JP2011230894A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of well forming an image on each sheet while suppressing the lowering of image productivity.SOLUTION: The image forming apparatus feeds a sheet to a resister roller 131 in a generally specified time from the start (a) of paper feed operation by a paper feed roller r1 stably without wastefully losing time. The apparatus includes a paper feed sensor S1 disposed, for example, between the paper feed roller r1 and the resister roller and a control unit Cont for controlling the paper feed operation of the paper feed roller. To sequentially supply sheets from a paper supply part 121 for continuously forming images, for each of second and subsequent sheets, the control unit Cont temporarily stops the paper feed operation after the sensor detects the front end of the sheet after the start of the paper feed operation by the paper feed roller, and then re-starts the paper feed operation. The control unit adopts, as a time from the start of paper feed operation to the re-start of paper feed operation, a specified time (a-d) set to the longest time or longer among the times required from the start of paper feed operation to the re-start of paper feed operation at a sheet front end stop position after the front end of the sheet is detected by the sensor which are obtained by taking at least one of the causes of a variation in the conveyance of sheets into account.

Description

  According to the present invention, a recording sheet, a recording sheet for an overhead projector (hereinafter collectively referred to as “sheet”) is supplied from a sheet supply unit to an image forming path passing through an image forming unit by a sheet feeding roller. The image can be formed on the sheet by passing the sheet, and before the sheet supplied by the sheet feeding roller is fed to the image forming path, the sheet is abutted against the stopped registration roller, and then the sheet The present invention relates to an image forming apparatus that activates a sheet conveying operation of a registration roller at a timing at which an image can be formed and sends the sheet to an image forming path.

  Such an image forming apparatus can be found in, for example, an electrophotographic copying machine, a printer, a facsimile machine, and a multi-function machine in which two or more of these are combined.

  In this type of image forming apparatus, when the paper is supplied from the paper supply unit to the registration roller by the paper supply roller, the front end position of the paper in the paper supply unit immediately before the paper supply by the paper supply roller is started, and the paper is conveyed. Due to various paper transport variations such as transport slip in rollers involved in rollers, roller outer diameter tolerance, and roller surface life deterioration, some sheets reach the registration rollers in a given time. It is known that variations such as reaching the registration rollers occur.

When such a sheet conveyance variation occurs, the following problems occur when sheets are sequentially supplied from the sheet supply unit for continuous image formation.
In other words, if a second sheet or later reaches the registration roller early, it overlaps with the preceding sheet and is sent to the image forming path by the registration roller together with the preceding sheet, resulting in an image formation defect. Even if there is no overlap with the preceding paper, the amount of bending of the paper for registration processing by stopping one end of the registration roller becomes too large, and the subsequent conveyance of the paper by the registration roller may be hindered. As a result, the subsequent image formation on the paper may be hindered. In addition, when mutual overlap occurs with the preceding paper, it is necessary to increase the paper feed interval in order to avoid the overlap, but doing so reduces the image productivity.

  Also, if the paper reaches the registration roller later than the conveyance of the preceding paper, the registration roller has already rotated since the timing at which the paper starts to be fed to the image forming path by the registration roller. Not only can the image be formed, but an image is formed on the paper supplied with a delay, and an image position shift occurs on the paper.

  Therefore, as one measure, Japanese Patent Laid-Open No. 2001-213537 discloses that a paper feed sensor is disposed downstream of a paper feed roller, a registration sensor is disposed downstream thereof, and a registration roller is disposed downstream thereof, so that the leading edge of the paper is fed. It monitors the time from the paper feed activation by the paper roller until it reaches the paper feed sensor, and judges whether the time is early or late with respect to a predetermined threshold time. It has been proposed to carry the paper as it is when it is late.

Japanese Patent Laid-Open No. 2001-213537

However, since a threshold is provided for control, a time loss occurs. For example, when the threshold value is 100 milliseconds, if the registration roller reaches the registration roller in 100 milliseconds, it is conveyed without stopping, and if it reaches the registration roller in 99 milliseconds, it is temporarily stopped and restarted. .
In that case, if the stop time is 20 milliseconds and the time required for restarting and starting (the time required to actually start rotation after turning on) is 20 milliseconds, a difference between 100 milliseconds and 139 milliseconds occurs. A time loss of 39 milliseconds occurs.

  Therefore, the present invention can form an image on the sheet by supplying the sheet from the sheet supply unit to the image forming path passing through the image forming unit by the sheet feeding roller, and passing the image forming path. Prior to feeding the sheet supplied by the printer to the image forming path, the sheet is abutted against the stopped registration roller, and then the sheet conveying operation of the registration roller is started at a timing at which image formation can be performed on the sheet. In the image forming apparatus, the second and subsequent sheets are fed from the start of the sheet feeding operation by the sheet feeding roller even when the sheets are sequentially fed from the sheet feeding unit for continuous image formation. It is possible to reach the registration roller that is still stopped for a certain period of time or substantially at a constant time and without incurring any time loss. And to provide an image forming apparatus capable of satisfactorily image formed on each of the paper while suppressing the lower.

  In order to solve the above problems, the present invention provides the following first, second and third image forming apparatuses.

(1) First image forming apparatus An image can be formed on the sheet by supplying the sheet from the sheet supply unit to the image forming path passing through the image forming unit by a paper feed roller and passing through the image forming path. Prior to feeding the paper supplied by the paper feed roller to the image forming path, the paper is abutted against the stopped registration roller, and then the paper conveyance operation of the registration roller is started at a timing when the image can be formed on the paper. An image forming apparatus for sending the paper to the image forming path,
A paper detection sensor disposed between the paper supply roller and the registration roller for detecting the leading edge of the paper supplied by the paper supply roller;
A control unit that controls a paper feeding operation of the paper feeding roller by controlling a paper feeding roller driving unit,
The controller is
In order to sequentially supply paper from the paper supply unit for continuous image formation, for each of the second and subsequent sheets,
After the paper feeding operation by the paper feeding roller is started, the paper feeding operation by the paper feeding roller is temporarily stopped after the leading edge of the paper fed by the paper feeding roller is detected by the paper detection sensor. Restart the paper feed operation using the paper feed roller,
The time from the start of the paper feed operation by the paper feed roller to the restart of the paper feed operation by the paper feed roller takes into account at least one predetermined factor among paper transport variation factors from the paper feed operation start to the An image forming apparatus that employs a predetermined time set to be longer than the longest time required for restarting the paper feeding operation at the paper leading edge stop position after the paper leading edge is detected by the paper detection sensor.

  According to the first image forming apparatus, when the sheets are sequentially supplied from the sheet supply unit for the continuous image formation, the first sheet may be used, but the second and subsequent sheets are detected at the latest. When it is detected by the sensor, it is stopped once and then transported again. At this time, the paper detected earlier by the paper detection sensor waits longer until the start of re-conveyance, while the paper detected later by the paper detection sensor starts re-conveyance earlier. For any paper, the time from the start of the paper feed operation by the paper feed roller to the restart of the paper feed operation by the paper feed roller is set to a fixed time. Therefore, even when the sheets are sequentially supplied from the sheet supply unit for continuous image formation, the second and subsequent sheets are stably transferred to the registration rollers within a predetermined time or substantially a fixed time from the start of the paper supply operation by the paper supply roller. Can be reached.

