Control method of driving device and robot system

Abstract

To provide: a control method of a piezoelectric drive unit capable of performing a stable activation; and a robot system.SOLUTION: A control method of a driving device including an ultrasonic actuator and a driven body driven receiving a driving force from the ultrasonic actuator, includes: an activation step of activating the ultrasonic actuator in a first driving mode; a driving mode switching step of switching driving modes of the ultrasonic actuator into a second driving mode that is different from the first driving mode in the case where the driven body does not come into a desired driving state at the activation; and a driving mode return step of switching the driving modes of the ultrasonic actuator into the first driving mode from the second driving mode in the case where the driven body comes into the desired driving state.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a control method for a drive device and a robot system. [Background technology]

[0002] For example, the fine motion mechanism described in Patent Document 1 includes a fixed base, a guide attached to the fixed base, a moving body that moves along the guide, a sliding member fixed to the moving body, and an ultrasonic actuator pressed against the sliding member. In this fine motion mechanism, the ultrasonic actuator is driven to advance the sliding member, and the moving body moves along the guide. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-27865 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, if dirt or other foreign matter adheres to the sliding surface of the sliding member, or if the sliding member and the ultrasonic actuator are stuck together due to not being driven for a long period of time, the actuator may start unstably or not start at all, making it impossible to achieve stable startup. [Means for solving the problem]

[0005] A method for controlling a driving device of the present invention is a method for controlling a driving device having an ultrasonic actuator and a driven body that is driven by receiving a driving force from the ultrasonic actuator, starting the ultrasonic actuator in a first drive mode; a drive mode switching step of switching a drive mode of the ultrasonic actuator to a second drive mode different from the first drive mode when the driven body does not reach a desired drive state at the time of the start-up; and a drive mode return step of switching the drive mode of the ultrasonic actuator from the second drive mode to the first drive mode when the driven body reaches the desired drive state.

[0006] The robot system of the present invention includes: a robot having a robot arm; a moving stage attached to the robot arm and equipped with a drive unit; a tool attached to the motion stage; The driving device includes an ultrasonic actuator, a driven body that receives a driving force from the ultrasonic actuator and is driven by the ultrasonic actuator, and a control device that controls the driving of the ultrasonic actuator, The control device activates the ultrasonic actuator in a first drive mode; if the driven body does not reach a desired drive state at the time of the start-up, a drive mode of the ultrasonic actuator is switched to a second drive mode different from the first drive mode; When the driven body reaches the desired drive state, the drive mode of the ultrasonic actuator is switched from the second drive mode to the first drive mode. [Brief description of the drawings]

[0007] [Figure 1] FIG. 2 is a plan view showing the drive device according to the first embodiment. [Diagram 2] FIG. 2 is a plan view of the ultrasonic actuator. [Diagram 3] FIG. [Figure 4] FIG. 4 is a diagram showing a driving voltage applied to an ultrasonic actuator. [Diagram 5] FIG. 2 is a plan view showing a driving state of the ultrasonic actuator. [Figure 6]FIG. 11 is a plan view showing a state in which a foreign object is attached to a slider. [Figure 7] 1 is a graph showing the relationship between driving voltage and thrust force. [Figure 8] 4 is a flowchart showing a control method for the drive device. [Figure 9] 1 is a graph showing the relationship between drive frequency and thrust force. [Figure 10] FIG. 13 is a plan view for explaining a control method for a drive device according to a fifth embodiment. [Figure 11] FIG. 13 is a plan view for explaining a control method for a drive device according to a fifth embodiment. [Figure 12] FIG. 13 is a plan view for explaining a control method for a drive device according to a fifth embodiment. [Figure 13] 4 is a flowchart for explaining a control method for the drive device. [Figure 14] FIG. 13 is a plan view showing a robot system according to a sixth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a control method for a driving device and a robot system according to the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

[0009] First Embodiment FIG. 1 is a plan view showing a drive device according to a first embodiment. FIG. 3 is a plan view of an ultrasonic actuator. FIG. 2 is an exploded perspective view of a piezoelectric drive unit. FIG. 4 is a diagram showing a drive voltage applied to an ultrasonic actuator. FIG. 5 is a plan view showing a drive state of an ultrasonic actuator. FIG. 6 is a plan view showing a state in which a foreign object is attached to a slider. FIG. 7 is a graph showing the relationship between drive voltage and thrust force. FIG. 8 is a flowchart showing a control method of the drive device.

[0010] In the following, the three mutually perpendicular axes are referred to as the X-axis, Y-axis, and Z-axis, and 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. The arrow side of each axis is also referred to as the "plus side," and the opposite side to the arrow is also referred to as the "minus side." The positive side of the Z-axis direction is also referred to as the "upper" and the negative side as the "lower," and the positive side of the X-axis direction is also referred to as the "tip" and the negative side as the "base."

[0011] 1 has a slider 2 which is a driven body that moves linearly in the Y-axis direction, and a piezoelectric driving unit 3 which abuts against the slider 2. The piezoelectric driving unit 3 also has an ultrasonic actuator 4 which abuts against the slider 2, a biasing member 6 which presses the ultrasonic actuator 4 against the slider 2, an encoder 8 which detects the amount of movement of the slider 2, and a control device 9 which controls the driving of the ultrasonic actuator 4.

[0012] However, the configuration of the driving device 1 is not particularly limited. For example, a plurality of piezoelectric driving units 3 may be arranged for the slider 2, and the slider 2 may be moved linearly by driving the plurality of piezoelectric driving units 3. In addition, the driven body may not move linearly like the slider 2, but may rotate like a rotor.

