JP5207643B2 - Image forming apparatus, voltage power supply apparatus, and control method thereof - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic process and a method thereof. In particular, the present invention relates to a voltage power supply apparatus that outputs a voltage used in an image forming apparatus and a method thereof.

  An electrophotographic image forming apparatus needs to generate a transfer voltage used when transferring an image to a recording material. This transfer voltage usually requires a voltage of 3 kV or more (required current is several μA). Conventionally, an image forming apparatus includes a voltage power supply device that uses a wound electromagnetic transformer to generate a desired voltage. However, since a very small current of about several μA is used in the image forming apparatus, it is necessary to reduce the leakage current as much as possible. Accordingly, the winding of the electromagnetic transformer is insulated by a mold or the like, and a larger transformer is required as compared with the supplied power, which hinders the reduction in size and weight of the voltage power supply device.

  In order to solve these problems, a voltage power supply device using a thin, lightweight, high-output piezoelectric transformer is known. Piezoelectric transformers do not require windings, and thus have a simple structure and are advantageous for reduction in thickness and weight. In addition, the piezoelectric transformer is advantageous in increasing the frequency and has a feature that electromagnetic noise is not generated. The piezoelectric transformer can generate a high voltage with a low voltage input by utilizing the resonance phenomenon of the piezoelectric vibrator.

Patent Document 1 shows a high-voltage power supply device that generates a drive frequency input to a piezoelectric transformer by a voltage-controlled oscillation circuit (VCO) that is an analog circuit. Since the piezoelectric transformer has a feature that the output voltage becomes maximum at the resonance frequency, the output voltage can be controlled by the frequency. The relationship between the drive frequency and the output voltage is characterized in that the output voltage becomes maximum at the resonance frequency, and the output voltage decreases as the frequency is higher than the resonance frequency or lower than the resonance frequency. Thereby, the high voltage power supply device described in Patent Document 1 controls the output voltage of the piezoelectric transformer by controlling the frequency output from the VCO.
JP-A-11-206113

  However, the prior art has the following problems. Usually, when increasing the output voltage of a piezoelectric transformer, the VCO is realized by changing the driving frequency of the piezoelectric transformer from higher to lower. The VCO controls the rise time of the output voltage by controlling the amount of frequency change that changes the frequency. Therefore, there is a problem that the rise time becomes longer as the desired voltage becomes higher.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus and a voltage power supply apparatus that reduce the rise time of a voltage output from a piezoelectric transformer.

In addition, the present invention controls, for example, a piezoelectric transformer that is driven at a frequency of an input signal and outputs a voltage corresponding to the frequency, and an output voltage from the piezoelectric transformer by controlling the frequency of the signal. And an image forming device to which the voltage output from the piezoelectric transformer is supplied, wherein the control device corresponds to each of the plurality of frequencies and the plurality of frequencies. Storage means for storing information indicating a correspondence relationship between output voltages, setting means for setting a frequency corresponding to the value of the output voltage instructed using information stored in the storage means, and the setting means And a switching means for switching the frequency of the signal by a predetermined amount of change. If, with the information stored in said storage means is information stored in association with the output voltage corresponding to each of a plurality of frequencies and a plurality of said frequency being switched for each of the amount of change, In the frequency region where the output voltage of the piezoelectric transformer is equal to or lower than a threshold value set between an output voltage corresponding to an unnecessary resonance frequency of the piezoelectric transformer and an output voltage corresponding to the resonance frequency of the piezoelectric transformer. A change amount for switching the frequency of the signal is set to a first change amount, and the change amount is set to a second change amount larger than the first change amount in a frequency region exceeding the threshold value.

  The present invention can provide, for example, an image forming apparatus and a voltage power supply apparatus that reduce the rise time of the voltage output from the piezoelectric transformer.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. The following embodiments do not limit the invention described in the claims, and all the combinations of features described in the embodiments are essential to the solution means of the present invention. Not exclusively. The present invention is realized by an electrophotographic printer as an application example. However, the present invention may be realized by an image forming apparatus employing another image forming method such as an ink jet printer.

  First, an outline of a printer will be described with reference to FIG. FIG. 1 is a diagram showing an outline of a printer according to the present invention. Here, description is mainly given about the element regarding this invention.

  The printer 100 includes image forming units 101a, 101b, 101c, and 101d that function as image forming units for each of yellow Y, magenta M, cyan C, and black B toners. The printer 100 also includes a transfer belt 107, a recording material cassette 108, and a fixing device 109. Further, the printer 100 includes a DC controller 110 that controls the printer 100, a voltage power supply device 113, and a video controller 115. In the printer 100, a plurality of rollers for conveying the recording material and a plurality of sensors for detecting the recording material are arranged.

