JPH10123794A - Transfer material carrying means, and image forming device provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the position of a transfer material carrying belt with a position detecting sensor in real time by printing a line having density gradient on the entire periphery of the belt. SOLUTION: The line 302 having density gradient is provided on the entire periphery of the belt 301, and the line 302 is detected by a belt position detecting means 303 for detecting the line 302 on the belt 301 along a direction crossing the moving direction of the belt 301. In such a case, the means 303 is constituted of an illuminating means 313 irradiating the belt 301 along the direction crossing the moving the direction of the belt 301 and a CCD(charge coupled element) array 314 sensing reflection light from the line 302 and converting it to an electric signal. The position and the moving direction of the belt 301 are detected by the means 303. Consequently, since the received quantity of light (density) by the sensor reflected from the line 302 on the belt 301 is changed in accordance with the meandering of the belt, the position of the belt 301 is detected by the density.

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 having a transfer material conveying means and forming an image on a transfer material such as paper using a plurality of photosensitive members, such as a color copying machine or a business color copying machine. About.

[0002]

2. Description of the Related Art As a conventional technique, a color copying machine has recently appeared in response to the color orientation of offices. One of the systems of this color copying machine is a four-tandem photoconductor drum tandem system. In this method, four photosensitive drums are arranged in parallel, a toner image is formed on each photosensitive drum using yellow, magenta, cyan, and black toners, and the toner images are sequentially formed on one transfer material. This is a method in which an image is transferred to obtain a color image.

In the four-tandem tandem system, a transfer material placed on a transfer material transport belt comes into contact with four photosensitive members one after another, and a toner image is transferred.

[0004] In the case other than the formation of a color image, for example, when forming only a black image, a toner image is not formed on three drums of yellow, magenta, and cyan, and the toner image is formed by black toner. Is formed and transferred to a transfer material to obtain an image of only black.

As described above, in the image forming apparatus employing the endless belt member for the transfer material conveying mechanism, the occurrence of the deviation and meandering of the belt at the time of driving, which is a defect peculiar to the belt mechanism, is suppressed. Some means will be essential. In other words, the drawbacks such as deviation and meandering during belt driving are caused by the mechanical accuracy of the belt itself, changes in belt characteristics, and the transfer material entering the transfer material transport belt from the transfer material supply mechanism, including the belt drive mechanism. Since it is generated by various external forces such as the vibration of the conveyor belt that occurs, it is impossible to prevent the belt from shifting or meandering without providing any means. Met.

Heretofore, when the belt has been shifted or meandering, the following method has been adopted as a means for correcting these problems.

(A) A method in which the diameter of the roller member holding the endless belt member is made larger at the center portion than at both end portions so that the roller member has a crown shape as a whole.

(B) A guide groove is provided in each roller member,
A method in which a guide rib is provided at a portion on the inner peripheral side of the endless belt member corresponding to the groove.

(C) A method of writing a registration mark on a belt member and correcting the relative positional deviation of the mark by optically feeding back the mark.

(D) A method in which a registration mark is written on a belt member, and the relative position of the belt holding member is changed based on the relative positional deviation of the mark.

(E) A method in which a biasing force is forcibly applied to the belt member to intentionally generate a bias, and the image forming timing is adjusted in accordance with the amount of belt deviation.

Here, as an example, a laser beam printer of a tandem type with four photosensitive drums will be described with reference to FIG.

This printer is provided with four image forming stations as image forming means including a developing device around an electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as a latent image carrier. The image formed on the photosensitive drum formed at each image forming station is transferred to a transfer material on a conveying means which moves and passes adjacent to the photosensitive drum.

