Image forming apparatus

Abstract

To solve a problem in which an optical sensor may falsely detect reflected light from a shutter as reflected light from test images.SOLUTION: An image forming apparatus comprises: image forming stations 114-117 that form images on an intermediate transfer belt 118 on the basis of an image forming condition; an optical sensor 141 that detects reflected light from test images formed on the intermediate transfer belt 118; a shutter 142 that prevents a light receiving surface of the optical sensor 141 from getting dirty; a shutter control unit 213 that controls the position of the shutter 142; and a CPU 203 that creates an image forming condition on the basis of a result of detection of the test images made by the optical sensor 141. The CPU 203 determines the timing to start an opening operation of the shutter 142 in detecting the test images, on the basis of the signal level of the optical sensor 141 acquired by executing the opening operation of the shutter 142 while a pattern image passes through an irradiation position of the optical sensor 141.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to control of a shutter that protects a sensor that detects an image on an image carrier. [Background technology]

[0002] Image forming devices such as copiers and printers are known that include an optical sensor that detects an image formed on an image carrier in order to calibrate the image forming device. For example, the image forming device forms a test image on the image carrier, receives reflected light from the test image with the optical sensor, and controls the density of the image formed by the image forming device based on the detection result of the reflected light from the test image detected by the optical sensor.

[0003] An optical sensor provided inside an image forming apparatus becomes dirty due to scattered toner. If the light receiving surface of the optical sensor becomes dirty, the optical sensor cannot detect reflected light from the test image with high accuracy. This may result in a decrease in image quality even though the image forming apparatus is performing calibration. In order to prevent the light receiving surface from becoming dirty due to scattered toner, a configuration is known in which the optical sensor has an openable and closable shutter (Patent Document 1). When the test image passes through an irradiation position where the optical sensor irradiates light, the shutter opens and the reflected light from the test image is received by the optical sensor, and during the period when the detection target does not pass through the irradiation position, the shutter closes to prevent the light receiving surface from becoming dirty. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-20187 A Summary of the Invention [Problem to be solved by the invention]

[0005] According to experiments by the inventors, there are individual differences in the time from when the shutter opening operation starts until the shutter opens to a position where the optical sensor can receive reflected light from the detection target. If the shutter is not open when the test image reaches the irradiation position, the optical sensor may erroneously detect the reflected light from the shutter as reflected light from the test image.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the image forming apparatus of the present invention is to appropriately control the timing at which the shutter starts to open. [Means for solving the problem]

[0007] In order to solve the above problems, the image forming apparatus of the present invention is an image forming apparatus that forms an image on a sheet, and includes an image carrier, an image forming means that forms an image on the image carrier based on image formation conditions, a light emitting unit that emits light toward the image carrier, and a light receiving unit that receives reflected light from a test image formed on the image carrier, and includes an output unit that outputs a signal according to the intensity of the light received by the light receiving unit, a shutter that is controlled to a first position facing the light receiving unit to prevent the light receiving unit from being soiled, and is controlled to a second position retracted from the first position so that the light receiving unit receives reflected light from the test image, a control unit that controls the shutter to the first position and the second position, and a front The present invention is characterized in that it has a generation means for causing the control means to start an opening operation to move the position of the shutter from the first position to the second position at a timing before the test image on the image carrier reaches an irradiation position where light from the light-emitting unit is irradiated, and generating the image formation conditions based on a signal corresponding to the intensity of reflected light from the test image output from the output means; and a determination means for causing the image forming means to form a pattern image, causing the control means to start the opening operation while passing the pattern image on the image carrier to the irradiation position, and determining the timing based on the time from when the opening operation starts to when the value of the signal output by the output means reaches a threshold value. Effect of the Invention

[0008] According to the present invention, the timing at which the shutter opening operation starts can be appropriately controlled. [Brief description of the drawings]

[0009] [Figure 1] Schematic cross-sectional view of an image forming apparatus [Diagram 2] Schematic cross-sectional view of an optical sensor [Diagram 3] Control block diagram of the printing device [Figure 4] Schematic perspective view of a sensor unit [Diagram 5] FIG. 11 is a flow chart showing an image forming operation including the formation of a test image. [Figure 6] FIG. 11 is a flow chart showing the reading control of a test image. [Figure 7] FIG. 11 is a flowchart showing a timing adjustment control for determining the start timing of the shutter opening operation. [Figure 8] FIG. 1 is a diagram for explaining a method for calculating a shutter open time. [Figure 9] A schematic diagram showing the difference in operation before and after adjusting the start timing of the shutter opening operation. [Figure 10] Another schematic diagram showing the difference in operation before and after adjusting the start timing of the shutter opening operation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the technical scope of the present invention is defined by the claims, and is not limited to the individual embodiments described below.

