JP2023085128A - Image formation device - Google Patents

Abstract

To suppress erroneous detection of an opening/closing state of a shutter regardless of a degree of durability of an intermediate transfer belt 109 in a configuration having the shutter 410 so that a toner concentration sensor 113 is not contaminated.SOLUTION: Presence/absence of abnormality in opening/closing operation of a shutter is determined based on an output of each sensor in a state where a shutter 410 is made to be a closed state and an open state while an intermediate transfer belt 109 is separated from a photosensitive drum 103 and an output of each sensor in a state where a shutter 410 is made to be a closed state and in an open state while the intermediate transfer belt 109 is in contact with the photosensitive drum 103.SELECTED DRAWING: Figure 9

Description

The present invention relates to an image forming apparatus having a shutter member provided facing a sensor for reading a toner image formed on an image carrier.

2. Description of the Related Art In recent years, electrophotographic image forming apparatuses such as color copiers and color printers capable of forming multicolor images have been developed. For example, an image forming apparatus forms a toner image for each color on a latent image carrier such as a photosensitive drum for each color, and transfers the toner image for each color to an intermediate transfer belt, which is an intermediate transfer member. Forms a multicolor image. The image forming apparatus then transfers the multicolor image formed on the intermediate transfer belt to a recording paper, which is a transfer paper, and fixes the multicolor image on the recording paper.

In this intermediate transfer type color image forming apparatus, automatic registration adjustment is performed in order to prevent color misregistration in the multicolor image formed on the intermediate transfer belt. In this automatic registration adjustment, the amount of misalignment between each color of the image transferred from the photosensitive drum for each color is measured. In order to measure the amount of this color misregistration, a pattern image for color misregistration measurement is formed on the intermediate transfer belt, and the pattern image is read using a sensor. A reflective optical sensor is used as the sensor.

Since toner scatters inside the machine during image formation, it is common to provide a shutter to prevent the toner from adhering to the detection surface of the optical sensor. When the optical sensor does not read the pattern image, the shutter is closed to prevent dirt from adhering to the detection surface of the optical sensor.

In order to detect whether or not the shutter is operating normally, a sensor reads reflected light from the intermediate transfer belt on which no toner is formed, and based on the reading result, determines whether the shutter is open or closed. (See Patent Document 1).

Japanese Patent Application Laid-Open No. 2001-100597

However, as the image forming apparatus is used for a long period of time, the surface of the intermediate transfer belt deteriorates due to durability, and the amount of reflected light from the intermediate transfer belt decreases as the durability progresses. As a result, even when the shutter is open, the amount of reflected light from the intermediate transfer belt may fall below the shutter open/close detection threshold, and the shutter may be erroneously detected as closed.

An object of the present invention is to suppress erroneous detection of the shutter open/closed state.

In order to solve the above problems, the image forming apparatus of the present invention includes:
an image forming means for forming a toner image on a photoreceptor;
an intermediate transfer member to which the toner image formed on the photoreceptor is transferred;
a contact/separation means for contacting and separating the intermediate transfer member from/to the photoreceptor;
a detecting means for irradiating the intermediate transfer body with light and detecting the reflected light;
Provided between the detection means and the intermediate transfer body, and can be opened and closed, in an open state the light from the detection means is irradiated onto the intermediate transfer body, and in a closed state the light from the detection means is transmitted to the intermediate transfer body. a shutter member that blocks irradiation of the body;
an opening/closing driving means for opening and closing the shutter member;
The opening/closing driving means is controlled to open and close the shutter member, and light is emitted from the detection means to close the shutter member while the intermediate transfer member is separated from the photoreceptor. and a first detection result of the detection means when the intermediate transfer member is in contact with the photosensitive member and the shutter member is closed. a detection result of 2, a third detection result of the detection means in a state in which the intermediate transfer member is separated from the photoreceptor and the shutter member is in an open state, and the intermediate transfer; Abnormal opening/closing operation of the shutter member is determined based on a fourth detection result of the detecting means when the body is in contact with the photoreceptor and the shutter member is opened. a control means;
characterized by having

According to the present invention, erroneous detection of the shutter opening/closing state can be suppressed regardless of the surface state of the intermediate transfer belt.

