Belt conveying device, image forming apparatus provided therewith and adjustment method of belt skew controller in belt conveyance device | Patent Number 07416074

A belt conveying device includes: at least three rollers, about which an endless belt to convey an object, is entrained, including an oscillation roller having a rotation shaft, whose one end is fixed and another end is oscillatably supported; a belt detection sensor provided adjacent to a side edge of the belt, which detects presence of the belt; and a belt skew controller which controls the oscillator to oscillate the oscillation roller according to a preset control value in a predetermined range to correct skew. The oscillator moves a rotation center of a movable edge of the oscillation roller along a tangential line of an ellipse having elliptical focuses corresponding to rotation centers of rotation shafts of the two rollers, other than the oscillation roller, positioned respectively in upstream and downstream of and adjacent to the oscillation roller in a belt conveyance direction.

This application is based on Japanese Patent Application Nos. 2006-223436 filed on Aug. 18, 2006, and 2007-164415 filed on Jun. 21, 2007, which are incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

This invention relates to a belt conveying device, image forming apparatus equipped therewith, and adjustment method of belt skew controller in the belt conveying device.

In the belt conveying device, in which an endless belt is entrained about predetermined number of rollers, one of which runs the endless belt as a drive roller, there is a case that what is called, belt skew occurs, which is a phenomenon that a running endless belt moves in the width direction (a direction perpendicular to the belt running direction).

In the image forming apparatus, such as an inkjet printer for forming an image onto a recording medium, which is closely contacted with the endless belt as an object to be conveyed, and onto which an image is formed by jetting ink drops of respective colors onto the recording medium while the recording medium is conveyed, this belt skew phenomenon allows the recording medium to meander and causes relative position deviations of respective color images, which forms an inferior image.

Once an abnormal situation of the belt skew occurs, there is a problem that the endless belt meanders in one direction, comes into contact with the frame holding rollers and destroys the rollers.

Thus, in a past, unexamined Japanese Patent Application No. 09-169449 discloses a belt conveying device having a function for detecting and controlling the belt skew to correct the belt skew by detecting at least two values from the group of a belt skew amount, a belt skew deviation amount and a belt skew speed and correcting the belt skew. Unexamined Japanese Patent Application No. 10-231041 discloses a belt conveying device having a function for detecting and controlling the belt skew by detecting a belt skew speed and a belt skew position to correct the skew.

In a belt conveying device, in which an endless belt is entrained between a drive roller and a driven roller, one end of the rotation shaft of the driven roller in a longitudinal direction is fixed and the other end is arranged to be capable of oscillating in direction parallel to the conveying direction of the object to be conveyed, the movement direction in the width direction of the endless belt is determined by the inclination of the driven roller, and belt skew is corrected by oscillating the other end of the driven roller in the direction parallel to the conveying direction.

Here, in the belt conveying device, in which a weight roller, other than the drive roller and the driven roller, is provided in order to give a predetermined tension to the endless belt in the lower direction, in the case when the driven roller is oscillated, the weight roller moves in an up and down directions in response to the oscillation amount of the driven roller.

This operation will be described by referring to

FIGS. 15(

FIG. 15(

FIG. 15(

In case when the endless belt 103 shifts in the left direction in

FIG. 15(

In this case, since the weight roller 102, normally, moves in the direction for relieving the tension of the endless belt 103, the left side in

FIG. 15(

FIG. 15(

However, in the case when dirt or dust of the belt adhered onto the internal surface of the endless belt 103 is adhered onto the drive roller 100 and the friction coefficient of the drive roller 100 decreases thereby, even though the driven roller 101 is controlled with the same control value, the shift direction of the endless belt 103 is reversed.

This will be illustrated in

FIG. 16

FIG. 16

As illustrated in

FIG. 16

FIG. 15(

As described above, in the case the situation becomes to the state that the friction coefficient of the drive roller 100 decreases, there has been a problem that when detecting the belt movement amount of the endless bet 103 and oscillating the driven roller 101 based on the predetermined control value as it has been, the endless belt 103 moves in the opposite direction to that for which it was intended to originally correct.

