阅读说明：本技术 压电驱动装置及其控制方法 (Piezoelectric driving device and control method thereof ) 是由 村上诚 于 2021-03-15 设计创作，主要内容包括：本公开涉及压电驱动装置及其控制方法。不论被驱动部的惯性的大小如何均能够进行高精度的位置控制。压电驱动装置的控制部进行以下控制：使用压电驱动装置与被驱动部之间的最大摩擦力和被驱动部的质量,计算压电驱动装置施加给被驱动部的最大减速度,计算从由位置传感器检测出的被驱动部的当前位置到目标位置为止的距离,使用最大减速度和从被驱动部的当前位置到目标位置为止的距离来计算被驱动部的基准速度,根据由位置传感器检测出的被驱动部的当前位置的时间变化来计算被驱动部的速度,在被驱动部的当前速度小于基准速度的情况下,从压电驱动装置向被驱动部施加驱动力,在当前速度为基准速度以上的情况下,从压电驱动装置向被驱动部施加制动力。(The present disclosure relates to a piezoelectric driving device and a control method thereof. The position control can be performed with high precision regardless of the magnitude of the inertia of the driven part. The control unit of the piezoelectric drive device performs the following control: the method includes calculating a maximum deceleration applied to a driven part by a piezoelectric driving device using a maximum frictional force between the piezoelectric driving device and the driven part and a mass of the driven part, calculating a distance from a current position of the driven part detected by a position sensor to a target position, calculating a reference speed of the driven part using the maximum deceleration and the distance from the current position of the driven part to the target position, calculating a speed of the driven part from a temporal change in the current position of the driven part detected by the position sensor, applying a driving force from the piezoelectric driving device to the driven part when the current speed of the driven part is less than the reference speed, and applying a braking force from the piezoelectric driving device to the driven part when the current speed is equal to or greater than the reference speed.)

1. A method for controlling a piezoelectric driving device, wherein the piezoelectric driving device drives a driven portion,

in the control method, the following control is performed:

calculating a reference velocity vth of the driven portion using a maximum deceleration a applied to the driven portion by the piezoelectric driving device and a distance Ln from a current position to a target position of the driven portion,

when the current speed vn of the driven part is less than the reference speed vth, a driving force is applied from the piezoelectric driving device to the driven part, and when the current speed vn is equal to or greater than the reference speed vth, a braking force is applied from the piezoelectric driving device to the driven part.

2. The control method of a piezoelectric driving apparatus according to claim 1,

the piezoelectric drive device includes:

a first piezoelectric element configured to apply a driving force by causing the piezoelectric driving device to perform bending vibration; and

a second piezoelectric element for applying a braking force by longitudinally vibrating the piezoelectric drive unit,

in the control method, the second piezoelectric element is longitudinally vibrated without bending vibration of the first piezoelectric element when the braking force is applied.

3. The control method of a piezoelectric driving apparatus according to claim 1 or 2,

in the control method, the maximum deceleration α is obtained using the mass m of the driven portion and the maximum frictional force F2max between the piezoelectric driving device and the driven portion.

4. The control method of a piezoelectric driving apparatus according to claim 1,

in the control method, the mass m of the driven part is calculated using the position of the driven part before driving the driven part, the position of the driven part after driving the driven part, the driving force to drive the driven part, and the time to drive the driven part.

5. The control method of a piezoelectric driving apparatus according to claim 1,

in the control method, the distance Ln and the reference speed vth are periodically obtained.

6. A piezoelectric driving device for driving a driven portion, the piezoelectric driving device comprising:

a vibration plate provided with a plurality of piezoelectric elements;

a protrusion provided on the vibration plate;

a driven portion contactable with the protrusion portion;

a control unit for controlling the operation of the piezoelectric drive device by controlling the voltage applied to the piezoelectric element; and

a position sensor that detects a current position of the driven portion,

the control unit performs the following control:

calculating a maximum deceleration a applied to the driven portion by the piezoelectric driving device using a maximum frictional force F2max between the piezoelectric driving device and the driven portion and a mass m of the driven portion,

calculating a distance Ln from a current position of the driven part detected by the position sensor to a target position,

calculating a reference speed vth of the driven part using a maximum deceleration a and a distance Ln from a current position to a target position of the driven part,

calculating a current velocity vn of the driven part based on a temporal change in the current position of the driven part detected by the position sensor,

when the current speed vn is lower than the reference speed vth, a driving force is applied from the piezoelectric driving device to the driven portion, and when the current speed vn is equal to or higher than the reference speed vth, a braking force is applied from the piezoelectric driving device to the driven portion.

7. The piezoelectric driving apparatus according to claim 6,

the piezoelectric drive device includes a plurality of the piezoelectric elements, each of which includes a first piezoelectric element that causes the piezoelectric drive device to vibrate in a bending manner and a second piezoelectric element that causes the piezoelectric drive device to vibrate in a longitudinal direction,

the control unit does not cause the first piezoelectric element to vibrate in a bending manner and causes the second piezoelectric element to vibrate in a longitudinal direction when the braking force is applied.

8. Piezoelectric driving device according to claim 6 or 7,

the piezoelectric driving device includes a maximum deceleration calculation unit that obtains a maximum deceleration α using a mass m of the driven unit and a maximum frictional force F2max between the piezoelectric driving device and the driven unit.

