US20090127974A1

US20090127974A1 - Small piezoelectric or electrostrictive linear motor

Info

Publication number: US20090127974A1
Application number: US12/357,438
Authority: US
Inventors: Vasiljef Piotr; Bo Keun Kim; Seok Min Yoon; Seong Yil Yoon
Original assignee: Piezoelectric Technology Co Ltd
Current assignee: Piezoelectric Technology Co Ltd
Priority date: 2004-03-02
Filing date: 2009-01-22
Publication date: 2009-05-21
Also published as: JP2007516688A; US20070120442A1; DE602005023129D1; ATE479201T1; WO2005083874A1; EP1721382A4; EP1721382A1; US7498719B2; EP1721382B1

Abstract

A piezoelectric/electrostrictive linear motor is provided. A movable shaft is coupled to a unimorph or bimorph, which is made by attaching a piezoelectric or electrostrictive substrate to an elastic body, so that a movable body provided with respect to the movable shaft is linearly moved along the movable shaft by the vibration or movement of the piezoelectric or electrostrictive substrate.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of and claims the benefit under 35 U.S.C. § 120 of a U.S. patent application Ser. No. 10/578,922 filed in the U.S. Patent and Trademark Office on May 9, 2006, which is a U.S. national stage application under 35 U.S.C § 371 of a PCT application number PCT/KR2005/00353 filed on Feb. 4,2005, and claims the benefit under 35 U.S.C. § 119(a) of a Korean patent application No. 10-2004-0014050 filed Mar. 2, 2004 and Korean patent application No. 10-2004-0040895 filed on Jun. 4,2004, in the Korean Intellectual Property Office, the entire disclosures of which are hereby incorporated by reference.

TECHNICAL FIELD

The following description relates to a piezoelectric/electrostrictive linear motor, and more particularly, to a small piezoelectric/electrostrictive ultrasonic linear motor which may be installed in cell phones or PDAs, etc., to drive, for example, their camera lenses and in which a movable shaft is coupled to a unimorph or bimorph, which is made by attaching a piezoelectric or electrostrictive substrate to an elastic body, so that a movable body fitted over the movable shaft is linearly moved along the movable shaft by vibration of the piezoelectric or electrostrictive substrate.

