JPH10282746A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an image from being deteriorated by rushing shock when the leading edge of the sheet material rushes into a fixing means, even when the length of sheet material in a carrying direction is shorter than a carrying distance between an image forming means and a fixing means. SOLUTION: This device is provided with a control part E which compares the length of recording paper in the carrying direction with the carrying distance L from the photoreceptor drum 11 of an image forming part to a fixing unit 27 so as to control the carrying speed of the recording paper, based on the comparison information. In the case of judging that the length of the recording paper in the carrying direction is shorter that the carrying distance L between the photoreceptor drum 11 of the image forming part and the fixing unit 27, the carrying speed of the recording paper is made slow at least in a given distance just before the leading edge of the recording paper reaches the fixing unit 27.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, etc., which forms an image on a sheet while conveying the sheet, and fixes the image on the sheet. is there.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, a printer, a facsimile machine, etc., particularly in an apparatus employing an electrophotographic system, image forming is performed while conveying a recording sheet as a sheet material by a conveying means. The image (toner image) formed by the means is transferred onto the recording paper, and the toner image is fixed on the recording paper by the fixing means.

Further, in the above-described image forming apparatus, in a device having a configuration in which a driving force is transmitted from a single driving source to a conveying unit, an image forming unit, and a fixing unit, the conveying speed of the recording paper is substantially constant. The transport speed is not switched (for example, reduced) according to the size of the recording paper.

[0004]

Therefore, in the above-mentioned conventional example, for example, when an image is formed on a recording sheet whose length in the conveying direction is shorter than the conveying distance between the image forming means and the fixing means, There is a possibility that the toner image transferred onto the recording paper may be deteriorated due to a rush shock when the leading edge of the recording paper rushes into the fixing unit. In particular, when the recording paper is thick, the rush shock when rushing into the fixing unit is further increased, so that there is a problem that the possibility of deteriorating the toner image on the recording paper is further increased.

Therefore, an object of the present invention is to provide an image forming apparatus in which, even when the length of a sheet in the conveying direction is shorter than the conveying distance between the image forming means and the fixing means, the leading end of the sheet is fixed to the fixing means. An object of the present invention is to prevent an image from deteriorating due to a rush shock when rushing into the camera.

[0006]

In order to achieve the above-mentioned object, a typical configuration of the present invention comprises a conveying means for conveying a sheet material, an image forming means for forming an image on the sheet material, and the sheet forming means. A fixing unit for fixing an image on the material, a length of the sheet material in a conveying direction is compared with a conveying distance from the image forming unit to the fixing unit, and a conveying speed of the sheet material is controlled based on the comparison information. Control means, and when it is determined that the length of the sheet material in the conveyance direction is shorter than the conveyance distance between the image forming means and the fixing means, at least the leading end of the sheet material reaches the fixing means. During a predetermined distance from immediately before, the conveying speed of the sheet material is reduced.

In the case where an image is continuously formed on a plurality of sheet materials, while the conveying means slows down the conveying speed of the preceding sheet material, the image forming on the next sheet material is performed. Is not performed.

According to the above arrangement, if it is determined that the length of the sheet in the conveying direction is shorter than the conveying distance between the image forming unit and the fixing unit, at least the leading end of the sheet reaches the fixing unit. Since the conveying speed of the sheet material is reduced for a predetermined distance from immediately before, the rush shock when the leading edge of the sheet material rushes into the fixing means is relieved, and as a result, a high quality image is obtained. Can be obtained.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image forming apparatus to which the present invention is applied will be specifically described below.

First Embodiment An image forming apparatus according to a first embodiment will be described in detail with reference to the drawings. still,
In the present embodiment, a case is described in which the present invention is applied to an electrophotographic copying machine as an image forming apparatus.

FIG. 1 is a schematic sectional view showing a schematic configuration of an image forming apparatus according to the present embodiment, FIG. 2 is an explanatory view of an operation panel of the apparatus, FIG. 3 is a block diagram showing a configuration of a control system of the apparatus, FIG. 4 is a timing chart showing the operation of the present apparatus by the control system.

First, a schematic configuration of the present apparatus will be described. The drive system of the present apparatus is divided into a main drive system for driving a feeding unit, a conveyance unit, an image forming unit (photosensitive drum, etc.) and a fixing unit, and an optical drive system for driving an optical system as a load. . As shown in FIG. 1, a driving source of a main driving system is a stepping motor M1, and a driving source of an optical driving system (including a mechanism for reading an image) is a stepping motor M1.
2 is adopted. These stepping motors M1, M2
Are controlled by the control unit E. The control unit E includes all drive circuits including a microcomputer, an extension IC unit, and the like.