[0011] (Explanation of Image Forming Apparatus) FIG. 1 is a schematic cross-sectional view of an image forming apparatus 101. The image forming apparatus 101 described in this embodiment includes a printing apparatus 102 that forms an image on a sheet, and a finisher 103 that stacks the sheets transported from the printing apparatus 102. The image forming station 114 forms a toner image using black toner. The image forming station 115 forms a toner image using cyan toner, the image forming station 116 forms a toner image using magenta toner, and the image forming station 117 forms a toner image using yellow toner. The toner images of each color are primarily transferred to an intermediate transfer belt 118 as an image carrier, and are supplied to a transfer nip portion where a secondary transfer roller 119 presses the intermediate transfer belt 118 as the intermediate transfer belt 118 rotates clockwise in the figure. On the other hand, in the printing apparatus 102, only the topmost sheet of a sheet stack accommodated in the paper feed decks 111 and 112 is separated by a separation roller (not shown) and transported to the transfer nip portion along a transport path 113. The timing and speed of conveying the sheet are controlled so that the toner image on the intermediate transfer belt 118 is transferred to the image forming area on the sheet. Then, a transfer voltage is applied to a secondary transfer roller 119, whereby the toner image is secondarily transferred from the intermediate transfer belt 118 to the sheet at the transfer nip.

[0012] The sheet onto which the toner image has been transferred in the transfer nip is transported to a fixing device 121. The fixing device 121 includes a pressure roller, a heating roller, and a heater, and as the sheet passes through the fixing nip between the pressure rollers, the toner is melted, thereby fixing the toner image to the sheet. The sheet that has passed through the fixing device 121 is transported to a transport path 125 via a transport path 122. Depending on the type of sheet, it may be necessary to apply more heat to the toner image to fix it to the sheet. For example, if the basis weight of the sheet is 300 [g / cm 2 When a toner image is fixed on a sheet of about 1 / 1000 mm in thickness, the toner image is not sufficiently fixed on the sheet by simply passing through the fixing device 121. In this case, the sheet that has passed through the fixing device 121 is conveyed to a second fixing device 123, passes through a conveying path 124, and is conveyed to a conveying path 125.

[0013] When a double-sided printing mode in which images are formed on both sides of a sheet is set, the sheet conveyed to conveying path 125 is conveyed to reversing path 126. The sheet conveyed to reversing path 126 is switched back by reverse rotation of the conveying roller. The sheet switched back in reversing path 126 is conveyed to conveying path 113 through conveying path 127. The sheet conveyed to conveying path 113 has been turned over, and the image of the second side (back side) is transferred from intermediate transfer belt 118 by secondary transfer roller 119.

[0014] The sheet that has passed through the transport path 125 is transported to the finisher 103 via a transport path 132. The finisher 103 is a post-processing device capable of stacking a large number of sheets. The finisher 103 has a stack tray 137 as a tray for stacking sheets. The sheet transported from the printing device 102 is stacked on the stack tray 137 via a transport path 135. The finisher 103 detects the passage of the sheet by transport sensors 133, 134, and 136. If the leading edge or trailing edge of the sheet does not arrive even after a predetermined time has elapsed, it is determined that a transport jam has occurred in the finisher 103, and the occurrence of the transport jam is notified on the display of the operation unit 206 of the printing device 102. The print status and print settings of the image forming device 101 are also displayed on the display of the operation unit 206.

[0015] On the intermediate transfer belt 118, a sensor unit 120 is disposed to detect reflected light from an image formed by the image forming stations 114 to 117. Here, it is known that the density of an image of the printing device 102 varies due to changes in the surrounding environment (temperature and humidity) and deterioration of the process parts of the image forming stations 114 to 117. Therefore, the printing device 102 forms a test image on the intermediate transfer belt 118, detects the test image by the sensor unit 120, and controls the image forming conditions based on the detection result of the test image by the sensor unit 120 so that the image density becomes the target density. Here, the image forming conditions are, for example, the exposure intensity when a laser scanner provided in the image forming station exposes a photoconductor. Also, the image forming conditions are, for example, a gradation correction table as a conversion condition used by the image processing unit 200 (FIG. 3) to convert image data. Also, for example, it may be both the exposure intensity of the laser scanner and the gradation correction table. For example, it may be a charging bias applied to a charger provided in the image forming station so that the charger charges the photoconductor.

[0016] (Explanation of optical sensor) 2 is a schematic cross-sectional view of the optical sensor 141 included in the sensor unit 120. The optical sensor 141 includes, for example, a light-emitting element as a light-emitting unit and a light-receiving element as a light-receiving unit. The optical sensor 141 described in this embodiment includes two LEDs as light-emitting elements and two PDs as light-receiving elements. LEDs 1 and 2 and PDs 1 and 2 are provided on a first surface of the substrate 501.