  Further, the predetermined time from the start of the paper feed operation by the paper feed roller to the restart of the paper feed operation by the paper feed roller can be set as short as possible within a range that does not interfere with the paper transport. It is also possible to increase the paper conveyance speed for conveying the paper to the system speed (the same as the paper conveyance speed when the image is formed on the paper in the image forming unit, the same as the paper conveyance speed by the registration roller). By adopting at least one, it is possible to cause the sheet to reach the resist roller that is still stopped without incurring a time loss (thus suppressing the decrease in image productivity).

  “From the start of the paper feed operation taking into account at least one predetermined factor among the paper transport variation factors as the time from the start of the paper feed operation by the paper feed roller to the restart of the paper feed operation by the paper feed roller A description will be further given of “adopting a fixed time set to the longest time or more of the time required for restarting the paper feeding operation at the paper leading edge stop position after the paper leading edge is detected by the paper detection sensor”.

  First, the “paper transport variation factor” refers to variations in the front end position of the paper in the paper supply unit immediately before the paper feed roller starts feeding, transport slip in the rollers involved in paper transport, outer diameter tolerance of the rollers involved in paper transport This is a factor that affects paper conveyance such as the life deterioration of the roller surface engaged in paper conveyance, and causes normal, fast, and slow paper conveyance.

  Which of the various paper transport variation factors should be taken into consideration may be determined in advance, for example, by determining what should be taken into consideration based on experiments and experiences. In any case, the one that greatly affects the paper transport will be considered.

  Further, the time required from the start of the paper feed operation to the restart of the paper feed operation at the paper front end stop position after the paper front end is detected by the paper detection sensor is calculated in advance for each of the paper transport variation factors, measured, etc. Find it and choose the longest time from the list.

Then, a fixed time equal to or longer than the longest time may be set as the time from the start of the paper feed operation by the paper feed roller to the restart of the paper feed operation by the paper feed roller.
This fixed time can be set as short as possible so that the registration roller can reach the registration roller before starting rotation for paper conveyance in order to take the timing of image formation on the paper. Since it is possible to increase the paper transport speed for transporting the paper to the registration rollers, the paper feed roller can be used without any time loss by adopting at least one of them. It is possible to reach the registration rollers that have been stopped stably in a certain time or substantially a certain time after the paper feeding operation is started.

  The same applies to the second and third image forming apparatuses described later.

  The control unit is configured such that a stop position of the leading edge of the paper when the leading edge of the paper supplied by the paper feeding roller is detected by the paper detection sensor is stopped by the paper detection sensor. A case where the sheet feeding operation by the sheet feeding roller is controlled so as to be between the registration rollers can be exemplified.

(2) Second image forming apparatus An image can be formed on the sheet by supplying the sheet from the sheet supply unit to the image forming path passing through the image forming unit by the paper feed roller and passing through the image forming path. Prior to feeding the paper supplied by the paper feed roller to the image forming path, the paper is abutted against the stopped registration roller, and then the paper conveyance operation of the registration roller is started at a timing when the image can be formed on the paper. An image forming apparatus for sending the paper to the image forming path,
A transport roller disposed between the paper feed roller and the registration roller;
A paper detection sensor disposed between the paper supply roller and the transport roller for detecting the leading edge of the paper supplied by the paper supply roller;
A control unit that controls a paper feeding operation of the paper feeding roller by controlling a paper feeding roller driving unit,
The controller is
In order to sequentially supply paper from the paper supply unit for continuous image formation, for each of the second and subsequent sheets,
After the paper feeding operation by the paper feeding roller is started, the paper feeding operation by the paper feeding roller is temporarily stopped after the leading edge of the paper fed by the paper feeding roller is detected by the paper detection sensor. Restart the paper feed operation using the paper feed roller,
The time from the start of the paper feed operation by the paper feed roller to the restart of the paper feed operation by the paper feed roller takes into account at least one predetermined factor among paper transport variation factors from the paper feed operation start to the An image forming apparatus that employs a predetermined time set to be longer than the longest time required for restarting the paper feeding operation at the paper leading edge stop position after the paper leading edge is detected by the paper detection sensor.

  Even in the second image forming apparatus, even when the paper is sequentially supplied from the paper supply unit for continuous image formation, the second and subsequent sheets are supplied for a certain time or substantially constant from the start of the paper feeding operation by the paper feeding roller. It is possible to reach the registration rollers that are still stopped in a stable manner and without incurring any time loss.

  In the second image forming apparatus, the control unit stops the leading edge of the sheet by stopping the feeding operation of the sheet feeding roller after the leading edge of the sheet supplied by the sheet feeding roller is detected by the sheet detection sensor. A case where the sheet feeding operation by the sheet feeding roller is controlled so that the position is between the sheet detection sensor and the transport roller can be exemplified.

The paper transport speeds of the paper feed roller, the transport roller, and the registration roller may be set such that the paper feed roller transport speed> the transport roller transport speed and the transport roller transport speed = the resist roller transport speed.
Here, the conveyance roller conveyance speed = registration roller conveyance speed includes substantially the same case where the conveyance roller conveyance speed and the registration roller conveyance speed may be considered to be practically the same.

  The control unit may be a control unit that controls the sheet conveyance operation of the conveyance roller by controlling the conveyance roller driving unit, and in that case, the control unit does not wait until the leading edge of the sheet reaches the conveyance roller. After the sheet conveying operation by the conveying roller is activated and the sheet feeding operation of the sheet feeding roller is restarted, the sheet feeding operation by the sheet feeding roller and the conveying roller are performed when the leading edge of the sheet advances a predetermined distance from the conveying roller. The sheet conveying operation may be stopped.

  In this case, it is possible to freely set the time from when the paper supplied by the paper feed roller enters the transport roller from the paper detection sensor to when the transport roller stops, so that the paper feed roller transport speed> the transport roller transport speed. Even in some cases, the slack due to the difference in the sheet conveyance speed between the conveyance rollers of the sheet fed to the conveyance roller can be suppressed, and the occurrence of excessive slack can be suppressed.

  Also, in this case, after the paper feeding operation of the paper feeding roller is restarted, the control unit performs the paper feeding operation by the paper feeding roller and the paper by the transport roller when the leading edge of the paper advances a predetermined distance from the transport roller. When stopping the transport operation, the time from the restart of the paper feed operation by the paper feed roller to the stop of the paper feed operation by the paper feed roller and the paper transport operation by the transport roller is preliminarily determined among the paper transport variation factors. Even when the leading edge of the paper arrives at the latest time with the most delay in consideration of at least one determined, a time set as the shortest time that the transport roller can transport the paper may be employed.

