JP2024031576A - High-voltage power supply device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-voltage power supply device that, in switching the polarity of high output voltage, can prevent a delay in start-up of bias and overshoot after the switching.

SOLUTION: A high-voltage power supply device has: a first transformer; first driving means that is connected with the transformer; first rectification and smoothing means that rectifies and smooths a voltage transformed by the first transformer; a second transformer; second driving means that is connected with the transformer; second rectification and smoothing means that rectifies and smooths a voltage transformed by the second transformer; an output voltage detection unit that detects output voltages rectified and smoothed by the first and second rectification and smoothing means; a control unit; and a transformer input voltage control circuit that generates transformer input voltage to be supplied to second input terminals of the first and second transformers. The high-voltage power supply device includes a voltage limit determination circuit that, when a result of detection performed by the output voltage detection unit is deviated from an output preset voltage by a predetermined amount or more, stops a driving pulse (POS_CLK) and a driving pulse (NEG_CLK).

SELECTED DRAWING: Figure 2

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a high voltage power supply device and an image forming apparatus.

In an electrophotographic image forming apparatus, an image is generally formed on recording paper through the steps of charging, exposure, development, transfer, and fixing.

The image forming apparatus includes a high voltage power supply device for supplying a high voltage (hereinafter referred to as high voltage) to a transfer roller provided at the peripheral edge of an image bearing member, such as a photosensitive drum.

During the image forming operation of the image forming apparatus, when the recording paper passes between the image bearing member and the transfer roller, the high voltage power supply unit supplies high voltage to the transfer roller with the opposite polarity to the toner image formed on the image bearing member. The toner image on the image carrier is transferred onto recording paper.

FIG. 6 is a circuit block diagram of a secondary transfer high voltage power supply device 60 according to conventional example 1 that supplies high voltage to the secondary transfer roller, including a secondary transfer high voltage control section 11, a positive high voltage generation section 12, and a positive bias transformer input voltage. It is composed of a control circuit 12a, a negative high voltage generation section 13, a negative bias transformer input voltage control circuit 13a, a load voltage detection circuit 14, and a load current detection circuit 15.

The positive high voltage generator 12 drives the gate of the FET Q21 using POS_CLK with a fixed frequency and duty. The drain of FET Q21 is connected to the primary winding of high voltage transformer 12c and resonance capacitor C21. The other end of the primary winding of the high voltage transformer 12c is connected to a transistor Q11, a capacitor C12, and a diode D11.

The electrolytic capacitor C12 is a smoothing capacitor for making the voltage input to the primary winding of the high voltage transformer 12c a stable DC voltage. In this way, by driving the primary winding of the high voltage transformer 12c with a predetermined control voltage based on the level of the control signal POS_CTRL, a high voltage DC bias corresponding to the control voltage is output to the output terminal Vout of the high voltage transformer 12c. .

The negative high voltage generator 13 drives the gate of the FET Q61 using a clock signal NEG_CLK with a fixed frequency and duty. The drain of FET Q61 is connected to the primary winding of high voltage transformer 13c and resonance capacitor C61. The other end of the primary winding of the high voltage transformer 13c is connected to a transistor Q51, a capacitor C52, and a diode D51.

The electrolytic capacitor C52 is a smoothing capacitor for making the voltage input to the primary winding of the high voltage transformer 13c a stable DC voltage. In this way, by driving the primary winding of the high voltage transformer 13c with a predetermined control voltage based on the level of the control signal NEG_CTRL, a high voltage DC bias corresponding to the control voltage is output to the output terminal Vout of the high voltage transformer 13c. .

Resistors R41 and R42 are high voltage bias output voltage detection resistors, and are connected to the Vsns terminal of the secondary transfer high voltage control section 11. The Isns terminal is a load current detection output terminal, and the load current detection circuit 15 includes a resistor R81, a current detection operational amplifier IC3, and a reference voltage DC1. The reference voltage for this circuit is Vs, which shows Vs when the load current is "zero" and increases as the positive load current increases. Also, when the load current increases, the voltage decreases.

