JPS6230267A - Developing bias controller for electrophotographic copying device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a black solid by supplying a bias voltage to a developing part through a switch means only when a picture signal is supplied and opening the switch means so as to make the developing part in a floating state when there is no picture signal. CONSTITUTION:In terms of a transfer operation a developing bias voltage V11 is supplied to a magnet sleeve 9 only when the picture signal is supplied to turn on a switch 13. During other periods the switch 13 is off. Accordingly the magnet sleeve 9 is in the floating state, and therefore its potential is the same as the surface of a photosensitive drum 1. As a result, the carrier sticking and the black solid, which are found in a conventional method, hardly occur, when a picture is not transferred.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention involves charging the surface of a photoreceptor and then exposing it to light to form an electrostatic latent image. The present invention relates to a developing bias control device in an electronic copying apparatus of a reversal development type that develops by attaching toner of a developer to a reversal latent image portion.

[Technical background of the invention and its problems] Normal development method
In other words, in an electronic copying machine that does not use a reversal development method,
The surface of a photosensitive drum charged with an electric charge is exposed to light to form an electrostatic latent image, and toner of a developing material consisting of a carrier and toner is adhered to this electrostatic latent image to develop it. In a reversal development type electronic copying apparatus using an OPC photosensitive drum, development is carried out by attaching developer toner to a reversal latent image portion on the exposed side of the photosensitive drum from which the charge has been removed. In other words, the developer toner is attached to the areas where the electric charge is removed and the potential becomes zero when exposed to light, but the electric charge remains in the areas that are not exposed to light, so this area is exposed to iron powder, etc. There is a problem that other carriers are easily attached. In particular, carriers tend to adhere to the boundary between a portion on the surface of the photosensitive drum that is charged to, for example, about 800 volts and a portion that has been exposed to light and has had its charge removed.

Further, the charger that charges the surface of the photosensitive drum is located in front of the developing section, and is pre-charged with 1? - After the photosensitive drum surface is charged, the charged photosensitive drum surface passes through an exposure section and further passes through a developing section, and when the charged photosensitive drum surface passes through the developing section, A developing bias voltage is applied to the developing section, but if a steep developing bias voltage is suddenly applied at this time, an electric field is suddenly generated on the photosensitive drum, causing the problem of carrier adhesion, where carriers adhere to the photosensitive drum. occurs.

In addition, if the photosensitive drum surface is charged too late than the time when the developing bias voltage is applied, when the uncharged photosensitive drum surface passes through the developing section to which the developing bias voltage has already been applied, the photosensitive drum surface Since the potential of the photosensitive drum is zero, which is the same as that when the photosensitive drum is exposed, there is a problem that toner adheres to the surface of the photosensitive drum, resulting in a solid black area, that is, a black area is formed on the copy paper.

Furthermore, when a jam occurs in the apparatus, at that point the apparatus simultaneously cuts off the power to all internal parts, ie, the charging section, the photosensitive drum section, the developing section, various drive motors, etc. For this reason, Ji1! The potential that existed on the surface of the photosensitive drum at the time when the problem occurred and all power supplies were cut off remains on the surface of the photosensitive drum. All power supplies are turned off with a potential remaining on the surface of the photosensitive drum, and when the jam is repaired in this state and the power of the device is turned on, the carrier is pulled by the potential remaining on the surface of the photosensitive drum. The same problem as described above of carrier adhesion to the photosensitive drum occurs. The problem of carrier adhesion caused by jams also occurs during power outages.

OBJECT OF THE INVENTION] The present invention has been made in view of the above, and its object is to prevent carrier adhesion and black spots by a simple and economical method, and to provide an electronic copying apparatus that operates properly. An object of the present invention is to provide a developing bias control device.

[Summary of the Invention] In order to achieve the above object, the surface of a photoreceptor is charged with an electric charge, and then exposed to light to form an electrostatic latent image. In a developing bias control device for an electronic copying apparatus using a reversal developing method that performs development in a developing section, the present invention operates in response to an image signal to supply a bias voltage to the developing section, and opens when there is no image signal. The gist is that a switch means is provided.

[Embodiments of the invention] Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a circuit diagram of a developing bias control device in an electronic copying apparatus according to an embodiment of the present invention. The electronic copying apparatus shown in the figure is a reversal development type electronic copying apparatus using an OPC photosensitive drum 1, and the surface of the photosensitive drum 1 is charged to, for example, a negative potential by a charging charger 3. The photosensitive drum 1 rotates counterclockwise as shown by the arrow 2 in the figure, and the electrostatic charge 11-
The surface of the photosensitive drum 1 charged at 3 is exposed at an exposure section 7 adjacent to the charging charger 3 to be exposed to light reflected from a copy document (not shown) as indicated by an arrow 5. As a result, the charges on the exposed surface of the photosensitive drum 1 are removed, and the remaining charges form an electrostatic latent image on the surface of the photosensitive drum. Further, next to the exposure section 7, a magnetic sleeve 9 constituting a developing section is disposed adjacent to the photosensitive drum 1. It is connected to a power supply unit 11 including a transformer that supplies a developing bias voltage V11 to the image forming apparatus. That is, the magnetic sleeve 9 is supplied with the developing bias voltage V11 from the power supply section 11 only when the switch 13 is closed. A control coil 15 of the switch 13 is excited by an image signal from a control section (not shown), and is thereby turned on and off.

