JP2008245350A - Ultrasonic motor and its drive method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic motor whose speed can be set not only arbitrarily, according to the requirement of a user, but also move a driven body at higher speed. <P>SOLUTION: This ultrasonic motor includes a rectangular flat piezoelectric plate formed by stacking piezoelectric ceramics; four drive electrodes formed in two lines and two rows on one main surface of the piezoelectric plate, where two surfaces having large area of the piezoelectric surface are regarded as the main surfaces and the stacked surface as side surfaces, common electrodes formed on the other main surface of the piezoelectric plate so as to face the drive electrodes sandwiching the piezoelectric plate; and two sliding members, which are provided on one side surface of the piezoelectric plate and contact a predetermined driven body. Arbitrary speed can be obtained, by selecting the installation position of the sliding member at an arbitrary distance from the end surface of the piezoelectric plate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ultrasonic motor using piezoelectric ceramics suitable for driving an XY stage and the like, a driving method thereof, and an ultrasonic motor apparatus for executing the driving method.

  Recently, ultrasonic motors using piezoelectric ceramics have been used for driving mechanisms such as an XY stage, a linear motor, and a rotary stage (see, for example, Patent Document 1). As shown in FIG. 4, the ultrasonic motor disclosed in Patent Document 1 has two rows and two columns on one main surface (surface having a large area) of a rectangular plate-shaped piezoelectric plate 91 formed by stacking piezoelectric ceramics. The four drive electrodes 92a to 92d are formed on the other main surface, a full-surface electrode (ground electrode; not shown) is formed on the other main surface, and an XY stage or the like is formed on one laminated surface of the piezoelectric plate 91. A head (sliding member) 93 for contacting the driven body 99 is attached.

  The four drive electrodes 92a to 92d are electrically connected to each other located diagonally, and two sets of drive electrode portions 94 and 95 are configured. In addition, the ultrasonic motor 90 is held by applying a preload by the spring 96 in the width direction (−X direction) of the piezoelectric plate 91 and simultaneously pressing the head 93 against the driven body 99 by the spring 97.

  In the ultrasonic motor 90, for example, a sine wave voltage is applied between one of the drive electrode portions 94 and 95 and the entire surface electrode, and the other drive electrode portion is in a floating state (a state where no voltage is applied). Thus, it can be driven. At this time, as shown in FIG. 4A, vibration in the expansion and contraction primary resonance (L1) mode occurs in the longitudinal direction of the piezoelectric plate 91, and as shown in FIG. B2) Mode vibration occurs.

  In the ultrasonic motor 90, an elliptical motion is generated in the head 93 due to the superposition (degeneration) of these vibration modes. The rotation direction of the elliptical motion can be reversed by switching the drive electrode portions 94 and 95 to which the voltage is applied. That is, whether the driven body 99 is moved in the + X direction or the −X direction is determined by which of the drive electrode portions 94 and 95 is applied with the drive voltage.

However, in the structure in which the head 93 is provided at the center of the end surface of the piezoelectric plate 91, the displacement of the piezoelectric plate 91 at the center of the end surface of the piezoelectric plate 91 is small, so the displacement of the head 93 in the X direction is very small. It is difficult to move at high speed. In addition, it is difficult to obtain an ultrasonic motor having an arbitrary maximum speed according to the required speed.
JP-A-7-184382

  The present invention has been made in view of such circumstances, and provides an ultrasonic motor that not only can arbitrarily set the maximum speed of the ultrasonic motor in accordance with the user's request but also moves the driven body at a higher speed. Objective.

  According to a first aspect of the present invention, there is provided a rectangular plate-like piezoelectric plate formed by laminating piezoelectric ceramics, and a piezoelectric plate having two major surfaces of the piezoelectric plate as a main surface and a laminated surface as a side surface. Four drive electrodes formed in two rows and two columns on one main surface of the piezoelectric plate, and a common electrode formed on the other main surface of the piezoelectric plate so as to face the drive electrode across the piezoelectric plate And two sliding members provided on one side surface of the piezoelectric plate and in contact with a predetermined driven body, and the installation position of the sliding member is selected at an arbitrary distance from the longitudinal center of the piezoelectric plate An ultrasonic motor characterized by obtaining an arbitrary maximum speed is provided. As a result, the driven body can be moved at the optimum speed required.

