JP4749276B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a digital copying machine or a laser printer, and more particularly to a method for stably transporting paper from a paper feed mechanism to an image forming unit.

  In conventional image forming apparatuses such as copying machines and printers, a sheet conveyed by a sheet feeding mechanism from a sheet feeding unit such as a sheet feeding cassette or a sheet feeding tray hits a pair of registration rollers on the upstream side of the image forming unit. After being stopped and skewing is corrected, the toner image is re-conveyed at a timing synchronized with the toner image formation on the surface of the photoconductor in the image forming unit, and the toner image on the surface of the photoconductor is transferred by the transfer unit. Thereafter, the paper passes through the fixing device, and the toner image is fixed. Then, the paper is discharged to the outside of the device.

  The configuration of a conventional paper feed cassette and paper feed mechanism is shown in FIG. The paper P set on the cassette base 10 a of the paper feed cassette 10 is applied to a pickup roller 29 provided on the apparatus main body side with a predetermined pressure by a paper stacking plate 28 urged upward by a conical compression spring 27. Pressed. When the print start button of the image forming apparatus is turned on, the pickup roller 29 and the driving roller 30a of the conveying roller pair 30 are rotationally driven in the direction of the arrow in the figure.

  As for the paper P set on the paper stacking plate 28, one or a plurality of upper sheets are usually sent to the conveying roller pair 30 by the pickup roller 29. When a plurality of sheets are sent to the conveying roller pair 30, only the uppermost sheet is separated and conveyed toward the sheet conveying path 12 by the separation roller 30b that rotates in the same direction as the stop or drive roller 30a. The Reference numeral 50 denotes a rear end cursor for aligning the rear ends of the paper P, and is provided so as to be movable in the paper transport direction (left-right direction).

  As described above, in the conventional paper feeding mechanism, a method is generally used in which the pickup roller 29 is brought into contact with the surface of the stacked paper and rotated in the paper feeding direction to feed the paper to the pair of transport rollers 30 on the downstream side. It is. At this time, if the pickup roller 29 slips or double feed (double field) of the paper occurs, the paper position at the start of paper feed varies.

  Such variations in the paper position lead to variations in the conveyance time from the start of paper feeding to the paper conveyance path 12, that is, the variation in paper feeding timing. As a result, the paper interval (inter-paper) during continuous printing and the arrival of the paper at the registration roller pair It causes time variation. If the gap between the papers becomes shorter during continuous printing, the amount of slackening when stopped by the pair of registration rollers will increase and the paper will wrinkle, or the following paper will be transported to the image forming unit following the preceding paper. , Paper jams may occur.

  On the other hand, when the interval between the sheets becomes long, the stop time of the registration roller pair cannot be sufficiently secured, the skew of the sheet cannot be corrected, or the sheet conveyance is performed at the image forming timing in the image forming unit. There may be a problem that the printing position is shifted in time. Also, if the interval between sheets becomes longer than a certain time, it is determined that a jam has occurred and the apparatus may stop during continuous printing. The problem described above becomes particularly noticeable in the case of a high-speed machine with a large number of processed sheets per unit time and a short interval between sheets.

  Accordingly, various methods for preventing variations in paper feed timing have been proposed. For example, Patent Document 1 discloses a first paper detection sensor on the downstream side of the paper feed means and a second paper detection on the upstream side of the registration roller pair. An image forming apparatus that includes sensors, determines whether to temporarily stop the sheet by the first sheet detection sensor, and corrects the stop time of the sheet based on the time until the sheet reaches the second sheet detection sensor Is disclosed.

