Power conversion device and image forming device

Abstract

To provide a power converter and an image-forming apparatus that can prevent ringing when switching is stopped, and in turn, prevent formation of an abnormal image.SOLUTION: A power converter of an embodiment comprises: a power conversion unit that controls a switching element based on a switching pulse signal, converts DC power to AC power, and outputs it to a power supply target; a storage unit that stores the AC current phase difference; a voltage detection unit that detects an AC voltage effective value; a current detection unit that detects an AC current effective value; and a control unit that stops output of the switching pulse signal at a timing when AC current becomes zero based on the current phase difference, AC voltage effective value, and AC current effective value.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a power conversion device and an image forming apparatus. [Background technology]

[0002] Conventionally, in a switching power supply device, a configuration has been disclosed in which a capacitor and a resistor are mounted in parallel with a filter L in order to quickly converge ringing when switching is stopped. Summary of the Invention [Problem to be solved by the invention]

[0003] However, from the viewpoint of preventing abnormal image formation (preventing abnormal discharge), the problem of the long time it takes to converge has not been solved.

[0004] The present invention has been made in consideration of the above, and aims to provide a power conversion device and an image forming device that can prevent ringing when switching is stopped, and ultimately prevent the formation of abnormal images. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems and achieve the object, the power conversion device of the embodiment includes a power conversion unit that controls switching elements based on switching pulse signals, converts DC power to AC power, and outputs the AC power to a power supply target, a memory unit that stores an AC current phase difference, a voltage detection unit that detects an AC voltage effective value, a current detection unit that detects the AC current effective value, and a control unit that stops output of the switching pulse signal at a timing when the AC current becomes zero based on the current phase difference, the AC voltage effective value, and the AC current effective value. [Effects of the Invention]

[0006] According to the present invention, it is possible to prevent ringing when switching is stopped, and as a result, it is possible to prevent the formation of abnormal images. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a partial cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing the general configuration of the high-voltage power supply device during shipping inspection. [Figure 3] FIG. 3 is a diagram illustrating the calculation of the AC current phase difference θ1. [Figure 4] FIG. 4 is a diagram illustrating the relationship between the AC output voltage, the AC output current, and the AC current phase difference θ1. [Figure 5] FIG. 5 is a diagram illustrating the calculation of the effective current. [Figure 6] FIG. 6 is a block diagram showing the general configuration of the high-voltage power supply device during normal operation. [Figure 7] FIG. 7 is a timing chart of the embodiment. [Figure 8] FIG. 8 is a timing chart of a conventional example. [Figure 9] FIG. 9 is a diagram illustrating the calculation of the AC current phase difference θ2. DETAILED DESCRIPTION OF THE INVENTION

[0008] Next, an embodiment will be described with reference to the drawings. FIG. 1 is a partial cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment. As shown in FIG. 1, the image forming apparatus 1 is configured as a digital multifunction peripheral.

[0009] That is, the image forming device 1 has a copy function, a printer function, a facsimile function, etc. The application switching key on the operation unit allows the user to switch between the copy function, printer function, and facsimile function in sequence, and when the copy function is selected, the device enters copy mode, when the printer function is selected, the device enters printer mode, and when the facsimile mode is selected, the device enters facsimile mode.

[0010] The flow of image formation in the image forming apparatus will be briefly explained using FIG. 1, taking the copy mode as an example.

[0011] In copy mode, a stack of documents is fed in order by the ADF 2 to the image reading device 3, and the image information is read by the image reading device. The read image information is then converted into optical information by the writing unit 4 as writing means via image processing means, and the photosensitive drum 6 is uniformly charged by the high-voltage power supply 10 as a power conversion device, and is then exposed to the optical information from the writing unit 4 to form an electrostatic latent image. This electrostatic latent image on the photosensitive drum 6 is developed into a toner image by the developing device 7. This toner image is transferred to a transfer paper by the transport belt 8, and the toner image is fixed on the transfer paper by the fixing device 9 before being discharged.

[0012] FIG. 2 is a block diagram showing the general configuration of the high-voltage power supply device during shipping inspection. The high-voltage power supply device 10 includes a drive unit 21, a smoothing circuit 22, a transformer 23, a voltage detection unit 24, a current detection unit 25, a direct current (DC) generation circuit 26, and a control CPU 27.

[0013] The drive unit 21 has an inverter circuit, and converts DC power into square-wave AC power using a switching element based on a switching pulse signal SP input from the control CPU 27 , and outputs the AC power to the smoothing circuit 22 . Here, as the switching element, a MOS transistor, an IGBT (insulated gate bipolar transistor), a SiC transistor, a GaN transistor, or the like is used.

