US20100148431A1 - Sheet feeding device and image forming apparatus provided with the sheet feeding device - Google Patents
Sheet feeding device and image forming apparatus provided with the sheet feeding device Download PDFInfo
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- US20100148431A1 US20100148431A1 US12/635,378 US63537809A US2010148431A1 US 20100148431 A1 US20100148431 A1 US 20100148431A1 US 63537809 A US63537809 A US 63537809A US 2010148431 A1 US2010148431 A1 US 2010148431A1
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- Prior art keywords
- sheet
- speed
- feeder
- gap
- feeding device
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H5/00—Feeding articles separated from piles; Feeding articles to machines
- B65H5/06—Feeding articles separated from piles; Feeding articles to machines by rollers or balls, e.g. between rollers
- B65H5/062—Feeding articles separated from piles; Feeding articles to machines by rollers or balls, e.g. between rollers between rollers or balls
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H7/00—Controlling article feeding, separating, pile-advancing, or associated apparatus, to take account of incorrect feeding, absence of articles, or presence of faulty articles
- B65H7/02—Controlling article feeding, separating, pile-advancing, or associated apparatus, to take account of incorrect feeding, absence of articles, or presence of faulty articles by feelers or detectors
- B65H7/14—Controlling article feeding, separating, pile-advancing, or associated apparatus, to take account of incorrect feeding, absence of articles, or presence of faulty articles by feelers or detectors by photoelectric feelers or detectors
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H2220/00—Function indicators
- B65H2220/03—Function indicators indicating an entity which is measured, estimated, evaluated, calculated or determined but which does not constitute an entity which is adjusted or changed by the control process per se
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H2301/00—Handling processes for sheets or webs
- B65H2301/40—Type of handling process
- B65H2301/44—Moving, forwarding, guiding material
- B65H2301/445—Moving, forwarding, guiding material stream of articles separated from each other
- B65H2301/4452—Regulating space between separated articles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H2511/00—Dimensions; Position; Numbers; Identification; Occurrences
- B65H2511/20—Location in space
- B65H2511/22—Distance
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H2511/00—Dimensions; Position; Numbers; Identification; Occurrences
- B65H2511/50—Occurence
- B65H2511/51—Presence
- B65H2511/514—Particular portion of element
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H2513/00—Dynamic entities; Timing aspects
- B65H2513/10—Speed
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H2515/00—Physical entities not provided for in groups B65H2511/00 or B65H2513/00
- B65H2515/70—Electrical or magnetic properties, e.g. electric power or current
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H2701/00—Handled material; Storage means
- B65H2701/10—Handled articles or webs
- B65H2701/13—Parts concerned of the handled material
- B65H2701/131—Edges
- B65H2701/1311—Edges leading edge
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H2701/00—Handled material; Storage means
- B65H2701/10—Handled articles or webs
- B65H2701/13—Parts concerned of the handled material
- B65H2701/131—Edges
- B65H2701/1313—Edges trailing edge
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H2801/00—Application field
- B65H2801/03—Image reproduction devices
- B65H2801/06—Office-type machines, e.g. photocopiers
Definitions
- the present invention relates to a sheet feeding device and an image forming apparatus provided with the sheet feeding device, and more particularly to a sheet feeding device for feeding sheets of printed medium successively and an image forming apparatus provided with the sheet feeding device.
- a sheet feeding device feeds a plurality of sheets successively
- the sheets are fed with no gaps among the sheets for the reasons below. If there are gaps among sheets, feed rollers and a transfer belt will rotate even while the gaps are passing thereby. Therefore, in this case, the drive distance of the feed rollers and the transfer belt is large, compared with the case wherein there are no gaps among sheets. Accordingly, when there are gaps among sheets, the feed rollers and the transfer belt are abraded shortly. Also, when there are gaps among sheets, the productivity becomes lower, compared with the case wherein there are no gaps among sheets. For these reasons, sheets are fed successively preferably with no gaps among the sheets.
- a sheet feeding device for example, a sheet feeding device as disclosed by Japanese Patent Laid-Open Publication No. 2006-232475 (Reference 1) is well known.
- a control unit controls a feed-out means to slow down the speed of the following sheet. With this control, it is possible to feed a plurality of sheets successively while keeping constant gaps among the sheets.
- An object of the present invention is to provide a sheet feeding device wherein the gaps among sheets successively fed can be made closer to zero and an image forming apparatus provided with the sheet feeding device.
- An embodiment of the present invention is a sheet feeding device that is suited to be used in an image forming apparatus comprising a printing section for printing an image on a sheet, and the sheet feeding device comprises: a first feeder for feeding the sheet at a first speed; a second feeder for feeding the sheet fed by the first feeder to the printing section at a second speed; a detector, which is located between the first feeder and the second feeder, for detecting a gap between a first sheet and a second sheet at a plurality of detection points while the first sheet is being fed by the second feeder and the second sheet is being fed by the first feeder; and a controller for controlling the first feeder or the second feeder, and when the detector detects that there is a gap between the first sheet and the second sheet, the controller controls the first feeder or the second feeder such that the first speed will be higher than the second speed.
- Another embodiment of the present invention is an image forming apparatus, and the image forming apparatus comprises the above-described sheet feeding device.
- FIG. 1 is a schematic view showing the general structure of an image forming apparatus according to an embodiment of the present invention
- FIG. 2 is an enlarged view of a sheet feeding device employed in the apparatus shown by FIG. 1 ;
- FIGS. 3 a - 3 c are illustrations showing operation of an overlap correction mechanism
- FIG. 4 is a flowchart showing a procedure that is carried out by a control unit while the sheet feeding device is feeding sheets successively;
- FIG. 5 is a graph showing waveforms of signals outputted from sensors
- FIGS. 6 a - 6 d are illustrations showing passing of two sheets by a light receiving element
- FIGS. 7 a - 7 d are illustrations showing passing of two sheets by a light receiving element
- FIGS. 8 a - 8 c are illustrations showing passing of two sheets by a light receiving element
- FIGS. 9 a - 9 c show modifications of the sensors provided for the sheet feeding device.
- FIG. 10 shows a modification of the overlap correction mechanism.
- a sheet feeding device and an image forming apparatus according to an embodiment of the present invention are hereinafter described.
- FIG. 1 an image forming apparatus 1 provided with a sheet feeding device according to an embodiment of the present invention is described.
- the image forming apparatus 1 is an electrophotographic color printer and forms a color image by combining four color (Y: yellow, M: magenta, C: cyan and K: black) images in a tandem method.
- the image forming apparatus 1 is to form an image on a sheet of paper P in accordance with image data, and comprises a printing section 2 , a feeding section 15 , a sheet feeding device 35 , a fixing device 22 and a printed-sheet tray 23 .
- the feeding section 15 is to supply sheets P one by one, and comprises a sheet tray 16 , a feed-out roller 17 and separation rollers 18 .
- a plurality of sheets to be subjected to printing is stacked in the sheet tray 16 .
- the feed-out roller 17 is to pick the sheets P out of the tray 16 one by one.
- the separation rollers 18 separate two or more sheets possibly picked out by the feed-out roller 17 and feed surely one sheet P forward.
- the sheet feeding device 35 comprises feed rollers 19 , timing rollers 20 , a control unit 30 , a driver 31 , a storage 32 , an overlap correction mechanism 40 , a route R and sensors Se 1 to Se 5 .
- the feed rollers 19 are rotated by the driver 31 to feed the sheet P at a speed “Va”.
- the driver 31 is, for example, a motor.
- the feed rollers 19 and the driver 31 form a feeder.
- the timing rollers 20 are rotated by another driver (not shown) to feed the sheet P fed thereto by the feed rollers 19 further to a printing section 2 at a speed “Vb”.
- the timing rollers 20 and the driver form another feeder.
- the route R is formed between the feed rollers 19 and the timing rollers 20 , and the sheet P travels therein.
- the sensors Se 1 to Se 5 are provided along the route R.
- the sensors Se 1 to Se 5 detect the gap between the sheets P 1 and P 2 . More specifically, while the sheet P 1 is being fed by the timing rollers 20 and while the sheet P 2 is being fed by the feed rollers 19 , the gap “g” between the trailing edge of the sheet P 1 and the leading edge of the sheet P 2 (which is hereinafter referred to as the gap “g” between the sheets P 1 and P 2 ) is detected by the plural sensors Se 1 to Se 5 provided along the route R.
- Each of the sensors Se 1 to Se 5 comprises a light source Se 1 - 1 (Se 2 - 1 , Se 3 - 1 , Se 4 - 1 or Se 5 - 1 ) and a light receiving element Se 1 - 2 (Se 2 - 2 , Se 3 - 2 , Se 4 - 2 or Se 5 - 2 ).
- the light source Se 3 - 1 and the light receiving element Se 3 - 2 are shown in the magnified view in FIG. 2 .
- the light sources Se 1 - 1 to Se 5 - 1 emit light.
- the light receiving elements Se 1 - 2 to Se 5 - 2 define detection points.
- the light receiving elements Se 1 - 2 to Se 5 - 2 receive the light emitted from the light sources Se 1 - 1 to Se 5 - 1 and send the control unit 30 output signals Sig 1 to Sig 5 in accordance with the quantities of received light. Specifically, when the light receiving elements Se 1 - 2 to Se 5 - 2 receive relatively large quantities of light, the elements Se 1 - 2 to Se 5 - 2 send output signals Sig 1 to Sig 5 of relatively high voltages, and when the light receiving elements Se 1 - 2 to Se 5 - 2 receive relatively small quantities of light, the elements Se 1 - 2 to Se 5 - 2 send output signals Sig 1 to Sig 5 of relatively low voltages. As shown in the magnified view in FIG.
- the light receiving elements Se 1 - 2 to Se 5 - 2 have a dimension (length) “l” in the sheet feeding direction.
- the sensors Se 1 to Se 5 are arranged at intervals larger than the initial gap “g” between the sheets P 1 and P 2 , so that the gap “g” will never be detected by two or more sensors concurrently.