  Since the image forming units 101 (a to d) have the same configuration, the details will be described here using the image forming unit 101a as an example. The image forming unit 101 a includes an exposure device 102, a photosensitive drum 103, a charging roller 104, a developing device 105, and a transfer roller 106. The charging roller 104 charges the photosensitive drum 103 uniformly. An electrostatic latent image is formed on the uniformly charged photosensitive drum 103 by exposure from the exposure device 102 based on the image signal to be formed. The developing device 105 includes a toner color developer in charge, and develops the electrostatic latent image formed on the photosensitive drum 103 by the developer. The transfer roller 106 transfers the developer image formed on the photosensitive drum 103 onto a recording material. Specifically, the recording material conveyed between the transfer roller 106 and the photosensitive drum 103 is nipped and conveyed, whereby the developer image formed on the photosensitive drum 103 is transferred to the recording material.

  The transfer belt 107 is disposed by a driving roller and a subordinate roller, and controls the conveyance of the recording material by the driving force of the driving roller. The recording material cassette 108 loads recording materials and supplies the recording materials to the image forming unit 101 according to a print job. The fixing device 109 fixes the developer image formed on the recording material output from the image forming unit 101a to the recording material by applying pressure and heating. The recording material output from the fixing device 109 is discharged out of the printer 100.

  The DC controller 110 includes a one-chip microcomputer (hereinafter referred to as CPU) 111, an application specific integrated circuit (hereinafter referred to as ASIC) 112, various input / output control circuits (not shown), RAM, ROM, and the like. Memory. Here, the ASIC 112 also functions as a control unit that controls the drive frequency input to the voltage power supply device 113 and controls the output voltage output from the voltage power supply device 113.

  The video controller 115 expands image data input from an external device 116 such as a personal computer into bitmap data, and converts it into an image signal for image formation. The video controller 115 converts image data read from a scanner included in the printer 100 into an image signal for image formation.

  A voltage power supply device (piezoelectric transformer type high voltage power supply device) 113 is a charging high voltage power source applied to the charging roller 104, a developing high voltage power source applied to the developer, and a transfer high voltage power source applied to the transfer roller 106 corresponding to each image forming unit 101. Is provided. Furthermore, the voltage power supply device 113 includes a piezoelectric transformer. Piezoelectric transformers are made of ceramic and can generate a high voltage with an efficiency higher than that of electromagnetic transformers. Further, the distance between the primary side electrode and the secondary side electrode can be increased, and it is not necessary to perform a special molding process for insulation, which is effective in reducing the size and weight of the voltage power supply device.

  Next, a voltage power supply apparatus 200 using a conventionally known voltage control oscillator (VCO) 210 will be described with reference to FIGS. FIG. 2 is a diagram illustrating a circuit of the voltage power supply apparatus 200 using the VCO 210. The VCO 210 is connected to the piezoelectric transformer 201 and controls the output voltage of the piezoelectric transformer 201 based on the transmission frequency.

  The voltage power supply device 200 includes a piezoelectric transformer 201, rectifier diodes 202 and 203, a smoothing capacitor 204, and resistors 205, 206, 207, 208 and 214. Furthermore, the voltage power supply apparatus 200 includes an operational amplifier 209, a transistor 211, an inductor 212, and a capacitor 213.

  Next, the operation of the voltage power supply apparatus 200 in the conventional example will be described. Here, the operation when generating the transfer voltage will be described as an example. First, an output control signal (hereinafter referred to as Vcont) that is an analog signal output from a controller (not shown) is input to the inverting input terminal (− terminal) of the operational amplifier 209 via the resistance element 214. On the other hand, a voltage obtained by dividing the output voltage (hereinafter referred to as Vout) by the resistors 205, 206, and 207 is input to the non-inverting input terminal (+ terminal) of the operational amplifier 209 through the protective resistor 208. Here, the operational amplifier 209 is connected from the output terminal so that the voltage value of Vcont input to the inverting input terminal (− terminal) is equal to the divided voltage obtained by dividing Vout by the resistors 205, 206, and 207. Output voltage. The output terminal of the operational amplifier 209 is connected to the VCO 210. The VCO 210 switches the transistor 211 at a frequency corresponding to the output voltage from the operational amplifier 209 and supplies a pulse to the primary side of the piezoelectric transformer 201. The piezoelectric transformer 201 vibrates according to the pulse supplied to the primary side, and generates an alternating voltage amplified at a step-up ratio corresponding to the size of the piezoelectric transformer 201 on the secondary side. The generated AC voltage is rectified and smoothed to a positive voltage by the rectifying diodes 202 and 203 and the smoothing capacitor 204 and supplied to the transfer roller 106.