The second image forming apparatus may be the following. A common drive motor is provided for the paper feed roller, the transport roller, and the registration roller,
The drive unit of the paper feed roller includes the common drive motor and a first electromagnetic clutch that switches between start and stop of paper feed operation of the paper feed roller by the drive motor,
The drive section of the transport roller includes the common drive motor and a second electromagnetic clutch that switches between starting and stopping the paper transport operation of the transport roller by the drive motor,
The registration roller drive unit includes the common drive motor and a third electromagnetic clutch that switches between starting and stopping the sheet transfer operation of the registration roller by the drive motor.
The control unit can control switching of feeding operation start and stop of the sheet feeding roller by turning on and off the first electromagnetic clutch, and starting sheet feeding operation by the feeding roller by turning on and off the second electromagnetic clutch. An image forming apparatus capable of switching control of stop and switching control of starting and stopping of a sheet conveying operation by the registration roller by turning on and off the third electromagnetic clutch.

(3) A third image forming apparatus.
Paper is supplied from the paper supply unit to the image forming path that passes through the image forming unit by the paper supply roller and passes through the image forming path, so that an image can be formed on the paper. Prior to feeding the sheet to the image forming path, the sheet is brought into contact with the stopped registration roller, and then the sheet conveying operation of the registration roller is started at a timing at which image formation can be performed on the sheet. An image forming apparatus to be sent to
A first transport roller disposed between the paper feed roller and the registration roller;
A second transport roller disposed between the first transport roller and the paper feed roller;
A first paper detection sensor disposed between the first transport roller and the second transport roller for detecting the leading edge of the supplied paper;
A second paper detection sensor disposed between the first paper detection sensor and the second transport roller for detecting the leading edge of the fed paper;
A control unit that controls a paper feeding operation of the paper feeding roller by controlling a paper feeding roller driving unit and a paper feeding operation of the second conveying roller by controlling a second conveying roller driving unit. And
The controller is
When supplying paper sequentially from the paper supply unit for continuous image formation, for the second and subsequent sheets,
After the start of the paper feeding operation by the paper feeding roller, the second paper detection sensor detects the leading edge of the paper fed by the paper feeding roller and sent by the paper transport operation of the second transport roller; The paper feeding operation by the paper feeding roller is stopped, the paper transporting operation of the second transport roller is stopped, and then the paper transporting operation of the second transport roller is restarted. Detection of the leading edge of the paper by the second paper detection sensor from the start of the paper feeding operation, taking into account at least one predetermined factor among the paper transport variation factors as the time from the start to the restart of the paper transport operation of the second transport roller An image forming apparatus that employs a fixed time set to be longer than the longest time required for restarting the paper transport operation of the second transport roller at a subsequent paper front end stop position.

  Even in the third image forming apparatus, even when the paper is sequentially supplied from the paper supply unit for continuous image formation, the second and subsequent sheets are supplied for a certain period of time or substantially constant from the start of the sheet feeding operation by the sheet feeding roller. It is possible to reach the registration rollers that are still stopped in a stable manner and without incurring any time loss.

  In the third image forming apparatus, the control unit is configured to stop the sheet conveying operation of the second conveying roller after the leading edge of the sheet supplied by the sheet feeding roller is detected by the second sheet detecting sensor. The sheet conveying operation by the second conveying roller may be controlled so that the stop position of the sheet leading edge is between the second sheet detecting sensor and the first sheet detecting sensor.

  The second transport roller drive unit may be a drive unit capable of switching a paper transport speed of the second transport roller between a high speed transport speed and a low speed transport speed lower than the paper transport speed, The sheet conveying speed of each of the second conveying roller, the first conveying roller, and the registration roller is: a sheet feeding roller conveying speed> a high conveying speed of the second conveying roller> a speed conveying speed of the second conveying roller, and The second conveyance roller speed conveyance speed = first conveyance roller conveyance speed = registration roller conveyance speed may be set.

  In this case, the second conveyance roller speed conveyance speed = first conveyance roller conveyance speed = registration roller conveyance speed includes the second conveyance roller velocity conveyance speed, the first conveyance roller conveyance speed, and the second conveyance roller passage. The high-speed conveyance speed and the registration roller conveyance speed, and the first conveyance roller conveyance speed and the registration roller conveyance speed are not exactly the same, but include substantially the same cases where they can be regarded as practically the same.

  The second transport roller drive unit is a drive unit capable of switching the paper transport speed of the second transport roller between two stages of a high speed transport speed and a low speed transport speed, and a paper feed roller transport speed> When the high-speed conveyance speed of the second conveyance roller> the high-speed conveyance speed of the second conveyance roller, and the high-speed conveyance speed of the second conveyance roller = the first conveyance roller conveyance speed = the registration roller conveyance speed, The control unit sets the sheet conveyance speed of the second conveyance roller to a high conveyance speed before stopping the sheet conveyance operation by the second conveyance roller by the sheet detection of the second sheet detection sensor upstream of the first sheet detection sensor. It may be set and set to a normal conveyance speed after restarting the sheet conveyance operation by the second conveyance roller.

  The second transport roller drive unit is a drive unit capable of switching the paper transport speed of the second transport roller between two stages of a high speed transport speed and a low speed transport speed, and a paper feed roller transport speed> When the high-speed conveyance speed of the second conveyance roller> the high-speed conveyance speed of the second conveyance roller, and the high-speed conveyance speed of the second conveyance roller = the first conveyance roller conveyance speed = the registration roller conveyance speed, The control unit sets the sheet conveyance speed of the second conveyance roller to a high conveyance speed before stopping the sheet conveyance operation of the second conveyance roller by the sheet detection of the second sheet detection sensor upstream of the first sheet detection sensor. After the sheet conveyance operation is restarted by the second conveyance roller, when the leading edge of the sheet is detected by the first sheet detection sensor, the sheet is passed from the high conveyance speed before entering the first conveyance roller. Speed It may be the one to switch to transmission speed.

  In the third image forming apparatus, the second conveying roller driving unit is a driving unit capable of switching the sheet conveying speed of the second conveying roller to a plurality of stages, and the control unit conveys the sheet to be conveyed. It may be possible to change and set the sheet conveying speed of the second conveying roller according to the direction length.

  In the third image forming apparatus, the second conveyance roller and the second sheet detection sensor on the downstream side of the second conveyance roller are provided as a set in a plurality of stages in the sheet conveyance direction. The sheet may be supplied to the image forming path using one or more of the plurality of sets under the control of the unit.

The third image forming apparatus may be the following.
The second transport roller drive unit includes a drive motor having a variable rotation speed,
A common drive motor is provided for the first conveying roller and the registration roller,
The drive section of the first transport roller includes the common drive motor and an electromagnetic clutch for the first transport roller that switches between starting and stopping the sheet transport operation of the first transport roller by the drive motor,
The registration roller drive unit includes the common drive motor, and a registration roller electromagnetic clutch that switches between starting and stopping the sheet conveyance operation of the registration roller by the drive motor,
The control unit can control the start and stop of the sheet conveying operation of the second conveying roller by controlling the second conveying roller driving unit, and can change the sheet conveying speed by the second conveying roller. ,
The first conveying roller electromagnetic clutch can be controlled to be turned on and off by turning on and off the first conveying roller electromagnetic clutch, and the sheet conveying operation can be activated by the registration roller by turning on and off the registration roller electromagnetic clutch. An image forming apparatus capable of switching and controlling the stop.

