JPH0117584B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transfer/separation device for an electrophotographic copying machine.

A transfer-type electrophotographic copying machine applies a transfer electric field to attract the toner adsorbed to the electrostatic latent image formed on the photoreceptor to the copy paper side, and performs the transfer. Copy paper sticks to the photoconductor. A separating device separates the copy paper from the photoreceptor, and in order to electrostatically apply the force for this separation, an electric charge is injected into the copy paper during transfer, and the copy paper is made into a conductor after transfer. It has been proposed to utilize the electrostatic attractive force between the charges and the induced charges generated in the conductor by bringing the charges close to each other.

FIG. 1 shows the principle of the transfer/separation device, which is the object of the present invention. Reference numeral 1 denotes a photoreceptor, which rotates in the direction of arrow A. The photoreceptor 1 carries an electrostatic latent image 2 of negative polarity, to which toner 3 of positive polarity is adsorbed. Copy paper 4 is fed toward the circumferential surface of photoreceptor 1 as shown by arrow B.
is injected with a negative charge by the corona discharger 5 to which a DC voltage is applied. As a result, toner 3
is attracted to copy paper 4 and transferred.
The copy paper 4 that has been transferred is attracted to the circumferential surface of the photoreceptor 1 and advances to a position where the conductive belt 6 is installed. The conductive belt 6 is running as shown by arrow C. Electrostatic induction occurs in the conductive belt 6 due to negative charges in the copy paper 4, and positive charges are induced in the portion facing the copy paper 4. Then, the copy paper 4 is attracted to the conductive belt 6 by the electrostatic attraction force acting between the two charges, and the copy paper 4 is separated.

Incidentally, the potential of the conductive belt 6 has a great influence on transfer and separation performance. conductive belt 6
When the conductive belt 6 is grounded, the negative charges generated in pairs with the positive charges due to the electrostatic induction immediately escape to the ground, so that the potential of the conductive belt 6 is maintained at zero. In this state, the separation performance is sufficient, but on the other hand, the suction force of the toner 3 to the copy paper 4 side is insufficient, and the toner 3 is retransferred to the photoreceptor 1 side, resulting in insufficient transfer performance. . If the conductive belt 6 is not grounded but left in a floating state, the negative charge generated by the electrostatic induction has nowhere to escape, thereby increasing the potential of the conductive belt 6 to a negative polarity. In this state, the transfer performance is sufficient, but the separation performance is insufficient.

In order to solve this problem, the present inventor invented a method of connecting an external DC power source to the conductive conveying member and controlling the potential so that it is low at the start of separation and becomes high thereafter, and has filed a separate application. . According to this invention, although transfer is insufficient for a short period of time at the start of separation, since a reliable separation force is obtained, the separation is reliably started, and even if the separation force decreases thereafter, the separation action once started is maintained. can be maintained as is, so it is possible to achieve both separation performance and transfer performance.

By the way, when the above invention was applied to a double-sided copying machine, it was found that separation was reliably performed when copying the front side, but separation was uncertain when copying the back side. Therefore, we investigated the cause and found the following. That is,
When copying the back side, the surface copying is performed beforehand, so the moisture content of the copy paper decreases, and furthermore, since toner and silicone oil are attached to the surface, the volume resistance of the copy paper is extremely low. It's getting expensive. Before surface copy
It has been actually measured that copy paper with a resistance of 10 ¹¹ Ω·cm becomes 10 ¹⁵ Ω·cm when copying on the back side. As a result, the amount of charge that the copy paper receives during transfer becomes larger when copying the back side than when copying the front side. As a result, after separation, the electrical repulsion between the electrically conductive conveying member and the transfer paper weakens the attraction force between the electrically conductive conveying member and the leading edge of the transfer paper, making the separation effect unstable. Conceivable.

The present invention has been made based on the above consideration, and the present invention has been made by making the external DC voltage applied to the conductive conveyance member during back copying smaller than that during front copying, thereby separating the separation during back copying. It is characterized by compensating for a decrease in performance.

Next, prior to explaining the present invention, the invention before the improvement will be explained with reference to FIGS. 2 to 5.

