JP2012088628A - Printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printer adopting an electrophotographic system especially realizing highly accurate control of an end margin position regardless of the strength or the surface characteristics of paper.SOLUTION: A printer which conveys a recording medium to an image forming part in a timing corresponding to an image formed on an image carrier comprises: first paper end detection means provided downstream in the paper conveyance direction of standby rolls which temporally stop the conveyance of the recording medium; rotation drive means for activating the rotation of rollers for conveying the recording medium; and control means which drives the rotation drive means in a state in which the end of the recording medium contacts with the standby rolls, and the conveyance of the recording medium is stopped, and which controls the drive of the rotation drive means according to the timing when the recording medium is detected by the first paper end detection means.

Description

  The present invention relates to a printing apparatus using an electrophotographic system.

  As a printing apparatus using an electrophotographic method, for example, a photosensitive drum is uniformly charged and initialized, an electrostatic latent image is formed on the photosensitive drum by optical writing, the electrostatic latent image is converted into a toner image, There is known a printer device that indirectly transfers the toner image to a recording medium such as paper, performs a heat fixing process, and prints it out.

  In this type of printing apparatus, for example, a toner image is temporarily transferred to an intermediate transfer medium such as a transfer belt (primary transfer), and then transferred to a recording medium such as paper (secondary transfer). A method of forming is adopted. FIG. 8 is a diagram showing a configuration in the vicinity of the secondary transfer unit in the printing apparatus of the above method.

  The secondary transfer unit 90 includes an intermediate transfer belt 91 and a secondary transfer roller 92, and a standby conveyance roller pair 93 is disposed upstream of the secondary transfer unit 90 in the sheet conveyance direction. A standby sensor 94 is disposed upstream of the standby conveyance roller pair 93 in the paper conveyance direction, and detects the leading edge of the paper conveyed toward the standby conveyance roller pair 93.

  The standby conveyance roller pair 93 obtains driving force from a motor (not shown) via a standby clutch 95, and after a predetermined time after the standby sensor 94 detects the leading edge of the paper, drives the standby conveyance roller pair 95. The sheet is conveyed to the secondary transfer unit 90. At this time, the skew of the sheet is corrected and the standby clutch 95 is driven to convey the sheet to the secondary transfer unit 90.

  FIG. 9 shows a time chart at this time. First, the motor is driven (turned on) at the timing a shown in the figure, and a photosensitive drum, a conveyance roller, etc. (not shown) are driven. Thereafter, exposure is sequentially performed based on the print data from four print heads of yellow (Y), magenta (M), cyan (C), and black (K) at the timings b to e in FIG. Perform primary image transfer.

  Thereafter, a paper feeding clutch (not shown) is driven at a predetermined timing (timing f shown in the figure), and the paper is carried into the apparatus. Then, for example, the standby sensor 94 detects the leading edge of the sheet at the timing g shown in the figure, the standby clutch 95 is driven at the timing h, and the sheet is fed again to the secondary transfer unit 90 at the timing i. At this time, the skew of the sheet is corrected as described above, and the sheet is conveyed to the secondary transfer unit 90.

  The invention according to Patent Document 1 is provided with a registration roller that locks the front end of the sheet and temporarily stands by, and further detects the front end detection sensor and the passage of the rear end of the sheet downstream from the roller. The trailing edge detection sensor is provided, and the sheet length is calculated based on the time from the start of the registration roller until the trailing edge of the sheet passes the trailing edge detection sensor, and the calculation result is obtained until the leading edge of the sheet reaches the leading edge detection sensor. The detection error is corrected due to the positional deviation of the leading edge of the sheet in comparison with the standard time.

  In an image forming apparatus provided with an image forming unit that forms an image on a sheet and a conveyance path having a bent part, the invention according to Patent Document 2 is provided on the upstream side in the sheet conveying direction and on the downstream side in the sheet conveying direction. Are provided with a first sensor and a second sensor for detecting the sheet, respectively, detecting a passage time for the sheet to pass between the first sensor and the second sensor, and determining the rigidity of the sheet based on the detected passage time. It has the determination means to determine.

JP 2009-107781 A JP 2006-267193 A

  However, in the conventional printing apparatus, when the paper is fed again by the standby conveyance roller pair 93, the skew of the paper is corrected. However, the paper once stopped by the standby conveyance roller pair 93 due to the rigidity and surface property of the paper. The tip position varies. In particular, when high-speed printing is performed such that the printing speed exceeds, for example, 50 ppm, the degree becomes remarkable, and there is a variation when re-feeding and aligning the position of the printed image and the paper in the secondary transfer unit 90. In some cases, the error may exceed the allowable range.

