Electrostatic motor drive circuit

Abstract

To prevent discharge between electrodes without reducing output.SOLUTION: An electrostatic motor drive circuit 1 drives an electrostatic motor 2 configured to obtain torque by electrostatic force generated between a rotor electrode 4 which is the electrode provided in a rotor and a stator electrode 5 which is the electrode provided in a stator. The electrostatic motor drive circuit 1 includes: a voltage application circuit 3 for applying drive voltage to the rotor electrode 4 and the stator electrode 5; and a voltage adjusting part 21 for adjusting drive voltage according to a change of an inter-electrode distance which is the distance between the rotor electrode 4 and the stator electrode 5.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electrostatic motor drive circuit for driving an electrostatic motor. [Background technology]

[0002] An electrostatic motor is configured to obtain a rotational force by an electrostatic force generated between a rotor electrode, which is an electrode provided on a rotor, and a stator electrode, which is an electrode provided on a stator. An electrostatic motor drive circuit for driving such an electrostatic motor applies a fixed voltage to one of the electrodes, and applies an A-phase voltage whose level is switched depending on the rotational position and a B-phase voltage whose phase is opposite to the A-phase voltage, to the other of the electrodes. Patent Document 1 discloses an electrostatic motor drive circuit that employs a circuit configuration of an isolated flyback converter. In the following description, the configuration disclosed in Patent Document 1 will be referred to as the prior art.

[0003] Generally, electrostatic motors have a low output, and high-output motors have not been realized. To realize high output from electrostatic motors, the output voltage of the drive circuit must be correspondingly high, for example, about 100 kV. However, as the output voltage of the drive circuit becomes higher, the possibility of discharge occurring when the electrodes approach each other increases. Discharge between electrodes can lead to a decrease in output and malfunction or failure of the equipment in which the electrostatic motor is installed, so measures must be taken to prevent this.

[0004] As a countermeasure, it is conceivable to adopt vacuum insulation for insulation between electrodes. When vacuum insulation is adopted, it is possible to significantly improve the dielectric strength voltage compared to when atmospheric insulation is adopted. However, even in a vacuum, in the case of a configuration having a complex electrode shape such as an electrostatic motor, discharge may occur due to factors such as electric field concentration due to the shape, electrode material, electrode surface state, outgassing, etc., and it is difficult to significantly reduce the risk of discharge. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-48557 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the prior art, in order to prevent discharge between the electrodes, the charge is removed in advance to reduce the voltage before the electrodes come close to each other. Although this reduces the risk of discharge, the reduction in voltage can cause other problems, such as a reduction in torque, i.e., a reduction in output.

[0007] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an electrostatic motor drive circuit that can prevent the occurrence of discharge between electrodes without causing a decrease in output. [Means for solving the problem]

[0008] The electrostatic motor drive circuit described in claim 1 drives an electrostatic motor (2) configured to obtain a rotational force by an electrostatic force generated between a rotor electrode (4) which is an electrode provided on a rotor and a stator electrode (5) which is an electrode provided on a stator, and includes a voltage application circuit (3, 3A, 3B, 3C, 3D) and a voltage adjustment unit (21, 21A, 21B, 21D, 33, 33A, 33B, 43). The voltage application circuit applies a drive voltage to the rotor electrode and the stator electrode.

[0009] In the above configuration, if the drive voltage does not exceed a withstand voltage determined according to the voltage at which discharge occurs between the rotor electrode and the stator electrode, discharge between the electrodes can be prevented. Furthermore, the withstand voltage changes according to changes in the inter-electrode distance. Therefore, the voltage adjustment unit adjusts the drive voltage according to changes in the inter-electrode distance, which is the distance between the rotor electrode and the stator electrode. With the above configuration, it is possible to adjust the drive voltage to a voltage value that provides a desired torque without exceeding the withstand voltage. Therefore, with the above configuration, the excellent effect of preventing discharge between the electrodes without causing a decrease in output can be obtained. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of an electrostatic motor drive circuit according to a first embodiment; [Diagram 2] FIG. 2 is a diagram showing a schematic configuration of each electrode of the electrostatic motor according to the first embodiment; [Diagram 3] FIG. 1 is a diagram showing an example of a specific electrode configuration of an electrostatic motor according to the first embodiment. [Figure 4] FIG. 2 shows an example of a specific electrode configuration of the electrostatic motor according to the first embodiment. [Diagram 5] FIG. 1 is a diagram showing a first specific configuration example of a voltage adjustment unit according to a first embodiment; [Figure 6] FIG. 11 is a diagram showing a second specific configuration example of the voltage adjustment unit according to the first embodiment; [Figure 7] FIG. 1 is a diagram showing an example of a relationship between an inter-electrode distance and an electrical angle in an electrostatic motor according to a first embodiment; [Figure 8] FIG. 1 is a diagram showing an example of a relationship between a withstand voltage and an electrical angle in an electrostatic motor according to a first embodiment; [Figure 9] FIG. 1 is a diagram showing an image of the operation of each electrode in a configuration in which the number of poles of the electrostatic motor according to the first embodiment is relatively small; [Figure 10] FIG. 1 is a diagram showing an image of the operation of each electrode in a configuration in which the number of poles of the electrostatic motor according to the first embodiment is relatively large; [Figure 11]FIG. 1 is a diagram showing a schematic flow of an operation for adjusting a drive voltage by a voltage adjusting unit according to a first embodiment; [Figure 12] FIG. 1 is a diagram showing an example of an operational waveform of each part according to the first embodiment; [Figure 13] FIG. 1 is a diagram showing an image of the operation of each electrode in the electrostatic motor according to the first embodiment; [Figure 14] FIG. 4 is a diagram showing schematic operational waveforms of each part according to the first embodiment and each comparative example. [Figure 15] FIG. 1 is a diagram illustrating a schematic configuration of a first modified example of a voltage application circuit according to a first embodiment; [Figure 16] FIG. 13 is a diagram illustrating a configuration of a second modified example of the voltage application circuit according to the first embodiment. [Figure 17] FIG. 13 is a diagram illustrating a configuration of a third modified example of the voltage application circuit according to the first embodiment. [Figure 18] FIG. 1 is a diagram showing an example of waveforms of a first fixed voltage, an A-phase voltage, and a B-phase voltage according to a first embodiment and a first modified example; [Figure 19] FIG. 13 is a diagram showing an example of waveforms of a first fixed voltage, an A-phase voltage, and a B-phase voltage according to a second modified example and a third modified example. [Figure 20] FIG. 13 is a schematic diagram showing a configuration of a modified example of a voltage adjusting unit and a voltage applying unit according to the first embodiment; [Figure 21] FIG. 11 is a diagram illustrating a configuration of an electrostatic motor drive circuit according to a second embodiment. [Figure 22] FIG. 13 is a diagram showing an example of a relationship between electrode capacitance and electrical angle in an electrostatic motor according to a second embodiment; [Figure 23] FIG. 13 is a diagram showing an example of waveforms of a drive signal and a drive voltage according to a second embodiment; [Figure 24] FIG. 11 is a diagram for explaining control of the waveform of a driving voltage by duty control according to the second embodiment; [Diagram 25] FIG. 11 is a diagram showing an example of an operational waveform of each part according to the second embodiment; [Figure 26] FIG. 13 is a diagram showing a first specific configuration example of a voltage adjustment unit according to a second embodiment; [Figure 27] FIG. 11 is a diagram showing a second specific configuration example of a voltage adjustment unit according to a second embodiment; [Figure 28] FIG. 13 is a diagram illustrating a flow of operations related to adjustment of a drive voltage by a voltage adjustment unit of a first configuration example according to a second embodiment; [Figure 29] FIG. 13 is a diagram illustrating a flow of operations related to adjustment of a drive voltage by a voltage adjustment unit of a second configuration example according to a second embodiment. [Diagram 30] FIG. 11 is a diagram showing schematic operational waveforms of each part according to the second embodiment and a comparative example. [Diagram 31] FIG. 11 is a schematic diagram showing detailed operational waveforms of each part according to the second embodiment and a comparative example. [Diagram 32] FIG. 11 is a diagram illustrating a configuration of an electrostatic motor drive circuit according to a third embodiment. [Diagram 33] FIG. 13 is a diagram showing a schematic flow of an operation for adjusting a drive voltage by a voltage adjusting unit according to a third embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, a number of embodiments will be described with reference to the drawings. Note that the same reference numerals are used to designate substantially the same components in the respective embodiments, and the description thereof will be omitted. (First embodiment) The first embodiment will be described below with reference to FIGS.