BACKGROUND

Small stepping motors, which may be installed in cell phones or PDAs, etc., to drive their camera lenses, are generally provided with reduction gears and cams to convert high speed rotation into linear motion. Furthermore, in conventional small stepping motors, when rotated or reversely rotated, backlash may occur, thus resulting in error. Therefore, such small stepping motors have been limitedly used. In addition, the small stepping motor is problematic in that high electric current is required and excessive heat is generated.
Generally, in methods of driving linear motors using piezoelectric or electrostrictive substrates, there are a driving method of using a traveling wave generated by a flexural wave, and a driving method which uses a standing wave and in which a linear motor is provided with both a longitudinal vibration actuator and a transverse vibration actuator so that a movable unit is operated by repeated vertical and horizontal vibration. Standing wave type linear motors are provided with vibrators having different operating modes and use multiple vibrations generated by them. Such a standing wave type linear motor includes a piezoelectric/electrostrictive actuator which vibrates vertically and horizontally, and a contact part which transmits mechanical displacement to a movable body which is moving. Longitudinal vibration of a piezoelectric vibrator is transmitted to the contact part at which the movable unit is coupled to the piezoelectric vibrator. The movable body is operated by friction at a junction between it and the movable unit. In the meantime, several other vibration transmitting methods have been proposed, but, because maintaining constant vibration amplitude is difficult due to wear resulting from repeated motion over a long period of time, it is very hard to put into practical use.
First, before exemplary embodiments are explained, a piezoelectric effect and vibration theory will be described herein below for comprehension of the exemplary embodiments.
Piezoelectric effect means that an electric charge is generated in a crystalline body when the crystalline body receives pressure, or, conversely, when an electric field is applied to the crystalline body, the crystalline body is mechanically displaced. A piezoelectric substrate having such piezoelectric effect is characterized in that mechanical displacement is induced according to the polarization direction and the direction of the electric field.
FIGS. 1( a) through 1(c) show mechanical displacement of a piezoelectric substrate 10 according to the polarization direction and the direction of the electric field.
FIG. 1( a) shows displacement of the piezoelectric substrate 10 when an electric field is applied to the piezoelectric substrate 10 polarized in a predetermined direction. When the polarization direction of the piezoelectric substrate 10 is the same as the direction of the electric field, the piezoelectric substrate 10 is expanded in a direction designated by the reference character z and is constricted by Poisson's ratio in a direction designated by the reference character x. When the polarization direction of the piezoelectric substrate 10 is opposite to the direction of the electric field, the piezoelectric substrate 10 is constricted in a direction z and is expanded in a direction x.
FIG. 1( b) illustrates displacement of the piezoelectric substrate 10 attached to an elastic body 20. In this case, the piezoelectric substrate 10 is displaced in the same manner as that described for the case of FIG. 1( a), and bending displacement of the elastic body 20 attached to the piezoelectric substrate 10 is induced by the expansion and constriction of the piezoelectric substrate 10.
The dotted line of FIG. 1( b) denotes the shape of the elastic body 20 bent when the piezoelectric substrate 10 is expanded in a direction z. Such bending displacement of the elastic body 20 is achieved by the expansion of the piezoelectric substrate 10 while a fixed edge 25 of the elastic body 20 is held at a predetermined position.
FIG. 1( c) illustrates the elastic body 20 bent in a direction z by the expansion of the piezoelectric substrate 10 in a direction x. When the direction of the electric field is instantaneously changed, the displacement state of the piezoelectric substrate 10, which was in the state of FIG. 1( b), is quickly changed. As a result, the elastic body 20 is quickly bent in a direction z by instantaneous acceleration and expansion of the piezoelectric substrate 10 in the direction x.
Although the bending displacement of the piezoelectric substrate, when an electric field is applied, has been described, even if an electrostrictive substrate is used in place of the piezoelectric substrate, the same bending displacement as that of the case of the piezoelectric substrate is induced. The electrostriction means that an electrostrictive body is mechanically displaced when an electric field is applied to the electrostrictive body. Even if the piezoelectric substrate of FIG. 1 is replaced with the electrostrictive substrate, the same bending displacement is induced.

