JP2003302878A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve accuracy in detecting the life of an ITB, prolong the life of the ITB, and reduce the cost of an image forming device. <P>SOLUTION: (1) The life of the ITB is detected by a density detecting sensor. (2) The life of the ITB is detected by using an optical sensor and a sheet counter. (3) A recovery operation for the surface of the ITB is carried out when the optical sensor detects a degree of the ITB soiling and it is determined that the ITB is heavily soiled. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art FIG. 9 shows a conventional image forming apparatus. Description will be given below with reference to the drawings. The photosensitive drum 1, which is an image carrier,
It is driven in the direction of the arrow in the figure by a driving means (not shown), and is uniformly charged by the primary charger 2. Next, the exposure device 3 irradiates the photosensitive drum 1 with a laser beam L according to a yellow image pattern, and a latent image is formed on the photosensitive drum 1. When the photosensitive drum 1 further advances in the direction of the arrow, the rotary support 1
Of the developing devices 4a, b, c, d supported by 1,
The developing device 4a containing the yellow toner is attached to the photosensitive drum 1.
And is visualized by the selected developing device 4a. The intermediate transfer belt 5 rotates in the arrow direction at substantially the same speed as the photosensitive drum 1, and the toner image formed and carried on the photosensitive drum 1 is made of resin by the primary transfer bias applied to the primary transfer roller 8a. Primary transfer is performed on the outer peripheral surface of the intermediate transfer belt 5. The above process is yellow,
By performing the processes for magenta, cyan and black, toner images of a plurality of colors are formed on the intermediate transfer belt 5. Next, the transfer material is fed from the transfer material cassette 12 by the pickup roller 13 at a predetermined timing. At the same time, the secondary transfer bias is applied to the secondary transfer roller 8b, and the toner image is transferred from the intermediate transfer belt 5 to the transfer material.

Further, the transfer material is conveyed to the fixing device 6 by the conveying belt 14 and melted and fixed to obtain a color image.

The transfer residual toner on the photosensitive drum 1 is cleaned by a cleaning device 7 of known blade means.

On the other hand, the transfer residual toner on the intermediate transfer belt 5 is cleaned by the intermediate transfer belt cleaner 15.

The intermediate transfer belt 5 is a consumable item,
It is set as a replaceable unit part. When the intermediate transfer belt is a consumable component in this way, the user needs to recognize that the intermediate transfer belt has reached the replacement time by some means, and regularly replace the intermediate transfer belt.

Therefore, the apparatus main body has a function of detecting the use status of the intermediate transfer belt and notifying the user when the life of the intermediate transfer belt is reached. More specifically, the usage time (or the number of prints) of the intermediate transfer belt is counted by the main body CPU, and when the total usage time of the intermediate transfer belt (or the total number of prints, etc.) reaches a predetermined value, , Is displayed on the operation panel 16 of the main body to prompt replacement of the intermediate transfer belt. The total use time of the intermediate transfer belt is stored in the non-volatile ROM 17 in the main body, and the internal value is rewritten and updated by the main body CPU every time the intermediate transfer belt is used. When the intermediate transfer belt is replaced, the value of the non-volatile ROM 17 is reset to 0 by the main body CPU.

[0008]

The intermediate transfer belt 5 is
Although it has already been described that it is a consumable item and needs to be regularly replaced, the reason why the intermediate transfer belt must be regularly replaced is as follows. Although the intermediate transfer belt 5 is cleaned by removing the transfer residual toner by the intermediate transfer belt cleaner 15, the intermediate transfer belt 5 is gradually contaminated by the components of the transfer material, discharge products, or the like and is exposed to light during repeated use. The surface of the drum 1 or the like may be scratched by rubbing against the contact member. When the surface of the intermediate transfer belt becomes contaminated, the surface resistance of the intermediate transfer belt is lowered and the transferability is deteriorated. This is because it will result in damage.

The deterioration of the surface properties (contamination, scratches) of the intermediate transfer belt causes a problem that the life of the intermediate transfer belt is shortened and the frequency of replacement of the intermediate transfer belt is increased.

On the other hand, in general, the degree of contamination and rubbing scratches on the intermediate transfer belt greatly differs depending on the use environment and use condition of the apparatus main body, and does not always correspond to the number of prints and the use time.