[0012] <Overall composition> As shown in FIG. 1, the electrostatic motor drive circuit 1 of this embodiment drives an electrostatic motor 2 and includes a voltage application circuit 3. In the following description, the electrostatic motor drive circuit 1 may be abbreviated as drive circuit 1. As shown in FIG. 2, the electrostatic motor 2 is configured to obtain a rotational force by an electrostatic force generated between a rotor electrode 4, which is an electrode provided on a rotor, and a stator electrode 5, which is an electrode provided on a stator. In this configuration, an electrode capacitance 6 is formed with the stator electrode 5 as one electrode and the rotor electrode 4 as the other electrode. In the following description, the rotor electrode 4 and the stator electrode 5 may be abbreviated as electrode 4 and electrode 5, respectively.

[0013] Specific electrode configurations of the electrostatic motor 2 can be, for example, those shown in Figures 3 and 4. In Figure 3, a large number of electrodes 4, 5 are arranged circumferentially, that is, in a direction parallel to the axis 7. In Figure 4, a large number of electrodes 4, 5 are arranged radially, that is, in a direction perpendicular to the axis 7. In this case, the voltage on the high potential side with respect to the ground, which is the reference potential of the circuit, is set to be a positive voltage.

[0014] The voltage application circuit 3 applies a drive voltage to the rotor electrode 4 and the stator electrode 5. Specifically, the voltage application circuit 3 applies a first fixed voltage and a second fixed voltage to the rotor electrode 4, and also applies an A-phase voltage and a B-phase voltage, the positive and negative of which are switched according to the rotational position of the electrostatic motor 2, to the stator electrode 5. The first fixed voltage is a positive fixed voltage, and the second fixed voltage is a voltage corresponding to ground. Thus, in this embodiment, the first fixed voltage, the second fixed voltage, the A-phase voltage, and the B-phase voltage correspond to the drive voltage. Note that in FIG. 1 and the like, the first fixed voltage is abbreviated as "positive", the second fixed voltage as "GND", the A-phase voltage as "A", and the B-phase voltage as "B".

[0015] The positive fixed voltage is a voltage that is constant at a voltage value higher than 0V, which is the potential of the ground 10. The negative fixed voltage is a voltage that is constant at 0V, which is the potential of the ground 10. The A-phase voltage and the B-phase voltage are voltages that alternate between a voltage value higher than 0V and 0V. However, the B-phase voltage is a voltage of opposite phase to the A-phase voltage. In other words, the A-phase voltage and the B-phase voltage are shifted in phase from each other by a half cycle.

[0016] The voltage application circuit 3 operates by receiving a power supply voltage VDD supplied from a DC power supply 8. The DC power supply 8 may be configured to be capable of boosting the voltage according to the output. The high-potential terminal of the DC power supply 8 is connected to a power supply line 9 via a resistor R1, and the low-potential terminal is connected to a ground 10. A capacitor C1 is connected between the power supply line 9 and the ground 10, which, together with the resistor R1, constitutes a filter circuit 11 for smoothing the power supply voltage VDD.

[0017] The voltage application circuit 3 includes half-bridge circuits 12 and 13, diodes D1 to D4, etc. The half-bridge circuit 12 includes two switching elements Q1 and Q2 connected in series between a power supply line 9 to which a power supply voltage VDD is applied and a ground 10. The switching elements Q1 and Q2 can be configured with transistors such as MOSFETs or IGBTs. In this case, both the switching elements Q1 and Q2 are N-channel MOSFETs.

[0018] The drain of switching element Q1 is connected to power line 9, and its source is connected to node N1. The drain of switching element Q2 is connected to node N1, and its source is connected to ground 10. Diode D1 is connected between node N1 and rotor electrode 4, with the node N1 side as the anode. Diode D2 is connected between node N1 and rotor electrode 4, with the rotor electrode 4 side as the anode.

[0019] A binary drive signal Sa output from the control circuit 14 is applied to the gate of the switching element Q1 via a buffer 15. A binary drive signal Sb output from the control circuit 14 is applied to the gate of the switching element Q2 via a buffer 16. With this configuration, the control circuit 14 controls the on / off of the switching elements Q1 and Q2. A rotation signal Sc indicating the rotation position of the electrostatic motor 2 is applied to the control circuit 14. The control circuit 14 controls the operation of the voltage application circuit 3 based on the rotation signal Sc so that the rotation position of the electrostatic motor 2 becomes a desired position.

