Patent Application
20110081181
1. Field of the Invention
The present invention relates to an image forming apparatus and a sheet conveying method, and in particular to an image forming apparatus and a sheet conveying method that correct for skew of a sheet being conveyed to an image forming unit.
2. Description of the Related Art
Image forming apparatuses such as copiers, printers, and facsimiles have a conveying unit that conveys a sheet such as a recording sheet or an OHP sheet to an image forming unit. According to those image forming apparatuses, a sheet is conveyed to the image forming unit by the conveying unit, and an image formed by the image forming unit is transferred to the sheet, so that an image is formed on the sheet.
Some of such image forming apparatuses having a conveying unit have a skew correction unit to correct for sheet skew so as to prevent a skewed sheet from being conveyed to the image forming unit, and correction systems using the skew correction unit include a loop forming system and an active registration system.
In the loop forming system, skew is corrected for by pressing a sheet onto a roller pair being at a standstill to form a loop in the sheet.
On the other hand, in the active registration system, skew is corrected for by turning a sheet while conveying it using two sensors and two roller pairs which are individually rotating (see Japanese Laid-Open Patent Publication (Kokai) No. H10-032682). Specifically, first, a skew amount of a sheet is computed based on a difference between generation timings of detection signals which are generated when a leading end of the sheet passes the two sensors provided on a common axis perpendicular to a sheet conveying direction of a sheet conveying path. Then, according to the computed skew amount, the rotational speeds of the respective two roller pairs provided at different locations in a direction perpendicular to the sheet conveying direction are individually controlled. For example, the rotational speed of one roller pair is controlled to be higher or lower than that of the other roller pair, so that skew of the sheet is corrected for.
Incidentally, to improve the performance of the image forming apparatuses, an image forming operation must be speeded up, but the above described loop forming system is not suitable because a sheet being conveyed must be temporarily stopped so as to form a loop in the sheet, and hence correction requires long time.
On the other hand, in the active registration system, skew of a sheet is corrected for without temporarily stopping conveyance of the sheet, and hence the time required for correction is shorter than in the loop forming system. Moreover, the sheet interval between a preceding sheet and a following sheet can be shortened as compared to the loop forming system, resulting in enhancement of sheet conveying efficiency.
However, as the sheet conveying speed increases, rollers contacting on a sheet become more prone to slip. The amount of slip is related to sheet surface characteristics. For example, when in double-sided recording, a sheet with an image transferred to a first side thereof is conveyed for image formation on a second side of the sheet, the amount of slip increases as the amount of toner used for image formation on the first side of the sheet increases. In this case, an image formed on the sheet is misaligned to a large degree, and hence even in the above described active registration system, it is difficult to correct for the misalignment.
The present invention provides an image forming apparatus and a sheet conveying method that can reliably correct for skew of a sheet being conveyed.
Accordingly, a first aspect of the present invention provides an image forming apparatus comprising a conveying unit configured to convey a sheet, a plurality of conveying roller pairs provided in a direction intersecting a direction in which the sheet is conveyed, and configured to be driven independently of each other, a skew amount detection unit configured to detect a skew amount of the sheet conveyed by the conveying unit, a toner amount determination unit configured to determine a toner amount for an image formed on the sheet, and a control unit configured to correct for skew of the sheet by controlling driving speeds for the plurality of roller pairs independently of each other based on the skew amount detected by the skew amount detection unit and the toner amount determined by the toner amount determination unit.
Accordingly, a second aspect of the present invention provides an image forming apparatus that forms images on both surfaces of a sheet, comprising an image forming unit, a conveying unit configured to convey the sheet to the image forming unit, a correction unit comprising a plurality of roller pairs provided in a direction intersecting a direction in which the sheet is conveyed, and individually adjusting a speed at which the sheet is conveyed, and configured to correct for skew of the sheet conveyed by the conveying unit, a skew amount detection unit configured to detect a skew amount of the sheet conveyed by the conveying unit, a toner amount determination unit configured to determine an amount of toner for an image formed on a first surface of the sheet, and a control unit configured to, in conveying the sheet with the image formed on the first surface thereof to the image forming unit so as to form an image on a second surface of the sheet, control the correction unit based on the skew amount detected by the skew amount detection unit and the toner amount determined by the toner amount determination unit.
