GB2224013A

GB2224013A - Image forming apparatus

Info

Publication number: GB2224013A
Application number: GB8923596A
Authority: GB
Inventors: Hiroshi Mori
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1988-10-24
Filing date: 1989-10-19
Publication date: 1990-04-25
Anticipated expiration: 2009-10-19
Also published as: DE3935231A1; GB2224013B; GB8923596D0; JPH02210368A; DE3935231C2

Description

1 1 is 2 224 0 13 "IMAGE FORMING APPARATUS" The present invention

generally relates to image forming apparatuses, and more particularly to an image forming apparatus having means for correcting a position of a recording sheet which is supplied from a duplex unit.

FIG.1 shows an essential part of a laser printer. The laser printer shown in FIG.1 has a main printer body'13, and a plurality of paper supply units (or paper supply cassettes) may be detachably connected to the main printer body 13.

A recording sheet 3 is supplied in a direction A from a first paper supply unit 1 or a second paper supply unit 2, and a resist roller pair 4 controls a timing with which the recording sheet 3 is transported to a photosensitive body 5. The photosensitive body 5 is rotated counterclockwise while a charger 6 charges a surface of the photosensitive body 5. A laser beam L from a laser optical system 7 is irradiated on the photosensitive body 5 to form thereon an electrostatic image.

The electrostatic image is visualized into a toner image by a developing unit S. The toner image is transferred onto the recording sheet 3 by a 2 1 is transfer charger 9, and the recording sheet 3 which is in contact with the photosensitive body 5 is separated from the photosensitive body 5 electrostatically. Thereafter, the recording sheet 3 is transported to a fixing unit 10 which fixes the toner image on the recording sheet 3. The recording sheet 3 having the fixed image is ejected in a direction B to an ejection part 11. On the other hand, after the toner image on the photosensitive body 5 is trhnsferred onto the recording sheet 3, cleaning blades of a cleaning unit 12 removes the residual toner on the surface of the photosensitive body 5 and the residual toner is recovered within the cleaning unit 12.

FIG.2 shows a duplex unit 20 for turning over (or reversing) the recording sheet 3 which has the image formed on a front side thereof so that an image can be formed on a back side of this recording sheet 3. The reversed recording sheet 3 is resupplied to the photosensitive body 5, the charger 6, the laser optical system 7, the developing unit 8, the transfer charger 9 and the like. The recording sheet 3 which has the image formed on the front side is supplied to a transport part of the duplex unit 20 via a path selector 14 and is supplied to a 3 1 switchback part 16 by transport rollers 15. Switch back rollers 18 make a reverse rotation when a predetermined time elapses after a rear end of the recording sheet 3 passes a switchback sensor 17. and the recording sheet 3 is supplied to the resist roller pair 4 of the main printer body 13 via a path selector 19. In this case, the position of the recording sheet 3 in the switchback part 16 slightly differs depending on whether the recording sheet 3 was supplied'from the first paper supply unit 1 or from the second paper supply unit 2.

In other words, when forming the image on the front side of the recording sheet 3, a deviation of the recording sheet 3 in the horizontal direction (hereinafter simply referred to as a horizontal deviation) while the recording sheet 3 is transported to the resist roller pair 4 slightly differs depending on whether the recording sheet 3 is supplied from the first paper supply unit 1 or from the second paper supply unit 2. The horizontal direction is perpendicular-to a direction in which the recording sheet 3 is transported.

In addition, when forming the image on the back side of the recording sheet 3. the recording sheet 3 is first reversed in the duplex unit 20 and 4 1 is then resupplied to the resist roller pair 4 in the reversed state. Because the transport path in which the recording sheet 3 is reversed is relatively long, the recording sheet 3 undergoes a horizontal deviation during the transport.

The horizontal deviation of the recording sheet 3 also differs depending on the inclination, mechanical characteristic and the like of the first and second paper supply units 1 and 2 and the duplex unit 20. Wh&n the horizontal deviation of the recording sheet 3 occurs, the positional relationship between the photosensitive body 5 and the recording sheet 3 changes and results in the image being formed on the recording sheet 3 at a position shifted from an intended or regular position. This shift of the image forming position is peculiar to each machine and must be accurately adjusted independently for each machine.