FIG. 7 is a circuit block diagram of a secondary transfer high voltage power supply device 70 of conventional example 2 that supplies high voltage to the secondary transfer roller, including a secondary transfer high voltage control section 11, a positive high voltage generation section 12, and a negative high voltage generation section. 13, a load voltage detection circuit 14, a load current detection circuit 15, and a transformer input voltage control circuit 17. The difference in the configuration of Conventional Example 2 from Conventional Example 1 is that in Conventional Example 1, each of the positive high voltage generation section 12 and the negative high voltage generation section 13 is provided with transformer input voltage control circuits 12a and 13a. The conventional example 2 is that the transformer input voltage control circuit 17 is shared by the positive high voltage generation section 12 and the negative high voltage generation section 13. In the circuit of Conventional Example 2, since the transformer input voltage control circuit 17 is shared, the circuit is simplified compared to Conventional Example 1, and thus downsizing and cost reduction are possible.

Japanese Patent Application Publication No. 2005-70083

Image forming apparatuses for such electrophotographic processes supply a positive bias to the secondary transfer roller in order to transfer the toner image from the intermediate transfer belt to the recording material. The density detection patch toner image formed at the position on the intermediate transfer belt corresponding to the space between the recording materials (paper gap) when transferring images to a secondary transfer belt for cleaning or when forming images on multiple recording materials continuously is Negative bias may be supplied to the secondary transfer roller in a process performed to prevent the image from being transferred to the secondary transfer roller when passing through the transfer roller section.

When performing such processing, some systems continuously switch the output polarity of the secondary transfer high voltage power source. In the secondary transfer high-voltage power supply device of conventional example 2 described above, the output voltage value of the high-voltage power supply device is controlled by controlling the voltage value input to the primary windings of the high-voltage transformer 12c and the high-voltage transformer 13c using the output control operational amplifier IC9. This is done by

When performing control to switch the polarity of the high voltage output voltage from positive to negative in this control method, the input voltage to the primary windings of the high voltage transformer 12c and high voltage transformer 13c at the timing of polarity switching is the desired value before the polarity switching is performed. The voltage level is equivalent to outputting a positive bias. After polarity switching, it is necessary to change the input voltage to the primary windings of high voltage transformers 12c and 13c to a level corresponding to outputting the desired negative bias after polarity switching.

High voltage transformers 12c and 13c whose input voltage levels to the primary windings of high voltage transformers 12c and 13c are equivalent to outputting the desired negative bias after polarity switching are equivalent to outputting the desired positive bias before polarity switching. When the input voltage level is lower than the input voltage level to the primary winding, the voltage supplied to the high voltage transformer 13c becomes excessive in a certain section immediately after polarity switching, causing an overshoot in the secondary transfer high voltage output Vout.

FIG. 8 is a sequence diagram of output polarity switching control in the high voltage power supply of Conventional Example 2.

In this sequence, control is performed to switch the polarity of the output voltage value to -600V for a predetermined time T1 from a state where the secondary transfer high voltage output voltage is outputting 3000V, and then switch the polarity of the output voltage value to 3000V again. . When switching the polarity from positive bias to negative bias, the set value of the positive bias output voltage setting signal CTRL is switched from the output voltage 3000V to -600V.

As mentioned above, the input voltage level to the primary windings of high voltage transformers 12c and 13c, which corresponds to outputting the desired negative bias after polarity switching, that is, the voltage level of electrolytic capacitor C92, corresponds to outputting the desired positive bias before polarity switching. If the level is lower than the level corresponding to the output, there is a problem that the voltage supply to the high voltage transformer 13c becomes excessive during the period T2 immediately after polarity switching, and the secondary transfer high voltage output overshoots. After T1 has elapsed since the polarity was switched from the positive bias to the negative bias, the polarity is switched from the negative bias to the positive bias, and the set value of the output voltage setting signal CTRL is switched from the output voltage -600V to 3000V. In this case, the electrolytic capacitor C92 is charged by the transistor Q91 to a voltage level corresponding to outputting a desired positive bias, and the output voltage is switched to 3000V.

When the input voltage control unit that supplies power to each transformer is shared by the positive bias circuit and the negative bias circuit as described above, the voltage of the electrolytic capacitor C92 is adjusted to the desired level as a way to avoid overshoot of the secondary transfer high voltage output voltage. The negative bias transformer drive NEG_CLK is stopped until the voltage level of the electrolytic capacitor C92 decreases to a voltage level corresponding to the negative bias output voltage, and the negative bias transformer drive NEG_CLK is stopped until the voltage of the electrolytic capacitor C92 decreases to a voltage level corresponding to the desired negative bias output voltage. Although there is a method for outputting the negative bias, the problem arises that the productivity of the device decreases because the start-up of the negative bias output is delayed.

