JPH09304997A - Picture image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid the occurrence of abnormal picture image due to unevenness in resistance value of an intermediate transfer belt. SOLUTION: A plurality of picture image density detection sensors 51 are provided at an interval in the longitudinal direction of an intermediate transfer belt 19 to detect density of toner picture image which is transferred on the intermediate transfer belt 19 by each picture image density detection sensor 51 at a plurality of sections in the longitudinal direction. Or, one picture image density detection sensor 51 may be provided and be scanned in the longitudinal direction of the intermediate transfer belt 19 to detect density of toner picture image which is transferred on the intermediate transfer belt 19 at a plurality of sections in the longitudinal direction. Each value detected by the picture image density detection sensor 51 is informed as it is, and the service life of the intermediate transfer belt 19 is judged based on the detected value. If the service life of the intermediate transfer belt 19 expires, it is informed.

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 using an electrophotographic system such as a copying machine, a printer, a facsimile machine (FAX).

[0002]

2. Description of the Related Art As an image forming apparatus as described above, the surface of a rotating photosensitive member is uniformly charged by a charging means,
Image light of a single color or a plurality of colors is sequentially written therein by an optical writing means to form an electrostatic latent image, and then developing means develops with a toner of a single color or different colors to form a toner image. After the toner images are sequentially transferred to the endless intermediate transfer belt using the medium resistance material by the first transfer means and superposed, the toner images are collectively transferred onto the transfer paper by the second transfer means using the paper transfer roller. (For example, Japanese Patent Laid-Open No. 2-50170)
Reference).

[0003]

However, this type of image forming apparatus has a problem that the resistance value on the end side of the intermediate transfer belt decreases. If there is a portion of the intermediate transfer belt where the resistance value has decreased, a current easily flows to that portion during the transfer process by the paper transfer roller, so the toner image of that portion is not reliably transferred to the transfer paper and an abnormal image Will be.

Here, it is considered that the resistance value of the end portion of the intermediate transfer belt (the portion that directly contacts the paper transfer roller when the transfer paper having the maximum paper-passing size or less is passed) is likely to decrease. This is because during the transfer process by the paper transfer roller, an electric current is more likely to flow in a portion of the intermediate transfer belt which is in direct contact with the paper transfer roller than is in contact with the paper transfer roller having high resistance.

There is no problem as long as the resistance value of the intermediate transfer belt is uniform throughout. However, for example, as shown in FIG. For example, as shown in Table 1, there is a difference in the resistance value between the non-sheet passing portion (end side) of the intermediate transfer belt 19 and the sheet passing portion. When the sheet-sized transfer sheet S2 is passed, the transfer bias by the sheet transfer roller is not evenly applied to the transfer sheet S2, and the contact portion of the transfer sheet S2 with the non-sheet passing portion (shaded lines are applied). (Shown) is blank, resulting in an abnormal image (uneven density).

[0006]

[Table 1]

The present invention has been made in view of the above problems, and an object of the present invention is to prevent the occurrence of an abnormal image due to the uneven resistance value of the intermediate transfer belt in the image forming apparatus as described above. To do.

[0008]

SUMMARY OF THE INVENTION According to the present invention, a rotating photoconductor, a charging means for uniformly charging the surface of the photoconductor, and a surface of the photoconductor charged by the means of a single color or a plurality of colors. An optical writing unit that sequentially writes image light to form an electrostatic latent image, and an electrostatic latent image that is sequentially formed on the surface of the photoconductor by the unit is developed with a toner of a single color or different colors to form a toner image. An endless medium using a medium resistance material that rotates adjacent to the developing means to be formed and is rotated adjacent to the photoconductor and superposes toner images of a single color or a plurality of colors that are sequentially formed on the surface of the photoconductor by the developing means. An intermediate transfer belt, a first transfer unit that transfers the toner image on the photoconductor to the intermediate transfer belt, and a second transfer unit that transfers the toner image on the intermediate transfer belt to a transfer sheet using a paper transfer roller. Image with In forming apparatus, in order to achieve the above object, it is characterized by providing the following means.

According to the invention of claim 1, a plurality of image density detecting means for detecting the density of the toner image transferred to the intermediate transfer belt are provided. According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, a plurality of image density detecting means are provided at intervals in a direction orthogonal to the rotation direction of the intermediate transfer belt (hereinafter referred to as "longitudinal direction"). Is.

