JPH07168467A - Electrophotographic recorder and transfer method - Google Patents

Abstract

PURPOSE:To execute an excellent transfer action even when a medium is special and the resistance of a transfer roller is different. CONSTITUTION:This electrophotographic recorder is provided with a photoreceptive drum, the transfer roller 13, a high-voltage power source circuit 48 impressing a transfer voltage on the roller 13 and a CPU controlling the whole of the electrophotographic recorder. By the power source circuit 48, an output voltage VO corresponding to a control signal from the CPU is outputted as the transfer voltage and impressed on the roller 13. At this time, an output current flowing to the roller 13 is outputted to the CPU as an output current detection signal SG2 by the power source circuit 48. On the other hand, the control signal SG1 corresponding to the signal SG2 from the power source circuit 48 is outputted to the power source circuit J18 by the CPU. Thus, even when the output current is changed according to the type of the printing medium or the resistance of the roller 13, the corresponding output voltage VO can be generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic recording device such as an electrophotographic printer or an electronic copying machine, and a transfer method in the same.

[0002]

2. Description of the Related Art An electrophotographic recording apparatus has a photosensitive drum,
The surface of this photosensitive drum is charged, and an electrostatic latent image is formed by selectively irradiating this surface with light by an exposure device, and the electrostatic latent image is developed by supplying toner to this surface by a developing device. Then, by passing a medium such as paper between the photosensitive drum and the developing device, the toner is sucked from the photosensitive drum toward the medium to transfer the toner to the medium, thereby performing printing.

FIG. 2 is a diagram for explaining the transfer process. In the figure, the electrostatic latent image formed on the photosensitive drum 11 is developed by the developing device 12. The developed toner image is transferred to the transfer roller 1 charged by the transfer power supply 14.
3 is transferred to the print medium 15 to form a toner image on the print medium 15. The toner 16 on the print medium 15 is
After that, it is fixed on the print medium 15 by a fixing device (not shown).

[0004]

The transfer efficiency of the toner 16 from the photosensitive drum 11 to the medium 15 depends on the transfer conditions,
For example, since it changes depending on the size of the medium, the thickness of the medium, the humidity of the atmosphere, and the temperature of the atmosphere, it is necessary to change the voltage value applied by the transfer power supply 14 to the transfer roller 13 according to these conditions. For example, an envelope requires a higher transfer voltage because it is narrower and thicker than an A4 cut sheet.

Therefore, it is an object of the present invention to detect a value corresponding to the resistance value of a print medium to be inserted and obtain a desired transfer voltage. Another object of the present invention is to detect the resistance value of the print medium by the high voltage power supply circuit itself used for transfer to obtain a desired transfer voltage. Still another object of the present invention is to obtain a desired transfer voltage by predicting the resistance value of the print medium even when direct resistance measurement cannot be performed because the current supplied to the print medium by the high voltage power supply circuit is not stable. .

[0006]

SUMMARY OF THE INVENTION The present invention is an electrophotographic recording apparatus comprising a photosensitive drum and a transfer roller provided so as to face the photosensitive drum, wherein a transfer voltage is supplied to the transfer roller. Control for inputting information of the high-voltage power supply circuit and information of the electrophotographic recording apparatus including at least one of output voltage value and output current value information of the high-voltage power supply circuit and controlling the output voltage value of the high-voltage power supply circuit A circuit, the control circuit calculates a value corresponding to a voltage value applied to the transfer roller based on a value that changes corresponding to the resistance value of the transfer roller and the resistance value of the print medium,
A control signal for controlling the voltage value supplied by the high-voltage power supply circuit is output based on the calculated value.

Another invention of the present application is a transfer method in an electrophotographic recording apparatus provided with a photosensitive drum and a transfer roller provided so as to face the photosensitive drum. Measuring the resistance value of the transfer roller; inserting a medium between the photosensitive drum and the transfer roller; applying a constant voltage V0 to the transfer roller; Between the current value B1 at the first time immediately after the medium is inserted between and the value A1 of the current that has changed during a minute time in the vicinity of the first time, and after the first time, the current Of the current value B2 at the second time before the change of the above is subsided and the value A2 of the current changed during the minute time in the vicinity of the second time, and the calculation formula Rm = {(B2 / B1) -1 } / {( 2 / A1)-(B2 / V0)} to calculate a resistance value Rm of the medium, and a voltage value corresponding to a combined resistance of the resistance value of the transfer roller and the resistance value of the medium is applied to the transfer roller. It is characterized by comprising the steps of:

[0008]

According to the present invention, the control circuit of the high-voltage power supply circuit is
The transfer voltage output from the high-voltage power supply circuit is controlled based on the value that changes according to the resistance value of the transfer roller and the value that changes according to the resistance value of the print medium. Regardless, the transfer can be performed with the optimum transfer voltage. Furthermore, even if the resistance value of the transfer roller changes due to aging, the transfer voltage can be applied according to the resistance value of the transfer roller, so that good transfer can be performed for a long period of time.