Generally, each machine is adjusted by making an accurate mechanical adjustment of the transport path. However, this adjustment requires both time and effort. Accordingly, it is possible to conceive a method of making no mechanical adjustment but to corect the shift of the image forming position in the optical system by adjusting a start position G 1 where the optical system starts to record the image so that the relative positional relationship between the recording sheet and the start position.

According to the conceivable method, the horizontal deviation is measured beforehand. In order to eliminate the shift in the start position where the recording of the image starts caused by the horizontal deviation, a correction quantity which corresponds to the horizontal deviation is set for each paper stpply unit and the duplex unit. A counting operation is started by a synchronous detection pulse and the recording start position in the horizontal direction is determined when the counted value reaches a predetermined reference value. The predetermined reference value is corrected depending on the set correction quantity.

But as described above, the degree of parallelism, mechanical characteristic and the like of each paper supply unit and the duplex unit of the image forming apparatus such as the laser printer differ slightly for each individual apparatus. The conceivable method adjusts the horizontal deviation which is caused by the inconsistent characteristics of each individual apparatus by setting the correction quantity for each paper supply unit and C 6 1 the duplex unit. However, when the reversed recording sheet is resupplied from the duplex unit, the position of the recording sheet within the duplex unit differs depending.on the paper supply unit from which the recording sheet was originally supplied.

For this reason, when the image forming apparatus has a plurality of paper supply units, the position of the recording sheet which is resupplied from the duplex unit cannot be corrected appropriately by the sole use of the correction quantity which is set with respect to the duplex unit. In other words, the conceivable method can only correct the position of the recording sheet to a certain extent which is still insufficient.

Accordingly, it is a general object of the present invention to provide a novel and useful image forming apparatus in which the problems described above are eliminated.

The present invention provides an image forming apparatus comprising a plurality of paper supply units for supplying recording sheets, a recording part including means for forming an image on a recording sheet, a duplex unit for reversing sides of a recording sheet which is recorded with an image on a front side by said recording part and for.

cl 7 resupplying the reversed recording sheet to said recording part for recording an image an a back side, transport means for transporting the recording sheet which is supplied from one of said paper supplying units and said duplex unit to said recording part, and correcting means for correcting a recording start position where said recording part starts to form the image based on a correction quantity which indicates a deviation of the recording sheet in a predetermined direction fr6m a regular position in said recording part, said predetermined direction being perpendicular to a direction in which the recording sheet is transported by said transport means, said correction quantity being set independently for each of said paper supply units and said duplex unit.

According to the image forming apparatus of the present invention, the correction quantity can be set independently for each transport path used to supply the recording sheet to the recording part. Hence, it is possible to constantly and accurately correct the recording start position of the recording part on the recording sheet.

other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with c a the accompanying drawings.

FIG.1 is a side view in cross section generally showing an essential part of a laser printer; FIG.2 is a side view in cross section generally showing an essential part of a duplex unit; FIG.3 is a system block diagram showing an embodiment of an image forming apparatus according to the present invention; FIC.4 is a flow chart showing an embodiment of an operation of the image forming apparatus shown in FIG.3; FIG.5 is a diagram for explaining a position adjustment; FIGS.6A through 6C are diagrams for explaining a recording start position; FIG.7 shows an embodiment of a main controller of the image forming apparatus shown in FIG.3; and FIG.8 is a flow chart showing another embodiment of an operation of the image forming apparatus shown in FIG.3.

FIG.3 shows a system block diagram of an embodiment of an image forming apparatus according to the present invention. In this embodiment, the 9 present invention is applied to a laser printer which has two paper supply units as shown in FIG.1 and a duplex unit as shown in FIG.2 described before.

In FIG.3, the laser printer comprises a host computer 21, a system controller 22, a main controller 23, a video controller 24, an optical write part 25, and dual-inline package switches (hereinafter simply referred to as DIP switches) 26 through 29 which are connected as shown. The system controller 22 converts character codes and the like received from the host computer 21 into a video signal having a dot pattern. The video signal is supplied to the video controller 24. The video controller 24 supplies the video signal to the optical write part 25 and synchronizes the write timing of the optical write part 25.

The DIP switches 26 through 29 are connected to the main controller 23. The DIP switches 26 and 27 are used to set correction quantities with respect to the corresponding paper supply units 1 and 2 shown in FIG.1. The DIP switch 28 is used to set the correction quantity for the case where the recording sheet which is supplied from the first paper supply unit I is resupplied from the duplex unit 20. In addition, the DIP switch 29 is c 1 used to set the correction quantity for the case where the recording sheet which is supplied from the second paper supply unit 2 is resupplied from the duplex unit 20.

