JP2001296720A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-quality color image where color slurring in a subscanning direction is moderated by restraining the torque fluctuation of a motor for driving a transfer belt or the like and restraining the fluctuation of the rotating speed of the belt without causing a cost rise at the time of turning on/off transfer bias. SOLUTION: In a transfer bias circuit, the transfer voltage is controlled by varying the on-duty of a PWM signal transmitted from the CPU of an image forming control part by a high voltage power source circuit constituted of a switching regulator circuit. At the time of turning on the transfer bias, control not only to transmit the PWM signal in duty width equivalent to target transfer voltage but also to widen the on-duty at three steps from D21 to D22 and D23 (D21<D22<D23) is performed. At the time of outputting the target voltage V23, the PWM signals at D21 and D22 are respedively outputted from the specified time T21 to the specified time T22 before the PWM signal is outputted at D23 equivalent to the voltage V23. At the time of turning off the transfer bias, control to narrow the on-duty is performed on the contrary.

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 having a belt member such as a transfer belt and a contact type transfer means such as a transfer blade, and more particularly to a method for reducing a speed fluctuation of the belt member.

[0002]

2. Description of the Related Art FIG. 12 shows a tandem type laser beam printer as a conventional image forming apparatus. The printer forms an image forming unit for each color of a yellow image (Y), a magenta image (M), a cyan image (C), and a black image (K) along a transfer belt 20 wrapped around a plurality of rollers. Provided.

Each image forming unit includes a photosensitive drum 18
(18a, 18b, 18c, 18d), the primary charger 16 (16a, 16b, 16) for uniformly charging the photosensitive drum
c, 16d), and a laser beam 13 (13a, 13a,
13b, 13c, 13d), a scanner unit 11 (11a, 11b, 11c, 11d) for forming a latent image,
Developing device 14 for developing the latent image and visualizing it as a toner image
(14a, 14b, 14c, 14d), a transfer device 19 (19a, 19b, 19c, 1) for transferring a toner image to transfer paper.
9d), a cleaner 15 (15a, 15b, 15c, 15d) for removing residual toner remaining on the photosensitive drum.

FIG. 13 is a perspective view showing a portion of the scanner unit 11. In FIG. 13, reference numeral 101 denotes an image signal (VDO signal) which is input to the laser unit 102 in the scanner unit 11 and
2 generates a laser beam 103 modulated on / off. The laser beam 103 is deflected by a rotating polygon mirror (polygon mirror) 105 which is constantly rotated by a scanner motor 104, and the deflected laser beam 13 is focused by a coupling lens 106 on a photosensitive drum 18 which is a surface to be scanned. Then, horizontal scanning (scanning in the main scanning direction) is performed on the photosensitive drum 18, and a latent image is formed on the photosensitive drum 18.

[0005] In FIG. 13, reference numeral 109 denotes a beam detection port, which takes in the laser beam 13 from the rotary polygon mirror 105 through the slit-shaped detection port 109, guides the laser beam 13 to the photoelectric conversion element 111 through the optical fiber 110, and the like. The laser beam is converted into an electric signal by the photoelectric conversion element 111, and after being amplified by an amplifier circuit (not shown), becomes a horizontal synchronization signal.

In FIG. 13, reference numeral P denotes a transfer sheet as a transfer material, and the transfer sheet P is fed from a cassette 22 shown in FIG. The fed transfer paper waits at the registration roller 21 shown in FIG. 12 in order to take timing with the image forming unit. In the vicinity of the registration roller 21, a first registration sensor 24 for detecting the leading end of the fed transfer paper is provided.

[0007] An image forming control section for controlling the image forming section includes:
Based on the detection result of the first registration sensor 24, the timing at which the leading edge of the transfer paper reaches the registration roller 21 is detected, and a first color (yellow in the example in the figure) toner image is formed on the photosensitive drum 18a. The temperature of the heater 23 (not shown) is controlled to a predetermined value.

The transfer paper on standby at the registration roller 21 is
By applying the detection result of the first registration sensor 24 and the timing of the image forming process to the transfer belt 20 arranged so as to penetrate the image forming portion of each color, and applying a suction bias to the axis of the suction roller 29. Thereby, the transfer paper is electrostatically attracted to the transfer belt 20 and held. The held transfer paper is conveyed to a photosensitive drum 18a by a transfer belt 20, and a transfer blade 19a to which a transfer bias is applied.
As a result, the first color toner image is transferred onto the transfer paper.

Similarly, the toner image of the second color (magenta in the illustrated example) is formed on the transfer paper conveyed by the transfer belt 20 at the timing of the image formation process of the second color and the detection result of the second registration sensor 25. Is superimposed and transferred from the first color toner image. Similarly, the toner image of the third color (cyan in the example in the figure) is changed to the toner image of the fourth color (black in the example in the figure) based on the detection result of the third registration sensor 26. Is superimposed and transferred onto a transfer sheet sequentially at a timing corresponding to each image forming process based on the detection result of.

The transfer paper onto which the four color toner images have been transferred is fused and fixed by a fixing device 23 having a built-in halogen heater, and then discharged outside the image forming apparatus.

