JP2002278231A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device by which the sticking of carrier and unnecessary toner consumption are eliminated, whose quality is high and which is efficient by keeping the proper balance of a potential difference between the surface potential of a photoreceptor and developing bias voltage. SOLUTION: In the image forming device having the photoreceptor, an electrifying means, an exposure means, a developing means and a developing bias means, control is performed by a controlling means so that the electrifying means is pressed in the rotating direction of an image carrier so as to raise surface potential at a non-image area formed before an image forming area on the image carrier to potential for image forming stepwise and also DC bias voltage raised stepwise similar to the surface potential raised stepwise is applied to a developer carrier when the non-image area passes a developing area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic system such as a copying machine and a printer, and more particularly to an image forming apparatus utilizing a reversal developing system.

[0002]

2. Description of the Related Art When an image is formed by an electrophotographic method,
An image bearing member (hereinafter, referred to as a photosensitive member) composed of a photoreceptor is charged by a charging unit to form a latent image by an exposing unit, and then a high-pressure developing bias having the same polarity as the charging polarity is applied to the developer carrying unit by a developing bias unit. A method is used in which a voltage is applied and toner is caused to adhere to the latent image portion by a developing unit. At this time, the surface of the photoconductor is generally charged at a potential higher than the developing bias voltage so that fog toner does not adhere to a region where the charging portion becomes a white background portion. However, if the white area is charged to an unnecessarily high potential, the carrier in the two-component developer may adhere to the surface of the photoconductor. Unnecessary toner adhesion is excessive consumption of toner, and carrier adhesion may damage the photoreceptor surface and the fixing roller surface.

In the conventional image forming apparatus, the time required for the photosensitive member to rotate from the position facing the charger to the developing area is set in advance, and the time required for the rotation of the photosensitive member from a control means comprising a control section of the main body of the image forming apparatus. There is a configuration in which an ON signal of a developing bias voltage is energized based on a charge ON signal.
In the image forming apparatus having such a configuration, variations in the rise of the high voltage power supply for charging in the non-image area formed before the image forming area on the image carrier, variations in the manufacturing of the charging device, or in the manufacturing of the photosensitive member. Due to variations in
In some cases, the balance between the charging potential and the developing bias voltage could not be maintained, causing some carriers to adhere, and others causing unnecessary toner adhesion. In particular, it is difficult to keep a proper balance between the charging potential and the developing bias voltage at the rise of the potential immediately after the charging is turned on, and problems such as the adhesion of the carrier and the adhesion of unnecessary toner are likely to occur.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above problems by maintaining an appropriate balance between the potential difference between the charged potential on the photosensitive member surface and the developing bias voltage in the non-image area, thereby preventing carrier adhesion and unnecessary It is an object of the present invention to provide a high quality and efficient image forming apparatus which consumes less toner.

[0005]

The object of the present invention can be achieved by the following constitution.

(1) An image carrier made of a photoreceptor, charging means for charging the surface of the image carrier, exposure means for exposing the charged image carrier surface to form a latent image, An image having developing means for developing the latent image with a developer carried on a developer carrying member, and developing bias means for applying a developing bias voltage having the same polarity as the charging polarity to the image carrying member to the developer carrying member; In the forming apparatus, the charging is performed so that a surface potential in a non-image area formed in front of an image forming area on the image carrier is gradually increased to a potential for image formation in accordance with a rotation direction of the image carrier. Energizing the means, and as the non-image area passes through the development area, similar to the stepwise increasing surface potential described above,
An image forming apparatus comprising: a control unit that controls a DC bias voltage that rises in a stepwise manner to be applied to the developer carrier.

(2) an image carrier made of a photoreceptor, charging means for charging the surface of the image carrier, exposure means for exposing the charged image carrier surface to form a latent image, Surface potential detecting means for detecting the potential of the surface of the image carrier on which the latent image has been formed; developing means for developing the latent image with a developer carried on a developer carrier; and charging polarity for the image carrier And a developing bias means for applying a developing bias voltage having the same polarity to the developer carrying member, the developing bias means being provided in front of an image forming area on the image carrying member in accordance with the rotation direction of the image carrying member. The surface potential in the image area is energized to gradually increase the potential for image formation to a potential for image formation, and when the non-image area passes through the development area, the surface potential detection means Before detection An image forming apparatus comprising similar to stepwise surface potential rises, that is controlled by the control means to apply a DC bias voltage to be stepwise increased in the developer carrier.