According to another invention of the present application, the resistance value of the transfer roller is measured before the printing medium is inserted, and the current value characteristic of the printing medium is detected immediately after the printing medium is inserted, and a predetermined calculation formula is used. Since the resistance value of the print medium is calculated by, the resistance value of the print medium can be calculated in an extremely short time, and the correct resistance value can be calculated even when the top margin of the print medium is small or when printing is performed at high speed. Obtainable. As a result, the transfer voltage can be applied according to the print medium.

[0010]

EXAMPLE An electrophotographic recording apparatus comprises a photosensitive drum 11, a developing device 12, a transfer roller 13 and a transfer power source 14 shown in FIG.
A control circuit as shown in FIG. 1 is provided in order to perform control for operating the above.

FIG. 1 is a block diagram of an electrophotographic recording apparatus for explaining the first embodiment of the present invention. The operation will be described by taking an electrophotographic printer as an example of the electrophotographic recording apparatus.

The control circuit for controlling the entire electrophotographic printer is composed of a single CPU 21, a control logic 22, an A / D converter 23 (A / D-C), and a pulse width modulation signal generator 24 (PWM-G). This is a CPU-LSI 28 which is a semiconductor integrated into one chip.

A control program for operating the CPU-LSI 28 is stored in the ROM 29, and printing is performed according to this control procedure.

The control logic 22 inputs the print data received from the host device such as a personal computer through the input interface 31. Furthermore, the detection information of the various medium sensors 37 and the operation panel 5
Enter the set value of 8. This control logic 22
Outputs dot data to be printed to the LED head 35 to perform exposure, and also outputs a control signal to the motor driver 42 to output the hopping motor 40 and the drum motor 41.
To control. Further, it outputs a control signal to the heat roller controller 53 to control the temperature of the fixing device 51. Further, a control signal is also output to the charging / developing power source 44 to control the voltage value for charging or developing.

The A / D converter 23 is a high-voltage power supply circuit 4
8 inputs a detection signal SG2 composed of a voltage value corresponding to the current value output to the transfer roller 13, and a voltage value corresponding to the temperature detected by the temperature measuring thermistor 52 provided in the fixing device 51 together with the heat roller controller 53. .

The pulse width modulation signal generator 24 outputs a pulse width modulation signal SG1 corresponding to the voltage value output from the high voltage power supply circuit 48.

Next, the operation of the CPU-LSI 28 will be described. The CPU-LSI 28 inputs the print information via the input interface and temporarily stores it in the RAM 32. The print information stored in the RAM 32 is stored in the ROM 29.
Converted to dot data based on the information stored in
Store again in another area of AM32. This dot data is transferred to the LED head 35 at a predetermined timing to perform exposure.

Further, the CPU-LSI 28 supplies printing paper into the printer in accordance with the conversion of this printing data. The CPU-LSI 28 inputs a detection signal output from a medium sensor 37 provided at each position for detecting the presence / absence of a medium, its width, suction from a paper cassette, and discharge from a discharge port of an electrophotographic printer, and is not shown. When a sheet is loaded in the sheet cassette, the hopping motor 40 and the drum motor 41 control the motor driver 42 to convey the medium in the printing direction.

The CPU-LSI 28 controls the high voltage power supply circuit 48 by outputting the pulse width modulation signal SG1 and applies a transfer voltage to the transfer roller 13. CPU-L
By performing such control, the SI 28 sequentially performs the exposure, development, transfer and fixing steps of the electrophotographic process, and performs printing.

The power supply circuit 55 is a commercial power supply.
High voltage power supply circuit 4
8 is a circuit for applying a power supply voltage to other blocks.

FIG. 3 is a circuit diagram of the high-voltage power supply circuit 48 in the first embodiment of the present invention. The high voltage power supply circuit 48 is
It has a transformer T1 composed of a primary coil L1 to which a + 5V power source E is input and a secondary coil L2 having a larger number of turns than this, and this transformer T1 produces a voltage larger than the primary voltage. Generate on the secondary side.

On the ground side of the primary coil L1, a diode D1 connected in the opposite direction and a resistor R on the base terminal are provided.
A transistor Tr1 for applying the pulse width modulation signal SG1 is connected via b. Further, a resonance capacitor C1 having an equivalent capacitance as seen from the distributed capacitance of the primary coil L1 is provided in parallel with the primary coil L1 to form a resonance circuit.