The feeding method of the feeding unit includes a feeding from the cassette 21 and a feeding from the multi-manual feeding unit 20, and any one of them can be selected. In the case of feeding from the cassette 21, a switch (not shown) for detecting the presence or absence of the cassette 21
The state is managed by a switch group 41 for detecting the size of the cassette 21 and a switch 42 for detecting the presence or absence of sheet material in the cassette 21. When an abnormality is detected by the above switch, the information is displayed on a display unit described later. Is displayed. In the case of multi-manual feeding, the state of the multi-manual feeding unit 20 is detected by the switch 43. This switch
Even when an abnormality is detected by 43, the information is displayed on a display unit described later.

The photosensitive drum 11 of the image forming section rotates in the direction of an arrow (clockwise) in FIG. The potential charged on the photosensitive drum 11 by the primary charger 12 is exposed by an optical system, developed by a developing unit 13, and transferred to a recording sheet as a sheet material sent from a feeding unit by a transfer unit 14. The image (toner image) is transferred. Then, the process of removing the residual toner from the photosensitive drum 11 after the transfer by the cleaning unit 15, removing the residual potential by the pre-exposure lamp 16, and forming an image again is repeated. The recording paper on which the image has been transferred as described above is placed on the transport belt 26 of the transport unit 25, and the fixing unit 27
The fixing unit 27 fixes the image.
The separation sensor 44 located immediately after the photosensitive drum 11 is a sensor that detects the state of the recording paper.

The fixing unit 27 has a driving roller 28, a tension roller 29, and a pressure roller 30. Further, a heater 31 having a resistor printed on a ceramic substrate is used as the heater, and this heater 31 is supported by a heat-resistant plastic supporter 32. Further, a metal stay (not shown) is attached to the plastic supporter 32 to make it stronger. The drive roller 28, the tension roller 29, and the heater 31 have an endless film 33.
Has been hung. A temperature detecting element (thermistor) 34 is attached to the metal stay.
Are in direct contact with the back surface of the heater 31. Still another temperature detecting element 35 is attached to the metal stay similarly to the temperature detecting element 34. The heater unit including the heater 31, the plastic supporter 32, and the metal stay and the endless film 33 press the pressing roller 30.

The recording paper that has passed through the fixing unit 27 is discharged onto a discharge tray 37 by discharge rollers 36. Also,
A discharge sensor 45 located immediately after the discharge roller 36 is a sensor for detecting whether or not the recording paper has normally passed through the fixing unit 27.

This device has a number of functions. Specifically, a stepping motor M2 of an optical drive system controls the position of the zoom lens 6 and the speed of the exposure units 2 to 5 to select a multi-stage magnification, and detects reflected light of the original placed on the original glass 1. A function of automatically selecting a density by an optical sensor 46, a function of automatically selecting a copy magnification (having communication means) by connecting to an external device (not shown),
Memory backup function for storing various states (for example, remaining number of sheets, magnification value, abnormality information, etc.) when an abnormality such as a paper jam occurs, and continuous page printing by controlling the position of the exposure lamp 2 by the stepping motor M2 function,
Further, a plurality of color images can be formed by exchanging the developing unit 13, and a switch 47 for detecting the exchanging of the developing unit 13 is provided, thereby having a function of switching control depending on this state.

Next, the operation of the present apparatus will be described.

A power cord (not shown) of the present apparatus is connected to a predetermined power supply. FIG. 2 shows an example of the operation panel, which is arranged on the upper surface of the apparatus shown in FIG. When power is supplied to the apparatus by pressing the power switch 51, the power indicator lamp 52 is simultaneously lit.

When the power is turned on, the display on the operation panel is set in the standard mode as follows. Number display 59
, 1 is displayed, the magnification display 67 is displayed at the same magnification, and the A of the automatic density adjustment display 76 is turned on.

The display of the start key 56 is displayed in red at the time of initial setting at the time of turning on the power (moving the lens to the same magnification position) and during copying. Indicates operable.