Therefore, in the method of determining the life of the intermediate transfer belt according to the usage time of the intermediate transfer belt as in the conventional image forming apparatus described above, the user can be notified of the replacement timing of the intermediate transfer belt at the optimum timing. could not.

The above-mentioned problems are not limited to the intermediary transfer belt, but also occur in other image bearing members such as photoconductors, transfer transfer belts, and the like.

The present invention has been proposed in view of the above problems, and is an image forming apparatus having the following configuration.

[0014]

[Means for Solving the Problems] (1) Surface characteristics of an image carrier or a transfer material carrier are detected by an optical sensor including a light emitting portion and a light receiving portion, and the image carrier or the transfer is detected according to the detection result. An image forming apparatus that determines the life of a material carrier.

(2) Detecting means for detecting the surface characteristics of the image bearing member or the transfer material bearing member by means of an optical sensor comprising a light emitting portion and a light receiving portion, and means for detecting the use time of the image bearing member or the transfer material bearing member. In the image forming apparatus having the image carrier or the transfer material carrier, the image carrier or the transfer material carrier is detected according to the detection result of the surface characteristics of the image carrier or the transfer material carrier and the detection result of the usage time of the image carrier or the transfer material carrier. Image forming device that determines the life of the device.

(3) The surface characteristics of the image bearing member or the transfer material bearing member are detected by an optical sensor including a light emitting portion and a light receiving portion, and the detection result of the surface characteristics of the image bearing member or the transfer material bearing member is a predetermined value. The image forming apparatus is characterized by performing a recovery operation of the surface characteristics of the image carrier or the transfer material carrier when the temperature reaches the value.

(4) The optical sensor is common with a sensor for detecting the optical characteristics of the toner image formed on the image carrier or the transfer material carrier (1), (2). The image forming apparatus according to (3).

(Operation) The life detection accuracy is improved by detecting the surface characteristics of the image carrier or the transfer material carrier by an optical sensor to determine the life.

Further, by detecting the surface characteristics of the image bearing member or the transfer material bearing member by an optical sensor, and at the same time detecting the usage time of the image bearing member or the transfer material bearing member to determine the life, the life detecting accuracy is obtained. Will be further improved.

Further, when the surface characteristics of the image carrier or the transfer material carrier are detected by an optical sensor and it is judged that the surface characteristics are deteriorated, a recovery operation of the surface characteristics is performed to perform the image carrier or transfer. The life of the material carrier can be extended.

Furthermore, by using the optical sensor in common with the toner image detecting sensor, the cost and size of the apparatus can be reduced.

[0022]

(First Embodiment) In the present embodiment,
A method of detecting the surface characteristics of the intermediate transfer belt with an optical sensor including a light emitting portion and a light receiving portion and determining the life of the intermediate transfer belt according to the detection result will be described.

FIG. 1 shows a sectional view of an image forming apparatus according to the present invention. It should be noted that the same components and members as those in the conventional image forming apparatus shown in FIG.
The description will be appropriately omitted.

The photosensitive drum 1 is arranged substantially in the center of the main body of the apparatus. The photosensitive drum 1 is rotatably supported,
Around the photosensitive drum 1, the charger 2, the exposure device 3, the developing devices 4a and 4b are sequentially arranged along the rotation direction (arrow direction).
An intermediate transfer belt 5, a cleaning device 7, and the like are provided. Further, the fixing device 6 is provided at the lower left of the main body of the apparatus.
Are arranged.

An optical sensor 9 is arranged downstream of the primary transfer portion (contact portion between the photosensitive drum 1 and the intermediate transfer belt 5) so as to face the surface of the intermediate transfer belt 5. The optical sensor 9 has a function of detecting the surface state of the intermediate transfer belt 5, and the first feature of the present embodiment is to detect the life of the intermediate transfer belt according to the detection result.

Further, the optical sensor 9 also has a function as a density sensor used for image density control. Generally, in an electrophotographic color image forming apparatus, the image density varies depending on various conditions such as changes in the environment in which it is used and the number of prints. Then, the original correct color tone cannot be obtained. Therefore, in this image forming apparatus, toner of each color is formed on the intermediate transfer belt 5 on a trial basis as density detection toner images (patches), the densities thereof are detected by the optical sensor 9, and the detection results are used for exposure. A stable image is obtained by feeding back the amount and the developing bias to control the image density. As described above, by using the optical sensor for detecting the surface state of the intermediate transfer belt 5 and the toner concentration sensor in common, the size and cost of the apparatus can be reduced. This is the second feature of this embodiment.