[0013] As shown in FIG. 2 , the ultrasonic actuator 4 has a vibration part 41, a support part 42 that supports the vibration part 41, a connection part 43 that connects the vibration part 41 and the support part 42, and a convex part 44 that protrudes from the tip of the vibration part 41 and transmits the vibration of the vibration part 41 to the slider 2.

[0014] The vibration part 41 has a thickness direction in the Z-axis direction and is plate-like extending in the XY plane including the X-axis and Y-axis. In plan view, the vibration part 41 is rectangular with the X-axis direction, which is the expansion and contraction direction, as the longitudinal direction. The vibration part 41 flexes and vibrates in an S-shape by expanding and contracting in the X-axis direction and bending in the Y-axis direction. However, the shape of the vibration part 41 is not particularly limited as long as it can perform its function.

[0015] The vibration section 41 also has a driving piezoelectric element 40 that causes the vibration section 41 to bend and vibrate. The piezoelectric element 40 has piezoelectric elements 4A and 4B as first piezoelectric elements, and piezoelectric elements 4C, 4D, 4E, and 4F as second piezoelectric elements. The piezoelectric elements 4A and 4B are arranged side by side in the X-axis direction at the center of the vibration section 41. The piezoelectric elements 4C and 4D are arranged side by side in the X-axis direction on the positive side of the Y-axis direction of the piezoelectric elements 4A and 4B, and the piezoelectric elements 4E and 4F are arranged side by side in the X-axis direction on the negative side of the Y-axis direction. Each of these piezoelectric elements 4A to 4F expands and contracts in the X-axis direction when electricity is applied.

[0016] Among the piezoelectric elements 4A to 4F, the piezoelectric elements 4A and 4B are piezoelectric elements for causing the vibration part 41 to expand and contract in the X-axis direction, and the piezoelectric elements 4C, 4D, 4E, and 4F are piezoelectric elements for causing the vibration part 41 to flex and vibrate in the Y-axis direction. However, the number and arrangement of the driving piezoelectric elements are not particularly limited.

[0017] 3, the vibration section 41 has a configuration in which a piezoelectric element layer 48 including the piezoelectric element 40 is sandwiched between a pair of substrates 49, 49. Each substrate 49 is, for example, a silicon substrate.

[0018] The piezoelectric element 40 has 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 examples of the material that can be used include 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 lead scandium niobate. In addition to the above-mentioned piezoelectric ceramics, the piezoelectric body may also be made of polyvinylidene fluoride, quartz, or the like.

[0019] The method for forming the piezoelectric body is not particularly limited, and the piezoelectric body may be formed from a bulk material, or may be formed using a sol-gel method or a sputtering method. In this embodiment, the piezoelectric body is formed using a sol-gel method. This makes it possible to obtain a thinner piezoelectric body than when the piezoelectric body is formed from a bulk material, for example, and to reduce the thickness of the ultrasonic actuator 4.

[0020] The protrusion 44 is provided at the tip of the vibrating part 41 and protrudes from the vibrating part 41 toward the positive side in the X-axis direction. The tip of the protrusion 44 is rounded in a semicircular shape. As shown in FIG. 1, the tip of the protrusion 44 is pressed against the side surface of the slider 2 by the biasing member 6. Therefore, the vibration of the vibrating part 41 is transmitted to the slider 2 via the protrusion 44. The material of the protrusion 44 is not particularly limited, and examples of the material include various ceramics such as zirconia, alumina, and titania. This results in the protrusion 44 having excellent durability. However, the configuration of the protrusion 44 is not particularly limited.

[0021] The support section 42 supports the vibration section 41. As shown in Fig. 2, the support section 42 is U-shaped and surrounds three sides of the vibration section 41. As shown in Fig. 3, the support section 42 has a configuration in which a spacer having approximately the same thickness as the piezoelectric element layer 48 is sandwiched between a pair of substrates 49, 49. However, the configuration of the support section 42 is not particularly limited as long as it can perform its function.

[0022] 2, the connection part 43 connects a part that becomes a node of the bending vibration of the vibrating part 41, that is, a central part in the X-axis direction, to the support part 42. However, the configuration of the connection part 43 is not particularly limited as long as it can perform its function.

[0023] The ultrasonic actuator 4 as described above is biased toward the slider 2 by the biasing member 6, so that the convex portion 44 is pressed against the slider 2. As shown in FIG. 3, a pair of biasing members 6 are provided so as to sandwich the ultrasonic actuator 4 from above and below. Each biasing member 6 has a support portion 61 that supports the ultrasonic actuator 4, a base 62 that fixes the piezoelectric driving unit 3 to the stage, and a plurality of plate-shaped spring portions 63 that connect the support portion 61 and the base 62. In the biasing member 6 configured as described above, the plate-shaped spring portions 63 are fixed to the stage in an elastically deformed state, so that the elasticity (restoring force) of the plate-shaped spring portions 63 can be used to press the convex portion 44 against the slider 2.

[0024] The biasing member 6 is a silicon substrate. This allows the biasing member 6 to have sufficient mechanical strength and elasticity. In addition, a silicon wafer process can be used, and the biasing member 6 can be manufactured with high processing accuracy. In addition, the difference in thermal expansion coefficient between the biasing member 6 and the ultrasonic actuator 4 is reduced, and thermal stress can be reduced. Therefore, deflection, distortion, etc. of the ultrasonic actuator 4 can be suppressed. However, the material of the biasing member 6 is not particularly limited.

[0025] The control device 9 is, for example, composed of a computer, and has a processor for processing information, a memory communicatively connected to the processor, and an external interface. The memory also stores programs executable by the processor, and the processor reads and executes the programs stored in the memory. Such a control device 9 receives commands (hereinafter also referred to as "drive commands") from a host computer (not shown), and controls the drive of the ultrasonic actuator 4 while feeding back the output of the encoder 8 to the commands.

