JPH05165287A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent sticking of positively-electrified carrier to a photosensitive drum which, when the door of a device is opened or the main power source of the device is shut off during the image forming operation, occurs since a negatively-electrified part on the photosensitive drum continuing to turn by means of the inertia of a driving system faces a developing sleeve. CONSTITUTION:The sticking of carrier to the surface of the photo-sensitive drum 1 is prevented by applying a -600V voltage, which is equal to that applied during the development, to the developing sleeve 21 during the time that the photosensitive drum 1 rotates only an angle of theta degrees by means of inertia after the supply of a voltage to the main drive motor is stopped during the image forming operation.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention, a copying machine, a facsimile,
Regarding the image forming apparatus such as a printer, more specifically, during the image forming operation in the image forming apparatus in which the polarity of uniform charging of the latent image carrier is opposite to the charging polarity of the carrier, that is, the charging polarity of the toner. The present invention relates to prevention of carrier adhesion on the latent image carrier when the apparatus door is opened or the apparatus main power is shut off.

[0002]

2. Description of the Related Art Conventionally, in this type of image forming apparatus,
After the latent image carrier is uniformly charged with a polarity opposite to the charge polarity of the carrier, the potential of a portion to which toner is to be attached (hereinafter referred to as a character portion, and a portion other than the character portion in the image is referred to as a background portion) is, for example, light. It is attenuated by irradiation to form a latent image,
The latent image is developed by applying a developing bias having a polarity opposite to the charging polarity of the carrier, that is, the same polarity as the charging polarity of the toner, to a developing sleeve having a magnetic brush formed of a two-component developer containing toner and carrier. (So-called reversal development).

In FIG. 4A, the uniform charging polarity is negative,
FIG. 6 shows an example of the relationship between the latent image potential and the developing bias in reversal development when the carrier has a positive polarity and the toner has a negative polarity. The upper half of the figure shows a latent image on which toner is attached in the shape of letter R as an example of the latent image on the latent image carrier, and the lower half of the figure shows the potential on the straight line aa of this latent image. And developing bias levels. In this example, the background part where the uniform charge remains as it is is minus 800V, and the character part is minus 100V.
V, the developing bias is minus 600V. By setting the potential of each part of the latent image and the developing bias as described above, the negatively charged toner on the developing sleeve receives the electrostatic force from the developing sleeve toward the character portion on the latent image carrier and adheres to the latent image carrier. To go. On the other hand, the positively charged carrier on the developing sleeve receives an electrostatic force toward the background portion on the latent image carrier, but it is still held on the developing sleeve by the magnetic force of the magnet for forming the magnetic brush on the developing sleeve. It does not adhere to the latent image carrier.

Further, in this type of image forming apparatus, for maintenance and inspection of the inside of the apparatus, a part of the side surface of the apparatus casing is formed with a door that can be opened and closed, and the apparatus door is opened. In order to ensure safety, a drive motor for driving the latent image carrier so that the surface of the latent image carrier is moved, or a high voltage power supply for developing bias, which is a door switch itself for detecting the opening / closing of the door or a switch for opening / closing by a signal from the door switch. And the like and the power source of the main body so that the voltage supply to the drive motor, the developing sleeve and the like is stopped when the door switch detects that the door is opened. When the device main power is cut off by turning off the device main switch or unplugging the device, not only the above-mentioned drive motor and high voltage power supply for developing bias but also control for the control unit consisting of a microcomputer, etc. The voltage supply from the power supply was also stopped.

[0005]

