Patent Application
20120001386
1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
In a conventional image forming apparatus such as a copying machine or a printer, a sheet whose one side has undergone image formation in an image forming unit is reversed, and conveyed again to the image forming unit via a reverse conveyance unit to perform image formation on the reverse side (two-sided printing). In such an image forming apparatus, there is a fear, at the time of two-sided printing, of the image formed on the sheet being deviated in the width direction, which is a direction orthogonal to the sheet conveyance direction.
This is due to the fact that, in the case of two-sided printing, the sheet conveyance path to be taken from the sheet feeding before the image formation on the second surface of the sheet is longer as compared with the case of one-sided printing. When the sheet conveyance path is thus long, the influence of minute misalignment of the conveyance rollers, distortion of the guide plate, etc. is added, sometimes resulting in gradual deviation of the sheet in the conveyance width direction.
In view of this, in the prior art, there is provided in the sheet conveyance path a detection sensor configured to detect a side edge position in the width direction of the sheet to detect the deviation amount in the width direction of the sheet. And, according to the deviation amount of the side edge position of the sheet thus detected by the detection sensor, the position of the latent image to be written to the photosensitive drum in the image forming unit is shifted, whereby the sheet is matched with the image forming position.
On the other hand, in recent image forming apparatuses, there is a demand for a further improvement in terms of user operability, in particular, of jamming handling property. In view of this, in more and more image forming apparatuses, the sheet conveyance apparatus is made detachable with respect to the image forming apparatus main body, and, when jamming has occurred, the sheet conveyance apparatus is drawn out to the front face, the rear face, or a side face of the apparatus main body, whereby the conveyance path is exposed to the exterior, thereby facilitating the jamming handling processing.
In such a detachable sheet conveyance apparatus, a detection sensor is arranged in the sheet conveyance path in the apparatus, and the position of a side edge position of the sheet is detected by this detection sensor. However, when the sheet conveyance apparatus is attached to the image forming apparatus main body, due to play between itself and the image forming apparatus main body and variation in component dimension, the sheet conveyance apparatus may be deviated in the sheet conveyance direction. In such cases, the detection sensor is also deviated with respect to the image forming apparatus main body, resulting in positional deviation between the detection sensor and the image forming unit.
In view of this, in a conventional image forming apparatus, the detection sensor is provided to be movable in the width direction; when detecting a sheet side edge position after the attachment of the sheet conveyance apparatus, the detection sensor is first moved toward the image forming apparatus main body to detect the position of a reference member provided in the image forming apparatus main body. And, after the position of the reference member is thus detected, the detection sensor is moved toward the sheet, whereby the sheet side edge position is detected (See Japanese Patent Application Laid-Open No. 2002-53246). Based on the movement amount of the detection sensor since the detection of the position of the reference member on the image forming apparatus main body side till the detection of the sheet side edge position, it is possible to obtain the actual sheet side edge position, in another words, the deviation amount of the sheet side edge position from the reference position. And, by adjusting the image writing position according to the deviation amount thus obtained, it is possible to correct the image forming position on the sheet.
As described above, in the conventional sheet conveyance apparatus and image forming apparatus as discussed in Japanese Patent Application Laid-Open No. 2002-53246, when detecting a sheet side edge position, the detection unit is first moved toward the reference member to detect the reference member. After this, to detect the side edge of the sheet, the detection unit is moved in the width direction of the sheet. However, when moving the sheet side end for detection after the movement of the detection unit toward the reference member to detect the reference member, it is necessary to secure a long movement distance for the detection unit for a case in which the sheet whose side edge position is to be detected is a sheet of a small width size. This involves a large-sized movement mechanism for moving the detection unit, resulting in an increase in the size of the apparatus.
The present invention is directed to an image forming apparatus of a small size and capable of detecting a sheet side edge position. Further, the present invention is directed to an apparatus of small in size and high accuracy capable of detecting a sheet side edge position.