SUMMARY

In one general aspect, there is provided a linear motor which induces bending displacement using the piezoelectric or electrostrictive substrate and converts the bending displacement into linear displacement.
In another aspect, there is provided a piezoelectric/electrostrictive linear motor, including a piezoelectric or electrostrictive substrate driven by a voltage applied thereto, an elastic body, to one surface or each of both surfaces of which the piezoelectric or electrostrictive substrate is attached, and a movable shaft coupled at an end thereof to the elastic body or the piezoelectric or electrostrictive substrate attached to the elastic body, the movable shaft being operated in conjunction with displacement of the piezoelectric or electrostrictive substrate, wherein a movable body provided with respect to the movable shaft is moved with respect to the movable shaft in response to the operation of the movable shaft.
The movable shaft may be moved in conjunction with bending displacement of the elastic body and the one or more piezoelectric or electrostrictive substrate attached thereto, to move the movable body.
A surface area of a largest surface of the elastic body may be greater than a surface area of a largest surface of the piezoelectric or electrostrictive substrate.
A portion of the elastic body and/or the piezoelectric or electrostrictive substrate may be fixed such that the movable shaft is moved in conjunction with bending displacement of the unfixed portion.
The movable shaft may be moved in conjunction with displacement of the piezoelectric or electrostrictive substrate between a first position and a second position, and the movable body may be moved along with a movement of the movable shaft in response to the piezoelectric or electrostrictive substrate being displaced toward the second position and the movable body may not moved back to a position of the movable shaft in response to the piezoelectric or electrostrictive substrate being displaced toward the first position.
The piezoelectric or electrostrictive substrate may be polarized.
The movable body may be moved with respect to the movable shaft in response to vibration of the movable shaft.
A weight of the movable body and a frictional force between the movable shaft and the movable body are provided so that the movable body may be moved with respect to the movable shaft when the movable shaft vibrates in conjunction with the displacement of the piezoelectric or electrostrictive substrate.
The movable body may include a friction member being in close contact with an outer surface of the movable shaft, a weight provided around an outer surface of the friction member, and an elastic shell fitted over an outer surface of the weight to hold both the friction member and the weight around the movable shaft, wherein the movable body is fitted over the movable shaft.
In still another aspect, there is provided a method of driving a piezoelectric/electrostrictive linear motor, the motor having an elastic body to which at least one piezoelectric or electrostrictive substrate is attached and a movable shaft coupled to the elastic body or the piezoelectric or electrostrictive substrate attached to the elastic body, wherein a movable body provided with respect to the movable shaft is to be moved with respect the movable shaft, the method including the step (a) of applying a voltage, which varies from a first voltage to a second voltage, to the piezoelectric or electrostrictive substrate during a first period, and the step (b) of applying a voltage, which varies from the second voltage to the first voltage, to the the piezoelectric or electrostrictive substrate during a second period after the step (a), wherein, the movable body is moved along with a movement of the movable shaft in conjunction with displacement of the piezoelectric or electrostrictive substrate during the step (a) or step (b), to move with respect to the movable shaft. The step (a) and step (b) may be repeated.
The movable body may be moved along with the movement of the movable shaft during one of the step (a) and step (b), and the movable body may not moved back to a position of the movable shaft during the other one of the step (a) and step (b).
The movable shaft may moved in conjunction with bending displacement of the elastic body and the piezoelectric or electrostrictive substrate, the piezoelectric or electrostrictive substrate may be displaced between a first position and a second position, and the movable body may be moved along with the movement of the movable shaft in response to the piezoelectric or electrostrictive substrate being displaced toward the second position and the movable body may not moved back to a position of the movable shaft in response to the piezoelectric or electrostrictive substrate being displaced toward the first position
The first period is longer than the second period. During the second period, the movable body may be moved along with the movement of the movable shaft, so that the movable body is moved along the movable shaft. The first period may be shorter than the second period. During the first period, the movable body may be moved along with the movement of the movable shaft, so that the movable body is moved along the movable shaft.
Other features will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the attached drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a) through 1(c) are diagrams illustrating a principle of bending movement of both a piezoelectric or electrostrictive substrate and an elastic body used in exemplary embodiments.

FIGS. 2( a) through 2(f) are diagrams illustrating a principle of a piezoelectric/electrostrictive ultrasonic linear motor according to an exemplary embodiment.

FIG. 3 is a diagram illustrating a saw-tooth pulse wave for driving a piezoelectric/electrostrictive ultrasonic linear motor according to an exemplary embodiment.

FIG. 4 is a diagram illustrating a piezoelectric/electrostrictive ultrasonic linear motor according to an exemplary embodiment.

FIG. 5 is a diagram illustrating a piezoelectric/electrostrictive ultrasonic linear motor according to another exemplary embodiment.

FIG. 6 is front and side views illustrating a piezoelectric/electrostrictive ultrasonic linear motor according still another exemplary embodiment.

FIGS. 7( a) and 7(b) are diagrams illustrating a movable body of a piezoelectric/electrostrictive ultrasonic linear motor according to an exemplary embodiment.

FIGS. 8( a) through 8(d) are diagrams illustrating a principle of movement of a movable body and a stator of a piezoelectric/electrostrictive ultrasonic linear motor according to an exemplary embodiment.