According to a third aspect of the present invention, there are provided image density detecting means for detecting the density of the toner image transferred to the intermediate transfer belt, and scanning means for scanning the image density detecting means in the longitudinal direction of the intermediate transfer belt. It is a thing.
According to a fourth aspect of the invention, in the image forming apparatus according to the third aspect,
At the time of scanning by the scanning means, a means for taking in the detection value by the image density detecting means each time the image density detecting means reaches each position corresponding to the usable transfer paper size is provided.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, there is provided means for stopping the rotation of the intermediate transfer belt during scanning by the scanning means.
According to a sixth aspect of the invention, in the image forming apparatus according to any one of the first to fifth aspects, belt life determining means for determining the life of the intermediate transfer belt based on a value detected by the image density detecting means is provided. .

According to a seventh aspect of the invention, in the image forming apparatus according to the sixth aspect, when the belt life determining means determines that the intermediate transfer belt has reached the end of its life, a means for notifying the fact is provided. The invention of claim 8 relates to claim 1
The image forming apparatus of any one of 7 is provided with a means for performing the image density detecting operation using the image density detecting means when the machine main body is powered on.

According to a ninth aspect of the present invention, the image forming apparatus according to any one of the first to seventh aspects is provided with a means for performing an image density detecting operation using the image density detecting means for every fixed number of sheets passed. is there. The invention of claim 10 relates to claims 1 to 7.
In any one of the above image forming apparatuses, a means is provided for performing the image density detecting operation using the image density detecting means for every constant number of transfer sheets of transfer paper having a size not larger than a predetermined size.

According to an eleventh aspect of the invention, in the image forming apparatus according to any one of the first to tenth aspects, prior to the image density detection operation using the image density detection means, the charging means, the optical writing means, and the developing means expose the photosensitive material. A means for forming a uniform halftone image on the surface of the body and transferring the halftone image to the intermediate transfer belt by the first transfer means is provided.

According to the image forming apparatus of the first and second aspects of the invention, since the plurality of image density detecting means are provided, the density of the toner image transferred to the intermediate transfer belt at a plurality of positions (the above-mentioned intermediate transfer belt is used). (Proportional to the resistance value at each location) can be detected. In this case, by providing a plurality of image density detecting means at intervals in the longitudinal direction of the intermediate transfer belt, it is possible to detect the densities at a plurality of positions in the longitudinal direction of the toner image transferred to the intermediate transfer belt.

According to the image forming apparatus of the third to fifth aspects, one image density detecting means is provided and is scanned in the longitudinal direction of the intermediate transfer belt, so that the image is transferred to the intermediate transfer belt in the same manner as described above. It is possible to detect the densities of a plurality of toner images in the longitudinal direction. Further, since only one image density detecting means is required, low cost can be realized.

In this case, at the time of scanning, the detection value by the image density detecting means is fetched each time the image density detecting means reaches each position (required position) corresponding to the usable transfer paper size. Since it is not necessary to take in a large number of densities in the longitudinal direction of the toner image transferred to the intermediate transfer belt, the processing efficiency does not decrease.

Further, by stopping the rotation of the intermediate transfer belt during the scanning, it is possible to easily detect the densities of a plurality of points on the same line (longitudinal direction) of the toner image transferred on the surface thereof. Moreover, since it is not necessary to form a toner image for density detection over a long span in the rotation direction of the intermediate transfer belt, it is possible to reduce the toner consumption amount.

Therefore, according to the image forming apparatus of the first to fifth aspects of the invention, each detected value by the image density detecting means is notified (displayed on the display portion or image-formed on the transfer paper,
Alternatively, it can be displayed on an external device display or the like), so that a user or a service person can know the resistance value unevenness in the longitudinal direction of the intermediate transfer belt, so that the intermediate transfer belt can be replaced before an abnormal image occurs. It will be possible.

According to the image forming apparatus of the sixth and seventh aspects of the invention, the life of the intermediate transfer belt can be determined based on the value detected by the image density detecting means. For example, the detected value may be compared with a predetermined condition, and when the condition is satisfied, it may be determined that the intermediate transfer belt has reached the end of its life. Then, when it is determined that the intermediate transfer belt has reached the end of its life, the user or the service person accurately knows the life of the intermediate transfer belt by notifying that fact,
Since the intermediate transfer belt can be immediately replaced, it is possible to prevent the occurrence of an abnormal image thereafter.

According to the image forming apparatus of the eighth aspect,
Since the image density detecting operation using the image density detecting means is performed when the power of the machine main body is turned on, it is possible to know the degree of deterioration of the intermediate transfer belt (uneven resistance value or life) without wasting time. According to the image forming apparatus of the ninth aspect of the present invention, the image density detecting operation using the image density detecting means is performed for each fixed number of sheets of paper, so that the degree of deterioration of the intermediate transfer belt can be surely grasped.