(3) an image carrier made of a photoreceptor, charging means for charging the surface of the image carrier, exposure means for exposing the charged image carrier surface to form a latent image; Surface potential detecting means for detecting the potential of the surface of the image carrier on which the latent image has been formed; developing means for developing the latent image with a developer carried on a developer carrier; and charging polarity for the image carrier And a developing bias means for applying a developing bias voltage having the same polarity to the developer carrying member, the developing bias means being provided in front of an image forming area on the image carrying member in accordance with the rotation direction of the image carrying member. After the surface potential in the image area is once charged by energizing the charging unit, the exposing unit is energized while gradually reducing the light amount so as to gradually increase to a potential for image formation. And the non-image area Control means for applying a stepwise increasing DC bias voltage similar to the stepwise rising surface potential detected by the surface potential detecting means to the developer carrying member when passing through the developing region. An image forming apparatus characterized in that the image forming apparatus is controlled by:

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention are described below.
Hereinafter, description will be given based on the drawings.

FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus such as a copying machine. In FIG. 1, a control unit (hereinafter, referred to as a main unit control unit) 1 including a control unit of the image forming apparatus main body includes a charging voltage control unit 7, an exposure light amount control unit 9, and a developing bias control unit 15. The charging voltage control unit 7 is a control unit including a grid voltage control for controlling the voltage of the charging high-voltage power supply 6 included in the charging unit 4, and the exposure light amount control unit controls the exposure light amount of the exposure unit 8. Alternatively, it is a control unit that employs a method of making the voltage variable, a pulse width modulation method, or the like. The developing bias control unit is a control unit configured to control the voltage of a developing bias power supply included in the developing bias unit, change the current or the voltage, and the like.

The main body control section 1 receives an image formation start signal in response to an input signal such as a turn-on of a copy switch (not shown), sends an electric signal to a driving means of a photoconductor driving motor (not shown), and outputs an image carrier (photosensitive member) comprising a photoconductor. The photoreceptor 2 is driven, and the charge removal lamp 3 is turned on to eliminate the influence of the surface potential of the previous image formed on the photoreceptor. Next, the surface of the photoconductor 2 is charged by the charging unit 4. The charging means 4 includes a box-shaped scorotron charger (hereinafter, referred to as a charger) 5 and a high-voltage power supply 6 for applying a voltage to the charger 5. The output voltage of the high-voltage power supply 6 is controlled by the main body control unit 1. The surface potential of the photosensitive member can be controlled to an arbitrary voltage between 0 and -1000 volts.

Photoconductor 2 whose surface is charged by charger 5
Continue rotating and reach a position facing the exposure means 8.
As the exposure means 8, a scanning method using a laser exposure system or the like is used. Since the exposure means 8 can change the exposure light quantity by the exposure light quantity control means 9, the surface potential of the photoreceptor changes from the charged potential to a limit potential at which the potential does not decrease even if exposure is continued further (hereinafter, this potential is set to the saturation exposure The potential level is changed to a potential level corresponding to the amount of exposure light until a potential image is formed.

In this embodiment, the exposure means is a scanning method using a laser exposure system, but an exposure method using an LED or the like is also applicable.

The photosensitive member 2 on which the latent image has been formed continues to rotate further, and reaches a position facing the surface potential detecting means 11 provided between the exposing means 8 and the developing means 10. The surface potential detecting means 11 has a high-voltage detecting unit (not shown),
The detected surface potential is sent as a signal to the main body control unit. Next, the photoconductor 2 enters the developing area 12. The latent image is visualized by the developing unit 10 in the developing area 12. The developing unit 10 includes a developer carrier 13 that holds and rotates and transports a two-component developer including a toner and a carrier.
And a developing bias power supply 14 capable of applying a high voltage to the developer carrier 13 and setting the output voltage to an arbitrary voltage value between 0 and -1000 volts.

