JP5310455B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus capable of simultaneously scanning a plurality of scanning lines with a plurality of laser light sources.

  In recent years, many full-color image forming apparatuses such as electrophotographic copying machines and printers have been put into practical use, and are provided with four photoconductors that form toner images of four colors (Y, M, C, K). The tandem method for synthesizing toner images formed on the body dominates.

  In response to the demand for high-speed and high-density image forming apparatuses, there has been a limit to high-speed and high-density in a single laser beam type exposure unit due to restrictions on the high rotation speed of the polygon motor. For this, there is a multi-beam technique in which a plurality of laser beams are used to simultaneously scan and expose a plurality of laser beams on a photosensitive member. An image forming apparatus that supports high-speed and high-density printing while suppressing the rotation speed of a polygon motor by using a multi-beam is disclosed (Patent Document 1).

  In addition, with the demand for higher functionality in image forming apparatuses, it is desired to support various types of transfer paper depending on the application. The characteristics of transfer paper used for image formation vary greatly depending on the type of paper used. An image forming apparatus that performs conveyance control according to the characteristics of a paper type when performing image formation on transfer paper of different paper types such as plain paper, tracing paper, and OHP sheet is disclosed (Patent Document 2, Patent Document 3).

JP 2008-139590 A JP 11-119598 A JP 2005-138575 A (particularly paragraph 0145)

  In an image forming apparatus using a multi-beam exposure unit, scanning exposure is simultaneously performed by the plurality of laser beams described above. When adjusting the leading edge timing of image writing, it is possible to correct the leading edge timing by adjusting the number of laser beams used for scanning the leading edge, but in this case, the characteristics of each laser beam are different. For this reason, a difference in color may occur.

  In the present invention, in view of such problems, when adjusting the tip timing by changing the writing position of the laser beam in the image forming apparatus, the characteristics of each laser beam are different, so that a difference in color occurs. The purpose is to prevent.

  The above object is achieved by the invention described below.

1. An image forming unit including a photoreceptor;
An exposure unit comprising a plurality of laser light sources, and simultaneously irradiating the photosensitive member with a plurality of laser beams to simultaneously perform scanning exposure of a plurality of scanning lines;
A transfer unit that transfers the image formed by the image forming unit to a sheet at a transfer position;
A paper feed tray for storing paper, a transport unit for transporting the paper in the paper feed tray to the transfer position,
An image forming apparatus comprising:
Adjustment of the leading edge timing of the image by changing the writing start position in the sub-scanning direction with an adjustment width that makes all of the scanning lines simultaneously scanned and exposed by the exposure unit with respect to the reference timing as a reference, and When adjusting the leading edge timing of the paper transported to the transfer position based on the leading edge timing adjustment value and synchronizing both leading edge timings,
The leading edge timing adjustment value set based on at least information about the sheet feeding tray or the paper stored in the sheet feeding tray is allocated to the adjustment of the leading edge timing of the image with the adjustment width, and the remaining less than the adjustment width An image forming apparatus, wherein an adjustment value is assigned to adjustment of the leading edge timing of the paper, and adjustment of the leading edge timing of the image and adjustment of the leading edge timing of the paper are performed based on the assigned adjustment value.

2. The transport unit includes a pair of registration rollers capable of changing a driving speed between the paper feed tray and the transfer position,
The stopped pair of registration rollers is brought into contact with the sheet conveyed from the sheet feeding tray, and the registration roller is started to rotate at a conveyance speed faster than the steady speed at the transfer position to convey the sheet, and the allocated adjustment value is set. 2. The image forming apparatus according to claim 1, wherein the leading edge timing of the sheet is adjusted by decelerating the conveyance speed to a steady speed at a timing based on the conveyance timing and conveying the sheet to the transfer position.

3. The transport unit includes a sensor that detects passage of a sheet between the registration roller and the transfer position;
3. The image forming apparatus according to 2, wherein the timing at which the registration roller decelerates to the steady speed based on the assigned adjustment value is corrected based on the output of the sensor.

4). A display unit that displays a setting screen for setting the timing adjustment value; and an input unit that can be input by an operator;
4. The image forming apparatus according to any one of 1 to 3, wherein a leading edge timing adjustment value can be changed by an input to the input unit.

