JPS6230266A - Development bias controller for electrophotographic copying device - Google Patents

Abstract

PURPOSE:To prevent a carrier from sticking to a photosensitive body by controlling such that the leading and traling times of a bias voltage supplied to a developing part can change gradually. CONSTITUTION:A voltage V11 is outputted from a power source part 11 at a time t1 after 0.3sec has passed since a charge was electrified on the surface so of a photosensitive drum. This voltage V11 is integrated by an integrating circuit 17 composed of a resistance 13 and a capacitor 15. A developing bias voltage V9 being the integrated output rises gradually in 0.2sec as times t1 and t3 show, and the tailing part of the end changes gradually in a longer time as times t5-t7 show. As a result, since the developing bias voltage V9 is not suddenly impressed like in a conventional method, an electric field does not occur abruptly in the photosensitive drum 1. Accordingly a carrier does not stick as seen in a conventional method.

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, and then forming a reversal latent image from which the charge is removed by exposure. The present invention relates to a development bias control device in an electronic copying apparatus of a so-called reversal development type that develops by attaching developer toner to an image area.

[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 by a charger is exposed to light to form an electrostatic latent image, and a toner of a developer consisting of a carrier and toner is adhered to this electrostatic latent image for development. In a reversal type electronic copying apparatus using an OPC photosensitive drum, development is performed by attaching toner of a developer to the reversed 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 tendency for Kireliya to be 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, a charging charger that charges the surface of the photosensitive drum is located in front of the developing section, and after the surface of the photosensitive drum is charged in advance by the charging charger, the charged surface of the photosensitive drum passes through the exposure section, and then passes through the developing section. When the charged photosensitive drum surface passes through the developing area, a developing bias voltage is applied to the developing area.At this time, if a steep developing bias voltage is suddenly applied, , an electric field is suddenly generated on the photosensitive drum, causing a problem of carrier adhesion, in which carriers adhere to the photosensitive drum.

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.

[Purpose of the invention]

The present invention has been made in view of the above, and the object thereof is to prevent carrier adhesion and black solids by a simple and economical method, and to operate a phenomenon bias control device in an electronic copying machine properly. Our goal is to provide the following.

[Summary of the invention]

In order to achieve the above purpose, the surface of the photoreceptor is charged with electric charge, and then exposed to light to form an electrostatic latent image, and this exposed and charge-removed reversed latent image portion is developed in a developing section. The gist of the present invention is to provide a developing bias control device for an electronic copying apparatus of the above-mentioned type, including a control circuit that controls the rise and fall times of the bias voltage supplied to the developing section so as to gradually change them.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be demonstrated 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 an arrow 2 in the figure, and the surface of the photosensitive drum 1 charged by the charging charger 3 is located at an exposure section 7 adjacent to the charging charger 3 as shown by an arrow 5 (not shown). It is designed to be exposed to light reflected from the copy original. 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 phenomenon section is arranged adjacent to the photosensitive drum 1.
3 and a capacitor 15, and includes a transformer that supplies a developing bias voltage to the magnetic sleeve 9 via the integrating circuit 17.
Connected to 1. That is, the magnetic sleeve 9
is the bias voltage output from the power supply section 11 to the integrating circuit 1
7, the rising and falling edges of the bias voltage are integrated, and the bias voltage is gradually changed over a longer period of time. Note that the rotation of the photosensitive drum 1 is such that the time T from when the surface of the photosensitive drum 1 passes the portion directly below facing the charging charger 3 to when the surface passes the portion facing the magnetic sleeve 9 is, for example, 0. It is set to 4 seconds. In addition, charging charger 3
As shown in FIG. 2, a timing circuit (not shown) performs timing control such as the timing at which the charging voltage is supplied to the magnetic sleeve 9 and the timing at which the developing bias voltage is applied to the magnetic sleeve 9.

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.

In FIG. 2, a charging voltage (3) is supplied to the charging charger 3 at time to, and the surface SO of the photosensitive drum 1 facing the charging charger 3 is charged with negative polarity. The surface of the charged photosensitive drum is exposed to light in the exposure section 7, the charge is removed by this exposure, an electrostatic latent image is formed in the portion where the charge remains, and the photosensitive drum 1 has a zero potential due to the removal of the charge. An inverted latent image, which is the opposite image to the electrostatic latent image, is formed on the surface of the electrostatic latent image.

Also, after the photosensitive drum surface sO is charged with a charge, it becomes 0.
At time t1 after 3 seconds have elapsed, the voltage V11 is applied from the power supply section 11.
is output. This voltage V11 is integrated by an integrating circuit 17 consisting of a resistor 13 and a capacitor 15, and the developing bias voltage V9, which is the integrated output, gradually rises over 0°2 seconds as shown from time t1 to t3, and then at the end. The falling portion also gradually changes in length as shown from time t5 to t7. As a result, the developing bias voltage v9 is not applied in 8-volts as in the conventional case.
Since an electric field is not suddenly generated on the photosensitive drum 1, the carry V marking as in the conventional case does not occur. The developing bias voltage ■9 that gradually changes in this way and rises completely at time t3 is applied to the magnetic sleeve 9,
A developer consisting of a carrier 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.
The toner is negatively charged.