9. The piezoelectric driving apparatus according to claim 6,

the piezoelectric driving device includes a mass calculation unit that calculates a mass m of the driven unit using a position of the driven unit before the driven unit is driven, a position of the driven unit after the driven unit is driven, a driving force for driving the driven unit, and a time for driving the driven unit.

10. The piezoelectric driving apparatus according to claim 6,

the control unit periodically obtains the distance Ln and the reference speed vth.

Technical Field

The present disclosure relates to a piezoelectric driving device and a control method thereof.

Background

Patent document 1 discloses a position control technique for an ultrasonic motor (piezoelectric motor). A drive device for an ultrasonic actuator is provided with: a component sensor that detects a current position of the moving component; an arithmetic unit that calculates a control target position of the moving member; a drive circuit that generates a drive voltage to drive the ultrasonic actuator in a predetermined resonance state; and a control circuit that controls a motion state of the moving member so that the moving member follows the control target position by adjusting one of physical quantities that determine the drive voltage according to a difference between the current position and the control target position as an operation physical quantity.

Patent document 1: japanese laid-open patent publication No. 2004-56878

However, in patent document 1, inertia of the moving member is not considered, and therefore, there is a problem as follows: when the inertia of the moving member is large, if the same control as that when the inertia of the moving member is small is performed, it takes time or the like until the moving member stops at the target position.

Disclosure of Invention

According to one aspect of the present disclosure, a method of controlling a piezoelectric driving device that drives a driven portion is provided. The control method performs the following control: a reference speed vth of the driven part is calculated using a maximum deceleration alpha applied to the driven part by the piezoelectric driving device and a distance Ln from a current position of the driven part to a target position, and when a current speed vn of the driven part is smaller than the reference speed vth, a driving force is applied from the piezoelectric driving device to the driven part, and when the current speed vn is equal to or greater than the reference speed vth, a braking force is applied from the piezoelectric driving device to the driven part.

Drawings

Fig. 1 is an explanatory view showing a piezoelectric driving device.

Fig. 2 is an explanatory diagram showing a schematic configuration of a control circuit of the piezoelectric drive device.

Fig. 3A is an explanatory diagram showing an operation of the first half of the vibration cycle of the piezoelectric drive device during driving.

Fig. 3B is an explanatory diagram showing an operation of the piezoelectric drive device in the second half of the vibration cycle during driving.

Fig. 4A is an explanatory diagram showing an operation of the piezoelectric drive device in the first half of the vibration cycle at the time of braking.

Fig. 4B is an explanatory diagram showing an operation of the piezoelectric drive device in the second half of the vibration cycle during braking.

Fig. 5 is an explanatory diagram showing a configuration of the control unit.

Fig. 6 is a flowchart of drive control repeatedly performed by the control unit.

Fig. 7 is a flowchart of the calculation of the mass m performed by the control unit.

Fig. 8 is an explanatory diagram showing the target position and the actual position of the driven part in the case of a high load.

Fig. 9 is an explanatory diagram showing the position and speed of the driven part and the force applied to the driven part in the case of a high load.

Fig. 10 is an enlarged view of the region Q2 of fig. 9.

Fig. 11 is an explanatory diagram showing a target position and an actual position of the driven part in the case of a medium load.

Fig. 12 is an explanatory diagram showing the position and speed of the driven part and the force applied to the driven part in the case of a medium load.

Fig. 13 is an enlarged view of the region Q3 of fig. 12.

Fig. 14 is an explanatory diagram showing the position, speed, and reference speed of the driven part in the case where the intermediate target position is not determined.

Description of the reference numerals

10 … piezoelectric drive; 20 … protrusions; 30 … piezoelectric actuator body; 40 … driven part; 50 … an object; a 60 … position sensor; 70 … control section; 71 … an intermediate target position calculating section; 72 … remaining distance calculating unit; 74 … maximum deceleration calculation section; 76 … speed calculating part; 78 … a reference speed calculating unit; 80 … voltage setting part; 82 … speed determination part; an 84 … switch; 86 … drive section; 87 … bending vibration driving part; 88 … longitudinal vibration drive; 89 … mass calculating part; 90 … upper control unit; 110a to 110f … piezoelectric elements; 200 … vibrating plate; 203 … long side; 204 … short side; 210 … support portion; 240 … recess.

Detailed Description

A. The first embodiment:

fig. 1 is an explanatory diagram showing a piezoelectric driving device 10. The piezoelectric driving device 10 is used for carrying an object 50. The piezoelectric drive device 10 includes a piezoelectric drive device main body 30, a driven unit 40, a position sensor 60, and a control unit 70. The piezoelectric driving device body 30 includes a diaphragm 200, six piezoelectric elements 110a, 110b, 110c, 110d, 110e, and 110f, and a protrusion 20. The vibration plate 200 has a substantially rectangular shape. The six piezoelectric elements 110a to 110f are arranged in a matrix on the diaphragm 200, specifically, two piezoelectric elements are arranged along the long side 203 in the a direction of fig. 1, and three piezoelectric elements are arranged along the short side 204 in the B direction of fig. 1. A support portion 210 is provided between the two piezoelectric elements arranged in the a direction of the diaphragm 200, specifically, outside the corresponding positions between the piezoelectric elements 110a and 110d and between the piezoelectric elements 110c and 110 f. When a voltage is applied to the piezoelectric elements 110a to 110f at an appropriate timing, the diaphragm 200 performs a bending motion with the support portion 210 as a joint.