  FIG. 3 is a diagram showing the relationship between the drive frequency of the piezoelectric transformer 201 and the output voltage. The horizontal axis represents the drive frequency [Hz] input to the piezoelectric transformer 201, and the vertical axis represents the voltage [V] output from the piezoelectric transformer 201. In general, the characteristics of the piezoelectric transformer 201 have such a shape that the output voltage becomes maximum at the resonance frequency f0 as shown in FIG. fZ is the lowest frequency operable with the VCO 210, and fA is the highest frequency operable with the VCO 210. Normally, the output voltage of the piezoelectric transformer is controlled by changing the drive pulse between the maximum frequency fH and the resonance frequency f0. Further, the spurious frequency shown in FIG. 3 indicates an unnecessary resonance frequency other than the resonance frequency f0.

  However, the voltage power supply device 200 using the VCO 210 takes a long time to control the drive frequency in order to obtain a desired voltage from the piezoelectric transformer 201. Specifically, the VCO 210 first inputs the highest frequency fA to the piezoelectric transformer 201. Thereafter, the VCO 210 decreases the drive frequency by a constant change amount until a desired voltage is output from the piezoelectric transformer 201. Therefore, the voltage power supply apparatus 200 requires more time to control the drive frequency input to the piezoelectric transformer 201 as the desired voltage is higher. Furthermore, when a desired voltage range is widely required, it is easily affected by the spurious frequency, and control at a low voltage is difficult.

  The printer 100 according to the present invention includes a digital circuit such as a CPU or ASIC that controls the piezoelectric transformer 201 instead of the VCO 210. In this case, the piezoelectric transformer is directly controlled by switching the transistor 211 with a clock or pulse output from the digital circuit. Furthermore, the printer 100 according to the present invention sets a driving frequency corresponding to a desired voltage value using a table in which a correspondence relationship between a plurality of driving frequencies and output voltages corresponding to the respective driving frequencies is defined in advance. Thereby, since the drive frequency input first to the piezoelectric transformer 201 is a drive frequency for obtaining a desired voltage, control of the subsequent drive frequency can be omitted. Hereinafter, the first embodiment will be described with reference to FIGS. 4 to 9.

[First Embodiment]
FIG. 4 is a circuit diagram of the voltage power supply device 113 according to the first embodiment. The same components as those of the voltage power supply device 200 described with reference to FIG.

  Unlike the voltage power supply apparatus 200, the voltage power supply apparatus 113 outputs a drive frequency from the ASIC 112 instead of the VCO 210. The ASIC 112 is connected to the voltage power supply device 113 by a feedback system so as to detect the voltage output from the piezoelectric transformer 201. Further, the ASIC 112 acquires a voltage value to be output from the CPU 111 and inputs a driving frequency corresponding to the acquired voltage value to the piezoelectric transformer 201.

  Next, with reference to FIG. 5, the configuration and characteristics of the control circuit of the voltage power supply in this embodiment will be described. FIG. 5 is a diagram showing detailed control blocks of the ASIC 112 according to the first embodiment.

  The ASIC 112 includes an acquisition unit 501, a selection unit 502, and a pulse generation unit 503. Further, the ASIC 112 includes a switching unit 504, an A / D converter 505, and a table generation unit 506 in order to generate a table in which a correspondence relationship between a plurality of drive frequencies and output voltages corresponding to the respective drive frequencies is defined in advance. . Further, the ASIC 112 includes a timing generation unit 507 and a RAM 508.

  The acquisition unit 501 functions as an acquisition unit that acquires a voltage value output from the piezoelectric transformer 201. Specifically, a desired voltage value notified from the CPU 111 (hereinafter referred to as a target voltage) is acquired. The selection unit 502 uses a lookup table (hereinafter referred to as LUT) in which a correspondence relationship between a plurality of drive frequencies and output voltages corresponding to each drive frequency is used, and drives corresponding to the acquired voltage values. It functions as a setting means for setting the frequency. Specifically, the selection unit 502 functions as a selection unit that selects a drive frequency corresponding to the voltage value acquired by the acquisition unit 501 from the LUT. The selection unit 502 notifies the pulse generation unit 503 of the selected drive frequency. Here, the LUT is generated by the table generation unit 506 in the initial process when the printer 100 is turned on, and stored in the RAM 508. The pulse generation unit 503 functions as a pulse generation unit that generates a pulse having a drive frequency input to the piezoelectric transformer 201 in accordance with the selected drive frequency.

  The switching unit 504 functions as switching means for switching the drive frequency by a predetermined change amount. Note that the pulse generation unit 503 generates a pulse by adding the change amount notified from the switching unit 504 to the current frequency according to the timing notified from the timing generation unit 507. The A / D converter 505 functions as a detection unit that detects the output voltage generated at the drive frequency switched by the switching unit 504. Specifically, the A / D converter 505 converts an input analog signal into a digital signal.

  FIG. 6 is a diagram illustrating the characteristics of the output voltage (Vout) with respect to the drive frequency of the piezoelectric transformer 201 according to the first embodiment. As shown in FIG. 6, the shape is such that the output voltage becomes maximum at the resonance frequency f0. fZ indicates the lowest frequency that can be generated by the ASIC 112, and fA indicates the highest frequency that can be generated by the ASIC 112.