SUMMARY OF THE INVENTION

It is therefore, an object of the present invention to provide a belt conveying device and an image forming apparatus therewith having a simple structure, which are capable of stabilizing the control of endless belt skew without depending on the friction coefficient of a drive roller.

Another object of this invention is to provide an adjustment method of a skew controller in the belt conveying device, which is capable of simply correcting a deviation amount of the center value of the control range, into which the skew of the endless belt is controlled.

Still another object will become clear in following embodiments.

An object described above will be attained by the following embodiments.

According to one embodiment of the present invention, a belt conveying device including, an endless belt capable of conveying an object to be conveyed, at least three rollers about which the endless belt is entrained for driving the endless belt, the three rollers including an oscillation roller having a fixed edge, which is one end of a shaft of the oscillation roller supported not to be moved, and a movable edge, which is another end of the shaft supported so as to be freely oscillated, an oscillator for oscillating the oscillation roller by moving the movable edge, a belt detection sensor for detecting a skew in a width direction of the endless belt, the belt detection sensor being arranged adjacent a side edge portion of the endless belt, and a skew controller for moving the movable edge of the oscillation roller for a predetermined distance to correct endless belt skew in the width direction of the endless belt by controlling the oscillator by using a preset control value in a predetermined range, wherein the oscillator moves a rotation center of the movable edge of the oscillation roller along a tangential line of an ellipse having elliptical focuses corresponding to rotation centers of rotation shafts of two rollers, other than the oscillation roller, which are positioned respectively in upstream and downstream of and adjacent to the oscillation roller in a conveyance direction of the endless belt.

According to another embodiment of the present invention, an adjustment method of a skew controller of a belt conveying device including, an endless belt capable of conveying an object to be conveyed, at least three rollers about which the endless belt is entrained for driving the endless belt, the rollers including an oscillation roller having a fixed edge, which is one end of a shaft of the oscillation roller supported not to be moved, and a movable edge, which is another end of the shaft supported so as to be freely oscillated, an oscillator for oscillating the oscillation roller by moving the movable edge of the oscillation roller, a belt detection sensor for detecting skew in a width direction of the endless belt, the belt detection sensor being set adjacent a side edge section of the endless belt, and a skew controller for moving the movable edge of the oscillation roller for a predetermined distance to correct skew in the width direction of the endless belt by controlling the oscillator by using a preset control value in a predetermined range, the adjustment method of the skew controller including the steps of:

providing a belt end measuring member for measuring an edge position in the width direction of the endless belt,

measuring respective positions of the endless belt in the width direction when conveying the endless belt for predetermined distances after oscillating the oscillation roller for predetermined distances with an upper limit value and a lower limit value of a preset control value in a predetermined range to operate the oscillator,

calculating a deviation amount of a control center value from respective conveyance distances of the endless belt at the upper limit value and the lower limit value of the preset control value and respective movement amounts in the width direction of the endless belt measured by the belt end measuring member, and

correcting a deviation amount of the control center value by using the calculated deviation amount.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention will be described by referring to drawings below.

FIG. 1

FIG. 2

In

FIG. 1

In

FIG. 1

It is preferable that a belt made of glass-cloth, onto which fluorine resin has been coated, structures the endless belt 14. There is no engagement between the endless belt 14 and the drive roller 11 and the driven roller 12 and the weight roller 13. The friction between the smooth rear surface of the endless belt 14 and the smooth outer surfaces of drive roller 11, the driven roller 12 and the weight roller 13 rotates and drives the endless belt 14.

The surface of the endless belt 14 has adhesiveness, which closely contacts with the recording medium P thereon. The recording medium P may be absorbed to the surface of the endless belt 14 by using electro-static absorption system.

With respect to the material of the recording material P, a recording material, which is normally used for an image forming application of the image forming apparatus, for example, paper, textile, plastic film and glass, may be used. The recording material P may be a sheet cut into a predetermined size or a long-rolled sheet continuously unrolled from a spool, onto which sheet is wound in a roll shape.