  As described above, according to the present invention, it is possible to form an image on a sheet by supplying the sheet from the sheet supply unit to the image forming path passing through the image forming unit by the paper feed roller and passing the image forming path. Prior to feeding the paper supplied by the paper feed roller to the image forming path, the paper is brought into contact with the resist roller that has stopped, and then the paper transport operation of the resist roller is performed at a timing at which image formation can be performed on the paper. An image forming apparatus that is activated and sends the paper to the image forming path, and even when the paper is sequentially supplied from the paper supply unit for continuous image formation, each of the second and subsequent sheets is fed by a paper feed roller. It is possible to reach the registration roller that is still stopped, stably and in a certain time since the start of the paper feeding operation, without incurring any time loss. It is possible to provide an image forming apparatus capable of satisfactorily image forming while suppressing a decrease in each sheet.

1 is a diagram schematically illustrating a configuration of an example of an image forming apparatus according to the present invention. FIG. 2 is a block diagram schematically showing a control circuit of the image forming apparatus in FIG. 1. 6 is a timing chart illustrating operation timings of related units in an example of paper supply control to an image forming pass. 12 is a timing chart showing operation timings of related units in another example of paper supply control to an image forming pass. 14 is a timing chart showing operation timings of related units in still another example of paper supply control to an image forming pass. 14 is a timing chart showing operation timings of related units in still another example of paper supply control to an image forming pass.

FIG. 1 shows a tandem type color punter which is an example of an image forming apparatus according to the present invention.
The printer 10 shown in FIG. 1 also includes a control unit Cont (see also FIG. 2) that controls the operation of the image forming apparatus 10. The operation of each part of the image forming apparatus, which will be described later, is performed under the instruction of the control part Cont.

  The printer 10 includes an image forming unit 11, a paper supply unit 12 below the image forming unit, and an image forming path 13. The image forming unit 11 includes an intermediate transfer belt 111 that is rotationally driven by a belt driving unit (not shown) and is wound around a driving roller d1 and a counter roller d2, and can be rotated in the counterclockwise direction α in the figure. Along the belt running direction, a yellow image forming unit Y, a magenta image forming unit M, a cyan image forming unit C, and a black image forming unit K are arranged in this order.

  The image forming unit in charge of each color is formed on the photoconductor PC by electrophotography based on image information from an image reading device (not shown) or image information transmitted from an external computer or an external facsimile machine (not shown). An electrostatic latent image corresponding to the assigned color image is formed, and the latent image is developed with the assigned color toner to form a toner image, which is applied with a primary transfer bias from a power supply (not shown). Primary transfer can be performed on the belt 111 at tr.

  When forming an image using the image forming unit, a monochrome toner image can be formed using any one of the four image forming units, or a color image can be formed using two or more image forming units. It can also be formed. When two or more image forming units are used, the color toner images formed by these image forming units are primarily transferred to the belt 111 at the timing of being superimposed on the belt 111.

  The image forming unit 11 further includes a secondary transfer roller TR facing the belt on the downstream side of the black image forming unit K in the rotation direction of the intermediate transfer belt 111 and a fixing device 112 disposed above the secondary transfer roller TR.

  As described above, the toner image primarily transferred onto the belt 111 is transferred onto the sheet conveyed along the image forming path 13 by the secondary transfer roller TR to which a secondary transfer bias is applied from a power supply (not shown). Secondary transferred.

  A sheet to be image-formed is supplied from a sheet supply unit 12 described below. The sheet supplied from the sheet supply unit 12 is abutted against a registration roller 131 positioned at the entrance of the image forming path 13 and temporarily stopped. The image forming unit 13 is sent to the image forming path 13 by the registration roller 131 at a timing at which an image can be formed at a predetermined position on the sheet.

  The toner image secondarily transferred to the paper in this way is fixed under heat and pressure by the fixing device 112 and is discharged to the discharge tray T together with the paper.

  In this example, the paper supply unit 12 below the image forming unit includes a supply unit 121 that supplies A4 size paper, a supply unit 122 that supplies B5 size paper, a supply unit 123 that supplies A3 size paper, and a B4 size paper. A supply unit 124 for supplying paper and a supply unit (manual tray) 125 for an operator to manually supply paper are included.

  The sheets in the sheet supply units 121, 122, 123, 124, and 125 can be sent out to the registration rollers 131 at the entrance of the image forming path 13 by the feed rollers r1, r2, r3, r4, and r5, respectively. Each of the rollers r1, r2, r3, r4, r5 can be rotationally driven by a paper feed roller driving unit r1D, r2D, r3D, r4D, r5D (see FIG. 2). The registration roller 131 can be rotationally driven by a registration roller driving unit 131D. These paper feed roller driving unit and registration roller driving unit can be controlled from the control unit Cont.

  In addition to the above, the paper supply unit 12 also includes a transport roller R1 (hereinafter referred to as “vertical transport roller R1”) for feeding the paper fed by the paper feed roller r2 or the paper feed roller r5 to the registration roller 131, It includes a transport roller R2 that feeds the paper fed by the paper roller r3 toward the vertical transport roller R1, and a transport roller R3 that feeds the paper sent by the paper feed roller r4 to the transport roller R2.

The vertical conveying roller R1 can be rotated by a vertical conveying roller driving unit R1D (see FIG. 2), and the conveying rollers R2 and R3 can be rotated at driving units R2D and R3D including stepping motors provided for the respective rollers. (See FIG. 2).
These roller driving units are also controlled by the control unit Cont.

The drive units r1D, r2D, and r5D of the paper feed rollers r1, r2, and r5, the drive unit 131D of the registration roller 131, and the drive unit R1D of the vertical conveyance roller R1 include a common drive motor M.
The drive units r1D, r2D, and r5D of the paper feed rollers r1, r2, and r5 have a common drive motor M and electromagnetic clutches CL1, CL2, and CL5 that switch a paper feed operation start and stop by the paper feed rollers r1, r2, and r5. Each is included (see FIG. 2).
The drive units r3D and r4D of the paper feed rollers r3 and r4 are drive units each including a stepping motor.

The drive unit 131D of the registration roller 131 includes a motor M that is common to the paper feed roller r1 and the like, and an electromagnetic clutch CL131 that switches between starting and stopping the sheet conveyance operation by the registration roller 131 (see FIG. 2).
The vertical conveyance roller drive unit R1D includes a common motor M and an electromagnetic clutch CLR1 that switches between starting and stopping the sheet conveyance operation by the vertical conveyance roller R1 (see FIG. 2).