  A circle (◯) shown in FIG. 6 indicates the drive frequency switched by the switching unit 504 when the LUT is generated. The number of circles (sampling number) shown in FIG. 6 is an example, and the switching unit 504 can control the sampling number by controlling the amount of change when sampling the voltage. The table generation unit 506 grasps the characteristics of the piezoelectric transformer 201 by sampling the output voltage output from the piezoelectric transformer 201 corresponding to a plurality of drive frequencies during the initial processing. Specifically, the printer 100 can specify the resonance frequency f0 and a plurality of spurious frequencies, and can control the output voltage even in a low voltage region where the spurious frequencies exist. Actually, the printer 100 according to the present embodiment controls the voltage output from the piezoelectric transformer 201 in the frequency range from fA to f0.

  FIG. 7 is a diagram showing the contents of the LUT 700 according to the first embodiment. Here, as an application example, an LUT 700 generated according to the address of the RAM 508 will be described. For example, the LUT 700 stores drive frequencies and output voltages in association with addresses 0, 1, and 2 in the RAM 508 in the order of addresses. Here, the LUT 700 holds 100 types of drive frequencies and output voltages. The number of 100 types is an example, and it is desirable that the number of types of output voltage and drive frequency held in the LUT in this embodiment is as large as possible. The selection unit 502 selects a drive frequency corresponding to the target voltage acquired by the acquisition unit 501 from the LUT 700. The RAM 508 also holds an area for storing other data set by the CPU 111, and each control block in the ASIC 112 detects the data and performs processing.

  Next, the generation process of the LUT 700 in this embodiment will be described with reference to FIG. FIG. 8 is a flowchart showing a processing procedure for generating the LUT 700 according to the first embodiment. Note that the ASIC 112 performs overall control of the processing described below.

  In step S801, the pulse generation unit 503 first generates a plurality of pulses at the maximum frequency fA during the initial process. The plurality of generated pulses are input to the primary side of the piezoelectric transformer 201 as a driving frequency. As a result, a voltage VA corresponding to the highest frequency fA is output from the secondary side of the piezoelectric transformer 201. Next, in step S802, the A / D converter 505 converts an analog signal input according to the output voltage into a digital signal in order to detect the output voltage. Thereafter, in step S <b> 803, the table generation unit 506 stores the output voltage VA converted into a digital value and the drive frequency fA generated by the pulse generation unit 503 at address 0 of the RAM 508.

  Subsequently, in step S <b> 803, the ASIC 112 determines whether or not the driving frequency input to the piezoelectric transformer 201 is a driving frequency fZ that can be generated by the ASIC 112. If it is the lowest drive frequency fZ, the ASIC 112 ends the process. On the other hand, if it is not the lowest frequency fZ, the ASIC 112 shifts the process to S805.

  In step S805, the pulse generation unit 503 acquires the timing signal generated by the timing generation unit 507. The pulse generation unit 503 switches the frequency of the generated pulse when the timing signal is acquired. Specifically, the timing generation unit 507 generates a timing signal after the drive frequency fA and the output voltage VA are stored at address 0. When this timing signal is notified, in step S806, the pulse generation unit 503 acquires the change amount of the drive frequency from the switching unit 504, and adds the acquired change amount to the current drive frequency fA. Further, in step S801, the pulse generation unit 503 generates a pulse at the switched drive frequency. Thereafter, the ASIC 112 detects the output voltage and stores it in the RAM 508. In this way, the ASIC 112 repeatedly executes the processing from S801 to S806 until the drive frequency reaches the lowest frequency fZ.

  Next, target voltage output processing in the present embodiment will be described with reference to FIG. FIG. 9 is a flowchart illustrating a processing procedure for outputting the target voltage of the printer 100 according to the first embodiment. Note that the ASIC 112 performs overall control of the processing described below.

  In step S901, the acquisition unit 501 acquires the target voltage VD shown in FIG. Specifically, first, the target voltage VD is sent from the CPU 111 to the RAM 508. The acquisition unit 501 acquires the target voltage VD stored in the RAM 508 and notifies the selection unit 502 of the target voltage VD.

  Subsequently, in step S902, the selection unit 502 searches the LUT 700 for a voltage value corresponding to the acquired target voltage. Here, as illustrated in FIG. 7, the selection unit 502 determines that the voltage value stored in the address 40 of the RAM 508 is the same as the target voltage. Therefore, the selection unit 502 acquires the drive frequency fD stored at the address 40 from the LUT 700. Further, the selection unit 502 notifies the pulse generation unit 503 of the drive frequency fD acquired from the LUT 700.

  Finally, in step S903, the pulse generation unit 503 changes the drive frequency to be generated to the drive frequency fD and inputs a pulse to the piezoelectric transformer 201. By performing the above processing, the printer 100 can output the target voltage VD from the piezoelectric transformer 201.