[0017] The LED1 irradiates light onto the surface of the intermediate transfer belt 118. The incident angle of the LED1 is, for example, 7°. The PD1 receives the specular reflected light of the light irradiated from the LED1 onto the intermediate transfer belt 118. The PD1 is provided at a position where it receives the light reflected from the intermediate transfer belt 118 at a reflection angle of 7°. The LED2 irradiates light onto the surface of the intermediate transfer belt 118. The incident angle of the LED2 is, for example, 35°. The PD2 receives the diffuse reflected light from the intermediate transfer belt 118 (or the test image on the intermediate transfer belt 118). The PD2 is located between the LED1 and the LED2 in the longitudinal direction of the substrate 201, and is provided at a position where it does not receive either the specular reflected light of the light irradiated from the LED1 onto the intermediate transfer belt 118 or the specular reflected light of the light irradiated from the LED2 onto the intermediate transfer belt 118. The PD2 is provided at a position where it receives the light reflected from the intermediate transfer belt 5 at a reflection angle of 18°.

[0018] It should be noted that LED1, LED2, PD1, and PD2 are all surface-mounted elements. LED1, LED2, PD1, and PD2 are arranged on the same surface of a substrate 501. A housing 503 is attached to the substrate 501. The housing 503 includes a light-shielding wall that forms a light guide path for each element, and a group of lenses 504a to 504d. As a result, the light emitted from LED1 travels in the direction of the optical axis (dotted line in the figure) and is irradiated onto the intermediate transfer belt 118. The position on the intermediate transfer belt 118 where the light from LED1 is irradiated is the irradiation position.

[0019] Light emitted from LED1 is irradiated to an irradiation position on intermediate transfer belt 118 by a light guide path and lens 504a in housing 403, and specular light of the reflected light is received by PD1 by a light guide path and lens 504b in housing 503. When a test image or a pattern image (patch pattern) is formed using black toner, image forming apparatus 101 described in this embodiment uses LED1 and PD1 to detect specular light from the test image or pattern image.

[0020] Moreover, the light emitted from the LED2 is irradiated to the irradiation position of the intermediate transfer belt 118 by the light guide path and the lens 504d in the housing 503, and the diffused light of the reflected light is received by the PD2 by the light guide path and the lens 504c in the housing 503. The light emitted from the LED2 is irradiated to the irradiation position of the intermediate transfer belt 118 by the light guide path and the lens 504d in the housing 503, and the diffused light of the reflected light is also received by the PD1 by the light guide path and the lens 504b in the housing 503. When a test image or a pattern image (patch pattern) formed using yellow toner is formed, the image forming apparatus 101 described in this embodiment uses the LED2 and the PD2 to detect the diffused light from the test image or the pattern image. The image forming apparatus 101 also uses the LED2 and the PD2 when a test image or a pattern image (patch pattern) formed using magenta or cyan toner is formed.

[0021] A connector 505, a control IC 507, and other mounted components 506 are mounted on the back side of the first surface (mounting surface) of the substrate 501 on which LED1, LED2, PD1, and PD2 are mounted. The control IC 507 has a core chip, which is an integrated circuit, connected to the substrate by wire bonding using a chip-on-board technique.

[0022] The connector 505 electrically connects the CPU 203 (FIG. 3) and the optical sensor 141. The control IC 507 communicates with the CPU 203 (FIG. 3) to control the emission of light from the LED 1 and the LED 2. The other mounted components 506 include, for example, a capacitor for stabilizing the power supplied to the control IC 507.

[0023] The substrate 501 also has a first positioning hole 502 a and a second positioning hole 502 b which are openings for mounting the optical sensor 141 to the printing device 102 .

[0024] 3 is a control block diagram of the printing device 102. The CPU 203 controls the printing device 102 and the finisher 103. The HDD 202 is a storage device in which programs and data are stored. The CPU 203 comprehensively controls image processing and printing based on the programs and the like stored in the HDD 202. The memory 204 stores programs and image data required when the CPU 203 performs various processes, and operates as a work area.

[0025] The communication interface (communication I / F) 201 functions as a reception unit that receives image data transmitted from a server or a PC. The image processing unit 200 executes image processing on the image data received by the communication I / F 201. The image processing unit 200 converts image signal values ​​included in the image data into output signal values ​​based on a gradation correction table. The output signal values ​​are used for exposure control in which the laser scanners of the image forming stations 114 to 117 expose the photoconductors. The image processing unit 200 may be realized by, for example, an ASIC.

[0026] The memory 204 stores programs and image data required when the CPU 203 performs various processes, and operates as a work area. The operation unit 206 accepts various setting inputs and operation instructions from a user. The operation unit 206 has a display for displaying setting information of the image forming apparatus 101, the processing status of a print job, and the like. The operation unit interface (operation unit I / F) 205 acquires various setting inputs and operation instructions input from the operation unit 206. The operation unit I / F 205 also outputs signals to the operation unit 206 for controlling the display of the operation unit 206.

