JP2004341142A - Image forming apparatus and sensor soil determination method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology that grasps soil of a sensor, in an image forming apparatus in which the sensor and a cleaning member are disposed close to each other. <P>SOLUTION: If the output voltage Vp of a sensor that receives reflected light from the surface of an intermediate transfer belt is within a predetermined range #1 when a light quantity control signal S1c is set to a predetermined value S1c(2), it is determined that the sensor is normal. If the output voltage Vp of the sensor is within a range #2 on the side where the light quantity is smaller than in the range #1, it is determined that the sensor is soiled with toner. Furthermore, if the output voltage Vp of the sensor is neither in the range #1 nor in the range #2, it is determined that the sensor is in failure. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus including a sensor that irradiates light to an image carrier, receives light emitted from the image carrier, and outputs a signal corresponding to the amount of received light.
[0002]
[Prior art]
2. Description of the Related Art An electrophotographic image forming apparatus such as a printer, a copying machine, and a facsimile machine includes a density sensor for detecting an image density of a toner image to be formed. As the density sensor, an optical method that irradiates light toward the surface of an image carrier that carries a toner image and detects light emitted from the surface is generally used. Then, various image forming conditions are adjusted based on the detection result of the image density detected by the density sensor, so that a predetermined image density can be stably obtained.
[0003]
The density sensor is disposed to face the image carrier. Regarding the mounting position, the applicant of the present application has proposed an image forming apparatus in which the density sensor is opposed to a region where the belt-shaped image carrier is wound around the roller. (See Patent Document 1). In the image forming apparatus configured as described above, since the image carrier at the position facing the density sensor is less likely to fluctuate, fluctuations in the distance between the density sensor and the image carrier are effectively suppressed, and the image density can be precisely controlled. Can be measured.
[0004]
Further, this type of image forming apparatus is provided with a cleaning member for removing toner remaining on the surface of the image carrier. In order to obtain a good toner removing effect, it is preferable that the cleaning member is also configured to abut on the surface of the image carrier in a region where the image carrier is wound around a roller with less flutter.
[0005]
[Patent Document 1]
JP-A-2002-214855 (FIG. 2)
[0006]
[Problems to be solved by the invention]
In recent years, demands for downsizing and cost reduction of image forming apparatuses have been increasing, and accordingly, there has been a demand for downsizing of parts constituting the apparatus and reduction of the number of parts. As a result, the degree of freedom of the mounting position of the above-described concentration sensor and the cleaning member is also restricted, and depending on the case, both may be forced to be arranged close to each other.
[0007]
As described above, when the sensor is disposed close to the cleaning member, the toner that has been scraped off from the surface of the image carrier and scattered around tends to adhere to the sensor. If the toner adheres to the sensor and the sensor becomes dirty, the light emitted from the sensor and the light incident on the sensor are blocked or scattered by the adhered toner, so that the amount of light received by the sensor does not accurately reflect the image density. I will. As a result, appropriate adjustment of image forming conditions cannot be performed, and the operation of the apparatus becomes unstable, and a problem such that a predetermined image quality cannot be obtained occurs.
[0008]
SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide a technique for grasping contamination of a sensor in an image forming apparatus in which a sensor and a cleaning member are arranged close to each other.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to the present invention is configured such that a belt-shaped image carrier wound around a roller and the image carrier out of a surface area of the image carrier are wound around the roller. Cleaning means for removing toner attached to the surface of the image carrier in contact with the wrapping area; and irradiating light to the surface of the image carrier, and irradiating light to the surface of the image carrier. A sensor that receives light emitted from the body and outputs a signal corresponding to the amount of received light; and a control unit that determines a degree of contamination of the sensor based on an output signal from the sensor. And
[0010]
According to the invention having such a configuration, the contamination of the sensor that is disposed near the cleaning unit and is likely to cause contamination due to toner adhesion is determined based on the output signal of the sensor itself. When the sensor becomes contaminated with toner, at least one of the light emitted from the sensor and the light emitted from the image carrier and incident on the sensor is blocked or scattered, so that the amount of light received by the sensor changes. Output signal also changes according to the degree of dirt. Therefore, by determining the degree of dirt on the sensor based on the output signal, it is possible to grasp the dirt on the sensor.
[0011]
For example, the sensor emits light toward the image carrier with a light amount corresponding to a light amount control signal given from the control unit, and receives light emitted from the image carrier. And a light receiving unit that outputs a signal corresponding to the amount of received light as the output signal, and the control unit is configured to provide the light emitting unit with the light amount control signal set to a predetermined set value. When the level of the output signal output from the light receiving unit is within a predetermined first range determined according to the set value, it is determined that the sensor is normal, while the light reception amount is lower than the first range. The sensor may be configured to determine that the sensor is dirty when the sensor is located in a second range adjacent to the first range.
[0012]
In the invention configured as described above, if the sensor is not contaminated, the level of the output signal should be within a predetermined range corresponding to the set value of the light intensity control signal. Therefore, this range is set as the first range, and when the level of the output signal is in the first range, it can be determined that the sensor is normal. On the other hand, if the sensor becomes dirty, the amount of received light decreases, so that the output signal of the sensor shifts to a lower amount of received light. Therefore, when the output signal of the sensor is in the second range adjacent to the first range on the light receiving amount side lower than the first range, it can be determined that the sensor is dirty. By doing so, it is possible to determine a normal state where the sensor is not dirty and a state where the sensor is dirty.
[0013]
Further, for example, the control unit may be configured to determine that the sensor has failed when the level of the output signal is not in any of the first range and the second range. . That is, the reason why the output signal of the sensor deviates from the predetermined range may be caused by a failure of the sensor itself in addition to the contamination of the sensor. If the sensor fails in this way, the output signal is considered to greatly deviate from the expected range. Therefore, when the level is not in any of the first and second ranges, the sensor fails and Likely to be.
[0014]
Further, the control unit previously acquires an output signal from the light receiving unit in a state where the light is not irradiated from the light projecting unit to the image carrier as a dark output signal, and the level of the dark output signal, or A level obtained by adding a predetermined offset value to the dark output signal may be set as a threshold on the low light receiving amount side in the level of the output signal in the second range. Even if the sensor is dirty, the output signal should not be lower than the level of the dark output signal as long as at least a part of the irradiation light from the light projecting unit is incident on the light receiving unit. Therefore, this dark output signal can be used as an index of the threshold value on the low light amount side in the range of the sensor output signal in which the sensor is determined to be dirty, that is, the second range.