Transfer from the photoreceptor 1 to the copy paper 4 is performed by charging the copy paper 4 with the corona discharger 5 in accordance with the principle described above. Feeding of copy paper 4 onto the circumferential surface of photoreceptor 1 is controlled by registration rollers 7 . That is, the registration roller 7
is waiting in a stopped state, and starts rotating when a resist clutch signal is applied as part of the copy cycle, and feeds the copy paper 4 to the circumferential surface of the photoreceptor 1 at a predetermined timing.

The conductive belt 6 is grounded via a power supply circuit 8, and its potential is controlled by the power supply circuit 8. Control of the power supply circuit 8 is performed by a timing control circuit 9 which starts operating when the registration roller 7 starts rotating.

FIG. 3 shows a power supply circuit 8 and a timing control circuit 9.
This is an example. When a resist clutch signal A (see Fig. 4, hereinafter the same) for starting the resist roller 7 is applied to the input terminal T, the transistor Tr ₁ is turned on, the electromagnetic clutch CL is connected, and the resist roller 7 is turned on. Rotation is started, and feeding of the copy paper 4 is started. When transistor Tr ₁ turns on, transistors Tr ₂ and Tr ₃ also turn on, and transistor Tr ₃ turns on.
The collector of changes from high level to low level as shown by b. This change causes capacitor C ₁
A differentiator circuit containing the trigger signal becomes the trigger signal and starts timer IC ₁ . Timer IC ₁ produces an output signal C for a time t ₁ and applies it to a second differentiator circuit including capacitor C ₂ . This second differentiating circuit generates a trigger signal T at the falling edge of the signal C, and supplies it to the second timer IC ₂ to start it. The second timer IC ₂ produces an output D, turning on the transistor Tr ₄ for a time t ₂ and energizing the relay RA.

A normally closed contact S of the relay RA is connected between the output terminal 10 of the power supply circuit 8 and the ground terminal via a resistor _R2 . The output terminal 10 is connected to a -600V DC power supply via a resistor _R1 . A constant voltage element Z is further connected between the output terminal 10 and the ground terminal.
A series circuit of a resistor R ₃ and a capacitor C ₃ is connected to each other. Until relay RA is energized, its contact S is closed, so power supply circuit 8
The potential at the output terminal 10 of the output terminal 10 exhibits a value close to zero. When relay RA is energized and contact S opens, capacitor
C ₃ is charged from a −600V DC power supply through resistor R ₁ ,
Since this is done via _R3 , the potential of the output terminal 10 gradually increases as shown by E and becomes constant at -600V. Since the conductive belt 6 is connected to the output terminal 10 of this power supply circuit 8, its potential is also the same.

FIG. 5 shows temporal changes in the potential of the conductive belt 6, and also shows the conveyance position of the copy paper 4. In FIG.

At time 0, the resist clutch signal A is given,
When the registration rollers 7 start rotating, the leading edge of the copy paper 4 starts running from a point _P1 on the registration rollers 7. At time _t3 , the leading edge of the copy paper 4 reaches the contact point _P2 between the conductive belt 6 and the photoreceptor 1.
However, since the power supply circuit 8 does not yet produce an output, the potential of the conductive belt 6 exhibits a value close to zero.
When time t ₁ , that is, the time t ₁ set by timer IC ₁ has elapsed since the start, relay RA is energized and its contact S opens, so power supply circuit 8
generates an output, and the potential of the conductive belt 6 gradually increases as shown in graph ho, reaching -600V.
When the time _{t2 set by the timer IC 2 has} elapsed from time _t1 , the copy paper 4 completes its passage, and the power supply circuit 8 returns to its original zero potential state again.
Get ready for the next start.

By the way, when the leading edge of the copy paper 4 reaches point _P2 , the potential of the conductive belt 6 is still zero, so sufficient separation performance is obtained, and the leading edge of the copy paper 4 separates from the photoreceptor 1. Then, it is attracted to the conductive belt 6 and transported in the direction of arrow C. At this time, the transfer performance is degraded and white spots occur at the leading edge of the copy paper 4, but since it is at the edge, there is no practical problem.

Since the potential of the conductive belt 6 begins to rise (in the negative direction) when the leading edge of the copy paper 4 reaches the _P3 point, the resulting suction force gradually decreases and the transfer performance recovers. Once the copy paper 4 is attracted to the conductive belt 6, it moves away from the photoreceptor 1, so even if the suction force decreases, the separation performance does not deteriorate and it continues to be attracted to the conductive belt 6, thereby being transported. be done.

