JPH0764360A - Image forming device - Google Patents

Abstract

PURPOSE:To perform steady electrification and transfer irrespective of a humidity change by the use of a contact-electrification method and, on the other hand, to remove toner on an electrifying member and a transfer member. CONSTITUTION:A voltage having the same polarity as that of electrified toner is supplied to an electrifying roller 5, which is in contact with a photoreceptor 1, by means of the positive voltage power source circuit 102 of a power source circuit 100, and the resistance value of the electrifying roller 5 is detected by a resistance value detecting circuit 106. At this time, the same voltage is supplied to a transfer roller 3 as well. The detected resistance value is compared with a reference value in a comparison circuit 107. Based on the result of the comparison, a control circuit 105 controls the output voltage of a negative voltage power source circuit 101 at the time of an image forming operation and supplies the voltage to the electrifying roller 5 and the transfer roller 3. At the time of the detection of the resistance value, toner sticking on the electrifying roller 5 and transfer roller 3 is transferred to the photoreceptor 1 by the application of the voltages having the same polarity of the electrified toner thereto, and the transferred toner is removed by a cleaning part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus for uniformly charging the surface of an image carrier and then transferring the image formed on the image carrier onto a transfer material.

More particularly, the present invention relates to an image forming apparatus which uses a contact charging device for charging the image carrier to charge the surface of the image carrier by bringing a charging member into contact with the image carrier.

[0003]

2. Description of the Related Art Corona discharge has hitherto been used as a charging device for charging an image carrier, a so-called photoconductor to a desired potential, and a transfer device for transferring a toner image formed on the photoconductor onto a transfer material. A corona discharge device using a has been used. However, this method requires a high voltage, and there is a fear that it may electrically affect a microcomputer or the like. Further, since a large amount of ozone is generated during corona discharge, there is an environmental problem. As means for solving such a problem, a charging member including a transfer member is brought into contact with a photoconductor to charge the surface of the photoconductor, and the transfer member is similarly brought into contact with the photoconductor to transfer a toner image to a transfer material. Methods have already been proposed.

A method using such a method is disclosed, for example, in JP-A-61-63867. This structural drawing is shown in FIG.

In FIG. 14, reference numeral 20 denotes a photosensitive member which constitutes an image carrier, and a conductive fiber aggregate (conductive member) 21 formed in a belt shape is bonded onto a conductive substrate 22 by a conductive adhesive. Thus, the charging member 23 is configured, and the conductive member is pressed against the photoconductor 20. By applying a voltage to the charging member 23, the surface of the photoconductor 20 is charged according to the supplied voltage. A transfer member (not shown) is also composed of a conductive fiber aggregate, and is brought into contact with the photoconductor 20 to transfer the toner image onto the transfer material.

[0006]

By the way, as in the above-mentioned Japanese Patent Laid-Open No. 61-63867, a so-called contact for charging the surface of the photosensitive member by bringing the charging member constituting the charging device into contact with the photosensitive member. In what is called a charging device, the resistance value of the conductive material of the charging member greatly changes due to changes in the environment, particularly humidity. When the resistance value of the conductive material of the charging member changes, the surface potential of the photoconductor also fluctuates accordingly, resulting in non-uniform charging and the occurrence of fogging.

It is known that in the case of such a charging device, the charging is performed by discharging in a gap near the contact point between the surface of the photosensitive member and the charging member and injecting charge at the contact point. ing. In the former case, the discharge starts when the voltage applied to the air gap near the contact point reaches a value determined by Paschen's discharge law shown in FIG. When the discharge starts, the charge moves from the charging member to the image carrier at once,
The surface potential of the image carrier becomes high and the discharge is stopped.

The state is shown in FIG.
When an arbitrary point A faces the tip of the conductive fiber 21a to which a voltage is applied across a gap of a certain size, the applied voltage is a discharge start voltage (determined by the photoconductor 20 and the gap). When it is higher than the charging start voltage / Vth), discharge is excited from the conductive fiber 21a and the photoconductor 20 starts to be charged (region C). The discharge is stopped when the charging potential (Vsp) rises and the difference between the applied voltage (Vap) and (Vsp) becomes equal to (Vth). That is, when the dark decay of the charging potential of the photoconductor 20 can be ignored, (Vsp) = (Va
p) − (Vth) holds.

After that, at point A, while keeping the charging potential,
It escapes from the region C where discharge is permitted and moves to a position (position B) where it comes into contact with the conductive fiber 21a. Needless to say, the potential difference between the conductive fiber 21a at the position B and the point A on the photoconductor 20 is Vth as described above. The charge moves to the point A, and the charging potential at the point A is further increased. That is, it is considered that the charging potential is given by the discharge phenomenon and the charge injection phenomenon.

Although the amount of charges transferred to the image carrier is smaller than that in discharging, the charging by charge injection depends on the surface resistance of the contact surface and the electrical characteristics of the photosensitive member, and is therefore easily affected by environmental changes. Therefore, when the environment changes, especially the humidity changes, the charge injection amount also changes, and as a result, uniform charging cannot be obtained.

For example, in a low-humidity environment, the resistance value of the conductive material of the charging member becomes high, it becomes difficult for the charge to move from the charging member to the photosensitive member, and the injection amount decreases. As a result, the surface potential of the photoconductor is lower than that under normal humidity. On the contrary, in a high-humidity environment, the resistance value becomes low, the charge easily moves from the charging member to the photoconductor, and the injection amount increases. As a result, the surface potential of the photoconductor becomes higher than that under normal humidity or low humidity.

With respect to these problems, the above-mentioned Japanese Patent Laid-Open No.
In the Japanese Laid-Open Patent Publication No. 1-63867, it is an object of the invention to prevent floating dust from adhering and to prevent the charger from being oxidized by the heat of discharge, and to solve uneven charging due to environmental changes. No mention of the method.

A means for solving such a problem is disclosed in, for example, Japanese Patent Laid-Open No. 56-132356. However, in this case, since constant current control is used as the power supply applied to the charging member, there is a problem of charge-up due to constant current flow, and it cannot be said to be an appropriate means.

On the other hand, the so-called contact, which is composed of the conductive fiber aggregate disclosed in the above-mentioned Japanese Patent Laid-Open No. 61-63867, transfers the toner image to the transfer material by contacting with the photoreceptor. Similarly to the contact charging device, in the transfer device, the resistance value of the conductive material greatly changes due to the change of environment, especially the change of humidity. Therefore, problems such as toner scattering and separation failure occur in a low humidity environment, and problems such as transfer failure occur in a high humidity environment.

A means for solving such a problem is disclosed, for example, in Japanese Patent Laid-Open No. 1-265282. However, in this case, a sensor is used as a means for detecting humidity, and as a method that does not use a sensor, a means is proposed in which a pair of electrodes is formed in the recording paper traveling path and the output voltage or output current is detected. is doing. The method of using such a sensor and the method of forming the electrode are not preferable because they complicate the structure and are disadvantageous in terms of cost.

Further, this publication refers to a change in the resistance of the recording paper due to environmental changes. What is meant by the present invention is that the applied voltage is determined by detecting the change in the resistance of the charging member or the transfer member. This is completely different from the method of doing.

In addition to the above, a number of inventions have been proposed to deal with such a situation, but all of them are limited to primary charging or transfer charging. It can be said that there was no control means for controlling the primary charging device and the transfer charging device by the same control device, which is the gist of the present invention.

Further, the present invention is a very effective invention which can obtain a great effect also with respect to another problem.

Another problem is that when a contact charging device is used, the toner adheres to the charging member due to residual toner not transferred to the transfer material on the photosensitive member or toner scattering in the image forming apparatus. Will end up. In the former case, most of the toner remaining on the photoconductor is collected by the cleaning blade, which is a cleaning unit. Therefore, the amount of residual toner that adheres to the material of the charging unit is extremely small, so that it adheres to the charging member even if there is no problem It can be considered that most of the toner is due to the latter. When the toner adheres to the charging member in this way, it enters the contact surface between the charging member and the photoconductor, scratches the surface of the photoconductor, and causes image unevenness due to poor charging.