[0015]
Further, if necessary, a notifying means for notifying a result of the determination by the control means in a mode according to the result of the determination may be further provided. By doing so, it is possible to notify the user of the state of contamination of the sensor and to urge the user to take appropriate measures according to the state.
[0016]
In addition, a method for determining sensor contamination according to the present invention is directed to a sensor for irradiating light toward the surface of an image carrier, receiving light emitted from the image carrier, and outputting a signal corresponding to the amount of received light. In order to achieve the above object, a sensor contamination determination method for determining contamination is characterized in that the degree of contamination of the sensor is determined based on an output signal from the sensor.
[0017]
In the invention thus configured, similarly to the above-described apparatus, when the sensor is contaminated with toner, at least one of light emitted from the sensor and light emitted from the image carrier and incident on the sensor. Is blocked or scattered, the amount of light received by the sensor changes, and the output signal from the sensor also changes according to the degree of dirt. Therefore, by determining the degree of dirt on the sensor based on the output signal, it is possible to grasp the dirt on the sensor.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
(1st Embodiment)
FIG. 1 is a diagram showing a first embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This apparatus 1 forms a full-color image by superimposing toners (developers) of four colors of yellow (Y), cyan (C), magenta (M), and black (K), or forms a black (K) toner. This is an image forming apparatus that forms a monochrome image using only the image forming apparatus. In the image forming apparatus 1, when an image signal is provided from an external device such as a host computer to the main controller 11, the engine controller 10 controls each unit of the engine unit EG in accordance with a command from the main controller 11 to generate a predetermined image. A forming operation is performed to form an image corresponding to the image signal on the sheet S.
[0019]
In the engine section EG, the photoreceptor 22 is provided rotatably in the direction of arrow D1 in FIG. A charging unit 23, a rotary developing unit 4, and a cleaning unit 25 are arranged around the photoconductor 22 along the rotation direction D1. The charging unit 23 is applied with a predetermined charging bias, and uniformly charges the outer peripheral surface of the photoconductor 22 to a predetermined surface potential. The cleaning unit 25 removes toner remaining on the surface of the photoconductor 22 after the primary transfer, and collects the toner in a waste toner tank provided inside. The photoconductor 22, the charging unit 23, and the cleaning unit 25 integrally constitute a photoconductor cartridge 2, and the photoconductor cartridge 2 is integrally detachable from the main body of the apparatus 1.
[0020]
Then, the light beam L is emitted from the exposure unit 6 toward the outer peripheral surface of the photoconductor 22 charged by the charging unit 23. The exposure unit 6 forms an electrostatic latent image corresponding to the image signal by exposing the light beam L onto the photoreceptor 22 in accordance with an image signal provided from an external device.
[0021]
The electrostatic latent image thus formed is developed by the developing unit 4 with toner. That is, in this embodiment, the developing unit 4 is configured as a support frame 40 provided rotatably about a rotation axis orthogonal to the paper surface of FIG. A yellow developing device 4Y containing a toner, a cyan developing device 4C, a magenta developing device 4M, and a black developing device 4K are provided. The developing unit 4 is controlled by the engine controller 10. Then, based on a control command from the engine controller 10, the developing unit 4 is driven to rotate, and the developing units 4Y, 4C, 4M, and 4K are selectively brought into contact with the photoconductor 22 or a predetermined gap is formed. When the developing device is positioned at a predetermined developing position facing away from the developing device, toner is applied to the surface of the photoconductor 22 from a developing roller provided in the developing device and carrying a toner of a selected color. As a result, the electrostatic latent image on the photoconductor 22 is visualized with the selected toner color.
[0022]
The toner image developed by the developing unit 4 as described above is primarily transferred onto the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer area TR1. The transfer unit 7 rotates the intermediate transfer belt 71 by a predetermined rotation by rotating the intermediate transfer belt 71, which corresponds to the “image carrier” of the present invention, and is wound around a plurality of rollers 72 to 75. And a drive unit (not shown) for rotating in the direction D2. When the color image is to be transferred to the sheet S, the toner images of each color formed on the photoreceptor 22 are superimposed on the intermediate transfer belt 71 to form a color image, and are taken out of the cassette 8 one by one. The color image is secondarily transferred onto the sheet S conveyed along the conveyance path F to the secondary transfer area TR2.
[0023]
At this time, in order to correctly transfer the image on the intermediate transfer belt 71 to a predetermined position on the sheet S, the timing for feeding the sheet S to the secondary transfer area TR2 is controlled. Specifically, a gate roller 81 is provided on the transport path F in front of the secondary transfer region TR2, and the sheet is rotated by the gate roller 81 in accordance with the timing of the orbital movement of the intermediate transfer belt 71. S is sent to the secondary transfer area TR2 at a predetermined timing.
[0024]
Further, the sheet S on which the color image has been formed is conveyed to the discharge tray 89 provided on the upper surface of the apparatus main body via the fixing unit 9, the pre-discharge roller 82 and the discharge roller 83. In the case where images are formed on both sides of the sheet S, when the rear end of the sheet S on which the image is formed on one side as described above is conveyed to the reverse position PR behind the pre-discharge roller 82. The rotation direction of the discharge roller 83 is reversed, whereby the sheet S is transported along the reverse transport path FR in the direction of arrow D3. Then, the sheet is again put on the transport path F before the gate roller 81. At this time, in the secondary transfer area TR2, the surface of the sheet S on which the image is transferred by contact with the intermediate transfer belt 71 is transferred first. It is the opposite side of the surface. Thus, an image can be formed on both sides of the sheet S.
[0025]
In addition, the device 1 includes a display unit 12 controlled by the CPU 111 of the main controller 11, as shown in FIG. The display unit 12 is configured by, for example, a liquid crystal display, and in accordance with a control command from the CPU 111, provides an operation guide to the user, a progress status of an image forming operation, and further indicates occurrence of an abnormality in the apparatus and replacement time of any unit. A predetermined message for notification is displayed.
[0026]
In FIG. 2, reference numeral 113 denotes an image memory provided in the main controller 11 for storing an image provided from an external device such as a host computer via the interface 112. Reference numeral 106 denotes a ROM for storing an operation program executed by the CPU 101 and control data for controlling the engine unit EG, and reference numeral 107 denotes a RAM for temporarily storing the operation results and other data in the CPU 101. is there.