A belt detection sensor 16 is provided adjacent the side edge of the endless belt 14. The belt detection sensor 16 is to detect the skew of the endless belt 14 by detecting the existence of the endless belt.

FIG. 3

The belt sensor 16 is provided adjacent a side edge section 14a of the endless belt 14, the belt sensor 16 being configured by three optical sensors 16a, 16b and 16c in order to detect the side edge section 14a. In the stable state where the skew of the endless belt 14 does not occur, a left edge sensor 16a is in an OFF state, which does not detect the side edge section 14a of the endless belt 14. A center sensor 16b positions substantially the same position as the side edge portion 14a of the endless belt 14. A right sensor 16c is in an ON state, which detects the endless belt 14.

The endless belt 14 is determined to be shifted to left viewed from the direction opposite to the direction of arrow A in case when the center sensor 16b of the belt sensor 16 is turned ON, and determined to be shifted to right in case when the center sensor 16b of the belt sensor 16 is turned OFF. The endless belt 14 is determined to be largely shifted to left in case when all the sensors 16a-16c are turned ON. The endless belt 14 is determined to be largely shifted to right in case when all sensors 16a-16c are turned OFF. Thus, the existence of the skew occurrence and the shift direction is determined by detecting the existence of the endless belt 14 by using the belt sensor 16.

Since the side edge section of the endless belt 14 is not always a straight line, the belt conveying device is normally arranged to correct the skew of the endless belt 14 by controlling the oscillation of the driven roller 12 so that the left sensor 16a is in a OFF state, the right sensor 16c is in a ON state and the center sensor 16b is in a degree where the center censor 16b periodically repeats the ON state and the OFF state.

As illustrated in

FIG. 12

The outline of the oscillation control for the driven roller 12 in this embodiment will be described here.

FIG. 4

FIG. 5

When oscillation control of this invention is performed, the rotation center “y†of the other end 12b of a rotation shaft of the driven roller 12, which corresponds to the oscillation roller in this invention, moves along a tangential line “OT†of ellipse “O†having elliptical focuses, which respectively correspond to rotation centers “x†and “z†of the other edge of respective rotation shafts of the drive roller 11 and the weight roller 13.

In general, an ellipse is a curve formed by a set of points on a plane where the sum of the distance from any point on the curve to two ellipitical focuses is constant. Thus, assuming that the rotation center “x†on the other end of the drive roller 11 and the rotation center “z†on the other end of the weight roller 13 respectively correspond to the elliptical focuses and the rotation center “y†on the other end of the driven roller 12 is set substantially on the elliptical locus of the ellipse “O†as the deployment relationship among the drive roller 11, the driven roller 12 and the weight roller 13, the sum of the distance between x and y, and the distance between y and z becomes constant as long as the “y†moves along the elliptical locus of the ellipse “O†. Thus, in the case when oscillating the driven roller 12, the rotation center “y†of the of the other end 12b of the driven roller 12 is arranged to move along the elliptical locus of the ellipse “O†, there is no tension difference practically occurs with the endless belt 14.

Thus, when oscillating the other end 12b of the rotation shaft of the driven roller 12 so as to move along the elliptical locus of the ellipse “O†, the movement of the endless belt 14 in the width direction is determined only by the deviation of alignment of the drive roller 11, the driven roller 12 and the weight roller 13. For example, as illustrated in

FIG. 5

Since the actual oscillation amount of the driven roller 12 is + or − (plus or minus) several mm, the movement along the elliptical locus of the ellipse “O†may be considered to be a straight line along the tangential line “OT†of the ellipse “O†.

FIGS. 6 and 7

FIG. 6

FIG. 7

In

FIG. 6

In

FIG. 6

Numeral 173 denotes a cam, which is provided so as to be capable of moving along a guide rail 174 in a C-direction, which is a horizontal direction. The upper surface of the cam 173 forms a cam surface 173a forming a slant surface inclining against the C-direction, which is a movement direction.

