IMAGE FORMING APPARATUS

An image forming apparatus includes an image carrier, an image forming unit, a measuring unit configured to measure the reflected light from the image carrier, a retaining member configured to retain the measuring unit, a shutter configured to block the light emitted from the light-emitting element, a spring member configured to pull the shutter to enter a closed state, a drive source, a drive control unit configured to control the drive source, a reference member, an adjustment unit configured to adjust the emitted light amount, and a control unit configured to control the image forming unit, the measuring unit, and the image forming unit, wherein, when the shutter enters the closed state from the open state, the drive control unit once stops the current supply to the drive source, then supplies a second current smaller than the first current to the drive source, and then stops the current supply again.

BACKGROUND

Field of the Disclosure

The present disclosure relates to control of opening and closing a shutter of a measuring unit provided on an image forming apparatus.

Description of the Related Art

To correct relative image positional deviations (referred to as color deviations) and densities for different color components, image forming apparatuses such as copying machines, printers, and facsimiles form a measurement image on an image carrier, and control color deviations and densities based on the result of the measurement of the measurement image by a measuring unit. An optical sensor known as a measuring unit measures a measurement image formed on an intermediate transfer member (or a photosensitive drum) as an image carrier.

The optical sensor irradiates the measurement image on the image carrier with light by using a light-emitting element, and measures the reflected light from the image carrier and the reflected light from the measurement image. An image forming apparatus controls color or density deviations based on the reflected light amount measured by the optical sensor.

It is, however, necessary to shorten the distance between the optical sensor and the measurement image to measure the measurement image. For this reason, there is an issue that the reflected light amount is reduced by an agent (toner or ink) which is scattered from the measurement image and adheres to the surface of the optical sensor.

An image forming apparatus discussed in Japanese Patent Application Laid-Open No. 02-111162 includes a reference member for adjusting the emitted light amount of an optical sensor. Before measuring the measurement image, the image forming apparatus discussed in Japanese Patent Application Laid-Open No. 02-111162 enables the optical sensor to measure the reflected light from the reference member and adjusts the emitted light amount of the optical sensor based on the result of the measurement of the reflected light from the reference member. The configuration discussed in Japanese Patent Application Laid-Open No. 02-111162 adjusts the emitted light amount to correct the reflected light amount reduced by the toner adhesion, making it possible to accurately measure the reflected light from the measurement image even if toner adheres to the optical sensor.

It was found that the emitted light amount of the light-emitting element cannot be suitably adjusted because of a slight change of the distance from the light-emitting element of the measuring unit to the reference member. An experiment of the inventor revealed that the reflected light amount changes by as large as 4% when the distance between the object under measurement and the optical sensor changes by 0.1 mm. The variation of the reflected light amount by the above-described distance exceeds the reflected light amount reduced by stain of toner.

When the measurement image is measured by the optical sensor, the reference member needs to be evacuated from the optical path for the light from the light-emitting element. For this reason, the image forming apparatus includes a drive source for controlling the shutter to enter an open state. The image forming apparatus includes a spring member for closing the shutter. When restoring the shutter from the open state to a closed state, the drive source control is stopped, and the spring member brings the shutter to into contact with an abutting portion. Then, the state of the shutter changes from the open state to the closed state.

In a configuration for closing the shutter by using the above-described spring member, the shutter collides with the abutting portion, causing a variation in the distance between the reference member of the shutter and the optical sensor. This variation of the distance may possibly inhibit the suitable adjustment of the light amount of the optical sensor.