Cross-sectional view of an image forming apparatus Schematic diagram showing an optical scanning device and a photosensitive drum Control block diagram of image forming apparatus Schematic diagram of toner concentration sensor A diagram showing the waveform of the toner density sensor and the method of calculating the amount of light when the amount of light is adjusted. Flowchart of conventional shutter open/close operation detection Diagram showing the regular reflection output of the toner density sensor when the shutter is opened and closed A diagram showing the regular reflection output of the toner density sensor due to the attachment and detachment of the primary transfer when the shutter is opened and closed. Flowchart of shutter opening/closing operation detection in the embodiment

FIG. 1 is a cross-sectional view showing the overall configuration of a color image forming apparatus 100 (hereinafter referred to as image forming apparatus 100) according to the present embodiment, and shows a schematic configuration of an electrophotographic full-color printer. The image forming apparatus 100 shown in FIG. 1 has a document reading section 101 and an image forming section 102 . A document image is read by a document reading unit 101, and an image forming unit 102 forms an image on a recording medium based on the read image data.

The image forming unit 102 includes four image forming stations 120Y, 120M, 120C, and 120Bk for forming toner images of yellow (Y), magenta (M), cyan (C), and black (Bk). It is The Y image forming station 120Y includes a photosensitive drum 103a as a photosensitive member, a charging device 104a for charging the photosensitive drum 103a, and a light beam for forming an electrostatic latent image on the charged photosensitive drum 103a. An emitting optical scanning device 105a is provided. The image forming station 120Y is further provided with a developing device 106a for developing the electrostatic latent image with toner, and a cleaning device 107a for cleaning residual toner on the photosensitive drum 103a. Other image forming stations 120M, 120C, and 120Bk also have the same configuration as the image forming station 120Y.

An image forming process performed at each image forming station will be described. Since the image forming processes performed in the respective image forming stations 120Y, 120M, 120C, and 120Bk are similar processes, the yellow image forming station 120Y will be described as an example.

The photosensitive drum 103a is charged by a charging device 104a. An electrostatic latent image is formed on the charged photosensitive drum 103a by a laser beam (light beam) emitted from an optical scanning device 105a having a laser light emitting portion as a light source. The formed electrostatic latent image is developed using yellow toner by the developing device 106a.

The yellow toner image developed on the photosensitive drum 103a is transferred to the intermediate transfer belt 109 (image carrier) by a transfer bias applied to the transfer blade 108a.

In the other image forming stations, toner images of respective colors are similarly formed and transferred onto the intermediate transfer belt 109 (on the image carrier). Four colors of the toner images transferred to the intermediate transfer belt 109 are collectively transferred onto the recording paper by the secondary transfer roller 110 in the secondary transfer portion T. FIG. After that, the recording paper carrying the toner image passes through the fixing device 111 and is subjected to fixing processing, and is discharged outside the device by the paper discharge roller 112 and the like. A cleaner blade 115 collects residual toner that has not been completely transferred at the secondary transfer portion T. As shown in FIG.

The black image forming station Bk is provided closer to the secondary transfer portion than the other chromatic image forming stations Y, M, and C in the rotation direction of the intermediate transfer belt 109 . By arranging them in this way, when forming a monochrome image, it is possible to reduce the time from when the user issues an image formation instruction to when the image is output.

A toner density sensor 113 is provided near the intermediate transfer belt 109 to detect a toner pattern for density deviation detection, which will be described later. The toner density sensor 113 is provided between the image forming station Bk for forming a black toner image and the secondary transfer roller 110 as shown in FIG. Further, when the toner image is transferred, the primary transfer roller 116 is raised toward the photosensitive drum 103 and the intermediate transfer belt 109 contacts the photosensitive drum 103 . At this time, the distance between the toner density sensor 113 and the intermediate transfer belt 109 is designed to be the focal length of the toner density sensor 113 . This state is referred to as a primary transfer adhesion state. Since the intermediate transfer belt 109 is designed not to contact the photosensitive drum 103 except during transfer, the distance between the toner density sensor 113 and the intermediate transfer belt 109 is at least the focal length. Let this state be When the distance between the intermediate transfer belt 109 and the toner density sensor 113 deviates from the focal length, the output fluctuates according to the deviated distance and the characteristics of the toner density sensor 113 . This characteristic is called distance characteristic.