[0020] The half-bridge circuit 13 includes two switching elements Q3 and Q4 connected in series between a power supply line 9 to which a power supply voltage VDD is applied and a ground 10. The switching elements Q3 and Q4 can be configured with transistors such as MOSFETs or IGBTs. In this case, the switching elements Q3 and Q4 are both N-channel MOSFETs. The drain of the switching element Q3 is connected to the power supply line 9, and the source of the switching element Q3 is connected to a node N2. The diode D3 is connected between the node N2 and the rotor electrode 4 with the node N2 side serving as the anode. The diode D4 is connected between the node N2 and the rotor electrode 4 with the rotor electrode 4 side serving as the anode.

[0021] The drain of switching element Q4 is connected to node N2, and its source is connected to ground 10. A binary drive signal Sd output from control circuit 14 is applied to the gate of switching element Q3 via buffer 17. A binary drive signal Se output from control circuit 14 is applied to the gate of switching element Q4 via buffer 18. With this configuration, the on / off of switching elements Q3 and Q4 is controlled by control circuit 14.

[0022] The voltage application circuit 3 outputs an A-phase voltage from a node N1 by complementarily turning on and off two switching elements Q1 and Q2 of the half-bridge circuit 12. In addition, the voltage application circuit 3 outputs a B-phase voltage from a node N2 by complementarily turning on and off switching elements Q3 and Q4 of the half-bridge circuit 13.

[0023] The voltage application circuit 3 is configured to output the output voltages of the half-bridge circuits 12, 13 outputted from a node N1 which is an interconnection node of the two switching elements Q1, Q2 and a node N2 which is an interconnection node of the two switching elements Q3, Q4 as the A-phase voltage and the B-phase voltage which are the drive voltages. The voltage application circuit 3 is also configured to output the voltages obtained by rectifying the A-phase voltage and the B-phase voltage with the diodes D1, D3, that is, the voltages at the cathodes of the diodes D1, D3, as the first fixed voltages, and to output the voltages obtained by rectifying the A-phase voltage and the B-phase voltage with the diodes D2, D4, that is, the voltages at the anodes of the diodes D2, D4, as the second fixed voltages.

[0024] The control circuit 14 controls the operation of the voltage application circuit 3 to generate a drive voltage to be applied to the rotor electrode 4 and the stator electrode 5, and has various functions for performing such control. As one of the above-mentioned functions, the control circuit 14 has a voltage adjustment unit 21 that adjusts the drive voltage according to a change in the inter-electrode distance between the rotor electrode 4 and the stator electrode 5. In this case, the voltage adjustment unit 21 functions in cooperation with various components provided outside the control circuit 14. The voltage adjustment unit 21 adjusts the drive voltage so that it does not exceed a withstand voltage determined according to the voltage at which a discharge occurs between the rotor electrode 4 and the stator electrode 5.

[0025] As a specific configuration of the voltage adjusting unit 21, for example, a first configuration example as shown in Fig. 5 or a second configuration example as shown in Fig. 6 can be adopted. Note that in Fig. 5 and Fig. 6, the half-bridge circuit 12 and a configuration corresponding to the half-bridge circuit 12, that is, a configuration for one phase, are illustrated and described, but the same applies to the half-bridge circuit 13 and a configuration corresponding to the half-bridge circuit 13.

[0026] [1] First configuration example of voltage adjustment unit In a first configuration example shown in Fig. 5 and a second configuration example shown in Fig. 6 described later, two resistors R2 and R3 that were omitted in Fig. 1 are shown. One terminal of the resistor R2 is connected to the source of the switching element Q1, and the other terminal is connected to a node N1. One terminal of the resistor R3 is connected to the node N1, and the other terminal is connected to the drain of the switching element Q2. The resistors R2 and R3 are resistors provided primarily for the purpose of protection, in order to prevent an excessive current from flowing through the half-bridge circuits 12 and 13.

[0027] 5, the control circuit 14A in the first configuration example includes a pulse generating unit 23, an OR circuit 24, a comparator 25, and a dielectric strength voltage calculating unit 26. In the first configuration example, the OR circuit 24, the comparator 25, and the dielectric strength voltage calculating unit 26 form a voltage adjusting unit 21A. The pulse generating unit 23 generates drive signals Sa and Sb. The drive signal Sa is input to the gate of the switching element Q1 via a buffer 15. The drive signal Sb is input to one input terminal of the OR circuit 24.

[0028] The output signal of the comparator 25 is input to the other input terminal of the OR circuit 24. The output signal of the OR circuit 24 is input to the gate of the switching element Q2 via the buffer 16. The A-phase voltage, which is the voltage of the node N1, that is, the drive voltage, is input to the non-inverting input terminal of the comparator 25. The upper limit voltage Va output from the insulation voltage calculation unit 26 is input to the inverting input terminal of the comparator 25. The insulation voltage calculation unit 26 calculates the inter-electrode distance and the insulation voltage based on the rotation signal Sc. Note that the insulation voltage corresponds to the above-mentioned withstand voltage, and therefore, hereinafter, the insulation voltage will be referred to as the withstand voltage.

[0029] The withstand voltage calculation unit 26 calculates the withstand voltage as follows. First, as shown in FIG. 7, in the electrostatic motor 2, the inter-electrode distance changes depending on the rotational position, that is, the electrical angle. The inter-electrode distance is determined with respect to the electrical angle by the structural design of the electrostatic motor 2. Also, as shown in FIG. 8, in the electrostatic motor 2, the withstand voltage changes depending on the electrical angle. The withstand voltage is determined by the electrode material, which is the material of the electrodes 4, 5, and the shapes of the electrodes 4, 5. Also, in a vacuum, the withstand voltage is proportional to the distance at 1 mm or less, and is proportional to the 0.5 to 0.7 power of the distance at 1 mm or more.

[0030] In this specification, for convenience, the rotational position is expressed in terms of electrical angle, but in reality, the withstand voltage between the electrodes, i.e., the withstand voltage, is determined according to the distance. It is necessary to note that the relationship between the electrical angle and the actual distance may differ depending on the electrode arrangement of the electrostatic motor 2. For example, the inner side of an electrode array motor is closer in distance. Therefore, basically, the inner side can be considered as the closest. Also, the electrical angle and the actual distance will change depending on the motor structure, specifically, the distance between the electrodes, the motor outer diameter, the number of poles, the number of electrodes, etc.

[0031] As shown in Figures 9 and 10, for example, when the number of poles is different, the correspondence relationship between the electrical angle and the distance is different. In this case, the number of poles is greater in the configuration shown in Figure 10 than in the configuration shown in Figure 9. As shown in Figures 9 and 10, even for the same electrical angle θ, the inter-electrode distance is shorter in a configuration with a relatively greater number of poles than in a configuration with a relatively smaller number of poles. Taking these points into consideration, the insulation withstand voltage calculation unit 26 calculates and acquires the withstand voltage based on the rotation signal Sc.

