JP4672828B2 - Ultrasonic motor and electronic device with ultrasonic motor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic motor and an electronic apparatus with an ultrasonic motor, and more particularly to precise positioning of a driven object by driving control of the ultrasonic motor.
[0002]
[Prior art]
In recent years, it has a piezoelectric vibrator that vibrates in the longitudinal direction that presses the driven object, and a piezoelectric vibrator that vibrates in the feed direction of the driven object, and the combined vibration of these two piezoelectric vibrators causes the vibrator to pass through. An ultrasonic motor for driving a driven object has been devised.
This type of ultrasonic motor is driven by applying a driving voltage whose phase is controlled to each piezoelectric vibrator.
[0003]
FIG. 8A shows the speed change of the ultrasonic motor by the conventional drive control method, and FIG. 8B shows the vibration displacement. As shown in FIG. 8, the conventional ultrasonic motor drive control is performed by inputting a voltage of the same magnitude from the start to the stop of the drive, so that the feed direction (X direction) of the driven object and the pressure contact with the driven object. Only when the ultrasonic motor is driven by exciting the vibration in the direction (Y direction) at the same magnitude, and the rotation direction of the ultrasonic motor is reversed, the phase of the drive voltage input to each piezoelectric vibrator is changed. It was a method to change.
[0004]
[Problems to be solved by the invention]
However, the conventional control driving method in which a driving voltage having the same magnitude as that of steady driving is input at the start or stop of driving of the ultrasonic motor has the following problems.
That is, at the time of start-up, the vibration displacement of the ultrasonic motor suddenly increases and, for example, stick slip occurs due to the difference between dynamic friction and static friction.
In addition, the portions where the moving body and the vibrating body come into contact with each other have some unevenness depending on the place. For this reason, at the time of low-speed rotation, the moving body and the vibrating body may be caught with each other and may not rotate smoothly.
Therefore, in practice, as shown in FIG. 8A, the ultrasonic motor may not start smoothly from a low speed and may suddenly start at a high speed or may not stop smoothly.
As a result, the driven object cannot be finely fed and the amount of overshoot with respect to the target position becomes large, so that the driven object cannot be positioned with high accuracy. For this reason, if it is going to position a driven object correctly, the establishment time to a target position was long.
[0005]
For the reasons described above, slipping occurs between the moving body and the vibrating body at the time of starting and stopping, the wear of the moving body and the vibrating body is large, and the life of the ultrasonic motor is shortened.
[0006]
An object of the present invention is to provide an ultrasonic motor that can start and stop smoothly and accurately position a driven object, and an electronic apparatus with an ultrasonic motor using the ultrasonic motor.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a super piezoelectric device having a first piezoelectric vibrator that vibrates in a direction in pressure contact with a driven object and a second piezoelectric vibrator that vibrates in a feeding direction of the driven object. In the sonic motor, the applied voltage to the first piezoelectric vibrator and the applied voltage to the second piezoelectric vibrator are separately controlled, and the magnitude and ratio of the pressure contact force and the feed force to the driven object are controlled. The phase difference is matched with the driving state of the driven object.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0009]
First, the configuration of the ultrasonic motor will be described.
[0010]
As shown in each drawing of FIG. 1 and FIG. 2, the ultrasonic motor 1 is in contact with the vibrating body 13 including the piezoelectric element 10, or the vibrating body 13 bonded to the piezoelectric element 10 and the vibrating body 13. The moving body 14 (driven object) and the pressurizing mechanism 15 that presses the moving body 14 against the vibrating body 13 are controlled by the control circuit 22 via the drive circuit 30.
That is, the ultrasonic motor 1 is a motor using the piezoelectric element 10 as a power source, and is an ultrasonic motor that moves the moving body 14 in a direction parallel to the end face of the piezoelectric element 10.