Each of these electromagnetic clutches is on / off controlled by the control unit Cont.
The electromagnetic clutches for the paper feed rollers r1, r2, and r5 can freely rotate in a non-energized off state.
A registration sensor SE is disposed in the vicinity of the upstream side of the registration roller 131 in the sheet conveyance direction.
A paper detection sensor S1 (hereinafter referred to as “paper feed sensor S1”) is disposed near the downstream side of the paper supply roller r1 of the paper supply unit 121.
A sheet detection sensor S2 (hereinafter referred to as “vertical conveyance sensor S2”) is disposed in the vicinity of the upstream side of the vertical conveyance roller R1, and the sheet detection sensors S3 and S3 are disposed in the vicinity of the downstream sides of the conveyance rollers 2 and 3, respectively. S4 (hereinafter referred to as “conveyance sensors S3, S4”) is arranged.
These sensors are connected to the control unit Cont.

  An operation panel PA for an operator is also connected to the control unit Cont. The operation panel PA is equipped with a key for selecting the size of paper used for image formation, a numeric keypad for setting the number of images to be formed, a print key for instructing start of printing, a display for displaying various information, and the like.

Next, the paper supply from the paper supply unit 12 will be described.
In the timing chart of FIG. 3, the sheet size A4 is selected on the operation panel PA, a plurality of A4 size sheets are sequentially supplied from the sheet supply unit 121, and the second and subsequent sheets are supplied continuously. The operation timing of each related part is shown. The same paper supply control may be performed from the first paper supply.

  First, the paper transport speed of the paper feed roller r1 is set to be higher than the paper transport speed of the registration rollers, and is not limited to this, but here, the paper feed roller speed is about 160 mm / sec. The speed is set to 320 mm / second.

In the following description, the indications (a), (b)... Indicate the positions in FIG.
After the second sheet of continuously fed sheets, the sheet feeding operation by the sheet feeding roller r1 is activated when the sheet feeding electromagnetic clutch CL1 is turned on (a). The leading edge of the sheet from the supply unit 121 conveyed thereby is detected by a sheet feeding sensor S1 disposed downstream of the sheet feeding roller r1 (b), and the sheet is fed at a fixed position (c) from the sheet leading edge detection. The electromagnetic clutch CL1 is turned off, and the paper feeding operation by the paper feeding roller r1 is stopped.

  Thereafter, after the elapse of a predetermined time (time between ad) from the start of the paper feed operation by the paper feed roller r1 (a) to the restart of the paper feed operation (d), the feed electromagnetic clutch CL1 is started. Then, the paper feeding operation activation by the paper feeding roller r1 is resumed. After the registration sensor SE detects the leading edge of the paper (e), the leading edge of the paper is abutted against the registration roller 131 that has stopped driving (f), and the skew correction deflection amount set in advance based on the detection of the leading edge of the paper by the registration sensor SE is used. After forming (f-g), the sheet feeding electromagnetic clutch CL1 is turned off (g), and the sheet feeding operation is stopped.

  Thereafter, substantially simultaneously, the sheet feeding electromagnetic clutch CL1 and the registration electromagnetic clutch CL131 are activated (h), the sheet conveying operation by the sheet feeding roller r1 and the registration roller 131 is activated, and then the sheet is about 10 mm (hi). ), The paper conveyance operation by the paper supply roller r1 is stopped (i), and the paper is conveyed to the image forming path 13 by the registration roller 131.

Next, another example of the paper supply control will be described with reference to the timing chart of FIG.
FIG. 4 shows a case where a paper size B5 is selected on the operation panel PA and a plurality of B5 size papers are sequentially supplied from the paper supply unit 122 to form images continuously, or a plurality of papers of a user desired size are placed on the manual feed tray 125. In the case of continuously forming images by mounting sheets, the operation timing of each related part in the paper supply control for the second and subsequent sheets is shown. The same paper supply control may be performed from the first paper supply.

  When the sheet conveyance speed of the sheet feeding roller r2 (or r5) is V1, the sheet conveyance speed by the vertical conveyance roller R1 is V2, and the sheet conveyance speed by the registration roller 131 is V3, V1> V2 and V2 = V3 are set. ing. V2 = V3 includes a case where V2 and V3 are substantially the same speed that can be regarded as the same speed in practice.

  Although not limited thereto, the sheet feeding speed V1 by the sheet feeding roller r1 (r5) is set to 320 mm / second, the sheet conveying speed V2 by the vertical conveying roller R1 and the sheet conveying speed V3 by the registration roller 131 are set to 160 mm / second, respectively. Has been.

In the following description, (a), (b)... Indicate positions in FIG.
After the second sheet of continuously fed sheets, the sheet feeding operation by the sheet feeding roller r2 (or r5) is started by turning on the sheet feeding electromagnetic clutch CL2 (or CL5) (a), and the sheet feeding roller r2 (or The leading edge of the sheet conveyed in r5) is detected by the vertical conveyance sensor S2 disposed upstream of the vertical conveyance roller R1 (b), and a certain amount is detected between the vertical conveyance roller R1 and the vertical conveyance sensor S2 from the detection by the sensor S2. At this position, the sheet feeding electromagnetic clutch CL2 (or CL5) is turned off to stop the sheet feeding operation by the sheet feeding roller (c).

  After that, when a predetermined time (ad) from the start of feeding (a) to the restarting elapses, the feeding electromagnetic clutch CL2 (or CL5) is restarted and the vertical transfer electromagnetic clutch CLR1 is started. Then, the paper conveyance operation by the paper feed roller r2 (or r5) and the vertical conveyance roller R1 is started, and the paper conveyance is resumed.

  Thereafter, when the leading edge of the sheet has passed 6.5 mm (ef) from the vertical conveying roller R1, the sheet feeding electromagnetic clutch CL2 (or CL5) is turned off to stop the sheet feeding operation by the sheet feeding roller (f). .

  Subsequent sheet conveyance is performed by the vertical conveyance roller R1, and after the registration sensor SE detects the leading edge of the sheet (g), the leading edge of the sheet abuts against the stopped registration roller 131 (h), and the leading edge of the sheet is detected by the registration sensor SE. The skew correction deflection amount (h−i) set in advance is formed with reference to, and then the longitudinal conveyance electromagnetic clutch CLR1 is turned off (i), and the sheet conveyance is stopped. Thereafter, the longitudinal conveyance electromagnetic clutch CLR1 and the registration electromagnetic clutch CL131 are activated substantially simultaneously to convey the paper.

Next, still another example of the paper supply control will be described with reference to the timing chart of FIG.
FIG. 5 shows the related parts in the paper supply control for the second and subsequent sheets when the paper size A3 is selected on the operation panel PA and a plurality of A3 size papers are sequentially supplied from the paper supply unit 123 to continuously form images. The operation timing is shown. The same paper supply control may be performed from the first paper supply.

  The paper transport speed of the paper feed roller r3 is V1, the high speed paper transport speed by the transport roller R2 is V2, the high speed paper transport speed by the transport roller R2 is V3, the paper transport speed by the vertical transport roller R1 is V4, and the paper by the registration roller 131 Assuming that the conveyance speed is V5, the relations V1> V2> V3 and V3 = V4 = V5 are set. V3 = V4 = V5 includes the case where V3, V4, and V5 have substantially the same speed that may be practically the same speed.

