KR20000044523A - Circuit for supplying voltage of apparatus for forming picture adopting method for developing electrophotography - Google Patents

Abstract

PURPOSE: A circuit for supplying voltage of an apparatus for forming picture adopting a method for developing electrophotography is provided to variably adjusting the density of toner by selectively applying a voltage to a developing roller according to temperature and humidity. CONSTITUTION: A circuit for supplying voltage of an apparatus for forming picture adopting a method for developing electrophotography includes a temperature sensor for outputting a temperature sensing signal by sensing temperature, a humidity sensor for outputting a humidity sensing signal by sensing humidity, a high voltage controller(10) for outputting a first selecting signal, a second selecting signal, and a high voltage generating signal at a predetermined period and whenever forming a picture by receiving the output signal from the temperature and humidity sensors, a high voltage generator(20) receiving the high voltage generating signal and generating a negative high voltage for outputting the generated high voltage to a developing roller, a first selecting part outputting a high or a low voltage according to the first selecting signal and connecting the output voltage with the output terminal of the high voltage part, and a second selecting part outputting a high or a low voltage according to the second selecting signal and connecting the output voltage with an anode of a second zener diode.

Description

Voltage supply circuit of an image forming apparatus employing an electrophotographic development method

The present invention relates to an image forming apparatus employing an electrophotographic development method, and more particularly to a circuit for selectively applying a voltage in the image forming apparatus.

In general, electrophotographic development methods are widely used in image forming apparatuses such as copiers, laser beam printers (LPP), LED print head (LPH) printers, plain paper fax machines, and the like. The electrophotographic development process consists of a process of "charge" → "exposure" → "developing" → "transfer" → "settlement".

FIG. 1 shows a schematic engine mechanism configuration of an image forming apparatus employing such an electrophotographic developing method and a bias voltage applied to each part. In FIG. 1, the developing unit 104 includes a developing roller 106, a supply roller 108, a toner regulating blade 110, and an agitator 112. The photosensitive drum 100, the charging roller 102, the developing roller 106, the supply roller 108, the transfer roller 116, etc., a drive system including an engine driving motor to correspond to the electrophotographic process progress (not shown) Rotate in the direction of the arrow shown in FIG. At this time, the paper is fed from a paper cassette (not shown) and conveyed along the paper feed path 118, and finally discharged to the outside of the image forming apparatus.

A typical electrophotographic process will now be described with reference to FIG. 1. First, in the charging process, the photosensitive drum 100 is charged by the charging roller 102 to a charging voltage Vch of negative bias, for example, about −1400 [V], thereby uniforming to a negative potential of about −800 [V]. One charge is formed on the surface. The surface of the photosensitive drum 100 charged as described above undergoes an exposure process as it rotates, and an electrostatic latent image is formed by being exposed to the image to be printed by the light L of an exposure apparatus (not shown). At this time, the original potential of the non-exposed region on the surface of the photosensitive drum 100 is maintained as it is, but the potential of the exposed image region is reduced to about several tens [V]. The exposure apparatus is, for example, a laser scanner unit in the LBP and an original scanner in the copier. As such, the surface of the photosensitive drum 100 having the electrostatic latent image reaches the developing region according to the rotation of the photosensitive drum 100. The developing area means an area where development is performed as a contact portion between the photosensitive drum 100 and the developing roller 106.

The surface of the photosensitive drum 100 that has reached the developing region in this manner is subjected to a developing process, and the electrostatic latent image formed on the photosensitive drum 100 is developed as a visible image by the toner on the developing roller 106. At this time, the toner 114 in the developing unit 104 is supplied to the developing roller 106 by the supply roller 106 and applied onto the developing roller 106. And the agitator 112 installed in the developing unit 104 stirs the toner 114 in the developing unit 104 by rotation so that the used toner and the new toner are mixed well.

In addition, the developing roller 106 has a negative developing potential by, for example, a developing voltage Vb of negative bias of -300 [V], and a negative bias voltage Vm of -500 [V], for example, of the supply roller 108. Is applied. Accordingly, the toner is negatively charged by the bias potential difference at the contact portion between the developing roller 106 and the supply roller 108 and adhered onto the developing roller 106 by ordinary force. The toner attached to the developing roller 106 is uniformly applied by the toner regulating blade 110. The toner applied to the developing roller 106 is developed by moving to the exposure area on the photosensitive drum 100 by an electrostatic force caused by a potential difference between the exposure potential of the photosensitive drum 100 and the developing potential of the developing roller 106. . The development method in which the development is performed while the surface of the developing roller 130 and the surface of the photosensitive drum 100 are in contact with each other is called a contact development method. In particular, a development method using only a nonmagnetic polymerized toner is a one-component nonmagnetic development method. This is called.