Further, the contact transfer device also has a problem that toner adheres to the transfer member. This is caused by the toner scattering in the image forming apparatus and the transfer material (sheet-shaped paper) when a jam occurs during the image forming process.
It is conceivable that the toner on the surface of the photoconductor adheres to the transfer member in the area where no image exists. Further, the latter has a much larger amount of adhesion than the former, and as a result, the toner adhering to the transfer member is transferred to the transfer material conveyed in the next image forming step, causing back stain.

According to the present invention, the toner attached to the charging member and the transfer member is a photosensitive member by applying a voltage having the same polarity as the toner to the charging member and the transfer member at least during non-image formation. Transfer to. One purpose is to scrape off and collect the toner adhering on the image carrier by a cleaning blade that is a cleaning means of the image carrier as the image carrier rotates.

Further, according to the present invention, the voltage applied to the charging member and the transfer member is applied from the same power source during non-image formation, and the resistance value of either one of the members when the voltage is applied is detected. It can be used as a part of the control means for controlling the applied voltage at the time of charging operation at the time of image formation and at the transfer processing step, and simplification of the structure and simplification of the control means can be achieved, and at the same time, such as humidity change. The purpose is to stabilize charging and transfer to an image carrier regardless of environmental changes.

Therefore, according to the present invention, at least at the time of non-image formation, a voltage having the same polarity as that of the toner is applied to the charging member and the transfer member to remove the toner adhering to the charging member and the transfer member. The resistance value of the member is detected, and based on the resistance value, the voltage applied to the charging member is determined so that the potential of the charging surface of the charging member during the charging operation during image formation is constant, and the By also determining the voltage applied to the transfer member, it is possible to remove the toner adhering to the charging member and the transfer member, and to provide a device that always obtains a stable charging potential and good transferability regardless of environmental changes. That is the purpose.

[0024]

According to the present invention, it is possible to suppress the occurrence of image unevenness due to uneven charging and back stain of the transfer material, simplify the control means, and change the environment, especially the influence of humidity. The first aspect of the present invention is made so that the resistance value of the conductive material of the charging member changes and the amount of charge injection that fluctuates accordingly is always constant.
The gist of the present invention is to expose the charged image bearing member surface to form an electrostatic latent image, develop the electrostatic latent image by a developing means to form a toner image, and transfer the toner image to a transfer material by a transfer means. In an image forming apparatus that obtains an image by fixing the transfer material onto the image carrier and fixing the transfer material by a fixing unit, the charging member and the transfer member are made of the same material, and both members are brought into contact with the surface of the image carrier. A means for detecting the resistance of the charging member or the transfer member, and a control means for controlling the voltage supplied to the charging member and the transfer member based on the resistance value detected by the detecting means. And

The above-mentioned control means controls the voltage based on the amount of change with respect to the reference value, using the resistance value at room temperature and normal humidity as a reference.

On the other hand, the detection means detects the resistance value and changes the current flowing when a voltage having the same polarity as the charged electric charge of the toner when the electrostatic latent image on the image carrier is developed during non-image formation is applied. It is detected as a resistance value or a voltage value according to.

In addition, the present invention has a second gist of the point that the toner adhering to the charging member and the transfer member is removed when the resistance value is detected in the first aspect of the present invention. A charging member which comes into contact with the surface of the carrier to be charged with a specific polarity, a means for exposing the image surface of the image with light, and a means for developing the electrostatic latent image formed on the surface of the image carrier with charged toner. A transfer member having the same configuration as the charging member for transferring the developed toner image onto a transfer material that comes into contact with the surface of the image carrier and is appropriately conveyed; and a cleaning unit for removing the toner remaining on the surface of the image carrier. And a detection means for detecting a resistance change of the charging member or the transfer member,
A controllable first power supply unit for applying a predetermined voltage to the charging member and the transfer member at the time of image formation, and detection by the detection unit by applying a predetermined voltage to the charging member or the transfer member at the time of non-image formation Second for applying a voltage to perform
Power source section, a switching means for switching and outputting the second power source section or the first power source section, and a switching means for switching to the second power source section during non-image formation. A control in which the voltage value of the first power supply unit is controlled by switching to the first power supply unit by the switching unit at the time of image formation based on the detected resistance value of the member to supply the voltage to the charging member and the transfer member. Means and are provided.

Specifically, the second power source section outputs a voltage having the same polarity as that of the toner charged by the developing means.

The detecting means detects a change in current according to a change in resistance value via the charging member or the transfer member, and converts the voltage into a voltage to detect the resistance value.

Further, the control means controls the voltage of the first power supply section based on the amount of change with respect to the reference value with the resistance value at room temperature and normal humidity as a reference.

When the developing means is the regular developing, the output of the first power source section has the opposite polarity to the charged toner, and when the developing means is the reversal developing, the first power source section is the same as the charged toner to the charging member. A voltage having a polarity opposite to that of the charged toner is output to the transfer member.

The control means supplies the voltage of the second power source to the charging member and the transfer member during non-image formation,
The image carrier is rotated at least once.

In the first and second aspects of the invention described above, as the charging member and the transfer member, a roller type in which a conductive fiber assembly or a conductive elastic member is coated around a conductive base, Alternatively, it is configured by a brush type in which a fiber assembly is attached to one side surface of the conductive base.

[0034]

According to the first aspect of the present invention, an image is formed by being charged by the charging member which is in contact with the image carrier.
At this time, the detection unit detects the resistance value of the charging member or the transfer member, and the voltage supplied to the charging member and the transfer member during image formation is controlled according to the detected resistance value. That is, the resistance values of the charging member and the transfer member greatly change according to the change in humidity, and the charging potential with respect to the image carrier changes. Therefore, the charging potential increases as the resistance decreases, but the charging potential can be made constant by controlling the voltage supplied at that time to be low. At this time, since the charging member and the transfer member have the same structure, the supply voltage can be controlled simultaneously, and the circuit structure can be simplified.

In this case, the resistance value is detected with reference to the resistance value of the charging member or the transfer member at room temperature and normal humidity, and the change amount is detected, and the voltage control can be performed according to the change amount. In particular, for resistance detection, for example, a detection voltage is applied to the charging member during non-image formation, and the current flowing through the charging member at this time can be detected as a change in resistance value.

According to the image forming apparatus of the second aspect of the invention, a predetermined voltage is applied to the charging member and the transfer member from the second power source section during non-image formation. When this voltage is applied, the detection means detects the resistance value of the charging member or the transfer member. The detected resistance value is processed as information for controlling the voltage value supplied to the charging member and the transfer member during image formation. That is, the control means simultaneously controls the voltage values supplied to the charging member and the transfer member according to the detected resistance value. In this way, by performing the voltage control according to the change in humidity, the charging potential of the charging member can be kept constant, and the transfer potential for transfer can be kept constant to prevent transfer defects.

The voltage supplied at the time of detecting the resistance value causes the electric charge of the developing toner to have a voltage value of the same polarity, so that the toner adhering to the charging member and the transfer member is detected at the same time as the resistance value is detected. Can be transferred to. The transfer toner is removed from the image carrier by the cleaning means, and the image can be formed in a clean state at the time of image formation. At this time, the toner attached to the surface of the image carrier can be completely cleaned by rotating the image carrier at least once. In particular, the transfer member does not stain the back surface of the transfer material with toner.

The detection of the resistance value by the detection means can be easily realized by changing the current flowing when the voltage is applied as the voltage value, and since the detection is performed at the time of non-image formation, there is no problem. Further, by comparing the resistance value of the charging member or the transfer member at room temperature and normal humidity with the detected resistance value as a reference, the value based on the resistance value change can be easily known.