Throughout the drawings and the detailed description, unless otherwise described or apparent, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The elements may be exaggerated for clarity and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the systems, apparatuses and/or methods described herein will be suggested to those of ordinary skill in the art. Also, descriptions of well-known functions and constructions are omitted to increase clarity and conciseness.
With reference to FIGS. 1( a) through 1(c), a piezoelectric or electrostrictive substrate 10 used in exemplary embodiments may be made of a single-crystalline ceramic, a polycrystalline ceramic or polymeric material. In the case of the piezoelectric substrate, the piezoelectric substrate may be polarized in a thickness direction of the substrate. An elastic body 20 may be made of an elastic member having a predetermined thickness. For example, phosphor bronze may be used as the material constituting the elastic body 20. Where a movable shaft is coupled to the elastic body 20, a coupling hole into which the movable shaft is inserted may be formed at the center on the elastic body 20.
As described above with reference to FIGS. 1( a) through 1(c), when an electric field is applied to both the elastic body 20 and the piezoelectric or electrostrictive substrate 10 which are attached to each other, bending vibration of both the elastic body 20 and the piezoelectric or electrostrictive substrate 10 is transmitted to the movable shaft. As a result, a movable body 40 linearly moves (see FIGS. 2( a) through 2(f). Here, the principle of moving the movable body 40 may be based on the law of inertia.
FIGS. 2( a) through 2(f) illustrate an exemplary driving mechanism of the movable body 40 fitted over a movable shaft 30. FIG. 3 shows an input pulse applied to the piezoelectric or electrostrictive substrate 10. As shown in the drawing, a repeated saw-tooth pulse may be used as a drive pulse.
Although not shown in FIGS. 2( a)-2(f), it is assumed that both the piezoelectric or electrostrictive substrate 10 and the elastic body 20 are coupled to a left end of the movable shaft 30 of FIGS. 2( a)-2(f) in the same manner as that shown in FIG. 4. The movement of the movable body 40 with respect to the movement of the movable shaft 30, when the saw-tooth pulse wave as shown in FIG. 3 is input as the drive pulse wave, will be explained herein below.
FIG. 2( a) and the point ‘a’ of FIG. 3 illustrate a start of an operation. The movable body 40 is placed on the movable shaft 30 at a position spaced apart from an end of the movable shaft 30 by a distance Sa.
FIG. 2( b) and the section between the point ‘a’ and the point ‘b’ of FIG. 3 illustrate a first step of FIG. 3 which is an inclined part of the saw-tooth pulse wave that represents an increase in voltage. That is, in the section in which the pulse wave from the point ‘a’ to the point ‘b’ is input, the movable body 40 linearly moves along with the movable shaft 30 in the direction of the x-axis by a distance A (Sa=Sb).
FIG. 2( c) and the section between the point ‘b’ and the point ‘c’ of FIG. 3 illustrate that the voltage of the saw-tooth pulse wave of FIG. 3 varies from the point ‘b’ to the point ‘c’ so that the voltage becomes zero. This means that the voltage applied to the piezoelectric or electrostrictive substrate becomes zero. At this time, as shown in FIG. 2( c), the movable shaft 30 instantaneously moves to the left by a distance 2A due to a restoring force of the elastic body. Because the movable shaft 30 instantaneously moves to the left, the movable body 40 having a predetermined weight stays at the position of the distance Sc according to the law of inertia. In other words, only the movable shaft 30 moves to the left (Sc>Sb).
FIG. 2( d) and the section between the point ‘c’ and the point ‘d’ of FIG. 3 illustrate that the movable shaft 30 moves along with the movable body 40 in the direction of the x-axis by a distance 2A (Sc=Sd).
FIG. 2( e) and the section between the point ‘d’ and the point ‘e’ of FIG. 3 illustrate that the movable shaft 30 and the movable body 40 move in the same manner as that described for the section between the point ‘b’ and the point ‘c.’