As shown in FIG. 6, photosensitive drums 101M, 101C, 101Y and 101K are arranged at image forming stations Pm, Pc, Py and Pk for forming images of magenta, cyan, yellow and black, respectively. Each photosensitive drum is rotatable in the direction of the arrow. Further, each of the photosensitive drums 101M, 101C, 10C
1Y and 101K, chargers 102M and 102M
C, 102Y, 102K and scanning optical devices 103M, 1M
03C, 103Y, 103K and developing device 104M,
104C, 104Y, 104K and cleaner 10
5M, 105C, 105Y, and 105K are sequentially provided along the rotation direction of the photosensitive drum, and a transfer unit 106 is provided below each photosensitive drum. The transfer unit 106 includes a transfer belt 106 a serving as a transfer material conveying unit common to each image forming station and the transfer charger 1.
06M, 106C, 106Y and 106K.

In the above-described printer, the transfer material P supplied from the paper feed cassette 107 serving as the transfer material supply means.
Is transported to each image forming station while being supported on the transfer belt 106a, and the toner images of each color formed on each photosensitive drum are sequentially transferred. When this transfer step is completed, the transfer material P is separated from the transfer belt 106a and is conveyed to a fixing device 108 as a fixing unit by a conveyance belt 109 as a transfer material guide unit, and a full-color image is formed on the transfer material P. .

[0016]

However, the conventional methods for correcting the belt deviation shown in (a) to (e) above have the following problems.

That is, the above-mentioned method (a) is the most widely used correction means, but the endless belt member is distorted by forming the roller member into a crown shape to generate an internal stress difference. Therefore, it is necessary to use a belt made of a material having sufficient elasticity in order to suppress the deviation of the belt.

In addition, since so-called permanent deformation of the belt member due to creep distortion is prevented while utilizing the strain generated in the belt member, for example, when a rubber belt is used, a material having a low rubber hardness and a high elasticity is used. It is necessary to adopt a material whose thickness is set to satisfy the mechanical strength. Therefore, since the thickness of the transfer material transport belt must be increased, the transfer current must be set large, which is not appropriate.

Next, in the above method (b), the bias of the belt member is suppressed by receiving the thrust force generated in the belt member at the end surface of the guide rib. The accuracy of the ribs determines the accuracy of the control of the moving speed of the belt member. However, since it is technically very difficult to attach the guide rib to the belt member on the inner peripheral side with high attachment accuracy, the movement speed of the belt member cannot be controlled with high accuracy, and it is not suitable for mass production. Absent.

In the above method (c), it takes time to perform feedback for adjusting the optical system, so that it is difficult to provide feedback every time an image is formed, and the belt is permanently used. The problem of offset and belt destruction cannot be solved by this method.

Next, the above method (d) is disclosed in
As described in Japanese Patent Application Laid-Open No. 71970/1995, the purpose of the belt is to travel substantially straight in the vicinity of the target position. There was a problem that the direction of the change and the degree of the progress did not follow the change.

Next, the method (e) has many advantages over the methods (a) to (d), and is more practical in terms of belt shift control. However, the above (e) also has the following problems.

First, depending on the environment where the device is placed,
The device body is twisted. Since the torsion also involves torsion of the belt supporting portion, the belt deviates from the deviation control amount set at the time of assembling the apparatus, and the belt moves only in one direction, and eventually breaks.

Secondly, the belt undergoes plastic deformation and the like due to endurance, causing a change in the shift of the belt. As a result, control over time such as destruction that deviates from the shift control amount set at the time of assembly as described above. Problem.

Therefore, according to the present invention, a transfer material transporting belt capable of detecting the belt position in real time by a position detection sensor by printing a line having a density gradient over the entire circumference of the transfer material transporting belt. It is intended to provide a means.

Further, a correction means is provided for the roller which is one of the support members of the belt, and a relational table between the deviation speed of the belt and the correction amount is stored in the memory, and the output value of the position detection sensor is compared with the relational table. Accordingly, it is an object of the present invention to provide a transfer material conveying unit that can quickly set a correction amount and can always control the position of the belt at the same position.

It is another object of the present invention to provide a transfer material conveying means capable of always detecting the position of the belt and correcting the deviation or meandering of the belt in real time, thereby preventing a deviation at the time of toner superposition.

