Image formation device

Abstract

To solve the problem in which an amount of light of measurement means is not properly adjusted because of a variation in a distance between a reference member and the measurement means.SOLUTION: An image formation device has a CPU 109 that: forms a detection pattern; causes a solenoid 214 to supply a first current so as to put a protection shutter 211 into an opening state; causes a pattern detection sensor 7 to measure reflection light from the detection pattern; and controls an image formation unit on the basis of a measurement result of the detection pattern by the pattern detection sensor 7. The CPU 109 is configured to, when the protection shutter 211 is controlled from the opening state to a closing state, supply a second current smaller than the first current to the solenoid 214 after stopping the current supply to the solenoid 214 once, and stop the current supply again after that.SELECTED DRAWING: Figure 15

Description

[Technical field]

[0001] The present invention relates to control of opening and closing of a shutter of a measuring device provided in an image forming apparatus. [Background technology]

[0002] In order to correct the relative positional shift (called color shift) and density of images for each color component, image forming devices such as copiers, printers, and facsimiles form a measurement image on an image carrier and control the color shift and density based on the measurement results of the measurement image by a measurement device. As the measurement device, an optical sensor that measures the measurement image formed on an intermediate transfer body (or a photosensitive drum) serving as an image carrier is known.

[0003] The optical sensor irradiates a measurement image on the image carrier with light using a light emitting element, and measures the reflected light from the image carrier and the reflected light from the measurement image. The image forming apparatus controls color shift or density shift based on the amount of reflected light measured by the optical sensor.

[0004] However, in order to measure the measurement image, the optical sensor needs to be close to the measurement image, which causes a problem that the agent (toner or ink) scattered from the measurement image adheres to the surface of the optical sensor, reducing the amount of reflected light.

[0005] The image forming apparatus described in Patent Document 1 has a reference member used to adjust the amount of light emitted by the optical sensor. Before measuring a measurement image, the image forming apparatus described in Patent Document 1 has the optical sensor measure the reflected light from the reference member, and adjusts the amount of light emitted by the optical sensor based on the measurement result of the reflected light from the reference member. According to the configuration of Patent Document 1, the amount of light emitted is adjusted to compensate for the reduced amount of reflected light due to the adhesion of toner, so that even if toner adheres to the optical sensor, the reflected light from the measurement image can be measured with high accuracy. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Utility Model Application Publication No. 02-111162 Summary of the Invention [Problem to be solved by the invention]

[0007] However, it was found that the amount of light emitted by the light-emitting element could not be adjusted appropriately due to a slight change in the distance from the light-emitting element of the measuring means to the reference member. According to the inventor's experiments, it was found that the amount of reflected light changes by as much as 4% when the distance between the measurement object and the optical sensor changes by 0.1 mm. The aforementioned amount of change in the amount of reflected light due to distance exceeds the reduction in the amount of reflected light caused by toner contamination.

[0008] Here, when the measurement image is measured by the optical sensor, it is necessary to move the reference member out of the optical path of the light from the light emitting element. For this purpose, the image forming device is provided with a drive source for controlling the shutter to an open state. The image forming device also has a spring member for closing the shutter. When returning the shutter from the open state to the closed state, the control of the drive source is stopped, and the spring member causes the shutter to abut against the abutment portion. This changes the shutter from the open state to the closed state.

[0009] However, in the above-described configuration in which the shutter is closed using a spring member, the shutter collides with the abutment portion, causing variation in the distance between the reference member of the shutter and the optical sensor. This variation in distance may cause the amount of light from the optical sensor to be improperly adjusted.

[0010] Therefore, an object of the present invention is to appropriately adjust the amount of light emitted by a measuring means. [Means for solving the problem]

[0011] In order to solve the above problems, an image forming apparatus of the present invention has an image carrier, an image forming means for forming an image on the image carrier, a light emitting element for emitting light toward the image carrier, and a light receiving element for receiving reflected light from the image carrier, and includes a measuring means for measuring the reflected light from the image carrier, a holding member for holding the measuring means, a shutter for blocking light emitted from the light emitting element of the measuring means toward the image carrier, a spring member for pulling the shutter so as to abut against an abutment portion of the holding member so as to be in a closed state in which the shutter blocks the light emitted from the light emitting element toward the image carrier, a drive source, and a drive control for controlling the drive source so as to move the shutter away from the abutment portion of the holding member against the pulling force of the spring member, thereby to be in an open state in which light from the light emitting element is irradiated to the image carrier. a measuring means for measuring the amount of light emitted by the light-emitting element of the measuring means, a reference member provided on the shutter, a reference member provided on the shutter, a reference member provided on the shutter, a reference member provided on the shutter, a reference member provided on the shutter, a reference member provided on the shutter, a reference member provided on the shutter, a reference member provided on the shutter, a reference member provided on the shutter, a reference member provided on the shutter, a reference member provided on the shutter, a reference member provided on the shutter, a reference member provided on the shutter, a reference member provided on the shutter, a reference member provided on the shutter, a reference member provided on the shutter, Effect of the Invention

