Control method of piezoelectric motor and piezoelectric motor

Abstract

The invention provides a control method of a piezoelectric motor and the piezoelectric motor, which can realize reduction of power consumption. A method for controlling a piezoelectric motor, characterized in that the piezoelectric motor has a piezoelectric vibrator that is provided with a piezoelectric element and vibrates by expansion and contraction of the piezoelectric element, and a drive circuit that is provided with an inductor that forms an LC circuit with the piezoelectric element, the piezoelectric vibrator is driven by applying an AC drive voltage to the piezoelectric element, and the resonant frequency of the LC circuit is changed by applying a DC bias voltage to the piezoelectric element such that the difference between the resonant frequency of the LC circuit and the drive frequency, which is the frequency of the drive voltage, is reduced.

Description

Technical Field

[0001] The invention relates to a control method of a piezoelectric motor and a piezoelectric motor. Background Art

[0002] For example, in the driving start method of an ultrasonic motor described in Patent Document 1, first, an oscillation circuit performs a downward sweep control to sweep the frequency of a driving signal (hereinafter also referred to as "driving frequency") downward from a pre-set initial frequency value to a peak frequency (resonance frequency of the ultrasonic motor) at a predetermined sweep rate. In addition, when the driving speed of the ultrasonic motor reaches a target speed, the oscillation circuit stops the downward sweep and switches to speed control that determines the driving frequency based on the difference between the speed information from the encoder and the target speed. According to such a method, the resonance of the ultrasonic motor can be gradually enhanced, and the driving start of the ultrasonic motor becomes stable. In addition, a driving frequency close to the peak frequency can be used, and the driving speed of the ultrasonic motor can be increased.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2016-13018

[0004] Here, the voltage amplification factor of the oscillation circuit changes according to the difference between the resonance frequency of the oscillation circuit and the driving frequency, and decreases as the difference increases. Therefore, in Patent Document 1, the voltage amplification factor of the oscillation circuit changes according to the change of the driving frequency, and it is not easy to continuously drive the ultrasonic motor with a high voltage amplification factor. Therefore, in Patent Document 1, there is a problem that it is difficult to achieve power saving. Summary of the invention

[0005] The control method of the piezoelectric motor involved in the present invention is characterized in that the piezoelectric motor has a piezoelectric vibrator and a driving circuit, the piezoelectric vibrator has a piezoelectric element and vibrates by the expansion and contraction of the piezoelectric element, and the driving circuit has an inductor that forms an LC circuit together with the piezoelectric element. In the control method of the piezoelectric motor, the piezoelectric vibrator is driven by applying an AC driving voltage to the piezoelectric element, and the resonant frequency of the LC circuit is changed by applying a DC bias voltage to the piezoelectric element in a manner that reduces the difference between the resonant frequency of the LC circuit and the frequency of the driving voltage, that is, the driving frequency.

[0006] The piezoelectric motor involved in the present invention has a piezoelectric vibrator and a driving circuit. The piezoelectric vibrator has a piezoelectric element and vibrates by the expansion and contraction of the piezoelectric element. The driving circuit has an inductor that forms an LC circuit together with the piezoelectric element. The piezoelectric motor drives the piezoelectric vibrator by applying an AC driving voltage to the piezoelectric element, and applies a DC bias voltage to the piezoelectric element in a manner that reduces the difference between the resonant frequency of the LC circuit and the frequency of the driving voltage, that is, the driving frequency, to change the resonant frequency of the LC circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a plan view showing the driving device according to the first embodiment.

[0008] Figure 2 It is a top view of the piezoelectric vibrator.

[0009] Figure 3 This is a three-dimensional exploded view of a piezoelectric motor.

[0010] Figure 4 This is a diagram showing the driving voltage applied to the piezoelectric vibrator.

[0011] Figure 5 It is a plan view showing a driving state of the piezoelectric vibrator.

[0012] Figure 6 is a block diagram showing a driving circuit.

[0013] Figure 7 : is a block diagram showing a modification example of the driving circuit.

[0014] Figure 8 This is a graph showing the relationship between the driving frequency and the moving speed of the slider.

[0015] Fig. 9 is a block diagram showing a conventional driving circuit.

[0016] Fig.10 It is a graph showing the moving speed of the slider and the voltage amplification factor of the LC circuit.

[0017] Fig.11 This is a graph showing the relationship between bias voltage and capacitance of a piezoelectric element.

[0018] Fig.12 This is a graph showing the relationship between the capacitance and voltage amplification factor of the piezoelectric element at a predetermined driving frequency and the driving voltage waveform signal.

[0019] Fig.13 This is a diagram showing a table showing the correspondence relationship between the driving frequency and the bias voltage.

[0020] Fig.14It is a diagram showing a plurality of tables set for each driving frequency.

[0021] Fig.15 It is a block diagram showing a driving circuit included in a driving device according to a second embodiment.

[0022] Fig.16 It is a plan view showing a robot system according to a third embodiment.

