Abstract:
A friction drive actuator, comprising: a vibration member which is configured to be driven to vibrate by expansion and contraction of a piezoelectric displacement portion which is included in the vibration member and driven by a driving signal; a sliding member which is in contact with the vibration member and is driven by the vibration member in a first direction with respect to the vibration member; a pressing member which causes the vibration member and the sliding member to come into a pressure contact therebetween; and a control member which is provided on each of the vibration member and the sliding member at a contact portion therebetween for controlling a relative movement of the sliding member with respect to the vibration member in a direction perpendicular to the first direction when the vibration member and the sliding member are pressedly contacted with each other by the pressing member.

Description:
This application claims priority on Japanese Patent Application No. 2007-048787 filed on Feb. 28, 2007, and on Japanese Patent Application No. 2008-005502 filed on Jan. 15, 2008, both in the Japanese Patent Office, the entire contents of which applications are hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to a friction drive actuator and more particularly to a friction drive actuator for causing a vibration member to make pressure contact with a sliding member to generate a relative movement. 
     BACKGROUND 
     Conventionally, use of a friction drive actuator for various moving devices has been tried. The friction drive actuator is generally comprised of a vibration member having a piezoelectric element which is an electromechanical energy conversion element and a sliding member for making contact with the vibration member in a pressurized state. The friction drive actuator is an actuator in which a relative movement between the vibration member and the sliding member in pressure contact with the vibration member is caused by an elliptical vibration (herein after, including a circular vibration) of a part of the vibration member, the elliptical vibration which is generated by inputting a drive signal into the piezoelectric element to expand and contract it. 
     The friction drive actuator is compact and excellent in silence, so that it is used as a drive mechanism for an electronic device such as an electronic camera, and in recent years, its applications have been spread more, and use thereof in a drive mechanism of a recording/reproducing head of an information recording apparatus such as a HDD and a DVD has been variously examined. 
     For example, there is known a vibration wave linear motor (a friction drive actuator) in which a vibration member is pressurized and held between two cylindrical guide shafts (sliding members), and due to an elliptical vibration generated in the drive contact portion of the vibration member, the vibration member and guide shafts make a relative movement in the axial direction (for example, refer to Unexamined Japanese Patent Application Publication No. 2005-57838). 
     Here, the schematic constitution of the vibration wave linear motor disclosed in Unexamined Japanese Patent Application Publication No. 2005-57838 will be explained by referring to  FIGS. 10   a ,  10   b .  FIG. 10   a  is a front sectional view of a vibration wave linear motor  46 , and  FIG. 10   b  is a cross sectional view along the line D-D′ in  FIG. 10   a.    
     On each of the upper and lower surfaces of a vibrator body  75 , provided is a connection type drive contact portion  93  in which a flat portion  92  and a drive contact portion  76  are unified with each other. Two upper and lower guide shafts  77  ( 77 - 1 ,  77 - 2 ) in contact with recessed portions  76   a  of the connection type drive contact portions  93  are supported by upright members  78 - 2  of support members  78 . The lower guide shaft  77 - 2  is pressed upwardly by a spiral spring  83 , thus a vibrator  70  is pressurized and held between the two guide shafts  77 . When AC voltages different in phase are applied to the vibrator body  75 , the vibrator body  75  generates a vibration wave, and an elliptical rotation vibration is generated in the drive contact portions  76 . By the elliptical rotation vibration, the vibrator  70  moves relatively to the two guide shafts  77  and support members  78  in the axial direction. By use of such a constitution, one part thereof is fixed, and the other part is connected to a driven member, thus the driven member can be driven to move. 
     Further, there is known a fine drive device (a friction drive actuator) for swinging a head arm (a sliding member) having a recording/reproducing head around a rotary shaft inserted through a rotation hole formed in the head arm, the drive device which is driven by an elliptical vibration generated in a vibration member in pressure contact with the head arm (for example, refer to Unexamined Japanese Patent Application Publication No. 2000-224876). 
     Further, there is known a rotary type ultrasonic actuator (a friction drive actuator) for rotating a rotor (a sliding member) born by ball bearings by a vibration member (for example, refer to Unexamined Japanese Patent Application Publication No. H06-78570). 
     Further, there is known an information recording/reproducing head drive device (a friction drive actuator) for swinging a head arm (a sliding member) around a V-shaped fulcrum formed in the head arm and supported by a wedge type support member by an elliptical vibration generated in a vibration member in pressure contact with the head arm (for example, refer to Unexamined Japanese Patent Application Publication No. 2001-222869). 
     On the other hand, in the information recording apparatus such as a HDD and a DVD, with the progress of higher recording density, the head drive mechanism is required to realize highly precise positioning of the head to the target position of a recording medium in submicron. Further, in correspondence with miniaturization and lower price of the information recording apparatus, further miniaturization and lower price are required for the drive mechanism. 