Next, the operation of the optical drive system after the power is turned on will be described. The exposure units 2 to 5 irradiate light from the exposure lamp 2 while scanning and moving rightward from the left end of FIG. 1 along the original on the original glass 1, and reflect the original image, which is the reflected light, to the first mirror 3, The photosensitive drum 11 is exposed through the second mirror 4, the third mirror 5, the zoom lens 6, the fourth mirror 7, the fifth mirror 8, and the sixth mirror 9. That is, the starting point of the movement of the exposure units 2 to 5 is set at the left end in FIG. 1, and this position is set as the home position (HP). This H
An HP sensor 49 is provided to detect P. Therefore, when the power is turned on, if the HP sensor 49 does not detect the position of the exposure lamp 2, the control unit E such as a microcomputer controls the rotation of the stepping motor M2 to move the exposure unit to the HP side.

When the exposure units 2 to 5 are located at the HP, the stepping motor M2 moves the zoom lens 6 to a predetermined position (equal magnification position). As described above, when the power is turned on, the equal magnification value is selected as the standard mode, and this equal magnification position is set to the zoom home position (ZH).
P). A ZHP sensor (not shown) is provided to detect the ZHP. Therefore, when the ZHP sensor does not detect the position of the zoom lens 6 when the power is turned on, the control unit E such as a microcomputer controls the rotation of the stepping motor M2 to move the zoom lens 6 to the ZHP side.

As described above, the preparation of the copying operation of the apparatus is completed by the end of the initial operation of the optical drive system.

Next, a copying operation by feeding from the cassette 21 will be described. When the copy start key 56 is pressed, the switches 41 for detecting the cassette size are used to set the recording paper size data according to the input signal, the number data set by the number key 54, and the magnification selection keys 61, 62, 64, 65, 66. The copying operation starts based on the magnification data and other data from the various mode selection means.

When the copy start key 56 is accepted, the display changes from green to red, and input of mode switching keys such as the numeric key 54 and magnification selection keys 61, 62, 64, 65, 66 is prohibited. Then, the stepping motor M1, which is the main drive source, starts rotating, and the feed roller 23, the photosensitive drum 11, the transport unit 25, the discharge roller 36, the fixing unit 27
And the like.

A feed solenoid (not shown) operates 0.5 sec after the start of the rotation of the stepping motor M 1, and the feed roller 22 rotates with the operation, and feeds the recording paper in the cassette 21 toward the feed roller 23. The recording paper feed amount of the feed roller 22 is controlled by cassette size data. That is, when the recording paper is larger than the predetermined value, the feeding amount is increased. When the recording paper reaches the feed roller 20, the recording paper is fed to the registration roller 24 by the feed roller 23, and stops when it reaches. Feed roller 23 and registration roller 24
The pre-registration sensor 48 installed between the first and second sensors detects the feeding state of the recording sheet, and measures the length of the recording sheet in the conveying direction while the registration roller 24 conveys the recording sheet.

At a predetermined timing until the recording paper is fed on the feeding path and reaches the registration roller 24, the exposure units 2 to 5 are allowed to start scanning the original. At this time,
The exposure lamp 2 is located at a position detected by the HP sensor 49. More specifically, at the time of the initial operation or the backward movement of the copy operation, the carriage is stopped at a position which is backward from the position detected by the HP sensor 49 by a distance corresponding to the selection magnification at that time.

When the scanning of the original is started, the stepping motor M2, which is the optical system driving source, moves in the direction in which the exposure units 2 to 5 move forward (to the right) until the driving pulse rate corresponding to the selected magnification value is reached. Pulse rate gradually increases
(Hereinafter referred to as slow-up control). That is, the moving speed is gradually accelerated and reaches the target speed.

The exposure units 2 to 5 start a scanning movement for a predetermined distance in accordance with cassette size data, magnification data, and the like, and at a predetermined timing, the start of conveyance of the recording paper by the registration rollers 24 is permitted. Is started. The exposure units 2 to 5 gradually decrease the pulse rate when reaching the target position (hereinafter, referred to as slowdown control).
After the stop, slow-up control and slow-down control are performed again in the direction of the HP sensor 49 to move the vehicle backward. And the HP sensor 49
Is detected, slowdown control for stopping at a position corresponding to the selected magnification is performed, and the exposure units 2 to 5 stop.

The present invention relates to control of the transport speed of recording paper in the above-described image forming apparatus, and the configuration and operation will be described in detail below.