FIG. 2 is a schematic view of the internal configuration of the optical scanning device 105a and a schematic view of the photosensitive drum 103a. Since the configurations of the optical scanning devices 105a to 105d are the same, the optical scanning device 105a will be described as an example. The optical scanning device 105 a includes a semiconductor laser 201 as a light source, a collimator lens 202 , an aperture stop 203 , a cylindrical lens 204 , a polygon mirror 205 , a polygon mirror driver 206 , a toric lens 207 and a diffraction optical element 208 .

A collimator lens 202 converts the light beam emitted from the semiconductor laser 201 into a parallel light beam. The aperture stop 203 restricts the luminous flux of the passing laser light. The cylindrical lens 204 has a predetermined refractive power only in the sub-scanning direction (photosensitive drum rotation direction), and directs the light beam that has passed through the aperture diaphragm 203 onto the reflecting surface of the polygon mirror 205 in the main scanning direction (photosensitive drum axial direction). is imaged as a long elliptical image. A polygon mirror 205, which is a rotating polygonal mirror, is rotated at a constant speed in the direction of arrow C in the drawing by a polygon mirror drive unit 206, and deflects and scans the laser beam imaged on the reflecting surface. The toric lens 207 is an optical element having an fθ characteristic and has different refractive indices in the main scanning direction and the sub-scanning direction. Both front and back lens surfaces in the main scanning direction of the toric lens 207 are aspherical. The diffractive optical element 208 is an optical element having an fθ characteristic and has different magnifications in the main scanning direction and the sub-scanning direction. A beam detector 209 (hereinafter referred to as a BD 209 ), which is a laser light detection means, is installed at a position corresponding to the outside of the image forming area of the photosensitive drum 103 a of the image forming apparatus 100 . A scanning timing signal (BD signal) is generated by detecting the laser light.

A spot of laser light emitted from the semiconductor laser 201 deflected by the rotationally driven polygon mirror 205 linearly moves (scans) on the photosensitive drum 103a in parallel with the axis of the photosensitive drum. The optical scanning device 105a in this embodiment uses a multi-beam laser that emits a plurality of beams as the semiconductor laser 201, and can form a plurality of line-shaped electrostatic latent images by one scanning. The photosensitive drum 103a is rotationally driven by the drum drive unit 211, and by this turning back the main scanning, image writing is performed in the sub-scanning direction (rotational direction of the photosensitive drum).

The diffractive optical element 208 is configured to be rotatable around an axis parallel to its optical axis. By rotating the diffractive optical element 208 around this axis, it is possible to correct the direction of the scanning line on the photosensitive drum 103a (the inclination of the scanning line with respect to the rotation axis of the photosensitive drum 103a). Moreover, the diffractive optical element 208 is configured to be rotatable around an axis parallel to the longitudinal direction of the diffractive optical element 208 . By rotating the diffractive optical element 208 about this axis, the curvature of the scanning line on the photosensitive drum 103a can be corrected. The diffractive optical element 208 is rotated by a diffractive optical element driving section 212 .

It is assumed that the semiconductor laser 201, the polygon mirror driving section 206, the drum driving section 211, and the diffraction optical element driving section 212 are controlled by a CPU, which will be described later.

After the surface of the photosensitive drum 103a is charged by the charging device 104a, the charged surface of the photosensitive drum 103a is exposed and scanned by laser light. The potential of the surface of the photosensitive drum 103a changes according to the intensity of the irradiated laser beam.

FIG. 3 is a control block diagram showing a configuration for executing shutter opening/closing operation detection control in the image forming apparatus of this embodiment. The CPU 301 executes shutter opening/closing operation detection control. A memory 302 stores a control program including processing for executing shutter opening/closing detection control. The shutter opening/closing mechanism 130 is a shutter opening/closing mechanism as opening/closing driving means for opening/closing the shutter 410 (to be described later). The contact/separation mechanism 140 is a contact/separation mechanism that causes the intermediate transfer belt 109 to contact and separate from the photosensitive member 103 .