The cam surface 173a always contacts with a slide roller 171b provided at the lower edge of the driven roller support plate 171 so as to be capable of rotating. In case when the cam 173 moves in the right direction along the guide rail 174 in

FIG. 6

FIG. 5

The guide rail 172 regulates the direction D, which is the movement direction of the driven roller support plate 171, so as to move substantially on the tangent “OT†of the elliptical locus “O†having elliptical focuses of the rotation center “x†of the drive roller 11 and the rotation center of the weight roller 13 as illustrated in

FIG. 4

An actuator 175 is fixed on the cam 173 via a bearing fixed thereon so as to be capable of rotating. One end of a rotation shaft 176, onto which a worm wheel gear 176a is fixed, is connected to the actuator 175. The worm wheel gear 176a meshes with a worm gear 177a. The worm gear 177a is fixed on a motor shaft 177 of a belt skew correction drive motor 216 (also referred to as a correcting member) provided so as to be perpendicular to the rotation shaft 176.

The belt skew correction drive motor is configured by a stepping motor. The belt skew correction drive motor rotates and drives a worm gear 177a in response to the pulse signals inputted thereto. Based on this operation, the worm wheel gear 176a meshed with the worm gear 177a rotates to rotate the rotation shaft 176. The actuator 175, which is connected to the front edge of the rotation shaft 176, moves back and forth based on the rotational direction of the rotation shaft 176.

The back and forth movement of the actuator 175 reciprocally moves the cam 173, onto which the actuator 175 is fixed, in the C-direction while the cam is guided by the guide rail 174. Based on this mechanism, the driven roller support plate 171 moves in the D-direction along the guide rail 172 while the driven roller plate 171 is guided by the cam surface 173a. As a result, the other end 12b of the driven roller 12 is oscillated.

A home position sensor 178 is provided adjacent the cam 173. The home position sensor 178 is an optical system sensor having a light emitting element 178a for emitting detecting light and a light receiving element 178b for receiving the detecting light. The home position sensor 178 detects the change of direction signals between the detection signals (Low) of the time when a shield plate 179, which is a detected member attached to the cam 173 as one body, shields the detecting light between the emitting element 178a and the light receiving element 178b, and the detection signals (High) at the time of receiving the detecting light when the cam 173 moves and shield plate 179 moves away from a position between the emitting element 178a and the light receiving element 178b. Based on this detection, the home position of the driven roller 12 can be detected.

The home position is a reference point of the control range of the oscillator 17 when oscillating the driven roller 12. The control range is defined by a movement amount of the cam 173 from the home position.

The home position may be defined as an edge portion, at which the detection signal (high) at the time when the shield plate 179 moves away from the point between the emitting element 178a and the light receiving element 178b changes to the detection signal (Low) at the time when the detecting light is shield by the shield plate 179. The home position is set to be a position where the other edge 12b of the driven roller 12 is positioned at a neutral position, which is not oscillated either (+) side or (−) side, and the endless belt 14 can be stably conveyed.

As illustrated in

FIG. 1

The carridge 3 is arranged to be capable of reciprocally moving along a guide rail 4 provided in the width direction of the endless belt 14 by the rotation drive of a primary scanning motor (not shown). The recording heads 2 reciprocally moves in a B-direction, which is the primary scanning direction.

The carridge 3 includes a belt edge position detection sensor 5. As illustrated in

FIG. 9

A linear encoder 6 for detecting the position of the carridge 3 detects position information. The linear encoder 6 is structured by a scale 6a provided parallel to a guide rail 4 and an encoder sensor 6b provided with the carridge 3 as one body. The encoder sensor 6b detects a pulse from the scale 6a as the carridge 3 moves. The position of the carridge 3 can be detected by counting the number of the pulse. Thus, when the belt edge detection sensor 5 detects the side edge portion 14a of the endless belt 14, the position of the side edge portion 14a of the endless belt 14 can be detected by detecting the position of the carridge 3 by detecting the number of pulses of the linear encoder 6.