FIG.4 shows an embodiment of an operation of the main controller 23. A step S1 makes initial settings of the laser printer, and a step S2 discriminates whether or not a print request is received from the system controller 22. When the discriminati6n result in the step S2 becomes YES, a step S3 confirms a paper supply start position. A step S4 discriminates whether or not the recording sheet is resupplied from the duplex unit 20. When the discrimination result in the step S4 is YES, a step S5 finds out the position where the supply of the recording sheet which is being resupplied originally started. A step S6 discriminates whether or not the supply of the recording sheet which is being resupplied originally started from the first paper supply unit 1 or the second paper supply unit 2. When the discrimination result in the step S6 is the first paper supply unit 1, a step S7 sets the value of the corresponding DIP switch 28 as the correction quantity. on the other hand, when the discrimination result in the step S6 is the second N 11 paper supply unit 2, a step S8 sets the value of the corresponding DIP switch 29 as the correction quantity.

When the discrimination result in the step S4 is NO, a step S9 discriminates whether the recording sheet which is being supplied is started from the first paper supply unit 1 or the second paper supply unit 2. When the discrimination result in the step S9 is the first paper supply unit 1, a step S10 setb the value of the corresponding DIP switch 26 as the correction quantity. on the other hand, when the discrimination result in the step S9 is the second paper supply unit 2, a step S11 sets the value of the corresponding DIP switch 27 as the correction quantity.

After the step S7, S8, S10 or S11, a step S12 carries out a print operation by controlling the recording start position along the horizontal direction by use of the correction quantity set by the corresponding one of the DIP switches 26 through 29. The horizontal direction is perpendicular to the direction in which the recording sheet 3 is transported. Accordingly, it is possible to independently set the correction quantity for the case where the recording sheet which is originally G 12 1 supplied from the first paper supply unit 1 is resupplied from the duplex unit 20 and for the case where the recording sheet which is originally supplied-from the second paper supply unit 2 is resupplied from the duplex unit 20, and the position of the recording sheet can be corrected with ease for each case.

Next, a description will be given of the setting of the correction quantity. FIG.5 shows the relationship'of a synchronous detection position P1, an image region P2 and a position adjusting width P3. An image recording start position is denoted by Z, and an image recording end position is denoted by W. FIG.6A shows a case where the image is recorded with the recording start position Z located at the regular (correct) position. FIGS.6B and 6C respectively show cases where the images are recorded with the recording start position Z shifted in the directions y and x shown in FIG.5.. In FIGS.6A through 6C, PS denotes the position of a synchronous detection sensor (not shown).

The recording start position Z is adjusted. as follows. When the main controller 23 receives the print request from the system controller 22, the main controller 23 if not in a busy state supplies a C.

13 control signal to the video controller 24 so as to drive the optical write part 25. When a synchronous detection signal SDS is output from the synchronous detection sensor, an image clock signal WCLK is generated. The synchronous detection signal SDS is generated in the optical write part 25 and is used as a reference for determining a write start position for each line of the image. The image clock signal WCLK is generated in the video controller 24 and is used as a reference for determining the timing with which the image data is transmitted.

FIG.7 shows an embodiment of the main controller 23. The main controller 23 comprises a multiplexer 23A which receives the output signals of the DIP switches 26 through 29, a programmable counter 23B, a decoder 23C and a main control unit 23D. The programmable counter 23B receives the image clock signal WCLK and the synchronous detection signal SDS. Vcc denotes a power source voltage. In addition, bo through b3 denote data terminals for receiving lower significant bits of the data and b4 through b7 denote data terminals for receiving upper significant bits of the data.

The main controller 23 detects whether the paper supply system selected by the user is the first G 14 is paper supply unit 1, the second paper supply unit 2 or the duplex unit 20. In order to select the value of the DIP switch which corresponds to the selected paper supply system, the main control unit 23D supplies a selection signal SEL to the multiplexer 23A. Based on the selection signal SEL, the multiplexer 23A sets the output signal of the selected one of the DIP switches 26 through 29 to the data terminals bO through b3 of the programmable counter 23B as an initial value. Thereafter, the programmable counter 23B starts to count the image clock signal WCLK from a time when the synchronous detection signal SDS is received. The programmable counter 23B outputs a carry signal when the counted value reaches 110OR11, and this carry signal is supplied to the main control unit 23D via the decoder 23C. The time when the carry signal is received by the main control unit 23D is set as the recording start position Z shown in FIG.5.