FIG. 14 is a schematic diagram of a wiring system of a motor drive circuit. The transfer belt motor drive circuit will be described below with reference to FIG.

The motor 205 of the motor unit 204 is
Outer rotary type DC brushless motor,
The transfer belt 20 is driven to rotate via a gear or the like. CPU 51 in a printer engine controller (not shown)
Controls image formation for each color. DSP (Digital S
ignal Processor. The motor controller 202 using the LSI for digital signal processing) is a CPU 51
And the motor 205 controls the rotation speed and phase of the motor 205 by PWM control via the motor driver 203.

As described above, by performing the feedback and the feedforward control using the DSP, the rotation speed control and the phase control can be performed without being affected by the load fluctuation of the motor.

A ferromagnetic magnetoresistive sensor (MR sensor) 206 in the motor unit 204 can read a pattern uniformly magnetized on the rotor of the motor as a sine wave corresponding to the rotation speed of the rotor. The motor controller 202 detects and controls the rotation speed of the motor based on the output signal S202 of the MR sensor 206 converted into a rectangular pulse wave (for example, 500 pulses / rotation) by the waveform converter 207.

The current I215 flowing through each phase of the motor 205
Flows from the resistor 208 to the ground (GMD) via the motor driver 203. The resistor 208 is a current detection resistor (for example, about 0.22Ω), and the voltage at both ends thereof increases as the current I215 flows. The motor controller 202 determines the current I 215 flowing to the motor based on the current detection signal (the voltage across the resistor 208) S 201.
Is detected at any time, and when the current is larger than a predetermined current value, an overcurrent protection function (not shown) is operated. Resistance 2
09 and 210 and the capacitor 211 constitute a filter circuit, and are provided for removing noise superimposed on the current detection signal S201.

Next, the transfer bias will be described with reference to FIGS. FIG. 15 is a schematic diagram of a wiring system of a transfer bias, and FIG. 16 is a schematic diagram of a wiring system of each image forming unit.

In FIG. 15, reference numeral 53 (53a to 53a)
d) is a transfer bias circuit, which is composed of a high voltage power supply circuit as a high voltage generating means for generating a transfer bias (transfer voltage). By applying the transfer bias output from the transfer bias circuit 53 to the transfer blade 19 (19a to 19d), the toner image formed on the photosensitive drum 18 (18a to 18d) is transferred onto the transfer belt 20. Transferred to paper.

As the transfer bias, a high voltage of a positive polarity is generally used in an image forming apparatus using a toner charged to a negative polarity. In addition, the voltage value is a signal (P) from a CPU 51 on an engine controller (not shown) that controls image formation in accordance with the usage environment of the device, the type of transfer paper, and the like.
WM signal) S51 (S51a to S51d).

When the transfer bias is applied, most of the transfer current Itr is transferred to the transfer bias circuit 5 as shown in FIG.
3 to transfer blade 19 of load 52 → transfer belt 20 →
It flows in the order of transfer paper → photosensitive drum 18 → photosensitive drum axis, and flows into the transfer bias circuit 53 via ground.

FIG. 17 shows an example of a transfer bias circuit constituted by a switching regulator circuit.

In FIG. 17, S82 is a clock signal of about 50 kHz transmitted from the CPU 51, and its frequency and on-duty are fixed to predetermined values. A switch 84 composed of a transistor or an FET is provided, and is turned on / off by a clock signal S82. By turning on and off the switch unit 84, the DC voltage supplied from the voltage control unit 81 becomes a switched pulse-like waveform, and is a switched pulse-like voltage waveform of the same cycle which is boosted via the transformer 85. Is transmitted from the primary side of the transformer 85 to the secondary side. The pulsed voltage transmitted to the secondary side is rectified and smoothed by a rectifying unit 86 composed of a diode and a ceramic capacitor, a switching frequency component is removed, and is output from a high voltage contact 88 as a high voltage DC voltage.

S51 is a clock signal of about 40 kHz (hereinafter referred to as PWM signal), which is transmitted from the CPU 51 to control the output voltage from the transfer bias circuit. The PWM signal S51 is smoothed to a DC voltage by a smoothing unit 83 including a resistor and a capacitor, and is input to a terminal of the comparator 82 to be a reference voltage of the comparator 82. The DC voltage and the reference voltage increase as the on-duty of the PWM signal S51 increases, and decrease as the on-duty decreases.

On the other hand, a voltage detecting section 87 is provided on the line connected to the high voltage contact 88, and detects the high voltage output to the high voltage contact 88 by dividing the output voltage by resistance. The output of the voltage detector 87 is input to the other terminal of the comparator 82, and is compared with a reference voltage based on the PWM signal S51. As a result of the comparison, when the detection voltage of the voltage detection unit 87 is smaller than the reference voltage, the comparator 82
Controls the voltage supplied from the voltage control unit 81 to the switch unit 84 to increase, and controls the voltage supplied to the switch unit 84 to decrease when the voltage detected by the voltage detection unit 87 is large. The balance is achieved when the voltages at the input terminals of the comparator 82 become substantially the same.

As described above, by varying the on-duty of the PWM signal S51, the primary voltage of the transformer 85 supplied to the switch section 84 is controlled, and the secondary high voltage, that is, the transfer voltage is controlled. Is possible.