[0023] Description of Reference Numerals

[0024] 1…driving device; 2…slider; 3…piezoelectric motor; 4…piezoelectric vibrator; 4A…piezoelectric element; 4B…piezoelectric element; 4C…piezoelectric element; 4D…piezoelectric element; 4E…piezoelectric element; 4F…piezoelectric element; 40…piezoelectric element; 41…vibrating portion; 42…support portion; 43…connecting portion; 44…convex portion; 48…piezoelectric element layer; 49…substrate; 6…force applying member; 61…support portion; 62…base; 63…plate spring portion; 8…encoder; 9…driving circuit; 9A…driving circuit; 91…voltage waveform generating circuit; 911…AC power supply; 912…DC power supply; 92…inductor; 93…resistor; 94…LC circuit; 95…capacitor; 99…capacitor; 1000…robot system; 1100…robot; 1110…base; 1120…robot arm; 1121…first arm; 1122…second arm; 1123…third arm; 1124…fourth arm; 1125…third arm Fifth arm; 1126…sixth arm; 1131…first arm rotation mechanism; 1132…second arm rotation mechanism; 1133…third arm rotation mechanism; 1134…fourth arm rotation mechanism; 1135…fifth arm rotation mechanism; 1136…sixth arm rotation mechanism; 1200…movable workbench; 1210…base; 1220…first workbench; 1230…second workbench; 1240…first workbench moving mechanism; 1250…second workbench moving mechanism structure; 1300…tool; 1310…inkjet head; 1400…control unit; Av…voltage amplification factor; DC…bias voltage; Sd…voltage waveform signal; T…table; T1…table; T2…table; T3…table; T4…table; U…first direction; V…second direction; V1…driving voltage; V2…driving voltage; V3…driving voltage; Vd…driving voltage; f1…frequency; f2…frequency; fd…frequency; fr…resonance frequency; frc…resonance frequency. DETAILED DESCRIPTION

[0025] Hereinafter, a piezoelectric motor control method and a piezoelectric motor according to the present invention will be described in detail based on the embodiments shown in the drawings.

[0026] <First Embodiment>

[0027] Figure 1It is a plan view showing the driving device according to the first embodiment. Figure 2 It is a top view of the piezoelectric vibrator. Figure 3 This is a three-dimensional exploded view of a piezoelectric motor. Figure 4 This is a diagram showing the driving voltage applied to the piezoelectric vibrator. Figure 5 It is a plan view showing a driving state of the piezoelectric vibrator. Figure 6 is a block diagram showing a driving circuit. Figure 7 is a block diagram showing a modified example of the driving circuit. Figure 8 This is a graph showing the relationship between the driving frequency and the moving speed of the slider. Fig. 9 is a block diagram showing a conventional driving circuit. Fig.10 It is a graph showing the moving speed of the slider and the voltage amplification factor of the LC circuit. Fig.11 This is a graph showing the relationship between bias voltage and capacitance of a piezoelectric element. Fig.12 This is a graph showing the relationship between the capacitance of the piezoelectric element at a predetermined driving frequency, the voltage amplification factor, and the voltage waveform signal. Fig.13 This is a diagram showing a table showing the correspondence relationship between the driving frequency and the bias voltage. Fig.14 It is a diagram showing a plurality of tables set for each driving frequency.

[0028] It should be noted that, hereinafter, three axes orthogonal to each other are set as the X-axis, the Y-axis, and the Z-axis, the direction along the X-axis is also referred to as the X-axis direction, the direction along the Y-axis is also referred to as the Y-axis direction, and the direction along the Z-axis is also referred to as the Z-axis direction. In addition, the arrow side of each axis is also referred to as the "positive side", and the side opposite to the arrow is also referred to as the "negative side". In addition, the positive side in the Z-axis direction is also referred to as the "upper", the negative side in the Z-axis direction is also referred to as the "lower", the positive side in the X-axis direction is also referred to as the "front end", and the negative side in the X-axis direction is also referred to as the "base end".

[0029] Figure 1 The driving device 1 shown has a slider 2 as a driven body that moves linearly in the Y-axis direction, and a piezoelectric motor 3 that abuts against the slider 2. In addition, the piezoelectric motor 3 has a piezoelectric vibrator 4 that abuts against the slider 2, a force applying member 6 that presses the piezoelectric vibrator 4 toward the slider 2, an encoder 8 that detects the amount of movement of the slider 2, and a driving circuit 9 that drives the piezoelectric vibrator 4.

[0030] However, the configuration of the driving device 1 is not particularly limited. For example, a plurality of piezoelectric motors 3 may be provided to the slider 2, and the slider 2 may be linearly moved by driving the plurality of piezoelectric motors 3. In addition, the driven body may not move linearly like the slider 2, but may rotate like a rotor.

[0031] In addition, if Figure 2As shown, the piezoelectric vibrator 4 includes a vibrating portion 41 , a supporting portion 42 supporting the vibrating portion 41 , a connecting portion 43 connecting the vibrating portion 41 and the supporting portion 42 , and a convex portion 44 protruding from the front end of the vibrating portion 41 and transmitting vibration of the vibrating portion 41 to the slider 2 .