[0032] The withstand voltage calculation unit 26 may be configured to acquire the withstand voltage by referring to a map that is created in advance with the above points in mind and that indicates the relationship between the electrical angle and the withstand voltage. The withstand voltage calculation unit 26 sets the voltage obtained by subtracting a predetermined margin from the acquired withstand voltage as the upper limit voltage. According to this first configuration example, when the drive voltage falls below the upper limit voltage, the switching element Q2 of the lower arm is turned on and off by the drive signal Sb. According to the first configuration example, when the drive voltage exceeds the upper limit voltage, the switching element Q2 of the lower arm is forced on and the charge of the electrode capacitance 6 is extracted, and as a result, the drive voltage is controlled to decrease to a voltage equal to or lower than the upper limit voltage, that is, to a target voltage that is a target voltage.

[0033] In this way, the voltage adjustment unit 21A of the first configuration example adjusts the drive voltage by turning on one of the two switching elements Q1 and Q2, that is, the switching element Q2, to discharge the electrode capacitance 6 formed between the rotor electrode 4 and the stator electrode 5. In the first configuration example, the time constant of the discharge of the electrode capacitance 6, that is, the slope of the decrease in the drive voltage, can be adjusted by the resistance value of the resistor R3. Furthermore, the voltage adjustment unit 21A of the first configuration example acquires the withstand voltage that changes according to the rotational position of the electrostatic motor 2, and adjusts the drive voltage so that it becomes a target voltage having a certain margin with respect to the acquired withstand voltage.

[0034] [2] Second configuration example of voltage regulator 6, the control circuit 14B in the second configuration example differs from the control circuit 14A in the first configuration example in that the OR circuit 24 is omitted. In this case, the drive signal Sb generated by the pulse generating unit 23 is input to the gate of the switching element Q2 via a buffer 16. Also, in this case, a switching element Q11, a resistor R11, and a buffer 27 are provided outside the control circuit 14B.

[0035] The switching element Q11 can be configured by a transistor such as a MOSFET or an IGBT. In this case, the switching element Q11 is an N-channel MOSFET. The drain of the switching element Q11 is connected to a node N1 via a resistor R11, and the source of the switching element Q11 is connected to a ground 10. The switching element Q11 functions as an adjustment switching element connected between the node N1, which is an interconnection node of the two switching elements Q1 and Q2 of the half-bridge circuit 12, and the ground 10. In this case, the output signal of the comparator 25 is input to the gate of the switching element Q11 via a buffer 27.

[0036] In the second configuration example, the voltage adjustment unit 21B is configured by the comparator 25, the withstand voltage calculation unit 26, the switching element Q11, the resistor R11, and the buffer 27. According to such a second configuration example, the switching element Q2 of the lower arm is turned on and off by the drive signal Sb regardless of the operation of the voltage adjustment unit 21B. Also, according to the second configuration example, when the drive voltage exceeds the upper limit voltage, the switching element Q11 functioning as an adjustment switching element is forcibly turned on to extract the charge of the electrode capacitance 6, and as a result, the drive voltage is controlled to decrease to a voltage equal to or lower than the upper limit voltage, that is, the target voltage which is the target voltage.

[0037] In this way, the voltage adjustment unit 21B of the second configuration example adjusts the drive voltage by turning on the switching element Q11, which is an adjustment switching element, to discharge the electrode capacitance 6 formed between the rotor electrode 4 and the stator electrode 5. In the second configuration example, the time constant of the discharge of the electrode capacitance 6, that is, the slope of the decrease in the drive voltage, can be adjusted by the resistance value of the resistor R11. Furthermore, the voltage adjustment unit 21B of the second configuration example obtains the withstand voltage that changes according to the rotational position of the electrostatic motor 2, and adjusts the drive voltage so that it becomes a target voltage with a certain margin relative to the obtained withstand voltage.

[0038] The flow of operations related to the adjustment of the drive voltage by the voltage adjustment unit 21A of the first configuration example and the voltage adjustment unit 21B of the second configuration example is shown in a flowchart in Fig. 11. As shown in Fig. 11, in step S101, data such as the inter-electrode distance and the withstand voltage are acquired. After step S101 is executed, the process proceeds to step S102, where it is determined whether the drive voltage is less than the upper limit voltage. If the drive voltage is less than the upper limit voltage, the result in step S102 is "YES", and the series of operations ends without executing steps S103 and thereafter.

[0039] On the other hand, if the driving voltage is equal to or higher than the upper limit voltage, the result in step S102 becomes "NO" and the process proceeds to step S103. In step S103, the lower arm switching element Q2 or the adjustment switching element Q11 is turned on, and the discharge of the electrode capacitance 6 is started. In FIG. 11 and other figures, the lower arm switching element is referred to as the lower SW, and the adjustment switching element is referred to as the adjustment SW. After step S103 is executed, the process proceeds to step S104, where it is determined whether the driving voltage is lower than the upper limit voltage. Here, if the driving voltage is equal to or higher than the upper limit voltage, the result in step S104 becomes "NO", and step S104 is executed again. On the other hand, if the driving voltage is lower than the upper limit voltage, the result in step S104 becomes "YES", and the process proceeds to step S105.

[0040] In step S105, the lower arm switching element Q2 or the adjustment switching element Q11 is turned off, and the discharge of the electrode capacitance 6 is stopped. After step S105 is executed, the series of operations is terminated. That is, in this case, after the discharge of the electrode capacitance 6 is started, the discharge continues as long as the drive voltage is equal to or higher than the upper limit voltage, but the discharge is stopped when the drive voltage falls below the upper limit voltage. Through this series of operations, feedback control is performed so that the drive voltage becomes less than the upper limit voltage.

[0041] Next, the operating waveforms of each part in the above configuration will be described with reference to Fig. 12. Note that, although the operating waveforms in the half-bridge circuit 12 will be described as an example here, the same applies to the operating waveforms in the configuration corresponding to the half-bridge circuit 13. Also, although the explanation will be given as an example here in which the second configuration example is adopted as the voltage adjustment unit 21, the same applies to the case in which the first configuration example is adopted as the voltage adjustment unit 21.

[0042] In Fig. 12 and other figures, the high level of each of the drive signals including the drive signals Sa and Sb is a level that turns on the switching element, and the low level is a level that turns off the switching element. Also, in Fig. 12, the on / off state of the adjustment switching element Q11 is expressed by a binary signal, specifically, a signal that indicates on by being at a relatively high level and off by being at a relatively low level. As shown in Fig. 12, when the drive signal Sa goes to a high level, the drive voltage rises to the power supply voltage VDD. Then, half a cycle later, when the drive signal Sb goes to a high level, the drive voltage drops to 0V.