Further, if a PWM signal S51 having a duty corresponding to a transfer bias of 0 V is sent, the transfer bias can be turned on and off.
Can be used as a transfer bias on / off signal.

Next, the relationship between the transfer voltage and the torque fluctuation will be described. FIG. 18 shows the relationship between the shaft torque of the motor driving the transfer belt and the transfer voltage. 18A shows a PWM signal, FIG. 18B shows a transfer voltage, and FIG. 18C shows a shaft torque.

When a transfer bias is applied while a motor for driving the transfer belt 20 is operated, the transfer blade 1
Attraction force acts between the transfer belt 9 and the transfer belt 20, and the frictional resistance therebetween increases. Therefore, the dynamic torque t1 of the motor shaft
Are larger than the dynamic torque t10 when no bias is applied while the bias is being applied. The dynamic torque increases as the transfer bias applied increases.

Therefore, there is the following relationship in FIG.

On-duty: D11 <D12 <D13 Transfer voltage: V11 <V12 <V13 Motor shaft torque: t11 <t12 <t13 For example, when the on-duty of the PWM signal is D11,
The transfer voltage becomes V11, and the dynamic torque of the motor shaft becomes t11. When the on-duty of the PWM signal is increased to D13, the transfer voltage increases to V13, and the dynamic torque of the motor shaft increases to t13.

Conventionally, when a transfer bias is turned on, a PWM signal having an on-duty width corresponding to a reference voltage, that is, a target transfer voltage, is simply sent.

[0031]

As described above, conventionally, when a transfer bias is turned on, a PWM signal having a duty width corresponding to a target transfer voltage is simply transmitted, and the transfer voltage is calculated from the time constant of the circuit. It was turned on and off with a relatively fast rise time and fall time determined.

However, in a tandem type image forming apparatus using the transfer blade 19 and the transfer belt 20,
Since an attractive force acts between the transfer blade and the transfer belt when the transfer bias is applied, if the transfer voltage fluctuation per unit time is large, the torque fluctuation per unit time of the transfer belt due to the fluctuation of the transfer voltage increases.

If the torque fluctuation per unit time is faster than the response speed of the motor control system, the control of the motor cannot catch up, and the rotation speed of the transfer belt fluctuates when the transfer bias is turned on or off. .

Therefore, when the four color toner images are sequentially transferred to the transfer paper, if the transfer bias is affected by the speed fluctuation of the transfer belt, each color is transferred in the transfer direction of the transfer paper (sub-scanning direction). (1) There was a problem that the color shift occurred and the image was defective.

A similar problem is that a plurality of color toner images on a plurality of photosensitive drums are temporarily superimposed on an
Also in an intermediate transfer type tandem type image forming apparatus which performs secondary transfer and then secondary transfer collectively to a transfer material, this occurs at the time of primary transfer.

An object of the present invention is to reduce the torque fluctuation of the driving motor for the transfer belt and the intermediate transfer belt without increasing the cost by devising an on / off control method when the transfer bias is turned on and off. An object of the present invention is to provide an image forming apparatus capable of obtaining a high-quality color image in which fluctuations in the rotational speed of the image are suppressed and color misregistration in the sub-scanning direction is reduced.

[0037]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
A plurality of image carriers, conveying means for carrying the transfer material and sequentially transporting the plurality of image carriers to the plurality of image carriers, and superimposing a plurality of color toner images formed on the plurality of image carriers on the transfer material; An image forming apparatus comprising: a plurality of transfer units for performing transfer by applying a transfer voltage to the plurality of transfer units; and a control unit that controls the high-voltage generation unit. An image forming apparatus characterized in that the high-voltage generating means is controlled so as to reduce rise time and fall time at the time of applying and stopping a voltage.

In the present invention, the rise time and the fall time of the transfer voltage are determined by a drive unit for driving the transfer unit in response to a torque change per unit time of the transfer unit which occurs when the transfer voltage is applied and stopped. Is the time during which the rotation speed control means can respond. The rise time and fall time of the transfer voltage are set longer as the absolute value of the transfer voltage is larger.

According to the present invention, the control means may control the high voltage generating means so as to apply and stop the transfer voltage stepwise when the transfer voltage is applied and stopped. When the transfer voltage is applied, a voltage having an absolute value smaller than the transfer voltage is applied, and then the transfer voltage is applied.When the transfer voltage is stopped, the absolute value of the transfer voltage is higher than the transfer voltage. Stop after applying a voltage with a small value. Alternatively, the control unit may control the high voltage generation unit so that the timings of applying and stopping the transfer voltage to the plurality of transfer units do not overlap. The transfer means has a belt shape. The transfer means has a blade shape.

Further, according to the present invention, a plurality of image carriers, an intermediate transfer member, and a plurality of color toner images formed on the plurality of image carriers are transferred onto the intermediate transfer member in a superimposed manner. An image forming apparatus comprising: a plurality of primary transfer units for applying a transfer voltage to the plurality of primary transfer units; and a control unit for controlling the high-voltage generation units. be able to.

[0041]

Embodiments of the present invention will be described below in more detail with reference to the drawings.