However, in the method of Patent Document 1, in order to determine whether or not to stop the paper using the first paper detection sensor provided on the downstream side of the paper feeding means, the paper supply in which the first paper detection sensor is arranged is used. Although the paper gap in the vicinity of the paper means can be kept constant, there is a possibility that the paper gap cannot be made constant in the vicinity of the registration roller pair in which the deviation in timing during paper conveyance is integrated. Further, the correction of the pause time based on the arrival time at the second paper detection sensor is executed every predetermined number of sheets, so that it was not possible to appropriately cope with the case where the paper gap suddenly shortened significantly.
JP 2005-31020 A

  In view of the above problems, an object of the present invention is to provide an image forming apparatus that can secure a paper gap between registration rollers to a certain level or more for each paper and can perform a stable paper feeding operation.

  In order to achieve the above object, the present invention provides a sheet feeding unit that feeds sheets one by one, an image forming unit that forms a predetermined image on the sheet fed by the sheet feeding unit, and the image forming unit. A registration roller pair that is arranged in the vicinity of the upstream side of the image forming unit and adjusts the conveyance timing of the sheet fed from the sheet feeding unit in accordance with the image formation timing in the image forming unit, and the registration roller pair and the sheet feeding One or more pairs of conveying rollers disposed between the sheet conveying unit, one or more sheet detecting units disposed in the vicinity of the pair of conveying rollers for detecting whether or not a sheet has passed, and the sheet feeding unit And an image forming apparatus comprising: a drive unit capable of independently driving the registration roller pair and the transport roller pair; and a control unit for controlling the drive unit. Depending on the detection timing of the means The inter-paper time during continuous printing is measured for each paper, and when the inter-paper time is shorter than a preset reference value, at least the transport roller pair and the paper feed upstream of the paper detection means The means is stopped by a time difference between the sheet interval time and the reference value.

  According to the present invention, in the image forming apparatus having the above-described configuration, when the time between sheets is longer than a preset reference value, the control unit sets the drive duration time of the pair of conveyance rollers and the sheet feeding unit. It is characterized by extending the time difference between the paper interval and the reference value.

  According to the present invention, in the image forming apparatus having the above-described configuration, the sheet interval time is measured using the sheet detection unit disposed in the vicinity of the upstream side of the conveyance roller pair positioned immediately before the registration roller pair. It is a feature.

  According to the present invention, in the image forming apparatus having the above-described configuration, a plurality of the sheet feeding units are provided, and are arranged on the downstream side of a merging point of a plurality of sheet conveying paths connecting the sheet feeding units and the registration roller pairs. The sheet interval time is measured using the sheet detecting means.

  According to the present invention, in the image forming apparatus configured as described above, the sheet detection unit is a reflective sensor.

  According to the first configuration of the present invention, even when the paper feeding timing is advanced due to the double feeding of paper and the paper gap becomes narrow, the paper gap time equal to or greater than the reference value can always be secured, so that the registration roller pair is reached. It is possible to effectively suppress the occurrence of jam by delaying the timing to perform. Further, since the sheet interval time is measured every time a sheet is conveyed, the sheet interval can be accurately corrected even when the sheet feeding timing is suddenly significantly advanced.

  According to the second configuration of the present invention, in the image forming apparatus having the first configuration, when the sheet interval time is longer than the reference value, the drive duration time of the conveying roller pair and the sheet feeding unit is set to the sheet interval. By extending the time difference between the time and the reference value, the amount of paper hitting the registration roller pair can be kept constant at all times, so paper skew and print misalignment due to delays in paper feed timing can be suppressed. it can.

  Further, according to the third configuration of the present invention, in the image forming apparatus having the first or second configuration, the paper is detected by using the paper detection unit in the vicinity of the upstream side of the conveyance roller pair positioned immediately before the registration roller pair. By measuring the interval time, it is possible to measure the interval time in the vicinity of the registration roller pair in which variations during sheet conveyance are integrated.

  According to the fourth configuration of the present invention, in the image forming apparatus having any one of the first to third configurations, the plurality of sheet conveyance paths connecting the plurality of sheet feeding units and the pair of registration rollers are joined. By measuring the sheet interval time using the sheet detection means on the downstream side of the point, the sheet interval time of sheets fed from a plurality of sheet supply units can be measured using one sheet detection sensor. .

