JPH10339988A - Toner image recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a toner image forming device capable of keeping the surface potential of a photoreceptor at a fixed voltage, even if a discharge voltage is changed and further, high printing quality, without being affected by an environmental condition such as humidity. SOLUTION: A fixed transfer current (i) is supplied to a photoreceptor drum 2 from a transfer roller 12, to obtain a transfer voltage value V0 in a state where the drum 2 is not electrified and a transfer voltage value V1 in a state where a previously set electrifying voltage is applied to the drum 2. Further, the V0 is subtracted from the V1, to obtain the surface potential of the drum 2 and an electrifying high-voltage power source 8 is reset with an electrifying control signal (b), so as to make the potential of the surface of the drum 2 become a desired value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner image forming apparatus used for an electrophotographic printer or the like.

[0002]

2. Description of the Related Art Conventionally, a toner image forming apparatus, for example, a toner image forming apparatus used in an electrophotographic printer, rotates in a predetermined direction by applying a voltage from a high voltage power supply for charging to a charger. The surface of the photoreceptor is uniformly charged with an electric charge, and an exposure device forms an electrostatic latent image having a potential of almost 0 V on the surface of the photoreceptor based on the print data, and charges the electrostatic latent image with a negative charge. The developed toner is supplied from a developing device and developed, and the developed toner on the surface of the photoreceptor is transferred to a transfer material by a transfer device.

[0003] The photoreceptor is mainly charged by discharge at and near the contact point between the charger and the photoreceptor. The potential obtained by subtracting the discharge starting voltage determined by Paschen's law or the like from the charging voltage of the charger is almost equal to the potential. It becomes the surface potential of the photoconductor.

The toner supplied from the developing device is pulled by the cloning force and adheres to the electrostatic latent image, and does not adhere to and repel other than the electrostatic latent image (printing background portion).

[0005]

In the conventional toner image forming apparatus, when the surface of the photosensitive member is charged with electric charge, even if the voltage of the charger is kept constant, the discharge voltage becomes lower than the humidity. The surface potential of the photoreceptor cannot be maintained at a predetermined voltage because it varies depending on environmental conditions, and when the potential is low, toner fogging occurs and print quality is degraded.

The present invention provides a toner image forming apparatus capable of maintaining the surface potential of a photoreceptor at a predetermined voltage even when a discharge voltage changes and maintaining good print quality without being affected by environmental conditions such as humidity. It is intended to provide.

[0007]

In order to achieve the above object, in a toner image forming apparatus according to the present invention, a predetermined voltage is applied to a charger to detect a surface potential of a photosensitive member. A potential detection means, and a discharge start voltage value for charging the surface of the photoreceptor is obtained from an output of the photoreceptor surface potential detection means, and a charging control signal is applied so that the surface of the photoreceptor has a predetermined surface potential. Charging control means for controlling the high-voltage power supply.

[0008]

Embodiments of the present invention will be described with reference to the drawings. Elements common to the drawings are denoted by the same reference numerals. First Embodiment FIG. 3 is a block diagram showing a configuration of a toner image forming apparatus. The toner image forming apparatus 1 includes a charger 3, an exposure device 4 (hereinafter, referred to as a recording head 4), a developing device 5, and a photosensitive member 2 (hereinafter, referred to as a photosensitive drum 2) rotating in the direction of arrow A.
A transfer device 6 is provided.

The charger 3 has a charging roller 7 which rotates in contact with the surface of the photosensitive drum 2 and a charging high-voltage power supply 8 which applies a high voltage to the charging roller 7. For example, the surface of No. 2 is uniformly charged with a charge of, for example, 800V.

The recording head 4 includes, for example, LED (light emitting diode) elements of the same number as the number of pixels for one line, and a potential of almost zero is applied to the surface of the photosensitive drum 2 based on print data.
A V electrostatic latent image is formed.

The developing device 5 includes a developing roller 9 which rotates in contact with the surface of the photosensitive drum 2, a blade 10 which contacts the surface of the developing roller 9, and a negative roller to the developing roller 9. A developing high-voltage power supply 11 for applying a high voltage;
The thickness of the toner is reduced between the blade and the blade 10, and a negative charge is charged by frictional charging. The negatively charged toner is attracted to and adheres to the electrostatic latent image due to the Cron's force, and repels and does not adhere to portions other than the electrostatic latent image (printing background portion).