  According to the present invention, the leading edge timing adjustment value is assigned to the adjustment of the leading edge timing of the image with an adjustment width that includes all of the scanning lines that are simultaneously scanned and exposed, and the remaining adjustment value that is less than the adjustment width is assigned to the sheet. Image forming apparatus capable of preventing color difference by adjusting the leading edge timing of the image and adjusting the leading edge timing of the paper based on the adjustment value assigned to each of the leading edge timing adjustments. Can be provided.

1 is an overall configuration diagram of an image forming system. FIG. 3 is a block diagram showing a control configuration of the image forming system. The structure of the exposure part 3 is shown. It is a detailed view of the setting screen A4 in the operation display section OP. It is a detailed view of the setting screen A4 in the operation display section OP. It is explanatory drawing of the control flow which the image forming apparatus A in this embodiment performs. FIG. 6 is a schematic diagram illustrating a relationship between a paper position and a writing start position. FIG. 6 is a diagram illustrating conveyance control for adjusting the leading edge timing of a sheet.

  Although the present invention will be described based on an embodiment, the present invention is not limited to the embodiment.

  FIG. 1 is an overall configuration diagram of an image forming system including an image forming apparatus A, a post-processing apparatus FNS, and a large-capacity paper feed tray LT. The illustrated image forming apparatus A is called a tandem color image forming apparatus, and includes an image forming unit A1, a scanner SC, an operation display unit OP, and an automatic document feeder ADF.

  The image forming unit A1 forms an image by an electrophotographic method, and includes an exposure unit 3, a plurality of image forming units 4Y (yellow), 4M (magenta), 4C (cyan), 4K (black), and a belt-like shape. It has an intermediate transfer belt 42, a paper feed tray 5a, a paper feed tray 5b, a paper feed means 50, a transport means 60, a fixing device 7, a paper discharge section 8, and an automatic double-sided copy transport section 9.

  The transport unit 60 includes a plurality of transport roller pairs 6a to 6h, and rotates by driving of a drive motor (not shown) to transport the paper S.

  In the specification of the present application, components are indicated by reference numerals with alphabetic suffixes omitted, and Y, M, C, K, or a to j are added to indicate individual components. It is indicated by a reference sign with a letter.

  An automatic document feeder ADF (ADF) is mounted on the upper part of the image forming apparatus A. A post-processing device FNS is connected to the left side of the image forming apparatus A in the drawing on the paper discharge unit 8 side.

  The document placed on the document table of the automatic document feeder ADF is conveyed in the direction of the arrow, and an image on one or both sides of the document is read by the optical system of the scanner SC, and is read by the CCD image sensor 1A.

  The analog signal photoelectrically converted by the CCD image sensor 1A is subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like in the memory control unit, and then sent to the exposure unit 3.

  In the exposure unit 3, output light from the semiconductor laser is applied to the photosensitive drum 41 of the image creation unit 4 to form a latent image. In the image creating unit 4, processes such as charging, exposure, development, transfer, separation, and cleaning are performed.

  Several hundred to 2,000 sheets can be stored in the sheet feeding tray 5, and the sheet S conveyed one by one by the sheet feeding unit 50 from the sheet feeding tray 5 is conveyed by the conveying roller pair 6 of the conveying unit 60. The The conveyance roller pair 6d on the upstream side of the image forming unit A1 functions as a registration roller (hereinafter, the conveyance roller pair 6d is also referred to as a registration roller pair 6d). The registration roller pair 6d is driven by an independent drive motor, and the sheet S conveyed from the paper feed tray 5 is brought into contact with the stopped registration roller pair 6d, and the driving of the registration roller pair 6d is started at a predetermined timing (hereinafter referred to as “registration roller pair 6d”). (Also referred to as re-conveyance), the leading edge timing of the conveyance of the sheet S to the transfer position N is adjusted, and synchronization with image formation by the image forming unit A1 is performed. The drive motor for driving the registration roller pair 6d is composed of a stepping motor or the like, and the resolution is equivalent to several μm in terms of the amount of movement on the surface of the registration roller pair 6d.

  In this embodiment, the tip timing is adjusted at the drive start timing, but in other embodiments described later, the tip timing is also adjusted by the deceleration timing of the drive motor. Here, the deceleration timing will be described (a specific example will be described later). The conveyance speed (rotational speed) of the registration roller pair 6d when the conveyance of the stopped sheet S is started is higher than the steady speed (also referred to as image forming speed) at the transfer position. The sheet is transported to the transfer position N after decelerating to a steady speed at a predetermined deceleration timing based on the timing adjustment value. The conveyance timing of the sheet to the transfer position N can be adjusted by moving the deceleration timing back and forth.