  Further, according to the fifth configuration of the present invention, in the image forming apparatus having any one of the first to fourth configurations, the detection timing of the paper is shifted by using the reflection type sensor as the paper detection unit. It becomes difficult to accurately measure the time between sheets.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side sectional view of an image forming apparatus according to a first embodiment of the present invention. In an image forming apparatus (for example, a printer) 100, when performing an image forming operation, a photosensitive drum 5 that rotates clockwise in the drawing is uniformly charged by a charging unit 4, and an exposure unit (laser scanning unit) based on document image data. Etc.) An electrostatic latent image is formed on the photosensitive drum 5 by the laser beam from 7, and a developer (hereinafter referred to as toner) is attached to the electrostatic latent image by the developing unit 8 to form a toner image.

  The toner is supplied to the developing unit 8 from the toner container 9. The image data is transmitted from a personal computer (not shown) or the like. Further, a static elimination device (not shown) for removing residual charges on the surface of the photosensitive drum 5 is provided on the downstream side of the cleaning device 15.

  A sheet is conveyed from the sheet feeding cassette 10 or the manual feed tray 11 via the sheet conveying path 12 and the registration roller pair 13 toward the photosensitive drum 5 on which the toner image is formed as described above, and the transfer roller 14 (image The toner image formed on the surface of the photosensitive drum 5 is transferred onto the sheet by the transfer unit. The sheet on which the toner image has been transferred is separated from the photosensitive drum 5 and conveyed to a fixing unit 16 having a fixing roller pair 17 to fix the toner image. When the paper is conveyed from the paper feed cassette 10, the paper on the paper stacking plate 28 is fed by a paper feed means composed of a pickup roller 29 and a paper feed roller pair 30 comprising a paper feed roller 30a and a separation roller 30b. Each sheet is separated and conveyed.

  The sheet that has passed through the fixing unit 16 is conveyed in the conveying direction by a sheet conveying roller 18 and a first conveying roller pair 20 and a second conveying roller pair 21 including a first pinch roller 19a and a second pinch roller 19b pressed against the sheet conveying roller 18. Is distributed. When an image is formed on only one side of the paper, the image is directed downward (hereinafter referred to as the following) through the feed roller pair 23 and the discharge roller pair 24 that are distributed to the paper transport path 22 by the first transport roller pair 20 and can rotate forward and backward. It is discharged onto the discharge tray 25 in a face-down manner. The paper transport path 22, the feed roller pair 23, and the discharge roller pair 24 also function as a switchback device that switches the paper transport direction.

  On the other hand, when images are formed on both sides of the paper, the paper that has passed through the fixing unit 16 is once distributed to the paper conveyance path 22 by the first conveyance roller pair 20. Then, after the trailing edge of the sheet has passed through the first conveying roller pair 20, the feed roller pair 23 and the discharge roller pair 24 are reversely rotated to switch the conveying direction. The image is distributed to the recording path 26 and is re-conveyed to the image forming unit including the photosensitive drum 5 and the developing unit 8 with the surface on which the image is not formed facing up. After the re-conveyed paper, the next image formed by the image forming unit is transferred by the transfer roller 14 and conveyed to the fixing unit 16 to fix the toner image, and then the first conveying roller pair 20 and the paper conveying path. Then, the paper is discharged onto the discharge tray 25 from the discharge roller pair 24 via 22.

  FIG. 2 is a cross-sectional view schematically showing a paper conveyance path from the paper feed cassette to the image forming unit in the image forming apparatus of the first embodiment. Portions common to FIG. 1 are denoted by the same reference numerals and description thereof is omitted. The image forming apparatus according to this embodiment includes a paper feed cassette 10, a manual feed tray 11, and a paper feed roller pair 30 including a pickup roller 29, a paper feed roller 30 a, and a separation roller 30 b. It is provided as a paper feeding means, and is arranged so that the pickup roller 29 is in contact with the upper surface end on the downstream side in the transport direction of the paper loaded on the paper feeding cassette 10 and the manual feed tray 11. The pickup roller 29 and the paper feed roller 30a rotate in conjunction with a drive transmission mechanism (not shown).