Next, a schematic structure of the image forming apparatus will be described by using the block diagram illustrated in

FIG. 10

In

FIG. 10

PC 201 has image data. The image data is transmitted to the main body of the image forming apparatus via the I/F section 202. The transmitted image data is processed into a format suitable for image formation at the recording head 2 in the image processing section 204 according to control signal from the controller 207. Since the print timing controller 203 controlled by the control signal from the controller 207, the same as above, outputs control signal at an appropriate timing to the image processing apparatus 204, drive signal is outputted to the recording head 2 from the head drive section 205. The recording head 2 jets ink drops according to the drive signal.

The reciprocal movement along the primary scanning direction of the recording head 2 is conducted by activating the primary scanning motor 210 via the primary scanning drive circuit 209 controlled by the primary scanning servo 208. The rotation amount of the primary scanning motor 210 is detected by a rotary encoder 211, transmitted to the primary scanning servo 208 and controlled by the controller 207. The position information along the primary scanning direction of the recording head 2 moved by the primary scanning motor 210 is transmitted from the linear encoder 6 for detecting the position of the carridege 3 (refer to

FIG. 1

On the other hand, the endless belt 14 included in the belt drive mechanics 217 together with the drive roller 11, the driven roller 12 and the weight roller 13 are driven and rotated by activating the secondary scanning motor 15 (refer to

FIG. 1

Further, the belt edge position detection sensor 5 included in the belt edge position detector 218 detects the existence of the side edge section 14a of the endless belt 14 and outputs the detection signal to the controller 207 while the carridge 3 moves in the primary scanning direction. In the case when the detection signal of the side edger section 14a of the endless belt 14 has been inputted from the belt position detector 218, the controller 207 measures the position of the side edge section 14a of the endless belt 14 based on the position information obtained from the linear encoder 6 at that time.

The belt skew correction motor 216 provided in the oscillator 17 is activated by the control signal through the belt skew correction motor drive circuit 215 controlled by the controller 207. The controller 207 obtains the determination whether there is existence of the movement of the endless belt 14 due to the oscillation of the driven roller 12 when the endless belt 14 moves in the width direction based on the information transmitted from the belt position detector 206 including the belt sensor 16. The controller 207 controls the drive of the belt skew correction motor 216 through the belt skew correction motor drive circuit 215 to correct the skew of the endless belt 14.

The control of the belt skew correction motor 216 by the controller 207 is conducted within a predetermined control value range (Pmin-Pmax), which has been set in advance, the predetermined control value range being in between a control value for moving the endless belt 14 in the right direction (+) in

FIG. 5

FIG. 11

While the endless belt 14 is stably rotating (S1), in case when skew occurs with the endless belt 14, the center sensor 16b of the belt detection sensor 16 is turned ON or OFF. When the center sensor 16b keeps the turn ON state for a predetermined period, it is detected that the endless belt 14 starts moving in a left direction in

FIG. 2

FIG. 6

FIG. 5

After the oscillation operation of the driven roller 12, when the skew of the endless belt 14 has been corrected, the center sensor is turned OFF again. Thus the controller 207 drives the belt skew correction motor 216 via the belt skew correction motor drive circuit 215 so as to gradually return the inclination of the driven roller 12 to the original state (S3).

On the other hand, in the case when the center sensor 16b becomes a situation where the center sensor 16b keeps a turn OFF state for a predetermined period from the stable state, it is detected that the endless belt 14 starts moving in a right direction in

FIG. 2

FIG. 6

FIG. 5

After the oscillation operation of the driven roller 12, when the skew of the endless belt 14 has been corrected, the center sensor 16b is turned ON again. Thus the controller 207 drives the belt skew correction motor 216 via the belt skew correction motor drive circuit 215 so as to gradually return the inclination of the driven roller 12 to the original state (S3).

