Ultrasonic motor system

Abstract

To provide an ultrasonic motor system in which an ultrasonic motor favorably operates.SOLUTION: An ultrasonic motor system 1 includes: an ultrasonic motor 10; and a motor drive circuit 60 configured to apply an AC voltage to the ultrasonic motor 10 so as to operate the ultrasonic motor 10. The motor drive circuit 60 is configured to change the operating status of the ultrasonic motor 10 by changing a drive frequency that is a frequency of the AC voltage and a phase of the drive voltage that indicates a phase difference between the AC voltage and a periodic reference signal of the drive frequency.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ultrasonic motor system, a driving device for an ultrasonic vibrator, and the like. [Background technology]

[0002] Ultrasonic motors have many advantages, such as being small, producing high torque, being very quiet, and providing a large holding force when not energized. However, controlling them is relatively difficult because the motor itself has nonlinear characteristics and many parameters are involved in its operation. For this reason, various studies have been conducted on controlling ultrasonic motors. For example, Patent Document 1 discloses generating a control signal for controlling an ultrasonic motor using a trained model obtained by deep reinforcement learning. Furthermore, Patent Document 2 discloses utilizing the output of a neural network determined by executing a genetic algorithm to control an ultrasonic motor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2023 / 068370 [Patent Document 2] International Publication No. 2007 / 049412 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention aims to improve the operation of ultrasonic equipment including ultrasonic motors. [Means for solving the problem]

[0005] According to one aspect of the present invention, an ultrasonic motor system includes an ultrasonic motor and a motor drive circuit configured to apply an AC voltage to the ultrasonic motor to operate the ultrasonic motor, and the motor drive circuit is configured to change the operating state of the ultrasonic motor by changing a drive frequency, which is the frequency of the AC voltage, and a phase of the drive voltage, which means the phase difference between a periodic reference signal of the drive frequency and the AC voltage. [Effects of the Invention]

[0006] According to the present invention, the operation of ultrasonic equipment including an ultrasonic motor can be improved. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram showing an outline of a configuration example of an ultrasonic motor system according to an embodiment. [Figure 2] FIG. 2 is a diagram showing an outline of a configuration example of a traveling wave type ultrasonic motor according to an embodiment. [Figure 3] FIG. 3 is a diagram showing an example of the relationship between the vibration amplitude and the drive frequency of the stator of the ultrasonic motor. [Figure 4] FIG. 4 is a schematic diagram for explaining the adjustment of the rotation speed of an ultrasonic motor, where (a) is a diagram showing a conventional case where only the drive frequency is changed, and (b) is a diagram showing a diagram showing a case where the drive frequency and the phase of the drive voltage are changed in one embodiment. [Figure 5] FIG. 5 is a diagram showing an example of the results of a numerical analysis of the time changes in the drive frequency and phase of the drive voltage of an ultrasonic motor, and the time changes in the current obtained at that time, in order to set a target current value proportional to the vibration amplitude of the stator. [Figure 6] FIG. 6 is a flowchart showing an outline of an example of the operation of the control device in controlling the ultrasonic motor. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment will be described with reference to the drawings. The embodiment relates to an ultrasonic motor system. The ultrasonic motor system includes an ultrasonic motor, and is configured to appropriately control the operation of the ultrasonic motor.

[0009] [System Configuration] 1 is a block diagram showing an outline of an example of the configuration of an ultrasonic motor system 1 according to this embodiment. The ultrasonic motor system 1 includes an ultrasonic motor 10, a control device 20, a motor drive circuit 60, and a group of sensors 70.

[0010] <Outline of the ultrasonic motor configuration> The ultrasonic motor 10 may be any type of ultrasonic motor that operates using ultrasonic vibrations, but in this embodiment, it is a rotary traveling wave ultrasonic motor, which is a form of vibration actuator. Figure 2 is a diagram showing an outline of an example of the configuration of the ultrasonic motor 10 according to this embodiment. Figure 2 shows the ultrasonic motor 10 in a cutaway state so that the structure of the ultrasonic motor 10 can be seen.

[0011] The ultrasonic motor 10 is constructed on a plate-shaped base 120, and its main parts are housed inside a cover 180 provided on the base 120. For the sake of explanation, only the rear half of the cover 180 is shown in FIG. 2. Also, for the sake of explanation, only the rear portions of the stator 130, rotor 140, bearing 160, disc spring 170, etc., which will be described later, are shown in FIG. 2 with the front portions cut away. All of these components have an approximate disk shape. The following components are provided in the space surrounded by the base 120 and the cover 180.