[0014] The smoothing circuit 22 smoothes the rectangular wave AC power, converts it into AC power with a waveform closer to an analog waveform, and outputs it to the transformer 23 . The transformer 23 converts the voltage of the AC power input to the primary coil and applies it to the photosensitive drum 6 via the secondary coil.

[0015] The voltage detector 24 detects the AC output voltage effective value V1 of the transformer 23 and outputs it to the control CPU 27. The current detector 25 detects an effective value I1 of the AC output current flowing through the secondary coil of the transformer 23 and outputs the detected value to the control CPU 27.

[0016] A direct current (DC) generating circuit 26 generates a DC voltage to be superimposed on the output voltage of the secondary coil of the transformer 23 . The control CPU 27 includes an effective current calculation unit 27A that calculates an effective current based on an input AC frequency command, a memory 27B that stores various information, and a pulse pattern control unit 27C that generates and outputs a switching pulse signal SP. Here, the memory unit 27B functions as a storage unit.

[0017] In addition, the inspection jig JG during shipping inspection has the function of detecting the AC voltage ACV applied to the photosensitive drum 6, detecting the AC current ACI supplied to the photosensitive drum 6, calculating the AC current phase difference θ1, and outputting it to the control CPU 27.

[0018] Next, the operation during shipping inspection will be described. The control CPU 27 of the high-voltage power supply device 10 generates a switching pulse signal SP for the pulse pattern control unit 27C to control the drive unit 21 based on an AC frequency command from the control unit (see Figure ##) of the image forming apparatus 1, and outputs it to the drive unit 21.

[0019] Based on a switching pulse signal SP input from the control CPU 27 , the drive unit 21 converts DC power into square-wave AC power using an inverter circuit and outputs the AC power to the smoothing circuit 22 .

[0020] The smoothing circuit 22 smoothes the rectangular wave AC power, converts it into AC power with a waveform closer to an analog waveform, and outputs it to the transformer 23 . The transformer 23 converts the voltage of the AC power input to the primary coil and applies it to the photosensitive drum 6 via the secondary coil.

[0021] As a result, the inspection jig JG detects the AC voltage ACV applied to the photosensitive drum 6, detects the AC current ACI supplied to the photosensitive drum 6, calculates the AC current phase difference θ1, and outputs it to the effective current calculation unit 27A of the control CPU 27.

[0022] FIG. 3 is a diagram illustrating the calculation of the AC current phase difference θ1. FIG. 4 is a diagram illustrating the relationship between the AC output voltage, the AC output current, and the AC current phase difference θ1.

[0023] More specifically, the relationship between the apparent power S, active power P, reactive power Q, and AC current phase difference θ1 of AC power is as shown in FIG. 3, and the inspection jig JG calculates the apparent power S and active power P based on the instantaneous value of the applied AC voltage ACV and the instantaneous value of the supplied AC current ACI, and calculates the AC current phase difference based on the following equation. θ1=cos-1(P / S)

[0024] As shown in FIG. 4, this AC current phase difference θ1 is expressed as the difference between the zero cross point of the phase of the output voltage and the zero cross point of the phase of the output current. In parallel with this, the voltage detection unit 24 of the high-voltage power supply device 10 detects the AC output voltage effective value V1 of the transformer 23 and outputs it to the active current calculation unit 27A of the control CPU 27.

[0025] Further, the current detection unit 25 detects an effective value I1 of the AC output current flowing through the secondary coil of the transformer 23 and outputs the detected value to an effective current calculation unit 27A of the control CPU 27. As a result, the active current calculation unit 27A calculates the active current Ir based on the AC output current effective value I1 input from the current detection unit 25 corresponding to the measurement timing of the AC current phase difference θ1, and stores the calculated active current Ir in the memory 27B.

[0026] FIG. 5 is a diagram illustrating the calculation of the effective current. As shown in FIG. 5, the AC current phase difference θ1 is expressed by the following equation. θ1=cos -1 (Ir / I1) Therefore, the effective current Ir is expressed by the following equation: Ir=I1·cosθ1

[0027] FIG. 6 is a block diagram showing the general configuration of the high-voltage power supply device during normal operation. In FIG. 6, the same parts as those in FIG. 1 are denoted by the same reference numerals. 6 differs from FIG. 1 in that the high-voltage power supply device 10 includes a stop timing calculation unit 27D in which the control CPU 27 calculates the stop timing of the switching pulse signal SP based on the AC frequency command ACFC, the stop command STP, and the phase correction mode command PA input from the control unit of the image forming apparatus 1, generates the stop command STP, and outputs it to the pulse pattern control unit 27C.