That is, since the sampling time for detecting the belt deviation speed by the timer can be changed, for example,
It is an object of the present invention to provide a transfer material conveying means capable of detecting a deviation speed at the same distance even when a process speed is changed between a full color copy mode and a mono color copy mode.

[0029]

According to the transfer material conveying means of the present invention, a plurality of rollers provided in parallel, and an endless transfer material conveying belt stretched over and stretched over these rollers. And a position detecting means for detecting the position of the transfer material conveying belt, wherein a line having a density gradient is printed on the transfer material conveying belt over the entire circumference of the belt. And

According to the transfer material conveying means of the second aspect,
One of a plurality of rollers on which the transfer material transport belt is stretched is provided with correction means for correcting the deviation of the belt, and a memory for storing a relationship between data detected by the position detection means and a correction amount is provided. And a correction amount is calculated from the data of the position detecting means.

According to the transfer material conveying means of the third aspect,
A plurality of image forming means which are provided in correspondence with the plurality of image carriers which are sequentially arranged, respectively form images on the respective image carriers, and sequentially transport a transfer material to each of the image carriers; 3. An image formed on each image carrier with respect to the transfer material transported by the transfer material transporter according to claim 2 and the transfer material transported by the transfer material transporter. And a plurality of transfer means for transferring each of them.

According to the transfer material conveying means of the fourth aspect,
It is characterized by including a timer that can set a sampling time for detecting the position of the transfer material transport belt.

According to the transfer material conveying means according to the first aspect,
By printing a line having a density gradient over the entire circumference of the transfer material conveying belt, the position of the belt can be detected in real time by the position detection sensor.

According to the transfer material conveying means of the second aspect,
A correction means is provided on a roller which is one of the support members of the belt,
Further, by storing a relational table between the shift speed of the belt and the correction amount in the memory and comparing the output value of the position detection sensor with the relational table, the correction amount can be set quickly, and the position of the belt is always controlled to the same position. be able to.

According to the image forming apparatus of the third aspect, the position of the belt can be always detected, and the deviation and meandering of the belt can be corrected in real time, so that the deviation at the time of toner superposition can be prevented.

According to the image forming apparatus of the present invention, since the sampling time for detecting the belt deviation speed by the timer can be changed, for example, when the process speed is changed between the full color copy mode and the mono color copy mode. However, the offset speed at the same distance can be detected.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG.
1 is a cross-sectional view illustrating a schematic configuration of a color printer according to an embodiment of the present invention. FIG. 2 is a schematic perspective view showing a belt and a belt holding mechanism according to the embodiment of the present invention. FIG. 3 is a diagram for explaining the movement of the correction roller in the apparatus of FIG. FIG. 4 is a diagram showing the relationship between the output of the CCD constituting the belt position detecting means in the apparatus of FIG. 1 and the lines on the belt. FIG. 5 is a block diagram showing a schematic configuration of the control means of the actuator for moving the correction roller in the apparatus shown in FIG.

An embodiment of the present invention will be described with reference to FIG.

FIG. 2 is a schematic sectional view of an apparatus in which the present invention is applied to an electrophotographic color printer. In the present embodiment, first, second, third and fourth four image stations Pa, Pb, Pc and P
The present invention is applicable to an image forming apparatus including one or more arbitrary number of image stations.

A paper feed mechanism 213 is provided on one right side in the main body 210 shown in FIG. 1, and a transfer material discharge port 214 is provided on the opposite side, that is, on the left side in FIG. Further, the fixing device 2
07 is provided. Further, on the lower side of the path from the paper feeding mechanism 213 to the fixing device 207 in the main body 210, a driven roller means, that is, an idler roller 212 is provided in proximity to the paper feeding mechanism 213, and the fixing device 20 is also provided.
7, the driving roller means, that is, the driving roller 211
Are provided, and these rollers 211 and 21 are provided.
A transport belt 208 is stretched between the two.