[0012] A stator 130 in the shape of an annular plate is fixed on the base 120. A shaft 150 is provided in the center of the stator 130, perpendicular to the base 120. The shaft 150 is rotatably supported by a bearing 160 fixed to a cover 180. A rotor 140 in the shape of an annular plate is fixed to the shaft 150. A contact portion 141 is provided on the outer ring portion of the rotor 140. The rotor 140 is pressed toward the stator 130 by a pressurizing member, such as a disc spring 170, and the contact portion 141 is in pressurized contact with a first surface 133 on the upper side of the stator 130.

[0013] Stator 130 has piezoelectric element 132 fixed to elastic body 131 made of, for example, a metal material. Elastic body 131 is provided on the rotor 140 side, and piezoelectric element 132 is provided on the opposite side. First surface 133 of elastic body 131 that comes into contact with rotor 140 has a comb-like uneven shape in which convex portions and concave portions that extend in the radial direction of annular elastic body 131 are repeatedly provided in the circumferential direction. When elastic body 131 vibrates, the comb-like shape of first surface 133 causes the tops of the convex portions that come into contact with contact portion 141 to undergo large displacement.

[0014] As will be described later, in order to generate a traveling wave with a wavelength λ in elastic body 131, piezoelectric element 132 has, for example, the following configuration. That is, in piezoelectric element 132, A-phase electrodes are provided in predetermined portions of the piezoelectric body, and B-phase electrodes are provided in other portions of the piezoelectric body. The piezoelectric body in the portions where the A-phase electrodes are provided is polarized so that the polarity changes alternately every length equivalent to 1 / 2λ in the circumferential direction. The piezoelectric body in the portions where the B-phase electrodes are provided is similarly polarized so that the polarity changes alternately every length equivalent to 1 / 2λ in the circumferential direction. A gap of a length equivalent to 1 / 4λ or 3 / 4λ is provided in the circumferential direction between the portions where the A-phase electrodes are provided and the portions where the B-phase electrodes are provided.

[0015] When an AC voltage is applied to the A-phase electrode and the B-phase electrode, adjacent sections of the piezoelectric element 132 are polarized in opposite directions, causing one section to expand and the other to contract. This expansion and contraction of the piezoelectric element 132 generates a bending vibration in the elastic body 131. At a predetermined frequency, the stator 130 enters a state close to resonance. When AC voltages with a phase difference of 90° are applied to the A-phase electrode and the B-phase electrode, respectively, the waves generated in the A-phase electrode and the B-phase electrode are combined, generating a traveling wave along the circumferential direction in the elastic body 131. At this time, the contact portion 141 of the rotor 140 is in pressure contact with the first surface 133 of the elastic body 131, so the rotor 140 rotates in the opposite direction to the generated traveling wave. When the rotor 140 rotates, the shaft 150 fixed to the rotor 140 rotates around its axis. In the ultrasonic motor 10, the shaft 150 serves as the output shaft, and the rotation of the shaft 150 is extracted as motor rotation.

[0016] <Outline of the configuration of the control device> As shown in Fig. 1, the control device 20 is a computer including various integrated circuits such as a processor 21, a memory 22, and a storage 23, an input interface (I / F) 24, an output interface (I / F) 25, and a bus line 26 connecting these. The control device 20 operates by these pieces of hardware working together. The specific configuration of the control device 20 may be any. For example, an SoC (System on a Chip) or the like may be used. Various programs and data are recorded in the control device 20, and the control device 20 operates using these programs and the like.

[0017] The control device 20 acquires target information, such as target values ​​for the operation of the ultrasonic motor 10, input from the outside via the input I / F 24. This target value may include values ​​such as the rotation speed, torque, and rotation position of the ultrasonic motor 10. The target information is information relating to the target state of the ultrasonic motor 10. The control device 20 determines a control command value that realizes the input target value. The control device 20 outputs the determined control command value via the output I / F 25. The control command value is transmitted to the motor drive circuit 60.

[0018] The control command value includes, for example, information related to the voltage, frequency, phase, etc. of the AC voltage applied to each of the A-phase electrodes and the B-phase electrodes of the ultrasonic motor 10. If the amplitude and frequency of the AC voltage applied to the A-phase electrodes are the same as those of the AC voltage applied to the B-phase electrodes, the control command value may include a single amplitude and frequency value without distinguishing between the A-phase and the B-phase. Regarding the phase, the control command value may include information related to the phase of each of the AC voltages applied to the A-phase electrodes and the B-phase electrodes, or may include information related to the phase and phase difference of either one of them. In addition, since the phase is changed in this embodiment as described below, the control command value may include information on the phase difference between a separately prepared periodic reference signal and the AC voltage to represent this phase.