FIG. 2( f) and the section between the point ‘e’ and the point ‘f’ of FIG. 3 illustrate that the movable shaft 30 and the movable body 40 move in the same manner as that described for the section between the point ‘c’ and the point ‘d.’
As such, the movable body 40 is moved by the drive of the saw-tooth pulse wave input into the piezoelectric or electrostrictive substrate 10, and by the elasticity of the elastic body 20, as well as according to the law of inertia. Such displacement is continuously and repeatedly induced by repeating the process in which the repeated bending motion of the piezoelectric or electrostrictive substrate 10 forming a unimorph or bimorph structure, that is, a single substrate or double substrate structure, is transmitted to the movable shaft 30. The movable body 40 moves from the left end to the right end of the movable shaft 30 using this principle.
In the same principle, when the direction of the saw-tooth pulse of FIG. 3 is changed and displacement induced by the changed pulse is transmitted to the movable shaft 30, the direction of the motion of the movable body 40 changes. Thus, the movable body 40 can move from the right end to the left end of the movable shaft 30. As such, an exemplary motor may be provided based on the law of inertia.
Accordingly, according to an exemplary embodiment, there is provided a piezoelectric/electrostrictive linear motor which is reversibly and linearly moved by an ultrasonic pulse voltage applied thereto, and which has a structure capable of precisely controlling the position by varying the period of the applied voltage and allows simplified manufacturing process thereof. The piezoelectric/electrostrictive linear motor may be installed in, for example, a cell phone or PDA, etc., to drive, for example, its camera lens.
A piezoelectric/electrostrictive linear motor having the above-mentioned construction uses bending movement of a unimorph or bimorph including both an elastic body 20 and a piezoelectric or electrostrictive substrate 10 as its driving source, so that a movable body 40 moves along a movable shaft 30. Thus, a small piezoelectric/electrostrictive linear motor may be provided. The manufacturing process of the small piezoelectric/electrostrictive linear motor may also be simplified, and the motor may be easily practicable according to a basic principle and have superior characteristics over known motors. Furthermore, the small piezoelectric/electrostrictive linear motor may be advantageous in that its thrust is superior for its size, operation is speedy, and the drive is stable.
According to an aspect, a fundamental construction of a piezoelectric/electrostrictive linear motor includes a piezoelectric or electrostrictive substrate, a movable body, a movable shaft and an elastic body. While various types of piezoelectric/electrostrictive linear motors may be provided based on the fundamental construction, three exemplary linear motors will be explained below.
FIGS. 4, 5 and 6 show three exemplary piezoelectric/electrostrictive ultrasonic linear motors, that is, three exemplary piezoelectric/electrostrictive linear motors driven by an ultrasonic pulse voltage applied thereto.
FIG. 4 shows a first exemplary embodiment which includes a piezoelectric or electrostrictive substrate 10, an elastic body 20 and a movable body 40. The assembly of the piezoelectric or electrostrictive substrate 10 and the elastic body 20 forms a unimorph having a disk shape. The elastic body 20 is not limited to a specific material, so long as the material has a predetermined thickness and is able to efficiently transmit vibration from the piezoelectric or electrostrictive substrate 10 thereto. The elastic body 20 may be made of phosphor bronze. Where the movable shaft 30 is directly attached to the elastic body, a protrusion 35 may be provided to support the movable shaft. In the case of the unimorph having a single piezoelectric or electrostrictive substrate 10, as shown in FIG. 4, the piezoelectric or electrostrictive substrate 10 and the movable shaft 30 may be provided on opposite sides of the elastic body 20. Alternatively, both the piezoelectric or electrostrictive substrate and the movable shaft may be provided on the same side of the elastic body. Furthermore, when the movable shaft is mounted to the center of the assembly of the piezoelectric or electrostrictive substrate and the elastic body, maximum displacement may be induced. Therefore, this case may be most effective.