[0028] Another difference from Figure 1 is that the image forming apparatus 1 includes a control unit 1A that controls the high-voltage power supply device 10 and a travel distance monitoring unit 1B that monitors the travel distance (driving time) of the photosensitive drum 6 and notifies the control unit 1A.

[0029] In this case, the photosensitive drum 6 can be modeled using capacitors 6A and 6B connected in series between the high-potential side power supply (output of the high-voltage power supply device) and the low-potential side power supply (ground), and a resistor 6C connected in parallel with the capacitor 6A.

[0030] Furthermore, the capacitors 6A and 6B can be regarded as variable capacitance capacitors whose capacitance changes as the cumulative travel distance (cumulative driving time) of the photosensitive drum 6 increases. As the capacitance of capacitors 6A and 6B changes, the AC current phase difference θ2 (→θ2=θ1 at the time of shipment from the factory) changes.

[0031] Next, the normal operation of the image forming apparatus will be described. In this case, it is assumed that the AC current phase difference θ2 (→θ2=θ1 at the time of shipment from the factory) at that time point is stored in the memory 27B.

[0032] When applying an AC voltage to the photosensitive drum 6, the control unit 1A outputs an AC frequency command ACFC to the control CPU 27 of the high-voltage power supply device 10.

[0033] As a result, the control CPU 27 of the high-voltage power supply device 10 generates a switching pulse signal SP for the pulse pattern control unit 27C to control the drive unit 21 based on the AC frequency command ACFC from the control unit of the image forming apparatus 1, and outputs it to the drive unit 21.

[0034] Based on a switching pulse signal SP input from the control CPU 27 , the drive unit 21 converts DC power into square-wave AC power using an inverter circuit and outputs the AC power to the smoothing circuit 22 .

[0035] The smoothing circuit 22 smoothes the rectangular wave AC power, converts it into AC power with a waveform closer to an analog waveform, and outputs it to the transformer 23 . The transformer 23 converts the voltage of the AC power input to the primary coil and applies it to the photosensitive drum 6 via the secondary coil, thereby forming an image.

[0036] Then, based on the monitoring result of the travel distance monitoring section 1B, the control section 1A outputs a stop command STP to the stop timing calculation section 27D of the control CPU 27 when it is time to end image formation.

[0037] As a result, the stop timing calculation unit 27D calculates the stop timing based on the AC current phase difference θ2 read from the memory 27B, the AC frequency command input from the control unit 1A, the AC output voltage effective value V1 input from the voltage detection unit, and the AC output current effective value I2 input from the current detection unit, and outputs a stop command STP to the pulse pattern control unit. As a result, the pulse pattern control unit stops outputting the switching pulse signal SP.

[0038] Next, the operation when the output of the switching pulse signal SP is stopped will be described in more detail. FIG. 7 is a timing chart of the embodiment. In the initial state, the high-voltage power supply device 10 is in steady operation, and the pulse pattern control unit 27C of the control CPU 27 outputs the switching pulse signal SP.

[0039] When a stop command STP is input from the control unit 1A of the image forming apparatus 1 at time t1, the stop timing calculation unit 27D of the control CPU 27 reads out the AC current phase difference θ2 stored in the memory 27B and calculates, based on the AC voltage phase managed inside the control CPU 27, a phase difference ΔP corresponding to the difference between the zero-cross point of the AC voltage phase managed inside the control CPU 27 and the zero-cross point of the output current.

[0040] In more detail, Phase difference ΔP=360°-θ2 Calculate.

[0041] Then, at time t2, which is the timing when the phase difference ΔP has elapsed from the zero-cross point of the AC voltage phase managed inside the control CPU 27, the stop timing calculation unit 27D controls the pulse pattern control unit to stop the output of the switching pulse signal SP.

[0042] Here, time t2 is the timing when the AC current becomes zero, and ideally, the timing when the phase of the AC current becomes 0°. Effectively, time t2 should be the timing when the phase of the AC current is within a predetermined phase range near 0°, and the predetermined phase range should be ±30°.

[0043] FIG. 8 is a timing chart of a conventional example. As shown in the conventional example in FIG. 8, when the output of the switching pulse signal SP is stopped at time t11, which is a timing when the AC output current is not at the zero-cross point, the output of the switching pulse signal SP is stopped while the AC output current is flowing. As a result, ringing occurs after time t11, as shown in FIG. 8, due to the remaining energy in the inductive component or capacitive component corresponding to the smoothing circuit or the photosensitive drum.

[0044] 8, the AC output voltage exceeds the discharge voltage, causing abnormal discharge, resulting in abnormal image formation, etc. Furthermore, the abnormal discharge can damage mechanical parts such as the photosensitive drum 6, shortening their lifespan and causing other problems.