[0019] <Outline of the motor drive circuit configuration> The motor drive circuit 60 acquires a control command value from the control device 20. Based on this control command value, the motor drive circuit 60 generates a drive voltage for operating the ultrasonic motor 10 and outputs it to the ultrasonic motor 10. The drive voltage is an AC voltage applied to the A-phase electrodes and an AC voltage applied to the B-phase electrodes of the ultrasonic motor 10. The frequency of the AC voltage is, for example, a frequency corresponding to the ultrasonic waves. The ultrasonic motor 10 is operated by the power output from this motor drive circuit 60.

[0020] <Outline of the sensor group configuration> The sensor group 70 may include various sensors that acquire information about the state of the ultrasonic motor 10.

[0021] The sensor group 70 may include a voltage sensor 71 that acquires a feedback voltage of the ultrasonic motor 10. For example, a piezoelectric element may be provided in the elastic body 131 of the stator 130 of the ultrasonic motor 10, and the voltage generated by this piezoelectric element due to distortion of the elastic body 131 may be acquired as the feedback voltage. Information regarding the characteristics and vibration state of the stator 130 can be obtained from the feedback voltage. A voltage sensor may also be provided separately from this for acquiring the voltage input to the ultrasonic motor 10. The sensor group 70 may include a current sensor 72 that acquires the drive currents associated with the above-mentioned A phase and B phase that flow through the piezoelectric element 132 of the ultrasonic motor 10. The drive currents may include information regarding the vibration amplitude of the stator 130.

[0022] The sensor group 70 may include an encoder 73 for acquiring the rotation speed, rotation position, etc. of the ultrasonic motor 10. The sensor group 70 may include a temperature sensor 74 for acquiring the temperature of the ultrasonic motor 10. The operation of the ultrasonic motor 10 is dependent on the vibration of the stator 130 at a frequency close to the resonant frequency, and is therefore temperature dependent.

[0023] The sensor group 70 may include a calculator 75 that calculates information such as amplitude and phase based on signals related to voltage and current acquired by the voltage sensor 71 and the current sensor 72. The calculator 75 may calculate information such as the vibration amplitude of the stator 130 of the ultrasonic motor 10 and other information on the state of the ultrasonic motor 10 based on output signals from the various sensors. The function of the calculator 75 may be included in the control device 20.

[0024] The sensor group 70 may include all or some of these sensors, etc. Status information regarding the status of the ultrasonic motor 10, such as output signals of various sensors acquired by the sensor group 70 and signals that have undergone predetermined processing based on the output signals, is input to the control device 20 via the input I / F 24.

[0025] [Ultrasonic motor control] <overview> The following describes the control of the ultrasonic motor 10 in the ultrasonic motor system 1 according to this embodiment. As described above, the ultrasonic motor 10 rotates the rotor 140 by vibrating the stator 130 at a frequency near the resonant frequency.

[0026] FIG. 3 shows an example of a resonance curve of the stator 130. That is, FIG. 3 shows an example of the relationship between the vibration amplitude of the stator 130 and the frequency of the AC voltage applied to the stator 130, i.e., the drive frequency. As shown in FIG. 3, the vibration amplitude of the stator 130 changes depending on the drive frequency. In general, in an ultrasonic motor 10, the vibration amplitude of the stator 130 is adjusted by adjusting the drive frequency, thereby adjusting the rotation speed of the ultrasonic motor 10 to a target value. In this case, the drive frequency is generally changed so that the frequency changes at a constant rate.

[0027] 3, the vibration amplitude and drive frequency of the stator 130 exhibit strong hysteresis. For this reason, in general, when obtaining a vibration amplitude of 2.3 μm indicated by a circle at startup, the drive frequency is swept from a high frequency to a low frequency to reach 42 kHz. If the drive frequency is swept from a low frequency to a high frequency, the vibration amplitude indicated by a square will be 0.8 μm even if the drive frequency is set to 42 kHz, and an appropriate vibration amplitude cannot be obtained. In other words, the drive voltage V applied to the A-phase electrode of the piezoelectric element 132 of the ultrasonic motor 10 A and the driving voltage V applied to the B-phase electrode B and V A = V0sin(2πft) V B = V0cos(2πft) At startup, the drive frequency f is changed over time from a high frequency to a low frequency.

