JPH0697363B2 - Color copier - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color copying machine, and more particularly to a color copying machine capable of excellent color copying even on an OHP sheet used in an overhead projector (OHP).

Conventional technology In a general copying machine using xerography,
An electrostatic latent image formed by exposure on a uniformly charged photoreceptor is developed into a toner image, and the toner image is transferred and fixed on an appropriate transfer material to obtain a copy. Of these series of steps, exposure is performed a plurality of times through a spectral means such as a color filter, and each latent image is developed with a developer containing a toner of a color corresponding to the spectral means. A color copy is obtained by multiple transfer onto the above. In a practical color copying machine, a transfer drum is used for multiple transfer, the transfer material is once carried on this transfer drum, and the toner image on the photoconductor is in the same position on the transfer material. Rotate in synchronization so that they overlap. Then, the transfer material onto which the toner images of the respective color components have been transferred in multiples is sent to the fixing device by a conveying means such as a suction belt,
It is fixed by heat, pressure, etc.

On the other hand, in recent years, OHP that projects an image drawn on a transparent film-like OHP sheet on a screen has been used in various fields, and it is possible to copy an original image such as a printed matter on the OHP sheet. Copiers that can be used are also in practical use.

Problems to be Solved by the Invention However, when an OHP sheet is used as a transfer material for a color copying machine, the heat capacity, the wettability to molten toner, and the like are different from those of ordinary paper, which may not be fixed properly. It was necessary to change the fixing conditions depending on whether the paper is a sheet or an OHP sheet. Therefore, for example, when using a fixing device of a type in which a transfer material is nipped and conveyed between a heat roller and a pressure roller that rotate while being in pressure contact with each other, the fixing condition can be changed by changing the rotation speed. There is.

Specifically, for example, the rotation speed of the transfer drum is always constant, and in the case of an OHP sheet, the driving speed of the conveying means and the fixing device which are interlocked with each other is set to one-sixth to one-fifth that of ordinary paper. It is slowing down. Therefore, if the timing of this deceleration is too early, the transport speed of the transport means is lower than the rotational speed of the transfer drum, so that the constituent members of the transfer drum catch up with the trailing end of the transfer material and collide there, causing a failure before fixing. The toner image was sometimes disturbed (smear). On the contrary, if the timing of deceleration is too late, the leading edge of the transfer material may pass through the fixing device without deceleration, and the portion may not be fixed well.

These problems are caused by simply increasing the length of the conveying path from the transfer drum to the fixing device, that is, the above-mentioned conveying means, or by using the heat generation variable type fixing device for any transfer material. This can be solved by keeping the fixing speed constant, but there is a problem in terms of downsizing of the apparatus or energy saving.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a color copying machine which does not cause the above-mentioned problems even if the conveying means has a limited length.

According to the present invention, a transfer drum that rotates in synchronism with a photoconductor while holding a transfer material, a fixing device that fixes a toner image transferred on the transfer drum onto the transfer material, In a color copying machine, the transfer material is conveyed from the peeling position of the transfer drum to the fixing device at the same speed as the transfer material passes through the fixing device. Detecting means for detecting the passage of a portion, and the fixing device and the conveying means after a predetermined time has elapsed from the time when the detecting means detects the passage of the specific portion a predetermined number of times after the transfer material is held on the transfer drum. The transfer drum further comprises a control means for reducing a driving speed of the cylindrical drum, and the transfer drum has a cylindrical drum and an end portion of which is fixed to a holding body fixing portion provided on the cylindrical drum. A transfer material holder wound around the transfer material holder, and the driving speed starts to decrease before the trailing edge of the transfer material passes through the peeling position for the predetermined time, and the holder fixing portion. Is provided so that the rear end of the transfer material passes through the peeling position before catching up with the rear end of the transfer material.

According to a preferred embodiment of the present invention, a protrusion is formed at a side end portion of the transfer drum to form a specific portion, and a photocoupler is provided at a position where the optical path is blocked by the passage of the protrusion to serve as a detection unit.

