light emitted from the LED as the light source of the reflection type optical sensor is reflected by the reference toner image carrying region in the intermediate transfer belt, and the obtained regular reflection light is detected by the regular reflection light receiving unit of the reflection type optical sensor. Based on the amount of received light, the position of the reference toner image on the intermediate transfer belt is grasped, and the amount of toner attached to the reference toner image is grasped. Thereafter, image forming conditions such as toner image formation timing, photosensitive member uniform charging potential, developing bias, and optical writing intensity with respect to the photosensitive member are adjusted based on the grasped results. Thereby, stable image quality can be maintained over a long period of time.

  If the light transmission / reception surface made of glass or the like of the reflection type optical sensor becomes dirty due to adhesion of toner, the surface of the intermediate transfer belt cannot be irradiated normally or the reflected light is received normally. It becomes impossible to do. Therefore, in the image forming apparatus described in Patent Document 1, a shutter member that covers the light transmitting / receiving surface of the reflective optical sensor so as to be openable and closable is provided on the support that supports the reflective optical sensor. When the reflective optical sensor is not used, the light transmission / reception surface is covered with a shutter member to suppress the adhesion of dirt to the light transmission / reception surface.

  In order to suppress the adhesion of dirt to the light transmitting / receiving surface as much as possible, it is necessary to shorten the opening time of the shutter member as much as possible. For this reason, it is desirable that the opening timing is limited only when the toner image on the intermediate transfer belt is detected or the toner adhesion amount on the toner image is detected.

  However, in the image forming apparatus described in Patent Document 1, it is necessary to open the shutter member when calibrating the reflective optical sensor in addition to detecting the toner image and the toner adhesion amount on the intermediate transfer belt. was there. Specifically, a light source such as an LED gradually decreases its light emission performance with long-term use, so that the amount of light emitted over time can be measured under the simple condition that a constant current is supplied. Will be reduced. In addition, since the light reflectivity of the surface of an image carrier such as an intermediate transfer belt generally decreases with time as the surface deteriorates, the amount of light emitted from the light source is constant over a long period of time. Even if maintained, the amount of reflected light on the surface of the image carrier decreases with time. For this reason, with respect to the reflection type optical sensor, calibration processing is periodically performed to adjust the light emission amount of the light source so that a predetermined amount of reflected light can be obtained on a solid surface that does not carry the toner image of the image carrier. There is a need. In this calibration process, the light emitted from the light source must reach the solid surface of the image carrier to obtain reflected light, so the shutter member must be opened.

  The present invention has been made in view of the above background, and an object of the present invention is to provide an image forming apparatus capable of shortening the opening time of the shutter member as compared with the prior art.

  The present inventor has completed the present invention by paying attention to the following phenomenon. That is, the light reflectivity of the surface of the image carrier gradually decreases over a long period, but hardly changes in a very short period such as several days. In the conventional image forming apparatus, the combination of the calibration process and the image forming condition adjustment process is performed at time intervals such as every several tens of prints. It is almost impossible to greatly change the reflectivity. For this reason, after adjusting the light emission amount of the light source so that a desired reflected light amount can be obtained on the solid surface of the image carrier by the calibration process, even if the next calibration process is performed, Sometimes, even if the formal calibration process of actually obtaining reflected light on the surface of the image carrier is not performed, the desired amount of reflected light can be obtained by emitting the light source with the same amount of light emission as immediately after the previous calibration process. be able to.

In order to achieve the above object, an invention according to claim 1 includes an image carrier that carries a toner image on its surface, a toner image forming unit that forms a toner image on the surface of the image carrier, and a light source. A reflection-type optical sensor that receives regular reflection light obtained by being reflected on the surface of the image carrier after being emitted from the light by a regular reflection light-receiving unit, and outputs a signal corresponding to the received light amount; and the reflection-type optical sensor A shutter member that covers the light transmission / reception surface of the sensor so as to be openable and closable, and for detecting a toner image formed on the surface of the image carrier based on the signal, or toner adhesion per unit area to the toner image The signal output from the specular reflection light receiving unit that receives the specular reflection light that is specularly reflected by the toner image non-carrying region on the surface of the image carrier and the arithmetic unit that performs arithmetic processing for obtaining the quantity The skin part that is A calibration unit that performs a calibration process for adjusting the light emission amount of the light source based on a reflection signal, wherein the calibration unit sets the regular reflection signal of the background portion to a predetermined value. First calibration processing for adjusting the light emission amount of the light source, and the light emitted from the light source under the condition of the light emission amount after the shutter member is closed and calibrated by the first calibration processing are reflected on the back surface of the shutter member. , combined conduct regular and the reflected light received by said signal storage processing for storing the back reflection signal is a signal output from the specular reflection light receiving unit in the data storage means, the implementation of the constant-term the combination During the timing, the light emission amount of the light source is adjusted so that the back surface reflection signal output from the regular reflection light receiving unit has the same value as the back surface reflection signal stored in the data storage means. Execute calibration process, and, during the continuous printing operation, out of the circumferential direction of the entire region in the endless moving surface of the image bearing member, corresponding to the recording sheet is caused to transfer the toner image on the surface of the image bearing member The second calibration process is performed when the sheet corresponding area to be moved is made to enter the position facing the reflective optical sensor .
The invention according to claim 2 is the image forming apparatus according to claim 1, wherein the proofreading unit obtains the background regular reflection signal acquired a plurality of times within a predetermined period in the first proofreading process. The light emission amount of the light source is adjusted so that the average value becomes the predetermined value.
According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, the shutter member having a polished back surface is used .
Also, the invention of claim 4, in any of the image forming apparatus according to claim 1 to 3,
The distance L ₀ between the reflective optical sensor and the image carrier and the distance L _c between the reflective optical sensor and the back surface have a relationship of “L _c / L _o > 0.2”. It is characterized by that.

  In these inventions, in the first calibration process, while the light emitted from the light source of the reflective optical sensor is actually reflected on the solid surface of the image carrier in the same manner as in the past, the amount of specular reflection is set to a desired value. Adjust the light emission amount of the light source so that In the signal storage process, the light emitted from the light source is reflected by the back surface of the shutter member under the condition of the light emission amount after calibration by the first calibration process, and is received by the regular reflection light receiving unit. At this time, the back surface reflection signal output from the regular reflection light receiving unit with a value corresponding to the light emission amount of the light source is stored in the data storage means. Thereafter, when the timing of the calibration process comes again, the second calibration process is performed instead of the first calibration process. In this second calibration process, the light emission amount of the light source is adjusted so that the back surface reflection signal obtained with the shutter member closed is the same value as the back surface reflection signal stored in the data storage means. The amount is set to the same value as immediately after the first calibration process. Thereby, the implementation frequency of the 1st calibration process which must be implemented in the state which opened the shutter member can be reduced compared with the past, and the opening time of a shutter member can be shortened compared with the past.

