Vibration driven motor

Abstract: A vibration driven motor can be driven with high torque at high rotation, and has a simple structure to be manufactured easily. The motor comprises a stator in a cylindrical form, a rotor disposed on the end surface of the stator, a first piezoelectric electro-mechanical converting element for generating torsional vibration around the axis of the stator, a second electro-mechanical converting element for generating longitudinal vibration in the axial direction of the stator, and a pressing member for pressing the rotor on the stator with pressure, wherein the stator consists of two semi-cylindrical members and the first or second piezoelectric element is one or more plate-like members sandwiched by the semi-cylindrical members of the stator.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a vibration driven motor which uses longitudinal vibration and torsional vibration. Related Background Art Fig. 13 is a perspective view showing a conventional example of a vibration driven motor of a longitudinal/torsional vibration type. In conventional vibration driven motors of this type, a stator 101 has a piezoelectric element 104 for torsional vibration sandwiched between two cylindrical vibration elements 102 and 103. Above the vibration element 103, a piezoelectric element 105 for longitudinal vibration is disposed. The piezoelectric element 104 for torsional vibration is polarized in the circumferential direction, and the piezoelectric element 105 for longitudinal vibration is polarized in the direction of thickness. Further, a rotor 106 is disposed above the piezoelectric element 105 for longitudinal vibration. The vibration elements 102 and 103 and the piezoelectric elements 104 and 105 which constitute the stator 101 are fixed to a shaft 107 (threadably engaged with a screw portion of the shaft 107). The rotor 106 is rotatably arranged on the shaft 107 through a ball bearing 108. The tip end of the shaft 107 is threadably engaged with a nut 110 through a spring 109, and the rotor 106 is brought into contact by pressure with the stator 101. The piezoelectric element 104 for torsional vibration and the piezoelectric element 105 for longitudinal vibration are driven by a phase control of a voltage having the single frequency oscillated from an oscillator 111 by a phase shifter 112. A mechanical displacement for rotating the rotor 106 is applied to the piezoelectric element 104 for torsional vibration. The piezoelectric element 105 for longitudinal vibration plays a role of converting the vibration into movement to one direction by synchronizing the frictional force working between the stator 101 and the rotor 106 with a period of the torsional vibration caused by the piezoelectric element 104 to fluctuate said frictional force periodically. Fig. 14 is a perspective view showing a developed state of the stator of the vibration driven motor of the prior art. Since the piezoelectric element 104 for torsional vibration is required to be polarized in the circumferential direction, a piezoelectric material thereof is once divided into six to eight fan-shaped pieces, as shown in Fig. 14. After being polarized, the pieces are assembled to a ring-shaped part for the second time. Note that a reference numeral 104a denotes an electrode. However, in the conventional vibration driven motor mentioned above, it is difficult to obtain a precision in shape when the piezoelectric element for torsional vibration is assembled in the ring form. On the other hand, each of the pieces of the piezoelectric elements for longitudinal vibration and torsional vibration is substantially equal to or smaller than a sectional piece of the stator. It is required to make holes at the central portions of the piezoelectric elements in order to pass the shaft therethrough. For this reason, the pieces of the piezoelectric elements become even smaller, so that it is difficult to attain high torque and high rotation for the motor. SUMMARY OF THE INVENTION It would be beneficial to provide a vibration driven motor which can solve the above-mentioned problems, can be driven at high rotation, and has a simple structure to be easily manufactured. According to the present invention, there is provided a vibration driven motor comprising: a bar-shaped stator assembly including a vibration element having a plurality of bar-shaped vibration members, and an electro-mechanical converting device disposed in contact with said vibration members; a relative moving element disposed on an end face of said bar-shaped stator assembly; and a pressing member for pressing said relative moving element against said vibration element; wherein said electro-mechanical converting device includes a first electro-mechanical converting element for generating a torsional vibration in said vibration element around an axis of said vibration element, and a second electro-mechanical converting element for generating a longitudinal vibration in said vibration element in an axial direction of said vibration