- the control unit 30 controls the driver 31 and the feed rollers 19 in accordance with the detection results of the sensors Se 1 to Se 5 .
- the storage 32 is, for example, a hard disk or a memory, and stores a table as shown by Table 1. The table shows the relationship between the size “L” of the gap “g” and the speed “Va”.
- the control unit 30 recognizes the size “L” of the gap “g” based on the output signals Sig 1 to Sig 5 from the sensors Se 1 to Se 5 and determines the speed “Va” with reference to the table.
- the control unit 30 controls the driver 31 and the feed rollers 19 such that the gap “g” detected by a more downstream sensor of the sensors Se 1 to Se 5 will be smaller than the gap “g” detected by a more upstream sensor of the sensors Se 1 to Se 5 .
- the control unit 30 controls the driver 31 and the feed rollers 19 such that the speed “Va” will be V 1 that is equal to the speed “Vb”.
- the overlap correction mechanism 40 is to correct an overlap of the sheets P 1 and P 2 .
- the overlap correction mechanism 40 is provided in a downstream position in the route R (near the timing rollers 20 ), and is a roller that has a cross section of a circle having a protrusion. If the sheets P 1 and P 2 reach the overlap correction mechanism 40 while overlapping with each other, the leading edge of the sheet P 2 is hooked by the protrusion of the overlap correction mechanism 40 as shown by FIG. 3 a . Then, as shown by FIG. 3 b , the sheet P 2 is pushed up by the force of the feed rollers 19 , and accordingly, the overlap correction mechanism 40 is rotated.
- the overlap correction mechanism 40 rotates by a specified amount, as shown by FIG. 3 c , the leading edge of the sheet P 2 is released from the protrusion of the overlap correction mechanism 40 , and the sheet P 2 is fed upward. Thereafter, the overlap correction mechanism 40 rotates further and returns to a state as shown by FIG. 3 a . In this way, the sheet P 2 slows down. Meanwhile, during the period from FIG. 3 a to FIG. 3 c , the sheet P 1 is fed upward without slowing down. Thereby, the overlap of the sheets P 1 and P 2 is corrected.
- the printing section 2 is to form a toner image on a sheet P fed from the timing rollers 20 .
- the printing section 2 comprises image forming units 24 Y, 24 M, 24 C and 24 K, first transfer rollers 8 Y, 8 M, 8 C and 8 K, an intermediate transfer belt 11 , a driving roller 12 , a driven roller 13 , a second transfer roller 14 , and a cleaning device 21 .
- the image forming units 24 Y, 24 M, 24 C and 24 K comprise photosensitive drums 4 Y, 4 M, 4 C and 4 K, electric chargers 5 Y, 5 M, 5 C and 5 K, exposure devices 6 Y, 6 M, 6 C and 6 K, developing devices 7 Y, 7 M, 7 C and 7 K, and cleaners 9 Y, 9 M, 9 C and 9 K, respectively.
- the photosensitive drums, the electric chargers, the exposure devices, the developing devices, the first transfer rollers, the cleaners and the image forming units are discussed generally, they are indicated as the photosensitive drum(s) 4 , the electric charger(s) 5 , the exposure device(s) 6 , the developing device(s) 7 , the first transfer roller(s) 8 , the cleaner(s) 9 and the image forming unit(s) 24 .
- the photosensitive drums When the photosensitive drums, the electric chargers, the exposure devices, the developing devices, the first transfer rollers, the cleaners and the image forming units are discussed individually, they are indicated as the photosensitive drums 4 Y, 4 M, 4 C and 4 K, the electric chargers 5 Y, 5 M, 5 C and 5 K, the exposure devices 6 Y, 6 M, 6 C and 6 K, the developing devices 7 Y, 7 M, 7 C and 7 K, the first transfer rollers 8 Y, 8 M 8 C and 8 K, the cleaners 9 Y, 9 M, 9 C and 9 K, and the image forming units 24 Y, 24 M, 24 C and 24 K.
- the electric chargers 5 charge the circumferential surfaces of the photosensitive drums 4 .
- the exposure devices 6 emit lasers controlled by an exposure control unit (not shown in the drawings). Thereby, electrostatic latent images are formed on the circumferential surfaces of the photosensitive drums 4 .
- the electric chargers 5 and the exposure devices 6 serve as a unit for forming electrostatic latent images on the circumferential surfaces of the photosensitive drums 4 .
- the developing devices 7 are to supply toner to the photosensitive drums 4 so as to form toner images on the circumferential surfaces of the photosensitive drums 4 . More specifically, the developing devices 7 store toner therein and charge the toner into the negative polarity by stirring the toner or the like. Developing rollers provided in the respective developing device 7 feed the toner toward the photosensitive drums 4 . At this time, the negative charged toner moves from the developing rollers to the photosensitive drums 4 influenced by the electric fields of the electrostatic latent images on the photosensitive drums 4 . In this way, toner images are formed on the circumferential surfaces of the photosensitive drums 4 .
- the intermediate transfer belt 11 is laid between the driving roller 12 and the driven roller 13 , and the toner images formed on the photosensitive drums 4 are transferred onto the intermediate transfer belt 1 such that the transferred images will be laid on one another to be combined into a full-color image (first transfer).
- the first transfer rollers 8 are located in contact with the inner surface of the intermediate transfer belt 11 .
- a first transfer voltage is applied from a voltage source (not shown in the drawings) to the first transfer rollers 8 , whereby the toner images formed on the photosensitive drums 4 are transferred onto the intermediate transfer belt 11 .
- the cleaners 9 are to collect residual toner remained on the photosensitive drums 4 after the first transfer.
- the driving roller 12 is rotated by an intermediate transfer belt driver (not shown in the drawings), whereby the intermediate transfer belt 11 is driven. Then, the intermediate transfer belt 11 carries the full-color toner image to the second transfer roller 14 .
- the second transfer roller 14 is located opposite the intermediate transfer belt 11 , and a nip portion N is formed between the second transfer roller 14 and the intermediate transfer belt 11 . While a sheet P fed from the timing rollers 20 is passing through the nip portion N, the second transfer roller 14 transfers the toner image carried by the intermediate transfer belt 11 onto the sheet P (second transfer). After the second transfer, the cleaning device 21 removes residual toner from the intermediate transfer belt 11 .
- the sheet P that has been subjected to the second transfer is fed to the fixing device 22 .
- the fixing device 22 applies a heating treatment and a pressing treatment to the sheet P so as to fix the toner image on the sheet P.
- the printed sheet P is ejected onto the printed-sheet tray 23 .
- the operation of the image forming apparatus 1 is generally described.
- the light receiving elements Se 1 - 2 to Se 5 - 2 receive relatively large quantities of light
- the light receiving elements Se 1 - 2 to Se 5 - 2 output signals Sig 1 to Sig 5 of relatively high voltages.
- the light receiving elements Se 1 - 2 to Se 5 - 2 receive relatively small quantities of light
- the light receiving elements Se 1 - 2 to Se 5 - 2 output signals Sig 1 to Sig 5 of relatively low voltages. Therefore, referring to FIG.
- the control unit 30 times the period and calculates the size “L” of the gap “g” between the sheets P 1 and P 2 , and in accordance with the calculation result, the control unit 30 controls the speed “Va”.
- the waveforms of the output signals Sig 1 to Sig 5 can be classified into three types. More specifically, the waveforms of the output signals Sig 1 and Sig 2 are trapezoidal. The waveform of the output signal Sig 3 is four-cornered with the upper side slanting. The waveform of the output signal Sig 4 is triangle. The output signal Sig 5 is constant and flat, which indicates that the gap “g” between the sheets P 1 and P 2 is zero.
- the reason why the output signals Sig 1 to Sig 5 have different waveforms is that the size “L” of the gap “g” is changeable. Specifically, as shown by FIGS. 6 a to 6 d , when the size “L” of the gap “g” is greater than the length “l” of the light receiving element Sen- 2 , the output signal “Sign” has such a waveform as those of the output signals Sig 1 and Sig 2 . As shown by FIGS. 7 a to 7 d , when the size “L” of the gap “g” is smaller than the size of the light receiving element Sen- 2 , the output signal “Sign” has such a waveform as that of the output signal Sig 3 . As shown by FIGS. 8 a to 8 c , when the gap “g” becomes zero while passing in front of the light receiving element Sen- 2 , the output signal “Sign” has such a waveform as that of the output signal Sig 4 . This is described in more details below.
- FIGS. 6 a to 6 d a case wherein the gap “g” is larger than the length “l” of the light receiving element Sen- 2 is described. While the trailing edge of the sheet P 1 is passing in front the light receiving element Sen- 2 (during the period from FIG. 6 a to FIG. 6 b ), the area of the light receiving element Sen- 2 covered by the sheet P 1 is decreasing. Accordingly, the voltage of the output signal “Sign” is increasing like the output signals Sig 1 and Sig 2 in the periods from “0” to “t 1 ” shown in FIG. 5 . Next, when and after the trailing edge of the sheet P 1 has completed passing by the light receiving element Sen- 2 (during the period from FIG. 6 b to FIG.
- the light receiving element Sen- 2 is covered neither by the sheet P 1 nor by the sheet P 2 . Accordingly, the voltage of the output signal “Sign” is fixed at a relatively high level like the output signals Sig 1 and Sig 2 in the periods from “t 1 ” to “t 2 ” shown in FIG. 5 .
- the area of the light receiving element Sen- 2 covered by the sheet P 2 is increasing. Accordingly, the voltage of the output signal “Sign” is decreasing like the output signals Sig 1 and Sig 2 in the periods from “t 2 ” to “t 3 ” shown in FIG. 5 .
- the voltage of the output signal “Sign” is fixed at a relatively low level like the signals Sig 1 and Sig 2 after “t 3 ” shown in FIG. 5 .