The diaphragm 200 has a recess 240 at the approximate center of the short side 204, and the protrusion 20 is provided in the recess 240. When the vibration plate 200 performs a bending motion, the protrusion 20 contacts and presses the driven portion 40, thereby driving the driven portion 40 in the B direction. The driven portion 40 has a flat plate shape with a mass m 1. The object 50 having the mass m2 is mounted on the driven unit 40 and is transported as the driven unit 40 moves. The position sensor 60 acquires the position of the driven part 40.

Fig. 2 is an explanatory diagram showing a schematic configuration of a control circuit of the piezoelectric drive device 10. In the piezoelectric driving device 10 of the present embodiment, the piezoelectric elements 110a and 110f are connected in parallel, the piezoelectric elements 110b and 110e are connected in parallel, and the piezoelectric elements 110c and 110d are connected in parallel, thereby forming three pairs. In the present embodiment, the piezoelectric elements of each pair are connected in parallel, but may be connected in series. The three pairs are connected to the control unit 70. The ground sides of the piezoelectric elements 110a to 110f are connected and shared. This can reduce the number of wirings. The ground sides of each pair may be independent. The position sensor 60 and the upper control unit 90 are connected to the control unit 70. The control unit 70 acquires the current position Pn of the driven unit 40 from the position sensor 60, acquires the final target position Pt from the upper control unit 90, and controls the driving of the piezoelectric elements 110a to 110 f.

Fig. 3A is an explanatory diagram showing an operation of the piezoelectric drive device 10 in the first half of the vibration cycle during driving. In the first half of the vibration period, a voltage is applied to two piezoelectric elements, for example, the piezoelectric element 110a and the piezoelectric element 110f, located at opposite corners of the vibration plate 200. The piezoelectric elements 110a and 110f are elongated as indicated by arrow x1, and the diaphragm 200 is bent. The protrusion 20 moves as indicated by an arrow y1 due to the bending of the vibration plate 200. At this time, if a voltage is also applied to the two piezoelectric elements 110b and 110e at the center in the short direction, the piezoelectric elements 110b and 110e also expand as indicated by arrow x 1. The protrusion 20 contacts the driven part 40, and presses the driven part 40 in the B direction with a force F1 (driving force F1). As a result, the driven portion 40 is driven in the B direction. It is not always necessary to apply a voltage to the piezoelectric elements 110b and 110 e. When the protrusion 20 is disposed in contact with the driven portion 40, the protrusion 20 is in contact with the driven portion 40 even when no voltage is applied.

The position of the driven portion 40 before the driving force F1 is applied is P0, and the intermediate target position at the end of the vibration cycle in the primary vibration is Pc 0. The distance L0 to the intermediate target position Pc0 is Pc 0-P0. When the first half of the vibration cycle ends, the driven part 40 reaches the position P1. The position P1 is a position forward of the intermediate target position Pc 0. The speed of the driven part 40 in the B direction increases from v0 to v 1.

Fig. 3B is an explanatory diagram showing an operation of the piezoelectric drive device 10 in the second half of the vibration cycle during driving. In the second half of the vibration cycle, a voltage is applied to the other two piezoelectric elements located at opposite corners of the vibration plate 200, that is, the piezoelectric element 110c and the piezoelectric element 110d, and no voltage is applied to the other piezoelectric elements 110a, 110b, 110e, and 110 f. The piezoelectric element 110c and the piezoelectric element 110d extend as indicated by arrow x2, the diaphragm 200 bends in the opposite direction, and the protrusion 20 moves as indicated by arrow y 2. However, since no voltage is applied to the two piezoelectric elements at the center in the short direction, that is, the piezoelectric element 110b and the piezoelectric element 110e, the protrusion 20 is separated from the driven part 40 and does not press the driven part 40. As a result, even if the projection 20 moves as indicated by arrow y2, no force is applied to the driven part 40. However, since the driven unit 40 moves at the velocity v1 due to inertia, it reaches the intermediate target position Pc0 at the end of the second half of the oscillation period. The protrusion 20 may be separated from the driven portion 40 by applying a voltage to the piezoelectric element 110b and the piezoelectric element 110e and compressing them.

Here, when the mass of the driven part 40 and the object 50 is small, that is, the inertia is small, the driven part 40 reaches the position P1 at the end of the first half of the vibration cycle and reaches the intermediate target position Pc0 at the end of the second half of the vibration cycle. However, when the driven part 40 and the object 50 have large masses, that is, when the inertia is large, the driven part 40 does not reach the position P1 at the end of the first half of the oscillation period and does not reach the intermediate target position Pc0 at the end of the second half of the oscillation period.

In the next vibration cycle, the next intermediate target position PC2 of the driven part 40 is set, and the driving is performed in the same manner. Note that, if the position of the driven unit 40 reaches Pc0 in the first vibration cycle, the distance L2 to the intermediate target position Pc2 is Pc2-Pc 0. On the other hand, if the position of the driven part 40 does not reach Pc0, the distance L2 to the intermediate target position Pc2 is greater than Pc2-Pc 0.

