JP4349950B2 - Ultrasonic motor - Google Patents

Description

  The present invention relates to an ultrasonic motor including a Langevin type ultrasonic transducer.

  As shown in FIG. 5, two ultrasonic transducers 101a and 101b, a holding member 102 that holds the ultrasonic transducers 101a and 101b at a predetermined angle (for example, 90 degrees), and a substantially V-shaped shape And a head 103 which is in contact with the slider 105 which is a driven body at the apex portion thereof, and which is connected to the ultrasonic transducers 101a and 101b at the end portion (the V-shaped open side). A resonance type ultrasonic motor 100 is known (see, for example, Patent Document 1).

  The ultrasonic transducer 101a includes a piezoelectric element 104a. The piezoelectric element 104a has a Langevin structure that is fastened with a predetermined force by a head 103 and a metal fitting 107a. Similarly, the ultrasonic transducer 101b includes a piezoelectric element 104b. The piezoelectric element 104b is fastened with a predetermined force by the head 103 and the metal fitting 107b.

  In the ultrasonic motor 100, when the ultrasonic vibrators 101a and 101b are driven with a resonance frequency voltage whose phase is shifted by 90 degrees, that is, when a resonance frequency voltage whose phase is shifted by 90 degrees is applied to the piezoelectric elements 104a and 104b, An elliptical motion occurs at the tip. Therefore, when the elliptically moving head 103 is pressed against the side surface of the slider 105 attached to the linear guide 106 with a certain force, a frictional force generated between the head 103 and the slider 105 causes the slider 105 to extend in the extending direction of the linear guide 106. A thrust is given, and the slider 105 can be moved by this.

  Here, each of the piezoelectric elements 104a and 104b has a structure in which two single-plate piezoelectric ceramics are stacked in order to obtain a ground (earth) to the head 103 and the metal fittings 107a and 107b. As described above, the piezoelectric elements 104a and 104b are respectively tightened with a predetermined force, and the piezoelectric elements 104a and 104b are required to have strength as mechanical parts. Is needed.

However, when the thickness of the single plate piezoelectric ceramic is large, there is a problem that the driving voltage becomes high. As a method for reducing the driving voltage of piezoelectric ceramics, a method of multilayering piezoelectric ceramics is known. However, the multilayer structure of piezoelectric elements 104a and 104b in the ultrasonic motor 100 has not been studied.
JP 2000-152671 A

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an ultrasonic motor including a Langevin type ultrasonic transducer having a laminated piezoelectric element having a structure optimized.

According to the present invention, there are two Langevin type ultrasonic transducers, a holding member that holds the two ultrasonic transducers at a predetermined angle, and a substantially V-shaped shape, and its apex portion An ultrasonic motor comprising: a head that is in contact with the driven body and has the two ultrasonic vibrators connected to the end thereof;
The ultrasonic transducer is formed by symmetrically laminating two laminated piezoelectric elements with a predetermined metal plate interposed therebetween, and each laminated piezoelectric element includes three or more odd-numbered piezoelectric ceramic layers and piezoelectric ceramics thereof. A multilayer piezoelectric element having a plurality of electrode layers sandwiching the layers and an external electrode connecting every other electrode layer;
An ultrasonic motor is provided in which a driving voltage is applied to an electrode layer provided on each end face of the multilayer piezoelectric element.

  In such an ultrasonic motor, it is preferable that the ultrasonic transducer is provided in a state where the two stacked piezoelectric elements are stacked via a metal plate. The multilayer piezoelectric element preferably has an integral structure in which the piezoelectric ceramic layer and the electrode layer are formed by integral firing.

