JPH085485Y2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an image forming apparatus such as a copying machine or a printer having a fixing device therein.

[Conventional technology]

Image forming apparatuses such as copying machines and various printers use a fixing device for fixing unfixed toner transferred onto a sheet. Conventionally, as the above-mentioned fixing device, heat and pressure are applied by carrying in the paper on which the unfixed toner is formed between a heat roll having a built-in heater and a pressure roll that presses a predetermined pressure against the heat roll. Has used a fixing device for fixing unfixed toner on a sheet. In such a fixing device, in order to surely fix the toner image on each sheet, the peripheral surface temperature of the heat roll is maintained at a high temperature, and the pressure contact force of both rolls is maintained in the strongly pressed state.

In addition to the so-called single-sided printing for printing on one side of paper, an image forming apparatus for two-color printing or so-called double-sided printing for printing on both sides of paper is also commercially available as the above-mentioned image forming apparatus. ing.

[Problems of conventional technology]

In such an image forming apparatus, after the unfixed toner of the first color or one side is fixed by the above fixing device, the image of the second color or the other side is formed again, and the unfixed toner of the second color or the other side is formed. The fixing process is performed by the above fixing device. However, the fixing device is controlled to be in a high temperature / high pressure contact state as described above, and therefore, the same sheet being conveyed through the fixing device twice causes wrinkles in the sheet. In addition, when the toner image is transferred to the second color or the other surface due to shrinkage of the paper due to the first fixing process, it is displaced from the transfer position of the toner image to the first color or the first print surface, which deteriorates the print quality. There is.

[Purpose of device]

In view of the above-mentioned conventional drawbacks, the present invention, even when performing two-color printing or double-sided printing, does not cause wrinkles on the paper,
Moreover, it is an object of the present invention to provide an image forming apparatus having excellent print quality.

[Key points of device]

In order to achieve the above object, the present invention arranges a charging means, an exposing means, a developing means, and a transferring means around an image carrier, and conveys a sheet having an unfixed image between a pair of rolls at least one of which is heated. In the image forming apparatus, the unfixed toner on the sheet is fixed and then stored in an intermediate tray in the machine, and an image is formed again on the sheet fed from the intermediate tray.
Paper side edge detecting means for detecting the side edge of the paper in the traveling direction, print position control means for controlling the side edge printing position of the paper by the exposing means based on the output of the paper side edge detecting means, and the first time The pressure between the rolls during fixing is set to the second
And a control means for making the pressure lower than the pressure between the rolls at the time of the fixing of the second time.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this embodiment, an image forming apparatus is used with single-sided printing.
1 illustrates an example of a printer device (hereinafter simply referred to as a printer) capable of color and double-sided printing.

FIG. 1 is an overall configuration diagram of this printer. In FIG. 1, the printer 1 is composed of an image forming unit 2 that forms a toner image on a sheet, and a conveyance mechanism 4 that conveys the sheet out of a sheet feed cassette 3 and conveys the inside of the printer 1.

The image forming unit 2 includes a photosensitive drum 5, a charging device 6, a print head 7, a first developing device 8, a second developing device 9, a transfer device 10, and a cleaner which are sequentially arranged near the peripheral surface of the photosensitive drum 5. It is composed of 11.

The charger 6 is a device that applies an initial charging voltage to the photosensitive surface of the photosensitive drum 5 that rotates in the direction of the arrow.
Is an apparatus for exposing a photosensitive surface based on image data.
The first developing device 8 and the second developing device 9 convert the electrostatic latent image formed on the photosensitive surface by the above-mentioned exposure into toner images (visualization) by using toners of different colors, and the transfer device 10 uses this toner. This is a device for transferring an image onto a sheet conveyed in the direction of arrow A.