[0027] The CPU 203 communicates with the control IC 507 (FIG. 2) to control the lighting of LED1 and LED2 of the optical sensor 141. The optical sensor 141 detects reflected light from the intermediate transfer belt 118 or a test image on the intermediate transfer belt 118, and outputs a voltage as a signal value based on the detection result (light reception result of PD1 or PD2). The voltage output by the optical sensor 141 is converted into a digital signal by an A / D converter (not shown) built into the CPU 203, and is acquired by the CPU 203 as a signal level. The shutter control unit 213 controls the voltage applied to the solenoid 143 according to an instruction from the CPU 203 in order to control the opening and closing operation of the shutter 142.

[0028] Next, the control of the CPU 203 will be described. The control of the CPU 203 is performed based on program data stored in the HDD 202. The CPU 203 also controls the image forming stations 114 to 117 to form a test image or a pattern image (hereinafter referred to as a patch pattern) on the intermediate transfer belt 118. The CPU 203 then causes the optical sensor 141 to detect the patch pattern, and controls the image forming conditions based on the detection result of the patch pattern by the optical sensor 141. Here, the test image formed on the intermediate transfer belt 118 by the printing device 102 will be described. The test image is, for example, an image having four densities of 70%, 50%, 30%, and 10% when the maximum density is 100%. The CPU 203 detects the patch pattern formed on the intermediate transfer belt 118 by the optical sensor 141, converts the voltage value of the optical sensor 141 into a digital value by an A / D converter (not shown), and acquires it as a signal level. CPU 203 converts the signal level into an image density value, obtains the gradation characteristics of image forming stations 114 to 117 from the density of the patch pattern, and generates a gradation correction table so that the gradation characteristics become ideal gradation characteristics. Alternatively, CPU 203 controls image forming conditions so as to achieve a target density based on the detection result of the patch pattern by optical sensor 141.

[0029] Next, a description will be given of the sensor unit 120. Fig. 4 is a schematic perspective view of the sensor unit 120 as a holding member that holds the optical sensor 141. The sensor unit 120 is an assembly part in which the optical sensor 141, the shutter 142, and a reference plate (not shown) provided on the back surface of the shutter 142 are unitized.

[0030] In addition to the optical sensor 141, the sensor unit 120 includes a frame 509, a sensor holder 510 to which the optical sensor 141 is attached, and a shutter 142. The shutter 142 is movable to a first position (closed position) facing the light receiving portion of the optical sensor 141 in order to prevent the light receiving surface of the optical sensor 141 from becoming dirty. The light receiving surface is the side on which the lens group 504a to 504d of the housing 203 (FIG. 2) are provided. When detecting reflected light from a test image, the shutter 142 is moved from the first position (closed position) facing the light receiving portion of the optical sensor 141 to a second position (open position) retreated therefrom.

[0031] The reference plate is provided on the surface of the shutter 142 facing the light receiving surface of the optical sensor 141. The sensor unit 120 includes a shutter moving mechanism 512 that opens and closes the shutter 142. The sensor unit 120 is assembled to the printing device 102 in a state in which a positioning portion 513 provided on a frame 509 is biased against a positioned portion (not shown) provided on the printing device 102. The sensor unit 120 is also disposed within the printing device 102 so as to maintain a predetermined distance between the intermediate transfer belt 118 and the optical sensor 141.

[0032] (Shutter movement mechanism) Next, the moving mechanism of the shutter 142 will be described with reference to FIGS.

[0033] The shutter 142 is opened and closed by a solenoid 143 and a link 515 provided in the shutter movement mechanism 512. The solenoid 143 is a drive source for transitioning the shutter 142 from a closed state to an open state. When the solenoid 143 is not attracted, the shutter 142 is pulled in the +X direction by a shutter spring (not shown) and is in a closed state, and when the solenoid 143 attracts the plunger, the shutter 142 moves in the -X direction via the link 515 and is in an open state. Here, the +X direction and the -X direction are directions that intersect with the direction of gravity. Note that the movement direction of the protective shutter 142 is not limited to a direction perpendicular to the vertical direction (horizontal direction).

[0034] When the shutter 142 moves from the open state to the closed state by the shutter spring (not shown), a part of the shutter 142 provided on the side of the opening 516 abuts against the frame 509 and the shutter 142 stops. This causes the shutter 142 to transition to the closed state, preventing the light receiving surface of the optical sensor 141 from being soiled by scattered toner. The shutter spring functions as a spring member that pulls the shutter 142 so that the shutter 142 abuts against the frame 509. The frame 509 functions as an abutment portion against which the shutter 142 abuts. When a voltage is applied to the solenoid 143, the solenoid 143 moves the shutter 142 away from the frame 509 against the tensile force of the shutter spring.