[0045] In contrast to this, according to this embodiment, as shown in FIG. 7, the timing when the phase of the AC output current is within a predetermined phase range near 0° is set as the timing to stop outputting the switching pulse signal SP.

[0046] That is, the output of the switching pulse signal SP is stopped at a timing when the AC output current is not flowing or at a timing when it can be considered that the AC output current is not flowing (=time t2 or a timing close to time t2).

[0047] Therefore, the AC output voltage immediately becomes 0 and remains in that state, and no ringing occurs, as shown in FIG. Here, the predetermined phase range is a range of ±30° with respect to the phase of the AC output current = 0°.

[0048] Within this range, the amount of residual energy in the inductive or capacitive component corresponding to the smoothing circuit or the photosensitive drum can be suppressed to a level that does not cause ringing.

[0049] That is, in the high-voltage power supply device 10, when the output of AC power is stopped, ringing of the AC output voltage and AC output current can be prevented. This in turn makes it possible to suppress generation of abnormal images in the image forming apparatus 1 and to suppress shortening of the lifespan of mechanical parts such as photoconductors.

[0050] Next, the operation in the phase correction mode will be described. Based on the output of the mileage monitoring unit, the control unit 1A of the image forming device 1 outputs a transition command PA to the stop timing calculation unit 27D to transition to the phase correction mode when the accumulated mileage since the previous phase correction mode (the first time is the factory shipping inspection) exceeds a predetermined value.

[0051] As a result, the stop timing calculation unit 27D calculates a new AC current phase difference θ2 in order to update the AC current phase difference θ2 stored in the memory 27B.

[0052] FIG. 9 is a diagram illustrating the calculation of the AC current phase difference θ2. At this time, the voltage detection unit 24 of the high-voltage power supply device 10 detects the AC output voltage effective value V1 of the transformer 23 and outputs it to the active current calculation unit 27A of the control CPU 27.

[0053] Further, the current detection unit 25 detects an effective value I2 of the AC output current flowing through the secondary coil of the transformer 23 and outputs the detected value to the stop timing calculation unit 27D of the control CPU 27. As a result, the stop timing calculation unit 27D calculates the active current Ir based on the AC output current effective value I2 input from the current detection unit 25.

[0054] Next, the stop timing calculation unit 27D calculates a new AC current phase difference θ2 based on the AC output current effective value I2 and the calculated active current Ir using the following equation. θ2=cos -1 (Ir / I2)

[0055] Then, the control CPU 27 records the calculated new AC current phase difference θ2 in the memory 27B for updating. Therefore, the AC current phase difference θ2 can always be kept optimal, and the stop timing calculation unit 27D always stops the output of the switching pulse signal SP using the latest AC current phase difference θ2.

[0056] As a result, it is possible to more reliably maintain a state in which the output of the switching pulse signal SP can be stopped at a timing when no AC output current is flowing. A state in which no ringing occurs in the AC output voltage waveform and the AC output current waveform can be maintained for a long period of time. Therefore, according to the above embodiment, it is possible to prevent ringing in the AC output voltage and AC output current when the output of the switching power supply device is stopped, and to suppress the formation of abnormal images and the shortening of the lifespan of mechanical parts such as photosensitive drums.

[0057] In the above explanation, we have described a case where the transition to phase correction mode is based on the photosensitive drum volume calculated travel distance, but since the capacitance characteristics of the photosensitive drum also change depending on the temperature and humidity, it is also possible to configure the system to transition to phase correction mode when the temperature exceeds a predetermined threshold temperature or when the humidity exceeds a predetermined threshold humidity.

[0058] More specifically, as shown in FIG. 6, a temperature sensor 1C serving as a temperature detection unit is provided near a photosensitive drum 6 to which power is supplied. Then, the temperature sensor 1C outputs a temperature detection signal TP to the control unit 1A to detect the ambient temperature of the photosensitive drum 6. When the temperature exceeds a predetermined threshold temperature, the control unit 1A may update the AC current phase difference θ2 because the error in the AC current phase difference θ2 increases.

[0059] As shown in FIG. 6, a humidity sensor 1D serving as a humidity detection unit is provided near the photosensitive drum 6 to which power is supplied. Then, the humidity sensor 1D outputs a humidity detection signal HM to the control unit 1A to detect the ambient humidity of the photosensitive drum 6. When the humidity exceeds a predetermined threshold humidity, the control unit 1A may update the AC current phase difference θ2 because the error in the AC current phase difference θ2 increases.