The capacitor _C3 in the power supply circuit 8 moderates the rise in potential of the conductive belt 6, thereby making the boundary of the white spot formed at the leading edge of the copy paper 4 less noticeable. Also, time t ₁ and t ₃
In the above example, t ₁ >t ₃ , but it may be t ₁ =t ₃ or t ₁ <t ₃ . They should be appropriately selected depending on the rising characteristics of the potential rise of the conductive belt 6.

Although the above is the invention before improvement, FIG. 6 shows an embodiment of the invention. A DC voltage of -600V is applied to the power supply circuit 8' via a resistor _R1 , and a DC voltage of -300V is applied via a resistor _R4 . Both resistors R ₁ and R ₄ are connected to the output terminal ₁₀ via the switching contact S 2 of the relay RA ₂ .
Relay RA ₂ is controlled by transistor Tr ₅ which is turned on by the back side copy signal. The relay RA for the normally closed contact S for grounding the output terminal 10 via the resistor R ₂ is energized by the output of the timing control circuit 9 as described above, but in this embodiment , it can be made inactive by closing the blank paper mode switch _S3 .

During surface copying, since there is no signal at the input terminal T ₁ , the transistor Tr ₅ is off and the relay RA ₂ is not energized, so the switching contact S ₂ enters the normally closed contact a side, and the output terminal 10 has a resistance R of ₁
is connected. Therefore, when the timing control circuit 9 issues a signal N, the normally closed contact S opens and the potential at the output terminal 10 gradually increases, causing -
The voltage remains constant at 600V, and the above-mentioned action takes place.

During backside copying, a signal is applied to input terminal T ₁ , which turns on transistor Tr ₅ ,
Since the relay RA ₂ is energized, the switching contact S ₂ switches to the normally open contact b side, and the resistor R ₄ is connected to the output terminal 10. Therefore, since the voltage that starts charging the capacitor _C3 when the normally closed contact S opens is -300V, the potential at the output terminal 10 increases toward -300V and becomes constant there. . In the end, as shown in FIG. 7, the potential of the conductive belt 6 is -600V when copying the front side, and -300V when copying the back side.
Therefore, even if the amount of charge on the copy paper 4 during back side copying is large, the conductive belt 6, which is suppressed to a low potential, exhibits sufficient separation performance.

In blank paper mode, in which the reverse side copy cycle is performed with a blank paper, blank paper mode switch S ₃
Turns on after surface copy is completed. As a result, relay RA remains inactive regardless of the presence or absence of the output from timing control circuit 9, so its normally closed contact S remains on and output terminal 10 is maintained at zero potential. Therefore, a reliable separation effect can be obtained, and no transfer is performed to the back side, resulting in a blank state.

As described above, in the present invention, the external DC voltage applied to the conductive conveying member during back side copying is made smaller than that during front side copying, so that sufficient separation force can be obtained even during back side copying, and both the front and back sides can be Sufficient separation performance and transfer performance can be obtained.

[Brief explanation of drawings]

Figure 1 is a front view showing the principle of the transfer/separation device;
Fig. 2 is a front view showing the invention before improvement, Fig. 3 is its circuit diagram, Fig. 4 is a timing chart, Fig. 5 is a graph showing potential changes, and Fig. 6 is a diagram showing the embodiment of the invention. The circuit diagram and FIG. 7 are graphs showing the potential changes. 1... Photoreceptor, 4... Copy paper, 5... Corona discharger, 6... Conductive belt, 8'... Power supply circuit, T ₁ ... Back side copy signal input terminal.

Claims (1)

[Claims] 1. Toner is attracted to the electrostatic latent image formed on the photoconductor, and the resulting toner image is transferred to copy paper in a transfer section under the application of a transfer electric field, and then the copy paper and conductive In a transfer/separation device of an electrophotographic copying machine that separates the copy paper from the photoreceptor by applying an electrostatic attraction force between the conveying members, an external DC power supply connected to the conveying member and A double-sided electrophotographic copying machine, characterized in that the double-sided electrophotographic copying machine is equipped with a means for switching the voltage from the external DC power supply so that it is lower during back-side copying than during front-side copying, using either a front-side copy signal or a back-side copy signal. Transfer/separation device.