[0035] Further, the shutter 142 has an opening 516 formed therein so that light from the optical sensor 141 can be irradiated onto the intermediate transfer belt 118 and reflected light from the detection target can be received by the optical sensor 141. When the shutter 142 is in an open state, the light receiving surface is exposed from the opening 516, and the optical sensor 141 can receive the test image or reflected light from the intermediate transfer belt 118.

[0036] On the other hand, when the shutter 141 is in the closed state, the shutter 142 blocks light emitted from the light emitting element (LED1 or LED2) of the optical sensor 141 to the intermediate transfer belt 118. Furthermore, when the shutter 142 is in the closed state, a reference plate provided on the shutter 141 faces the optical sensor 141. This allows the optical sensor 141 to detect the reference plate when the shutter 142 is in the closed state.

[0037] (Image formation operation involving formation of a test image) 5 is a flow chart showing an image forming operation in which the image forming apparatus 101 forms a user image. In the image forming operation described in this embodiment, while a user image is continuously formed on a plurality of sheets based on image data input as a print job, a test image for density control is formed between a plurality of image forming areas aligned in the rotation direction of the intermediate transfer belt 118. Here, the image forming area is the range of the intermediate transfer belt 118 that is transferred onto one sheet. The area between the image forming area corresponding to the image on the Nth page and the image forming area corresponding to the image on the N+1th page is also called an inter-sheet area.

[0038] When the CPU 203 receives image data through the communication I / F 201, the CPU 203 determines whether the update conditions for updating the image forming conditions are satisfied (S501). In step S501, if the CPU 501 can detect all of the test images of four densities for each color formed after the image forming conditions were last updated, the CPU 203 determines that the update conditions are satisfied. If the CPU 203 can detect all of the test images of four densities for each color in step S501, the CPU 203 updates the image forming conditions based on the densities of the test images of the four densities (S502). In step S502, the image forming conditions are, for example, a gradation correction table used by the image processing unit 200 for image processing. The CPU 203 obtains gradation characteristics from the detection results of test images of multiple different densities, and generates a gradation correction table so that the gradation characteristics become ideal gradation characteristics.

[0039] Next, CPU 203 forms a user image based on the image data (S503). In step S503, CPU 203 controls image forming stations 114-117 based on the latest image forming conditions to form a user image based on the image data. Since the image forming conditions described in this embodiment are tone correction tables, CPU 203 converts the image data using image processing unit 200 based on the latest tone correction table, and controls image forming stations 114-117 based on the converted image data to form a user image. When formation of one page of user image starts, CPU 203 measures time using a timer (not shown).

[0040] If the update conditions are not satisfied in step S501, CPU 203 shifts the process to step S503. In other words, if the detection results of the test images of the four densities have not been acquired, CPU 203 causes image forming stations 114 to 117 to form a user image based on image data without updating the image formation conditions.

[0041] Based on the time measured by the timer, the CPU 203 determines whether the time T1 has elapsed since the formation of one page of user image was started (S504). The time T1 is a time that specifies the timing to start forming the test image between sheets. Therefore, the time T1 is determined in advance for each type and size of sheet. The CPU 203 does not start forming the test image until the time T1 has elapsed in step S504. Then, in response to the elapse of the time T1, the CPU 203 causes the image forming stations 114, 115, 116, and 117 to form the test image (S505). In step S505, the test image is formed following the user image, and both the user image and the test image are transferred to the intermediate transfer belt 118.

[0042] Here, in the printing device 102 of this embodiment, the number of test images formed in step S505 is, for example, one. A test image with a yellow density of 70% is formed following the user image of the first page, and a test image with a yellow density of 50% is formed following the user image of the second page. Next, a test image with a yellow density of 30% is formed following the user image of the third page, and a test image with a yellow density of 10% is formed following the user image of the fourth page. As a result, when the test image following the user image of the fourth page is detected by the optical sensor 141, the update condition for yellow is satisfied. After this, a yellow gradation correction table is generated.

[0043] Then, a magenta test image with a density of 70% is formed following the user image on the 5th page, and a magenta test image with a density of 50% is formed following the user image on the 6th page. In other words, when the test image following the user image on the 8th page is detected by the optical sensor 141, the magenta update condition is met. When user images are formed on the 9th to 12th pages, four cyan test images are formed, and when user images are formed on the 13th to 16th pages, four black test images are formed. From the 17th page onwards, test images are repeatedly formed in the same order as for the 1st page.

[0044] After the test image has been formed, the CPU 203 starts measuring time with a timer. This is because the time measured by the timer is used to determine the timing for controlling the opening and closing of the shutter 142 and the sampling timing of the test image in the test image reading control described below.