Additionally, in order to prevent the productivity of the device from decreasing, it is possible to add a circuit such as a forced discharge circuit to accelerate the discharge of the electrolytic capacitor C92 at the timing of switching from positive bias to reverse bias. However, the problem arises that adding a circuit increases costs.

An object of the present invention is to provide a high-voltage power supply device and image forming device that can prevent delays in bias rise and overshoot after switching polarity of high-voltage output voltage without increasing costs due to addition of circuits such as forced discharge circuits. The goal is to provide equipment.

In order to achieve the above object, the high voltage power supply device of the present invention drives the first transformer (12c) with a first drive pulse (POS_CLK), and drives the first transformer (12c) with a first drive pulse (POS_CLK). a first driving means (Q21) connected to a first input terminal of the transformer (12c); and a first driving means (Q21) connected to the first and second output terminals of the first transformer (12c); A first rectifying and smoothing means (12d) that rectifies and smoothes the voltage converted by the transformer (12c), a second transformer (13c), and a second drive pulse (NEG_CLK) that rectifies and smoothes the voltage converted by the transformer (12c). and a second driving means (Q61) connected to the first input terminal of the second transformer (13c), and the first and second output terminals of the second transformer (13c). a second rectifying and smoothing means (13d) connected to and rectifying and smoothing the voltage converted by the second transformer (13c), the first rectifying and smoothing means (12d), and the second rectifying and smoothing means. an output voltage detection section (14) that detects the output voltage rectified and smoothed by the means (13d), and controls the output voltage to the target value based on the output voltage target value and a signal (Vsns) from the output voltage detection section (14). a control section (19) that generates a control signal (CTRL) for controlling the output voltage; and a control section (19) that receives the control signal (CTRL) outputted from the control section (19), In a high voltage power supply device (20) having a transformer input voltage control circuit (17) that generates a transformer input voltage to be supplied to a second input terminal of the first transformer (12c) and the second transformer (13c), the output It is characterized by comprising a voltage limit determination circuit (19a) that stops the drive pulse (POS_CLK) and the drive pulse (NEG_CLK) when the detection result by the voltage detection unit (14) deviates from the output setting voltage by a predetermined amount or more. do.

According to the present invention, when switching the polarity of the output voltage of the high voltage power supply, control is performed to stop the transformer drive CLK when the voltage exceeds the target voltage by a predetermined value or more. This makes it possible to prevent a delay in the rise of the bias after switching and an overshoot when switching the polarity of the high-voltage output voltage, without increasing the cost due to the addition of a circuit such as a forced discharge circuit.

FIG. 1 is an explanatory diagram of the configuration of an image forming apparatus in this embodiment. FIG. 2 is a circuit block diagram of a secondary transfer high-voltage power supply device in this embodiment. FIG. 7 is a diagram illustrating a sequence during a paper patch holding operation in this embodiment. FIG. 3 is a diagram showing a sequence of high voltage polarity switching control in this embodiment. It is a flowchart of high voltage polarity switching control in this example. 2 is a circuit block diagram of a secondary transfer high-voltage power supply device of Conventional Example 1. FIG. FIG. 2 is a circuit block diagram of a secondary transfer high-voltage power supply device of Conventional Example 2. FIG. 7 is a diagram showing a sequence of high-voltage polarity switching control in Conventional Example 2.

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

FIG. 1 is a schematic configuration diagram of an image forming apparatus 100 using an electrophotographic process in this embodiment. In FIG. 1, 1a to 1d are photosensitive drums, 2a to 2d are charging rollers, 3a to 3d are laser scanners, 4a to 4d are developing devices, 5 is an intermediate transfer belt, 6a to 6d are primary transfer rollers, 7 is a 2 This is the next transfer roller. Further, this apparatus is a color copying machine, and a to d represent yellow, magenta, cyan, and black, respectively, but this is not the case.