Accordingly, a third aspect of the present invention provides a sheet conveying method for an image forming apparatus which has an image forming unit, a conveying unit that conveys a sheet, and a correction unit that has a plurality of roller pairs provided in a direction intersecting a direction in which the sheet is conveyed, and individually adjusting a speed at which the sheet is conveyed, and corrects for skew of the sheet conveyed by the conveying unit, and forms images on both surfaces of the sheet, comprising a skew amount detection step of detecting a skew amount of the conveyed sheet, a toner amount determination step of determining atoner amount for an image formed on a first surface of the sheet, and a control step of, in conveying the sheet with the image formed on the first surface thereof to the image forming unit so as to form an image on a second surface of the sheet, controlling the correction unit based on the skew amount detected in the skew amount detection step and the toner amount determined in the toner amount determination step.
Accordingly, a fourth aspect of the present invention provides a sheet conveying method for an image forming apparatus which has a conveying unit that conveys a sheet, and a plurality of conveying roller pairs provided in a direction intersecting a direction in which the sheet is conveyed, and are driven independently of each other, comprising a skew amount detection step of detecting a skew amount of the sheet conveyed by the conveying unit, a toner amount determination step of determining a toner amount for an image formed on the sheet, and a control step of correcting for skew of the sheet by controlling driving speeds for the plurality of roller pairs independently of each other based on the skew amount detected in the skew amount detection step and the toner amount determined in the toner amount determination step.
According to the present invention, because skew of a sheet is corrected for based on the skew amount of the sheet and the amount of toner used for an image formed on the sheet, skew of a sheet during conveyance of the sheet having an image formed on a first surface thereof so as to form an image on a second surface of the sheet can be reliably corrected for.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
The present invention will now be described in detail with reference to the drawings showing embodiments thereof.
Referring to
The image control unit 7 generates a horizontal synchronizing signal based on a laser beam detection signal sent from a laser scanner 4, described later, and in synchronization with the horizontal synchronizing signal, sends an image pulse to the laser scanner 4. Also, the image control unit 7 sends an image request signal and a horizontal synchronizing signal to the controller 8, and converts image data sent from the controller 8 into an image pulse having a pulse width corresponding to a data level of the image data. The image request signal is generated by, for example, the image control unit 7 receiving a trigger signal from a CPU, not shown, that performs a sequence of the whole apparatus. It should be noted that the CPU controls the overall operation of the image forming apparatus 500.
Further, in the case of forming an image on one surface (second surface) of the sheet S having an image formed on the other surface (first surface) thereof, the image control unit 7 determines and stores the amounts of toner used in respective regions where the surface on which the image has been formed and a pair of skew correction rollers 2R and 2L, described later, contact on each other (hereafter referred to as “the amounts of toner used”). The amounts of toner used are sent to a first variable speed determination unit 103R and a second variable speed determination unit 103L, respectively, of a first driving control unit 9, described later. In this case, the image control unit 7 acts as a toner amount determination unit.
The controller 8 temporarily stores image data sent from a PC or a reader, not shown, in an image memory, not shown, and sends the image data to the image control unit 7 in synchronization with an image request signal and a horizontal synchronizing signal from the image control unit 7. After a predetermined number of pulses in the horizontal synchronizing signal have been counted based on the image request signal, the controller 8 synchronizes the image data with the horizontal synchronizing signal and sends the image data to the image control unit 7 every predetermined number of lines.
The image forming unit 300 has the laser scanner 4 and a photoconductive drum 16, which is an image supporting member. A charging unit 20, a developing unit 22, a primary transfer charging unit 24, and a cleaner 26 are disposed around the photosensitive drum 16 and in the rotational direction thereof.