[0045] The CPU 203 starts the test image reading control (S506) and determines whether image formation on all sheets included in the print job is completed (S507). When the start of the reading control in step S506 is instructed, the CPU 203 executes the test image reading control shown in FIG. 6 in parallel with the image forming operation shown in FIG. 5. The test image reading control will be described in FIG. 6, and therefore will not be described here. If image formation on all sheets included in the print job is completed in step S507, the CPU 203 ends the image forming operation process after the sheet on which the image of the last page of the print job is formed is stacked on the stack tray 137 of the finisher 103. On the other hand, if image formation on all sheets included in the print job is not completed in step S507, the CPU 203 shifts the process to step S501. As a result, the CPU 203 repeatedly executes the processes from step S501 to step S507 until image formation on all sheets included in the print job is completed.

[0046] Fig. 6 is a flow chart showing the reading control started in step S506 in Fig. 5. CPU 203 judges whether or not time T2 has elapsed since one test image was formed based on the time measured by the timer (S601). Time T2 is the time from the start of test image formation to the timing of starting the opening operation of moving shutter 142 from the closed position to the open position in order to detect the test image by optical sensor 141. In the present invention, time T2 is determined in the subsequent timing adjustment control (Fig. 7). Here, it will be described that time T2 is predetermined.

[0047] In response to the passage of time T2 from the start of formation of the test image in step S601, the CPU 203 applies a voltage to the solenoid 143 by the shutter control unit 213 to start the opening operation of the shutter 142 (S602). When a voltage is applied to the solenoid 143 in step S602, the solenoid 143 attracts the plunger and starts the opening operation of the shutter 142 via the link 515. Here, when the CPU 203 starts the opening operation of the shutter 142, it starts measurement by a timer. Note that in order to maintain the shutter 142 in the open state, the shutter control unit 213 continues to apply a voltage to the solenoid 143 until a closing operation command is received from the CPU 203.

[0048] Next, the CPU 203 determines whether or not the shutter open time T3 has elapsed since the opening operation of the shutter 142 started based on the time measured by the timer (S603). The shutter open time T3 is the shutter open time required from the start of the opening operation of the shutter 142 until the shutter 142 finishes opening to the open position. When the shutter open time T3 has elapsed since the start of the opening operation of the shutter 142, the CPU 203 starts sampling by the optical sensor 141 (S604). At this time, the CPU 203 starts measurement by the timer. The sampling time described in this embodiment is the time Tsamp. The time Tsamp is also predetermined based on the type and size of the sheet. The CPU 203 determines whether or not the time Tsamp has elapsed since the sampling by the optical sensor 141 started based on the time measured by the timer (S605).

[0049] After the time Tsamp has elapsed since the start of sampling in step S605, the CPU 203 ends the sampling by the optical sensor 141. Then, the CPU 203 stops the application of voltage to the solenoid 143 by the shutter control unit 213 in order to close the shutter 142 (S606). After that, the CPU 203 ends the reading control of the test image. Note that the reading control in FIG. 6 is repeatedly executed every time a test image is formed. That is, when a test image is formed in each of a plurality of inter-paper regions, the opening operation of the shutter 142 is started every time the time T2 has elapsed since the formation of each test image, the sampling of the test image is performed, and the closing operation of the shutter 142 is executed. The shutter 142 is opened and closed every time the test image on the intermediate transfer belt 118 passes the irradiation position.

[0050] Incidentally, there are individual differences in the opening and closing mechanism including the solenoid 143 that opens and closes the shutter 142. Therefore, there is a difference in the time from when the opening operation of the shutter 142 starts until the shutter 142 finishes opening to a position where the optical sensor 141 can receive the reflected light from the test image on the intermediate transfer belt 118. The image forming apparatus 101 described in this embodiment executes timing control that can suppress erroneous detection of the reflected light from the shutter 142 as the reflected light from the test image, even if there are individual differences in the time at which the shutter 142 opens.

[0051] (Timing adjustment control) 7 is a flowchart showing timing adjustment control that determines the start timing of the opening operation of the shutter 142. The timing adjustment control may be performed, for example, after the printing device 102 is assembled in a factory, or may be performed when a user or a service person inputs an instruction to perform the timing adjustment control from the operation unit 206.

[0052] When CPU 203 receives an instruction to execute timing adjustment control, it causes one of image forming stations 114 to 117 to form a patch pattern (S701). The patch pattern is, for example, a band image of uniform density formed using toner of one color. The longitudinal direction of the patch pattern (band image) is the rotation direction of intermediate transfer belt 118. When formation of the patch pattern starts, CPU 203 starts measuring time with a timer.

[0053] Based on the time measured by the timer, the CPU 203 determines whether the time Ta has elapsed from the start of patch pattern formation (S702). The time Ta is the time from the start of patch pattern formation until the patch pattern reaches the irradiation position of the optical sensor 141. In the timing adjustment control, the rotation speed of the intermediate transfer belt 118 is controlled to a predetermined rotation speed. Therefore, the time Ta is predetermined.