According to an aspect of the present invention, an image forming apparatus includes: an image forming apparatus main body having an image forming unit configured to form an image on a sheet; and a sheet conveyance apparatus provided to be detachable with respect to the image forming apparatus main body and configured to convey the sheet to the image forming unit, wherein the sheet conveyance apparatus includes a sheet conveyance path through which the sheet passes, and a detection unit including a light emitting unit and a light receiving unit, opposed to the light emitting unit across the sheet conveyance path therebetween, configured to receive light from the light emitting unit, wherein the detection unit is configured to detect a reference and to detect an edge position of the conveyed sheet in a width direction of the sheet orthogonal to the sheet conveyance direction, the image forming apparatus further comprising a control unit configured to determine a position of the sheet based on detections of the reference and the edge position of the conveyed sheet by the detection unit, and wherein the light receiving unit of the detection unit is composed of a plurality of light receiving elements configured to receive light from the light emitting unit and arranged in the width direction on a same substrate.
Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention.
Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings.
Further, the apparatus main body 1 is equipped with a transfer roller 9b, which abuts on the photosensitive drum 9a and forms a transfer unit together with the photosensitive drum 9a, and a fixing device 11 configured to fix a toner image transferred by the transfer unit to the sheet P. Further, between the image forming unit 1A and the sheet feeding cassette 2, there is arranged to be detachable to the apparatus main body 1 a two-sided unit 20, which is a sheet conveyance apparatus configured to reverse and convey a sheet whose first side has undergone image formation and having a reverse conveyance path R that is a sheet conveyance path for conveying the sheet to the image forming unit 1A again.
The image forming unit 1A is equipped with a process cartridge 9 having the photosensitive drum 9a, a charger (not illustrated), a development sleeve, a cleaning unit, etc. Further, there is provided a laser scanner 10 which is an exposure unit configured to cause the surface of the photosensitive drum 9a to be exposed and to form an electrostatic latent image on the photosensitive drum 9a.
The sheet feeding apparatus 1B is equipped with a pickup roller 5, which is a feeding member configured to feed out the sheets P stacked in the sheet feeding cassette 2 starting from the uppermost one. Further, the sheet feeding apparatus 1B is equipped with a separation roller 6 which is held in press contact with the pickup roller 5 and configured to separate and convey one by one, together with the pickup roller 5, the sheets P fed out by the pickup roller 5. The sheet feeding cassette 2 is provided with a sheet stacking plate 2a, and a pressurization spring pressurizing the lower surface of the sheet stacking plate 2a upwardly; owing to the pressurization spring 2b, the uppermost sheet P on the sheet stacking plate 2a is held in press contact with the pickup roller 5. In
Next, the image forming operation of the image forming apparatus 100, constructed as described above, will be illustrated. When the image forming operation is started, the photosensitive drum 9a first rotates in the direction of the arrow, with its surface being charged by a charger (not illustrated) ; after this, a laser beam is emitted to the photosensitive drum 9a from the laser scanner 10 based on image information. As a result, an electrostatic latent image is formed on the photosensitive drum. Next, as a development sleeve (not illustrated) rotates, toner, which is charged to an appropriate degree, is supplied onto the photosensitive drum 9a, whereby the electrostatic latent image is developed to be visualized as a toner image.
In the meantime, in parallel with this toner image forming operation, the pickup roller 5 is driven by a driving motor (not illustrated) and is rotated, thereby feeding out the uppermost sheet P in the sheet feeding cassette 2. And, the sheet P thus fed out by the pickup roller 5 is conveyed while separated by a separation unit 3, which is configured with the pickup roller 5 and the separation roller 5, and is conveyed to a registration roller pair 8 at rest via a conveyance roller pair 7. After this, leading edge alignment (skew feed correction) is performed by the registration roller pair 8.
Next, in the image forming unit 1A, the sheet P is conveyed to the transfer unit by the registration roller pair 8 in conjunction with the image formed on the photosensitive drum 9a, and the image on the photosensitive drum 9a is transferred to the sheet P by the transfer roller 9b. After this, the sheet P, to which the toner image has been transferred, is conveyed to the fixing device 11, where the unfixed toner image is fixed to the sheet surface through heating/pressurization.