  Although not limited thereto, here, the sheet feeding speed V1 by the sheet feeding roller r3 = 320 mm / sec, the high speed conveying speed V2 by the conveying roller R2 = 320 mm / sec, the speed conveying speed V3 by the conveying roller R2 = the vertical conveying roller R1. Is set such that the conveyance speed V4 = the conveyance speed V5 by the registration roller 131 = 160 mm / second.

In the following description, the indications (a), (b)... Indicate the positions in FIG.
Starting with the second and subsequent sheets of continuously fed sheets, the sheet feeding operation by the sheet feeding roller r3 is started by starting the motor of the driving unit r3D (a). At this time, since the transport roller R2 has already been rotated by the prior activation of the stepping motor of the drive unit R2D, the paper is transferred to the transport roller R2 (b).

When the conveyance sensor S3 detects the leading edge of the sheet after the leading edge of the sheet has passed the conveying roller R2, the driving unit r3D of the sheet feeding roller r3 is turned off to stop the sheet feeding operation by the roller r3 (c).
After that, the sheet is continuously conveyed by the conveying roller R2, and when the sheet advances a certain distance (cd) after the leading edge of the sheet is detected by the conveying sensor S3, the conveying roller R2 is stopped (d) and the sheet is conveyed. Stop.

  Thereafter, when a predetermined time (ae) from the start of paper feeding to the restart of the paper transport operation elapses, the paper transport operation by the transport roller R2 is restarted (e), and the paper transport is resumed. In this example, at this time, the vertical conveyance electromagnetic clutch CLR1 for the vertical conveyance roller R1 is activated and the vertical conveyance roller R1 starts to be driven.

  Thereafter, when the vertical conveyance sensor S2 detects the leading edge of the paper, the conveyance roller R2 is decelerated, and the paper conveyance speed of the conveyance roller R2 is changed to the high-speed conveyance speed before the vertical conveyance roller R1 (g) enters the paper (f). If the conveying roller R1 is not decelerated, excessive sheet loosening due to the difference in speed between the high-speed conveying speed of the conveying roller R2 and the conveying speed of the vertical conveying roller R1 after the vertical conveyance roller R1 enters the sheet is prevented.

  Thereafter, after the registration sensor SE detects the leading edge of the paper (i), it abuts against the registration roller 131 that stops the paper (j), and the skew correction deflection is preset based on the detection of the leading edge of the paper by the registration sensor SE. The amount (j−k) is formed, and then the sheet conveying operation by the conveying roller R2, the vertical conveying roller R1, and the registration roller 131 is started substantially simultaneously.

Next, still another example of the paper supply control will be described with reference to the timing chart of FIG.
FIG. 6 shows the related parts in the paper supply control for the second and subsequent sheets when the paper size B4 is selected on the operation panel PA and a plurality of B4 size papers are sequentially supplied from the paper supply unit 124 to continuously form images. The operation timing is shown. The same paper supply control may be performed from the first paper supply.

  The paper transport speed of the paper feed roller r4 is V1, the high speed paper transport speed of the transport rollers R2 and R3 is V2, the high speed paper transport speed of the transport rollers R2 and R3 is V3, the paper transport speed of the vertical transport roller R1 is V4, and the resist Assuming that the sheet conveyance speed by the roller 131 is V5, the relations V1> V2> V3 and V3 = V4 = V5 are set. V3 = V4 = V5 includes a case where V3, V4, and V5 are substantially the same speed that can be regarded as practically the same speed.

  Although not limited thereto, here, the feeding speed V1 of the feeding roller r4 = 320 mm / second, the high speed paper feeding speed of the feeding rollers R2 and R3 is V2 = 320 mm / sec, and the high speed paper feeding of the feeding rollers R2 and R3. The speed is set such that V3 = paper transport speed by the vertical transport roller R1 is V4 = paper transport speed by the registration roller 131 is V5 = 160 mm / sec.

In the following description, (a), (b)... Indicate positions in FIG.
Starting with the second and subsequent sheets of continuously fed sheets, the sheet feeding operation by the sheet feeding roller r4 is started by starting the motor of the driving unit r4D (a). In this example, at this time, since the transport rollers R3 and R2 have already been rotated by the prior activation of the stepping motors of the drive units R3D and R2D, the paper is transferred to the transport roller R3 (b).

When the conveyance sensor S4 detects the leading edge of the sheet after the leading edge of the sheet has passed the conveying roller R3 (c), the driving unit r4D of the sheet feeding roller r4 is turned off to stop the sheet feeding operation by the roller r4.
After that, when the paper passes through the transport roller R2 by the paper transport by the transport rollers R3 and R2, and the transport sensor S3 detects the leading edge of the paper (e), the transport proceeds when the paper advances a certain distance (ef). The rollers R3 and R2 are stopped (f), and the paper conveyance is stopped.

  Thereafter, when a predetermined time (a-g) from the start of paper feeding to the restart of the paper transport operation elapses, the paper transport operations of the transport rollers R2 and R3 are started substantially simultaneously (g), and the paper transport is resumed. . In this example, at this time, the vertical conveyance electromagnetic clutch CLR1 for the vertical conveyance roller R1 is activated and the vertical conveyance roller R1 starts to be driven.

  Thereafter, when the front edge of the paper is detected by the vertical conveyance sensor S2 (h), the conveyance rollers R2 and R3 are decelerated, and the paper conveyance speed of the conveyance rollers R2 and R3 is increased before the vertical conveyance roller R1 (i) enters the paper. If the conveying speed is set to (h) and the conveying rollers R2 and R3 are not decelerated, it is caused by a difference in speed generated between the high conveying speed of the conveying rollers R2 and R3 and the conveying speed of the vertical conveying roller R1 after the vertical conveying roller R1 enters the sheet. Prevent excessive paper slack.

  Then, after the registration sensor SE detects the leading edge of the sheet (k), the sheet is abutted against the stopped registration roller 131 (l), and the skew correction deflection is set in advance based on the detection of the leading edge of the sheet by the registration sensor SE. Then, the sheet conveying operation by the conveying rollers R2, R3, the vertical conveying roller R1, and the registration roller 131 is started substantially simultaneously.

  In the paper supply control example described above, the paper feed operation is restarted from the start of the paper feed operation by the paper feed roller ((ad) in FIG. 3, (ad) in FIG. 4, (ae) in FIG. 5). In FIG. 6, (a-g)] is a fixed time (however, based on experiments, etc.) that is longer than the longest time required from the start of paper feed to the restart of paper transport, taking into account the factors of paper transport variation. Is set to a certain period of time that is not too long for the student).

  Although the present invention is not limited to the paper transport variation factor, here, from experiments, the variation in the front end position of the paper in the paper supply unit immediately before the paper feeding by the paper feeding roller is 20 mm, and the slip rate of the paper feeding roller is Assuming that the diameter of the sheet feeding roller varies from an outer diameter of 20 mm to an outer diameter of 19 mm due to 5% life deterioration, and taking these into account as factors for variation in sheet conveyance, the longest time is calculated in advance, and based on the start of sheet feeding A certain period of time is required until the paper transport is restarted.