[0032] The vibration part 41 is a plate-shaped part extending in the XY plane including the X-axis and the Y-axis with the Z-axis direction as the thickness direction. In addition, the vibration part 41 is a rectangle with the X-axis direction as the expansion direction as the long side when viewed from above. In addition, the vibration part 41 is bent and vibrated in an S-shape by expanding and contracting in the X-axis direction while bending in the Y-axis direction. However, the shape of the vibration part 41 is not particularly limited as long as it can exert its function.

[0033] In addition, the vibration part 41 has a piezoelectric element 40 for driving the vibration part 41 to perform bending vibration. The piezoelectric element 40 has six piezoelectric elements 4A, 4B, 4C, 4D, 4E, and 4F. In the central part of the vibration part 41, the piezoelectric elements 4A and 4B are arranged in the X-axis direction. In addition, on the positive side of the Y-axis direction of the piezoelectric elements 4A and 4B, the piezoelectric elements 4C and 4D are arranged in the X-axis direction, and on the negative side of the Y-axis direction, the piezoelectric elements 4E and 4F are arranged in the X-axis direction. These piezoelectric elements 4A to 4F expand and contract in the X-axis direction by energizing each other.

[0034] In addition, among the piezoelectric elements 4A to 4F, the piezoelectric elements 4A and 4B are piezoelectric elements for causing the vibration part 41 to perform expansion and contraction vibration in the X-axis direction, and the piezoelectric elements 4C, 4D, 4E, and 4F are piezoelectric elements for causing the vibration part 41 to perform bending vibration in the Y-axis direction. However, the number and arrangement of the piezoelectric elements for driving are not particularly limited.

[0035] like Figure 3 As shown, the vibration part 41 is configured by sandwiching a piezoelectric element layer 48 including the piezoelectric element 40 between a pair of substrates 49, 49. Each substrate 49 is, for example, a silicon substrate.

[0036] In addition, the piezoelectric element 40 is a structure in which a piezoelectric body is sandwiched between a pair of electrodes. The material constituting the piezoelectric body is not particularly limited, and for example, piezoelectric ceramics such as lead zirconate titanate (PZT), barium titanate, lead titanate, potassium niobate, lithium niobate, lithium tantalate, sodium tungstate, zinc oxide, barium strontium titanate (BST), strontium bismuth tantalate (SBT), lead metaniobate, and scandium lead niobate can be used. In addition to the above-mentioned piezoelectric ceramics, polyvinylidene fluoride, quartz, etc. can also be used as the piezoelectric body.

[0037] In addition, the method for forming the piezoelectric body is not particularly limited, and the piezoelectric body can be formed from a bulk material, or can be formed using a sol-gel method or a sputtering method. In the present embodiment, the piezoelectric body is formed using a sol-gel method. Thus, for example, compared with the case where the piezoelectric body is formed from a bulk material, a thin piezoelectric body can be obtained, and the piezoelectric vibrator 4 can be made thinner.

[0038] The convex portion 44 is provided at the front end portion of the vibration portion 41 and protrudes from the vibration portion 41 toward the positive side in the X-axis direction. Figure 1 As shown in FIG. 1 , the front end of the protrusion 44 is pressed toward the side of the slider 2 by the force applying member 6. Therefore, the vibration of the vibrating portion 41 is transmitted to the slider 2 via the protrusion 44. The material constituting the protrusion 44 is not particularly limited, but various ceramics such as zirconium oxide, aluminum oxide, and titanium dioxide can be cited, for example. Thus, the protrusion 44 has excellent durability. However, the structure of the protrusion 44 is not particularly limited.

[0039] The support portion 42 supports the vibration portion 41. Figure 2 As shown in FIG. 4 , the support portion 42 is a U-shape surrounding three sides of the vibration portion 41. Figure 3 As shown, the support portion 42 is formed by sandwiching a spacer having substantially the same thickness as the piezoelectric element layer 48 between a pair of substrates 49, 49. However, the structure of the support portion 42 is not particularly limited as long as the function thereof can be achieved.

[0040] In addition, if Figure 2 As shown, the connection portion 43 connects the portion of the vibrating portion 41 that becomes a node of bending vibration, that is, the central portion in the X-axis direction, to the supporting portion 42. However, the configuration of the connection portion 43 is not particularly limited as long as it can exert its function.

[0041] The piezoelectric vibrator 4 as described above is urged toward the slider 2 by the urging member 6, so that the protrusion 44 is pressed toward the slider 2. Figure 3 As shown, a pair of the urging members 6 are provided so as to sandwich the piezoelectric vibrator 4 from above and below. Each urging member 6 includes a support portion 61 for supporting the piezoelectric vibrator 4, a base 62 for fixing the piezoelectric motor 3 to the workbench, and a plurality of plate-shaped spring portions 63 connecting the support portion 61 and the base 62. In the urging member 6 having such a configuration, by fixing the plate-shaped spring portion 63 to the workbench in a state where the plate-shaped spring portion 63 is elastically deformed, the convex portion 44 can be pressed toward the slider 2 by utilizing the elasticity (restoring force) of the plate-shaped spring portion 63.