On the downstream side of the fixing device 11, there are provided a triple driving roller 12 configured to rotate counterclockwise, and a triple driven roller A 12a and triple driven roller B 12b, which are held in press contact with the triple driving roller 12. And, as the tripe driving roller 12 rotates, the triple driven roller A 12a and the triple driven roller B 12b rotate clockwise. Owing to this construction, in the case of one-sided printing, the sheet P, to which the toner image has been fixed, is conveyed via a conveyance roller pair 13 and a discharge roller pair 14 by the triple driving roller 12 and the tripe driven roller A 12a, and is successively stacked on a discharge tray 15 on the upper surface of the apparatus main body, with the printed surface down.
On the other hand, in the case where image formation is performed on both sides of the sheet P, after the trailing edge of the sheet whose first surface has undergone image formation has passed the triple driving roller 12 and the tripe driven roller A 12a, a driving motor (not illustrated) is reversed to cause reverse rotation of the conveyance roller pair 13 and the discharge roller pair 14. As a result, the sheet P whose one surface has undergone image formation is conveyed, starting with the trailing edge as a leading edge, toward the nip portion between triple driving roller 12 and triple driven roller B 12b.
At this time, the triple driving roller 12 continues to rotate counterclockwise, so that the sheet P, which has been conveyed to the nip portion between the triple driving roller 12 and the triple driven roller B 12b, is conveyed toward a two-sided unit 20. And, the reversed sheet P is conveyed to a conveyance roller pair 7 in the apparatus main body via conveyance roller pairs 21 and 22 provided in the two-sided unit. After this, the sheet P is conveyed to the transfer unit again via a registration roller pair 8, with the first printed surface down, then the toner image is transferred to the second surface. As in the case of one-sided printing, the sheet to whose both sides toner images have been transferred is conveyed via the fixing device 11, the conveyance roller pair 13, and the discharge roller pair 14 and is successively stacked on the discharge tray 15.
As described above, the two-sided unit 20 is detachably attached to the apparatus main body 1. And, when jamming occurs in the apparatus main body, the two-side unit 20 is drawn out of the apparatus main body 1 as illustrated in
Further, on the downstream side in the sheet conveyance direction of the conveyance roller 22, the two-sided unit 20 has a side edge detection sensor unit 30 configured to detect one side edge position in the width direction, which is orthogonal to the conveyance direction of the sheet P passing through the reverse conveyance path R. And, in the case of two-sided printing, the sheet having passed through the reverse conveyance path R is conveyed, with a side edge position thereof being detected by the side edge detection sensor unit 30. To make the influence of skew feed during sheet conveyance up to the image forming unit 1A as small as possible, the side edge detection sensor unit 30 can be arranged at a position as close as possible to the image forming unit 1A.
When attaching the two-sided unit 20 to the apparatus main body 1, as illustrated in
Here, assuming that the sheet conveyance direction is the X-direction, that the width direction is the Y-direction, and that the apparatus height direction is the Z-direction, a Y-direction positioning portion 18b of the positioning pin 18 and a Y-direction positioning surface 24b of the positioning member 24 perform poisoning in the width direction on the two-sided unit 20. Further, an XZ-direction positioning shaft portion 18a of the positioning pin 18 and an XZ-direction positioning hole portion 24a perform positioning on the two-side unit 20 in the sheet conveyance direction and the apparatus height direction. Further, in the state in which positioning has been effected on the two-sided unit 20, the connector 25 provided on the two-sided unit 20 illustrated in
In
As illustrated in
Further, below, there is provided a light receiving unit 36 having a substrate 36b on which there are arranged in series a plurality of light receiving elements 36a and arranged to face the sheet passing the reference plate 16a and the reverse conveyance path R. And, between the light emitting unit 35 and the light receiving unit 36, there exists a space G through which one side edge portion in the width direction of the sheet P passes and which the forward end of the reference plate 16a provided on the rear side plate 16 enters. The length of the light emitting unit 35 and the light receiving unit 36 in the width direction is large enough to cover the side edge of a sheet of a minimum size to the side edge of a sheet of a maximum size conveyable and the forward end portion of the reference plate 16a that has entered the space G.
