JP4454930B2 - Ultrasonic motor and electronic device with ultrasonic motor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic motor that frictionally drives a moving body by vibration of the vibrating body, and more particularly to an ultrasonic motor that drives the moving body by exciting expansion and contraction vibration and bending vibration in the same in-plane direction.
[0002]
[Prior art]
An ultrasonic motor using the resonance mode of an elastic body has excellent controllability, and has attracted attention as a precision positioning actuator. In particular, linear actuators are often required as actuators for various stages, and many types have been proposed and studied. Among them, various ultrasonic motors utilizing the combined vibration of the longitudinal (extension / contraction) vibration and bending vibration of a rectangular plate have been studied. Among these, ultrasonic motors using laminated piezoelectric elements are: (1) Low voltage drive, (2) Small size and high output, (3) Excellent controllability, (4) Simple structure, (5) Less manufacturing process, etc. (For example, refer patent document 1).
[0003]
The structure and driving principle will be described below. In FIG. 4, the vibrating body 40 is configured by stacking two types of piezoelectric elements 13 and 8 in the thickness direction. FIG. 4A is a view of the vibrating body 40 as viewed from above, and the first piezoelectric element 13 has four regions formed by connecting the centers of the length and width of the piezoelectric element 13. The polarization direction is changed and the polarization is performed in the thickness direction as shown in FIG. Electrodes 9b, 9c, 9d, and 9e are provided on one surface of the piezoelectric element 13 so as to correspond to each polarization region. On the other surface of the piezoelectric element 13, an electrode 9f is provided almost entirely. By applying a drive signal between the pressure electrodes 9b, 9c, 9d, 9e and the electrode 9f, bending vibration is excited in a direction perpendicular to the thickness. FIG. 4C is a view of the vibrating body 40 as viewed from below, and the second piezoelectric element 8 is polarized in the same direction throughout. Electrodes 9a and 9f are provided on almost the entire front and back surfaces of the piezoelectric element 8. By applying a drive signal between the electrodes 9a and 9f, expansion (longitudinal) vibration is excited in a direction perpendicular to the thickness. To do. Therefore, the electrode 9 f is a common electrode for the piezoelectric elements 13 and 8.
[0004]
As a driving method, for example, as shown in FIG. 4B, a signal obtained by amplifying the signal from the oscillation circuit 12 by the amplification circuit A 10a is applied to the first piezoelectric element 13, and the signal from the oscillation circuit 12 is transferred. For example, when a signal whose phase is shifted by 90 degrees by the phase circuit 11 and a signal amplified by the amplifier circuit B10b are applied to the second piezoelectric element 8, longitudinal vibrations and bending vibrations having different phases can be excited. The side surface of 40 moves elliptically as shown in FIG. Accordingly, the moving body in contact with the vibrating body 40 operates.
[0005]
In addition, with such a structure, expansion / contraction (longitudinal) vibration and bending vibration can be controlled independently, so that the shape of the ellipse formed by the displacement can be controlled, and the motor characteristics (speed, propulsive force) can be varied over a wide range. At the same time, highly accurate positioning is possible.
[0006]
[Patent Document 1]
Japanese Unexamined Patent Publication No. 2000-116162 (page 5-7, FIGS. 4 and 5)
[0007]
[Problems to be solved by the invention]
However, as shown in FIG. 4, when a vibrating body is formed by simply stacking and laminating two longitudinal vibration exciting piezoelectric elements and bending vibration exciting piezoelectric elements, the following phenomenon is likely to occur. (1) Unnecessary modes such as bending vibration in the thickness direction are excited in the vicinity of the use resonance point. (2) A mode coupled with an unnecessary mode is excited, including bending vibration in the thickness direction. An example of these is shown based on the analysis result by the finite element method. The analyzed model has the same configuration as that shown in FIG. 4, and has a length of 20 mm, a width of 5.45 mm, and a thickness of 2 mm (two piezoelectric elements are each 1 mm).