[0026] For example, when the driving voltage V1 shown in Fig. 4 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. 5, the vibrating portion 41 vibrates in an inverted S-shape in the Y-axis direction while stretching and vibrating in the X-axis direction, and these vibrations are combined, causing the tip of the convex portion 44 to move elliptically in an elliptical orbit in the counterclockwise direction as shown by the arrow. This causes the slider 2 to be sent out and move linearly in the positive direction of the Y-axis. Conversely, when the waveforms of the driving voltages V2 and V3 are switched, the slider 2 moves linearly in the negative direction of the Y-axis.

[0027] The configuration of the driving device 1 has been described above. Next, a control method of the driving device 1 will be described. For example, as shown in FIG. 6, if foreign matter Q such as dirt or dust is attached to the surface of the slider 2, the convex portion 44 will get caught on the foreign matter Q when the ultrasonic actuator 4 is started, making the start of the movement of the slider 2 unstable. In addition, for example, if the slider 2 is stopped for a long period of time and the convex portion 44 and the slider 2 are stuck together, the start of the movement of the slider 2 will also become unstable. In such a case, the driving device 1 will determine that an abnormality has occurred and will emergency stop the drive of the ultrasonic actuator 4 (hereinafter, also referred to as "error stop"). The above-mentioned "unstable start of movement" also includes a case where the convex portion 44 cannot overcome the foreign matter Q and the slider 2 does not start moving, or a case where the slider 2 starts moving but stops immediately.

[0028] Therefore, the driving device 1 of this embodiment has a driving mode that attempts to resolve unstable start of the movement of the slider 2 at the time of startup due to factors such as a foreign object Q. With this configuration, it is possible to suppress the occurrence of error stop at the time of startup. This will be described in detail below.

[0029] The control device 9 has a first drive mode and a second drive mode as drive modes for driving the ultrasonic actuator 4. Of these, the first drive mode is a normal drive mode, and the ultrasonic actuator 4 is started in the first drive mode first. In contrast, the second drive mode is a drive mode used when the drive of the slider 2 is unstable and the desired drive state is not reached when the ultrasonic actuator 4 is started in the first drive mode. In the following, for convenience of explanation, the case where the slider 2 reaches the desired drive state when started in the first drive mode is also called a "normal state", and the case where the desired drive state is not reached is also called an "abnormal state". In other words, the second drive mode is a drive mode for eliminating the abnormal state and returning to the normal state.

[0030] The "desired driving state" refers to a state in which the slider 2 reaches a desired moving speed, for example, the moving speed of the slider 2 assumed when driven in the first driving mode, or a threshold value set based on this moving speed. Alternatively, it refers to a state in which the slider 2 reaches a desired moving distance, for example, the moving distance of the slider 2 assumed when driven in the first driving mode, or a threshold value set based on this moving distance. In particular, in this embodiment, it is said to be a state in which both of these are satisfied. This makes it possible to easily and accurately determine an abnormal state. The moving speed and moving distance of the slider 2 can be obtained from the output of the encoder 8.

[0031] 7, the force (hereinafter also referred to as "thrust") that sends out the slider 2 increases as the driving voltages V2 and V3, which are voltages that control the amplitude of the bending vibration, are increased. In contrast, since the driving voltage V1 is a voltage that controls the amplitude of the stretching vibration, the thrust hardly changes even if the driving voltage V1 is changed. Therefore, in this embodiment, in both the first and second driving modes, the driving voltage V1 is kept constant, and the thrust is controlled by changing the driving voltages V2 and V3.

[0032] In the first drive mode, the drive voltages V2 and V3 are changed within a variable range Sv from the voltage value Vmin to the voltage value Vmax to adjust the thrust and increase or decrease the moving speed of the slider 2. Here, by setting the variable range Sv low, it is possible to prevent the ultrasonic actuator 4 from overheating due to excessive power. Therefore, it is possible to prevent failure and shortening of the lifespan of the ultrasonic actuator 4, and stable drive for a long period of time is possible.

[0033] In contrast, in the second drive mode, the drive voltages V2 and V3 are set higher than the variable range Sv of the first drive mode. Therefore, a higher thrust force can be obtained than in the first drive mode, and even if a foreign object Q is attached to the slider 2, the protrusion 44 can easily overcome the foreign object Q, and the protrusion 44 is less likely to get caught on the foreign object Q. This increases the likelihood that the slider 2 will start moving smoothly. In other words, it increases the likelihood that the abnormal state can be resolved and the normal state can be transitioned to, and the occurrence of an error stop can be more effectively suppressed.

[0034] In particular, the second drive mode of this embodiment has a first voltage value Va, a second voltage value Vb greater than the first voltage value Va, and a third voltage value Vc greater than the second voltage value Vb. In the second drive mode, first, the ultrasonic actuator 4 is driven at the first voltage value Va to attempt to eliminate the abnormal state. If the abnormal state is not eliminated at the first voltage value Va, the ultrasonic actuator 4 is driven at the second voltage value Vb to attempt to eliminate the abnormal state again. If the abnormal state is not eliminated at the second voltage value Vb, the ultrasonic actuator 4 is driven at the third voltage value Vc to attempt to eliminate the abnormal state again. In this way, by gradually increasing the drive voltages V2 and V3 in the order of Va → Vb → Vc, it is possible to prevent excessive drive voltages V2 and V3 greater than the magnitude capable of eliminating the abnormal state from being applied to the ultrasonic actuator 4, and overheating of the ultrasonic actuator 4 can be effectively suppressed. In addition, overheating of the ultrasonic actuator 4 can be effectively suppressed by not changing the drive voltage V1 that does not affect the thrust. It is also possible to suppress runaway of the slider 2.