The toner of the developer supplied to the magnetic sleeve 9 in this way is exposed by the exposure unit 7, and the charge is removed, and the toner adheres to the surface portion of the photosensitive drum 1 that has become zero potential, that is, the inverted latent image portion, and the surface of the photosensitive drum 1 is removed. Develop a reversal latent image of
A reversal development is formed on the surface of the photosensitive drum. 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).

As mentioned above, the developing bias voltage V9 supplied to the magnetic sleeve 9 starts to rise at time t1, which is 0.3 seconds after time to, and completely rises at time t3, which is another 0.2 seconds after time to. However, the center time of this rise is the surface S of the photosensitive drum 1 that was first negatively charged by the charging charger 3 at time to.
This corresponds to time t2 when O rotates and reaches a position facing the magnetic sleeve 9 after 0.4 seconds have elapsed from time to.

Considering this time relationship centering on the position facing the magnetic sleeve 9, at time to, the charging charger 3
Even if charging voltage V3 is supplied at time to, only the surface SO of photosensitive drum 1 facing charging charger 3 is charged at time to, and 0.4 seconds elapse from time to (before 2, the magnetic sleeve Since the surface of the photosensitive drum 1 passing through the position facing the magnetic sleeve 9 has not yet been charged, it is thought that the charging voltage v3 has not yet been supplied to the position facing the magnetic sleeve 9. and magnetic sleeve 9
For charging the position opposite to □Pressure V
3 is the waveform of the charging voltage V3 in FIG. 2, which can be considered as being supplied at time t2 as indicated by a two-dot chain line 21.

Therefore, considering the position facing the magnetic sleeve 9' as the center, the developing bias voltage 9 starts to rise at time t1, which is 0.1 seconds earlier than the time t1 when the charging voltage v3 is supplied. It completely rises at time t3, which is 0°1 second later than time t2 when v3 is supplied.

That is, at time t3 when the developing bias voltage V9 is completely supplied, the charging voltage 3 is completely supplied and the voltage facing the magnetic sleeve 9 is
The surface of the photosensitive drum 1 is completely charged. As a result, at the time when the developing bias voltage v9 is supplied as in the conventional case, the surface portion of the photosensitive drum 1 facing the magnetic sleeve 9 will not be charged and have zero potential.
This prevents solid black from appearing in this area as in the past. Moreover, as can be seen from FIG. 2, this time relationship is the same for the trailing edge portions of each signal.

FIG. 3 is a circuit diagram of a developing bias control device in an electronic copying machine according to a further embodiment of the present invention. The circuit shown in this embodiment differs from the circuit shown in FIG. The configuration is such that the fall time can be set separately for each. That is, the integrating circuit 27 of the circuit shown in FIG. 3 is constructed by connecting diodes 35, 39 in series with each resistor 33, 37,
The rise time is controlled by the time constant of the resistor 37 and capacitor 15 connected to the diode 39, and the fall time is controlled by the time constant of the resistor 33 and capacitor 15 connected to the diode 35.
It is determined by which time constant it is controlled.

[Effects of the Invention] As explained above, according to the present invention, since the rise and fall times of the bias voltage supplied to the developing section are controlled to gradually change, sudden electric fields on the photoreceptor are prevented. Because there is no generation of carriers, there is no possibility of carriers adhering to the photoreceptor. In addition, the saturation point of the falling portion of the bias voltage supplied to the developing section is after the point at which the charging voltage is applied to the charging section to charge the surface of the photoreceptor, so the bias voltage has completely risen. Because the surface of the photoreceptor is not charged and is not at zero potential at the moment the bias voltage rises, toner may adhere to the surface of the photoreceptor at zero potential after the bias voltage rises, resulting in solid black. do not have.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a developing bias control device in an electronic copying machine showing one embodiment of the present invention, FIG. 2 is a waveform diagram showing the operation of the circuit shown in FIG. 1, and FIG. 3 is another embodiment of the present invention. FIG. 2 is a circuit diagram of a developing bias control device in an electronic copying apparatus showing an example. 1... Photosensitive drum 3... Charging charger 9... Magnetic sleeve 11... Power supply part 13... Resistor 15...
Capacitor 17...Integrator circuit Figure 1 to t1t2t3 t4
t5t6t7 Figure 2

Claims (3)

[Claims] (1) Electronic copying 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 this exposed and charge-removed reversal latent image portion is developed in a developing section. 1. A developing bias control device for an electronic copying apparatus, comprising a control circuit that controls the rise and fall times of a bias voltage supplied to a developing section so as to gradually change. (2) The phenomenon bias control device for an electronic copying machine according to claim 1, wherein the control circuit is constituted by an integrating circuit. (3) The saturation point of the rising portion of the bias signal is after the point in time when a charging voltage is applied to the charging section to charge the surface of the photoreceptor. A developing bias control device in an electronic copying apparatus according to item 2.