[0027]
A cleaner 76 is arranged near the roller 75. The cleaner 76 can be moved toward and away from the roller 75 by an electromagnetic clutch (not shown). Then, while moving to the roller 75 side, the blade of the cleaner 76 contacts the surface of the intermediate transfer belt 71 wrapped around the roller 75, and the toner remaining on the outer peripheral surface of the intermediate transfer belt 71 after the secondary transfer. Is removed. The cleaner 76 functions as the "cleaning means" of the present invention. As described above, by bringing the cleaner 76 into contact with the area around the roller 75 in the surface area of the intermediate transfer belt 71, the cleaner 76 is not affected by the fluttering caused by the rotation of the belt 71, and thus has a constant effect. With this pressure, the cleaner 76 can be brought into contact with the intermediate transfer belt 71, so that an excellent toner removing effect can be obtained.
[0028]
Further, a density sensor 60 is disposed near the roller 75. The density sensor 60 is provided to face the surface of the intermediate transfer belt 71, and measures the optical density of a toner image formed on the outer peripheral surface of the intermediate transfer belt 71 as necessary. Based on the measurement results, the apparatus 1 adjusts operating conditions of each section of the apparatus that affect image quality, for example, development bias applied to each developing unit, intensity of the exposure beam L, and the like.
[0029]
If the distance between the density sensor 60 and the intermediate transfer belt 71 fluctuates, the result of the density measurement is affected. Therefore, it is desirable that the distance between the two is constant. For this purpose, it is desirable to dispose the density sensor 60 so as to face a portion of the surface area of the intermediate transfer belt 71 that is wound around any of the rollers 72 to 75. However, generally, it is difficult to secure a sufficient arrangement space in the vicinity of the primary transfer region TR1 and the secondary transfer region TR2, and as in this embodiment, the position of the density sensor 60 is substantially the position of the cleaner 76. In many cases, it is limited to the vicinity.
[0030]
FIG. 3 is a diagram showing a configuration of the density sensor. The density sensor 60 has a light emitting element 601 such as an LED that irradiates light to a winding area 71 a wound around the roller 75 in the surface area of the intermediate transfer belt 71. The density sensor 60 is provided with a polarizing beam splitter 603 to adjust the irradiation light amount of the irradiation light in accordance with a light amount control signal Slc provided from the CPU 101 via a light amount control signal conversion unit 680 as described later. A light quantity monitoring light receiving unit 604 and an irradiation light quantity adjustment unit 605 are provided. The light amount control signal converter 680 outputs a light amount control signal Slc based on two types of 8-bit digital signals DA1 and DA2 output from the CPU 101 to control the irradiation light amount. The configuration of the light amount control signal converter 680 will be described later in detail.
[0031]
The polarizing beam splitter 603 is disposed between the light emitting element 601 and the intermediate transfer belt 71 as shown in FIG. It is split into p-polarized light having a polarization direction parallel to the plane and s-polarized light having a perpendicular polarization direction. Then, while the p-polarized light is incident on the intermediate transfer belt 71 as it is, the s-polarized light is extracted from the polarization beam splitter 603 and then is incident on the light receiving unit 604 for monitoring the irradiation light amount, and the light receiving element 642 of the light receiving unit 604 , A signal proportional to the irradiation light amount is output to the irradiation light amount adjustment unit 605.
[0032]
The irradiation light amount adjustment unit 605 feedback-controls the light emitting element 601 based on the signal from the light receiving unit 604 and the light amount control signal Slc from the light amount control signal conversion unit 680 to irradiate the intermediate transfer belt 71 from the light emitting element 601. Is adjusted to a value corresponding to the light amount control signal Slc. As described above, in this embodiment, the irradiation light amount can be appropriately changed and adjusted over a wide range by the output signal from the CPU 101.
[0033]
In this embodiment, the input offset voltage 641 is applied to the output side of the light receiving element 642 provided in the irradiation light quantity monitoring light receiving unit 604, and the light emitting element is controlled as long as the light quantity control signal Slc does not exceed a certain signal level. 601 is configured to be maintained in a light-off state. The specific electrical configuration is as shown in FIG.
[0034]
FIG. 4 is a diagram showing an electrical configuration of the light receiving unit 604 employed in the density sensor 60 of FIG. In the light receiving unit 604, the anode terminal of the light receiving element PS such as a photodiode is connected to the non-inverting input terminal of the operational amplifier OP constituting the current-voltage (I / V) conversion circuit, and is grounded via the offset voltage 641. Connected to potential. In addition, the cathode terminal of the light receiving element PS is connected to the inverting input terminal of the operational amplifier OP and is connected to the output terminal of the operational amplifier OP via the resistor R. Therefore, when light is incident on the light receiving element PS and the photocurrent i flows, the output voltage VO from the output terminal of the operational amplifier OP becomes
VO = iR + Voff (Equation 1)
(However, Voff is an offset voltage value.)
And a signal corresponding to the amount of reflected light is output from the light receiving unit 604. The reason for this configuration will be described below.
[0035]
FIG. 5 is a diagram showing light quantity control characteristics in the density sensor of FIG. When the input offset voltage 641 is not applied, the light intensity characteristic as shown by the broken line in FIG. 5 is exhibited. That is, when the light quantity control signal Slc (0) is supplied from the CPU 101 to the irradiation light quantity adjustment unit 605, the light emitting element 601 is turned off, and when the signal level of the light quantity control signal Slc is increased, the light emitting element 601 is turned on and the intermediate transfer belt 601 is turned on. The amount of light irradiated on 71 also increases almost in proportion to the signal level. However, the light amount characteristics may be shifted in parallel as indicated by a one-dot chain line or a two-dot chain line shown in FIG. 5 depending on the influence of the ambient temperature, the configuration of the irradiation light amount adjustment unit 605, and the like. In this case, the light-emitting element 601 may be turned on even though a light-off instruction, that is, a light-quantity control signal Slc (0) is given from the CPU 101 via the light-quantity control signal converter 680.
[0036]
On the other hand, as in the present embodiment, when the input offset voltage 641 is applied and shifted in advance to the right hand side in the figure to provide a dead zone (signal levels Slc (0) to Slc (1)) (FIG. (Solid line), the light-emitting element 601 can be reliably turned off by giving a light-off instruction from the CPU 101, that is, a light amount control signal Slc (0), and malfunction of the device can be prevented beforehand.