In this state, the paper fed from the paper cassette is transferred to the transfer roller 116. After the exposure and development process described above, if the photosensitive drum 100 continues to rotate to reach the transfer position, a transfer process is performed. At this time, a transfer voltage Vt of positive bias of several hundred [KV] to several thousand [KV] is applied to the transfer roller 116. As a result, transfer is performed by transferring the toner attached to the photosensitive drum 100 to the paper by an electromotive force due to the potential difference between the transfer roller 116 and the photosensitive drum 100. The toner transferred to the paper in this manner is fixed to the paper by the pressure and heat of the fixing unit (not shown). Then, the paper on which the fixing is completed is discharged to the outside, and the above processes are continuously performed until the printing on one sheet of paper is completed.

As can be seen from the above description, the transfer voltage of the developing roller is fixed to a constant voltage value through firmware (Firm-Ware). However, there is a case where the output is unstable depending on the state of the developing roller 106, and there is a problem in that the amount of toner is not properly maintained as the temperature and humidity are varied. In particular, when the temperature is low and low, it is more difficult to supply the toner, and even when an increase in the amount of the toner is required, the toner cannot be supplied smoothly. Therefore, it is impossible to supply as much toner as desired through the developing roller 106, so that the image quality of the printed image is lighter than the normal case, or the image quality is poor because it is not normally printed on paper.

As described above, in the image forming apparatus employing the electrophotographic developing method, the voltage of the developing roller is kept constant, resulting in unstable output depending on the resistance of the developing roller or the state of the material. There was a problem that the toner was not smoothly supplied when increasing, i.e., increasing the density.

Accordingly, an object of the present invention is to provide a circuit capable of selectively supplying a voltage applied to a developing roller according to temperature and humidity in an image forming apparatus employing an electrophotographic developing method.

1 is a view showing a schematic engine mechanism configuration of an image forming apparatus employing an electrophotographic development method and a bias voltage applied to each part;

2 is a detailed circuit diagram of a voltage supply circuit for applying a voltage to a developing roller according to a preferred embodiment of the present invention.

The present invention for achieving the above object is a voltage supply circuit to a developing roller of an image forming apparatus employing an electrophotographic developing method, a temperature sensor for sensing a temperature and outputting a temperature sensing signal, and a humidity sensing signal for sensing humidity A high voltage controller configured to receive a humidity sensor for outputting a first signal, a high voltage controller configured to receive output signals of the temperature sensor and the humidity sensor and output a first selection signal, a second selection signal, and a high voltage generation signal every predetermined period and image formation; A high voltage generator for outputting the generated high voltage to the developing roller by receiving a high voltage generation signal output from the high voltage controller; and outputting a high voltage or a low voltage according to a first selection signal output from the high voltage controller; The output voltage is connected to an output terminal of the high voltage unit and an output terminal of the high voltage unit. An anode of a first zener diode having a predetermined breakdown voltage is connected, and an anode of a second zener diode having a breakdown voltage different from that of the first zener diode is connected to a cathode of the first zener diode. A cathode of the zener diode is grounded, and a high voltage or low voltage is output according to a second selection signal output from the high voltage controller, and the output voltage is configured as a second selection unit connected to an anode of the second zener diode. It is characterized by.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

2 is a detailed circuit diagram of a voltage supply circuit for applying a voltage to a developing roller according to a preferred embodiment of the present invention. Hereinafter, the configuration and operation of the circuit will be described in detail with reference to FIG. 2. In addition, the image forming apparatus employing the electrophotographic development method according to the present invention includes a sensor for sensing the temperature and a sensor for sensing the humidity.

The high voltage controller 10 outputs a high voltage generation signal when an image forming signal is received or when it is time to supply a voltage to the developing roller 106. Since this is a well known technique, a detailed description thereof will be omitted. In addition, the high voltage controller 10 receives the temperature and humidity signals according to the present invention and checks whether the internal voltage is below a set value provided therein. The selection signal is output to the selection terminals A and B for selectively outputting the temperature output according to the inspection result. The high voltage unit 20 generates and outputs a voltage of -350 [V] rather than a voltage of -300 [V] which is generally output according to the present invention. Next, the configuration of a circuit for selectively supplying a voltage according to the present invention will be described.