[0042] The force-applying member 6 is a silicon substrate. Thus, a force-applying member 6 having sufficient mechanical strength and elasticity can be obtained. In addition, the force-applying member 6 can be manufactured with high processing accuracy by using a silicon wafer process. In addition, the difference in thermal expansion coefficient with the piezoelectric vibrator 4 becomes smaller, and thermal stress can be reduced. Therefore, the deflection, deformation, etc. of the piezoelectric vibrator 4 can be suppressed. However, the constituent material of the force-applying member 6 is not particularly limited.

[0043] For example, when Figure 4 When the driving voltage V1 is applied to the piezoelectric elements 4A and 4B, the driving voltage V2 is applied to the piezoelectric elements 4C and 4F, and the driving voltage V3 is applied to the piezoelectric elements 4D and 4E, as shown in FIG. Figure 5 As shown, the vibrating portion 41 performs expansion and contraction vibration in the X-axis direction and bending vibration in the Y-axis direction in an inverted S shape, and these vibrations are synthesized so that the front end of the convex portion 44 performs elliptical motion in a manner of describing an elliptical orbit in the counterclockwise direction as shown by the arrow. As a result, the slider 2 is sent out and moves linearly in the positive side of the Y-axis direction. In addition, when the waveforms of the driving voltages V2 and V3 are switched, on the contrary, the slider 2 moves linearly in the negative side of the Y-axis direction.

[0044] The driving circuit 9 is a circuit for driving the piezoelectric vibrator 4. Figure 6 As shown, the driving circuit 9 has a voltage waveform generating circuit 91 that generates a voltage waveform signal Sd having a voltage waveform having a driving voltage Vd, an inductor 92, and a resistor 93. In addition, an RLC series resonance circuit is formed by connecting the inductor 92, the resistor 93, and the piezoelectric element 40 in series. It should be noted that the RLC series resonance circuit is also referred to as "LC circuit 94" below. The LC circuit 94 functions as a voltage amplifier circuit that amplifies the voltage of the voltage waveform signal Sd generated by the voltage waveform generating circuit 91 to generate a driving voltage Vd. In addition, the current flowing to the piezoelectric element 40 is reduced by the inductor 92, so that the power consumption of the driving circuit 9 can be reduced. It should be noted that the LC circuit 94 is not particularly limited, for example, Figure 7 As shown, a capacitor 99 connected in parallel with the piezoelectric element 40 may be further provided.

[0045] The voltage waveform generating circuit 91 includes an AC power supply 911 and a DC power supply 912. The AC power supply 911 is a power supply for applying an AC voltage to the piezoelectric element 40. The DC power supply 912 is a power supply for applying a DC bias voltage DC to the piezoelectric element 40. The magnitude of the bias voltage DC can be freely changed.

[0046] It should be noted that the driving voltage Vd generated by the driving circuit 9 is equivalent to any one of the driving voltages V1 to V3 described above. Therefore, the piezoelectric motor 3 may also be configured to have three driving circuits 9 to generate the driving voltages V1 to V3. In addition, the piezoelectric motor 3 may also generate three driving voltages V1 to V3 having different phases based on the driving voltage Vd generated by one driving circuit 9 using a phase adjustment circuit that adjusts the phase of the driving voltage Vd.

[0047] Figure 8 It is a graph showing the relationship between the frequency of the driving voltage Vd, that is, the driving frequency fd, and the moving speed of the slider 2. As shown in the figure, in the region on the low-frequency side lower than the resonance frequency fr of the piezoelectric vibrator 4, as the driving frequency fd moves away from the resonance frequency fr, the moving speed of the slider 2 decreases sharply. In contrast, in the region on the high-frequency side higher than the resonance frequency fr, as the driving frequency fd moves away from the resonance frequency fr, the moving speed of the slider 2 decreases slowly. That is, compared with the region on the low-frequency side lower than the resonance frequency fr, the movement speed of the slider 2 in the region on the high-frequency side higher than the resonance frequency fr changes less with respect to the driving frequency fd, and it is easy to control the movement speed of the slider 2. Therefore, in the piezoelectric motor 3, as Figure 8 As shown by the hatched lines in , the driving frequency fd higher than the resonance frequency fr is used to control the driving of the piezoelectric vibrator 4. However, this is not limited to this, and the driving frequency fd lower than the resonance frequency fr may be used to control the driving of the piezoelectric vibrator 4.

[0048] Next, the starting method of the piezoelectric vibrator 4 is described. When the piezoelectric motor 3 starts the piezoelectric vibrator 4 from a stopped state, the driving frequency fd is set to a frequency f1 higher than the resonance frequency fr and the driving is started. Then, a "downward sweep control" is performed in which the driving frequency fd is gradually swept downward from the frequency f1 at a predetermined sweep rate to approach the resonance frequency fr. Then, when the driving frequency fd reaches a preset frequency f2 (fr<f2<f1), the downward sweep control is terminated and the control is transferred to a "frequency speed control" in which the driving frequency fd is determined based on the difference between the speed information of the slider 2 obtained from the output of the encoder 8 and the target speed.