Action The transfer drum also starts to rotate with a series of operations for forming a toner image on the photoconductor, and the transfer material is carried on the transfer drum. The toner images on the photoconductor are sequentially and multiple-transferred onto the transfer material as the transfer drum rotates, and during this time, the rotation of the transfer drum is detected by the detecting means. When the transfer drum is rotated by a predetermined number of revolutions and the transfer is completed, the transfer material is conveyed to the fixing device by the conveying means so that the formed toner image is not disturbed,
It is fixed by heat. In the present invention, as described above, the fixing device and the transporting device are decelerated at a predetermined timing based on the detection of the specific portion of the transfer drum by the detecting device. Further, among the setting modes of this timing, the reduction of the driving speed is started before the trailing edge of the transfer material passes through the peeling position, whereby the conveying means can be configured to be short. In addition, since the trailing edge of the transfer material passes through the peeling position before the holding portion of the transfer drum catches up with the trailing edge of the transfer material, the image due to the collision between the holding portion of the holding member and the trailing edge of the transfer material can be obtained. Disturbance can be prevented.

Embodiments Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

Referring to FIG. 3, there is shown a color copying machine constructed by applying the present invention, which is an original table 2 made of transparent glass or the like.
When a document is placed on the upper surface of the document and the document cover 4 is set to start the copying operation, the exposure lamp 6 including a halogen lamp or the like starts scanning and exposing the document. The light emitted from the exposure lamp 6 to the original directly or through the reflector 8 becomes light corresponding to the original image and is reflected by the lens system 16 and further the reflecting mirrors 18, 20 via the reflecting mirrors 10, 12, 14. Then, it is sent to the spectral filter 22. In this case, the exposure lamp 6, the reflector 8, and the reflecting mirror 10 move to the right in the figure, and the reflecting mirrors 12 and 14 also move to the right at a speed half the moving speed of the reflecting mirror 10. . Therefore, during scanning exposure, the optical path length from the document surface to the lens system 16 is kept constant.

In the spectral filter 22, of the blue, green, and red filters 22a, 22b, and 22c, first the blue filter 2
An optical image obtained by transmitting light into 2a and separating the light is reflected by the reflecting mirror 24 and sent to the photosensitive drum 26. The photosensitive drum 26 having a surface made of a photoconductive material forms an optical image from the spectral filter 22 while rotating clockwise in the figure after the surface is uniformly charged by the charging corotron 28, and the original document An electrostatic latent image corresponding to the image and the filter 22a is formed.

The electrostatic latent image formed on the photosensitive drum 26 is developed and visualized by the developing device 30 that supplies yellow toner.

Next, after performing the transfer described later, the irradiation lamp 6, the reflector 8 and the reflecting mirrors 10, 12 and 14 are reset to their original positions again, and the spectral filter 22 is set to the green filter 22b, and the same as above. By performing the scanning exposure of, an electrostatic latent image is formed on the photosensitive drum 26.
The latent image is developed and visualized by the developing device 32 that supplies magenta toner.

Similarly, at the time of the third scanning exposure, the developing device 3 is switched to the red filter 22c to supply the cyan toner.
4 is set to work.

On the other hand, the transfer material (not shown) placed on the paper feed tray 36 is sent to the inside of the copying machine by the feed roller 38, and after being accurately timed by the registration roller 40, on the rotating peripheral surface of the transfer drum 42. The tip of the gripper 44 is sandwiched by a plurality of grippers 44 provided in the width direction.

The transfer drum 42 has a structure as shown in FIGS. 4 and 1, for example, and 62 is a cylindrical drum having a shape in which a side surface of a cylindrical member made of a conductor such as aluminum is cut away. . The cylindrical drum 62 has a flange that forms its side end.
621 and a tie bar 6 formed between the flange pair
22 and a bearing member 623 for rotatably supporting the shaft. A plurality of grippers 44 are provided near the edge of the tie bar 622 in the longitudinal direction, and sandwich the end of the transfer material by the action of a biasing member (not shown). Reference numeral 64 denotes a transfer material holder that is wound and stretched between a pair of flanges 621 from an edge of the tie bar 622 on the side where the flipper 44 is formed to a groove 624 formed on the opposite side, and the cylindrical drum 62. Together with this, the transfer drum 42 is configured. The transfer material holder 64 is formed by knitting a polymeric resin material such as nylon into a fiber or forming it into a sheet so that the discharge of the transfer corotron 50 or the like provided in the transfer drum can reach the transfer material well. ing. In this example,
The groove portion 624 of the cylindrical drum 62 corresponds to the holding body fixing portion described above. When the end portion of the transfer material holding body 64 is fixed to the cylindrical drum 62 by using an adhesive tape, a clip or other members without forming the groove portion 624 in the cylindrical drum 62, the member is the holding member. It corresponds to the fixed part.