  The sheet fed from the sheet feeding cassette 10 or the manual feed tray 11 passes through the sheet conveying path 12 and is conveyed to the registration roller pair 13. The registration roller pair 13 is disposed in the vicinity of the upstream side of the photosensitive drum 5 (see FIG. 1), temporarily stops the conveyed paper, and transfers in synchronization with the image formation timing on the surface of the photosensitive drum 5. Re-convey to roller 14 (see FIG. 1). Further, the registration roller pair 13 abuts against the leading edge of the paper to form a slack, and also serves to correct the skew of the paper.

  Between the paper feed cassette 10 and the registration roller pair 13, conveyance roller pairs 31 a and 31 b are arranged in order from the upstream side along the paper conveyance path 12, and between the manual feed tray 11 and the registration roller pair 13. A conveying roller pair 31c is arranged. A registration sensor 32 that detects passage of the registration roller pair 13 near the upstream side of the registration roller pair 13 is disposed, and the upstream side of the conveyance roller pairs 31a, 31b, and 31c is disposed near the conveyance roller pairs 31a to 31a. Paper detection sensors 33a, 33b, and 33c for detecting the passage of the paper 31c are arranged.

  The paper feed roller pair 30, the transport roller pairs 31a to 31c, and the registration roller pair 13 are connected to a drive motor 37 (see FIG. 3) via an electromagnetic clutch (not shown), and are controlled by ON / OFF control of the electromagnetic clutch. The roller pair can be driven independently. In addition, it is good also as a structure which provides the motor which drives each roller pair separately.

  In the present embodiment, the time from the trailing edge detection of the preceding sheet to the leading edge detection of the succeeding sheet during continuous printing using the sheet detection sensor 33b disposed in the vicinity of the conveyance roller pair 31b immediately before the registration roller pair 13. (Paper interval time) is measured for each sheet, and when the paper interval time is shorter than a preset reference value, the conveyance roller pairs 31a and 31b and the supply roller are fed by the time difference between the measured paper interval time and the reference value. The paper roller pair 30 is stopped.

  As a result, even when the paper feeding timing is advanced due to double feeding of the paper and the paper gap becomes narrower, a paper gap time that is equal to or greater than the reference value can always be secured, so the timing at which the paper reaches the registration roller pair 13 is delayed. Generation of paper wrinkles and jams can be effectively suppressed. Further, since the sheet interval time is measured every time a sheet is conveyed, the sheet interval can be accurately corrected even when the sheet feeding timing is suddenly significantly advanced.

  Further, the sheet detection sensors 33a and 33b are generally arranged on the conveyance roller pairs 31a and 31b, respectively, and the sheet interval correction is performed by using the sensors that are normally arranged without providing the sensors separately. Therefore, it is possible to avoid a complicated configuration and an increase in cost.

  Here, it is possible to measure the inter-sheet time by using the sheet detection sensor 33a in the vicinity of the downstream side of the conveying roller pair 31a and perform the same control. Therefore, it is preferable to measure the sheet interval time in the vicinity of the registration roller pair 13.

  On the other hand, when the sheet interval time is measured using the registration sensor 32, the sheet interval time is compared with the reference value after the preceding sheet passes through the registration roller pair 13, and if it is shorter than the reference value, the conveyance roller pair 31a is compared. 31b is transmitted. Therefore, when the conveying roller pair 31a, 31b stops, the leading edge of the succeeding paper reaches the registration roller pair 13, and it becomes impossible to secure a gap between the registration roller pair 13, and the registration roller pair 13 is loosened. There is a possibility that the formation time may not be sufficient and a timing failure may occur during re-conveyance. Further, when the registration sensor 32 is disposed at a position away from the registration roller pair 13, there is a concern that the detection timing of the paper passing through the registration roller pair 13 may be poor.