  The inventions according to Patent Documents 1 and 2 use two sensors, but the invention according to Patent Document 1 is an invention that corrects a detection error due to misalignment, and the invention according to Patent Document 2 reduces the rigidity of the paper. It is an invention to judge.

  Therefore, the present invention provides a printing apparatus with excellent print quality by controlling the position of the leading edge margin with high accuracy regardless of the stiffness and surface quality of the paper, even for a high-speed printing apparatus.

  According to the first aspect of the present invention, there is provided a printing apparatus for carrying a recording medium into an image forming unit at a timing coincident with an image formed on an image carrier, and a standby roll for temporarily stopping the conveyance of the recording medium. A first sheet leading edge detecting unit provided on the downstream side in the sheet conveying direction; a rotation driving unit that rotates a roller that conveys the recording medium; and a leading end of the recording medium is in contact with the standby roll; Control means for driving the rotation driving means in a state in which the conveyance of the recording medium is stopped, and for controlling the driving of the rotation driving means in accordance with the timing when the recording medium is detected by the first sheet leading edge detection means. This can be achieved by providing a printing device.

  According to a second aspect of the present invention, there is provided a second sheet leading edge detecting means on the upstream side of the standby roll in the sheet conveying direction, and the second sheet leading edge detecting means is provided on the standby roll. This can be achieved by providing a printing apparatus used for setting the standby amount of the recording medium.

  According to a third aspect of the present invention, the control means stops the rotation driving means after receiving a detection signal from the first paper leading edge detection means, and sends the image to the transfer section. This can be achieved by providing a printing apparatus that resumes driving of the rotation driving means again at a timing that matches the data.

  According to a fourth aspect of the present invention, the rotation drive means can be achieved by providing a printing apparatus that is a motor.

  According to a fifth aspect of the present invention, the above object can be achieved by providing a printing apparatus in which the image carrier is a photoreceptor or a transfer belt.

  According to the present invention, the sensor provided on the downstream side of the standby roller in the sheet conveyance direction calculates the sheet conveyance time to the sensor, compares it with a preset time based on the calculation result, and determines the skew of the sheet. By adjusting the delay of the conveyance time due to the line or the like, the sheet can be accurately guided to the secondary transfer position and the transfer process can be performed. Therefore, high-quality image formation can be performed on the paper.

It is sectional drawing explaining the structure of the printing apparatus of this embodiment. FIG. 4 is a configuration diagram in the vicinity of a standby conveyance roller pair and a secondary transfer roller. It is a circuit block diagram of a printing apparatus. It is a flowchart explaining the process of this embodiment. It is a time chart explaining the process of this embodiment. It is a figure explaining the modification of the printing apparatus of this embodiment. It is a figure explaining the other modification of the printing apparatus of this embodiment. FIG. 6 is a configuration diagram in the vicinity of a conventional standby conveyance roller pair and a secondary transfer roller. It is a time chart explaining the conventional process.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view illustrating a configuration of a full-color image forming apparatus (hereinafter simply referred to as a printer apparatus) according to the present embodiment.

  A printer apparatus 1 shown in the figure is an electrophotographic secondary transfer tandem type color image forming apparatus, and includes an image forming unit 2, a transfer belt unit 3, a toner supply unit 4, a paper feeding unit 5, a belt type. The fixing unit 6 and the duplex printing transport unit 7 are configured.

  The image forming unit 2 is in contact with the lower running unit surface 8a of the transfer belt 8 of the transfer belt unit 3 and multi-stages four developing devices 9 (9m, 9c, 9y, 9k) from right to left in FIG. It consists of a side-by-side configuration. The image forming unit 2 is held by the main body frame of the printer apparatus 1 so as to be movable up and down from a printing execution position shown in FIG. 1 to a maintenance position below it.

  Of the four developing devices 9, the three developing devices 9m, 9c, and 9y on the downstream side (the right side in the figure) are magenta (M), cyan (C), and yellow (Y ) Color toner is formed, and the developing device 9k forms a monochrome image using black (K) toner mainly used for dark portions of characters and images.

  Each of the developing devices 9 has the same configuration except for the color of the toner that develops the image. Therefore, the configuration of the developing device 9k for black (K) toner will be described below as an example.