After the photosensitive drums 1a to 1d are uniformly charged by the charging rollers 2a to 2d, electrostatic latent images are formed on the photosensitive drums 1a to 1d by exposing them to light according to image signals by the laser scanners 3a to 3d. It is formed. Thereafter, the toner images are developed by the developing devices 4a to 4d, and the toner images on the photosensitive drums 1a to 1d are multiple-transferred onto the intermediate transfer belt 5 by the primary transfer rollers 6a to 6d. The toner image transferred to the intermediate transfer belt 5 is conveyed to the secondary transfer section 7. Further, the recording material P is conveyed from the paper cassette 10 to the secondary transfer section 7. Here, the recording material P is conveyed between the secondary transfer roller 7a and the secondary transfer opposing roller 7b. In the secondary transfer section 7, a voltage is applied to the secondary transfer roller 7a by the secondary transfer high voltage generation circuit 8, and the toner image on the intermediate transfer belt 5 is electrostatically transferred onto the recording material P. Thereafter, the toner image transferred to the recording material P is fixed by the fixing device 9 to obtain a color image.

Next, a secondary transfer high-voltage power supply device for applying voltage to the secondary transfer roller 7a will be described using FIG. 2. FIG. 2 is a circuit block diagram of the secondary transfer high voltage power supply device in this embodiment.

The secondary transfer high voltage generation circuit 18 operates when the secondary transfer high voltage control section 19 outputs a positive high voltage based on commands regarding the target voltage and operation timing output by the copying machine control section 16 that controls the entire copying machine 100. operates by outputting a high voltage control signal CTRL and a transformer drive signal POS_CLK. The copying machine control unit 16 manages the output voltage (Vout) of the secondary transfer high voltage generation circuit 18 to be applied to the secondary transfer roller 7a and its output timing. The secondary transfer high voltage control unit 19 performs digital feedback control on the secondary transfer high voltage generation circuit 18 so that the output voltage (Vout) of the secondary transfer high voltage generation circuit 18 becomes the target voltage given from the copying machine control unit 16. do. The secondary transfer high voltage generation circuit 18 generates a high voltage based on the signal input from the secondary transfer high voltage control section 19, and applies the voltage to the secondary transfer roller 7a. Further, the output voltage (Vout) and current (Iout) are respectively converted into detection signals (Vsns, Isns) and input to the secondary transfer high voltage control section 19. The output current detection signal (Isns) of the secondary transfer high voltage generation circuit 18 is input to the copying machine control section 16 after being subjected to digital filter processing such as averaging processing in the secondary transfer high voltage control section 19 .

Next, the secondary transfer high voltage generation circuit 18 will be explained in detail. The secondary transfer high voltage generation circuit 18 mainly includes a positive high voltage generation section 12 that generates a voltage (transfer bias) for transferring a toner image onto the recording material P, and a positive high voltage generation section 12 that mainly generates a voltage (transfer bias) for transferring a toner image onto the recording material P. A voltage transferred to the transfer belt 5 for cleaning (cleaning bias) and a toner patch formed on the intermediate transfer belt 5 for density detection are held on the intermediate transfer belt 5 when the patch passes through the secondary transfer roller 7a section ( The transformer input voltage control circuit 17 includes a negative high voltage generation section 13 that generates a voltage to prevent the patch from being transferred to the secondary transfer roller 7a, an output voltage detection section 14, an output current detection section 15, and a transformer input voltage control circuit 17.

The positive high voltage generation section 12 and the negative high voltage generation section 13 are connected to a transformer input voltage control circuit 17. The positive high voltage generation section 12, the negative high voltage generation section 13, and the transformer input voltage control circuit 17 are driven by a signal input from the secondary transfer high voltage control section 19.

The positive high voltage generating section 12 includes a transformer drive circuit 12b, a step-up transformer 12c, and a high voltage smoothing circuit 12d.

The transformer input voltage control circuit 17 generates a voltage Vin at a level whose output voltage (Vout) corresponds to a desired voltage value based on the output voltage control signal CTRL output from the secondary transfer high voltage control unit 19, and generates a positive high voltage. 12. The positive high voltage generating section 12 generates a positive high voltage by inputting the input voltage (Vin) generated by the transformer input voltage control circuit 17 and inputting the transformer drive signal POS_CLK. Here, the POS_CTRL signal is a PWM signal with a frequency of 50 kHz, and the POS_CLK signal is a fixed rectangular wave with a frequency of 25 kHz, and the duty ratio is normally 50%.

