JPH0330148B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color electrophotographic copying apparatus.

There are various types of color electrophotographic copying devices, such as those using an electrostatic latent image transfer method and those using a visible image transfer method. , the color original image is separated into color components using, for example, blue, green, and red color separation filters, the photoreceptor is exposed to this color-separated light, and each static image obtained by this exposure is The electro-latent image,
A color copy image is obtained by making an image visible using yellow, magenta, and cyan color developers, which are complementary colors to each of the above colors, and sequentially overlappingly transferring this to a transfer sheet held on a transfer drum. It is something.

FIG. 1 shows an example of this type of color electrophotographic copying apparatus, and first, a copying process performed by the copying apparatus will be described. First, a color original is placed at a predetermined position on the original placing glass 1, and the original holding plate 2 is placed over it. Next, when you press the print button (not shown) on this device,
The photosensitive drum 8 begins to rotate in the direction of the arrow. Correspondingly, a holding member 5 equipped with an illumination light source 3 and a first mirror 4 is attached to a guide shaft 6.
The holding member 10 equipped with the second mirror 7 is moved on the same axis 6 in the same direction.
It moves forward with a speed ratio of 1.

As the illumination light source 3 performs illumination scanning of the document, the first mirror 4, the second mirror 7, the lens system 9, the blue separation filter 12a,
Color separation slit exposure is performed through the fourth mirror 13 and the fifth mirror 14, and the charger 15
First, an electrostatic latent image corresponding to the blue color separation is formed at a predetermined position on the circumferential surface of the photoreceptor drum which has been charged with electricity. This electrostatic latent image is immediately visualized by a developing device 16 containing yellow toner which is a complementary color to the above color.

During this time, the transfer sheet S on the paper feed tray 22 is fed from the paper feed tray 22 by the paper feed roller 23, passes through a pair of registration rollers 24, and its leading end rotates in synchronization with the drum 8 in the direction of the arrow. The tip clamper 26 on the transfer drum 25 is clamping the transfer drum 25 . The transfer sheet is squeezed by the squeezing roller 27 so as to come into close contact with the circumferential surface of the drum 25, and the tip side of the transfer sheet and the tip of the visible image forming area on the photoreceptor drum 8 mentioned above are connected to the transfer section 25. From this state, the visible image is transferred to the transfer sheet by the transfer charger 29 fixed to the drum 25. After this transfer, residual toner and residual charges on the photosensitive drum 8 are removed by a cleaning device 19 and a static elimination charger 20, respectively.

When the photosensitive drum 8 completes its first rotation, the scanning optical system consisting of the illumination light source 3, the first mirror 4, the second mirror 7, etc. is moved back to the position shown in the figure from the position where it finished its forward movement. Drum 8
As it enters its second rotation, the scanning optical system starts to move forward again, and this time, the static image on the photoreceptor drum 8 is filtered through the green color separation filter 12b, which has already been switched. An electrostatic latent image corresponding to green color separation is formed at the same position as the electrostatic latent image forming position.

The electrostatic latent image is visualized by a developing device 17 containing magenta toner having a complementary color relationship with the above color. This visible image is transferred to the transfer sheet on the transfer drum 25, which has entered its second rotation, and is superimposed on the first transferred image on this sheet. As the drum 8 enters the third rotation, an electrostatic latent image corresponding to red separation is formed at the same position on the photosensitive drum 8 via the red separation filter 12c, and this electrostatic latent image is visualized by a developing device 18 containing cyan toner having a complementary color relationship with the above color. This visible image is transferred to the transfer sheet on the transfer drum 25, which has entered its third rotation, and is further superimposed on the superimposed transfer image.

Then, the transfer sheet is released from the front end clamper 26 by suction by the separation charger 31, and is completely separated from the drum 25 by the pick-off claw 32. Thereafter, the transfer sheet is sent toward the fixing device 33, where it is fixed, and then discharged to the outside of the machine by a pair of discharge conveyance rollers 34. In the manner described above, color copies can be obtained by this copying apparatus. Note that after the third transfer, the toner and charges attached to the transfer drum 25 are removed by a transfer drum cleaning device 35 and a transfer drum static elimination charger 36, respectively. Also, regarding the photosensitive drum 8,
During the fourth rotation, the attached toner and residual charges are removed by the cleaning device 19 and the static eliminating charger 20, respectively.