  The developing device 9 includes a photosensitive drum 10 at the top. The photosensitive drum 10 has a peripheral surface made of, for example, an organic photoconductive material. A cleaner 11, a charging roller 12, an optical writing head 13, and a developing roller 15 of the developing device 14 are disposed around the periphery of the photosensitive drum 10.

  The developing device 14 includes a housing 16 that covers the outside, a partition wall 17 provided inside, a developing roller 15, a first stirring and conveying screw 18, and a second stirring and conveying screw 19. Although not specifically shown, the first and second agitating and conveying screws 18 and 19 include a screw shaft and a fin that is integrally formed with the screw shaft and rotates.

  The developing unit 14 includes a reserve tank, which will be described later in detail, and a magenta (M), cyan (C), yellow (Y), and magenta (M) as shown by M, C, Y, and K in FIG. Either black (K) toner is supplied.

  The transfer belt unit 3 has an endless transfer belt 8 that extends in the shape of a flat loop in the left-right direction in the figure at approximately the center of the main unit, and the transfer belt 8 is stretched over the transfer belt 8. A driving roller 21 and a driven roller 22 that circulate in a counterclockwise direction indicated by an arrow p in the figure are provided.

  The above-described transfer belt 8 is directly transferred to the surface of the belt that circulates below by a primary transfer roller 20 that is integrated with the unit and pressed against the photosensitive drum 10 via the transfer belt 8 (primary transfer). Then, the toner image is conveyed to the secondary transfer unit 23 to the paper for further transfer (secondary transfer) to the paper.

  The transfer belt unit 3 is provided with a belt cleaner 24 having a cleaning blade that comes into contact with the surface of the drive roller 21. A waste toner collection container 25 is detachably disposed below the belt cleaner 24.

  In the belt cleaner 24, the cleaning blade comes into contact with the surface of the transfer belt 8 to scrape and remove the waste toner, and the waste toner is sent to a waste toner collection container 25 below by a conveying screw.

  The toner supply unit 4 includes four reserve tanks 26 (26m, 26c, 26y, and 26k) disposed above the upper running unit of the transfer belt 8, and is detachably disposed on the reserve tanks 26, respectively. And a toner cartridge 27 (27m, 27c, 27y, 27k) for toner replenishment.

  The four toner cartridges 27m, 27c, 27y, and 27k accommodate magenta (M), cyan (C), yellow (Y), and black (K) toners, respectively, and four reserve tanks 26 (26m, 26c). , 26y, and 26k) are replenished with toner from the toner cartridge 27 mounted thereon.

  These four reserve tanks 26 are hidden behind the opposite side of the transfer belt unit 3 in FIG. 1, but are connected to the corresponding developing devices 14 of the developing device 9 by toner supply paths.

  Although not particularly shown, the toner supply unit 4 is held on the frame of the printer 1 main body so as to be able to be raised and lowered from the printing execution position shown in FIG. 1 to a maintenance position above it.

  Two electrical parts 30 are disposed on the left side of the toner supply unit 4 from the left side of the belt cleaner 24 to above the drive roller 21. The electrical unit 30 includes a circuit board on which a control device composed of a plurality of electronic components, which will be described in detail later, is mounted.

  The paper feed unit 5 includes two paper feed cassettes 29 (29a, 29b) arranged in two upper and lower stages. A paper take-out roller 31, a feed roller 32, a separating roller 33, and a standby conveyance roller pair 34 are disposed in the vicinity of the paper feed opening (right side of the drawing) of the two paper feed cassettes 29, respectively.

  A secondary transfer roller 35 that is in pressure contact with the driven roller 22 via the transfer belt 8 is disposed in the paper transport direction (vertically upward in the drawing) of the standby transport roller pair 34, and the secondary transfer onto the paper described above. Part 23 is formed.

  A belt-type heat fixing unit 6 is disposed downstream (upward in the drawing) of the secondary transfer portion. On the further downstream side of the belt-type heat fixing unit 6, a pair of carry-out rollers 36 for carrying out the fixed paper from the belt-type heat fixing unit 6, and a paper discharge tray 37 formed on the upper surface of the apparatus. A paper discharge roller pair 38 for paper discharge is provided.

  The conveyance unit 7 for double-sided printing also serves as an opening / closing member whose outer surface (right outer surface in the drawing) opens or shields the inside of the printer apparatus 1 from the side surface to the outside.

  This duplex printing transport unit 7 has a start return path 39a that branches rightward in the figure from just before the paper discharge roller pair 38, an intermediate return path 39b that bends downward, and a left lateral direction opposite to the above. Thus, a return path 39 including a terminal return path 39c for finally inverting the return sheet is provided.