1 is a schematic configuration diagram showing a copier according to an embodiment. FIG. 2 is an enlarged configuration diagram illustrating an enlarged configuration of a printing unit of the copier. FIG. 3 is an enlarged configuration diagram illustrating an image forming unit in the print unit. The front view which shows the optical sensor unit of the same printing part with an intermediate transfer belt. FIG. 3 is an enlarged configuration diagram showing a first end photosensor of the optical sensor unit together with an intermediate transfer belt. Expanded configuration diagram showing the Y photosensor of the optical sensor unit together with the intermediate transfer belt FIG. 3 is an enlarged side view showing the optical sensor unit together with an intermediate transfer belt. FIG. 3 is an enlarged side view showing the optical sensor unit with an intermediate transfer belt in a state where a shutter member is closed. 6 block diagram showing a part of an electric circuit in the copier. FIG. 4 is a plan view showing an intermediate transfer belt and a patch pattern image for detecting the toner adhesion amount of each color formed on the surface of the intermediate transfer belt. 6 is a graph showing a target image density characteristic curve and an actual image density characteristic curve immediately before the first image forming condition adjustment processing is performed. 6 is a graph showing a target image density characteristic curve and an actual image density characteristic curve immediately after performing the first image forming condition adjustment process. FIG. 6 is a plan view showing a patch pattern image for toner adhesion amount detection formed by a first image forming condition adjustment process performed during a continuous printing operation. The top view which shows the patch pattern image for position shift detection formed by the 2nd image formation condition adjustment process with an intermediate transfer belt. 6 is a graph showing the relationship between the cumulative number of prints made by this copying machine and the background regular reflection output voltage from various photosensors of the optical sensor unit. The graph which shows the relationship between the cumulative number of printed sheets and the LED light emission amounts of various photosensors. The expanded block diagram which shows the Y photosensor which is made to light-emit LED in the state in which the shutter member is closed. The graph which shows the relationship between LED light emission amount of various photosensors, and back surface reflective output voltage. The graph which shows the relationship between a back surface regular reflection output voltage and a background part regular reflection output voltage. 6 is a flowchart showing a control flow of image forming condition adjustment processing performed by the control unit of the copier. The expanded block diagram which shows Y photosensor 154Y when implementing the 1st calibration process. The flowchart which shows the flow of the 1st calibration process and signal storage process which are implemented by the control part. The flowchart which shows the flow of the 2nd calibration process implemented by the control part. The graph which shows the relationship between shutter distance _Lc and back surface reflective output voltage. The graph which shows the time-dependent change of the background regular reflection output voltage from the photo sensor which makes the test object the intermediate transfer belt whose surface deterioration has advanced. 9 is a timing chart showing various operation timings when a patch image formed in the inter-paper corresponding area of the intermediate transfer belt is detected by a photosensor during the first image forming condition adjustment processing.

  Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of a so-called tandem type full-color electrophotographic copying machine (hereinafter simply referred to as “copying machine”) provided with a plurality of photosensitive members will be described. First, a basic configuration of the copying machine according to the embodiment will be described. FIG. 1 is a schematic configuration diagram illustrating a copying machine according to an embodiment. In FIG. 1, a copying machine includes a printing unit 100 that forms an image, a paper feeding device 200 on which the printing unit 100 is mounted and that supplies recording paper 5 as a recording member to the printing unit 100, and a printing unit. A scanner 300 that is mounted on 100 and reads a document image, and an automatic document feeder (ADF) 400 that is mounted on the scanner 300 are provided. The printing unit 100 is provided with a manual feed tray 6 for manually feeding the recording paper 5 and a paper discharge tray 7 for discharging the recording paper 5 on which an image has been formed.

  FIG. 2 is an enlarged configuration diagram illustrating the configuration of the printing unit 100 in an enlarged manner. The print unit 100 is provided with an endless intermediate transfer belt 10 which is an intermediate transfer member and an image carrier. The material of the intermediate transfer belt 10 is made of polyimide that has excellent mechanical characteristics in order to prevent displacement due to belt elongation.

  The intermediate transfer belt 10 is endlessly moved in the clockwise direction in the figure by the rotational drive of any one of the support rollers in a state of being stretched around the three support rollers 14, 15, and 16. As shown in FIG. 2, yellow (Y), cyan (C), and magenta are provided on the belt stretched portion between the first support roller 14 and the second support roller 15 among the support rollers 14, 15, and 16. Four image forming units 18Y, 18C, 18M, and 18K of (M) and black (K) are arranged side by side. In addition, a belt patch portion between the second support roller 15 and the third support roller 16 detects a reference patch image, which is a reference toner image formed on the intermediate transfer belt 10, and attaches toner to the reference patch image. An optical sensor unit 150 for detecting the amount is attached.

  A laser writing device 21 is provided above the image forming units 18Y, 18C, 18M, and 18K as shown in FIG. The laser writing device 21 emits writing light by driving a semiconductor laser (not shown) by a laser control unit (not shown) based on the image information of the original read by the scanner 300. Then, the writing light exposes and scans the drum-shaped photoconductors 20Y, 20C, 20M, and 20K, which are latent image carriers provided in the image forming units 18Y, 18C, 18M, and 18K, and electrostatically scans the photoconductors. A latent image is formed. Note that the light source of the writing light is not limited to the laser diode, and may be an LED, for example.

  FIG. 3 is an enlarged configuration diagram showing two of the four image forming units 18Y, 18C, 18M, and 18K. The four image forming units 18Y, 18C, 18M, and 18K have the same configuration except that the colors of the toners used are different from each other. Therefore, in FIG. The subscripts Y, C, M, and K are omitted. In the following description, these subscripts are omitted as appropriate.

  In the image forming unit 18, a charging device 60, a developing device 61, a photoconductor cleaning device 63, and a charge removal device 64 are provided around the photoconductor 20. A primary transfer device 62 is provided at a position facing the photoconductor 20 via the intermediate transfer belt 10.

  The charging device 60 is of a contact charging type employing a charging roller, and uniformly charges the surface of the photoconductor 20 by applying a voltage in contact with the photoconductor 20. As the charging device 60, a non-contact charging type using a non-contact scorotron charger or the like can be used.

  The developing device 61 uses a two-component developer composed of a magnetic carrier and a non-magnetic toner. As the developer, a one-component developer may be used. The developing device 61 can be broadly divided into a stirring unit 66 and a developing unit 67 provided in the developing case 70. In the agitating unit 66, a two-component developer (hereinafter simply referred to as “developer”) is conveyed while being agitated and supplied onto a developing sleeve 65, which will be described later, as a developer carrying member. The stirring unit 66 is provided with two parallel screws 68, and a partition plate is provided between the two screws 68 for partitioning so that both ends communicate with each other. Further, a toner concentration sensor 71 for detecting the toner concentration of the developer in the developing device 61 is attached to the developing case 70. On the other hand, in the developing unit 67, the toner in the developer attached to the developing sleeve 65 is transferred to the photoconductor 20. The developing portion 67 is provided with a developing sleeve 65 facing the photoreceptor 20 through the opening of the developing case 70, and a magnet (not shown) is fixedly disposed in the developing sleeve 65. A doctor blade 73 is provided so that the tip of the developing sleeve 65 approaches.