The photoreceptor 2 on which a visible image (toner image) is formed by the developing means 10 is further rotated to transfer the toner image to recording paper (not shown) by a transfer means (not shown) in a transfer area (not shown). The recording paper is heated and fixed by a fixing device (not shown) and discharged to a discharge tray (not shown).

FIG. 2 is a diagram showing a rising state of a charging potential and a developing bias voltage in a non-image area according to a conventional method.

In the figure, three vertical broken lines (straight lines)
Among them, the broken line on the left side indicates the time t0 when the non-image area of the photosensitive member 2 comes to the position facing the charger 5, and the time t0
Indicates the charging start position, and the second broken line from the left indicates the time when the time Ts has elapsed since the start of charging. This time Ts is also the transit time of the non-image area on the photoconductor and the charging is performed. It is also a time representing the rise time of the potential. The broken line on the right is the time t when the photosensitive member 2 enters the developing area.
3 and a line indicating the time at which the developing bias voltage is turned on. The three curves on the left are lines indicating the rise of the surface potential of the photosensitive member 2 charged by the charger 5, and the three curves on the right correspond to the three curves on the left at a position facing the charger. 7 is a curve showing a state when the photoconductor 2 having a surface potential that has reached the developing area after the time Ta (Ta = t3−t0).

As shown in the figure, in the conventional method, when the charged potential rises from the uncharged state to the charged potential after the completion of charging by turning on the charging high-voltage power supply, there are some cases where the rise is slow or steep.

FIG. 2A shows a case where the rising of the charging potential is slow, FIG. 2B shows a case where the rising is proper, and FIG. 2C shows a case where the rising is steep.

In FIG. 2A, Vcc is a voltage for instructing the charging high-voltage power supply to turn on from the main body control unit (hereinafter referred to as charging instruction voltage), V0 is the potential of the photosensitive member surface in an uncharged state, and Vh is the charging completion. The subsequent charging potential is shown. As can be seen from the figure, the charging potential on the photoreceptor surface gradually rises from the uncharged state V0 to the charging potential Vh after the completion of charging. Therefore, during the time x from when the photosensitive member 2 reaches the developing area and the developing bias voltage is turned on to when the potential of the charged portion of the photosensitive member rises to a potential at which no fogging occurs, the charged potential of the photosensitive member is not changed. This indicates that fogging is likely to occur.

In FIG. 2B, the rising of the charging potential at the charger position is proper, the developing bias voltage and the charging potential in the developing area rise in a well-balanced manner, and the occurrence of fogging and toner adhesion is prevented. It represents a small state.

In FIG. 2C, since the rise of the charging potential at the charger position is rapid, it is difficult to turn on the developing bias voltage in the developing area, and the rising timing of the developing bias voltage is too late. in case of,
The time difference y between the timing of the rise of the charging potential and the timing of the rise of the developing bias voltage indicates that carrier adhesion is likely to occur. On the contrary, the timing of the rising of the developing bias voltage is too early. Tends to cause toner adhesion.

FIG. 3 is a view for explaining a first embodiment according to the present invention. In the non-image area where the charged potential of the photoreceptor surface can be set before the image forming area on the image carrier, FIG. 5 is a diagram illustrating a change in the potential of the photoconductor surface and a change in a developing bias voltage when the potential is gradually increased to the potential for image formation.