As shown in FIG. 2, the optical sensor 9 comprises a light emitting element 91 such as an LED, a light receiving element 92 such as a photodiode, and a holder 93.
The infrared light from No. 1 is applied to the surface of the intermediate transfer belt 5 or the toner image P for density detection, and the light reflected from the infrared light is measured by the light receiving element 92. By doing so, the surface characteristics of the intermediate transfer belt 5 or the density of the toner image P for density detection can be measured. The light emitting element 91 and the light receiving element 92 are arranged opposite to each other at an angle of 45 ° with reference to the normal line 1, and the regular reflection light from the intermediate transfer belt and the toner image is measured.

Next, the method of detecting the life of the intermediate transfer belt in this embodiment will be described in detail with reference to the flowchart of FIG.

In the present embodiment, the detection of the life of the intermediate transfer belt is executed immediately after the printing operation and when the power of the apparatus main body is turned on.

First, when an instruction to detect the life of the intermediate transfer belt is input to the main body CPU, the intermediate transfer belt life detecting sequence is started.

STEP 1 First, the reflection output A of the intermediate transfer belt is measured by the optical sensor 9.

The sensitivity of the optical sensor 9 is adjusted in advance so that the reflected output from the unused (new) intermediate transfer belt is about 5V.

STEP2 Determine the life of the intermediate transfer belt.

The reflectance of the surface of the intermediate transfer belt used in this embodiment gradually decreases as it is used. This is because the surface of the intermediate transfer belt is contaminated by printing or the surface is scratched by rubbing. Therefore, the reflection output A of the intermediate transfer belt
The value of becomes smaller as the intermediate transfer belt is used (FIG. 4).

Here, when the reflection output A of the intermediate transfer belt is less than 2 V, the surface properties (contamination and scratches) of the intermediate transfer belt are remarkably deteriorated. When printing is performed in this state, a good image is obtained. It is difficult to obtain. Therefore, the process advances to STEP 3 to display the life of the intermediate transfer belt.

STEP 3 Since it is necessary to replace the intermediate transfer belt, the life of the intermediate transfer belt is displayed on the display panel 16 (user interface panel).

As described above, in the present embodiment, the surface characteristics of the intermediate transfer belt are detected by the optical sensor, and the life of the intermediate transfer belt is judged according to the detection result, thereby improving the accuracy of detecting the life of the intermediate transfer belt. I explained how to do it.

The present embodiment is applied to a system in which the main factor that determines the life of the intermediate transfer belt is the change (deterioration) of the surface characteristics, and mechanical changes such as belt elongation do not affect the life so much. It is preferable.

(Embodiment 2) In the present embodiment, the surface characteristics of the intermediate transfer belt are detected by an optical sensor consisting of a light emitting portion and a light receiving portion, and the usage time of the intermediate transfer belt is detected, and both detection results are obtained. A method of determining the life of the intermediate transfer belt will be described.

FIG. 5 is a sectional view of the image forming apparatus according to the present invention. It should be noted that members having the same configurations and functions as those of the image forming apparatus of FIG. 1 described in the first embodiment are denoted by the same reference numerals, and description thereof will be appropriately omitted.

Also in this embodiment, the optical sensor 9 is used.
Has a function of detecting the surface state of the intermediate transfer belt 5 and a function of a density sensor used for image density control at the same time.

In addition, a non-volatile ROM for storing the cumulative print use number T of the intermediate transfer belt in the main body of the apparatus.
17 are provided. Value T in non-volatile ROM 17
Is rewritten and updated by the main body CPU each time the intermediate transfer belt is used. Further, when the intermediate transfer belt is replaced, the value T is reset to 0 by the main body CPU.

Next, the method of detecting the life of the intermediate transfer belt in this embodiment will be described in detail with reference to the flowchart of FIG.

In the present embodiment, the detection of the life of the intermediate transfer belt is performed immediately after the printing operation and when the power of the apparatus main body is turned on.