However, according to the above construction, if the apparatus door is opened or the apparatus main power supply is shut off during the image forming operation for some reason, the carrier on the developing sleeve carries the latent image. There is a problem that it may adhere to the body and cause various problems. That is, the latent image carrier is driven by the drive motor during the image forming operation, and the drive system of the latent image carrier including such a drive motor has a certain inertia. In particular, the inertia becomes large when a flywheel or the like is adopted to make the latent image carrier surface move at a constant speed. For this reason, even after the voltage supply to the drive motor and the high voltage power source for developing bias is stopped by opening the device door or shutting off the device mains power during the image forming operation, the latent amount is equal to the inertia. The surface of the image carrier moves. During the movement of the latent image carrier surface for this inertia, if a portion of the latent image carrier on which the uniform charging potential remains is opposed to the developing sleeve, for example,
As shown in FIG. 4B, between the developing sleeve in which the supply of the developing bias is stopped and the developing voltage is 0 V and the latent image carrier, the strong force in the direction of moving the carrier on the developing sleeve to the latent image carrier side. An electric field is formed. Accordingly, the electric field causes the carrier on the developing sleeve to adhere to the surface of the latent image carrier. For example, in FIG. 5, the horizontal axis represents the absolute value of the potential difference between the latent image carrier and the developing sleeve potential, and the vertical axis represents the latent image when the latent image carrier and the developing sleeve face each other with such potential difference. 6 is a graph showing the relationship between the above potential difference and the number of carriers attached to a latent image carrier by taking the number of carriers that have adhered to the carrier. From this graph,
It can be seen that when the potential difference is about 500 V or more, the number of carriers adhering to the latent image carrier increases rapidly. In this way, the carrier itself adhering to the latent image carrier may not only reduce the amount of carrier in the developing device and change the developing characteristics, but also adhere to the latent image carrier. When the carrier is sandwiched between the latent image carrier surface and the cleaning blade of the cleaning device, the latent image carrier surface or the cleaning blade may be damaged,
Further, the image quality is remarkably deteriorated by moving to a fixing device through a transfer paper or the like and damaging the fixing roller.

The latent image bearing member is not limited to the one using the reversal development as described above, but may be a latent image bearing member formed on the latent image bearing member by a magnetic brush for various reasons. The carrier may adhere to the above and cause the above problems.

The present invention has been made in view of the above problems. A first object of the present invention is to carry a latent image carrier when the apparatus door is opened or the apparatus main power source is shut off during image forming operation. An object of the present invention is to provide an image forming apparatus capable of preventing the carrier from being attached to the upper part, and the second purpose thereof is
An object of the present invention is to provide an image forming apparatus that can appropriately remove the carrier even when the carrier adheres to the latent image carrier to reduce the problems caused by the carrier adhesion as compared with the conventional case.

[0008]

In order to achieve the above-mentioned first object, the invention of claim 1 has a latent image carrier whose surface is moved by a drive motor and has opposite polarities. A developing sleeve having a magnetic brush formed of a two-component developer containing a charged carrier and toner;
After the latent image carrier is uniformly charged to the opposite polarity to the carrier, the potential of the portion to which the toner should be attached is attenuated to form a latent image, and the latent image is charged to the developing sleeve by carrier charging. In an image forming apparatus for applying a developing bias having a polarity opposite to that of the polarity for developing, drive control for stopping power supply to the drive motor in response to detection of opening of an apparatus opening / closing door by an apparatus door switch Means and delay control means for supplying a predetermined voltage from the high voltage power source for developing bias to the developing sleeve for a predetermined period after the supply of power to the drive motor is stopped. The invention of Item 2 forms a magnetic brush composed of a latent image carrier that is driven by a drive motor so that the surface moves, and a two-component developer containing a carrier and a toner that are charged with opposite polarities. A latent image carrier having a developing sleeve is uniformly charged to a polarity opposite to the charge polarity of the carrier, and then the potential of a portion to which toner is to be attached is attenuated to form a latent image. In an image forming apparatus for developing by applying a developing bias having a polarity opposite to the charging polarity of the carrier to the developing sleeve, the internal power source and the internal power source are used for a predetermined period during a predetermined period after the main power source of the apparatus is shut off. A delay control means for supplying a voltage is provided.

In order to achieve the above-mentioned second object, the invention of claim 3 is such that a latent image carrier which is driven by a drive motor so that its surface moves, a carrier and a toner which are charged with opposite polarities. And a developing sleeve formed with a magnetic brush made of a two-component developer containing a toner, and the latent image formed on the latent image carrier is developed with toner in the magnetic brush. It is characterized in that a drive control means for reversing the latent image carrier is provided for a predetermined period after the start of the image forming operation.