Also, an analog signal output from the toner concentration sensor 113 is input to the CPU 301 . The toner concentration sensor 113 is arranged downstream of the photosensitive drum 103d in the movement direction of the intermediate transfer belt 109 as shown in FIG. 1, and includes a toner concentration sensor 113a and a toner concentration sensor 113b. The toner concentration sensor 113a is arranged on one end side of the intermediate transfer belt 109 in the direction orthogonal to the moving direction, and the toner concentration sensor 113b is arranged on the other end side. In order to adjust the toner concentration sensor 113, the CPU 301 adjusts the amount of emitted light from the optical sensor 113 based on the analog signal input from the toner concentration sensor 113 so that the output of the toner concentration sensor 113 becomes a predetermined value. . The CPU 301 also determines whether the shutter should be opened or closed based on the analog signal input from the optical sensor 113 .

Next, the configuration of the toner density sensor 113 related to the toner density measurement technique will be described. A toner density sensor 113 measures the density of the toner image formed on the intermediate transfer belt 109 . The structure of the toner density sensor 113 will be described with reference to FIG.

4A and 4B are cross-sectional views of the toner concentration sensor 113 viewed from the upstream side with respect to the moving direction of the intermediate transfer belt 109. FIG. 4A shows a state in which the intermediate transfer belt 109 is in contact with the photosensitive drum 103 (primary transfer state), and FIG. 4B shows a state in which the intermediate transfer belt 109 is separated from the photosensitive drum 103 ( (primary transcription de-state). A distance Y between the intermediate transfer belt 109 and the shutter 410 in the primary transfer off state is larger than a distance X between the intermediate transfer belt 109 and the shutter 410 in the primary transfer on state. The toner concentration sensor 113 includes a light emitting diode (hereinafter referred to as LED) 401 and a photodiode (hereinafter referred to as PD) 402 and PD 403 . The LED 401 is arranged so as to emit infrared light at an incident angle (angle with respect to an imaginary line perpendicular to the surface of the intermediate transfer belt 109) of about 15°. The PD 402 is arranged so as to receive the reflected light of the light emitted from the LED 401 onto the intermediate transfer belt 109 and the toner image 409 at the position of the specular reflection angle. The PD 403 is arranged so as to receive the reflected light of the light emitted from the LED 401 onto the intermediate transfer belt 109 and the toner image 409 and scattered light at the position of the irregular reflection angle.

A shutter 410 as a shutter member is arranged between the toner density sensor 113 and the intermediate transfer belt 109 and can be opened and closed. The shutter member 410 irradiates the intermediate transfer belt 109 with light from the LEDs 401 in the open state, and blocks the light from the LEDs 401 from reaching the intermediate transfer belt 109 in the closed state. When the reflected light from the intermediate transfer belt 109 and the toner image is received, the shutter 410 is moved to the position indicated by the solid line as shown in FIG. 4 and the shutter 410 is opened. Except when receiving reflected light from the intermediate transfer belt 109 and the toner image, the shutter 410 is moved to the position indicated by the dotted line in FIG. To prevent the lens 404 from becoming dirty.

The electric substrate 407 of the toner concentration sensor 113 is mounted with a light receiving circuit having a conversion function of converting a current flowing in accordance with the amount of light received by the PDs 401 and 402 into voltage. A lens 404 is an optical component molded from epoxy resin to create a path for light emitted from the LED 401 and light received by the PDs 402 and 403 . A shielding member 405 made of black resin is provided to prevent the light emitted by the LED 401 from directly entering the PDs 402 and 403 . The toner concentration sensor 113 configured as described above can measure both specularly reflected light and irregularly reflected light. A PD 402 that receives specularly reflected light and a PD 403 that receives irregularly reflected light measure reflected light from the intermediate transfer belt 109 and reflected light from the toner image 409 . When a toner image is formed on the intermediate transfer belt 109, the PD 402 that receives specularly reflected light reduces the amount of reflected light according to the toner density. On the other hand, a small amount of light is scattered from the intermediate transfer belt 109 and the black toner image formed on the intermediate transfer belt 109 and enters the PD 403 that receives irregularly reflected light. On the other hand, the scattered light from the yellow, magenta, and cyan toner images formed on the intermediate transfer belt 109 is received by the PD 402 more than the scattered light from the black toner image. As the area density of the color toner increases, the scattered light also increases, so the amount of light received by the PD 403 increases. An image for measurement is formed on the intermediate transfer belt 109, the density of the image for measurement is measured using the specularly reflected light and the irregularly reflected light, and the intensity of the laser beam of the optical scanning device 105a is changed based on the measured value. Performing density correction.