Here, the movable body 14 of the ultrasonic motor 1 is provided with a position sensor 21 such as an encoder that detects the position or rotational speed of the movable body 14. As will be described in detail later, the control circuit 22 controls the first piezoelectric vibrator 11 and the second piezoelectric vibrator 12 via the drive circuit 30 in accordance with a signal input from the position sensor 21. The drive circuit 30 includes a first signal generator 31 for driving the first piezoelectric vibrator 11 and a second signal generator 32 for driving the second piezoelectric vibrator 12.
[0011]
The piezoelectric element 10 is formed by stacking a plurality of piezoelectric vibrators 12 (second piezoelectric vibrators) as vibration sources in the feed direction, and a piezoelectric vibrator 11 (first piezoelectric vibrator) as a vibration source in the pressure contact direction thereon. A structure in which a plurality of vibrators are stacked. In FIG. 1, for convenience, the piezoelectric vibrators 11 and 12 are provided one by one. The piezoelectric element 10 has electrodes whose details will be described later.
Here, a protrusion that is driven in contact with the moving body 14 may be provided at substantially the center of the end face.
In addition, these two piezoelectric vibrators 11 and 12 ensure insulation from adjacent piezoelectric vibrators or electrodes by sandwiching an insulator 18, for example.
[0012]
As shown in FIGS. 1 and 3B, the piezoelectric vibrator 12 has four polarization regions 12a, 12b, and 12c that are generated by being divided into two parts in the vertical direction and two parts in the horizontal direction. The polarization region 12d has a structure in which the polarization direction is alternately reversed in the stacking direction. That is, the polarization region 12a and the polarization region 12d are polarized such that the upper surface becomes +, for example, and the polarization region 12b and the polarization region 12c are polarized such that the upper surface becomes −, for example.
Further, as shown in FIG. 3D and FIG. 3E, the piezoelectric vibrator 11 is polarized so that almost the entire surface is one polarization region, for example, the upper surface becomes + in the stacking direction.
[0013]
As shown in FIG. 1, the piezoelectric element 10 includes an electrode 16a, an electrode 16b, an electrode 16c, an electrode 16d, an electrode 16e, an electrode 16f, and an electrode 16g.
Among these, the electrodes 16 a to 16 e are electrodes for inputting signals to the piezoelectric vibrator 11, and the electrodes 16 f and 16 g are electrodes for inputting signals to the piezoelectric vibrator 12.
[0014]
The electrode 16a substantially covers the upper surface of the polarization region 12a of the piezoelectric vibrator 12, and a part thereof is drawn out to the side surface 10a. That is, the upper surfaces of the polarization regions 12a of the piezoelectric vibrators 12 are all at the same potential by the electrodes 16a that are continuous through the portion drawn out to the side surface 10a.
[0015]
Similarly, the electrode 16b substantially covers the upper surface of the polarization region 12b of the piezoelectric vibrator 12, and a part thereof is drawn out to the side surface 10a. In other words, the upper surfaces of the polarization regions 12b of the piezoelectric vibrators 12 all have the same potential due to the electrodes 16b that are continuous through the portion drawn to the side surface 10a.
[0016]
The electrode 16c substantially covers the upper surface of the polarization region 12c of the piezoelectric vibrator 12, and a part thereof is drawn out to the side surface 10b. That is, the upper surfaces of the polarization regions 12c of the piezoelectric vibrators 12 are all at the same potential by the electrodes 16c that are continuous through the portion drawn out to the side surface 10b.
[0017]
Similarly, the electrode 16d substantially covers the upper surface of the polarization region 12d of the piezoelectric vibrator 12, and a part thereof is drawn out to the side surface 10b. That is, the upper surfaces of the polarization regions 12d of the piezoelectric vibrators 12 are all set to the same potential by the electrodes 16d that are continuous through the portion drawn to the side surface 10b.
[0018]
The electrode 16e covers all the lower surfaces of the polarization regions 12a, 12b, 12c, and 12d of the piezoelectric vibrator 12, and a part thereof is drawn out to the side surface 10a. In other words, the lower surfaces of the four polarization regions of each piezoelectric vibrator 12 are all at the same potential by the electrode 16d that is continuous through the portion drawn out to the side surface 10a.