  In the developing device 61, the developer is conveyed and circulated while being stirred by the two screws 68 and supplied to the developing sleeve 65. The developer supplied to the developing sleeve 65 is pumped up to the sleeve surface by the magnetic force generated by the magnet roller disposed in the developing sleeve 65. The developer pumped up by the developing sleeve 65 is conveyed along with the rotation of the developing sleeve 65 and is regulated to an appropriate amount by the doctor blade 73. The regulated developer is returned to the stirring unit 66. Thus, the developer conveyed to the developing area facing the photoconductor 20 becomes a spiked state by the magnetic force generated by the magnet roller, and forms a magnetic brush. In the developing region, a developing electric field that moves the toner in the developer to the electrostatic latent image portion on the photoreceptor 20 is formed by the developing bias applied to the developing sleeve 65. As a result, the toner in the developer is transferred to the electrostatic latent image portion on the photoreceptor 20, and the electrostatic latent image on the photoreceptor 20 is visualized to form a toner image. The developer that has passed through the developing region is transported to a portion where the magnetic force of the magnet is weak, and thus is separated from the developing sleeve 65 and returned to the stirring unit 66. When the toner concentration in the stirring unit 66 becomes light by repeating such an operation, the toner concentration sensor 71 detects this, and the toner is supplied to the stirring unit 66 based on the detection result.

  As the primary transfer device 62, a primary transfer roller is adopted, and is installed so as to be pressed against the photoconductor 20 with the intermediate transfer belt 10 interposed therebetween. The primary transfer device 62 may not be a roller shape, but may be a conductive brush shape, a non-contact corona charger, or the like.

  The photoconductor cleaning device 63 includes a cleaning blade 75 made of, for example, polyurethane rubber, which is disposed so that the tip thereof is pressed against the photoconductor 20. In this embodiment, in order to improve the cleaning performance, a conductive fur brush 76 that contacts the photoconductor 20 is also used. The toner removed from the photoconductor 20 by the cleaning blade 75 and the fur brush 76 is accommodated in the photoconductor cleaning device 63.

  The static eliminator 64 including a static eliminator lamp irradiates light to initialize the surface potential of the photoreceptor 20. The image forming unit 18 is provided with a potential sensor 120 facing the photoconductor 20. The potential sensor 120 is provided so as to face the photoconductor 20 and detects the surface potential of the photoconductor 20.

  The surface of the photoconductor 20 is uniformly charged to, for example, −700 V by the charging device 60, and the potential of the electrostatic latent image portion irradiated with the laser light from the laser writing device 21 is, for example, −120 V. On the other hand, the developing bias is −470 V, for example, and a developing potential of 350 V acts between the electrostatic latent image and the developing sleeve.

  In FIG. 1 described above, the image forming unit 18 first charges the surface of the photoconductor 20 uniformly by the charging device 60 as the photoconductor 20 rotates. Next, based on the image information read by the scanner 300, laser writing light is emitted from the laser writing device 21 to form an electrostatic latent image on the photoconductor 20. Thereafter, the electrostatic latent image is visualized by the developing device 61 to form a toner image. This toner image is primarily transferred onto the intermediate transfer belt 10 by the primary transfer device 62. The transfer residual toner remaining on the surface of the photoconductor 20 after the primary transfer is removed by the photoconductor cleaning device 63, and then the surface of the photoconductor 20 is discharged by the charge removal device 64 and used for the next image formation. The

  In FIG. 2, a secondary transfer roller 24 as a secondary transfer device is provided at a position facing the third support roller 16 among the three support rollers. When the toner image on the intermediate transfer belt 10 is secondarily transferred onto the recording paper 5, the secondary transfer roller 24 is pressed against the portion of the intermediate transfer belt 10 wound around the third support roller 16. Next transfer nip is formed. The secondary transfer device may not be configured using the secondary transfer roller 24 but may be configured using, for example, a transfer belt or a non-contact transfer charger. The secondary transfer roller 24 is in contact with a roller cleaning unit 91 that cleans toner adhering to the secondary transfer roller 24.

  An endless belt-like transport belt 22 is disposed between the two rollers 23a and 23b on the downstream side of the secondary transfer roller 24 in the recording paper 5 transport direction. Further, a fixing device 25 for fixing the toner image transferred onto the recording paper 5 is provided further downstream in the transport direction. The fixing device 25 has a configuration in which a pressure roller 27 is pressed against the heating roller 26. Further, a belt cleaning device 17 is provided at a position facing the second support roller 15 among the support rollers of the intermediate transfer belt 10. The belt cleaning device 17 is for removing residual toner remaining on the intermediate transfer belt 10 after the toner image on the intermediate transfer belt 10 is transferred to the recording paper 5.

  As shown in FIG. 1, the printing unit 100 is provided with a conveyance path 48 that guides the recording paper 5 fed from the paper feeding device 200 to the paper discharge tray 7 via the secondary transfer roller 24. Yes. Along the conveyance path 48, a conveyance roller 49a, a registration roller 49b, a discharge roller 56, and the like are also provided. A switching claw 55 is provided on the downstream side of the conveyance path 48 to switch the conveyance direction of the recording paper 5 after transfer to the paper discharge tray 7 or the sheet reversing device 93. The paper reversing device 93 reverses the recording paper 5 and sends it again to the secondary transfer roller 24.

  The print unit 100 is also provided with a manual paper feed path 53 that joins from the manual feed tray 6 to the transport path 48, and a sheet of recording paper 5 set on the manual feed tray 6 is disposed upstream of the manual paper feed path 53. A paper feed roller 50 and a separation roller 51 are provided for feeding paper one by one.

  The paper feeding device 200 includes a plurality of paper feeding cassettes 44 for storing the recording paper 5, a paper feeding roller 42 and a separation roller 45 for feeding the recording papers stored in the paper feeding cassettes 44 one by one, and the fed recording paper Is composed of a transport roller 47 that transports the paper along the paper feed path 46. The paper feed path 46 is connected to the transport path 48 of the printing unit 100.

  The scanner 300 reciprocates the first and second traveling bodies 33 and 34 mounted with a document illumination light source and a mirror in order to read and scan a document (not shown) placed on the contact glass 31. Let The image information scanned by the traveling bodies 33 and 34 is collected by the imaging lens 35 on the imaging surface of the reading sensor 36 installed behind the imaging lens 35 and read by the reading sensor 36 as an image signal.

  When copying a document using the copying machine, first, the document is set on the document table 30 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 31 of the scanner 300, and the automatic document feeder 400 is closed and pressed by it. Thereafter, when the user presses a start switch (not shown), when the document is set on the automatic document feeder 400, the document is conveyed onto the contact glass 31. Then, the scanner 300 is driven and the first traveling body 33 and the second traveling body 34 start traveling. Thereby, the light from the first traveling body 33 is reflected by the document on the contact glass 31, and the reflected light is reflected by the mirror of the second traveling body 34 and guided to the reading sensor 36 through the imaging lens 35. . In this way, the image information of the original is read.