The transformer input voltage control circuit 17 will be explained. The transformer input voltage control circuit 17 is a series regulator circuit that controls the voltage input to the transformer using the CTRL signal. The CTRL signal has an amplitude of 3.4 V, is smoothed by a resistor R91 and a capacitor C91, and is input to the operational amplifier IC9 as a voltage signal of 0 to 3.4 V. The operational amplifier IC9 and the resistors R92 (10 kΩ) and R93 (2 kΩ) form a non-inverting amplifier circuit with a six-fold amplification degree, and the output voltage is 0 to 20.4 V. The output of operational amplifier IC9 is connected to the primary side of transformer 12c and C92 for voltage stabilization via transistor Q91 for current amplification. Therefore, when the duty ratio of the CTRL signal increases, the voltage input to the primary side of the step-up transformer 12c increases, and the AC voltage output from the step-up transformer 12c also increases.

The transformer drive circuit 12b will be explained. The transformer drive circuit 12b is a circuit for driving the transformer 12c by switching operation. The transformer drive circuit 12b includes a FET Q21 and a capacitor C21. The transformer drive circuit 12b is connected to the primary winding side of the step-up transformer 12c, and its end is opposite to the transformer input voltage control circuit 12a. In the transformer drive circuit 12b, the FETQ21 is operated by inputting the POS_CLK signal to the FETQ21, and the transformer 12c operates in flyback resonance as the capacitor C21 and the primary winding of the transformer 12c resonate.

The high voltage smoothing circuit 12d will be explained. The high voltage smoothing circuit 12d is a circuit for rectifying and smoothing the AC voltage boosted by the step-up transformer 12c. The AC voltage boosted by the step-up transformer 12c is rectified to a positive high voltage by the diode D31, and smoothed by the capacitor C31. Further, the high voltage smoothing circuit 12d has a bleeder resistor R31.

The negative high voltage generating section 13 has the same configuration except that the rectifying polarity of the high voltage smoothing circuit 13d is opposite to that of the positive high voltage generating section 12, so a description thereof will be omitted.

The high voltage generated by the positive high voltage generation section 12 is the voltage (Vba) at point a in the secondary transfer high voltage generation circuit 18 with point b as the reference voltage. The high voltage generated by the negative high voltage generation section 13 is the voltage at point b (Vgb) with the ground as a reference voltage. The output voltage (Vout) of the secondary transfer high voltage generation circuit 18 is a voltage at point c with the ground as a reference voltage, and its value is Vgb+Vba.

The output voltage detection unit 14 that detects the output voltage (Vout) of the secondary transfer high voltage generation circuit 18 will be described. The output voltage (Vout) is divided in the range of 0 to 3.4 V by the voltage dividing resistors R41 and R42 of the output voltage detection unit 14, and is input to the secondary transfer high voltage control unit 19 as an output voltage detection signal (Vsns). be done.

The output current detection unit 15 that detects the output current (Iout) flowing to point c of the secondary transfer high voltage generation circuit 18 will be described. The output current detection section 15 includes an operational amplifier IC3, a current detection resistor R81, and a reference voltage DC1. The current detection resistor R81 is installed on a path through which a current flows between the ground and point c, and connects the output terminal of the operational amplifier IC3 and the -input terminal by negative feedback. Therefore, the output voltage of the operational amplifier IC3 changes according to the current flowing through the current detection resistor R51 with reference to the reference voltage DC1 inputted to the + input terminal. This voltage is input to the secondary transfer high voltage control section 11 as an output current detection signal (Isns).

Next, the secondary transfer high voltage control section 19 will be explained in detail. The secondary transfer high voltage control unit 19 performs digital feedback control so that the output voltage (Vout) of the secondary transfer high voltage generation circuit 18 becomes the target voltage. A target voltage signal and an operation timing signal are input to the secondary transfer high voltage control section 19 from the copying machine control section 16 via serial communication. The operation timing signal is a timing signal related to ON/OFF of the voltage output (Vout) and switching of the output voltage (Vout). Further, the secondary transfer high voltage control unit 19 receives an output voltage detection signal (Vsns) and an output current detection signal (Isns) from the secondary transfer high voltage generation circuit 18 . The secondary transfer high voltage control unit 19 A/D converts the output voltage detection signal (Vsns) and the output current detection signal (Isns), and converts the A/D conversion results into corresponding output voltage values and output current values. After conversion, average processing is performed. As a result, an output voltage value (Vval) and an output current value (Ival) are obtained. The secondary transfer high voltage control section 19 performs feedback calculation based on the deviation between the target voltage input from the copying machine control section 16 and the output voltage value (Vval), and controls the ON time or duty ratio of the CTRL signal. This controls the output voltage (Vout) of the secondary transfer high voltage generation circuit 8. Further, the output voltage value and the output current value (Ival) are input to the copying machine control section 16 through serial communication.