- the gap “g” is smaller than the length “l” of the light receiving element “Sen- 2 ”, the leading edge of the sheet P 2 starts passing in front of the light receiving element Sen- 2 before the trailing edge of the sheet P 1 completes passing in front of the light receiving element Sen- 2 . Therefore, during the period “t 1 ” to “t 2 ”, the voltage of the output signal “Sign” is not fixed but is gradually decreasing.
- the leading edge of the sheet P 2 comes to the light receiving element Sen- 2 while the trailing edge of the sheet P 1 is still passing in front of the light receiving element Sen- 2 .
- the speed “Va” is higher than the speed “Vb”
- the covered area of the light receiving element Sen- 2 is gradually increasing. Accordingly, the voltage of the output signal “Sign” is gradually decreasing like the output signal Sig 5 in the period from “t 1 ” to “t 3 ” shown in FIG. 5 .
- the leading edge of the sheet P 2 catches up with the trailing edge of the sheet P 1 as shown by FIG. 8 c , and thereafter, the light receiving element Sen- 2 is entirely covered by the sheets P 1 and P 2 . Accordingly, the voltage of the output signal “Sign” is fixed at a relatively low level like the output signal Sig 4 after “t 3 ” shown in FIG. 5 .
- the timings of the passing of the trailing edge of the sheet P 1 and the passing of the leading edge of the sheet P 2 in front of the light receiving element Sen- 2 depend on the size “L” of the gap “g”.
- the control unit 30 recognizes the passing of the trailing edge of the sheet P 1 and the passing of the leading edge of the sheet P 2 , based on the waveform of the output signal “Sign” from the light receiving element Sen- 2 . Referring to FIG. 4 , the operation of the image forming apparatus 1 is hereinafter described, focusing on this point.
- the control unit 30 sets N to 1 at step S 1 .
- This step S 1 is carried out, for example, based on the time when the leading edge of the sheet P 1 is detected by the sensor Se 5 located the most downstream in the route R.
- the control unit 30 judges whether the sensor “Sen” (n: integer from 1 to 5) detects the trailing edge of the sheet P 1 during a period when the trailing edge of the sheet P 1 is expected to come thereto (step S 2 ). While the trailing edge of the sheet P 1 is passing in front of the light receiving element Sen- 2 , the covered area of the light receiving element Sen- 2 is decreasing, and the quantity of light received by the light receiving element Sen- 2 is increasing. Accordingly, the voltage of the output signal “Sign” from the light receiving element Sen- 2 is increasing.
- the control unit 30 judges the up-edge of the output signal “Sign” as the time when the sensor “Sen” starts detecting the trailing edge of the sheet P 1 . Thereafter, the processing goes to step S 4 . On the other hand, when the trailing edge of the sheet P 1 is not detected, the control unit 30 judges that there is no gap between the sheets P 1 and P 2 . Then, the processing goes to step S 3 .
- the control unit 30 sets the speed “Va” to V 1 at step S 3 .
- the control unit 30 judges that there is no gap between the sheets P 1 and P 2 . Therefore, the control unit 30 sets the speed “Va” to V 1 that is equal to the speed “Vb”. Thereafter, the processing goes to step S 18 .
- step S 7 This judgment is made at step S 7 that will be described later.
- the processing goes to step S 6 .
- the processing returns to step S 5 .
- the process at step S 5 is repeated.
- step S 6 the control unit 30 takes in a value of the time “t 1 ” (see FIG. 5 ) when the increase in the voltage of the output signal “Sign” stops.
- the control unit 30 judges whether the value “t 1 ” is equal to a value “ta” (step S 7 ).
- the value “ta” is obtained by dividing the length “l” of the light receiving element “Sen- 2 ” by the speed “Vb”, and therefore, the value “ta” indicates the time that is necessary for the trailing edge of the sheet P 1 to complete passing by the light receiving element “Sen- 2 ”.
- the speed “Vb” is a fixed value known to the control unit 30 .
- step S 7 by judging whether the value “t 1 ” is equal to the value “ta”, the control unit 30 judges whether the stop of the increase in the voltage of the output signal “Sign” is due to the completion of the passing of the trailing edge of the sheet P 1 by the light receiving element “Sen- 2 ” as shown by FIG. 6 b or due to the arrival of the leading edge of the sheet P 2 at the light receiving element “Sen- 2 ” as shown by FIGS. 7 b and 8 b . In other words, the control unit 30 judges which waveform of the output signals Sig 1 to Sig 4 shown in FIG. 5 the output signal “Sign” has.
- step S 8 the control unit 30 judges that the stop of the increase in the voltage of the output signal “Sign” is due to the arrival of the leading edge of the sheet P 2 at the light receiving element “Sen- 2 ” (see the waveforms of signals Sig 3 and Sig 4 in FIG. 5 ). Thereafter, the processing goes to step S 10 .
- the control unit 30 judges at step S 8 whether the sensor “Sen” has detected the leading edge of the sheet P 2 .
- the area of the light receiving element “Sen- 2 ” covered by the sheet P 2 is increasing. Accordingly, the quantity of light received by the light receiving element “Sen- 2 ” is decreasing, and the voltage of the output signal “Sign” from the light receiving element “Sen- 2 ” is decreasing like the output signals Sig 1 and Sig 2 for the periods from “t 2 ” to “t 3 ”.
- the control unit 30 judges the down-edge of the output signal “Sign” as the time when the leading edge of the sheet P 2 has reached the light receiving element “Sen- 2 ”.
- the process at step S 8 is repeated until the sensor “Sen” starts detecting the leading edge of the sheet P 2 .
- the processing goes to step S 9 .
- step S 10 the control unit 30 subsequently judges whether the time “t 1 ” is smaller than “ta” (step S 10 ).
- the time “ta” is a time that is necessary for the trailing edge of the sheet P 1 to complete passing by the light receiving element “Sen- 2 ”. Therefore, in the normal state, the time “t 1 ” is equal to or smaller than “ta”, and it never happens that the time “t 1 ” is greater than “ta”. Accordingly, when it is judged that the time “t 1 ” is greater than “ta” (“NO” at step S 10 ), the control unit 30 judges that an error has occurred. Then, the processing is terminated. On the other hand, when the time “t 1 ” is smaller than “ta”, the processing goes to step S 11 .
- the control unit 30 judges whether the trailing edge of the sheet P 1 has completed passing by the light receiving element “Sen- 2 ”.
- the light receiving element “Sen- 2 ” is covered by only the sheet P 2 as shown by FIG. 7 c . Because the sheet P 2 travels in such a direction as to cover more part of the light receiving element “Sen- 2 ”, the voltage of the output signal “Sign” is steeply decreasing like the output signal Sig 3 in the period from “t 2 ” to “t 3 ” shown in FIG. 5 .
- control unit 30 judges whether the trailing edge of the sheet P 1 has completed passing by the light receiving element “Sen- 2 ” by judging whether the decreasing speed in the voltage of the output signal “Sign” is accelerated.
- the processing goes to step S 9 .
- the processing goes to step S 12 .
- step S 12 the control unit 30 judges whether the voltage of the output signal “Sign” is zero. In other words, at step S 12 , the control unit 30 judges whether the leading edge of the sheet P 2 has caught up with the trailing edge of the sheet P 1 while the light receiving element “Sen- 2 ” is detecting the trailing edge of the sheet P 1 and the leading edge of the sheet P 2 as shown by the output signal Sig 4 in FIG. 5 and FIGS. 8 a - 8 c . When the voltage of the output signal “Sign” is zero at step S 12 , the control unit 30 judges that the leading edge of the sheet P 2 has caught up with the trailing edge of the sheet P 1 . Thereafter, the processing goes to step S 13 .
- step S 12 when the voltage of the output signal “Sign” is not zero at step S 12 , the control unit 30 judges that the leading edge of the sheet P 2 has not caught up with the trailing edge of the sheet P 1 . Thereafter, the processing returns to step S 11 .
- step S 13 When the voltage of the output signal “Sign” is zero, the size “L” of the gap “g” between the sheets P 1 and P 2 is judged to be zero (step S 13 ). Thereafter, the processing goes to step S 17 .
- the control unit 30 takes in a value of the time “t 2 ” (see FIG. 5 ) when the voltage of the output signal “Sign” starts decreasing due to the detection at step S 8 or the detection at step S 11 . Thereafter, at step S 14 , the control unit 30 judges whether the leading edge of the sheet P 2 has completed passing by the light receiving element “Sen- 2 ”. When and after the leading edge of the sheet P 2 has completed passing by the light receiving element “Sen- 2 ”, the light receiving element “Sen- 2 ” is completely covered by the sheet P 2 . Accordingly, the quantity of light received by the light receiving element “Sen- 2 ” becomes zero, and the voltage of the output signal “Sign” becomes zero.
- control unit 30 judges whether the leading edge of the sheet P 2 has completed passing by the light receiving element “Sen- 2 ” by judging whether the voltage of the output signal “Sign” has become zero.
- the processing goes to step S 15 .
- the process at step S 14 is repeated until it is judged that the leading edge of the sheet P 2 has completed passing by the light receiving element “Sen- 2 ”.
- step S 15 the control unit 30 takes in a value of the time “t 3 ” (see FIG. 5 ) when the leading edge of the sheet P 2 has completed passing by the light receiving element “Sen- 2 ”.
- control unit 30 calculates the size “L” of the gap “g” between the sheets P 1 and P 2 from the length “l” of the light receiving element “Sen- 2 ”, the speed “Vb” and the time “t 3 ”. Specifically, the control unit 30 figures out the size “L” of the gap “g”, based on the following expression (1).
- step S 17 the control unit 30 controls the driver 31 and the feed rollers 19 to adjust the speed “Va” in accordance with the size “L” of the gap “g”. More specifically, the control unit 30 specifies a value for the speed “Va”, referring to Table 1, and the control unit 30 controls the driver 31 and the feed rollers 19 so that the sheet P 2 will be fed at the specified speed “Va”. Since the speeds V 2 , V 3 , V 4 and V 5 in Table 1 are larger than the speed “Vb”, the gap “g” between the sheets P 1 and P 2 will be decreasing. Then, the processing goes to step S 18 .