  In the middle of the return path 39, five pairs of return rollers 41 (41a, 41b, 41c, 41d, 41e) are arranged. The exit of the end return path 41e joins the conveyance path to the standby conveyance roller pair 34 corresponding to the sheet feeding cassette 29b below the sheet feeding section 5.

  FIG. 2 is a diagram for explaining in detail the configuration around the standby conveyance roller pair 34 and the secondary transfer roller 35 in the printer apparatus 1 having the above configuration. As shown in the figure, a sensor 40a for detecting the leading edge of the sheet is disposed upstream of the standby conveyance roller pair 34 in the sheet conveyance direction, and similarly, the leading edge of the sheet is disposed downstream of the standby conveyance roller pair 34 in the sheet conveyance direction. A sensor 40b for detecting the above is disposed.

  The standby conveyance roller pair 34 is driven by a standby motor 68, and the transfer belt 8 is in contact with the secondary transfer roller 35 to constitute the secondary transfer unit 23.

  FIG. 3 is a block diagram illustrating an internal circuit of the printer apparatus 1 having the above configuration. As shown in the figure, the printer apparatus 1 has a central processing unit (CPU) 55 as a center, and an interface controller (I / F_CONT) 56 and a head controller (HEAD_CONT) 57 are connected to the CPU 55 via data buses. Has been. A printer printing unit 58 is connected to the HEAD_CONT 57.

  The CPU 55 is connected to a ROM (read only memory) 59, an EEPROM (electrically erasable programmable ROM) 61, an operation panel 62 of the main body operation unit, and a sensor unit 63 to which outputs from sensors arranged in the respective units are input. ing. The sensor unit 63 also receives a detection signal when the sensors 40a and 40b detect the leading edge of the sheet.

  The ROM 59 stores a system program, and the CPU 55 performs processing by controlling each unit in accordance with the system program.

  That is, in each unit, first, the I / F_CONT 56 converts print data supplied from a host device such as a personal computer into bitmap data and develops it in the frame memory 65. In the frame memory 65, a storage area is set for each of black (K), magenta (M), cyan (C), and yellow (Y), and data of each color is developed in the corresponding area.

  The data developed in the frame memory 65 is output to the HEAD_CONT 57, and is output from the HEAD_CONT 57 to the printer printing unit 58. The EEPROM 61 stores information of times T1 to T3 described later.

  The printer printing unit 58 includes a rotation driving system (not shown) including the photosensitive drum 10 and the primary transfer roller 20 shown in FIG. 1, an image forming unit having driven parts such as the charging roller 12 and the optical writing head 13, A driving unit (not shown) for driving the transfer belt unit 3 to move up and down and the rotation of the transfer belt 8 is provided.

  Further, the printer printing unit 58 includes a belt driving unit 66 that drives the belt of the belt-type fixing unit 6 and a standby motor driving unit 67 that drives a standby roller. The standby motor drive unit 67 drives the standby motor 68 described above.

  Further, the printer printing unit 58 outputs a drive output to a process load such as a conveyance mechanism including rotationally driven parts such as the paper take-out roller 22 to the paper discharge roller pair 31, and a belt-type fixing unit 6 that is driven and heated. To control.

  The black (K), magenta (M), cyan (C), and yellow (Y) data output from the HEAD_CONT 57 are respectively sent from the printer printing unit 58 to the corresponding optical writing heads 13 shown in FIG. To be supplied.

In the above configuration, the processing operation of the printing apparatus of this embodiment will be described below.
FIG. 4 is a flowchart for explaining the processing operation of this example, and FIG. 5 is a time chart for explaining the processing operation of this example.

  First, a main motor (not shown) is driven (turned on), and driving of the photosensitive drum 10 and the developing roller 15 is started, and yellow (Y), magenta (M), cyan (C), and black (K) are started. Print data is transmitted to the four print heads, the transfer belt 8 is exposed, and the toner image is primarily transferred to the transfer belt 8. Thereafter, a paper supply clutch (not shown) is driven to feed the paper into the apparatus. The paper fed into the machine reaches the sensor 40a through the paper transport path.

  The sensor 40a detects the timing of the leading edge of the paper rising through the paper conveyance path at j shown in FIGS. As a result of this detection, a paper leading edge detection signal is transmitted from the sensor 40a to the CPU 55 via the sensor unit 63 described above. Under the control of the CPU 55, the leading edge of the paper comes into contact with the standby conveying roller pair 34 after a preset time has elapsed. Stop paper transport.