The gripper 44 is a cam 46 provided inside the transfer drum 42.
And 48 are opened when they are in contact with the cams 48 and 48, and they are closed when they are disengaged from the cams. Further, the cams move inward of the transfer drum 42 so as not to act on the gripper 44 if necessary. Has become. 625 is a protrusion formed at the end of the flange, and the rotational position of the transfer drum is made clear by being detected by the detecting means described later.

The transfer material whose tip is gripped by the gripper 44 is held so as to be wound around the transfer drum as the transfer drum 42 rotates. Next, a transfer corotron provided inside the transfer drum 42 at a position facing the photosensitive drum 26.
When the transfer material passes between the photosensitive drum 26 and the photosensitive drum 26, the yellow toner image formed on the photosensitive drum 26 is first transferred. The toner remaining on the photoconductor drum after transfer is removed by the cleaner 60, and after being uniformly exposed again, magenta and cyan toner images are sequentially formed on the surface of the photoconductor drum, and the toner images are transferred over the yellow toner. To be done.

Thus, the transfer material on which the toners of three colors are transferred in multiplex is gripped when the tip of the transfer material reaches the position corresponding to the cam 48.
44 is opened, the gripped state is released, and the sheet is delivered onto the transport device 52. The transfer material, which is transported to the left in the figure by the transport device 52, is fixed on the toner overlapping layer as a multiple transfer image with heat and pressure when passing through the fixing device 54 including the heat roller 541 and the pressure roller 542. It is discharged to the tray 58.

All of the above operations are controlled by a control unit (not shown). When the transfer material is a normal sheet, each device of the transfer material transport system, that is, the feed roller 38, the registration roller 40, the transfer drum 42, the transport device. The drive speeds of 52 and the fixing device 54 are set to be equal to the peripheral speed of the photosensitive drum 26.

When the transfer material is an OHP sheet, the transport device 52 and the fixing device 5
4 is designed to decelerate at a predetermined timing, and a drive mode characteristic of the present invention will be described with reference to FIGS. 1 and 2.

76 is, for example, a DC servo motor 72 and a PLL (Phase
Locked Loop) controlling motor drive unit 74, and the rotation shaft of the motor 72 is driven by the drive roller 52 of the conveyance device 52 via a reduction means (not shown) having the same reduction ratio.
1, and is connected to a heat roller 541 and a pressure roller 542 which constitute the fixing device 54. Reference numeral 68 denotes a transfer drum position sensor including a photocoupler having a light emitting means and a light receiving means, and one pulse signal is generated when the protrusion 625 formed on the flange 621 of the transfer drum passes. Reference numeral 70 denotes a control unit that controls the drive start timing and drive speed of the drive means 76, and is composed of an electronic circuit using a one-chip microcomputer or the like. The signal pulses from the sensor 68 are counted by the control unit 70, and the driving means 76 is decelerated after a predetermined time has elapsed since the signal was input a predetermined number of times. The formation position of the projection 625 is selected such that the gripper 44, that is, the tip of the transfer material passes through the sensor 68 when it reaches the vicinity of the peeling claw 66. Also, the transport device
The length of 52, that is, the pair of drive rollers 521, 521 of the conveyance device 52.
The distance between them may be sufficiently shorter than the length of the transfer material in the conveying direction, which allows downsizing of the entire apparatus.

FIG. 2 is a graph showing the timing of deceleration and the position of the OHP sheet with respect to the output signal of the sensor 68, and the vertical axis is
The passing position corresponding to the position coordinate of the transfer material on the conveying path, the driving speed, and the output level of the sensor 68 are shown, and the horizontal axis shows the elapsed time.