Embodiment 1 According to the present invention, when the transfer bias is turned on and off, the on / off control method is devised to suppress the torque fluctuation of the driving motor of the transfer belt and the intermediate transfer belt without increasing the cost. It is characterized in that fluctuations in the rotational speed of the belt are suppressed, and color shift in the sub-scanning direction of a color image is reduced.

This embodiment shows a case in which the present invention is applied to the laser printer shown in FIG. 12 as a conventional example of a tandem type image forming apparatus. The configuration of the laser printer and the image forming operation are the same as those described in the conventional example, and thus will not be described. Hereinafter, FIG. 12 and the like will be referred to as needed for the description.

In this embodiment, as shown in FIG. 1, a PWM signal S71 transmitted from the CPU 51 of the image forming control unit for controlling image formation to the comparator 82 of the transfer bias circuit is used.
As in the case of the conventional PWM signal S51 shown in FIG. 17, the transmission is not simply performed with the duty width corresponding to the target transfer voltage, but is performed with the duty width changed at the time of on / off.

The configuration of the transfer bias circuit itself shown in FIG. 1 is the same as that of the transfer bias circuit shown in FIG. 17, and comprises a high voltage power supply circuit as a high voltage generating means for generating a transfer bias (transfer voltage). It is composed of a regulator circuit. Since the transfer bias circuit has already been described in the related art, a detailed description thereof will be omitted.

According to the transfer bias circuit, the CPU 5
By varying the on-duty of the PWM signal S71 from 1, the primary-side voltage of the transformer 85 supplied to the switch 84 constituting the high-voltage generation circuit of the transfer bias circuit is controlled, and the secondary-side high-voltage, The transfer bias (transfer voltage) can be controlled.

A control method for turning on and off the transfer bias in this embodiment will be described.

In FIG. 15, the transfer bias circuit 63
(63a, 63b, 63c, 63d) are used to transfer the toner image formed on the photosensitive drum 18 (18a, 18b, 18c, 18d) of FIG. A bias is generated and applied to the transfer blade 19 (19a, 19b, 19c, 19d). As the transfer bias, in an image forming apparatus using a toner charged to a negative polarity, a high voltage of a positive polarity is generally used.

In this embodiment, as shown in FIG. 2, when the transfer bias is turned on and off, a predetermined rise time T1 and a rise time T1 are provided to suppress the voltage fluctuation of the transfer bias per unit time. is there.

The rise time T1 is, for example, the time from when the voltage rises from 0 V to the target transfer voltage V1 until the voltage reaches 10% to 90% of the target voltage V1, and the fall time T1.
1 is a time when the voltage falls from the target voltage V1 to 0 V, for example, from 90% to 10% of the target voltage V1.

The rise and fall time T1 needs to be at least a time (for example, several tens msec to several hundred msec) at which the control system of the drive motor of the transfer belt 20 can sufficiently catch up with the torque fluctuation due to the transfer voltage fluctuation. is there.

Next, a method of controlling the PWM signal for setting the start-up time to a predetermined time will be described with reference to FIG.

In this embodiment, as shown in FIG.
The on-duty of the PWM signal S71 is changed from D21 to D2.
2. Control is performed to widen to D23 in three stages (D21 <D22 <D23). Note that FIG. 3A is schematically shown with emphasis on the description, and it is obvious that the frequency is about 40 kHz.
The PWM signal of z (period: 25 μsec) does not look like a pulse as shown on the horizontal axis in the order of msec.

In the method of this embodiment, when the target voltage V23 of the transfer bias is output, the output voltage is turned on for a predetermined time T21, T22 before the PWM signal S71 is output at the on-duty D23 corresponding to the target voltage V23. Duty D21, D22
Are output, respectively.

Referring to FIG. 4, a method of controlling the on / off of the transfer bias according to the present embodiment will be described.

In FIG. 4, the motor for the transfer belt (transfer material transfer belt) is turned on (step S501),
The CPU 51 in the image forming control unit of FIG.
= 0 (S502). The CPU calculates the target transfer voltage V23
PW with on-duty D21 corresponding to lower voltage than
An M signal S71 is output, and time counting is performed until the counter t1 reaches a predetermined time T21 (S503 to S505). Next, C
The PU sets the counter to t2 = 0 (S506).

Similarly, when the on-duty D22 corresponds to a voltage lower than the target voltage V23 and is shorter than D21, the PW
The M signal S71 is output, and time counting is performed until the counter t2 reaches a predetermined time T22 (S507 to S509). Then C
The PU sets the counter to t3 = 0 (S510). PWM signal S with on-duty D23 corresponding to target voltage V23
71, and counts the time until the counter t3 reaches a predetermined time T23 (S511 to S513).

The above-described control is performed by controlling the target transfer voltage V23.
Before reaching the target, it is equivalent to providing two target voltages. However, since the output transfer voltage has a time constant of the transfer bias circuit, the output voltage does not become stair-like when the duty of the PWM signal is switched, and rises smoothly over a predetermined time as shown in FIG. , The rise time can be made gradual.