[0035] However, the second driving mode is not particularly limited, and the driving voltages V2 and V3 may be fixed to any one of the first voltage value Va, the second voltage value Vb, and the third voltage value Vc. Also, the driving voltages V2 and V3 may be increased continuously from the first voltage value Va to the third voltage value Vc.

[0036] Hereinafter, the control method of the drive device 1 will be specifically described with reference to the flowchart shown in Fig. 8. The control method of the drive device 1 includes a start-up step S1 for starting the ultrasonic actuator 4 in a first drive mode, a drive mode switching step S2 for switching the drive mode of the ultrasonic actuator 4 to the second drive mode if the slider 2 does not reach a desired drive state at the time of start-up, and a drive mode return step S3 for switching the drive mode of the ultrasonic actuator 4 to the first drive mode if the slider 2 reaches a desired drive state.

[0037] <Start-up step S1> In the start-up step S1, as step S11, the control device 9 first starts the ultrasonic actuator 4 in the first drive mode and starts the movement of the slider 2. Next, as step S12, the control device 9 detects the movement speed and movement distance of the slider 2 based on the output of the encoder 8. The method of detecting the movement speed is not particularly limited, but for example, the slider 2 is moved a predetermined distance and the movement speed can be detected from the time required for the movement. Also, the method of detecting the movement distance is not particularly limited, but the slider 2 is driven for a predetermined time and the movement distance can be detected as the distance moved within that time. Next, as step S13, the control device 9 judges whether the slider 2 is in a normal state or an abnormal state based on the detected movement speed and movement distance. If the slider 2 is in a normal state, the control device 9 continues driving in the first drive mode as it is. On the other hand, if the slider 2 is in an abnormal state, the control device 9 proceeds to the drive mode switching step S2.

[0038] <<Drive mode switching step S2>> In the drive mode switching step S2, the control device 9 first switches the drive mode of the ultrasonic actuator 4 from the first drive mode to the second drive mode and sets the drive voltages V2 and V3 to the first voltage value Va as step S21. This generates a thrust force larger than that in the first drive mode, and attempts to bring the slider 2 from an abnormal state to a normal state. Next, as step S22, the control device 9 detects the moving speed and moving distance of the slider 2 based on the output of the encoder 8. Next, as step S23, the control device 9 determines whether the slider 2 is in a normal state or an abnormal state based on the detected moving speed and moving distance. If the slider 2 is in a normal state, the control device 9 proceeds to the drive mode return step S3.

[0039] On the other hand, if the slider 2 remains in the abnormal state, then in step S24, the control device 9 sets the drive voltages V2 and V3 to the second voltage value Vb. This further increases the thrust force, and attempts to bring the slider 2 from the abnormal state to the normal state. Next, in step S25, the control device 9 detects the moving speed and moving distance of the slider 2 based on the output of the encoder 8. Next, in step S26, the control device 9 determines whether the slider 2 is in a normal state or an abnormal state based on the detected moving speed and moving distance. If the slider 2 is in a normal state, the control device 9 proceeds to the drive mode return step S3.

[0040] On the other hand, if the slider 2 remains in the abnormal state, in step S27, the control device 9 sets the driving voltages V2 and V3 to the third voltage value Vc. This further increases the thrust force, and attempts to make the slider 2 go from the abnormal state to the normal state. Next, in step S28, the control device 9 detects the moving speed and moving distance of the slider 2 based on the output of the encoder 8. Next, in step S29, the control device 9 determines whether the slider 2 is in a normal state or an abnormal state based on the detected moving speed and moving distance. If the slider 2 is in a normal state, the control device 9 proceeds to the drive mode return step S3. On the other hand, if the slider 2 remains in the abnormal state, the control device 9 stops the ultrasonic actuator 4 due to an error because the driving voltages V2 and V3 cannot be increased any further.

[0041] <<Drive mode return step S3>> In the drive mode return step S3, the control device 9 switches the drive mode of the ultrasonic actuator 4 from the second drive mode to the first drive mode. This makes it possible to suppress the drive voltages V2 and V3, and effectively suppress overheating of the ultrasonic actuator 4. Note that since the moving speed of the slider 2 is sufficiently high when switching to the first drive mode, switching to the first drive mode does not cause the slider 2 to return to an abnormal state again. According to the above-mentioned control method, even if the slider 2 is in an abnormal state in the startup step S1, an attempt can be made to eliminate the abnormal state and return it to a normal state, and therefore the occurrence of an error stop at startup can be suppressed.

[0042] The control method of the drive device 1 has been described above in detail. As described above, the control method of the drive device 1 includes the ultrasonic actuator 4 and the slider 2, which is a driven body that receives a driving force from the ultrasonic actuator 4 and is driven by the ultrasonic actuator 4. The control method of the drive device 1 includes a start-up step S1 for starting the ultrasonic actuator 4 in a first drive mode, a drive mode switching step S2 for switching the drive mode of the ultrasonic actuator 4 to a second drive mode different from the first drive mode when the slider 2 does not reach a desired drive state at the start-up, and a drive mode return step S3 for switching the drive mode of the ultrasonic actuator 4 from the second drive mode to the first drive mode when the slider 2 reaches a desired drive state. As a result, even if the slider 2 is in an abnormal state in the start-up step S1, it is possible to try to eliminate the abnormal state and return it to a normal state, and it is possible to suppress the occurrence of an error stop at the time of start-up.

[0043] As described above, the desired driving state is when the slider 2 has reached the desired moving distance or moving speed, which makes it possible to easily and accurately determine whether an abnormal state has occurred.

[0044] As described above, the drive voltages V2 and V3 in the second drive mode are greater than the drive voltages V2 and V3 in the first drive mode in the startup step S1. This provides a higher thrust than in the startup step S1, increasing the possibility that the abnormal state will be resolved and the normal state will be restored. This makes it possible to more effectively suppress the occurrence of error stops.