[0028] Furthermore, when changing the rotation speed of the ultrasonic motor 10 after it has been started, the drive frequency is swept to change the vibration amplitude of the stator 130, thereby adjusting the rotation speed of the ultrasonic motor 10 to the desired value. To reverse the rotation of the ultrasonic motor 10, it is sufficient to invert the phase of only one of the drive voltages. To stop the rotation of the ultrasonic motor 10, it is sufficient to stop the application of the AC voltage. While it generally takes only about 1 ms at most to stop an ultrasonic motor, starting an ultrasonic motor can take as long as 50 ms depending on the conditions.

[0029] Generally, as described above, the rotation speed of the ultrasonic motor 10 is controlled by adjusting the drive frequency. In contrast, in the ultrasonic motor system 1 of this embodiment, the rotation speed of the ultrasonic motor 10 is controlled by adjusting the drive frequency and the phase of the drive voltage. That is, the drive voltage V applied to the A-phase electrode of the piezoelectric element 132 of the ultrasonic motor 10 of this embodiment is A and the driving voltage V applied to the B-phase electrode B and V A = V0sin(2πft + θ) V B = V0cos(2πft + θ) The rotation speed of the ultrasonic motor 10 is controlled by adjusting the drive frequency f and the phase θ of the drive voltage. As is clear from the above formula, changing the phase of the drive voltage in the description of this embodiment means shifting the phase by a phase angle θ with respect to a periodically changing reference phase. In other words, the drive voltage V applied to the A-phase electrode A When the periodic reference signal of the drive frequency separately prepared for this is set to s = sin(2πft), the drive voltage V applied to the A-phase electrode is A = V0 sin(2πft + θ) has a phase difference θ with the reference signal s, and changing the phase θ of the drive voltage means changing the phase difference θ with this reference signal s.

[0030] For example, as shown in FIG. 4(a), when adjusting the rotation speed of the ultrasonic motor 10, the driving voltage V applied to the A-phase electrode is generally A and the driving voltage V applied to the B-phase electrode B In contrast to this, in this embodiment, as shown in FIG. 4(b), the drive frequency of the drive voltage V applied to the A-phase electrode is adjusted. A and the driving voltage V applied to the B-phase electrode B In the example of Figure 4(b), not only the driving frequency but also the time T A and time T B As shown in FIG. 4(b), the phase of the drive voltage is changed. That is, the phase difference with respect to the reference signal is changed. The phase of the drive voltage may be adjusted to take discrete values, or may be swept to change at a constant rate, or may be adjusted to change the rate of change. The drive frequency may also be swept to change at a constant rate, or may be adjusted to change the rate of change.

[0031] <Analysis example> The vibration state of the stator 130 when an AC voltage was applied to the piezoelectric element 132 of the stator 130 was determined by numerical analysis. For the numerical analysis, a simplified voltage-current model was used that omitted the rotation, torque, etc. of the ultrasonic motor 10, and only the vibration of the stator 130 was calculated. Since the vibration amplitude of the stator 130 is proportional to the current flowing through the piezoelectric element 132, this current value was evaluated.

[0032] The following analysis was performed. A target value for the rotation speed, i.e., a target value for the current value flowing through the piezoelectric element 132, was determined. The optimal change patterns for the frequency (drive frequency) and phase (phase difference from the reference signal) of the drive voltage to achieve this target value were determined as follows: From the current state, the drive frequency was changed to 100 different values ​​between 38 kHz and 41 kHz. For each change, the phase of the drive voltage was changed to 100 different values ​​between -180° and 180°, and 10,000 different current values ​​were calculated after 1 ms had elapsed. From these, the drive frequency and drive voltage phase for which the current value representing the vibration amplitude after 1 ms had elapsed was closest to the target value was determined as the drive frequency and drive voltage phase to be applied during that 1 ms. The state 1 ms later, using these drive frequency and drive voltage phase, was determined as the current state. Similarly, the drive frequency and drive voltage phase to be applied during the next 1 ms were determined from the 100 drive frequencies and 100 drive voltage phases. By repeating such exhaustive calculations, the optimum driving frequency and driving voltage phase change pattern were determined.

[0033] As a comparative example, the phase was kept constant and the same calculation was performed while changing only the frequency, to determine the optimum driving frequency change pattern when the phase was constant.

[0034] FIG. 5 shows an example of the results of the numerical analysis. The middle graph in FIG. 5 shows the drive frequency versus time. The bottom graph in FIG. 5 shows the phase of the drive voltage (phase difference with respect to the reference signal) versus time. The top graph in FIG. 5 shows the results of the numerical analysis of the current flowing at that time. This current is proportional to the vibration amplitude of the stator 130.