A rectifying diode D2 and a smoothing capacitor C4 are provided on the output side of the secondary coil L2, and a noise filter capacitor C3 is provided in series with the smoothing capacitor C4.

A current detecting resistor Rs is connected between the power source E and the ground side end of the smoothing capacitor C4, and a bypass capacitor C2 for the high voltage power source circuit 48 is connected between the power source E and the ground. To be done.

The operation of this high-voltage power supply circuit will be described with reference to FIGS. FIG. 4 is a time chart of the high voltage power supply circuit 48. The pulse width modulation signal SG1 as shown in FIG. 4 is applied to the base terminal of the transistor Tr1 shown in FIG. 3 via the resistor Rb. The resistor Rb is provided to limit the base current of the transistor Tr1. The pulse width modulation signal SG1 has a predetermined cycle T, and is controlled to lengthen the on-time t in this cycle T when it is desired to output a high voltage and to shorten the on-time t when it is desired to output a low voltage. That is, the level of the output voltage is controlled by the ratio of the ON time and the OFF time. Then, the current from the power source E intermittently flows through the primary coil L1 of the transformer T1 by turning on / off the transistor Tr1.

The transformer T1 multiplies the voltage of the primary coil L1 by the winding number ratio and outputs it to the secondary coil L2. The current flowing through the secondary coil L2 is rectified by the rectifying diode D2. The output voltage V0 is output after being smoothed by the smoothing capacitor C4, and this output voltage V0 is applied to the transfer roller 13.

At this time, the current flowing through the transfer roller 13, that is, the output current, passes through the current detection resistor Rs. Therefore,
Assuming that the resistance value of the current detection resistor Rs is rs, the voltage Vsg2 of the output current detection signal SG2 is Vsg2 = 5-I0.rs, as shown in FIG.

FIG. 5 is a diagram showing the relationship between the current I0 output by the high-voltage power supply circuit 48 and the detected current Vsg2. As shown in the figure, for example, if rs = 500 [kΩ] I0 = 10 [μA], then Vsg2 = 0 [V], and if I0 = 0 [μA], then Vsg2 = 5 [V]. . Therefore, the CPU-LSI 28 can detect the voltage Vsg2 by the A / D converter 23 and monitor the output voltage I0.

As shown in FIG. 4, the pulse width modulation signal SG1
Thus, when the transistor Tr1 is turned on, a current flows through the primary coil L1, and when the inductance of the primary coil L1 is L1, the current value increases with time, and at time t, Ic = Et / L1.

After that, when the transistor Tr1 is turned off, the capacitance C of the resonance capacitor C1 which is an equivalent capacitance viewed from the distribution capacitance of the primary coil L1 of the transformer T1.
Resonance occurs between 1 and the inductance L1 of the primary coil L1. At this time, the peak value V of the collector voltage Vc
cpeak is the peak value Icpeak of the collector current Ic, √
(L1 / C1) times, Vcpeak = Icpeak√ (L1 / C1) = Et / √ (L1C1) (1), and the frequency fv of about 1 / 2π√ (L1C1) Resonance is generated. In this case, the negative side of the vibration waveform is clamped by the diode D1 shown in FIG.
The collector voltage Vc is rapidly attenuated.

It can be seen from the equation (1) that the collector voltage Vcpeak increases in proportion to the time during which the collector current Ic flows.

Here, the period T of the pulse width modulation signal SG1
Is 50 [μs], the frequency f is 20 [kHz], the maximum value of the time t is 25 [μs], the primary side inductance L1 of the transformer T1 is 500 [μH], and the primary side coil L1 of the transformer T1 is Equivalent capacitance C1 seen from distributed capacitance is 2
000 [pF], power supply voltage E 5 [V], transformer T1
When the winding ratio is 1:30, the resonance cycle Tv = 6.3 [μs], the peak value Icpeak of the collector current Ic = 250 [mA] (average maximum value 63 [mA]), and the peak of the collector voltage Vc. The value Vcpeak = 125 [V] and the maximum value of the output voltage V0 = 3.75 [kV] (Vcpeak × 30).

At this time, the current I0 flowing through the transfer roller 13
Since the print medium 15 is inserted between the transfer roller 13 and the photosensitive drum 11 during printing, the output current is very small and is several [μA] to 10 [μA]. mW]. In contrast,
The input energy is 0.25 [A] × (1/2) × (1/2) × 5 [V] = 312 [mW], which is sufficiently large. Therefore, even if the output current I fluctuates, sufficient power is supplied from the primary coil L1, so that the voltage fluctuation of the output voltage V0 becomes extremely small.