[0012] According to the present invention, the amount of light emitted by the measuring means can be appropriately adjusted. [Brief description of the drawings]

[0013] [Figure 1] Cross-sectional view of the main part of an image forming apparatus [Diagram 2] Schematic cross-sectional view of an optical sensor [Diagram 3] Control block diagram of an image forming apparatus [Figure 4] Schematic diagram of color misregistration detection pattern [Diagram 5] FIG. 13 is a diagram showing an example of detection results of a color shift detection pattern. [Figure 6] Schematic diagram of concentration detection pattern [Figure 7] FIG. 13 is a diagram showing an example of a detection result of a density detection pattern. [Figure 8] FIG. 1 is a schematic perspective view of a sensor unit including an optical sensor; [Figure 9] Schematic perspective view of the sensor holder [Figure 10] Schematic diagram of the main part of the sensor unit including the protective shutter movement mechanism [Figure 11] Enlarged view of the sensor unit's protective shutter [Figure 12] FIG. 1 is a diagram for explaining the variation in the position of a protective shutter; [Figure 13] Example of distance characteristics of optical sensor [Figure 14] FIG. 1 is a diagram for explaining the timing of opening and closing a protective shutter. [Figure 15] Flowchart showing the opening and closing control of the protective shutter [Figure 16] Flowchart showing the adjustment of the amount of light from the optical sensor DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] (First embodiment) 1 is a cross-sectional view of a main part of an image forming apparatus 100. The image forming apparatus 100 includes an image forming unit that forms images of yellow (Y), cyan (C), magenta (M), and black (K), an intermediate transfer belt 5, and a transfer roller 4 that transfers the image on the intermediate transfer belt 5 to a sheet.

[0015] The image forming unit includes photoconductor drums 1a, 1b, 1c, and 1d, chargers (not shown), laser scanners 15a, 15b, 15c, and 15d, developers 16a, 16b, 16c, and 16d, and a primary transfer device (not shown). The photoconductor drums 1a, 1b, 1c, and 1d rotate counterclockwise in FIG. 1. The chargers charge the photoconductor drums 1a, 1b, 1c, and 1d. The laser scanners 15a, 15b, 15c, and 15d expose the photoconductor drums 1a, 1b, 1c, and 1d charged by the chargers to form electrostatic latent images on the photoconductor drums 1a, 1b, 1c, and 1d. The latent images on the photoconductor drums 1a, 1b, 1c, and 1d are developed by the developers 16a, 16b, 16c, and 16d. As a result, images of each color are visualized on the photosensitive drums 1a, 1b, 1c, and 1d.

[0016] The primary transfer device transfers the images on the photosensitive drums 1a, 1b, 1c, and 1d from the photosensitive drums 1a, 1b, 1c, and 1d to the intermediate transfer belt 5. The images of each color formed on the photosensitive drums 1a, 1b, 1c, and 1d are transferred in sequence onto the intermediate transfer belt 5 in a superimposed manner, so that a full-color image 6 is carried on the intermediate transfer belt 5. Here, the intermediate transfer belt 5 is an intermediate transfer body onto which the image is transferred.

[0017] The intermediate transfer belt 5 is passed around a number of rollers including a belt support roller. An image 6 is secondarily transferred from the intermediate transfer belt 5 to a sheet at a nip between the intermediate transfer belt 5 and the transfer roller 4. The sheet onto which the image has been transferred is conveyed by a conveyor belt 12 to a fixing device (not shown), where the image is fixed onto the sheet by heat and pressure from the fixing device. The sheet onto which the image has been fixed is then discharged onto a paper output tray of the image forming apparatus 100.

[0018] Incidentally, in the image forming apparatus 100, deviations occur in the relative positions of the images of each color due to manufacturing variations in the laser scanners 15a-d and the photosensitive drums 1a-d, component deformation due to temperature rise, transport variations in the intermediate transfer belt 5, and the like. This deviation in the relative positions of the images of each color is called color shift. For this reason, the image forming apparatus 100 forms a color shift detection pattern, detects the color shift detection pattern by the pattern detection sensor 7, and performs color shift correction based on the detection result of the color shift detection pattern by the pattern detection sensor 7 so as to suppress the color shift.