Fig. 4A is an explanatory diagram showing an operation of the piezoelectric drive device 10 in the first half of the vibration cycle at the time of braking. In the first half of the vibration period, a voltage is applied to two piezoelectric elements located at the center in the short side direction of the vibration plate 200, specifically, the piezoelectric element 110b and the piezoelectric element 110 e. The piezoelectric elements 110b and 110e extend in the longitudinal direction as indicated by the arrow x3, and the diaphragm 200 also extends in the longitudinal direction. Thereby, the protrusion 20 comes into contact with the driven portion 40. Braking is performed by a frictional force F2 between the protrusion 20 and the driven portion 40. The frictional force F2 is also referred to as "braking force F2".

The position of the driven portion 40 before the application of the frictional force F2 is P3, and the intermediate target position at the end of the oscillation period in the primary oscillation is Pc 3. The distance L3 to the target position Pc3 is Pc 3-P3. When the first half of the vibration cycle ends, the driven part 40 reaches the position P4. The position P4 is a position forward of the target position Pc 3. The speed of the driven part 40 in the B direction is reduced from v3 to v 4.

Fig. 4B is an explanatory diagram showing an operation of the piezoelectric drive device 10 in the second half of the vibration cycle during braking. In the second half of the vibration period, the application of the voltage to the piezoelectric element 110b and the piezoelectric element 110e is stopped. The piezoelectric elements 110b and 110e become shorter in the longitudinal direction as indicated by the arrow x4, and the diaphragm 200 also becomes shorter in the longitudinal direction. Thus, the projection 20 is no longer in contact with the driven portion 40, and the braking force F2 is not applied to the driven portion 40. However, since the driven unit 40 moves at the velocity v4 due to inertia, it reaches the intermediate target position Pc3 at the end of the second half of the oscillation period. When the protrusion 20 is disposed in contact with the driven portion 40, the protrusion 20 may be separated from the driven portion 40 by applying a voltage to the piezoelectric element 110b and the piezoelectric element 110e and compressing them in the longitudinal direction indicated by the arrow x 4.

Here, when the mass of the driven part 40 and the object 50 is small, that is, the inertia is small, the driven part 40 reaches the position P4 at the end of the first half of the vibration cycle and reaches the intermediate target position Pc3 at the end of the second half of the vibration cycle. However, when the driven part 40 and the object 50 have large masses, that is, when the inertia is large, the driven part 40 exceeds the position P4 at the end of the first half of the oscillation period and exceeds the intermediate target position Pc3 at the end of the second half of the oscillation period. The present disclosure provides a control method that can stop at the final target position Pt even when the inertia of the driven portion 40 is large. Therefore, in the middle of the final target position Pt, even if the driven part 40 exceeds the intermediate target position, the driven part 40 may stop at the final target position Pt.

Fig. 5 is an explanatory diagram showing the configuration of the control unit 70. Control unit 70 includes an intermediate target position calculation unit 71, a remaining distance calculation unit 72, a maximum deceleration calculation unit 74, a speed calculation unit 76, a reference speed calculation unit 78, a voltage setting unit 80, a speed determination unit 82, a switch 84, and a drive unit 86.

In this specification, the time required for one position control is referred to as one cycle. The intermediate target position calculation unit 71 calculates an intermediate target position Pcn after one cycle using the final target position Pt acquired from the upper control unit 90 and the current position Pn acquired from the position sensor 60. The remaining distance calculation unit 72 calculates the difference between the intermediate target position Pcn and the current position Pn after one cycle, that is, the distance Ln to the intermediate target. That is to say that the first and second electrodes,

Ln＝Pcn-Pn…(1)。

the maximum deceleration calculating section 74 calculates the maximum deceleration α of the driven section 40 by the following equation using the mass m and the maximum frictional force F2 max. The maximum frictional force F2max is also referred to as "maximum braking force F2 max".

α＝F2max/m…(2)

Here, the mass m is the sum of the mass m1 of the driven portion 40 and the mass m2 of the object 50. The mass m1 of the driven portion 40 is known. The mass m2 of the object 50 conveyed by the drive unit 40 is not known, but can be easily calculated as described later. The maximum frictional force F2max is a frictional force between the protrusion 20 and the driven portion 40, and can be measured experimentally and is known.

The velocity calculation unit 76 calculates the velocity vn of the driven unit 40 from the temporal change in the current position Pn.

The reference speed calculation unit 78 calculates the reference speed vth by the following equation using the distance Ln to the target and the maximum deceleration α.

vth＝(2·α·Ln)^1/2…(3)

If the speed vn of the driven portion 40 is the reference speed vth, the driven portion 40 can be decelerated at the deceleration α and stopped at the final target position Pt by applying the maximum frictional force F2max from the projection portion 20 to the driven portion 40.