SUMMARY

According to an aspect of the present disclosure, an image forming apparatus includes an image carrier, an image forming unit configured to form an image on the image carrier, a measuring unit provided with a light-emitting element for emitting light to the image carrier and a light-receiving element for receiving reflected light from the image carrier, and configured to measure the reflected light from the image carrier, a retaining member configured to retain the measuring unit, a shutter configured to block the light emitted from the light-emitting element of the measuring unit to the image carrier, a spring member configured to pull the shutter so that the shutter comes into contact with an abutting portion of the retaining member to enter a closed state where the shutter blocks the light emitted from the light-emitting element to the image carrier, a drive source, a drive control unit configured to control the drive source to separate the shutter from the abutting portion of the retaining member against a pulling force of the spring member so that the shutter enters an open state where the image carrier is irradiated with the light from the light-emitting element, a reference member disposed on the shutter, an adjustment unit configured to cause the light-emitting element of the measuring unit to emit light, cause the light-receiving element of the measuring unit to receive reflected light from the reference member, and adjust the emitted light amount of the light-emitting element based on a result of the measurement of the reference member by the measuring unit, and a control unit configured to control the image forming unit to form a measurement image, control the drive control unit to supply a first current to the drive source so that the shutter enters the open state, control the measuring unit to measure reflected light from the measurement image, and control the image forming unit based on a result of the measurement of the measurement image by the measuring unit, wherein, in a case where the shutter is controlled to enter the closed state from the open state, the drive control unit once stops the current supply to the drive source, then supplies a second current smaller than the first current to the drive source, and then stops the current supply again.

DESCRIPTION OF THE EMBODIMENTS

A first exemplary embodiment will be described below.FIG.1is a cross-sectional view illustrating an essential part of an image forming apparatus100. The image forming apparatus100includes an image forming unit for forming a yellow (Y) image, a cyan (C) image, a magenta (M) image and a black (K) image, an intermediate transfer belt5, and a transfer roller4for transferring the images on the intermediate transfer belt5to a sheet.

The image forming unit includes photosensitive drums1a,1b,1cand1d, a charging unit (not illustrated), laser scanners15a,15b,15c, and15d, developing devices16a,16b,16c, and16d, and a primary transfer unit (not illustrated). Referring toFIG.1, the photosensitive drums1a,1b,1c, and1drotate in the counterclockwise direction. The charging unit charges the photosensitive drums1a,1b,1c, and1d. The laser scanners15a,15b,15c, and15dexpose the photosensitive drums1a,1b,1c, and1dcharged by the charging unit to light to form electrostatic latent images on the photosensitive drums1a,1b,1c, and1d, respectively. The latent images on the photosensitive drums1a,1b,1c, and1dare developed by the developing devices16a,16b,16c, and16d, respectively. The images of different colors are visualized on the photosensitive drums1a,1b,1c, and1d.

The primary transfer unit transfers the images on the photosensitive drums1a,1b,1c, and1dfrom the photosensitive drums1a,1b,1c, and1dto the intermediate transfer belt5. When the images of different colors formed on the photosensitive drums1a,1b,1c, and1dare sequentially transferred onto the intermediate transfer belt5in an overlapped way, a full-color image6is carried on the intermediate transfer belt5. The intermediate transfer belt5is an intermediate transfer member to which images are transferred.

The intermediate transfer belt5is stretched by a plurality of rollers including a belt support roller. The image6is secondarily transferred from the intermediate transfer belt5to a sheet at the nip portion between the intermediate transfer belt5and the transfer roller4. The sheet with the image6transferred thereto is conveyed to a fixing unit (not illustrated) by a conveyance belt12. The image is fixed to the sheet with the heat and pressure from the fixing unit. The sheet with the image fixed thereto is discharged onto a discharge tray of the image forming apparatus100.

The image forming apparatus100produces relative positional deviations between images of different colors by manufacturing dispersion or errors of the laser scanners15ato15dand the photosensitive drums1ato1d, parts distortion caused by temperature rise, and conveyance dispersion of the intermediate transfer belt5. These relative positional deviations between images of different colors are referred to as color deviations. Accordingly, the image forming apparatus100forms a color deviation detection pattern, detects the color deviation detection pattern by using a pattern detection sensor7, and performs color deviation correction based on the result of the detection of the color deviation detection pattern by using the pattern detection sensor7to prevent color deviations.