  A leading edge detection sensor TS1 is provided on the downstream side of the registration roller pair 6d, and the passage of the sheet conveyed from the registration roller pair 6d can be detected.

  The transfer roller 43 functions as a transfer unit, and the toner image is transferred to the sheet S conveyed by the conveying unit 60 at the transfer position N of the transfer roller 43, and the toner image is fixed by the fixing device 7 on the downstream side. Then, it is sent from the paper discharge unit 8 to the post-processing device FNS.

  When images are formed on both the front and back sides of the sheet S, after one-sided image formation is performed by the conveyance path switching gate, the sheet S is conveyed downward immediately after passing through the fixing device 7 and sent to the automatic duplex copy sheet feeding unit 9. After reversing the front and back, the image creating unit 4 again processes the back surface image and then ejects the paper from the paper discharge unit 8, and the post-processing device FNS performs post-processing.

  The operation display unit OP functions as an “input unit” and a “display unit”, and includes a touch panel in which a touch screen is arranged on a liquid crystal (LCD) panel. The user (operator) can input print conditions and post-processing setting information in a post-processing apparatus described below by inputting or selecting various settings through the operation display unit OP.

  The large-capacity paper feed tray LT is provided in each of the paper feed trays 5c, 5d, and 5e, and each of these paper feed trays 5, and feeds the top sheet of the paper bundle in the paper feed tray 5 one by one. A paper means 50 is provided. A large number of sheets S in the sheet feeding tray 5 are continuously fed and sent to the image forming apparatus A.

  In the sheet post-processing device FNS, an insertion sheet feeding means 40, a stacking means 30, and a stapling means 20 containing insertion sheets (used for a front cover, a back cover, etc.) are arranged in a substantially vertical direction from the top in the figure. They are arranged in columns.

  An entrance conveyance unit 70 is disposed on the upper right side of the sheet post-processing device FNS in the figure. In addition, a movable paper discharge tray 81 for discharging and stacking printed paper is disposed on the left side of the paper post-processing device FNS. The movable paper discharge tray 81 can accommodate up to about 3000 sheets (A4 size, B5 size) on which images are formed.

  FIG. 2 is a block diagram showing a control configuration of the image forming system. In FIG. 2, image data processing is mainly described, and a configuration such as sequence control is illustrated in a simplified manner.

  2, the image forming apparatus A includes an image processing control unit 100, a printer control unit 110, a scanner control unit 120, and an operation panel control unit 130. Each control unit includes an ADF control unit 140 connected to the main body, The LT control unit 150 and the FNS control unit 160 are connected by a serial communication line indicated by a dotted line. In FIG. 2, only the image processing control unit 100 shows a CPU (image control CPU) and a memory (nonvolatile memory 102) for storing a program. A memory is included, and these perform sequence control in cooperation with each other through a serial communication line.

  A printer controller 200 connected to the image forming apparatus A is connected to an external personal computer PC via a LAN line, receives print data from the personal computer PC, and performs image processing. The printer controller 200 may be externally attached to the main body or installed as a substrate inside.

  Since the print data created by the personal computer PC is described in a page description language such as PS or PCL, the printer controller 200 has a function of analyzing the print data and converting it into bitmap data. In addition, the printer controller 200 executes processing for adjusting an image such as screen processing, conversion of character data into a built-in font, and the like. In such processing, the DRAM control IC 201 is executed using the DRAM as a memory under the control of the controller control CPU.

  The DRAM control IC 201 of the printer controller 200 is connected to the DRAM control IC 101 of the image processing control unit 100 via a PCI bus (indicated by a thick line), and transfers the converted image data and various information set by the printer driver of the personal computer PC. .

  Under the control of the image control CPU of the image processing control unit 100, the DRAM control IC 101 temporarily stores the received data in a page memory as a buffer, sends it to a compression IC, compresses the data, and then stores it in the compressed memory of the DRAM. save.

  The data in the compressed memory is sent to the decompression IC in accordance with the control sequence, decompressed, and supplied to the laser light source LD for image writing through the write processing unit.