The laser scanner 4 is comprised of a laser beam emitting unit, a polygon mirror, a laser beam detecting sensor, and so on, which are not shown. Based on an image pulse from the image control unit 7, the laser scanner 4 irradiates laser beam onto the photosensitive drum 16 charged by the charging unit 20, thus forming an electrostatic latent image on the photosensitive drum 16. At this time, the polygon mirror deflects and reflects the laser beam emitted from the laser beam emitting unit, and the laser beam detecting sensor sends a laser beam detection signal to the image control unit 7 when detecting the laser beam.
The photosensitive drum 16 is rotated by a motor, not shown, in a direction indicated by an arrow in the figure, and is uniformly charged to a predetermined potential by the charging unit 20 to which a charged bias is applied. The developing unit 22 accommodates toner and forms a toner image by attaching toner to an electrostatic latent image on the photosensitive drum 16. The primary transfer charging unit 24 is disposed at a location opposed to the photosensitive drum 16 such that it can contact on the photosensitive drum 16 via an endless transfer belt 14 tightly stretched between three rollers 12a to 12c, and constitutes a primary transfer unit for transferring a toner image on the photosensitive drum 16 to the transfer belt 14.
The cleaner 26 cleans the surface of the photosensitive drum 16 by scraping off toner remaining on the photosensitive drum 16 without being transferred to the transfer belt 14. A secondary transfer roller 28 is disposed at a location opposed to the roller 12c located at a lower position as viewed in the figure such that it can contact on the roller 12c via the transfer belt 14, and constitutes a secondary transfer unit for transferring a toner image 31 from the transfer belt 14 to the sheet S. The conveying unit 400 has a sheet feeding unit 301 and a sheet conveying unit 302. The sheet feeding unit 301 has a cassette 50 that is attachable and detachable to and from an apparatus main body, not shown, and accommodates a plurality of sheets S, and a sheet feeding roller 51 that conveys the sheets S one by one to the sheet conveying unit 302.
The sheet conveying unit 302 has a conveying roller pair 52, a conveying roller pair 53, and a skew correction unit 303. The conveying roller pair 52 conveys the sheet S fed from the sheet feeding unit 301 to the conveying roller pair 53, and the conveying roller pair 53 conveys the sheet S to the secondary transfer unit where the secondary transfer roller 28 and the roller 12c contact on each other. The conveying roller pairs 52 and 53 each acts as a conveying unit. It should be noted that the sheet S is conveyed using the middle in the width direction perpendicular to the sheet conveying direction as a conveyance reference.
The skew correction unit 303 has a first sensor unit 6, a second sensor unit 5 as a detecting unit, a skew correction roller unit comprised of cut rollers 2 and driven rollers 2a, a timing roller unit comprised of cut rollers 1 and driven rollers 1a, the first driving control unit 9 that controls the operation of the skew correction roller unit, and a second driving control unit 10 that controls the operation of the timing roller unit. It should be noted that the skew correction roller unit acts as a correction unit. A detailed description will now be given of the skew correction unit 303 with reference to
Referring to
The skew correction roller unit controlled by the first driving control unit 9 is comprised of, for example, a first skew correction roller pair 2R and a second skew correction roller pair 2L which are disposed on the right and left with respect to the direction in which the sheet S is conveyed. The skew correction roller pairs 2R and 2L are each comprised of the cut roller 2 and the driven roller 2a, which is disposed such as to face the cut roller 2 across the sheet S being conveyed and follows the cut roller 2. It should be noted that there may be a plurality of skew correction roller units. The skew correction roller pairs 2R and 2L are electrically connected to a first motor 122R and a second motor 122L, respectively, which are drive units, and the motors 122R and 122L are driven by a first driver 121R and a second driver 121L, respectively. The skew correction roller pairs 2R and 2L separately rotate with driving operations of the drivers 121R and 121L, whereby conveying speeds on both sides of the sheet S, which contact on the respective skew correction roller pairs 2R and 2L, in the conveying direction are separately adjusted.
The first sensor unit 6 is comprised of a sensor 6L and a sensor 6R. The sensors 6R and 6L detect a leading end of the sheet S being conveyed, and send sheet detection signals to the first driving control unit 9.