  According to such an ultrasonic motor, since the drive voltage can be lowered, the step-up transformer is downsized or the step-up transformer becomes unnecessary. Further, by adopting a configuration in which two stacked piezoelectric elements are stacked via a metal plate, it is easy to take out the electrodes on the high voltage side and the ground side, and the disconnection of the lead wire can be prevented. Furthermore, by using an integrated structure manufactured by an integral firing method as a laminated piezoelectric element, vibration transmission efficiency is maintained high, and spurious vibrations that are likely to occur when multiple piezoelectric ceramic plates are used are suppressed. be able to.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic structure of the ultrasonic motor 10. The ultrasonic motor 10 has the same structure as the ultrasonic motor 100 shown in FIG. 5 except that the structure of the piezoelectric element is different. The structure will also be described in detail.

  The ultrasonic motor 10 is in contact with two driven vibrators 15, two ultrasonic vibrators 11 a and 11 b having a Langevin structure, a holding member 12 that holds the ultrasonic vibrators 11 a and 11 b at an angle of 90 degrees. And a head 13 having a substantially V-shape. A pressing mechanism 14 is attached to the holding member 12, and the pressing mechanism 14 presses the head 13 against the driven body 15 with a predetermined force.

  The ultrasonic vibrator 11a includes a bolt 21 having both ends threaded, a cap nut 22 having a screw hole screwed into a screw groove of the bolt 21, and two ring-shaped laminated molds through which the bolt 21 can pass. It has piezoelectric elements 23a and 23b and ring-shaped metal plates 24a and 24b. Similar to the ultrasonic transducer 11a, the ultrasonic transducer 11b includes a bolt 21 ', a cap nut 22', two ring-shaped stacked piezoelectric elements 23a 'and 23b', and a ring-shaped metal plate 24a. '· 24b'. The structure of the laminated piezoelectric element 23a and the like will be described in detail later.

  The holding member 12 is provided with holes for allowing the bolts 21 and 21 'to pass therethrough. The head 13 connects the contact portion 13a in contact with the driven body 15, the connection portions 13b and 13b 'connected to the ultrasonic transducers 11a and 11b, and the contact portion 13a and the connection portions 13b and 13b'. Neck portions 13c and 13c 'are formed, and screw holes that are screwed into the screw grooves of the bolts 21 and 21' are formed in the connecting portions 13b and 13b ', respectively.

  The laminated piezoelectric elements 23a and 23b are fastened with a predetermined force by the connecting portion 13b of the cap nut 22 and the head 13, whereby a Langevin type ultrasonic transducer 11a is obtained. Similarly, the laminated piezoelectric elements 23a ′ and 23b ′ are fastened with a predetermined force by the cap nut 22 ′ and the connecting portion 13b ′ of the head 13, whereby a Langevin type ultrasonic transducer 11b is obtained.

  Thus, in the ultrasonic motor 10, the connecting portion 13b of the head 13 is also a component of the ultrasonic transducer 11a, and similarly, the connecting portion 13b 'is also a component of the ultrasonic transducer 11b. That is, the head 13 not only gives thrust to the driven body 15 but also plays a role as a member constituting a Langevin type vibrator by tightening the laminated piezoelectric element 23a and the like.

  For the head 13, a metal material such as stainless steel or cemented carbide having excellent wear resistance is preferably used. In this case, it is easy to form screw grooves for connecting the bolts 21 and 21 'to the connecting portions 13b and 13b'. It is also preferable to apply a ceramic coating excellent in wear resistance such as silicon nitride on the surface of the contact portion 13a in the head 13. As will be described later, since the internal electrode 32a used as the ground electrode is formed on the end face of the laminated piezoelectric element 23a / 23a 'on the head 13 side, the head 13 is held at the ground potential.

  Metal materials are also used for the bolts 21 and 21 ′, the cap nuts 22 and 22 ′, and the holding member 12. Accordingly, the head 13 and the cap nuts 22 and 22 'are electrically connected via the bolts 21 and 21', and the cap nuts 22 and 22 'and the holding member 12 are grounded. Will be retained. For this reason, the metal plates 24b and 24b 'that are in contact with the holding member 12 are used as ground electrodes. In other words, the structure of the laminated piezoelectric element 23 and the like must be set so that the metal plates 24b and 24b 'can be used as ground electrodes.