Below the idler roller 212, there is provided an adjusting roller 209 which comes into contact with the transport belt 208 from the inner peripheral side of the transport belt 208 to freely adjust the tension of the transport belt 208. On the other hand, above the path from the idler roller 212 to the drive roller 211, the first, second, third and fourth image stations Pa are arranged in order from the paper feed mechanism 213 in the vicinity of the transport belt 208. , Pb, Pc and Pd are arranged side by side.

The transport belt 208 is frictionally driven by a drive roller 211 in a direction indicated by an arrow Z in FIG. 2, and carries the transfer material P fed through the paper feed mechanism 213.
The sheet is sequentially conveyed to the above-described image forming stations Pa, Pb, Pc, and Pd.

The paper supply mechanism 213 includes a paper supply cassette 223 detachable from the main body 210, a rotatable paper supply roller 220 provided at a mounting portion of the main body 210 for mounting the paper supply cassette 223, By body 2
Paper feed guide 2 for guiding transfer material P sent into
22, a pair of registration rollers 221 for receiving the transfer material P guided by the paper feed guide 222 and sending it to the idler roller 212 side at a predetermined timing, and a leading end of the transfer material P moving in the paper feed guide 222 And a sensor (not shown) for outputting a predetermined signal when detecting the signal. The paper feed mechanism 213 performs a function of placing the transfer material P on the transport belt 208 from the idler roller 212 side.

The fixing device 207 receives the transferred transfer material P from the drive roller 211 side, and transfers the image material to each image station P.
In a, Pb, Pc, and Pd, the visible images superimposed and transferred on the transfer material P are fixed collectively to form a permanent image. Then, the transfer material P carrying the permanent image is discharged from a transfer material discharge port 214 onto a paper discharge tray 230 detachably attached to the copying machine main body 210.

Each of the image stations Pa, Pb, Pc and Pd has substantially the same configuration, and is a photosensitive drum 201a, 201b, 2 which is driven to rotate in the direction of arrow F shown in FIG.
01c and 201d, and around each photosensitive drum,
Chargers 215a and 215 for uniformly charging the photosensitive drum
b, 215c and 215d, developing devices 203a, 203b and 20 for developing the electrostatic latent image formed on the photosensitive drum
3c and 203d, transfer material dischargers 204a, 204b, 204c and 2 for transferring the developed visual image to the transfer material P
04d, cleaning means 205a, 205b, 205c and 205 for removing toner remaining on the photosensitive drum
d are sequentially arranged in the drum rotation direction.

Each photosensitive drum 201a, 201b,
Above 201c and 201d, an imaging lens 217a,
217b, 217c and 217d and laser beam scanners 216a, 216b, 216c and 216d are provided, respectively.

The developing device 203a contains magenta toner, the developing device 203b contains cyan toner, the developing device 203c contains yellow toner, and the developing device 203
03d contains black toner, respectively. The above laser beam scanners 216a, 216b, 216
c and 216d are a semiconductor laser, a polygon mirror, f
lens, etc., and receives the input of an electric digital image signal and modulates the laser beam corresponding to this signal via the imaging lenses 217a, 217b, 217c and 217d, respectively, to the chargers 215a, 215b, 2
15c and 215d and developing devices 203a, 203b, 2
Between 03c and 203d, the drum surface is exposed by scanning in the drum genera direction.

The laser beam scanner 216a has a pixel signal corresponding to a magenta component image of a color image, the laser beam scanner 216b has a pixel signal corresponding to a cyan component image, and the laser beam scanner 216c has a pixel signal corresponding to a yellow component image. A pixel signal is input to the laser beam scanner 216d, and a pixel signal corresponding to the black component image is input to the laser beam scanner 216d. Further, between the first image forming station Pa and the paper feeding mechanism 213, the paper suction charger 2 is provided.
06, and the attraction charger 206 transfers the transfer material P supplied from the paper feed mechanism 213 to the transport belt 2.
Corona discharge is performed in order to surely adsorb 08.

On the other hand, a static eliminator (not shown) is provided almost directly above the drive roller 211 between the fourth image station Pd and the fixing device 207. An alternating current is applied to separate the attracted transfer material P.