The image forming apparatus100is known to produce varying density of an image because of variations of the ambient environment (temperature and humidity) and the abrasion of photosensitive layers of the photosensitive drums1ato1d. For this reason, the image forming apparatus100forms a density detection pattern, detects the density detection pattern by using the pattern detection sensor7, and controls image forming conditions based on the result of the detection of the density detection pattern by using pattern detection sensor7to achieve a target image density. Examples of the image forming conditions include the exposure intensities of the laser scanners15ato15d, and a gradation correction table of an image processing unit (not illustrated) for subjecting image data to image processing. Examples of the image forming conditions further include both the exposure intensities of the laser scanner15ato15dand the gradation correction table, and a charging bias applied to enable the charging unit (not illustrated) to charge the photosensitive drums1ato1d.

The pattern detection sensor7is an optical sensor for detecting the reflected light from the detection pattern (the density detection pattern or the color deviation detection pattern) formed on the intermediate transfer belt5. The detection pattern is equivalent to the measurement image.FIG.2is a cross-sectional view schematically illustrating the pattern detection sensor7. The pattern detection sensor7includes, for example, Light Emitting Diodes (LEDs) as light-emitting elements, and photodiodes (PDs) as light-receiving elements. The pattern detection sensor7includes two LEDs and two PDs. LEDs1and2and PDs1and2are disposed on the first surface of a substrate201.

The LED1irradiates the surface of the intermediate transfer belt5with light, for example, at an incident angle of 7 degrees. The PD1receives, from the intermediate transfer belt5, normal reflection light of the light radiated from the LED1onto the intermediate transfer belt5. The PD1is disposed at a position where the PD1receives the light reflected by the intermediate transfer belt5at a reflection angle of 7 degrees. The LED2irradiates the surface of the intermediate transfer belt5with light, for example, at an incident angle of 35 degrees.

The PD2is a light-receiving element for receiving diffused reflected light from the intermediate transfer belt5(or the detection pattern on the intermediate transfer belt5). The PD2is positioned between the LEDs1and2in the longitudinal direction of the substrate201, and is disposed at a position where the PD2receives neither the normal reflection light of the light radiated from the LED1onto the intermediate transfer belt5nor the normal reflection light of the light radiated from the LED2onto the intermediate transfer belt5. The PD2is disposed at a position where the PD2receives the light reflected by the intermediate transfer belt5at a reflection angle of 18 degrees.

All of the LEDs1and2and the PD1and2are surface-mounted elements disposed on the same surface of the substrate201. The substrate201is provided with a housing203. The housing203includes a shading wall and a lens group204for forming a light guide path for each element. Thus, the light emitted from the LED1advances in the direction of the optical axis (the dotted line inFIG.2) and then radiated onto the intermediate transfer belt5.

The light emitted from the LED1advances almost in the direction of the optical axis (the dotted line inFIG.2) through a light guide path and a lens unit near the LED1of the lens group204in the housing203, passes through a light guide path and a lens unit near the PD1of the lens group204in the housing203, and then reaches the PD1. The light emitted from the LED2advances in the direction of the optical axis (solid line inFIG.2) through a light guide path and a lens unit near the LED2of the lens group204in the housing203, and then is radiated onto the intermediate transfer belt5. The PD2receives diffused reflected light of the light radiated from the LED2onto the intermediate transfer belt5through a light guide path and a lens unit near the PD2of the lens group204in the housing203.

A connector205, a control integrated circuit (IC)207, and other surface-mounted components206are mounted on the back surface of the first surface (mount surface) of the substrate201where the LEDs1and2and the PDs1and2are mounted. The control IC207as an IC core chip is connected with the substrate201with wire bonding by using a chip-on-board method.

The connector205electrically connects a Central Processing Unit (CPU)109(FIG.3) for controlling the entire image forming apparatus100and the pattern detection sensor7. The control IC207communicates with the CPU109to control the light emission of the LEDs1and2. Other surface-mounted components206include, for example, a capacitor for stabilizing the power to be supplied to the control IC207.

