JPS624714B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a copying apparatus having a fixing device that fixes a toner image by sandwiching and conveying a toner image support material between a pair of rollers.

For example, in an electrophotographic copying machine, first and second rollers (at least one of which is heated from the inside or outside, and at least one of which is covered with a releasable elastic material such as silicone rubber) A fixing device is often used, which grips and conveys a toner image support material, heats and melts the toner, and fixes the toner onto the support material. However, if the two rollers are kept in pressure contact with each other at all times, the surface of the roller coated with a heat-resistant release material such as silicone rubber will change due to heat and pressure. For this reason, it is well known in the prior art to prevent deformation of the roller by releasing the pressure upon completion of a set copying cycle.

However, since this pressure release is performed at the same time as the conventionally set copy cycle ends, the frequency or number of pressurization and release operations is high. In particular, when single copies are made repeatedly while replacing originals one after another, mechanical noise is generated due to the repetition of pressure release and pressure application during each copying cycle.Today, there is a desire for a quieter electrophotographic copying machine as an office machine. Contrary to.

In addition, in order to prevent the fixing performance from deteriorating even when pressurizing and releasing operations are performed frequently as described above, mechanical durability must be considered, which not only requires a large-scale configuration but also requires a pressure mechanism. The parts used for this also tend to be expensive in terms of durability.

The main objective of the present invention is therefore to overcome the above-mentioned disadvantages. Here, the copying apparatus of the present invention is a copying apparatus having a fixing device which is a pair of rollers that are selectively pressurized and released, and which fixes a toner image on a supporting material when the pressure is applied. means for maintaining the pressurized state of the pair of rollers for a predetermined period of time even after the end of the set copying cycle; The next copying cycle is started while maintaining the pressurized state of the roller pair, but if the next copying cycle start signal is not given within the predetermined time, the pressurized state of the roller pair is released after the elapse of the predetermined time. It is characterized by the fact that it is made to do so. As a result, the above-mentioned noise can be reduced, and the durability of the fixing device can be easily improved, making it possible to obtain good quality copied images over a long period of time.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram of an example of an electrophotographic copying apparatus to which the present invention can be applied. Reference numeral 1 denotes a drum having an electrophotographic photoreceptor 1' having a conductive layer, a photoconductive layer, and a transparent insulating layer laminated in this order on its circumferential surface, and is driven to rotate in the direction of the arrow. As it rotates, photoreceptor 1' is pre-exposed with lamp 2 to erase the photohistory of said photoconductive layer. Simultaneously with this pre-exposure, the surface of the photoreceptor is neutralized by an AC corona discharger 2'. The photoreceptor 1' is then charged by a DC corona discharger 3 according to the characteristics of said photoconductive layer, and then charged by an AC or discharger 3 of opposite polarity.
At the same time, it receives a corona discharge from the DC corona discharger 4 and, at the same time, receives optical image exposure of the original 7 placed on the original platen 6 via the lens 5. The document table 6 moves in the direction of the arrow in synchronization with the rotation of the drum 1, whereby the document 7 is scanned while being illuminated by the lamp 6', but when scanning is completed, the document table 6 moves in the opposite direction to the arrow. and return to the home position. In any case, a charge pattern corresponding to the original is formed on the photoreceptor by the above-mentioned light image exposure, but the photoreceptor 1' is further uniformly exposed over the entire surface by the lamp 8, and thus the photoreceptor has a high contrast electrostatic potential. An image is formed.
As the drum 1 rotates, the latent image is transferred to the developing device 9.
The toner image thus formed is transferred onto a transfer paper 11 under the action of a corona discharger 10 which attracts the paper 11 to the photoreceptor 1'. The transfer paper 11 is taken out from the cassette 12 by a roller 13, conveyed by a pair of register rollers 14 in synchronization with the rotation of the drum 1, and brought into alignment with the toner image on the photoreceptor 1'. After the transfer, the transfer paper is separated from the photoreceptor 1' by the separation means 15, guided by the guide 16, and reaches the fixing device. On the other hand, after the transfer, the photoreceptor 1' is cleaned of residual toner by a cleaning device 17.