[0043] 12, the upper limit voltage, i.e., the target voltage, reaches a maximum value when the drive signal Sa or Sb changes from low level to high level, and then gradually decreases to a minimum value after a half cycle. In this case, during the period when both the drive signals Sa and Sb are off, the switching element Q11 is repeatedly turned on and off so that the drive voltage is less than the target voltage. When the first configuration example is adopted as the voltage adjustment unit 21, the switching element Q2 of the lower arm is repeatedly turned on and off during the above period.

[0044] According to the present embodiment described above, the following effects can be obtained. The drive circuit 1 of this embodiment includes a voltage application circuit 3 that applies a drive voltage to the rotor electrodes 4 and the stator electrodes 5, and a voltage adjustment unit 21 that adjusts the drive voltage in response to changes in the inter-electrode distance. With this configuration, it is possible to adjust the drive voltage to a voltage value that provides a desired torque without exceeding the withstand voltage. Therefore, this embodiment has the excellent effect of preventing discharge between the electrodes without causing a decrease in output.

[0045] The effect obtained by this embodiment becomes clearer when compared with the conventional technology. Therefore, the effect obtained by this embodiment will be described in detail below with reference to Figs. 13 and 14 while comparing this embodiment with two comparative examples corresponding to the conventional technology. Fig. 13 shows an image of the operation of the electrodes of the electrostatic motor 2, which is a schematic representation of the rotor electrode 4 and the stator electrode 5, and indicates that the voltage applied to each electrode is "positive" by adding "+" and that it is "GND" by adding [-]. Fig. 14 shows an image of the operation of the electrodes, which is a linear representation of the operation image shown in Fig. 13.

[0046] As shown in FIG. 13 and FIG. 14, in the electrostatic motor 2, when the electrical angle is 0°, 180°, or 360°, the inter-electrode distance is the smallest, that is, the electrodes are at the closest positions. At the closest positions, discharge is most likely to occur. However, at the closest positions, the torque in the rotational direction is zero. The first comparative example is configured in such a way that no measures are taken to prevent discharge between the electrodes. In the first comparative example, the drive voltage is not lowered between the closest positions, so that the waveform of the drive voltage is a square wave whose level is inverted at the closest positions. Therefore, in the first comparative example, the drive voltage may exceed the withstand voltage at around the electrical angle of 180°, which may result in discharge between the electrodes.

[0047] In the second comparative example, in order to prevent discharge between the electrodes, a measure is taken to remove the charge and reduce the voltage before the electrodes approach each other. In the second comparative example, the drive voltage is completely reduced from "positive" to 0V, which is "GND", a little before the electrical angle of 180°. Therefore, in the second comparative example, the drive voltage does not exceed the withstand voltage near the electrical angle of 180°, and as a result, no discharge occurs between the electrodes. However, in the second comparative example, the drive voltage is completely reduced to 0V a little before the electrical angle of 180°, so the torque also decreases to 0. In the electrostatic motor 2, the peak of the electrostatic force is at the approach position, but in the second comparative example, such electrostatic force is not fully used.

[0048] In contrast, in this embodiment, like the first comparative example, the waveform of the drive voltage is such that the level is inverted at the closest position, but unlike the first comparative example, the drive voltage is reduced between the closest positions so as not to exceed the withstand voltage. Therefore, in this embodiment, the drive voltage does not exceed the withstand voltage in the entire period including the vicinity of the electrical angle of 180°, and as a result, no discharge occurs between the electrodes. Moreover, in this embodiment, the drive voltage is not completely reduced to 0V between the closest positions, but is maintained at a level as high as possible within the range that does not exceed the withstand voltage. Therefore, according to this embodiment, it is possible to improve the torque while using up the withstand voltage and suppressing discharge between the electrodes.

[0049] As specific configurations of the voltage adjustment unit 21, a first configuration example shown in FIG. 5 and a second configuration example shown in FIG. 6 can be adopted. The voltage adjustment unit 21A of the first configuration example and the voltage adjustment unit 21B of the second configuration example each have the following advantages. According to the first configuration example, the electrode capacitance 6 is discharged using the switching elements Q2 and Q4 of the half-bridge circuits 12 and 13 that are originally provided, so that the circuit scale can be kept small compared to a configuration in which a switching element for discharging is separately provided. According to the second configuration example, the switching speed of the switching element Q11 for discharging the electrode capacitance 6 and the time constant for discharging the electrode capacitance 6 can be changed without affecting the characteristics of the half-bridge circuits 12 and 13.

[0050] The voltage adjustment unit 21 adjusts the drive voltage so that it becomes a target voltage with a certain margin with respect to the withstand voltage. With this configuration, it is possible to include error factors, specifically factors such as the dimensions of each part and electric field concentration, in the margin, and it is possible to prevent the drive voltage from exceeding the withstand voltage due to such errors and causing discharge between the electrodes.

[0051] <Modifications of the voltage application circuit> The voltage application circuit 3 may be configured to apply a first fixed voltage and a second fixed voltage to one of the electrodes 4, 5, and to apply an A-phase voltage and a B-phase voltage to the other of the electrodes 4, 5. Several modified examples of the voltage application circuit 3 will be described below with reference to Figs. 15 to 20.

[0052] [1] First modified example of the voltage application circuit 15, the voltage application circuit 3A of the first modified example is different from the voltage application circuit 3 in the connection form with the electrostatic motor 2. That is, in the voltage application circuit 3A, the nodes N1 and N2 are connected to the rotor electrode 4, and the cathodes of the diodes D1 and D3 and the anodes of the diodes D2 and D4 are connected to the stator electrode 5. In this manner, the voltage application circuit 3A is configured to apply an A-phase voltage and a B-phase voltage to the rotor electrode 4, and to apply a first fixed voltage and a second fixed voltage to the stator electrode 5.

[0053] [2] Second variant of voltage application circuit As shown in FIG. 16, the voltage application circuit 3B of the second modification is different from the voltage application circuit 3 in that the diodes D1 to D4 are omitted. In the voltage application circuit 3B, the node N1 and the node N2 are connected to the stator electrode 5. That is, the voltage application circuit 3B is configured to output the output voltages of the half-bridge circuits 12 and 13 outputted from the node N1, which is the interconnection node of the two switching elements Q1 and Q2, and the node N2, which is the interconnection node of the two switching elements Q3 and Q4, as the A-phase voltage and the B-phase voltage, which are the drive voltages. In addition, in the voltage application circuit 3B, the power supply line 9 and the ground 10 are connected to the rotor electrode 4. That is, the voltage application circuit 3B is configured to output the voltage supplied from the DC power supply 8 as the first fixed voltage and the second fixed voltage, which are the drive voltages.