Next, sensor output fluctuation due to durability will be described. When the image forming apparatus is used for a long period of time from the initial state of use, the window surface of the toner concentration sensor 113 is stained with toner, paper dust, and the like. As a result, the output of the toner density sensor 113 decreases when detecting reflected light from the intermediate transfer belt 109, so there is a concern that the dynamic range in measuring the toner density will become smaller. Therefore, it is necessary to adjust the amount of light to return to the output before the endurance test. The light quantity adjustment control will be described below.

FIG. 5 is a diagram showing the output waveform of the toner density sensor 113 and the light amount calculation method when light amount adjustment is executed. The amount of light of the toner density sensor 113 is adjusted by changing the current applied to the LED 401 of the toner density sensor 113 in three steps when the reflected light from the intermediate transfer belt 109 is detected. FIG. 5(a) shows the output waveform of the toner concentration sensor 113 when light amount adjustment is executed.

The current is changed in three stages in the region indicated by the arrow in FIG. , a third current value larger than the second current value is set in the period from t3 to t4. P11 to P38 indicate sampling timings of the output of the density sensor 113. FIG.

FIG. 5(b) shows a method of calculating the target light amount. The toner density sensor 113 detects each output level at three levels of set current in FIG. , P38) are detected. The CPU 301 calculates average values (P1ave, P2ave, P3ave) from the values of each 8 points. FIG. 5(b) shows the result of calculating the output level at the current value changed in three steps. The CPU 301 determines the amount of light from the three average values so that the output level of the toner concentration sensor 113 becomes the target sensor output in FIG. 5(b). If the output level is the target value, the corresponding light amount should be set. Also, by performing linear interpolation based on a straight line determined from the three average values, the amount of light is determined so that the output level of the toner density sensor 113 becomes the target value. If the target output level is not reached even if the current value is the maximum value that can be set, the output gain of the toner concentration sensor 113 is switched, and the light amount is determined by performing the light amount adjustment control again. A well-known technique may be used for the method of switching the output gain.

By adjusting the light amount through the light amount adjustment control as described above, even if the surface (window surface) of the lens 404 of the toner concentration sensor 113 is stained with toner or the like, the dynamic range can be returned to the state before endurance.

However, if the shutter 410 does not open due to a failure of the opening/closing mechanism of the shutter 410 during light amount adjustment or density correction, the intermediate transfer belt 109 and the toner image are not irradiated with light. cannot be performed normally. As a result, density deviation occurs in the formed image. Further, if the shutter 410 continues to be open, the degree of dirt on the window surface of the toner density sensor 113 becomes too large, and there is a possibility that the light amount adjustment and the density correction control cannot be performed correctly. Therefore, it is important to half-open or close the shutter 410, and it is desirable to reduce the cost of the configuration for this purpose.

FIG. 6 shows a flowchart of known shutter opening/closing operation detection as a comparative example. First, the toner density sensor 113 is lit with a predetermined amount of light (S602). Next, the shutter 410 is closed, and the specular reflection output Vc from the toner density sensor 113 is stored (S604). In the shutter closed state, the toner density sensor 113 measures the density of the back side of the shutter 410 (the side opposite to the intermediate transfer belt 109 side). In this embodiment, the distance between the shutter 410 and the toner density sensor 113 is less than the focal length, so when the shutter is closed, the specular reflection output is small as indicated by the solid line in FIG. After that, when the shutter 410 is opened, the specular reflection output Vo of the toner density sensor 113 is stored (S605). In the shutter open state, the toner density sensor 113 measures the density of the intermediate transfer belt 109 . Since the surface of the intermediate transfer belt 109 used in the present embodiment is prone to specular reflection, when the shutter is open, specular reflection output is greater than when the shutter is closed, as indicated by the solid line in FIG. It is determined whether the stored specular reflection output Vc of the toner density sensor 113 when the shutter is closed is less than or equal to a predetermined value (S606). If it is equal to or greater than the predetermined value, it is determined that there is a shutter closing failure (S610). If the regular reflection output Vc when the shutter is closed is less than or equal to a predetermined value, it is determined whether or not the stored regular reflection output Vo when the shutter is open is greater than or equal to a predetermined value (S607). If the specular reflection output Vo when the shutter is open is equal to or less than a predetermined value, it is determined that there is a failure in the shutter opening operation (S609). If the specular reflection output Vo when the shutter is open is equal to or greater than a predetermined value, it is determined that the shutter opening/closing operation is normally performed (S608).