Similarly, when the transfer voltage falls, P
The WM signal S71 may be provided with three levels of on-duty, and control may be performed to gradually reduce the on-duty. The fall can be made smooth over a predetermined time, and the fall time can be made gradual.

The rise time and fall time are as follows:
Since it is provided in order to reduce the voltage fluctuation of the transfer bias per unit time, it is necessary to increase the transfer voltage as the target voltage increases.

FIG. 5 is a diagram showing the difference between the rise time and the fall time depending on the magnitude of the target transfer voltage. As shown in the figure, when the target transfer voltage V3> V2, the rise and fall times are controlled so that T3> T2.

As described above, according to the present embodiment, when the transfer bias is turned on and off, the transfer bias is controlled by devising the transfer bias on and off so that the rise and fall of the transfer bias become gentle. Therefore, fluctuations in the rotation speed of the transfer belt when the transfer bias is turned on and off can be suppressed, and a high-quality color image with reduced color shift in the sub-scanning direction can be obtained.

Embodiment 2 Another embodiment of the present invention will be described with reference to FIGS. FIG. 6 is an explanatory diagram of the on / off control method of the transfer bias, and FIG. 7 is a flowchart at that time.

The image forming operation of the laser printer is the same as that described in the conventional example, and will not be described. The transfer bias circuit is the same as that in the first embodiment, and a description thereof will be omitted.

In order to reduce the torque fluctuation per unit time of the shaft of the drive motor of the transfer belt, it is necessary to suppress the voltage fluctuation of the transfer bias per unit time. In the present embodiment, as shown in FIG.
And a voltage V4 having an absolute value lower than that of the voltage V2 is provided, so that the voltage fluctuation of the transfer bias per unit time is suppressed to be small.

In the figure, a small voltage V4 is applied for a predetermined time T4 before transfer, and a transfer voltage V5 is applied for a predetermined time T5 at a timing when the toner image on the photosensitive drum 18 is transferred onto transfer paper. After the transfer, a small voltage V5 is applied again at a predetermined time T4 to turn off the transfer bias.

In this case, when the low voltage V4 and the transfer voltage V5 are switched, the belt torque fluctuates due to this voltage fluctuation. At least, the transfer voltage V is selected so that the control system of the belt drive motor can sufficiently follow the torque fluctuation.
It is necessary to set a difference between 5 and the low voltage V4. In addition, it is necessary to set the low voltage V4 to a voltage level that does not affect the photosensitive drum, and take care not to affect the toner image during image formation.

The control of this embodiment will be described with reference to FIG.

In FIG. 7, the conveyor belt motor is ON.
(Step S601), the CP in the image forming control unit
U (not shown) sets the counter to t4 = 0 (S60
2). The CPU outputs the PWM signal S71 with the on-duty D4 corresponding to the voltage V4 lower than the transfer voltage V5, and counts the time until the counter t4 reaches a predetermined time T4 (S603 to S605). Next, the CPU sets the counter to t5 = 0 (S606).

The CPU sets the transfer voltage V higher than the voltage V4.
PWM signal S71 with on-duty D4 corresponding to 5
Is output and the time is counted until the counter t5 reaches a predetermined time T5 (S607 to S609). Next, the CPU sets the counter to t4 = 0 (S610). The CPU operates at the voltage V4
The PWM signal S71 is output with the on-duty D4 corresponding to the above, and the time is counted until the counter t4 reaches a predetermined time T4 (S611 to S613).

Thereafter, the CPU outputs the PWM signal S71 with the on-duty D0 corresponding to the voltage of 0 V, and stops outputting the transfer voltage (S614). The motor for the conveyor belt is stopped (S615).

As described above, in this embodiment, the control method is devised so that the transfer voltage is applied stepwise when the transfer bias is applied and when the transfer bias is stopped. It is possible to suppress fluctuations in the rotation speed of the transfer belt at the time of on / off, and to obtain a high-quality color image in which color shift in the sub-scanning direction is reduced.

Further, when the control method of the first embodiment is combined with the control method of the present embodiment, fluctuations in the rotation speed of the transfer belt per unit time can be further reduced.

Embodiment 3 Still another embodiment of the present invention will be described with reference to FIGS. FIG. 8 is an explanatory diagram of a method of controlling the on / off of the transfer bias applied to the four color image forming units, and FIG. 9 is a flowchart at that time.

The image forming operation of the laser printer is the same as that described in the conventional example, and a description thereof will be omitted. The transfer bias circuit is the same as that in the first embodiment, and a description thereof will be omitted.

In order to reduce the torque fluctuation per unit time of the shaft of the belt drive motor, it is necessary to suppress the voltage fluctuation of the transfer bias per unit time. In this embodiment, four colors of yellow, magenta, cyan, and black are used.
When a transfer bias is applied to each of the color image forming units, voltage fluctuation of the transfer bias per unit time is suppressed by controlling the on / off timing of each transfer bias so as not to overlap.

The four-color transfer blade 19 (19a) shown in FIG.
19d), the transfer force is simultaneously applied to each of the transfer biases, and an attraction force acts between the transfer blades 19 and the transfer belts 20 of the four colors. The torque increases. For this reason, if the transfer biases of the four colors are started at the same timing, the fluctuation in torque per unit time naturally increases.