  Therefore, the configuration of this embodiment in which the sheet interval time is measured by using the sheet detection sensor 33b in the vicinity of the upstream side of the conveyance roller pair 31b disposed immediately before the registration roller pair 13 and the sheet interval control is performed is preferable. In addition, here, when the sheet interval time is shorter than the reference value, both the conveyance roller pairs 31a and 31b are stopped. However, the sheet detection sensor 33b is positioned upstream from the conveyance roller pair 31b (for example, the conveyance roller). If the sheet can be stopped before the paper is nipped by the conveyance roller pair 31b, only the conveyance roller pair 33a and the feed roller 30a are stopped, and the conveyance roller pair 31b continues. Can also be driven.

  As the paper detection sensors 33a and 33b, various sensors that can detect whether paper has passed or not can be used. For example, an arm-type sensor that directly detects the paper and detects it, or light is emitted from the light emitting unit to the paper. In addition, a reflection type sensor that detects reflected light from the surface of the paper with a light receiving unit is used. In this example, a reflective sensor is used that can reliably detect a sheet as long as the sheets do not completely overlap, and that hardly causes a shift in detection timing.

  In this embodiment, as shown in FIG. 2, the paper conveyance path 12 connected to the manual feed tray 11 is branched from the downstream side of the conveyance roller pair 31 b, and the paper detection sensor 33 b detects when paper is fed from the manual feed tray 11. I do not do it. Normally, the paper feed speed from the manual feed tray 11 is set slower than the paper feed speed from the paper feed cassette 10, and it is possible to provide a margin between the papers. This is because sometimes it is not necessary to perform the sheet gap control of the present invention. Therefore, for example, even when the paper transport path 12 of the manual feed tray 11 is branched from the upstream side of the transport roller pair 31b, it is not necessary to perform the paper spacing control when feeding from the manual feed tray 11.

  When a reflection type sensor is used as the paper detection sensor 33b, there is a possibility that an OHP sheet detection failure may occur. However, since the OHP sheet is generally fed from the manual feed tray 11, no particular problem occurs.

  FIG. 3 is a block diagram illustrating a control path of the image forming apparatus according to the first embodiment, and FIG. 4 is a flowchart illustrating a paper gap control procedure performed by the image forming apparatus according to the first embodiment. With reference to FIG. 2 and FIG. 3, the procedure for adjusting the sheet interval time will be described according to the steps in FIG. First, when a paper feed signal is transmitted to the control unit 35 by a print start command or the like, the drive motor 37 is driven to rotate by the control signal transmitted from the control unit 35, and the pickup roller 29 on the paper feed cassette 10 side and the paper feed. The roller 30a rotates counterclockwise to start feeding (step S1).

  Next, it is determined whether or not the print command is continuous printing (step S2). If it is a single print command, it is not necessary to perform the sheet interval control, so the sheet is conveyed to the image forming unit 40 via the registration roller pair 13 at a predetermined timing to form an image, and the process is terminated. On the other hand, when continuous printing is instructed, the paper interval time T (seconds) with the subsequent paper is measured using the paper detection sensor 33b (step S3). The measured inter-paper time T is transmitted to the control unit 35. Then, the reference value T0 (seconds) stored in advance in the storage unit 39 is read, and the control unit 35 compares the paper interval time T with the reference value T0 to determine whether T <T0. (Step S4).

  When the inter-paper time T is shorter than the reference value T0, the succeeding paper has reached the paper detection sensor 33b earlier than usual, so the transport roller pair 31a, 31b and the paper feed roller 30a are set to T0-T (seconds). ) Only (step S5). Thereafter, when the transport roller pairs 31a and 31b and the paper feed roller 30a are driven again (step S6), the paper reaches the registration roller pair 13 at the same timing as usual (step S7).