In this embodiment, the programmable counter 23B is an 8-bit counter and the value of the DIP switch is set to the data terminal bO through b3 while the data terminals b4 through b7 are fixed to the power source voltage Vcc.

When it is assumed for the sake of 1 X 1 convenience that the regular value of the DIP switch when the recording start position Z is located at the regular position is 118H",, the programmable counter 23B outputs the carry signal at a position indicated by a one-dot chain line which is a predetermined distance from a left end of the recording sheet indicated by a solid line in FIG.6A.

When the recording start position Z shifts in the direction y as shown in FIG.6B, the value of the DIP switch is set smaller than the regular value 118H". In this case, the programmable counter 23B outputs the carry signal after the counted value reaches a value greater than that of the case where the regular value is set in the DIP switch. As a result, as indicated by a broken line in FIG.6B, the adjustment is made so that the recording start position Z relative to the recording sheet (indicated by the solid line) is correct.

When the recording start position Z shifts in the direction x as shown in FIG.6C, the value of the DIP switch is set greater than the regular value 118H". In this case, the programmable counter 23B outputs the carry signal before the counted value reaches a value equal to that of the case where the regular value is set in the DIP switch. As a result, C 16 1 26 as indicated by a broken line in FIG.6C, the adjustment is made so that the recording start position Z relative to the recording sheet (indicated by the solid line) is correct.

After the programmable counter 23B outputs the carry signal at the recording start position Z, the programmable counter 23B continues to count and the decoder 23C supplies a signal which indicates the recording end position W to the main control unit 23D when the counted value in the programmable counter 23B reaches a predetermined value. The recording end position W differs depending on the size (width) of the recording sheet. Hence, the predetermined value to be decoded in the decoder 23C is set depending on a detection made by a paper size detecting means which is provided in the paper supply unit, so that the recording end position is accurately set for the recording sheets of various sizes.

The DIP switch is provided with respect to all of the units in the paper supply system which affect the supply of the recording sheet, including the duplex unit 20. For this reason, the horizontal deviation of the recording sheet can be adjusted depending on the characteristics of each unit by merely setting the value of the DIP switch. As a 1 17 C.

result, it is possible to constantly and accurately set the recording start position and the recording end position on the recording sheet regardless of which unit supplies the recording sheet.

Next, a description will be given of another embodiment of the operation of the main controller 23, by referring to FIG.S. In FIG.8, those steps which are the same as those corresponding steps in FIG.4 are designated by the same reference numerals, and a description thereof will be omitted.

According to this embodiment, it is possible to omit the DIP switch 29 shown in FIG.3.

For example, it is assumed for the sake of convenience that the correction quantity is 2 mm for the case where the printing is carried out with respect to the recording sheet 3 which is supplied from the first paper supply unit 1 and the correction quantity is 3 mm for the case where the printing is carried out with respect to the recording sheet 3 which is supplied from the second paper supply unit 2. In this case, when the paper supply is started from the first paper supply unit 1 and after an image is recorded on the front side of the recording sheet this recording sheet is transported to the duplex unit 20 which resupplies this recording sheet for 18 C 1 recording an image on a back side of the recording sheet, the horizontal shift introduced by the duplex unit 20 alone is 1 mm if the total horizontal shift is 3 mm. In other words, the correction quantity is 1 mm for the duplex unit 20. Therefore, the correction quantity for the first paper supply unit 1 alone is set to 2 mm, the correction quantity for the duplex unit 20 alone is set to I mm, and the total correction quantity is set to 3 mm.

Sitilarly, when the paper supply is started from the second paper supply unit 2 and after an image is recorded on the front side of the recording sheet this recording sheet is transported to the duplex unit 20 which resupplies this recording sheet for recording an image on a back side of the recording sheet, the horizontal shift introduced by the duplex unit 20 alone is 1 mm if the total horizontal shift is 4 mm. In other words, the correction quantity is 1 mm for the duplex unit 20. Therefore, the correction quantity for the second paper supply unit 2 alone is set to 3 iti, the correction quantity for the duplex unit alone is set to 1 mm, and the total correction quantity is set to 4 mm.