The transfer unit 6 has a transfer roller 12 which rotates in contact with the surface of the photosensitive drum 2 and a transfer high-voltage power supply 13 for applying a positive high voltage to the transfer roller 12. The developing toner 14 is transferred to the printing paper 15 from the surface of the body drum 2.

FIG. 1 is a charge control circuit diagram according to the first embodiment. The control unit 20 has a microprocessor,
A surface potential detection signal a is input from the transfer high voltage power supply 13 via the A / D converter 21, and the charging control signal b and the transfer control signal c are supplied to the charging high voltage power supply 8 and the transfer high voltage power supply 13, respectively.
Is output.

The charging voltage applied from the charging high-voltage power supply 8 to the charging roller 7 is controlled based on a charging control signal b. Similarly, the transfer voltage applied from the transfer high-voltage power supply 13 to the transfer roller 12 is controlled based on a transfer control signal c.

The voltage feedback signal d from the high voltage power supply 13 for transfer is input to the high voltage control circuit 22 and the A / D
The signal is input to the converter 21 and converted into a surface potential detection signal a. The output of the high voltage control circuit 22 is input to the base terminal of the transistor TR1, and the amplified collector current flows through the primary winding N1 of the transformer T1. The output of the secondary winding N2 of the transformer T1 is a diode D1, a capacitor C1,
The positive output that is input to the smoothing circuit made up of the resistor R1 and smoothed is applied to the transfer roller 12 as a transfer voltage.

The negative side of the resistor R1 is grounded via a current detecting resistor Rs and the buffer amplifier BF
Entered into 1. The transfer current i passes through the current detection resistor Rs, and the voltage applied to the current detection resistor Rs is proportional to the transfer current i. Therefore, the transfer current i is input to the high voltage control circuit 22 as a current feedback signal e.

The output of the secondary winding N3 of the transformer T1 is input to a smoothing circuit consisting of a diode D2, a capacitor C2 and a resistor R2. The output of the smoothing circuit is passed through a buffer amplifier BF2 to a voltage feedback signal. d. Since the windings N2 and N3 are connected in the transformer T1, the transfer voltage is proportional to the voltage feedback signal d, and the transfer voltage can be detected from the voltage feedback signal d.

The high-voltage control circuit 22 drives the transistor TR1 to a predetermined voltage or current while monitoring the voltage feedback signal d and the current feedback signal e based on the transfer control signal c.

Therefore, the voltage value and the current value of the output of the transfer high-voltage power supply 13 are determined by the transfer control signal c, and the output voltage can be detected by the surface potential detection signal a.

FIG. 2 is an explanatory diagram showing the relationship between the transfer voltage and the transfer current. Curves B and C indicate whether or not the photosensitive drum 2 is charged.
Has the relationship shown in FIG. The transfer voltage difference ΔV when the transfer current value is constant is substantially equal to the surface potential of the photosensitive drum 2. Accordingly, in order to determine the surface potential of the photosensitive drum 2, a predetermined transfer current is supplied to the photosensitive drum 2 from the transfer high-voltage power supply 13, and the surface of the photosensitive drum 2 is charged by applying a predetermined voltage. The transfer voltage difference .DELTA.V between the transfer voltage value V0 in the state where the charging is not performed and the transfer voltage value V1 in the state where the surface of the photosensitive drum 2 is charged by the charging roller 7 may be obtained.

Next, the operation will be described with reference to FIG.
FIG. 4 is a flowchart showing the operation of the first embodiment. In step S1, the control unit 20 rotates the photosensitive drum 2 together with the start of warm-up before the start of printing.

In step S2, the control unit 20 controls the high voltage power supply 13 for transfer so that a constant transfer current i (for example, 4 .mu.A) flows through the transfer roller 12 based on the transfer control signal c, as shown in FIG. The detected transfer voltage V0 is detected.

In step S3, the control unit 20 sets the desired potential on the surface of the photosensitive drum 2 to 800 V and sets the discharge starting voltage to 50.
0 V, and the high voltage power supply for charging 8 based on the charging control signal b.
Charge voltage applied to the charging roller 7 from 800 to 500
= 1300V is set.

In step S4, the control unit 20 determines in step S4
2, the transfer voltage V1 shown in FIG. 2 is detected, and the voltage value V0 is subtracted from the voltage value V1 to determine the surface potential ΔV of the photosensitive drum 2.