That is, when the control coil 15 is excited by the image signal, the switch 13 is closed.

Next, the operation of the developing bias control device in the electronic copying apparatus shown in FIG. 1 will be explained with reference to the waveforms in FIG. 2.

When the apparatus starts, each drive motor for the photosensitive drum 1 and the magnetic sleeve 9 rotates, and as shown in FIG. 2, a charging voltage V3 is supplied to the charging charger 3.
As a result, the surface of the photosensitive drum 1 facing the charging charger 3 is charged to a negative potential, and the power supply section 11 generates a developing bias voltage V11. Even if the developing bias voltage V11 is generated from the power supply unit 11, the switch 13 remains open, so the voltage V11 is applied to the magnetic sleeve 9.
11 is not supplied, and the magnetic sleeve 9 is in a floating state.

When the magnetic sleeve 9 is in a floating state as described above, the magnetic sleeve 9 is drawn to the surface potential of the adjacent photosensitive drum 1 and has the same potential as the surface potential of the photosensitive drum 1, so that the magnetic sleeve 9 and the photosensitive drum 1 are connected to each other. There is no potential difference between them.

In this way, since there is no potential difference between the two, carriers and toner are not attracted to the other,
Conventional problems such as carrier adhesion and black spots are completely eliminated.

As described above, when the charging voltage V3 is supplied to the charging charger 3, and thereby the surface of the photosensitive drum 1 facing the charging charger 3 is charged to a negative potential, the charged surface of the photosensitive drum 1 is placed in the exposed area. 7, the charge is removed by this exposure, an electrostatic latent image is formed on the part where the charge remains, and an image opposite to the electrostatic latent image is formed on the surface part of the photosensitive drum 1 where the charge is removed and becomes zero. An inverted latent image is formed.

On the other hand, an image signal is sent to the control coil 15 from a control section (not shown).
is supplied and energized, this causes switch 13
operates only while this image signal is being generated and is turned on as shown in FIG. A developer consisting of a carrier such as iron powder and toner is supplied to the magnetic sleeve 9 from a hopper (not shown) or the like. In this case, since a negative bias voltage is supplied to the magnetic sleeve 9, the carrier is positively charged and the toner is negatively charged.

As described above, the toner of the developer supplied to the magnetic sleeve 9 is exposed to light by the exposure unit 7, and the surface portion of the photosensitive drum 1 has a zero potential due to the removal of electric charges.
That is, it adheres to the reverse latent image portion, develops the reverse latent image on the surface of the photosensitive drum 1, and forms a reverse developed image on the surface of the photosensitive drum 1. After the reverse development is formed in this manner, the reverse image is copied onto the copy paper by a transfer section, a fixing section, etc. (not shown).

This copying operation is performed only while the image signal is supplied and the switch 13 is on, and stops when the switch 13 is turned off. For example, when copying many originals, this image signal is supplied each time one original is copied, and when the switch 13 is turned on and one copy is made, the image signal disappears and the switch 13 is also turned off.

Further, when the next image signal is supplied to copy the next document, the switch 13 is turned on again and the copying operation is performed.

As a result, in this copying operation, the developing bias voltage V11 is supplied to the magnetic sleeve 9 only when the image signal is supplied and the switch 13 is on, but since the switch 13 is off during other periods, the magnetic sleeve 9 9 is in a floating state, so that the potential of the magnetic sleeve 9 is the same as the potential of the surface of the photosensitive drum 1. For this reason, when an image is not copied, carrier adhesion and solid black do not occur as in the conventional method.

Note that when a jam occurs, all power supplies are cut off, and in this state, charges remain on the surface of the photosensitive drum 1. Then, after the jam is repaired, the power is turned on again, but at this time, the charge remaining on the surface of the photosensitive drum 1 would have drawn in carriers and caused carrier adhesion in conventional devices; In this device, when the power is turned on again, the switch 13 is not turned on and the magnetic sleeve 9 is in a floating state.
Since the potential is the same as that of the photosensitive drum 1, the problem of carriers being drawn in and attached by charges remaining on the surface of the photosensitive drum 1 is eliminated.

This effect is the same even when a power outage occurs, and carrier adhesion does not occur even during a power outage.

[Effects of the Invention] As explained above, according to the present invention, the bias voltage is supplied to the developing section via the switch means only when an image signal is supplied, and the switch means is opened when there is no image signal. Since the developing section is in a floating state, the potential of the developing section is the same as the potential of the facing photoreceptor in this floating state, so when the power is turned on again after a jam or a power outage, the developing section is in a floating state. This prevents carriers and toner from the developing section from adhering to the photoreceptor, and from causing black solids, even when this happens, and at other times as well.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a developing bias control device in an electronic copying apparatus showing an embodiment of the present invention, and FIG. 2 is a waveform diagram showing the operation of the circuit shown in FIG.

Claims (1)

[Claims] Development in an electronic copying device using a reversal development method, in which the surface of a photoreceptor is charged with an electric charge, then exposed to light to form an electrostatic latent image, and the exposed and charge-removed portion of the reversal latent image is developed in a developing section. The bias control device operates in response to an image signal to supply a bias voltage to the developing section;
1. A developing bias control device for an electronic copying machine, comprising a switch means that is open when there is no image signal.