In the color printer having the above structure, a cut sheet is used as the transfer material P, and the transfer material P is sent out from the paper feed cassette 223 and
13, the leading end is detected by the sensor (not shown), and each of the image stations Pa,
Pb, Pc and Pd photosensitive drums 201a, 201b,
201c and 201d start rotating. Drive roller 2
11 is also driven at the same time, and the conveyor belt 208 is
Is driven in the arrow Z direction. The transfer material P is supplied to the sheet feeding guide 22.
2 and is placed on the transport belt 208 and is received on the transport belt 208 by corona discharge from the attraction charger 206.

Further, at a predetermined timing with the drive timing of the registration roller pair 221 as a base point, the photosensitive drum 2
The image forming processes for 01a, 201b, 201c and 201d are sequentially started. That is, the magenta image is formed on the photosensitive drum 201a of the first image station Pa, and the photosensitive drum 201b is formed on the photosensitive drum 201b of the second image station Pb.
, A yellow image is formed on the photosensitive drum 201c of the third image station Pc, and a black image is formed on the photosensitive drum 201d of the fourth image station Pd. The principle of image formation in these image stations Pa, Pb, Pc and Pd is already well known as the Carlson process, and therefore, the description thereof is omitted.

The transfer material P is moved by the movement of the transport belt 208.
Are sequentially passed under the photosensitive drums 201a to 201d of the first to fourth image stations Pa to Pd and conveyed toward the fixing device 207, and are transferred to the transfer dischargers 204a, 204b, 204c and 204c of each image station. 20
By 4d, the visible images of each color formed in each image forming unit are sequentially transferred onto the transfer material P in a superimposed manner, and a color image is synthesized. After passing through the fourth image forming station Pd, the transfer material P is neutralized by the neutralizer (not shown) to which the AC voltage is applied, and is separated from the transport belt 208. The transfer material P separated from the transport belt 208 is sent to the fixing device 207, and after the developed image transferred in the fixing device 207 is fixed, the transfer material P is discharged from the transfer discharge port 214 to the paper discharge tray 230, and thus is transferred. One image forming cycle ends.

Next, the present invention will be described in detail with reference to FIG. 2 showing a detailed structure of a belt and a belt holding mechanism, which is the gist of the present invention.

The drive roller 211 in FIG. 1 corresponds to the drive roller 304 in FIG. 2, and the idler roller 212 in FIG. 1 corresponds to the driven roller 307 in FIG. The adjustment roller 209 in FIG. 1 corresponds to the correction roller 306 in FIG.

Each of the rollers constituting the belt holding mechanism is rotatably supported by a shaft, and the driving roller 304 and the driven roller 307 are arranged in a corresponding relationship, and all are fixed at predetermined positions. A drive motor 308 for rotating the drive roller 304 in the direction of arrow B shown in the figure is connected to the rotation shaft of the drive roller 304. The correction roller 306 corrects a problem such as deviation or meandering of the belt 301. One end of the rotation shaft of the correction roller 306 is provided by a pivot bearing 312, and the other end is provided by a bearing 309. Supported. The bearing 309 is connected to a rod 311 coaxially coupled to an operating shaft of an actuator 310 serving as a variable adjusting means. The operating shaft of the actuator 310 reciprocates along a belt 301 as indicated by X in FIG. By moving, the bearing 309 moves the rod 3
As shown by AA ′ in FIG. 3 together with the correction roller 306 via the reference numeral 11, it is configured to move in a slightly circular arc.

That is, since the pivot roller 312 is fixed to the correction roller 306, the pivot roller 3
The other end side (that is, the bearing 309 side) is moved in an arc in the direction (along the belt 301) as indicated by an arrow AA ′ in FIG. Thus, the rotation center axis of the correction roller 306 can be at an arbitrary angle with respect to the original position of the correction roller 306 in the direction along the belt 301.