Moreover, by making the charging member and the transfer member roller-type, the charging member and the transfer member can be rotated, and the charging instability due to charge injection can be set by appropriately setting the contact time with the image carrier. It is effective in blocking. Further, by rotating the transfer member in the same direction as the transfer material carrying-in direction to the transfer member, it is useful for reducing conveyance failure such as jam. Moreover, the structure can be simplified by using a brush type.

In the first and second aspects of the invention, since the change state of the charging member or the transfer member is directly detected, the control for charging and transfer is made more effective in contact with the image carrier. Become.

[0041]

First, an example of an image forming apparatus of the present invention will be described with reference to FIG. As the charging member, it is possible to use the one having the structure shown in the conventional example, but it is difficult to cause uneven charging, and from the viewpoint of long life etc., the one using conductive fibers planted in a roller shape is illustrated. Shows. Although this image forming apparatus is an optical printer, particularly a laser printer, the image forming apparatus is not limited to this and can be applied to an electrophotographic copying apparatus.

Data relating to image formation from a host computer (not shown) is processed by the controller 16. Next, the image formation start signal is sent to the engine controller 1.
Sent to 7. From this, the operation proceeds according to a predetermined process.

The transfer materials stored in the transfer material cassette 7 are drawn out one by one by the paper feeding roller 8 and are conveyed by the conveying rollers 9 and 10 to the position before the registration roller 11. The drum-shaped photoconductor 1 forming the image carrier is driven to rotate at a constant speed by a rotation mechanism (not shown). Similarly, the charging roller 5 also rotates at a constant speed. The rotation of the charging roller 5 may be the same as the rotation peripheral speed of the photoconductor 1, but may be configured to be driven at different rotation speeds.

The photosensitive member 1 can be charged to a specific polarity by applying a voltage while the charging roller 5 as the charging device is in contact with the photosensitive member 1 as the image carrier.

As shown in FIG. 2, the charging roller 5 used here is an assembly of conductive fibers which becomes a contact in which the resistance value is adjusted to a desired value by adjusting the dispersion amount of carbon in rayon, for example. An electroconductive core metal 5a having a diameter of 6 mm is used as a substrate by forming an electroconductive base cloth 5a into which a band is formed in a width of 10 mm.
It is wound around c. Here, the resistance of the charging roller is set to about 100 kΩ, the single fiber diameter of the conductive fibers is 20 μm, and the planting density is 8000 fibers / inch.
^{2. The} fiber length was 3 mm.

On the other hand, in the developing device 2, the magnet roller 2d
The upper toner is appropriately sent from the toner storage tank 2e to the developing tank 2f by the supply roller 2d so as to have a predetermined concentration, and is agitated by the mixer roller 2c. At this time, the toner is charged to the same polarity as the photoconductor charging potential when the reversal development is performed. When a value close to the charging potential of the photoconductor 1 is applied to the magnet roller 2d, the toner adheres to the portion irradiated by the exposure / writing head 6 and is reversely developed. When the toner is attached to the unexposed area, the developing device 2 can perform regular development by developing using charged toner having a polarity opposite to the charging potential.

The transfer material is conveyed by the registration roller 11 at a timing corresponding to the image position on the photosensitive member 1. The transfer material is nipped and conveyed by the photoconductor 1 and the transfer roller 3. At this time, a voltage having a polarity opposite to that of the toner is applied to the transfer roller 3. Therefore, the toner on the photoconductor 1 is transferred onto the transfer material. The transfer roller 3 has the same structure as the charging roller 5.

The toner on the transfer material is internally heated by the heater 12.
The toner is nipped and conveyed by the heat roller 12a and the pressure roller 12b containing c, and the toner is fused and fixed on the transfer material by passing between the rollers. The transfer material is the transport roller 1.
3. The paper is delivered to the stack guide 15 by the paper discharge roller 14.

On the other hand, the toner not transferred on the photoconductor 1 is scraped off from the photoconductor 1 by the cleaning blade 4a of the cleaning unit 4 and the toner screw 4 is removed.
b, it is sent to a toner waste container (not shown).

The charging roller 5 and the transfer roller 3 are both connected to a rotation driving means such as a motor, and are rotationally driven by the motor. In particular, when the transfer roller 3 is rotated along the transfer material transport direction, the transfer material transportability is dramatically improved, and jams are less likely to occur.

On the other hand, in the charging roller 5, the photosensitive member 1
If the contact time at the contact point with is longer, the time for injecting charges becomes longer, and the charging potential may become unstable. Therefore, the rotation direction, rotation speed, etc. of the charging roller 5 are appropriately set so that the contact time with the photoconductor 1 is shortened.

Then, the electrostatic latent image is formed by charging the photosensitive member 1 and exposing the image, and the latent image is developed as a toner image by the developing device 2 and then conveyed through the registration roller 11. The toner image is transferred onto the transfer material by the transfer roller 3
Is transcribed by the action of. In this case, when the charging roller 5 charges the photoconductor 1 to, for example, a negative polarity, a voltage having a negative polarity is applied to the charging roller 5. Then, if the portion corresponding to the image is not exposed by the image exposure (in the case of a normal copying machine), it is a positive image as an electrostatic latent image, and this is positively charged by the developing device 2. It will be developed with toner. Further, in order to transfer the toner image to the transfer material, it is necessary to apply a voltage having a polarity opposite to that of the toner from the back surface of the transfer material to the transfer roller 3, and a negative voltage is applied to the transfer roller 3. Conversely, when the photoconductor 1 is positively charged, the toner of the developing device 2 is negatively charged, and the transfer roller 3
Is applied with a positive voltage.

The present invention detects the resistance value of the charging roller 5 or the transfer roller 3 having the same material and the same structure in the image forming apparatus having the above-described structure, and based on this resistance value, the charging roller 5 and the transfer roller 3 are detected. The applied voltage (supply voltage) is controlled. This stabilizes the charging potential and the transfer operation without being affected by environmental changes such as humidity changes. Examples for that purpose are specified below.

<Embodiment 1> FIG. 3 is a circuit diagram showing the detection of the resistance values of the charging roller 5 and the transfer roller 3 and the voltage control based thereon.

In the figure, 100 is a power supply circuit,
Reference numeral 101 is a negative voltage power supply circuit, and 102 is a positive voltage power supply circuit. 103 and 104 are charging roller 5 or transfer roller 3
A change-over switch for supplying a negative voltage or a positive voltage to the switch, which switch is controlled by the control circuit 105. The control circuit 105 controls the changeover of the changeover switches 103 and 104 during an image forming operation or during non-image forming according to a command from the control unit of the image forming apparatus main body.
The control circuit 105 also supplies a negative or positive voltage power supply based on the comparison information (comparison signal) from the comparison circuit 107 that compares the resistance value detected by the resistance value detection circuit 106 with, for example, a reference value. It controls the output voltage of the circuits 101 and 102.

The resistance value detection circuit 106 detects the electric resistance of the charging roller 5 in particular, and an example thereof is shown in FIG. In the figure, .DELTA.R is the electric resistance value of the charging roller 5, which is affected by humidity and the like and changes. The charging roller 5 is 100 k as described above at room temperature and humidity.
Shows a resistance value of about Ω.

The changing resistance value ΔR of the charging roller 5 is
The other resistors R1 to R3 form a bridge circuit, and the voltage from the power supply circuit 100 is supplied to the connection point between the resistors ΔR and R2. The Zener diode ZD is provided to convert the current flowing in the bridge circuit into a voltage and protect the CPU (control circuit 105) against an overcurrent. This Zener diode ZD has, for example, 5.5.
A voltage of V is used, and the voltage between the diodes ZD is input to the analog input terminal of the CPU via the transistor Tr.