[0019] It is also known that the image density of the image forming apparatus 100 varies due to changes in the surrounding environment (temperature and humidity) and wear of the photosensitive layers of the photosensitive drums 1a to d. Therefore, the image forming apparatus 100 forms a density detection pattern, detects the density detection pattern by the pattern detection sensor 7, and controls the image forming conditions based on the detection result of the density detection pattern by the pattern detection sensor 7 so that the image density becomes the target density. Here, the image forming conditions are, for example, the exposure intensity of the laser scanners 15a to d. Also, the image forming conditions are, for example, a gradation correction table of an image processing unit (not shown) that performs image processing on image data. Or, for example, it may be both the exposure intensity and the gradation correction table of the laser scanners 15a to d. Or, for example, it may be a charging bias applied to charge the photosensitive drums 1a to d by a charger (not shown).

[0020] The pattern detection sensor 7 is an optical sensor that detects reflected light from a detection pattern (density detection pattern or color shift detection pattern) formed on the intermediate transfer belt 5. The detection pattern corresponds to a measurement image. FIG. 2 is a schematic cross-sectional view of the pattern detection sensor 7. The pattern detection sensor 7 includes, for example, an LED as a light-emitting element and a PD as a light-receiving element. The pattern detection sensor 7 includes two LEDs and two PDs. LEDs 1 and 2, and PDs 1 and 2 are provided on a first surface of the substrate 201.

[0021] LED1 irradiates light onto the surface of the intermediate transfer belt 5. The incident angle of LED1 is, for example, 7°. PD1 receives the specularly reflected light of the light irradiated from LED1 onto the intermediate transfer belt 5. PD1 is provided at a position to receive the light reflected from the intermediate transfer belt 5 at a reflection angle of 7°. LED2 irradiates light onto the surface of the intermediate transfer belt 5. The incident angle of LED2 is, for example, 35°. PD2 is a light receiving element that receives diffusely reflected light from the intermediate transfer belt 5 (or the detection pattern on the intermediate transfer belt 5). PD2 is located between LED1 and LED2 in the longitudinal direction of the substrate 201, and is provided at a position that does not receive either the specularly reflected light of the light irradiated from LED1 onto the intermediate transfer belt 5 or the specularly reflected light of the light irradiated from LED2 onto the intermediate transfer belt 5. PD2 is provided at a position to receive the light reflected from the intermediate transfer belt 5 at a reflection angle of 18°.

[0022] 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 201. A housing 203 is attached to the substrate 201. Inside the housing 203, there are light-shielding walls and a lens group 204 that form light guide paths for each element. This allows the light emitted from LED1 to travel in the direction of the optical axis (dotted line in the figure) and irradiate the intermediate transfer belt 5.

[0023] Light emitted from LED1 travels generally in the direction of the optical axis (dotted line in the figure) through the light guide path in housing 203 and the lens portion of lens group 204 near LED1, and reaches PD1 through the light guide path in housing 203 and the lens portion of lens group 204 near PD1. Light emitted from LED2 travels in the direction of the optical axis (solid line in the figure) through the light guide path in housing 203 and the lens portion of lens group 204 near LED2, and is irradiated onto intermediate transfer belt 5. PD2 receives diffuse reflection light of light irradiated from LED2 onto intermediate transfer belt 5 by the light guide path in housing 203 and the lens portion of lens group 204 near PD2.

[0024] A connector 205, a control IC 207, and other mounted components 206 are mounted on the back side of the first surface (mounting surface) of the substrate 201 on which LED1, LED2, PD1, and PD2 are mounted. The control IC 207 has a core chip, which is an integrated circuit, connected to the substrate by wire bonding using a chip-on-board technique.

[0025] A connector 205 electrically connects a CPU 109 (FIG. 3) that controls the entire image forming apparatus 100 to the pattern detection sensor 7. A control IC 207 communicates with the CPU 109 to control the emission of LED1 and LED2. Other mounted components 206 include, for example, a capacitor for stabilizing the power supplied to the control IC 207.

[0026] The substrate 201 also has a first positioning hole 202(a) and a second positioning hole 202(b), which are openings for mounting the pattern detection sensor 7 to the image forming apparatus 100.

[0027] 3 is a control block diagram of the image forming apparatus 100. The CPU 109 communicates with the control IC 207 to control the lighting of LED1 and LED2 of the pattern detection sensor 7. The pattern detection sensor 7 measures the reflected light received from the intermediate transfer belt 5 or the detection pattern on the intermediate transfer belt 5, and outputs a voltage as an output value based on the measurement result (light reception result of PD1 or PD2). The voltage output by the pattern detection sensor 7 is converted into a digital signal by an A / D converter 110 built in the CPU 109, and is acquired by the CPU 109 as a reading level.

[0028] CPU 109 controls laser scanners 15a-d via laser writing control unit 112, controls developers 16a-d via developer control unit 113, and controls photoconductor drums 1a-d via photoconductor drum control unit 114. Furthermore, CPU 109 controls the rotation of the drive roller of intermediate transfer belt 5 via intermediate transfer belt drive unit 115.