[0049] It should be noted that since the piezoelectric vibrator 4 is pressed toward the slider 2 by the force applying member 6, the Q value of the piezoelectric vibrator 4 is low. Therefore, even if a driving frequency fd of a frequency f2 close to the resonance frequency fr is suddenly applied at the time of starting, the piezoelectric vibrator 4 may not oscillate and start. Therefore, by performing the aforementioned downward sweep control to gradually enhance the resonance, the piezoelectric vibrator 4 can be started more reliably and stably.

[0050] Furthermore, in the piezoelectric motor 3, the resonant frequency frc of the LC circuit 94 is changed to follow the change of the driving frequency fd as described above. Here, the resonant frequency frc = 1 / {2π√(LC)}... Formula (1), although it can also be obtained by calculation, in the present embodiment, the piezoelectric motor 3 is actually driven, and the frequency at which the voltage amplification factor in the LC circuit 94 becomes the maximum, that is, the frequency at which the voltage applied to the piezoelectric element 40 reaches the maximum, is determined as the resonant frequency frc. That is, the resonant frequency frc may sometimes become a value different from the calculation result according to formula (1). According to such a method, individual differences can be eliminated, and an accurate resonant frequency frc can be set for each piezoelectric motor 3 in each piezoelectric motor 3. In addition, since there is no need to prepare a new circuit other than the driving circuit 9 for measurement, the resonant frequency frc can be simply measured. However, the method for setting the resonant frequency frc is not particularly limited, for example, it can also be determined as a value calculated using formula (1).

[0051] For example, Fig. 9 is a block diagram showing a conventional drive circuit 9A. Fig.10 9A is a graph showing the moving speed of the slider 2 and the voltage amplification factor Av of the LC circuit 94. In the conventional drive circuit 9A, the resonance frequency frc is constant. Fig.10 As shown in FIG. 1 , the LC circuit 94 may be configured so that the resonance frequency frc coincides with the frequency f1 at the time of activation. This allows the piezoelectric vibrator 4 to be activated stably with a large force.

[0052] However, since the voltage amplification factor Av gradually decreases after starting, downward sweep control and frequency speed control in the area with low voltage amplification factor Av are forced to be performed, so excellent driving efficiency cannot be obtained. That is, if the moving speed of the slider 2 is the same, a larger driving voltage Vd is required, and more power is consumed accordingly. Therefore, in this embodiment, a DC power supply 912 is provided in addition to the AC power supply 911 in the voltage waveform generating circuit 91, and a DC bias voltage DC is applied to the piezoelectric element 40 to change the capacitance of the piezoelectric element 40, thereby changing the resonance frequency frc. Fig.11 As shown, the larger the bias voltage DC is, the smaller the capacitance of the piezoelectric element 40 is, and as can be seen from equation (1), the higher the resonance frequency frc is.

[0053] In addition, in the driving of the piezoelectric vibrator 4, in either the down sweep control or the frequency speed control, the piezoelectric motor 3 changes the magnitude of the bias voltage DC so that the difference Δf between the resonance frequency frc and the drive frequency fd becomes smaller than when the bias voltage DC is zero or constant. In the driving of the piezoelectric vibrator 4, the magnitude of the bias voltage DC is preferably changed in a manner that maintains the difference Δf within a prescribed range, and more preferably in a manner that maintains the difference Δf at zero. According to such a control method, since the piezoelectric vibrator 4 can be continuously driven at a high voltage amplification factor Av, the power consumption of the drive circuit 9 can be reduced.

[0054] As a specific example, Fig.12 The relationship between the capacitance of the piezoelectric element 40, the voltage amplification factor Av, and the voltage waveform signal Sd at a predetermined driving frequency fd is shown. In this figure, the following situation is shown: for example, when the capacitance of the piezoelectric element 40 is 80nF, since the voltage amplification factor Av is about 1.5 times, in order to set the slider 2 to a predetermined moving speed, it is necessary to generate a voltage waveform signal Sd of about 15V. In such a case, if a bias voltage DC is applied to change the capacitance of the piezoelectric element 40 to 45nF, the difference Δf becomes smaller, and the voltage amplification factor Av rises to about 7 times its peak value. Therefore, in order to set the slider 2 to a predetermined moving speed, it is sufficient to generate a voltage waveform signal Sd of about 3V. In this way, by applying a bias voltage DC to the piezoelectric element 40 to reduce Δf, the power consumption of the drive circuit 9 can be reduced.

[0055] It should be noted that after the piezoelectric element 40 is charged, since no current of the bias voltage DC flows, no power consumption occurs in the DC power supply 912. Therefore, even if the power consumption caused by the DC power supply 912 (power consumption until the piezoelectric element 40 is charged) is taken into account, the power consumption of the drive circuit 9 can be reduced.