Next, the sequence during the sheet spacing patch holding operation in this embodiment will be explained using FIG. 3. In an electrophotographic image forming apparatus, in order to adjust the toner density to the optimum value when forming an image on a recording material, a toner patch is formed under specified conditions on an intermediate transfer belt, and the density detection result is read by a patch detection sensor. There are some that adjust the toner density inside the developing device.

In some cases, the toner patch is formed at a position on the intermediate transfer belt corresponding to between the recording materials (between the sheets) when images are formed on multiple recording materials, and the toner patch is formed on the secondary roller 7a. In order to prevent the image from being transferred to the secondary transfer roller 7a when passing through the position, as shown in FIG. Vout is switched from positive bias to negative bias, and switched from negative bias to positive bias when moving from the inter-paper area to the image forming area.

When the recording material P1 is being conveyed to the position of the secondary transfer roller 7a, the output voltage (Vout) is set to 3000 V in order to transfer the image forming toner image formed on the intermediate transfer belt 5 to the recording material P1. This voltage value is supplied to the secondary transfer roller 7a.

When the paper gap is at the position of the secondary transfer roller 7a, in order to hold the toner image for patch formation formed on the intermediate transfer belt 5 on the intermediate transfer belt 5 (to prevent it from being transferred to the secondary transfer roller 7a). b) The output voltage (Vout) is set to -600V, and this voltage value is supplied to the secondary transfer roller 7a.

When the recording material P2 is being conveyed to the position of the secondary transfer roller 7a, the output voltage (Vout) is set to 3000 V in order to transfer the image forming toner image formed on the intermediate transfer belt 5 to the recording material P2. This voltage value is supplied to the secondary transfer roller 7a.

It is necessary to raise the transfer bias target voltage (3000 V) corresponding to the next recording material P2 before the recording material P2 is conveyed to the secondary transfer roller 7a.

Here, assuming that the paper interval time is 130 ms and the patch forming time is 50 ms, the secondary transfer high voltage generation circuit 18 needs to complete the falling and rising of the output voltage (Vout) within 80 ms. For example, it is necessary to complete switching of the output voltage (Vout) from positive bias to negative bias in 50 ms, and from negative bias to positive bias in 30 ms.

Next, the control sequence of the secondary transfer high voltage control section 19 when forming the inter-sheet patch will be explained using FIG. 4. FIG. 4 is a diagram showing a sequence when the high-voltage polarity switching control in this embodiment is used when forming an inter-paper patch.

In FIG. 4, first, the secondary transfer high voltage control section 19 outputs a POS_CLK signal at a frequency of 25 kHz and a duty ratio of 50% to drive the step-up transformer 12c. Then, the duty ratio of the CTRL signal is PID-controlled by the secondary transfer high voltage control section 19 based on the deviation between the output voltage (Vout) detected by the output voltage detection section 14 and the first target voltage (3000 V). As a result, the output voltage (Vout) can be feedback-controlled, and the first target voltage (3000 V) can be output from point c of the secondary transfer high voltage generation circuit 18.

Next, in order to form a paper patch, the secondary transfer high voltage control unit 19 turns off the POS_CLK signal, turns on the NEG_CLK signal, and sets the output value to CTRL: 3000 V when the toner image has been transferred to the recording material P1. The secondary transfer high voltage control unit 11 performs PID control on the duty ratio of the CTRL signal based on the deviation between the output voltage (Vout) detected by the output voltage detection unit 14 and the target voltage (-600V). Thereby, the output voltage (Vout) can be feedback-controlled and the target voltage (-600V) can be output from point c of the secondary transfer high voltage generation circuit 18.

When switching the output control voltage from the target voltage (3000 V) during image formation to the target voltage (-600 V) for holding the inter-paper patch on the intermediate transfer belt, the secondary transfer high voltage control unit 19 uses the voltage shown in FIG. The output state (ON/OFF) of the NEG_CLK signal is controlled based on the determination result of the limit determination section 19a.

As mentioned above, in the control method of Conventional Example 2, the input voltage (Vin) level to the primary windings of the high voltage transformers 12c and 13c, which corresponds to outputting the desired negative bias after polarity switching, that is, the electrolytic capacitor C92 If the voltage level of the electrolytic capacitor C92 is lower than the voltage level of the electrolytic capacitor C92 corresponding to outputting the desired positive bias before the polarity switching, an excessive voltage is supplied to the high voltage transformer 13c during the period T2 after the polarity switching, causing a secondary Overshoot occurs in the transfer high voltage output. Therefore, in order to prevent overshoot, it is necessary to take measures such as turning off NEG_CLK until Vin drops to a desired value, or adding a discharge circuit to speed up the time for lowering Vin.