The average value determination unit 100, which is a passage timing detection unit, counts the number of pulses in a horizontal synchronizing signal from the image control unit 7, which are shown in
The average value (TAVE) is timing of the sheet S passing a middle point of a line connecting the sensor 6R and the sensor 6L, and this middle point is set as a reference point for determining whether sheet being conveyed is lagging or leading. It should be noted that the reference point should not necessarily be set in this way, but for example, a sensor capable of detecting the middle in the width direction of the sheet S may be disposed, and a signal from this sensor may be set as a reference point.
The comparative determination unit 101 compares the average value (TAVE) determined by the average value determination unit 100 and a target passage count value (T1IDEAL) shown in
The first skew amount counter 102R acting as a skew amount determination unit determines whether or not the output of the sheet detection signal from the sensor 6R precedes the output of the sheet detection signal from the sensor 6L, and determines a skew amount (see
The second skew amount counter 102L acting as a skew amount determination unit determines whether or not the output of the sheet detection signal from the sensor 6L precedes the output of the sheet detection signal from the sensor 6R, and determines a skew amount based on the determination result. Also, after the determination, the second skew amount counter 102L outputs a preceding/following flag L (precede: 1 or following: 0), the skew amount, and a skew flag L (skewed: 1 or not-skewed: 0) as determination signals to the second variable speed determination unit 103L.
Based on the lag/lead amount and the lag/lead flag from the comparative determination unit 101 and the preceding/following flag, the skew amount, and the skew flag from the first skew amount counter 102R, the first variable speed determination unit 103R determines a target speed Vs1 of sheet conveyance by the first skew correction roller pair 2R. Also, when receiving data on the amount of toner used from the image control unit 7, described later, the first variable speed determination unit 103R determines a target speed Vs3 based on the various signals from the comparative determination unit 101, the various signals from the first skew amount counter 102R, and the amount of toner used from the image control unit 7. The target speed is sent to the first motor pulse control unit 120R.
Similarly to the first variable speed determination unit 103R, the second variable speed determination unit 103L determines a target speed Vs2 of sheet conveyance by the second skew correction roller pair 2L based on the various signals sent from the comparative determination unit 101 and the various signals sent from the second skew amount counter 102L. Also, when receiving data on the amount of toner used from the image control unit 7, described later, the second variable speed determination unit 103L determines a target speed Vs4 based on the various signals from the comparative determination unit 101, the various signals from the second skew amount counter 102L, and the amount of toner used from the image control unit 7. The target speed is sent to the second motor pulse control unit 120L.
Based on the received sheet detection signal and target speed, the first motor pulse control unit 120R acting as a control unit controls the periods of step pulses sent from the first driver 121R to the first motor 122R. This controls the rotational speed of the first skew correction roller pair 2R during sheet conveyance.
Based on the received sheet detection signals and target speeds, the second motor pulse control unit 120L acting as a control unit controls the periods of step pulses sent from the second driver 122L to the second motor 122L. This controls the rotational speed of the second skew correction roller pair 2L during sheet conveyance.
Moreover, on standby for sheet conveyance, the motor pulse control units 120R and 120L receive mark detection signals from home position sensors, not shown, which have detected marks, not shown, provided in the respective skew correction roller pairs 2R and 2L. The motor pulse control units 120R and 120L having received the mark detection signals control the respective motors 122R and 122L via the respective drivers 121R and 121L so that the skew correction roller pairs 2R and 2L stop with the cut portions of the cut rollers 2 turned up. In this case, the cut roller 2 and the driven roller 2a of each of the skew correction roller pairs 2R and 2L are spaced apart from each other.