According to the image forming apparatus of the tenth aspect of the present invention, the image density detecting operation using the image density detecting means is performed every fixed number of transfer sheets of transfer paper having a size not larger than a predetermined size. It is possible to reliably grasp the degree of deterioration of the intermediate transfer belt at an appropriate time without performing the image density detection operation.

According to the image forming apparatus of the eleventh aspect of the present invention, prior to the image density detecting operation using the image density detecting means, a uniform halftone is formed on the surface of the photoconductor by the charging means, the optical writing means and the developing means. Since the image is formed and the halftone image is transferred to the intermediate transfer belt by the first transfer means, it is possible to more accurately grasp the degree of deterioration of the intermediate transfer belt.

[0024]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 3 is a schematic configuration diagram showing a mechanical portion of a digital color copying machine according to an embodiment of the present invention, and FIG. 4 is a partially enlarged view around the photosensitive drum and the intermediate transfer belt.

The color scanner 1 illuminates the lower surface (color image) of the original 3 with the illumination lamp 4 and reflects the reflected light through the mirrors 5a, 5b, 5c and the lens 6 to CC.
By forming an image on the color line sensor 7 composed of D, the color image of the original 3 is converted into three primary colors R (red) and G.
It is decomposed into (green) and B (blue), read, and output as R, G, and B image data (electrical signals).

Then, the R, G, B image data is subjected to color conversion processing in the image processing section, and C of the three primary colors of the subtractive method is applied.
(Cyan), M (magenta), Y (yellow), and K (black) image data are obtained, temporarily stored in the image memory, read out, and output to the color printer 2 to obtain C, M, Y, and K toners. An image is formed and overlaid to form a full color image.

The color printer 2 is provided with a photosensitive drum 9 inside, and a cleaning unit 10, a discharging lamp 11, a charging charger 12, a potential sensor 13 and K are provided around the photosensitive drum 9.
Developing device 14, C developing device 15, M developing device 16, Y developing device 1
7, a development density pattern detector 18, an endless intermediate transfer belt 19 using a medium resistance material, and the like are arranged.

In order to develop the electrostatic latent image, each of the developing devices 14 to 17 develops sleeves 14a to 17a which rotate so as to bring the toner into contact with the photosensitive drum 9, and developing paddles 14b to 17b which scoop and agitate the toner. And toner concentration detection sensors 14c to 17c and the like. In this embodiment, K, C, M, and Y represent the order of writing and development (color image forming order) by the laser light.

When the copy operation is started, the color scanner 1 converts the color image of the original 3 into R (red), G (green),
The image is separated into B (blue) and read, and the R, G, B image data is converted into K, C, M, Y image data and output to the color printer 2. On the other hand, in the color printer 2, the photosensitive drum 9 is rotated in the arrow A direction, and the surface thereof is uniformly charged by the charging charger 12.

Further, the color printer 2 causes the laser writing unit 8 to generate a corresponding laser beam in accordance with the K image data first sent from the color scanner 1, and writes it on the charged surface of the photosensitive drum 9. Form an electrostatic latent image. The tip of the electrostatic latent image (K latent image) is
When the developing position of the K developing device 14 is reached, the K latent image begins to be developed with the K toner by the rotating developing sleeve 14a, and when the rear end portion of the K latent image passes the developing position, the K developing ends and A toner image is formed.

Then, the K toner image on the photosensitive drum 9 is transferred onto the intermediate transfer belt 19 which is rotated adjacent to the photosensitive drum 9. This intermediate transfer is performed by applying a predetermined bias voltage to the intermediate transfer roller 20 when the photosensitive drum 9 and the intermediate transfer belt 19 contact each other. After that, the residual toner on the photoconductor drum 9 is removed by the cleaning unit 10, the charge is removed by the charge removal lamp 11, and then the charging by the charging charger 12 is started again. Writing by the laser light, development, intermediate transfer,
Repeat the cleaning and subsequent cycle.

As a result, the K, C, M, and Y toner images sequentially formed on the photosensitive drum 9 are sequentially aligned and transferred onto the intermediate transfer belt 19 to transfer an intermediate transfer image of four colors. (Toner image) is formed, and it is collectively transferred onto a transfer paper. Therefore, the intermediate transfer belt 1
When the K step of forming the K toner image on the image forming device 9 is completed, the process proceeds to the C step of forming the C toner image on the intermediate transfer belt 19, but the front end of the C toner image and the K image on the intermediate transfer belt 19 are formed. Make sure that the leading edge of the toner image matches
The timing of starting writing by the laser beam for the C latent image by the laser writing unit 8 is adjusted.