Therefore, in the present invention, a limit is set on the output voltage value of the high voltage power supply, and control is performed to stop the transformer drive CLK when the output voltage deviates from the target voltage by a predetermined value or more when switching the polarity of the output voltage. As a result, even when the voltage level input to the negative bias transformer is higher than the voltage equivalent to outputting negative bias, a limiter is set on the output voltage value, and when the limit value is exceeded, the transformer drive CLK is turned OFF to output the output voltage. It becomes possible to suppress voltage overshoot.

In FIG. 4, the solid line waveform of the secondary transfer high voltage output Vout in period T2 immediately after switching the target voltage from 3000V to -600V is when the method of this embodiment is used, and the dotted line is when the conventional method is used ( NEG_CLK signal output is held ON). In this way, by using this embodiment, it is possible to start up while suppressing the overshoot of the negative bias high voltage output (Vout).

In this embodiment, the negative bias output voltage limit value is set to a target value of -100V, and when the voltage exceeds -700V, the NEG_CLK signal output is turned off.

After the output voltage (Vout) of the secondary transfer high voltage generation circuit 18 converges to the negative bias target voltage (-600 V), the toner patch formed on the intermediate transfer belt remains unchanged even after passing the position of the secondary transfer roller 7a. It is held on an intermediate transfer belt.

Next, in order to form a toner image on the recording material P2, the secondary transfer high voltage control unit 19 turns on the POS_CLK signal, turns off the NEG_CLK signal, and changes the output value setting from POS_CTRL: -600V to 3000V when the paper interval is finished. The secondary transfer high voltage control unit 19 performs PID control on the duty ratio of the POS_CTRL signal based on the deviation between the output voltage (Vout) detected by the output voltage detection unit 14 and the target voltage (3000V). As a result, the output voltage (Vout) can be feedback-controlled, and the target voltage (3000 V) can be output from point c of the secondary transfer high voltage generation circuit 18.

Next, in the operation of the copying machine, FIG. I will explain. 5(a) shows the operation of the entire copying machine 100, FIG. 5(b) shows the operation of the secondary transfer high-voltage control unit 19 during a print job, and FIG. 5(c) shows the operation of the paper gap patch on the intermediate transfer belt. The following description focuses on the operation of the secondary transfer high voltage control section 19 when the negative bias output operation is executed.

First, the operation of the copying machine 100 of this embodiment will be explained using FIG. 5(a). First, when the main power switch (not shown) of the copying machine 100 is operated by the user and the power is turned on, the copying machine control unit 16 executes initialization processing (s11) and then enters a standby state, which is a standby state for image forming processing. The process moves to (s12). Thereafter, the process waits (s13) until a print job instructing image formation is received from a user interface (not shown) of the copying machine 100 or a personal computer (not shown) connected via a network system. When the copying machine 100 receives a print job, the copying machine 100 performs the print job, and after the print job is completed, it shifts to a standby state (s12), and waits until it receives a print job again (s13).

The control flow during a print job will be explained using FIG. 5(b). At this time, feedback control of the output voltage (Vout) of the secondary transfer high voltage generation circuit 18 is performed by the secondary transfer high voltage control section 19, but the timing to start output and the target voltage value are given by the copying machine control section 16. . When a print job is started, the secondary transfer high voltage generation circuit 18 outputs a transfer bias for transferring the toner image on the intermediate transfer belt 5 to the recording material P by driving the positive high voltage generation section 12. (s21). Thereafter, the copying machine control unit 16 determines whether or not it is necessary to perform a negative bias output operation to hold the paper patch on the intermediate transfer belt (s22). The condition for determining whether it is necessary to perform the paper patch retention bias is the number of continuous image formation sheets. The number of sheets is set to 50 so that the temperature and humidity within the copying machine 100 do not change excessively. As a result of the condition judgment (s22), if it is necessary to execute the paper patch retention bias (s22: Yes), the paper patch retention bias is executed (s23), and if there is no need to execute the paper patch retention bias ( s22: No) Proceed to the next process (S24). At the end, it is determined whether all image formation included in the print job has been completed (S24), and if it has not been completed (s24: No), the image formation process (s21) is executed again, and if it has been completed ( s24: Yes), the print job is finished.