FIG. 3 is a block diagram of a control system of the present apparatus. In the figure, a thin arrow indicates an electric action, and a thick arrow indicates a mechanical action. In FIG. 3, M1 is a stepping motor as a main drive source, which is controlled by the control unit E, and at the time of constant speed rotation, the rotation speed A or the rotation speed B (A> B).
Rotate at. Reference numeral 24 denotes a registration roller that conveys the recording paper to the photosensitive drum 11. Reference numeral 24c denotes a registration clutch, which is controlled by the control unit E and is turned on by the registration roller 24 during ON.
To the drive of the stepping motor M1. The registration clutch 24c is synchronized with the optical drive as described above.
N, and the registration rollers 24 start conveying the recording paper, thereby starting a series of image formation. Reference numeral 11 denotes a photosensitive drum, which forms a toner image on recording paper as described above. Reference numeral 25 denotes a transport unit including a transport belt and the like, which transports the recording paper from the photosensitive drum 11 to the fixing unit 27. A fixing unit 27 fixes the toner image on the recording paper as described above, and discharges the recording paper. Reference numeral 48 denotes a pre-registration sensor, which is disposed immediately before the registration roller 24 and has a function of detecting the presence or absence of a recording sheet in front of the registration roller and detecting the length of the conveyed recording sheet in the conveyance direction. I have. 44 is a separation sensor, which is a photosensitive drum
It is disposed immediately after 11 and detects the state of the recording paper and the trailing edge of the recording paper. The control unit E controls the registration clutch 24c, the display unit, and other functions based on the pre-registration sensor 48, the separation sensor 44, the sensors and the operation keys, and the like. Has a function of controlling the stepping motor M1 by comparing the length of the recording paper in the transport direction detected by the above with the transport distance from the photosensitive drum 11 to the fixing unit 27.

The above-described registration roller 24, photosensitive drum 1
1. The transport unit 25 and the fixing unit 27 rotate according to the rotation speed of the stepping motor M1. Further, the driving of the stepping motor M1 is selectively transmitted to the registration roller 24 by the registration clutch 24c.

The operation of this apparatus by the above control system will be described with reference to the timing chart of FIG.

When the start key is pressed (a), the stepping motor M1 starts rotating at the rotation speed A after predetermined slow-up control, and the feeding of the recording paper is started (b). The fed recording paper is conveyed to the registration roller 24 and stops in a state of waiting for the registration clutch 24c to be turned on (c). While the registration clutch 24c waits for the ON state, the pre-registration sensor 48 detects the presence of the recording paper.
When the registration clutch 24c is turned on at a predetermined timing synchronized with the exposure unit (d), the registration roller 24 starts conveying the recording paper to the photosensitive drum 11, and a series of image forming operations is started. (E).

Here, the control section E operates from (d) to (f) until the registration roller sensor 24 detects the absence of the recording paper (ie, detects the trailing edge of the recording paper) from the start of the conveyance of the recording paper by the registration roller 24. The length of the recording sheet in the transport direction is calculated from the number of stepping motor drive pulses output in step (1), and is compared with a predetermined transport distance L from the photosensitive drum 11 to the fixing unit 27. The length of the recording paper is equal to the transport distance L.
If the stepping motor M is longer than
The rotation speed change control of 1 is not performed, and the rotation speed remains unchanged at A. If the length of the recording paper is shorter than the transport distance L, a rotation speed non-change distance is calculated by subtracting a predetermined slowdown distance from the difference, and the stepping motor drive pulse at the rotation speed A is calculated. Calculate the number. That is, at the end of the slowdown control, the leading end of the recording paper
, The number of drive pulses at the rotation speed A for controlling the motor to be positioned immediately before is calculated. Hereinafter, drive control when the length of the recording paper is shorter than the transport distance L will be described.

The separation of the recording paper passing through the photosensitive drum 11 from the photosensitive drum 11 is confirmed by a separation sensor 44,
It is transported to the transport unit 25 (g). When the transfer of the toner image onto the recording paper is completed, the rear end of the recording paper is detected by the separation sensor 44 (h), and the recording paper is completely transported to the transport unit 25.
When the recording paper is conveyed upward, the leading end of the recording paper
During a predetermined distance from immediately before reaching 27, the conveying speed of the recording paper is reduced. That is, the control unit E outputs the drive pulses of the rotation number A by the previously calculated number of drive pulses, performs the predetermined slowdown control, and then performs the rotation number B (B <B) by the predetermined number of drive pulses. A) The drive pulse of A) is output, and after performing predetermined slow-up control, drive control (rotation speed change control) of the stepping motor M1 is performed so as to return to the rotation speed A again (h to i). ).