[0056] It should be noted that the method of changing the bias voltage DC so as to reduce the difference Δf is not particularly limited. Fig.13 The table T showing the correspondence between the driving frequency fd and the bias voltage DC such that the difference Δf converges within the prescribed range is shown. In addition, the piezoelectric motor 3 determines the magnitude of the bias voltage DC based on the current driving frequency fd and the table T, and applies the bias voltage DC of the determined magnitude to the piezoelectric element 40. By repeatedly performing such control at a prescribed cycle, the difference Δf between the resonance frequency frc and the driving frequency fd can be continuously kept small during the driving of the piezoelectric vibrator 4, and the power consumption of the driving circuit 9 can be reduced.

[0057] Such a table T is preferably prepared based on data obtained by actually driving the piezoelectric vibrator 4, for example. Thus, it is less likely to be affected by individual differences. However, the method for preparing the table T is not particularly limited, and for example, it can also be prepared based on data obtained by simulation. In addition, in the illustrated table T, the voltage value of the bias voltage DC is set for every 1.0 kHz of the drive frequency fd, but it is not limited to this, and can be appropriately set based on, for example, the required characteristics, etc.

[0058] Here, the resonance frequency frc varies not only according to the magnitude of the bias voltage DC but also according to the magnitude (amplitude) of the drive voltage Vd. Fig.13 Table T shown. In this embodiment, Fig.14 As shown, 0V to 40V is divided into 10V intervals, and there is a table T1 used when the driving voltage Vd is 0V or more and less than 10.0V, a table T2 used when the driving voltage Vd is 10.0V or more and less than 20.0V, a table T3 used when the driving voltage Vd is 20.0V or more and less than 30.0V, and a table T4 used when the driving voltage Vd is 30.0V or more and less than 40.0V. Thus, in the present embodiment, a table is made for every 10V, but it is not limited thereto, and it can be appropriately set based on the required characteristics, etc. Therefore, for example, a table can be made for every 5V, a table can be made for every 1V, or a table can be made for every 0.1V.

[0059] The above describes a method for determining the bias voltage DC using the table T, but the method for determining the bias voltage DC is not particularly limited. For example, by substituting the magnitude of the drive frequency fd and the drive voltage Vd, a relational expression that can be used to find the magnitude of the bias voltage DC can be created, and the bias voltage DC can be determined using the relational expression.

[0060] The control method of the piezoelectric motor 3 and the piezoelectric motor 3 according to the present embodiment have been described above. As described above, the control method of the piezoelectric motor 3 is a control method of the piezoelectric motor 3 having the piezoelectric vibrator 4 and the drive circuit 9, wherein the piezoelectric vibrator 4 includes the piezoelectric element 40 and vibrates by the expansion and contraction of the piezoelectric element 40, and the drive circuit 9 includes the inductor 92 that forms the LC circuit 94 together with the piezoelectric element 40. In the control method of the piezoelectric motor 3, the piezoelectric vibrator 4 is driven by applying the AC drive voltage Vd to the piezoelectric element 40, and the DC bias voltage DC is applied to the piezoelectric element 40 so that the difference Δf between the resonance frequency frc of the LC circuit 94 and the frequency of the drive voltage Vd, that is, the drive frequency fd, is reduced, thereby changing the resonance frequency frc of the LC circuit 94. According to the control method, the difference Δf between the resonance frequency frc and the drive frequency fd can be kept small while the piezoelectric vibrator 4 is driven, and the power consumption of the drive circuit 9 can be reduced.

[0061] As described above, the bias voltage DC is changed according to the driving frequency fd in the control method of the piezoelectric motor 3. According to such a control method, the difference Δf can be reduced more reliably with simple control.

[0062] As described above, in the control method of the piezoelectric motor 3 , the bias voltage DC is changed according to the magnitude of the drive voltage Vd. The resonance frequency frc of the LC circuit 94 also changes according to the magnitude of the drive voltage Vd. Therefore, according to such a control method, the difference Δf can be reduced more reliably.

[0063] In addition, as described above, in the control method of the piezoelectric motor 3, the magnitude of the bias voltage DC is determined by referring to the table T showing the relationship between the driving frequency fd and the bias voltage DC. According to such a control method, the control becomes simple. In particular, by using the data obtained by actually driving the piezoelectric vibrator 4 to prepare the table T, individual differences can be eliminated.

[0064] As described above, in the control method of the piezoelectric motor 3, a plurality of tables T are prepared for each magnitude of the drive voltage Vd. According to such a control method, since the table T corresponding to the magnitude of the drive voltage Vd can be selected and used, control becomes simple.

[0065] As described above, in the control method of the piezoelectric motor 3, the driving frequency fd is higher than the resonance frequency fr of the piezoelectric vibrator 4. According to such a control method, the piezoelectric vibrator 4 is easier to control than when the driving frequency fd is lower than the resonance frequency fr of the piezoelectric vibrator 4.

[0066] As described above, in the control method of the piezoelectric motor 3, when the piezoelectric vibrator 4 is started from a stopped state, a downward sweep control is performed to bring the driving frequency fd close to the resonance frequency fr of the piezoelectric vibrator 4. According to such a control method, the start of the piezoelectric vibrator 4 is stabilized.

