JPH07302006A - Image forming device - Google Patents

Abstract

PURPOSE:To stably obtain effective transfer efficiency with a simple constitution. CONSTITUTION:In a normal control operation, a transfer current applied to a transfer roller 38 is controlled with a constant current at a prescribed constant current control value I0. A combined resistance vlaue R in a transfer part is lowered by material changes in a transfer material 50 and environment where the image forming device is placed, etc., and when a transfer voltage V1 in the control with the constant current becomes a reference voltage V0 or below, the transfer current I1 is increased and the transfer voltage V1 is controlled so as to obtain the transfer voltage V1 to the reference voltage V0 or above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus,
In particular, the present invention relates to an image forming apparatus applied to, for example, a copying machine, a printer or a facsimile.

[0002]

2. Description of the Related Art An example of a conventional image forming apparatus of this type is
It is disclosed in JP-A-3-213888. In this conventional technique, constant voltage control is performed on the charging member (transfer means) while the image area is located in the transfer area for the purpose of preventing a decrease in transfer efficiency due to a change in transfer material resistance.
The constant current control is performed in the other period, and the voltage value during the constant voltage control is changed according to the voltage value obtained during the constant current control.

[0003]

In the prior art, since the voltage value during constant voltage control is changed according to the voltage value obtained during constant current control, the power supply device for controlling the transfer bias is provided. However, there is a problem in that it is complicated and costly. Further, since the constant voltage control is performed while the image area is located in the transfer area, when the resistance value of the transfer portion changes due to the change of the transfer material type or the environment, the current value flowing into the transfer area fluctuates greatly. However, there is also a problem in that the intended purpose of preventing a decrease in transfer efficiency cannot be achieved.

Therefore, a main object of the present invention is to provide an image forming apparatus capable of stably obtaining effective transfer efficiency with a simple structure.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to an image carrier,
Exposure means for exposing the surface of the image carrier to form an electrostatic latent image, developing means for developing the electrostatic latent image with toner, and a transfer electrode pressed against the surface of the image carrier and a bias connected to the transfer electrode. In an image forming apparatus having a power source and a transfer unit for transferring a toner image formed on the surface of an image carrier to a recording material, a bias power source controls a transfer current applied to a transfer electrode to a predetermined value. Current control means and voltage control means for controlling the transfer voltage applied to the transfer electrode so as not to fall below a predetermined value, and when the transfer voltage decreases in the constant current control by the constant current control means, the voltage control means The image forming apparatus is characterized in that the transfer voltage is controlled.

[0006]

The current control means controls the transfer current to a predetermined value. If the combined resistance value of the transfer part decreases due to changes in the type of transfer material or environment (humidity, etc.), and the transfer voltage decreases accordingly, the voltage control means prevents the transfer voltage from falling below a predetermined value (reference voltage). To control. The reference voltage is set to, for example, the minimum value of the transfer voltage with which the effective transfer efficiency can be obtained when the resistance value of the transfer portion becomes the smallest.

Therefore, the constant current control by the current control means can widely cope with the change in the resistance value of the transfer portion, and when the resistance value is extremely lowered, it can be coped with by the voltage control by the voltage control means.

[0008]

According to the present invention, effective transfer efficiency can be stably obtained with a simple structure. The above-mentioned objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments with reference to the drawings.

[0009]

EXAMPLE An image forming apparatus 10 of this example shown in FIG.
Is applied to a printer, a copier, a facsimile, or the like, and includes a photosensitive drum 12 rotated by a motor (not shown) in the arrow direction. Photoconductor drum 12
Is a photosensitive substrate such as OPC formed on the surface of a conductive substrate made of metal or the like, and around it, the charger 14, the developing device 16, the transfer device 18, and the cleaning device 20 from the upstream side in the rotation direction. Are arranged in this order. Developing device 1
6 includes a toner box 26 having an opening 22 on the side surface thereof and containing a toner 24 therein. A developing roller 28 that supplies the toner 24 to the photosensitive drum 12 is provided in the opening 22 of the toner box 26, and a supply roller 30 that supplies the toner 24 to the developing roller 28 is provided inside the toner box 26. Furthermore, opening 2
2 is provided with a blade 32 that regulates the thickness of the toner 24 attached to the developing roller 28.

The transfer device 18 includes a transfer roller 38 in which a roller 36 made of a conductive material such as conductive urethane rubber is formed around a central shaft 34 made of a highly rigid material such as iron. The pressing means (not shown) presses the photosensitive drum 12 with a predetermined pressure. A bias power supply 40 is connected to the transfer roller 38. The bias power supply 40 includes a power supply 42 and a voltage detection unit 4
The output of the power supply 42 is controlled by the control unit 46 including MPU (microprocessor unit) and the like. When the negative polarity toner is used as the toner 24, the positive bias voltage is output from the power supply 42, and when the positive polarity toner is used, the negative bias voltage is output.