Since the side edge section of the endless belt 14 is not always a straight line, the center sensor 16b of the belt detection sensor 16 repeats detection and non-detection operations of the side edge portion 14a of the endless belt 14 in a predetermined period. Thus, after gradually having moved the inclination of the driven roller 12 back to the original state, in case when the center sensor 16b has become to a state that the center sensor 16b repeats ON and OFF operations, the controller 207 determines that the endless belt 14 is positioned on substantially neutral position, and controls the oscillation of the driven roller 12 to be stopped.

Since the oscillator 17 moves the rotation center “y†of the other end 12b of the driven roller 12 along the locus “O†of the ellipse having elliptical focuses of the rotation center “x†of the drive roller 11 and the rotation center “z†of the weight roller 13, the oscillation control of the driven roller 12 does not practically generate the tension difference between the drive roller 11 and the driven roller 12 and weight roller 13, about which the endless belt 14 is entrained, and the skew of the endless belt 14 is corrected by only the deviation of alignment of respective rollers. Thus, irrespective to the existence of the friction resistance of the drive roller 11, it is possible to coincide the oscillation direction of the driven roller 12 to the movement direction of the endless belt 14.

FIG. 12

As understood from this graph, even though the friction coefficient μ of the drive roller 11 changes, for example, the friction coefficient μ equals to 0.2 or 0.7, in the case when the same control value is outputted, the movement direction of the endless belt 14 does not change and the relationship between the conveyance amount and the movement amount in the width direction is kept substantially the same state. Thus, it is apparent that according to a belt conveying device 1 of the invention, it becomes possible to stabilize the skew control of the endless belt 14 irrespective to the friction coefficient of the drive roller 11 by applying the oscillator 17.

In order to stabilize the skew correction of the endless belt 14 by the oscillation of the driven roller 12, it is preferable that the center value of the predetermined control range of the oscillator 17 coincides to the neutral position of the endless belt 14. In order to coincide both of them, following operation is necessary. Oscillate the driven roller 12 for respective predetermined distances with the upper limit value and the lower limit value of the control value range. Then obtain the deviation amount between the center value of the control range of the oscillator 17 and the neutral position of the endless belt 14 from the conveyance amount and shift amount in the width direction of the endless belt 14 after oscillating the driven roller 12 for a predetermined distance with the predetermined upper limit value and lower limit value of the control value range of the oscillator 17. Then correct the control center value of the oscillator 17 based on the deviation amount.

This operation will be described referring to the correction process flow illustrated in

FIG. 13

Firstly, set the upper limit value (Pmax) of the range of the control value set in advance to the belt skew correction motor 216 of the oscillator 17 and oscillate the driven roller 12 for the predetermined distance (S10). Then, output the control signal corresponding to the predetermined step number to the secondary scanning motor 15 to convey the endless belt 14 for a predetermined distance in the conveyance direction (S11).

Based on this operation, since the endless belt 14 moves in the width direction by the oscillation operation of the driven roller 12, measure the position of the endless belt 14 in the width direction. The position of the endless belt 14 in the width direction can be measured by the controller 207 by moving the carriage 3 in the width direction, detecting the side edge section 14a of the endless belt 14 by the belt edge position detection sensor 5 and detecting the position of the carriage 3 when detected by a linear encoder 6. The movement amount of the endless belt 14 in the width direction can be measured by measuring the position of the endless belt 14 in the width direction.

Next, the same as above, set the lower limit value the (Pmin) of the range of the control value set in advance to the belt skew correction motor 216. Based on this operation, the driven roller 12 is oscillated to the opposite direction described above for the predetermined distance (S13). Then, convey the endless belt 14 for a predetermined distance in the conveyance direction (S14). Then, measure the position of the moved endless belt 14 in the width direction and measure the movement amount of the endless belt 14 in the width direction (S15).

Based on this operation, for example as illustrated in

FIG. 12

Here, in case when the center value of the control range of the oscillator 17 coincides with the neutral position of the endless belt 14, the relationship between the conveyance amount and the movement amount in the width direction of the endless belt 14 should be symmetric with respect to a horizontal axis in

FIG. 15

FIG. 15

Thus, the controller 207 detects the deviation amount based on the relationship between the respective conveyance amounts and the respective movement amounts of the endless belt 14 at the upper limit value and the lower limit value in the control range and calculates the deviation amount of the control center value of the oscillator 17 based on the detected deviation amount (S16). After that, the control center value of the oscillator 17 is corrected in response to the calculated deviation amount, thereby making to coincide with the neutral position of the endless belt 14 (S17).