Therefore, the total correction quantity C 19 can be set independently for the case where the duplex unit 20 resupplies the recording sheet which is originally supplied from the first paper supply unit 1 and the case where the duplex unit 20 resupplies the recording sheet which is originally supplied from the second paper supply unit 2.

In FIG.8, when the discrimination result in the step S6 is the first paper supply unit 1, a step S27 sets as the correction quantity a sum of the values of thd DIP switches 26 and 28. on the other hand, when the discrimination result in the step S6 is the second paper supply unit 2, a step S28 sets as the correction quantity a sum of the values of the DIP switches 27 and 28. In other words, the correction quantity is automatically set to a new value which corresponds to the sum of the values of two DIP switches.

Therefore, according to this embodiment, it is possible to omit the DIP switch 29 which is provided with respect to the duplex unit 20 because the total correction quantity for the case where the recording sheet is resupplied from the duplex unit 20 is automatically set by adding the correction quantity with respect to the duplex unit 20 along to the correction quantity of the paper supply unit 1 along which originally started the paper supply.

In the described embodiments, the number of paper supply units is two. However, it is of course possible to apply the present invention to cases where the number of paper supply units is greater than two.

Further, the present invention is not limited to these embodiments, but various variations and modifications may be made without departing from the scope of'the present invention.

1 k 21

Claims

1 WHAT WE CLAIM IS:

1. An image forming apparatus comprising:

a plurality of paper supply units for supplying recording sheets; recording part including means for forming an image on a recording sheet; duplex unit for reversing sides of a recording sheet which is recorded with an image on a front side by said recording part and for resupplying the reversed recording sheet to said recording part for recording an image on a back side; transport means for transporting the recording sheet which is supplied from one of said paper supplying units and said duplex unit to said recording part; and correcting means for correcting a recording start position where said recording part starts to form the image based on a correction quantity which indicates a deviation of the recording sheet in a predetermined direction from a regular position in said recording part, said predetermined direction C' 22 being perpendicular to a direction in which the recording sheet is transported by said transport means, said correction quantity being set independently for each of said paper supply units and said duplex unit.

2. The image forming apparatus as claimed in claim 1 wherein said correction quantity is set to a first value when said recording part receives the recording sheet which is supplied directly from a first paper supply unit, a second value when said recording part receives the recording sheet which is supplied directly from a second paper supply unit, a third value when said recording part receives the recording sheet which is originally supplied from said first paper supply unit and is received via said duplex unit, and a fourth value when said recording part receives the recording sheet which is originally supplied from said second paper supply unit and is received via said duplex unit.

t C 23

3. The image forming apparatus as claimed in claim 2 which further comprises setting means for independently setting said first through fourth values into said correcting means.

4. The image forming apparatus as claimed in claim 3 wherein said setting means comprises four dual-inline package switches for setting said first through fourth values.

5. The image forming apparatus as claimed in claim 2 which further comprises means for detecting the unit from which said recording part receives the recording sheet.

6. The image forming apparatus as claimed f 24 1 in claim 1 which further comprises setting means for independently setting a first value into said correcting means as said correction quantity for a case where said recording part receives the recording sheet which is supplied directly from a first paper supply unit, a second value into said correcting means as said correction quantity for a case where said recording part receives the recording sheet which is received directly from a second paper supply unit, and a third value into said correcting means as said correction quantity for a case where said recording part receives the recording sheet which is originally supplied from one of said paper supply units and is received via said duplex unit.

7. The image forming apparatus as claimed in claim 6 wherein said setting means comprises three dual-inline package switches for setting said first through third values.

1 1

8. The image forming apparatus as claimed in claim 6 wherein said correction quantity is set to a first value when said recording part receives the recording sheet which is supplied directly from a first paper supply unit. a second value when said recording part receives the recording sheet which is supplied directly from a second paper supply unit, a sum of the first and third values when said recording part receives the recording sheet which is originally supplied from said first paper supply unit and is received via said duplex unit, and a sum of the second and third values when said recording part receives the recording sheet which is originally supplied from said second paper supply unit and is received via said duplex unit.

9. The image forming apparatus as claimed in claim 6 which further comprises means for detecting the unit from which said recording part receives the recording sheet.

26 C lo. An image forming apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

Published 1990 atThe Patent Office, State House, 66171 High Holborn, LondonWCIR4TP. Further copiesinaybeobtainedfrom The PatentOffice. Sales Branch. St Mary Cray, Orpington. Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1187