  When the start switch is pressed by the user, a drive motor (not shown) is driven, and one of the support rollers 14, 15, 16 is rotationally driven to rotate the intermediate transfer belt 10. At the same time, the photosensitive members 20Y, 20C, 20M, and 20K of the image forming units 18Y, 18C, 18M, and 18K are also rotationally driven. Thereafter, based on the image information read by the reading sensor 36 of the scanner 300, the writing light is applied from the laser writing device 21 onto the photoreceptors 20Y, 20C, 20M, 20K of the image forming units 18Y, 18C, 18M, 18K. Are each irradiated. As a result, electrostatic latent images are formed on the respective photoreceptors 20Y, 20C, 20M, and 20K, and are visualized by the developing devices 61Y, 61C, 61M, and 61K. Then, yellow, cyan, magenta, and black toner images are formed on the photoreceptors 20Y, 20C, 20M, and 20K, respectively.

  Each color toner image formed in this way is primarily transferred by the primary transfer rollers 62Y, 62C, 62M, and 62K so as to sequentially overlap the intermediate transfer belt 10. As a result, a composite toner image in which the toner images of the respective colors overlap is formed on the intermediate transfer belt 10. The transfer residual toner remaining on the intermediate transfer belt 10 after the secondary transfer is removed by the belt cleaning device 17.

  When the user presses the start switch, the paper feeding roller 42 of the paper feeding device 200 corresponding to the recording paper 5 selected by the user rotates and the recording paper 5 is sent out from one of the paper feeding cassettes 44. The fed recording paper 5 is separated into one sheet by the separation roller 45 and enters the paper feed path 46, and is conveyed by the conveyance roller 47 to the conveyance path 48 in the printing unit 100. The recording paper 5 thus transported is stopped when it hits the registration roller 49b.

  The registration roller 49 b starts to rotate in accordance with the timing at which the composite toner image formed on the intermediate transfer belt 10 as described above is conveyed to the secondary transfer unit facing the secondary transfer roller 24. The recording paper 5 sent out by the registration roller 49 b is sent between the intermediate transfer belt 10 and the secondary transfer roller 24, and the secondary transfer roller 24 causes the composite toner image on the intermediate transfer belt 10 to be transferred onto the recording paper 5. Secondary transfer is performed. Thereafter, the recording paper 5 is conveyed to the fixing device 25 while being attracted to the secondary transfer roller 24, and heat and pressure are applied by the fixing device 25 to perform a toner image fixing process. The recording paper 5 that has passed through the fixing device 25 is discharged to the paper discharge tray 7 by the discharge roller 56 and stacked. When image formation is performed also on the back surface of the surface on which the toner image is fixed, the conveying direction of the recording paper 5 that has passed through the fixing device 25 is switched by the switching claw 55 and sent to the paper reversing device 93. The recording paper 5 is then reversed and guided again to the secondary transfer roller 24.

  FIG. 4 is a front view showing the optical sensor unit 150 together with the intermediate transfer belt 10. The optical sensor unit 150 is disposed below the intermediate transfer belt 10 in the vertical direction. A plurality of photosensors fixed to the support member 157, a shutter member 156, a shutter solenoid (not shown), and the like are included. Specifically, the photosensors fixed to the support member 157 include a first end photosensor 151, a center photosensor 152, a second end photosensor 153, a Y photosensor 154Y, a C photosensor 154C, and an M photosensor. 154M and K photosensor 154K. Of these seven, the first end photosensor 151, the center photosensor 152, the second end photosensor 153, the Y photosensor 154Y, the C photosensor 154C, and the M photosensor 154M are respectively multi-reflection type optical sensors. Become. The K photosensor is a regular reflection type optical sensor.

  The copying machine forms a K-patch toner image (K patch image) for detecting misregistration and a K patch image for detecting the toner adhesion amount on the surface of the intermediate transfer belt 10 in an image forming condition adjusting process described later. The first end photosensor 151 is for detecting a K-patch image for misregistration detection formed at one end in the width direction of the intermediate transfer belt 10. The center photosensor 152 is for detecting a K-patch image for detecting misregistration formed at the center in the width direction of the intermediate transfer belt 10. The second end photosensor 153 is for detecting a K-patch image for detecting misregistration formed at the other end in the width direction of the intermediate transfer belt 10. The K photo sensor 154K is for detecting the K toner adhesion amount with respect to the K patch image for toner adhesion amount detection formed on the surface of the intermediate transfer belt 10. The Y, C, and M photosensors 154Y, C, and M indicate Y, C, and M toner adhesion amounts with respect to Y, C, and M patch images for toner adhesion amount detection formed on the surface of the intermediate transfer belt 10, respectively. It is for detection.

  FIG. 5 is an enlarged configuration diagram showing the K photo sensor 154K together with the intermediate transfer belt 10. As shown in FIG. The K photosensor 154K made up of a regular reflection type optical sensor has an LED 154aK as a light source and a regular reflection light receiving unit 154bK. Then, the regular reflection light received from the LED 154aK and regularly reflected on the surface of the intermediate transfer belt 10 is received by the regular reflection light receiving unit 154bK, and a voltage corresponding to the amount of received light is output from the regular reflection light receiving unit 154bK. A control unit (not shown) of the copier is a timing at which the K patch image Kpg formed on the intermediate transfer belt 10 enters just above the K photosensor 154 based on the change in the output voltage value from the regular reflection light receiving unit 154bK. Or the amount of adhesion of K toner per unit area with respect to the K patch image Kpg.

  FIG. 6 is an enlarged configuration diagram showing the Y photosensor 154Y together with the intermediate transfer belt 10. As shown in FIG. The Y photosensor 154Y formed of a multi-reflection optical sensor includes an LED 161Y that is a light source, a regular reflection light receiving unit 162Y, and a diffuse reflection light reception unit 163Y. Then, the regular reflection light that has been emitted from the LED 161Y and specularly reflected on the surface of the intermediate transfer belt 10 is received by the regular reflection light receiving unit 162Y, and a voltage corresponding to the amount of received regular reflection light is received. Output from. Further, the diffuse reflection light received from the LED 161Y and diffusely reflected on the surface of the intermediate transfer belt 10 is received by the diffuse reflection light receiving unit 163Y, and a voltage corresponding to the amount of the diffuse reflected light is received. Output from. A control unit (not shown) of the copier applies the Y patch image Ypg formed on the intermediate transfer belt 10 based on the output voltage value from the regular reflection light receiving unit 162Y and the output voltage value from the diffuse reflection light receiving unit 163Y. The amount of Y toner attached per unit area is grasped. Since how to determine the Y toner adhesion amount based on the above two output voltage values is disclosed in detail in Japanese Patent Application Laid-Open No. 2007-33770, description thereof is omitted. Although the Y photosensor 154Y has been described, the C photosensor 154C, the M photosensor 154M, the first end photosensor 151, the center photosensor 152, and the second end photosensor 153 that are multi-type optical sensors are similarly configured. It is possible to detect the toner adhesion amount or to detect the toner image.