Similarly, the M step and the Y step are performed,
An intermediate transfer image of four colors is formed on the intermediate transfer belt 19. However, the image forming order is not limited to K, C, M, and Y, and the image forming order is predetermined according to the characteristics of the toner and the finishing effect of the color image finally formed on the transfer paper. To be done. The intermediate transfer belt 19 is stretched around an intermediate transfer roller 20, a drive roller 21, and a driven roller group, and is rotated in the direction of arrow B by a drive motor (not shown).

The belt cleaner 22 is a brush roller 22.
a, rubber blade 22b, and contact / separation mechanism 2 from the belt
2c and the like, which is in contact with the intermediate transfer belt 19 before the first intermediate transfer of the K toner image, but is separated from the belt surface by the contact / separation mechanism 22c when the intermediate transfer is started.

The paper transfer unit 23 includes a paper transfer roller 23.
a, a roller cleaning blade 23b, and a mechanism 23c for contacting and separating from the belt. The paper transfer roller 23a is normally separated from the intermediate transfer belt 19. However, when the four-color superposed intermediate transfer images formed on the intermediate transfer belt 19 are collectively transferred onto the transfer paper, the transfer paper 24a is timed. Is pressed against the intermediate transfer belt 19 and a predetermined bias voltage is applied to the roller 23a to transfer the intermediate transfer image onto the transfer paper 24.

Incidentally, the transfer paper 24 is a paper feed roller 25.
And the registration roller pair 26, the intermediate transfer belt 1
The four-color superimposing intermediate transfer image of No. 9 is fed at the timing when the front end portion reaches the transfer position. When the four-color superimposed intermediate transfer image (toner image) starts to be transferred to the transfer paper, the belt cleaner 22 contacts the intermediate transfer belt 19 that has finished the paper transfer by the contact / separation mechanism 22c, and the brush roller 22a and the rubber blade 22b are connected to each other. Cleaning is performed by collecting the remaining toner by.

Here, the operation of forming an intermediate transfer image of four-color superimposition on the intermediate transfer belt (hereinafter also simply referred to as "belt") 19 will be described in a little more detail. 1
The following three methods are conceivable as the operation after the intermediate transfer of the K toner image of the color is completed up to the trailing edge. One of these methods or a point of the copy speed depending on the transfer paper size (copy size), etc. The most efficient method is combined and operated.

(1) Constant-speed forward movement method Even after the intermediate transfer of the K toner image, the arrow mark B is kept at the constant speed.
Continue to rotate (forward) in the direction. When the front end portion of the K intermediate transfer image on the belt 19 reaches the intermediate transfer position where it comes into contact with the photosensitive drum 9 again, the front end portion of the next C toner image on the photosensitive drum 9 will be exactly at that position. In addition, the image is formed with a timing. Therefore, the C toner image is intermediately transferred onto the belt 19 while being accurately aligned with the K intermediate transfer image.

After that, similarly, M and Y steps are performed to obtain a full-color four-color superimposed intermediate transfer image. Subsequent to the Y process for the fourth color, the intermediate transfer images of the four colors superimposed on the belt 19 are collectively transferred onto the transfer paper 24 while moving forward at a constant speed.

(2) Skip forward movement method After the intermediate transfer of the K toner image is completed, the K toner image is separated from the photosensitive drum 9 and is skipped at a high speed for a predetermined distance in the forward movement direction, and then returned to the initial forward movement speed. Then, the belt 19 is brought into contact with the photosensitive drum 9 again. The subsequent steps are the same as those of the constant speed forward method.

(3) Reciprocation When the intermediate transfer of the K toner image is completed, the toner image is separated from the photosensitive drum 9, and the forward movement is temporarily stopped, and at the same time, it is returned at a high speed in the opposite direction (direction of arrow C). The front end portion of the K intermediate transfer image on the belt 19 passes through the intermediate transfer position and further moves by a preset distance, and then is stopped and put in a standby state.

Next, when the front end portion of the C toner image on the photosensitive drum 9 reaches the intermediate transfer position, K on the belt 19 is reached.
The belt 19 is restarted at a constant speed in the forward direction (arrow B direction) at the same timing so that the front ends of the toner images coincide with each other, and the belt 19 is again brought into contact with the photosensitive drum 9. Therefore, the C toner image is intermediately transferred while being accurately aligned with the K intermediate transfer image.

After that, the M and Y processes are similarly performed while repeating the quick return, and a full-color four-color superimposing intermediate transfer image is obtained. Is the same as the constant speed forward method.