As shown in FIG. 4, the movable shaft 30 may be attached to a surface opposite another surface of the elastic body 20 to which the piezoelectric or electrostrictive substrate 10 is attached. Alternatively, as shown in FIG. 5, the movable shaft 30 may be attached to the same surface of the elastic body 20 to which the piezoelectric or electrostrictive substrate 10 is attached. In this case, the piezoelectric or electrostrictive substrate 10 may be attached to a region of the surface of the elastic body 20 other than a region of the surface of the elastic body 20 to which the movable shaft 30 is attached.
The piezoelectric or electrostrictive substrate 10 is polarized in a thickness direction. Furthermore, the piezoelectric or electrostrictive substrate 10 having the disk shape vibrates according to an input saw-tooth pulse wave in a direction from the outer diameter to the inner diameter or in a direction from the inner diameter to the outer diameter, thereby executing a unimorph bending movement.
In the first exemplary embodiment of FIG. 4, the piezoelectric or electrostrictive substrate 10 is attached to a surface of the elastic body 20. A coupling hole is formed at the center on an opposite surface of the elastic body 20 so that the movable shaft 30 is fitted into the coupling hole of the elastic body 20. The elastic body has an outer diameter larger than that of the piezoelectric or electrostrictive substrate 10 such that the elastic body is supported by a support surface. For example, a fixed edge 25 may be provided around the circumference of the elastic body 20 to fasten the linear motor to the support surface. The fixed edge 25 may serve to prevent the linear motor from undesirably moving due to the vibration of the piezoelectric or electrostrictive substrate 10.
The movable shaft 30 is several times lighter than a bimorph which is a double structure of the elastic body 20 coupled to the piezoelectric or electrostrictive substrate 10. The movable shaft 30 has a structure capable of efficiently transmitting vibration generated by the piezoelectric or electrostrictive substrate 10. Furthermore, the movable shaft 30 is manufactured such that the movable body 40 fitted over the movable shaft 30 may move along the movable shaft 30. For example, a hollow shaft is used as the movable shaft 30. Electrodes, which are provided on both surfaces of the piezoelectric or electrostrictive substrate 10, are connected to a saw-tooth pulse voltage source (U), so that a drive pulse is input through the electrodes.
FIG. 5 shows a second exemplary embodiment. A linear motor according to the second exemplary embodiment is a bimorph having two piezoelectric or electrostrictive substrates 10. Such structure is able to operate using reduced voltage, thus extending the lifetime of the linear motor. The piezoelectric or electrostrictive substrates 10 may be polarized in a thickness direction. Here, the polarization direction of the pair of piezoelectric or electrostrictive substrates 10 is appropriately adjusted such that generated vibration is able to reach the maximum value. Furthermore, an earth terminal is connected to the elastic body 20, so that, when a saw-tooth pulse is applied to upper and lower electrodes of the piezoelectric or electrostrictive substrates 10, the linear motor is actuated. In the second exemplary embodiment, the piezoelectric or electrostrictive substrate 10, which is placed at the same side as a movable shaft 30, may be attached to a region of the surface of the elastic body 20 other than a region of the surface of the elastic body 20 to which the movable shaft 30 is attached. Alternatively, the movable shaft 30 may be attached to an outer surface of the piezoelectric or electrostrictive substrate 10, not the elastic body 20.
FIG. 6 shows a third exemplary embodiment. In a linear motor according to the third exemplary embodiment, each of an elastic body 20 and a piezoelectric or electrostrictive substrate 10 has a rectangular plate shape, not a disk shape. This linear motor may be used in a place the length of one side of which is limited. In this embodiment, the linear motor is operated by the bending movement of a unimorph, which consists of the elastic body 20 and the piezoelectric or electrostrictive substrate 10 and has a rectangular plate shape and a size of a×b. The third embodiment may be also manufactured as the bimorph type shown in FIG. 5. In this case, the bimorph may have the same arrangement as that described for FIG. 6.