On the other hand, the paper transport mechanism 4 is disposed between a transport direction switching roller 13, which will be described in detail later, a paper feed roller 12 for transporting the paper from the paper feed cassette 3, and between the paper feed roller 12 and the transport direction switching roller 13. Standby roll 14, guide plate 15a, fixing roll 16,
The guide plate 15b, the conveying direction switching roller 13 and the face-down discharged sheet (hereinafter, referred to as FD) tray 17, the conveying roll 18, the guide plate 19, the sheet discharging roll 20, the conveying direction switching roller 13 and the face. Up discharge paper (hereinafter referred to as FU)
A guide plate 22 arranged between the trays 21, a paper discharge roll 23,
A guide plate 24, a transport roll 25, an intermediate tray 26, a transport roll 27, and a guide plate 28, which are arranged between the transport direction switching roller 13 and the waiting roll 14 in order to re-feed the sheet to the image forming unit 2.
It is composed of Each of the transport rolls 18, 23, 25, 27 applies a transporting force to the sheet, and in particular, the transport roll 18 is directly connected to a forward / reverse rotation control motor, which will be described later in detail, and can also apply a transporting force in the reverse direction. The waiting roll 14 applies a conveying force to the paper and controls the image matching between the leading edge of the paper and the toner image on the photosensitive surface. Further, the fixing roll 16 thermally fixes the unfixed toner attached to the paper. In addition, the waiting roll 14
A paper detection sensor 29 is arranged on the upstream side of the paper conveyance direction, a paper detection sensor 30 is arranged between the fixing roll 16 and the conveyance direction switching roller 13, and a paper detection sensor 30 is arranged between the conveyance direction switching roller 13 and the conveyance roll 18. A paper detection sensor 31 is provided.

The transport direction switching roller 13 is a transport direction switching member for branching the paper transported from the fixing roll 16 side to the guide plate 19 or 22 or 24, for example, and FIG. 2 shows an enlarged sectional view thereof. As shown in the figure, two sheet guide grooves 13a and 13b are formed inside the conveyance direction switching roller 13. The paper guide openings 13a ′ and 13a ″ at both ends of the paper guide groove 13a are formed at an angle of 120 °, and the paper guide openings 13b ′ and 13b ″ at both ends of the paper guide groove 13b are formed at an angle of 150 °. Has been formed. Further, the angle between the paper guide openings 13a 'and 13b' and the angle between the paper guide openings 13a "and 13b" are both set to 45 °.

Further, as shown in the perspective view of FIG. 3, the conveyance direction switching roller 13 is rotationally controlled by a step motor 32 in which a rotation shaft (not shown) is fixedly mounted on the roller shaft 13c. An initial position setting switch 33 serving as a reference for setting a predetermined position of the transport direction switching roller 13 is provided at the side end of the transport direction switching roller 13.

On the other hand, FIG. 4 is a perspective view of the fixing roll 16 described above,
The fixing roll 16 includes a heat roll 16a and a pressure roll 16b,
The heat roll 16a is heated by the heater 16a '. Further, the heat roll 16a is set to a predetermined temperature during the fixing operation, and this temperature control is performed by the printer controller described later. The pressure roll 16b is a roller for applying a predetermined pressure to the heat roll 16a, and rotates following the heat roll 16a. Bearings 34a, 34b are conventionally mounted on the rotary shaft 16b 'of the pressure roll 16b, and the bearings 34a, 34b are respectively attached to the levers 35a, 35b. Holes 35a 'and 35b' are provided at one ends of the levers 35a and 35b and are pivotally supported by a fulcrum shaft (not shown). Also, one end of the compression springs 36a, 36b is locked to the lower ends of the other ends of the levers 35a, 35b, and the other ends of the compression springs 36a, 36b are connected to cams 38a, 38b fixed to the rotary shaft 37a of the step motor 37. Pressed. cam
38a, 38b are formed with convex portions 38a ', 38b' having a trapezoidal cross section,
By rotating the step motor 37, the compression force of the springs 36a and 36b can be changed in two steps. The rotation angle of the step motor 37 is a convex portion 37b 'formed on the peripheral surface of a rotation angle setting disk 37b fixed to the rotation shaft 37a.
Detected by pressing 39b. And spring 36
Lever 35a, 35 by controlling the compression force of a, 36b in two stages
b, the heat roll 16a of the pressure roll 16b through the bearings 34a, 34b
The pressure contact force against can be controlled in two steps. In the present embodiment, as will be described later, the case where both rolls 16a and 16b have a predetermined pressure contact force for completely fixing the unfixed toner on the paper is described as strong pressure contact.

Next, the structure of the paper detection sensor 29 will be described with reference to FIGS.