During the rotation speed change control, the recording paper is conveyed by the conveyance unit 25, and when the driving at the rotation speed B is started, the leading end of the recording paper is located immediately before the fixing unit 27 (j). While the recording paper is conveyed at a rotation speed B for a predetermined distance, the leading end thereof enters the fixing unit 27 (k),
Thereafter, conveyance at the rotation speed A is started again (i). Further, the recording paper is completely discharged onto the discharge tray after the entire fixing operation is completed (l). Then, after a lapse of a predetermined time, a predetermined slowdown control is performed to stop the stepping motor M1, and a series of image forming operations is completed (m).

When an image is continuously formed on a plurality of recording sheets, the image formation on the next recording sheet is not performed while the conveying speed of the preceding recording sheet is reduced. Is controlled as follows. For example, the n-th sheet (n = 1, 2, 3,...)
..), Feeding of the (n + 1) th recording sheet is started at a predetermined timing during a series of image forming operations of the recording sheet, and fixing operation of the (n + 1) th recording sheet is started. Until (k), the registration clutch is on standby. Then, after the stepping motor M1 starts to rotate at the rotation speed A after the fixing operation of the n-th recording sheet is started,
At a predetermined timing synchronized with the exposure unit, the registration clutch 24c is turned on. That is, at a predetermined timing after the rotation speed of the stepping motor M1 returns to A, n
The image forming operation of the (+1) th recording sheet is started.

The above-described operation is repeated until the final recording sheet. After the final recording sheet is completely discharged and a predetermined time has elapsed, a predetermined slowdown control is performed, the stepping motor M1 is stopped, and a series of image forming operations is performed. Ends.

As described above, by controlling the conveying speed of the recording paper, when the length of the recording paper in the conveying direction is shorter than the conveying distance L from the photosensitive drum 11 to the fixing unit 27, the toner image is controlled. It is possible to relieve the rush shock when the recording paper enters the fixing unit 27 without changing the conveyance speed of the recording paper during execution of the main image forming process such as forming and fixing (excluding a part of the leading end of the recording paper). it can.
As a result, deterioration of the image due to the rush shock can be prevented, and a high-quality image can be obtained.

Second Embodiment An image forming apparatus according to a second embodiment will be described in detail with reference to the drawings. FIG.
Is a block diagram showing a configuration of a control system of the present apparatus, and FIG. 6 is a timing chart showing an operation of the present apparatus by the control system. Note that the schematic configuration and the basic operation of the image forming apparatus according to this embodiment are the same as those of the above-described embodiment described with reference to FIGS.

The second embodiment of the present invention relates to the control of the transport speed of recording paper in the above-described image forming apparatus (feeding from a cassette), and the configuration and operation will be described in detail below.

FIG. 5 is a block diagram of a control system of the present apparatus. In the figure, a thin arrow indicates an electric action, and a thick arrow indicates a mechanical action. In FIG. 5, M1 is a stepping motor as a main drive source, which is controlled by the control unit E, and at the time of constant speed rotation, the rotation speed A or the rotation speed B (A> B).
Rotate at. Reference numeral 24 denotes a registration roller that conveys the recording paper to the photosensitive drum 11. Reference numeral 24 denotes a registration clutch, which is controlled by the control unit E and is turned on during the ON state.
To the drive of the stepping motor M1. The registration clutch 24c is synchronized with the optical drive as described above.
N, and the registration rollers 24 start conveying the recording paper, thereby starting a series of image formation. Reference numeral 11 denotes a photosensitive drum, which forms a toner image on recording paper as described above. Reference numeral 25 denotes a transport unit including a transport belt and the like, which transports the recording paper from the photosensitive drum 11 to the fixing unit 27. A fixing unit 27 fixes the toner image on the recording paper as described above, and discharges the recording paper. A recording paper size detection switch 40 detects the size of the recording paper being conveyed. 44 is a separation sensor, which is a photosensitive drum
It is disposed immediately after 11 and detects the state of the recording paper and the trailing edge of the recording paper. The control unit E controls the registration clutch 24c, the display unit, and other loads based on the recording paper size detection switch 40, the separation sensor 44, the above-described sensors, operation keys, and the like. The length of the recording paper in the transport direction is calculated from the size of the recording paper detected by the size detection switch 40, and the length of the recording paper in the transport direction is compared with the transport distance L from the photosensitive drum 11 to the fixing unit 27. Further, it has a function of controlling the stepping motor M1 and the like.