In the figure, the vertical direction represents a change in potential,
The horizontal direction indicates the time required for the photoconductor to move from the start of charging to the completion of development in accordance with the rotation direction of the photoconductor. Of the three broken lines in the vertical direction, the leftmost line indicates the time t0 when the non-image portion of the photoreceptor 2 comes to a position facing the charger 5, and the central line indicates
The time t2 at which the photoreceptor 2 comes to a position facing the surface potential detecting means 11 is shown.
The time t3 when the vehicle has come to the position opposite to. Reference numeral a denotes a graph in which the charging instruction voltage Vcc is stepwise increased, and reference numeral b denotes a high voltage from the charging high-voltage power supply 6 energized by the charging instruction voltage Vcc. The potential of the charged photoreceptor surface is increased stepwise from the potential V0 in the uncharged state to the charging potential Vh after the completion of the charging.
FIG. Reference numeral c is a graph showing the potential Vhi detected by the surface potential detecting means of the charging potential of the surface of the photoconductor rising stepwise.
Reference numeral d is a graph having a tendency similar to the charging potential, which represents a state in which the developing bias voltage (DC bias voltage) Vd in the developing region is gradually increased, and a constant potential difference Vm with respect to the charging potential Vhi. It shows that it changes with. When this is represented by an equation, | Vd | = |
Vhi | -Vm, where 50 volts ≦ Vm ≦ 200 volts.

In the first embodiment, the case where the charging potential and the developing bias voltage are increased with respect to the non-image area formed before the image forming area on the photosensitive member has been described. In the direction, the charging potential and the developing bias voltage with respect to the non-image area formed behind the image forming area on the photoreceptor may also decrease gradually in the same manner as the rising. Unnecessary toner adhesion and carrier adhesion can be prevented by maintaining the balance between the charging potential and the developing bias voltage.

On the other hand, when the image area of the photosensitive member 2 reaches the development area, the developability is improved (the adhesion of toner is improved).
Therefore, a method of superimposing an AC component in addition to a DC bias voltage (also referred to as a DC component of a developing bias voltage) may be used. In the present invention, the alternating current component is superimposed when the charging potential Vhi rises or falls and becomes | Vhi | ≧ | Vh | −50 volts. As the value of the AC component, a value in the range of 1 to 3 kV is usually used.

FIG. 4 is a diagram for explaining a second embodiment according to the present invention. In the non-image area formed before the image forming area on the photoconductor, the surface of the photoconductor once activated is charged. The potential Vh is changed to the light quantity at the time of full exposure using the exposure means (the light quantity at the time of full exposure means the maximum exposure light quantity as the exposure means capable of setting the charging potential to the saturation exposure potential).
FIG. 9 is a diagram showing that the charging potential Vhi and the developing bias voltage Vd of the photoreceptor surface are stepwise increased by stepwise decreasing from Ls to the light amount L0 in the non-exposure non-lighting state.

In the figure, the meaning of the vertical and horizontal positions is the same as in FIG. Also, 4 in the vertical direction
Of the dashed lines, the leftmost dashed line indicates time t0 when the photoconductor 2 comes to the position facing the charger 5, and the time t0 also indicates that it is also the charging start position. Indicates the time t1 when the photoconductor 2 comes to the position facing the exposure means 8, the third broken line from the left indicates the time t2 when the photoconductor 2 comes to the position facing the surface potential detecting means 11, The right end line indicates a time t3 when the photoconductor 2 comes to a position facing the development area 12. Reference numeral e is a graph in which the charging instruction voltage Vcc is instantaneously increased, and reference numeral f is a switch that turns on the charger 5 with a high voltage from the charging high-voltage power supply 6 energized by the charging instruction voltage Vcc. 4 is a graph showing a rise in the rise of the charged photoconductor surface potential (from a potential V0 in an uncharged state to a charge potential Vh after completion of charging). Reference numeral g indicates that once the potential of the photoconductor surface is charged to the charging potential Vh after the completion of the charging, the exposure unit exposes the photoconductor surface from the light amount Ls at the time of the full exposure to the light amount L0 at the non-exposure state. It is a graph showing the change (fall) of the exposure light amount irradiated while decreasing stepwise, and reference numeral h denotes a charge potential Vhj of the photoreceptor surface receiving the stepwise change (fall) exposure light amount. It is a graph which shows the state which changes (rises) stepwise according to it. Reference numeral i is a graph showing a potential Vhj obtained by detecting the charging potential of the photoreceptor surface, which gradually changes (increases), by a surface potential detecting means. Reference numeral j is a graph showing a state in which the developing bias voltage (DC bias voltage) Vd in the developing area gradually increases in a manner similar to the charging potential graph d, and is constant with respect to the charging potential Vhj. It shows that the transition occurs with the potential difference Vm. When this is represented by an equation, | Vd | = | Vhj
| -Vm, (however, 50 volts ≦ Vm ≦ 200 volts)
Becomes