Therefore, in this embodiment, as shown in FIG. 8, at the timing when the toner image on each photosensitive drum is transferred onto the transfer paper, respective transfer voltages V6, V7, V8,
By turning on V9 and controlling the on / off timing of the transfer bias so as not to overlap in time, torque fluctuation per unit time is reduced.

FIG. 8 shows that the transfer voltage for yellow (first color) is V6, the transfer voltage for magenta (second color) is V7, the transfer voltage for cyan (third color) is V8, and black (fourth color).
In this case, the transfer voltage is set to V9, and the transfer voltage is sequentially increased by about 500 V from the first color to the fourth color.

The control of this embodiment will be described with reference to FIG.

In FIG. 9, the transfer belt motor is turned on.
Then, the transfer bias for yellow is turned on (S702). This yellow transfer bias O
The transfer bias for magenta of the second color is turned on so as not to overlap with N (S703). Similarly, the transfer bias for cyan is turned on (S704).

In this embodiment, since the transfer of the first color yellow has been completed at the timing of turning on the cyan transfer bias, the transfer bias for yellow is turned off (S705). Next, the transfer timing of the fourth color black is set, and the transfer bias for black is turned on so as not to overlap with the turning off of the biases of the other colors (S70).
6). Thereafter, the transfer biases for magenta, cyan, and black are sequentially turned off, and the transfer ends (S707).
To S709). Finally, the transfer belt motor is turned off (S710).

As described above, in this embodiment, the cost is increased by devising a control method at the time of applying and stopping the transfer bias so that the on / off timing of each transfer bias does not overlap. Without this, fluctuations in the rotation speed of the transfer belt when the transfer bias is turned on and off can be suppressed, and a high-quality color image with reduced color shift in the sub-scanning direction can be obtained.

The control method of this embodiment is similar to those of the first and second embodiments.
By combining the above control methods, the fluctuation in the rotation speed of the transfer belt per unit time can be further reduced.

Embodiment 4 FIG. 10 is a schematic view showing a transfer bias wiring system according to still another embodiment of the present invention.

[0086] The image forming operation of the laser printer is the same as that described in the conventional example, and therefore will not be described. Further, the transfer bias circuit is the same as that in the first embodiment, and the description is omitted.

In this embodiment, the transfer bias circuit includes a common transfer bias circuit 53a for three colors of yellow, magenta and cyan, and a dedicated transfer bias circuit 53 for black.
d is provided. Transfer bias circuit 53a for three colors
Are the loads 52a, 52 of yellow, magenta, and cyan.
b, 52c, and the transfer bias circuit 53d for black is connected only to the black load 52d.
The transfer bias circuits 53a and 53d are grounded.

This is because, in the case of an apparatus in which the monochrome mode (only black is used) is set, the transfer bias circuit is reduced for cost reduction, and the transfer bias circuit for the color (yellow, magenta, cyan) is used in the monochrome mode. This is a configuration that allows turning off.

The transfer voltage value of each of the transfer bias circuits 53a and 53d is determined by a PWM signal from the CPU 51 on an engine controller (image formation control unit) for controlling image formation in accordance with the use environment of the apparatus and the type of transfer paper. S71
e, and can be controlled by S71d.

This embodiment is applied to a transfer bias circuit having such a configuration. As in the first, second, and third embodiments, the torque fluctuation per unit time when the transfer bias is applied is reduced.
The rotation speed fluctuation of the transfer belt can be suppressed.

Embodiment 5 FIG. 11 is a schematic view showing an image forming apparatus according to still another embodiment of the present invention.

The present embodiment differs from the image forming apparatuses of the first to fourth embodiments in that an intermediate transfer belt 30 is provided as an intermediate transfer member in the image forming apparatus, and an image forming operation of an intermediate transfer system is performed.

The intermediate transfer belt 30 is wrapped around a plurality of rows, and along the transfer belt 30, an image forming unit for each color of yellow (Y), magenta (M), cyan (C), and black (K) is formed. is set up. The basic configuration of each image forming unit is the same as that of the conventional image forming apparatus shown in FIG. 11, the same reference numerals as those shown in FIG. 15 indicate the same members.

The image forming control section for controlling the image forming section includes:
When a print signal is received from a host computer (not shown), formation of a first color (yellow in the illustrated example) toner image on the photosensitive drum 18a is started, and the heater of the fixing unit 23 is controlled to a predetermined temperature.

When forming the first color image, the intermediate transfer belt 3 in which only the first color photosensitive drum 18a passes through each image forming portion
Contact 0. The intermediate transfer belt 30 is driven to rotate with the rotation of the photosensitive drum, and a primary transfer bias is applied to a primary transfer blade 39a disposed on the back surface of the intermediate transfer belt 30 of the primary transfer portion in contact with the photosensitive drum 18a. When the voltage is applied, the first color toner image formed on the photosensitive drum 18a is transferred onto the intermediate transfer belt based on the reference position of the intermediate transfer belt.