[0037]
On the other hand, when the light amount control signal Slc (2) exceeding the signal level Slc (1) is given to the irradiation light amount adjustment unit 605, the light emitting element 601 is turned on, and the intermediate transfer belt 71 is irradiated with p-polarized light as irradiation light. Then, the p-polarized light is reflected by the intermediate transfer belt 71, the amount of p-polarized light and the amount of s-polarized light among the light components of the reflected light are detected by the reflected light amount detection unit 607, and a signal corresponding to each light amount is sent to the CPU 101. Is output.
[0038]
As shown in FIG. 2, the reflected light amount detection unit 607 receives a polarized light beam splitter 671 disposed on the optical path of the reflected light, and p-polarized light passing through the polarized light beam splitter 671, and responds to the light amount of the p-polarized light. And a light receiving unit 670s that receives the s-polarized light split by the polarization beam splitter 671 and outputs a signal corresponding to the amount of the s-polarized light. In the light receiving unit 670p, the light receiving element 672p receives the p-polarized light from the polarizing beam splitter 671, amplifies the output from the light receiving element 672p by the amplifier circuit 673p, and then converts the amplified signal to a signal corresponding to the amount of p-polarized light. Is output from the light receiving unit 670p. The light receiving unit 670s has a light receiving element 672s and an amplifier circuit 673s, like the light receiving unit 670p. For this reason, the light amounts of two component lights (p-polarized light and s-polarized light) different from each other among the light components of the reflected light can be obtained independently.
[0039]
In this embodiment, the output offset voltages 674p and 674s are applied to the output sides of the light receiving elements 672p and 672s, respectively, and the output voltages Vp and Vs of the signals supplied to the CPU 101 from the amplifier circuits 673p and 673s are shown in FIG. It is offset to the plus side as shown.
[0040]
FIG. 6 is a graph showing how the output voltage changes with respect to the amount of reflected light in the density sensor of FIG. The specific electrical configuration of each of the light receiving units 670p and 670s is the same as that of the light receiving unit 604, and a description thereof is omitted here. Also in the light receiving units 670p and 670s configured as described above, similarly to the light receiving unit 604, even when the amount of reflected light is zero, each output voltage Vp and Vs has a value of zero or more, and The output voltages Vp and Vs also increase in proportion to the increase in the amount of light. By applying the output offset voltages 674p and 674s in this manner, the influence of the dead zone in FIG. 5 can be reliably eliminated, and an output voltage corresponding to the amount of reflected light can be output.
[0041]
FIG. 7 is a diagram showing a light quantity control signal converter in this embodiment. The light amount control signal converter 680 supplies a light amount control signal Slc having a voltage value corresponding to two kinds of digital signals DA1 and DA2 output from the CPU 101 for light amount control to the irradiation light amount adjustment unit 605 of the density sensor 60. Is what you do. The light amount control signal converter 680 is provided with two D / A (digital / analog) converters 681 and 682 for converting the two digital signals DA1 and DA2 from the CPU 101 into analog signal voltages VDA1 and VDA2, respectively. . Then, these analog signals VDA1 and VDA2 are input to the arithmetic unit 690 via the buffers 683 and 684, respectively.
[0042]
In this embodiment, the D / A converters 681 and 682 both have an 8-bit resolution and operate on a single + 5V power supply. That is, these output voltages VDA1 and VDA2 take 256 discrete values from 0V to + 5V in accordance with the value (0 to 255) of the 8-bit digital signal DA1 or DA2 from the CPU 101. For example, when the digital signal DA1 from the CPU 101 is 0, the output voltage VDA1 of the D / A converter 681 becomes 0V. Then, each time the value of the digital signal DA1 increases by 1, the output voltage VDA1 increases by a minimum voltage step ΔVDA = (5/255) V. When the digital signal DA1 is 255, the output voltage VDA1 of the D / A converter 681 increases. Becomes + 5V. The same applies to the output voltage VDA2 of the D / A converter 682. As described above, the output voltage VDA1 of the D / A converter 681 and the output voltage VDA2 of the D / A converter 681 can each take 256 discrete values corresponding to an 8-bit digital signal.
[0043]
Here, in order to finely control the amount of light emitted by the light emitting element 601, it is desirable that the light amount control signal Slc can be set in multiple steps in steps as small as possible. If the data bit length of the digital signals DA1 and DA2 is increased, finer settings can be made, but this is not practical in terms of device cost. That is, it is necessary to use D / A converters 681 and 682 having a larger number of input bits and higher resolution, but such devices are expensive. In particular, for a CPU, it is necessary to use a product having a data bit length of 16 bits in order to handle data exceeding 8 bits. Such a product is very expensive compared to a product having a data bit length of 8 bits. turn into.
[0044]
Therefore, in this embodiment, the arithmetic unit 690 performs a predetermined operation on the output voltages of these two D / A converters 681 and 682, and the result of the operation is used as the light amount control signal Slc, thereby obtaining the data bit length. Is limited to 8 bits so that the light amount can be controlled with high resolution while suppressing the apparatus cost.
[0045]
The operation unit 690 is a subtraction circuit including four resistors 691 to 694 and an operational amplifier 695. Of the four resistors 691 to 694, two resistors 691 and 694 have the same resistance value R1, and the other two resistors 692 and 693 have the same resistance value R2 (where R2> R1). have. In such a configuration, the output voltage Vout output from the arithmetic unit 690 is expressed by the following equation:
Vout = VDA1− (R1 / R2) VDA2 (Expression 2)
Is represented by This output voltage Vout is input to the irradiation light amount adjustment unit 605 of the density sensor 60 as the light amount control signal Slc.
[0046]
By doing so, it is possible to set the light quantity control signal Slc in the voltage range of 0 to 5 V and in the minimum voltage step (R1 / R2) ΔVDA. Here, since R1 <R2, the light amount control signal Slc can be set more finely than in the case where control is performed using an 8-bit digital signal and one D / A converter. It becomes. More specifically, the resolution of the light quantity control signal Slc can be substantially improved (R2 / R1) times.
[0047]
When the set value of the light amount control signal Slc is set to a value exceeding the above-described signal level Slc (1) by the combination of the two 8-bit digital signals (DA1, DA2), the light emitting element is driven by the light amount corresponding to the set value. 601 emits light, and a part of the light is emitted toward the surface of the intermediate transfer belt 71 as described above. Then, the light reflected on the surface of the intermediate transfer belt 71 is received by the light receiving units 670p and 670s.