As described above, in this color electrophotographic copying apparatus, the scanning optical system reciprocates three times, and the photosensitive drum 8 and transfer drum 25 each move four times.
By rotating it several times, one color copy can be obtained.

By the way, in FIG. 1, the photosensitive drum 8
and the transfer drum 25 have the same diameter,
The transfer drums 25 are designed to rotate in the direction of the arrow in synchronization with each other, and a second roller is provided on the circumferential surface of the transfer drum 25.
As shown in the figure, the transfer sheet S is wrapped around the transfer sheet S, and the peripheral surface portion corresponding to the angle θ becomes a non-image area.

On the other hand, as shown in FIG. 3, the scanning optical system is composed of an illumination light source 3, a first mirror 4, and a second mirror 7, of which the illumination light source 3 and first mirror 4 are integrated. Similarly, the second mirror 7 also moves forward in the direction of the solid arrow, and after the forward movement is completed, it moves back in the direction of the dotted arrow.

Now, assuming that the stroke amount of the illumination light source 3 and the first mirror 4 is St, while the drum 25 shown in FIG. 2 rotates by θ, the illumination light source 3 and the first mirror 4
and moves back from the virtual line position to the solid line position. FIG. 4 shows this relationship as a timing diagram.

By the way, in this type of color electrophotographic copying apparatus, the copying speed determines the performance of the copying apparatus to some extent. The copy speed in this case is
Assuming that the drum diameter of the photosensitive drum is a predetermined diameter, it may be considered that this corresponds to the peripheral speed of the drum. In this case, the transfer drums also have the same diameter, and the same concept can be applied.Hereafter, for convenience, the explanation will be continued by applying the transfer drums.

As mentioned above, in order to improve one of the performances of the copying apparatus, it is a good idea to increase the copying speed, so to speak, the peripheral speed of the transfer drum. However, it is impossible to increase the circumferential speed without limit, and the circumferential speed is naturally limited by the following conditions.

1 Problems with the spectral sensitivity of the photoreceptor 2 Problems with the output of the illumination light source 3 Problems with fixing capacity and fixing time 4 Problems with development speed Normally, in this type of color electrophotographic copying device, if the copying speed is made faster than necessary, The color image quality will be greatly degraded, and the so-called copy level will not be satisfactory as a color image unless it is several steps higher than the copy level of a monochrome copying device. In addition,
The copy level mentioned here includes the following characteristics.

1. Image gradation for faithfully reproducing light and dark areas 2. Reproducibility of fine details such as fine lines and fine lines 3. Reproducibility of uniform density of solid areas These points depend on the spectral sensitivity of the photoreceptor and , and depends on conditions such as exposure and scanning speed, and the peripheral speed of the transfer drum cannot be increased unnecessarily.
In addition, color copying machines require a color separation process compared to monochrome copying machines, so the amount of exposure per unit time to the photoreceptor is
A larger amount of light is required, and from this point of view, the circumferential speed of the drum is naturally limited.

By the way, assuming that the number of rotations of the transfer drum is constant, if the diameter of the drum is made smaller in design, the peripheral speed increases accordingly. However, as mentioned earlier, the circumferential speed is
It cannot be made infinitely fast, but is set at a certain appropriate speed. In other words, the diameter of the drum cannot be made very small.

Nowadays, it has become extremely important to miniaturize not only monochrome copying machines but also color copying machines. This largely depends on the space occupied by the photosensitive drum, the transfer drum, etc., and in particular, making both drums as small as possible is extremely effective in downsizing the device. Therefore, reducing the drum diameter to the minimum possible size while balancing the relationship with the circumferential speed described above will greatly contribute to the miniaturization of the device, and will also maintain the color image quality at a certain level. becomes possible.

However, if the diameter of the drum is reduced in consideration of the circumferential speed as described above, a new copying problem will arise as described below.

As shown in FIG. 5a, on the transfer drum 25,
Assuming that a B4 size transfer sheet S ₁ is wound, the scanning optical system will move backward while the drum 25 rotates by an angle θ ₁ of the non-image area.
Further, as shown in FIG. 5b, a transfer sheet S ₂ of A3 size larger than the above sheet is placed on the transfer drum 25.
is wound, the scanning optical system must be moved back while the drum 25 rotates by an angle θ ₂ . Naturally, in this case, the relationship θ ₁ >θ ₂ holds true.