Referring next to
Referring to
The timing roller unit controlled by the second driving control unit 10 is comprised of, for example, a timing roller pair 1R and a timing roller pair 1L which are disposed on the right and left with respect to the direction in which the sheet S is conveyed. The timing roller pairs 1R and 1L are each comprised of the cut roller 1 and the driven roller 1a, which is disposed such as to face the cut roller 1 across the sheet S being conveyed and follows the cut roller 1. The timing roller pairs 1R and 1L are rotated by a motor 205, which is driven by a driver 204. The timing roller pairs 1R and 1L rotate with driving operations of the driver 204, whereby the sheet S contacting on the timing roller pairs 1R and 1L is conveyed.
The second sensor unit 5 detects the leading end of the sheet S being conveyed, and sends a sheet detection signal to the second driving control unit 10.
The counter 200 of the second driving control unit 10 having received the sheet detection signal counts the number of pulses in a horizontal synchronizing signal using an image request signal sent from the image control unit 7 (see
The comparative determination unit 201 compares the count value of the sheet detection signal and a target passage count value (T2IDEAL) with each other. Here, the target passage count value (T2IDEAL) is timing in which the leading end of the sheet S should pass the second sensor unit 5 so that the leading end of the toner image 31 on the transfer belt 14 and the leading end of the sheet S can correspond to each other in the secondary transfer unit. Based on the comparison result, the comparative determination unit 201 determines the amount of lag/lead of the timing in which the sheet S passes the second sensor unit 5 relative to the target passage count value, and outputs a lag/lead flag (lag: 0 or lead: 1) and a lag/lead amount to the variable speed determination unit 202.
Based on the lag/lead flag and the lag/lead amount from the comparative determination unit 201, the variable speed determination unit 202 determines a target speed V1 of sheet conveyance by the timing roller pairs 1R and 1L, and sends the target speed V1 to the motor pulse control unit 203.
Based on the received target speed V1 sent from the variable speed determination unit 202, the motor pulse control unit 203 controls the periods of step pulses sent from the driver 204 to the motor 205. This controls the rotational speed of the timing roller pairs 1R and 1L in a direction indicated by an arrow in the figure during sheet conveyance.
Moreover, on standby for sheet conveyance, the motor pulse control unit 203 receives mark detection signals from home position sensors, not shown, which have detected marks, not shown, provided in the respective timing roller pairs 1R and 1L. The motor pulse control unit 203 having received the mark detection signals controls the motors 205 via the driver 204 so that the timing roller pairs 1R and 1L stop with the cut portions of the cut rollers 1 turned up. In this case, the cut roller 1 and the driven roller 1a of each of the timing roller pairs 1R and 1L are spaced apart from each other.
Next, a description will be given of an image forming process carried out by the image forming apparatus 500 according to the present embodiment.
First, a description will be given of a case where an image is formed on one surface of the sheet S.
When receiving a trigger signal sent from the CPU, not shown, the image control unit 7 (see
The laser scanner 4 having received the image pulse irradiates laser beam corresponding to the image pulse onto the photosensitive drum 16 which has been charged in advance by the charging unit 20 and is rotating. An electrostatic latent image is formed on the photosensitive drum 16 irradiated with the laser beam.
Then, the developing unit 22 attaches toner to the electrostatic latent image, whereby a toner image is formed on the photosensitive drum 16. The toner image formed on the photosensitive drum 16 is transferred onto the transfer belt 14 by the action of a primary transfer bias voltage applied to the primary transfer charging unit 24 in the primary transfer unit. The toner image 31 transferred onto the transfer belt 14 moves in a direction indicated by an arrow A in
In order that the leading end of the sheet S reaches the secondary transfer unit in timing with the leading end of the toner image 31 reaching the secondary transfer unit, the feeding roller 51 feeds the sheet S held in the cassette 50 toward the closest conveying roller pair 52 in synchronization with the trigger signal sent from the CPU. Sensors, not shown, are disposed in the vicinity of the conveying roller pairs 52, and when detecting the passage of the sheet S, each sensor sends a detection signal to the CPU. The CPU having received the detection signal from each sensor causes a driving control unit, not shown, to drive each conveying roller pair 52. The sheet S is conveyed toward the conveying roller pair 53 with rotation of the driven conveying roller pairs 52, and conveyed toward the skew correction unit 303 by the conveying roller pair 53.