First, when an instruction for detecting the life of the intermediate transfer belt of the main body CPU is input, an intermediate transfer belt life detecting sequence is started.

STEP 1 First, the reflection output A of the intermediate transfer belt is measured by the optical sensor 9.

As with the first embodiment, the optical sensor 9
The sensitivity is adjusted in advance so that the reflection output for the unused (new) intermediate transfer belt is about 5V.

STEP2 The life of the intermediate transfer belt is judged. Here, when the reflection output A of the intermediate transfer belt is smaller than 2 V, the surface property (contamination or scratch) of the intermediate transfer belt is remarkably deteriorated. When printing is performed in this state, a good image can be obtained. Is in a difficult state. Therefore, in STEP 5, the life of the intermediate transfer belt is displayed.

STEP 3 The CPU of the main body reads the cumulative print use number T of the intermediate transfer belt from the non-volatile ROM 17.

STEP 4 The life of the intermediate transfer belt is judged based on the cumulative number of prints used T of the intermediate transfer belt.

In the intermediate transfer belt of the image forming apparatus used in this embodiment, the maximum allowable number of prints is 1000
It is set to 00. This value is set to a value that allows the intermediate transfer belt used in this embodiment to maintain sufficient mechanical strength. If the cumulative number of prints used on the intermediate transfer belt exceeds 100,000, there is a possibility that the belt may break or the belt may grow unacceptably.
Therefore, when the cumulative number of prints used T exceeds 100,000, it is determined that the intermediate transfer belt has reached the end of its life, and the process proceeds to STEP 5 for displaying the life of the intermediate transfer belt.

STEP 5 Since it is necessary to replace the intermediate transfer belt, the life of the intermediate transfer belt is displayed on the display panel 16 (user interface panel).

As described above, in the present embodiment, the surface characteristics of the intermediate transfer belt are detected by the optical sensor including the light emitting portion and the light receiving portion, the operating time of the intermediate transfer belt is detected, and the intermediate value is detected according to both detection results. The method for determining the life of the transfer belt has been described.

In this embodiment, it is uncertain whether the final factor that determines the life of the intermediate transfer belt is the change (deterioration) of the surface characteristics or the deterioration of the mechanical strength characteristics. It is preferably used in a system.

(Embodiment 3) In the present embodiment, the surface characteristics of the intermediate transfer belt are detected by an optical sensor, and when it is judged that the surface characteristics have deteriorated, a recovery operation of the surface characteristics is performed to perform the intermediate transfer. A method for achieving a long service life of the belt will be described.

FIG. 7 shows a sectional view of the image forming apparatus according to the present invention. It should be noted that members having the same configurations and functions as those of the image forming apparatus of FIG. 1 described in the first embodiment are denoted by the same reference numerals, and description thereof will be appropriately omitted.

Also in this embodiment, the optical sensor 9
Has a function of detecting the surface state of the intermediate transfer belt 5 and a function of a density sensor used for image density control at the same time.

In addition, a non-volatile ROM for storing the cumulative print use number T of the intermediate transfer belt is provided in the main body of the apparatus.
17 are provided. Value T in non-volatile ROM 17
Is rewritten and updated by the main body CPU each time the intermediate transfer belt is used. Further, when the intermediate transfer belt is replaced, the value T is reset to 0 by the main body CPU.

Further, in this embodiment, the intermediate transfer belt polishing roller 18 for recovering the surface property of the intermediate transfer belt is provided so as to be able to contact / separate from the intermediate transfer belt 5. The intermediate transfer belt polishing roller 18 is a metal roller made of aluminum and is usually separated from the intermediate transfer belt 5. Further, when the operation of recovering the surface characteristics of the intermediate transfer belt is performed, the intermediate transfer belt contacts the intermediate transfer belt and rotates in the opposite direction at the same speed as the moving speed of the intermediate transfer belt. By doing so, contaminants such as discharge products and paper dust that have adhered to the surface of the intermediate transfer belt are stripped from the belt surface, and the surface property of the intermediate transfer belt is restored.

Next, the sequence for performing the recovery operation execution determination and the life determination of the intermediate transfer belt surface characteristic will be described with reference to the flowchart of FIG.

Note that this sequence is executed immediately after the printing operation and when the power of the apparatus main body is turned on.