  Further, in this ultrasonic motor, it is desirable that the installation position of the sliding member is at or near the end of the piezoelectric plate. The displacement of the sliding member is determined by the distance from the center of the piezoelectric plate in the longitudinal direction. This is because the displacement amount of the sliding member is the largest and the maximum speed is obtained.

  In this ultrasonic motor, it is preferable that the value obtained by dividing the length in the width direction of the piezoelectric plate by the length in the longitudinal direction of the piezoelectric plate is 0.272, so that the displacement in the longitudinal direction of the piezoelectric plate shown in FIG. The resonance frequency that maximizes the displacement of a certain L1 mode and the resonance frequency that maximizes the displacement of the B2 mode, which is the displacement in the width direction of the piezoelectric plate shown in FIG. 5B, are substantially the same frequency. Both the displacement in the longitudinal direction of the piezoelectric plate and the displacement in the width direction of the piezoelectric plate are maximized, and a large displacement can be transmitted to the sliding member in both the front-rear direction and the left-right direction.

  According to a second aspect of the present invention, this ultrasonic motor driving method, that is, a rectangular plate-shaped piezoelectric plate made of piezoelectric ceramics and one main surface of this piezoelectric plate are provided in two rows and two columns, Four drive electrodes that are electrically connected to each other at diagonal positions and divided into two sets of drive electrode portions, and opposite to the drive electrodes with the piezoelectric plate sandwiched between the other main surfaces of the piezoelectric plate A method of driving an ultrasonic motor, comprising: a common electrode provided to be arranged; and two sliding members provided at arbitrary positions on a side surface of the piezoelectric plate from a center in a longitudinal direction. An ultrasonic motor driving method is provided in which a voltage is not applied to the other driving electrode portion while a predetermined voltage is applied to one of the driving electrodes.

  The ultrasonic motor according to the present invention has an excellent effect that it is possible to obtain a maximum speed optimum for a required speed and to obtain a maximum speed for moving the driven body at a high speed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a schematic configuration of an ultrasonic motor device. The ultrasonic motor device 100 includes an ultrasonic motor 10, a casing unit 20 for holding the ultrasonic motor 10, and a drive power supply unit 30 for driving the ultrasonic motor 10. As shown in FIG. 1, the three-dimensional orthogonal coordinate axes of the X axis, the Y axis, and the Z axis are defined.

  The ultrasonic motor 10 includes a rectangular plate-shaped piezoelectric plate 11 made of piezoelectric ceramics, and four drives formed in two rows and two columns on one main surface (Y-direction surface; Z-X surface) of the piezoelectric plate 11. A common electrode (not shown) formed almost entirely on the other main surface of the piezoelectric plate 11 so as to face the drive electrodes 12a to 12d across the piezoelectric plate 11 and the electrodes 12a to 12d; Sliding members (hereinafter referred to as “heads”) 13a and 13b provided on the side surfaces (thickness direction; Z direction surface in FIG. 1; XY surface) and output surfaces facing the driven body 50 are provided. ing. The heads 13a and 13b are installed equidistantly, that is, line-symmetrically with a longitudinal middle line of the piezoelectric plate 11.

  The piezoelectric ceramic material used for the piezoelectric plate 11 is not particularly limited, but lead zirconate titanate piezoelectric ceramics are usually used. The piezoelectric plate 11 preferably has a shape in which a value obtained by dividing the width (length in the Z direction) by the length (length in the X direction) is 0.272. By adopting such a shape, as described later, the L1 mode and the B2 mode can be excited simultaneously at the same frequency to obtain a large vibration displacement.