[0019]
Further, in the piezoelectric vibrator 12, when the same drive signal is input to the electrodes 16a, 16b, 16c, and 16d using the electrode 16e as a reference electrode, the polarization regions 12b and 12c contract when the polarization regions 12a and 12d expand, Conversely, when the polarization regions 12a and 12d contract, the polarization regions 12b and 12c expand. Accordingly, the piezoelectric vibrator 12 performs bending vibration in the lateral direction.
[0020]
That is, since the drive signals input to the same polarization region are the same, all the piezoelectric vibrators 12 bend and vibrate in the same direction. Therefore, a large bending vibration, that is, a vibration in the direction of sending the moving body 14 is generated in the piezoelectric element 10.
[0021]
The electrode 16f substantially covers the upper surface of the polarization region 11a of the piezoelectric vibrator 11, and a part thereof is drawn out to the side surface 10b. That is, the upper surfaces of the polarization regions 11a of the piezoelectric vibrators 11 are all set to the same potential by the electrodes 16e that are continuous through the portion drawn to the side surface 10b.
[0022]
Similarly, the electrode 16g substantially covers the lower surface of the polarization region 11a of the piezoelectric vibrator 11, and a part thereof is drawn out to the side surface 10a. In other words, the lower surface of the polarization region 11a of the stacked piezoelectric vibrator 11 has the same potential due to the electrode 16g continuous through the portion drawn out to the side surface 10a.
[0023]
Further, in the piezoelectric vibrator 11, when a drive signal is input to the electrode 16 f with the electrode 16 g as a reference, the polarization region 11 a expands or contracts. Therefore, the piezoelectric vibrator 11 has a longitudinal extension motion, that is, a vibrating body 13. A vibration in a direction in which the movable body 14 is pressed against the moving body 14 is generated.
[0024]
As shown in FIG. 1, the electrode 16e of the piezoelectric vibrator 12 is connected to the AC power source 6 via the switch 17b, and the electrodes 16a, 16b, 16c and 16d are connected to the AC power source 6 via the switch 17a. The electrode 16f of the piezoelectric vibrator 11 is directly connected to the output side of the AC power source 6, and the electrode 16g is directly connected to the reference potential side. Therefore, the connection direction of the electrodes 16a to 16e, that is, whether these electrodes are connected to the output side of the AC power supply 6 or to the ground potential side is switched by the switch 17a and the switch 17b. Therefore, the ultrasonic motor 1 rotates the moving body 14 in the opposite direction only by switching both the switches 17a and 17b.
[0025]
Next, the operation of the control circuit 22 of the ultrasonic motor 1 will be described.
In the following drawings, the vibration displacement in the X direction is a vibration component in the feed direction of the moving body 14 due to the vibration of the second piezoelectric vibrator 12, and its magnitude is calculated from the second signal generator 32 to the second. Is proportional to the voltage applied to the piezoelectric vibrator 12.
Further, the vibration displacement in the Y direction is a vibration component in a direction in which the moving body 14 is pressed by vibration of the first piezoelectric vibrator 11, and the magnitude thereof is from the first signal generator 31 to the first piezoelectric vibration. It is proportional to the voltage applied to the child 11.
[0026]
FIG. 4A shows the behavior until the driven object of the ultrasonic motor according to the drive control system of the present invention is established at the target position, and FIGS. 4B and 4C show the vibration displacement. In FIG. 4B, first, as shown in (1) in the figure, the ultrasonic motor 1 is started only by vibration displacement in the Y direction. Here, as shown in (2) in the figure without the state of FIG. (1), the vibration displacement in the X direction that is extremely small with respect to the vibration displacement in the Y direction, for example, the minimum X direction vibration that can operate the moving body 14 In some cases, it is activated with displacement.