[0054] [3] Third variant of voltage application circuit 17, the voltage application circuit 3C of the third modified example differs from the voltage application circuit 3B of the second modified example in the connection form with the electrostatic motor 2. That is, in the voltage application circuit 3C, the node N1 and the node N2 are connected to the rotor electrode 4, and the power line 9 and the ground 10 are connected to the stator electrode 5. In this manner, the voltage application circuit 3C is configured to apply an A-phase voltage and a B-phase voltage to the rotor electrode 4, and to apply a first fixed voltage and a second fixed voltage to the stator electrode 5.

[0055] Even when the configurations of the first to third modified examples are adopted for the voltage application circuit 3, the electrostatic motor 2 is driven in the same manner as in the above embodiment, and the same actions and effects as in the above embodiment can be obtained. However, when the configurations of the second and third modified examples are adopted for the voltage application circuit 3, the following ingenuity is required. That is, in the configuration in which the first fixed voltage is generated by rectifying the voltages at the nodes N1, N2 with the diodes D1, D3, as in the above embodiment and first modified example, the first fixed voltage, the A-phase voltage, and the B-phase voltage have waveforms as shown in FIG.

[0056] That is, when the above embodiment and the first modified example are adopted, if the withstand voltage of the A-phase voltage and the B-phase voltage with respect to GND is ensured, it is guaranteed that the voltage between the electrodes 4, 5 will be equal to or lower than the withstand voltage. Therefore, when the above embodiment and the first modified example are adopted, the voltage adjustment unit 21 only needs to be configured to adjust the drive voltage by turning on the lower arm switching elements Q2, Q4 or the adjustment switching element Q11 to discharge the electrode capacitance 6.

[0057] In contrast, in the case of a configuration in which the voltage supplied from the DC power supply 8 is output as the first fixed voltage, as in the second and third modified examples, it is necessary to ensure a withstand voltage for the first fixed voltage, i.e., the positive fixed voltage. Therefore, when the second and third modified examples are adopted, the voltage adjustment unit 21 must further adjust the drive voltage by turning on the switching elements Q1 and Q3 of the upper arm to charge the electrode capacitance 6.

[0058] When the second or third modified example is adopted, a switching element for adjustment may be provided separately connected in parallel to the switching elements Q1 and Q3 of the upper arm, and the voltage adjustment unit 21 may adjust the drive voltage by turning on the switching element for adjustment to charge the electrode capacitance 6. The concept of such control regarding the charging of the electrode capacitance 6 is similar to the control regarding the discharging of the electrode capacitance 6 described in the above embodiment. When the second or third modified example is adopted, the voltage adjustment unit is also configured to perform the above control, so that the first fixed voltage, the A-phase voltage, and the B-phase voltage have waveforms as shown in FIG.

[0059] <Modifications of the Voltage Regulator> In the above embodiment, the voltage adjustment unit 21 adjusts the drive voltage applied to one of the electrodes 4 and 5, but it can be modified to adjust the drive voltage applied to both the electrodes 4 and 5. However, when adopting such a modified voltage adjustment unit, it is necessary to change the voltage application circuit as well. That is, as shown in FIG. 20, when adopting a voltage adjustment unit 21D that adjusts the drive voltage applied to both the electrodes 4 and 5, the voltage application circuit 3D includes, in addition to the half-bridge circuits 12 and 13, half-bridge circuits 12D and 13D that have the same configuration as the half-bridge circuits 12 and 13.

[0060] In other words, the voltage application circuit 3D has two sets of half-bridge circuits added to the voltage application circuit 3. Such a modified voltage adjustment unit 21D makes it possible to simultaneously adjust the drive voltages applied to both electrodes 4 and 5, and as a result, the adjustment range for the withstand voltage can be halved compared to the voltage adjustment unit 21 of the above embodiment. The contents of control related to the adjustment of the drive voltage can be the same as those described in each of the above embodiments.

[0061] Second embodiment The second embodiment will be described below with reference to FIGS. 21, the drive circuit 31 of the present embodiment differs from the drive circuit 1 of the first embodiment in that it includes a control circuit 32 instead of the control circuit 14. The control circuit 32 includes a voltage adjustment unit 33 as one of its functions.

[0062] The voltage adjustment unit 33 adjusts the drive voltage in the same manner as the voltage adjustment unit 21 of the first embodiment. However, the voltage adjustment unit 33 adjusts the drive voltage by utilizing a change in electrode capacitance according to a change in the inter-electrode distance. The voltage adjustment unit 33 also adjusts the drive voltage by duty controlling the on / off of two switching elements provided in each of the half-bridge circuits 12 and 13. Such adjustment of the drive voltage is performed based on the following concept.

[0063] That is, as shown in Fig. 22, the capacitance value of the electrode capacitance 6 changes according to the electrical angle. Therefore, it can be said that the electrode capacitance 6 is a variable capacitance that changes according to the electrical angle, that is, the electrode position. And, as shown in the following formulas (1) and (2), the voltage V of the electrode capacitance 6 becomes smaller as the capacitance C becomes larger, where Q is the electric charge. Q = C × V … (1) V = Q / C … (2)

[0064] 23, during the period when the drive voltage is applied between the electrodes 4 and 5, the voltage of the electrode capacitance 6 is constant at the applied voltage, i.e., the power supply voltage VDD or 0 V. However, when the application of the drive voltage is stopped, the voltage of the electrode capacitance 6 changes according to the inter-electrode distance, i.e., the capacitance value of the electrode capacitance 6. Specifically, the voltage of the electrode capacitance 6 decreases as the inter-electrode distance decreases, i.e., the capacitance value of the electrode capacitance 6 increases. In this embodiment, the drive voltage is adjusted by utilizing such characteristics of the electrode capacitance 6.

[0065] As shown in Fig. 24, in the above configuration, the output voltage of the half-bridge circuits 12 and 13, i.e., the waveform of the drive voltage, can be controlled by changing the pulse width, i.e., the duty, of the drive signals Sa, Sb, Sd, and Se. In this specification, "duty" refers to the ratio of the period during which the drive signal is at a level that turns on the switching element in one cycle of the drive signal, i.e., the on-duty. Note that in Fig. 24, the change in the drive voltage on the 0V side is omitted.

[0066] 24 and 25, the smaller the duty is, the earlier the timing at which the drive voltage drops from the power supply voltage VDD becomes, and the lower the drive voltage becomes when the electrical angle is 180°, compared to when the duty is greater. According to the method for adjusting the drive voltage of this embodiment, the drive voltage waveform can be made to have a gentle decreasing curve similar to the curve showing the relationship between the electrical angle and the withstand voltage shown in FIG. As a specific configuration of the voltage adjusting unit 33, for example, a first configuration example as shown in FIG. 26 or a second configuration example as shown in FIG. 27 can be adopted.