[0010]

In the image forming apparatus according to claim 1, the drive control means, in response to the detection of the opening of the apparatus opening / closing door by the apparatus door switch, supplying power to the drive motor for driving the latent image carrier. Stop the supply. Even after the power supply is stopped, the latent image carrier moves by the inertia of the drive motor. Due to the movement of the latent image carrier surface corresponding to the inertia, the delay control means is operated by the delay control means for a predetermined period during which the latent image carrier part in which the potential charged with a polarity opposite to the charge polarity of the carrier remains facing the developing sleeve. A predetermined voltage is supplied from the high voltage power source for developing bias to the developing sleeve so that the potential difference between the potential of the latent image bearing member and the developing sleeve potential does not cause carrier adhesion to the latent image bearing member.

In the image forming apparatus of the second aspect, the main power source of the apparatus is shut off and the power supply to the drive motor for driving the latent image carrier is stopped. Even after the power supply is stopped, the latent image carrier moves by the inertia of the drive motor.
Due to the movement of the latent image carrier surface corresponding to the inertia, the delay control means is operated by the delay control means for a predetermined period during which the latent image carrier part in which the potential charged with a polarity opposite to the charge polarity of the carrier remains facing the developing sleeve. A predetermined voltage is supplied to the developing sleeve by using an internal power source so that the potential difference between the potential of the latent image bearing member and the developing sleeve potential does not cause carrier adhesion to the latent image bearing member.

According to another aspect of the image forming apparatus of the present invention, the latent image carrier is reversed by the drive control means for a predetermined period after the main power source of the apparatus is turned on and before the image forming operation is started. When the power is turned on, the surface portion of the latent image carrier on the downstream side of the developing sleeve in the direction of movement of the latent image carrier in the forward direction is opposed to the developing sleeve, and the carrier attached to the surface portion is placed on the developing sleeve. Recovered by the magnetic force that forms the magnetic brush.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter referred to as a copying machine) which is an image forming apparatus will be described below. FIG. 1 is a front view showing a schematic configuration of a main part of a copying machine according to this embodiment. The photosensitive drum 1 as a latent image carrier is rotationally driven in the clockwise direction by an arrow by a main drive motor (not shown). A developing device 2 is arranged on the right side of the photosensitive drum 1. The developing device 2 includes two developing sleeves 21 and 21 facing the surface of the photosensitive drum 1.
A magnetic brush composed of a two-component developer containing a carrier and a toner is formed on the surface of the photosensitive drum 1 to visualize the electrostatic latent image formed thereon. As a structure for forming the magnetic brush on the developing sleeve 21 in this manner, various known structures can be adopted. For example, a fixed magnet is provided inside the hollow of the developing sleeve 21, and the magnetic force causes the magnetic carrier to which toner is attached by electrostatic force or the like to be attracted onto the developing sleeve 21 in a spike shape. A developing bias is applied to the developing sleeve 21 from a high voltage power source for developing bias. The developing device 2 shown in the figure also includes a stirring member 22 for stirring the developer in the casing, a separator 23 for collecting the developer on the developing sleeve 21 while guiding it to the lower portion of the casing, and the like. Around the photosensitive drum 1, in addition to the developing device 2, a uniform charger, an image exposure optical system, a transfer separation device, a cleaning device, which are not shown in order to execute a well-known electrophotographic process. A static eliminator or the like is provided. Further, a sheet feeding and conveying device (not shown) for feeding the transfer sheet to the transfer position on the surface of the photosensitive drum 1, a fixing device for fixing the toner on the transfer sheet separated from the surface of the photosensitive drum 1, and the like are also provided.

Image formation of this copying machine is performed as follows. First, the surface of the photosensitive drum 1 is uniformly charged by the uniform charger to about −800 V, and then the portion to which the toner is to be attached by the image exposure optical system is irradiated with, for example, laser light,
The potential is attenuated to about −100 V, and thereby an electrostatic latent image is formed. This electrostatic latent image is applied to the developing sleeve 21 by a developing device 2 in which a developing bias of −600 V is applied.
Reverse development with. That is, the negatively charged toner is attached to the character portion of about minus 100V. At this time, the relationship between the potential of the electrostatic latent image and the developing bias has the relationship shown in FIG. Further, the carrier is positively charged, which has the opposite polarity to the toner. The toner image formed on the photosensitive drum 1 by this development is transferred to the transfer paper at the transfer position, and is fixed to the transfer paper by the fixing device. On the other hand, the surface of the photosensitive drum 1 after the toner image is transferred onto the transfer paper is cleaned of residual toner by a cleaning device, and then the residual charge is neutralized by a neutralization device to prepare for the next image formation.