At this time, since the vibration displacement in the Y direction of the ultrasonic motor 1 is large, the vibration body 13 is sufficiently in pressure contact with the moving body 14 without being affected by the roughness or undulation of the contact surfaces of the vibrating body 13 and the moving body 14. At this time, even if the moving body 14 is not operating, the moving body 14 and the vibrating body 13 are not in a completely static friction state, but are in a state where the moving body 14 is operating, that is, static friction and dynamic friction are mixed. Therefore, the stick slip can be suppressed, and the vibration displacement in the X direction is small and can be driven at an extremely low speed, so that the ultrasonic motor 1 can be started smoothly and a sticky slip is generated between the moving body 14 and the vibrating body 13. It is difficult to improve the durability of the ultrasonic motor 1.
[0027]
Next, as shown in (2) to (3) in the figure, the vibration displacement in the X direction is gradually increased by controlling the voltage applied to the second piezoelectric vibrator 12, and the rotational speed of the ultrasonic motor 1 is increased. To the steady drive state indicated by (4) in the figure.
[0028]
When the distance between the current position of the moving body 14 and the target position becomes smaller than a predetermined value (5 in the figure), the vibration displacement in the X direction is reduced by controlling the voltage applied to the second piezoelectric vibrator 12. The size is gradually reduced to prevent the moving body 14 from overshooting from the target position. When the moving body 14 reaches the target position, the application of voltage to the first piezoelectric vibrator 11 and the second piezoelectric vibrator 12 is stopped, and the ultrasonic motor 1 is completely stopped.
[0029]
At this time, after the voltage application is stopped, the moving body 14 stops after passing the target position due to inertia.
Therefore, in order to correct the position of the moving body 14, as shown in (6) in the figure, the ultrasonic motor 1 is first activated only by displacement in the Y direction, and then the ultrasonic motor is moved by small vibration displacement as in (7). After starting 1 in the reverse rotation direction, the ultrasonic motor 1 is completely stopped.
Further, as shown in (8) and (9) in the figure, after starting the ultrasonic motor 1 with a vibration displacement smaller than in the case of (7) in the figure, the ultrasonic motor 1 is completely stopped.
[0030]
Accordingly, when the position of the moving body 14 is corrected, only the vibration displacement in the Y direction or only a very small displacement in the X direction is adjusted and the ultrasonic motor 1 is activated to prevent stick slip and to operate at a very low speed. High-precision positioning is possible. In addition, the target position can be set in a short time.
[0031]
Note that, as shown in FIG. 4C, even if both the vibration displacement in the X direction and the vibration displacement in the Y direction are both changed, the same effect as the above-described example is obtained.
Therefore, as shown in FIG. 4A, the ultrasonic motor 1 can be started smoothly, and the movable body 14 can be positioned with high accuracy. Moreover, since the amount of overshoot can be reduced when stopping at the target position, the establishment time to the target position can be shortened.
In such a control, the vibration in the Y direction becomes small at the start and at the end of driving, so that the piezoelectric element 11 does not press the vibrating body 13 more than necessary. Therefore, the point that the amount of slip coming from the small amount of overshoot is small, the wear between them is reduced, and the life of the ultrasonic motor 1 is extended.
In this case, the second signal generator 32 can be omitted, and the output voltage from the first signal generator 31 can be applied to the second piezoelectric vibrator 12 via a phase shifter (not shown). Therefore, the circuit can be miniaturized.
[0032]
As shown in FIG. 5A, when starting the ultrasonic motor 1, the phase difference between the voltage applied to the first piezoelectric vibrator 11 and the voltage applied to the second piezoelectric vibrator 12 is calculated. It may be gradually increased (from 0 ° to 90 ° in the figure). Furthermore, in this case, since the vibration displacement in the X direction and the vibration displacement in the Y direction can be controlled separately, only the amplitude in the X direction can be increased while fixing the amplitude in the Y direction. Therefore, the ultrasonic motor 1 can be started smoothly as in the example described above.