FIG. 5 is a block diagram of the paper detection sensor 29, and FIG. 6 is a schematic sectional view of FIG. In both figures, the paper detection sensor 29 includes a plurality of LEDs 40, a printed circuit board (hereinafter referred to as a PCB) 42 on which an LED driver 41 and the like are arranged, and an LED 40.
The image forming lens array 43 on which the emitted light is incident, the optical transmission rod 44 on which the light reflected by the paper is incident, and the phototransistor 46 that detects the emitted light from the optical transmission rod 44. The LEDs 40 arranged on the PCB 42 are 16 LEDs 40a to 40p.
And are arranged in a line in a direction orthogonal to the conveying direction of the paper P (direction of arrow A). This LED 40a-40
p lights up sequentially by PCB42. Also, imaging lens array
The position of the guide plate 28 to which the light is radiated via 43 is, for example, black-painted so that the portion without the paper does not reflect the light.

The light transmission rod 44 is composed of a cylindrical rod whose inner peripheral surface totally reflects light, and is arranged parallel to the arrangement direction of the LEDs 40a to 40p described above. In addition, a mirror 44b that reflects internal light is arranged at one end of the light transmission rod 44, and the other end faces the phototransistor 46 described above. Further, diffusion fringes 44a are formed on the opposite peripheral surface of the light transmission rod 44 on which the reflected light of the light emitted via the imaging lens array 43 is incident, and the reflected light from the paper incident on the light transmission rod 44 is formed. The scattered light is scattered into the light transmission rod 44 and the scattered light is transmitted to the light transmission rod 44.
It is configured to lead to the phototransistor 46 along.

On the other hand, the other paper detection sensors 30 and 31 are composed of photo interrupters and the like, and can detect the leading edge and the trailing edge of the passing paper.

The printer 1 having the above-described mechanical structure has a built-in printer control circuit having the structure shown in the block diagram of FIG. The printer control circuit 54 includes a video interface (hereinafter referred to as video I / F) 47, left and right end print area control unit 48, front and rear end print area control unit 49, print head interface (hereinafter referred to as print head I / F) 50, CPU
(Central processing unit) 51 and input / output interface 52. The video I / F 47 is connected to an interface controller (hereinafter, I / F controller) 53 also provided in the printer 1, and the print head I / F 50 is connected to the print head 7 described in FIG. The interface 52 is connected to various sensors / loads and the paper detection sensor 29 including the step motors 32 and 37 described above.

The CPU 51 controls all the driving of the printer 1 of this embodiment, and controls each part according to a program stored in a ROM (read only memory) not shown. For example, the CPU 51 writes the above video signal input via the video I / F 47 to the left and right edge print area control unit 48 and the front and rear edge print area control unit 49, and detects the side edge of the sheet detected by the sheet detection sensor 29. And the data after the front end are output to the left and right end print area control unit 48 or the front and rear end print area control unit 49.

The left and right end print area control unit 48 outputs a video signal in accordance with the above-mentioned side end data of the paper output from the CPU 51.
The output to the I / F 50, and the front and rear end print area control unit 49 controls the output of the video signal output to the print head I / F 50 in accordance with the above-described front and rear end data of the paper output from the CPU 51. The print head I / F 50 outputs the above video signal to the print head 7 and prints an image on a sheet.

In addition, the above-mentioned various sensors / load and paper detection sensors 29
The specific circuit of is composed of the circuit shown in FIG. As shown in the figure, the step motor 37 is
Is connected to a driver circuit 56 that controls the driving of the motors, and the rotation is controlled according to the outputs from the inverters 59 and 60. That is, the switch 39a is the convex portion 37 formed on the above-mentioned disc 37b.
When pressed down to b ′, the + 5V voltage (high signal) supplied to the input of the inverter 59 via the pull-up resistor R ₁ changes to the ground level (low signal), and the inverter 59 changes to the printer controller 54 (input / output interface). A high signal is output to 52) to control the driver circuit 56 to stop the rotating step motor 37 at a predetermined position. This position is a position where both rolls 16a, 16b are in strong pressure contact, as will be described later in detail. Similarly, when the switch 39b is pressed to the convex portion 37b 'formed on the disk 37b, the high signal supplied to the input of the inverter 60 via the pull-up resistor R ₂ changes to a low signal, and A high signal is output from 60 to the input / output interface 52 to control the driver circuit 56 to stop the step motor 37 at a predetermined position. This position is a position where both rolls 16a and 16b are in weak contact, as will be described later in detail.