[0029] Next, the control of CPU 109 will be described. The control of CPU 109 is performed based on program data stored in ROM 111. CPU 109 also controls the image forming unit to form a detection pattern, which will be described later, on intermediate transfer belt 5 based on pattern image data. CPU 109 then causes pattern detection sensor 7 to detect the detection pattern, and controls image formation conditions based on the detection result of pattern detection sensor 7.

[0030] Next, a description will be given of the detection pattern that the image forming apparatus 100 forms on the intermediate transfer belt 5 when detecting color misregistration. Fig. 4 is a schematic diagram of a color misregistration detection pattern 401 used to detect color misregistration. Fig. 5 illustrates an example of the detection result of the color misregistration detection pattern 401 detected by the pattern detection sensor 7 (output waveform of the pattern detection sensor 7). To detect the color misregistration detection pattern 401, the pattern detection sensor 7 causes the LED1 to emit light, and outputs a voltage value (output value) based on the light reception result of the PD1.

[0031] In the area where the color misregistration detection pattern 401 of the intermediate transfer belt 5 is not formed, the reflectance of the surface of the intermediate transfer belt 5 is higher than that of the color misregistration detection pattern 401 (toner image), so the voltage value of PD1 that receives the specular reflected light is high. Therefore, the reading level is also increased. On the other hand, in the area where the color misregistration detection pattern 401 is formed, the reflectance of the color misregistration detection pattern 401 (toner image) is lower than that of the surface of the intermediate transfer belt 5, so the voltage value of PD1 is low. Therefore, the reading level is decreased. In color misregistration detection, the reading level is compared with a threshold value to detect the position of the image for each color included in the color misregistration detection pattern 401, as shown in FIG. 5.

[0032] The difference between the image position for each color and the ideal position is detected as the amount of color shift from the output waveform of the pattern detection sensor 7. In color shift correction, the CPU 109 controls the writing timing of the laser scanners 15a to 15d by the laser writing control unit 112 based on the detected color shift.

[0033] Next, a detection pattern that the image forming apparatus 100 forms on the intermediate transfer belt 5 when performing density detection will be described. Fig. 6 is a schematic diagram of a density detection pattern 601 used for detecting density. The density detection pattern 601 has a gradation pattern that results in four densities of 70%, 50%, 30%, and 10%, when the maximum density is 100%.

[0034] CPU 109 detects density detection pattern 601 formed on intermediate transfer belt 5 by pattern detection sensor 7, converts the voltage value of pattern detection sensor 7 into a digital value by A / D converter 110, and acquires it as a reading level. CPU 109 converts the reading level into an image density value (not shown), obtains the gradation characteristics of the image forming unit from the density of density detection pattern 601, and generates a gradation correction table so that the gradation characteristics become ideal gradation characteristics. Alternatively, CPU 109 controls image formation conditions so that a target density is achieved based on the detection result of pattern detection sensor 7.

[0035] 7 illustrates an example of the detection result (output waveform of the pattern detection sensor 7) of the yellow density detection pattern 601 detected by the pattern detection sensor 7. To detect the density detection pattern 601, the pattern detection sensor 7 causes the LED2 to emit light and outputs a voltage value (output value) based on the light reception result of the PD2. Note that although the detection results of the density detection patterns 601 of other colors have different voltage values, the shapes of the output waveforms are the same, so a description thereof will be omitted here.

[0036] An image formed to have a density of 70% included in the density detection pattern 601 has a large amount of toner, so the amount of diffusely reflected light reflected by the yellow (Y) toner increases. As the amount of light received by PD2 increases, the voltage value of the pattern detection sensor 7 increases. As a result, the reading level also increases. An image formed to have a density of 10% included in the density detection pattern 601 has a small amount of toner, so the amount of diffusely reflected light reflected by the yellow (Y) toner decreases. As the amount of light received by PD2 increases, the voltage value of the pattern detection sensor 7 decreases. As a result, the reading level also decreases.

[0037] (Light intensity correction for pattern detection sensor 7) Since the pattern detection sensor 7 is disposed near the intermediate transfer belt 5, it becomes dirty with toner scattered from the detection pattern. This reduces the amount of reflected light. For example, when the above-mentioned density detection is performed, the reading level is reduced as shown by the dashed line in FIG. 7. Therefore, the image forming apparatus 100 executes control (FIG. 16) to adjust the amount of emitted light of the pattern detection sensor 7 at any timing.

[0038] The light amount adjustment will be described below with reference to the control flow chart of FIG.

[0039] When the main power supply of the image forming apparatus 100 is turned on, the CPU 109 determines whether it is the time of initial manufacture or whether a part has been replaced (Setp501). When it is the time of initial manufacture or a part has been replaced, the CPU 109 sets the amount of emitted light to a specified value (Step 502) and causes the pattern detection sensor 7 to measure the reflected light from the reference plate 221 (FIG. 11) (Step 503). The CPU 109 stores the measurement value acquired in Step 503 in a memory (not shown) as a reference value (Step 504). Here, the reference plate 221 functions as a reference member used to acquire the reference value.