The above-described registration roller 24, photosensitive drum 1
1. The transport unit 25 and the fixing unit 27 rotate according to the rotation speed of the stepping motor M1. Further, the driving of the stepping motor M1 is selectively transmitted to the registration roller 24 by the registration clutch 24c.

The operation of this apparatus by the above control system will be described with reference to the timing chart of FIG.

When the start key is depressed (a), the stepping motor M1 starts rotating at a rotation speed A after predetermined slow-up control, and the feeding of the recording paper is started (b). At this time, the recording paper size detection switch 40 detects the size of the fed recording paper. The fed recording paper is conveyed to the registration roller 24 and stops in a state of waiting for the registration clutch 24c to be turned on (c). When the registration clutch 24c is turned on at a predetermined timing synchronized with the exposure unit (d), the registration roller 24 starts conveying the recording paper to the photosensitive drum 11, and a series of image forming operations is started. (E).

Here, the control unit E calculates the length of the recording paper in the conveying direction from the size of the recording paper detected by the recording paper size detection switch 40, and moves the predetermined photosensitive drum 11 to the fixing unit. Compare with the transport distance L up to 27. If the length of the recording paper is longer than the transport distance L, the rotation speed change control of the stepping motor M1 described below is not performed, and the rotation speed remains unchanged at A. If the length of the recording paper is shorter than the transport distance L, a rotation speed non-change distance is calculated by subtracting a predetermined slowdown distance from the difference, and the stepping motor drive pulse at the rotation speed A is calculated. Calculate the number. That is, the number of drive pulses at the rotation speed A for controlling the leading end of the recording paper to be located immediately before the fixing unit 27 at the end of the slowdown control is calculated. Hereinafter, drive control when the length of the recording paper is shorter than the transport distance L will be described.

The recording paper that has passed through the photoconductor drum 11 is separated from the photoconductor drum 11 by a separation sensor 44, and is checked.
It is transported to the transport unit 25 (g). When the transfer of the toner image onto the recording paper is completed, the rear end of the recording paper is detected by the separation sensor 44 (h), and the recording paper is completely transported to the transport unit 25.
When the recording paper is conveyed upward, the leading end of the recording paper
During a predetermined distance from immediately before reaching 27, the conveying speed of the recording paper is reduced. That is, the control unit E outputs the drive pulses of the rotation number A by the previously calculated number of drive pulses, performs the predetermined slowdown control, and then performs the rotation number B (B <B) by the predetermined number of drive pulses. A) The drive pulse of A) is output, and after performing predetermined slow-up control, drive control (rotation speed change control) of the stepping motor M1 is performed so as to return to the rotation speed A again (h to i). ).

During the rotation speed change control, the recording paper is conveyed by the conveyance unit 25, and when the driving at the rotation speed B is started, the leading end of the recording paper is located immediately before the fixing unit 27 (j). While the recording paper is conveyed at a rotation speed B for a predetermined distance, the leading end thereof enters the fixing unit 27 (k),
Thereafter, conveyance at the rotation speed A is started again (i). Further, the recording paper is completely discharged onto the discharge tray after the entire fixing operation is completed (l). Then, after a lapse of a predetermined time, a predetermined slowdown control is performed to stop the stepping motor M1, and a series of image forming operations is completed (m).

When an image is continuously formed on a plurality of recording sheets, the image formation on the next recording sheet is not performed while the conveying speed of the preceding recording sheet is reduced. Is controlled as follows. For example, the n-th sheet (n = 1, 2, 3,...)
..), Feeding of the (n + 1) th recording sheet is started at a predetermined timing during a series of image forming operations of the recording sheet, and fixing operation of the (n + 1) th recording sheet is started. Until (k), the registration clutch is on standby. Then, after the stepping motor M1 starts to rotate at the rotation speed A after the fixing operation of the n-th recording sheet is started,
At a predetermined timing synchronized with the exposure unit, the registration clutch 24c is turned on. That is, at a predetermined timing after the rotation speed of the stepping motor M1 returns to A, n
The image forming operation of the (+1) th recording sheet is started.

The above operation is repeated until the final recording paper is discharged. After the final recording paper is completely discharged and a predetermined time has elapsed, a predetermined slowdown control is performed, the stepping motor M1 is stopped, and a series of image forming operations is performed. Ends.