Incidentally, the bias applied to the developing sleeve 21 is minus 600 V as described above during the development in which the electrostatic latent image on the photosensitive drum 1 is opposed,
When the trailing edge of the electrostatic latent image passes, the voltage is switched to -100V. This is to prevent toner from adhering to the surface of the photosensitive drum 1 having a potential of 0 V after the trailing edge of the electrostatic latent image.

In such a copying machine, when the voltage supply to the main drive motor is stopped for some reason during the image forming operation, the photosensitive drum 1 is inertia even after the voltage supply to the main drive motor is stopped. The rotation is continued for a predetermined time and then stopped. The angle θ in the figure indicates the rotation angle due to this inertia. During the rotation of the inertia, the surface portion of the photosensitive drum 1 which is already charged to −800 V by the uniform charger may pass through the developing sleeve 21. Therefore, if the voltage supply to the developing sleeve is stopped at the same time as the voltage supply to the main drive motor is stopped as in the conventional case, it is about minus 800 as described above.
The developing sleeve 21 having 0V on the surface of the V photosensitive drum 1
The positive charge carrier on the top will stick. Therefore, in the present embodiment, during the rotation of the inertia, the potential of the developing sleeve 21 is minus 80 due to the uniform charger.
The bias is continuously applied to the developing sleeve 21 so that the potential does not adhere to the surface portion of the photosensitive drum 1 which is charged to 0V. Hereinafter, a specific example for this will be described.

First, the first specific example will be described. In this example, when detecting the opening of an openable / closable device door forming the side surface of the copying machine to stop the voltage supply to the main motor, during the rotation of the inertia of the photosensitive drum 1,
The voltage of minus 600 V, which is the same as during development, is continuously applied to the developing sleeve 21. For this,
In this example, unlike the drive power source for the main motor, the drive power source for the developing bias high-voltage power source is directly supplied from the DC power source in the device without the door switch that opens when the device door is opened. Wire as you would. And
The door switch is controlled so as to continue to apply the voltage of −600 V to the developing sleeve 21 for a certain period of time after it is detected that the door of the apparatus 8 is opened.
For example, as shown in FIG. 2 (a), a microcomputer or the like is configured to accept an interrupt by a signal (door open signal) that the door switch detects that the device door is opened, and execute the next subroutine A. CP consisting of
Configure (program) the U unit. In this subroutine A, waiting for a certain period of time from the time when the door open signal is received, for example, a period slightly longer than the rotation time for inertia of the photoconductor drum 1 which is obtained in advance by an experiment (step A1). ), The developing bias OFF signal is output to the developing bias high-voltage power supply circuit after the elapse of the certain time (step A2). The delay control means is realized by the above interrupt processing. The above CP
As in the conventional case, the control power of the U unit is configured to be directly supplied from the DC power supply in the device without using a door switch that opens when the device door is opened. Further, in this example, the developing bias ON signal output port to the developing bias high-voltage power supply circuit of the CPU unit is composed of a latch circuit, and once this is turned on, the port is switched to the off state until it is switched to the off state. Stay in the state.

By the way, depending on a specific timing (for example, a timing immediately after the end of development) during the image forming operation in which the apparatus door is opened, the photosensitive member facing the developing sleeve 21 is rotated during the inertia of the photosensitive drum 1. Drum 1
There are cases where the surface potential is 0V. Even in this case, if the developing sleeve 21 is applied during the rotation of the inertia of the photoconductor drum 1, the toner is minute (because the rotation of the inertia is minute), but toner is not present on the surface of the photoconductor drum 1 of 0V. It will stick. However, according to the example of the flowchart shown in the figure, if the development bias of minus 600V is being applied to the development sleeve 21 when the interruption is accepted, the minus 600V is maintained for the predetermined time.
After maintaining V, bias application is stopped, and conversely, when the interruption is accepted and the developing bias of minus 600 V is not being applied, the bias application is stopped after maintaining the bias state as it is for the predetermined time. .. Therefore,
Even if it is not judged whether the developing bias of minus 600V is being applied when the door open signal is received, the above toner adhesion can be prevented or reduced.