However, the surface of the intermediate transfer belt 109 becomes rougher due to friction with the cleaner blade 115 and adherence of paper dust as the durability of the intermediate transfer belt 109 progresses. FIG. 7 shows the output of the toner concentration sensor 113 due to the change in the surface property of the intermediate transfer belt 109 by a broken line. When the roughness of the surface of the intermediate transfer belt 109 increases due to durability, the specular reflection output of the toner concentration sensor 113 when the shutter is open becomes smaller than before the durability, as indicated by the dashed line in FIG. As a result, even if the shutter 410 is open, it may be erroneously detected that the shutter 410 is closed. Therefore, it is difficult to determine the open/closed state of the shutter 410 using the measurement result of the back side of the shutter 410 and the measurement result of the intermediate transfer belt 109 . Therefore, in the present embodiment, a mechanism for attaching and detaching the intermediate transfer belt 109 is used to detect the opening/closing operation of the shutter.

FIG. 8 shows specular reflection outputs of the toner concentration sensor 113 when the shutter is open and when the shutter is closed. FIG. 8A shows the specular reflection output of the toner density sensor 113 due to the attachment and detachment of the primary transfer when the shutter is closed. When the shutter 410 is closed, the toner density sensor 113 measures the density (reflected light) behind the shutter. Since the positional relationship between the shutter 410 and the toner density sensor 113 does not change even if the intermediate transfer belt 109 is attached or detached, the specular reflection output does not fluctuate between the primary transfer attached state and the primary transfer off state. Therefore, by detecting that the specular reflection output does not change when the intermediate transfer belt 109 is attached and detached, it is determined that the shutter is in the closed state.

FIG. 8B shows the specular reflection output of the toner concentration sensor 113 due to the attachment and detachment of the primary transfer when the shutter is open. When the shutter 410 is open, the toner density sensor 113 measures the density (reflected light) of the intermediate transfer belt 109 . When the intermediate transfer belt 109 is attached and detached, the positional relationship between the intermediate transfer belt 109 and the toner concentration sensor 113 changes, so the specular reflection output of the toner concentration sensor 113 fluctuates. The solid line indicates the specular reflection output in the initial state, and the dashed line indicates the specular reflection output after the endurance test. When the surface of the intermediate transfer belt 109 becomes rough due to durability, the specular reflection output decreases both when the primary transfer is attached and removed compared to before the durability. This is because the output fluctuation at the time of attachment and detachment of the primary transfer depends on the distance characteristic of the toner density sensor 113 . That is, by detecting a change in the specular reflection output when the intermediate transfer belt 109 is attached and detached, it is possible to determine whether the shutter is open regardless of the surface condition of the intermediate transfer belt 109 .

A shutter opening/closing operation detection sequence by the CPU 301 in this embodiment will be described with reference to FIG. This control is executed before executing the density correction process described above.

First, the CPU 301 puts the intermediate transfer belt 109 in the primary transfer disengaged state (S901). The CPU 301 turns on the light source of the toner concentration sensor 113 with a predetermined amount of light (S902), acquires the specular reflection output Vc1, which is the detection result of the toner concentration sensor 113 in the shutter closed state, and stores it in the memory 302 (S903). At this time, since the toner density sensor 113 measures the density behind the shutter 410, the specular reflection output is relatively small as described above. The CPU 301 turns on the toner concentration sensor 113 with the light amount determined by the light amount adjustment (S904). Note that the light amount adjustment is performed after the power of the apparatus is turned on or each time a predetermined number of sheets are printed. Then, the CPU 301 opens the shutter 410, acquires the specular reflection output Vo1 of the toner concentration sensor 113, and stores it in the memory 302 (S906). At this time, no toner image is formed on the area of the intermediate transfer belt 109 measured by the toner density detection sensor 113 . After that, the CPU 301 shifts the intermediate transfer belt 109 to the primary transfer contact state (S907), and lights the light emitting portion of the toner concentration sensor 113 with a predetermined amount of light (S908). The CPU 301 acquires the specular reflection output Vo2 of the toner concentration sensor 113 when the shutter 410 is open, and stores it in the memory 302 (S909). At this time, no toner image is formed on the area of the intermediate transfer belt 109 measured by the toner density detection sensor 113 . Next, the CPU 301 lights the toner density sensor 113 with the light amount after the light amount adjustment (S910). The CPU 301 closes the shutter 410, acquires the specular reflection output Vc2 of the toner concentration sensor 113, and stores it in the memory 302 (S912). Then, the CPU 301 determines whether there is an abnormality in the shutter opening/closing operation.