  FIG. 7 is an enlarged side view showing the optical sensor unit 150 together with the intermediate transfer belt 10. In the drawing, seven photosensors (151, 152, 153, 154Y to K) are fixed to the side surface of the support member 157 in such a posture that the light transmission / reception surface made of glass faces the intermediate transfer belt 10. A shutter solenoid 155 is fixed on the upper surface of the support member 157. The shutter member 156 is fixed to the drive shaft of the shutter solenoid 155 so as to be present at a position interposed between the light transmission / reception surface of each photosensor and the intermediate transfer belt 10. When the shutter solenoid 155 is not driven and the drive shaft is extended as shown in the figure, the shutter member 156 is positioned directly above the light transmitting / receiving surface of each of the seven photosensors. Cover the surface. Thus, the light transmitting / receiving surface is protected so that the toner scattered from the intermediate transfer belt 10 does not adhere to the light transmitting / receiving surface of the photosensor. When the shutter solenoid 155 is driven and its drive shaft contracts, the shutter member 156 is retracted from right above each photosensor as shown in FIG. Thereby, the light irradiation with respect to the belt by each photosensor becomes possible.

  FIG. 9 is a block diagram showing a part of an electric circuit in the copying machine. In the figure, a control unit 190 as a calculation unit includes a CPU 190a, a ROM 190c that stores a control program and various data, and a RAM 190b that temporarily stores various data. The control unit 190 includes an optical writing control circuit 192 dedicated to controlling the laser writing device, each photo sensor of the optical sensor unit 150, a shutter solenoid 155, various power sources, various motors, each color toner density sensor, and the like. It is connected via an I / O interface 191 for exchanging signals with peripheral devices.

  The optical writing control circuit 192 controls the driving of the laser writing device (21 in FIG. 1) based on a command input from the control unit 190 via the I / O interface 191. The various power sources shown in the figure are each color developing bias power source for individually outputting the developing bias applied to the developing sleeve of each color image forming unit (18Y, C, M, K), each color primary transfer roller (62Y, C, M, and K) primary transfer bias power sources for each color for individually outputting primary transfer biases to be applied. The various motors shown in the figure are each color process motor for individually driving the image forming units of each color, a belt drive motor for driving the intermediate transfer belt 10, and the like. Each color toner density sensor includes a Y toner density sensor for detecting the Y toner density of the developer in the Y developing apparatus, a C toner density sensor for detecting the C toner density of the developer in the C developing apparatus, and the M developing apparatus. An M toner density sensor for detecting the M toner density of the developer, and a K toner density sensor for detecting the K toner density of the developer in the K developing device. In addition to these various devices, a toner replenishing device (not shown) for replenishing Y, C, M, and K toners to Y, C, M, and K developing devices is also connected to the I / O interface 191. Yes.

  The copying machine is configured to perform the following image forming condition adjustment processing immediately after the power is turned on or every time a predetermined number of prints are performed. That is, in this image forming condition adjustment process, a first image forming condition adjustment process related to the image density and a second image forming condition adjustment process related to the image position are performed. In the first image formation condition adjustment process, a patch pattern image for toner adhesion amount detection is formed on the surface of the intermediate transfer belt 10 in the second image formation condition adjustment process. .

  In the first image forming condition adjustment process, Y, C, M, and K patch pattern images made of Y, C, M, and K toners are formed as patch pattern images for detecting the toner adhesion amount. Each of these patch pattern images consists of 10 patch images. For example, taking a K patch pattern image PK as an example, as shown in FIG. 10, this is 10 K patches, Y patch images PK1, PK2,. It consists of a statue. The output voltage from the regular reflection light receiving unit of the K photo sensor 154K when these K patch images respectively enter the position facing the K photo sensor 154K of the optical sensor unit is sent to the control unit 190 via the I / O interface 191. Sent to the RAM 190a. Similarly to K, for Y, C, and M, 10 Y, C, and M patch images respectively enter Y, C, and M when Y, C, and M photosensors 154Y, C, and M are opposed to Y. Output voltages from the regular reflection light receiving units of the C and M photosensors 154Y, C and M are stored in the RAM 190a. In addition, in Y, C, and M, in addition to the output voltage from the regular reflection light receiving unit, the output voltage from the diffuse reflection light reception unit is also stored in the RAM 190a.

  Based on the output voltage from the various photosensors stored in the RAM 190b and the algorithm stored in advance in the ROM 190c2, the control unit 190 sets the output voltage for each of Y, C, M, and K to Y per unit area. , C, M, and K are converted into toner adhesion amounts and stored in the RAM 190b.

  For each color of Y, C, M, and K, the control unit 190 controls the toner adhesion amount of each patch image stored in the RAM 203 and the development potential (development bias and latent image potential) when the patch image is formed. The linear function formula y = ax + b of the development characteristic indicating the relationship between the toner adhesion amount and the development potential is obtained based on Then, based on the slope a in this linear function equation, the image forming conditions such as the developing potential, laser beam writing intensity, developer toner density and the like are adjusted for each color. Details thereof are described in Japanese Patent Application Laid-Open No. 9-2111911 and the like, and thus description thereof is omitted.

FIG. 11 is a graph showing a target image density characteristic curve and an actual image density characteristic curve immediately before the first image forming condition adjustment process is performed. The image density characteristic indicates the relationship between the target value and the actual output value for various image densities. In an electrophotographic image forming apparatus, if the environment (temperature / humidity) fluctuates or heat is generated during continuous operation, the actual image density characteristic curve is L with respect to the target image density characteristic curve L ₀ . coming shift as ₁ and _{L 2.} If left unshifted, the image density cannot be reproduced normally. Therefore, the first image forming condition adjustment process is performed. Thus, as shown in FIG. 12, the image density characteristic curve deviates from the target as L ₁ and L _2, close to the target image density characteristic curve L _0, to stabilize the image density reproducibility be able to.

  The copying machine has two types of first image forming condition adjustment processing: one that is performed during a continuous printing operation, and one that is performed immediately after the power is turned on or immediately after a print job is performed. Yes. FIG. 10 shows a patch pattern image formed in the first image forming condition adjustment process performed immediately after power-on or immediately after a print job is executed. In the first image forming condition adjustment process performed during the continuous printing operation, a patch pattern image shown in FIG. 13 is formed instead of the patch pattern image shown in FIG. That is, ten patch images included in the patch pattern image are formed in different inter-paper corresponding areas on the intermediate transfer belt 10. When the execution timing of the first image formation condition adjustment processing has arrived, the control unit 190 replaces the patch pattern image shown in FIG. 10 with the patch pattern shown in FIG. Form an image.

  When the control unit 190 finishes the first image formation condition adjustment process, the control unit 190 performs a second image formation condition adjustment process. In the second image formation condition adjustment process, a patch pattern image for detecting misregistration as shown in FIG. 14 is formed at one end, the center, and the other end of the intermediate transfer belt 10 in the width direction. Each patch pattern image has a patch image Py1, Pc1, Pm1, Pk1 of each color extending in a posture inclined by 45 [°] from the belt width direction, and each color extending in a posture inclined by about −45 [°]. Patch image Patch image Py2, Pc2, Pm2, and Pk2.