element; and said first electro-mechanical converting element includes at least one plate-shaped sandwiched by two of said vibration members, and facing surfaces of said plate-shaped member and said two vibration members are substantially orthogonal to said end face of said bar-shaped stator assembly. It is possible to provide a shaft to be inserted through substantially the center of said vibration element, and to insert this shaft to said vibration element in a not-passing-through state to project it only from one end of the vibration element so as to rotatably insert said relative moving element in this projecting part. Also, both said bar-shaped stator assembly and said bar-shaped vibration members may be formed in a rectangular pillar shape. The bar-shaped stator assembly may be formed in a cylindrical shape with three bar-shaped vibration members, and may also be formed in a cylindrical shape with four bar-shaped vibration members. It is also possible to form said bar-shaped stator assembly in a quadrangular shape with four bar-shaped vibration members. According to an embodiment of the present invention, the first and second electro-mechanical converting elements are plate-like members sandwiched between bar-shaped vibration members each constituting a vibration element so that assembly is very easy. Further, if the second electro-mechanical converting element is disposed in the axial direction on the outer peripheral side of said vibration element, assembly becomes easier. Since the plate-like member is used as the first electro-mechanical converting element, it is possible to reduce the cost of the electro-mechanical converting element. Also, since each electro-mechanical converting element can be arranged to have a large area, it is possible to realize a high-rotating motor with high torque. When the bar-shaped stator assembly is formed in a rectangular pillar shape, only a plane processing is required to manufacture the vibration element, which results in easy processing of the vibration element and is advantageous in term of mass production. Also, since only the plane processing is required, it is easy to improve the precision in processing of the bonding face of the piezoelectric element which requires flatness. Furthermore, if the number of parts constituting the vibration element is increased, the area of the electro-mechanical converting elements in contact with the vibration element becomes larger. As a result, a force for generating vibration by the electro-mechanical converting elements becomes greater so that it is possible to increase an output of the motor. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view for showing a first embodiment of the vibration driven motor according to the present invention in its developed state; Fig. 2 is a perspective view for showing the vibration driven motor of Fig. 1 in its assembled state; Figs. 3A to 3C are views for showing arrangements of piezoelectric elements of the vibration motor according to the first embodiment; Figs. 4A and 4B are views for showing a direction of polarization and an arrangement of an electrode of the piezoelectric element (for torsional vibration) used in the vibration motor according to the present embodiment, and a deformation upon voltage application thereof; Figs. 5A and 5B are views for showing a direction of polarization and an arrangement of an electrode of the piezoelectric element (for longitudinal vibration) used in the vibration motor according to the present embodiment, and a deformation upon voltage application thereof; Figs. 6A and 6B are charts for showing voltage wave forms to be applied to the piezoelectric elements of the vibration motor according to the present embodiment; Fig. 7 is a perspective view for showing a second embodiment of the vibration driven motor according to the present invention in its developed state; Fig. 8 is a perspective view for showing a third embodiment of the vibration driven motor according to the present invention in its developed state; Fig. 9 is a perspective view for showing a fourth embodiment of the vibration driven motor according to the present invention in its developed state; Fig. 10 is a view for showing an arrangement of the piezoelectric elements of the vibration motor in which a stator is formed of three bar-shaped members according to a fifth embodiment; Fig. 11 is a view for showing an arrangement of the piezoelectric elements of the vibration motor in which the stator is formed of four bar-shaped members according to a fifth embodiment; Fig. 12 is a view for showing an arrangement of the piezoelectric elements of the vibration motor in which the stator of Fig. 11 is formed in a rectangular pillar shape; Fig. 13 is a perspective view for showing a vibration driven motor of a longitudinal/torsional vibration type according to the prior art; and Fig. 14 is a perspective view for showing a rotor of the vibration driven motor of the prior art in its developed state. DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] Embodiments