The resistors R1 to R3 forming the bridge circuit
Is set so that, for example, when the conductive resistance value ΔR of the charging roller 5 in a high humidity state decreases, the current flowing through the bridge circuit becomes small. Further, the values of the resistors R1 to R3 are appropriately set so that a large amount of current flows through the bridge circuit as the resistance ΔR of the charging roller 5 increases in the low humidity state. So, for example, at room temperature and humidity (2
The voltage of the Zener diode ZD is set to, for example, about 2.5 V to 3.0 V at 5 ° C. and 50% RH.

Therefore, the CPU inputs a voltage generated in the Zener diode ZD supplied through the transistor Tr, and thereby a reference value, for example, a voltage value (2) corresponding to a resistance value of 100 kΩ at room temperature and normal humidity. 0.5V-3.
0V) is included, and the voltage applied to the transfer roller 3 as well as the voltage applied to the charging roller 5 is controlled according to the magnitude of the comparison result. Output the command to change.

The reference value is the charging roller 5
Since the change in resistance ΔR of the above is converted into a voltage value and processed, a reference voltage (2.5
V to 3.0 V) is stored in advance in the RAM or ROM.

When the resistance of the charging roller 5 is detected by the resistance detecting circuit 105, a voltage having the same polarity as the charging polarity of the toner of the developing device 2 is applied to the charging roller and the transfer roller 3. Therefore, if the toner of the developing device 2 has a positive charging polarity, a positive voltage is supplied to the charging roller 5 and the transfer roller 3. Therefore, the control circuit 105, which is a CPU, switches the changeover switches 103 and 104 to the positive voltage power supply circuit 102 so that a predetermined voltage is supplied from the positive voltage power supply circuit 102 side of the power supply circuit 100, and the charging and transfer rollers 5 and 3 are switched. Supply positive voltage.

At this time, the current flowing through the charging roller 5 is detected by the Zener diode ZD of the resistance value detection circuit 106,
The resistance value of the charging roller 5 can be known. in this case,
The photoconductor 1 is rotated at least once as in the image forming operation. Therefore, the positively charged toner attached to the charging roller 5 and the transfer roller 3 is transferred to the surface of the photoconductor 1. This toner is removed by the cleaning blade 4a of the cleaning unit 4 as the photoconductor 1 rotates.

Next, in order to deepen the above understanding, one operation example will be described.

First, at the time of non-image formation, the positive voltage power supply circuit 10
FIG. 5 shows the surface potential of the photoconductor 1 generated by switching to 2 and changing the voltage output from the circuit 102.
FIG. 5 shows a photosensitive member which is a charging surface that comes into contact with the conductive fiber assembly when a positive DC voltage is applied to the charging roller 5 in a room temperature and normal humidity environment where the temperature is 25 ° C. and the humidity is 50% RH. It represents the surface potential.

Here, when the potential of the charged surface of the conductive fiber assembly becomes +600 V at room temperature and normal humidity, the charging roller 5 is applied with a voltage.
The resistance value of is used as the reference value. According to this, the applied voltage is +9
It can be seen that when the voltage is 00V, the potential of the charged surface of the conductive fiber assembly becomes + 600V. Therefore, at the time of non-image formation, + 900V is applied from the positive voltage power supply circuit 102 to the photosensitive member 1.
Was applied to the charging roller 5 and the transfer roller 3 for at least one rotation. At this time, the charging roller 5 and the transfer roller 3
The toner adhered to the surface of the photoconductor 1 is transferred to the cleaning blade 4a of the cleaning unit 4 on the surface of the photoconductor 1.
It is removed and collected by.

On the other hand, when the above voltage is applied, the resistance value detection circuit 106 detects the resistance value of the charging roller 5.
This detection is converted into a voltage value as shown in FIG. 4, and this value is supplied to the comparison circuit 107 in the CPU. In the comparison circuit 107, the potential of the charged surface of the conductive fiber aggregate in the environment of normal temperature and normal humidity which is input in advance is +600.
The resistance value of the charging roller 5 when the voltage when it becomes V is applied to the charging roller 5 (reference value) is compared with the detected resistance value, and the variation value thereof is calculated. The calculated fluctuation value is sent to the control circuit 105. In the control circuit 105,
The voltage applied to the charging roller 5 during the charging operation during image formation and the voltage applied to the transfer roller 5 during the transfer process are set in advance, and the applied voltage is determined each time according to the level of the variation value. .

In the case of FIG. 7, the applied voltage is set so as to correspond to three types of low humidity environment, normal humidity environment and high humidity environment, and the applied voltage is determined in each environment. The set values at this time are shown in Table 1 below.

[0068]

[Table 1]

The voltage values set in Table 1 above were obtained from FIG. 6 showing the potential of the charging surface of the charging member in each environment. FIG. 6 shows the voltage applied to the charging roller 5 in the embodiment of the present invention, and the surface potential of the photoconductor 1 which is the charged surface of the conductive fiber assembly under each environment when the applied voltage is changed. Is represented. This graph can also be applied to the voltage applied to the transfer roller 3 made of the same material as the charging roller 5.

In the characteristic diagram of FIG. 6, what is indicated by a solid line is a characteristic diagram in a normal humidity environment where the temperature is 25 ° C. and the humidity is 50% RH, and the charging potential of the photoconductor 1 of this embodiment is −600.
When trying to obtain V, the applied voltage is -900V,
This can also be applied to the voltage applied to the transfer roller 3 during the transfer process. On the other hand, what is indicated by a broken line is a characteristic diagram in a low humidity environment where the temperature is 20 ° C. and the humidity is 20% RH.
It is necessary to apply a voltage of -1000V. Further, what is indicated by a dashed line is a characteristic diagram in a high humidity environment where the temperature is 30 ° C. and the humidity is 80% RH. When the charging potential of the photoconductor 1 is to be obtained, a voltage of −800 V is applied. There is a need.

The cause of the difference in the voltage value among these three is that the resistance of the conductive member fluctuates due to the change in humidity, and the charge injection amount also fluctuates accordingly.

Therefore, the control circuit 105 performs the voltage switching control shown in Table 1 in order to keep the charging potential to the photosensitive member 1 constant and to perform the transfer satisfactorily regardless of the environmental change. That is,
If the control circuit 105 determines that the resistance value detected by the resistance value detection circuit 106 is in an environment of normal temperature and normal humidity,
When a surface potential of −600V is desired as indicated by the solid line in FIG. 6, a voltage of −900V is applied to the charging roller 5 and the transfer roller 3.
The output voltage of the negative voltage power supply circuit 101 is controlled to be applied to.

Further, since the resistance becomes low under the environment of high temperature and high humidity, the control circuit 105 applies a voltage of about -1000 V to the charging roller and the transfer roller 3 as shown by the broken line in FIG.
The output voltage of the negative voltage power supply circuit 101 is controlled to be applied to.

Further, since the resistance becomes high at low temperature and low humidity, the resistance value detection circuit 106 detects the state, and the control circuit 105 determines that the resistance value is high.
The comparison section determines the supply voltage during image formation. In this case, the output voltage of the negative voltage power supply circuit 101 is controlled to −800 V, and the changeover switches 103 and 104 are turned on.
The voltage (-800 V) corresponding to the resistance value detected by the charging roller 5 and the transfer roller 3 is supplied during the image forming operation.

To explain the above in more detail, in a low humidity environment, the resistances of the charging roller 5, the transfer roller 3, and the conductive member increase, and the charging roller 5 causes the photosensitive member 1 or
It becomes difficult for the charges to move from the transfer roller 3 to the transfer material. Conversely, in a high-humidity environment, the resistance of the conductive member drops, and it becomes easy for charges to move from the charging roller 5 to the photoconductor 1 or from the transfer roller 3 to the transfer material. The charge injection amount has a great influence, and in the charging process, the charge potential of the photoconductor 1 increases due to the increase of the charge injection amount, and thus the photoconductor 1 causes a dielectric breakdown and causes a problem such as a pinhole. Further, a decrease in the charge potential of the photoconductor 1 due to a decrease in the charge injection amount causes a problem that fog occurs due to insufficient charge.