  As the pressing mechanism 14, for example, an air cylinder, a hydraulic cylinder, a spring coil, or the like is used.

  Next, the structure of the multilayer piezoelectric element 23a and the like will be described. As described above, since the structures of the ultrasonic transducers 11a and 11b are substantially the same, the laminated piezoelectric elements 23a and 23b constituting the ultrasonic transducer 11a will be described below. FIG. 2 is a sectional view showing a schematic structure of the multilayer piezoelectric elements 23a and 23b.

  The multilayer piezoelectric element 23a has a structure in which a plurality of piezoelectric ceramic layers 31 are sandwiched between internal electrodes 32a and 32b, and the internal electrodes 32a and the internal electrodes 32b are alternately provided in the stacking direction. The plurality of internal electrodes 32a are electrically connected by the external electrode 33a, and the plurality of internal electrodes 32b are electrically connected by the external electrode 33b. The internal electrodes 32a and 32b are not exposed on the inner hole side so that the bolt 21 (not shown in FIG. 2) inserted into the multilayer piezoelectric element 23a and the internal electrodes 32a and 32b are not electrically connected.

  As is generally known, the multilayer piezoelectric element 23a is formed by first forming a piezoelectric ceramic powder into a sheet shape to produce a green sheet, and printing the electrode paste on the green sheet by a screen printing method. After laminating and integrating by thermocompression bonding, calcining and firing under predetermined conditions, and cutting and grinding the obtained fired body, an external electrode paste is applied to a predetermined position on the side surface, and a predetermined temperature is applied. Can be manufactured by baking. According to such an integral firing method, it is easy to form the piezoelectric ceramic layer 31 thin.

  The number of stacked piezoelectric ceramic layers 31 is an odd number. As a result, the internal electrode 32a is exposed at one of the end faces in the stacking direction of the multilayer piezoelectric element 23a, and the internal electrode 32b is exposed at the other. In FIG. 2, since the internal electrode 32a is in contact with the head 13, as described above, the metal plate 24b that is electrically connected to the head 13 through the bolt 21, the cap nut 22, and the holding member 12 is used as the ground electrode. On the other hand, since the metal plate 24a is in contact with the internal electrode 32b, the metal plate 24a is used as a high-voltage side electrode.

  The laminated piezoelectric element 23b has the same structure as the laminated piezoelectric element 23a, and sandwiches the metal plate 24a so that the internal electrode 32a is in contact with the metal plate 24b and the internal electrode 32b is in contact with the metal plate 24a. The multilayer piezoelectric element 23a is arranged symmetrically. The piezoelectric ceramic layers 31 of the multilayer piezoelectric elements 23a and 23b are previously polarized with a predetermined voltage using the internal electrode 32b as the high-voltage side and the internal electrode 32a as the ground electrode.

Lead wires (not shown in FIG. 2) are attached to the metal plates 24a and 24b, respectively, and drive voltages are applied using these lead wires to drive the stacked piezoelectric elements 23a and 23b simultaneously (see FIG. 1). . For example, the multilayer piezoelectric elements 23a and 23b constituting the ultrasonic transducer 11a are expanded and contracted by, for example, V ₁ = V ₀ sin2πft (f: resonance frequency), and the multilayer piezoelectric element 23a ′ of the ultrasonic transducer 11b is expanded. 23b ′ is expanded or contracted by V ₂ = V ₀ cos 2πft. As a result, an elliptical motion can be generated in the contact portion 13a of the head 13, and the driven body 15 can be moved using the frictional force between the driven body 15 and the contact portion 13a.