[0035] The target current value is shown by a gray dotted line in the upper graph of Figure 5. That is, for 10.0 ms from the start of control in the stopped state, i.e., when the elapsed time was 0.0 ms to 10.0 ms, the target current value was set to 0.6 A. After that, for 10.0 ms, i.e., when the elapsed time was 10.0 ms to 20.0 ms, the target current value was set to 0.3 A.

[0036] The gray dashed line in Fig. 5 indicates the optimal change pattern of the drive frequency and drive voltage phase obtained as described above. The black solid line in Fig. 5 indicates the optimal change pattern of the drive frequency obtained as described above when the phase is kept constant and only the drive frequency is changed according to the comparative example.

[0037] In the case of the comparative example shown by the solid line, the drive frequency fluctuated, rising and falling, as shown in the middle graph of Fig. 5, and the current value was unstable, as shown in the top graph of Fig. 5. It was particularly unstable when the target current value was relatively low. This was thought to be because the current value was being forcibly maintained without a steady-state solution being obtained.

[0038] On the other hand, when the phase of the drive frequency and drive voltage was adjusted, as shown in the lower graph of FIG. 5, by changing the phase, the drive frequency became relatively stable, as shown in the middle graph of FIG. 5, and the current value also stably matched the target value, as shown in the upper graph of FIG. 5. Even when the target current value was relatively low, the current value stably matched the target value. In addition, the transient response to changing the target current value was also faster than in the comparative example. This is thought to be because the ability to manipulate the phase allows any position on the complex plane to be set as a steady-state solution, and obtaining a steady-state solution allows for a stable current value.

[0039] As described above, in contrast to conventional control methods that attempt to obtain a target rotation speed by changing the drive frequency, the control method according to this embodiment obtains the target rotation speed by changing the drive frequency and the phase of the drive voltage. It has become clear that changing the drive frequency and the phase of the drive voltage achieves stable control and high-speed responsiveness.

[0040] As described above, there are combinations of drive frequency and drive voltage phases that can stably obtain the target rotation speed depending on the target rotation speed, and there are also change patterns of the drive frequency and drive voltage phase when the target rotation speed changes. These can be obtained in advance. Furthermore, because the resonant frequency changes depending on, for example, the temperature of the ultrasonic motor 10, the combination of the drive frequency and drive voltage phase may differ depending on various conditions, such as the temperature of the ultrasonic motor 10. However, it is possible to obtain in advance the optimal combination of drive frequency and drive voltage phase for each case depending on the conditions.

[0041] Control Method The operation of the ultrasonic motor 10 according to this embodiment will be described below. Fig. 6 is a flowchart showing an outline of the operation of the control device 20 of the ultrasonic motor 10.

[0042] In step S101, the control device 20 externally acquires a target value for the operation of the ultrasonic motor 10, such as the rotation speed. In step S102, the control device 20 acquires state information such as the outputs of various necessary sensors from the sensor group 70.

[0043] In step S103, the control device 20 determines an optimal control method for appropriately achieving the target value of operation in the situation identified by the status information acquired from the sensor group 70. The control device 20 determines the drive frequency and the phase of the drive voltage based on, for example, the target rotation speed, the difference between the target rotation speed and the current rotation speed, the temperature of the ultrasonic motor 10, and the like. The optimal control method may be determined by selecting an appropriate one from among combinations of drive frequency and drive voltage phases prepared in advance for each current state and target state. Alternatively, the optimal control method may be determined by selecting an appropriate one from among combinations of drive frequency and drive voltage phases prepared in advance for each difference between the target state and the current state. The optimal control method may also be calculated and determined using a predetermined method using, for example, the acquired target information for the operation of the ultrasonic motor 10 and the status information acquired from the sensor group 70. The determination of these optimal control methods is performed within a short period of time equal to or shorter than the time constant of the ultrasonic motor 10, for example, 1 ms or less.

[0044] In step S104, the control device 20 creates a control command value for implementing the determined optimal control method and outputs it to the motor drive circuit 60. This control command value may include, for example, information related to the drive voltage, drive frequency, and phase of the drive voltage. Having acquired the control command value, the motor drive circuit 60 outputs a corresponding drive voltage to the ultrasonic motor 10 based on the control command value, thereby operating the ultrasonic motor 10. As a result, the ultrasonic motor 10 operates based on the optimal control method.