The voltage setting unit 80 calculates the voltage V of the drive signal for driving the piezoelectric elements 110a to 110f, using the distance Ln to the intermediate target position Pcn and the current speed vn of the driven unit 40. The voltage V corresponds to the driving force F1 and the braking force F2. The voltage setting unit 80 performs the following settings: increasing the voltage as the distance Ln to the intermediate target position Pcn increases; the higher the current speed vn of the driven part 40, the lower the voltage. However, when the voltage V exceeds the voltage Vlim, the voltage Vlim is limited to the voltage Vlim that generates the maximum frictional force F1max or F2max to the frictional force between the protrusion 20 and the driven portion 40. The sliding between the protrusion 20 and the driven portion 40 can be suppressed. Note that the maximum frictional forces F1max and F2max are predetermined known values.

The speed determination unit 82 compares the current speed vn of the driven unit 40 with the reference speed vth, and turns on a switch 84, which will be described later, if vn < vth, and turns off the switch 84, which will be described later, if vn ≧ vth.

If vn < vth, the switch 84 turns on the drive signal for causing the drive section 86 to perform bending vibration, and if vn ≧ vth, the drive signal for causing the drive section 86 to perform bending vibration is turned off. The drive signal for causing the driving unit 86 to perform the longitudinal vibration is not turned off in accordance with the magnitude relationship between the current speed vn of the driven unit 40 and the reference speed vth.

The driving unit 86 includes a bending vibration driving unit 87 and a longitudinal vibration driving unit 88. The bending vibration driving unit 87 drives the piezoelectric elements 110a, 110c, 110d, and 110f, and the longitudinal vibration driving unit 88 drives the piezoelectric elements 110b and 110 e. The piezoelectric elements 110a, 110c, 110d, and 110f cause the diaphragm 200 to vibrate in a bending manner, and the piezoelectric elements 110b and 110e cause the diaphragm 200 to vibrate in a longitudinal direction.

The mass calculating section 89 calculates the mass m. The mass calculating section 89 calculates the mass m using the position P0 before the driving force F1 is applied to the driven section 40 and the position P1 after the application. Specifically, let tst be the time at which the driving force F1 is applied, β be the acceleration, and Lst be the interval between the position P0 and the position P1.

Because Lst is beta (b) ((b))tst)²Therefore, the mass calculation unit 89 calculates the acceleration β by the following equation.

β＝2·Lst/(tst)²…(4)

Further, the relationship between the force F1, the acceleration β, and the mass m is:

F1＝β·m…(5)

therefore, the mass calculating section 89 calculates the mass m by the following equation.

m＝F1/β…(6)

Fig. 6 is a flowchart of driving control repeatedly performed by the control unit 70. In step S100, the maximum deceleration calculating section 74 of the control section 70 calculates the maximum deceleration α of the driven section 40 using the mass m and the maximum frictional force F2 max. In addition, this step S100 may be performed only for the first time. This is because, if the mass m is constant, the maximum deceleration α is constant.

In step S105, the control unit 70 acquires the final target position Pt of the driven unit 40 from the upper control unit 90. In step S110, the control unit 70 acquires the current position Pn of the driven unit 40 from the position sensor 60.

In step S120, the control unit 70 determines whether or not the difference | Pt-Pn | between the final target position Pt of the driven unit 40 and the current position Pn of the driven unit 40 is equal to or less than the threshold Lth. When | Pt — Pn | is equal to or less than the threshold Lth, the control unit 70 ends the processing in the flowchart because the position of the driven unit 40 is within the error range with respect to the final target position Pt. If | Pt — Pn | exceeds the threshold Lth, the control unit 70 proceeds to step S130.

In step S130, the speed calculation unit 76 of the control unit 70 calculates the speed vn of the driven part 40 using the position P (n-1) of the driven part 40 in the previous cycle and the position Pn of the driven part 40 in the previous cycle.

In step S140, the intermediate target position calculation unit 71 of the control unit 70 calculates the intermediate target position Pcn of the driven unit 40 after one cycle using the final target position Pt of the driven unit 40 acquired from the upper control unit 90 and the position Pn of the driven unit 40 acquired from the position sensor 60.

In step S150, the remaining distance calculating unit 72 of the control unit 70 calculates the distance Ln from the current position Pn of the driven unit 40 to the intermediate target position Pcn.

In step S160, the voltage setting unit 80 of the control unit 70 calculates the voltage V for driving the piezoelectric elements 110a to 110f using the distance Ln to the intermediate target position Pcn and the current speed vn of the driven unit 40. The voltage V corresponds to the driving force F1 and the braking force F2. When the calculated voltage V exceeds the voltage Vlim, the voltage setting unit 80 limits the voltage V for driving the piezoelectric elements 110a to 110F to the voltage Vlim that generates the maximum frictional force (the maximum driving force F1max or the maximum braking force F2max) in the frictional force between the protrusion 20 and the driven portion 40. The voltage Vlim is a known value predetermined by an experiment or the like.

In step S170, the reference speed calculation unit 78 of the control unit 70 calculates the reference speed vth using the distance Ln to the intermediate target position Pcn and the maximum deceleration α.

In step S180, the speed determination unit 82 of the control unit 70 compares the current speed vn of the driven unit 40 with the reference speed vth, and if vn < vth, the process proceeds to step S190, and if vn ≧ vth, the process proceeds to step S195.