In operation, when the surface of the photoconductor drum 12 uniformly charged by the charger 14 is irradiated with a light image 48 by an exposure device (not shown), the photoconductor drum 12 is exposed.
An electrostatic latent image is formed on the surface of the film according to its photoconductive characteristics. This electrostatic latent image is toner-developed by the developing device 16, and the toner image is attracted to the electric field of the transfer device 18 and transferred to the recording material 50 such as recording paper. The recording material 50 on which the image is transferred is discharged to the outside after the image is fixed by a fixing device (not shown). After the transfer process is completed, the toner 24 remaining on the surface of the photoconductor drum 12 is scraped off by the blade 52 of the cleaning device 20.

In the transfer step, the transfer roller 38 is applied so that effective transfer efficiency (ratio of the amount of toner transferred to the recording material 50 to the amount of toner attached to the surface of the photosensitive drum 12) can be obtained. transfer current I _t and the transfer voltage V _t to is controlled by the control unit 46. In the control unit 46, the constant current control value I ₀ and the reference voltage V ₀ are set in advance. Here, the constant current control value I ₀ is set to a value that can obtain effective transfer efficiency in the normal environment and the low temperature and low humidity environment, and the reference voltage V _{0 is set.}
Is set to the minimum value of the voltage that can obtain effective transfer efficiency in the high temperature and high humidity environment where the resistance value is the smallest. Such constant current control value I ₀ and reference voltage V
₀ can be found from the transfer current-transfer efficiency graph as shown in FIG. 2 and the transfer voltage-transfer efficiency graph as shown in FIG. 3, and in this embodiment, the constant current control value I ₀ is −.
It is set to 4 μA (FIG. 2) and the reference voltage V ₀ is set to 120 V (FIG. 3).

Note that the characteristics shown in the graphs of FIGS. 2 and 3 are characteristics obtained as a result of using a specific photoconductor, transfer roller, toner, recording material, etc., so if these elements are changed. , Constant current control value I ₀ and reference voltage V ₀
Will be changed as a matter of course. Further, the fluctuations in the transfer current-transfer efficiency characteristic and the transfer voltage-transfer efficiency characteristic due to environmental changes are due to fluctuations in the combined resistance value R from the central shaft 34 of the transfer roller 38 to the ground potential of the photosensitive drum 12. Such a variation in the combined resistance value R can also occur due to a change in the material of the recording material 50.

[0014] In the control operation, the transfer roller 38 as the transfer current I _t to be added to (FIG. 1) is the constant current control value I ₀ (FIG. 2), the output of the power supply 42 by the control unit 46 of the bias power supply 40 Is controlled. If the transfer voltage V _t detected by the voltage detection unit 44 becomes equal to or lower than the reference voltage V ₀ (FIG. 3) due to a decrease in the combined resistance value R due to an environmental change or the like, the transfer voltage V _t ≧ the reference voltage V ₀ is satisfied. Transfer roller 38
The transfer current I _t given to is increased. For example, in FIG.
As shown in the transfer current-transfer voltage graph of No. 3, when the combined resistance value R is extremely reduced in a high temperature and high humidity environment, the transfer voltage V is increased in the constant current control with the constant current control value I ₀ (−4 μA).
_{Since t} falls below the reference voltage V ₀ (120 V), it becomes impossible to obtain effective transfer efficiency. In such a case, in order to obtain efficient transcription efficiency, the transfer current I _t is increased to -5 .mu.A, the transfer voltage V _t is increased to the reference voltage V ₀ (120V).

According to this embodiment, the effective transfer is performed by the constant current control in the normal environment and the low temperature and low humidity environment, that is, when the combined resistance value R is large, and by the constant voltage control when the high temperature and high humidity environment, that is, when the combined resistance value R is small. You can get efficiency. Further, according to this embodiment,
Since the control operation of the transfer current I _t and the transfer voltage V _t is simple, the configuration can be simplified and the manufacturing cost can be reduced.

Although the transfer roller is used as the transfer electrode in the above embodiment, a knife-edge transfer electrode or the like may be used instead. Further, in the above embodiment, so as to control by the MPU of the control section 46 of the transfer current I _t and the transfer voltage V _t (microprocessor unit), instead of this, the power supply circuit shown in FIG. 5 You may make it control using 56. The power supply circuit 56 includes a boost rectifier circuit 58. The step-up rectifier circuit 58 includes two transformers 60 and 62. The primary coils of the transformers 60 and 62 are turned on / off by the transistors 64 and 66, and the boosted AC voltage is output to the secondary coil. . This AC voltage is rectified by the rectifier circuits 68 and 70 and output as a DC voltage. A pulse signal for turning on / off the transistors 64 and 66 is applied from the MPU, for example, through the input terminal 74 of the polarity switching circuit 72.
The input terminal 76 of the polarity switching circuit 72 is supplied with a high level polarity signal from the MPU when outputting a positive polarity voltage and a low level polarity signal when outputting a negative polarity voltage.