[0040] Next, CPU 109 determines whether it is time to correct dirt (Step 505). In Step 505, for example, if the detection pattern is to be read, CPU 109 shifts the process to Step 506 in order to adjust the amount of light before the detection pattern is read. Note that CPU 109 may shift the process to Step 506 when, for example, the number of images printed since the previous light amount adjustment has been performed reaches a predetermined number.

[0041] CPU 109 sets the amount of emitted light to a specified value (Step 506), and causes pattern detection sensor 7 to measure the reflected light from reference plate 221 (FIG. 11) (Step 507). CPU 109 then calculates the difference between the reference value stored in Step 504 and the current measured value, and adjusts the amount of emitted light so that the measured value of reference plate 221 (FIG. 11) becomes the reference value (Step 508). Thereafter, CPU 109 causes pattern detection sensor 7 to detect the detection pattern based on the adjusted amount of emitted light (Step 509). If the detection of the detection pattern is successful, CPU 109 controls the image formation conditions based on the detection result of the detection pattern.

[0042] Next, a description will be given of the sensor unit 200. Fig. 8 is a schematic perspective view of the sensor unit 200 serving as a holding member for holding the pattern detection sensor 7. Fig. 9 is a schematic perspective view of the sensor holder 210. The sensor unit 200 is an assembly part in which the pattern detection sensor 7, a protective shutter 211, and a reference plate 221 are integrated into a unit.

[0043] In addition to the pattern detection sensor 7, the sensor unit 200 includes a frame 209, a sensor holder 210 to which the pattern detection sensor 7 is attached, and a protective shutter 211 to protect a sensor surface 208 of the pattern detection sensor 7. The sensor surface 208 is the side on which the lens group 204 (FIG. 2) of the housing 203 (FIG. 2) is provided. The protective shutter 211 has a reference plate 221 (FIG. 11) on a surface facing the sensor surface 208 of the pattern detection sensor 7. The sensor unit 200 further includes a shutter moving means 212 for opening and closing the protective shutter 211. The sensor unit 200 is assembled to the image forming apparatus 100 in a state in which a frame positioning portion 213 provided on the frame 209 is biased against a positioning portion (not shown) provided on the image forming apparatus 100. The sensor unit 200 is disposed in the image forming apparatus 100 so as to maintain a predetermined distance between the intermediate transfer belt 5 and the pattern detection sensor 7.

[0044] (Protective shutter movement mechanism) Next, the moving mechanism of the protective shutter 211 will be described with reference to FIGS.

[0045] The protective shutter 211 is opened and closed by a solenoid 214 and a link 215 provided on the shutter moving means 212. The solenoid 214 is a drive source for shifting the protective shutter 211 from a closed state to an open state. When the solenoid 214 is not attracted, the protective shutter 211 is biased in the X direction by the shutter spring 217 and is in a closed state, and when the solenoid 214 attracts the plunger, the protective shutter 211 moves in the Y direction via the link 215 and is in an open state. Note that the X direction and the Y direction are directions that intersect with the direction of gravity, and the movement direction of the protective shutter 211 is not limited to a direction perpendicular to the vertical direction (horizontal direction).

[0046] Further, an opening 216 is formed in the protective shutter 211 so that the pattern detection sensor 7 can detect the surface of the intermediate transfer belt 5. When the protective shutter 211 is in an open state, the sensor surface 208 is exposed from the opening 216, and the pattern detection sensor 7 can receive reflected light from the intermediate transfer belt 7. Due to the presence of the opening 216, the pattern detection sensor 7 can detect the detection pattern on the intermediate transfer belt 5 when the protective shutter 211 is in an open state.

[0047] On the other hand, when the protective shutter 211 is in the closed state, the protective shutter 211 blocks light emitted from the light emitting element (LED1 or LED2) of the pattern detection sensor 7 toward the intermediate transfer belt 5. Furthermore, when the protective shutter 211 is in the closed state, a reference plate 221 (FIG. 11) provided on the protective shutter 211 faces the pattern detection sensor 7. This allows the pattern detection sensor 7 to detect the reference plate 221 (FIG. 11) when the protective shutter 211 is in the closed state.

[0048] 11 is an enlarged view of a main part of the sensor unit 200. FIG. 11(a) shows the protective shutter 211 in a closed state, and FIG. 11(b) shows the protective shutter 211 in an open state. When the protective shutter 211 moves from an open state to a closed state by the shutter spring 217, the shutter positioning portion 218 provided on the side of the opening 216 abuts against the shutter abutment portion 219 provided on the frame 209, and the protective shutter 211 stops. This causes the protective shutter 211 to transition to a closed state, preventing the pattern detection sensor 7 from being soiled by scattered toner. The shutter spring 217 functions as a spring member that pulls the protective shutter 211 so that the shutter positioning portion 218 abuts against the shutter abutment portion 219.