By constructing the high-voltage power supply circuit 48 in this way, it is not necessary to constantly detect the output voltage for feedback control to a constant voltage, and therefore it is not necessary to separately provide a circuit for feedback control. Also, instead of separately providing a control circuit for feedback, CPU-L
There is no need to burden SI28. Therefore, the high-voltage power supply circuit 48 that outputs a stable high-voltage power supply can be realized by a simple circuit.

As described above, the output voltage V0 is the inductance L1 and the equivalent capacitance C1 used as the resonance capacitor.
, Power supply voltage E and time t. As a result, the relationship between the pulse width modulation signal SG1 and the output voltage V0 of the high voltage power supply circuit 48 becomes as shown in FIG. Figure 6
FIG. 6 is a characteristic diagram of a pulse width modulation signal and an output voltage of the high voltage power supply circuit 48 in the first embodiment of the present invention. As shown, the output voltage V0 has a proportional relationship with the pulse width modulation signal SG1.

An example in which the equivalent capacitance of the primary coil L1 is used as the resonance capacitor C1 has been described, but if this alone does not provide a sufficient capacitance value, it is necessary to separately provide a capacitor in parallel.

Next, the operation of the transfer roller 13 in the first embodiment of the present invention will be described. FIG. 7 shows a time chart of the output voltage and the output current in the first embodiment of the present invention. In FIG. 7, V0 on the vertical axis indicates the output voltage value of the high-voltage power supply circuit, I0 indicates the output current value, and the horizontal axis indicates the time.

First, when the printing operation is started and the photosensitive drum 11 shown in FIG. 2 starts to rotate, the pulse width modulation signal S generated by the pulse width modulation signal generator 24 shown in FIG.
G1 is generated, and the high voltage power supply circuit 48 outputs the output voltage V0.
The voltage V1 corresponding to the pulse width signal SG1 is output only during the time ta. At this time, the current value of the output current I0 becomes I1, and this current value I1 is the output current detection signal SG2.
Is input to the CPU-LSI 28 and monitored. Thereby, the resistance value of the transfer roller 13 alone can be calculated.

Next, when the print medium 15 is fed and inserted between the photosensitive drum 11 and the transfer roller 13, the high-voltage power supply circuit 48 outputs the output voltage V0 to the voltage value V for the time tb.
Change to 2. At this time, the value of the output current I0 becomes I2, and this current value I2 is similarly input to the CPU-LSI 28 as the output current detection signal SG2 and monitored. This makes it possible to calculate a combined resistance value of the transfer roller 13 and the print medium 15.

The CPU-LSI 28 has the print medium 15
The resistance value of the print medium 15 can be calculated from the resistance value in the absence state and the resistance value in the presence state of the print medium 15.
The voltage VTR during printing can be calculated according to this resistance value. Specifically, since I1 and I2 are detected for the predetermined voltage values V1 and V2, respectively, the voltage VTR at the time of printing can be obtained from the table shown in FIG. 8 without calculating the resistance value. .

FIG. 8 is a diagram showing a transfer voltage calculation table in the first embodiment of the present invention. This calculation table can be stored in the ROM 29 shown in FIG. 1, and the voltage VTR at the time of printing is read based on the detected current values I1 and I2. Then, the pulse width modulation signal generator 24 generates the pulse width modulation signal SG1 corresponding to the voltage value VTR, and outputs the output voltage V0 in response to the pulse width modulation signal SG1 of the high voltage power supply circuit 48 box during the time tc. Keep on VTR. At this time, the current value of the output current I0 becomes ITR.

In this embodiment, the voltage value V1 is 50
0 [V] and the voltage value V2 are 1 [kV], and the calculation table of FIG. 8 shows the voltage value VTR calculated under this condition.

The calculation table of FIG. 8 is set so that the voltage value VTR increases as the current values I1 and I2 of the output current I0 decrease. This means that the resistance of the transfer roller 13 is large when the current value I1 when the output voltage V0 is the voltage value V1 is small when the photosensitive drum 11 and the transfer roller 13 are in direct contact with each other. In this case, it is necessary to set the voltage value VTR large. Further, when the print medium 15 is inserted between the photosensitive drum 11 and the transfer roller 13 and the current value I2 when the output voltage V0 is the voltage value V2 is small,
This means that the resistance of the print medium 15 is large. In this case, it is necessary to set the voltage value VTR large.