As described above, by controlling the transport speed of the recording paper, the toner image can be transferred when the length of the recording paper in the transport direction is shorter than the transport distance L from the photosensitive drum 11 to the fixing unit 27. It is possible to relieve the rush shock when the recording paper enters the fixing unit 27 without changing the conveyance speed of the recording paper during execution of the main image forming process such as forming and fixing (excluding a part of the leading end of the recording paper). it can.
As a result, deterioration of the image due to the rush shock can be prevented, and a high-quality image can be obtained.

[Other Embodiments] In the above embodiment,
The separation sensor is used to detect that the trailing edge of the recording paper has passed the photosensitive drum. However, the present invention is not limited to this. It is also possible to configure so as to detect that the rear end has passed the photosensitive drum.

In the above-described embodiment, the stepping motor is used as the driving source and the transport distance is controlled by the number of steps. However, the present invention is not limited to this. The method of detecting the leading edge of the recording paper by providing the detecting means, the method of controlling the transport distance by time control, and the like can be controlled in the same manner as in the above-described embodiment regardless of the type of the motor.

In the above-described embodiment, a copying machine is exemplified as an image forming apparatus. However, the present invention is not limited to this, and it is needless to say that the present invention can be used for other image forming apparatuses such as a printer and a facsimile machine. It is possible.

[0057]

As described above, according to the present invention,
If it is determined that the length of the sheet material in the conveyance direction is shorter than the conveyance distance between the image forming unit and the fixing unit, the sheet is at least a predetermined distance immediately before the leading end of the sheet material reaches the fixing unit. Since the conveyance speed of the sheet material is controlled to be slow, the rush shock when the leading end of the sheet material rushes into the fixing unit is relieved, and as a result,
High quality images can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a schematic configuration of an image forming apparatus to which the present invention is applied.

FIG. 2 is an explanatory diagram of an operation panel of the apparatus.

FIG. 3 is a block diagram showing a configuration of a control system of the apparatus according to the first embodiment.

FIG. 4 is a timing chart showing an operation of the apparatus by the control system.

FIG. 5 is a block diagram showing a configuration of a control system of the device according to the second embodiment.

FIG. 6 is a timing chart showing the operation of the device by the control system.

[Explanation of symbols]

E: controller M1, M2: stepping motor 1: original glass 2-5: exposure unit (2: exposure lamp, 3-5: mirror) 6: zoom lens 7-9: mirror 11: photosensitive drum 12: primary charging Unit 13 Developing unit 14 Transfer unit 15 Cleaning unit 16 Pre-exposure lamp 20 Multi-manual feed unit 21 Cassette 22 Feed roller 23 Feed roller 24 Registration roller 25 Transport unit 26 Transport belt 27 Fixing Unit 28 Drive roller 29 Tension roller 30 Pressure roller 31 Heater 32 Plastic supporter 33 Endless film 34, 35 Temperature detecting element (thermistor) 36 Discharge roller 37 Discharge tray 40 Recording paper size detection switch 41 ... Switch group 42,43 ... Switch 44 ... Separation sensor 45 ... Ejection sensor 46 ... Optical sensor 47 ... Switch 48 ... Pre-registration sensor 49 ... H Sensor 51 ... power switch 52 ... power indicator 54 ... numeric keys 56 ... start key 59 ... number indicator 61,62,64,65,66 ... magnification selection key 67 ... magnification display 76 ... automatic density adjustment indicator

Claims (2)

[Claims] A conveying unit configured to convey a sheet material; an image forming unit configured to form an image on the sheet material; a fixing unit configured to fix an image on the sheet material; and a length of the sheet material in a conveying direction. A control unit that compares a conveyance distance from the image forming unit to the fixing unit and controls a conveyance speed of the sheet material based on the comparison information, wherein the length of the sheet material in the conveyance direction is the image. When it is determined that the conveyance distance is shorter than the conveyance distance between the forming unit and the fixing unit, the conveyance speed of the sheet material is reduced at least for a predetermined distance immediately before the leading end of the sheet material reaches the fixing unit. Image forming apparatus. 2. An image forming method according to claim 1, wherein, when image forming is continuously performed on a plurality of sheet materials, image forming on a next sheet material is performed while said conveying means reduces the conveying speed of the preceding sheet material. The image forming apparatus according to claim 1, wherein the image forming apparatus does not perform the processing.