[0054] When the time Ta has elapsed from the start of formation of the patch pattern, the CPU 203 applies a voltage to the solenoid 143 by the shutter control unit 213 to start the opening operation of the shutter 142 (S703), and starts sampling by the optical sensor 141 (S704). In steps S703 and S704, the CPU 203 causes the shutter control unit 213 to start the opening operation while passing the patch pattern through the irradiation position, and acquires a signal level converted from the output voltage of the optical sensor 141. This uses the difference between the reflectance of the back surface of the shutter 142 facing the light receiving surface side and the reflectance of the patch pattern to measure the time required for the shutter 142 to open to the open position from the start instruction of the opening operation of the shutter 142.

[0055] The CPU 203 determines whether time Tp has elapsed since the start of sampling of the patch pattern (S705). Time Tp is sufficiently longer than the time it takes for the shutter 142 to finish opening to a position where the optical sensor 141 can receive reflected light from the test image on the intermediate transfer belt 118. Note that the longitudinal length of the patch pattern and time Tp are predetermined so that the patch pattern does not finish passing the irradiation position during sampling.

[0056] After the time Tp has elapsed since the start of sampling of the patch pattern, CPU 203 ends sampling by optical sensor 141 and stops application of voltage to solenoid 143 by shutter control unit 213 to close shutter 142 (S706). CPU 203 then determines the time required for the opening operation of shutter 142 from the multiple signal levels acquired in step S705, determines time T2 from the time required for the opening operation of shutter 142 (S707), and ends the timing adjustment control process.

[0057] (How to calculate the shutter open time) A method for calculating the shutter open time T3 in this embodiment will be described with reference to Fig. 8. Fig. 8 shows the transition of the signal level acquired from step S704 to S705 in Fig. 7. In Fig. 8, the horizontal axis represents time, and the vertical axis represents signal level. Fig. 8 also includes schematic diagrams of patch patterns.

[0058] In step S707 in FIG. 7, CPU 203 first calculates a reference signal level (hereinafter referred to as REF data). CPU 203 calculates the average value of the signal levels sampled between time TREF1 and time TREF2 as REF data. The REF data is a value equivalent to the sampling result when shutter 142 is in a completely open state. Next, CPU 203 calculates a threshold value for the signal level. For example, CPU 203 multiplies the REF data by a predetermined value smaller than 1 to calculate the threshold value. Here, the predetermined value is, for example, 0.9.

[0059] CPU 203 searches for a signal level exceeding the threshold value among the data sampled between time 0 and time TREF1, and determines the time when the signal level first exceeds the threshold value as shutter open time T3. Shutter open time (T3) is the time required from when solenoid 143 starts the opening operation of shutter 142 until shutter 142 is in the open state and optical sensor 141 can properly detect the test image formed on intermediate transfer belt 118.

[0060] Then, CPU 203 determines time T2 by subtracting the shutter open time (T3) from the time from when the test image is formed until the test image reaches the irradiation position. Note that the time from when the test image is formed until the test image reaches the irradiation position differs depending on the type (grammage) and size of the sheet. CPU 203 determines time T2 according to the type (grammage) and size of the sheet.

[0061] (Difference in operation before and after adjustment) 9 is a schematic diagram showing the difference in operation before and after adjusting the time T2 in the timing adjustment control when the shutter open time T3 is longer than the design value. As explained in the test image reading control (FIG. 6), a test image is formed between multiple user images.

[0062] 9(a) shows the solenoid signal for causing solenoid 143 to perform an opening operation and the state of shutter 142 before timing adjustment control is performed. Before adjustment shown in FIG. 9(a), shutter open time T3 is longer than the design value, so even though the test image has reached the irradiation position, the opening operation of shutter 142 has not been completed. In this case, CPU 203 erroneously detects the detection result of reflected light from shutter 142 as the detection result of reflected light from the test image. This makes it impossible to control the density of images formed by image forming stations 114-117 with high accuracy.

[0063] FIG. 9B shows a solenoid signal for causing the solenoid 143 to perform an opening operation and a state of the shutter 142 after the timing adjustment control is performed. After the adjustment shown in FIG. 9B is performed, the start timing (time T2) of the opening operation is determined so that the opening operation of the shutter 142 is completed before the test image reaches the irradiation position. As shown in FIG. 9, according to the image forming apparatus 101 described in this embodiment, even if the shutter opening time T3 is longer than the design value, the opening operation of the shutter 142 is completed before the test image reaches the irradiation position. As a result, according to the image forming apparatus 101 described in this embodiment, erroneous detection by the optical sensor 141 can be suppressed and the density of the image formed by the printing device 102 can be controlled with high accuracy.

[0064] Fig. 10 is a schematic diagram showing the difference in operation before and after adjusting the time T2 in the timing adjustment control when the shutter open time T3 is shorter than the design value. As in Fig. 9, a test image is formed between multiple user images as described in the test image reading control (Fig. 6).

