Ultrasonic motor system

Abstract

To provide an ultrasonic motor system in which an ultrasonic motor favorably operates when started.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 lower a drive frequency that is a frequency of the AC voltage from a predetermined frequency to a frequency at which a target status of the ultrasonic motor 10 can be obtained when the ultrasonic motor 10 is started. The lowering of the drive frequency has a change pattern varying a frequency changing rate such that the frequency changing rate is fast at high frequencies and is slow at low frequencies.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 start-up operation of an ultrasonic device including an ultrasonic motor. [Means for solving the problem]

[0005] According to one aspect of the present invention, an ultrasonic motor system comprises 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, when the ultrasonic motor is started, reduce the drive frequency, which is the frequency of the AC voltage, from a predetermined frequency to a frequency at which a target ultrasonic motor state is obtained, and the reduction in the drive frequency has a change pattern in which the change rate of the frequency changes, with a fast change rate at high frequencies and a slow change rate at low frequencies. [Effects of the Invention]

[0006] According to the present invention, the operation of an ultrasonic device including an ultrasonic motor at startup 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 diagram showing an example of the results of a numerical analysis of the time change in the drive frequency of the ultrasonic motor and the time change in the current proportional to the vibration amplitude of the stator obtained at that time. [Figure 5] FIG. 5 is a flowchart showing an outline of an example of the operation related to the startup control by the control device when the ultrasonic motor is started. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment will be described with reference to the drawings. This embodiment relates to an ultrasonic motor system. This ultrasonic motor system includes an ultrasonic motor and is configured to appropriately control the operation of the ultrasonic motor. The ultrasonic motor system of this embodiment is particularly excellent in operation at startup.

[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 the amplitude and frequency 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 only to the phase difference therebetween, or may include information related to either one of the phases and the phase difference.

[0019] <Outline of the configuration of the motor drive circuit> 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] [Control of ultrasonic motor startup] <overview> The following describes the control at the time of startup 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) where 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] When high response is required at startup, it may seem that a faster sweep of the drive frequency is better. However, the inventors' investigation revealed that if the frequency sweep is too fast, the intended vibration amplitude cannot be obtained. This is thought to be because, for example, when the drive frequency is reduced to 42 kHz, if the frequency sweep is slow enough, a vibration amplitude of 2.3 μm, as indicated by the circles, is obtained. However, if the frequency sweep is too fast, the vibration amplitude of 0.8 μm, as indicated by the squares, is obtained. When the stator 130 is not properly excited in this way, the rotor 140 does not rotate properly.

[0030] Furthermore, according to the inventor's investigations, it has become clear that, on the high frequency side where the change in vibration amplitude relative to the change in frequency is relatively small, the desired vibration amplitude can be obtained even if the frequency sweep is relatively fast, but near the resonant frequency where the change in vibration amplitude relative to the change in frequency is relatively large, the desired vibration amplitude cannot be obtained if the frequency sweep is fast.

[0031] Therefore, in this embodiment, when the ultrasonic motor 10 is started, the drive frequency is reduced from a predetermined frequency on the high frequency side to a frequency that achieves the target state of the ultrasonic motor 10, such as a target rotation speed. At this time, the drive frequency is reduced in a frequency change pattern in which the change rate is fast at high frequencies and slow at low frequencies. For example, the drive frequency is swept toward the low frequency side, and the frequency sweep is initially relatively fast and then slowed. Note that the frequency change pattern, in which the change rate is fast at high frequencies and slow at low frequencies, does not necessarily have to be exactly like that, and includes a change pattern that generally has such a tendency.

[0032] <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.

[0033] Figure 4 shows an example of the results of a numerical analysis. The bottom graph in Figure 4 shows the relationship between the frequency of the AC voltage applied to the piezoelectric element 132 of the stator 130, i.e., the drive frequency, and the elapsed time. The top graph in Figure 4 shows the results of a numerical analysis of the current that flows at that time. This current is proportional to the vibration amplitude of the stator 130.

[0034] In one analysis, we analyzed the change in current value when the drive frequency was reduced stepwise at a constant rate of 0.16 kHz from 40.0 kHz to 39.2 kHz. The solid black line shows the results when the drive frequency was reduced in 0.4 ms increments over 2 ms, the dashed line shows the results when the drive frequency was reduced in 0.6 ms increments over 3 ms, the dotted line shows the results when the drive frequency was reduced in 1.0 ms increments over 5 ms, and the dash-dot line shows the results when the drive frequency was reduced in 2.0 ms increments over 10 ms.

[0035] These results also showed that when the drive frequency was decreased relatively slowly from 40.0 kHz to 39.2 kHz over 10 ms, the current value stabilized at a large value, such as 0.75 A, approximately 16 ms after the start of AC voltage application. On the other hand, when the drive frequency was decreased relatively quickly from 40.0 kHz to 39.2 kHz over 5 ms, the current value increased rapidly, and from 1.5 ms to 6.0 ms after the start, the current value was higher than when the drive frequency was decreased over 10 ms. However, after 6.0 ms, the current value decreased, and the stator 130 was not properly excited. When the drive frequency was decreased more quickly from 40.0 kHz to 39.2 kHz, i.e., over 2 ms or 3 ms, the current value did not increase significantly, and the current value decreased, and the stator 130 was not properly excited.