Thereafter, the CPU-LSI 28 controls the high-voltage power supply circuit 48 to apply the voltage value VTR to the transfer roller 13 as a transfer voltage to start printing, and when the printing is completed, the output voltage V0 of the high-voltage power supply circuit 48. Voltage value of 0
Return to V.

The voltage value VTR set in the calculation table can be changed by operating the operation panel 58. Further, the calculation table can be switched and changed according to other printing conditions such as the type and size of the print medium 15. Further, the voltage value VTR can be calculated by a predetermined formula corresponding to the result of this table without reading it by the calculation table.

FIG. 9 is a characteristic diagram of the electrophotographic printer according to the first embodiment of the present invention. In FIG. 9, a solid line curve indicates a range in which transfer is favorably performed when thin paper, thick paper, and an envelope are used as each medium in a normal transfer roller, and a broken line curve is about 1 to 2 digits. The following shows a range in which transfer is favorably performed when thin paper and thick paper are used as each medium when the transfer roller has a large resistance value. Further, M in parentheses indicates that the atmosphere around the electrophotographic printer is in a normal temperature and normal humidity state, and L indicates that it is low temperature and low humidity.

In this way, good transfer can be performed by calculating the impedance of the medium and selecting the transfer voltage suitable for it.

The above control is summarized as follows.
FIG. 10 is a flowchart illustrating the above series of controls.

Step S1: The rotation of the photosensitive drum 11 is started. Step S2: The high voltage power supply circuit 48 (FIG. 1) outputs the output voltage V
Let 0 be the voltage value V1 for the time ta (FIG. 7). Step S3: The print medium 15 is fed and inserted between the photosensitive drum 11 and the transfer roller 13. Step S4: The high-voltage power supply circuit 48 sets the output voltage V0 to the voltage value V2 for the time tb. Step S5: The CPU-LSI 28 has current values I1 and I1.
The voltage value VTR corresponding to 2 is read from the calculation table shown in FIG. Step S6: The high-voltage power supply circuit 48 sets the output voltage V0 to the voltage value VTR for the time tc. Step S7: Start printing. Step S8: It is judged whether or not printing is completed. When printing is completed, the process proceeds to step S9. Step S9: The high voltage power supply circuit 48 returns the voltage value of the output voltage V0 to 0V.

As described above, according to the present embodiment, the high-voltage power supply circuit 48 outputs the current value at the time of outputting the predetermined voltage as the detection signal SG2 to the A / D converter 23, and the impedance of the transfer roller 13 and the printing are performed. Since the impedance of the medium 15 can be easily calculated and the transfer voltage can be set according to the impedance, good transfer can be performed by the simple high-voltage power supply circuit 48.

Next, a second embodiment of the present invention will be described.
FIG. 11 is a circuit diagram of a high voltage power supply circuit for explaining the second embodiment of the present invention. High-voltage power supply circuit 48 of this embodiment
In addition to the configuration of the high-voltage power supply circuit 48 of the first embodiment, -2 includes a sensor coil L3 for detecting the output voltage, and has a rectifying diode D3 and a smoothing capacitor C5 at its output terminal. The output voltage detection signal SG3 is output. Since the voltage value of the output voltage detection signal SG3 is proportional to the output voltage V0, the CPU-LSI 28 can detect the voltage value of the output voltage detection signal SG3 by the A / D converter 23 and monitor the output voltage V0.

In this way, it is possible to monitor the relationship between the pulse width modulation signal SG1 and the output voltage V0 due to variations in the characteristics of the components forming the high voltage power supply circuit 48-2. Since the pulse width modulation signal SG1 and the output voltage V0 have a linear relationship, the relationship between the pulse width modulation signal SG1 and the output voltage V0 is monitored at one point and calibration is performed to improve the accuracy of the output voltage V0. Can be made.

As described above, the transfer voltage corresponding to the fed medium is applied to the transfer roller 13 by detecting the resistance value of the medium fed into the electrophotographic recording apparatus or the value corresponding thereto. However, the accuracy of transfer can be improved. However, when the number of printed sheets per unit time is increased, it becomes difficult to measure the resistance value of the medium or the value corresponding thereto.

In order to solve this, the resistance of the medium is calculated by calculation from the change in the current before the medium is fed and the current immediately after the medium is fed. Therefore, the resistance value of the medium is measured as in the third embodiment below.

First, the problem in measuring the resistance value of the print medium 15 at high speed will be described. FIG. 12 is a circuit diagram showing an equivalent circuit of the transfer device. In FIG. 12, Rd is the equivalent resistance of the photosensitive drum 11, Cm is the equivalent capacity of the medium, and R
m is the equivalent resistance of the medium, and Rr is the equivalent resistance of the transfer roller 13.