  As described above, the printer 100 according to the present embodiment does not require the control to switch the drive frequency a plurality of times to approach the target voltage, and generates a pulse at the drive frequency corresponding to the target voltage from the beginning by using the LUT 700. Is possible. Therefore, even if the target voltage is a relatively high voltage among the output voltages of the piezoelectric transformer 201, the piezoelectric transformer 201 can be started up at high speed.

[Second Embodiment]
Next, a second embodiment will be described with reference to FIGS. In the present embodiment, the amount of change in frequency when generating the LUT 1200 is set larger than that in the first embodiment. Therefore, it is assumed that the target voltage and the voltage value stored in the LUT 1200 do not correspond one-to-one. In such a case, in the present embodiment, the drive frequency corresponding to the target voltage is derived from the plurality of output voltages and drive frequencies stored in the RAM 508 and the target voltage.

  FIG. 10 is a diagram showing detailed control blocks of the ASIC 1001 according to the second embodiment. Here, only the control block different from the control block of the ASIC 112 according to the first embodiment shown in FIG. 5 will be described.

  The ASIC 1001 includes a derivation unit 1002 instead of the selection unit 502 of the ASIC 112. The derivation unit 1002 has the same function as the selection unit 502 in the sense that it functions as a setting unit that sets a drive frequency corresponding to the target voltage using the LUT 1200. However, unlike the selection unit 502, the deriving unit 1002 functions as deriving means for extracting each driving frequency corresponding to a plurality of voltage values close to the target voltage from the LUT 1200 and deriving the driving frequency corresponding to the target voltage. . That is, the LUT 1200 according to the present embodiment does not necessarily define the drive frequency corresponding to the target voltage.

  The deriving unit 1002 derives a drive frequency fD for outputting the target voltage VD from the plurality of output voltages and the drive frequency stored in the RAM 508. For example, the deriving unit 1002 derives the drive frequency fD corresponding to the target voltage VD by performing proportional integration using the plurality of output voltages and the drive frequency stored in the RAM 508.

  The derivation unit 1002 may select a drive frequency corresponding to the output voltage closest to the target voltage from the output voltages stored in the RAM 508 and notify the pulse generation unit 503 of the drive frequency. In this case, it is desirable that the ASIC 1001 notifies the derivation unit 1002 of the difference between the voltage value detected by the A / D converter 505 and the target voltage value, and causes the derivation unit 1002 to adjust the drive frequency again. Further, the ASIC 1001 outputs the target voltage by repeating such processing until the output voltage from the piezoelectric transformer 201 approaches the target voltage. Thereby, the printer 100 according to the present embodiment can reduce the processing time of the initial process for creating the LUT as compared with the first embodiment. Furthermore, the printer 100 may reduce the processing time for obtaining the target voltage VD as compared with the method of setting the initial drive frequency to the highest frequency fA of the ASIC 1001 and then detecting and adjusting the output voltage. it can. Of course, the processing time for obtaining the target voltage VD depends on the number of samples when the LUT is generated.

  Next, the LUT 1200 according to the present embodiment will be described with reference to FIGS. 11 and 12. FIG. 11 is a diagram illustrating the characteristics of the output voltage (Vout) with respect to the drive frequency of the piezoelectric transformer 201 according to the second embodiment. FIG. 12 is a diagram showing the contents of the LUT 1200 according to the second embodiment.

  The table generation unit 506 samples the output voltage from the piezoelectric transformer 201 at a larger interval than in FIG. 6, as indicated by a circle (◯) illustrated in FIG. 11. As a result, the number of sampling of the output voltage is reduced as compared with the first embodiment. The adjustment of the sampling number is determined by the amount of change set by the switching unit 504. As shown in FIG. 12, the LUT 1200 has an output voltage sampling number of 20 between the highest drive frequency fA and the lowest drive frequency fZ as an example.

  Next, output processing of the target voltage VD in the present embodiment will be described with reference to FIG. Here, only the processing different from the generation processing of the LUT 700 in the first embodiment will be described. That is, only the processing in S902 will be described.

  In step S902, the derivation unit 1002 acquires from the LUT 1200 a plurality of output voltages close to the target voltage VD acquired in S901 and a plurality of drive frequencies corresponding thereto. Subsequently, the deriving unit 1002 derives a driving frequency corresponding to the target voltage VD by performing, for example, proportional integration using the acquired plurality of output voltages, a plurality of driving frequencies, and the target voltage VD. . Thereafter, the derivation unit 1002 notifies the pulse generation unit 503 of the derived drive frequency fD.