The first selection terminal A of the high voltage controller 10 is grounded through the first resistor R01 and the second resistor R02. The base terminal of the first transistor Q1, which is an NPN transistor, is connected to the contact point of the first resistor R01 and the second resistor R02. In addition, a third resistor R03 connected in series with the first selection terminal A and a fourth resistor R04 are connected to the emitter terminal of the second transistor Q2 configured as a PNP transistor. The emitter terminal and the base terminal of the second transistor Q2 are connected through a fifth resistor R05, and the base terminal of the second transistor Q2 is connected to the first transistor R06 through a sixth resistor R06. It is connected to the collector end of Q1). The emitter end of the first transistor Q1 is grounded. The collector terminal of the second transistor Q2 is grounded through the seventh resistor R07 and the first capacitor C1. The seventh resistor R07 is connected to an output terminal Vb for applying a voltage to the developing roller 106. Three zener diodes ZD1, ZD2, and ZD3 that are reverse biased are connected in series between the output terminal Vb and ground. In the following description, the first resistor R01 through the seventh resistor R07, the first capacitor C1, the first transistor Q1, and the second transistor Q2 are collectively referred to as a 'first selector'. It is called '.

In addition, the second selection terminal B is grounded through an eleventh resistor R11 and a twelfth resistor R12, and the contacts of the eleventh resistor R11 and the twelfth resistor R12 are NPN transistors. It is connected to the base end of the three transistors Q3. In addition, the emitter terminal of the third transistor Q3 is grounded. The second selection terminal B is connected to the emitter terminal of the fourth transistor Q4, which is a PNP transistor, through a thirteenth resistor R13 and a fourteenth resistor R14. The emitter terminal and the base terminal of the fourth transistor Q4 are connected through a fifteenth resistor R15, and the base terminal of the fourth transistor Q4 is connected to the third transistor Q3 through a sixteenth resistor R16. Is connected to the collector stage. The collector terminal of the fourth transistor Q4 is connected to a contact point of the second zener diode ZD2 and the third zener diode ZD3 through a seventeenth resistor R17. Then, the breakdown voltage of each zener diode is examined. The first zener diode ZD1 and the second zener diode ZD2 each have a breakdown voltage of 150 [V], and the third zener diode ZD3 has a breakdown voltage of 50 [V]. Therefore, one zener diode having a breakdown voltage corresponding to the sum of the first zener diode ZD1 and the second zener diode ZD3 may be configured. That is, in this embodiment, since the breakdown voltage is 300 [V], one zener diode having a breakdown voltage of 300 [V] can be used. In the following description, the eleventh resistors R11 to 17th resistors R17, the third transistor Q3, and the fourth transistor Q4 are collectively referred to as a 'second selection unit'.

Next, the operation according to the configuration of FIG. 2 will be described. The high voltage controller 10 outputs a high voltage to the first selection terminal A to output a voltage of -350V when the temperature and humidity are lower than the set reference value, and to the second selection terminal B. Output low voltage. In contrast, when the temperature and humidity are higher than the set reference value, the high voltage controller 10 outputs a low voltage to the first selection terminal A to output a voltage of -300 [V], and the second selection terminal B. Outputs a high voltage. Among the outputs, a case where the temperature and humidity are low, that is, a high voltage is output to the first selection terminal A and a low voltage is output to the second selection terminal B will be described.

First, the operation of the second voltage converter connected to the first selection terminal A will be described. The high voltage output from the first selection terminal A is voltage-divided through the first resistor R01 and the second resistor R02 and applied to the base terminal of the first transistor Q1. A high voltage is applied through the third resistor R03, the fourth resistor R04, the fifth resistor R05, and the sixth resistor R06. At this time, since the first transistor Q1 is turned off, a high voltage is applied to the collector terminal of the first transistor Q1. In addition, since the voltage divided by the first resistor R01 and the second resistor R02 is applied to the base terminal of the first transistor Q1, the first transistor Q1 is turned on. When the first transistor Q1 is turned on, the second transistor Q2 is biased by the fifth resistor R05. Therefore, the second transistor Q2 is turned on. When the second transistor Q2 is turned on, the first to third zener diodes ZD1, ZD2, and ZD3 are positively biased and grounded. That is, the ground point moves to the position of the anode of the first zener diode ZD1. This is actually a virtual ground point because there is a voltage difference of 2.1 [V] but negligible.