  On the other hand, if the sheet interval time T is equal to or greater than the reference value T0 in step S4, the pair of conveying rollers 31a and 31b and the sheet feeding roller 30a are driven as they are without performing the sheet interval control, thereby causing the registration roller pair 13 to move to the sheet. Arrives (step S7). The registration roller pair 13 conveys the sheet to the image forming unit 40 at a predetermined timing, and image formation is performed in the image forming unit 40. Thereafter, it is determined whether or not the continuous printing is continued (step S8). If the paper feeding is finished, the process is finished as it is. If printing continues, the process returns to step S2, and the same procedure is repeated thereafter (steps S2 to S7).

  By the above control procedure, the reduction of the paper interval time due to the double feeding of the paper is automatically detected for each paper, and the paper interval time can always be adjusted to the reference value T0 or more. It is possible to effectively prevent defects such as jams and jams. The reference value T0 may be appropriately set according to the specifications of the image forming apparatus, such as the paper size used and the image processing speed.

  FIG. 5 is a flowchart showing another sheet spacing control procedure by the image forming apparatus of the present invention. With reference to FIG. 2 and FIG. 3, the procedure for adjusting the sheet interval time will be described according to the steps of FIG. The procedure (steps S1 to S3) from the start of paper feeding by a print start command or the like to the measurement of the inter-paper time T (seconds) in the case of continuous printing is the same as in FIG.

  Then, the reference value T0 is read from the storage unit 39, and the control unit 35 determines whether or not the paper interval time T is equal to the reference value T0 (step S4). If T ≠ T0, it is next determined whether T <T0 or not (step S5). If T <T0, the succeeding paper has arrived at the paper detection sensor 33b earlier than usual, and therefore the conveying roller pair 31a, 31b and the paper feed roller 30a are stopped for T0-T (seconds) (step). S6). Thereafter, when the transport roller pairs 31a and 31b and the paper feed roller 30a are driven again (step S7), the paper reaches the registration roller pair 13 at the same timing as usual (step S8).

  If T> T0 in step S5, the subsequent paper reaches the paper detection sensor 33b later than usual, and therefore the drive time of the transport roller pair 31a, 31b and the paper feed roller 30a is set to T-T0 (seconds). ) (Step S9). As a result, the sheet reliably reaches the registration roller pair 13 (step S8), and the same slack as usual is formed.

  On the other hand, if T = T0 in step S4, the succeeding paper has normally reached the paper detection sensor 33b, and therefore the pair of transport rollers 31a and 31b and the paper feed roller 30a are left as they are without performing the paper gap control. By driving, the sheet reaches the registration roller pair 13 at a normal timing and a predetermined slack is formed (step S7). Then, the sheet is conveyed from the registration roller pair 13 to the image forming unit 40 at a predetermined timing to form an image. Thereafter, it is determined whether or not the continuous printing is continued (step S8). If the paper feeding is finished, the process is finished as it is. If printing continues, the process returns to step S2, and the same procedure is repeated thereafter (steps S2 to S7).

  In the control procedure of FIG. 5, when the paper interval time T is longer than the reference value T0, the drive duration time of the conveying roller pairs 31a and 31b and the paper feed roller 30a is extended by T-T0. As a result, the extension of the inter-sheet time caused by slipping of the pickup roller 29 is automatically detected for each sheet, and the conveyance roller pair 31a, 31b and the feed roller 30a are driven by the amount of the increased inter-sheet time. The paper can be surely made to reach the registration roller pair 13 and the amount of slackness of the paper can be kept constant at all times. It is possible to effectively suppress paper skew and printing misalignment.