In this embodiment, the actuator 31
As 0, a linear stepping motor is used, and the moving amount of the rotation center axis of the correction roller 306 is set as
This can be easily performed by changing the number of pulses of a drive command signal (pulse signal) output to the linear stepping motor.

A line 302 having a density gradient over the entire circumference is provided on the belt 301, and the line 302 is moved with respect to the moving direction of the belt 301.
Line 30 on belt 301 along the direction crossing it
2 is detected by a belt position detecting means 303 for detecting the second position. In the present embodiment, the belt position detecting means 303 is connected to the illuminating means 313 for irradiating the belt 301 in a direction crossing the moving direction of the belt 301 and the line 30.
CCD which detects reflected light from 2 and converts it into electric signal
(Charge-coupled device) It is composed of an array 314.

In the above configuration, the actuator 31
0, the center of rotation of the correction roller 306 is moved from the original position C indicated by the dotted line to the position C 'indicated by the solid line in the moving direction of the belt 301 as shown in FIG. Is the + direction), the correction roller 306
3 is different from the original position, a twist angle occurs between the rollers 301 and the other rollers. Therefore, the winding position of the belt 301 shifts from the position indicated by the broken line to the position indicated by the solid line in FIG. (Indicated by the distance α), the belt 301 is shifted.

Conversely, when the rotation center axis of the correction roller 306 is moved from the original position C indicated by the dotted line in the direction opposite to the moving direction of the belt 301 (this moving direction is referred to as the minus direction),
Similarly, unlike the case where the correction roller 306 is at the original position, a twist angle occurs between the correction roller 306 and the other rollers. Therefore, the winding position of the belt 301 moves from the position shown by the broken line in FIG. (To the right) and the belt 301 is shifted in the opposite direction.

Therefore, if the belt 301 is offset in the + direction, the correction roller 306 is tilted to move the belt 301 in the-direction, and if the belt 301 is offset in the-direction, the correction roller 306 is tilted in the opposite direction to move in the + direction. In other words, the belt 301 can always be driven at the same position, and an accident such as breakage of the belt 301 can be prevented.

The position and the moving direction of the belt 301 are detected by the belt position detecting means 303. FIG. 4 is a diagram showing the line density distribution in the belt width direction and the detection values of the sensor. The amount of light (density) of the sensor reflected from the line 302 on the belt 301 changes according to the deviation of the belt. An accurate position of the belt 301 can be detected from the density (detected value).

For example, the sensor sets the line density from 0 to 25.
Assuming that the detection and input are performed in 256 steps of 5 bits, the line density detection value of the sensor at the belt position (the sensor is located at the center of the line) before the belt is shifted is 128.
If the belt shifts in the direction A in FIG. 4, if the sensor inputs a detection value smaller than 128 bits of the low density portion in FIG. 4, and if the belt shifts in the B direction,
Conversely, the sensor inputs a detection value higher than 128 bits of the high density portion.

Since the position in the line width direction and the detection value of the sensor correspond to each other, if the line width is 25.6 mm, a calculation in which a deviation of 0.1 mm occurs due to a change of 1 bit of the detection value. That is, when the sensor inputs a detection value of 120 bits, it can be seen that a deviation of 0.8 mm occurs in the A direction.

By appropriately setting the time (speed detection time) of the timer shown in FIG. 5, it also serves as a belt shift speed detecting means for detecting the moving direction and the shift speed (shift amount / speed detection time) of the belt 301.

For example, if the process speed during color printing is 5
When 0 mm / sec, the speed detection time is 1 sec, and the belt width and the detected value are the same as above, the sensor is 1 s.
The line density is detected every ec (at intervals of 50 mm on the belt). Now, the detection value becomes 11 after 1 second from 120 bits.
Assuming 7 bits, 0.3m in A direction per second
m, the deviation speed is 0.3 mm in the A direction.
/ Sec.

Further, the process speed 1 in the case of mono color
Even if it is different from the color mode at 00 mm / sec, by setting the speed detection time to 0.5 sec, the offset speed can be detected at 50 mm intervals on the belt as in the color mode.