[0033]
Further, the phases of the voltage applied to the first piezoelectric vibrator 11 and the voltage applied to the second piezoelectric vibrator 12 are synchronized, and the amplitude ratio of each applied voltage is changed while maintaining the synchronized state. However, as shown in FIG. 5B, since the vibration displacement in the X direction and the vibration displacement in the Y direction can be controlled separately, only the amplitude in the X direction can be increased while the amplitude in the Y direction is fixed. Therefore, the ultrasonic motor 1 can be started smoothly as in the example described above.
[0034]
Further, as shown in FIG. 6A, as the moving body 14 approaches the target position, only the vibration displacement in the Y direction is gradually reduced by controlling the voltage applied to the second piezoelectric vibrator 12. Since the transmitted force is reduced, the inertia of the moving body 14 when the ultrasonic motor 1 is stopped is reduced, and the amount of overshoot with respect to the target position can be reduced. Therefore, the establishment time can be shortened.
[0035]
Further, as shown in FIG. 6B, the voltage applied to the second piezoelectric vibrator 12 is controlled to gradually reduce the vibration displacement in the Y direction ((1) to (3) in the figure). Then, by controlling the voltage applied to the first piezoelectric vibrator 11 to gradually reduce the vibration displacement in the Y direction ((3) to (5) in the figure), the ultrasonic motor 1 is suddenly moved at the target position. Compared to the case of stopping, the amount of overshoot is extremely small, and precise positioning is possible.
[0036]
In the example of FIGS. 5A and 5B described above, the control at the time of starting the ultrasonic motor 1 is the control at the time of positioning by reversing the procedure. For example, in FIG. 5A, the start-up time is reduced by starting with the vibration displacement in the Y direction being small at the time of position correction, so that the rise time of the moving body 14 is delayed, but the static torque does not change. The amount of overshoot is smaller than the amount of movement when the body 14 rises, and the movable body 14 can be positioned more accurately than in the past. In FIG. 5B, the ultrasonic motor 1 is activated by gradually increasing the phase difference. Conversely, the phase difference is gradually decreased at the end of driving, and the rotational speed of the ultrasonic motor 1 is increased. You may slow down gradually. Also in this case, the movable body 14 can be positioned with higher accuracy than in the past.
[0037]
In the example of FIGS. 6A and 6B described above, the control at the time of positioning the ultrasonic motor 1 is the control at the time of activation by reversing the procedure. For example, in FIG. 6A, positioning control is performed by gradually reducing the vibration displacement in the Y direction. Conversely, even if the ultrasonic motor 1 is started while gradually increasing the vibration displacement in the Y direction. Good. By this control, the ultrasonic motor 1 can be started smoothly.
[0038]
Further, the drive control method according to the present invention is not limited to the ultrasonic motor 1 shown in the present embodiment, and the vibration component in the direction in which it is pressed against the driven body and the vibration component in the feed direction of the driven body are represented. As long as the ultrasonic motor can be controlled independently, the principle and structure are not limited. For example, the ultrasonic motor can be applied to the ultrasonic motor 2 shown in FIG. In this case, the piezoelectric vibrator 24 that generates vibration in the twisting direction corresponds to the piezoelectric vibrator 11 in the ultrasonic motor 1, and the piezoelectric vibrator 23 that expands and contracts in the vertical direction corresponds to the piezoelectric vibrator 11.
[0039]
Furthermore, when the moving body 14 is a driving object included in, for example, a stage of a semiconductor manufacturing apparatus, a measuring instrument, a camera, a printer, a printing machine, a machine tool, a robot, a moving device, or a storage device, these electronic devices with ultrasonic motors Performance and durability are improved.
[0040]
【The invention's effect】
According to the present invention, the ultrasonic motor can be started smoothly by controlling the magnitude and ratio of the pressure contact force to the driven object in accordance with the driving condition of the driven object, and the driven object can be highly accurate. Can be positioned.