In step S190, the control unit 70 drives both the bending vibration driving unit 87 and the longitudinal vibration driving unit 88 of the driving unit 86. Thereby, the driving force F1 is applied to the driven portion 40. In step S195, the control unit 70 drives only the longitudinal vibration driving unit 88 of the driving unit 86. This applies a braking force F2 to the driven portion 40.

Fig. 7 is a flowchart of the calculation of the mass m performed by the control unit 70. As described above, the mass m is the sum of the mass m1 of the driven portion 40 and the mass m2 of the object 50. In step S200, the control unit 70 acquires a position P0 before the driving force is applied to the driven unit 40. Before the driving force is applied to the driven part 40, the speed of the driven part 40 is zero. This is because the speed of the driven portion 40 is zero when the mass m changes, that is, when the driven portion 40 grips or releases the object 50 to cause the mass m to change.

In step S210, the control portion 70 drives the driven portion 40 with the driving force F1. In step S220, the control unit 70 acquires the position P1 of the driven unit 40 after driving. In step S230, the control section 70 acquires the distance Lst between the position P0 and the position P1.

In step S240, the control unit 70 calculates the acceleration β of the driven unit 40. If the time when the force based on the driving force F1 is applied is t and the acceleration is β, the acceleration β can be calculated using equation (4).

In step S250, the control unit 70 calculates the mass m. From the relationship between the driving force F1, the acceleration β, and the mass m, the mass m is calculated using equation (6). The control unit 70 uses the calculated mass m in step S100 of fig. 6. Note that, when the mass m2 of the object 50 is known, the upper control unit 90 may give a result that the mass m2 of the object 50 is much smaller than the mass m1 of the driven unit 40, for example, when the mass m is 1/1000 or less, and the mass m1 of the driven unit 40 may be used as the mass m.

Fig. 8 is an explanatory diagram showing the target position Pcn and the actual position Pn of the driven part 40 in the case of a high load. The high load means a case where the mass m is large, that is, a case where the inertia is large. In this case, even if the frictional force between the protrusion 20 and the driven portion 40 is driven as the maximum driving force F1, the driven portion 40 cannot be sufficiently accelerated. Therefore, as shown in fig. 8, the distance Ln from the current position Pn of the driven part 40 to the target position Pcn gradually increases. In addition, the driven portion 40 cannot be decelerated sufficiently even at the time of braking. Therefore, the control unit 70 starts braking from time t2 before the driven unit 40 reaches the final target position Pt in order to stop the driven unit 40 at the final target position Pt.

Fig. 9 is an explanatory diagram showing the position and speed of the driven part 40 and the force applied to the driven part 40 in the case of a high load, and fig. 10 is an enlarged view of a region Q2 of fig. 9. In the case of a high load, the driving force F1 at time t0 is calculated from the distance Ln to the intermediate target position Pcn and the current speed vn of the driven portion 40, and is a driving force smaller than the maximum driving force F1 max.

In the subsequent cycle, the driven part 40 does not reach the intermediate target position Pcn, and therefore the distance Ln from the current position Pn of the driven part 40 to the intermediate target position Pcn becomes large. Therefore, in the case of a high load, the driving force F1 gradually becomes large. Further, if the driving force calculated using the distance Ln to the intermediate target position Pcn and the current speed vn of the driven portion 40 is equal to or greater than the maximum driving force F1max, the control portion 70 drives the driven portion 40 at the maximum driving force F1 max. After time t1, the intermediate target position Pcn coincides with the final target position Pt. Therefore, the distance Ln increases before the time t1 and decreases thereafter.

Since the driven portion 40 is driven at the maximum driving force F1max, the speed vn of the driven portion 40 increases linearly. On the other hand, as can be seen from equation (3), the reference velocity vth is proportional to the square root of the distance Ln. As a result, the speed vn of the driven portion 40 exceeds the reference speed vth at time t 2. Note that, while the distance Ln gradually decreases from the time t1 to the time t2, the reference speed vth is always larger than the speed vn of the driven portion 40.

If the speed vn of the driven unit 40 exceeds the reference speed vth at time t2, the braking is performed by the braking force F2max by the single vibration in the subsequent cycle through the processing of steps S180 and S195 in fig. 6. Here, the reference speed vth is a value at which the speed vn of the driven portion 40 becomes zero when the driven portion 40 reaches the final target position Pt when the driven portion 40 decelerates due to the maximum frictional force F2max, and therefore the speed vn of the driven portion 40 is not less than the reference speed vth before the time t3 at which the driven portion 40 reaches the final target position Pt.

Under high load, before time t2, driving is performed with the maximum driving force F1max, and before time t2 to t3, braking is performed with the braking force F2 max. At time t3, the driven unit 40 reaches the final target position Pt, and the speed vn of the driven unit 40 becomes zero.

Fig. 11 is an explanatory diagram showing the target position and the actual position of the driven part 40 in the case of the medium load. Fig. 12 is an explanatory diagram showing the position, speed, and force applied to the driven portion 40 of the driven portion 40 in the case of a medium load, and fig. 13 is an enlarged view of a region Q3 of fig. 12.