Here, the scanning optical system will move backward within the rotation time corresponding to θ ₁ or θ ₂ .
In any case, the scanning optical system must be moved back all at once in an extremely short period of time. It is not easy to instantaneously move a scanning optical system having a predetermined mass back. There are extremely troublesome technical issues such as the problem of the movement inertia of the scanning optical system and the shock when stopping.In particular, for example, it is difficult to design the scanning optical system based on A3 size, that is, the reconstruction of the scanning optical system using θ ₂ . Compared to the design method based on B4 size, the moving method is extremely disadvantageous in terms of reciprocal movement of the scanning optical system.
A B4 size format is a good idea. However,
If you do this, you will not be able to reproduce A3 size. This is because, as shown in FIG. 5b, the portion of the transfer sheet corresponding to (θ ₁ −θ ₂ ) is
This is because it will no longer be exposed to light.

From this point of view, the conventional design technology has been to maintain the angle θ ₁ while increasing the diameter of the transfer drum in order to make copies of the maximum copy size, for example, A3 size. . From this point of view, it has been difficult to downsize the drum.

On the other hand, from the perspective of customers who use this type of color copying device, for example, the frequency of making A3 size copies is relatively low, and the frequency of making copies of B4 size or smaller is high.
The idea that it is more advisable to use size as a design standard has also been proposed as one criterion for judgment.

The present invention has been made in view of the above-mentioned points, and it is possible to perform both a copy of a predetermined size and a copy of a smaller size at the same copying speed, and to is set at a speed that allows the above-mentioned small-sized copies to be made, and the diameters of the transfer drum and photoreceptor drum are minimized while maintaining the image quality at a certain level.
The purpose is to downsize the entire device and reduce the cost of the device.

Hereinafter, the present invention will be explained specifically and in detail based on Examples.

In FIG. 6, a gear 8a that is integral or substantially integral with the photosensitive drum 8 meshes with a pinion gear 38 on the driving side, and also meshes with a gear 25a that is integral or substantially integral with the transfer drum 25. It fits.

The clutch wheel 39 and the gear 40 are integrated, and are rotatably supported on a shaft 41 whose one shaft end 41a is fixed to an immovable support member 42. At one location on the circumferential surface of the clutch wheel 39,
Locked recess 3 in the shape of a concave groove along the axial direction of the same wheel 39
9b is formed, and this shape is tapered at a predetermined angle θ such that it opens linearly toward the outer periphery of the clutch wheel 39, as shown in FIG. Also, a wheel 3 adjacent to the locked recess 39b and located in the rotational direction of the clutch wheel 39
A flat cutout portion 39a lower than the peripheral surface is formed in a portion of the peripheral surface of 9.

A wire drum 44 adjacent to the clutch wheel 39
A gear 43 is integrally formed with the shaft 41, and these are rotatably supported by a shaft 41, as shown in FIG. Shaft 4 passing through wire drum 44
A clutch lever 45 is fixed to one shaft end of 4a, and a clutch wheel 39 is attached to one end of this lever.
A locking claw 45a that can be freely locked and detached from the locking recess 39b.
and a protrusion 45b are formed. Pins 45d and 44b are fixed to the clutch lever 45 and gear 43, respectively, as shown in FIG.
6 is attached to the clutch lever 45 due to the elasticity of the spring 46, as shown in FIG. 9a.
It has a habit of rotating counterclockwise about the axis of the shaft 44a. Note that the locking claw 45a
is in a state separated from the circumferential surface of the clutch ring 39 during normal life. Note that this will be described later.

Shaft 4 to which clutch lever 45 is fixed to one shaft end
The base end of a release lever 47 is fixed to the other shaft end of 4a, and the free end of the release lever 47 has a
A roller 47a arranged in a direction perpendicular to the axial direction of the shaft 41 is rotatably mounted. As shown in FIG. 10, a release ring 48 is fitted into the boss portion 44c of the wire drum 44.
c, it is slidable in this axial direction.