  In a conventionally known multilayer piezoelectric element, lead wires are soldered to external electrodes. However, in the ultrasonic motor 10, in order to generate large displacement vibrations in the laminated piezoelectric elements 23a and 23b, when the lead wires are attached to the external electrodes 33a and 33b by soldering or the like as in the prior art, a short time is required. As a result of driving, the lead wire is detached at this attachment portion. Further, when the number of piezoelectric ceramic layers 31 included in the multilayer piezoelectric elements 23a and 23b is an even number, the same internal electrode (that is, either the internal electrode 32a or 32b) is formed on both surfaces of the multilayer piezoelectric elements 23a and 23b. 1) is exposed, a lead wire must be attached to either one of the external electrodes 33a and 33b, and the above-described problem of lead wire detachment cannot be avoided.

For this reason, in the ultrasonic motor 10, by setting the number of piezoelectric ceramic layers to an odd number, the internal electrodes exposed to the end faces of the multilayer piezoelectric elements 23a and 23b without attaching lead wires to the external electrodes 33a and 33b. The drive voltage can be applied to the electrodes 32a and 32b via the metal plates 24a and 24b. Thereby, the ultrasonic motor 10 can have a long life . Further, in the ultrasonic motor 10, the driving voltage can be lowered by using the laminated piezoelectric elements 23a and 23b for the ultrasonic transducer 11a.

  As the stacked piezoelectric elements 23a and 23b, so-called adhesive stacked piezoelectric elements can be used. The adhesive laminated piezoelectric element that can be used in the ultrasonic motor 10 is such that a piezoelectric ceramic plate having a predetermined thickness with electrode films formed on the front and back surfaces is symmetrical with respect to the direction of polarization across the electrode film. It has a structure in which an external electrode film is formed on the side surface thereof. That is, conventionally, an adhesive-type laminated piezoelectric element having a structure in which a metal foil is sandwiched between piezoelectric ceramic plates is known. In such a structure, the adhesive layer is doubled to increase spurious. Since there is a problem that vibration is easily generated and the adhesive layer suppresses transmission of vibration of the piezoelectric ceramic plate, there is substantially no merit to use in the ultrasonic motor 10.

  For this reason, even when an adhesive-type laminated piezoelectric element is used, the number of piezoelectric ceramic plates needs to be an odd number, so that the metal plate 24a. 24b can be used as a drive electrode. In addition, in the case of the adhesive-type laminated piezoelectric element, there is a limit to thinning the piezoelectric ceramic plate from the viewpoint of handling during the bonding process, but the voltage is lower than that in the case of using a thick single-plate piezoelectric element. Driving becomes possible.

  As mentioned above, although embodiment of this invention has been described, this invention is not limited to such a form. For example, the head 13 can be made of ceramics such as alumina, silicon nitride, or silicon carbide. When the head 13 is made of an insulating material such as alumina, for example, the connecting portions 13b and 13b ′ of the head 13 are connected to the internal electrodes 32a of the stacked piezoelectric elements 23a and 23a ′ that are in contact with the head 13 for grounding. Instead of directly forming a screw hole, for example, a hexagonal column-shaped hole is formed, and a metal nut to be screwed into the bolts 21 and 21 'is inserted and fixed, and laminated with the connecting portions 13b and 13b'. What is necessary is just to make it the structure which inserts a metal plate between each type | mold piezoelectric element 23a * 23a ', and these metal plates and a nut conduct | electrically_connect.

  (A) Single plate type piezoelectric element (thickness: 8 mm), (b) monolithic fired laminated piezoelectric element (thickness of piezoelectric ceramic layer: 640 μm, number of laminated layers: 14 layers), (c) adhesive laminated type Three types of ultrasonic motors were produced using each of the piezoelectric elements (thickness of piezoelectric ceramic layer: 750 μm, number of layers: 10 layers). FIG. 3 shows the stage drive characteristics when the alumina stage is moved using each ultrasonic motor. Here, the head of each ultrasonic motor is pressed against the stage with a preload of 120 N.