The sensors 6L and 6R detect the leading end of the sheet S being conveyed, and send sheet detection signals to the average value determination unit 100 and the respective skew amount counters 102R and 102L (see
On the other hand, the first skew amount counter 102R and the second skew amount counter 102L having received the sheet detection signals determine lag/lead directions and skew amounts of the sheet S based on the times at which the sensors 6R and 6L detect the leading end of the sheet S. The first skew amount counter 102R and the second skew amount counter 102L output preceding/following flags, skew flags, and skew amounts to the variable speed determination units 103R and 103L, respectively. Based on the lag/lead flag and the lag/lead amount from the comparative determination unit 101 and the preceding/following flags, the skew flags, and the skew amounts from the skew amount counter 102R and 102L, the variable speed determination units 103R and 103L determine target speeds Vs1 and Vs2, respectively.
Referring now to
Each figure A of
Firstly, referring to
In such a leading state, as shown in
Secondly, referring to
In such a lagging state, as shown in
Thirdly, referring to
In such a leading state, as shown in
Fourthly, referring to
In such a lagging state, as shown in
Fifthly, referring to
In such a leading state, as shown in
Sixthly, referring to
In such a lagging state, as shown in
The variable speed determination units 103R and 103L having determined the target speeds as described above send the determined target speeds to the motor pulse control units 120R and 120L, respectively. Based on the received target speeds, the motor pulse control units 120R and 120L control the rotational speeds of the respective skew correction rollers 2R and 2L via the respective drivers 121R and 121L. As a result, the skew of the sheet S is corrected for, and the degree of lagging or leading is corrected for or reduced.
The sheet S of which skew has been corrected for and of which degree of lagging or leading has been reduced by the first driving control unit 9 is conveyed toward the timing roller pairs 1R and 1L, and the second sensor unit 5 detects the leading end of the conveyed sheet S and sends a sheet detection signal to the counter 200 (see
The counter 200 having received the sheet detection signal latches a count value when the second sensor unit 5 detects the leading end of the conveyed sheet S, and sends the count value to the comparative determination unit 201. The comparative determination unit 201 compares the count value from the counter 200 with the ideal passage count value T2IDEAL from the image control unit 7, and sends a lag/lead flag and a lag/lead amount as comparison results to the variable speed determination unit 202. The variable speed determination unit 202 determines the target speed V1 based on the lag/lead flag and the lag/lead amount from the comparative determination unit 201.
For example, when the sheet S is being conveyed in a state shown in
Also, for example, when the sheet S is being conveyed in a state shown in
The variable speed determination unit 202 having determined the target speed V1 sends the determined target speed V1 to the motor pulse control unit 203. Based on the received target speed V1, the motor pulse control unit 203 controls the rotational speeds of the timing roller pairs 1R and 1L via the driver 204. Then, the motor pulse control unit 203 corrects for the lagging or leading of the sheet S, then resets the conveying speed for the sheet S to the steady-state speed V0, and conveys the sheet S to the secondary transfer unit.
The secondary transfer roller 28 transfers the toner image 31 to the sheet S conveyed to the secondary transfer unit. The sheet S to which the toner image has been transferred is conveyed to a fixing unit, not shown, and the toner image is fixed on a surface of the sheet S by the fixing unit heating and pressurizing the sheet S.
Next, a description will be given of an operation in which images are formed on both of front and back surfaces of the sheet S.
This operation is basically the same as the image forming operation in the above described operation in which an image is formed on one surface, and hence description of corresponding operations is omitted, only different operations being described below.
By the same operation as described above, a toner image is formed on the photosensitive drum 16, and further, the toner image 31 is transferred onto the transfer belt 14. On this occasion, the image control unit 7 determines amounts of toner used DR and DL in respective diagonally shaded regions 11R and 11L shown in
Based on the received amounts of toner used DR and DL, the respective variable speed determination units 103R and 103L obtain an amount of toner used difference correction value α from a table shown in
Vs3=Vs1+αVc (1)
Vs4=Vs2−αVc (2)
Here, Vc is an adjustment value for correcting for a difference between a computed correction result and an actual correction result, and correcting for subtle apparatus-to-apparatus variations such as mounting positions of sensors and drive rollers.