In addition, when a high voltage is applied to the first selection terminal A, a low voltage is applied to the second selection terminal B at the same time. Next, when the low voltage is applied to the second selection terminal B, the operation of the second selection unit will be described. When the low voltage is applied to the second selection C, since no current flows through the eleventh resistor R11 and the twelfth resistor R12, the third transistor Q3 maintains the off state. Since the third transistor Q3 maintains the off state, the fourth transistor Q4 maintains the off state. No current flows through the collector terminal of the fourth transistor Q4.

On the contrary, when a low voltage is applied to the first selection terminal A and a high voltage is applied to the second selection terminal B, the opposite phenomenon occurs. That is, the first transistor Q1 and the second transistor Q2 are turned off, and the third transistor Q3 and the fourth transistor Q4 are turned on. Therefore, current flows to the anode of the third zener diode ZD3 through the resistor R17 connected to the collector terminal of the fourth transistor Q4. Therefore, the third zener diode ZD3 is positively biased and turned on. In addition, the first transistor Q1 and the second transistor Q2 of the first selector maintain a turn-off state. Therefore, no current flows through the second transistor Q2.

Therefore, since the current flowing through the fourth transistor flows to the ground point through the third zener diode, the anode of the third zener diode ZD3 becomes the virtual ground point, and the voltage output from the high voltage unit 20 is the second voltage. Only the voltage of -300 [V] applied in the reverse direction to the first zener diode ZD1 and the second zener diode ZD2 is output. In this way, the voltage applied to the developing roller 106 may be selectively caused by temperature and humidity.

As described above, in the image forming apparatus employing the electrophotographic developing method, there is an advantage in that the density of the toner can be variably controlled by allowing voltage to be selectively applied to the developing roller according to temperature and humidity.

Claims (5)

In a voltage supply circuit to a developing roller of an image forming apparatus employing an electrophotographic developing method, A temperature sensor for sensing a temperature and outputting a temperature detection signal; A humidity sensor that detects humidity and outputs a humidity detection signal; A high voltage controller which receives the output signals of the temperature sensor and the humidity sensor and outputs a first selection signal, a second selection signal, and a high voltage generation signal every predetermined period and during image formation; A high voltage generator for receiving a high voltage generation signal output from the high voltage controller and generating a negative high voltage to output the generated high voltage to the developing roller; A first selector configured to output a high voltage or a low voltage according to a first select signal output from the high voltage controller, and the output voltage is connected to an output terminal of the high voltage unit; An anode of a first zener diode having a predetermined breakdown voltage is connected to an output terminal of the high voltage unit, and an anode of a second zener diode having a breakdown voltage different from that of the first zener diode is connected to a cathode of the first zener diode. Connected and the cathode of the second zener diode is grounded, According to the second selection signal output from the high voltage controller, a high voltage or a low voltage is output, and the output voltage comprises an electrophotographic development method comprising a second selection unit connected to an anode of the second zener diode. Voltage supply circuit in the image forming apparatus employed. The method of claim 1, And a high voltage output from the high voltage section is -350V. The method of claim 1, And a breakdown voltage of the first zener diode is 300V, and a breakdown voltage of the second zener diode is 50V. The method of claim 1, wherein the first selection unit, Grounded through a first resistor and a second resistor connected in series to a first selection terminal for outputting the first selection signal of the high voltage controller; The base of the first transistor of the type EN is connected to the contact of the first resistor and the second resistor, the collector terminal of the first transistor is grounded, A third resistor and a fourth resistor at the first selection terminal and connected to an emitter of a second transistor of a PNP type; A fifth resistor is connected between the base and the base of the second transistor, The base end of the second transistor is connected to the collector end of the first transistor through a sixth resistor, And a collector terminal of the second transistor is connected to an output terminal of the high voltage unit through a seventh resistor. The method of claim 1, wherein the second selection unit, Grounded through a first resistor and a second resistor connected in series to a second selection terminal for outputting the second selection signal of the high voltage controller; The base of the first transistor of the type EN is connected to the contact of the first resistor and the second resistor, the collector terminal of the first transistor is grounded, A third resistor and a fourth resistor at the second selection terminal, and are connected to an emitter of a second transistor of a PNP type; A fifth resistor is connected between the base and the base of the second transistor, The base end of the second transistor is connected to the collector end of the first transistor through a sixth resistor, And a collector end of the second transistor is connected to an anode of the second zener diode through a seventh resistor.