  In this way, even if there is a paper feed variation factor, the time from the start of paper feed to the restart is set in consideration of the longest time of the variance, so that the leading edge of the paper moves from the feed start to the registration roller. The time until arrival can be made constant, and the sheet interval can be freely set according to the set value of the sheet feeding speed by making the sheet feeding speed higher than the system speed.

  As a result, even when sheets are sequentially supplied from the sheet supply unit for continuous image formation, each of the second and subsequent sheets can be stably and stably received within a certain time from the start of the sheet feeding operation by the sheet feeding roller. It can reach the registration roller without incurring time loss, and image formation can be performed as well.

  The image forming apparatus described with reference to FIG. 1 is a tandem type color printer, but the present invention is also applicable to other types of color image forming apparatuses such as a so-called four-sill type, and also to a monochrome image forming apparatus. it can. The present invention can be applied not only to a printer, but also to a copying machine, a facsimile machine, a multifunction machine, and the like.

  Therefore, the present invention can form an image on the sheet by supplying the sheet from the sheet supply unit to the image forming path passing through the image forming unit by the sheet feeding roller, and passing the image forming path. Prior to feeding the sheet supplied by the printer to the image forming path, the sheet is abutted against the stopped registration roller, and then the sheet conveying operation of the registration roller is started at a timing at which image formation can be performed on the sheet. In the image forming apparatus, the second and subsequent sheets are fed from the start of the sheet feeding operation by the sheet feeding roller even when the sheets are sequentially fed from the sheet feeding unit for continuous image formation. The present invention can be used to provide an image forming apparatus that can reach a registration roller stably in a fixed time and without incurring time loss.

10 Image forming device (printer)
DESCRIPTION OF SYMBOLS 11 Image forming part 12 Paper supply part 131 Registration roller 131D Registration roller drive part CL131 Registration roller electromagnetic clutch 121 A4 size paper supply part r1 Paper feed roller r1D Paper feed roller r1 drive part CL1 Paper feed roller r1 electromagnetic clutch M Drive motor 122 common to paper rollers r1, r2, etc. B5 size paper supply unit r2 Paper supply roller r2D Drive unit CL2 of paper supply roller r2 Electromagnetic clutch 123 for paper supply roller r2 A3 size paper supply unit r3 Paper supply roller r3D Paper supply Driving unit 124 of roller r3 B4 size paper supply unit r4 Paper feeding roller r4D Driving unit 125 of paper feeding roller r4 Manual paper feeding unit r5 Paper feeding roller r5D Driving unit CL5 of paper feeding roller r5 Electromagnetic clutch R1 for paper feeding roller r5 Roller (vertical conveyance roller)
R1D Longitudinal Conveying Roller Drive CLR1 Vertical Conveying Roller Electromagnetic Clutch R2, R3 Conveying Roller R2D, R3D Conveying Roller Driving Unit SE Registration Sensor S1 Paper Detection Sensor
S2 Paper detection sensor (vertical conveyance sensor)
S3, S4 Paper detection sensor (conveyance sensor)

Claims (17)