[0008]
FIG. 5 shows the relationship between frequency and admittance when a signal is applied to the piezoelectric element for longitudinal vibration excitation (indicated by a thick line in the figure), but unnecessary vibration is also generated near the resonance point (around 80 KHz) of longitudinal vibration (around 81 KHz). That is, the bending vibration in the thickness direction shown in FIG. 6 has been excited.
[0009]
FIG. 7 shows the side surface of the vibrating body at the resonance point of bending vibration when a drive signal is applied to the actual use state, that is, the longitudinal vibration exciting piezoelectric element and the bending vibration exciting piezoelectric element. It can be seen that the film is bent and deformed, and bending vibration in the thickness direction is also excited.
[0010]
As shown in FIG. 5, when the unnecessary mode is excited near the resonance point to be used, that is, near the driving frequency, the displacement of the unnecessary mode is superimposed on the vibration displacement, so an unnecessary displacement component is added to the moving body, Drive efficiency decreases. Further, the influence of this unnecessary mode also causes a characteristic variation because the degree of influence changes greatly due to a slight difference in frequency. Furthermore, self-excited oscillation driving becomes difficult due to the influence of unnecessary modes.
[0011]
The same applies to the state shown in FIG. In addition, when coupled with the unnecessary mode, the electromechanical coupling coefficient of the vibrating body is lowered, so that the speed and propulsive force of the moving body are lowered. Since the vibration displacement includes a component of an unnecessary mode displacement, an unnecessary displacement component is added to the moving body, and the driving efficiency is lowered.
[0012]
Although an example of the influence of the unnecessary mode has been described above, it is affected by various vibration modes depending on the shape of the vibrator.
[0013]
Similar problems may also occur in ultrasonic motors that drive by applying drive signals to some of the piezoelectric elements provided. This is because the stress generated by the piezoelectric element is not evenly applied to the entire vibrating body, so that bending vibration in the thickness direction may be excited.
[0014]
[Means for Solving the Problems]
Therefore, the piezoelectric actuator of the present invention is configured by laminating a plurality of types of piezoelectric elements having mutually different polarization regions to constitute a vibrating body, and in contact with the vibrating body by vibration displacement generated in a direction perpendicular to the stacking direction. In the ultrasonic motor for driving the body or the vibrator itself, the plurality of types of piezoelectric elements are alternately stacked in a predetermined order.
Alternatively, an ultrasonic motor having an elastic body and a vibrating body that is disposed so as to sandwich the elastic body and has the same piezoelectric element joined to one surface and the other surface of the elastic body, The moving body in contact with the vibrating body or the vibrating body itself is driven by the vibration displacement generated in the direction orthogonal to the stacking direction.
[0015]
Alternatively, a vibrating body is configured by laminating a plurality of types of piezoelectric elements or by laminating piezoelectric elements and an elastic body, and an operating body in contact with the vibrating body by vibration displacement generated in a direction orthogonal to the laminating direction, or the vibrating body itself The plurality of types of piezoelectric elements excite different vibrations, and are arranged so as to sandwich the stacked piezoelectric elements, and one surface of the stacked piezoelectric elements An ultrasonic motor having a vibrating body made of an elastic body joined to the other surface is used.
[0016]
As another solution, a vibrating body is configured by laminating a plurality of types of piezoelectric elements, and the moving body in contact with the vibrating body or the vibrating body itself is driven by vibration displacement generated in a direction perpendicular to the stacking direction. In the ultrasonic motor, the vibration is a stretching vibration and a bending vibration, and the natural frequency of the bending vibration in the thickness direction of the vibrating body is not located near the natural frequency of the stretching vibration and the bending vibration. Determine the thickness.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described based on the drawings with a focus on differences from the conventional example.
(Embodiment 1)
FIG. 1 shows a vibrating body of an ultrasonic motor according to the present invention. The vibrating body 10 is configured by stacking two types of piezoelectric elements 1 and 2 in the thickness direction. In the first piezoelectric element 1 (1a, 1b), the polarization direction is changed in the thickness direction as indicated by + and-in the figure in the four regions formed by connecting the centers of the length and width of the piezoelectric element 1. Polarized. Although not shown, bending vibration is excited in a direction orthogonal to the thickness by applying a drive signal to electrodes provided on the front and back surfaces of the piezoelectric element 1. The second piezoelectric element 2 is polarized in the same direction throughout. Although not shown, expansion and contraction (longitudinal) vibration is excited in a direction orthogonal to the thickness by applying a drive signal to electrodes provided on the front and back surfaces of the piezoelectric element 2.