  The driving electrodes 12a to 12d are electrically connected to each other at diagonal positions, and are divided into two sets of driving electrode portions, ie, a driving electrode 12a / 12d set and a driving electrode 12b / 12c set. A lead portion 15 for applying a drive voltage to the set of 12c is attached to the drive electrode 12c, and a lead portion 16 for applying a drive voltage to the set of the drive electrodes 12a and 12d is attached to the drive electrode 12d, respectively. . The drive electrodes 12a to 12d are equal in size, narrow as long as the gap width between the drive electrodes 12a to 12d does not cause dielectric breakdown, and the area occupied on the main surface of the piezoelectric plate 11 is as wide as possible. It is preferable that the vibration displacement clamp by the piezoelectric inactive region of the piezoelectric plate 11 is reduced.

  The casing portion 20 that holds the piezoelectric plate 11 includes a concave base portion 21, two first elastic members 22 a attached to the bottom wall of the base portion 21, and one side wall of the base portion 21. The attached second elastic member 22b and a columnar member 23 provided between the other side wall of the base portion 21 and the piezoelectric plate 11 are provided.

  The base 21 is made of engineering plastic or metal. As the first and second elastic members 22a and 22b, a coil spring, a leaf spring, an elastic resin (rubber), or the like is used. The two first elastic members 22 a are in contact with the side surface of the piezoelectric plate 11 where the heads 13 a and 13 b are not attached, and press the heads 13 a and 13 b against the driven body 50. The second elastic member 22b presses one end face (X direction plane; YZ plane) of the piezoelectric plate 11 in the X direction, whereby the piezoelectric plate 11 is connected to the base portion via the cylindrical member 23. 21 is pressed against the other side wall. The thickness (length) direction of the cylindrical member 23 is parallel to the Y direction, and is frictionally held between the side wall of the base portion 21 and the piezoelectric plate 11 by urging by the second elastic member 22b, and at the same time, The holding member that is not held is held so that it cannot move in the Z direction.

  The drive power supply unit 30 includes an AC power supply 31 and a switch 32. The AC power supply 31 outputs a sine wave voltage having a frequency for exciting the ultrasonic motor 10 to resonate in the L1 mode and the n-order (n is an integer) bending resonance mode. Preferably, a secondary bending resonance mode (B2 mode described above with reference to FIG. 5B) is preferably used as the resonance mode of the nth order bending.

  When driving the ultrasonic motor 10, the switch 32 energizes one of the lead portions 15 and 16 with a voltage output from the AC power supply 31. That is, while a predetermined voltage is applied to one drive electrode portion of two sets of drive electrode portions (a set of drive electrodes 12a and 12d and a set of drive electrodes 12b and 12c), a voltage is applied to the other drive electrode portion. Is not applied.

  FIG. 2A schematically shows the movement of the ultrasonic motor 10 and the driven body 50 when a voltage is applied to the pair of drive electrodes 12a and 12d. When a voltage having a resonance frequency that simultaneously generates resonance in the L1 mode and the B2 mode is applied to the drive electrodes 12a and 12d, the piezoelectric plate 11 can obtain the maximum amplitude in both the X direction and the Z direction. -The diagonal length in which 12d is provided expands and contracts, and correspondingly, shear deformation occurs in which the diagonal length in which drive electrodes 12b and 12c are provided expands and contracts.

  The displacement of the head 13a is indicated by arrows D1a and D1b according to this deformation, and the displacement of the head 13b is indicated by arrows D2a and D2b according to this deformation. Since the diagonal displacement amount of the drive electrodes 12a and 12d to which the voltage is applied is larger than the diagonal displacement amount of the drive electrodes 12b and 12c to which no voltage is applied, the displacement amount of the head 13a is the displacement of the head 13b. Larger than the amount.