After that, the transfer paper on which the intermediate transfer images of four colors are transferred together is transferred from the intermediate transfer belt 19 to the fixing unit 28 by the transfer belt 27, and the fixing roller 28a and the pressure roller controlled at a predetermined temperature are pressed. With 28b, the toner image is fused under pressure and fixed, and is carried out to the copy tray 29 to obtain a full-color copy.

By the way, at the time of repeat copying for obtaining a plurality of copies from the same original, the color scanner 1 operates only for the first original, and the stored color image data forms an image on the photosensitive drum 9. Is the first Y
Following the (fourth color) process, the process proceeds to the second K (first color) process at a predetermined timing. In addition, the intermediate transfer belt 19
Follows the batch transfer of the first four-color superimposing intermediate transfer image onto the transfer sheet, and then the second K toner image is intermediately transferred to the area whose surface is cleaned by the belt cleaner 22. . After that, the operation is the same as that of the first sheet. The third and subsequent sheets are similar to the second sheet.

The transfer sheet cassettes 30 to 33 each store transfer sheets of various sizes, and the transfer sheet cassettes 30 to 33 store timings from the cassettes that store transfer sheets of a size designated by an operation signal from an operation unit (not shown). It is fed to the pair of registration rollers 26. Reference numeral 34 is a manual paper feed tray for OHP paper or thick paper.

In this digital color copying machine, as shown in FIG. 1, for example, a plurality of image density detection sensors 51 for detecting the density (toner amount) of the toner image transferred onto the intermediate transfer belt 19 are provided. Are provided at intervals in the longitudinal direction (direction orthogonal to the rotation direction). Here, the maximum sheet-passable size is A3 vertical, and two image density detection sensors 51 are provided so as to face the inner and outer surfaces of the A4 vertical range in the longitudinal direction of the intermediate transfer belt 19.

Alternatively, for example, as shown in FIG. 2, one image density detection sensor 51 may be provided so as to be capable of scanning (moving) in the longitudinal direction of the intermediate transfer belt 19. The image density detection operation using the image density detection sensor 51 will be described in detail later.

In the above, the case of the copy mode for obtaining four full colors has been described, but in the case of the three-color copy mode or the two-color copy mode, the same operation is performed for the designated color and the number of colors. In the single-color copy mode, only the developing device of the designated color is operated until the predetermined number of sheets are finished, and the intermediate transfer belt 19 is in contact with the photosensitive drum 9 in the arrow B direction (forward direction). The belt cleaner 22 is driven at a constant speed and operates while the belt cleaner 22 is still in contact with the intermediate transfer belt 19.

FIG. 5 is a block diagram showing the control system of this digital copying machine. The control section of this digital copying machine
A system controller 61, a scanner controller 62, an image processor 63, a laser driver 64, an intermediate transfer belt controller 65,
It is composed of an AC load control unit 66 and the like. The system control unit 61 centrally controls the entire digital copying machine.

The scanner control unit 62 includes a scanner motor 7
Drive control of No. 1 and image reading control by the color line sensor 7, and the read image data of R, G, B and a signal indicating the reading timing are supplied to the image processing unit 6.
Send to 3. The image processing unit 63 performs color conversion processing on the R, G, and B image data to obtain K, which is the three primary colors of the subtractive color method.
After the C, M, and Y image data are obtained and once stored in the image memory, the image data of each color are sequentially read out and sent to the laser drive unit 64.

The laser driving unit 64 includes a synchronization detection sensor 72.
The laser diode 68 in the laser writing unit 8 shown in FIG. 3 is driven to be modulated (ON / OFF) according to the synchronization detection signal from the image processing unit 63 and the image data of each color from the image processing unit 63, and the image is output from the laser diode 68. The laser light modulated according to the data is generated. Sync detection sensor 72
Detects the laser light reflected by a polygon mirror (not shown) in the laser writing unit 8 outside the image forming area before the start of image formation in order to make the image forming start position on the photosensitive drum 9 constant. Output the sync detection signal.

The polygon motor 73 has a system controller 6
The polygon mirror is rotated by rotating at the number of rotations corresponding to the drive signal from 1. The intermediate transfer belt control unit 65 turns on the belt drive motor 74 according to the drive signal from the system control unit 61 and the timing signal from the mark sensor 50.
The rotation of the intermediate transfer belt 19 is set to N to start the rotation, or the belt drive motor 74 is turned off at a predetermined timing to stop the rotation of the intermediate transfer belt 19.