The paper patch holding bias output (s23) shown in FIG. 5(b) will be explained using FIG. 5(c). When paper patch retention bias output is started, the copying machine control unit 16 first sends a signal indicating the secondary transfer negative bias high voltage output limiter value (target value -100V) to the secondary transfer high voltage control unit 19, and the secondary transfer starts. A limiter value is set in the voltage limit determination section in the high voltage control section 19 (s31), and when the toner image on the intermediate transfer belt 5 has been transferred to the recording material P, the CTRL signal level is switched from 3000V to -600V. , POS_CLK is turned OFF and NEG_CLK is turned ON (s32).

Next, it is determined whether the secondary transfer high voltage output exceeds the limit value (-700V = -600V - 100V) (s33), and if the secondary transfer high voltage output exceeds the limit value, NEG_CLK is turned OFF ( s34), and if the limit value is not exceeded, NEG_CLK is kept ON (s35).

If T1 has not elapsed since the output polarity switching timing, the processes from s33 to s35 are repeated, and when T1 has elapsed, the process moves to the next step of setting the two-turn high voltage output setting value (s36).

Next, when the holding operation of the toner patch on the intermediate transfer belt 5 is finished, the CTRL signal level is switched from -600V to 3000V, POS_CLK is turned ON, NEG_CLK is turned OFF (s37), and the paper patch holding bias output is ended. do.

As described above, according to the present invention, when switching the polarity of the output voltage of the high-voltage power supply, control is performed to stop the transformer drive CLK when the target voltage exceeds a predetermined value.

As a result, even if the input voltage level to the primary winding of the high-voltage transformer that corresponds to outputting the bias after polarity switching is lower than the voltage level equivalent to outputting bias before polarity switching, the output voltage value will not change. A limiter is provided to control the transformer drive CLK to be turned off when the output voltage value exceeds the limit value, making it possible to prevent delays in bias rise and overshoot after switching when switching the polarity of the high voltage output voltage. Become.

Furthermore, it is possible to start high voltage output in a short time without increasing costs due to the addition of a forced discharge circuit or the like.

In this embodiment, as an example of high-voltage output switching control, control for holding the paper patch of secondary transfer high voltage on the intermediate transfer belt is described, but other output voltage switching control of secondary transfer high voltage, charging roller, etc. It is also possible to use this control when switching the output voltage of a high-voltage power supply device that supplies high voltage to the developing device.

100 Image forming devices 1a to 1d Photosensitive drums 2a to 2d Charging rollers 3a to 3d Laser scanners 4a to 4d Developing device 5 Intermediate transfer belt 6a to 6d Primary transfer roller 7 Secondary transfer roller

Claims (4)

a first transformer; a first driving means for driving the first transformer with a first driving pulse and connected to a first input terminal of the first transformer; a first rectifying and smoothing means that is connected to the first and second output terminals and rectifies and smoothes the voltage converted by the first transformer;
a second transformer; a second driving means for driving the second transformer with a second drive pulse and connected to a first input terminal of the second transformer; a second rectifying and smoothing means that is connected to the first and second output terminals and rectifies and smoothes the voltage converted by the second transformer;
an output voltage detection section that detects the output voltage rectified and smoothed by the first rectification and smoothing means and the second rectification and smoothing means;
a control unit that generates a control signal for controlling the output voltage to the target value based on the output voltage target value and the signal from the output voltage detection unit;
Inputting the control signal output from the control unit, generating a transformer input voltage to be supplied to second input terminals of the first transformer and the second transformer in order to control the output voltage to a target value. In a high voltage power supply device having a transformer input voltage control circuit,
A high-voltage power supply device comprising a voltage limit determination circuit that stops a drive pulse (POS_CLK) and a drive pulse (NEG_CLK) when a detection result by an output voltage detection section deviates from an output setting voltage by a predetermined amount or more. The high voltage power supply device according to claim 1,
A high-voltage power supply device characterized in that a limiter value of the voltage limiter determination circuit is switched at a timing when a target value of an output voltage is changed. An image forming apparatus comprising the high voltage power supply device according to claim 1 or 2. The image forming apparatus according to claim 3,
The image forming apparatus is characterized in that the high voltage power supply device outputs a high voltage for the secondary transfer roller of the image forming apparatus.