  On the other hand, the original image data read by the CCD of the scanner SC passes through the reading processing unit and the compression IC, and is similarly stored in the compression memory. Like the print data, the image data from the decompression IC and the writing processing unit is transferred to the laser light source LD. Supplied. Various setting information when the document is read by the image reading unit SC is input from the operation display unit OP and transferred from the panel control unit 130. In the figure, a thin solid line is a data transfer line connecting each component and circuit.

  As described above, the print image data from the personal computer PC or the original image data obtained by reading the original is subjected to various processes, compressed and expanded, and finally written on the photosensitive drum 41 by the laser light source LD. Various setting information in the personal computer PC and the operation display unit OP is sent to the control unit of each unit together with the sequence control information through a dotted serial communication line.

  FIG. 3 shows the configuration of the exposure unit 3. The exposure unit 3 irradiates a plurality of laser beams and simultaneously scans a plurality of scanning lines in the main scanning direction on the photosensitive drum 41 to perform writing. As shown in FIG. 29, a collimator lens 21, a slit 22, a cylindrical lens 23, a polygon mirror 24, an fθ lens 25, a cylindrical lens 26, a mirror 27, a light receiving sensor 28, and the like.

  The laser light source unit 29 includes a plurality of laser light sources LD such as four, eight, and sixteen, for example. In FIG. 3, an example in which four laser light sources LD1 to LD4 are provided will be described. Further, the mirror 27 and the light receiving sensor 28 are provided at positions outside the image forming area of the photosensitive drum 41. The plurality of laser light sources LD1 to LD4 are numbered in order of the moving direction of the image, that is, from the front in the sub-scanning direction, and the number is reflected at the end of the code.

  The exposure of the laser beam from the exposure unit 3 to the photosensitive drum 41 is performed as follows. First, the four laser beams exposed from each of the first to fourth laser light sources LD1 to LD4 are converted into parallel beams by the collimator lens 21, and the collimator lens 21 is formed by the slit 22 for shaping the beam spot of the photosensitive drum 41. Transmission of the four beams exposed from is limited.

  The four beams transmitted through the slit 22 are imaged on the mirror surface of the rotating polygon mirror 24 by the cylindrical lens 23 and deflected by being reflected by the mirror surface. The reflecting mirror surface of the polygon mirror 24 can be regarded as a virtual light source. Since the distance from the virtual light source to the surface of the photosensitive drum 41 varies depending on the direction of the opposite mirror surface, the influence on the main scanning speed of the beam exposed from the virtual light source by the fθ lens 25 is corrected.

  The four beams exposed from the fθ lens 25 are imaged on the photosensitive drum 41 by the cylindrical lens 26. The four laser beams imaged on the photosensitive drum 41 are scanned along the scanning lines S1 to S4 shown in FIG. Further, some of the four laser beams reflected from the polygon mirror 24 are reflected by the mirror 27 and detected by the light receiving sensor 28.

  As described above, in the image forming apparatus A including the exposure unit 3 of FIG. 3, scanning exposure in the main scanning direction is performed by the rotation of the polygon mirror 24, and moved in the sub scanning direction by the rotation of the photosensitive drum 41. An image is formed.

  3 shows an example in which four (or eight) laser beams transmitted through the slit 22 are scanned in the main scanning direction by the polygon mirror 24 having eight mirror surfaces. The number of mirror surfaces is as follows. There is no particular limitation. Further, the laser light source unit 29 is not limited to one, and two or more semiconductor laser units having a laser light source may be provided.

  Also, each optical system (collimator lens 21, slit 22, cylindrical lens 23, polygon mirror 24, fθ lens 25, cylindrical so that the optical center of the optical system is positioned at the center of the arrangement direction of the four laser light sources LD1 to LD4. The lens 26) is arranged.

[Timing adjustment value setting]
Next, the setting of the tip timing adjustment value will be described. The leading edge timing adjustment value can be set individually or in combination depending on (1) the paper feed tray 5 to be used, (2) the type of paper to be used, (3) front / back, and (4) paper size. , (1) to (4) are used to determine the tip timing adjustment value. In the present application, the timing adjustment value in each element (1) to (4) is simply referred to as “adjustment value” or “tip timing adjustment value”, and the sum of these values is referred to as “tip timing adjustment value”. .

  4 and 5 are detailed views of the setting screen A4 in the operation display unit OP. In the example shown below, the setting is performed using the operation display unit OP provided in the image forming system. However, the setting is not limited thereto, and the setting may be performed from a personal computer PC connected to the image forming apparatus A. .