An elastic spring 49 is attached between the wire drum 44 and the release wheel 48, and the elasticity of this spring 49 causes the release wheel 48 to slide to the right in FIG. A behavior is given, and the movement due to this behavior is caused by the locking plate 6.
It is blocked by 8. In this state, Koro 4
7a rides on the circumferential portion 48b of the release ring 48, and is attached to the locking pawl 45a of the clutch lever 45.
is spaced apart from the circumference of the clutch ring 35 as shown in FIG. 9a.

In FIG. 6, a solenoid 65 is connected to an operating rod 64 whose base end is pivotally connected to a shaft 63. A compressible spring 66 is attached to the operating rod 64, and the elasticity of the spring 66 gives the stopper piece 64a at the free end the tendency to rotate in the direction away from the protrusion 48c. Rotation due to habit is prevented by a stopper pin 67.

A gear 53, an electromagnetic clutch 54, and a gear 55 are each mounted on a shaft 52 disposed parallel to the shaft 41, of which gear 53 is a driving pinion gear 56, and gear 55 is a driving pinion gear 56. 43 are interlocked with each other.

A wire 57 is wound around the wire drum 44. One end of this wire is locked to a pin 61a of the device frame plate 61 via a fixed pulley 58 and a moving pulley 59, and the other end is connected to a fixed pulley 62 and a moving pulley 59. It is locked to a pin 61b of the device frame plate 61 via a pulley 59. The movable pulley 59 is attached to the holding member 10 via the shaft 10a. Further, a wire 57 is secured to the lower part of the mounting plate 5a (see FIG. 1) fixed to the holding member 5.

Here, in FIG. 6, when a print button (not shown) of the apparatus is pressed, a copy start command signal is output, and the drive motor 69 starts rotating. Along with this, the pinion gear 38 on the drive side rotates in the direction of the arrow, and accordingly, the photosensitive drum 8 and the transfer drum 25 are rotated in the direction of the arrow, respectively, by the gear 8a and the gear 25a. Further, the clutch wheel 39 integrated with the gear 40 rotates in the direction of the arrow. Furthermore, the rotation of the drive motor 69 causes the pinion gear 56 and the gear 53 to rotate in the directions indicated by the dotted arrows, but the electromagnetic clutch 54 is in an OFF state and the gear 55 remains stopped.
Note that, due to the rotation of the pinion gear 38, both the gears 8a and 25a are engaged with each other, so that the photosensitive drum 8 and the transfer drum 25 rotate in the directions of the arrows in complete synchronization. Note that when the clutch wheel 39 rotates once, the photosensitive drum 8 and the transfer drum 25 also rotate once.

In the initial state, the clutch ring 39 and the wire drum 44 are in the position shown in FIG. 9a, and the locking pawl 45a is separated from the clutch ring 39. Here, as mentioned earlier, when the copy start command signal is output, the clutch wheel 39 starts rotating in the direction of the arrow.
At the same time or immediately after this, the solenoid 65 shown in FIG. 6 is energized by a separate operating signal, and as a result, the operating rod 64
3 in the direction of arrow A against the elasticity of spring 66. During this rotation, the stopper piece 64a in FIG. 10 moves to the left, as shown in FIG.
Push and move the protrusion 48c to move the release ring 48.
It is moved against the elasticity of the spring 49 to the position shown in the figure. The release wheel 48 is shown in FIGS. 10 to 11.
When moved to the position shown in the figure, the roller 47a slides relative to the circumferential portion 48b of the release ring 48,
It descends slightly to the position shown by the solid line in FIG.

The lowering of the roller 47a means that the release lever 47 in FIG. 6, the shaft 44a, and the clutch lever 45 move together counterclockwise in FIG. 9a due to the elasticity of the spring 46 (see FIG. 7). These rotate until the locking pawl 45a abuts against the clutch wheel 39, as shown in FIG. 9b.

When the clutch wheel 39 rotates from this state to the position shown in FIG. 9c, the locking pawl 45a engages with the locked recess 39b of the clutch wheel 39 through the notched flat portion 39a as shown in the figure. . In this state, the first
The roller 47a of the release lever 47 in FIG. 1 descends from the solid line position to the imaginary line position.