On the other hand, in the transfer processing step, an increase in the charge injection amount causes a problem such as transfer failure, and a decrease in the charge injection amount causes problems such as toner scattering and separation failure.

Therefore, the resistance value of the conductive member is detected in advance during non-image formation, and each time, the voltage value applied to the charging roller 5 during the charging operation during image formation and the transfer roller 3 during the transfer processing step. By determining the applied voltage value of, the photosensitive member 1 can always obtain a stable surface potential irrespective of the change of the charge injection amount due to the change of environment, and a good transfer property can be obtained in the transfer processing step. Obtainable. Further, by controlling the voltage of the charging device and the transfer device by the same control circuit 105, the device can be simplified.

Furthermore, another object of the present invention is to
By applying a positive voltage, which is a voltage having the same polarity as the charging polarity of the toner, to the charging roller 5 and the transfer roller 3 during non-image formation, the toner adhered to the conductive member in contact with the photoconductor 1 of both rollers. Was transferred onto photoreceptor 1. As a result, even if 20 k sheets are continuously printed, the charging roller 5
Since the toner attached to the transfer roller 3 is removed each time, the toner enters the contact surface between the charging roller 5 and the photoconductor 1 and damages the surface of the photoconductor 1 or causes image unevenness due to poor charging. In addition, a good image was obtained without causing stains on the back of the transfer material.

In this embodiment, the resistance change of the charging roller 5 and the transfer roller 3 due to the humidity change is detected, and the voltage control is carried out in three stages at low humidity, normal humidity and high humidity. With this, the constituent circuit of the control circuit 105 can be simplified and sufficient control can be performed according to the change in humidity. However, if more accurate control is desired, the voltage switching control can be realized by dividing the voltage switching control into three or more stages and setting the voltage accordingly. For example, when comparing the output voltage of the resistance value detection circuit 106 from 0 to 5.5 V, the output voltage of the resistance value detection circuit 106 may be compared in 0.5 V units, more finely in 0.1 units, and the voltage control may be performed accordingly.

Further, according to this embodiment, the negative voltage power supply circuit 101 side is a controllable power supply section, and the positive voltage power supply circuit 102 is a power supply section for resistance value detection.

<Embodiment 2> FIG. 8 shows a second embodiment of the present invention, in which a conductive fiber assembly (conductive member) 51 having a width of 10 is used.
A strip-shaped charging member 50 having a brush structure was formed by forming the strip-shaped member having a size of mm and adhering it to a conductive substrate 52 made of a metal such as aluminum with a conductive adhesive. On the other hand, a conductive fiber aggregate 31 also formed in a strip shape having a width of 10 mm was adhered onto a conductive substrate 32 made of metal with a conductive adhesive to form a transfer member 30 having a brush structure.

Both are conductive fiber aggregates (conductive members)
Reference numerals 51 and 31 are those having a fiber length of 4 mm, which is made conductive by sandwiching carbon formed in an extremely fine rod shape in nylon. The resistance value is 1 at room temperature and humidity.
The diameter of the single fiber of the conductive fiber was 20 μm, and the planting density was 8000 fibers / inch ² .

The photoconductor 1 is negatively charged by the charging member 50, the surface of the photoconductor 1 is exposed to form an electrostatic latent image, and the developing device 2 forms a toner image. The container 2 performs reversal development in which the toner is negatively charged.

In the case of reversal development, a negative voltage is applied to the charging member 50 at the time of image formation, and a voltage having a polarity opposite to the charging polarity of the toner is applied to the transfer member 30 at the transfer processing step. At the time of non-image formation, in order to transfer the toner adhered to both members 50 and 30 onto the photoconductor 1, a voltage having the same polarity as the charging polarity of the toner is applied. Therefore, the charging member 50
A negative voltage is applied to the transfer member 30.

The control of the voltage supplied to the charging member 50 and the transfer member 30 at the time of image formation based on the above-mentioned voltage switching and environmental change has the same circuit configuration as in FIG. 3, and the same portions are denoted by the same reference numerals. The details of the circuit are as described above. The resistance value detection circuit 106 also uses the circuit configuration itself shown in FIG.

First, the changeover switch 103 during non-image formation.
9 is changed to the negative voltage power supply circuit 101 side, and the potential change on the surface of the photoconductor 1 when the voltage of the power supply circuit 101 is changed by applying it to the charging member 50 is shown in FIG. The temperature in FIG. 9 is 25
This is a graph showing the surface potential of the photoreceptor 1 when a negative DC voltage is applied to the charging member in a normal temperature and normal humidity environment of ° C and humidity of 50% RH. Here, the resistance value of the charging member 50 when the surface potential of the photoconductor becomes −600 V in the normal temperature and normal humidity environment when the charging member 50 is applied is used as a reference value. According to this, the applied voltage is -10
It can be seen that the surface potential of the photoconductor 1 becomes -600V when the voltage is 00V.

Therefore, at the time of non-image formation, −1000 V was applied to the charging member 50 and the transfer member 30 from the negative voltage power supply circuit 102 only while the photoconductor 1 made at least one revolution.
At this time, the toner attached to the charging member and the transfer member is transferred onto the photoconductor 1 and is collected by the cleaning blade 4a which is the cleaning means 4 for cleaning the surface of the photoconductor 1.

On the other hand, the resistance value detection circuit 106 detects the resistance value of the charging member 50 and transmits the result to the comparison circuit 107 formed in the control circuit 105 including a CPU. In the comparison circuit 107, the voltage when the potential of the surface of the photoconductor due to the conductive fiber assembly becomes −600 V, which is input in advance in the normal temperature and normal humidity environment, is applied to the charging member 5.
The stored reference resistance value of the charging member when applied to 0 is compared with the detected resistance value ΔR, and the variation value is obtained. In accordance with the calculated variation value, the control circuit 105
The voltage value supplied to the charging member 50 and the transfer member 30 during the image forming operation is set, and thereby the changeover switches 103 and 104 are switched to the negative voltage power supply circuit 102 and the positive voltage power supply circuit 101, respectively, to control the output voltage thereof. .

FIG. 10 is a diagram showing the surface potential of the photosensitive member 1 when the voltage supplied to the charging member 50 is changed in this embodiment, and the solid line shows a normal humidity environment where the temperature is 25 ° C. and the humidity is 50% RH. The surface potential of the photoreceptor 1 at
The surface potential of the photoconductor 1 in a low humidity environment of 0 ° C. and a humidity of 20% RH, and the alternate long and short dash line represents the surface potential of the photo conductor 1 in a high humidity environment of an air temperature of 30 ° C. and a humidity of 80% RH. This graph can also be applied to the voltage applied to the transfer member 30 made of the same material as the charging member 50 by reversing the polarity of the applied voltage.

Therefore, with respect to the voltage value supplied to the charging member 50 for setting the surface potential of the photosensitive member 1 to -600 V during the image forming operation, the power source is in accordance with the humidity environment of each diagram. Table 2 below shows the voltages supplied to the charging member 50 and the transfer member 30 in a low humidity environment (broken line in FIG. 10), a normal humidity environment (solid line in FIG. 10), and a high humidity environment (dotted line in FIG. 10). ), And the case of setting in five different ways between the low humidity environment and the normal humidity environment, and between the normal humidity environment and the high humidity environment.