[0067] In addition, as described above, the inductor 92 is connected in series with the piezoelectric element 40. Thus, the LC circuit 94 functions as a voltage amplifier circuit, thereby reducing the power consumption of the drive circuit 9.

[0068] In addition, as described above, the piezoelectric motor 3 includes: the piezoelectric vibrator 4, which includes the piezoelectric element 40, and the piezoelectric vibrator 4 vibrates by the expansion and contraction of the piezoelectric element 40; and the drive circuit 9, which includes the inductor 92 that forms the LC circuit 94 with the piezoelectric element 40, and drives the piezoelectric vibrator 4 by applying the AC drive voltage Vd to the piezoelectric element 40, and applies the DC bias voltage DC to the piezoelectric element 40 so that the difference Δf between the resonance frequency frc of the LC circuit 94 and the frequency of the drive voltage Vd, that is, the drive frequency fd, becomes small, thereby changing the resonance frequency frc of the LC circuit 94. According to such a configuration, during the driving of the piezoelectric vibrator 4, the difference Δf between the resonance frequency frc and the drive frequency fd can be kept small, and the power consumption of the drive circuit 9 can be reduced.

[0069] <Second Embodiment>

[0070] Fig.15 It is a block diagram showing a driving circuit included in a driving device according to a second embodiment.

[0071] The driving device 1 of this embodiment is the same as the driving device 1 of the first embodiment described above, except that the structure of the LC circuit 94 is different. In the following description, the driving device 1 of this embodiment is mainly described with respect to the differences from the first embodiment described above, and the description of the same matters is omitted. In addition, in the drawings of this embodiment, the same reference numerals are attached to the same structures as those in the above embodiment.

[0072] like Fig.15As shown, in the LC circuit 94 of the present embodiment, the inductor 92 is connected in parallel with the piezoelectric element 40, and the capacitor 95 is connected in series with the inductor 92. In such a configuration, the LC circuit 94 does not function as a voltage amplifier circuit that amplifies the voltage of the voltage waveform signal Sd. Therefore, the voltage waveform signal Sd is directly applied to the piezoelectric element 40 as the drive voltage Vd. In such a configuration, the current flowing to the piezoelectric element 40 can be reduced by the inductor 92 and the capacitor 95. However, the LC circuit 94 is not particularly limited, for example, the capacitor 95 can also be omitted. With such a configuration, as in the aforementioned first embodiment, in the driving of the piezoelectric vibrator 4, the difference Δf between the resonance frequency frc and the drive frequency fd can be continuously kept small, and the power consumption of the drive circuit 9 can be reduced.

[0073] As described above, in the control method of the piezoelectric motor 3 of the present embodiment, the inductor 92 is connected in parallel with the piezoelectric element 40. With such a configuration, the power consumption of the drive circuit 9 can also be reduced.

[0074] According to the second embodiment as described above, it is possible to achieve the same effects as those of the first embodiment described above.

[0075] <Third Embodiment>

[0076] Fig.16 It is a plan view showing a robot system according to a third embodiment.

[0077] Fig.16 The robot system 1000 shown includes a robot 1100, a mobile workbench 1200 mounted on the robot 1100, a tool 1300 mounted on the mobile workbench 1200, and a control unit 1400 for controlling their driving. The robot system 1000 is capable of performing operations such as supplying, unloading, conveying, and assembling precision equipment and parts constituting the precision equipment.

[0078] The robot 1100 is a six-axis robot having six joints, and includes a base 1110 fixed to a floor or a ceiling, and a robot arm 1120 connected to the base 1110. The robot arm 1120 includes a first arm 1121 rotatably connected to the base 1110, a second arm 1122 rotatably connected to the first arm 1121, a third arm 1123 rotatably connected to the second arm 1122, a fourth arm 1124 rotatably connected to the third arm 1123, a fifth arm 1125 rotatably connected to the fourth arm 1124, and a sixth arm 1126 rotatably connected to the fifth arm 1125. The sixth arm 1126 is provided with a hand connection portion, and the mobile workbench 1200 is mounted on the hand connection portion.

[0079] In addition, the robot 1100 has: a first arm rotation mechanism 1131, which is arranged at the joint portion between the base 1110 and the first arm 1121, so that the first arm 1121 rotates relative to the base 1110; a second arm rotation mechanism 1132, which is arranged at the joint portion between the first arm 1121 and the second arm 1122, so that the second arm 1122 rotates relative to the first arm 1121; a third arm rotation mechanism 1133, which is arranged at the joint portion between the second arm 1122 and the third arm 1123, so that the third arm 1123 rotates relative to the second arm 1121. 22 rotation; the fourth arm rotation mechanism 1134 is arranged at the joint between the third arm 1123 and the fourth arm 1124, so that the fourth arm 1124 rotates relative to the third arm 1123; the fifth arm rotation mechanism 1135 is arranged at the joint between the fourth arm 1124 and the fifth arm 1125, so that the fifth arm 1125 rotates relative to the fourth arm 1124; and the sixth arm rotation mechanism 1136 is arranged at the joint between the fifth arm 1125 and the sixth arm 1126, so that the sixth arm 1126 rotates relative to the fifth arm 1125.