The step motor 32 is connected to a driver circuit 57 that controls the drive of the step motor 32, and the initial position setting switch 33
After the button is pressed, the step motor
Stop rotation of 32. That is, when the high signal supplied to the input of the inverter 61 via the pull-up resistor R ³ is changed to the low signal by pressing the initial position setting switch 33, the inverter 61 outputs the input / output interface.
A high signal is output to 52 to drive the driver circuit 57 to rotate the step motor 32 by a predetermined angle and then stop.

Forward / reverse control motor (hereinafter simply referred to as motor) 55
Is a motor axially attached to the above-described transport roll 18, and the driver circuit 58 controls forward rotation or reverse rotation.
Control of forward / reverse rotation of the motor 55 is performed by the CPU 51 which will be described later.
And the output signal from the inverter 62. When the high signal is output from the inverter 62, the above-described paper detection sensor 31 detects the passage of the rear end of the paper and is turned on. In this case, the pull-up resistor R ₄ output to the inverter 62 is output. This is because the high signal from the sensor changes to a low signal via the paper detection sensor 31.

Further, the connection configuration of the paper detection sensor 29 is such that the LEDs 40a to 40p are connected to the input / output interface 52 via the inverters 63a to 63p, and the LED drive signal output from the CPU 51 causes the LE
The drive signals are sequentially output to D40a to 40p, and the LEDs 40a to 40p are sequentially turned on.

In the printer 1 having the above configuration, the print processing operation will be described focusing on the control operation of the pressure contact force between the heat roll 16a and the pressure roll 16b.

First, a case will be described in which one-color printing is performed on one side of a sheet and the sheet is discharged to the FD tray 17 (hereinafter, the print processing in this case is referred to as a single-color single-sided print mode). When the print switch is pressed after the printer 1 is set to the above-described single-color single-sided print mode by operating the mode setting key (not shown) in advance, this process is executed according to the time chart shown in FIG. That is, the CPU 51 outputs a drive signal to a driver circuit (not shown) via the input / output interface 52 by inputting a start signal (low signal) by pressing the print switch, and rotates the main motor. The rotation of the main motor causes the photosensitive drum 5 to start rotating in the direction of the arrow, and at the same time, by turning on a clutch (not shown), the rotational force of the main motor is transmitted to the paper feed roller 12 to rotate the paper feed roller 12. The paper is unloaded from the paper feed cassette 3.

At the same time when the main motor starts rotating, the step motors 32, 37 and the motor 55 also start rotating.
The rotation of the step motors 32, 37 and 55 is started by the CPU.
This is performed by the rotation start signal output from 51 to the corresponding driver circuits 56, 57, 58. After that, for example, the step motor 32 stops rotating after the time t ₁ after turning on the initial setting switch 33. The position of the conveyance direction switching roller 13 when the step motor 32 stops rotating is the position shown in FIG. That is, if the transport direction switching roller 13 located at the position shown in FIG. 9 is the initial position, this time t ₁ is changed from the position shown in FIG.
This is the time required to rotate to the position shown in FIG. 11 (however, the transport direction switching roll 13 is supposed to rotate in the direction of arrow B shown in FIG. 9). Also, the step motor 37 is the CPU 5
After the rotation is started by the rotation start signal from 1, the above-mentioned convex portion 37b 'presses the switch 39a and rotates until the high signal is input from the inverter 59 to the CPU 51. The position where the convex portion 37b 'depresses the switch 39a is shown in FIG. 4 and the convex portions of the cams 38a, 38b.
38a 'and 38b' are in pressure contact with the compression springs 36a and 36b, and at this time, the heat roll 16a and the pressure roll 16b are in strong pressure contact as described above. This strong pressure contact state means that the unfixed toner on the sheet is set in a state in which it can be thermally fixed by a predetermined pressure contact force, as described above. Further, the motor 55 also starts rotating in accordance with the rotation start signal input to the driver circuit 58, and causes the transport roll 18 to rotate forward.

After that, when the leading edge of the paper carried out by the paper feed roller 12 is detected by the paper detection sensor 29, the I / F controller 5
Vertical sync signal ▲ ▼ is output to 3 and then I / F
The video signal is output from the controller 53 to the video I / F 47. A bias voltage (-voltage) is applied to the developing roller 8a of the first developing device 8 at the same time when the sheet detecting sensor 29 detects the leading edge of the sheet.