The AC load control unit 66 is the system control unit 6
The fixing roller 28 shown in FIG.
The energization to the AC load 75 including the heater built in a is controlled. The copy process device 76 includes the charger 12, the developing devices 14 to 17, the paper transfer unit 23, etc., and is driven according to a timing signal from the system control unit 61.

The sequence device 77 is various motors other than the scanner motor 71, the polygon motor 73, and the belt drive motor 74, solenoids, clutches, etc., which are driven in response to a timing signal from the system controller 61. The operation unit 78 includes a display device that displays the display information from the system control unit 61 and a key that inputs various information.

The sensors and switches 79 are various sensors and switches except the color line sensor 7, the synchronization detection sensor 72, the mark sensor 50, and the image density detection sensor 51. The sensor movement motor 52 is used when one image density detection sensor 51 is provided so as to be capable of scanning (moving) in the longitudinal direction of the intermediate transfer belt 19 as shown in FIG. 2, but as shown in FIG. Multiple image density detection sensors 5
Not used when 1s are spaced apart.

Next, the control according to the present invention by the system controller 61 will be described. The system control unit 61
When a plurality of image density detection sensors 51 are arranged at intervals as shown in FIG. 1, the charger 12, the laser writing unit 8, the developing device (K developing device 14, C developing device 15, M developing device 1
6, or Y developing device 17) forms a predetermined toner image on the surface of the photosensitive drum 9, and transfers the toner image to the intermediate transfer belt 19 by the paper transfer unit 23 using the paper transfer roller 23a. An image density detection operation is performed in which the image density detection sensors 51 detect the densities at a plurality of points in the longitudinal direction, and the detected values are displayed on the display of the operation unit 78.

Alternatively, as shown in FIG. 2, when one image density detection sensor 51 is provided so that it can be scanned in the longitudinal direction of the intermediate transfer belt 19 by a drive unit including a sensor movement motor 52, a predetermined image density detection sensor 51 is provided. A predetermined toner image is formed on the surface of the photoconductor drum 9 by the charging charger 12, the laser writing unit 8, and the developing device at a timing, and the toner image is formed by the paper transfer unit 23 using the paper transfer roller 23a. After the transfer, the image density detection sensor 51 is scanned in the longitudinal direction (at this time, the rotation of the intermediate transfer belt 19 is stopped), and the image density detection sensor 51 has a sheet-passable size (usable transfer paper). Each position according to size), eg A
The image density detection operation of fetching the detection value by the image density detection sensor 51 is performed every time a required position is reached, such as a position corresponding to 4 vertical, B4 vertical, A5 vertical, A5 horizontal, B5 vertical, and B5 horizontal. Each detected value is displayed on the display of the operation unit 78.

Therefore, the user or the service person can check the displayed content of the display of the operation unit 78, that is, the toner concentration detection values at a plurality of positions in the longitudinal direction of the intermediate transfer belt 19 to determine the toner density in the longitudinal direction of the intermediate transfer belt 19. Since the unevenness of the resistance value can be known, it becomes possible to replace the intermediate transfer belt 19 with a new one before an abnormal image occurs.

When the image density detection sensor 51 is scanned to detect the image density at a plurality of positions in the longitudinal direction of the toner image transferred to the intermediate transfer belt 19, the following (1) to (4) are shown. The effect is also obtained. (1) Since only one image density detection sensor 51 is required, low cost can be realized.

(2) During scanning of the image density detection sensor 51, the detected value of the image density detection sensor 51 is fetched each time the image density detection sensor 51 reaches each position corresponding to the usable transfer paper size. That is, since it is not necessary to take in a large number of detection values by the image density detection sensor 51, the processing efficiency does not decrease. (3) Since the intermediate transfer belt 19 is stopped during the scanning of the image density detection sensor 51, it is possible to easily detect the densities of a plurality of points on the same line (longitudinal direction) of the toner image transferred to the intermediate transfer belt 19. it can.

(4) Since the intermediate transfer belt 19 is stopped during the scanning of the image density detecting sensor 51, the amount of toner consumption can be reduced. That is, when detecting the densities of the toner image transferred to the intermediate transfer belt 19 at a plurality of positions in the longitudinal direction, the time required for the scanning operation of the image density detection sensor 51 and the process of fetching the detection value by the image density detection sensor 51. Intermediate transfer belt 1
When 9 rotates, the density detection range of the toner image transferred on the surface (rotation direction of the intermediate transfer belt 19) becomes wide. Therefore, by stopping the intermediate transfer belt 19 during the scan, the detection density range can be narrowed, and it is not necessary to form a toner image over a long span in the rotation direction of the intermediate transfer belt 19. The toner consumption can be reduced.