- Step S 18 the control unit 30 judges whether N is equal to five.
- Step S 18 is a process to judge whether the processes from step S 2 to step S 17 have been carried out with regard to all the sensors Se 1 to Se 5 .
- N is equal to five
- the procedure is completed.
- N is not equal to five
- the processing goes to step S 19 .
- step S 19 the control unit 30 resets the timer. Subsequently, the control unit 30 makes an increment of N at step S 20 . Thereafter, the processing returns to step S 2 .
- the gap “g” detected by a more downstream sensor of the sensors Se 1 to Se 5 is smaller than the gap “g” detected by a more upstream sensor.
- the gap “g” between two sheets P 1 and P 2 that are sequentially fed can be made closer to zero.
- a plurality of sensors Se 1 to Se 5 are provided in the sheet route R at a plurality of locations, and the control unit 30 can adjust the speed “Va” of the sheet P 2 fed by the feed rollers 19 at a plural number of times. Accordingly, the sheet feeding device 35 can control the speed “Va” more precisely, compared with the sheet feeding device disclosed by Reference 1 that detects the gap between sheets only once.
- the sheet feeding device 35 and the image forming apparatus 1 provided with the sheet feeding device 35 consequently, it is possible to make the gap “g” between sheets P 1 and P 2 closer to zero. Thereby, the lives of the feed rollers 19 and the intermediate transfer belt 11 are prolonged, and the productivity is improved.
- the gap “g” between sheets P 1 and P 2 can be made closer to zero, and even if the speeds “Va” and “Vb” are low, the productivity can be maintained high. If the speeds “Va” and “Vb” are low, the speed of a sheet traveling in the fixing device 22 is also low, which permits the fixing temperature of the fixing device 22 to be set low. Thereby, the power consumption of the image forming apparatus 1 can be lowered.
- the speed “Va” is accelerated, and when the gap “g” between sheets becomes relatively small, the speed “Va” is decelerated.
- the speed “Va” is decelerated so that the sheet P 1 and the sheet P 2 are prevented from overlapping with each other.
- an overlap correction mechanism 40 is provided, and even if the sheets P 1 and P 2 overlap with each other, the overlap can be corrected by the overlap correction mechanism 40 .
- the sheet feeding device 35 and the image forming apparatus 1 provided with the sheet feeding device 35 are not limited to the embodiment above. Modifications are possible within the scope of the invention. In the following, modifications of the sheet feeding device 35 and the image forming apparatus 1 provided with the sheet feeding device 35 is described.
- FIGS. 9 a - 9 c show modifications of the sensors Se 1 to Se 5 for the sheet feeding device 35 .
- a light receiving member Se 1 - 2 may be provided for the light sources Se 1 - 1 to Se 5 - 1 .
- a camera “C” may be provided instead of the sensors Se 1 to Se 5 .
- the camera “C” is preferably located in a position suited to take pictures mainly around the timing rollers 20 as shown by FIG. 9 c . This is because the target is that the gap “g” becomes zero before the gap “g” comes to the timing rollers 20 .
- control unit 30 adjusts the speed “Va” while fixing the speed “Vb”.
- speed “Vb” may be adjusted, while the speed “Va” may be fixed.
- the control unit 30 controls the timing rollers 20 and a driver for the timing rollers 20 so that the speed “Vb” will be lower than the speed “Va”.
- the control unit 30 may control the feed rollers 19 and the driver 31 or the timing rollers 20 and the driver for the timing roller 20 so that the speed “Va” will be lower than the speed “Vb”.
- the control unit 30 makes a control so as to form a gap “g” between the sheets P 1 and P 2 once and then to close the gap “g”. Thereby, the sheets P 1 and P 2 can be prevented from going out of the route R while overlapping with each other.
- control unit 30 may control the feed rollers 19 and the driver 31 or the timing rollers 20 and the driver for the timing rollers 20 so that the speed “Va” will be lower than the speed “Vb”.
- the overlap correction mechanism 40 is not limited to have the structure shown by FIG. 2 .
- FIG. 10 shows a modified overlap correction mechanism 40 ′.
- the overlap correction mechanism 40 ′ is made by bending a guide plate that is a component of the route R. The leading edge of the sheet P 2 is hooked by the guide plate, and thereby, an overlap of the sheets P 1 and P 2 is corrected.
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Control Or Security For Electrophotography (AREA)
- Paper Feeding For Electrophotography (AREA)
- Controlling Sheets Or Webs (AREA)
- Delivering By Means Of Belts And Rollers (AREA)
- Sheets, Magazines, And Separation Thereof (AREA)
Abstract
A sheet feeding device that is suited to be employed in an image forming apparatus having a printing section for printing an image on a sheet. The sheet feeding device has feed rollers for feeding a sheet at a speed “Va” and timing rollers for feeding a sheet fed by the feed rollers to the printing section at a speed “Vb”. Sensors are provided between the feed rollers and the timing rollers, so that the gap between a foregoing sheet and a following sheet can be detected at a plurality of detection points while the foregoing sheet is being fed by the timing rollers and the following sheet is being fed by the feed rollers. When one of the sensors detects that there is a gap between the sheets, a control unit controls the feed rollers such that the speed “Va” will be higher than the speed “Vb”.
Description
- This application is based on a Japanese patent application No. 2008-317144 filed on Dec. 12, 2008, the content of which is incorporated herein by reference.
- 1. Field of the Invention
- The present invention relates to a sheet feeding device and an image forming apparatus provided with the sheet feeding device, and more particularly to a sheet feeding device for feeding sheets of printed medium successively and an image forming apparatus provided with the sheet feeding device.
- 2. Description of Related Art
- When a sheet feeding device feeds a plurality of sheets successively, it is preferred that the sheets are fed with no gaps among the sheets for the reasons below. If there are gaps among sheets, feed rollers and a transfer belt will rotate even while the gaps are passing thereby. Therefore, in this case, the drive distance of the feed rollers and the transfer belt is large, compared with the case wherein there are no gaps among sheets. Accordingly, when there are gaps among sheets, the feed rollers and the transfer belt are abraded shortly. Also, when there are gaps among sheets, the productivity becomes lower, compared with the case wherein there are no gaps among sheets. For these reasons, sheets are fed successively preferably with no gaps among the sheets.
- As a conventional sheet feeding device, for example, a sheet feeding device as disclosed by Japanese Patent Laid-Open Publication No. 2006-232475 (Reference 1) is well known. In this sheet feeding device, when a detector detects that the gap between two sheets (a foregoing sheet and a following sheet) that are successively fed is lower than a specified value, a control unit controls a feed-out means to slow down the speed of the following sheet. With this control, it is possible to feed a plurality of sheets successively while keeping constant gaps among the sheets.
- Thus, in the sheet feeding device disclosed by
Reference 1, the gaps among sheets are kept constant. However,Reference 1 is silent about controlling the gaps closer to zero. - An object of the present invention is to provide a sheet feeding device wherein the gaps among sheets successively fed can be made closer to zero and an image forming apparatus provided with the sheet feeding device.
- An embodiment of the present invention is a sheet feeding device that is suited to be used in an image forming apparatus comprising a printing section for printing an image on a sheet, and the sheet feeding device comprises: a first feeder for feeding the sheet at a first speed; a second feeder for feeding the sheet fed by the first feeder to the printing section at a second speed; a detector, which is located between the first feeder and the second feeder, for detecting a gap between a first sheet and a second sheet at a plurality of detection points while the first sheet is being fed by the second feeder and the second sheet is being fed by the first feeder; and a controller for controlling the first feeder or the second feeder, and when the detector detects that there is a gap between the first sheet and the second sheet, the controller controls the first feeder or the second feeder such that the first speed will be higher than the second speed.
- Another embodiment of the present invention is an image forming apparatus, and the image forming apparatus comprises the above-described sheet feeding device.
- This and other objects and features of the present invention will be apparent from the following description with reference to the accompanying drawings, in which:
-
FIG. 1 is a schematic view showing the general structure of an image forming apparatus according to an embodiment of the present invention; -
FIG. 2 is an enlarged view of a sheet feeding device employed in the apparatus shown byFIG. 1 ; -
FIGS. 3 a-3 c are illustrations showing operation of an overlap correction mechanism; -
FIG. 4 is a flowchart showing a procedure that is carried out by a control unit while the sheet feeding device is feeding sheets successively; -
FIG. 5 is a graph showing waveforms of signals outputted from sensors; -
FIGS. 6 a-6 d are illustrations showing passing of two sheets by a light receiving element; -
FIGS. 7 a-7 d are illustrations showing passing of two sheets by a light receiving element; -
FIGS. 8 a-8 c are illustrations showing passing of two sheets by a light receiving element; -
FIGS. 9 a-9 c show modifications of the sensors provided for the sheet feeding device; and -
FIG. 10 shows a modification of the overlap correction mechanism. - A sheet feeding device and an image forming apparatus according to an embodiment of the present invention are hereinafter described.