The variable speed determination units 103R and 103L having determined the target speeds send the determined target speeds to the respective motor pulse control units 120R and 120L. Based on the received target speeds, the motor pulse control units 120R and 120L control the rotational speeds of the respective skew correction roller pairs 2R and 2L.
The sheet S of which skew and lagging or leading have been corrected for with consideration given to the amount of toner used for the toner image transferred to the sheet S as described above is conveyed to the timing roller pairs 1R and 1L, and an image is formed on the other surface of the sheet S in the same way as described above, which completes image formation on both surfaces of the sheet S.
Referring next to
Referring to
The average value determination unit 100 determines the average value (TAVE) based on the received sheet detection signals (S1502), and sends the determined average value (TAVE) to the comparative determination unit 101. On the other hand, the skew amount counters 102R and 102L detect sheet lagging/leading directions and skew amounts based on the received sheet detection signals (S1503), and send preceding/following flags, skew flags, and skew amounts to the respective variable speed determination units 103R and 103L.
Also, the comparative determination unit 101 determines a lag/lead amount based on the received average value (TAVE) and the target passage count value T1IDEAL from the image control unit 7 (S1503), and sends a lag/lead flag and a lag/lead amount to the variable speed determination units 103R and 103L.
Then, the variable speed determination units 103R and 103L determine the target speeds Vs1 and Vs2 based on the lag/lead amount received from the comparative determination unit 101 and the skew amounts received from the skew amount counters 102R and 102L (S1504). After that, the variable speed determination units 103R and 103L determine whether or not they have received data on the amount of toner used from the image control unit 7 (S1505). When the variable speed determination units 103R and 103L have not received data on the amount of toner used, the variable speed determination units 103R and 103L send the determined target speeds Vs1 and Vs2 to the respective motor pulse control units 120R and 120L.
On the other hand, when the variable speed determination units 103R and 103L have received data on the amount of toner used, the variable speed determination units 103R and 103L determine the target speeds Vs3 and Vs4 based on the lag/lead amount, the skew amounts, and the data on the amount of toner used (S1506), and send the determined target speeds Vs3 and Vs4 to the respective motor pulse control units 120R and 120L.
Then, the motor pulse control units 120R and 120L control conveying speeds (rotational speeds) of the respective skew correction roller pairs 2R and 2L based on the received target speeds (S1507). Through the control of the skew correction roller pairs 2R and 2L, the sheet S of which skew and amount of lag/lead relative to the toner image has been adjusted is conveyed toward the timing roller pairs 1R and 1L.
Then, when detecting the leading end of the sheet S conveyed toward the timing roller pairs 1R and 1L (S1508), the second sensor unit 5 sends a sheet detection signal to the counter 200. The counter 200 sends a count value based on the sheet detection signal to the comparative determination unit 201.
The comparative determination unit 201 determines a lag/lead amount based on the count value from the counter 200 and the target passage count value T2IDEAL from the image control unit 7 (S1509), and sends the determined lag/lead amount and a lag/lead flag to the variable speed determination unit 202. The variable speed determination unit 202 determines the target speed V1 based on the received lag/lead amount and lag/lead flag (S1510), and sends the determined target speed V1 to the motor pulse control unit 203.
Then, the motor pulse control unit 203 controls the conveying speeds (rotational speeds) of the timing roller pairs 1R and 1L based on the received target speed V1 (S1511). Through the control of the timing roller pairs 1R and 1L, the sheet S of which lagging or leading amount has been adjusted so that the leading end of the sheet S and the leading end of the toner image on the photosensitive drum 16 can coincide with each other is conveyed toward the secondary transfer unit 28. Then, in the secondary transfer unit 28, the toner image is transferred to the sheet S (S1512).
Next, a description will be given of a second embodiment of the present invention.
