SMALL PIEZOELECTRIC OR ELECTROSTRICTIVE LINEAR MOTOR
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.
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 FIELDThe 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.
BACKGROUNDSmall 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.
The dotted line of
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
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.
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 DESCRIPTIONThe 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
As described above with reference to
Although not shown in
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
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.
As shown in
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
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.
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.
The structure of the movable body 40 of
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
Referring to
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.
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.
Type: Application
Filed: Jan 22, 2009
Publication Date: May 21, 2009
Inventors: Vasiljef Piotr (Vilius), Bo Keun Kim (Seongnam), Seok Min Yoon (Seoul), Seong Yil Yoon (Seoul)
Application Number: 12/357,438
International Classification: H02N 2/04 (20060101);