The fixing device has two rollers 18 and 19. The roller 18 is a fixing roller with which the toner image surface of the transfer paper is pressed, and is a tubular metal roll coated with a thin coating of tetrafluoroethylene resin, silicone rubber, or the like. A heater 20 is installed in the hollow of this roller 18.
is arranged to heat the circumferential surface of the roller 18 to a temperature at which the toner can be melted and fixed onto the support paper 11. 21 is roller 1 to prevent toner from adhering.
8. This is a means of applying an offset prevention liquid such as silicone oil to the circumferential surface. Roller 19 is transfer paper 1
1 is pressed against the roller 18, and is made of a metal core roll covered with a thick silicone rubber layer.
When pressurized by the roller 18, it deforms elastically as shown in the figure.
Forms a nip that pinches the transfer paper. In this fixing device, a fixing roller arranged at a fixed position is rotationally driven by a main motor (not shown), and a pressure roller is driven to rotate by frictional force. The transfer paper 11 sent from the drum 1 by rotation in the direction is conveyed by both rollers under pressure, and at this time, the toner image is transferred to the transfer paper 1.
Melt and fix on 1. Reference numeral 22 is a claw-like member that contacts the roller 18 and reliably separates the transfer paper that has passed through the nip portion from the fixing roller 18. roller pair 18,
The transfer paper that has passed between the rollers 19 and 23 then passes through the pair of ejection rollers 23.
is discharged onto the tray 24.

In the copying apparatus described above, the drum 1 and the rollers 18 and 23 are rotationally driven by the same main motor via a power transmission mechanism composed of a gear train, a chain sprocket mechanism, etc., and while the motor is rotating, That is, while the drum 1 is rotating, the rollers 18, 2
3 always rotates, and when the motor stops rotating, that is, when the drum 1 stops rotating, the rollers 18 and 2 rotate.
3 also appears to have stopped rotating. On the other hand, the document table 6 and rollers 13 and 14 are also driven by the motor via a power transmission mechanism composed of a gear train, a chain sprocket mechanism, etc., but in this case, a clutch is provided in the power transmission mechanism. Under the control of this clutch means, the platform 6 and rollers 13 and 14 are driven at predetermined timings relative to the rotation of the drum 1. The motor starts rotating in response to a copy start signal obtained by the operator pressing a copy button provided on the operation panel. Rotation stops at the end of the copy cycle. The time length of one copy cycle can be easily set using a timer.

One copying cycle of the apparatus shown in FIG. 1 consists of the following steps. When the copy button is turned on, the main motor starts rotating and the drum 1 starts rotating, but at this time the platform 6 has not yet started moving and the lamp 6' remains off. However, lamp 2,
8 and the lamp 25 that illuminates the photoreceptor through the slit of the charger 4 in the same way as the imaging light beam of the original is turned on.
Corona dischargers 2', 3, and 4 also discharge. This erases the residual charge on the photoreceptor 1', erases the optical memory of the photoconductive layer, lowers the resistance value, and optimizes and stabilizes the sensitivity of the photoreceptor. The above preparatory process prior to latent image formation is performed by rotating the drum 1 a predetermined number of times. This is called forward rotation of the drum 1. During the pre-rotation of the drum 1, the roller 13 operates to transport the transfer paper to the register roller 14 position and stop it there.

When the previous rotation of the drum 1 is completed, the lamp 25
is turned off, the lamp 6' is turned on, the table 6 starts moving, and a copy image is obtained by the above-described steps.

Even after the transfer of the toner image is completed in the transfer process and the trailing edge of the transfer paper is separated from the photoreceptor, the drum 1 continues to rotate a predetermined number of times. This is called post-rotation of the drum. Lamps 2 and 8 remain lit during the subsequent rotation, and before the start of the post-rotation, the table 6 enters the double movement process and the lamp 6' is extinguished, and the lamp 25 is lit instead. . At the same time, each discharger 2', 3, and 4 continues discharging. By this post-rotation, the photoreceptor 1' is subjected to post-processing after image formation.
It is electrostatically cleaned. Before the end of the post-rotation, the paper supporting the fixed toner image is discharged onto the tray 24 by the roller 23. When the drum 1 has rotated a predetermined number of times, the motor stops. At this time, the lamps 2, 8, and 25 are also turned off, and each corona discharger also stops discharging. (Part 2 above)
See diagram. The solid lines in the figure indicate the time during which each means is in operation. ) In the case of so-called multi-copying, in which multiple copies are made consecutively from one original, after the drum front rotates,
The processes of latent image formation, development transfer, and fixing are repeated a number of times set by the operator, and after the last transfer is completed, the drum rotates backward as described above to complete the copying cycle. It is. The steps involved in copy image formation, whether single copy or multi-copy, as described above, are well known.