Similarly, at the time of forming the second color (magenta in the illustrated example) image, the second color photosensitive drum 18 is placed on the intermediate transfer belt.
b, and the magenta toner image on the photosensitive drum 18b is superimposed and transferred onto the intermediate transfer belt from the first color toner image based on the reference position of the intermediate transfer belt. Thereafter, similarly, the photosensitive drum 18c and the photosensitive drum 18d abut on the intermediate transfer belt 30, respectively, and the third color toner image (cyan in the example in the figure) formed on the photosensitive drum 18c and the fourth color toner image formed on the photosensitive drum 18d (In the illustrated example, black) are sequentially transferred onto the intermediate transfer belt 30 in a superimposed manner.

The 4 superimposedly transferred on the intermediate transfer belt 30
The color toner image is transferred onto the transfer paper P conveyed to the secondary transfer section where the intermediate transfer belt 30 and the secondary transfer roller 31 face each other.
Secondary transfer is collectively performed by the secondary transfer roller 31. The secondary transfer roller 31 is retracted to a position separated from the intermediate transfer belt 30 during image formation.

The transfer paper P is conveyed from the transfer material cassette 22 to the secondary transfer section, and is once waited by the registration rollers 21. In the vicinity of the registration roller 21, a registration sensor 24 for detecting the leading end of the fed transfer paper is provided. The transfer paper waiting at the registration roller 21 is conveyed to the secondary transfer unit at a timing between the detection result of the registration sensor 24 and the image forming process. At the same time, when the secondary transfer roller 31 comes into contact with the intermediate transfer belt 30 and a secondary transfer bias is applied to the secondary transfer roller, the four color toner images on the intermediate transfer belt are collectively transferred onto the transfer paper. Is done.

The transfer paper to which the four color toner images have been transferred is fused and fixed by the fixing device 23 with a built-in halogen heater, and is discharged outside the image forming apparatus.

In this embodiment, the intermediate transfer belt 3
In the tandem type image forming apparatus using 0, the transfer bias circuit of the primary transfer blade 39 (39a to 39d) for each color is controlled to be on / off as described in the first, second, third or fourth embodiment. I have. Therefore, fluctuations in the rotation speed of the drive motor for the intermediate transfer belt can be reduced, and the same effects as in the first to fourth embodiments can be obtained.

[0101]

As described above, according to the present invention,
In a tandem-type color image forming apparatus with a transfer belt and an intermediate transfer belt, when forming a color image, when the transfer bias is turned on and off, the on / off control of the rise and fall of the transfer bias is devised. Therefore, it is possible to obtain a color image in which fluctuations in the rotation speed of the belt are suppressed and color misregistration in the sub-scanning direction is reduced without increasing the cost.

[Brief description of the drawings]

FIG. 1 shows a transfer bias circuit according to an embodiment of the present invention;
FIG. 9 is an explanatory diagram showing that a PWM signal with a changed duty width is transmitted thereto.

FIG. 2 is an explanatory diagram showing that a predetermined rise time and a fall time are provided in the transfer bias on / off control method in the embodiment of FIG. 1;

FIG. 3 shows a PW for setting a rise time to a predetermined time.
FIG. 4 is an explanatory diagram illustrating a control method of an M signal.

FIG. 4 is a flowchart showing a control method in the embodiment of FIG.

FIG. 5 is a diagram illustrating a difference between a rise time and a fall time depending on the magnitude of a target transfer voltage.

FIG. 6 is an explanatory diagram showing that a transfer voltage is applied and stopped stepwise by a transfer bias on / off control method according to another embodiment of the present invention.

FIG. 7 is a flowchart showing a control method in the embodiment of FIG.

FIG. 8 is an explanatory diagram showing that on / off timings of transfer voltages of four colors are not overlapped by a transfer bias control method according to still another embodiment of the present invention.

FIG. 9 is a flowchart showing a control method in the embodiment of FIG.

FIG. 10 is a schematic diagram showing a wiring system of a transfer bias according to still another embodiment of the present invention.

FIG. 11 is a schematic configuration diagram showing an image forming apparatus according to still another embodiment of the present invention.

FIG. 12 is a schematic view showing a conventional image forming apparatus.

FIG. 13 is a perspective view illustrating a scanner unit of the image forming apparatus of FIG. 12;

FIG. 14 is a schematic diagram showing a wiring system of a motor drive circuit.

FIG. 15 is a schematic diagram showing a wiring system of a transfer bias.

FIG. 16 is a schematic diagram illustrating a wiring system of a transfer bias of each image forming unit.

FIG. 17 is an explanatory diagram illustrating a transfer bias circuit.

FIG. 18 is a diagram illustrating a relationship between a PWM signal of a transfer bias circuit, a transfer voltage, and a shaft torque of a belt drive motor.