The correction amount of the correction roller 306 centered on the original position C is stored in advance in the memory of FIG. 5 in relation to the deviation speed and the correction amount, and the deviation and the deviation speed detected from the CCD are stored in advance. Determined by comparison.

In addition, the present invention is not limited to the embodiment described above and shown in the drawings, and it is needless to say that the present invention can be appropriately modified and implemented without departing from the scope of the invention.

[0070]

According to the transfer material conveying means according to the first aspect of the present invention, a line having a density gradient is printed over the entire circumference of the transfer material conveying belt, so that the belt can be detected in real time by the position detection sensor. Can be detected.

According to the transfer material conveying means of the second aspect of the present invention, the correction means is provided on the roller which is one of the belt supports, and the memory has a relational table between the speed of the belt shift and the correction amount. By comparing the output value of the position detection sensor with the relation table, the correction amount can be set quickly,
The position of the belt can always be controlled to the same position.

According to the image forming apparatus of the third aspect of the invention, the position of the belt can always be detected, and the deviation or meandering of the belt can be corrected in real time, so that the deviation at the time of toner superposition can be prevented.

According to the image forming apparatus of the present invention, since the sampling time for detecting the belt deviation speed by the timer can be changed, for example, the process speed is changed between the full color copy mode and the mono color copy mode. In this case, it is possible to detect the deviation speed at the same distance.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a color printer according to an embodiment of the present invention.

FIG. 2 is a schematic perspective view showing a belt and a belt holding mechanism according to one embodiment of the present invention.

FIG. 3 is a view for explaining the movement of a correction roller in the apparatus of FIG. 2;

FIG. 4 is a diagram showing a relationship between an output of a CCD constituting a belt position detecting means in the apparatus of FIG. 1 and a line on a belt.

FIG. 5 is a block diagram showing a schematic configuration of a control means of an actuator for moving a correction roller in the apparatus of FIG. 2;

FIG. 6 is a cross-sectional view showing a schematic configuration of a conventional tandem-type laser beam printer with four photosensitive drums.

[Explanation of symbols]

 201 Printer main body 208 Conveyor belt 210 Copy machine main body 211 Drive roller 212 Idler roller 213 Supply mechanism 301 Belt 302 Line 303 Belt position detecting means 304 Drive roller 307 Followed roller 306 Correction roller 313 Lighting means 314 CCD array

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kazumi Irie Inside Sharp Co., Ltd. 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka

Claims (4)

[Claims] 1. An image forming apparatus comprising: a plurality of rollers provided in parallel; an endless transfer material transport belt stretched over and stretched over these rollers; and a position detecting means for detecting a position of the transfer material transport belt. A transfer material transporting means, wherein a line having a density gradient is printed on the transfer material transport belt over the entire circumference of the belt. 2. A method according to claim 1, wherein one of a plurality of rollers on which the transfer material conveying belt is stretched has a correcting means for correcting a deviation of the belt, and a memory for storing a relationship between data detected by the position detecting means and a correction amount. 2. The transfer material conveying means according to claim 1, wherein the correction amount is calculated from the data and the data of the position detecting means. 3. A plurality of image forming means provided corresponding to a plurality of image carriers sequentially disposed, respectively, for forming images on the respective image carriers, and a plurality of image forming means for each of the image carriers. A transfer material transporting means for sequentially transporting the transfer material, the transfer material transporting means comprising a correcting means for correcting a deviation of the belt on one of a plurality of rollers on which a transfer material transporting belt is stretched; A memory for storing the relationship between the data detected by the detecting means and the correction amount, and calculating the correction amount from the data and the data of the position detecting means; provided for each of the image carriers; An image forming apparatus, comprising: a plurality of transfer units for respectively transferring images formed on the respective image carriers to a transfer material conveyed by the transfer material conveying unit. 4. The image forming apparatus according to claim 3, further comprising a timer capable of setting a sampling time for detecting a position of the transfer material transport belt.