The above-described paper detection sensor 29 detects not only the leading edge of the paper but also the side edge of the conveyed paper. This detection operation
CPU51 to input / output interface 52, inverter 63a ~
This is performed by sequentially lighting the LEDs 40a to 40p by sequentially outputting drive signals to the LEDs 40a to 40p via 63p. LED40a
The emitted light of ˜40p is applied to the guide plate 28 via the imaging lens array 43 as shown in FIG. 5, and the light of the LED 40 applied to the guide plate 28 on which the paper is present is transmitted by the optical transmission rod 44.
The light that has been incident on the light transmission rod 44 is guided to the light transmission rod 44 and is incident on the phototransistor 46 as described above. Therefore, the CPU 51 can detect the side edge of the sheet being conveyed by the lighting timing of the LEDs 40a to 40p and the detection timing of the reflected light at the phototransistor 43.
This side edge data is output to the left and right edge print area control unit 48 described above, and the left and right edge print area of the paper is controlled by the data. The print head 7 exposes the photosensitive surface based on the video signal output from the print head I / F 50.

During that time, the paper is sent to the standby roll 14 and waits there, and the standby roll 14 starts rotating at the timing when the image position on the photoconductor drum 5 and the leading edge position of the paper match, and the paper is transferred to the photoconductor drum 5. Sent between vessels 10. At this time, a toner image is formed on the photosensitive surface by the charging device 6, the print head 7, and the first developing device 8 described above, and the toner image transferred onto the paper by the transfer device 10 is further conveyed through the guide plate 15a. The heat is fixed by the fixing roll 16. At this time, the heat roll 16a and the pressure roll 1 which constitute the fixing roll 16 as described above.
6b is in strong pressure contact, and the unfixed toner on the sheet conveyed between the rolls 16a and 16b is completely fixed on the sheet by heat and a predetermined pressure.

After that, the paper reaches the paper guide opening 13a 'of the conveyance direction switching roller 13 set in the state shown in FIG. 11 as described above, and is guided through the paper guide opening 13a' → the paper guide groove 13a → the paper guide opening 13a ". The sheet is guided to the plate 19. Then, as described above, the sheet is further conveyed upward in the guide plate 19 by the conveyance roll 18 which rotates in the forward direction, and is ejected to the FD tray 17 by the sheet ejection roll 20.

The output of the bias voltage applied to the developing roll 8a is stopped when a predetermined time has elapsed after the print data for one sheet of paper was output. Further, the strong pressure contact between the heat roll 16a and the pressure roll 16b is also rotated again by the rotation start signal to the step motor 37 output from the CPU 51 after the fixing of the paper is completed,
By depressing the switch 39b, a weak pressure contact state is established.

Next, a case where two-color printing is performed and the paper is discharged to the FD tray 17 (this case is called a two-color print mode) will be described.

In this case, if the print switch is pressed after operating the mode setting key (not shown) to set the printer 1 to the two-color print mode, each process is executed according to the time chart shown in FIG. That is, in the same manner as described above, when the start signal (low signal) is input by pressing the print switch, the CPU 51 causes the input / output interface 52 to
Output a drive signal to a driver circuit (not shown) via
The main motor is rotated, the photosensitive drum 5 is rotated in the direction of the arrow, and the paper is carried out by the paper feed roller 12.

Further, similarly to the above, the step motors 32, 37 and the motor 55 are also started to rotate at the same time when the main motor starts to rotate. At this time, the step motor 32 stops rotating after a time t ₂ after turning on the initial setting switch 33. The position of the conveyance direction switching roller 13 when the step motor 32 stops rotating is the position shown in FIG. That is, this time t ₂ is the time required to rotate the transport direction switching roller 13 from the initial setting position shown in FIG. 9 to the position shown in FIG. Further, the step motor 37 rotates until the above-mentioned convex portion 37b 'presses the switch 39b and a high signal is input from the inverter 60 to the CPU 51. The position where the convex portion 37b 'depresses the switch 39b is a state in which the convex portions 38a', 38b 'of the cams 38a, 38b are not in pressure contact with the compression springs 36a, 36b as shown in FIG.
The a and the pressure roll 16b maintain a weak pressure contact state during idling.