[0060] In the above description, the high-voltage power supply device 10 updates the AC current phase difference θ2 when the control unit 1A of the image forming apparatus 1 instructs it to transition to the phase update mode. However, the AC current phase difference θ2 may be calculated at a predetermined check timing, and the AC current phase difference θ2 may be updated when the amount of change in the AC current phase difference θ2 since the previous update exceeds a predetermined threshold change amount.

[0061] Furthermore, although the above explanation has been given for the case where a photosensitive drum is used as a load, it can be similarly applied to any configuration (load having a capacitive component) in which ringing occurs when the switching operation of the switching power supply device is stopped. The image forming apparatus of this embodiment is equipped with a control device such as a CPU, a storage device such as a ROM (Read Only Memory) or RAM, an external storage device such as an HDD, a display device such as a display device, and an input device such as an operation panel, and has a hardware configuration that utilizes a normal computer.

[0062] In the above embodiment, the image forming apparatus of the present invention has been described as being applied to a multifunction peripheral having at least two of the functions of a copy function, a printer function, a scanner function, and a facsimile function, but the present invention can be applied to any image forming apparatus such as a copier, printer, scanner device, or facsimile device. [Explanation of symbols]

[0063] 1. Image forming device 1A Control section 1B Odometer monitoring unit 1C temperature sensor 1D Humidity Sensor 2 ADF 3. Image reader 4 Write Unit 6 Photosensitive drum 6A capacitor 6C resistor 7. Developing device 8 conveyor belt 9 Fixing device 10 High-voltage power supply (power conversion device) 21 Drive section 22 Smoothing circuit 23 Transformer 24 Voltage detection section 25 Current detection section 26 Generator Circuit 27 Control CPU 27A active current calculation unit 27B memory 27C Pulse pattern control section 27D Stop timing calculation unit ACI supply alternating current ACV Applied AC voltage HM Humidity detection signal Ir effective current I1 effective value I2 AC output current effective value JG inspection jig PA Transition Order SP Switching pulse signal SP Switching pulse signal STP stop command TP Temperature detection signal V1 AC output voltage effective value ΔP phase difference θ1 AC current phase difference (initial value) θ2 AC current phase difference [Prior art documents] [Patent documents]

[0064] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-211877

Claims

1. a power conversion unit that controls a switching element based on a switching pulse signal, converts DC power into AC power, and outputs the AC power to a power supply target; a storage unit that stores the AC current phase difference; a voltage detection unit that detects an effective AC voltage value; a current detection unit that detects an effective value of an AC current; a control unit that stops output of the switching pulse signal at a timing when the AC current becomes zero based on the AC current phase difference, the AC voltage effective value, and the AC current effective value; A power conversion device comprising:

2. The timing at which the AC current becomes zero is the timing at which the phase of the AC current is within a predetermined phase range near 0°. The power conversion device according to claim 1 .

3. The predetermined phase range is set to ±30°. The power conversion device according to claim 2 .

4. the power conversion unit is connected to a DC power supply and has a drive unit that drives the switching element based on the switching pulse signal; a smoothing circuit that smoothes the output of the drive unit; a transformer that converts the voltage output from the smoothing circuit and outputs the converted voltage; The power conversion device according to claim 1 , comprising:

5. an updating unit that, when an update instruction is input, calculates an effective current value based on the AC effective current value, calculates an AC phase difference based on the AC effective current value and the effective current value, and updates the AC phase difference in the storage unit; The power conversion device according to claim 1 .

6. a temperature detection unit that detects a temperature of the object to be supplied with power or an ambient temperature of the object to be supplied with power, the update unit updates the AC current phase difference when the detected temperature exceeds a predetermined threshold temperature. The power conversion device according to claim 5 .

7. a humidity detection unit that detects the humidity around the target to be supplied with power; the updating unit updates the AC current phase difference when the detected humidity exceeds a predetermined threshold humidity. The power conversion device according to claim 5 .

8. a calculation unit that calculates an effective current value based on the AC effective current value, and calculates an AC phase difference based on the AC effective current value and the effective current value; an updating unit that updates the AC current phase difference in the storage unit with the AC current phase difference calculated by the calculating unit when a change in the AC current phase difference from a previous update exceeds a predetermined threshold change amount; The power conversion device according to claim 1 .

9. The power conversion device according to any one of claims 1 to 8; a photosensitive drum as the power supply target; An image forming apparatus comprising:

10. The power conversion device according to claim 5 ; a photosensitive drum as the power supply target; a travel distance monitoring unit that calculates a travel distance of the photosensitive drum and monitors the travel distance; a control unit that outputs the update instruction when the mileage exceeds a predetermined mileage; An image forming apparatus comprising:

Images