  Each patch image of the patch pattern image formed at one end in the belt width direction is detected by the first end photosensor 151. Further, each patch image of the patch pattern image formed at the center in the belt width direction is detected by the center photosensor 152. Each patch image of the patch pattern image formed at the other end in the belt width direction is detected by the second end photosensor 153. If the patch image formation timing of each color is appropriate, the detection time intervals of the patch images are equal to each other. If inappropriate, the patch image formation intervals are non-uniform. And the detection time interval also becomes non-uniform. Also, if there is no skew in the optical system for optical writing, patch images of the same color are detected at the same timing among the three patch pattern images, but the detection timing differs if there is a skew. Come. The control unit 190 uses an optical mirror as an imaging condition based on the detection time interval and detection timing deviation of each patch image in the main scanning direction (same as the belt width direction) and the sub-scanning direction (same as the belt movement direction). Or the optical writing timing as an image forming condition is corrected. By such second image forming condition adjustment processing, it is possible to suppress overlay deviation and image skew of each color.

  It should be noted that the length of the patch pattern image for detecting misregistration in the belt circumferential direction is larger than the normal inter-paper area. For this reason, when forming the patch pattern image for misregistration detection during the continuous printing operation, the control unit 190 expands the inter-paper area more than usual and only detects the misregistration within the inter-paper. A patch pattern image can be formed.

  In this copying machine, when each patch pattern image is formed, the secondary transfer roller 24 shown in FIG. 1 is separated from the intermediate transfer belt 10 to avoid transfer of the patch image to the secondary transfer roller 24. It is supposed to be.

  As described above, the first end photosensor 151, the center photosensor 152, the second end photosensor 153, the Y photosensor 154Y, the C photosensor 154C, the M photosensor 154M, and the K photosensor 154K in the optical sensor unit 150. Each has a regular reflection light receiving part that is regularly reflected on the belt surface. The specular reflectivity on the belt surface of the specularly reflected light received by the specular reflection light receiving portion changes with time.

  FIG. 15 is a graph showing the relationship between the cumulative number of prints made by the copying machine and the background regular reflection output voltage from the various photosensors of the optical sensor unit 150. The background portion regular reflection output voltage is a voltage output from the regular reflection light receiving portion in a state where the regular reflection light is received on the solid surface of the intermediate transfer belt 10 that does not carry the toner image. As the amount of received light increases, the voltage value increases. The graph of FIG. 15 is created based on the results of experiments in which the background regular reflection output voltage is measured over time in a state where the light emission amounts of the LEDs of various photosensors are kept constant. As shown in the figure, the regular reflection output voltage of the background portion decreases as the cumulative number of prints of the copying machine increases even though the light emission amount of the LED is kept constant. This is because as the cumulative number of prints increases, the surface deterioration of the intermediate transfer belt 10 progresses and the light regular reflection on the belt surface decreases.

  FIG. 16 is a graph showing the relationship between the cumulative number of prints and the LED light emission amount of the optical sensor unit 150. This graph is created based on the result of an experiment in which the amount of light emitted from an LED is measured over time under the condition of supplying a constant power supply current to the LED. As shown in the figure, under the condition of supplying a constant power supply current to the LED as the light source, the light emission amount of the LED decreases as the cumulative lighting time of the LED increases. This is because the LED deteriorates with the increase in the cumulative lighting time and its light emission performance decreases. Regardless of the cumulative lighting time, in order to make the light emission amount of the LED constant, it is necessary to increase the power supply current with the deterioration of the LED.

  As shown in FIG. 15, the light regular reflection property of the intermediate transfer belt 10 is lowered with time, and the light emitting performance of the LED is lowered with time as shown in FIG. 16. It is necessary to perform calibration processing periodically. Therefore, prior to performing the first image formation condition adjustment process in the image formation condition adjustment process, the control unit 190 performs the calibration process for each of the seven photosensors. In this calibration process, the control unit 190 causes the LED to emit light and irradiates light onto the solid surface of the intermediate transfer belt 10, so that a background regular reflection output voltage of a predetermined value is output. Adjust the power control signal for the sensor. The power control signal is a signal for controlling the current value output to the LED from the power adjustment circuit built in the photosensor. By changing the value of the power supply control signal, the light emission amount of the LED can be adjusted by changing the current value for the LED from the power supply adjustment circuit of the photosensor. By performing such a calibration process, the background regular reflection output voltage can be maintained constant over a long period of time.

  In the conventional image forming apparatus, in the calibration process, it is necessary to open the shutter member 156 of the optical sensor unit 155 in order to obtain specular reflection light on the belt surface. Therefore, the shutter opening time is increased by performing the calibration process. There has been a problem of facilitating the adhesion of dirt to the light transmission / reception surfaces of various photosensors.

Next, a characteristic configuration of the copier according to the embodiment will be described.
In FIG. 7 described above, the shutter member 156 of the optical sensor unit 150 has its back surface opposed to the light transmitting / receiving surfaces of various photosensors. The shutter member 156 is made of a metal such as aluminum and has a back surface subjected to polishing processing (for example, mirror processing) for improving light reflectivity. For this reason, when the shutter member 156 is closed as shown, the light emitted from the LEDs of the various photosensors can be reflected well on the back surface.

  FIG. 17 is an enlarged configuration diagram illustrating the Y photosensor 154Y that causes the LED 161Y to emit light with the shutter member 156 closed. The regular reflection light receiving unit 162 </ b> Y is disposed at a position where the most regular reflection light regularly reflected on the surface of the intermediate transfer belt 10 can be received. The shutter member 156 is located closer to the Y photosensor 154Y than the intermediate transfer belt 10. For this reason, most of the regular reflection light regularly reflected by the back surface of the shutter member 156 proceeds toward a position different from the regular reflection light receiving unit 162Y. However, a part of the regular reflection light is received by the regular reflection light receiving unit 162Y.

  FIG. 18 is a graph showing the relationship between the LED light emission amounts of the various photosensors and the back surface reflection output voltage. The back surface reflection output voltage is an output voltage from a regular reflection light receiving unit that receives regular reflection light that is regularly reflected by the back surface of the shutter member 156 in a closed state. As illustrated, a proportional relationship is established between the light emission amount of the LED and the back surface reflection output voltage. This is because the regular reflection light quantity on the back surface of the shutter member 156 increases as the light emission amount of the LED increases.

FIG. 19 is a graph showing the relationship between the backside regular reflection output voltage and the background regular reflection output voltage. This graph is created based on the results of measuring the backside regular reflection output voltage and the background regular reflection output voltage under various LED light emission conditions. As shown in the figure, the background regular reflection output voltage increases as the back surface reflection output voltage increases. This indicates that, if the light regular reflection property of the belt surface is the same, the background regular reflection output voltage can be obtained based on the back surface reflection output voltage. In other words, if the light regular reflection property of the belt surface is the same, the intermediate transfer belt 10 is configured by configuring the photosensor so that the back surface reflection output voltage of, for example, A ₁ [V] can be obtained with the shutter member 156 closed. For example, a desired background regular reflection output voltage of A ₂ [V] can be obtained on the solid surface.

  The control unit 190 includes two types of calibration processes for various photosensors, a first calibration process and a second calibration process, which are alternately performed. Specifically, if the first flag, which is a parameter variable stored in the RAM 190b, is turned on when the execution timing of the image formation condition adjustment process arrives, the first image formation condition adjustment process is performed. Before performing the first calibration process, the first calibration process is performed as the calibration process. On the other hand, when the first flag is off, the second calibration process is performed as the calibration process before the first image forming condition adjustment process. The first flag is turned on from off immediately after the second calibration process is performed. Further, immediately after the first calibration process is performed, the first calibration process is turned off.