[0049] (Timing of opening and closing the protective shutter 211) Next, the opening and closing timing of the protective shutter 211 will be described. The protective shutter 211 has the function of preventing contamination in addition to detecting the detection pattern and the reference plate 221 described above. Therefore, except when detecting the detection pattern, it is basically in a closed state. In other words, the pattern detection sensor 7 faces the reference plate 221 so that the pattern detection sensor 7 can measure the reference plate 221 during the period when the detection pattern is not being detected.

[0050] Furthermore, in recent years, users have been demanding increasingly high productivity. For this reason, a detection pattern is formed between images formed on the intermediate transfer belt 5. The suction action of the solenoid 214 (plunger) opens the protective shutter 211 in about several tens of msec, and the suction state is maintained. After that, after the measurement of the detection pattern is completed, the shutter spring 217 transitions from the open state to the closed state in several tens of msec. At this time, as described above, the protective shutter 211 (positioning portion 218) collides with the abutment portion 219 due to the short-term closing action.

[0051] Here, according to an experiment by the inventor, it was found that the protective shutter 211 moves in the vertical direction when it closes in a short time. FIG. 12(a) shows the ideal stop position of the protective shutter 211 in the closed state. Meanwhile, FIG. 12(b) shows the stop position of the protective shutter 211 when it stops displaced in the vertical direction from the ideal stop position. The protective shutter 211 is biased by the shutter spring 217 while abutting against the abutment portion 219. Therefore, as shown in FIG. 12(b), due to the frictional force acting between the abutment portion 219 and the positioning portion 218 of the protective shutter 211, the protective shutter 211 stops at a position displaced in the vertical direction from the ideal stop position. This causes the distance between the reference plate 221 and the pattern detection sensor 7 to be different from the ideal distance.

[0052] Fig. 13 shows the distance characteristics of the pattern detection sensor 7 that the inventors found through experiments. The distance characteristics indicate the change in the amount of reflected light relative to the distance from the pattern detection sensor 7 to the target object. Fig. 13 shows that the amount of reflected light changes significantly depending on the distance from the pattern detection sensor 7 to the target object. Specifically, when the target object is located 3 mm from the pattern detection sensor 7, a change of 0.1 mm changes the amount of reflected light by as much as 4%.

[0053] Therefore, the image forming apparatus 100 performs the suction operation of the solenoid 214 (plunger) again (operation to open the protective shutter 211) after the positioning portion 218 of the protective shutter 211 hits the hitting portion 219 by the shutter spring 217. This is called the post-operation. In the post-operation, the protective shutter 211 moves to such an extent that the sensor surface 208 is not entirely exposed from the opening 216. In other words, the movement amount of the protective shutter 211 in the post-operation is smaller than the movement amount of the protective shutter 211 when the protective shutter 211 changes from the closed state to the open state in order for the pattern detection sensor 7 to detect the detection pattern on the intermediate transfer belt 5. When the post-operation is completed, the positioning portion 218 hits the hitting portion 219 by the shutter spring 217, and the protective shutter 211 transitions to the closed state again. When the post-operation is performed, the impact when the positioning portion 218 hits the abutment portion 219 is reduced compared to the impact caused by the closing operation immediately after detecting the detection pattern, so the protective shutter 211 is positioned at an ideal stop position in the closed state. By performing the post-operation, fluctuations in the distance from the pattern detection sensor 7 to the reference plate 221 are suppressed when the light amount adjustment of the pattern detection sensor 7 is performed, and the pattern detection sensor 7 can appropriately adjust the emitted light amount.

[0054] (Protective shutter 211 opening and closing operation) A control for positioning the protective shutter 211 at a target position by performing a post-operation will be described. When a post-operation is performed, the current applied to the solenoid 214 is made lower than the current applied to the solenoid 214 when reading the detection pattern. When a post-operation is performed, the time during which a current is applied to the solenoid 214 (application time) is further made shorter than the time during which a current is applied to the solenoid 214 when reading the detection pattern (application time).

[0055] An example will be described with reference to FIG. 14. Period A indicates the length of time during which the operation of opening and closing the protective shutter 211 is performed when reading the detection pattern, and the magnitude of the current applied to the solenoid 214. Period B indicates the length of time during which the post-operation is performed, and the magnitude of the current applied to the solenoid 214. The applied current during the post-operation (period B) is lower than the applied current when reading the detection pattern (period A), and the applied current is turned off in a shorter time during period B than during period A. Here, the current applied to the solenoid 214 during the post-operation is, for example, about 60% of the current applied to the solenoid 214 when reading the detection pattern. The application time during period B is, for example, 100 msec.