  On the setting screen A4 shown in FIG. 4, the user can set (1) an adjustment value in the paper feed tray 5. The setting screen A4 includes a numeric key K1, a numeric value column K2 for displaying a numeric value input by the numeric key K1, and a set button K3 for setting the numeric value in the numeric value column K2 to the selected paper feed tray 5. The adjustment value column K4 indicates the adjustment value currently set in the paper feed tray 5 displayed in the adjacent left paper feed tray column K10. In the example shown in the figure, the uppermost paper feed tray 1 (corresponding to the paper feed tray 5a in FIG. 1) is selected, and when the user operates the set button K3, the display value in the numerical value column K2 is It is set in the adjustment value column K4 of the paper feed tray 1. The adjustment value of each paper feed tray 5 can be set in units of 0.1 mm within a range of +6.00 mm to −6.00 mm.

  In the setting screen A4 shown in FIG. 5, the adjustment value for the leading edge timing at the time of image formation on the back side of the paper (side 2 of the paper) can be set by the adjustment value column K6. In addition, the adjustment value column K5 can set an adjustment value for the leading edge timing depending on the combination of paper size (large size, small size), paper type (thick paper, plain paper), and front and back. The adjustment value columns K4, K5, and K6 can be adjusted independently, and the total of the setting values in these adjustment value columns becomes the leading edge timing adjustment value depending on the conditions during image formation. For example, if the adjustment values for the paper feed tray 1, back surface, small size, and plain paper are +0.60 mm, +0.30 mm, +0.50 mm, and +0.00 mm, respectively, the leading edge when image formation is performed under these conditions The timing adjustment value is +1.40 mm. Each set adjustment value is stored in the nonvolatile memory 102 that functions as a “storage unit” by converting the unit from length (mm) to the number of pixels. For example, if the resolution is 1200 dpi (21.2 μm), +1.40 mm is 66 dots.

  The size of the paper stored in each paper feed tray 5 is automatically detected by a size detection mechanism (not shown), and the correspondence with the type of paper stored is input by a user instruction to the operation display unit OP. It is done by.

[Control flow]
FIG. 6 is an explanatory diagram of a control flow performed by the image forming apparatus A in the present embodiment. In step S10, a print job is input in response to a print start instruction from the personal computer PC or the operation display unit OP.

  In step S11, the print job conditions (paper tray used, paper size, paper type, paper front and back) input in step S10 are matched with the leading edge timing adjustment values set in FIGS. These total values are used as the tip timing adjustment value ux.

  In step S12, the leading edge timing adjustment value ux is assigned to the leading edge timing adjustment value u1 and the leading edge timing adjustment value u2.

  The leading edge timing adjustment value ux that is set based on the information on the paper feed tray 5 used when forming an image or the paper S stored in the paper feeding tray 5 is also allocated to the leading edge timing adjustment value u2 of the image. This is because the leading edge timing of the image can be drawn from LD1 of the eight laser light sources LD1 to LD8. As a result, the tip timing can be adjusted with high accuracy.

  In the present embodiment, there are eight scanning lines that are simultaneously scanned and exposed by the exposure unit 3, and the adjustment width p that is a set of all eight that are simultaneously scanned and exposed is 8 Line (169.4 μm: 8-pixel size of 1200 dpi). ).

  For example, when the leading edge timing adjustment value ux is 66Line as in the above example, the adjustment value p2 is assigned to the leading edge timing adjustment value u2 (writing start position in the sub-scanning direction) with the adjustment width p (8Line). is there. Since the remaining adjustment value 2Line less than the adjustment width is assigned to the adjustment value u1 of the leading edge timing of the sheet, the adjustment value u1 is 2Line.

  Specifically, u1 = mod (ux, p) and u2 = ux−u1. Here, mod (x, y) indicates a remainder when x is divided by y.

  Steps S13 to S14 are control of the paper transport system, and the leading edge timing of the paper is adjusted based on the adjustment value u1. Steps S21 to S23 are control of the image processing system, and the leading edge timing of the image is adjusted based on the adjustment value u2. In this way, the timings of both tips are synchronized. This will be described below.