By the way, the reason why the notched flat portion 39a is provided in the clutch wheel 39 described above is as follows. That is, since this drive mechanism is operated at a relatively high speed, the vibrations generated during high-speed operation cause the locking pawl 45a to overcome the locked recess 39b by the shock when the locking pawl 45a is engaged. There is a risk of it getting lost. In order to prevent such points,
This is because the cutout flat portion 39a is provided.

The reason why the locked recess 39b is tapered as shown in FIG. 8 is as follows. That is, at the same time as the locking pawl 45a engages with the locking recess 39b, the scanning optical system, which is a moving object, starts to move forward, as described in the next paragraph. This shock may cause the scanning optical system to move ahead of the other, which may cause blur in the copied image. Further, due to load fluctuations during engagement, the scanning optical system itself, which is a driven object, may shake, causing a problem in the mechanical system. Locked recess 39b
By making it tapered, the above-mentioned problems can be prevented, and play during engagement can be eliminated. In other words, there is no backlash, and the engagement and disengagement operations become easier.

Now, returning to the original explanation, as shown in FIG. Take it with you and rotate it in the direction of the arrow. That is, in FIG. 6, the wire drum 44 rotates in the direction indicated by the solid line arrow, and therefore the gear 55 rotates in the direction opposite to the direction indicated by the dotted line arrow. However, the electromagnetic clutch 54 is off and has no effect on the rotation of the gear 53. As described above, when the wire drum 44 rotates in the direction of the solid arrow, the holding member 10 begins to move forward in the direction of the arrow via the wire 57, fixed pulley 58, fixed pulley 62, movable pulley 59, etc. At the same time, the mounting plate 5a, which locks the wire 57, ie, the holding member 5 in FIG. 1, also begins to move in the same direction as above. In this case, the speed ratio between the holding members 5 and 10 is 2:1. In this way, the locking pawl 45a of the clutch lever 45 engages with the locked recess 39b of the clutch wheel 39, so that
The illumination light source 3, first mirror 4, and second mirror in FIG.
The scanning optical system comprising the mirror 7 and the like starts this forward movement, which corresponds to the timing at which exposure scanning of the color separation slits on the photosensitive drum 8 starts.

Here, the clutch wheel 39 and the wire drum 44 rotate together in the direction of the arrow from the position shown in FIG. 9c, and when both rotate to the position shown in FIG. 9d, the clutch lever 45 is released. The locking pawl 4 of the lever 45 is rotated clockwise by the pin 51 (see FIG. 6) about the axis of the shaft 44a against the elasticity of the spring 46.
5a is removed from the locked recess 39b of the clutch wheel 39 as shown in the figure. Therefore, the rotation of only the wire drum 44 is temporarily stopped, and the forward movement of the scanning optical system is therefore stopped, and the first document illumination scan is completed at this stage. That is, the first electrostatic latent image formation on the drum 8 is completed. In addition, clutch ring 3
9 continues to rotate in the direction of the arrow even though the wire drum 44 has stopped.

In FIG. 9d, the clutch lever 45 is connected to the shaft 4.
When the protrusion 45b turns around the axis of the clutch 4a to the position shown in the figure, the protrusion 45b pushes the actuator of the micro switch MS, which is a detection means for detecting that the clutch is turned off, and generates a switching signal. With this signal, the 6th
The electromagnetic clutch 54 in the figure is turned on, and as a result, the rotational driving force of the normally rotating gear 53 is transmitted to the gear 55, which rotates in the direction of the dotted arrow. Therefore, the wire drum 44 integrally equipped with the gear 43 rotates in the direction of the dotted arrow, which is the opposite direction. Therefore, the scanning optical system starts the backward movement from the position where the forward movement has ended.

On the other hand, the wire drum 44, which has stopped once at the position shown in FIG. During this reverse rotation, the side edge of the clutch lever 45 moves while slidingly contacting the pin 51, which is the clutch release means, and gradually moves away from the pin 51. Therefore, the locking pawl 45a of the clutch lever 45 comes into pressure contact with the circumferential surface of the clutch wheel 39, which is rotating in the direction of the arrow. In this state, the roller 47a of the release lever 47 in FIG. 11 is held in the position shown by the solid line. And clutch lever 4
5 reaches the position shown in FIG. 9b, and at the same time, the clutch wheel 39, which has continued to rotate, reaches the position shown in FIG. 9b and completes its first rotation. In this state, the photosensitive drum 8 also completes its first rotation. It should be noted that when the clutch lever 45 reaches the position shown in FIG. 9b, the electromagnetic clutch 54 is turned off, the reverse rotation of the wire drum 44 is completed, and the drum 44 is temporarily stopped.