Unlike the example of the flow chart shown in the figure, when the door open signal is received, it is judged whether or not the developing bias of minus 600V is being applied. The application may be controlled so that the application of the developing bias of minus 600V is continued unless the application of the bias of minus 600V is being continued. Further, at the time of receiving the door oven signal, whether or not the minus 800 V charging area on the surface of the photosensitive drum 1 passes through the portion facing the developing sleeve 21 during rotation of the inertia of the photosensitive drum 1, Is determined from the sequence timing to apply minus 600V to the developing sleeve 21 only while the minus 800V charging area on the surface of the photosensitive drum 1 passes through the portion facing the developing sleeve 21. Is also good.

Next, the second specific example will be described. In this example, when the apparatus main power supply is cut off (AC power supply to the main body is cut off) by turning off the apparatus main switch or pulling out the plug, the developing process is performed during the rotation of the inertia of the photosensitive drum 1. The voltage of minus 600 V, which is the same as during development, is continuously applied to the sleeve 21. Therefore, in this example, a power supply switching circuit as shown in FIG. 3, for example, is configured. That is, in FIG. 3, a + 24V internal battery 13 and a + 5V internal battery 14 which are internal power supplies are provided so as to be connected to the developing bias high-voltage power supply circuit 10 and the CPU unit 11 via the switch circuit 12. The voltages of these internal batteries 13 and 14 are made to correspond to the voltage of the main body power source, which will be described later. As shown in FIG. 3, the switch circuit 12 supplies the developing bias high-voltage power source driving power source (+24 V) and the CPU unit control power source (+5 V) from the apparatus main power source to the developing bias voltage as shown in FIG. High-voltage power supply circuit 10
Are connected to the CPU unit 11, and in the operating state switched as indicated by arrow B in the figure, the internal batteries 13 and 14 are connected.
Is connected to the developing bias high-voltage power supply circuit 10 and the CPU unit 11 by, for example, a relay switch. In addition, the AC cutoff detection sensor 15 is replaced with the transformer 15
a and a rectifier circuit 15b, and the output g of the rectifier circuit 15b is used as a cutoff detection signal. This output g is the CPU
It is output to the unit 11 and is also used to switch the switch circuit 12 from the inactive state to the active state.
Further, there is also provided a timer circuit (not shown) for switching the switch circuit 12 to the inactive state when a predetermined time t _{1 has} elapsed after the switch circuit 12 was switched to the operating state. This timer circuit is also driven by the internal battery. This timer circuit, the switch circuit 12, and the AC cutoff sensor 1
5, the internal battery 13, the high voltage power source circuit for developing bias 10 and the CPU unit 11 are kept for a certain time t ₁ after the AC is cut off.
A timer unit 16 for supplying power from 14 is configured. The fixed time t ₁ is set to be longer than the developing bias application time t ₂ described later. Also in this example, the developing bias ON signal output port to the developing bias high-voltage power supply circuit of the CPU unit 11 is composed of a latch circuit, and once this is turned ON, switching to the OFF state or the like is performed. Maintain that state until. Then, from the time when the AC power cutoff sensor 15 detects that the AC power supply is cut off, a constant time t _{2 is applied} , and if necessary, the developing sleeve 21 is subjected to minus 600
Control is performed so that the voltage of V is continuously applied. For example, in FIG.
As shown in (b), when the signal g from the AC cutoff sensor 15 switches to the internal batteries 13 and 14, and the CPU unit 11 receives this signal g, the following subroutine B is executed. In addition, a CPU unit including a microcomputer is configured (programmed). In this subroutine B, the developing bias ON signal is output to the developing bias high-voltage power supply circuit 10 for a fixed time t ₂ which is slightly longer than the rotation time for the inertia of the photosensitive drum 1 (steps B1 and B2), and this constant time is reached. When t _{2 has} elapsed, the developing bias OFF signal is output (step B3). Here, the developing bias ON signal is output in step B1 of the flowchart shown in the flowchart when this subroutine switches the control power supply of the CPU unit 11 from the main body power supply (+ 5V) to the internal battery 14. This is because the CPU unit 11 may be reset at the time of this switching. That is, if the CPU unit 11 is reset at the time of this switching, the developing bias ON signal output port of the CPU unit 11 is reset even when the developing bias of −600 V is being applied at the time of this switching, and the developing bias remains as it is. This is because no voltage is applied. The delay control means is realized by the above processing and the power supply switching circuit.