When the print medium 15 enters between the photosensitive drum 11 and the transfer roller 13, the equivalent resistance Rm of the medium and the equivalent capacity of the medium are placed between the equivalent resistance Rd of the photosensitive drum 11 and the equivalent resistance Rr of the transfer roller 13. Cm is inserted, switch S
This corresponds to the state where Wm is turned off. When the switch SWm is turned off, the transfer voltage Vtr increases by the equivalent resistance Rm of the medium. Therefore, if Vtr is maintained during printing, the transfer voltage corrected for the resistance Rm is applied.

However, the print medium 15 is the photosensitive drum 11
At the moment of being inserted between the transfer roller 13 and the transfer roller 13, even if an attempt is made to detect a change in the voltage Vtr by supplying a predetermined current value to the transfer roller 13, the change in the voltage Vtr is delayed due to the equivalent capacitance Cm of the print medium 15. This state is shown in FIG.

FIG. 13 is a waveform diagram showing changes in the voltage Vtr when a predetermined current is supplied to the transfer roller 13.
As shown in the figure, it can be seen that it takes time for the voltage to stabilize after the print medium 15 is inserted. Therefore, in the electrophotographic recording apparatus having a high printing speed, since the time from the insertion of the medium to the start of printing is short, the electrophotographic recording apparatus reaches the printing area before the voltage Vtr becomes stable, and this voltage difference causes an error. In order to avoid this, the resistance of the print medium 15 is calculated as follows.

In the equivalent circuit of FIG. 12, when the resistance Rd of the photosensitive drum 11 is negligibly smaller than the other resistances, the current characteristics shown in the graph of FIG. 14 are obtained.

FIG. 14 is a graph showing changes in the current flowing through the transfer roller 13 when the medium is inserted. This current value is
It is a current value when the voltage V0 is applied to the transfer roller 13 and can be detected by the detection signal SG2.
The change in the current i from the detection point (1) corresponding to the time when the print medium is inserted (t = 0) is i = V0 {Rr + Rm · exp (-t / τ)} / {(R
r + Rm) · Rr}, and the current change di / dt is di / dt = −V0 · Rm · exp (−t / τ) /
It becomes {(Rr + Rm) · Rr · τ}.

The current change at the detection point (1) is A1, the current value is B1, and the current at the detection point (2) (after an arbitrary time before the current becomes stable and t = t1) Assuming that the change is A2 and the current value is B2, A1 = -V0.Rm / {(Rr + Rm) .Rr..tau.} (A) B1 = V0 / Rr ... (b) A2 = -V0.Rm.exp (-T1 / .tau.) / {(Rr + Rm) .Rr..tau.} (C) B2 = V0. {Rr + Rm.exp (t1 / .tau.)} / (Rr + Rm) .Rr (d)

From (a), (c) shows that A2 = A1.exp
Since (−t1 / τ), exp (−t1 / τ) = A2 / A1 (c ′).

From (c '), since (d) is B2 = V0. {Rr + (A2 / A1) .Rm} / {(Rr + Rm) .Rr} (d'), Rm = {(B2 / V0) .Rr-1} / {(A2 / A1)-(B2 / V0)} (d '') Substituting (b) into this, Rm = {(B2 / B1) -1 } / {(A2 / A1)-(B2 / V0)}.

As a result, the current value before the print medium 15 is inserted, the current value at an arbitrary time t1 before the current stabilizes, and the resistance of the medium before the current value stabilizes due to the applied voltage V0. Rm can be calculated.

The specific control will be described below. First, the current is measured before the print medium 15 is inserted (B1), and the current value is measured twice with a slight shift immediately after the medium is inserted. The difference between the two current values and the time are measured. The rate of change in current (A1) is calculated from

Next, the current value is measured twice at an arbitrary time before the print medium 15 reaches the printing position, and the current change rate (A2) is obtained from the difference between the two current values and the time.
The average current value at this time or one of the current values is the current value (B2) at this time. Current value B1 and B
The average value is preferable when calculating 2, but the change in the current value during this time is smaller than the current value, so either value may be used.

Next, before the print position is reached, the resistance value of the print medium 15 is obtained by the above formula, and the resistance value of the transfer roller 13 obtained from the current value before the medium enters and the calculated resistance of the print medium 15 are obtained. Then, the optimum transfer voltage corresponding to the combined resistance value is obtained from the table of the first embodiment by a table or calculation formula in which the search key is changed so as to calculate the voltage value from the resistance value. Then, the high-voltage power supply circuit 48 is controlled to have this voltage.