Now, as described above, the roller pair of the fixing device, especially the roller 19, is elastically deformed when pressed by the roller 18. If this pair of rollers is constantly pressurized, the roller 19 will suffer permanent deformation as described above, which will hinder fixing. For this reason, in the past, the pressure on the rollers 18 and 19 was released and they were separated from each other at the same time as the end of the set copy cycle, that is, the end of the post-rotation of the photoreceptor, but this caused noise as described above. Moreover, in order to prevent breakdowns, the mechanical strength of parts had to be increased, leading to increased costs. Therefore, in the apparatus shown in FIG. 1, the roller pair 18, 19 is pressurized and released as follows.

First, reference numeral 26 in FIG. 1 is an arm that rotatably supports the roller 19. This arm 26 is fixed to a shaft 27, and by rotating this shaft by a predetermined angle clockwise in the figure, the arm 26 presses the roller 19 against the roller 18 against the tension spring 28. The shaft 27 is fixed in this state, and when this fixation is released, the arm 26 is rotated counterclockwise in the figure by the force of the spring 28, and the roller 19 is rotated counterclockwise in the figure.
distance from.

A mechanism for pressurizing the roller 19 against the roller 18 and releasing the pressure will be described below with reference to FIGS. 3, 4, and 5. FIG. 3 shows the pressurization being released, FIG. 4 the pressurization operation in progress, and FIG. 5 the pressurization in progress.

When the copy button is turned on, the shaft 29 is rotationally driven by the main motor via a chain sprocket mechanism, and a gear 30 connected to this shaft via a spring clutch is rotated in the direction of arrow a. Rotate in the direction of arrow b.
As the pressure lever 32 rotates, the pressure lever 32 is rotated clockwise around the rotation center 27 by being pushed by a pressure roller 34 implanted in a notched disk 33 fixed to the gear 31. First, the fixing device lever 35 shown by the two-dot chain line in the figure is rotated clockwise to apply pressure to the fixing device pressure roller 19 (not shown). That is, the above-mentioned lever 3 is attached to the shaft 27 in FIG.
5 is fixed, and this lever 35 has a roller 3.
6 is implanted, and this roller 36 is pushed by the pressure lever 32 and rotates clockwise. A pressure lever 32 is loosely fitted to the shaft 27.
It also serves as the center axis of rotation. On the other hand, the stopper lever 38, which rotates around the shaft 37, is given a clockwise rotational habit by the spring 39, but when the copying switch is turned on, the plunger 40 is actuated, and the lever 38 is rotated by the spring 39. It rotates counterclockwise by a predetermined angle against the force. As a result, a stopper roller 44, which is rotatably connected to the lever 38 by a shaft 41 and implanted in an arm 43 biased counterclockwise by a spring 42, is brought to a predetermined locking position. As the pressure lever 32 rotates as described above, the stopper roller 44 is caught on the hook portion of the pressure lever 32, and the pressure lever 32 is rotated.
is fixed at the position shown in FIG. 5, and the fixing device lever 35 is also fixed, so that the pressure roller 19 of the fixing device remains pressed against the fixing roller 18. Reference numeral 45 designates a clutch controller for disconnecting and connecting the aforementioned spring clutch, which is rotatably supported by a shaft 46 and given a clockwise rotational tendency by a spring 47. A clutch release pawl 48 and a leaf spring 49 are fixed to the controller 45. Further, the pressure lever 32 and the clutch controller 45 are connected to the control arm 5.
After the pressure lever 32 is fixed as described above, the clutch controller 45 is actuated to turn off the spring clutch and the shaft 29 is connected to the shaft 29.
Although the rotation of the main motor is transmitted to the main motor, the gear 30 and therefore the gear 31 are prevented from rotating. This maintains the pressure applied to the rollers 18 and 19. The timing of the operation of this clutch controller 45 is determined by a control plate 33 attached to the gear 31.
controlled by The leaf spring 49 of the clutch controller 45, which is rotated clockwise by a torsion spring 47, falls into the notch of the control plate 33, and the pawl 48 at the other end stops the spring clutch control ring (not shown) and locks the spring clutch.
Turn it off. Gear 3 after the copy button is turned on
1 rotates once and stops, but the pressure applied by the rollers 18 and 19 has been completed before that stop. Furthermore, gear 3
0 and 31 stop rotating, but the main motor is rotating, which drives the fixing roller 18 to rotate, and the pressure roller 19 that is in pressure contact with the fixing roller 18.
The above-mentioned fixing process is performed because the rotation is driven.