[0045] As described above, the drive voltages V2 and V3 in the second drive mode are greater than the variable range Sv of the drive voltages V2 and V3 in the first drive mode, which makes it possible to more reliably make the drive voltages V2 and V3 in the second drive mode greater than the drive voltages V2 and V3 in the startup step S1.

[0046] As described above, the ultrasonic actuator 4 has the vibration part 41, the piezoelectric elements 4A and 4B which are the first piezoelectric elements that vibrate the vibration part 41 in an expanding and contracting manner, and the piezoelectric elements 4C, 4D, 4E, and 4F which are the second piezoelectric elements that vibrate the vibration part 41 in a bending manner. The driving voltages V2 and V3 of the piezoelectric elements 4C, 4D, 4E, and 4F in the second driving mode are greater than the driving voltages V2 and V3 of the piezoelectric elements 4C, 4D, 4E, and 4F in the first driving mode in the startup step S1. This allows the thrust generated in the second driving mode to be greater than the thrust generated in the first driving mode with simple control.

[0047] <Second embodiment> The drive device 1 of this embodiment is similar to the drive device 1 of the first embodiment described above, except for the control method. In the following description, the drive device 1 of this embodiment will be described focusing on the differences from the first embodiment described above, and a description of the similarities will be omitted.

[0048] In the first embodiment described above, the driving voltages V2 and V3 in the second driving mode are made larger than the driving voltages V2 and V3 in the first driving mode to increase the thrust in the second driving mode and to eliminate the abnormal state. In contrast, in the present embodiment, the driving voltage V1 in the second driving mode is made larger than the driving voltage V1 in the first driving mode to increase the amplitude of the stretching vibration of the convex portion 44 in the second driving mode, making it easier for the convex portion 44 to overcome the foreign object Q, thereby attempting to eliminate the abnormal state.

[0049] Specifically, the larger the driving voltage V1, the larger the amplitude of the stretching vibration of the convex portion 44. Therefore, the driving voltage V1 in the second driving mode is set higher than the driving voltage V1 in the first driving mode. As a result, in the second driving mode, the convex portion 44 vibrates more greatly in the X-axis direction than in the first driving mode, making it easier for the convex portion 44 to overcome the foreign object Q. Therefore, the possibility that the abnormal state will be resolved and the normal state will be restored is increased, and the occurrence of an error stop at start-up can be more effectively suppressed.

[0050] In addition, in the drive mode switching step S2, as in the first embodiment described above, there are a first voltage value, a second voltage value larger than the first voltage value, and a third voltage value larger than the second voltage value. Then, first, the ultrasonic actuator 4 is driven with the first voltage value to attempt to eliminate the abnormal state. If the abnormal state is not eliminated with the first voltage value, the ultrasonic actuator 4 is driven with the second voltage value to attempt to eliminate the abnormal state again. If the abnormal state is not eliminated with the second voltage value, the ultrasonic actuator 4 is driven with the third voltage value to attempt to eliminate the abnormal state again. In this way, by gradually increasing the drive voltage V1, it is possible to prevent an excessive drive voltage V1 that is greater than or equal to the magnitude capable of eliminating the abnormal state from being applied to the ultrasonic actuator 4, and it is possible to effectively prevent overheating of the ultrasonic actuator 4. In addition, it is possible to effectively prevent overheating of the ultrasonic actuator 4 by not changing the drive voltages V2 and V3.

[0051] However, the second driving mode is not particularly limited and may be fixed to any one of the first voltage value, the second voltage value, and the third voltage value, or the driving voltage V1 may be increased continuously from the first voltage value to the third voltage value.

[0052] The second embodiment as described above can also achieve the same effects as the first embodiment.

[0053] <Third embodiment> FIG. 9 is a graph showing the relationship between the drive frequency and the thrust force.

[0054] The driving device 1 of this embodiment is similar to the driving device 1 of the first embodiment described above, except for the control method. In the following description, the driving device 1 of this embodiment will be described focusing on the differences from the first embodiment described above, and the description of the similar points will be omitted. In the drawings of this embodiment, the same reference numerals are used for the same configurations as the above-mentioned embodiment.

[0055] In this embodiment, an attempt is made to transition from an abnormal state to a normal state by changing the frequency of the drive voltages V1, V2, and V3 in the second drive mode from the frequency of the drive voltages V1, V2, and V3 in the first drive mode. A detailed explanation will be given below, but for convenience of explanation, the frequency of the drive voltages V1, V2, and V3 will be referred to as the "drive frequency f."

[0056] As shown in FIG. 9, the thrust is maximum when the drive frequency f coincides with the resonance frequency fr of the ultrasonic actuator 4. In addition, the thrust drops sharply on the low frequency side of the resonance frequency fr, and drops gently on the high frequency side of the resonance frequency fr. Therefore, in the first drive mode, the drive frequency f is set close to the resonance frequency fr and on the high frequency side of the resonance frequency fr. This makes the change in the moving speed of the slider 2 with respect to the drive frequency f gentle, and the moving speed of the slider 2 can be controlled with high accuracy. In addition, a sufficient margin is set between the drive frequency f and the resonance frequency fr to maintain the relationship of resonance frequency fr<drive frequency f even if the resonance frequency fr fluctuates during driving.

[0057] In contrast, in the second drive mode, the drive frequency f is made lower than the drive frequency f in the first drive mode and made closer to the resonance frequency fr, which generates a larger thrust than in the first drive mode, increases the possibility that the abnormal state will be resolved and the normal state will be restored, and makes it possible to more effectively suppress the occurrence of an error stop at start-up.