- Referring to
FIG. 1 , animage forming apparatus 1 provided with a sheet feeding device according to an embodiment of the present invention is described. - The
image forming apparatus 1 is an electrophotographic color printer and forms a color image by combining four color (Y: yellow, M: magenta, C: cyan and K: black) images in a tandem method. Theimage forming apparatus 1 is to form an image on a sheet of paper P in accordance with image data, and comprises aprinting section 2, afeeding section 15, asheet feeding device 35, afixing device 22 and a printed-sheet tray 23. - The
feeding section 15 is to supply sheets P one by one, and comprises asheet tray 16, a feed-out roller 17 andseparation rollers 18. A plurality of sheets to be subjected to printing is stacked in thesheet tray 16. The feed-outroller 17 is to pick the sheets P out of thetray 16 one by one. Theseparation rollers 18 separate two or more sheets possibly picked out by the feed-outroller 17 and feed surely one sheet P forward. - As
FIG. 2 shows, thesheet feeding device 35 comprisesfeed rollers 19,timing rollers 20, acontrol unit 30, adriver 31, astorage 32, anoverlap correction mechanism 40, a route R and sensors Se1 to Se5. Thefeed rollers 19 are rotated by thedriver 31 to feed the sheet P at a speed “Va”. Thedriver 31 is, for example, a motor. Thefeed rollers 19 and thedriver 31 form a feeder. Thetiming rollers 20 are rotated by another driver (not shown) to feed the sheet P fed thereto by thefeed rollers 19 further to aprinting section 2 at a speed “Vb”. Thetiming rollers 20 and the driver form another feeder. The route R is formed between thefeed rollers 19 and thetiming rollers 20, and the sheet P travels therein. - The sensors Se1 to Se5 are provided along the route R. When two sheets P1 and P2 are fed successively as shown by
FIG. 2 , the sensors Se1 to Se5 detect the gap between the sheets P1 and P2. More specifically, while the sheet P1 is being fed by thetiming rollers 20 and while the sheet P2 is being fed by thefeed rollers 19, the gap “g” between the trailing edge of the sheet P1 and the leading edge of the sheet P2 (which is hereinafter referred to as the gap “g” between the sheets P1 and P2) is detected by the plural sensors Se1 to Se5 provided along the route R. Each of the sensors Se1 to Se5 comprises a light source Se1-1 (Se2-1, Se3-1, Se4-1 or Se5-1) and a light receiving element Se1-2 (Se2-2, Se3-2, Se4-2 or Se5-2). The light source Se3-1 and the light receiving element Se3-2 are shown in the magnified view inFIG. 2 . The light sources Se1-1 to Se5-1 emit light. The light receiving elements Se1-2 to Se5-2 define detection points. The light receiving elements Se1-2 to Se5-2 receive the light emitted from the light sources Se1-1 to Se5-1 and send thecontrol unit 30 output signals Sig1 toSig 5 in accordance with the quantities of received light. Specifically, when the light receiving elements Se1-2 to Se5-2 receive relatively large quantities of light, the elements Se1-2 to Se5-2 send output signals Sig1 to Sig5 of relatively high voltages, and when the light receiving elements Se1-2 to Se5-2 receive relatively small quantities of light, the elements Se1-2 to Se5-2 send output signals Sig1 to Sig5 of relatively low voltages. As shown in the magnified view inFIG. 2 , the light receiving elements Se1-2 to Se5-2 have a dimension (length) “l” in the sheet feeding direction. In this embodiment, the sensors Se1 to Se5 are arranged at intervals larger than the initial gap “g” between the sheets P1 and P2, so that the gap “g” will never be detected by two or more sensors concurrently. - The
control unit 30 controls thedriver 31 and thefeed rollers 19 in accordance with the detection results of the sensors Se1 to Se5. Thestorage 32 is, for example, a hard disk or a memory, and stores a table as shown by Table 1. The table shows the relationship between the size “L” of the gap “g” and the speed “Va”. -
TABLE 1 Size “L” of Gap “g” Speed “Va” 0 V1 0 < L ≦ L1 V2 L1 < L ≦ L2 V3 L2 < L ≦ L3 V4 L3 < L V5 - The
control unit 30 recognizes the size “L” of the gap “g” based on the output signals Sig1 to Sig5 from the sensors Se1 to Se5 and determines the speed “Va” with reference to the table. In Table 1, the values meet the conditions L1<L2<L3, V1<V2<V3<V4 and V1=Vb. That is, the speed “Va” is equal to or greater than the speed “Vb” at all times. Thereby, when there is a gap between the sheets P1 and P2 (L>0), thecontrol unit 30 controls thedriver 31 and thefeed rollers 19 such that the gap “g” detected by a more downstream sensor of the sensors Se1 to Se5 will be smaller than the gap “g” detected by a more upstream sensor of the sensors Se1 to Se5. On the other hand, when one of the sensors “Sen” detects no gap between the sheets P1 and P2 (L=0), thecontrol unit 30 controls thedriver 31 and thefeed rollers 19 such that the speed “Va” will be V1 that is equal to the speed “Vb”. - The
overlap correction mechanism 40 is to correct an overlap of the sheets P1 and P2. Specifically, as shown inFIGS. 1 and 2 , theoverlap correction mechanism 40 is provided in a downstream position in the route R (near the timing rollers 20), and is a roller that has a cross section of a circle having a protrusion. If the sheets P1 and P2 reach theoverlap correction mechanism 40 while overlapping with each other, the leading edge of the sheet P2 is hooked by the protrusion of theoverlap correction mechanism 40 as shown byFIG. 3 a. Then, as shown byFIG. 3 b, the sheet P2 is pushed up by the force of thefeed rollers 19, and accordingly, theoverlap correction mechanism 40 is rotated. When theoverlap correction mechanism 40 rotates by a specified amount, as shown byFIG. 3 c, the leading edge of the sheet P2 is released from the protrusion of theoverlap correction mechanism 40, and the sheet P2 is fed upward. Thereafter, theoverlap correction mechanism 40 rotates further and returns to a state as shown byFIG. 3 a. In this way, the sheet P2 slows down. Meanwhile, during the period fromFIG. 3 a toFIG. 3 c, the sheet P1 is fed upward without slowing down. Thereby, the overlap of the sheets P1 and P2 is corrected. - The
printing section 2 is to form a toner image on a sheet P fed from the timingrollers 20. As shown inFIG. 1 , theprinting section 2 comprisesimage forming units first transfer rollers intermediate transfer belt 11, a drivingroller 12, a drivenroller 13, asecond transfer roller 14, and acleaning device 21. Theimage forming units photosensitive drums electric chargers exposure devices devices cleaners photosensitive drums electric chargers exposure devices devices first transfer rollers 8 M 8C and 8K, thecleaners image forming units - The
electric chargers 5 charge the circumferential surfaces of thephotosensitive drums 4. Theexposure devices 6 emit lasers controlled by an exposure control unit (not shown in the drawings). Thereby, electrostatic latent images are formed on the circumferential surfaces of thephotosensitive drums 4. Thus, theelectric chargers 5 and theexposure devices 6 serve as a unit for forming electrostatic latent images on the circumferential surfaces of thephotosensitive drums 4. - The developing
devices 7 are to supply toner to thephotosensitive drums 4 so as to form toner images on the circumferential surfaces of thephotosensitive drums 4. More specifically, the developingdevices 7 store toner therein and charge the toner into the negative polarity by stirring the toner or the like. Developing rollers provided in the respective developingdevice 7 feed the toner toward thephotosensitive drums 4. At this time, the negative charged toner moves from the developing rollers to thephotosensitive drums 4 influenced by the electric fields of the electrostatic latent images on thephotosensitive drums 4. In this way, toner images are formed on the circumferential surfaces of thephotosensitive drums 4. - The
intermediate transfer belt 11 is laid between the drivingroller 12 and the drivenroller 13, and the toner images formed on thephotosensitive drums 4 are transferred onto theintermediate transfer belt 1 such that the transferred images will be laid on one another to be combined into a full-color image (first transfer). Thefirst transfer rollers 8 are located in contact with the inner surface of theintermediate transfer belt 11. A first transfer voltage is applied from a voltage source (not shown in the drawings) to thefirst transfer rollers 8, whereby the toner images formed on thephotosensitive drums 4 are transferred onto theintermediate transfer belt 11. The cleaners 9 are to collect residual toner remained on thephotosensitive drums 4 after the first transfer. The drivingroller 12 is rotated by an intermediate transfer belt driver (not shown in the drawings), whereby theintermediate transfer belt 11 is driven. Then, theintermediate transfer belt 11 carries the full-color toner image to thesecond transfer roller 14. - The
second transfer roller 14 is located opposite theintermediate transfer belt 11, and a nip portion N is formed between thesecond transfer roller 14 and theintermediate transfer belt 11. While a sheet P fed from the timingrollers 20 is passing through the nip portion N, thesecond transfer roller 14 transfers the toner image carried by theintermediate transfer belt 11 onto the sheet P (second transfer). After the second transfer, thecleaning device 21 removes residual toner from theintermediate transfer belt 11. - The sheet P that has been subjected to the second transfer is fed to the fixing
device 22. The fixingdevice 22 applies a heating treatment and a pressing treatment to the sheet P so as to fix the toner image on the sheet P. The printed sheet P is ejected onto the printed-sheet tray 23. - The operation of the
image forming apparatus 1 provided with thesheet feeding device 35 is hereinafter described with reference to the drawings. - First, referring to
FIGS. 5 to 8 , the operation of theimage forming apparatus 1 is generally described. When the light receiving elements Se1-2 to Se5-2 receive relatively large quantities of light, the light receiving elements Se1-2 to Se5-2 output signals Sig1 to Sig5 of relatively high voltages. When the light receiving elements Se1-2 to Se5-2 receive relatively small quantities of light, the light receiving elements Se1-2 to Se5-2 output signals Sig1 to Sig5 of relatively low voltages. Therefore, referring toFIG. 5 , while the output signals Sig1 to Sig5 are high (during the periods between time “0” to time “t3”), the gap “g” between the sheets P1 and P2 are passing in front of the light receiving elements Se1-2 to Se5-2, respectively. That is, the size “L” of the gap “g” can be judged from the length of the period when the voltage of the output signal Sig1 to Sig5 is high. Thecontrol unit 30 times the period and calculates the size “L” of the gap “g” between the sheets P1 and P2, and in accordance with the calculation result, thecontrol unit 30 controls the speed “Va”. - As shown in
FIG. 5 , the waveforms of the output signals Sig1 to Sig5 can be classified into three types. More specifically, the waveforms of the output signals Sig1 and Sig2 are trapezoidal. The waveform of the output signal Sig3 is four-cornered with the upper side slanting. The waveform of the output signal Sig4 is triangle. The output signal Sig5 is constant and flat, which indicates that the gap “g” between the sheets P1 and P2 is zero. - The reason why the output signals Sig1 to Sig5 have different waveforms is that the size “L” of the gap “g” is changeable. Specifically, as shown by
FIGS. 6 a to 6 d, when the size “L” of the gap “g” is greater than the length “l” of the light receiving element Sen-2, the output signal “Sign” has such a waveform as those of the output signals Sig1 and Sig2. As shown byFIGS. 7 a to 7 d, when the size “L” of the gap “g” is smaller than the size of the light receiving element Sen-2, the output signal “Sign” has such a waveform as that of the output signal Sig3. As shown byFIGS. 8 a to 8 c, when the gap “g” becomes zero while passing in front of the light receiving element Sen-2, the output signal “Sign” has such a waveform as that of the output signal Sig4. This is described in more details below. - Referring to