of the present invention will be described more fully in the following, with reference to the drawings, etc. Fig. 1 is a perspective view showing the first embodiment of the vibration driven motor according to the present invention in its developed state, while Fig. 2 is a perspective view showing the vibration driven motor of Fig. 1 in its assembled state. In the first embodiment, a stator 1 has four plate-like piezoelectric elements 4 and 5 sandwiched between semi-cylindrical members 2 and 3 (arrangement of the piezoelectric elements will be described with reference to Figs. 3A to 3C), and a shaft 7 is inserted through the center of the stator 1. A rotor 6 is rotatably inserted into the shaft 7. On one side of the shaft 7, there are formed two projections 7a in the axial direction of the outer periphery, and a screw portion 7b is formed on the other side thereof. On the semi-cylindrical members 2 and 3, grooves 2a and 3a to which the projections 7a of the shaft 7 are fitted are formed in parallel with the central axis of the rotor 1. Also on the piezoelectric elements 4 and 5, cut-away portions 4a and 5a are formed at positions into which the projection 7a of the shaft 7 is inserted. Note that since the shaft 7 is in contact with the cut-away portions 4a and 5a of the piezoelectric elements, a molded portion 7d may be formed on the side surface thereof. On the semi-cylindrical members 2 and 3, bolt halls 2b and 3b are also formed in a direction perpendicular to the central axis of the stator 1. These semi-cylindrical members 2 and 3 sandwich the piezoelectric elements 4 and 5 and are fastened to be fixed by a bolt 13 and a nut 14 in the state in which the shaft 7 is fitted. The rotor 6 is inserted into the shaft 7 to be in contact with the end of the stator 1. However, in this embodiment, a sliding member 15 made of PPS or the like is inserted therebetween. Moreover, a sliding member 16, a spring 9 and a washer 17 are inserted into the shaft 7 in the named order on the opposite side of the rotor 6, and are fastened by a nut 10, thereby pressing the rotor 6 on the stator 1 with pressure. Figs. 3A to 3C are views showing arrangements of piezoelectric elements of the vibration motor according to the first embodiment. The piezoelectric element 4 is a device for torsional vibration, while the piezoelectric element 5 is a device for longitudinal vibration. Two of the piezoelectric element 4 are arranged in the upper left part of Fig. 3A and the other two in the lower right part. Two of the piezoelectric element 5 are arranged in the upper right part of Fig. 3A and the other two in the lower left part. An electrode 4b is disposed between the two piezoelectric elements 4, and an electrode 5b is disposed between the two piezoelectric elements 5. The electrodes 4b and 5b are formed by metallic foil such as phosphor bronze, and are bonded and fixed to the piezoelectric elements 4 and 5 or fastened and fixed to the bolt 13 and the nut 14. A portion between the piezoelectric elements 4 and 5 and the semi-cylindrical members 2 and 3 is grounded. A portion between the piezoelectric element 4 and the piezoelectric element 5 is also grounded via a grounding electrode. Fig. 3A shows a case in which the thickness of the piezoelectric element 4 for torsional vibration is different from that of the piezoelectric element 5 for longitudinal vibration. Fig. 3B shows a case in which the both thicknesses are equal to each other. The case in Fig. 3A is advantageous in that a large amplitude of the torsional vibration can be obtained. Fig. 3C shows a direction of polarization of the piezoelectric element 4 for torsional vibration and that of the piezoelectric element 5 for longitudinal vibration. The piezoelectric element 4 for torsional vibration is polarized in the axial direction of the motor and the piezoelectric element 5 for longitudinal vibration is polarized in the direction of thickness of the element. Figs. 4A and 4B and Figs. 5A and 5B are views showing a direction of polarization and an arrangement of electrodes of the piezoelectric elements used in the vibration motor according to the present embodiment, and deformation upon voltage application thereof. The piezoelectric element 4 for torsional vibration is polarized in the direction of length of the flat plane, as shown in Fig. 4A. When voltage is applied by use of the electrode of Fig. 4A, the stator 1 can be torsionally vibrated by use of the shearing deformation, as shown in Fig. 4B. The piezoelectric element 5 for longitudinal vibration is polarized in the direction of thickness of the flat plane, as shown in Fig. 5A. When voltage is applied by use of the electrode of Fig. 5A, the piezoelectric element is elongated and deformed, as shown in Fig. 5B. The stator 1 can be longitudinally vibrated by use of this deformation of the piezoelectric element 5. In order to drive the motor with efficiency, it is desirable to make the oscillation frequency of the torsional vibration of the motor substantially