[0036] Another analysis was conducted in which the drive frequency was initially reduced quickly and then reduced slowly, as in this embodiment. The drive frequency change pattern was determined as follows: The drive frequency was changed from the current state to 100 different values ​​between 38 kHz and 41 kHz, and 100 current values ​​were calculated after 1 ms had elapsed. The drive frequency that produced the largest current value representing the vibration amplitude after 1 ms was determined as the drive frequency to be applied for that 1 ms. The state after 1 ms of applying this drive frequency was determined as the current state, and the drive frequency to be applied for the next 1 ms was similarly determined from the 100 drive frequencies. By repeating this exhaustive calculation, the optimal drive frequency change pattern was determined.

[0037] The gray solid line in Figure 4 represents the optimal drive frequency change pattern obtained as described above. As shown in the bottom graph of Figure 4, it was found that optimal control was achieved by gradually decreasing the drive frequency. In this case, as shown in the top graph of Figure 4, the current value, i.e., the vibration amplitude of the stator 130, rose quickly and stabilized at a high value of 0.75 A approximately 8.5 ms after the start of AC voltage application. The results showed both a high rise characteristic similar to that obtained when the drive frequency was changed from 40.0 kHz to 39.2 kHz over 5 ms (dotted line) and a high stability similar to that obtained when the drive frequency was changed from 40.0 kHz to 39.2 kHz over 10 ms (dashed line).

[0038] As described above, there are drive frequency change patterns that can quickly obtain a high vibration amplitude, and these patterns can be obtained in advance. For example, because the resonant frequency changes depending on the temperature of the ultrasonic motor 10, the optimal drive frequency change pattern 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 drive frequency change pattern for each case depending on the conditions.

[0039] Control Method The operation of the control device 20 when starting up the ultrasonic motor 10 according to this embodiment will be described. When the ultrasonic motor 10 of this embodiment is started from a stopped state, the ultrasonic motor 10 is controlled by the startup control described here during startup, which exhibits a complex transient response. Once the operation of the ultrasonic motor 10 is started by the startup control and an input target value, such as a predetermined rotation speed, is achieved, the control mode switches to another stable control mode. The stable control is performed by, for example, a known control method.

[0040] FIG. 5 is a flowchart showing an outline of the operation of the control device 20 relating to the start-up control when the ultrasonic motor 10 is started.

[0041] 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 status information, such as the output of various necessary sensors, from the sensor group 70. For example, the control device 20 acquires temperature information of the ultrasonic motor 10 from the temperature sensor 74.

[0042] 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. As the optimal control method, the control device 20 determines, for example, a drive frequency change pattern over time when the drive frequency is reduced from a relatively high predetermined frequency to a predetermined frequency at which the target rotation speed is achieved. The optimal control method may be determined by selecting an appropriate one from multiple pre-prepared drive frequency change patterns based on the acquired target information of the operation of the ultrasonic motor 10 and the status information acquired from the sensor group 70. Multiple pre-prepared drive frequency change patterns may be prepared and finely changed depending on the target information and the status information. Alternatively, multiple pre-prepared drive frequency change patterns may be prepared that are suitable for the target value of the operation of the ultrasonic motor 10 and the status of the ultrasonic motor 10, even if they are not necessarily optimal, and an appropriate one may be selected from among them depending on the target information and the status information. The optimal control method may also be determined by calculation using a predetermined method, for example, using the acquired target information of the operation of the ultrasonic motor 10 and the status information acquired from the sensor group 70. The determination of these optimum control methods is carried out in a short time equal to or shorter than the time constant of the ultrasonic motor 10, for example, 1 ms or less.

[0043] 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 and drive frequency. 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, causing the ultrasonic motor 10 to operate. As a result, the ultrasonic motor 10 starts up and operates based on the optimal control method. Once the state of the ultrasonic motor 10 corresponding to a target value such as a specified rotation speed is obtained, the control mode of the ultrasonic motor 10 switches to another stable control mode.

[0044] <Modification of Control Method> A modified example of the startup control described above will now be described. Machine learning or the like may be used to determine the optimal control pattern for startup control. For example, when there are few parameters, such as when determining a drive frequency change pattern for optimal control depending on the temperature of the ultrasonic motor 10, it is possible to prepare in advance a relationship between the temperature of the ultrasonic motor 10 and the optimal change pattern, for example, using the analysis described above. On the other hand, when there are more parameters, such as when further depending on the load torque applied to the ultrasonic motor 10, or when adaptively changing the optimal change pattern based on status information obtained from the sensor group 70, which can change from moment to moment, it is difficult to prepare a change pattern in advance. In such cases, the use of machine learning or the like is effective.

[0045] 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, or state information obtained using the sensor group 70. 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 state information.

[0046] 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.

[0047] The trained model may be created by any machine learning technique, including, but not limited to, deep reinforcement learning.