[0048]
When detecting the amount of light reflected from the surface of the intermediate transfer belt 71 or the toner image formed on the surface of the intermediate transfer belt 71 using the density sensor 60 configured as described above, sampling is performed at a plurality of locations to improve measurement accuracy. It is preferable to statistically process the sampled data, for example, determine an average value and use the averaged value for the subsequent processing.
[0049]
Here, as described above, the density sensor 60 is disposed close to the cleaner 76. In addition to the fact that the residual toner is scraped off from the surface of the intermediate transfer belt 71 by the cleaner 76 and the cleaner 76 performs the separating and contacting operation with respect to the intermediate transfer belt 71, the toner is easily scattered in the vicinity of the cleaner 76. . Due to this, contamination of the density sensor 60 due to toner adhesion is likely to occur.
[0050]
FIG. 8 is a partial sectional view of the density sensor 60. As shown in FIG. 8, the main part of the concentration sensor 60 is housed inside the housing 60. Further, a transparent sheet 600a made of, for example, polycarbonate is attached to the main surface of the housing 600 facing the intermediate transfer belt surface 71a. The transparent sheet 600a allows light emitted from the light emitting elements 601 toward the intermediate transfer belt surface 71a and light reflected from the belt surface 71a to pass therethrough, while preventing dust and scattered toner from entering the inside of the density sensor 60. Is preventing. As described above, the toner T scattered from the intermediate transfer belt surface 71a easily adheres to the surface of the transparent sheet 600a facing the intermediate transfer belt surface 71a.
[0051]
When the toner T adheres to the surface of the transparent sheet 600a as described above, light is blocked or scattered. For example, as shown in FIG. 8, a predetermined amount of light L1 emitted from the light emitting element 601 toward the intermediate transfer belt 71 is blocked and scattered by the toner T, and as a result, the amount of light L2 reaching the intermediate transfer belt surface 71a Becomes smaller than the predetermined light amount. Similarly, the amount of light L4 transmitted through the transparent sheet 600a and entering the density sensor 60 from the intermediate transfer belt surface 71a is smaller than the amount of light L3 emitted from the intermediate transfer belt surface 71a. Such a phenomenon causes an error in the density detection result.
[0052]
FIG. 9 is a diagram showing the relationship between the light quantity control signal and the sensor output voltage. Here, the output voltage Vp of the light receiving unit 670p corresponding to the p-polarized component will be described as a representative, but the same discussion holds for the output voltage Vs corresponding to the s-polarized component. However, since the intensity of the s-polarized light component is lower than that of the p-polarized light component, and the S / N ratio of the measurement is easily reduced, the processing is performed based on the p-polarized light component in this embodiment.
[0053]
If the density sensor 60 is not stained by the toner T, the change of the sensor output voltage Vp with respect to the light quantity control signal Slc is as shown by the solid line in FIG. That is, when the level of the light quantity control signal is equal to or lower than Slc (1) (FIG. 5), the light emitting element 601 is turned off, and at this time, the output voltage Vp becomes a value Vp0 corresponding to the offset voltage Voff shown in FIG. The output signal at this time corresponds to the “dark output signal” of the present invention. Then, when a light quantity control signal Slc exceeding the level Slc (1) is given, the light emitting element 601 emits light with a light quantity corresponding to the signal level, so that the output voltage Vp also increases according to the light quantity control signal Slc. It saturates at the upper limit Vprim based on the device configuration and does not increase any more.
[0054]
Therefore, when the light quantity control signal Slc is set to a predetermined value Slc (2) exceeding the level Slc (1), the sensor output voltage Vp is set to a predetermined voltage range corresponding to the set value Slc (2) of the light quantity control signal. Should be in # 1. Here, the reason why the voltage range # 1 has a width is to allow a change in output due to dirt that does not adversely affect the measurement accuracy and to consider a deviation due to a characteristic variation of each part of the sensor. is there.
[0055]
On the other hand, when the density sensor 60 is contaminated with toner, the output voltage Vp for the same set value of the light quantity control signal Slc becomes a lower value than when there is no contaminant, for example, as shown by a dashed line in FIG. Further, an abnormal voltage may be output due to the failure of the concentration sensor 60. For example, when the light emitting element 601 stops emitting light for some reason, the output signal Vp is set to the level Vp0 of the dark output signal irrespective of the set value of the light amount control signal Slc, as shown by the two-dot chain line in FIG. It will be a close value. In addition to the above, there is a case where the light amount cannot be adjusted or a failure occurs on the light receiving side due to a failure of a component constituting the concentration sensor 60, a short circuit of the wiring, a disconnection, and the like. Accordingly, the output voltage Vp becomes an extremely large value, or conversely, becomes an extremely small value.
[0056]
Therefore, in this embodiment, the upper limit value Vpmax and the lower limit value Vpmin of the output signal Vp that can be regarded as normal operation of each part of the density sensor 60 are set in accordance with the set value Slc (2) of the light amount control signal Slc. When the actually detected output signal Vp is within the range # 1 defined by these values, it is determined that the density sensor 60 is normal. Here, “normal” means a state in which each part of the density sensor 60 is operating properly, and of course, contamination by toner does not affect the measurement.
[0057]
On the other hand, when the output voltage Vp is within the range # 2 defined by the level Vpth obtained by adding the offset value corresponding to the measurement error to the level Vp0 of the dark output signal and the level Vpmin, the density sensor 60 is dirty. Judge. This category corresponds to a state where the density sensor 60 is operating normally, but the measurement accuracy may be reduced due to contamination by toner. Further, when the output voltage Vp is not in either of the ranges # 1 and # 2, it is determined that some abnormality has occurred in the density sensor 60.
[0058]
More specifically, the CPU 101 provided in the engine controller 10 executes a program stored in the ROM 106 in advance to perform a sensor check operation shown in FIG. 10 prior to measuring the density of the toner image. The degree of contamination of the density sensor 60 and the presence or absence of a failure are determined. Thus, in this embodiment, the CPU 101 functions as the “control unit” of the present invention.