[0065] 10A shows a solenoid signal for causing the solenoid 143 to perform an opening operation and the state of the shutter 142 before the timing adjustment control is performed. Before the adjustment shown in FIG. 10A is performed, the shutter open time T3 is shorter than the design value, so the opening operation is completed while the user image is passing the irradiation position. As a result, there is a possibility that the toner adhering to the optical sensor 141 and the shutter 142 will fall onto the user image on the intermediate transfer belt 118 due to the impact when the shutter 142 reaches the closed position. If the fallen toner is fixed to the sheet together with the user image, a defective image with toner stains will be formed on the printed matter.

[0066] FIG. 10B shows a solenoid signal for causing the solenoid 143 to perform an opening operation and a state of the shutter 142 after the timing adjustment control is performed. After the adjustment shown in FIG. 10B is performed, the start timing (time T2) of the opening operation of the shutter 142 is determined so that the opening operation of the shutter 142 is completed after the user image downstream of the test image in the rotation direction of the intermediate transfer belt 118 has passed the irradiation position. According to the image forming apparatus 101 described in this embodiment, even if the shutter opening time T3 is shorter than the design value, it is possible to prevent the toner attached to the optical sensor 141 or the shutter 142 from falling onto the area on the intermediate transfer belt 118 on which the user image is carried. As a result, according to the image forming apparatus 101 described in this embodiment, it is possible to prevent erroneous detection by the optical sensor 141 and to prevent the formation of a defective image in which the printed matter is stained with toner.

[0067] Furthermore, in the image forming apparatus 101 described in this embodiment, the timing at which the shutter 142 of the optical sensor 141 that detects reflected light from a test image or a pattern image (patch pattern) formed on the intermediate transfer belt 118 is controlled. However, the optical sensor 141 may be configured to detect reflected light from a test image or a pattern image (patch pattern) on an image carrier possessed by each of the image forming stations 114 to 117. The image carrier possessed by each of the image forming stations 114 to 117 is a photosensitive member. [Explanation of symbols]

[0068] 114~117 Image forming station 118 Intermediate transfer belt 141 Optical Sensor 142 Shutter 203 CPU 213 Shutter control section

Claims

1. An image forming apparatus for forming an image on a sheet, An image carrier; an image forming means for forming an image on the image carrier based on image forming conditions; an output unit having a light emitting unit that emits light toward the image carrier and a light receiving unit that receives reflected light from a test image formed on the image carrier, and outputting a signal corresponding to the intensity of the light received by the light receiving unit; a shutter that is controlled to a first position facing the light receiving unit to prevent the light receiving unit from being soiled, and that is controlled to a second position retracted from the first position so that the light receiving unit receives reflected light from the test image; a control means for controlling the shutter to the first position and the second position; a generating means for causing the control means to start an opening operation for moving the position of the shutter from the first position to the second position at a timing before the test image on the image carrier reaches an irradiation position where the light from the light emitting unit is irradiated, and generating the image forming conditions based on a signal corresponding to the intensity of the reflected light from the test image output from the output means; a determination means for causing the image forming means to form a pattern image, causing the control means to start the opening operation while passing the pattern image on the image carrier to the irradiation position, and determining the timing based on the time from when the opening operation starts to when the value of the signal output by the output means reaches a threshold value.

2. 2. The image forming apparatus according to claim 1, wherein the determining unit determines the timing such that the shutter finishes moving to the second position before the test image reaches the irradiation position.

3. The image forming apparatus according to claim 2, characterized in that the determination means determines the timing so that the position of the shutter reaches the second position after an image formed downstream of the test image in the rotational direction of the image carrier has finished passing through the irradiation position.

4. 2. The image forming apparatus according to claim 1, wherein the timing is controlled based on a time from when the formation of the test image starts.

5. 2. The image forming apparatus according to claim 1, wherein a value of the signal corresponding to the intensity of the reflected light from the pattern image is different from a value of the signal corresponding to the intensity of the reflected light from the rear surface of the shutter.

6. a value of a signal corresponding to the intensity of reflected light from the pattern image is greater than the threshold value; 2. The image forming apparatus according to claim 1, wherein a value of the signal corresponding to the intensity of the reflected light from the rear surface of the shutter is smaller than the threshold value.

7. a spring member that pulls the shutter so that the shutter abuts against an abutment portion; a solenoid that separates the shutter from the abutment portion against the tensile force of the spring member, 2. The image forming apparatus according to claim 1, wherein the first position is a position of the shutter when the shutter abuts against the abutment portion.

8. 2. The image forming apparatus according to claim 1, wherein the test image is formed in an area on the image carrier between an image to be transferred to a sheet and an image to be transferred to a sheet following the sheet.

Images