The substrate201has a first positioning hole202(a) and a second positioning hole202(b) as openings for attaching the pattern detection sensor7to the image forming apparatus100.

FIG.3is a control block diagram illustrating the image forming apparatus100. The CPU109communicates with the control IC207to control the lighting of the LEDs1and2of the pattern detection sensor7.

The pattern detection sensor7measures the reflected light from the intermediate transfer belt5or the detection pattern on the intermediate transfer belt5, and outputs a voltage as an output value based on the result of the measurement (the result of the light reception of the PD1or2). The voltage output by the pattern detection sensor7is converted into a digital signal by an analog-to-digital (A/D) converter110built in the CPU109and then acquired as a read level by the CPU109.

The CPU109controls the laser scanners15ato15dvia a laser write control unit112, controls the developing devices16ato16dvia a developing device control unit113, and controls the photosensitive drums1ato1dvia a photosensitive drum control unit114. The CPU109controls the rotation of the drive rollers of the intermediate transfer belt5via an intermediate transfer belt drive unit115.

Control by the CPU109will be described below. Control by the CPU109is performed based on program data stored in a Read Only Memory (ROM)111. The CPU109controls the image forming unit to form a detection pattern (described below) on the intermediate transfer belt5based on pattern image data. The CPU109controls the pattern detection sensor7to detect the detection pattern and controls the image forming conditions based on the result of the detection of the detection pattern by the pattern detection sensor7.

A detection pattern formed on the intermediate transfer belt5by the image forming apparatus100at the time of color deviation detection will be described below.FIG.4schematically illustrates a color deviation detection pattern401used to detect color deviations.FIG.5illustrates an example of a result of the detection of the color deviation detection pattern401by the pattern detection sensor7(an output waveform of the pattern detection sensor7). To detect the color deviation detection pattern401, the pattern detection sensor7causes the LED1to emit light and outputs a voltage value (output value) based on the result of the light reception by the PD1.

In regions on the intermediate transfer belt5where the color deviation detection pattern401is not formed, the reflection factor of the surface of the intermediate transfer belt5is higher than that of the color deviation detection pattern401(toner image), resulting in a high voltage value of the PD1that receives normal reflection light and therefore resulting in an increased read level. On the other hand, in regions where the color deviation detection pattern401is formed, the reflection factor of the color deviation detection pattern401(toner images) is smaller than that of the surface of the intermediate transfer belt5, resulting in a low voltage value of the PD1and therefore resulting in a decreased read level. In the color deviation detection, the CPU109compares the read level with a threshold value to detect the positions of the images of different colors included in the color deviation detection pattern401, as illustrated inFIG.5.

Based on the output waveform of the pattern detection sensor7, the CPU109detects the difference between the positions of the images of different colors and ideal positions, as the amounts of color deviations. In the color deviation correction, the CPU109controls the write timings of the laser scanners15ato15dbased on the detected color deviations via the laser write control unit112.

A detection pattern formed on the intermediate transfer belt5by the image forming apparatus100at the time of density detection will be described below.FIG.6schematically illustrates a density detection pattern601used for density detection. The density detection pattern601includes a gradation pattern having four different densities as 70%, 50%, 30%, and 10% of the maximum density (100%).

The CPU109detects the density detection pattern601formed on the intermediate transfer belt5via the pattern detection sensor7and converts the voltage value of the pattern detection sensor7into a digital value via the A/D converter110to acquire a read level. The CPU109converts the read level into an image density value (not illustrated), obtains the gradation characteristics of the image forming unit based on the density of the density detection pattern601, and generates a gradation correction table so that the gradation characteristics are ideal gradation characteristics. Alternatively, the CPU109controls the image forming conditions based on the result of the detection of the pattern detection sensor7to achieve a target density.

FIG.7illustrates an example of a result of the detection of the density detection pattern601of yellow detected by the pattern detection sensor7(an output waveform of the pattern detection sensor7). To detect the density detection pattern601, the pattern detection sensor7causes the LED2to emit light and outputs a voltage value (output value) based on the result of the light reception by the PD2. For the density detection pattern601of other colors, the detection result has different voltage values and the same output waveform, and redundant descriptions of the other colors will be omitted.