Next, pressure release will be explained. plunger 4
0 is cut off, the coil spring 39
As a result, the stopper lever 38 is rotated clockwise about the fulcrum 37, and the stopper roller 44 is removed from the hook portion of the pressure lever 32. The pressure lever 32 detached from the stopper roller 44 has a torsion spring 3 that gives it a counterclockwise rotational habit.
5' and the fixing side pressure release spring 28, it is rotated counterclockwise, and the pressure roller 34 acts as a stopper and stops. At this time, the control arm 50 moves upward in the figure along with the movement of the pressure lever 32, disengaging the pawl 48 of the clutch controller 45 from the spring clutch, and turning the clutch into the ON state. When the _T2 brake plunger 40 is turned off, the main motor is already turned off as described below, so the gears 30 and 31 do not rotate.

Next, operation control of the plunger 40 and the main motor will be explained.

FIG. 6 is a block diagram of the control circuit, and FIG. 7 is a timing chart of drive signals for the main motor M and plunger 40. Reference numeral 51 in FIG. 6 is a copying machine control circuit, which generates a main motor drive signal and drives the main motor M by a main motor drive circuit 52 when the copy button B is turned on. Further, 53 is a delay circuit that receives a main motor drive signal from the circuit 51 and generates a plunger drive signal to be described later, and transmits the drive signal to the plunger drive circuit 54 to operate the plunger 40. The timing of the signals generated by the circuits 51 and 53 is as shown in FIG. That is, the circuit 51 calculates the time required from the time _T1 when the copy button is turned on to the time _T2 when the copying cycle corresponding to the set number of copies is completed, whether it is single copy or multi-copy, that is, the time required before the drum Rotation is started, the number of copies set by the operator is completed, and a time signal required for the end of the drum's subsequent rotation is oscillated. (Signal A) However, although the circuit 53 is the same as the circuit 51 when the signal oscillation starts, the end of the signal oscillation is delayed from that of the circuit 51, and the timing
It is _T3 . (Signal B) By the way, the main motor M stops at time _T2 , and therefore the drum 1 and the fixing and pressure rollers 18 and 19 also stop rotating. However, since the plunger 40 continues to operate until time _T3 , the pressurized state of the rollers 18 and 19 is maintained even if the main motor is stopped. The time from this point _T2 to _T3 , that is, the time during which the pressurized state of the rollers 18 and 19 is maintained after the end of the copying cycle, is set to a constant time within the range of 5 to 30 seconds, preferably 10 to 20 seconds. be done. This is because it is known from experience when using a copying machine that the time for exchanging originals on the original table is within the above-mentioned fixed time. In any case, even if the copying cycle has ended within the above time t, the roller pair 1
8 and 19, the pressure remains pressurized without being released, so if the original is replaced and the next copy is made during that time, mechanical noise is often generated when the pressure is released or when the pressure is applied, as in the past. It is possible to continue the copy operation without any problems.
Furthermore, the durability of pressure mechanisms or pressure release mechanisms that normally use mechanical parts such as cams and springs decreases each time the mechanism operates, but the above-mentioned As shown in FIG.
Although rollers 8 and 19 are in pressure contact, they are not rotating, so there is no effect on the durability of the rollers, and due to idle rotation, excessive silicone oil is applied to the roller 18, which may stain the paper or damage the silicone oil. Of course, inconveniences such as swelling of the rubber roller and increased oil consumption can also be prevented. It goes without saying that the above-mentioned fixed time t is within a time period in which permanent deformation of the releasable elastic material such as silicone rubber constituting the roller surface cannot occur.

[Brief explanation of the drawing]

FIG. 1 shows a copying apparatus to which the present invention can be applied, FIG. 2 shows a copying cycle, FIGS. 3, 4, and 5 show a roller pressure mechanism, FIG. 6 shows a control circuit, and FIG. 7 shows signal timing. FIG. 18 is a fixing roller, 19 is a pressure roller, 40 is a plunger, 51 is a control circuit, 53 is a delay circuit, and M is a main motor.

Claims (1)

[Scope of Claims] 1. In a copying machine having a fixing device which is a pair of rollers that selectively apply and release pressure, and which fixes a toner image to its support material when the pressure is applied, comprising means for maintaining the pressurized state of the pair of rollers for a predetermined period of time even after the set copying cycle ends;
If a start signal for the next copying cycle is given within the predetermined time after the copying cycle ends, the next copying cycle starts while maintaining the pressurized state of the pair of rollers, but the next copying cycle does not start within the predetermined time. A copying apparatus characterized in that, if a cycle start signal is not given, the pressurized state of the pair of rollers is released after the predetermined time has elapsed. 2. The copying apparatus according to claim 1, wherein the pair of rollers is stopped from rotating after a set copying cycle is completed, and the pressurized state is maintained for a predetermined period of time in this stopped rotation state. 3. The copying apparatus according to claim 1 or 2, wherein the predetermined time is 5 to 30 seconds.