[0067] [1] First configuration example of voltage adjustment unit As shown in FIG. 26, a control circuit 32A of the first configuration example differs from the control circuit 14A of the first embodiment in that a pulse generating section 34 is provided instead of the pulse generating section 23.

[0068] The pulse generating unit 34 generates the drive signals Sa and Sb. The drive signal Sa is input to the gate of the switching element Q1 via the buffer 15. The drive signal Sb is input to the gate of the switching element Q2 via the buffer 16. In this case, the output signal of the comparator 25 is input to the pulse generating unit 34. The pulse generating unit 34 controls the duty of the drive signals Sa and Sb based on the output signal of the comparator 25. In the first configuration example, the comparator 25, the insulation withstand voltage calculating unit 26, and the pulse generating unit 34 form a voltage adjusting unit 33A.

[0069] The voltage adjustment unit 33A utilizes the change in the drive voltage caused by the change in the capacitance value of the electrode capacitance 6 to control the duty of the drive signals Sa, Sb so that the drive voltage becomes a target voltage having a certain margin with respect to the withstand voltage. The flow of operations related to the adjustment of the drive voltage by the voltage adjustment unit 33A of the first configuration example is shown in a flowchart in Figure 28. The flow of operations shown in Figure 28 differs from the flow of operations in the first embodiment shown in Figure 11 in that step S203 is provided instead of step S103 and step S105 is omitted.

[0070] In step S203, the duty of the drive signal is changed to be lower by a predetermined value, that is, the duty of the drive signal is reduced. After step S203 is executed, the process proceeds to step S104, where it is determined whether the drive voltage is less than the upper limit voltage. If the drive voltage is equal to or greater than the upper limit voltage, the result is "YES" in step S104, and the process returns to step S203, where the duty of the drive signal is further reduced. On the other hand, if the drive voltage is less than the upper limit voltage, the result is "NO" in step S104, and the series of operations ends.

[0071] In the voltage adjustment unit 33A of the first configuration example, the duty considered to be optimal is determined in advance in consideration of characteristics such as the change in the capacitance value of the electrode capacitance 6, and the switching elements Q1 and Q2 are controlled to be turned on and off, and then, if the drive voltage exceeds the upper limit voltage during actual operation, the duty is dynamically controlled to be lowered. By such control, the voltage adjustment unit 33A of the first configuration example prevents the drive voltage from rising beyond the upper limit voltage, and as a result, discharge between the electrodes is prevented.

[0072] [2] Second configuration example of voltage regulator 27, the control circuit 32B of the second configuration example differs from the control circuit 32A of the first configuration example in that the comparator 25 is omitted and a duty calculation unit 35 is added. The duty calculation unit 35 calculates an optimal duty such that the drive voltage does not exceed an upper limit voltage. The duty calculation unit 35 can also be configured to obtain the duty by referring to a map that indicates the relationship between the electrical angle and the optimal duty, which is created in advance.

[0073] A power supply voltage VDD is input to the control circuit 32B. Although details will be described later, the duty calculation unit 35 determines whether or not to perform duty calculation based on the voltage value of the power supply voltage VDD. The duty calculation unit 35 outputs a signal representing the calculated or acquired duty to the pulse generation unit 34. The pulse generation unit 34 generates drive signals Sa, Sb based on the signal representing the duty provided from the duty calculation unit 35. In the second configuration example, the insulation withstand voltage calculation unit 26, the pulse generation unit 34, and the duty calculation unit 35 form a voltage adjustment unit 33B.

[0074] The flow of operations related to the adjustment of the drive voltage by the voltage adjustment unit 33B of the second configuration example is shown in a flowchart in Fig. 29. The flow of operations shown in Fig. 29 differs from the flow of operations in the first configuration example shown in Fig. 28 in that steps S302, S303, and S304 are provided instead of steps S102, S203, and S104. In step S302, it is determined whether the voltage value of the power supply voltage VDD is smaller than the closest proximity withstand voltage, which is the withstand voltage when the electrodes are at the closest position, that is, the maximum withstand voltage.

[0075] Here, if the voltage value of the power supply voltage VDD is equal to or greater than the closest withstand voltage, the result in step S302 is "NO" and the process proceeds to step S303. In step S303, the duty is calculated as described above. After step S303 is executed, the process proceeds to step S304, where the drive signals Sa, Sb having the calculated duty are generated. On the other hand, if the voltage value of the power supply voltage VDD is smaller than the closest withstand voltage, the result in step S302 is "YES", and the process skips step S303 and proceeds to step S304. In this case, in step S304, the duty is not reduced and drive signals Sa, Sb having a duty of 100% are generated. After step S304 is executed, the series of operations ends.

[0076] The voltage adjustment unit 33B of the second configuration example controls the on / off of the switching elements Q1 and Q2 by calculating or obtaining from a map a duty that is considered to be optimal, without measuring and feeding back the drive voltage. With this control, the voltage adjustment unit 33B of the second configuration example prevents the drive voltage from rising above the upper limit voltage, and as a result, discharge between the electrodes is prevented. In the first place, when the power supply voltage VDD is a voltage value less than the closest withstand voltage, there is no possibility of discharge occurring between the electrodes.

[0077] Therefore, in the voltage adjustment unit 33B of the second configuration example, when the power supply voltage VDD is a voltage value less than the closest withstand voltage, the drive signals Sa, Sb are generated without reducing the duty. Note that the voltage adjustment unit 33B of the second configuration example can also be modified to perform duty calculation even when the power supply voltage VDD is a voltage value less than the closest withstand voltage. When modified in this way, step S303 in FIG. 29 can be omitted.

[0078] This embodiment can also provide the same effect as the first embodiment. The effect provided by this embodiment becomes clearer when compared with the conventional technology. Therefore, the effect provided by this embodiment will be described in detail below with reference to Figs. 30 and 31 while comparing this embodiment with a comparative example corresponding to the conventional technology. The comparative example performs control that does not reduce the duty of the drive signal, that is, square wave control that sets the duty of the drive signal to 100%.

[0079] As shown in Figs. 30 and 31, in the comparative example, the drive voltage is limited by the withstand voltage at the closest position, which is the position where the electrical angle is 180°, so that there is a possibility that sufficient torque cannot be obtained. In contrast, in this embodiment, the duty is controlled so that the drive voltage does not exceed the withstand voltage at each position, including the position where the electrical angle is 180°, so that the drive voltage is maintained at a level as high as possible within a range where the drive voltage does not exceed the withstand voltage. Therefore, according to this embodiment, it is possible to improve the torque per cycle while suppressing discharge between the electrodes. Furthermore, according to this embodiment, such discharge suppression can be achieved only by duty control, which is relatively easy to control.