Now, the OHP sheet is fed in, and the tip of it is gripper 4
The first pulse is counted the first time the protrusion 625 passes the sensor 68 after being gripped at 4. At this time,
Although the OHP sheet is located at the transfer position, transfer is not yet performed in this embodiment. Then, when the second to fourth pulses are counted during three rotations and multiple transfer is performed,
The peeling claw 66 contacts the transfer drum, and the OHP sheet 72 is released from the gripper 44 to be in the state shown in FIG. This state is immediately after the fifth pulse is counted, and after the lapse of t ₁ seconds from the rising edge of this pulse, the driving means 76
Is slowed down. However, due to the inertial force of the motor 72 or the like, this deceleration is not instantaneously achieved, and the driving speed becomes a predetermined value after t ₂ . After this, the OHP sheet progresses at low speed,
Since the transfer drum 42 is rotating at the original speed, the rear end of the transfer material holder 64, that is, the groove portion 624 of the transfer drum catches up with the rear end of the OHP sheet. However, this point is a point amm rearward of the peeling point B as shown in FIG. 2, and the rear end of the OHP sheet does not hit the groove portion 624 again. In Fig. 2, the rear end of the OHP sheet is peeling point B after the fixing device is decelerated.
The period prior to the arrival of the sheet is a state in which the leading edge of the OHP sheet sent from the high-speed transfer drum is rate-controlled by the low-speed fixing device and the transport device.
The trailing edge of the sheet is slipping on the transfer drum. In the prior art, the groove portion 624 (mesh end) of the transfer drum may collide with the rear end of the OHP sheet before the rear end of the OHP sheet reaches the peeling point B. This phenomenon is caused by the present invention as described above. Is solved by.

In this embodiment, the effective diameter of the transfer drum 42 is set to 202 mm like the photosensitive drum 26, and the normal speed is 159 mm / sec. Therefore, the interval of the detection signal of the sensor 68 is 4.0 sec.
Further, t ₂ varies depending on the fixing load fluctuation and the like, but according to the experiment, it is within a range of approximately 0.28 to 0.40 seconds, for example, t ₁ is 1.
When set to 48 seconds, the distance a described above is 1.0 to 7.4 mm.

Further, in this embodiment, since the length of the conveying device 52, that is, the distance from the peeling point B to the fixing device passage point C is made as small as possible, the portion b which has passed through the fixing device before deceleration is achieved. Results in poor fixing, and this value is 9.7 to 10 under the above conditions.
It is 0 mm. However, although not shown, this copying machine is provided with an erasing means for erasing the edge 10 mm of the image, for example, an LED or the like, and since a toner image is not formed on the edge, there is no problem.

EFFECTS OF THE INVENTION As described above, according to the present invention, the driving speed of the fixing device and the conveying means starts to decrease before the trailing edge of the transfer material passes through the peeling position. Since it can be made short, and the rear end of the transfer material passes through the peeling position before the rear end of the transfer material catches up with the rear end of the transfer material, the rear end of the transfer material passes through the peeling position. The effect that the image disturbance due to the edge collision is prevented occurs.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a drive system of a conveying device and a fixing device, which are features of the present invention, and FIG. 2 is a graph showing deceleration timing and OHP sheet position with respect to an output signal of a sensor, FIG. FIG. 4 is a schematic configuration diagram of a color copying machine to which the present invention is applied, and FIG. 4 is an exploded view of a transfer drum. 26 ... Photosensitive drum, 42 ... Transfer drum, 44 ... Gripper, 625 ... Projection, 52 ... Conveying device, 54 ... Fixing unit, 70 ... Control unit, 72 ... OHP sheet, 76 ... Drive means.

Claims (1)

[Claims] 1. A transfer drum that holds a transfer material and rotates in synchronism with a photoconductor, a fixing device that fixes the toner image transferred on the transfer drum onto the transfer material, and the transfer material passes through the fixing device. In a color copying machine having a conveying unit that conveys the transfer material from the peeling position of the transfer drum to the fixing unit at the same speed as that of the detecting unit, a detecting unit that detects passage of a specific portion formed on the transfer drum. And a control means for reducing the driving speed of the fixing device and the conveying means after a predetermined time elapses after the detection means detects the passage of the specific portion a predetermined number of times after the transfer material is held on the transfer drum. The transfer drum further includes: a cylindrical drum; and a transfer material holder whose end is fixed to a holder fixing portion provided on the cylindrical drum and which is wound around the cylindrical drum. To However, during the predetermined time, the reduction of the driving speed is started before the trailing edge of the transfer material passes through the peeling position, and before the holding body fixing portion catches up with the trailing edge of the transfer material. A color copying machine, wherein the rear end of the transfer material is set so as to pass through the peeling position.