  In particular, in color image forming apparatuses such as color printers and color copiers, image formation starts simultaneously with the start of paper feed, so when the paper feed timing is delayed, the image formed on the photosensitive drum is discarded, Although it is necessary to form a new image in a state where the sheet is kept on standby by the pair of registration rollers 13, by performing the control of FIG. 5, the delay in the sheet feeding timing is eliminated and wasteful toner consumption is reduced and printing is performed. The waiting time can be shortened.

  FIG. 6 is a cross-sectional view schematically showing a paper conveyance path from the paper feed cassette to the image forming unit in the image forming apparatus according to the second embodiment of the present invention. Portions common to FIG. 2 of the first embodiment are denoted by the same reference numerals and description thereof is omitted. The image forming apparatus according to the present embodiment includes two paper feed cassettes 10, and the paper detection sensor 33 b used for measuring the time between papers is connected from the junction 12 a of the paper conveyance path 12 from each paper feed cassette 10. Is also arranged downstream.

  Thus, the sheet interval time of sheets fed from both sheet cassettes 10 can be measured using one sheet detection sensor 33b, and the sheet interval can be controlled without adding an expensive sensor. . The specific paper spacing control procedure is the same as that shown in FIGS. Here, the configuration provided with two paper feed cassettes 10 has been described, but the same applies to the case where three or more paper feed cassettes are provided, since all the paper transport paths from the respective paper feed cassettes merge. Also, the sheet interval control may be performed using a sheet detection sensor on the downstream side.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in each of the above-described embodiments, three transport roller pairs 31a to 31c are arranged on the upstream side of the registration roller pair 13, but the transport roller pair may be one set or two sets, or four sets. You may provide above. Further, it is not necessary to provide one sheet detection sensor for each pair of transport rollers. If at least one sheet detection sensor is provided, sheet spacing control is possible.

  Further, the paper transport path 12 of the manual feed tray 11 is branched from the downstream side of the transport roller pair 31b, but the manual feed tray 11 is joined by joining the paper transport path 12 of the manual feed tray 11 to the upstream side of the transport roller pair 31b. The sheet spacing control can also be executed for sheet feeding from the sheet, and if an arm type sensor is used as the sheet detection sensor 33b, the OHP sheet can be detected.

  Although the monochrome printer has been described as an example of the image forming apparatus here, the present invention can be applied to other image forming apparatuses such as monochrome and color copiers, color printers, and facsimiles.

  The present invention provides a sheet feeding unit that feeds sheets one by one, an image forming unit that forms a predetermined image on the sheet fed by the sheet feeding unit, and an upstream side of the image forming unit A registration roller pair that adjusts the conveyance timing of the sheet fed from the sheet feeding unit in accordance with the image formation timing in the image forming unit, and one disposed between the registration roller pair and the sheet feeding unit The transport roller pair described above, one or more paper detection means arranged near the transport roller pair for detecting whether or not the paper has passed, a paper feed roller pair, a registration roller pair, and a transport roller pair In an image forming apparatus including an independently drivable drive unit and a control unit that controls the drive unit, the control unit determines a sheet interval during continuous printing according to a detection timing of a predetermined sheet detection unit. Measure every time and between paper If shorter than a preset reference value during stops the conveying roller pair and the sheet feeding means upstream of the at least the paper detecting means by the time difference between sheet time and the reference value.

  As a result, the paper interval time is measured using the normally disposed paper detection sensor, and if it is shorter than the reference value, the conveying roller pair and the paper feeding means on the upstream side of the sensor are stopped so that the registration roller pair always It is possible to provide an image forming apparatus that can secure a paper interval time that is equal to or greater than a reference value, and that can effectively suppress the narrowing of the paper space and the occurrence of paper wrinkles and jams resulting therefrom. In addition, since the sheet interval time is measured for each sheet, it is possible to cope with a case where the sheet feeding timing is suddenly advanced. Furthermore, when the paper interval time is longer than the reference value, if the control is performed to extend the drive duration time of each roller pair by the time difference between the paper interval time and the reference value, the skew of the paper due to the delay of the paper supply timing The image forming apparatus can also suppress printing misalignment.