coincident with that of the longitudinal vibration so as to enlarge an amplitude of the rotational displacement and an amplitude of the longitudinal vibration simultaneously. In order to make these oscillation frequencies substantially the same, it is required to obtain the optimal condition by varying a material and a shape of the stator 1, a material and a shape of the rotor 6, a material and a shape of the sliding members 15 and 16, a pressing force, and the like. Next, a timing of the torsional vibration and that of the longitudinal vibration will be described. As shown in Figs. 6A and 6B, since a displacement of the piezoelectric element 5 for longitudinal vibration is the positive direction (the direction in which the stator 1 and the rotor 6 are brought into contact) when a rotational displacement of the piezoelectric element 4 for torsional vibration is the positive direction, the torsional vibration of the stator 1 is transmitted to the rotor 6 to rotate it in the positive direction. Since a displacement of the piezoelectric element 5 for longitudinal vibration is the negative direction (the direction in which the stator 1 is separated away from the rotor 6) when a rotational displacement of the piezoelectric element 4 for torsional vibration is the negative direction, the torsional vibration of the stator 1 is not transmitted to the rotor 6 and the rotor does not rotate. By repeating this operation, the rotor 6 is rotated in a predetermined direction. In order to obtain the torsional vibration and the longitudinal vibration as mentioned above, an alternating voltage having a phase shifted by about 90° is applied to the piezoelectric element 4 for torsional vibration and the piezoelectric element 5 for longitudinal vibration. It is possible to improve the torque, the number of rotations, and the efficiency of the motor by adjusting the phase difference and selecting the optimal value. The above-mentioned phase difference can be changed from 90° to -90° by reversing the rotational direction of the motor. By this change, the direction of the torsional vibration to be transmitted to the rotor 6 is reversed to make a reverse rotation. [Second Embodiment] Fig. 7 is a perspective view showing the second embodiment of the vibration driven motor according to the present invention in its developed state. In the embodiment described below, portions performing the same functions as those in the foregoing first embodiment are given the same referential numbers, and description thereof will be omitted. In the second embodiment, the piezoelectric element 4 for torsional vibration is sandwiched between semi-cylindrical members 2-1 and 3-1. However, the piezoelectric element 5 for longitudinal vibration is disposed on molded portions 2-1a and 3-1a which are formed in the axial direction of the outer periphery of the semi-cylindrical members 2-1 and 3-1. Further, the semi-cylindrical members 2-1 and 3-1 and a shaft 7-1 are connected to each other by spring portions 2c, 3c and 7c. In this case, it is preferable to form the spring portions 2c and 3c after fastening the semi-cylindrical members 2-1 and 3-1 by the bolt 13 and the nut 14. Other structures and operations are substantially the same as those in the first embodiment. [Third Embodiment] Fig. 8 is a perspective view of a stator used in the third embodiment of the vibration driven motor according to the present invention. The third embodiment is different from the first embodiment only in that the shape of the stator is an angular pillar. Other structures and operations are substantially the same as those in the first embodiment. Therefore, portions performing the same functions as those in the foregoing first embodiment are given the same referential numbers, and description thereof will be omitted. In this third embodiment, the stator is divided into angular pillar members 2-2 and 3-2. For this reason, the stator can be produced only by conducting a plane processing, whereby the stator can be easily processed, which is advantageous in terms of a mass production. Since the stator can be produced only by the plane processing, it becomes easy to improve a precision in processing a bonding surface of the piezoelectric element which requires the flatness. [Fourth Embodiment] Fig. 9 is a perspective view of a stator used in the fourth embodiment of the vibration driven motor according to the present invention. The fourth embodiment is different from the second embodiment only in that the shape of the stator is an angular pillar. Other structures and operations are substantially the same as those in the second embodiment. Therefore, portions performing the same functions as those in the foregoing second embodiment are given the same referential numbers, and description thereof will be omitted. In this fourth embodiment, the stator is divided into angular pillar members 2-3 and 3-3. For this reason, the stator can be produced only by conducting the plane processing, whereby the stator can be easily processed, which is