[0080] Third embodiment The third embodiment will be described below with reference to FIGS. 32, a drive circuit 41 of the present embodiment differs from the drive circuit 1 of the first embodiment in that a control circuit 42 is provided instead of the control circuit 14. The control circuit 42 includes a voltage adjustment unit 43 as one of its functions. The voltage adjustment unit 43 has the functions of both the voltage adjustment unit 21 of the first embodiment and the voltage adjustment unit 33 of the second embodiment.

[0081] The voltage adjustment unit 43 controls the duty, i.e., the pulse width, of the drive signal by utilizing a change in the drive voltage caused by a change in the capacitance value of the electrode capacitance 6. When there is a possibility that the drive voltage will exceed the withstand voltage, the voltage adjustment unit 43 drives the lower arm switching elements Q2, Q4, etc. to control the discharge of the charge of the electrode capacitance 6 so that the drive voltage will be below the withstand voltage. The flow of operations related to the adjustment of the drive voltage by the voltage adjustment unit 43 is shown in a flowchart in Figure 33.

[0082] The operation flow shown in Fig. 33 differs from the operation flow in the first configuration example shown in Fig. 11 in that steps S403 and S405 are provided instead of steps S103 and S105. In step S403, duty control is performed similarly to that of the voltage adjustment unit 33 in the second embodiment. After step S403 is executed, the process proceeds to step S104, where it is determined whether the drive voltage is less than an upper limit voltage.

[0083] In this case, if the driving voltage is equal to or greater than the upper limit voltage, step S104 becomes "NO" and the process proceeds to step S405. In step S405, discharge control is performed similarly to that of the voltage adjustment unit 21 in the first embodiment. After step S405 is performed, the series of operations ends. On the other hand, if the driving voltage is less than the upper limit voltage, step S104 becomes "YES" and the series of operations ends.

[0084] According to this embodiment, basically, the same actions and effects as those of the second embodiment can be obtained. Furthermore, according to this embodiment, even if the accuracy of the control similar to that of the second embodiment, that is, the duty control based on the relationship between the characteristics of the electrode capacitance 6 and the withstand voltage, is not sufficient, or even if the voltage reduction by the duty control alone is insufficient to reduce the driving voltage below the withstand voltage, the discharge control of the electrode capacitance 6 described in the first embodiment is performed, so that the occurrence of discharge can be reliably prevented.

[0085] (Other embodiments) The present invention is not limited to the embodiments described above and shown in the drawings, and can be modified, combined, or expanded as desired without departing from the spirit and scope of the present invention. The numerical values ​​and the like shown in the above embodiments are merely examples and are not intended to be limiting.

[0086] Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, and other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure. [Explanation of symbols]

[0087] 1...electrostatic motor drive circuit, 2...electrostatic motor, 3, 3A, 3B, 3C, 3D...voltage application circuit, 4...rotor electrode, 5...stator electrode, 6...electrode capacitance, 9...power supply line, 10...ground, 12, 13, 12D, 13D...half bridge circuit, 21, 21A, 21B, 21D, 33, 33A, 33B, 43...voltage adjustment section, Q1, Q2, Q3, Q4...switching element, Q11...switching element.

Claims

1. An electrostatic motor drive circuit for driving an electrostatic motor (2) configured to obtain a rotational force by an electrostatic force generated between a rotor electrode (4) which is an electrode provided on a rotor and a stator electrode (5) which is an electrode provided on a stator, comprising: a voltage application circuit (3, 3A, 3B, 3C, 3D) that applies a drive voltage to the rotor electrodes and the stator electrodes; a voltage adjusting unit (21, 21A, 21B, 21D, 33, 33A, 33B, 43) for adjusting the drive voltage in response to a change in an inter-electrode distance between the rotor electrode and the stator electrode; 1. An electrostatic motor drive circuit comprising:

2. 2. The electrostatic motor drive circuit according to claim 1, wherein the voltage adjustment unit adjusts the drive voltage so that the drive voltage does not exceed a withstand voltage determined according to a voltage at which a discharge occurs between the rotor electrode and the stator electrode.

3. The voltage application circuit includes: A half-bridge circuit (12, 13, 12D, 13D) including two switching elements (Q1, Q2, Q3, Q4) connected in series between a power supply line (9) to which a power supply voltage is applied and a ground (10) serving as a reference potential of the circuit, an output voltage of the half-bridge circuit output from an interconnection node of the two switching elements or a voltage generated using the output voltage is output as the drive voltage, 3. The electrostatic motor drive circuit according to claim 1, wherein the voltage adjustment unit adjusts the drive voltage by turning on one of the two switching elements to discharge or charge an electrode capacitance formed between the rotor electrode and the stator electrode.

4. The voltage application circuit includes: A half-bridge circuit (12, 13, 12D, 13D) including two switching elements (Q1, Q2, Q3, Q4) connected in series between a power supply line (9) to which a power supply voltage is applied and a ground (10) serving as a reference potential of the circuit, an output voltage of the half-bridge circuit output from an interconnection node of the two switching elements or a voltage generated using the output voltage is output as the drive voltage, The voltage adjustment unit (21B) a switching element (Q11) for adjustment connected between an interconnection node of the two switching elements and the power supply line or the ground; 3. The electrostatic motor drive circuit according to claim 1, wherein the drive voltage is adjusted by turning on the adjustment switching element to discharge or charge an electrode capacitance formed between the rotor electrode and the stator electrode.

5. The voltage adjustment unit is 4. The electrostatic motor drive circuit according to claim 3, wherein the drive voltage is adjusted by utilizing a change in the electrode capacitance in accordance with a change in the inter-electrode distance.

6. The voltage adjustment unit is 5. The electrostatic motor drive circuit according to claim 4, wherein the drive voltage is adjusted by utilizing a change in the electrode capacitance in accordance with a change in the inter-electrode distance.

7. The voltage adjustment unit is 6. The electrostatic motor drive circuit according to claim 5, wherein the drive voltage is adjusted by duty controlling the on / off of the two switching elements.

8. The voltage adjustment unit is 7. The electrostatic motor drive circuit according to claim 6, wherein the drive voltage is adjusted by duty controlling the on / off of the two switching elements.

9. 3. The electrostatic motor drive circuit according to claim 2, wherein the voltage adjustment unit acquires the withstand voltage, which changes depending on the rotational position of the electrostatic motor, and adjusts the drive voltage so that the drive voltage becomes a target voltage having a certain margin with respect to the acquired withstand voltage.

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