FIGS. 6 a to 6 d, a case wherein the gap “g” is larger than the length “l” of the light receiving element Sen-2 is described. While the trailing edge of the sheet P1 is passing in front the light receiving element Sen-2 (during the period fromFIG. 6 a toFIG. 6 b), the area of the light receiving element Sen-2 covered by the sheet P1 is decreasing. Accordingly, the voltage of the output signal “Sign” is increasing like the output signals Sig1 andSig 2 in the periods from “0” to “t1” shown inFIG. 5 . Next, when and after the trailing edge of the sheet P1 has completed passing by the light receiving element Sen-2 (during the period fromFIG. 6 b toFIG. 6 c), the light receiving element Sen-2 is covered neither by the sheet P1 nor by the sheet P2. Accordingly, the voltage of the output signal “Sign” is fixed at a relatively high level like the output signals Sig1 and Sig2 in the periods from “t1” to “t2” shown inFIG. 5 . Next, while the leading edge of the sheet P2 is passing in front of the light receiving element Sen-2 (during the period fromFIG. 6 c toFIG. 6 d), the area of the light receiving element Sen-2 covered by the sheet P2 is increasing. Accordingly, the voltage of the output signal “Sign” is decreasing like the output signals Sig1 and Sig2 in the periods from “t2” to “t3” shown inFIG. 5 . Finally, when and after the leading edge of the sheet P2 has completed passing by the light receiving element Sen-2 (afterFIG. 6 d), the light receiving element Sen-2 is entirely covered by the sheet P2. Accordingly, the voltage of the output signal “Sign” is fixed at a relatively low level like the signals Sig1 and Sig2 after “t3” shown inFIG. 5 . - Next, referring to
FIGS. 7 a to 7 d, a case wherein the gap “g” is smaller than the length “l” of the light receiving element Sen-2 is described. In a first part of the period when the trailing edge of the sheet P1 is passing in front of the light receiving element Sen-2 (during the period fromFIG. 7 a toFIG. 7 b), the area of the light receiving element Sen-2 covered by the sheet P1 is decreasing. Accordingly, the voltage of the output signal “Sign” is increasing like the output signal Sig3 in the period from “0” to “t1” shown inFIG. 5 . Thereafter, as shown byFIG. 7 b, the leading edge of the sheet P2 comes to the light receiving element Sen-2 while the trailing edge of the sheet P1 is still passing in front of the light receiving element “Sen-2”. In this moment, because the speed “Va” is higher than the speed “Vb”, the covered area of the light receiving element Sen-2 covered by the sheets P1 and P2 is gradually increasing. Accordingly, the voltage of the output signal “Sign” is gradually decreasing like the output signal Sig3 in the period from “t1” to “t2” shown inFIG. 5 . Next, when and after the trailing edge of the sheet P1 has completed passing by the light receiving element Sen-2 (afterFIG. 7 c), only the leading edge of the sheet P2 passes in front of the light receiving element Sen-2, and accordingly, the voltage of the output signal “Sign” is steeply decreasing like the signal Sig3 in the period from “t2” to “t3” shown inFIG. 5 . Finally, when and after the leading edge of the sheet P2 has completed passing by the light receiving element “Sen-2” (afterFIG. 7 d), the light receiving element Sen-2 is entirely covered by the sheet P2. Accordingly, the voltage of the output signal “Sign” is fixed at a relatively low level like the signal Sig3 after “t3” shown inFIG. 5 . Thus, when the gap “g” is smaller than the length “l” of the light receiving element “Sen-2”, the leading edge of the sheet P2 starts passing in front of the light receiving element Sen-2 before the trailing edge of the sheet P1 completes passing in front of the light receiving element Sen-2. Therefore, during the period “t1” to “t2”, the voltage of the output signal “Sign” is not fixed but is gradually decreasing. - Next, referring to
FIGS. 8 a to 8 c, a case wherein the gap “g” becomes zero while the gap “g” is passing in front of the light receiving element Sen-2 is described. In a first part of the period when the trailing edge of the sheet P1 is passing in front of the light receiving element Sen-2 (during the period fromFIG. 8 a toFIG. 8 b), the area of the light receiving element Sen-2 covered by the sheet P1 is decreasing. Accordingly, the voltage of the output signal “Sign” is increasing like the output signal Sig5 in the period from “0” to “t1” shown inFIG. 5 . Thereafter, as shown byFIG. 8 b, the leading edge of the sheet P2 comes to the light receiving element Sen-2 while the trailing edge of the sheet P1 is still passing in front of the light receiving element Sen-2. In this moment, because the speed “Va” is higher than the speed “Vb”, the covered area of the light receiving element Sen-2 is gradually increasing. Accordingly, the voltage of the output signal “Sign” is gradually decreasing like the output signal Sig5 in the period from “t1” to “t3” shown inFIG. 5 . Next, the leading edge of the sheet P2 catches up with the trailing edge of the sheet P1 as shown byFIG. 8 c, and thereafter, the light receiving element Sen-2 is entirely covered by the sheets P1 and P2. Accordingly, the voltage of the output signal “Sign” is fixed at a relatively low level like the output signal Sig4 after “t3” shown inFIG. 5 . - As described above, the timings of the passing of the trailing edge of the sheet P1 and the passing of the leading edge of the sheet P2 in front of the light receiving element Sen-2 depend on the size “L” of the gap “g”. The
control unit 30 recognizes the passing of the trailing edge of the sheet P1 and the passing of the leading edge of the sheet P2, based on the waveform of the output signal “Sign” from the light receiving element Sen-2. Referring toFIG. 4 , the operation of theimage forming apparatus 1 is hereinafter described, focusing on this point. - The
control unit 30 sets N to 1 at step S1. This step S1 is carried out, for example, based on the time when the leading edge of the sheet P1 is detected by the sensor Se5 located the most downstream in the route R. - Next, in order to judge the presence or non-presence of a gap “g” between the sheets P1 and P2, the
control unit 30 judges whether the sensor “Sen” (n: integer from 1 to 5) detects the trailing edge of the sheet P1 during a period when the trailing edge of the sheet P1 is expected to come thereto (step S2). While the trailing edge of the sheet P1 is passing in front of the light receiving element Sen-2, the covered area of the light receiving element Sen-2 is decreasing, and the quantity of light received by the light receiving element Sen-2 is increasing. Accordingly, the voltage of the output signal “Sign” from the light receiving element Sen-2 is increasing. Therefore, thecontrol unit 30 judges the up-edge of the output signal “Sign” as the time when the sensor “Sen” starts detecting the trailing edge of the sheet P1. Thereafter, the processing goes to step S4. On the other hand, when the trailing edge of the sheet P1 is not detected, thecontrol unit 30 judges that there is no gap between the sheets P1 and P2. Then, the processing goes to step S3. - When the trailing edge of the sheet P1 is not detected, the
control unit 30 sets the speed “Va” to V1 at step S3. In this procedure, when thecontrol unit 30 judges that there is no gap between the sheets P1 and P2, thecontrol unit 30 judges that adjustment of the speed “Va” is not necessary. Therefore, thecontrol unit 30 sets the speed “Va” to V1 that is equal to the speed “Vb”. Thereafter, the processing goes to step S18. - When the trailing edge of the sheet P1 is detected, the
control unit 30 starts a timer (step S4). As shown byFIG. 5 , thecontrol unit 30 starts timing with the time of the up-edge of the output signal “Sign” defined to be t=0. Next, thecontrol unit 30 judges whether the increase in the voltage of the output signal “Sign” has stopped (step S5). As shown byFIG. 6 b, when the trailing edge of the sheet P1 has completed passing by the light receiving element “Sen-2, the sheet P1 stops covering the light receiving element “Sen-2”, and the quantity of light received by the light receiving element “Sen-2” stops increasing. Accordingly, the increase in the voltage of the output signal “Sign” stops. As shown byFIGS. 7 b and 8 b, when the leading edge of the sheet P2 has reached the light receiving element “Sen-2”, the light receiving element “Sen-2” starts to be covered by the sheet P2. Therefore, at this time, also, the quantity of light received by the light receiving element “Sen-2” stops increasing, and accordingly, the increase in the voltage of the output signal “Sign” stops. At step S5, however, thecontrol unit 30 cannot judge whether the stop of the increase in the voltage of the output signal “Sign” is due to the completion of the passing of the trailing edge of the sheet P1 by the light receiving element “Sen-2” or due to the arrival of the leading edge of the sheet P2 at the light receiving element “Sen-2”. This judgment is made at step S7 that will be described later. When the increase in the voltage of the output signal “Sign” stops, the processing goes to step S6. Unless the increase in the voltage of the output signal “Sign” stops, the processing returns to step S5. Until the increase in the voltage of the output signal “Sign” stops, the process at step S5 is repeated. - At step S6, the
control unit 30 takes in a value of the time “t1” (seeFIG. 5 ) when the increase in the voltage of the output signal “Sign” stops. - Next, the
control unit 30 judges whether the value “t1” is equal to a value “ta” (step S7). The value “ta” is obtained by dividing the length “l” of the light receiving element “Sen-2” by the speed “Vb”, and therefore, the value “ta” indicates the time that is necessary for the trailing edge of the sheet P1 to complete passing by the light receiving element “Sen-2”. The speed “Vb” is a fixed value known to thecontrol unit 30. Thus, at step S7, by judging whether the value “t1” is equal to the value “ta”, thecontrol unit 30 judges whether the stop of the increase in the voltage of the output signal “Sign” is due to the completion of the passing of the trailing edge of the sheet P1 by the light receiving element “Sen-2” as shown byFIG. 6 b or due to the arrival of the leading edge of the sheet P2 at the light receiving element “Sen-2” as shown byFIGS. 7 b and 8 b. In other words, thecontrol unit 30 judges which waveform of the output signals Sig1 to Sig4 shown inFIG. 5 the output signal “Sign” has. When the value “t1” is equal to the value “ta”, thecontrol unit 30 judges that the stop of the increase in the voltage of the output signal “Sign” is due to the completion of the passing of the trailing edge of the sheet P1 by the light receiving element “Sen-2” (see the waveforms of the signals Sig1 and Sig2 inFIG. 5 ). Thereafter, the processing goes to step S8. On the other hand, when the value “t1” is not equal to the value “ta”, thecontrol unit 30 judges that the stop of the increase in the voltage of the output signal “Sign” is due to the arrival of the leading edge of the sheet P2 at the light receiving element “Sen-2” (see the waveforms of signals Sig3 and Sig4 inFIG. 5 ). Thereafter, the processing goes to step S10. - When it is judged that the time “t1” is equal to the time “ta”, the