[0058] In particular, in the drive mode switching step S2, there are a first frequency f1, a second frequency f2 closer to the resonance frequency fr than the first frequency f1, and a third frequency f3 closer to the resonance frequency fr than the second frequency f2. Then, first, the ultrasonic actuator 4 is driven at the first frequency f1 to attempt to eliminate the abnormal state. If the abnormal state is not eliminated at the first frequency f1, the ultrasonic actuator 4 is driven at the second frequency f2 to attempt to eliminate the abnormal state again. If the abnormal state is not eliminated at the second frequency f2, the ultrasonic actuator 4 is driven at the third frequency f3 to attempt to eliminate the abnormal state again. In this way, runaway of the slider 2 can be suppressed by gradually bringing the drive frequency f closer to the resonance frequency fr.

[0059] However, the second driving mode is not particularly limited, and the driving frequency f may be fixed to any one of the first frequency f1, the second frequency f2, and the third frequency f3. Also, the driving frequency f may be changed continuously from the first frequency f1 to the third frequency f3.

[0060] As described above, in the control method of the drive device 1 of this embodiment, in the second drive mode, the drive frequency f of the ultrasonic actuator 4 is changed to approach the resonance frequency fr of the ultrasonic actuator 4. This generates a thrust force larger than that in the first drive mode, increasing the possibility that the slider 2 will go from an abnormal state to a normal state. Therefore, the occurrence of an error stop can be more effectively suppressed.

[0061] The third embodiment as described above can also achieve the same effects as the first embodiment described above.

[0062] <Fourth embodiment> The drive device 1 of this embodiment is similar to the drive device 1 of the first embodiment described above, except for the control method. In the following description, the drive device 1 of this embodiment will be described focusing on the differences from the first embodiment described above, and a description of the similarities will be omitted.

[0063] In this embodiment, the phase difference between the drive voltages V1, V2, and V3 in the second drive mode is changed from the phase difference between the drive voltages V1, V2, and V3 in the first drive mode to attempt a transition from an abnormal state to a normal state. Specifically, the phase difference between the drive voltages V2 and V3 is fixed at about 180°, while the phase difference θ (see FIG. 4) between the drive voltages V1 and V2 and V3 is changed. By changing the phase difference θ, the elliptical orbit of the convex portion 44 changes, and there is a possibility that the convex portion 44 is less likely to get caught on the foreign object Q when the slider 2 starts moving, and more likely to overcome it. Therefore, the possibility that the abnormal state is resolved and the normal state is restored is increased, and the occurrence of an error stop can be more effectively suppressed.

[0064] As described above, in the control method of the drive device 1 of this embodiment, the ultrasonic actuator 4 has the vibration part 41, the piezoelectric elements 4A and 4B that vibrate the vibration part 41 in an expanding and contracting manner, and the piezoelectric elements 4C, 4D, 4E, and 4F that vibrate the vibration part 41 in a bending manner. In the second drive mode, the phase difference θ between the drive voltage V1 of the piezoelectric elements 4A and 4B and the drive voltages V2 and V3 of the piezoelectric elements 4C, 4D, 4E, and 4F is changed. In this way, by changing the phase difference θ, the elliptical orbit of the convex part 44 changes, and the convex part 44 is less likely to get caught on the foreign object Q when the slider 2 starts moving, and may easily overcome the foreign object Q. Therefore, the possibility that the abnormal state is resolved and the normal state is restored is increased, and the occurrence of an error stop can be more effectively suppressed.

[0065] The fourth embodiment as described above can also achieve the same effects as the first embodiment described above.

[0066] <Fifth embodiment> Fig. 10 to Fig. 12 are plan views for explaining a method of controlling the drive device according to the fifth embodiment, and Fig. 13 is a flowchart for explaining a method of controlling the drive device.

[0067] The driving device 1 of this embodiment is similar to the driving device 1 of the first embodiment described above, except for the control method. In the following description, the driving device 1 of this embodiment will be described focusing on the differences from the first embodiment described above, and the description of the similar points will be omitted. In the drawings of this embodiment, the same reference numerals are used for the same configurations as the above-mentioned embodiment.

[0068] For example, as shown in FIG. 10, even if the ultrasonic actuator 4 is driven while the convex portion 44 is in contact with a foreign object Q adhering to the slider 2, and an attempt is made to send the slider 2 in the positive direction of the Y axis, the momentum of the slider 2 may be insufficient for the convex portion 44 to overcome the foreign object Q, and the slider 2 may not start moving.

[0069] Therefore, in this embodiment, as shown in Fig. 11, the slider 2 is first moved in the direction opposite to the moving direction in the start-up step S1, that is, to the negative Y-axis direction to sufficiently separate the protrusion 44 from the foreign object Q, and then the slider 2 is sent out to the positive Y-axis direction as shown in Fig. 12. This sufficiently increases the moving speed of the slider 2 before the protrusion 44 comes into contact with the foreign object Q, and this momentum makes it easier for the protrusion 44 to overcome the foreign object Q. This increases the possibility that the abnormal state will be resolved and the normal state will be restored, and the occurrence of an error stop can be more effectively suppressed.

[0070] Hereinafter, a specific description will be given of a control method for the drive device 1 based on the flowchart shown in Fig. 13. As in the first embodiment described above, the control method for the drive device 1 includes a start-up step S1, a drive mode switching step S2, and a drive mode return step S3.

[0071] <Start-up step S1> In the start-up step S1, the control device 9 first starts the ultrasonic actuator 4 in the first drive mode and starts moving the slider 2 as step S101. Next, as step S102, the control device 9 detects the moving speed and moving distance of the slider 2 based on the output of the encoder 8. Next, as step S103, the control device 9 determines whether the slider 2 is in a normal state or an abnormal state based on the detected moving speed and moving distance. If the slider 2 is in a normal state, the control device 9 continues driving in the first drive mode as it is. On the other hand, if the slider 2 is in an abnormal state, the control device 9 proceeds to the drive mode switching step S2.