As such, the shape of both a piezoelectric or electrostrictive substrate and an elastic body may be changed such that the shape of the piezoelectric/electrostrictive ultrasonic linear motor is suitable for a particular device. Furthermore, the shape may be changed to various shapes other than the disclosed circular or rectangular shape.
FIG. 7 shows an example of a movable body 40 fitted over a movable shaft 30. When an input pulse is applied to a piezoelectric or electrostrictive substrate, the piezoelectric or electrostrictive substrate vibrates along with an elastic body. This vibration is transmitted to the movable shaft 30. Then, the movable body 40 moves along the movable shaft 30. As such, the vibration of the piezoelectric or electrostrictive substrate is converted into the linear motion of the movable body 40.
The structure of the movable body 40 of FIG. 7 is merely one example of the movable body. Therefore, the movable body 40 is not limited to a specific structure, so long as predetermined friction between the movable shaft 30 and the movable body 40 is maintained and the movable body 40 has a predetermined weight.
The movable body 40 is a metal body or substance having a predetermined weight. In addition, the movable body 40 is in close contact with the movable shaft 30 and is manufactured such that constant friction is maintained at a junction between the movable shaft 30 and the movable body 40. Furthermore, the movable body 40 may be a single body.
The movable body 40 is in close contact with the outer surface of the movable shaft 30 to cover at least part of the movable shaft 30, thus maintaining constant friction. For example, the movable body 40 has a structure capable of being fitted over the movable shaft 30. Furthermore, the movable body 40 must be manufactured such that it is applicable to the law of inertia using the frictional force and the predetermined weight.
As shown in FIG. 7, the movable body 40 includes a friction member 42 which is in close contact with the outer surface of the movable shaft 30, thus providing the constant friction. The movable body 40 further includes a weight 44 which is provided around an outer surface of the friction member 42 and covers at least part of the friction member 42. The weight 44 may be made of metal of a predetermined weight. The movable body 40 further includes an elastic shell 46 which is fitted over an outer surface of the weight 44 to reliably couple the weight 44 to the friction member 42.
Referring to FIG. 7, the movable body 40 may consist of two subcylindrical bodies, each of which has a friction member being in contact with the movable shaft 30 and a metal body that has a predetermined weight and is provided around an outer surface of the friction member. The subcylindrical bodies are held around the movable shaft by the elasticity of the elastic spring 46.
When the movable body 40 is held around the movable shaft 30 by an optimum force, superior performance of the linear motor is achieved. For this, the elastic spring 46 having a predetermined elasticity is fitted over the movable body 40, thus providing the optimum holding force by which the movable body 40 is held around the movable shaft 30.
For example, a nonmetallic member having a braking function is used as the friction member. The weight may be made of dense metal.
FIG. 8 shows a movement of the movable body 40 fitted over the movable shaft 30 of a linear motor (unimorph or bimorph) according to an exemplary embodiment. In this drawing, the movement of both the movable shaft 30 and the movable body 40, which depends on the movable shaft 30, by the bending movement of the unimorph or bimorph is illustrated. It is understood that the movable body 40 is moved by the displacement of the unimorph or bimorph.
A number of exemplary embodiments have been described above. Nevertheless, it will be understood that various modifications may be made. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the following claims.