After that, when the front end of the paper carried out by the paper feed roller 12 is detected by the paper detection sensor 29 as described above, a vertical synchronization signal is output, and a video signal is output from the I / F controller 53 to the video I / F 47. It In addition, the paper detection sensor 29
A bias voltage (-voltage) is applied to the developing roller 8a of the first developing device 8 at the same time when the leading edge and the side edge of the sheet are detected. After that, the photosensitive surface drum 5 is exposed in the same manner as described above, and the first
While the toner image is formed by the developing device 9, the paper stands by on the standby roll 14, and when the standby roll 14 starts to rotate, the paper is sent between the photoconductor drum 5 and the transfer device 10 to form a toner image (for example, on the paper). Black toner image) is transferred to the fixing roll 16
Is heat fixed in. At this time, since the heat roll 16a and the pressure roll 16b are in weak contact with each other as described above, the unfixed toner on the paper is not completely fixed on the paper, but the contact pressure is weak,
The paper is sent to the conveyance direction switching roller 13 without causing wrinkles or the like on the paper. Since the conveyance direction switching roller 13 is set to the position shown in FIG. 13 as described above, the paper reaching the paper guide opening 13a ″ is set in the paper guide groove 13a → the paper guide opening 13
It is guided to the guide plate 24 via a '. After that, the paper is further carried by the carrying roll 25 and carried to the intermediate tray 26. The paper transported to the intermediate tray 26 is further transported by the transport roll.
It is conveyed upward by 27 and reaches the sheet detection sensor 29 again via the guide plate 28.

In the 2-color print mode, the print start signal output to the CPU 51 again becomes low level and the CPU 5
1 again outputs the rotation start signal to the above step motors 32 and 37, and resets the position of the transport direction switching roller 13 and the pressure contact state of the fixing roll 16. That is, the step motor 32 rotates, and stops the rotation at time t after _one after turning on the initial setting switch 33. The position of the conveyance direction switching roller 13 when the step motor 32 stops rotating is the position shown in FIG.

Further, the step motor 13 rotates until the above-mentioned convex portion 37b 'depresses the switch 39a and a high signal is input from the inverter 59 to the CPU 51. The position where the convex portion 37b 'depresses the switch 39a is in a state where the heat roll 16a and the pressure roll 16b are in strong pressure contact with each other as described above.

After that, the video signal from the I / F controller 53
Output to / F47, and at the same time when the paper detection sensor 29 detects the leading edge of the paper, a bias voltage (-
Voltage) is applied. At this time, the position of the side edge of the paper is also detected as described above, and the side edge data obtained here is output to the left and right edge print area control unit 48, and the side edge data obtained when printing the first color and this side The amount of misalignment of the sheet is corrected from the edge data.

FIGS. 14 (a) and 14 (b) are diagrams for explaining this, and FIG. 14 (a) shows the positional relationship between the LEDs 40a to 40p and the paper in the printing of the first color, and the LED 40a in the printing of the second color.
The positional relationship between .about.40p and the paper is shown in FIG. Here, the side edge data obtained for the first color is A, and the side edge data obtained for the second color is B. From the figure, the paper passage position is deviated from the first color passage position A ′ to the position A ″ on the right side. In this case, the video data output for each line in the second color is corrected, for example, by shifting it to the right side of the AB (x) dot for output, and the control for obtaining the same margin width M _L is performed. .

The print head 7 performs exposure based on the video data whose displacement amount has been corrected in this manner. And
The toner image of the second color (for example, a red toner image) adhered on the photosensitive surface by the print head 7 and the second developing device 9 is transferred onto the paper by the transfer device 10 and is completely heat-fixed by the fixing roll 16 which is in strong pressure contact. . At this time, the toner of the first color is also completely fixed on the paper. After that, the paper is transferred to the transfer direction switching roller 13
11 is set to the position shown in FIG. 11, so that the conveyance roll is guided to the guide plate 19 through the paper guide port 13a ′ → the paper guide groove 13a → the paper guide port 13a ″, and further rotates as described above. It is further conveyed in the guide plate 19 by 18,
The paper is discharged to the FD tray 17 by the paper discharge roll 20. afterwards,
The output of the bias voltage applied to the developing roll 9a is stopped, and the strong pressure contact between the heat roll 16a and the pressure roll 16b is also controlled to the weak pressure contact during idling.

Finally, a case where double-sided printing is performed and the paper is discharged to the FD tray 17 (hereinafter referred to as a double-sided print mode) will be described.