Returning to the original explanation, when the clutch wheel 39 continues to rotate from the position shown in FIG. 9d,
The locking pawl 45a of the clutch lever 45 placed in the position shown in FIG.
is engaged with the locked recess 39b again. In this state, the scanning optical system starts the second forward movement, and a second electrostatic latent image is formed on the photosensitive drum 8, and the above-described operation is then repeated. moreover,
The series of operations described above is repeated in the same manner during the formation of the third electrostatic latent image. Note that the photosensitive drum completes its third rotation, and in its fourth rotation, cleaning, static electricity removal, etc. are performed, and during this period, the transfer sheet is conveyed to the fixing device 33 (see FIG. 1) side. There are, but
During this time, there is no need to scan the original with illumination.
The clutch lever 45 is designed not to engage the clutch wheel 39.

That is, when the final document illumination scan is completed and the wire drum 44 is reversed from the position shown in FIG. 9 d to the position shown in FIG. In addition, the solenoid 65 shown in FIG. 6 is demagnetized by an appropriate operation signal, and along with this, the solenoid 65 shown in FIG.
Stopper piece 64a that has been pushing the protrusion 48c until now
Due to the elasticity of the spring 66, the operating rod 64 has a
Turn in the direction opposite to the direction of arrow A.

That is, in FIG. 11, the stopper piece 64a of the operating rod 64 moves to the right to the position shown in FIG. 10, and by the retracting operation of the stopper piece 64a,
Due to the elasticity of the spring 49, the release ring 48
Slide from FIG. 11 to the position shown in FIG. 10. During this sliding, the roller 47a of the release lever 47 passes through the conical inclined part 48a of the release wheel 48 and rides on the circumferential part 48b as shown in FIG.

In this position, as shown in FIG. 9a, the locking claw 45a of the clutch lever 45 is separated from the circumferential surface of the clutch ring 39, and this state is maintained thereafter. That is, even when the clutch wheel 39 starts rotating for the fourth time, the locking pawl 45a no longer engages with the locked recess 39b, the wire drum 44 does not rotate, and the scanning optical system stops. Maintain posture.

On the other hand, the clutch wheel 39 enters its fourth rotation from the position shown in FIG. 9a, and after making one revolution, it stops at the position shown in FIG. 9a to prepare for the next copy.

In addition, in FIG. 9d, the clutch lever 45
The state of engagement with the clutch wheel 39 is released by the action of the clutch lever release pin 51, which is movable in the circumferential direction of the clutch wheel 39, as shown in FIG. Moreover, it can be fixed at a selective position in that direction, for example, to perform short return of the scanning optical system, and the desired sheet size can be adjusted according to instructions from the person in charge of copying. can get.

Here, in FIG. 5a, it is assumed that, for example, a B4 size transfer sheet _S1 is wound around the transfer drum 25. Then, the range of θ ₁ becomes a non-image area. In the copying apparatus according to the embodiment of the present invention,
The scanning optical system is designed to move backward in the range of θ ₁ . This relationship is shown in FIG.

That is, in the case of B4 size or less, when the copy start command signal is output in FIG. 12, the solenoid 65 in FIG.
is excited, and the excited state is maintained until the transfer drum 25 completes its third rotation. During this time, the clutch lever 45 is allowed to engage the clutch wheel 39, and the scanning optical system repeats the reciprocating operation three times. When the excitation state of the solenoid 65 is released, the clutch lever 45 can no longer engage the clutch wheel 39, and the scanning optical system is stopped and held at the starting position shown in FIG. At this point, the transfer sheet is discharged, the two drums are neutralized, and cleaning is performed.

Next, when copying a transfer sheet of a larger size than the above-mentioned transfer sheet, for example, A3, which is the largest size sheet used in this copying device,
As shown in the lower part of FIG. 12, an idle rotation process of the transfer drum is provided.