  In step S13, the conveyance of the sheet S from the sheet feed tray 5 is started based on the contents of the print job. In step S14, the leading edge timing of the sheet is adjusted so that the sheet S is conveyed to the transfer position N at a timing shifted by the adjustment value u1 with respect to the reference timing as a reference. The adjustment of the leading edge timing of the sheet may be performed by controlling the re-conveying timing of the registration roller pair 6d by controlling the driving motor, or the deceleration timing may be controlled as described later. For example, if the adjustment value u1 is +2 Line, the sheet S is transported so as to reach the transfer position N later by the time of 2 Line than the reference timing.

  In the image processing system, in step S21, the image data of the print job is expanded. In step S22, each color exposure unit 3 changes the writing start position at a timing shifted by the adjustment value u2 with respect to the reference timing. For example, if the adjustment value u2 is 64Line, exposure of the leading edge of the image is started with a delay of 8 sets for the time of 64Line, that is, 8 sets for the adjustment width p of 8 sets.

  In step S24, the latent images formed on the photosensitive drums 41 of the respective colors in step S23 are developed by the image creating units 4Y, 4M, 4C, and 4K, and sequentially transferred to the intermediate transfer belt 42 to form a superimposed toner image. To do.

  In step S16, the sheet S is conveyed at the transfer position N at the leading edge timing of the sheet adjusted in the sheet conveying system up to step S15, and formed at the leading edge timing of the image adjusted in the image processing system up to step S23. The transferred image is transferred by the transfer roller 43.

[Reason for adjusting with the adjustment width that makes all eight exposed at the same time as one set]
Next, the reason why adjustment is performed with the adjustment width p, which is a set of eight laser beams that are simultaneously scanned and exposed, will be described. FIG. 7 is a schematic diagram showing the relationship between the paper position and the writing start position. FIG. 7A shows an example in which the leading end position of the sheet coincides with the writing start position (the writing position of LD1), and FIG. 7B shows a deviation of 6 lines because the leading end position of the sheet does not match the writing start position. An example is shown. FIG. 7B is a comparative example.

  In FIG. 7B, all the eight light sources are not combined into one set, and the laser light sources LD1 to LD6 are not irradiated in one scanning of the front end (writing position 1), and only the two light sources from the laser light sources LD7 and LD8 are exposed. Thus, it is possible to make the writing start position coincide with the position of the leading edge of the paper. However, in that case, since the characteristics of the laser light source LD1 to the laser light source LD8 are different from each other, a difference in color may occur. When the same image data is repeatedly used for continuous printing, the laser light source LD for writing out the leading edge of the paper is different for each image formation, and the color is different between adjacent papers, making it easy to recognize. The problem arises.

  In this embodiment shown in FIGS. 1 to 6, such a problem can be prevented by adjusting the tip timing with a plurality of laser beams as a set.

[Other Embodiments]
In the embodiment shown in FIGS. 1 to 6, the leading edge timing of the sheet is adjusted by controlling the re-conveying timing of the registration roller pair 6d. However, in the other embodiment described with reference to FIG. The leading edge timing of the paper is adjusted by controlling. This will be described below. Except for the configuration described with reference to FIG. 8, the embodiment is the same as the embodiment described with reference to FIGS.

  FIG. 8 is a diagram for explaining conveyance control for adjusting the leading edge timing of a sheet. In FIG. 8, the vertical axis represents the conveyance speed (unit: mm / sec) of the registration roller pair 6d, and the horizontal axis represents time (msec).

  The first transport speed (steady speed) at the image forming and transfer position N is 301.5 mm / sec, and the second transport speed of the pair of registration rollers 6d for transporting the paper S is 1 higher than the first transport speed. For example, it is set to 361.5 mm / sec.

  In FIG. 8, when the drive start signal t1 output from the control unit is input to the drive motor that drives the registration roller pair 6d, the drive motor starts to be driven with a slight time difference, and the registration roller pair 6d Accelerated to the second transport speed.

  First, “a system that does not consider correction by the tip detection sensor TS1” will be described. By starting to drive the registration roller pair 6d, the sheet S is conveyed at a high second conveyance speed. After the leading edge of the sheet S is detected by the leading edge detection sensor TS1 (timing t2), the sheet S is decelerated at a deceleration timing t3 after a predetermined time has elapsed. In FIG. 8, the solid line shows the deceleration timing when the leading edge timing adjustment value u1 is zero. The t3 corresponds to the reference timing. When the adjustment value u1 is zero, the deceleration timing matches the reference timing.