[0056] The reason why the applied current in period B is 60% of the applied current in period A is to make the attractive force of the solenoid 214 (plunger) almost equal to the force of the urging shutter spring 217. As a result, the protective shutter 211 moves within the application time of 100 msec with a force almost equal to the force applied by the shutter spring 217. In reality, the attractive force for opening the protective shutter 211 and the force by the shutter spring 217 to close are almost equal, so the protective shutter 211 hardly moves at all.

[0057] When the applied voltage is turned off after the post-operation is completed, the positioning portion 218 of the protective shutter 211 abuts against the abutment portion 219 again due to the shutter spring 217, and the protective shutter 211 returns to the closed position. With this operation, the protective shutter 211, which moved vertically due to an impact when the protective shutter 211 is opened or closed after detecting the detection pattern, moves to an ideal vertical position due to its own weight. Furthermore, since there is almost no movement within 100 msec even after the applied voltage is turned off, the impact when the positioning portion 218 abuts against the abutment portion 219 is reduced. Therefore, the positions of the protective shutter 211 and the pattern detection sensor 7 are stable and ideal in the closed state after the post-operation.

[0058] (Protective shutter opening and closing control) In the following, the opening and closing control of the protective shutter will be described with reference to the control block diagram of FIG. 3 and the flow chart diagram of FIG. 15. First, the CPU 109 starts a job in which the image forming apparatus 100 forms an image on a sheet (Step 701). While the job is being executed, the CPU 109 causes the image forming unit to form a detection pattern when the number of pages on which images have been printed reaches a predetermined number (Step 702). The CPU 109 applies a current to the solenoid 214, and causes the protective shutter 211 to transition from a closed state to an open state (Step 703). In Step 703, the current applied to the solenoid 214 is, for example, 800 mA. The CPU 109 functions as a drive control unit that controls the solenoid 214 as a drive source. As a result, the positioning portion 218 of the protective shutter 211 moves away from the abutment portion 219.

[0059] Next, the CPU 109 causes the light emitting element (LED 1 or 2) to emit light based on the amount of emitted light adjusted by correcting for sensor dirt, and causes the pattern detection sensor 7 to measure the detection pattern (Step 704). In Step 704, since a current of 800 mA continues to be applied to the solenoid 214, the protective shutter 211 remains open. After the detection pattern has passed the detection position of the pattern detection sensor 7, the CPU 109 turns off the current applied to the solenoid 214 (Steps 705 and 706). This causes the shutter spring 217 to return the protective shutter 211 to its original position.

[0060] The CPU 109 waits for 100 msec until the state of the protective shutter 211 becomes stable (Step 707). After that, the CPU 109 applies current to the solenoid 214 again to perform the post-operation (Step 708). In Step 708, the applied current is, for example, 500 mA. Here, the CPU 109 stops the current supply to the solenoid 214 once, and then supplies a current of 500 mA to the solenoid 214 again.

[0061] After waiting for 100 msec with the current applied in Step 708 (Step 709), the CPU 109 turns off the current applied to the solenoid 214 (Step 710). After that, the CPU 109 waits for 100 msec (Step 711) and causes the pattern detection sensor 7 to measure the reference plate 221 in order to perform light amount adjustment (Step 712).

[0062] The vertical positions of the reference plate 221 and the pattern detection sensor 7 are moved to ideal positions by subsequent operations (the processing of Steps 707 to 710). Therefore, the processing of Step 712 may be performed, for example, after the processing of Step 702 is executed. In other words, when the distance between the reference plate 221 and the pattern detection sensor 7 is stable, the CPU 109 may be configured to cause the pattern detection sensor 7 to measure the reference plate 221 immediately before measuring the detection pattern.

[0063] 15, the pattern detection sensor 7 measures the reference plate 221 every time a detection pattern is measured, but it is not necessary to execute the processes of Steps 707 to 712 every time. For example, if only a small number of sheets have been printed since the previous light amount adjustment, the processes of Steps 707 to 712 may be skipped. Furthermore, detection pattern measurement is not limited to only when a job is being executed, and the light amount adjustment and detection pattern measurement may be executed when the user instructs detection pattern measurement.

[0064] In the above description, the current value (500 mA) applied to the solenoid 214 in the post-operation is set to be lower than the current value (800 mA) applied to the solenoid 214 when measuring the detection pattern. However, if the current value (or voltage value) applied to the solenoid 214 cannot be changed, a configuration may be used in which only the application time is shortened. The same effect can be obtained with this configuration.

[0065] In addition, to improve the stability of the position of the reference plate 221, the current value applied to the solenoid 214 in the post-operation is set to 500 mA, but the optimal current value to be applied to the solenoid 214 varies depending on individual differences in the solenoid 214 and the shutter spring 217. Therefore, for example, a mode for determining the current value to be applied to the solenoid 214 in the post-operation may be provided. In this mode, for example, the CPU 109 may perform Steps 703 to 712 in FIG. 15 multiple times while changing the applied current, and determine the optimal current value based on the measurement result of the reference plate 221 by the pattern detection sensor 7.