[0045] In step S105, the control device 20 determines whether to end the operation based on whether the input of the target value for the operation has been stopped or not. If the target value for the operation has been input and the operation is not to be ended, the process returns to step S101. Thereafter, the above-described process is repeated. On the other hand, if the operation is to be ended, the series of operations ends.

[0046] <Modification of Control Method> A modified example of the operation of the ultrasonic motor 10 described above will now be described. Machine learning or the like may be used to determine the optimal control method. Determining the optimal combination of drive frequency and drive voltage phases based on the current rotation speed, temperature, load torque, etc. of the ultrasonic motor 10, as in this embodiment, tends to involve many parameters and result in complex calculations. For this reason, the use of machine learning or the like is effective in this embodiment.

[0047] In this modification, a trained model is installed in the control device 20. This trained model is configured to output information on an optimal control method for the ultrasonic motor 10 to achieve the target value state in response to input of a target value for the state of the ultrasonic motor, such as a target rotation speed, and state information obtained using the sensor group 70. The information on the optimal control method includes information on the drive frequency and the phase of the drive voltage. The control device 20 can create a control command value related to the AC voltage to be applied to the piezoelectric element 132 of the ultrasonic motor 10 based on the information on the optimal control method output from the trained model. The trained model may be configured to output a control command value in response to input of a target value and state information.

[0048] In the ultrasonic motor system 1 according to this modification, when a target value for the state of the ultrasonic motor input from outside or state information acquired using the sensor group 70 is input to the control device 20 equipped with a trained model, a control command value is output at high speed from the control device 20. This control command value is input to the motor drive circuit 60, and the operation of the ultrasonic motor 10 can be controlled quickly and appropriately by the output of the motor drive circuit 60 based on the control command value.

[0049] The trained model may be created by any machine learning technique, including, but not limited to, deep reinforcement learning.

[0050] In deep reinforcement learning, for example, a neural network including an input layer, multiple intermediate layers, and an output layer is provided, and this neural network is used by the agent to determine its behavior. In this deep reinforcement learning, for example, a target value of the operating state, such as a target rotation speed, and a value related to state information obtained using the sensor group 70 can be used as the state. Information on the drive frequency and the phase of the drive voltage, or a value related to the corresponding control command value, can be used as the behavior. A value related to the difference between the rotation speed when the ultrasonic motor 10 is operated by the control command value and the target rotation speed can be used as the reward. For example, a trained model created by such deep reinforcement learning can be installed in the control device 20.

[0051] This deep reinforcement learning is not limited to being performed using an actual ultrasonic motor 10. Deep reinforcement learning may also be performed using a simulation that uses, for example, an equivalent circuit model based on an LCR circuit. By performing machine learning using a simulation followed by machine learning using an actual ultrasonic motor 10, machine learning becomes faster and a highly reliable trained model can be quickly obtained.

[0052] The control device 20 may continue to re-learn the learned model while the ultrasonic motor 10 is operating. By continuing the learning, it is possible to deal with cases where the state of the hardware of the ultrasonic motor 10 changes, such as when the wear surface of the ultrasonic motor 10 changes, or when the environment in which the ultrasonic motor 10 is used changes.

[0053] [About ultrasonic motor systems] The ultrasonic motor system 1 according to this embodiment determines the optimal drive frequency and drive voltage phase to achieve a target state of the ultrasonic motor 10, such as rotation speed, output torque, and rotational position, during operation of the ultrasonic motor 10, and then changes the drive frequency and drive voltage phase. This type of control allows for more stable operation and faster response than, for example, control that involves changing only the drive frequency. For example, when starting the ultrasonic motor 10 from a stopped state to a predetermined target rotation speed, or when changing the target rotation speed, the ultrasonic motor 10 can quickly transition to the target rotation speed. Furthermore, when a constant rotation speed is required, the rotation speed can remain constant without change. A stable rotation speed can be achieved, especially at low rotation speeds, which tend to be unstable.

[0054] High operational stability and high responsiveness are required in various usage situations of ultrasonic motors. For example, stability and response speed also affect the controllability of a positioning device. According to this embodiment, an ultrasonic motor system 1 that achieves high stability and high responsiveness can be realized.