In the above-described second embodiment, the case where the charging potential and the developing bias voltage increase in the non-image area formed before the image forming area on the photosensitive member has been described. Similarly to the embodiment, when the charging potential and the developing bias voltage for the non-image area formed behind the image forming area decrease, it is possible to gradually decrease the charging potential and the developing bias voltage as in the case of the increase. It is.

When the image area of the photoreceptor 2 reaches the developing area, the charging potential Vhj reaches the value of the charging potential Vh after the completion of charging.
When the charging potential Vhj becomes | Vhj | ≧ | Vh | −50 volts, the control is configured to superimpose the AC component. That is, the surface potential detecting means 11 detects the surface potential of the photoreceptor 2, and when the difference between the value and the charging potential Vh after completion of charging is 50 volts or less, the AC component of the developing bias is superimposed.

In the present invention, the value of the charging potential Vh after the completion of charging is -650 to -1000 volts,
In the embodiment, the number of steps of the charging potential that changes stepwise is set in 5 to 10 steps, and the difference Vm between the charging potential that changes stepwise and the developing bias voltage is set in the range of 50 to 200 volts. Excellent results without unnecessary toner adhesion and carrier adhesion are obtained.

In this embodiment, reversal development has been described. However, regular development (combination of plus charge and minus toner, or minus charge and plus toner)
Can also be applied.

[0033]

According to the present invention, it is possible to provide a high quality and efficient image forming apparatus with less carrier adhesion and unnecessary toner consumption.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus.

FIG. 2 is a diagram showing how a charging potential and a developing bias voltage rise in a non-image area according to a conventional method.

FIG. 3 is a diagram for explaining a first embodiment according to the present invention.

FIG. 4 is a diagram for explaining a second embodiment according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 control means (main body control unit) 2 image carrier (photoconductor) 5 box-shaped scorotron charger (charger) 6 charging high-voltage power supply 8 exposure means 10 developing means 11 surface potential detection means 12 developing area 13 developer carrier 14 Development bias power supply

Continued on the front page F term (reference) 2H027 DA02 EA01 EA05 EA07 EC20 ED03 ED07 EE02 EE07 EF09 2H073 AA03 AA05 BA02 BA23 CA03 2H077 AD06 AD35 DB08 DB12 DB13 DB14 EA03 GA17 2H200 FA08 GA45 GA53 GA56 GB02 HA12 HA29 NA29

Claims (9)