[Brief description of the drawings]
1A, 1B, and 1C are schematic views of an ultrasonic motor 1 as viewed from above, side, and below, respectively, and FIG. 1D is a vibration displacement of the ultrasonic motor 1; FIG.
FIG. 2 is a block diagram showing a configuration of an ultrasonic motor.
3 is a diagram showing the piezoelectric element 10 and the piezoelectric vibrators 11 and 12 of FIG.
FIG. 4 is a diagram showing behavior until a driven object is established at a target position according to the ultrasonic motor drive control method of the present invention, and vibration displacement of the ultrasonic motor.
FIG. 5 is a diagram showing vibration displacement of the ultrasonic motor according to the ultrasonic motor drive control method of the present invention.
FIG. 6 is a diagram showing vibration displacement of the ultrasonic motor according to the drive control method of the ultrasonic motor of the present invention.
7 is an external view showing an ultrasonic motor 2. FIG.
FIG. 8 is a diagram illustrating a vibration displacement of an ultrasonic motor and a speed change of the ultrasonic motor by a conventional ultrasonic motor drive control method.
[Explanation of symbols]
1 Ultrasonic Motor 6 AC Power Supply 10 Piezoelectric Element 11 First Piezoelectric Vibrator 12 Second Piezoelectric Vibrator 13 Vibrating Body 14 Moving Body 15 Pressure Mechanisms 16a to 16g Electrodes 17a and 17b Switch 21 Position Sensor 22 Control Circuit 23 Piezoelectric Vibrator 24 Piezoelectric vibrator 30 Drive circuit 31 First signal generator 32 Second signal generator

Claims (8)

In an ultrasonic motor having a first piezoelectric vibrator that vibrates in a direction in pressure contact with a driven object, and a second piezoelectric vibrator that vibrates in a feeding direction of the driven object,
As the driven object approaches the target position, the applied voltage to the second piezoelectric vibrator is controlled to gradually reduce the vibration component in the feed direction, and then the applied voltage to the first piezoelectric vibrator is reduced. An ultrasonic motor comprising drive control means for controlling and gradually reducing a vibration component in a pressure contact direction. In an ultrasonic motor having a first piezoelectric vibrator that vibrates in a direction in pressure contact with a driven object, and a second piezoelectric vibrator that vibrates in a feeding direction of the driven object,
After starting the ultrasonic motor only with the vibration in the direction of pressure contact with the driven object or with the vibration in the feed direction of the driven object, the voltage applied to the second piezoelectric vibrator is controlled. An ultrasonic motor comprising drive control means for gradually increasing only the vibration component in the feed direction. In an ultrasonic motor having a first piezoelectric vibrator that vibrates in a direction in pressure contact with a driven object, and a second piezoelectric vibrator that vibrates in a feeding direction of the driven object,
An ultrasonic motor while gradually increasing the phase difference between the voltage applied to the first piezoelectric vibrator (vibration component in the pressure contact direction) and the voltage applied to the second piezoelectric vibrator (vibration component in the feed direction). An ultrasonic motor comprising drive control means for activating the motor. The ultrasonic motor according to any one of claims 1 to 3 ,
The drive control means starts or ends the drive control of each ultrasonic motor when the parameter reaches a predetermined value. The ultrasonic motor according to claim 4 ,
The ultrasonic motor, wherein the parameter is a distance from a current position of the driven object to a target position. The ultrasonic motor according to claim 4 ,
The ultrasonic motor, wherein the parameter is a speed of the ultrasonic motor. The ultrasonic motor according to any one of claims 1 to 6 ,
When the driven object reaches a target position, the drive control means stops applying the voltage to each piezoelectric vibrator to completely stop the driven object, and then starts the ultrasonic motor in the reverse direction. And correcting the position of the driven object. Ultrasonic electronic apparatus equipped with a motor and having an ultrasonic motor according to any one of claims 1 to 7.

Images