[0059]
FIG. 10 is a flowchart showing a sensor check operation in this embodiment. In this sensor check operation, first, in a state where the light emitting element 601 does not emit light, that is, in a state where the light amount control signal Slc is set to a value equal to or lower than the level Slc (1), the level Vp0 of the output signal from the sensor corresponding to the dark output signal is obtained. Is detected (step S1). Here, the dark output signal should be at a level corresponding to the offset voltage 674p given to the light receiving unit 670p, and the level Vp0 falls within a certain range even if a characteristic variation or a measurement error of each part is included. Should be. Therefore, it is checked whether or not the level Vp0 of the dark output signal is within a predetermined range (step S2). If the determination here is YES, that is, if the dark output signal level Vp0 is within the predetermined range, the process proceeds to step S3, but if not, it is determined that there is some abnormality in the density sensor, and the operations from step S21 onward described below are executed. I do.
[0060]
On the other hand, when the dark output signal is within the above range, next, a predetermined light amount control signal Slc (2) is given to the irradiation light amount adjustment unit 605 to cause the light emitting element 605 to emit light, and the sensor output voltage Vp at that time. Is detected. Then, the level is sequentially compared with the levels Vpth, Vpmax, and Vpmin (steps S4 to S6).
[0061]
As a result of these comparisons, it is understood how the sensor output voltage Vp is related to each of the voltage levels shown in FIG. 9, and the subsequent processing differs depending on the result. That is, when the determinations in steps S4 to S6 are all YES, the value of the sensor output voltage Vp is within the range # 1, and at this time, the density sensor 60 is operating normally and there is no influence of sensor contamination. It can be determined (step S7). Therefore, at this time, the subsequent image forming operation is permitted, and the sensor check operation ends (step S8).
[0062]
On the other hand, if the determination in any of steps S4 and S5 is NO, the value of sensor output voltage Vp is not in any of ranges # 1 and # 2. It is highly likely that the sensor output greatly deviates from the range of the assumed value because some abnormality has occurred in the density sensor 60. Therefore, in this case, it is determined that the sensor has failed (step S21). Then, a service call to the user, that is, a message urging the user to contact the service center and request an investigation is displayed on the display unit 12 (step S22), and the subsequent image forming operation is performed until the abnormality is resolved. Is not executed (step S23). This is because, when the density measurement of the toner image by the density sensor 60 cannot be performed correctly, the operation conditions of the apparatus cannot be properly set, and as a result, the obtained image quality cannot be guaranteed.
[0063]
When the result of the determination in step S6 is NO, the sensor output voltage Vp is within the range # 2. At this time, although it can be estimated that the density sensor 60 is operating normally, its output voltage is too low, so it is considered that the toner is attached and contaminated. Therefore, in this case, it is determined that the density sensor 60 is dirty (step S11), and a message for urging the user to perform a cleaning request, that is, to clean the density sensor 60, is displayed on the display unit 12 (step S12). ).
[0064]
It is preferable that a cleaning tool such as a brush or a sponge is provided as an accessory of the apparatus 1 so as to be used for a sensor cleaning operation by a user. Further, after the cleaning operation by the user is performed, it is desirable to execute the sensor check again. Here, when the user performs the opening / closing operation of the cover, it is presumed that some measure has been taken, and at this time, the above processing is executed again. That is, by monitoring the output signal of an open / close sensor (not shown) for detecting the open / close of the cover that covers the engine unit EG, waits for the open / close of the cover, and when it is determined that the open / close operation has been performed, The above processing is executed again from step S1 (step S13).
[0065]
Further, when it is determined that the density sensor 60 is dirty, whether or not to allow execution of the subsequent image forming operation may be determined according to the specifications of the apparatus. In other words, from the viewpoint of guaranteeing good image quality, it is preferable not to perform image formation. On the other hand, in order to meet the demand for image formation even if the image quality is somewhat inferior, execution of image formation is allowed. It may be.
[0066]
As described above, in the image forming apparatus according to the first embodiment of the present invention, the degree of contamination of the sensor is determined based on the output voltage from the density sensor 60 disposed near the cleaner 76. More specifically, the output voltage Vp output from the light receiving unit 670p when the light emitting element 601 emits light with a predetermined light amount is detected. When the value is within the range # 1 set in accordance with the set value of the light amount control signal Slc, the sensor is determined to be normal, while the value is set to a lower light amount side than the range # 1. When it is in # 2, it is determined that the sensor is dirty. Further, when the sensor output is not in either of the ranges # 1 and # 2, it is determined that the sensor has failed.
[0067]
In this way, by determining the degree of dirt on the basis of the detection result of the sensor output, the degree of dirt on the sensor can be grasped, and necessary measures can be taken promptly according to the result. It becomes. Further, since the toner image density is measured after checking the dirt on the sensor, the density of the toner image can be accurately measured, and the operating conditions of the apparatus can be appropriately adjusted based on the measurement result. it can. In addition, since the toner image density is measured while checking the sensor for contamination as needed, the cleaner 76, which easily scatters the toner, and the density sensor 60 can be arranged close to each other, and the apparatus can be downsized.
[0068]
As described above, in this embodiment, the intermediate transfer belt 71, the cleaner 76, the density sensor 60, and the CPU 101 serve as the "image carrier", "cleaning unit", "sensor", and "control unit" of the present invention, respectively. It is functioning. In addition, the light emitting element 601 and the irradiation light amount adjustment unit 605 function as a “light projecting unit” of the present invention, while the reflected light amount detection unit 607 functions as a “light receiving unit” of the present invention. Further, the display unit 12 functions as the “notifying unit” of the present invention. Further, the ranges # 1 and # 2 of the sensor output voltage Vp correspond to the “first range” and the “second range” of the present invention, respectively.
[0069]
(2nd Embodiment)
Next, a second embodiment of the image forming apparatus according to the present invention will be described. The configuration of the apparatus in this embodiment is the same as that of the image forming apparatus of the first embodiment described above, and a description thereof will be omitted. In this embodiment, prior to the measurement of the density of the toner image, a light amount setting process described below is performed. This light amount setting process adjusts the light emission amount of the light emitting element 601 so that the sensor output Vp when detecting light incident on the reflected light amount detection unit 607 from the surface of the intermediate transfer belt 71 not carrying the toner image becomes a predetermined value. This is the process to perform.
[0070]
In this way, by controlling the sensor output Vp to a constant value in a state where the toner does not adhere to the intermediate transfer belt 71, the relationship between the sensor output and the density of the toner image can be uniquely expressed, and the subsequent processing And the measurement can be performed in a region where the sensitivity of the light receiving elements 672p and 672s is good, so that improvement in measurement accuracy can be expected. Further, as described later, in this embodiment, the check of the density sensor 60 is performed together with the light amount setting processing.