advantageous in terms of a mass production. Since the stator can be produced only by the plane processing, it becomes easy to improve a precision in processing a bonding surface of the piezoelectric element which requires the flatness. Further, since the piezoelectric element for longitudinal vibration is disposed on the outer periphery of the stator, the assembling becomes easier. [Fifth Embodiment] Figs. 10, 11 and 12 are views showing arrangements of piezoelectric elements of a stator used in the fifth embodiment of the vibration driven motor according to the present invention. In the fifth embodiment, the stator is constituted by three or more components. Other structures and operations are substantially the same as those in the first embodiment. Therefore, portions performing the same functions as those in the foregoing first embodiment are given the same referential numbers, and description thereof will be omitted. In Fig. 10, the stator 18 is constituted by combining three bar-shaped members 18a to 18c each of which has substantially a fan-shaped cross section. In this case, the piezoelectric elements 4, 5 and the shaft 7-1 are preferably fixed by bonding. In Fig. 11, the stator 19 is constituted by combining four bar-shaped members 19a to 19d each of which has substantially a quarter-circular cross section. In Fig. 12, the stator 20 is constituted by combining four bar-shaped members 20a to 20d and arranged to have a rectangular form. In the fifth embodiment, since the area of each of the piezoelectric elements which is in contact with the stator becomes larger, the force for generating the vibration by the piezoelectric elements becomes greater. For this reason, an output of the motor can be increased. Note that, in the fifth embodiment, like in the second or fourth embodiment, the piezoelectric element for longitudinal vibration may be disposed on the outer periphery of the stator. The present invention is not limited to the embodiments described above, but various variations or modifications can be feasible. For example, the foregoing embodiments use piezoelectric elements as electro-mechanical converting elements for converting the electric energy into mechanical energy. However, electrostrictive elements may be used instead. As fully described above, according to the present invention, assembling of the vibration driven motor becomes very easy. Further, since plate-like members are used as the electro-mechanical converting elements, the cost for the electro-mechanical converting elements can be reduced. Further, since the electro-mechanical converting elements can be arranged to have a large area, a high torque vibration driven motor at high rotation can be realized.

Claims: A vibration driven motor comprising: a bar-shaped stator assembly (1) including a vibration element having a plurality of bar-shaped vibration members (2, 3, 18a-c, 19a-d, 20a-d), and an electro-mechanical converting device disposed in contact with said vibration members; a relative moving element (6) disposed on an end face of said bar-shaped stator assembly; and a pressing member (9) for pressing said relative moving element against said vibration element; wherein said electro-mechanical converting device includes a first electro-mechanical converting element (4) for generating a torsional vibration in said vibration element around an axis of said vibration element, and a second electro-mechanical converting element (5) for generating a longitudinal vibration in said vibration element in an axial direction of said vibration element; and said first electro-mechanical converting element includes at least one plate-shaped member (4) sandwiched by two of said vibration members, and facing surfaces of said plate-shaped member and said two vibration members are substantially orthogonal to said end face of said bar-shaped stator assembly. A vibration driven motor according to claim 1, wherein said second electro-mechanical converting element includes at least one plate-shaped member (5) sandwiched by two of said vibration members, and facing surfaces of said plate-shaped member of said second electro-mechanical converting element and said two vibration members are substantially orthogonal to said end face of said bar-shaped stator assembly. A vibration driven motor according to claim 1, wherein said second electro-mechanical converting element includes at least one plate-shaped member (5) disposed on an outer surface of one of said plurality of vibration members, and said outer surface of said one vibration member and a facing surface of said plate-shaped member of said second electro-mechanical converting element are substantially orthogonal to said end face of said bar-shaped stator assembly. A vibration driven motor according to claim 2, said bar-shaped stator assembly being shaped cylindrically and including a vibration element having two substantially semi-cylindrical vibration members (2, 3), and wherein said first and second electro-mechanical converting elements each