  When the adjustment value u1 is positive instead of zero, the deceleration starts at a deceleration timing t4 that is earlier than the reference timing t3 by a time corresponding to the adjustment value u1. The broken line in FIG. 4 shows the change in speed when the vehicle is decelerated at the deceleration timing t4. By making the deceleration timing earlier than the reference timing, the conveyance time of the sheet S to the transfer position N can be delayed. Similarly, when the adjustment value u2 is negative, the conveyance time of the sheet S to the transfer position N can be shortened by increasing the deceleration timing.

  Next, the “system that considers correction by the tip detection sensor TS1” will be described. The reference timing t3 is corrected by the detection timing of the tip detection sensor TS1. As a result of correcting the reference timing t3, the deceleration timing t4 is also corrected.

  For example, when normal conveyance is performed and the set reference time and the measurement time by the tip detection sensor TS1 are the same, it is not necessary to correct the reference timing t3.

  On the other hand, when the conveyance start of the sheet S is delayed due to slippage between the sheet S and the registration roller pair 6d, the detection time t2 of the sheet S by the leading edge detection sensor TS1 is delayed from the reference timing. Corresponding to this delay, the reference time t3 is corrected.

  For example, from the start of driving of the registration roller pair 6d, the leading edge of the paper S conveyed at the first conveyance speed by the registration roller pair 6d is detected by the leading edge detection sensor TS1, and the time required until that time is a preset reference timing. On the other hand, for example, when delayed by 1.0 msec, the driving of the registration roller pair 6d corresponding to the second conveyance speed of 361.5 mm / sec is delayed by 6.0 msec from the reference timing t3.

  In this way, the leading edge detection sensor TS1 corrects the reference timing t3 for calculating deceleration, thereby adjusting the leading edge timing of the paper with higher accuracy in synchronization with the image processing system and the paper conveying system. It becomes possible.

A1 Image forming unit A4 Setting screen 3 Exposure unit 29 Laser exposure unit LD1 to LD8 Laser light source 4, 4Y, 4M, 4C, 4K Image creation unit 5, 5a to 5e Paper feed tray 6d Registration roller pair 42 Intermediate transfer belt 43 Transfer roller N Transcription position

Claims (4)

An image forming unit including a photoreceptor;
An exposure unit comprising a plurality of laser light sources, and simultaneously irradiating the photosensitive member with a plurality of laser beams to simultaneously perform scanning exposure of a plurality of scanning lines;
A transfer unit that transfers the image formed by the image forming unit to a sheet at a transfer position;
A paper feed tray for storing paper, a transport unit for transporting the paper in the paper feed tray to the transfer position,
An image forming apparatus comprising:
Adjustment of the leading edge timing of the image by changing the writing start position in the sub-scanning direction with an adjustment width that makes all of the scanning lines simultaneously scanned and exposed by the exposure unit with respect to the reference timing as a reference, and When adjusting the leading edge timing of the paper transported to the transfer position based on the leading edge timing adjustment value and synchronizing both leading edge timings,
The leading edge timing adjustment value set based on at least information about the sheet feeding tray or the paper stored in the sheet feeding tray is allocated to the adjustment of the leading edge timing of the image with the adjustment width, and the remaining less than the adjustment width An image forming apparatus, wherein an adjustment value is assigned to adjustment of the leading edge timing of the paper, and adjustment of the leading edge timing of the image and adjustment of the leading edge timing of the paper are performed based on the assigned adjustment value. The transport unit includes a pair of registration rollers capable of changing a driving speed between the paper feed tray and the transfer position,
The stopped pair of registration rollers is brought into contact with the sheet conveyed from the sheet feeding tray, and the registration roller is started to rotate at a conveyance speed faster than the steady speed at the transfer position to convey the sheet, and the allocated adjustment value is set. The image forming apparatus according to claim 1, wherein the leading edge timing of the sheet is adjusted by decelerating a conveyance speed to a steady speed at a timing based on the conveyance timing and conveying the sheet to the transfer position. The transport unit includes a sensor that detects passage of a sheet between the registration roller and the transfer position;
The image forming apparatus according to claim 2, wherein the timing at which the registration roller decelerates to the steady speed is corrected based on the assigned adjustment value based on the output of the sensor. A display unit that displays a setting screen for setting the timing adjustment value; and an input unit that can be input by an operator;
The image forming apparatus according to claim 1, wherein a leading edge timing adjustment value can be changed by an input to the input unit.

Images