In this way, the resistance of the medium can be calculated by observing the current and the change in the current before printing. Therefore, even in a high-speed electrophotographic recording apparatus in which the resistance of the medium cannot be directly measured, A proper transfer voltage can be obtained.

In the high voltage power supply circuits of the first and second embodiments, the PWM signal is used as the control signal. However, the output voltage may be directly feedback-controlled by a digital value.

FIG. 15 is a circuit diagram of a high voltage power supply circuit according to the fourth embodiment of the present invention. In FIG. 15, the high voltage power supply circuit includes a sensor coil L for monitoring the output voltage.
3 and divides this voltage by resistors R70 and R71 and connects it to one input terminal of the comparator 68.
A desired reference voltage output from the D / A converter 64 of the one-chip microcomputer 60 is connected to the other terminal of the comparator 68. The comparator 68 outputs a logic "H" when the detected voltage is higher than the reference voltage, and outputs a logic "L" when the detected voltage is lower than the reference voltage. This output is connected to the input of the 3-input AND circuit 69. The signal line output from the I / O 66 of the one-chip microcomputer 60 and the output of the oscillation circuit 67 are connected to the other input of the AND circuit 69. When the one-chip microcomputer 60 controls to turn on the high voltage output, a logical "H" is output from the I / O 66, and this I / O
When 66 becomes logic “H” and the logic of the comparator 68 is “H”, the clock of the oscillation circuit 67 is output as the output of the AND circuit 69. Oscillation circuit 6
While the clock 7 is applied to the transistor Tr1, power is supplied to the transformer T1 and a high voltage is output as V0.

The output current is the resistance R73, R74,
The one-chip microcomputer 6 is converted into a voltage by the current-voltage conversion circuit composed of the R75 and the operational amplifier 81.
0 is input to the A / D converter 65 and monitored.

The one-chip microcomputer 60 is a CP
It has a U 61, a RAM 62, and a ROM 63, and is connected to the CPU-LSI 28 via an I / O 66. By using the high-voltage power supply circuit as in the present embodiment, good printing can be performed without lowering the output voltage even in an electrophotographic recording apparatus that consumes a large amount of current because high-speed printing is performed.

[0073]

As described above, according to the present invention, the control circuit of the high voltage power supply circuit changes the value corresponding to the resistance value of the transfer roller and the value corresponding to the resistance value of the print medium. Since the transfer voltage output from the high-voltage power supply circuit is controlled based on the above, it is possible to perform transfer at an optimum transfer voltage regardless of the size and characteristics of the printing paper. Furthermore, even if the resistance value of the transfer roller changes due to aging, the transfer voltage can be applied according to the resistance value of the transfer roller, so that good transfer can be performed for a long period of time.

According to another invention of the present application, the resistance value of the transfer roller is measured before the printing medium is inserted, and the current value characteristic of the printing medium is detected immediately after the printing medium is inserted, and the predetermined calculation formula is used. Since the resistance value of the print medium is calculated by, the resistance value of the print medium can be calculated in an extremely short time, and the correct resistance value can be calculated even when the top margin of the print medium is small or when printing is performed at high speed. Obtainable. As a result, the transfer voltage can be applied according to the print medium.

[Brief description of drawings]

FIG. 1 is a block diagram of an electrophotographic recording apparatus for explaining a first embodiment of the present invention.

FIG. 2 is a schematic view of an electrophotographic recording apparatus for explaining a transfer process.

FIG. 3 is a circuit diagram of a high-voltage power supply circuit according to the first embodiment of the present invention.

FIG. 4 is a time chart of a high voltage power supply circuit.

FIG. 5 is a graph showing the relationship between the current output by the high-voltage power supply circuit and the detected current.

FIG. 6 is a characteristic diagram of a pulse width modulation signal and an output voltage of a high voltage power supply circuit according to the first embodiment of the present invention.

FIG. 7 is a time chart of an output voltage and an output current according to the first embodiment of the present invention.

FIG. 8 is a diagram showing a transfer voltage calculation table according to the first embodiment of the present invention.

FIG. 9 is a characteristic diagram of the electrophotographic printer according to the first embodiment of the present invention.

FIG. 10 is a flow chart for explaining control in the first embodiment of the present invention.

FIG. 11 is a circuit diagram of a high voltage power supply circuit according to a second embodiment of the present invention.

FIG. 12 is a circuit diagram showing an equivalent circuit of a transfer device.

FIG. 13 is a diagram showing a change in voltage Vtr when a predetermined current is supplied to the transfer roller.

FIG. 14 is a graph showing a change in current flowing through a transfer roller when a medium is inserted.