When the head 13a is displaced in the direction of the arrow D1a approaching the driven body 50, the head 13b is displaced in the direction of the arrow D2a so as to be separated from the driven body 50, and conversely, the arrow in which the head 13a is separated from the driven body 50. When displacing in the direction of D1b, the head 13b is displaced in the direction of the arrow D2b so as to approach the driven body 50.
The head 13a repeatedly strikes the driven body 50 by repeating the displacement of the arrows D1a and D1b at a constant short time interval according to the driving frequency. The striking force that the head 13a applies to the driven body 50 includes a leftward component in the X direction, and a frictional force acts between the head 13a and the driven body 50 at the moment of the hitting. It can be moved to the left in FIG. 2A.

  The amount of displacement of the heads 13a and 13b differs depending on the installation positions of the heads 13a and 13b. That is, the magnitude of the displacement varies depending on the distance from the center in the longitudinal direction of the piezoelectric plate 11 (X direction in FIG. 1). FIG. 3 is a diagram showing the relationship between the installation position of the sliding member (head) and the maximum speed of the driven body when the piezoelectric plate (piezoelectric element) is driven at a resonance frequency of 50 kHz. The position from the center of the element (piezoelectric plate) indicates the distance from the center in the longitudinal direction of the piezoelectric plate 11. The maximum speed is the maximum driving speed of the driven body 50. As shown in FIG. 3, when the driven body 50 is moved at a specific resonance frequency, the speed at which the driven body 50 is moved depends on the distance from the center of the longitudinal direction of the piezoelectric plate 11 (X direction in FIG. 1). come. According to FIG. 3, it can be seen that as the distance from the center in the longitudinal direction increases, the maximum speed increases in proportion to the distance. Further, since the piezoelectric plate 11 is driven at a specific resonance frequency that provides the maximum amplitude, it is necessary to adjust the installation positions of the heads 13a and 13b in order to adjust the speed of the driven body. Therefore, by using FIG. 3, it is possible to determine the optimum head position for the maximum driving speed to be determined, and to design an ultrasonic motor having an arbitrary maximum driving speed.

  FIG. 2B schematically shows the movement of the ultrasonic motor 10 and the driven body 50 when a voltage is applied to the set of the drive electrodes 12b and 12c. At this time, the vibration generated in the ultrasonic motor 10 is symmetrical in the X direction in the form shown in FIG. 2A. That is, when the L1 mode and B2 mode resonances are generated simultaneously in the drive electrodes 12b and 12c, the diagonal length of the piezoelectric plate 11 provided with the drive electrodes 12b and 12c expands and contracts. As a result, shear deformation occurs in which the length in the diagonal direction where the drive electrodes 12a and 12d are provided expands and contracts.

  The displacement of the head 13a is indicated by arrows D1a and D1b according to this deformation, and the displacement of the head 13b is indicated by arrows D2a and D2b according to this deformation. Since the diagonal displacement amount of the drive electrodes 12b and 12c is larger than the diagonal displacement amount of the drive electrodes 12a and 12d, the displacement amount of the head 13b is larger than the displacement amount of the head 13a.

When the head 13b is displaced in the direction of the arrow D2b approaching the driven body 50, the head 13a is displaced in the direction of the arrow D1b so as to be separated from the driven body 50, and conversely, the arrow in which the head 13b is separated from the driven body 50. When displacing in the direction of D2a, the head 13a is displaced in the direction of arrow D1a so as to approach the driven body 50.
The head 13b repeatedly strikes the driven body 50 by repeating the displacement of the arrows D2a and D2b at regular short time intervals according to the driving frequency. The striking force applied to the driven body 50 by the head 13b includes a rightward component in the X direction, and a frictional force acts between the head 13b and the driven body 50 at the moment of the hitting. It can be moved to the right in FIG. 2B.

  The heads 13a and 13b actually have a motion to draw an elliptical trajectory having a major axis in the directions of the arrows D1a, D1b, D2a, and D2b, depending on the shape accuracy and the holding state of the ultrasonic motor 10, respectively. Although it may occur, even in that case, the driving characteristics of the driven body 50 are not greatly affected.

  The configuration of the drive power supply unit 30 is not limited to that shown in FIG. 1. For example, the lead units 15 and 16 are each provided with an AC power supply connected via an on / off switch, and control of the on / off switch is performed. Thus, one of the two sets of drive electrode portions may be driven.