In the case of the medium load, the driving force F1 from the time t0 to the time t4 is calculated from the distance Ln to the intermediate target position Pcn and the current speed vn of the driven portion 40, and is a driving force smaller than the maximum driving force F1 max. However, in each cycle, the driven part 40 does not reach the intermediate target position Pcn, and thus the distance Ln to the intermediate target position Pcn gradually increases. Therefore, the driving force F1 also becomes gradually larger. At time t4, the driving force F1 becomes the maximum driving force F1 max.

The driving force F1 from the time t4 to the time t5 is the maximum driving force F1 max. During this time, as in the case of a high load, since the driven portion 40 is driven at the maximum driving force F1max, the speed vn of the driven portion 40 linearly increases. On the other hand, as can be seen from equation (3), the reference velocity vth is proportional to the square root of the distance Ln. As a result, the speed vn of the driven portion 40 at time t5 substantially matches the reference speed vth.

From time t5 to time t6, the driven part 40 is driven with the maximum driving force F1max or braked with the maximum frictional force F2max, according to the result of comparison between the speed vn and the reference speed vth. During this period, the distance Ln is substantially constant, and the reference speed vth is also substantially constant. If the speed vn of the driven portion 40 does not satisfy the reference speed vth, the driving is performed at the maximum driving force F1max, and if the speed vn of the driven portion 40 exceeds the increased reference speed vth, the braking is performed at the maximum frictional force F2 max.

After time t6, since intermediate target position Pcn matches final target position Pt, distance Ln gradually decreases, and reference speed vth also gradually decreases. After time t6, the driven unit 40 is braked by the maximum frictional force F2 max. At time t7, the driven unit 40 reaches the final target position Pt, and the speed vn of the driven unit 40 becomes zero.

As described above, according to the present embodiment, the control unit 70 calculates the reference speed vth of the driven unit 40 at which the driven unit 40 can be stopped at the final target position Pt at the time of braking with the maximum frictional force, acquires the current speed vn of the driven unit 40, applies the driving force, which is the smaller one of the driving force F1 calculated from the distance Ln and the speed vn and the maximum driving force F1max between the piezoelectric driving device and the driven unit 40, to the driven unit 40 from the piezoelectric driving device main body 30 when the current speed vn of the driven unit is less than the reference speed vth, and applies the braking force to the driven unit 40 from the piezoelectric driving device main body 30 when the current speed vn of the driven unit is equal to or greater than the reference speed vth, and thus can stop the driven unit 40 at the target position Pt. That is, the position control can be performed with high accuracy regardless of the magnitude of the inertia of the driven portion 40.

In the above embodiment, the driving force is applied with the smaller one of the driving force F1 calculated from the distance Ln and the velocity vn and the maximum driving force F1max between the piezoelectric driving device and the driven portion 40, but the maximum driving force F1max may be applied. The driving force F1 need not be calculated from the distance Ln and the velocity vn. On the other hand, when the driving force F1 calculated from the distance Ln and the velocity vn is applied, unnecessary acceleration can be suppressed.

In the present embodiment, when the driven portion 40 is braked, the diaphragm 200 is vibrated in the longitudinal direction by applying a voltage to the piezoelectric elements 110B and 110e and then not applying a voltage as described in fig. 4A and 4B, but the piezoelectric elements 110B and 110e may be extended by continuing to apply a voltage to the piezoelectric elements 110B and 110 e. Braking may also be performed in the second half of the cycle.

In the present embodiment, when the driven unit 40 is braked, a voltage may be applied to all the piezoelectric elements 110a to 110f, or may be applied to the piezoelectric elements 110a, 110c, 110d, and 110 f. In this case, since the piezoelectric elements at mutually symmetrical positions with respect to the a direction are simultaneously driven, longitudinal vibration is performed without performing bending vibration.

In the present embodiment, the graph is created on the premise that the maximum driving force F1max and the maximum frictional force F2max are equal to each other, but the maximum driving force F1max and the maximum frictional force F2max may not be equal to each other. In the case of a high load, the position, speed vn and timing of the driven portion 40 at the time of switching from driving to braking change, but the control does not change. The same applies to the driving force F1 and the frictional force F2. For example, in the case of the medium load shown in fig. 12 and 13, the driving force F1 and the frictional force F2 are alternately applied during the period from time t5 to time t6, and when F1 is 2 · F2, the controller 70 performs two-cycle braking after performing one-cycle driving, that is, the speed vn of the driven unit 40 can be set to zero after three cycles. When 2 · F1 is 3 · F2, the controller 70 can zero the speed vn of the driven part 40 after five cycles by performing driving, braking, driving, and braking. When the ratio of F1 to F2 is n: m, the speed vn of the driven part 40 can be made zero after n + m cycles in the same manner.

In the above description, the moving direction of the driven part 40 is not mentioned, but the force of m · g · sin θ is increased or decreased depending on the moving direction. Note that θ is 0 in the horizontal direction and 90 ° in the vertical direction. In this case, the expression (5) is the following expressions (7) and (8) depending on the moving direction of the driven part 40.

F1+m·g·sinθ＝β1·m…(7)

F1-m·g·sinθ＝β2·m…(8)

Since the unknowns are m and θ and there are two equations, both the masses m and θ can be obtained. Hereinafter, the driving force F1 may be set to F1+ m · g · sin θ or F1-m · g · sin θ depending on the moving direction of the driven part 40 during the control. The same applies to the braking force F2.