[0071]
FIG. 11 is a principle diagram for explaining the light quantity setting processing in the second embodiment according to the present invention, and FIG. 12 is a flowchart showing the light quantity setting processing. FIG. 13 is a flowchart showing a light amount detection operation performed in the light amount setting process. The basic concept of the output voltage Vp of the density sensor 60 and the state determination of the sensor based on the output voltage Vp in the light amount setting process is the same as that described in the first embodiment. Therefore, for the processing based on the same principle as that of the first embodiment, the description of the first embodiment is referred to, and the detailed description is omitted here.
[0072]
As shown in FIG. 11, the sensor output voltage Vp is controlled by the light amount control signal in a region Z1 on the low level side due to the provision of the dead zone (FIG. 5) and a region Z2 between the region Z3 where the output voltage is saturated in the circuit configuration. It changes in proportion to Slc. This is because the amount of light emitted from the light emitting element 601 is proportional to the amount of light control signal Slc (FIG. 5), and the sensor output voltage Vp is proportional to the amount of light reflected from the intermediate transfer belt 71 (FIG. 6). The characteristics shown in FIG. 11 fluctuate due to variations in characteristics of components, changes over time, and contamination of the sensor. However, if the relationship between the light quantity control signal Slc and the sensor output voltage Vp is actually measured at two points in the area Z2, the characteristics can be grasped. From the result, the value of the light amount control signal Slc (ref) for controlling the sensor output voltage Vp to the predetermined reference value Vpref can be obtained.
[0073]
A specific method of obtaining the light quantity control signal Slc (ref) will be described with reference to FIGS. First, similarly to the sensor check operation in the first embodiment, a dark output signal is detected. That is, the level Vp0 of the output signal from the sensor is detected while the light emitting element 601 does not emit light (step S101), and it is determined whether or not the level is within a predetermined range (step S102). Here, when the dark output signal voltage Vp0 is not in the above range, it is determined that the sensor has failed (step S121), and processing according to the determination result (steps S122 and S123) is executed.
[0074]
If the dark output signal voltage Vp0 is within the normal range, the light quantity control signal Slc is set to the value Slc (3) shown in FIG. 11 (step S103), and the light quantity detection subroutine shown in FIG. 13 is called (step S103). S104). By setting the light quantity control signal Slc in this way, the light emitting element 601 emits light with a predetermined light quantity.
[0075]
In the light amount detection routine, a sensor output voltage Vp3 corresponding to the above light emission amount is detected (step S201). Then, similarly to the sensor check in the first embodiment, the detected voltage Vp3 is compared with the levels Vpth, Vpmax, and Vpmin determined according to the set value of the light amount control signal Slc (steps S202 to S204). ). Further, based on the result of the comparison, it is determined whether the density sensor 60 is normal, dirty, or malfunctioning (steps S205 to S207), and the process returns to the light amount setting process of FIG.
[0076]
In the next step S105, the subsequent processing is made different depending on the determination result in the light quantity detection routine. That is, if the determination result is “normal”, the process proceeds to step S106, the light amount control signal Slc is set to the value Slc (4) shown in FIG. 11 (step S106), and the light amount detection routine is called again (step S107). . The light quantity control signal Slc (4) is a value larger than the value Slc (3) set previously, and therefore, the light emitting element 601 emits light with a higher light quantity. The content of the light quantity detection routine executed in this state is the same as that at the time of the first call described above, but the values Vpth, Vpmax, and Vpmin to be compared with the sensor output voltage Vp4 are the set values of the light quantity control signal Slc. Can be changed as necessary according to the difference.
[0077]
Then, the determination result is checked even after the execution of the light amount detection routine (step S108). If the sensor output voltages Vp3 and Vp4 detected by the execution of the two light quantity detection routines are both values indicating that the sensor is normal, that is, values belonging to the range # 1 in FIG. The process proceeds to compare these two output voltages (step S109). Here, from the relationship shown in FIG. 11, the output voltage Vp4 when set to the light quantity control signal Slc (4) should be higher than the output voltage Vp3 when set to the light quantity control signal Slc (3). is there. Therefore, as a result of the comparison, if the voltage Vp4 is higher, it is determined that the measurement has been properly performed, and the reference light amount control signal Slc (ref) for obtaining the reference light amount is calculated (step S110).
[0078]
This calculation is performed based on the results Vp3 and Vp4 of the two light quantity detections and the relationship shown in FIG.
Slc (ref) = Slc (3) + {Slc (4) −Slc (3)} × (Vpref−Vp3) / (Vp4−Vp3) (Equation 3)
Can be obtained by If the light amount control signal Slc given from the CPU 101 to the irradiation light amount adjustment unit 605 is set to the reference value Slc (ref) thus obtained, the sensor output when no toner adheres to the surface area 71a of the intermediate transfer belt 71 becomes the reference value Vpref. It becomes. Therefore, when the optical density of the toner image is obtained, the actually measured value Vp of the sensor output is evaluated based on this value Vpref, so that the toner density can be stably measured without being affected by the variation in sensor characteristics and the contamination by toner. Image density measurement can be performed.
[0079]
In order to set the light quantity control signal Slc to the reference value Slc (ref), an 8-bit digital signal supplied from the CPU 101 to the irradiation light quantity adjustment unit 605 is set so that the light quantity control signal Slc becomes closest to the reference value Slc (Ref). The signals DA1 and DA2 may be determined. Further, since the degree of contamination of the density sensor 60 changes every moment, it is desirable to execute the reference light amount control signal Slc (ref) before each measurement of the density of the toner image.
[0080]
On the other hand, in step S105 or S108, when the result of the determination is "dirty", that is, indicating that the sensor is dirty, the process proceeds to step S131, and a "cleaning request" message is displayed on the display unit 12, and the first This is the same as in the case of the embodiment. That is, after the cover opening / closing operation is performed by the user, the above-described processing from step S101 is executed again (step S132). If the result of the determination is "failure", a message prompting a service call is displayed (step S122), and execution of the subsequent image forming operation is prohibited (step S123), and the light amount setting process ends.
[0081]
Further, if the magnitude relationship between the two sensor output voltages is different from the original in step S109, it is considered that the density sensor 60 is abnormal. Execute the accompanying process.