The detection values of the image density detection sensor 51 can be formed on transfer paper by the color printer 2 or displayed on a display of an external device. Further, the life of the intermediate transfer belt 19 can be determined based on each detection value of the image density detection sensor 51.

Here, each detected value is checked against a predetermined condition, and when the condition is satisfied, that is, when the difference (density difference) between the detected values exceeds a predetermined reference value. First, it may be determined that the intermediate transfer belt 19 has reached the end of its life. This is because an abnormal image may occur when a density difference exceeding the reference value occurs.

For example, as shown in FIG. 6, the detected values (sensor output) by the image density detection sensors 51 inside and outside the position corresponding to the A4 length (transfer paper size) on the surface (toner image) of the intermediate transfer belt 19. Value) is very different,
Since the difference is about 0.5 (V), the intermediate transfer belt 1
The reference value for determining whether 9 has reached the end of life is 0.
In the case of 4 (V), it is determined that the intermediate transfer belt 19 has reached the end of its life.

When it is determined that the intermediate transfer belt 19 has reached the end of its life, the fact is notified (displayed on the display of the operation unit 78, image formation on the transfer paper by the color printer 2, external device). Display on the display), the user or service person can know the life of the intermediate transfer belt 19 accurately and can immediately replace the intermediate transfer belt 19, so that the occurrence of abnormal images thereafter can be prevented. be able to. In this case, it is not necessary to notify each detection value by the image density detection sensor 51.

Further, the image density detecting operation using the image density detecting sensor 51 can be performed when the power of the machine body is turned on. By doing so, without wasting time,
The degree of deterioration of the intermediate transfer belt 19 (uneven resistance value or life) can be known. Alternatively, the image density detection operation using the image density detection sensor 51 can be performed every fixed number of sheets passed. As a result, even if the digital copying machine is left for a long period of time with the power of the machine main body turned on, it is possible to reliably grasp the degree of deterioration of the intermediate transfer belt 19.

Alternatively, the image density detecting operation using the image density detecting sensor 51 can be performed every time a fixed number of transfer sheets having a size smaller than a predetermined size are passed. For example, assuming that the maximum paper-passage size of the machine is A3, resistance unevenness does not occur on the intermediate transfer belt 19 as long as the A3-size transfer paper is being passed. Therefore, the above-described image density detection operation is performed for every fixed number of transfer sheets of less than A3. As a result, it is possible to reliably grasp the degree of deterioration of the intermediate transfer belt 19 at an appropriate time, without wastefully performing the image density detection operation.

Further, prior to the image density detecting operation using the image density detecting sensor 51, the charger 12, the laser writing unit 8, the developing device (K developing device 14, C developing device 1).
5, M developing device 16 or Y developing device 17) to form a uniform halftone image on the surface of the photosensitive drum 9,
The halftone image can also be transferred to the intermediate transfer belt 19 by the paper transfer unit 23 using the paper transfer roller 23a, and then the deterioration degree of the intermediate transfer belt 19 can be grasped more accurately.

Although the embodiment in which the present invention is applied to the digital color copying machine using the intermediate transfer belt has been described above, the present invention is not limited to this, and other copying machines or laser printers using the intermediate transfer drum etc. The present invention can be applied to various image forming apparatuses.

[0071]

As described above, according to the image forming apparatus of the present invention, it is possible to avoid the occurrence of an abnormal image due to the uneven resistance value of the intermediate transfer belt.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a positional relationship between an intermediate transfer belt 19 and a plurality of image density detection sensors 51 shown in FIG.

FIG. 2 is a perspective view showing an example of the positional relationship between the intermediate transfer belt 19 and one image density detection sensor 51.

FIG. 3 is a schematic configuration diagram showing a mechanical portion of a digital color copying machine according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating a photosensitive drum 9 and an intermediate transfer belt 19 of FIG.
FIG.

5 is a block diagram showing a control system of the digital copying machine of FIG.

FIG. 6 shows a relationship between a position corresponding to a plurality of transfer paper sizes on the surface (toner image) of the intermediate transfer belt 19 shown in FIG. 1 or 2 and a detection value (sensor output value) by the image density detection sensor 51. It is a diagram showing an example.

FIG. 7 shows an example of a relationship between a transfer sheet S1 having a size (A4 portrait) or smaller and a non-sheet passing portion (end portion side) of the intermediate transfer belt 19 and a sheet passing portion in a conventional image forming apparatus. It is a perspective view.