Thus, in the case when skew occurs with the endless belt 14, the deviation can be stably corrected in both directions in the width direction by controlling the oscillator 17 by using predetermined control values.

In step S17, it is preferable to change the home position of the driven roller 12 in order to correct the deviation amount of the control center value of the oscillator 17. With respect to the method of changing the home position of the driven roller 12, following methods are listed. (1) To move the position of the home position sensor 178 for detecting the home position of the driven roller 12 along the C-direction in

FIG. 6

FIG. 6

In the case of (1), the home position sensor 178 may be provided so as to be capable of moving along the C-direction. In the case of (2), the shield plate 179 may be provided so as to be capable of moving along C-direction. In the case of (3), the step number may be changed in response to the deviation amount from the home position, for example, in the controller 207.

The adjustment method of a skew controller for correcting the deviation amount of a control center value of the oscillator 17 may be executed when the product is shipped from the factory or at the time of maintenance service by a service person. This adjustment method can be applied to the belt conveying device for correcting skew by shifting an endless belt in the width direction by controlling the inclination of any one of a plurality of rollers, about which the endless belt is entrained, by using a control value within a predetermined range.

In the belt conveying device 1 described above, the endless belt 14 is entrained about three rollers, which are the drive roller 11, the driven roller 12 and the weight roller 13. In this invention, the number of roller, about which the endless belt 14 is entrained is at least three. Thus the number of roller, about which the endless belt 14 is entrained may be equal to or more than four.

FIG. 14

In case when the roller 182 is assumed to be an oscillation roller in four rollers 181, 182, 183 and 184, in order to correct the skew of the endless belt 14, a rotation center “y†of the other end of the rotation shaft of the oscillation roller 182 may be moved along a tangential line “OT†of ellipse “O†having elliptical focuses corresponding to rotation centers “x†and “z†of rotation shafts of respective two rollers 181 and 183, other than the roller 182, adjacent to each other positioned in upstream and downstream with respect to the oscillation roller 182 in a conveyance direction of the endless belt 14.

In case when the number of rollers further increases, the effect of this invention can be obtained by controlling the oscillation roller in the same manner.

Among the rollers, which are equal to or more than three rollers, about which the endless belt 14 is entrained, any one of rollers may be an oscillation roller. However, in case the oscillation roller is the driven roller, the oscillator 17 may be easily set, which is preferable.

Further, it is preferable that the oscillation roller may be a roller, which should be selected from other than two rollers utilized for structuring the platen surface, onto which recording medium P is placed. For example, in

FIG. 14

A belt conveying device of the invention is not limited to the one utilized for the conveyance of the recording medium when recording an image onto the recording medium. For example, a belt conveying device of this invention can be widely applied to a field where skew phenomenon of the endless belt has become problematic in addition to the fixing apparatus for conducting fixing of the recording medium after image formation, and an intermediate transfer apparatus for an electro-photographic printer.

Further, an image forming apparatus of this invention can be widely applied to an image forming apparatus including a belt conveying mechanism for conveying recording medium, such as an inkjet printer, an inkjet textile printing apparatus, an electro-photographic printer and an image exposing apparatus.

According to an embodiment of the present invention, it becomes possible to provide a belt conveying device having a simple structure, which is capable of stabilizing the skew control of the endless belt independent of the friction coefficient of the drive roller and an image forming apparatus therewith.

According to an embodiment of the invention, there is provided an image forming apparatus having a simple structure, which is capable of stabilizing a skew control of an endless belt independent for the friction coefficient of a drive roller.

Further, according to an embodiment of the invention, there is provided an adjustment method of a skew controller of a belt conveying device, which is capable of simply correcting the deviation of the center value of the control range for controlling the skew of the endless belt.