Second embodiment:

in the first embodiment, the intermediate target position Pcn is set and the position and speed of the driven part 40 are controlled using the distance Ln from the current position Pn to the intermediate target position Pcn, but in the second embodiment, the intermediate target position Pcn is not set and the position and speed of the driven part 40 are controlled using the distance from the current position Pn to the final target position Pt. The control flowchart of the second embodiment is substantially the same as the flowchart shown in fig. 6, but the distance Ln to the final target position Pt is calculated in step S150 without executing step S140.

Fig. 14 is an explanatory diagram showing the position Pn, the velocity vn, and the reference velocity vth of the driven unit 40 in the case where the intermediate target position Pcn is not determined. Since the driven part 40 approaches the final target position as time passes, the distance Ln becomes smaller. As a result, the reference speed vth monotonically decreases. On the other hand, the driven portion 40 receives the driving force F1 according to the distance Ln, and thus becomes monotonously fast. The driving force F1 is, for example, the maximum driving force F1 max. At time t8, since the speed vn of the driven portion 40 exceeds the reference speed vth, braking is performed by the friction force F2 at and after time t 8. As a result, at time t9, the driven unit 40 reaches the final target position Pt and the velocity vn becomes zero.

The operation under high load when the intermediate target position Pcn of the first embodiment is determined is compared with the operation when the intermediate target position Pcn is not determined, and the same is true except for the following two points.

(a) The driving force F1 at time t0 may be calculated from the distance Ln to the intermediate target position Pcn and the current speed vn of the driven portion 40 to be a driving force less than the maximum driving force F1max in the case of a high load, but is the maximum driving force F1max in the case where the intermediate target position Pcn is not determined.

(b) In the case of a high load, the reference speed vth increases before the middle (time t2) and decreases thereafter, but in the case where the middle target position Pcn is not determined, the reference speed vth is maximum at t0 and then monotonically decreases.

As described above, it is understood that the control can be performed in the same manner regardless of whether the intermediate target position Pcn is determined or not. In the case where the intermediate target position Pcn is determined, the driving force F1 can be reduced when the mass m is light, and therefore the driven portion 40 is easily suppressed from exceeding the stop position. When the intermediate target position Pcn is not determined, the intermediate target position calculation unit 71 is not necessary.

The present disclosure is not limited to the above-described embodiments, and can be implemented in various ways within a scope not departing from the gist thereof. For example, the present disclosure can also be achieved in the following manner. Technical features in the above-described embodiments that correspond to technical features in the respective embodiments described below can be appropriately replaced or combined in order to solve part or all of the problems of the present disclosure or to achieve part or all of the effects of the present disclosure. Note that, if this feature is not described as an essential feature in the present specification, it can be appropriately deleted.

(1) According to one aspect of the present disclosure, a method of controlling a piezoelectric driving device that drives a driven portion is provided. The control method performs the following control: a reference speed vth of the driven part is calculated using a maximum deceleration alpha applied to the driven part by the piezoelectric driving device and a distance Ln from a current position of the driven part to a target position, and when a current speed vn of the driven part is smaller than the reference speed vth, a driving force is applied from the piezoelectric driving device to the driven part, and when the current speed vn is equal to or greater than the reference speed vth, a braking force is applied from the piezoelectric driving device to the driven part. According to this aspect, the piezoelectric driving device calculates the reference speed of the driven part that can stop the driven part at the final target position when braking is performed with the maximum frictional force, and acquires the current speed of the driven part, and the piezoelectric driving device can stop the driven part at the target position because the driving force is applied to the driven part from the piezoelectric driving device when the current speed of the driven part is smaller than the reference speed, and the braking force is applied to the driven part from the piezoelectric driving device when the current speed of the driven part is equal to or greater than the reference speed. That is, the position control can be performed with high accuracy regardless of the magnitude of the inertia of the driven portion.

(2) In the above aspect, the piezoelectric driving device may include: a first piezoelectric element configured to apply a driving force by causing the piezoelectric driving device to perform bending vibration; and a second piezoelectric element that vibrates the piezoelectric drive device in a longitudinal direction to apply a braking force, and vibrates the second piezoelectric element in the longitudinal direction without causing the first piezoelectric element to vibrate in a bending manner when the braking force is applied. According to this aspect, the braking force can be applied by vibrating the second piezoelectric element in the longitudinal direction.

(3) In the above aspect, the maximum deceleration α may be obtained using the mass m of the driven portion and the maximum frictional force F2max between the piezoelectric driving device and the driven portion. According to this aspect, even if the mass m changes, the maximum deceleration α can be obtained.

(4) In the above aspect, the mass m of the driven part may be calculated using the position of the driven part before the driven part is driven, the position of the driven part after the driven part is driven, the driving force for driving the driven part, and the time for driving the driven part. According to this aspect, the mass m of the driven portion can be easily calculated.

(5) In the above aspect, the distance Ln and the reference speed vth may be periodically obtained. According to this aspect, the driven portion can be controlled with high accuracy.

The present disclosure can also be implemented in various ways other than the control method of the piezoelectric drive device. For example, the present invention can be realized by a piezoelectric driving device, a motor provided with a piezoelectric driving device, a robot, or the like.