[0091]

[Table 2]

In order to distinguish each humidity environment of Table 2, in the circuit of FIG. 4, when the voltage generated by the resistance value detection circuit 106 (voltage between Zeners) is, for example, 0 to 1.5 V, in a high humidity environment, 1 Between 0.5 and 2.5V, it is in the middle of high humidity environment and high humidity environment, when it is 2.5 to 3.0V, it is normal humidity environment, and when it is 3.0 to 4.0V, it is normal humidity environment and low humidity environment. In the middle of time, when the voltage is 4.0 to 5.5 V, the control circuit 105 can perform the voltage control shown in Table 2 by distinguishing it from the low humidity environment. At this time, the voltage supplied to the transfer member 30 is similarly controlled.

The detection of the resistance value, that is, the timing of detecting the resistance value of the charging member in order to know the environmental condition is the same as that in the first embodiment, and it is during non-image formation, for example, before starting the image forming operation. To do. This is the changeover switch 103, 1
04 is switched to the negative voltage power supply circuit 102 side according to the instruction of the control circuit 105, and the charging member 50 and the transfer member 30 are set to 1
Supply voltage of 000V. As a result, the voltage corresponding to the resistance value of the charging member 50 is detected by the resistance value detection circuit 106, and the voltage value under each environment shown in Table 2 is set based on the detected value. Then, when the image forming operation is started, the control circuit 105 switches the changeover switch 103 to the side of the negative voltage power supply circuit 101 and the changeover switch 104 to the side of the positive voltage power supply circuit 102, and sets the negative voltage to the charging member 50.
A positive voltage is supplied to the transfer member 30. In this case, the positive and negative voltage power supply circuits 101 and 102 are controlled to a voltage according to each environment as shown in Table 2 and output the voltage. The positive and negative voltage power supply circuits 101 and 102 at this time constitute a power supply unit that can be controlled.

As described above, the temperature is 25 ° C. and the humidity is 50% RH.
In the normal humidity environment, when it is attempted to obtain the charging potential of the photoreceptor 1 of the present embodiment of -600V, the voltage applied to the charging member 50 is -1000V, and the polarity of this voltage is reversed. As a result, it can be applied to the voltage applied to the transfer member 30 during the transfer process. On the other hand, the temperature is 20 ℃,
In a low humidity environment with a humidity of 20% RH, when an attempt is made to obtain the charging potential of the photoconductor 1, the charging member 50 has -1100.
It is necessary to apply a voltage of V, and +1 is applied to the transfer member 30.
It is necessary to apply a voltage of 100V. Furthermore, temperature 3
In a high humidity environment of 0 ° C. and a humidity of 80% RH, the photoreceptor 1
When trying to obtain the charging potential of -9, the charging member 50 has a -9
It is necessary to apply a voltage of 00V, and the transfer member 30
It is necessary to apply a voltage of 900V.

The cause of the difference between the voltage values of these three factors is that the resistance of the conductive member of the charging member and the transfer member fluctuates due to the change of humidity as described in the first embodiment. This is because the amount of charge input fluctuates. Therefore, in a low-humidity environment, the resistance of the conductive member increases, and it becomes difficult to move the charge from the charging member 50 to the photoconductor 1 or from the transfer member 30 to the transfer material. Conversely, in a high-humidity environment, the resistance of the conductive member drops, and it becomes easy for charges to move from the charging member 50 to the photoconductor 1 or from the transfer member 30 to the transfer material. The charge injection amount has a great influence, and in the charging process, the charge potential of the photoconductor 1 increases due to the increase of the charge injection amount, and thus the photoconductor 1 causes a dielectric breakdown and causes a problem such as a pinhole. Further, a decrease in the charge potential of the photoconductor 1 due to a decrease in the charge injection amount causes a problem that fog occurs due to insufficient charge. On the other hand, in the transfer processing step, an increase in the charge injection amount causes a problem such as transfer failure, and a decrease in the charge injection amount causes problems such as toner scattering and separation failure.

Therefore, as described above, the resistance value of the conductive member is detected in advance during non-image formation, and each time, the voltage value applied to the charging member 50 during the charging operation during image formation, and the transfer processing step. By determining the value of the voltage applied to the transfer member 30, the photosensitive member 1 can always obtain a stable surface potential irrespective of the change of the charge injection amount due to the change of the environment, and it is possible to obtain a good surface potential during the transfer process. Transferability can be obtained. Further, by controlling the charging device and the transfer device by the same control means (control circuit 105), the device can be simplified. Further, as in the present embodiment, it is possible to perform the control with higher accuracy by further setting the applied voltage between the low humidity environment and the normal humidity environment and between the normal humidity environment and the high humidity environment.

Further, in order to perform control with high accuracy, the detection value of the resistance value detection circuit 106 is finely divided and the voltage control is executed according to each divided value.

On the other hand, another object of the present invention is to apply a negative voltage, which is the voltage of the charging polarity of toner during non-image formation, to the charging member 50 and the transfer member 30.
The toner attached to both members was transferred onto the photoconductor 1. As a result, even if continuous printing of 25 k sheets is performed, the toner attached to the charging member 50 and the transfer member 30 is removed each time, so that the toner enters the contact surface between the charging member 50 and the transfer member 30, and the photoreceptor 1 A good image was obtained without damaging the surface or causing unevenness in the image due to poor charging, and without causing stains on the back of the transfer material.

The negative voltage power supply circuit 10 is used during non-image formation.
The changeover switches 103 and 104 are switched to the 1 side to supply a predetermined negative voltage to the charging member 50 and the transfer member 30. At this time, the power supply circuit 101 that supplies voltage supplies a power supply unit for resistance value detection. Will be configured.

<Embodiment 3> FIG. 11 is a third embodiment of the present invention, in which carbon is dispersed in an elastic body such as rubber or urethane to form a conductive roll-like elastic layer 51-1 made of metal or the like. Of the charging member 50-1 by covering the conductive core member 52-1 of
Configured 1. On the other hand, a conductive elastic layer 31-1 also made of the same material as the charging member was coated on the conductive core member 32-1 to form a transfer member 30-1.

The photoconductor 1 is negatively charged, and the surface of the photoconductor 1 is exposed to form an electrostatic latent image, and the developing device 2 forms a toner image. Reversal development is performed in which the toner is negatively charged. In the case of reversal development, the charging member 50-1 is used during the charging operation during the image forming operation.
A negative voltage is applied to the transfer member 30-1, and a positive voltage having a polarity opposite to the charging polarity of the toner is applied to the transfer member 30-1 during the transfer process. Both members 50-1 and 30-1 during non-image formation
In order to transfer the toner adhered to the photosensitive member 1 onto the photoconductor 1, a voltage having the same polarity as the charging polarity of the toner is applied. Therefore, a negative voltage is applied to the charging member 50-1 and the transfer member 30-1. The circuit configuration similar to that in FIG. 3 (and FIG. 8) is used for switching the voltage to be supplied to the charging member 50-1 and the transfer member 30-1 and controlling the voltage to be supplied during the image forming operation according to the environmental change. The same parts are designated by the same reference numerals, and the details of the circuit are as described above. Further, the resistance value detection circuit 106 has the same configuration as that in FIG. Particularly, in this embodiment, the resistance value of the transfer member 30-1 is detected, which is different from the first and second embodiments in this respect.

Therefore, the changeover switch 1 is used during non-image formation.
04 to the negative voltage power supply circuit 101 side to transfer the transfer member 30.
FIG. 12 shows the potential change on the surface of the photosensitive member 1 when the voltage of the power supply circuit 101 is variously changed by applying the voltage to -1. FIG. 1
Reference numeral 2 represents the surface potential of the photoconductor 1 which is the charged surface when a negative DC voltage is applied to the transfer member 30-1 in a room temperature and normal humidity environment where the temperature is 25 ° C. and the humidity is 50% RH. . Here, the resistance value of the transfer member 30-1 when a voltage when the potential of the charged surface of the conductive elastic body becomes −600 V is applied to the transfer member 30-1 in a normal temperature and normal humidity environment is a reference value. And According to this, the applied voltage is -1100
It can be seen that when the voltage is V, the surface potential of the photoconductor 1 becomes −600V.