[0080] In addition, a driving device 1 is mounted as a power source in a part or all of the first arm rotation mechanism 1131 to the sixth arm rotation mechanism 1136, and the first arm 1121 to the sixth arm 1126 of the object are rotated by the driving of the driving device 1. Therefore, the robot 1100 can enjoy the effect of the above-mentioned piezoelectric motor 3. However, this is not limited to this, and the driving device 1 may not be mounted on any of the first arm rotation mechanism 1131 to the sixth arm rotation mechanism 1136.

[0081] The movable workbench 1200 comprises: a base 1210 connected to the hand connection part of the sixth arm 1126; a first workbench 1220, which moves in a first direction U relative to the base 1210; a second workbench 1230, which moves in a second direction V orthogonal to the first direction U relative to the first workbench 1220; a first workbench moving mechanism 1240, which moves the first workbench 1220 in the first direction U relative to the base 1210; and a second workbench moving mechanism 1250, which moves the second workbench 1230 in the second direction V relative to the first workbench 1220.

[0082] In addition, the driving device 1 is mounted as a power source in one or both of the first table moving mechanism 1240 and the second table moving mechanism 1250, and the first table 1220 and the second table 1230 of the object are moved by the driving of the piezoelectric motor 3. Thus, the effect of the piezoelectric motor 3 can be enjoyed.

[0083] In addition, a tool 1300 is mounted on the second workbench 1230. The tool 1300 is not particularly limited and varies depending on the content of the target operation, but in this embodiment, it is an inkjet head 1310. In the robot system 1000, the inkjet head 1310 ejects ink to perform a printing operation on the object. As described above, the movable workbench 1200 is interposed between the robot 1100 and the inkjet head 1310. Therefore, for example, when the robot 1100 is stopped, the inkjet head 1310 can be moved by the movable workbench 1200. Thus, a stable printing operation can be performed.

[0084] According to the third embodiment, the same effects as those of the first embodiment can be achieved.

[0085] The control method of the piezoelectric motor and the piezoelectric motor of the present invention are described above based on the illustrated embodiments, but the present invention is not limited thereto, and the configuration of each part can be replaced with any configuration having the same function. In addition, other arbitrary configurations may be added to the present invention. In addition, the various embodiments may be appropriately combined. In addition, in the aforementioned embodiments, the configuration of applying the piezoelectric motor to a robot system is described, but the piezoelectric motor can also be applied to various electronic devices that require driving force, such as printers, projectors, and the like.

Claims

1. A method for controlling a piezoelectric motor, characterized in that: The piezoelectric motor includes a piezoelectric vibrator and a drive circuit. The piezoelectric vibrator includes a piezoelectric element and vibrates by the expansion and contraction of the piezoelectric element. The drive circuit includes an inductor that forms an LC circuit with the piezoelectric element. In the control method of the piezoelectric motor, the piezoelectric vibrator is driven by applying an AC driving voltage to the piezoelectric element, and the resonant frequency of the LC circuit is changed by applying a DC bias voltage to the piezoelectric element in a manner that reduces the difference between the resonant frequency of the LC circuit and the frequency of the driving voltage, i.e., the driving frequency.

2. The control method of the piezoelectric motor according to claim 1, characterized in that: The bias voltage is varied according to the driving frequency.

3. The control method of the piezoelectric motor according to claim 2, characterized in that: The bias voltage is varied according to the magnitude of the driving voltage.

4. The control method of the piezoelectric motor according to claim 3, characterized in that: The magnitude of the bias voltage is determined by referring to a table showing the relationship between the driving frequency and the bias voltage.

5. The control method of the piezoelectric motor according to claim 4, characterized in that: A plurality of the tables are prepared according to the magnitude of the driving voltage.

6. The control method of a piezoelectric motor according to claim 1, characterized in that: The driving frequency is higher than the resonance frequency of the piezoelectric vibrator.

7. The control method of the piezoelectric motor according to claim 6, characterized in that: When the piezoelectric vibrator is started from a stopped state, downward sweep control is performed to bring the driving frequency close to the resonance frequency of the piezoelectric vibrator.

8. The control method of a piezoelectric motor according to claim 1, characterized in that: The inductor is connected in series with the piezoelectric element.

9. The control method of a piezoelectric motor according to claim 1, characterized in that: The inductor is connected in parallel with the piezoelectric element.

10. A piezoelectric motor, characterized in that: The piezoelectric motor includes a piezoelectric vibrator and a drive circuit. The piezoelectric vibrator includes a piezoelectric element and vibrates by the expansion and contraction of the piezoelectric element. The drive circuit includes an inductor that forms an LC circuit with the piezoelectric element. The piezoelectric motor drives the piezoelectric vibrator by applying an AC driving voltage to the piezoelectric element, and changes the resonant frequency of the LC circuit by applying a DC bias voltage to the piezoelectric element in a manner that reduces the difference between the resonant frequency of the LC circuit and the frequency of the driving voltage, i.e., the driving frequency.

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