  In addition, since the sheet interval time is measured using the sheet detecting means disposed in the vicinity of the upstream side of the conveyance roller pair positioned immediately before the registration roller pair, the sheet interval time in the vicinity of the registration roller pair, which is likely to vary, is accurately determined. It becomes possible to measure. Further, when a plurality of sheet feeding units are provided, if the sheet detecting unit downstream of the merging point of the plurality of sheet conveying paths connecting each sheet feeding unit and the registration roller pair is used for measuring the time between sheets, An image forming apparatus capable of measuring the sheet interval time of sheets fed from a plurality of sheet feeding units using one sheet detection sensor.

  In addition, since the reflection type sensor is used as the detection means, it is difficult for the detection timing of the paper to shift, and the time between papers can be detected reliably.

1 is a side cross-sectional view showing an overall configuration of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing a paper feed mechanism from a paper feed cassette to an image forming unit in the image forming apparatus of the first embodiment. FIG. 3 is a block diagram illustrating a control path of the image forming apparatus according to the first embodiment. These are the flowcharts which show the paper gap control procedure by the image forming apparatus of 1st Embodiment. These are the flowcharts which show the other paper spacing control procedure by the image forming apparatus of 1st Embodiment. These are sectional views schematically showing a paper feed mechanism from the paper feed cassette to the image forming unit in the image forming apparatus of the second embodiment of the present invention. These are side surface sectional drawings which show the structure of the conventional paper feed cassette and paper feed mechanism.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Paper feed cassette 11 Manual feed tray 13 Registration roller pair 29 Pickup roller (paper feed means)
30 Paper feed roller pair (paper feed means)
30a Paper feed roller 30b Separation rollers 31a to 31c Conveying roller pair 32 Registration sensor 33a to 33c Paper detection sensor (paper detection means)
35 Control unit (control means)
37 Drive motor (drive means)
39 Storage Unit 40 Image Forming Unit 100 Image Forming Apparatus

Claims (4)

Paper feeding means for feeding paper one by one;
An image forming unit that forms a predetermined image on a sheet fed by the sheet feeding unit;
A registration roller pair disposed in the vicinity of the upstream side of the image forming unit and for adjusting the conveyance timing of the sheet fed from the sheet feeding unit in accordance with the image forming timing in the image forming unit;
One or more transport roller pairs disposed between the registration roller pair and the paper feeding means;
One or more paper detection means disposed in the vicinity of the pair of transport rollers for detecting whether or not the paper has passed;
Drive means capable of independently driving the paper feed means, the registration roller pair, and the transport roller pair;
An image forming apparatus comprising: a control unit that controls the driving unit;
The control means measures the sheet interval during continuous printing for each sheet at the detection timing of the predetermined sheet detector, and at least the sheet when the sheet interval is shorter than a preset reference value When the conveyance roller pair and the paper feeding unit on the upstream side of the detection unit are stopped by a time difference between the paper interval time and the reference value, and the paper interval time is longer than a preset reference value, an image forming apparatus comprising that you extended by the time difference between the reference value and between the paper time driving duration of the transport roller pair and said sheet feeding means. 2. The image forming apparatus according to claim 1, wherein the sheet interval time is measured using the sheet detection unit disposed in the vicinity of the upstream side of the pair of conveying rollers positioned immediately before the pair of registration rollers . A plurality of the sheet feeding means are provided, and the sheet interval time is determined by using the sheet detecting means disposed downstream of the merging point of a plurality of sheet conveying paths connecting the sheet feeding means and the registration roller pair. The image forming apparatus according to claim 1, wherein the image forming apparatus is measured. The image forming apparatus according to claim 1 , wherein the sheet detection unit is a reflective sensor .

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