FIG. 15 is a circuit diagram of a high voltage power supply circuit according to a fourth embodiment of the present invention.

[Explanation of symbols]

 11 Photosensitive Drum 12 Developing Device 13 Transfer Roller 14 Transfer Power Supply 15 Printing Medium 16 Toner 21 CPU 22 Control Logic 23 A / D Converter 24 Pulse Width Modulation Signal Generator 28 CPU-LSI 48 High Voltage Power Supply Circuit 51 Fixer 52 Temperature Measuring Thermistor 53 Heat roller controller 55 Power supply circuit 56 AC input

Claims (9)

[Claims] 1. An electrophotographic recording apparatus comprising a photosensitive drum and a transfer roller provided opposite to the photosensitive drum, wherein a high voltage power supply circuit for supplying a transfer voltage to the transfer roller, and a high voltage power supply circuit And a control circuit for controlling the output voltage value of the high-voltage power supply circuit while inputting the information of the electrophotographic recording apparatus including the information of the output current value, wherein the control circuit prints the resistance value of the transfer roller and the printing value. Control for calculating a value corresponding to the voltage value applied to the transfer roller based on a value that changes corresponding to the resistance value of the medium, and controlling the voltage value supplied by the high-voltage power supply circuit based on the calculated value An electrophotographic recording device characterized by outputting a signal. 2. The electrophotographic recording apparatus according to claim 1, wherein the control circuit further receives an output of the medium sensor, calculates a width of the medium according to the output, and a resistance value of the transfer roller and a print medium. And a value corresponding to the voltage value applied to the transfer roller based on the width of the medium, and an electrophotographic recording apparatus. 3. The electrophotographic recording apparatus according to claim 1, wherein the control circuit further receives an operation panel setting, and a value that changes corresponding to a resistance value of the transfer roller and a resistance value of a print medium, An electrophotographic recording apparatus, wherein a value corresponding to a voltage value applied to the transfer roller is calculated based on the setting of the operation panel. 4. The electrophotographic recording apparatus according to claim 1, wherein the electrophotographic recording apparatus includes a memory device that stores information for operating the control circuit, and the control circuit is configured to operate from the memory device. An electrophotographic recording apparatus, wherein a calculation formula for calculating the value is read and the value is calculated based on the calculation formula. 5. The electrophotographic recording apparatus according to claim 1, wherein the electrophotographic recording apparatus includes a memory device that stores information for operating the control circuit, and the control circuit calculates the value. An electrophotographic recording apparatus, wherein the value is calculated with reference to a table stored in the memory device for performing the operation. 6. The electrophotographic recording apparatus according to claim 1, wherein the control circuit has a pulse width modulation signal generator that outputs a control signal to the high-voltage power supply circuit, and the pulse width modulation signal generator outputs the control signal based on the pulse width of the control signal. An electrophotographic recording device characterized by controlling the voltage of a high-voltage power supply circuit. 7. The electrophotographic recording apparatus according to claim 6, wherein the high-voltage power supply circuit includes a first coil having a first number of turns and a second number of turns having a greater number of turns than the first number of turns. Second
A transformer having a coil, a switch element for inputting an output signal of the pulse width modulation signal generator and controlling a current supplied to the first coil, a smoothing circuit connected to the second coil, An electrophotographic recording apparatus having a first detection terminal that outputs a voltage value corresponding to a current value supplied from a high-voltage power supply circuit. 8. The electrophotographic recording apparatus according to claim 7, wherein the high-voltage power supply circuit further includes a second detection terminal that outputs a voltage value corresponding to a voltage value supplied from the high-voltage power supply circuit. Recording device. 9. A transfer method in an electrophotographic recording apparatus comprising a photosensitive drum and a transfer roller provided opposite to the photosensitive drum, wherein a resistance value of the transfer roller is measured before sucking a print medium. A step of inserting a medium between the photosensitive drum and the transfer roller, a step of applying a constant voltage V0 to the transfer roller, and a step immediately after inserting the medium between the photosensitive drum and the transfer roller. A step of detecting a current value B1 at a first time and a current value A1 changed during a minute time in the vicinity of the first time; and a second step after the first time and before a change in the current is stopped. A step of detecting a current value B2 at time and a current value A2 changed during a minute time in the vicinity of the second time, and a calculation formula Rm = {(B2 / B1) -1} / {(A2 / A1)- (B2 / 0)} is used to calculate a resistance value Rm of the medium, and a voltage value corresponding to a combined resistance of the resistance value of the transfer roller and the resistance value of the medium is applied to the transfer roller. Method.