[Explanation of symbols]

 18a-18d Photosensitive drum 19a-19d Transfer blade 20 Transfer belt 30 Intermediate transfer belt 39a-39d Primary transfer blade 51 CPU 81 Voltage controller 82 Comparator 85 Transformer S71 PWM signal

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 21/00 398 G03G 21/00 372 F term (Reference) 2H027 DE07 DE09 EA03 EA15 EB04 EC06 EC09 EC20 ED16 ED24 EE01 EE03 EE04 EE07 ZA01 2H030 AA01 AB02 AD05 AD17 AD19 BB02 BB23 BB42 BB44 BB46 BB54 2H032 AA05 AA15 BA09 BA18 CA02 CA13

Claims (16)

[Claims] 1. A plurality of image carriers, a conveying unit that carries a transfer material and sequentially conveys the plurality of image carriers, and transfers a plurality of color toner images formed on the plurality of image carriers. An image forming apparatus comprising: a plurality of transfer units configured to transfer images in a superimposed manner on a material; a high voltage generation unit configured to apply a transfer voltage to the plurality of transfer units; and a control unit configured to control the high voltage generation unit. The image forming apparatus controls the high voltage generating means so as to reduce a rise time and a fall time when the transfer voltage is applied and when the transfer voltage is stopped. 2. The method according to claim 1, wherein a rise time and a fall time of the transfer voltage are determined by a rotation of a drive unit that drives the transfer unit with respect to a torque change per unit time of the transfer unit that occurs when the transfer voltage is applied and stopped. 2. The image forming apparatus according to claim 1, wherein the time is a time during which the speed control means can respond. 3. The image forming apparatus according to claim 1, wherein a rise time and a fall time of the transfer voltage are longer as an absolute value of the transfer voltage is larger. 4. A plurality of image carriers, conveying means for carrying a transfer material and sequentially conveying the transfer materials to the plurality of image carriers, and transferring a plurality of color toner images formed on the plurality of image carriers. An image forming apparatus comprising: a plurality of transfer units configured to transfer images in a superimposed manner on a material; a high voltage generation unit configured to apply a transfer voltage to the plurality of transfer units; and a control unit configured to control the high voltage generation unit. The means performs the application and stop of the transfer voltage stepwise when applying and stopping the transfer voltage,
An image forming apparatus for controlling the high-pressure generating means. 5. When the transfer voltage is applied, a voltage having an absolute value smaller than the transfer voltage is applied, and then the transfer voltage is applied. When the transfer voltage is stopped, the transfer voltage is continuously applied. 5. The image forming apparatus according to claim 4, wherein the image forming apparatus stops after applying a voltage whose absolute value is smaller than the transfer voltage. 6. A plurality of image carriers, conveying means for carrying a transfer material and sequentially conveying the plurality of image carriers, and transferring toner images of a plurality of colors formed on the plurality of image carriers. An image forming apparatus comprising: a plurality of transfer units configured to transfer images in a superimposed manner on a material; a high voltage generation unit configured to apply a transfer voltage to the plurality of transfer units; and a control unit configured to control the high voltage generation unit. The image forming apparatus controls the high voltage generating means so that timings of applying and stopping the transfer voltage to the plurality of transfer means do not overlap. 7. The image forming apparatus according to claim 1, wherein said conveying means has a belt shape. 8. The image forming apparatus according to claim 1, wherein said transfer unit has a blade shape. 9. A plurality of image transfer members, an intermediate transfer member, and a plurality of primary transfer members which transfer toner images of a plurality of colors formed on the plurality of image support members in an overlapping manner on the intermediate transfer member. Means, a high voltage generating means for applying a transfer voltage to the plurality of primary transfer means, and a control means for controlling the high voltage generating means. An image forming apparatus, wherein the high-voltage generating means is controlled so as to reduce a rise time and a fall time at the time of stopping. 10. A drive unit for driving the intermediate transfer body in response to a change in torque per unit time of the intermediate transfer body that occurs when the transfer voltage is applied and when the transfer voltage is stopped. 10. The image forming apparatus according to claim 9, wherein the rotation speed control unit is responsive. 11. The image forming apparatus according to claim 9, wherein a rising time and a falling time of the transfer voltage are set longer as the absolute value of the transfer voltage is larger. 12. A plurality of image transfer members, an intermediate transfer member, and a plurality of primary transfer units which transfer toner images of a plurality of colors formed on the plurality of image transfer members in a superimposed manner on the intermediate transfer member. Means, a high voltage generating means for applying a transfer voltage to the plurality of primary transfer means, and a control means for controlling the high voltage generating means. And during the stop, the transfer voltage is applied and stopped stepwise,
An image forming apparatus for controlling the high-pressure generating means. 13. When the transfer voltage is applied, a voltage whose absolute value is smaller than the transfer voltage is applied, and then the transfer voltage is applied. When the transfer voltage is stopped, the transfer voltage follows the transfer voltage. 13. The image forming apparatus according to claim 12, wherein the image forming apparatus stops after applying a voltage whose absolute value is smaller than the transfer voltage. 14. A plurality of image transfer members, an intermediate transfer member, and a plurality of primary transfer units for transferring a plurality of color toner images formed on the plurality of image support members by superimposing and transferring them on the intermediate transfer member. Means, a high voltage generating means for applying a transfer voltage to the plurality of primary transfer means, and a control means for controlling the high voltage generating means, wherein the control means comprises: An image forming apparatus, wherein the high-voltage generating means is controlled so that the timing of applying and stopping the transfer voltage to the means does not overlap. 15. The image forming apparatus according to claim 9, wherein the intermediate transfer member has a belt shape. 16. The image forming apparatus according to claim 9, wherein said primary transfer means has a blade shape.