An image forming apparatus according to the second embodiment controls the skew correction roller pairs 2R and 2L based on the amount of toner used of an image formed on one surface of the sheet S and sheet surface characteristics.
The overall arrangement of the image forming apparatus according to the present embodiment is the same as that of the image forming apparatus 500 according to the first embodiment, and description of corresponding operations is omitted, only different operations being described below.
This image forming apparatus has an operation/display unit as shown in
When the sheet S with an image formed thereon is to be conveyed, the variable speed determination units 103R and 103L determine the target speeds Vs1 and Vs2 and amounts of toner used DR and DL in the regions 11R and 11L in the same way as described above. Also, based on the sheet surface friction coefficient μ and the amounts of toner used DR and DL, the variable speed determination units 103R and 103L obtain respective friction coefficient correction values βR and βL, from a table shown in
Based on the friction coefficient correction values βR and βL, the variable speed determination units 103R and 103L obtain a correction value γ from a table shown in
Vs5=Vs1+γVd (3)
Vs6=Vs2−γVd (4)
Here, Vd is an adjustment value for correcting for a difference between a computed correction result and an actual correction result, and correcting for subtle apparatus-to-apparatus variations such as mounting positions of sensors and drive rollers.
The variable speed determination units 103R and 103L send the determined target speeds to the respective motor pulse control units 120R and 120L. Based on the received target speeds, the motor pulse control units 120R and 120L control the rotational speeds of the respective skew correction roller pairs 2R and 2L.
Referring next to
Referring to
On the other hand, when the variable speed determination units 103R and 103L have received data on the amount of toner used from the image control unit 7, they determine the target speeds Vs5 and Vs6 based on the lag/lead amount, the skew amounts, and the data on surface characteristics (S1906), and send the determined target speeds Vs5 and Vs6 to the respective motor pulse control units 120R and 120L.
According to the first embodiment, when the sheet S having an image formed on the first surface thereof is conveyed so as to form an image on the second surface of the sheet S, skew and lagging/leading of the sheet S are corrected for with consideration given to a difference in the amount of slip due to a difference in the amount of toner used in regions where the respective skew correction roller pairs 1R and 1L and the sheet S contact on each other. Thus, skew during conveyance for image formation on the second surface can be reliably corrected for.
According to the second embodiment, when the sheet S having an image formed on the first surface thereof is conveyed so as to form an image on the second surface of the sheet S, skew and lagging/leading of the sheet S are corrected for with consideration given to a difference in the amount of slip due to a difference in the amount of toner used and a friction coefficient as sheet surface characteristics. Thus, as is the case with the first embodiment, skew during conveyance for image formation on the second surface can be reliably corrected for. Moreover, the sheet characteristics for use in determining the targets speeds Vs5 and Vs6 is not limited to a friction coefficient, but may be the presence or absence of a coating.
Moreover, although in the above described embodiments, the speed at which an image is transferred to the sheet S in the secondary transfer unit (transfer speed) is the steady-state speed V0, the transfer speed and the steady-state speed may not be equal. For example, it may be arranged such that the steady-state speed is set to be higher than the transfer speed and switched to the transfer speed by the timing roller pairs 1R and 1L correcting for lagging/leading of the sheet S and lowering the steady-state speed, and the sheet S is conveyed to the secondary transfer unit.
Moreover, in the above described embodiments, skew of the sheet S is corrected for using the skew correction roller pairs 2R and 2L to reduce the degree of lagging/leading of the sheet S to some extent, and then lagging/leading of the sheet S is reliably corrected for using the timing roller pairs 1R and 1L. In the above described embodiments, however, sheet skew and lagging/leading may be corrected for in parallel using, for example, the skew correction roller pairs 2R and 2L.
Moreover, in place of the sensors 6R and 6L that detect the leading end of the sheet S, a line sensor using a CCD (charge-coupled device) may be provided in a direction perpendicular to the sheet conveying direction so as to detect the leading end of the sheet S.
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 such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2009-231326 filed Oct. 5, 2009, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-231326 | Oct 2009 | JP | national |