Paper is supplied from the paper supply unit to the image forming path that passes through the image forming unit by the paper supply roller and passes through the image forming path, so that an image can be formed on the paper. Prior to feeding the sheet to the image forming path, the sheet is brought into contact with the stopped registration roller, and then the sheet conveying operation of the registration roller is started at a timing at which image formation can be performed on the sheet. An image forming apparatus to be sent to
A paper detection sensor disposed between the paper supply roller and the registration roller for detecting the leading edge of the paper supplied by the paper supply roller;
A control unit that controls a paper feeding operation of the paper feeding roller by controlling a paper feeding roller driving unit,
The controller is
In order to sequentially supply paper from the paper supply unit for continuous image formation, for each of the second and subsequent sheets,
After the paper feeding operation by the paper feeding roller is started, the paper feeding operation by the paper feeding roller is temporarily stopped after the leading edge of the paper fed by the paper feeding roller is detected by the paper detection sensor. Restart the paper feed operation using the paper feed roller,
The time from the start of the paper feed operation by the paper feed roller to the restart of the paper feed operation by the paper feed roller takes into account at least one predetermined factor among paper transport variation factors from the paper feed operation start to the An image forming apparatus characterized in that a fixed time set longer than the longest time among times required for restarting the paper feeding operation at a paper front end stop position after detection of a paper front end by a paper detection sensor is adopted.   The control unit is configured such that a stop position of the leading edge of the paper when the leading edge of the paper supplied by the paper feeding roller is detected by the paper detection sensor is stopped by the paper detection sensor. The image forming apparatus according to claim 1, wherein a sheet feeding operation by the sheet feeding roller is controlled to be between the registration rollers.   3. The image forming apparatus according to claim 1, wherein a sheet conveyance speed of the sheet feeding roller is set to be higher than a sheet conveyance speed of the registration roller. Paper is supplied from the paper supply unit to the image forming path that passes through the image forming unit by the paper supply roller and passes through the image forming path, so that an image can be formed on the paper. Prior to feeding the sheet to the image forming path, the sheet is brought into contact with the stopped registration roller, and then the sheet conveying operation of the registration roller is started at a timing at which image formation can be performed on the sheet. An image forming apparatus to be sent to
A transport roller disposed between the paper feed roller and the registration roller;
A paper detection sensor disposed between the paper supply roller and the transport roller for detecting the leading edge of the paper supplied by the paper supply roller;
A control unit that controls a paper feeding operation of the paper feeding roller by controlling a paper feeding roller driving unit,
The controller is
In order to sequentially supply paper from the paper supply unit for continuous image formation, for each of the second and subsequent sheets,
After the paper feeding operation by the paper feeding roller is started, the paper feeding operation by the paper feeding roller is temporarily stopped after the leading edge of the paper fed by the paper feeding roller is detected by the paper detection sensor. Restart the paper feed operation using the paper feed roller,
The time from the start of the paper feed operation by the paper feed roller to the restart of the paper feed operation by the paper feed roller takes into account at least one predetermined factor among paper transport variation factors from the paper feed operation start to the An image forming apparatus characterized in that a fixed time set longer than the longest time among times required for restarting the paper feeding operation at a paper front end stop position after detection of a paper front end by a paper detection sensor is adopted.   The control unit is configured such that a stop position of the leading edge of the paper by stopping the paper feeding operation after the leading edge of the paper supplied by the paper feeding roller is detected by the paper detection sensor and the paper detection sensor. The image forming apparatus according to claim 4, wherein a sheet feeding operation by the sheet feeding roller is controlled so as to be between the conveying rollers.   The paper transport speed of each of the paper feed roller, the transport roller, and the registration roller is set such that the paper feed roller transport speed> the transport roller transport speed and the transport roller transport speed = the resist roller transport speed. The image forming apparatus according to 4 or 5.   The control unit is a control unit that controls the sheet conveyance operation of the conveyance roller by controlling the conveyance roller driving unit, and the control unit conveys the sheet by the conveyance roller until the leading edge of the sheet reaches the conveyance roller. The operation is started, and after the sheet feeding operation of the sheet feeding roller is restarted, the sheet feeding operation by the sheet feeding roller is stopped when the leading end of the sheet advances a predetermined distance from the transport roller. Image forming apparatus.   The control unit, after restarting the paper feeding operation of the paper feeding roller, stops the paper feeding operation by the paper feeding roller when the leading edge of the paper advances a predetermined distance from the transport roller. The time until the paper feed operation by the paper feed roller is stopped after the paper operation is restarted, the front end of the paper arrives most late to the transport roller in consideration of at least one predetermined factor of paper transport variation. 8. The image forming apparatus according to claim 7, wherein the time set as the shortest time during which the transport roller can transport the paper is employed. Paper is supplied from the paper supply unit to the image forming path that passes through the image forming unit by the paper supply roller and passes through the image forming path, so that an image can be formed on the paper. Prior to feeding the sheet to the image forming path, the sheet is brought into contact with the stopped registration roller, and then the sheet conveying operation of the registration roller is started at a timing at which image formation can be performed on the sheet. An image forming apparatus to be sent to
A first transport roller disposed between the paper feed roller and the registration roller;
A second transport roller disposed between the first transport roller and the paper feed roller;
A first paper detection sensor disposed between the first transport roller and the second transport roller for detecting the leading edge of the supplied paper;
A second paper detection sensor disposed between the first paper detection sensor and the second transport roller for detecting the leading edge of the fed paper;
A control unit that controls a paper feeding operation of the paper feeding roller by controlling a paper feeding roller driving unit and a paper feeding operation of the second conveying roller by controlling a second conveying roller driving unit. And
The controller is
When supplying paper sequentially from the paper supply unit for continuous image formation, for the second and subsequent sheets,
After the start of the paper feeding operation by the paper feeding roller, the second paper detection sensor detects the leading edge of the paper fed by the paper feeding roller and sent by the paper transport operation of the second transport roller; The paper feeding operation by the paper feeding roller is stopped, the paper transporting operation of the second transport roller is stopped, and then the paper transporting operation of the second transport roller is restarted. Detection of the leading edge of the paper by the second paper detection sensor from the start of the paper feeding operation, taking into account at least one predetermined factor among the paper transport variation factors as the time from the start to the restart of the paper transport operation of the second transport roller A fixed time set longer than the longest time among times required for restarting the paper transport operation of the second transport roller at a subsequent paper front end stop position is adopted. Forming apparatus.   The control unit is configured such that the stop position of the leading edge of the sheet due to the stop of the sheet conveying operation of the second conveying roller after the leading edge of the sheet supplied by the sheet feeding roller is detected by the second sheet detecting sensor, The image forming apparatus according to claim 9, wherein a sheet conveying operation by the second conveying roller is controlled so as to be between a second sheet detecting sensor and the first sheet detecting sensor.   The second transport roller drive unit is a drive unit capable of switching the paper transport speed of the second transport roller between two stages of a high speed transport speed and a low speed transport speed, the paper feed roller, the second The sheet conveyance speed of each of the conveyance roller, the first conveyance roller, and the registration roller is as follows: the feed roller conveyance speed> the high-speed conveyance speed of the second conveyance roller> the high-speed conveyance speed of the second conveyance roller, and the second conveyance The image forming apparatus according to claim 9, wherein the roller conveying speed is set to the first conveying roller conveying speed = the registration roller conveying speed.   The control unit sets the sheet conveyance speed of the second conveyance roller to a high-speed conveyance speed before stopping the sheet conveyance operation by the second conveyance roller based on the sheet detection of the second sheet detection sensor upstream of the first sheet detection sensor. The image forming apparatus according to claim 11, wherein after the restart of the sheet conveying operation by the second conveying roller, the continuous conveying speed is set.   The control unit sets the sheet conveyance speed of the second conveyance roller to a high-speed conveyance speed before stopping the sheet conveyance operation of the second conveyance roller based on the sheet detection of the second sheet detection sensor upstream of the first sheet detection sensor. After the restart of the sheet conveying operation by the second conveying roller, when the leading edge of the sheet is detected by the first sheet detecting sensor, the high speed conveying speed is detected before the leading edge of the sheet enters the first conveying roller. The image forming apparatus according to claim 11, wherein the image forming apparatus is switched to a normal conveyance speed.   The second conveying roller driving unit is a driving unit capable of switching the sheet conveying speed of the second conveying roller to a plurality of stages, and the control unit is configured to change the second conveying roller according to the conveying direction length of the sheet to be conveyed. The image forming apparatus according to claim 9, wherein the sheet conveyance speed can be changed and set.   The second conveyance roller and the second sheet detection sensor on the downstream side of the second conveyance roller are provided as a set in a plurality of stages in the sheet conveyance direction, and are controlled by the control unit. The image forming apparatus according to claim 9, wherein the sheet is supplied to the image forming path using one or more of a plurality of sets. A common drive motor is provided for the paper feed roller, the transport roller, and the registration roller,
The drive unit of the paper feed roller includes the common drive motor and a first electromagnetic clutch that switches between start and stop of paper feed operation of the paper feed roller by the drive motor,
The drive section of the transport roller includes the common drive motor and a second electromagnetic clutch that switches between starting and stopping the paper transport operation of the transport roller by the drive motor,
The registration roller drive unit includes the common drive motor and a third electromagnetic clutch that switches between starting and stopping the sheet transfer operation of the registration roller by the drive motor.
The control unit can control switching of feeding operation start and stop of the sheet feeding roller by turning on and off the first electromagnetic clutch, and starting sheet feeding operation by the feeding roller by turning on and off the second electromagnetic clutch. 9. The image forming apparatus according to claim 4, wherein the stop can be switched and the sheet conveyance operation start and stop by the registration roller can be switched by turning on and off the third electromagnetic clutch. The second transport roller drive unit includes a drive motor having a variable rotation speed,
A common drive motor is provided for the first conveying roller and the registration roller,
The drive section of the first transport roller includes the common drive motor and an electromagnetic clutch for the first transport roller that switches between starting and stopping the sheet transport operation of the first transport roller by the drive motor,
The registration roller drive unit includes the common drive motor, and a registration roller electromagnetic clutch that switches between starting and stopping the sheet conveyance operation of the registration roller by the drive motor,
The control unit can control the start and stop of the sheet conveying operation of the second conveying roller by controlling the second conveying roller driving unit, and can change the sheet conveying speed by the second conveying roller. ,
The first conveying roller electromagnetic clutch can be controlled to be turned on and off by turning on and off the first conveying roller electromagnetic clutch, and the sheet conveying operation can be activated by the registration roller by turning on and off the registration roller electromagnetic clutch. The image forming apparatus according to claim 9, wherein the stop can be switched and controlled.

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