In step S5, the control unit 20 determines that the surface potential Δ
The actual discharge start voltage is obtained from V, the charging voltage is reset based on the charging control signal b, and the process is terminated.

For example, if the detected surface potential of the photosensitive drum 2 is .DELTA.V = 900 V, it is detected that the actual discharge start voltage is 1300-900 = 400 V. 400 + 800 = 1200
The charging control signal b is controlled so as to apply a charging voltage of V.

According to the first embodiment, the photoreceptor surface potential detecting means for detecting the surface potential of the photoreceptor is also used as a high voltage power supply for transfer, so that an expensive surface voltmeter is not newly provided. As a result, it is possible to provide an inexpensive toner image recording apparatus while reducing the size of the recording apparatus.

Second Embodiment FIG. 5 is a charge control circuit diagram according to a second embodiment.
The control unit 30 has a microprocessor, and outputs a surface potential detection signal f from the charging high-voltage power supply 8 through the A / D converter 31.
, And outputs a charging control signal g and a potential detection signal h to the high voltage control circuit 32 and the sine wave oscillator 33, respectively.

The charging output (charging voltage) j applied from the charging high-voltage power supply 8 to the charging roller 7 is controlled based on a charging control signal g.

The output of the high voltage control circuit 32 is a transistor T
The collector current input to the base terminal of R2 and amplified, flows through the primary winding N1 of the transformer T2. Transformer T
The output of the secondary winding N2 is input to a smoothing circuit comprising a diode D3, a capacitor C3, and resistors R4 and R5.
The charge output j is applied to the transfer roller 7.

The resistors R4 and R5 constitute a voltage dividing circuit at the same time as the discharging resistance of the capacitor C3, and divide the charging output j. The divided voltages are averaged by the capacitor C5 and input to the buffer amplifier BF3. The output of the buffer amplifier BF3 becomes a voltage feedback signal k, which is input to the high voltage control circuit 32 and the A / D converter 31.
Is converted into a surface potential detection signal f.

That is, the voltage feedback signal k is obtained by dividing the charging output j and averaging it, and is proportional to the charging output j. The control unit 30 receives the surface potential detection signal f and can detect the charging output j applied to the charging roller 7.

The high-voltage control circuit 32 drives the transistor TR2 based on the charging control signal g so as to monitor the voltage feedback signal k so that the charging output j has a predetermined voltage value. Accordingly, the voltage value of the charging output j is determined by the charging control signal k, and the voltage value can be detected by the voltage feedback signal k.

The primary side of the transformer T3 is connected so that a sine wave is input from a sine wave oscillator 33.
The sine wave AC voltage output from the secondary side can be applied to the charging roller 7 via the capacitor C4. The control unit 30 controls the start and stop of the oscillation of the sine wave oscillator 33 based on the potential detection signal h.

FIG. 6 is a waveform diagram of a sine wave alternating current output from the secondary side of the transformer T3, in which the discharge start voltage has + α, for example, several hundred volts.

Next, the operation will be described with reference to FIG.
FIG. 9 is a flowchart for explaining the second embodiment. In step S1, the control unit 30 sets the password before starting printing.
The photoreceptor drum 2 is rotated at the same time as the start of operation.

In step S2, the control section 20 applies a predetermined voltage to the charging roller 7 from the charging high voltage power supply 8 based on the charging control signal g. For example, the desired potential on the surface of the photosensitive drum 2 is 800 V, the discharge starting voltage is 500 V, and the charging voltage applied to the charging roller 7 is 800 + 500 = 13.
Set to 00V.

After the photosensitive drum 2 has rotated one or more turns and the entire circumference has been charged, in step S3, the control unit 20 stops applying a voltage to the charging roller 7 by the charging control signal g.

In step S4, the control section 20 starts oscillating the sine wave oscillator 33 in response to the potential detection signal h. From the secondary side of the transformer T3, a sine wave AC signal m as shown in FIG.
However, as shown in FIG.
Is applied to Electric discharge is started between the charging roller 7 and the photosensitive drum 2, and the average of the potential of the charging roller 7 and the surface potential of the photosensitive drum 2 become substantially equal. This is because the magnitude of the surface potential of the photosensitive drum 2 is reflected on the potential of the charging roller 7 irrespective of the discharge start voltage value since the sine wave AC voltage value exceeds the discharge start voltage value. .