An image having the 70% density included in the density detection pattern601has a large amount of toner, providing a large amount of diffused reflected light reflected by the yellow (Y) toner. With the increase in the received light amount of the PD2, the voltage value of the pattern detection sensor7increases to increase the read level. An image having the 10% density included in the density detection pattern601has a small amount of toner, providing a small amount of diffused reflected light reflected by the yellow (Y) toner. With the increase in the received light amount of the PD2, the voltage value of the pattern detection sensor7decreases to decrease the read level.

(Light Amount Correction for Pattern Detection Sensor7)

Since the pattern detection sensor7is disposed in the vicinity of the intermediate transfer belt5, the sensor7is stained by toner scattered from the density detection pattern601, resulting in a reduced reflected light amount. For example, as a result of the above-described density detection, the read level is lowered as drawn by the broken lines inFIG.7. Accordingly, the image forming apparatus100performs control to adjust the emitted light amount of the pattern detection sensor7at an optional timing (FIG.16).

The light amount adjustment will be described below with reference to the control flowchart inFIG.16.

When the main power of the image forming apparatus100is turned ON, then in step S501, the CPU109determines whether the apparatus100is in the initial production or the parts replacement state. When the apparatus100is in the initial production or the parts replacement state (YES in step S501), the processing proceeds to step S502. In step S502, the CPU109sets the emitted light amount to a predetermined value. In step S503, the CPU109controls the pattern detection sensor7to measure the reflected light from a reference plate221(FIGS.11A and11B). In step S504, the CPU109stores the measured value acquired in step S503in a memory (not illustrated) as a reference value. The reference plate221functions as a reference member for acquiring a reference value.

In step S505, the CPU101determines whether the current timing is a stain correction timing. For example, when the detection pattern601is to be read (YES in step S505), the CPU109performs the light amount adjustment before the detection pattern reading is started. Then, the processing proceeds to step S506. For example, the processing may proceed to step S506when the number of sheets on which printing has been completed since the light amount adjustment is started reaches a predetermined number.

In step S506, the CPU109sets the emitted light amount to a predetermined value. In step S507, the CPU109controls the pattern detection sensor7to measure the reflected light from the reference plate221(FIGS.11A and11B). In step S508, the CPU109obtains the difference between the reference value stored in step S504and the present measured value, and adjusts the emitted light amount so that the measured value of the reference plate221(FIGS.11A and11B) becomes the reference value. In step S509, the CPU109controls the pattern detection sensor7to detect the detection pattern based on the adjusted emitted light amount. When the detection of the detection pattern is successful, the CPU109controls the image forming conditions based on the result of the detection of the detection pattern.

A sensor unit200will be described below.FIG.8is a perspective view schematically illustrating the sensor unit200as a retaining member for retaining the pattern detection sensor7.FIG.9is a perspective view schematically illustrating a sensor holder210. The sensor unit200is an assembly part for unitizing the pattern detection sensor7, a protection shutter211, and the reference plate221.

The sensor unit200includes the pattern detection sensor7, a frame209, the sensor holder210for attaching the pattern detection sensor7, and the protection shutter211for protecting a sensor surface208of the pattern detection sensor7. The sensor surface208is the side where the lens group204(FIG.2) of the housing203(FIG.2) is disposed. The protection shutter211is provided with the reference plate221(FIGS.11A and11B) on the surface facing the sensor surface208of the pattern detection sensor7.

The sensor unit200includes a shutter moving unit212for opening and closing the protection shutter211. With the sensor unit200, a frame positioning portion213disposed on the frame209is attached to the image forming apparatus100in a state of being biased by a positioning portion (not illustrated) disposed on the image forming apparatus100. The sensor unit200is disposed in the image forming apparatus100to maintain a predetermined distance between the intermediate transfer belt5and the pattern detection sensor7.