[Claims] An image bearing member comprising a photoreceptor; charging means for charging a surface of the image bearing member; exposure means for exposing the charged image bearing member surface to form a latent image; An image forming apparatus comprising: developing means for developing a latent image with a developer carried on a developer carrier; and developing bias means for applying a developing bias voltage having the same polarity as the charging polarity to the image carrier to the developer carrier. In the apparatus, the charging unit is configured to gradually increase a surface potential in a non-image area formed in front of an image forming area on the image carrier according to a rotation direction of the image carrier to a potential for image formation. And applying a stepwise increasing DC bias voltage to the developer carrier similar to the stepwise increasing surface potential described above when the non-image area passes through the developing area. Control An image forming apparatus characterized in that controlled by the stage. 2. An image carrier comprising a photoreceptor, charging means for charging a surface of the image carrier, exposure means for exposing the charged image carrier surface to form a latent image, Surface potential detecting means for detecting the potential of the surface of the image carrier on which the latent image is formed; developing means for developing the latent image with a developer carried on a developer carrier; and charging polarity for the image carrier. A developing bias means for applying a developing bias voltage of the same polarity to the developer carrier, wherein a non-image formed before the image forming area on the image carrier according to a rotation direction of the image carrier. The charging unit is energized so as to gradually increase the surface potential in the region to a potential for image formation, and is detected by the surface potential detecting unit when the non-image region passes through the developing region. Said earlier Similar to the surface potential rises Kaiteki, the image forming apparatus, wherein the controlling by the control means to apply a DC bias voltage to be stepwise increased in the developer carrier. 3. An image carrier comprising a photoreceptor, charging means for charging the surface of the image carrier, exposure means for exposing the charged image carrier surface to form a latent image, Surface potential detecting means for detecting the potential of the surface of the image carrier on which the latent image is formed; developing means for developing the latent image with a developer carried on a developer carrier; and charging polarity for the image carrier. A developing bias means for applying a developing bias voltage of the same polarity to the developer carrier, wherein a non-image formed before the image forming area on the image carrier according to a rotation direction of the image carrier. The surface potential in the area, once charged by charging the charging means, and then biasing the exposure means while gradually reducing the amount of light so as to gradually increase to a potential for image formation, And the non-image area is When passing through the image area, the control means applies a stepwise increasing DC bias voltage similar to the stepwise rising surface potential detected by the surface potential detecting means to the developer carrier. An image forming apparatus characterized by controlling. 4. The charging device according to claim 1, wherein the charging unit controls the charging unit so that a surface potential in a non-image area formed behind the image forming area on the image carrier decreases stepwise to a saturation exposure potential in accordance with a rotation direction of the image carrier. And applying a stepwise falling DC bias voltage to the developer carrier, similar to the stepwise falling surface potential described above, when the non-image area passes through the developing area. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled by a control unit. 5. The charging device according to claim 1, wherein the charging unit controls the surface potential in a non-image area formed behind the image forming area on the image carrier in a stepwise manner to a saturation exposure potential in accordance with a rotation direction of the image carrier. Energizing, and when the non-image area passes through the developing area, a DC bias voltage that decreases stepwise, similar to the stepwise surface potential detected by the surface potential detecting means, is applied to the developer. 3. The image forming apparatus according to claim 2, wherein the control unit controls the voltage so as to apply the voltage to the carrier. 6. A method according to claim 1, wherein the surface potential in a non-image area formed behind the image forming area on the image carrier is temporarily charged by energizing the charging unit in accordance with a rotation direction of the image carrier. The exposure means is urged while gradually increasing the lateral width so as to gradually decrease to the saturation exposure potential, and when the non-image area passes through the development area, the above-described detection is performed by the surface potential detection means. 4. The image forming apparatus according to claim 3, wherein the controller is controlled to apply a stepwise decreasing DC bias voltage similar to the stepwise decreasing surface potential to the developer carrier. apparatus. 7. The developing device according to claim 6, wherein the DC bias voltage is a developing bias voltage applied to the developer carrier, Vd is a surface potential of the image carrier which rises in a stepwise manner, and the developing bias voltage Vd and the surface potential are Vhi. 2. The control means according to claim 1, wherein, when a potential difference from Vm is Vm, | Vd | = | Vhi | -Vm (where 50 V ≦ Vm ≦ 200 V). 2, Claim 4
The image forming apparatus according to claim 5. 8. The developing device according to claim 1, wherein the DC bias voltage is a developing bias voltage applied to the developer carrier, Vhj is a surface potential of the image carrier that rises in a stepwise manner, and the developing bias voltage Vd and the surface potential Vhj. 4. The control means according to claim 3, wherein, when a potential difference from Vm is Vm, | Vd | = | Vhj | -Vm (where 50 V ≦ Vm ≦ 200 V). 7. The image forming apparatus according to 6. 9. The step of claim 8, wherein the DC bias voltage is Vh, the surface potential of the stepwise-varying image carrier according to claim 7 is Vhi, and the surface potential of the image carrier after stepwise completion is Vhi. Vhj represents the surface potential of the image carrier that changes in time, and | Vh | − | Vhi | ≦ 50 volts or | V
9. The method according to claim 2, wherein when h |-| Vhj | ≦ 50 volts, the control means controls the AC component so that the AC component is superimposed on the developer carrier. The image forming apparatus according to claim 1.