Specifically, the CPU 301 determines whether or not the ratio of Vc1 and Vc2 (Vc1/Vc2) is within a predetermined range (0.9 or more and 1.1 or less) (S913). If Vc1/Vc2 is not less than 0.9 and not less than 1.1, the sensor output fluctuates even though the shutter is closed, that is, the shutter 410 is open. The CPU 301 determines that the shutter 410 fails to close (S917). If Vc1/Vc2 is 0.9 or more and 1.1 or less, the CPU 301 determines whether Vo1/Vo2 is 0.9 or more and 1.1 or less (S914). When Vo1/Vo2 is 0.9 or more and 1.1 or less, the sensor output does not fluctuate even though the shutter is open, which means that the shutter 410 is closed. The CPU 301 determines that there is a failure in the shutter opening operation (S915). If Vo1/Vo2 is not less than 0.9 and not less than 1.1, the CPU 301 determines that the shutter opening/closing operation is normal (S916).

When a failure of the shutter opening/closing operation is detected, the CPU 301 sets a failure flag in the memory 302 or displays an alarm on a display unit (not shown) of the image forming apparatus 101 so that service parts can be replaced. In this case, image formation can be executed without density correction.

As described above, according to the present embodiment, by using the primary transfer attachment/detachment state of the intermediate transfer belt 109, the opening/closing operation of the shutter 410 can be checked with a low-cost configuration without separately providing a sensor for detecting opening/closing of the shutter. It can be performed. As a result, conventional erroneous detection of shutter opening/closing can be suppressed.

109 intermediate transfer belt 113 toner concentration sensor 120 opening/closing driving mechanism 130 contact/separation mechanism 301 CPU
302 memory 410 shutter

Claims (5)

an image forming means for forming a toner image on a photoreceptor;
an intermediate transfer member to which the toner image formed on the photoreceptor is transferred;
a contact/separation means for contacting and separating the intermediate transfer member from/to the photoreceptor;
a detecting means for irradiating the intermediate transfer body with light and detecting the reflected light;
Provided between the detection means and the intermediate transfer body, and can be opened and closed, in an open state the light from the detection means is irradiated onto the intermediate transfer body, and in a closed state the light from the detection means is transmitted to the intermediate transfer body. a shutter member that blocks irradiation of the body;
an opening/closing driving means for opening and closing the shutter member;
The opening/closing driving means is controlled to open and close the shutter member, and light is emitted from the detection means to close the shutter member while the intermediate transfer member is separated from the photoreceptor. and a first detection result of the detection means when the intermediate transfer member is in contact with the photosensitive member and the shutter member is closed. a detection result of 2, a third detection result of the detection means in a state in which the intermediate transfer member is separated from the photoreceptor and the shutter member is in an open state, and the intermediate transfer; Abnormal opening/closing operation of the shutter member is determined based on a fourth detection result of the detecting means when the body is in contact with the photoreceptor and the shutter member is opened. a control means;
An image forming apparatus comprising: 3. The control means determines that the shutter member fails to close when the ratio between the first detection result and the second detection result is not within a predetermined range. 1. The image forming apparatus according to 1. 3. The control means determines that the shutter member fails to open when the ratio between the third detection result and the fourth detection result is not within a predetermined range. 1. The image forming apparatus according to 1. The control means causes the image forming means to form an image for measurement on the intermediate transfer member, causes the detection means to detect reflected light from the image for measurement, and controls the image forming means based on the detection result. 4. The image forming apparatus according to any one of claims 1 to 3, wherein the image forming apparatus executes a density correction process to correct the density, and determines whether the shutter member is abnormal before executing the density correction process. . 5. The image forming apparatus according to claim 1, wherein the controller determines whether the opening and closing operation of the shutter member is abnormal when no toner image is formed on the intermediate transfer member. Device.

Images