[0018]
As shown in FIG. 1A, the first piezoelectric elements 1a and 1b are stacked so as to sandwich the front and back of the second piezoelectric element 2. As a bonding method, in addition to bonding, a sheet of piezoelectric elements manufactured using a sheet process may be stacked and then fired. The two piezoelectric elements 1 and 2 are arranged symmetrically in the front and back direction when viewed from the center of the thickness of the vibrating body 10. As long as this rule is observed, the number, thickness, and arrangement of the piezoelectric elements 1 and 2 are arbitrary. Also, an electrode (not shown) and a method for short-circuiting between the electrodes are arbitrary, and an insulating layer may be provided between the piezoelectric elements 1 and 2. When the drive signal is applied, the two piezoelectric elements 1 and 2 generate different stresses, but such an arrangement does not generate stress that causes bending displacement in the thickness direction. Therefore, the unnecessary mode is not excited near the resonance point to be used, that is, in the vicinity of the resonance point of the bending vibration mode in the direction orthogonal to the longitudinal vibration mode and the stacking direction. Moreover, it is not combined with an unnecessary mode.
[0019]
Here, a rectangular plate vibrating body has been described. For example, an ultrasonic motor using an in-plane bending vibration and an in-plane vibration of a disk or an annular vibrating body, an in-plane bending vibration or an in-plane vibration, and the like. It can also be applied to piezoelectric devices such as piezoelectric transformers to be used.
[0020]
Further, as shown in FIG. 9, even if a plurality of types of piezoelectric elements 1 and 2 are alternately laminated to form a vibrating body, the same effect can be obtained because the force generated by each piezoelectric element is equalized.
[0021]
(Embodiment 2)
FIG. 2 shows a second example of the vibrator of the ultrasonic motor of the present invention. The vibrating body 20 is configured by laminating two types of piezoelectric elements 3 and 4 and two elastic bodies 5a and 5b in the thickness direction. The first piezoelectric element 3 is polarized in the thickness direction by changing the polarization direction in four regions formed by connecting the length and width centers of the piezoelectric element 3 as indicated by + and-in the figure. . Although not shown, bending vibration is excited in a direction perpendicular to the thickness by applying a drive signal to electrodes provided on the front and back surfaces of the piezoelectric element 3. The second piezoelectric element 4 is polarized in the same direction throughout. Although not shown, expansion and contraction (longitudinal) vibration is excited in a direction orthogonal to the thickness by applying a drive signal to electrodes provided on the front and back surfaces of the piezoelectric element 2.
[0022]
As shown in FIG. 2A, the two elastic bodies 5a and 5b are joined so as to sandwich the upper and lower surfaces of the first piezoelectric element 3 and the second piezoelectric element 4 that are joined together. As described above, in this embodiment, the two types of piezoelectric elements 3 and 4 are not arranged symmetrically with respect to the stacking direction, but the stress is maximum when a stress that causes bending displacement in the thickness direction is applied. By providing the elastic bodies 5a and 5b having the same thickness on the upper and lower surfaces, it becomes possible to minimize the generation of unnecessary modes due to the stress and the influence of coupling between the use mode and the unnecessary mode.
[0023]
The elastic bodies 5 a and 5 b are made of a metal such as an aluminum alloy or stainless steel, and are preferably thicker than the piezoelectric elements 3 and 4.
[0024]
(Embodiment 3)
FIG. 3 shows another example of the vibrator of the ultrasonic motor of the present invention. The vibrating body 30 is formed by joining two identical piezoelectric elements 6 a and 6 b so as to sandwich the upper and lower surfaces of the elastic body 7. The piezoelectric element 6 is polarized in the same direction in the thickness direction as shown by + in the figure in all four regions formed by connecting the length and width centers of the piezoelectric element 6. Although not shown, four divided electrodes are provided on one surface of the piezoelectric element 6 and electrodes are provided on the other surface over the front surface. By applying a drive signal to two diagonal regions among the four divided regions, bending vibration and expansion / contraction (longitudinal) vibration are simultaneously excited in a direction orthogonal to the thickness.