Therefore, during non-image formation, the negative voltage power supply circuit 101 applies -1100 V to the charging member 50-1 and the transfer member 30-1 for one rotation of the photoconductor 1. At this time, in the supply voltage, the negative voltage power supply circuit 101
The resistance value of the transfer member 30-1 constitutes a power supply unit for detecting voltage. The output voltage of the negative voltage power supply circuit 101 is set to the charging member 5
The toners attached to the charging member 50-1 and the transfer member 30-1 are transferred onto the photoconductor 1 by being supplied to the 0-1 and the transfer member 30-1, and the cleaning means 4 for cleaning the surface of the photoconductor 1 is performed. It is collected by the blade 4a.

On the other hand, the resistance value detection circuit 106 detects the resistance value of the transfer member 30-1 and transmits the result to the comparison circuit 107 formed in the control circuit 105 including a CPU. In the comparison circuit 107,
The voltage when the potential of the surface of the photoconductor 1 due to the conductive fiber assembly becomes −600 V in the normal humidity environment is set to the transfer member 30.
A resistance value, which is a prestored reference value of the transfer member when applied to -1, and the detected resistance value are compared,
The variation value is calculated.

Based on the calculated variation value, the control circuit 10
Reference numeral 5 denotes a charging member 50-1 and a transfer member 30 during image formation.
The voltage value supplied to -1 is set, and the output voltage of the negative voltage power supply circuit 101 and the positive voltage power supply circuit 102 is controlled by this. At this time, the changeover switches 103 and 104 are changed over according to their polarities.

FIG. 13 is a diagram showing the surface potential of the photosensitive member 1 when the voltage supplied to the charging member 50-1 is changed in this embodiment, and the solid line shows the temperature of 25 ° C. and the humidity of 5
The surface potential of the photoconductor 1 in a normal humidity environment of 0% RH is
The broken line is a graph showing the surface potential of the photoconductor 1 in a low humidity environment where the temperature is 20 ° C. and the humidity is 20% RH, and the dashed line is a graph showing the surface potential of the photo conductor 1 in the high humidity environment where the temperature is 30 ° C. and the humidity is 80% RH. is there. This graph can also be applied to the voltage applied to the transfer member 30-1 made of the same material as the charging member 50-1 by reversing the polarity of the applied voltage.

Therefore, the voltage value supplied to the charging member material 50-1 for setting the surface potential of the photosensitive member 1 to -600 V during the image forming operation is a voltage according to the humidity environment of each diagram. Table 3 below shows the voltages supplied to the charging member 50-1 and the transfer member 30-1 for charging the surface potential of the photoconductor 1 to -600 V in each humidity environment based on FIG. In particular, the supply voltage is constant in a low humidity environment (broken line in FIG. 13), in a normal humidity environment (solid line in FIG. 13), in a high humidity environment (dashed line in FIG. 13), and during a low humidity environment and a normal humidity environment. It is set according to five kinds of environmental conditions between the wet environment and the high humidity environment.

[0108]

[Table 3]

In order to distinguish each humidity environment in Table 3, the voltage generated by the resistance value detection circuit 106 (voltage between Zener diodes ZD) in the circuit of FIG. 4 is, for example, 0 to 1.5V.
Is in a high-humidity environment, 1.5-2.5V is in a high-humidity environment and a normal-humidity environment, 2.5-3.0V is in a normal-humidity environment, and 3.0-4.0V is in a normal environment. The control circuit 105 can perform the voltage control shown in Table 3 by distinguishing between the low humidity environment and the low humidity environment between 4.0 and 5.5 V between the humidity environment and the low humidity environment. At this time, the voltage supplied to the transfer member 30-1 is similarly controlled.

The detection of the resistance value, that is, the timing of detecting the resistance value of the transfer member 30-1 in order to know the environmental condition is the same as in the first embodiment during non-image formation, for example, before starting the image forming operation. To do. This is the changeover switch 10
3, 104 is switched to the negative voltage power supply circuit 101 side according to the instruction of the control circuit 105, and a voltage of -1100 V is supplied to the charging member 50-1 and the transfer member 30-1. The voltage supplied by the negative voltage power supply circuit 101 at this time constitutes a power supply unit for detecting the resistance value. As a result, the transfer member 3
The voltage corresponding to the resistance value of 0-1 is the resistance value detection circuit 106.
The voltage value under each environment shown in Table 3 is set based on the detected value.

When the image forming operation is started, the control circuit 105 sets the changeover switch 103 to the negative voltage power supply circuit 101 side and the changeover switch 104 to the positive voltage power supply circuit 1.
02 side, respectively, and a negative voltage is supplied to the charging member 50-1 and a positive voltage is supplied to the transfer member 30-1. In this case, the positive and negative voltage power supply circuits 101 and 102 are controlled to a voltage according to each environment as shown in Table 3 and output the voltage.
The negative and positive voltage power supply circuits 101 and 102 form a controllable power supply unit during image formation.

As described above, the temperature is 25 ° C. and the humidity is 50% RH.
In the normal humidity environment, when it is attempted to obtain the charging potential of the photoreceptor 1 of the present embodiment of -600V, the voltage applied to the charging member 50-1 is -1100V, and the polarity of this voltage is reversed. Therefore, it can be applied to the voltage applied to the transfer member 30-1 during the transfer process. On the other hand, the temperature is 20
In a low-humidity environment of 20 ° C. and a humidity of 20% RH, when it is attempted to obtain the charging potential of the photoconductor 1, the charging member 50-1 has −
It is necessary to apply a voltage of 1200 V, and the transfer member 30
It is necessary to apply a voltage of + 1200V to -1. Furthermore, in a high humidity environment where the temperature is 30 ° C. and the humidity is 80% RH,
To obtain the charging potential of the photoconductor 1, it is necessary to apply a voltage of -1000V to the charging member 50-1 and a voltage of + 1000V to the transfer member 30-1. This allows stable image formation.

Therefore, the cause of the above-mentioned voltage difference is that the charging member and the transfer member are changed due to the change in humidity as described in the first and second embodiments. This is because the resistance of the conductive member fluctuates and the charge injection amount accordingly fluctuates. Therefore, in a low-humidity environment, the resistance of the conductive member increases, and it becomes difficult for the charge to move from the charging member 50-1 to the photoconductor 1 or from the transfer member 30-1 to the transfer material. On the contrary, in a high humidity environment, the resistance of the conductive member drops, and the charge is easily transferred from the charging member 50-1 to the photoconductor 1 or from the transfer member 30-1 to the transfer material. This charge injection amount has a great influence, and if the supply voltage is kept constant, in the charging processing step, the charge potential of the photoconductor 1 increases due to the increase in the charge injection amount, and the photoconductor 1 causes a dielectric breakdown to cause pinholes. Problems such as the occurrence of
In addition, a decrease in the charge injection amount causes a decrease in the charging potential of the photoconductor 1, which causes a problem that fog occurs due to insufficient charging. On the other hand, at the time of the transfer processing step, an increase in the charge injection amount causes problems such as transfer failure, and a decrease in the charge injection amount causes problems such as toner scattering and separation failure.

On the other hand, as described above, the resistance value of the conductive member is detected in advance during non-image formation, and each time, the voltage value applied to the charging member 50-1 during the charging operation during image formation and the transfer value are transferred. By determining the voltage value applied to the transfer member 30-1 during the processing step, the photoconductor 1 can always obtain a stable surface potential regardless of the change in the charge injection amount due to the change in the environment. Good transferability can be obtained during the process. In addition, by controlling the charging device and the transfer device by the same control means, the device can be simplified.

Further, as in this embodiment, by setting the applied voltage corresponding to the middle of the low humidity environment and the normal humidity environment, and the middle of the normal humidity environment and the high humidity environment, it is possible to obtain high accuracy. You can control. In order to perform control with higher precision, it is possible to divide the detection value of the resistance value detection circuit 106 into fine parts and execute control according to each divided value.