By the way, according to the example of the flow chart shown in the above, depending on the specific timing during the image forming operation in which the AC power supply is cut off (for example, the timing immediately after the completion of the development), the amount of inertia of the photosensitive drum 1 may be increased. In some cases, the electric potential of the surface of the photosensitive drum 1 facing the developing sleeve 21 is 0 V during the rotation of, and although it is minute as described above, there is a possibility that toner adheres to the surface of the photosensitive drum 1 of 0 V. is there. In order to prevent or reduce this toner adhesion, as described in connection with the first specific example,
When the AC power interruption is detected, it is judged whether or not the developing bias of minus 600V is being applied to the developing sleeve 21, and when the minus 600V is being applied, the minus 600V is applied for the constant time t ₂ . After that, the bias application is stopped, and conversely, when the negative 600 V is not being applied, the bias application may be stopped after maintaining the bias state as it is for the predetermined time.

Next, another embodiment of the present invention will be described. In contrast to the above-described embodiment, the carrier is prevented from adhering to the surface of the photosensitive drum 1 when the voltage supply to the main drive motor is stopped during the image forming operation. Even when such carrier adhesion occurs, it is intended to prevent the occurrence of defects due to the carrier adhesion in the image forming operation performed thereafter. Therefore, in this embodiment, the photosensitive drum 1 is rotated in the opposite direction (counterclockwise) for a predetermined period after the main power source of the apparatus is turned on and before the image forming operation is started, so that the photosensitive drum 1 is rotated. The photosensitive drum 1 surface portion on the downstream side of the developing sleeve 21 in the direction of normal rotation is opposed to the developing sleeve, and the carrier attached to the surface portion forms a magnetic brush on the developing sleeve 21. It is recovered by a magnetic force (for example, a magnetic force of a magnet provided inside the hollow inside of the developing sleeve 21). Specifically, the drive system is configured so that the rotation of the photosensitive drum 1 can be rotated in the forward and reverse directions independently of other drive members (for example, the fixing roller in the fixing device, the rotating fur brush roller in the cleaning device, etc.). Keep it. For example, a forward / reverse rotation motor dedicated only to the photoconductor drum 1 may be provided, or a rotation direction reversing mechanism and an electromagnetic clutch for inserting / removing the mechanism in / from the drive transmission system from the drive motor to the photoconductor drum 1 may be provided. Then, after the main power supply of the apparatus is turned on, for a predetermined time, for example, only a time during which the photosensitive drum 1 can be rotated by an amount corresponding to the inertia,
A CPU unit including a microcomputer or the like is configured (programmed) so that the photosensitive drum 1 is reversely controlled. It is desirable that the developing sleeve 21 be rotated (for example, forward) during the reverse rotation of the photosensitive drum 1. For this purpose, the developing sleeve 21 is also configured to be driven independently of the other driving members in the same manner as the photosensitive drum 1. In this case, the photosensitive drum 1 and the developing sleeve 2
A dedicated drive motor for 1 may be provided. The developing sleeve 21 and the developing system such as the stirring member 22 may be driven in the same way. Further, during the reverse rotation of the photosensitive drum 1, a negative voltage may be applied to the developing sleeve 21 so as to promote the movement of the carrier to the developing sleeve 21 side. The value of the minus voltage may be set to minus 600V like the developing bias, or may be set to a value smaller than this in order to prevent or reduce toner adhesion.

[0023]

According to the first aspect of the invention, the inertia of the drive system for driving the latent image carrier after the opening / closing door of the apparatus is opened to stop the power supply to the drive motor for driving the latent image carrier. The surface of the latent image carrier moves by an amount corresponding to the charge polarity of the carrier, and the potential of the latent image carrier that has a potential opposite to the charging polarity of the carrier remains facing the developing sleeve for a predetermined period of time. Since a predetermined voltage that makes the potential difference between the potential and the developing sleeve potential not cause carrier adhesion to the latent image carrier is supplied from the high voltage power source for developing bias to the developing sleeve, carrier adhesion to the latent image carrier is achieved. Can be prevented.