[0025]
In this way, it is possible to construct a vibrating body using only a piezoelectric element, but in that case, in order to obtain mechanical strength, the thickness of the piezoelectric element has to be increased, and the polarization voltage becomes higher, which makes it difficult to manufacture. In addition to this, the drive voltage also increases. Therefore, a thin piezoelectric element may be used by being bonded to an elastic body such as a metal. However, in this case, since the structure is a unimorph structure, it becomes easy to excite bending vibration in the thickness direction, which is unnecessary vibration. Here, this phenomenon can be mitigated if the piezoelectric element is bonded to both surfaces of the elastic body, but when a piezoelectric element having a different polarization direction in the surface is used, or as shown in the example of FIG. When applied, there is a risk of exciting flexural vibration.
[0026]
Therefore, in this embodiment, the bending vibration in the thickness direction is suppressed by setting the thickness of the elastic body 7 so that the bending rigidity in the thickness direction of the elastic body 7 is larger than the bending rigidity of the entire piezoelectric elements 6a and 6b. The The piezoelectric element is not limited to the present embodiment, and the same configuration can be adopted for a method of exciting different vibrators as shown in FIG. The same configuration can be applied to an ultrasonic motor of a type in which a piezoelectric element is bonded to both ends of an elastic body and one of them is driven.
[0027]
As described above, not only is it not affected by the unnecessary mode, but also there are advantages of low voltage driving and high output by providing a plurality of thin piezoelectric elements.
[0028]
(Embodiment 4)
As a measure that is not affected by coupling of unnecessary modes, excitation, etc., it is also possible to cope with a specific shape of the vibrating body.
[0029]
An example is shown below based on the analysis result by the finite element method. The analyzed model has the same configuration as that shown in FIG. 4, has a length of 20 mm, a width of 5.45 mm, and an eigenvalue analysis by changing the thickness (the thickness of the two piezoelectric elements is equal) to 1 mm, 2 mm, and 4 mm. FIG. 8 shows the result when the above is performed.
FIG. 8A shows the longitudinal vibration mode when the thickness is 1 mm, FIG. 8B shows the case when the thickness is 2 mm, and FIG. 8C shows the longitudinal vibration mode when the thickness is 3 mm. It can be seen that thickness direction bending displacement components are mixed except for (c). Incidentally, under the above conditions, the bending vibration was a normal shape (pure bending vibration mode) that was not affected by unnecessary vibration in any case.
[0030]
These are considered to have occurred because the resonance frequencies of the bending vibration modes in various thickness directions in which the resonance frequency changes depending on the thickness approached the resonance frequencies of the vibration modes to be used, although the resonance frequencies of the vibration modes to be used hardly depend on them. Therefore, for example, the unnecessary mode is determined by determining the thickness of the vibrating body so that the natural frequency of the bending vibration mode in the thickness direction of the vibrating body is not located near the natural frequency of the stretching vibration and bending vibration as in the condition of (c). Can be unaffected.
[0031]
Note that this embodiment can also be applied to an ultrasonic motor in which a piezoelectric element and an elastic body are stacked by means such as bonding, and vibration in an in-plane direction orthogonal to the stacking direction is used.
[0032]
(Embodiment 5)
An example in which an electronic apparatus is configured using the piezoelectric actuator of the present invention will be described with reference to FIG. FIG. 10 shows the positioning drive of the read head in the hard disk drive mechanism using the ultrasonic motor of the present invention. The read head 16b on the disk 15 is attached to the tip of the arm 16a. The other end of the arm 16a is provided with a rotating plate 16c that is fixed to a bearing that serves as a rotation center of the arm 16a and that rotates about a bearing (not shown). The vibrating body 50 is guided so as to be movable in the longitudinal direction by the guide members 18a and 18b at the central portion serving as a vibration node. A protrusion 17 joined to the vibrating body 50 is brought into contact with the outer peripheral portion of the rotating plate 16c under the force of the spring 14. The rotating plate 16 c operates by receiving the force of the protrusion 17. Since this ultrasonic motor can extremely reduce the feed amount per one drive signal cycle, the positioning accuracy of the rotary plate 16c, that is, the head 16b is extremely high, and the recording density of the disk 15 can be remarkably increased.