control unit 30 judges at step S8 whether the sensor “Sen” has detected the leading edge of the sheet P2. As shown byFIGS. 6 c and 6 d, while the leading edge of the sheet P2 is passing by the light receiving element “Sen-2”, the area of the light receiving element “Sen-2” covered by the sheet P2 is increasing. Accordingly, the quantity of light received by the light receiving element “Sen-2” is decreasing, and the voltage of the output signal “Sign” from the light receiving element “Sen-2” is decreasing like the output signals Sig1 and Sig2 for the periods from “t2” to “t3”. Thecontrol unit 30 judges the down-edge of the output signal “Sign” as the time when the leading edge of the sheet P2 has reached the light receiving element “Sen-2”. The process at step S8 is repeated until the sensor “Sen” starts detecting the leading edge of the sheet P2. Then, when thecontrol unit 30 judges that the leading edge of the sheet P2 has reached the light receiving element “Sen-2”, the processing goes to step S9. - When it is judged at step S7 that the time “t1” is not equal to “ta”, the
control unit 30 subsequently judges whether the time “t1” is smaller than “ta” (step S10). The time “ta” is a time that is necessary for the trailing edge of the sheet P1 to complete passing by the light receiving element “Sen-2”. Therefore, in the normal state, the time “t1” is equal to or smaller than “ta”, and it never happens that the time “t1” is greater than “ta”. Accordingly, when it is judged that the time “t1” is greater than “ta” (“NO” at step S10), thecontrol unit 30 judges that an error has occurred. Then, the processing is terminated. On the other hand, when the time “t1” is smaller than “ta”, the processing goes to step S11. - At step S11, the
control unit 30 judges whether the trailing edge of the sheet P1 has completed passing by the light receiving element “Sen-2”. When and after the trailing edge of the sheet P1 has completed passing by the light receiving element “Sen-2”, the light receiving element “Sen-2” is covered by only the sheet P2 as shown byFIG. 7 c. Because the sheet P2 travels in such a direction as to cover more part of the light receiving element “Sen-2”, the voltage of the output signal “Sign” is steeply decreasing like the output signal Sig3 in the period from “t2” to “t3” shown inFIG. 5 . Thus, thecontrol unit 30 judges whether the trailing edge of the sheet P1 has completed passing by the light receiving element “Sen-2” by judging whether the decreasing speed in the voltage of the output signal “Sign” is accelerated. When the completion of the passing of the trailing edge of the sheet P1 by the light receiving element “Sen-2” is judged at step S11, the processing goes to step S9. When the completion of the passing of the trailing edge of the sheet P1 is not judged at step S11, the processing goes to step S12. - At step S12, the
control unit 30 judges whether the voltage of the output signal “Sign” is zero. In other words, at step S12, thecontrol unit 30 judges whether the leading edge of the sheet P2 has caught up with the trailing edge of the sheet P1 while the light receiving element “Sen-2” is detecting the trailing edge of the sheet P1 and the leading edge of the sheet P2 as shown by the output signal Sig4 inFIG. 5 andFIGS. 8 a-8 c. When the voltage of the output signal “Sign” is zero at step S12, thecontrol unit 30 judges that the leading edge of the sheet P2 has caught up with the trailing edge of the sheet P1. Thereafter, the processing goes to step S13. On the other hand, when the voltage of the output signal “Sign” is not zero at step S12, thecontrol unit 30 judges that the leading edge of the sheet P2 has not caught up with the trailing edge of the sheet P1. Thereafter, the processing returns to step S11. - When the voltage of the output signal “Sign” is zero, the size “L” of the gap “g” between the sheets P1 and P2 is judged to be zero (step S13). Thereafter, the processing goes to step S17.
- At step S9, the
control unit 30 takes in a value of the time “t2” (seeFIG. 5 ) when the voltage of the output signal “Sign” starts decreasing due to the detection at step S8 or the detection at step S11. Thereafter, at step S14, thecontrol unit 30 judges whether the leading edge of the sheet P2 has completed passing by the light receiving element “Sen-2”. When and after the leading edge of the sheet P2 has completed passing by the light receiving element “Sen-2”, the light receiving element “Sen-2” is completely covered by the sheet P2. Accordingly, the quantity of light received by the light receiving element “Sen-2” becomes zero, and the voltage of the output signal “Sign” becomes zero. Therefore, thecontrol unit 30 judges whether the leading edge of the sheet P2 has completed passing by the light receiving element “Sen-2” by judging whether the voltage of the output signal “Sign” has become zero. When the completion of the passing of the leading edge of the sheet P2 by the light receiving element “Sen-2” is judged at step S14, the processing goes to step S15. The process at step S14 is repeated until it is judged that the leading edge of the sheet P2 has completed passing by the light receiving element “Sen-2”. - At step S15, the
control unit 30 takes in a value of the time “t3” (seeFIG. 5 ) when the leading edge of the sheet P2 has completed passing by the light receiving element “Sen-2”. - Then, the
control unit 30 calculates the size “L” of the gap “g” between the sheets P1 and P2 from the length “l” of the light receiving element “Sen-2”, the speed “Vb” and the time “t3”. Specifically, thecontrol unit 30 figures out the size “L” of the gap “g”, based on the following expression (1). -
L=t3×Vb−1 (1) - Next, at step S17, the
control unit 30 controls thedriver 31 and thefeed rollers 19 to adjust the speed “Va” in accordance with the size “L” of the gap “g”. More specifically, thecontrol unit 30 specifies a value for the speed “Va”, referring to Table 1, and thecontrol unit 30 controls thedriver 31 and thefeed rollers 19 so that the sheet P2 will be fed at the specified speed “Va”. Since the speeds V2, V3, V4 and V5 in Table 1 are larger than the speed “Vb”, the gap “g” between the sheets P1 and P2 will be decreasing. Then, the processing goes to step S18. - At step S18, the
control unit 30 judges whether N is equal to five. Step S18 is a process to judge whether the processes from step S2 to step S17 have been carried out with regard to all the sensors Se1 to Se5. When N is equal to five, the procedure is completed. When N is not equal to five, the processing goes to step S19. - At step S19, the
control unit 30 resets the timer. Subsequently, thecontrol unit 30 makes an increment of N at step S20. Thereafter, the processing returns to step S2. - In this way, all the sensors Se1 to Se5 are subjected to the same processing. Accordingly, as shown by
FIG. 5 , the gap “g” detected by a more downstream sensor of the sensors Se1 to Se5 is smaller than the gap “g” detected by a more upstream sensor. - In the
sheet feeding device 35 or in theimage forming apparatus 1 provided with thesheet feeding device 35, the gap “g” between two sheets P1 and P2 that are sequentially fed can be made closer to zero. In thesheet feeding device 35, a plurality of sensors Se1 to Se5 are provided in the sheet route R at a plurality of locations, and thecontrol unit 30 can adjust the speed “Va” of the sheet P2 fed by thefeed rollers 19 at a plural number of times. Accordingly, thesheet feeding device 35 can control the speed “Va” more precisely, compared with the sheet feeding device disclosed byReference 1 that detects the gap between sheets only once. In thesheet feeding device 35 and theimage forming apparatus 1 provided with thesheet feeding device 35, consequently, it is possible to make the gap “g” between sheets P1 and P2 closer to zero. Thereby, the lives of thefeed rollers 19 and theintermediate transfer belt 11 are prolonged, and the productivity is improved. - In the
sheet feeding device 35 and in theimage forming apparatus 1 provided with thesheet feeding device 35, the gap “g” between sheets P1 and P2 can be made closer to zero, and even if the speeds “Va” and “Vb” are low, the productivity can be maintained high. If the speeds “Va” and “Vb” are low, the speed of a sheet traveling in the fixingdevice 22 is also low, which permits the fixing temperature of the fixingdevice 22 to be set low. Thereby, the power consumption of theimage forming apparatus 1 can be lowered. - In the
sheet feeding device 35 and in theimage forming apparatus 1 provided with thesheet feeding device 35, when the gap “g” between sheets is relatively large, the speed “Va” is accelerated, and when the gap “g” between sheets becomes relatively small, the speed “Va” is decelerated. When the leading edge of the sheet P2 is catching up with the trailing edge of the sheet P1, the speed “Va” is decelerated so that the sheet P1 and the sheet P2 are prevented from overlapping with each other. - Further, in the
sheet feeding device 35 and theimage forming apparatus 1 provided with thesheet feeding device 35, anoverlap correction mechanism 40 is provided, and even if the sheets P1 and P2 overlap with each other, the overlap can be corrected by theoverlap correction mechanism 40. - The
sheet feeding device 35 and theimage forming apparatus 1 provided with thesheet feeding device 35 are not limited to the embodiment above. Modifications are possible within the scope of the invention. In the following, modifications of thesheet feeding device 35 and theimage forming apparatus 1 provided with thesheet feeding device 35 is described. -
FIGS. 9 a-9 c show modifications of the sensors Se1 to Se5 for thesheet feeding device 35. AsFIG. 9 a shows, a light receiving member Se1-2 may be provided for the light sources Se1-1 to Se5-1. AsFIG. 9 b shows, a camera “C” may be provided instead of the sensors Se1 to Se5. In this case, the camera “C” is preferably located in a position suited to take pictures mainly around the timingrollers 20 as shown byFIG. 9 c. This is because the target is that the gap “g” becomes zero before the gap “g” comes to thetiming rollers 20. - In the embodiment above, the
control unit 30 adjusts the speed “Va” while fixing the speed “Vb”. However, the speed “Vb” may be adjusted, while the speed “Va” may be fixed. In this case, when there is a gap “g” between sheets P1 and P2, thecontrol unit 30 controls the timingrollers 20 and a driver for the timingrollers 20 so that the speed “Vb” will be lower than the speed “Va”. - Additionally, when the most upstream sensor Se1 detects no gap between the sheets P1 and P2, the
control unit 30 may control thefeed rollers 19 and thedriver 31 or the timingrollers 20 and the driver for thetiming roller 20 so that the speed “Va” will be lower than the speed “Vb”. When the sensor Se1 detects no gap between the sheets P1 and P2, there is a possibility that the sheets P1 and P2 may overlap with each other. For this reason, thecontrol unit 30 makes a control so as to form a gap “g” between the sheets P1 and P2 once and then to close the gap “g”. Thereby, the sheets P1 and P2 can be prevented from going out of the route R while overlapping with each other. Further, when any other sensors Set to Se5 than the sensor Se1 detect no gap between the sheets P1 and P2, thecontrol unit 30 may control thefeed rollers 19 and thedriver 31 or the timingrollers 20 and the driver for the timingrollers 20 so that the speed “Va” will be lower than the speed “Vb”. - The
overlap correction mechanism 40 is not limited to have the structure shown byFIG. 2 .FIG. 10 shows a modifiedoverlap correction mechanism 40′. Theoverlap correction mechanism 40′ is made by bending a guide plate that is a component of the route R. The leading edge of the sheet P2 is hooked by the guide plate, and thereby, an overlap of the sheets P1 and P2 is corrected. - Although the present invention has been described with reference to the embodiments above, it is to be noted that various changes and modifications are possible to those who are skilled in the art. Such changes and modifications are to be understood as being within the scope of the present invention.