(Moving Mechanism of Protection Shutter)

The moving mechanism of the protection shutter211will be described below with reference toFIGS.8and10.

The protection shutter211is opened and closed by a solenoid214and a link215disposed on the shutter moving unit212. The solenoid214is a drive source for changing the protection shutter211from the closed state to the open state. When the solenoid214is not absorbed, the protection shutter211is biased in the X direction by the shutter spring217to enter the closed state. When the solenoid214absorbs the plunger, the protection shutter211moves in the Y direction via the link215to enter the open state. The X and Y directions intersect with the gravity direction. The moving direction of the protection shutter211is not limited to the direction (horizontal direction) perpendicularly intersecting the vertical direction.

The protection shutter211is provided with an opening216to enable the pattern detection sensor7to detect the surface of the intermediate transfer belt5. When the protection shutter211is in the open state, the sensor surface208is exposed from the opening216, enabling the pattern detection sensor7to receive the reflected light from the intermediate transfer belt5. The opening216enables the pattern detection sensor7to detect the detection pattern on the intermediate transfer belt5when the protection shutter211is in the open state.

On the other hand, when the protection shutter211is in the closed state, the protection shutter211blocks the light emitted from the light-emitting element (LED1or2) of the pattern detection sensor7to the intermediate transfer belt5. When the protection shutter211is in the closed state, the protection shutter211disposed on the reference plate221(FIGS.11A and11B) faces the pattern detection sensor7. This enables the pattern detection sensor7to detect the reference plate221(FIGS.11A and11B) when the protection shutter211is in the closed state.

FIGS.11A and11Bare enlarged views illustrating an essential part of the sensor unit200.FIG.11Aillustrates the protection shutter211in the closed state, andFIG.11Billustrates the protection shutter211in the open state. When the protection shutter211is changed from the open state to the closed state by the shutter spring217, the shutter positioning portion218disposed on the lateral surface of the opening216comes into contact with a shutter abutting portion219disposed on the frame209, and the protection shutter211stops. Thus, the protection shutter211enters the closed state to prevent the pattern detection sensor7from being stained by scattered toner. The shutter spring217functions as a spring member for pulling the protection shutter211so that the shutter positioning portion218comes into contact with the shutter abutting portion219.

(Opening and Closing Operations of Protection Shutter211)

The timing of opening and closing the protection shutter211will be described below. The protection shutter211has a function of preventing stain in addition to a function of detecting the above-described detection pattern and a function of detecting the reference plate221. Accordingly, the protection shutter211is basically closed other than in a case of detecting the detection pattern. More specifically, the pattern detection sensor7faces the reference plate221to enable measuring the reference plate221in a time period during which the detection pattern is not detected.

In recent years, users have demanded higher productivity. For this reason, the detection pattern is formed between images formed on the intermediate transfer belt5. The absorption operation of the solenoid214(plunger) opens the protection shutter211for about several ten milliseconds and then maintains the absorption state. Then, upon completion of the detection pattern measurement, the protection shutter211is changed from the open state to the closed state by the shutter spring217. As described above, the protection shutter211(the positioning portion218of the protection shutter211) collides with the abutting portion219in a short-time closing operation.

An experiment by the inventor revealed that the short-time closing operation of the protection shutter211caused the vertical movement of the protection shutter211.FIG.12Aillustrates an ideal stop position in the closed state of the protection shutter211. On the other hand,FIG.12Billustrates the stop position of the protection shutter211when the protection shutter211stops at a position vertically deviated from the ideal stop position. The protection shutter211is biased by the shutter spring217while the protection shutter211is in contact with the abutting portion219. Accordingly, as illustrated inFIG.12B, the protection shutter211stops at a position vertically deviated from the ideal stop position because of the frictional force applied between the abutting portion219and the positioning portion218of the protection shutter211. This means that the distance between the reference plate221and the pattern detection sensor7is not the ideal distance.