  As shown in FIG. 3, in an ultrasonic motor using an integrally fired laminated piezoelectric element, a sufficient moving speed can be obtained at a low voltage, and the driven body can be moved at a high speed by increasing the driving voltage. It was confirmed that It has been confirmed that even an ultrasonic motor using an adhesive-type laminated piezoelectric element can reduce the drive voltage as compared with a conventional ultrasonic motor using a single-plate piezoelectric element.

  FIG. 4 shows mechanical load characteristics when the head of each ultrasonic motor is pressed against the stage with a preload of 150 N and the drive voltage is 70V. In FIG. 4, since the value of the intersection with the horizontal axis (mechanical load) when each plot is extrapolated is considered to be the thrust applied to the stage, even a heavier stage can be moved at a higher speed as this value increases. . As shown in FIG. 4, an improvement in mechanical load was confirmed with an ultrasonic motor using a laminated piezoelectric element compared to an ultrasonic motor using a single-plate piezoelectric element. It was confirmed that an ultrasonic motor using a laminated piezoelectric element can obtain high mechanical load characteristics.

  An ultrasonic motor using an integrally fired multilayer piezoelectric element having an odd number of piezoelectric ceramic layers and an ultrasonic motor using an even fired multilayer piezoelectric element having an even number of layers are preloaded. Was 120 N, the driving voltage was 70 V, and the lifetime was measured when the stage was driven. In addition, in an integrally fired laminated piezoelectric element having an even number of piezoelectric ceramic layers, lead wires are connected to one external electrode formed on the side surface in order to use both internal electrodes exposed on the end face as ground electrodes. By soldering, a driving voltage on the high voltage side can be applied. As a result, in the integrally fired multilayer piezoelectric element having an even number of ceramic layers, the lead wire was detached at the soldered portion in about 10 hours. In the multilayer piezoelectric element, no characteristic deterioration or failure occurred after 100 hours.

  The ultrasonic motor of the present invention is suitable as a driving device for an XY stage equipped in a semiconductor manufacturing apparatus or the like.

Sectional drawing which shows schematic structure of the ultrasonic motor which concerns on this invention. FIG. 2 is a cross-sectional view showing a schematic structure of a multilayer piezoelectric element constituting the ultrasonic motor of FIG. 1. Explanatory drawing which shows the stage drive characteristic by various ultrasonic motors. Explanatory drawing which shows the mechanical load characteristic of various ultrasonic motors. Explanatory drawing which shows schematic structure of the conventional ultrasonic motor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10; Ultrasonic motor 11a * 11b; Ultrasonic vibrator 12; Holding member 13; Head 13a; Contact part 13b * 13b '; Connection part 13c * 13c'; Neck part 14; Pressing mechanism 15; 21 '; Bolts 22 and 22'; Cap nuts 23a, 23b, 23a ', and 23b'; Piezoelectric plates 24a, 24b, 24a ', and 24b'; Metal plates 31; Piezoelectric ceramic layers 32a and 32b; Internal electrodes 33a and 33b; External electrodes 100; ultrasonic motors 101a and 101b; ultrasonic transducers 102; holding members 103; heads 104a and 104b; piezoelectric elements 105; sliders 106; linear guides 107a and 107b;

Claims (2)

It has two Langevin type ultrasonic transducers, a holding member that holds the two ultrasonic transducers at a predetermined angle, and a substantially V-shaped shape. And an ultrasonic motor comprising a head to which the two ultrasonic transducers are connected at an end thereof,
The ultrasonic transducer, while stacking the two product layers piezoelectric elements symmetrically about a predetermined metal plate, each laminated piezoelectric element, of three or more odd number layers piezoelectric ceramic layers and these piezoelectric A laminated piezoelectric element having a plurality of electrode layers sandwiching a ceramic layer and an external electrode connecting every other electrode layer;
An ultrasonic motor, wherein a driving voltage is applied to an electrode layer provided on each end face of the multilayer piezoelectric element.   The ultrasonic motor according to claim 1, wherein the multilayer piezoelectric element has an integral structure in which the piezoelectric ceramic layer and the electrode layer are formed by integral firing.

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