  Next, from this state, the standby motor 68 is driven at a timing k shown in FIGS. 9A to 9C, and the paper is fed again to the secondary transfer unit 23. The process of the flowchart shown in FIG. 4 is started by refeeding the sheet.

  First, the re-fed paper reaches the sensor 40b. The sensor 40b stores the time T at which the leading edge of the paper has arrived (step (hereinafter referred to as S) 1), and determines whether this time T is shorter than the preset time T3 (S2).

  The time T3 is the shortest of the preset times T1 to T3 as described above. In this case, the timing of the time chart shown in FIG. 5C corresponds, and the drive of the standby motor 68 is immediately stopped. (S3, timing l shown in FIG. 4C). In this case, for example, when the paper is fed again from the standby conveyance roller pair 34, the leading edge of the sheet slightly protrudes and the leading edge of the sheet reaches the sensor 40b in a short time.

  Therefore, after that, the standby motor 68 is driven again at the time Tx shown in FIG. With this configuration, even when the leading edge of the sheet reaches the sensor 40b in a short time, the secondary transfer can be performed at an accurate position by stopping the first drive of the standby motor 68 at a corresponding timing. it can.

  Next, when the time T detected by the sensor 40b is longer than the preset time T3 (S2 is NO), it is further determined whether the time T detected by the sensor 40b is T2 ≦ T <T1 (S5). The time T1 is the longest time among the preset times T1 to T3, and the time T2 is the next longest time. Here, when the time T detected by the sensor 40b is T2 ≦ T <T1 (S5 is YES), the drive of the standby motor 68 is stopped (S6, timing m shown in FIG. 5B), and thereafter The standby motor 68 is driven again at the time Tx shown in FIG.

  With this configuration, for example, when refeeding from the standby conveyance roller pair 34, even if it takes a long time for the leading edge of the paper to reach the sensor 40b due to paper slip or the like, the standby motor is provided for the corresponding time. By performing the first drive 68 for a long time, the secondary transfer can be performed at an accurate position.

  On the other hand, if the time T detected by the sensor 40b is not T2 ≦ T <T1 (S5 is NO), it is further determined whether the time T detected by the sensor 40b is T3 ≦ T <T2 (S8). Here, when the time T detected by the sensor 40b is T3 ≦ T <T2 (S8 is YES), the drive of the standby motor 68 is stopped (S9, timing n shown in FIG. 5A), and thereafter The standby motor 68 is re-driven at the time Tx shown in FIG. With this configuration, for example, when paper is re-feeded from the standby conveyance roller pair 34, the time until the leading edge of the paper reaches the sensor 40b is within a normal range, and the initial time of the standby motor 68 for the corresponding time. By performing this driving, secondary transfer can be performed at an accurate position.

  When the time T detected by the sensor 40b exceeds T3 (S8 is NO), this time T1 is the longest time among the preset times T1 to T3 as described above, and the paper jam occurs. For example, it is determined that it has occurred, and for example, the driving of the printing apparatus is stopped (S11), and an error display is performed.

  As described above, according to the present embodiment, when re-feeding the stopped paper to the standby conveyance roller pair 34, the time T that reaches the sensor 40b from the interrupt control unit 34 is measured, and preset times T1 to T1 are measured. By sequentially comparing with T3, a delay in conveyance time such as skew of the paper in the standby conveyance roller pair 34 is grasped, the drive time of the standby conveyance roller pair 34 is adjusted, and the secondary transfer position to the paper Can be set accurately. Therefore, high-quality image formation can be performed on the paper.

  FIG. 6 is a diagram illustrating a modification of the printing apparatus according to the present embodiment, and is a diagram illustrating a configuration example of a printing apparatus that does not use a transfer belt. In the drawing, the sheet unloaded from the sheet feeding cassette 70 by the sheet feeding roller 71 is detected by the sensor 73 and temporarily stopped by the standby conveying roller pair 74 as described above. Thereafter, the standby motor 72 is driven, and the sheet is conveyed to a transfer unit including a photosensitive drum 76 as an image carrier and a transfer unit 77. At this time, the time T is detected by the sensor 75 in the same manner as described above, and the print position is adjusted based on the skew of the paper by performing comparison processing with the preset times T1 to T3. The toner image can be transferred to a proper printing position. Thereafter, the paper on which the toner image has been transferred is subjected to a heat fixing process by a heat fixing device 78.