Claims (14)
1. A sheet feeding device that is suited to be used in an image forming apparatus comprising a printing section for printing an image on a sheet;
a first feeder for feeding the sheet at a first speed;
a second feeder for feeding the sheet fed by the first feeder to the printing section at a second speed;
a detector, which is located between the first feeder and the second feeder, for detecting a gap between a first sheet and a second sheet at a plurality of detection points while the first sheet is being fed by the second feeder and the second sheet is being fed by the first feeder; and
a controller for controlling the first feeder or the second feeder,
wherein when the detector detects that there is a gap between the first sheet and the second sheet, the controller controls the first feeder or the second feeder such that the first speed will be higher than the second speed.
2. A sheet feeding device according to claim 1 , wherein the controller controls the first feeder or the second feeder such that the gap detected at a more downstream detection point of the plurality of detection points will be smaller than the gap detected at a more upstream detection point of the plurality of detection points.
3. A sheet feeding device according to claim 1 , wherein when the detector detects that there is no gap between the first sheet and the second sheet, the controller controls the first feeder or the second feeder such that the first speed and the second speed will be equal to each other.
4. A sheet feeding device according to claim 1 , wherein when the detector detects at the most upstream detection point that there is no gap between the first sheet and the second sheet, the controller controls the first feeder or the second feeder such that the first speed will be lower than the second speed.
5. A sheet feeding device according to claim 1 ,
wherein each of the detection points has a specified length;
wherein the controller calculates the first speed, the second speed and a size of the gap at each of the detection points as follows:
the controller calculates the second speed, based on a time necessary for a trailing edge of the first sheet to complete passing by the detection point and the specified length of the detection point;
the controller calculates the first speed, based on a time necessary for a leading edge of the second sheet to complete passing by the detection point and the specified length of the detection point; and
the controller calculates the size of the gap, based on the specified length of the detection point, the second speed and a time necessary for the gap to complete passing by the detection point; and
wherein the controller controls the first feeder or the second feeder in accordance with the size of the gap to adjust the first speed or the second speed.
6. A sheet feeding device according to claim 1 , further comprising a corrector for correcting an overlay of the first sheet and the second sheet.
7. A sheet feeding device according to claim 1 , wherein the first speed is fixed.
8. An image forming apparatus comprising a printing section for printing an image on a sheet, said image forming apparatus comprising:
a sheet feeding device comprising:
a first feeder for feeding the sheet at a first speed;
a second feeder for feeding the sheet fed by the first feeder to the printing section at a second speed;
a detector, which is located between the first feeder and the second feeder, for detecting a gap between a first sheet and a second sheet at a plurality of detection points while the first sheet is being fed by the second feeder and the second sheet is being fed by the first feeder; and
a controller for controlling the first feeder or the second feeder,
wherein when the detector detects that there is a gap between the first sheet and the second sheet, the controller controls the first feeder or the second feeder such that the first speed will be higher than the second speed.
9. An image forming apparatus according to claim 8 , wherein the controller of the sheet feeding device controls the first feeder or the second feeder such that the gap detected at a more downstream detection point of the plurality of detection points will be smaller than the gap detected at a more upstream detection point of the plurality of detection points.
10. An image forming apparatus according to claim 8 , wherein when the detector of the sheet feeding device detects that there is no gap between the first sheet and the second sheet, the controller of the sheet feeding device controls the first feeder or the second feeder such that the first speed and the second speed will be equal to each other.
11. An image forming apparatus according to claim 8 , wherein when the detector of the sheet feeding device detects at the most upstream detection point that there is no gap between the first sheet and the second sheet, the controller controls the first feeder or the second feeder such that the first speed will be lower than the second speed.
12. An image forming apparatus according to claim 8 ,
wherein each of the detection points in the sheet feeding device has a specified length;
wherein the controller of the sheet feeding device calculates the first speed, the second speed and a size of the gap at each of the detection points as follows:
the controller calculates the first speed, based on a time necessary for a trailing edge of the first sheet to complete passing by the detection point and the specified length of the detection point:
the controller calculates the second speed, based on a time necessary for a leading edge of the second sheet to complete passing by the detection point and the specified length of the detection point; and
the controller calculates the size of the gap, based on the specified length of the detection point, the second speed and a time necessary for the gap to complete passing by the detection point; and
wherein the controller of the sheet feeding device controls the first feeder or the second feeder in accordance with the size of the gap to adjust the first speed or the second speed.
13. An image forming apparatus according to claim 8 , wherein the sheet feeding device further comprises a corrector for correcting an overlap of the first sheet and the second sheet.
14. An image forming apparatus according to claim 8 , wherein the first speed is fixed.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2008-317144 | 2008-12-12 | ||
JP2008317144A JP4650564B2 (en) | 2008-12-12 | 2008-12-12 | Sheet conveying apparatus and image forming apparatus provided with the same |
Publications (1)
Publication Number | Publication Date |
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US20100148431A1 true US20100148431A1 (en) | 2010-06-17 |
Family
ID=42026862
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US12/635,378 Abandoned US20100148431A1 (en) | 2008-12-12 | 2009-12-10 | Sheet feeding device and image forming apparatus provided with the sheet feeding device |
Country Status (4)
Country | Link |
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US (1) | US20100148431A1 (en) |
EP (1) | EP2196420A3 (en) |
JP (1) | JP4650564B2 (en) |
CN (1) | CN101746627B (en) |
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US20110089629A1 (en) * | 2009-10-20 | 2011-04-21 | Canon Kabushiki Kaisha | Sheet detecting device and image forming apparatus |
US20140042693A1 (en) * | 2012-08-07 | 2014-02-13 | Canon Kabushiki Kaisha | Method for controlling sheet conveyance in image forming apparatus |
US20170329269A1 (en) * | 2016-05-11 | 2017-11-16 | Canon Kabushiki Kaisha | Image forming apparatus |
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JP5825267B2 (en) * | 2013-01-21 | 2015-12-02 | コニカミノルタ株式会社 | Image processing apparatus and motor rotation control method |
CN104660855A (en) * | 2013-11-20 | 2015-05-27 | 崴强科技股份有限公司 | Correction device and correction method for scanning images |
JP6472276B2 (en) * | 2015-03-05 | 2019-02-20 | キヤノン株式会社 | Image forming apparatus |
JP6164246B2 (en) * | 2015-04-27 | 2017-07-19 | コニカミノルタ株式会社 | Image forming apparatus |
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US20110089629A1 (en) * | 2009-10-20 | 2011-04-21 | Canon Kabushiki Kaisha | Sheet detecting device and image forming apparatus |
US8172227B2 (en) * | 2009-10-20 | 2012-05-08 | Canon Kabushiki Kaisha | Sheet detecting device and image forming apparatus |
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US20170329269A1 (en) * | 2016-05-11 | 2017-11-16 | Canon Kabushiki Kaisha | Image forming apparatus |
US10534302B2 (en) * | 2016-05-11 | 2020-01-14 | Canon Kabushiki Kaisha | Image forming apparatus |
Also Published As
Publication number | Publication date |
---|---|
JP4650564B2 (en) | 2011-03-16 |
CN101746627A (en) | 2010-06-23 |
EP2196420A3 (en) | 2011-02-23 |
JP2010137974A (en) | 2010-06-24 |
EP2196420A2 (en) | 2010-06-16 |
CN101746627B (en) | 2013-04-17 |
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