Next, a sheet side edge position detecting operation by the side edge detection sensor unit 30, which is a detection unit for simultaneously detecting the reference plate 16a and the side edge position in the width direction of the sheet, will be described. As illustrated in
Thus, as illustrated in
In this way, in the present exemplary embodiment, the sheet side edge position and the reference position (the reference plate 16a) of the apparatus main body 1 are simultaneously read by the plurality of light receiving elements 36a mounted on the same substrate 36b. And, owing to this construction, it is possible to detect the sheet side edge position in a short time. Specifically, in the present exemplary embodiment, the light receiving unit 36 of the side edge detection sensor unit 30 is configured with the plurality of light receiving elements 36a arranged in series on the same substrate 36b, whereby it is possible to detect the sheet side edge position in a short time.
Further, the light receiving elements 36a read the reference position (the reference plate 16a), whereby it is possible to cancel positional deviation due to play between the units of the apparatus main body 1 and variation in component dimension. As a result, it is possible to detect the sheet side edge position without being affected by positional deviation between the apparatus main body 1 and the unit. Thus, by controlling the unit dimension of the plurality of light receiving elements 36a, it is possible to detect the sheet side edge position with high precision, and the image forming position on the sheet can be optimized.
Next, the second exemplary embodiment of the present invention will be described.
In
The sensor holder 43 is constantly held in contact with the cam 42 by the biasing force of a spring 44. Owing to this construction, when the cam 42 receives a drive force from a gear row (not illustrated) and rotates, the sensor holder 43 performs sliding operation. The gear row (not illustrated) is connected with a driving gear row driving a conveyance roller pair 21, 22 of the two-side unit 20.
As illustrated in
As described above, as the cam 42 rotates, the sensor holder 43 makes a sliding motion, so that the light receiving unit 46 and the light emitting unit 45 make an integral sliding motion. In the present exemplary embodiment, the first light receiving element S0, which is nearest to the reference plate 16a, serves to detect the reference plate 16a, and the others, i.e., the second through fourth light receiving elements S1 through S3, serve to detect the side ends of sheets of different sizes. And, using the light receiving element S0 as a reference, the light receiving elements S1 through S3 are mounted on the substrate 46a at distances D1, D2, and D3 in conformity with the sheet sizes so that they can detect the side edge positions of sheets of different lengths in the width direction. While in the present exemplary embodiment the four light receiving elements S0 through S3 are arranged in line in the width direction on the substrate 46a, it is also possible to increase the number of light receiving elements according to the sheet sizes that can be dealt with by the apparatus. Here, the arrangement in the width direction signifies that the positions in the width direction of the four light receiving elements S0 through S3 differ from each other; it is also possible for the four light receiving elements S0 through S3 to be offset from each other in the conveyance direction.
In this way, in the side edge detection sensor unit 40, the point light sources L0 through L3 and the light receiving elements S0 through S3 are arranged in the sheet width direction corresponding to the different sheet sizes and configured to slide in width direction. Specifically, the pairs formed by the point light sources L0 through L3 and the light receiving elements S0 through S3 are set at positions corresponding to the different sheet sizes. The sliding distance of the side edge detection sensor unit 40 is approximately ±3 to ±6 mm with respect to designed value for sheet sizes. However, there are no particular limitations regarding the sliding distance if setting is made such that the sliding amount increases in correspondence with the addition of the tolerance of the sheet dimension, the skew feed amount, etc. However, the above-mentioned sliding amount helps to achieve a reduction in the size of the sliding mechanism. For example, it is possible to perform sliding operation using a cam, thus a reduction in the size of the sliding mechanism can be achieved.
Next, the sheet side edge position detecting operation by the side edge detection sensor unit 40 will be described.