[0072] <<Drive mode switching step S2>> In the drive mode switching step S2, the control device 9 switches the drive mode of the ultrasonic actuator 4 from the first drive mode to the second drive mode. In the second drive mode, first, in step S201, the slider 2 is moved in the opposite direction to that in the start-up step S1. Next, in step S202, the slider 2 is moved in the same direction as that in the start-up step S1. Next, in step S203, the control device 9 detects the movement speed and movement distance of the slider 2 based on the output of the encoder 8. Next, in step S204, the control device 9 determines whether the slider 2 is in a normal state or an abnormal state based on the detected movement speed and movement distance. If the slider 2 is in a normal state, the control device 9 proceeds to the drive mode return step S3.

[0073] On the other hand, if the slider 2 remains in the abnormal state, the amount of movement in the opposite direction is increased from the previous time, and steps S201 to S204 are repeated a predetermined number of times. If the abnormal state is not resolved even after the predetermined number of repetitions, an error stop is performed.

[0074] <<Drive mode return step S3>> In the drive mode return step S3, the control device 9 switches the drive mode of the ultrasonic actuator 4 from the second drive mode to the first drive mode.

[0075] As described above, in the second drive mode of this embodiment, the ultrasonic actuator 4 is driven so that the slider 2 moves in the direction opposite to the movement direction in the startup step S1, and then the slider 2 is driven so that the slider 2 moves in the same direction as the movement direction in the startup step S1. This makes it possible to sufficiently increase the movement speed of the slider 2 before the convex portion 44 comes into contact with the foreign object Q in the drive mode switching step S2, and this momentum makes it easier for the convex portion 44 to overcome the foreign object Q. This increases the possibility that the abnormal state will be resolved and the normal state will be restored, and the occurrence of an error stop can be more effectively suppressed.

[0076] The fifth embodiment can also achieve the same effects as the first embodiment described above.

[0077] Sixth Embodiment FIG. 14 is a plan view showing a robot system according to the sixth embodiment.

[0078] The robot system 1000 shown in FIG. 14 has a robot 1100, a movable stage 1200 attached to the robot 1100, a tool 1300 attached to the movable stage 1200, and a control unit 1400 that controls the driving of these, and can perform tasks such as supplying, removing, transporting, and assembling precision equipment and the parts that make up the equipment.

[0079] The robot 1100 is a six-axis robot with six joints, and includes a base 1110 fixed to a floor or 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 connector, and a moving stage 1200 is attached to the hand connector.

[0080] The robot 1100 also includes a first arm rotation mechanism 1131 that is disposed at a joint between the base 1110 and the first arm 1121 and rotates the first arm 1121 relative to the base 1110, a second arm rotation mechanism 1132 that is disposed at a joint between the first arm 1121 and the second arm 1122 and rotates the second arm 1122 relative to the first arm 1121, and a third arm rotation mechanism 1133 that is disposed at a joint between the second arm 1122 and the third arm 1123 and rotates the third arm 1123 relative to the second arm 1122. the fourth arm rotation mechanism 1134 is arranged at the joint between the third arm 1123 and the fourth arm 1124 and rotates the fourth arm 1124 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 and rotates the fifth arm 1125 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 and rotates the sixth arm 1126 relative to the fifth arm 1125.

[0081] A driving device 1 is mounted on some or all of the first to sixth arm rotation mechanisms 1131-1136 as a power source, and the corresponding arms 1121-1126 rotate when driven by the driving device 1. Therefore, the robot 1100 can enjoy the effects of the driving device 1 described above, and can demonstrate high reliability. However, the present invention is not limited to this, and the driving device 1 does not have to be mounted on any of the first to sixth arm rotation mechanisms 1131-1136.

[0082] The moving stage 1200 has a base 1210 connected to the hand connection portion of the sixth arm 1126, a first stage 1220 that moves in a first direction U relative to the base 1210, a second stage 1230 that moves in a second direction V perpendicular to the first direction U relative to the first stage 1220, a first stage moving mechanism 1240 that moves the first stage 1220 in the first direction U relative to the base 1210, and a second stage moving mechanism 1250 that moves the second stage 1230 in the second direction V relative to the first stage 1220.

[0083] One or both of the first and second stage moving mechanisms 1240 and 1250 are equipped with a driving device 1 as a power source, and the target stages 1220 and 1230 are moved by driving the piezoelectric driving unit 3. This allows the effects of the driving device 1 to be enjoyed, and high reliability can be achieved. For example, when the driving device 1 is mounted on the first stage moving mechanism 1240, the ultrasonic actuator 4 is fixed to the base 1210, the slider 2 is fixed to the first stage 1220, and the control device 9 performs the same control as in the first embodiment described above. Also, when the driving device 1 is mounted on the second stage moving mechanism 1250, the ultrasonic actuator 4 is fixed to the first stage 1220, the slider 2 is fixed to the second stage 1230, and the control device 9 performs the same control as in the first embodiment described above.

[0084] Further, a tool 1300 is attached to the second stage 1230. The tool 1300 is not particularly limited and varies depending on the contents of the target work, but in this embodiment, it is an inkjet head 1310. In the robot system 1000, a printing work is performed on an object by ejecting ink from the inkjet head 1310. As described above, the moving stage 1200 is interposed between the robot 1100 and the inkjet head 1310. Therefore, for example, while the robot 1100 is stopped, the inkjet head 1310 can be moved by the moving stage 1200. This allows a stable printing work to be performed.