[0055] Furthermore, with ultrasonic motors such as those described in this embodiment, when an external load torque is applied while the motor is stopped, a phenomenon is known in which, when attempting to rotate in the opposite direction to the load torque, the motor temporarily rotates in the reverse direction due to the load torque, and then rotates in the desired direction. This phenomenon is believed to occur as follows, and analysis by the inventors supports this theory. Specifically, when the motor is stopped, the shaft is locked by friction between the stator and rotor. When the ultrasonic motor starts, a state in which the stator amplitude is small occurs as the stator transitions to an appropriate vibration. At this time, the friction between the stator and rotor that locked the shaft decreases, causing the ultrasonic motor to lose its holding force, and the ultrasonic motor is unable to generate enough torque to counteract the load torque and rotate the shaft in the desired direction. In other words, the ultrasonic motor enters a neutral state. As a result, the ultrasonic motor rotates in the reverse direction due to the load torque. After that, when the stator reaches an appropriate vibration state with sufficient amplitude, the ultrasonic motor rotates the shaft in the desired direction against the load torque.

[0056] For example, if a robot arm is operated using an ultrasonic motor, the ultrasonic motor will be subjected to a load torque due to the robot arm's own weight. The above-mentioned phenomenon of the motor reversing causes the robot arm to move in the opposite direction to the desired direction, for example, when the robot arm starts to move. One of the advantages of ultrasonic motors is that they can obtain a high holding force when stationary without using any other device, so it is desirable to avoid the above-mentioned reverse rotation.

[0057] According to the ultrasonic motor system 1 of this embodiment, the ultrasonic motor 10 can be started more quickly than before, so the reverse rotation described above can be almost completely prevented. This prevention of reverse rotation also has an excellent effect in utilizing the ultrasonic motor 10.

[0058] The present invention has been described above by showing preferred embodiments, but it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

[0059] For example, the above-described technology relates to excitation of an ultrasonically vibrating component such as the stator 130. Therefore, the above-described technology is not limited to rotary traveling-wave ultrasonic motors, but can also be applied to linear traveling-wave ultrasonic motors. Similarly, the above-described technology is not limited to ultrasonic motors using the vibration of a circular flat plate as in the above-described embodiment, but can also be applied to mode rotation ultrasonic motors using flexural vibration of a cylinder. Similarly, the above-described technology is not limited to traveling-wave ultrasonic motors, but can also be applied to standing-wave ultrasonic motors. Standing-wave ultrasonic motors include, for example, linear ultrasonic motors that combine longitudinal and flexural vibrations, and rotary ultrasonic motors that combine longitudinal and torsional vibrations. These include mode conversion and composite mode ultrasonic motors, such as mode conversion ultrasonic motors that combine a longitudinal vibrator and a flexural vibrating element, and composite vibrator ultrasonic motors that combine a longitudinal piezoelectric element and a torsional piezoelectric element. In other words, the ultrasonic motor may be any type of ultrasonic motor that utilizes ultrasonic vibration.

[0060] Furthermore, the above-described technology can be applied not only to the ultrasonically vibrating vibrator included in the above-described ultrasonic motor, but also to controlling the operation of various ultrasonic vibrators, such as various ultrasonic vibrators including Langevin vibrators. The applicability of the above-described technology to Langevin vibrators and the like can be understood, for example, from the analysis example shown in FIG. 5 . That is, for example, by adjusting the drive frequency and the phase of the drive voltage so that the vibration amplitude of the piezoelectric element is set to a target value, the vibration of the ultrasonic vibrator can be appropriately controlled. Furthermore, the above-described technology can be applied not only to ultrasonic motors, but also to controlling the operation of various ultrasonic devices equipped with ultrasonic vibrators such as ultrasonic vibrators. That is, the above-described technology can also be applied to driving devices for these ultrasonic vibrators. Ultrasonic devices include, for example, ultrasonic cleaners, ultrasonic processing machines, ultrasonic welding machines, ultrasonic bonders, medical ultrasonic diagnostic devices, ultrasonic imaging devices, pulverizers, sonar, fish finders, and the like.

[0061] As in the case of ultrasonic motors, the application of the above-described technology to the control of the operation of various ultrasonic vibrators and various ultrasonic devices can provide the following advantages. That is, the time required for the vibration amplitude of the ultrasonic vibrator or the like to reach the desired amplitude at startup can be shortened. Furthermore, in these operations, the response to fluctuations in environmental conditions and target values ​​during operation can be accelerated. As a result, for example, improved processing accuracy can be achieved in ultrasonic processing machines, improved welding quality in ultrasonic welding machines, shorter diagnosis times can be achieved in ultrasonic diagnostic devices, improved crushing capabilities can be achieved in crushing devices, and similar improvements in various other performances of various devices can be realized. [Explanation of symbols]