  As described above, the printer 100 according to the present embodiment reduces the number of output voltage samplings for generating the LUT 1200 and derives the driving frequency corresponding to the target voltage from a plurality of values. Accordingly, the printer 100 according to the present embodiment can reduce the processing time of the initial process and can bring the output voltage from the piezoelectric transformer 201 close to the target voltage in a short time. Furthermore, the printer 100 according to the present embodiment can reduce the capacity of the RAM 508 as compared with the first embodiment.

[Third Embodiment]
Next, a third embodiment will be described with reference to FIG. The printer 100 according to the present embodiment creates an LUT that reduces the influence of spurious frequencies. FIG. 13 is a diagram illustrating the characteristics of the output voltage (Vout) with respect to the drive frequency of the piezoelectric transformer 201 according to the third embodiment.

  The drive circuit of the piezoelectric transformer 201 forms an LC resonance type flyback converter using a transistor 211, an inductor 212, and a piezoelectric transformer input capacitor (not shown). This configuration is effective in that it is inexpensive and a high effective input voltage value can be obtained. However, since the voltage waveform includes a harmonic component as shown in FIG. 13, the voltage waveform is easily affected by spurious frequencies (unnecessary resonance frequencies other than the resonance frequency f0) generated by the structural characteristics of the piezoelectric transformer 201. End up. In this case, if the range of the target voltage is widened, it is difficult to control at a low voltage because it is affected by the spurious frequency.

  As shown in FIG. 13, the characteristics of the piezoelectric transformer 201 have a flared shape including a spurious frequency that maximizes the output voltage at the resonance frequency f0. Here, a problem related to the control of the voltage power supply apparatus 200 that controls the piezoelectric transformer 201 by the VCO 210 shown in FIG. 2 will be described. Hereinafter, a case where the transfer voltage is controlled within the range of the output voltage Vlow shown in FIG. 13 will be described.

  Usually, the operating frequency of the VCO 210 is set to be wide so that the resonance frequency f0 does not fall outside the operating range due to individual variations of the piezoelectric transformer 201, and includes the spurious frequency. In FIG. 13, when the control is performed on the higher frequency side than the resonance frequency f0, the drive frequency starts from the higher frequency side. Therefore, when the voltage VL within the Vlow range is required, the control is established at the point of the drive frequency fL1. . However, when the load on the transfer roller 106 or the like becomes slightly heavier at the driving frequency fL1, the frequency characteristic curve 1301 instantaneously drops to a lower voltage like the frequency characteristic curve 1302. At this time, since the spurious voltage (output voltage at the spurious frequency) becomes lower than the voltage VL, the control point moves from the driving frequency fL1 to the driving frequency fL3. Accordingly, voltage fluctuation is involved in the process of control from the drive frequency fL1 to the drive frequency fL3, and thus defects such as image defects may occur. When the load on the transfer roller 106 or the like is restored, the operating point becomes the drive frequency fL2. That is, when the control is started from the high frequency side and the voltage VL is output, it can be said that stable control cannot be performed unless the voltage is higher than the spurious voltage.

  In the printer 100 according to the present embodiment, when the target voltage is a low voltage, the output voltage can be stabilized without being affected by the spurious frequency. Specifically, as in the first and second embodiments, the printer 100 according to the present embodiment stores the drive frequency and the output voltage in the RAM 508 during the initial processing after the power is turned on, and generates an LUT.

  When generating the LUT, the pulse generator 503 first generates a pulse at the drive frequency fA. Further, the switching unit 504 sets the change amount of the drive frequency to a small value that becomes the first change amount, that is, a value that can detect the characteristic curve of the spurious frequency. Further, the CPU 111 notifies the ASIC 112 of the threshold value VT shown in FIG. 13 for the purpose of detecting the spurious frequency. Here, as shown in FIG. 13, the threshold value VT is set between the output voltage at the spurious frequency and the output voltage at the resonance frequency f0. The ASIC 112 uses the selection unit 502 or the derivation unit 1002 to compare the output voltage and the threshold value VT. The switching unit 504 sets the change amount to the above-described first change amount while the output voltage from the piezoelectric transformer 201 is equal to or less than the threshold value VT. On the other hand, when the output voltage exceeds the threshold value VT, the switching unit 504 sets the change amount to the second change amount that is larger than the first change amount.

  As described above, when generating the LUT, the printer 100 according to the present embodiment samples with a smaller amount of change than the normal change amount in the frequency region where the spurious frequency exists, and normal in the frequency region where the spurious frequency does not exist. Sampling by the amount of change. Therefore, when the target voltage is equal to or lower than the threshold VT, the selection unit 502 or the derivation unit 1002 acquires a plurality of drive frequencies corresponding to the target voltage from the LUT. In this case, the selection unit 502 or the derivation unit 1002 selects the drive frequency on the lowest frequency side from the plurality of drive frequencies and notifies the pulse generation unit 503 of it. Thus, the printer 100 according to the present embodiment can output a voltage stably without being affected by the spurious frequency when outputting a low voltage.