FIG. 8 shows a problem when a transfer sheet S2 having a maximum sheet-passing size is passed when there is a difference in resistance between the non-sheet-passing portion and the paper-passing portion of the intermediate transfer belt 19 shown in FIG. It is a figure for explaining.

[Explanation of symbols]

 1: Color Scanner 2: Color Printer 8: Laser Writing Unit 9: Photosensitive Drum 12: Charging Charger 14: K Developing Device 15: C Developing Device 16: M Developing Device 17: Y Developing Device 19: Intermediate Transfer Belt 23: Paper transfer unit 23a: Paper transfer roller 51: Image density detection sensor 52: Sensor movement motor 61: System control unit 65: Intermediate transfer belt control unit 74: Belt drive motor 78: Operation unit

Claims (11)

[Claims] 1. A rotating photoconductor, charging means for uniformly charging the surface of the photoconductor, and image data of a single color or a plurality of colors sequentially written on the surface of the photoconductor charged by the means. An optical writing unit for forming an electrostatic latent image, and a developing unit for developing the electrostatic latent image sequentially formed on the surface of the photoconductor by the unit with toner of a single color or different colors to form a toner image. An endless intermediate transfer using a medium resistance material that rotates adjacent to the photoconductor and holds the toner images of a single color or a plurality of colors sequentially formed on the surface of the photoconductor by the developing means in an overlapping manner. A belt, a first transfer unit that transfers the toner image on the photoconductor to the intermediate transfer belt, and a second transfer unit that transfers the toner image on the intermediate transfer belt to a transfer sheet using a paper transfer roller.
In the image forming apparatus, the image forming apparatus is provided with a plurality of image density detecting means for detecting the density of the toner image transferred to the intermediate transfer belt. 2. The image forming apparatus according to claim 1, wherein
An image forming apparatus, wherein the plurality of image density detecting means are provided at intervals in a direction orthogonal to a rotating direction of the intermediate transfer belt. 3. A rotating photoconductor, charging means for uniformly charging the surface of the photoconductor, and image data of a single color or a plurality of colors sequentially written on the surface of the photoconductor charged by the means. An optical writing unit for forming an electrostatic latent image, and a developing unit for developing the electrostatic latent image sequentially formed on the surface of the photoconductor by the unit with toner of a single color or different colors to form a toner image. An endless intermediate transfer using a medium resistance material that rotates adjacent to the photoconductor and holds the toner images of a single color or a plurality of colors sequentially formed on the surface of the photoconductor by the developing means in an overlapping manner. A belt, a first transfer unit that transfers the toner image on the photoconductor to the intermediate transfer belt, and a second transfer unit that transfers the toner image on the intermediate transfer belt to a transfer sheet using a paper transfer roller.
In the image forming apparatus, the image density detecting unit detects the density of the toner image transferred to the intermediate transfer belt, and the image density detecting unit is orthogonal to the rotating direction of the intermediate transfer belt. An image forming apparatus comprising: a scanning unit configured to scan in a direction. 4. The image forming apparatus according to claim 3, wherein
The image forming apparatus is characterized in that when scanning by the scanning means, means is provided for taking in a detection value by the image density detecting means each time the image density detecting means reaches each position corresponding to a usable transfer paper size. . 5. The image forming apparatus according to claim 4, wherein
An image forming apparatus, comprising means for stopping rotation of the intermediate transfer belt during scanning by the scanning means. 6. The image forming apparatus according to claim 1, further comprising belt life determining means for determining the life of the intermediate transfer belt based on a value detected by the image density detecting means. An image forming apparatus characterized by the above. 7. The image forming apparatus according to claim 6, wherein
An image forming apparatus provided with means for notifying that the intermediate transfer belt has reached the end of its life by the belt life judging means. 8. The image forming apparatus according to claim 1, further comprising means for performing an image density detecting operation using the image density detecting means when the machine main body is powered on. A characteristic image forming apparatus. 9. The image forming apparatus according to claim 1, further comprising means for performing an image density detecting operation using the image density detecting means for every fixed number of sheets passed. A characteristic image forming apparatus. 10. The image forming apparatus according to claim 1, wherein an image density detecting operation using the image density detecting unit is performed for a predetermined number of transfer sheets of a transfer paper having a size equal to or smaller than a predetermined size. An image forming apparatus, characterized in that it is provided with means for carrying out each. 11. The image forming apparatus according to claim 1, wherein the charging means, the optical writing means, and the developing means are used before the image density detecting operation using the image density detecting means. A uniform halftone image is formed on the surface of the photoconductor, and the halftone image is first formed.
An image forming apparatus comprising means for transferring to the intermediate transfer belt by the transfer means.