  FIG. 20 is a flowchart illustrating a control flow of the image forming condition adjustment process performed by the control unit 190. When the execution timing of the image forming condition adjustment processing arrives (Y in Step 1; hereinafter, Step is referred to as S), the control unit 190 determines whether or not the first flag is turned on (S2). If it is turned on (Y in S2), after the combination of the first calibration process and the signal storage process described later (S3), after turning off the first flag (S4), The first image forming condition adjustment process (S5) and the second image forming condition adjustment process (S6) are sequentially performed. On the other hand, if the first flag is not turned on (N in S2), after the second calibration process is performed (S7), the first flag is turned on (S8), and then the first image formation is performed. Condition adjustment processing and second image formation condition adjustment processing are performed (S5, S6).

  The first calibration process is performed from a regular reflection light receiving unit that receives regular reflection light actually obtained on the surface of the intermediate transfer belt 10 for each of the various photosensors of the optical sensor unit 150, as in the conventional calibration process. This is processing for adjusting the power supply control signal so that the output of the regular reflection output voltage of the background portion is a predetermined value. For example, with respect to the Y photosensor 154Y, as shown in FIG. 21, the LED 161Y is turned on with a shutter member (not shown) opened, and the specularly reflected light obtained on the solid surface of the intermediate transfer belt 10 is specularly reflected. Light is received by the light receiving unit 162Y. Then, the power control signal for the Y photosensor 154Y is adjusted so that the background specular reflection output voltage output from the regular reflection light receiving unit 162Y has a predetermined value.

  As shown in FIG. 20, the controller 190 executes the first calibration process as a set together with the signal storage process (S3). The signal storage process is a process of storing the back surface reflection output voltage in the RAM 190b as a data storage unit for each of various photosensors in the optical sensor unit 150. The back surface reflected output voltages of various photosensors are obtained as follows. That is, after the first calibration process is performed, the shutter member 156 that has been opened is closed, and then the light emitted from the LED (for example, 161Y) under the condition of the light emission after calibration (the condition of the power control signal after calibration). Is reflected by the back surface of the shutter member 156. And the voltage output from the regular reflection light-receiving part (for example, 162Y) which received the reflected light is acquired as a back surface reflection output voltage.

  FIG. 22 is a flowchart showing the flow of the first calibration process and the signal storage process. This flow is performed in parallel for each of the seven photosensors in the optical sensor unit (150). When the first calibration process is started, the control unit 190 first opens the shutter member (156) (S3a), and then determines whether or not a continuous printing operation is being performed (S3b). If the continuous printing operation is in progress (Y in S3b), the continuous printing operation is interrupted (S3c). More specifically, the page from the photoconductor to the image page that is primarily transferred to the intermediate transfer belt is used as a partition, and the image of the subsequent page is interrupted. Then, after the image of the page being formed is secondarily transferred to the recording paper, the printing operation is interrupted. However, the intermediate transfer belt (10) continues to be driven.

  Thereafter, the control unit 190 lights the LED while the intermediate transfer belt (10) is running (S3d), and then samples the background regular reflection output voltage five times at a predetermined time interval (S3e). Then, it is determined whether the average of the five sampling values is within the target range (S3f). If not within the target range, the power control signal is adjusted (S3g), and the control flow is changed to S3e. Loop and sample the back surface regular reflection output voltage again 5 times. In this way, sampling and adjustment of the power control signal are repeated until the average value falls within the target range.

  When the average value of the regular reflection output voltage of the background portion falls within the target range (Y in S3f), if the printing operation is interrupted, the continuous printing operation is resumed (S3h, S3i). This is the first calibration process. When the first calibration process is completed, a signal storage process is performed next. In the signal storage process, after the shutter member is closed (S3j), the back surface reflection output voltage is acquired and stored in the RAM 190b in a state where the LED is turned on by the power control signal after calibration in the first calibration process (S3k). .

  FIG. 23 is a flowchart showing the flow of the second calibration process. This flow is also performed in parallel for each of the seven photosensors in the optical sensor unit (150). When starting the second calibration process, the controller 190 turns on the LED with the shutter member (156) closed (S7a). At this time, the power control signal to the photo sensor is the same as the value calibrated in the previous first calibration process. Next, the back surface reflection output voltage is acquired, and it is determined whether or not the value is the same as that stored in the RAM (190b) (S7b). If they are not the same, after adjusting the power control signal (S7c), loop the control flow to S7b, and the back reflection output voltage is the same as that stored in the RAM (190b)? It is determined again whether or not. In this way, the adjustment of the power supply control signal is repeated until the back surface reflection output voltage becomes the same as the value in the RAM.

  In the copying machine having the above-described configuration, after the first calibration process similar to the conventional one is performed, the second calibration process is performed instead of the first calibration process when the execution timing of the calibration process comes again. Thereby, the implementation frequency of the 1st calibration process which must be implemented in the state which opened the shutter member can be reduced compared with the past, and the opening time of a shutter member can be shortened compared with the past.

Hereinafter, (see e.g., _{L c} of FIG. 17) in various photosensors in the optical sensor unit (150), a light transmitting and receiving surface of the photo sensor, the distance between the rear surface of the shutter member (156), that the shutter distance _{L c} . The distance between the light transmission / reception surface of the photosensor and the surface of the intermediate transfer belt (10) is referred to as a belt surface distance L _o (see, for example, L _o in FIG. 21). FIG. 25 is a graph showing the relationship between the shutter distance _Lc and the back surface reflection output voltage in various photosensors. From a state where the shutter distance L _c to zero (a state of being in contact with the shutter member to the light transmitting and receiving surface of the photosensor), the shutter distance L _c is gradually increased, eventually, from the regular reflection light receiving portion of the photosensor The output back-surface reflected output voltage starts to rise rapidly. Shutter distance L _c of the time is the minimum required distance. As illustrated, the minimum required distance was 1 [mm]. At that time, the belt surface distance _Lo was set to 5 [mm]. Therefore, in order to obtain the back surface reflection output voltage, it has been found that the relationship of “L _c / L _o > 0.2” must be provided. Therefore, the copying machine according to the embodiment has a relationship of “L _c / L _o > 0.2”. More specifically, L _c = 2.5 [mm] and L _o = 10 [mm].

FIG. 25 is a graph showing the temporal change in the regular reflection output voltage of the background portion from the photosensor whose test target is the intermediate transfer belt (10) whose surface deterioration has progressed. In this graph, the timing (reference timing t ₀ ) at which the reference position in the circumferential direction of the intermediate transfer belt is a test object is 0 [second]. The present inventor makes a predetermined time interval from the reference timing t ₀ to t ₁ (t ₀ + Δt), t ₂ (t ₁ + Δt), t ₃ (t ₂ + Δt), and so on. The experiment for measuring the regular reflection output voltage of the background portion was performed 10 times. Then, based on values (t _1Ave , t _2Ave , t _3Ave ...) _Obtained by averaging 10 measurement results at each measurement timing (t ₁ , t ₂ , t ₃ ...), FIG. Created a graph. As shown in the figure, the intermediate transfer belt with advanced surface deterioration has a considerable variation in the regular reflection of light in the circumferential direction. It is assumed that the belt portion that is the subject to be examined when the background regular reflection output voltage is obtained is the location where the light reflectivity is worst or the best location around the belt. In such a case, if the photosensor is calibrated based only on the background regular reflection output voltage, the detection accuracy of the toner adhesion amount is significantly deteriorated.