  Next, a specific configuration and characteristics of the ultrasonic motor 10 will be described. A length of 16.5 mm × width 4.5 mm × thickness 3 mm (width / length = 0.272) of the piezoelectric plate 11 made of lead zirconate titanate-based piezoelectric ceramics is vertically 1.6 mm long. X Driving electrodes 12a to 12d having a width of 7.8 mm were formed, and a full surface electrode was formed on the other main surface. The drive electrodes 12a and 12d are connected, the drive electrodes 12b and 12c are connected, and lead portions 15 and 16 are provided on the drive electrodes 12c and 12d, respectively, and polarization treatment is performed in the thickness direction of the piezoelectric plate 11. . Further, alumina heads 13a and 13b were attached to both ends of the side surface of the piezoelectric plate 11 using an epoxy adhesive.

  The ultrasonic motor 10 thus manufactured is pressed against a metal slider 5 mm × 3 mm × 60 mm slidably held on a guide rail with a constant force, and a sine wave voltage having a frequency of 100 kHz and a voltage of 60 Vrms is applied to the lead portion 15. Thus, resonance vibrations in the L1 mode and the B2 mode were generated simultaneously. By adjusting the force for pressing the ultrasonic motor 10 against the slider, the slider could be moved at a maximum speed of 100 mm / sec.

The schematic block diagram of an ultrasonic motor. The figure which shows typically a motion of an ultrasonic motor and a to-be-driven body. The figure which shows typically a motion of an ultrasonic motor and a to-be-driven body. The figure which shows the relationship between the position of a sliding member, and the maximum speed. The top view which shows the structure of the conventional ultrasonic motor. The figure which shows the expansion-contraction primary resonance (L1) mode of a piezoelectric plate. The figure which shows the bending secondary resonance (B2) mode of a piezoelectric plate.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Ultrasonic motor, 11 ... Piezoelectric plate, 12a-12d ... Drive electrode, 13a * 13b ... Head, 15 * 16 ... Lead part, 20 ... Casing part, 21 ... Base part, 22a ... 1st elastic member, 22b ... 2nd elastic member, 23 ... Cylindrical member, 30 ... Drive power supply part, 31 ... AC power supply, 32 ... Switch, 50 ... Driven body.

Claims (4)

In a rectangular flat plate-like piezoelectric plate formed by laminating piezoelectric ceramics, and a piezoelectric plate having two major surfaces of the piezoelectric plate as a main surface and a laminated surface as a side surface,
Four drive electrodes formed in two rows and two columns on one main surface of the piezoelectric plate;
A common electrode formed on the other main surface of the piezoelectric plate so as to face the drive electrode across the piezoelectric plate;
Two sliding members provided on one side surface of the piezoelectric plate and in contact with a predetermined driven body;
An ultrasonic motor characterized in that an arbitrary maximum speed is obtained by selecting an arbitrary distance from the longitudinal center of the piezoelectric plate as an installation position of the sliding member.   The ultrasonic motor according to claim 1, wherein the installation position of the sliding member is at or near the end of the piezoelectric plate.   The ultrasonic motor according to claim 1, wherein a value obtained by dividing the width of the piezoelectric plate by the length of the piezoelectric plate is 0.272. A rectangular plate-shaped piezoelectric plate made of piezoelectric ceramics and two main electrodes on one main surface of this piezoelectric plate are connected in two rows and two columns, and the diagonally-connected ones are electrically connected to two sets of drive electrode portions. Four divided drive electrodes, a common electrode provided to face the drive electrode with the piezoelectric plate sandwiched between the other main surface of the piezoelectric plate, and an arbitrary side surface of the piezoelectric plate from the longitudinal center A driving method of an ultrasonic motor comprising two sliding members respectively provided at positions,
A method of driving an ultrasonic motor, wherein a voltage is not applied to the other drive electrode portion while a predetermined voltage is applied to one of the two sets of drive electrodes.

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