Here, a case where a high-level polarity signal is applied to the input terminal 76, that is, a case where a positive voltage is output will be described. At this time, the transistors 78 and 80 connected to the input terminal 76 are turned on,
Transistor 66 is forced to the off state. Therefore, the transformer 62 does not operate. On the other hand, transistor 7
When the transistor 8 is turned on, the transistor 82 is turned off and the transistor 64 can be turned on / off.
When a pulse signal is input from the input terminal 74 in that state, the transistor 64 is turned on / off according to the ON / OFF state of the pulse signal.
Is turned on / off, the primary coil of the transformer 60 is interrupted, and an AC voltage is output to the secondary coil. This AC voltage is converted into a DC voltage by the rectifier circuit 68 and output to the output terminal.

Since the output of the rectifier circuit 68 is applied to the current detection circuit 84 through the rectifier circuit 70, at the connection point P of the current detection circuit, the positive DC current output from the rectifier circuit 68, that is, the transfer current I. A voltage corresponding to the size of _t can be obtained. The voltage is amplified to a predetermined voltage V ₁ through the buffer section 88 included in the level shift circuit 86, and then input to one input terminal of the comparison circuit 90. However, the input voltage V ₁ is set to be smaller than the reference voltage V ₂ set by the resistors 92a and 92b.
The difference between the reference voltage V ₂ and the voltage V ₁ input to each input terminal is output from the comparison circuit 90, and this output voltage is input to the voltage control circuit 94. Here, when the voltage V ₁ is high, the output voltage of the comparison circuit 90 is low, and when the voltage V ₁ is low, the output voltage of the comparison circuit 90 is high.

The voltage control circuit 94 turns on the input voltage.
The amplified voltage is amplified by the amplifier 96.
To the voltage constantly generated by the diode 98, etc.
Then, this is output to the connection point Q. Therefore, the rectifier circuit
Transfer current I output from 68 _tChanges depending on
The base voltage of transistor 100 changes, which causes
Electricity applied to the center tap of the primary coil of the lance 60
The pressure changes and the magnitude of the AC voltage of the secondary coil changes.
It For example, the transfer current I_tBecomes smaller, the transformer
The voltage at the center tap of the primary coil of 60 increases,
The AC voltage increases. Therefore, the transfer current I_tIs large
I hear On the contrary, the transfer current I_tBecomes larger,
The voltage applied to the primary coil of the coil 60 becomes small,
The AC voltage of the next coil also decreases, and the transfer current I_tIs small
Become In this way, the output current from the rectifier circuit 68
That is, the transfer current I_tIs controlled to be almost constant.

The combined resistance value R of the transfer portion due to environmental changes, etc.
There decreases, the output current of the transfer current I _t That rectifier circuit 68 is greatly increased, reduced significantly the output voltage from the comparator circuit 90. Even in such a case, the diode 98 or the like in the voltage control circuit 94 operates as a lower limit limiter of the voltage, so that the DC output voltage (transfer voltage V _t ) of the rectifier circuit 68 is the minimum voltage required to obtain effective transfer efficiency. It does not become smaller than the value (reference voltage V ₀ ).

[Brief description of drawings]

FIG. 1 is an illustrative view showing one embodiment of the present invention.

FIG. 2 is a graph showing the relationship between transfer current and transfer efficiency in the example of FIG.

FIG. 3 is a graph showing the relationship between transfer voltage and transfer efficiency in the embodiment of FIG.

FIG. 4 is a graph showing the relationship between transfer current and transfer voltage in the embodiment of FIG.

FIG. 5 is a circuit diagram showing a power supply circuit applied to the embodiment in FIG.

[Explanation of symbols]

 10 ... Image forming device 12 ... Photosensitive drum 14 ... Charging device 16 ... Developing device 18 ... Transfer device 20 ... Cleaning device 24 ... Toner 26 ... Toner box 28 ... Developing roller 38 ... Transfer roller 40 ... Bias power supply 50 ... Recording material 56 … Power supply circuit

Claims (2)

[Claims] 1. An image carrier, an exposing means for exposing the surface of the image carrier to form an electrostatic latent image, a developing means for developing the electrostatic latent image with toner, and a pressure contact with the surface of the image carrier. And a bias power source connected to the transfer electrode, and further comprising a transfer unit that transfers the toner image formed on the surface of the image carrier to a recording material. The power supply includes current control means for controlling the transfer current applied to the transfer electrode to a predetermined value, and voltage control means for controlling the transfer voltage applied to the transfer electrode so as not to fall below a predetermined value. An image forming apparatus, wherein the transfer voltage is controlled by the voltage control means when the transfer voltage is lowered in the constant current control by the control means. 2. The image forming apparatus according to claim 1, wherein the voltage control unit includes a voltage limiter unit that constantly generates a voltage equal to or higher than a predetermined value.