In this case, when the print switch is pressed after the printer 1 is set to the double-sided print mode by the mode setting key (not shown), each process is executed according to the time chart shown in FIG. That is, similarly to the above, when the start signal (low signal) is input by pressing the print switch, the CPU 51 rotates the main motor and causes the paper feed roller 12 to carry out the paper.

Further, similarly to the above, the rotation of the main motor is started at the same time as the rotation of the step motors 32, 37 and the motor 55, and the time t ₁ is set after the initialization switch 33 of the step motor 32 is turned on.
After that, the rotation is stopped and the state shown in Fig. 11 is set. Also, the step motor 37 is the same as in the two-color mode described above, and the heat roll 16
The pressure a and the pressure roll 16b are controlled so as to be in a weak pressure contact state.
Further, the motor 55 also starts to rotate according to the control signal input to the driver circuit 58, and causes the transport roll 18 to rotate forward.

After that, when the front end of the paper carried out by the paper feed roller 12 is detected by the paper detection sensor 29 as described above, a vertical synchronization signal is output and a video signal is output from the I / F controller 53 to the video I / F 47. To be done. In addition, the paper detection sensor 2
At the same time when the leading edge of the paper 9 is detected, the developing roll 8 of the first developing device 8
A bias voltage (-voltage) is applied to a.

After that, the standby roll 14 stands by for a predetermined time, and when the paper is conveyed again, the paper is sent between the photoconductor drum 5 and the transfer device 10, the toner image is transferred onto the paper, and the fixing roll 16 thermally fixes it. At this time, since the heat roll 16a and the pressure roll 16b are in weak pressure contact with each other as described above, the unfixed toner on the paper is not completely fixed to the paper, but the press contact force is weak, so wrinkles may occur in the paper. Instead, the paper is sent to the transport direction switching roller 13.

Since the conveyance direction switching roller 13 is set to the position shown in FIG. 11 as described above, the sheet is guided to the guide plate 19 through the sheet guide groove 13a → the sheet guide port 13a ″. When the sheet is conveyed upward by 18 and the trailing edge of the sheet is detected by the sheet detection switch 31, the rotation direction of the motor 55 is reversed after a predetermined time as shown in the time chart of Fig. 15. The step motor 32 is also It is rotationally driven and stopped ₃ hours after turning on the initial position detection switch 33 to bring the conveyance direction switching roller 13 to the state shown in Fig. 16. Therefore, the paper in the guide plate 19 is fed backward and conveyed. Paper is sent to the switching roller 13 and the paper guide opening 13a 'is turned to the paper guide groove 13a.
→ It is conveyed to the intermediate tray 26 through the paper guide port 13a ″. The sheet conveyed to the intermediate tray 26 is further conveyed to the conveyance roll.
It is conveyed upward by 27 and reaches the sheet detection sensor 29 again via the guide plate 28.

In the double-sided print mode, the print start signal goes low again as in the two-color print mode.
The CPU 51 outputs the control signal to the above step motors 32 and 37 again to reset the position of the transport direction switching roller 13 and the pressure contact state of the fixing roll 16. That is, after rotating the step motor 32 and turning on the initial setting switch 33, the rotation is stopped after time t ₁ , and the position of the conveyance direction switching roller 13 when the step motor 32 stops rotating is set to the state shown in FIG. To do.

Further, the step motor 37 is also rotated until the above-mentioned convex portion 37b 'pushes down the switch 39a to bring the heat roll 16a and the pressure roll 16b into a strong pressure contact state. Further, the motor 55 also starts to rotate according to the control signal input to the driver circuit 58, and causes the transport roll 18 to rotate forward.

Thereafter, a video signal is output from the I / F controller 53, and a bias voltage (-voltage) is applied to the developing roller 8a of the first developing device 8 at the same time when the leading edge and the side edge of the sheet of the sheet detecting sensor 29 are detected. Then, the print head 7 and the first developing device 8
As a result, the second toner deposited on the photosensitive surface is transferred onto the sheet by the transfer device 10 and is completely thermally fixed by the fixing roll 16 which is in strong contact with the sheet. In this case, the second toner image is printed on the surface opposite to the surface on which the first toner image is applied, from the above-described sheet conveyance path. Then, the first toner image is also completely fixed on the sheet at this time. afterwards,
The paper is guided to the guide plate 19 through the paper guide port 13a 'of the transfer direction switching roller 13 → the paper guide groove 13a → the paper guide port 13a ″, and further inside the guide plate 19 by the transfer roll 18 which rotates in the forward direction as described above. Is discharged to the FD tray 17 by the paper discharge roll 20. After that, the output of the bias voltage applied to the developing roll 9a is stopped, and the heat roll 16
The high pressure contact between a and the pressure roll 16b is also controlled to be the weak pressure contact during idling.