Claims

1. A piezoelectric/electrostrictive linear motor, comprising:

a piezoelectric or electrostrictive substrate driven by a voltage applied thereto;

an elastic body, to one surface or each of both surfaces of which the piezoelectric or electrostrictive substrate is attached; and

a movable shaft coupled at an end thereof to the elastic body or the piezoelectric or electrostrictive substrate attached to the elastic body, the movable shaft being operated in conjunction with displacement of the piezoelectric or electrostrictive substrate, wherein a movable body provided with respect to the movable shaft is moved with respect to the movable shaft in response to the operation of the movable shaft.

2. The piezoelectric/electrostrictive linear motor of claim 1, wherein the movable shaft is moved in conjunction with bending displacement of the elastic body and the one or more piezoelectric or electrostrictive substrate attached thereto, to move the movable body.

3. The piezoelectric/electrostrictive linear motor of claim 2, wherein a surface area of a largest surface of the elastic body is greater than a surface area of a largest surface of the piezoelectric or electrostrictive substrate.

4. The piezoelectric/electrostrictive linear motor of claim 2, wherein a portion of the elastic body and/or the piezoelectric or electrostrictive substrate is fixed such that the movable shaft is moved in conjunction with bending displacement of the unfixed portion.

5. The piezoelectric/electrostrictive linear motor of claim 1, wherein the movable shaft is moved in conjunction with displacement of the piezoelectric or electrostrictive substrate between a first position and a second position, and the movable body is moved along with a movement of the movable shaft in response to the piezoelectric or electrostrictive substrate being displaced toward the second position and the movable body is not moved back to a position of the movable shaft in response to the piezoelectric or electrostrictive substrate being displaced toward the first position.

6. The piezoelectric/electrostrictive linear motor of claim 1, wherein the piezoelectric or electrostrictive substrate is polarized.

7. The piezoelectric/electrostrictive linear motor of claim 1, wherein the movable body is moved with respect to the movable shaft in response to vibration of the movable shaft.

8. The piezoelectric/electrostrictive linear motor of claim 1, wherein a weight of the movable body and a frictional force between the movable shaft and the movable body are provided so that the movable body is moved with respect to the movable shaft when the movable shaft vibrates in conjunction with the displacement of the piezoelectric or electrostrictive substrate.

9. The piezoelectric/electrostrictive linear motor of claim 1, wherein the movable body comprises: a friction member being in close contact with an outer surface of the movable shaft; a weight provided around an outer surface of the friction member; and an elastic shell fitted over an outer surface of the weight to hold both the friction member and the weight around the movable shaft, wherein the movable body is fitted over the movable shaft.

10. A method of driving a piezoelectric/electrostrictive linear motor, the motor having an elastic body to which at least one piezoelectric or electrostrictive substrate is attached and a movable shaft coupled to the elastic body or the piezoelectric or electrostrictive substrate attached to the elastic body, wherein a movable body provided with respect to the movable shaft is to be moved with respect the movable shaft, the method comprising:

the step (a) of applying a voltage, which varies from a first voltage to a second voltage, to the piezoelectric or electrostrictive substrate during a first period; and

the step (b) of applying a voltage, which varies from the second voltage to the first voltage, to the the piezoelectric or electrostrictive substrate during a second period after the step (a), wherein,

the movable body is moved along with a movement of the movable shaft in conjunction with displacement of the piezoelectric or electrostrictive substrate during the step (a) or step (b), to move with respect to the movable shaft.

11. The method of claim 10, wherein the step (a) and step (b) are repeated.

12. The method of claim 10, wherein the movable body is moved along with the movement of the movable shaft during one of the step (a) and step (b), and the movable body is not moved back to a position of the movable shaft during the other one of the step (a) and step (b).

13. The method of claim 10, wherein the movable shaft is moved in conjunction with bending displacement of the elastic body and the piezoelectric or electrostrictive substrate, the piezoelectric or electrostrictive substrate is displaced between a first position and a second position, and the movable body is moved along with the movement of the movable shaft in response to the piezoelectric or electrostrictive substrate being displaced toward the second position and the movable body is not moved back to a position of the movable shaft in response to the piezoelectric or electrostrictive substrate being displaced toward the first position

14. The method of claim 10, wherein the first period is longer than the second period.

15. The method of claim 10, wherein, during the second period, the movable body is moved along with the movement of the movable shaft, so that the movable body is moved along the movable shaft.

16. The method of claim 10, wherein the first period is shorter than the second period.

17. The method of claim 10, wherein, during the first period, the movable body is moved along with the movement of the movable shaft, so that the movable body is moved along the movable shaft.