[0082]
As described above, in the light amount setting process according to the second embodiment, the light emitting element 601 is caused to emit light with two types of light amounts, the sensor output voltages Vp of the light emitting elements 601 are detected, and based on the detection results, the light output during the concentration measurement is determined. The irradiation light amount is set. Therefore, the sensor output in a state where the toner does not adhere always has a constant reference value Vpref, and the influence of the sensor characteristic variation is small. As a result, the density of the toner image can be accurately and stably measured. Further, since the state of the density sensor 60 is determined based on the sensor output, the degree of sensor contamination can be accurately grasped. Then, since a necessary message is displayed according to the determination result, it is possible to promptly notify the user of the abnormality of the sensor and prompt the user to perform a necessary measure.
[0083]
(Other)
After performing the state determination of the density sensor 60 and the light amount adjustment in addition thereto as described above, the density of the toner image is measured, and the operation conditions of each unit of the apparatus can be adjusted based on the result. Numerous proposals and disclosures have been made on various kinds of adjustment techniques, and a description thereof will be omitted.
[0084]
Note that the present invention is not limited to the above-described embodiment, and various changes other than those described above can be made without departing from the gist of the present invention. For example, the configuration of the density sensor 60 is not limited to those described in each of the above embodiments, and irradiates light to the image carrier and detects light emitted from the irradiation area. As long as it detects the optical density, it may have a configuration different from the above.
[0085]
Further, in each of the above-described embodiments, when the sensor output is in the range # 2 shown in FIG. 9, the sensor is uniquely determined to be “dirty”. The range # 2 in which the sensor is determined to be dirty may be further subdivided, such as "no dirt". Then, the subsequent processing may be made different depending on the classification.
[0086]
Further, in each of the above-described embodiments, the abnormality of the sensor is displayed as a message on the display unit 12 to notify the user, but other than this, for example, a voice message or an alarm sound recorded in advance may be used to notify the user. It may be.
[0087]
In addition, when it is determined that the sensor is faulty, not only simply notifying the occurrence of the fault, but also which of the above-described steps has been determined to be faulty to help the serviceman identify the fault location. An identifiable error code may be displayed together.
[0088]
Further, in each of the above-described embodiments, the density sensor 60 that detects the amount of the received two polarized light components (p, s) is provided. In addition, for example, only the single light component is detected. The present invention can be applied to an apparatus including the density sensor described above.
[0089]
In each of the above embodiments, the present invention is applied to an apparatus that forms an image using four color toners of yellow, magenta, cyan, and black. However, the type and number of toner colors are limited to the above. It is not what is done. For example, the present invention can be applied to an apparatus capable of forming only a black-and-white monochrome image. In addition to the rotary developing system of the present invention, a so-called tandem type image forming apparatus in which developing units corresponding to respective toner colors are arranged so as to be arranged in a line in the sheet conveying direction. The present invention is also applicable. Further, the present invention is not limited to the electrophotographic apparatus as in the above embodiment, but is applicable to all image forming apparatuses.
[Brief description of the drawings]
FIG. 1 is a diagram showing a first embodiment of an image forming apparatus according to the present invention.
FIG. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus of FIG. 1;
FIG. 3 is a diagram illustrating a configuration of a density sensor.
4 is a diagram showing an electrical configuration of a light receiving unit employed in the density sensor of FIG.
FIG. 5 is a diagram showing a light amount control characteristic in the density sensor of FIG. 3;
FIG. 6 is a graph showing how an output voltage changes with respect to the amount of reflected light in the density sensor of FIG. 3;
FIG. 7 is a diagram showing a light quantity control signal conversion unit in this embodiment.
FIG. 8 is a partial cross-sectional view of the density sensor.
FIG. 9 is a diagram illustrating a relationship between a light quantity control signal and a sensor output voltage.
FIG. 10 is a flowchart showing a sensor check operation in this embodiment.
FIG. 11 is a principle diagram for explaining a light amount setting process in a second embodiment according to the present invention.
FIG. 12 is a flowchart illustrating a light amount setting process.
FIG. 13 is a flowchart illustrating a light amount detection operation performed in the light amount setting process.
[Explanation of symbols]
12 display unit (notification means), 60 density sensor (sensor), 71 intermediate transfer belt (image carrier), 76 cleaner (cleaning means), 101 CPU (control means), 601 light emitting element (light emitting element) 605: Irradiation light amount adjustment unit (light emitting unit), 607: Reflected light amount detection unit (light receiving unit)

Claims (6)

A belt-shaped image carrier wound around rollers,
Cleaning means for removing toner adhered to the surface of the image carrier by abutting the winding area around which the image carrier is wound around the roller in the surface area of the image carrier;
A sensor that is disposed near the cleaning unit and irradiates light toward the surface of the image carrier, receives light emitted from the image carrier, and outputs a signal corresponding to the amount of received light;
An image forming apparatus comprising: a control unit that determines a degree of contamination of the sensor based on an output signal from the sensor. A light projecting unit that irradiates the image carrier with light with a light amount corresponding to a light amount control signal given from the control unit; and a light receiving unit that receives light emitted from the image carrier, And a light receiving unit that outputs a signal corresponding to the output signal as the output signal.
The control means,
The level of the output signal output from the light receiving unit when the light amount control signal set to a predetermined set value is given to the light projecting unit is within a predetermined first range determined according to the set value. 2. The sensor according to claim 1, wherein when it is determined that the sensor is normal, the sensor is determined to be dirty when the sensor is in a second range adjacent to the first range on a light receiving amount lower side than the first range. 3. Image forming apparatus. The image forming apparatus according to claim 2, wherein the control unit determines that the sensor has failed when the level of the output signal is not in any of the first range and the second range. The control means previously acquires an output signal from the light receiving unit in a state where the light is not irradiated from the light projecting unit to the image carrier as a dark output signal, and obtains the level of the dark output signal or the dark output signal. The image forming apparatus according to claim 2, wherein a level obtained by adding a predetermined offset value to the output signal is set as a threshold on the low light receiving amount side in the level of the output signal in the second range. 5. The image forming apparatus according to claim 1, further comprising a notification unit configured to notify a determination result by the control unit in a mode according to the determination result, as needed. A sensor dirt determination method for irradiating light toward the surface of the image carrier, receiving light emitted from the image carrier, and outputting a signal corresponding to the amount of received light to determine dirt on the sensor.
A sensor contamination determination method, wherein a degree of contamination of the sensor is determined based on an output signal from the sensor.

Images