According to the image forming apparatus of the second aspect, after the main power source of the apparatus is shut off, the surface of the latent image carrier is moved by the inertia of the drive system for driving the latent image carrier, and the charge polarity of the carrier is changed. The potential difference between the potential of the latent image carrier portion and the developing sleeve potential is held by the delay control means during the predetermined period in which the latent image carrier portion where the potential charged with the opposite polarity remains faces the developing sleeve. Since a predetermined voltage that does not cause carrier adhesion to the body is supplied to the developing sleeve using an internal power supply, carrier adhesion to the latent image carrier can be prevented.

According to another aspect of the image forming apparatus of the present invention, the latent image carrier is reversed by the drive control means for a predetermined period after the main power source of the apparatus is turned on and before the image forming operation is started. When the power is turned on, the surface portion of the latent image carrier on the downstream side of the developing sleeve in the direction of movement of the latent image carrier in the forward direction is opposed to the developing sleeve, and the carrier attached to the surface portion is placed on the developing sleeve. Since it is recovered by the magnetic force that forms the magnetic brush, it is possible to prevent or reduce problems caused by carrier adhesion to the latent image carrier.

[Brief description of drawings]

FIG. 1 is a front view showing a schematic configuration of a copying machine according to an embodiment.

FIG. 2A is a flowchart of control according to the embodiment,
6B is a flowchart of control according to another embodiment.

FIG. 3 is a circuit diagram according to another embodiment.

FIG. 4A is an explanatory diagram for explaining a relationship between a latent image potential during development and a developing bias, and FIG. 4B is a latent image carrier potential when carrier adhesion to the latent image carrier occurs. Explanatory drawing for demonstrating the relationship with a developing bias.

FIG. 5 is a graph showing the relationship between the potential difference between the latent image carrier and the developing bias potential, and the carrier adhesion to the latent image carrier.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Photoconductor drum, 2 Developing device 10 High voltage power supply circuit for developing bias, 11 C
PU unit 12 switch circuit, 13, 14
Internal power supply 21 Development bias

Claims (3)

[Claims] 1. A latent image carrier that is driven by a drive motor so that its surface moves, and a developing sleeve having a magnetic brush formed of a two-component developer containing a carrier and a toner charged to opposite polarities. The latent image carrier is uniformly charged to a polarity opposite to the charge polarity of the carrier, and then the potential of the portion to which the toner should be attached is attenuated to form a latent image,
In an image forming apparatus that develops the latent image by applying a developing bias having a polarity opposite to the charging polarity of the carrier to the developing sleeve, in response to the device door switch detecting that the device opening / closing door is opened. Drive control means for stopping the power supply to the drive motor, and delay control means for supplying a predetermined voltage from the high voltage power supply for developing bias to the developing sleeve during a predetermined period after stopping the power supply to the drive motor. An image forming apparatus characterized by being provided. 2. A latent image carrier that is driven by a drive motor so that its surface moves, and a developing sleeve having a magnetic brush formed of a two-component developer containing a carrier and a toner charged with opposite polarities. The latent image carrier is uniformly charged to a polarity opposite to the charge polarity of the carrier, and then the potential of the portion to which the toner should be attached is attenuated to form a latent image,
In an image forming apparatus for developing the latent image by applying a developing bias having a polarity opposite to the charging polarity of the carrier to the developing sleeve, the internal power source is used for a predetermined period after the main power source of the apparatus is shut off. An image forming apparatus, comprising: delay control means for supplying a predetermined voltage to the developing sleeve. 3. A latent image carrier driven by a drive motor so that its surface moves, and a developing sleeve having a magnetic brush formed of a two-component developer containing a carrier and a toner charged to opposite polarities. In an image forming apparatus having a latent image formed on a latent image carrier with toner in the magnetic brush, after the apparatus main power is turned on and before the image forming operation is started,
An image forming apparatus comprising drive control means for reversing the latent image carrier during a predetermined period.