[Fourth Embodiment]
Next, a fourth embodiment will be described with reference to FIG. The printer 100 according to the present embodiment generates the LUT when the CPU 111 detects the replacement of the process cartridge, which is the image forming unit 101, separately from the generation of the LUT during the initial process. FIG. 14 is a diagram illustrating the characteristics of the output voltage (Vout) with respect to the drive frequency of the piezoelectric transformer 201 according to the fourth embodiment. Hereinafter, the necessity of generating an LUT when a process cartridge is replaced will be described.

  A frequency characteristic curve 1401 shows an output voltage with respect to a driving frequency after the process cartridge is replaced and used for a certain period of time. A frequency characteristic curve 1402 indicates the output voltage with respect to the drive frequency immediately after the process cartridge is replaced. As shown in FIG. 14, as the frequency of use of each process cartridge increases, the photosensitive drum 103 of the process cartridge is scraped, so that the output voltage from the piezoelectric transformer 201 also decreases as the impedance on the load side viewed from the high voltage output decreases. descend. For example, the output voltage at the resonance frequency f0 decreases from the output voltage V02 immediately after replacement to the output voltage V01 as the number of uses increases. Therefore, when the target voltage is generated, the state of the device at the time of initial processing that generated the LUT is different from the current state of the device, and the accuracy of voltage control is reduced. For example, when the drive frequency corresponding to the output voltage VD1 is defined as fD1 during the initial process, the output voltage corresponding to the drive frequency fD1 becomes VD2 when the process cartridge is replaced.

  Therefore, the CPU 111 according to the present embodiment manages information about the process cartridge for each toner color. When the CPU 111 detects the replacement of the process cartridge from this information, it requests the ASIC 112 to generate an LUT. The ASIC 112 generates the LUT by any one of the methods in the first to third embodiments. Thereby, the printer 100 according to the present embodiment can cope with a change in the frequency characteristics of the piezoelectric transformer 201 when the process cartridge is replaced, and can output a stable voltage.

  In each of the embodiments described above, an ASIC is used as a digital circuit that is a means for generating a drive frequency to be input to the piezoelectric transformer 201, but a one-chip microcomputer can be used instead. Further, although the output voltage and the drive frequency are stored in the RAM 508 on the ASIC, the RAM may be held on the CPU 111.

1 is a diagram showing an outline of a printer according to the present invention. It is a figure which shows the circuit of the voltage power supply device 200 using VCO210. FIG. 6 is a diagram showing the relationship between the drive frequency of the piezoelectric transformer 201 and the output voltage. 2 is a circuit diagram of a voltage power supply device 113 according to the first embodiment. FIG. It is a figure which shows the detailed control block of ASIC112 which concerns on 1st Embodiment. FIG. 6 is a diagram illustrating a characteristic of an output voltage (Vout) with respect to a driving frequency of the piezoelectric transformer 201 according to the first embodiment. It is a figure which shows the content of LUT700 which concerns on 1st Embodiment. It is a flowchart which shows the process sequence which produces | generates LUT700 which concerns on 1st Embodiment. 3 is a flowchart illustrating a processing procedure for outputting a target voltage of the printer 100 according to the first embodiment. It is a figure which shows the detailed control block of ASIC1001 which concerns on 2nd Embodiment. FIG. 6 is a diagram illustrating a characteristic of an output voltage (Vout) with respect to a driving frequency of a piezoelectric transformer 201 according to a second embodiment. It is a figure which shows the content of LUT1200 which concerns on 2nd Embodiment. FIG. 6 is a diagram illustrating a characteristic of an output voltage (Vout) with respect to a driving frequency of a piezoelectric transformer 201 according to a third embodiment. It is the figure which showed the characteristic of the output voltage (Vout) with respect to the drive frequency of the piezoelectric transformer 201 which concerns on 4th Embodiment.

Explanation of symbols

100: Printer 110: DC controller 111: CPU
112: ASIC
113: Voltage power supply device 201: Piezoelectric transformer

Claims (8)