On the other hand, another object of the present invention is to apply a negative voltage having the same polarity as the charging polarity of the toner to the charging member 50-1 and the transfer member 30-1 during non-image formation. Then, the toner attached to both members was transferred onto the photoconductor 1. As a result, even if continuous printing of 25 k sheets is performed, the toner attached to the charging member 50-1 and the transfer member 30-1 is removed each time, so that the charging member 50-1 is removed.
-1 does not enter the contact surface between the photosensitive member 1 and the photosensitive member 1 and does not damage the surface of the photosensitive member 1 or cause image unevenness due to charging failure. Was obtained.

The numerical values illustrated in each of the above-described embodiments, that is, the voltage values supplied to the charging member and the transfer member are examples, and the type of the photoconductor, the material of the conductive member constituting the charging member, and the like. Different in different. Therefore, the supply voltage for obtaining the surface potential suitable for various photoconductors is as shown in FIGS.
It can be realized by experimentally obtaining characteristic diagrams such as 3.

Further, the negative or positive voltage power supply circuits 101 and 102 of the power supply circuit 100 can be similarly implemented by superposing an AC voltage on a DC voltage. Particularly for voltage control, the DC voltage side may be controlled in the same manner as in the first to third embodiments, and the AC voltage may be kept constant.

[0119]

In the image forming apparatus using the contact charging method, it is possible to always obtain a stable image without being influenced by environmental changes due to humidity changes.

Further, the voltage control of the charging and transfer means can be controlled by the same controller, so that the circuit structure can be simplified.

Further, when the resistance value of the conductive member such as the charging member is detected, the toner adhered to the charging member and the transfer member is transferred to the image carrier side and is removed by the cleaning, so that the transfer material is not polluted. At the same time, it is possible to prevent the image carrier from being damaged by the charging member and the transfer member.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of an image forming apparatus according to the present invention.

FIG. 2 is a perspective view showing an example of a charging member (or a transfer member) according to the present invention.

FIG. 3 is a circuit configuration diagram showing an example of control of a voltage supplied to a charging member and a transfer member in the first embodiment according to the present invention.

FIG. 4 is a circuit diagram showing a specific example of a detection circuit for detecting a resistance value of a charging member or a transfer member of the present invention.

FIG. 5 is a characteristic diagram showing a surface potential when a positive voltage is applied to the charging member in the first embodiment of the present invention.

FIG. 6 is a characteristic diagram showing how the surface potential changes due to environmental changes in the first embodiment of the present invention.

FIG. 7 is a flowchart relating to voltage control according to the first embodiment of the present invention.

FIG. 8 is a circuit configuration diagram for controlling a supply voltage to a charging member and a transfer member according to a second embodiment of the present invention.

FIG. 9 is a characteristic diagram showing the surface potential when a negative voltage is applied to the charging member in the second embodiment of the present invention.

FIG. 10 is a characteristic diagram showing how the surface potential changes due to environmental changes in the second embodiment of the present invention.

FIG. 11 is a circuit configuration diagram for controlling the supply voltage to the charging member and the transfer member in the third embodiment of the present invention.

FIG. 12 is a characteristic diagram showing changes in the surface potential when a negative voltage is applied to the transfer member in the third embodiment of the present invention.

FIG. 13 is a characteristic diagram showing how the surface potential changes due to environmental changes in the third embodiment of the present invention.

FIG. 14 is a perspective view showing a configuration example of a conventional contact charging member.

FIG. 15 is a discharge characteristic diagram based on Paschen's law.

FIG. 16 is a configuration diagram for explaining a method of charging a charging member (or a transfer member) using conductive fibers.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor (image bearing member) 2 Developing device 3 Transfer roller (transfer member) 4 Cleaning unit 5 Charging roller (charging member) 6 Exposure means 30,30-1 Transfer member 50,50-1 Charging member 100 Power supply circuit 101 Negative Voltage power supply circuit 102 Positive voltage power supply circuit 103, 104 Changeover switch 105 Control circuit 106 Resistance value detection circuit 107 Comparison circuit ΔR Charging member (or resistance value of transfer member) ZD Zener diode for resistance value detection

Claims (11)

[Claims] 1. A contact type charging means for charging an image bearing member to a specific polarity, a means for exposing the charged image bearing member, and an electrostatic latent image formed on the image bearing member in response to the exposure. An image forming apparatus comprising: a developing unit that develops an image with a charged toner; and a contact-type transfer unit that appropriately transfers the developed toner image onto a transfer material that is conveyed. The members are made of the same material and have the same structure, a detection means for detecting the resistance value of the charging member or the transfer member is provided, and the voltage supplied to the charging member and the transfer member based on the resistance value detected by the detection means. An image forming apparatus comprising a control unit configured to simultaneously control the image forming apparatus and the image forming apparatus. 2. The control means includes means for comparing the resistance value of the charging member or the transfer member at room temperature and normal humidity with the resistance value detected by the detection means as a reference, and comparing The image forming apparatus according to claim 1, wherein voltage control is performed according to a result. 3. The detection unit detects a resistance value by detecting a current or a voltage generated by supplying a voltage having a specific polarity to a charging member or a transfer member during non-image formation. The image forming apparatus described. 4. When the developing means carries out regular development,
2. The image forming apparatus according to claim 1, wherein a voltage from the same power source is supplied to the charging member and the transfer member under the control of the control means. 5. A contact type charging means for charging an image carrier to a specific polarity, a means for exposing the charged image carrier, and an electrostatic latent image formed on the image carrier according to the exposure. Developing means for developing the image with charged toner, contact-type transfer means for appropriately transferring the developed toner image to a transfer material conveyed, and cleaning means for removing the toner remaining on the image carrier. In an image forming apparatus comprising: a charging member and a transfer member, which are made of the same material and have the same structure, a detection unit which detects a resistance value of the charging member or the transfer member, and when the image is formed on the charging member and the transfer member. A controllable first power supply unit for supplying a predetermined voltage, and a second power supply unit for supplying a voltage to the resistance member and the transfer member to detect a resistance value by the detection unit during non-image formation. , The first Switching means for supplying one of the source portion and the second power source portion to the charging member and the transfer member, and the first means based on the resistance value detected by the detection means while controlling the switching means. An image forming apparatus comprising: a control unit that controls a voltage of a power supply unit. 6. The image forming apparatus according to claim 5, wherein the second power supply section outputs a voltage having the same polarity as the charged toner of the developing means. 7. The control means includes means for comparing the reference resistance value with the detection resistance value detected by the detection means with reference to the resistance value of the charging member or the transfer member at room temperature and normal humidity, The image forming apparatus according to claim 5, wherein the voltage of the first power supply unit is controlled according to the comparison result. 8. The detection unit detects the resistance value by detecting the current or voltage generated in the charging member or the transfer member in a state where the voltage from the second power supply unit is supplied to the charging member and the transfer member during non-image formation. The image forming apparatus according to claim 5, wherein the image is converted and detected. 9. When the developing unit is a regular developing unit, the output voltage of the first power source unit has a polarity opposite to that of the charged toner, and when the developing unit is a reversal developing unit, the first power source unit is the same as the charged toner unit. The image forming apparatus according to claim 5, wherein a voltage having a polarity is output to the charging member and a voltage having a polarity opposite to that of the charged toner is output to the transfer member. 10. The image forming apparatus according to claim 5, wherein the control means rotates the image carrier at least once while the voltage of the second power source is being supplied to the charging member and the transfer member during non-image formation. 11. The charging member and the transfer member are a roller type in which a conductive fiber assembly or a conductive elastic layer is wound around or covered with a conductive base portion, or a brush type in which a fiber assembly is attached to a conductive base portion. The image forming apparatus according to claim 1.