STEP 1 First, the reflection output A of the intermediate transfer belt is measured by the optical sensor 9.

As with the first embodiment, the optical sensor 9
The sensitivity is adjusted in advance so that the reflection output for the unused (new) intermediate transfer belt is about 5V.

STEP 2 It is determined whether or not the surface property recovery operation of the intermediate transfer belt is to be executed. Here, the reflection output A of the intermediate transfer belt is 2
When it is smaller than V, the surface property (contamination or scratch) of the intermediate transfer belt is remarkably deteriorated, and when printing is performed in this state, it is judged that it is difficult to obtain a good image. Therefore, the operation proceeds to the intermediate transfer belt surface property recovery operation in STEP3.

STEP3 The intermediate transfer belt surface property recovery operation is executed. The specific method of operation is as follows. First, the metal polishing roller 18 is brought into contact with the intermediate transfer belt. Subsequently, the intermediate transfer belt 5 is rotated, and the polishing roller 18 is rotated in the opposite direction at the same speed as the moving speed of the intermediate transfer belt for 2 minutes. By doing so, contaminants such as discharge products and paper dust that have adhered to the surface of the intermediate transfer belt are stripped from the belt surface, and the surface property of the intermediate transfer belt is restored.

STEP 4 The optical sensor 9 allows the reflection output A of the intermediate transfer belt to be reflected.
To measure again. This is performed to confirm that the surface property of the intermediate transfer belt has been recovered by the operation of recovering the surface property of the intermediate transfer belt in STEP3.

STEP 5 The life of the intermediate transfer belt is judged. The judgment method is as follows. First, the reflection output A of the intermediate transfer belt measured in STEP 4 and a predetermined value (= 3)
V). When the reflection output A is smaller than 3V, it is judged that the surface property of the intermediate transfer belt cannot be sufficiently restored, that is, the intermediate transfer belt has reached the end of its life.
Proceed to STEP 8 to display the life of the intermediate transfer belt. Incidentally, in the present embodiment, the judgment threshold value of the reflected output A is set to 3V,
If this value is made small (close to the judgment threshold value of STEP2: 2V), the life of the intermediate transfer belt can be extended, but on the other hand, the execution interval of the surface property recovery operation becomes short and the user is uncomfortable. Become. On the contrary, if the threshold value is increased (reflected output of a new intermediate transfer belt: close to 5 V), the life of the intermediate transfer belt is shortened. Therefore, it is preferable that the judgment threshold value is set to an optimum value according to the image forming apparatus used.

STEP 6 The CPU of the main body reads the cumulative number of prints used T of the intermediate transfer belt T from the nonvolatile ROM 17.

STEP7 The service life of the intermediate transfer belt is determined based on the cumulative number of prints used T of the intermediate transfer belt.

Here, the cumulative print use number T is 10
If it exceeds 00000, it is determined that the intermediate transfer belt has reached the end of its life, and the process proceeds to STEP 8 for displaying the life of the intermediate transfer belt.

STEP 8 Since it is necessary to replace the intermediate transfer belt, the life of the intermediate transfer belt is displayed on the display panel 16 (user interface panel).

As described above, in the present embodiment, the surface characteristics of the intermediate transfer belt are detected by the optical sensor, and when it is determined that the surface characteristics are deteriorated, the surface characteristics recovery operation is performed to lengthen the intermediate transfer belt. The method of achieving a longer life has been described.

The present embodiment is applied to a system in which the surface characteristics of the intermediate transfer belt are significantly changed (deteriorated) or the degree of changes (deterioration) of the surface characteristics of the intermediate transfer belt is greatly different depending on the usage conditions of the apparatus. It is preferable to use.

In the first to third embodiments, the method for improving the accuracy of detecting the life of the intermediate transfer belt and extending the life of the intermediate transfer belt have been described above. It is also applicable to a transfer material carrier such as a carrier or a transfer belt.

Further, although the surface condition of the intermediate transfer belt is detected immediately after the printing operation and when the power of the apparatus main body is turned on, it may be detected at another timing. For example, if the surface of the intermediate transfer belt (base of the toner image) is measured by the optical sensor during the image density control described in the first embodiment, the surface property of the intermediate transfer belt is determined based on the measured value. Is also good. By doing so, the control of the present invention and the image density control can be performed at the same time, and the total control time can be shortened.