include at least one plate-shaped member (4, 5) sandwiched between flat portions of said vibration members. A vibration driven motor according to claim 3, wherein said bar-shaped stator assembly being shaped cylindrically and including a vibration element having two substantially semi-cylindrical vibration members (2, 3), and said first electro-mechanical converting elements includes at least one plate-shaped member sandwiched between flat portions of said vibration members. A vibration driven motor according to claim 2 or 3, further comprising a shaft (7) inserted into said vibration element substantially along the axis of said vibration element, so as not to pass through said vibration element and project from only one end of said vibration element, and wherein said relative moving element is rotatably disposed on a projecting portion of said shaft. A vibration driven motor according to one of claims 2, 3 or 6, wherein said bar shaped stator assembly and said vibration members are of rectangular pillar shape. A vibration driven motor according to any preceding claim, wherein said vibration element has a drive surface substantially orthogonal to said axial direction and which transmits drive forces created by said torsional vibration and said longitudinal vibration to said relative moving element; and said torsional vibration is generated by shearing-deformation of said first electro-mechanical converting element in a direction substantially orthogonal to said drive surface, and said longitudinal vibration is generated by elongation deformation of said second electro-mechanical converting element in a direction substantially orthogonal to said drive surface. A vibration driven motor according to any preceding claim, wherein said first electro-mechanical converting element and said second electro-mechanical converting element are bonded to said vibration element, and the bonding surface therebetween is disposed substantially in parallel to the axial direction of said vibration element. A vibration driven motor according to claim 1, wherein said first electro-mechanical converting element includes first plate-like members (4) and said second electro-mechanical converting element includes second plate-like members (5), and said first and second plate-like members are divided into an arrangement having two groups disposed on opposite sides of an axial plane of said vibration element, respectively, each groups being constituted by a laminate of at least one first plate-like member (4) and at least one second plate-like member (5) and being sandwiched between opposed surfaces of a pair of said vibration members, which surfaces are substantially parallel to the axis of said vibration element; and an order of lamination along a direction perpendicular to the axis of said vibration element in said axial plane is different in said two groups. A vibration driven motor according to claim 1, wherein said bar-shaped stator assembly includes a connecting member (13) connecting said vibration members to each other in a direction perpendicular to an axis of said vibration element, such that facing surfaces of said electro-mechanical converting member and said vibration members are substantially orthogonal to said end face of said bar-shaped stator assembly. A vibration driven motor according to claim 1, wherein said bar-shaped stator assembly is cylindrical and said vibration element has only three of said vibration members (18a-c). A vibration driven motor according to claim 1, wherein said bar-shaped stator assembly is cylindrical and said vibration element has only four of said vibration members (19a-d). A vibration driven motor according to claim 1, wherein said bar-shaped stator assembly is quadrangular pillar shape and has only four of said vibration members (20a-d) . A vibration driven motor according to claim 1, wherein: said first electro-mechanical converting element (4) generates torsional vibration by applying a first alternating voltage (T) and said second electro-mechanical converting element (4) generates a longitudinal vibration by applying a second alternating voltage (L) of different phase than said first alternating voltage; each of said first and second electro-mechanical converting elements (4, 5) has a two-layered structure including two plate-like electro-mechanical converting members laminated together and sandwiched by two of said plurality of bar-shaped vibration members in a direction transverse to an axis of two vibration members; and said first alternative voltage is applied between one of said vibration members and an electrode disposed between the plate-like electro-mechanical converting members of said first electro-mechanical converting element.

Inventors: ASHIZAWA TAKATOSHI, OKAZAKI MITSUHIRO, SUGAYA ISAO, TAKAGI TADAO, TOMIKAWA YOSHIRO, ASHIZAWA, TAKATOSHI, OKAZAKI, MITSUHIRO, SUGAYA, ISAO, TAKAGI, TADAO, TOMIKAWA, YOSHIRO
Applicants: NIPPON KOGAKU KK, NIKON CORPORATION
Application year: 1995
Main classification: H01L41
IPC codes: H02N2, H01L41