When making a copy using an A3 size sheet, if the scanning optical system is moved back within the range of θ ₁ as shown in Figure 5b, the range of (θ ₁ - _{θ 2} ) will be exposed. Otherwise, it becomes an untransferred part. Therefore, as shown in FIG. 12, the forward movement time of the scanning optical system is extended by (θ ₁ -θ ₂ ). As this means, the clutch lever release pin 5 shown in FIG.
One example is a method in which the clutch wheel 39 is selectively displaced in the rotational direction of the clutch wheel 39. In this way, the locked recess 3 of the clutch lever 45
The timing of detachment from the pin 9b can be delayed, and the timing of the end of forward movement of the scanning optical system is delayed according to the amount of movement of the pin 51.

On the other hand, in FIG. 12, the scanning optical system starts the backward movement immediately after completing the forward movement, and this backward movement time corresponds to θ ₁ . This backward movement process causes the drum to become wedged during the second idle rotation.

Then, at the same time as the scanning optical system completes its backward movement, the excitation state of the solenoid 65 is released. Then, when the drum enters the third rotation, solenoid 6
5 is energized again. That is, during this time, the clutch lever 45 cannot engage with the clutch wheel 39, so the scanning optical system remains stopped at the starting position, and as a result, exposure scanning is not performed and the electrostatic latent image is Since it is not formed, it does not disturb the previously formed electrostatic latent image.

Idle rotation refers to the time when the drum rotates as part of the electrostatic latent image forming process. Note that the process of operating the scanning optical system and the solenoid is repeated thereafter as shown in the figure. Also, the drum 6
During the rotation, ejection of the transfer sheet, neutralization of the two drums, cleaning, etc. are performed. Note that the end timing of the backward motion of the scanning optical system for A3 size may be at least earlier than the timing indicated by the symbol B.

As mentioned above, the drum diameter can be set based on the B4 size, and the drum diameter can be set based on the A3 size.
It can be made smaller compared to what is set using the size standard method. Since the transfer drum rotates at the same speed both in A3 and B4, the circumferential speed is constant and the copying speed is the same. Also,
Since the backward movement time of the scanning optical system also corresponds to at least θ ₁ , it is possible to reduce the movement inertia of the scanning optical system, and to prevent vibrations and the like when the scanning optical system is stopped.

On the other hand, as shown in FIG. 5b, when the scanning optical system is moved back in the range of θ ₂ , the above-mentioned problem occurs. If the drum diameter is set such that θ ₁ can be ensured, the drum diameter becomes correspondingly large. In addition, _the color separation filters 12a, 12b, 12c shown in _FIG .
Since the position can be changed, there is no need for the drive mechanism to be very fast-moving.

In FIG. 6, the clutch wheel 39 and the clutch lever 45 connect and disconnect the drive transmission relationship between the drive source such as the drive motor 69 and the document scanning moving body such as the scanning optical system. , constitutes a kind of clutch mechanism that transmits the driving force from the drive source to the document scanning moving body to drive the document scanning moving body placed at the starting position.

Additionally, a release lever 47, a release wheel 48,
The operating rod 64, solenoid 65, spring 66, etc. rotate to form electrostatic latent images in accordance with the number of color separations with each rotation when transferring a large size transfer sheet such as A3 size. After forming each electrostatic latent image on the photoreceptor drum 8, the photoreceptor drum is transferred to the transfer drum 2 as an electrostatic latent image non-forming process.
5, the clutch mechanism is cut and held so that the original scanning moving body is stopped at the starting position so that it idles once with 5, and a transfer sheet such as B4 size, which is smaller than the above-mentioned large size transfer sheet, is cut and held. When performing transfer using the clutch mechanism, the clutch mechanism is operated in a continuous manner to continuously drive the original scanning moving body.

In addition, as a fixing device, reference numeral 3 in FIG.
When copying a large number of sheets in succession using a fixing roller installed in the fixing device as shown in 3 and using a large size transfer sheet such as A3 size, as shown in Fig. 12. As shown, since there is idle rotation time, as a result, the conveyance time from both drums 8 and 25 to the fixing device 33 becomes longer, and heat can be sufficiently supplied to the sheet within a sufficient amount of time. Therefore, the fixing power supply capacity does not need to be very large, and fixing is efficient and economical. On the other hand, if there is no idling process, the sheets will be ejected one after another from both drums in a short period of time, and the time for the sheets to pass through the fixing device will accordingly become shorter.