In the state illustrated in
In
In the present exemplary embodiment, the control unit 101 can recognize the side edge of the reference plate 16a, in other words, the 0-reference, from the rising edge from Low to High of the output signal from the first light receiving element S0. As illustrated in
In
When the sensor holder 43 slides in the state of
The sliding distance of the light receiving elements S0 through S3 according to the motor step number is previously computed from the configuration of the cam 42, and, by counting the step number, it is possible to calculate the sliding amount (distance) of the light receiving elements S0 through S3. Thus, the sheet side edge position (the distance D to the sheet side edge position when the reference plate is regarded as 0) can be calculated from the following equation:
D=D1+K1 (equation 1)
Where K1 is a value calculated from the sliding distance of the light receiving elements S0 through S3 according to the motor step number previously calculated, and from the motor step number C1 actually measured. D1 is the distance from the light receiving element S0 to the light receiving element S1 illustrated in
D=D2−K2 (equation 2)
Specifically, the sheet side end position D can be calculated by subtracting the distance K2 calculated from the motor step number from the inter-light-receiving element distance D2. And, based on the sheet side edge position thus calculated, the image writing position is corrected by an image writing control unit (not illustrated), whereby an optimized image can be formed on the sheet having passed the side edge detection sensor unit 40.
As described above, in the present exemplary embodiment, a plurality of light receiving elements S0 through S3 are arranged on the same substrate 46a at positions where it is possible to detect the reference plate 16a and the side edge positions of sheets of different lengths in the width direction, thus reading the sheet side edge position and the position of the reference plate 16a. And, owing to this construction, it is possible to detect the sheet side edge position in a short time. Further, by controlling the dimension between the light receiving elements of the plurality of light receiving elements S0 through S3 on the substrate 46a, the precision with which the sheet side edge position is detected is enhanced, and the image forming position on the sheet can be optimized.
In the present exemplary embodiment, in the calculation of the sheet side edge position, it is possible not only to utilize the initial detection value (T1) in
Next, the third exemplary embodiment of the present invention will be described with reference to the drawings.
In
Here,
Next, the sheet side end position detecting operation by the side end detection sensor unit 50, constructed as described above, will be described. First, by the time the sheet leading edge reaches the side edge detection sensor 50, the time T0 in
Next, when the sheet leading edge reaches the side edge detection sensor unit 50, the cycle of the time T0 gets out of order, and a Low-High rising edge signal appears at a time interval shorter than the time T0. Using this point in time of change as a trigger, the sheet side edge position detection is executed. Specifically, the time T1 in
In this case, the sheet side end position detection and the side edge position detection of the reference plate 16a are executed by the single light receiving element S0, so that D1 in equation 1 described above is 0, and only the K factor calculated from the motor step number remains. In the case where the sheet side edge detection is effected by the other light receiving elements S2 and S3, the procedures involved are the same as those of the second exemplary embodiment described above.
Here, in the construction of the present exemplary embodiment also, a plurality of light receiving elements S1 through S3 are arranged on the same substrate to be capable of detecting the side edge positions of sheets of different lengths in the width direction, and, at the same time, the side edge position of the sheet and the reference position (the reference plate 16a) of the apparatus main body are read. And, owing to this construction, it is possible to detect the side edge position of a sheet in a short time. Further, by controlling the dimension between the light receiving elements of the plurality of light receiving elements S1 through S3 on the substrate 46a, it is possible to detect the sheet side edge position with high precision, whereby the image forming position on the sheet can be optimized.
Next, the fourth exemplary embodiment of the present invention will be described with reference to the drawings.
In
Numeral 60c denotes a sheet side edge position reference edge of the reference plate member 60; this sheet side edge position reference edge 60c serves in the same way as the side edge of the reference plate of the first through third exemplary embodiments described above, and is arranged between the light emitting unit 45 and the light receiving unit 46. Specifically, the light emitting unit 45 and the light receiving unit 46 detect the sheet side edge position reference edge 60c to detect the side edge of the reference plate member 60. The sliding motion of the light emitting unit 45, the light receiving unit 46, and the sensor holder 43 and the side edge position detecting method are the same as those of the second exemplary embodiment described above, and a description will be omitted.
In this way, in the present exemplary embodiment, the reference plate member 60 having the sheet side edge position reference edge 60c is supported in the two-sided unit 20 to be sliable in the sheet width direction, and is caused to directly abut on the rear side plate 16. Owing to this construction, it is possible to enhance the positional precision of the sheet side edge position reference edge 60c.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures, and functions.
This application claims priority from Japanese Patent Application No. 2010-150247 filed Jun. 30, 2010, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-150247 | Jun 2010 | JP | national |