  On the other hand, FIG. 7 is a view showing another modified example of the printing apparatus of the present embodiment, in which a sheet conveying belt is used instead of the transfer belt. In other words, the leading edge of the sheet carried out from the sheet feeding cassette 80 by the sheet feeding roller 81 is detected by the sensor 83 and is temporarily stopped by the standby conveying roller pair 84 as described above. After that, the standby motor 82 is driven to feed the paper onto the conveying belt 86, and magenta (M), cyan (C), yellow (Y), and black (K) print heads 87M and 87C from a photosensitive drum (not shown). , 87Y and 87K. At this time, the time T is detected by the sensor 85 in the same manner as described above, and the print position on the paper is adjusted based on the skew of the paper by performing comparison processing with the preset times T1 to T3. Is called. After the exposure to the paper, a heat fixing process by the heat fixing device 88 is performed.

DESCRIPTION OF SYMBOLS 1 Printer apparatus 2 Image formation part 3 Transfer belt unit 4 Toner supply part 5 Paper feed part 6 Belt type fixing unit 7 Conveyance unit for double-sided printing 8 Transfer belt 8a Lower travel part surface 9 (9m, 9c, 9y, 9k) Developing device DESCRIPTION OF SYMBOLS 10 Photosensitive drum 11 Cleaner 12 Charging roller 13 Optical writing head 14 Developer 15 Developing roller 16 Housing | casing 17 Partition 15 Developing roller 18 1st stirring conveyance screw 19 2nd stirring conveyance screw 20 Primary transfer roller 21 Driving roller 22 Follower roller 23 Secondary transfer section 24 Belt cleaner 25 Waste toner collection container 26 (26m, 26c, 26y, 26k) Reserve tank 27 (27m, 27c, 27y, 27k) Toner cartridge 29 (29a, 29b) Paper feed cassette 30 Electrical equipment Part 31 Paper take-out roller 32 Feed Roller 33 Rolling roller 34 Standby conveyance roller pair 35 Secondary transfer roller 36 Unloading roller pair 37 Paper discharge tray 38 Paper discharge roller pair 39 Return path 39a Start return path 39b Intermediate return path 39c End return path 41 (41a, 41b, 41c, 41d, 41e) Return roller pair 42 Toner transport path 43 Toner supply mechanism 44 Cartridge motor 45 Fin screw 46 Reserve tank motor 47 Toner 48 Fin screw 49 Developer motor 50 Opening 51 Toner density sensor 52 Detected part 53 Detecting part 54 Detection Device 55 CPU (central processing unit)
56 Interface Controller (I / F_CONT)
57 Printer controller (PR_CONT)
58 Printer printing section 59 ROM (read only memory)
61 EEPROM (electrically erasable programmable ROM)
62 Operation Panel 63 Sensor Unit 65 Frame Memory 66 Belt Drive Unit 67 Standby Motor Drive Unit 70 Paper Feed Cassette 71 Paper Feed Roller 72 Standby Motor 73 Sensor 74 Standby Transport Roller Pair 75 Sensor 76 Photosensitive Drum 77 Transfer Device 78 Thermal Fixing Device 80 Feed cassette 81 Feed roller 82 Standby motor 83 Sensor 84 Standby transport roller pair 85 Sensor 86 Transport belts 87M, 87C, 87Y, 87K Print head 88 Thermal fixing device

Claims (5)

In a printing apparatus for carrying a recording medium into an image forming unit at a timing coincident with an image formed on an image carrier,
First paper leading edge detection means provided on the downstream side in the paper conveyance direction of the standby roll for temporarily stopping the conveyance of the recording medium;
Rotation driving means for rotating a roller for conveying the recording medium;
In a state where the leading edge of the recording medium is in contact with the standby roll and conveyance of the recording medium is stopped, the rotation driving unit is driven, and the recording medium is detected by the first sheet leading edge detecting unit. Control means for performing drive control of the rotation drive means according to timing;
A printing apparatus comprising:   A second paper leading edge detection unit is provided on the upstream side of the standby roll in the sheet conveyance direction, and the second sheet leading edge detection unit is used for setting a standby amount of the recording medium in the standby roll. The printing apparatus according to claim 1.   The control unit stops driving the rotation driving unit after receiving the detection signal from the first sheet leading end detection unit, and drives the rotation driving unit again at a timing coincident with the image data sent to the transfer unit. The printing apparatus according to claim 1, wherein the printing apparatus is restarted.   The printing apparatus according to claim 1, wherein the rotation driving unit is a motor.   The printing apparatus according to claim 1, wherein the image carrier is a photoconductor or a transfer belt.