FIG.13illustrates the distance characteristics of the pattern detection sensor7obtained through an experiment by the inventor. The distance characteristics indicate the variation of the reflected light amount with respect to the distance from the pattern detection sensor7to a target object.FIG.13illustrates that the reflected light amount largely is changed by the distance from the pattern detection sensor7to the target object. More specifically, when the target object is located at a position 3 mm from the pattern detection sensor7, the reflected light amount changes by as large as 4% with respect to a 0.1-mm variation.

After the positioning portion218of the protection shutter211is brought into contact with the abutting portion219by the shutter spring217, the image forming apparatus100performs the absorption operation of the solenoid214(plunger) (operation for opening the protection shutter211). This operation is referred to as a post operation. In the post operation, the protection shutter211moves to an extent that the sensor surface208is not entirely exposed from the opening216. More specifically, the moving amount of the protection shutter211in the post operation is smaller than that of the protection shutter211when the protection shutter211changes from the closed state to the open state to enable the pattern detection sensor7to detect the detection pattern on the intermediate transfer belt5. When the post operation is completed, the positioning portion218is brought into contact with the abutting portion219by the shutter spring217, and the protection shutter211enters the closed state again. After the post operation is performed, the impact occurring when the positioning portion218is brought into contact with the abutting portion219is smaller than the impact caused by the closing operation immediately after the detection of the detection pattern. Accordingly, the protection shutter211is positioned at the ideal stop position in the closed state. Performing the post operation can prevent the variation of the distance from the pattern detection sensor7to the reference plate221during execution of the light amount adjustment of the pattern detection sensor7, so that the pattern detection sensor7can suitably adjust the emitted light amount.

(Opening and Closing Operations of Protection Shutter211)

Control for positioning the protection shutter211at the target position through the post operation will be described below. The current applied to the solenoid214at the time of the post operation is made smaller than that at the time of detection pattern reading. The application time duration of the current applied to the solenoid214at the time of the post operation is made shorter than that of the current applied to the solenoid214at the time of detection pattern reading.

An example will be described below with reference toFIG.14. A time period A indicates the time duration during which the opening and closing operation of the protection shutter211is performed at the time of detection pattern reading, and the magnitude of the current applied to the solenoid214. A time period B indicates the time duration during which the post operation is performed, and the magnitude of the current applied to the solenoid214. The applied current in the post operation (time period B) is made smaller than that at the time of detection pattern reading (time period A), and the applied current in the time period B is turned OFF in a shorter time than in the time period A. For example, the current applied to the solenoid214in the post operation is set to about 60% of that at the time of detection pattern reading. The current application time duration in the time period B is, for example, is 100 milliseconds.

The reason why the current applied in the time period B is set to about 60% of that in the time period A is to almost equalize the absorption force of the solenoid214(plunger) and the biasing force of the shutter spring217. Thus, during the 100-ms current application time duration, the protection shutter211moves by almost the same force as the biasing force of the shutter spring217. Actually, the absorption force required to open the protection shutter211and the force of the shutter spring217required to close the protection shutter211are almost the same, and therefore the protection shutter211hardly moves.

When the applied voltage is turned OFF after completion of the post operation, the positioning portion218is brought into contact with the abutting portion219again by the shutter spring217, and the protection shutter211returns to the position of the closed state. After this operation, the protection shutter211, which has vertically moved by the impact occurring when the protection shutter211is opened or closed after the detection of the detection pattern, moves to the ideal vertical position by its own weight. The protection shutter211hardly moves in the 100-ms period even after turning OFF the applied voltage, and hence the impact occurring when the positioning portion218is brought into contact with the abutting portion219decreases. For this reason, the positions of the protection shutter211and the pattern detection sensor7are stably set to the ideal positions in the closed state after the post operation.