In the embodiments described so far, a full-color copying method in which yellow, magenta, and cyan development are sequentially performed was applied, but in addition, single-color copying of each of yellow, magenta, cyan, etc. It is also applicable to the following two-color copying method and the following two-color copying method.

1 Yellow + Magenta 2 Magenta + Cyan 3 Yellow + Cyan In this case, for example, in the method 1), the cyan process in FIG.
At the second time, sheet ejection, static neutralization, cleaning, etc. may be performed.

As described above, according to the present invention, copying of a predetermined size,
In addition to making it possible to make both smaller-sized copies at the same copying speed, this copying speed is set as a reference speed that allows the above-mentioned smaller-sized copies to be made, and the image quality is maintained at a constant level. Since the diameters of the transfer drum and photoreceptor drum can be minimized while maintaining the same level, the overall size of the device and the cost of the device can be reduced.
In addition, even when copying is performed using transfer sheets of different sizes, stable color images with no difference can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a color electrophotographic copying apparatus embodying the present invention, and FIG. 2 is a transfer sheet and non-image area on a transfer drum used to explain the background of the present invention. Diagram showing the relationship between
The figure is a schematic diagram of the reciprocating operation of the scanning optical system, Figure 4 is an operation timing diagram of the transfer drum and scanning optical system used to explain the background of the present invention, and Figures 5 a and b 6 is a diagram used to explain the background of the present invention, showing the relationship between transfer sheets of different sizes and non-image areas on a transfer drum, and FIG. 6 is a color electrophotographic copying apparatus of the present invention. FIG. 7 is a perspective view showing a wire drum portion in the drive mechanism, which is a perspective view showing a drive mechanism for a scanning optical system, a photoreceptor drum, and a transfer drum, which is included in the drive mechanism;
FIG. 8 is an enlarged view of the main part of the clutch wheel, and FIGS. 9 a to 9 d are action diagrams for explaining the clutch engagement action by the clutch wheel and clutch lever, respectively.
FIG. 10 is a side sectional view of the clutch mechanism operation control mechanism, and FIG. 11 is a side sectional view of the clutch mechanism operation control mechanism, and FIG.
FIG. 12 is a diagram showing the operation timing of the transfer drum, scanning optical system, etc. according to the size classification of the transfer sheet. 3, 4, 7... Original scanning moving body, 8... Photosensitive drum, 25... Transfer drum, 39... Clutch wheel, 45... Clutch lever, 47... Release lever, 48... Release wheel, 64 ...operating rod,
65... Solenoid, 66... Spring, 69... Drive motor as a drive source.

Claims (1)

[Scope of Claims] 1. To perform exposure scanning with a photosensitive drum on which an electrostatic latent image is repeatedly formed every rotation according to the number of color separations by the color separation exposure action of a color original. , a document scanning moving body that is driven reciprocatingly from its starting position for a predetermined distance and moves back at a speed greater than the forward movement speed; a transfer drum that rotates in contact and has a circumference somewhat longer than the length of the maximum usable transfer sheet; a drive source for driving the document scanning moving body, the photosensitive drum, and the transfer drum; , a clutch that connects and disconnects the drive transmission relationship between the drive source and the original scanning moving body, which transmits the driving force from the driving source to the original scanning moving body when connected, and transmits the driving force from the driving source to the original scanning moving body, and A first clutch that moves the original scanning moving body placed in a forward position and is disconnected when the forward movement of the original scanning moving body is completed, and drive transmission between the driving source and the original scanning moving body. A clutch that connects and disconnects the relationship, which is connected after the first clutch is disengaged, transmits the driving force from the drive source to the document scanning movable body, and moves the document scanning movable body forward. A second clutch that moves back from the end position to the starting position, and when performing transfer using the maximum size transfer sheet, the document scanning moving body that has made one reciprocating movement is stopped and waiting at the starting position. When the first clutch is held in a disengaged state so that the transfer drum idles once, and a transfer sheet of a smaller size than the maximum size transfer sheet is used for transfer, each rotation of the transfer drum above 1st
A color electrophotographic copying apparatus comprising a clutch actuation control mechanism that allows engagement of a clutch.