As described above, in the printer 1 of this embodiment, when the same sheet is conveyed twice through the fixing roll 16 in the two-color print mode and the double-sided print mode, the step motor 37 is controlled to control the first color (or the first color). At the time of printing, the heat roll 16a and the pressure roll 16b are put into a weak pressure contact state, and 2
Both rolls 16a, 16b when printing the color (or second time)
Is a technique in which the toner images of two colors or both sides are reliably fixed and the wrinkles are not generated on the paper by making the state of strong pressure contact (predetermined pressure contact state).

In this embodiment, the case where the paper is discharged to the FU tray 21 is not described, but in this case, the conveyance direction switching roller 13 is set to the initial setting position (state of FIG. 9) and the paper is discharged. Just paper.

[Advantages of the Invention] As described in detail above, according to the present invention, even when the same sheet is fixed twice, since the fixing is performed with a strong pressure only during the second fixing, the sheet is wrinkled. Does not occur.

Further, since the roll in the fixing device is not in pressure contact with a predetermined pressure (strong pressure contact) except during the second fixing, deterioration of the roll is delayed and the life of the fixing device can be extended.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of the printer device of this embodiment, FIG. 2 is a cross-sectional view of the transport direction switching roller, and FIG. 3 is a perspective view of the transport direction switching roller used in the printer device of this embodiment. FIG. 5 is a perspective view of a fixing roll used in the printer device of the present embodiment, FIG. 5 is a configuration diagram of the paper detection device, FIG. 6 is a schematic sectional view of FIG. 5, and FIG. 7 is a printer of the present embodiment. FIG. 8 is a circuit block diagram of the apparatus, FIG. 8 is a circuit diagram of various sensors / load circuits, FIG. 9, FIG. 11, FIG. 13 and FIG. 16 are diagrams for explaining the setting position of the conveyance direction switching roller, and FIG. , FIG. 12 and FIG. 15 are time charts showing the operation timing of the printer apparatus of the present embodiment, and FIGS. 14 (a) and 14 (b) are diagrams for explaining misregistration correction of paper. 1 ... Printer, 2 ... Image forming device, 4 ... Paper transport mechanism, 16 ... Fixing device, 16a ... Heat roll, 16b ... Pressure roll, 34a, 34b ... Bearing, 35a, 35b ... Lever, 35a ′, 35
b ′ …… hole, 36a, 36b …… spring, 37 …… step motor,
37a ... Rotation axis, 37b ... Disc, 37b '... Convex part, 38a, 38b
...... Cam, 38a ', 38b' ...... Convex part, 39a, 39b ...... Switch, 54 ...... Printer controller, 59,60 ...... Inverter.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location G03G 15/20 107 109 (56) References JP-A-55-15122 (JP, A) JP-A-SHO 56-106267 (JP, A) JP 58-87564 (JP, A) JP 59-57260 (JP, A) JP 60-103377 (JP, A) JP 55-35504 (JP, A) JP 60-164769 (JP, A) JP 61-62066 (JP, A) JP 61-174576 (JP, A) JP 60-142373 (JP, A) JP 63 -182683 (JP, A) JP-A 63-206789 (JP, A) JP-A 60-150072 (JP, A) JP-A 60-44062 (JP, A) JP-A 58-169169 (JP, A) )

Claims (1)

[Scope of utility model registration request] 1. A charging unit, an exposing unit, a developing unit, and a transferring unit are arranged around an image carrier, and a sheet having an unfixed image is conveyed between a pair of rolls, at least one of which is heated, and the unfixed sheet on the sheet is undecided. In an image forming apparatus for fixing the deposited toner to an intermediate tray in the machine and forming an image again on the sheet fed from the intermediate tray, a sheet side edge detecting means for detecting the side edge in the traveling direction of the sheet. A print position control means for controlling the side edge print position of the paper by the exposure means based on the output of the paper side edge detection means, and a pressure between the rolls in the first fixing
An image forming apparatus comprising: a control unit configured to weaken the pressure between the rolls in the second fixing.