[0033]
Here, the hard disk drive mechanism is shown as an example, but the present invention can also be applied to a feeding mechanism, a manipulator and the like in a processing apparatus.
[0034]
【The invention's effect】
According to the present invention, the unnecessary mode is not excited near the use resonance point. Further, a mode coupled with an unnecessary mode is not excited. Therefore, self-excited oscillation driving is facilitated, the characteristic variation of each actuator is small, and only the displacement of the target vibration mode can be transmitted to the moving body, so that high driving efficiency can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a vibrating body of an ultrasonic motor according to Embodiment 1 of the present invention.
FIG. 2 is a diagram showing a configuration of a vibrating body of an ultrasonic motor according to a second embodiment of the present invention.
FIG. 3 is a diagram showing a configuration of a vibrating body of an ultrasonic motor according to a third embodiment of the present invention.
FIG. 4 is a diagram showing a configuration of a conventional ultrasonic motor.
FIG. 5 is a diagram illustrating an example of a frequency response analysis result of a vibration body of a conventional ultrasonic motor.
FIG. 6 is a diagram illustrating an example of an eigenvalue analysis result of a vibrating body of a conventional ultrasonic motor.
FIG. 7 is a diagram illustrating another example of the eigenvalue analysis result of a vibration body of a conventional ultrasonic motor.
FIG. 8 is a diagram illustrating a result of vibration analysis of a vibrating body of a conventional ultrasonic motor.
FIG. 9 is a diagram showing another configuration of the vibrating body of the ultrasonic motor according to the first embodiment of the present invention.
FIG. 10 is a diagram showing an electronic apparatus using the ultrasonic motor of the present invention.
[Explanation of symbols]
1, 2, 3, 4, 6, 8, 13 Piezoelectric elements 5, 7 Elastic body 9 Electrodes 10, 20, 30, 40, 50 Vibrating body 14 Screw 15 Disk 16 Arm 17 Protrusion 18 Guide member

Claims (5)

A plurality of types of piezoelectric elements having different polarization regions are stacked in the thickness direction to form a vibrating body, and come into contact with the vibrating body by vibration displacement by combining two different vibrations generated in a direction perpendicular to the stacking direction. An ultrasonic motor that drives the moving body or the vibrating body itself,
The ultrasonic motor according to claim 1, wherein the vibrating body has an elastic body bonded to both ends in the stacking direction of the stacked piezoelectric elements that generate the vibration displacement . An ultrasonic motor having an elastic body and a vibrating body having a piezoelectric element bonded to one surface and the other surface of the elastic body so as to sandwich both ends in the thickness direction of the elastic body ,
The piezoelectric element generates a vibration displacement by combining two different vibrations in a direction orthogonal to the thickness direction,
2. The ultrasonic motor according to claim 1, wherein a bending stiffness in the thickness direction of the elastic body is greater than a bending stiffness in the thickness direction of the piezoelectric element . 2. The ultrasonic motor according to claim 1, wherein the plurality of types of piezoelectric elements having different polarization regions are a piezoelectric element that generates stretching vibration and a piezoelectric element that generates bending vibration . A plurality of types of piezoelectric elements having different polarization regions are stacked in the thickness direction, or a piezoelectric element and an elastic body are stacked in the thickness direction to form a vibrating body, and stretching vibration and bending generated in a direction perpendicular to the stacking direction. An operating body that is in contact with the vibrating body by vibration displacement due to vibration synthesis, or an ultrasonic motor that drives the vibrating body itself,
The ultrasonic motor is characterized in that the thickness of the vibrating body is such that the natural frequency of the bending vibration in the thickness direction of the vibrating body is not located near the natural frequency of the stretching vibration and bending vibration . An electronic apparatus comprising the ultrasonic motor according to any one of claims 1 to 4.

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