(Opening and Closing Control of Protection Shutter)

Opening/closing control of the protection shutter will be described below with reference to the control block diagram inFIG.3and the flowchart inFIG.15. In step S701, the CPU109starts a job in which the image forming apparatus100forms an image on a sheet. When the number of pages on which image printing has been completed reaches a predetermined number during execution of the job (YES in step S702), the processing proceeds to step S703. In step S703, the CPU109instructs the image forming unit to form a detection pattern. In step S703, the CPU109applies a current to the solenoid214to change the protection shutter211from the closed state to the open state. In step S703, the CPU109applies, for example, an 800-mA current to the solenoid214. The CPU109functions as a drive control unit for controlling the solenoid214as a drive source. Thus, the positioning portion218of the protection shutter211separates from the abutting portion219.

In step S704, the CPU109controls the light-emitting element (LED1or2) to emit light based on the emitted light amount adjusted by the sensor stain correction, and controls the pattern detection sensor7to measure the detection pattern. In step S704, because the 800-mA current is kept being applied to the solenoid214, the protection shutter211remains open. After the detection pattern has passed through the detection position of the pattern detection sensor7, then in steps S705and S706, the CPU109turns OFF the current applied to the solenoid214. Thus, the shutter spring217restores the protection shutter211to the former position.

In step S707, the CPU109waits for 100 milliseconds until the state of the protection shutter211stabilizes. In step S708, to perform the post operation, the CPU109applies a current, for example, a 500-mA current to the solenoid214again. After once stopping the current supply to the solenoid214, the CPU109supplies the 500-mA current to the solenoid214again.

In step S709, the CPU109waits for 100 milliseconds while maintaining the current applied in step S708. In step S710, the CPU109turns OFF the current applied to the solenoid214. In step S711, the CPU109waits for 100 milliseconds. In step S712, the CPU109controls the pattern detection sensor7to measure the reference plate221to perform the light amount adjustment.

The vertical positions of the reference plate221and the pattern detection sensor7are moved to the ideal positions through the post operation (the processing in steps S707to S710). Accordingly, the processing of step S712may be performed, for example, after completion of the processing in step S702. More specifically, when the distance between the reference plate221and the pattern detection sensor7is stable, the CPU109may be configured to control the pattern detection sensor7to measure the reference plate221before the detection pattern measurement.

Although, in the flowchart inFIG.15, the pattern detection sensor7measures the reference plate221each time the detection pattern measurement is performed, the CPU109does not need to perform the processing in steps707to712each time. For example, if a small number of sheets have been printed since the last light amount adjustment, the CPU109may skip the processing in steps S707to S712. The timing of the detection pattern measurement is not limited to the job execution timing. The light amount adjustment and detection pattern measurement may be performed when the user issues an instruction for the detection pattern measurement.

In the above descriptions, the current value (500 mA) applied to the solenoid214in the post operation is made smaller than the current value (800 mA) applied to the solenoid214at the time of the detection pattern measurement. However, if the current value (or voltage value) to be applied to the solenoid214cannot be changed, only the application time duration may be reduced. This configuration also enables obtaining similar effects.

A 500-mA current is to be applied to the solenoid214in the post operation to improve the stability of the position of the reference plate221. However, the most suitable current value to be applied to the solenoid214depends on individual differences of the solenoid214and the shutter spring217. Accordingly, for example, there may be provided a mode for determining the current value to be applied to the solenoid214in the post operation. For example, the CPU109needs to perform steps S703to S712inFIG.15several times while varying the applied current and then determine the most suitable current value based on the result of the measurement of the reference plate221by the pattern detection sensor7.

Although, in the above descriptions, the CPU109controls the value of the current to be applied to the solenoid214to drive the protection shutter211, the value of the applied voltage may be controlled. In this configuration, the CPU109may control the voltage to be applied to the solenoid214so that the applied voltage in the post operation becomes smaller than that at the time of detection pattern measurement.

The present disclosure makes it possible to suitably adjust the light amount of the measuring unit.

OTHER EMBODIMENTS

This application claims the benefit of Japanese Patent Application No. 2022-178639, filed Nov. 8, 2022, which is hereby incorporated by reference herein in its entirety.