[0048] 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 related to a change pattern of the drive frequency, or a value related to a 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.

[0049] 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.

[0050] 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.

[0051] [About ultrasonic motor systems] The ultrasonic motor system 1 according to this embodiment changes the drive frequency to lower when the ultrasonic motor 10 is started, but this drive frequency is not lowered at a constant pace, but rather at an optimal speed that varies. Therefore, in the ultrasonic motor system 1 according to this embodiment, the start-up time until the ultrasonic motor 10 reaches a predetermined target state, such as reaching a target rotation speed, is shorter than in the conventional case where the drive frequency is lowered at a constant pace.

[0052] High responsiveness is required in various usage situations of ultrasonic motors. For example, the response speed also affects the controllability of a positioning device. According to this embodiment, an ultrasonic motor system 1 that achieves high responsiveness can be realized.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] For example, the above-described technology relates to excitation of an ultrasonically vibrating component, such as the stator 130, at startup. 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.

[0058] 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. 4. That is, for example, by adjusting the driving frequency change pattern according to conditions so that the vibration amplitude at the time of starting the piezoelectric element reaches a target value, the vibration of the ultrasonic vibrator at the time of starting 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, crushing devices, sonar, fish finders, and the like.

[0059] 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 a desired amplitude upon startup can be shortened. 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 can be realized in various other performance aspects of various devices. [Explanation of symbols]

[0060] 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 reduce a drive frequency, which is the frequency of the AC voltage, from a predetermined frequency to a frequency at which a target ultrasonic motor state is obtained when the ultrasonic motor is started, and the reduction in the drive frequency has a change pattern in which the change speed of the frequency changes, with the change speed being fast at high frequencies and slow at low frequencies. 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 relating to a target state of the ultrasonic motor and the state information, determine an optimum change pattern for the drive frequency based on the target information and the state information, and output a control command value relating to the optimum change pattern for the drive frequency to the motor drive circuit; The ultrasonic motor system of claim 1 further comprising:

3. The ultrasonic motor system according to claim 2 , wherein the status information includes information about a temperature of the ultrasonic motor or information about a load applied to the ultrasonic motor.

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

5. 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, When the ultrasonic motor is started, acquiring status information relating to a status of the ultrasonic motor and target information relating to a target status of the ultrasonic motor; an optimal change pattern for a drive frequency, which is the frequency of the AC voltage, is determined based on the target information and the state information, and the optimal change pattern for the drive frequency is a change pattern in which the drive frequency is decreased from a predetermined frequency to a frequency at which a target state of the ultrasonic motor is obtained, and the decrease in the drive frequency has a change pattern in which the change speed of the frequency is changed such that the change speed is fast at high frequencies and slow at low frequencies; Outputting a control command value relating to the optimum change pattern of the drive frequency The control device is configured as follows.

6. A control method for controlling an AC voltage applied to an ultrasonic motor to operate the ultrasonic motor, the method comprising: and when starting the ultrasonic motor, reducing a drive frequency, which is a frequency of the AC voltage, from a predetermined frequency to a frequency at which a target state of the ultrasonic motor is obtained, The reduction in the driving frequency has a change pattern in which the change rate of the frequency is fast at high frequencies and slow at low frequencies. A method for controlling an ultrasonic motor.

7. 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 including the following steps being executed by the computer when the ultrasonic motor is started: 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 optimum change pattern for the drive frequency, which is the frequency of the AC voltage, based on the target information and the state information, the optimum change pattern for the drive frequency being a change pattern in which the drive frequency is reduced from a predetermined frequency to a frequency at which a target state of the ultrasonic motor is obtained, and the reduction in the drive frequency has a change pattern in which the change speed of the frequency is fast at high frequencies and slow at low frequencies; outputting a control command value relating to an optimum change pattern of the drive frequency; A control program for executing the above.

8. The control program according to claim 7, wherein the change pattern is determined using a trained model configured to output information regarding an optimal change pattern of the drive frequency in response to input of the target information and the state information.

9. 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 reduce a drive frequency, which is the frequency of the AC voltage, from a predetermined frequency to a frequency at which a target state of the ultrasonic vibrator is obtained when the ultrasonic vibrator is activated, and the reduction in the drive frequency has a change pattern in which the change speed of the frequency changes, with the change speed being fast at high frequencies and slow at low frequencies. A driving device for ultrasonic vibrators.

10. The driving device described in claim 9 further comprises 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 an optimal change pattern of the driving frequency based on the status information and the target information, and output a control command value regarding the optimal change pattern of the driving frequency to the driving circuit.

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

12. The ultrasonic device is an ultrasonic motor.

12. The ultrasound machine system of claim 11.

13. 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: and when starting the ultrasonic vibrator, lowering the drive frequency, which is the frequency of the AC voltage, from a predetermined frequency to a frequency at which a target ultrasonic motor state is obtained, The reduction in the driving frequency has a change pattern in which the change rate of the frequency is fast at high frequencies and slow at low frequencies. A method for controlling an ultrasonic vibrator.

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