[0062] 1: Ultrasonic motor system 10: ultrasonic motor, 120: base, 130: stator, 131: elastic body, 132: piezoelectric element, 133: first surface, 140: rotor, 141: contact portion, 150: shaft, 160: bearing, 170: disc spring, 180: cover 20: control device, 21: processor, 22: memory, 23: storage, 24: input I / F, 25: output I / F, 26: bus line 60: Motor drive circuit 70: Sensor group, 71: Voltage sensor, 72: Current sensor, 73: Encoder, 74: Temperature sensor, 75: Calculator

Claims

1. an ultrasonic motor; a motor drive circuit configured to apply an AC voltage to the ultrasonic motor to operate the ultrasonic motor; Equipped with The motor drive circuit is configured to change the operating state of the ultrasonic motor by changing a drive frequency, which is the frequency of the AC voltage, and a phase of the drive voltage, which is the phase difference between a periodic reference signal of the drive frequency and the AC voltage. Ultrasonic motor system.

2. a sensor for acquiring status information relating to the status of the ultrasonic motor; a control device configured to acquire target information and state information relating to a target state of the ultrasonic motor, determine an optimum drive frequency and a phase of the drive voltage based on the target information and the state information, and output control command values ​​relating to the optimum drive frequency and the phase of the drive voltage to the motor drive circuit; The ultrasonic motor system of claim 1 further comprising:

3. 3. The ultrasonic motor system according to claim 2, wherein the control device is equipped with a trained model configured to output the optimal drive frequency and drive voltage phase in response to input of the target information and the state information.

4. A control device that controls an AC voltage applied to an ultrasonic motor to operate the ultrasonic motor, and controls the operation of the ultrasonic motor, acquiring status information relating to a status of the ultrasonic motor and target information relating to a target status of the ultrasonic motor; determining an optimal drive frequency, which is the frequency of the AC voltage, and an optimal phase of the drive voltage, which is the phase difference between a periodic reference signal of the drive frequency and the AC voltage, based on the target information and the state information; Outputting a control command value relating to the optimum drive frequency and phase of the drive voltage The control device is configured as follows.

5. A control method for controlling an AC voltage applied to an ultrasonic motor to operate the ultrasonic motor, the method comprising: changing a drive frequency, which is the frequency of the AC voltage, and a phase of the drive voltage, which means a phase difference between a periodic reference signal of the drive frequency and the AC voltage, to change the operating state of the ultrasonic motor; A method for controlling an ultrasonic motor.

6. A control program for causing a computer to control an AC voltage applied to an ultrasonic motor to operate the ultrasonic motor, thereby controlling the operation of the ultrasonic motor, the control program comprising: acquiring status information relating to a status of the ultrasonic motor and target information relating to a target status of the ultrasonic motor; determining an optimal drive frequency, which is the frequency of the AC voltage, and an optimal phase of the drive voltage, which is the phase difference between a periodic reference signal of the drive frequency and the AC voltage, based on the target information and the state information; outputting a control command value relating to the optimum drive frequency and phase of the drive voltage; A control program for executing the above.

7. The control program of claim 6, wherein determining the optimal drive frequency and the phase of the drive voltage is performed using a trained model configured to output the optimal drive frequency and the phase of the drive voltage in response to input of the target information and the state information.

8. A driving device including a driving circuit configured to apply an AC voltage to an ultrasonic vibrator so as to vibrate the ultrasonic vibrator, The drive circuit is configured to change the operating state of the ultrasonic vibrator by changing a drive frequency, which is the frequency of the AC voltage, and a phase of the drive voltage, which is the phase difference between a periodic reference signal of the drive frequency and the AC voltage. A driving device for ultrasonic vibrators.

9. The driving device according to claim 8, further comprising a control device configured to acquire status information regarding the status of the ultrasonic vibrator and target information regarding a target state of the ultrasonic vibrator, determine the optimal driving frequency and phase of the driving voltage based on the status information and the target information, and output control command values ​​regarding the optimal driving frequency and phase of the driving voltage to the driving circuit.

10. A drive device according to claim 8 or 9; an ultrasonic device including the ultrasonic vibrator; An ultrasound device system comprising:

11. The ultrasonic device is an ultrasonic motor.

11. The ultrasound machine system of claim 10.

12. A control method for controlling vibration of an ultrasonic vibrator by controlling an AC voltage applied to the ultrasonic vibrator so as to vibrate the ultrasonic vibrator, comprising: changing a driving frequency, which is the frequency of the AC voltage, and a phase of the driving voltage, which means a phase difference between a periodic reference signal of the driving frequency and the AC voltage, to change the operating state of the ultrasonic vibrator; A method for controlling an ultrasonic vibrator.

Images