Further, in detecting the surface state of the intermediate transfer member, an optical sensor of the type which detects the specularly reflected light from the surface of the intermediate transfer belt was used, but the optical sensor applicable to the present invention is The type is not limited to the specular reflection light detection type, and other types of optical centers may be used. For example, an irregularly reflected light (diffused light) detection type optical sensor may be used. Further, when a transparent or translucent intermediate transfer belt is used, a transmissive optical sensor may be used.

Further, the number of prints is used as the usage time of the image bearing member or the transfer material bearing member, but the rotation time or the rotation number of the image bearing member or the transfer material bearing member may be used.

[0078]

As described above, according to the present invention, the accuracy of life detection is improved by detecting the surface characteristics of the image carrier or the transfer material carrier by an optical sensor to determine the life.

Further, by detecting the surface characteristics of the image bearing member or the transfer material bearing member by an optical sensor and at the same time detecting the usage time of the image bearing member or the transfer material bearing member to judge the life, the life detecting accuracy is obtained. Has been further improved.

If the surface characteristics of the image carrier or the transfer material carrier are detected by the optical sensor and it is determined that the surface characteristics have deteriorated, a recovery operation of the surface characteristics is performed to perform the image carrier or transfer. The life of the material carrier has been extended.

Furthermore, by using the optical sensor in common with the sensor for detecting the toner image, the cost and size of the apparatus can be reduced.

[Brief description of drawings]

FIG. 1 illustrates an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 represents an optical sensor.

FIG. 3 represents a flowchart of the first embodiment of the present invention.

FIG. 4 shows a change in reflected output value of the intermediate transfer belt.

FIG. 5 illustrates an image forming apparatus according to a second exemplary embodiment of the present invention.

FIG. 6 represents a flowchart of a second embodiment of the present invention.

FIG. 7 illustrates an image forming apparatus according to a third exemplary embodiment of the present invention.

FIG. 8 represents a flowchart of a third embodiment of the present invention.

FIG. 9 illustrates a conventional image forming apparatus.

[Explanation of symbols]

1 photosensitive drum 2 Primary charger 3 exposure equipment 4 Phenomenon device 5 Intermediate transfer belt 6 fixing device 7 Cleaning device 8a Primary transfer roller 8b Secondary transfer roller 9 Optical sensor 16 Operation panel 17 Non-volatile ROM 18 Polishing roller

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koichi Hiroshima             Kyano, 3-30-2 Shimomaruko, Ota-ku, Tokyo             Within the corporation F-term (reference) 2H027 DA09 DA38 DA45 DE02 DE07                       DE10 EC06 EC14 EC18 EF01                       EF11 HB01 HB02 HB16                 2H200 FA02 GA23 GA44 JC03 JC09                       JC12 JC20 LB11 LB20 LB39                       LB40 PA27 PA28 PB24 PB33                       PB35

Claims (4)

[Claims] 1. A surface characteristic of an image carrier or a transfer material carrier is detected by an optical sensor including a light emitting unit and a light receiving unit, and the life of the image carrier or the transfer material carrier is determined according to the detection result. Image forming apparatus. 2. A detecting means for detecting the surface characteristics of the image bearing member or the transfer material bearing member by an optical sensor comprising a light emitting portion and a light receiving portion, and a means for detecting the usage time of the image bearing member or the transfer material bearing member. In the image forming apparatus having the image carrier or the transfer material carrier, the image carrier or the transfer material carrier is detected according to the detection result of the surface characteristics of the image carrier or the transfer material carrier and the detection result of the usage time of the image carrier or the transfer material carrier. Image forming device that determines the life of the device. 3. The surface characteristic of the image bearing member or the transfer material bearing member is detected by an optical sensor including a light emitting portion and a light receiving portion, and the detection result of the surface characteristic of the image bearing member or the transfer material bearing member reaches a predetermined value. When reaching, the image forming apparatus is characterized by performing a recovery operation of the surface characteristics of the image carrier or the transfer material carrier. 4. The optical sensor according to claim 1, wherein the optical sensor is common with a sensor for detecting optical characteristics of a toner image formed on the image carrier or the transfer material carrier. The image forming apparatus described.