With this potential, the capacitors C3 and C4 are charged, and the capacitor C3 is averaged as a signal n as shown in FIG. 8 through the resistor R3, and is further divided by the resistors R4 and R5. Capacitor C5
Are further averaged, and reflected on the surface potential detection signal f as described above.

In step S5, the control unit 20 detects the surface potential of the photosensitive drum 2 from the surface potential detection signal f, and
As described in the embodiment, the actual discharge start voltage is obtained, and the charging voltage is reset based on the charging control signal b.
The process ends.

The sine wave AC voltage was provided to the charging high voltage power supply 8 and applied to the charging roller 7. However, the direction of the diode D3 in the circuit diagram shown in FIG. 13
The sine wave oscillator 33, transformer T3 and capacitor C4 are deleted from the circuit diagram shown in FIG.
The sine wave AC voltage may be supplied from the transfer roller 12.

According to the second embodiment, the photoreceptor surface potential detecting means for detecting the surface potential of the photoreceptor is also used as a high-voltage power supply for charging, so that an expensive surface voltmeter is not required. As a result, it is possible to provide an inexpensive toner image recording apparatus while reducing the size of the recording apparatus.

[0044]

Since the present invention is configured as described above, it has the following effects. A photoreceptor surface potential detecting means for detecting the surface potential of the photoreceptor; and a discharge starting voltage value when a voltage is applied to the surface of the photoreceptor by the charger, from the surface potential of the photoreceptor. By providing a charging control means for controlling a charging high-voltage power supply by a charging control signal so as to reach a surface potential, the surface potential of the photoreceptor can be maintained at a predetermined voltage even when the discharge voltage changes, and humidity and the like can be maintained. And good print quality can be maintained without being affected by the environmental conditions.

[Brief description of the drawings]

FIG. 1 is a charge control circuit diagram according to a first embodiment.

FIG. 2 is an explanatory diagram showing a relationship between a transfer voltage and a transfer current.

FIG. 3 is a block diagram illustrating a configuration of a toner image forming apparatus.

FIG. 4 is a flowchart showing the operation of the first embodiment.

FIG. 5 is a charge control circuit diagram according to a second embodiment.

FIG. 6 is a waveform diagram of a sine wave alternating current.

FIG. 7 is a waveform diagram of a sine wave alternating current applied to a charging roller.

FIG. 8 is a waveform diagram of a sine wave alternating current passing through capacitors C3 and C4.

FIG. 9 is a flowchart showing the operation of the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Toner image recording device 8 High voltage power supply for charging 13 High voltage power supply for transfer 20, 30 Control unit 21, 31 A / D converter 33 Sine wave oscillator

Claims (5)

[Claims] 1. A voltage is applied to a charger from a high voltage power supply for charging to charge a surface of a photoreceptor rotating in a predetermined direction to a uniform potential, and a static electricity based on print data is exposed by an exposure device. In a toner image forming apparatus for forming an electrostatic latent image, supplying charged toner from a developing device to the electrostatic latent image to develop the toner, and transferring the developed toner to a transfer material by a transfer device, a predetermined image is formed. Photoreceptor surface potential detection means for applying the applied voltage to the charger to detect the surface potential of the photoreceptor; and a discharge starting voltage value for charging the surface of the photoreceptor from the output of the photoreceptor surface potential detection means. A charging control means for controlling a charging high-voltage power supply by a charging control signal so that the surface of the photosensitive member has a predetermined surface potential. 2. The photosensitive member surface potential detecting means supplies a predetermined transfer current to the photosensitive member from the transfer device, and determines a transfer voltage value when the surface of the photosensitive member is not charged, 2. The toner image recording apparatus according to claim 1, wherein a surface potential of the photosensitive member is obtained from a difference from a transfer voltage value in a state where the charging is performed by applying a predetermined voltage by the charger. 3. The photosensitive member surface potential detecting means supplies a sine wave alternating current having an amplitude greater than a discharge starting voltage value to the surface of the charged photosensitive member supplied with a predetermined charging voltage from the charger. 2. The toner image recording apparatus according to claim 1, wherein a voltage value which is substantially equal to the surface potential of the photoconductor by discharging on the surface of the photoconductor is determined as the surface potential of the photoconductor. 4. The toner image recording apparatus according to claim 3, wherein said sine wave alternating current is supplied from said charger. 5. The toner image recording apparatus according to claim 3, wherein the sine wave alternating current is supplied from the transfer device.