[0085] As described above, the robot system 1000 of this embodiment includes the robot 1100 having the robot arm 1120, the moving stage 1200 attached to the robot arm 1120 and equipped with the driving device 1, and the tool 1300 attached to the moving stage 1200. The driving device 1 also includes the ultrasonic actuator 4, the slider 2 that receives driving force from the ultrasonic actuator 4 and drives it, and the control device 9 that controls the driving of the ultrasonic actuator 4. The control device 9 starts the ultrasonic actuator 4 in the first driving mode, and if the slider 2 does not reach a desired driving state at the time of starting, switches the driving mode of the ultrasonic actuator 4 to a second driving mode different from the first driving mode, and if the slider 2 reaches a desired driving state, switches the driving mode of the ultrasonic actuator 4 from the second driving mode to the first driving mode. With this configuration, the robot system 1000 can enjoy the effects of the piezoelectric driving unit 3 described above and exhibits high reliability.

[0086] The sixth embodiment can also achieve the same effects as the first embodiment described above.

[0087] The control method for the drive device and the robot system of the present invention have been described above based on the illustrated embodiment, but the present invention is not limited thereto, and the configuration of each part can be replaced with any configuration or process having a similar function. Any other configuration or process may be added to the present invention. The embodiments may be appropriately combined. In the above embodiment, the configuration in which the drive device is applied to a robot system has been described, but the drive device can also be applied to various electronic devices that require driving force, such as printers and projectors. [Explanation of symbols]

[0088] 1...drive device, 2...slider, 3...piezoelectric drive unit, 4...ultrasonic actuator, 4A...piezoelectric element, 4B...piezoelectric element, 4C...piezoelectric element, 4D...piezoelectric element, 4E...piezoelectric element, 4F...piezoelectric element, 40...piezoelectric element, 41...vibration unit, 42...support unit, 43...connection unit, 44...protrusion, 48...piezoelectric element layer, 49...substrate, 6...biasing member, 61...support unit, 62...base, 63...plate spring unit, 8...encoder, 9...control device, 1000...robot system, 1100...robot, 1110...base, 1120...robot arm, 1121...first arm, 1122...second arm, 1123...third arm, 1124...fourth arm, 1125...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...moving stage, 1210...base, 1220...first stage, 1230...second stage, 1 240...first stage moving mechanism, 1250...second stage moving mechanism, 1300...tool, 1310...inkjet head, 1400...control unit, Q...foreign matter, S1...startup step, S101...step, S102...step, S103...step, S11...step, S12...step, S13...step, S2...driving mode switching step, S201...step, S202...step, S203...step, S204...step, S21...step, S22...step, S23... step, S24...step, S25...step, S26...step, S27...step, S28...step, S29...step, S3...drive mode return step, Sv...variable range, U...first direction, V...second direction, V1...drive voltage, V2...drive voltage, V3...drive voltage, Va...first voltage value, Vb...second voltage value, Vc...third voltage value, Vmax...voltage value, Vmin...voltage value, f...drive frequency, f1...first frequency, f2...second frequency, f3...third frequency, fr...resonant frequency, θ...phase difference

Claims

1. A method for controlling a driving device having an ultrasonic actuator and a driven body that receives a driving force from the ultrasonic actuator and is driven, comprising the steps of: starting the ultrasonic actuator in a first drive mode; a drive mode switching step of switching a drive mode of the ultrasonic actuator to a second drive mode different from the first drive mode when the driven body does not reach a desired drive state at the time of the start-up; a drive mode return step of switching the drive mode of the ultrasonic actuator from the second drive mode to the first drive mode when the driven body reaches the desired drive state.

2. 2. The method for controlling a drive device according to claim 1, wherein the desired drive state is a state in which the driven body has reached a desired moving distance or moving speed.

3. The method for controlling a drive device according to claim 1 , wherein the drive voltage in the second drive mode is greater than the drive voltage in the first drive mode in the starting step.

4. The method for controlling a drive device according to claim 3 , wherein the drive voltage in the second drive mode is greater than a variable range of the drive voltage in the first drive mode.

5. The ultrasonic actuator has a vibration section, a first piezoelectric element that vibrates the vibration section in an expansion and contraction manner, and a second piezoelectric element that vibrates the vibration section in a bending manner, 5. The method for controlling a drive device according to claim 3, wherein a drive voltage of the second piezoelectric element in the second drive mode is greater than a drive voltage of the second piezoelectric element in the first drive mode in the starting step.

6. The method for controlling a driving device according to claim 1 , wherein in the second driving mode, a driving frequency of the ultrasonic actuator is changed so as to approach a resonant frequency of the ultrasonic actuator.

7. The ultrasonic actuator has a vibration section, a first piezoelectric element that vibrates the vibration section in an expansion and contraction manner, and a second piezoelectric element that vibrates the vibration section in a bending manner, 2. The method for controlling a drive device according to claim 1, wherein in the second drive mode, a phase difference between a drive voltage for the first piezoelectric element and a drive voltage for the second piezoelectric element is changed.

8. 2. The control method for a drive device according to claim 1, wherein in the second drive mode, the ultrasonic actuator is driven so that the driven body moves in a direction opposite to the movement direction in the startup step, and then the driven body is driven so that the driven body moves in the same direction as the movement direction in the startup step.

9. A robot having a robot arm; a moving stage attached to the robot arm and equipped with a drive unit; a tool attached to the motion stage; The driving device includes an ultrasonic actuator, a driven body that receives a driving force from the ultrasonic actuator and is driven by the ultrasonic actuator, and a control device that controls the driving of the ultrasonic actuator, The controller activates the ultrasonic actuator in a first drive mode; if the driven body does not reach a desired drive state at the time of the start-up, a drive mode of the ultrasonic actuator is switched to a second drive mode different from the first drive mode; a drive mode of the ultrasonic actuator being switched from the second drive mode to the first drive mode when the driven body reaches the desired drive state.

Images