  Therefore, in this copying machine, as shown in FIG. 22, in the first calibration process, the background regular reflection output voltage is sampled five times at predetermined time intervals, and the photo is taken so that the average value is within the target range. The sensor is calibrated (S3e, S3f, S3g). In such a configuration, it is possible to suppress deterioration in detection accuracy of the toner adhesion amount due to variations in light reflectivity in the circumferential direction of the belt. Instead of the average value of the five sampling results, an average value of the two to four sampling results or an average value of the six or more sampling results may be employed.

  FIG. 26 shows various operation timings when the photo sensor detects a patch image (see FIG. 13) formed in the inter-paper corresponding area of the intermediate transfer belt during the continuous printing operation in the first image forming condition adjustment processing. It is a timing chart. During continuous printing, as shown in the uppermost part of the timing chart, with respect to the position facing the optical sensor unit (hereinafter referred to as reflected light measurement position), the recording paper corresponding area and the inter-paper corresponding area in the intermediate transfer belt Alternately enter. Since the patch images of the respective colors for detecting the toner adhesion amount are formed in the inter-paper corresponding area, as shown in the lowermost stage, the control unit (190) is the timing at which the inter-paper corresponding area enters the reflected light measurement position. The shutter member is opened and the sensor output voltage is sampled. On the other hand, at the timing when the recording paper corresponding area enters the reflected light measurement position, the shutter member is closed to protect the sensor. Before starting the sampling of the sensor output voltage, the recording paper corresponding area adjacent to the paper gap corresponding area where the first patch image is formed on the upstream side in the belt moving direction has entered the reflected light measurement position. The second calibration process described above is performed at the timing. Thereby, the lighting of the LED is started at the timing immediately before the measurement of the toner adhesion amount is started and the calibration of the photosensor is started, so that the lighting time of the LED can be reduced as much as possible.

  So far, a copying machine has been described in which a patch image formed on the intermediate transfer belt 10 serving as an image carrier and the toner adhesion amount to the photo image sensor are detected by a photosensor. The present invention can also be applied to a configuration in which a patch image on the surface of the image carrier and the toner adhesion amount to the image are detected by a photo sensor.

  As described above, in the copying machine according to the embodiment, the control unit 190 serving as the calibration unit performs the regular reflection output voltage (skin part normal reflection) acquired multiple times (five times) within the predetermined period in the first calibration process. The light emission amount (power control signal) of the LED of the photosensor is adjusted so that the average value of the reflected output signal) falls within the target range. With this configuration, as already described, it is possible to suppress deterioration in detection accuracy of the toner adhesion amount due to variations in light reflectivity in the circumferential direction of the belt.

  In the copying machine according to the embodiment, since the back surface of the shutter member 156 is polished, the light from the LED is favorably reflected by the back surface of the shutter member 156. Thereby, a favorable correlation can be caused between the LED light emission amount and the back surface reflection output voltage, and the accuracy of the second calibration process can be improved.

  In the copier according to the embodiment, the control unit 190 causes the recording paper corresponding area, which is the sheet corresponding area, out of all the areas in the circumferential direction of the intermediate transfer belt 10 that is the image carrier to enter the reflected light measurement position. The second calibration process is performed. In such a configuration, it is possible to start the LED lighting at the timing immediately before the start of the measurement of the toner adhesion amount and start the calibration of the photosensor, thereby reducing the LED lighting time as much as possible.

Further, since the copier according to the embodiment has the relationship of “L _c / L _o > 0.2”, the back reflection light from the shutter can be reliably received by the regular reflection light receiving unit.

10: Intermediate transfer belt (image carrier)
18Y, C, M, K: Image forming unit (part of toner image forming means)
21: Laser writing device (part of toner image forming means)
151: First end photosensor (reflection type optical sensor)
152: Central photosensor (reflective optical sensor)
153: Second end photosensor (reflection type optical sensor)
154Y, C, M, K: Y, C, M, K photo sensor (reflection type photo sensor)
154aK: LED (light source)
154bK: Regular reflection light receiving unit 156: Shutter member 161Y: LED (light source)
152Y: Regular reflection receiving unit 190: Control unit (calculation means, calibration means)
190b: RAM (data storage means)

JP 2006-349808 A

Claims (4)

An image carrier that carries a toner image on its surface, a toner image forming unit that forms a toner image on the surface of the image carrier, and a light source that is reflected on the surface of the image carrier. The specular reflection light is received by the specular reflection light receiving unit, and a reflection type optical sensor that outputs a signal corresponding to the amount of received light, a shutter member that covers the light transmission / reception surface of the reflection type optical sensor so as to be openable and closable, And a calculation means for performing a calculation process for detecting a toner image formed on the surface of the image carrier or for obtaining a toner adhesion amount per unit area with respect to the toner image; The amount of light emitted from the light source is adjusted based on the regular reflection signal of the background that is the signal output from the regular reflection light receiving unit that receives regular reflection light that is regularly reflected by the toner image non-carrying region on the surface of the carrier. in order to An image forming apparatus comprising a calibration unit for performing a positive process,
A first calibration process in which the calibration means adjusts the light emission amount of the light source so that the background specular reflection signal becomes a predetermined value; and the light emission after the shutter member is closed and calibrated by the first calibration process. A signal storage that reflects light emitted from the light source under the condition of the amount on the back surface of the shutter member and stores a back surface reflection signal that is a signal output from the regular reflection light receiving unit that receives the reflected light in the data storage means the combination of the processing is performed on a regular basis in between execution timing of the constant-term the combination, wherein the back reflection signal said data storage means back reflection signals stored in the output from the specular reflection light receiving portion and performing a second calibration process of adjusting the light emission amount of the light source so that the same value as, and, during the continuous printing operation, the entire region circumferential direction of the endless moving surface of the image bearing member , In which case, the carrying out said second calibration process is caused to enter the sheet corresponding region corresponding to the recording sheet is caused to transfer the toner image on the surface of the image bearing member to a position facing the reflective-type optical sensor An image forming apparatus, comprising: The image forming apparatus according to claim 1,
In the first calibration process, the calibration means adjusts the light emission amount of the light source so that an average value of the regular reflection signal acquired over a plurality of times within a predetermined period becomes the predetermined value. An image forming apparatus. The image forming apparatus according to claim 1 or 2,
An image forming apparatus characterized in that a back surface of the shutter member is polished. The image forming apparatus according to any one of claims 1 to 3 ,
The distance L ₀ between the reflective optical sensor and the image carrier and the distance L _c between the reflective optical sensor and the back surface have a relationship of “L _c / L _o > 0.2”. An image forming apparatus.

Images