A piezoelectric transformer that is driven at a frequency of an input signal and outputs a voltage corresponding to the frequency, a control unit that controls an output voltage from the piezoelectric transformer by controlling a frequency of the signal, and the piezoelectric transformer An image forming apparatus provided with an image forming unit to which the voltage output from is supplied,
The control means includes
Storage means for storing information indicating a correspondence relationship between the plurality of frequencies and the output voltage corresponding to each of the plurality of frequencies;
Setting means for setting a frequency corresponding to the value of the instructed output voltage, using information stored in the storage means;
Signal generating means for outputting the signal having the frequency set by the setting means to the piezoelectric transformer;
Switching means for switching the frequency of the signal by a predetermined amount of change,
The information stored in the storage means is information stored by associating a plurality of frequencies switched for each change amount and an output voltage corresponding to each of the plurality of frequencies,
In the frequency region where the output voltage of the piezoelectric transformer is equal to or lower than a threshold value set between an output voltage corresponding to an unnecessary resonance frequency of the piezoelectric transformer and an output voltage corresponding to the resonance frequency of the piezoelectric transformer. The amount of change for switching the frequency of the signal is set to a first change amount, and the change amount is set to a second change amount larger than the first change amount in a frequency region exceeding the threshold value. apparatus.   The image forming apparatus according to claim 1, wherein the information is generated at least one of a case where power is supplied to the image forming apparatus and a case where a process cartridge included in the image forming apparatus is replaced. apparatus. The setting means includes
The image forming apparatus according to claim 1, further comprising a selection unit that selects the frequency corresponding to the specified output voltage using the information.   In the information stored in the storage means, each frequency corresponding to a plurality of voltage values close to the specified output voltage value is extracted, and the specified output voltage value is determined from the extracted plurality of frequencies. The image forming apparatus according to claim 1, further comprising a derivation unit that derives a frequency to be transmitted.   5. The image forming apparatus according to claim 1, wherein the setting unit, the signal generation unit, and the switching unit are circuits that process digital data. A piezoelectric transformer which outputs a voltage corresponding to the frequency is driven at the frequency of the inputted signal, by controlling the frequency of the signal, electric wherein Ru and control means for controlling the output voltage from the piezoelectric transformer A source device,
The control means includes
Storage means for storing information indicating a correspondence relationship between the plurality of frequencies and the output voltage corresponding to each of the plurality of frequencies;
Setting means for setting a frequency corresponding to the value of the instructed output voltage, using information stored in the storage means;
Signal generating means for outputting the signal having the frequency set by the setting means to the piezoelectric transformer;
Switching means for switching the frequency of the signal by a predetermined amount of change,
The information stored in the storage means is information stored by associating a plurality of frequencies switched for each change amount and an output voltage corresponding to each of the plurality of frequencies,
In the frequency region where the output voltage of the piezoelectric transformer is equal to or lower than a threshold value set between an output voltage corresponding to an unnecessary resonance frequency of the piezoelectric transformer and an output voltage corresponding to the resonance frequency of the piezoelectric transformer. set the amount of change for switching the frequency of the signal to the first change amount, electrostatic you and sets the amount of change in the second amount of change larger than said first change amount in the frequency domain exceeding the threshold Source equipment. A piezoelectric transformer that is driven at a frequency of an input signal and outputs a voltage corresponding to the frequency, a control unit that controls an output voltage from the piezoelectric transformer by controlling a frequency of the signal, and the piezoelectric transformer A method of controlling an image forming apparatus including an image forming unit to which a voltage output from
The control means is
A storage step of storing in a storage means information indicating a correspondence relationship between the plurality of frequencies and the output voltage corresponding to each of the plurality of frequencies;
A setting step of setting a frequency corresponding to the value of the output voltage instructed using the information stored in the storage means;
A signal generating step of outputting the signal having the frequency set in the setting step to the piezoelectric transformer;
A switching step of switching the frequency of the signal by a predetermined amount of change, and
The information stored in the storage means is information stored by associating a plurality of frequencies switched for each change amount and an output voltage corresponding to each of the plurality of frequencies,
The switching step is performed in a frequency region where the output voltage of the piezoelectric transformer is equal to or lower than a threshold value set between an output voltage corresponding to an unnecessary resonance frequency of the piezoelectric transformer and an output voltage corresponding to the resonance frequency of the piezoelectric transformer. A change amount for switching the frequency of the signal is set to a first change amount, and the change amount is set to a second change amount larger than the first change amount in a frequency region exceeding the threshold value. A piezoelectric transformer which outputs a voltage corresponding to the frequency is driven at the frequency of the inputted signal, by controlling the frequency of the signal, electric wherein Ru and control means for controlling the output voltage from the piezoelectric transformer A method for controlling a source device comprising:
The control means is
A storage step of storing in a storage means information indicating a correspondence relationship between the plurality of frequencies and the output voltage corresponding to each of the plurality of frequencies;
A setting step of setting a frequency corresponding to the value of the output voltage instructed using the information stored in the storage means;
A signal generating step of outputting the signal having the frequency set in the setting step to the piezoelectric transformer;
A switching step of switching the frequency of the signal by a predetermined amount of change, and
The information stored in the storage means is information stored by associating a plurality of frequencies switched for each change amount and an output voltage corresponding to each of the plurality of frequencies,
The switching step is performed in a frequency region where the output voltage of the piezoelectric transformer is equal to or lower than a threshold value set between an output voltage corresponding to an unnecessary resonance frequency of the piezoelectric transformer and an output voltage corresponding to the resonance frequency of the piezoelectric transformer. A change amount for switching the frequency of the signal is set to a first change amount, and the change amount is set to a second change amount larger than the first change amount in a frequency region exceeding the threshold value.

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