[0066] In the above description, the protective shutter 211 is driven by controlling the value of the current applied to the solenoid 214, but the solenoid 214 may be configured to control the value of the voltage applied thereto. In this case, the CPU 109 may control the voltage applied to the solenoid 214 so that the voltage applied in the post-operation is smaller than the voltage applied when measuring the detection pattern. [Explanation of symbols]

[0067] 7 Pattern detection sensor 109 CPU 211 Protective shutter 214 Solenoid

Claims

1. an image carrier; an image forming means for forming an image on the image carrier; a measuring means for measuring the reflected light from the image carrier, the measuring means including a light-emitting element for emitting light toward the image carrier and a light-receiving element for receiving the reflected light from the image carrier; a holding member for holding the measuring means; a shutter that blocks light emitted from the light emitting element of the measuring means toward the image carrier; a spring member that pulls the shutter so that the shutter abuts against an abutment portion of the holding member so that the shutter is in a closed state in which the shutter blocks light emitted from the light-emitting element toward the image carrier; A driving source; a drive control unit that controls the drive source to move the shutter away from the abutting portion of the holding member against the tensile force of the spring member, thereby bringing the shutter into an open state in which light from the light-emitting element is irradiated onto the image carrier; and a reference member provided on the shutter; an adjusting means for adjusting the amount of light emitted from the light-emitting element based on the measurement result of the reference member by causing the light-emitting element of the measuring means to emit light and the light-receiving element of the measuring means to receive reflected light from the reference member; a control means for controlling the image forming means to form a measurement image, for controlling the drive control means to supply a first current to the drive source so as to open the shutter, for controlling the measurement means to measure reflected light from the measurement image, and for controlling the image forming means based on a measurement result of the measurement image by the measurement means; an image forming apparatus characterized in that, when the shutter is controlled from the open state to the closed state, the drive control means stops the supply of current to the drive source once, then supplies a second current to the drive source that is smaller than the first current, and then stops the supply of current again.

2. An image forming device as described in claim 1, characterized in that by supplying the first current and then stopping it, the shutter changes from a closed state to a first open state and then to a closed state, and by supplying the second current and then stopping it, the shutter again changes from a closed state to a second open state in which the amount of movement of the shutter is smaller than in the first open state and then to a closed state.

3. 2. The image forming apparatus according to claim 1, wherein the driving source is a solenoid having a plunger.

4. 2. The image forming apparatus according to claim 1, wherein the shutter is controlled to the open state by moving from the closed state in a direction intersecting the direction of gravity.

5. an image carrier; an image forming means for forming an image on the image carrier; a measuring means for measuring the reflected light from the image carrier, the measuring means including a light-emitting element for emitting light toward the image carrier and a light-receiving element for receiving the reflected light from the image carrier; a holding member for holding the measuring means; a shutter that blocks light emitted from the light emitting element of the measuring means toward the image carrier; a spring member that pulls the shutter so that the shutter abuts against an abutment portion of the holding member so that the shutter is in a closed state in which the shutter blocks light emitted from the light-emitting element toward the image carrier; A driving source; a drive control unit that controls the drive source to move the shutter away from the abutting portion of the holding member against the tensile force of the spring member, thereby bringing the shutter into an open state in which light from the light-emitting element is irradiated onto the image carrier; and a reference member provided on the shutter; an adjusting means for adjusting the amount of light emitted from the light-emitting element based on the measurement result of the reference member by causing the light-emitting element of the measuring means to emit light and the light-receiving element of the measuring means to receive reflected light from the reference member; a control means for controlling the image forming means to form a measurement image, for controlling the drive control means to supply a first voltage to the drive source so as to open the shutter, for controlling the measurement means to measure reflected light from the measurement image, and for controlling the image forming means based on a measurement result of the measurement image by the measurement means; an image forming apparatus characterized in that, when the shutter is controlled from the open state to the closed state, the drive control means stops the supply of voltage to the drive source once, then supplies a second voltage to the drive source that is smaller than the first voltage, and then stops the supply of voltage again.

6. An image forming device as described in Claim 5, characterized in that by supplying the first voltage and then stopping it, the shutter changes from a closed state to a first open state and then to a closed state, and by supplying the second voltage and then stopping it, the shutter again changes from a closed state to a second open state in which the amount of movement of the shutter is smaller than in the first open state and then to a closed state.

7. 6. The image forming apparatus according to claim 5, wherein the driving source is a solenoid having a plunger.

8. 6. The image forming apparatus according to claim 5, wherein the shutter is controlled to the open state by moving from the closed state in a direction intersecting the direction of gravity.

Images