     In the vibration wave linear motor disclosed in Unexamined Japanese Patent Application Publication No. 2005-57838, as shown in  FIG. 10   b , the contact surfaces between the guide shafts  77  ( 77 - 1 ,  77 - 2 ) and the drive contact portions  76  are formed in a cylindrical shape with the same radius. However, when joining the two, unless the radii of the recessed portions  76   a  of the drive contact portions  76  are made larger than the radii of the guide shafts  77  ( 77 - 1 ,  77 - 2 ), and gaps are formed between the two, the two cannot be joined. Therefore, even if the two are processed highly precisely, gaps of microns are generated, and backlash is caused. 
     Further, the guide shaft  77 - 2  is supported by a bearing slotted hole  81  formed in the upright member  78 - 2  and is pressed up by the spiral spring  83 . However, the support member is required to have a fitting backlash of microns, and an inclination of the vibrator  70  with respect to the guide shaft  77 , which is equivalent to the fitting backlash, is generated and the relative position between the vibrator  70  and the guide shaft  77  fluctuates. 
     Therefore, in the vibration wave linear motor having such a constitution, due to various types of backlash of microns generated between the vibrator  70  and the guide shaft  77 , it is difficult to set highly precisely the relative position between the two in microns which is required for the information recording apparatus. 
     Further, in the fine drive device disclosed in Unexamined Japanese Patent Application Publication No. 2000-224876, although the mechanism constitution is not described in detail, the head arm has a bearing mechanism of the rotary shaft, so that it can be inferred easily that backlash is caused in the bearing section. Further, the vibration member is structured so as to incline also in a direction other than the pressing direction, and for example, the head arm may rotate in a slightly twisted direction with respect to the rotary shaft. Therefore, there is a possibility that the head section provided at the end of the head arm may collide with the recording surface of the disk. Further, the constitution having no bearing mechanism is disclosed, though even in these constitutions, by the out-of-roundness and abrasion condition of the guide member and a shift of the shaft center due to a dent caused by an impact load, it may be considered that the positioning is affected greatly. 
     Further, in the rotary type ultrasonic actuator disclosed in Unexamined Japanese Patent Application Publication No. H06-78570, the members such as the ball bearings for bearing the rotor are used, so that backlash between the balls and the inner and outer walls cannot be avoided. The backlash component in the direction of the rotary shaft is biased, though the backlash component in the radial direction cannot be biased. These gaps are ones in microns and influence greatly the positioning. Further, at time of drive start of the vibration member, the gaps are first biased and then the drive in a desired direction is started, so that a problem arises that the startup characteristic is influenced. Further, when a highly rigid load support member is structured by such a mechanism, there is a possibility that complication and high price of the device due to enlargement of the apparatus and an increase in the mechanical parts may be caused. 
     Further, in the information recording/reproducing head drive apparatus disclosed in Unexamined Japanese Patent Application Publication No. 2001-222869, due to the pressure contact of the vibration member, the compression pressure to the V-shaped fulcrum by the wedge type support member is increased, thus there is a possibility that the fulcrum may be abraded. As a result, the position of the head mounted on the end of the arm is changed. 
     SUMMARY 
     In view of the forgoing problems, an object of the present invention is to provide a friction drive actuator for realizing highly precise positioning without causing complication and high price. 
     In view of forgoing, one embodiment according to one aspect of the present invention is a friction drive actuator, comprising: 
     a vibration member which is configured to be driven to vibrate by expansion and contraction of a piezoelectric displacement portion which is included in the vibration member and driven by a driving signal; 
     a sliding member which is in contact with the vibration member and is driven by the vibration member in a first direction with respect to the vibration member; 
     a pressing member which causes the vibration member and the sliding member to come into a pressure contact therebetween; and 
     a control member which is provided on each of the vibration member and the sliding member at a contact portion therebetween for controlling a relative movement of the sliding member with respect to the vibration member in a direction perpendicular to the first direction and parallel to a surface of the sliding member when the vibration member and the sliding member are pressedly contacted with each other by the pressing member. 
     According to another aspect of the present invention, another embodiment is a friction drive actuator, comprising: 
     a vibration member which is configured to be driven to vibrate by expansion and contraction of a piezoelectric displacement portion which is included in the vibration member and driven by a driving signal; 
     a sliding member which is formed to be circular, disposed in pressure contact with the vibration member at an inner circumferential surface of the sliding member so as to be elastically deformed, and rotates in a first direction with respect to the vibration member when driven by the vibration member; and 
     a control portion which is provided on each of the vibration member and the sliding member at a contact portion therebetween for controlling a relative movement of the sliding member with respect to the vibration member in a direction perpendicular to the first direction and parallel to a surface of the sliding member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1   a ,  1   b  are entire schematic views of a friction drive actuator of Embodiment 1 of the present invention, 
         FIGS. 2   a ,  2   b ,  2   c  are external views showing the constitution of a vibration member of Embodiment 1, 
         FIGS. 3   a ,  3   b ,  3   c  are drawings showing the situation of a modification of the vibration member in the resonance mode of Embodiment 1, 
         FIGS. 4   a ,  4   b  are entire schematic views of a friction drive actuator of Modification 1 of Embodiment 1, 
         FIGS. 5   a ,  5   b  are entire schematic views of a friction drive actuator of Modification 2 of Embodiment 1, 
         FIGS. 6   a ,  6   b ,  6   c  are entire schematic views of the friction drive actuator of Embodiment 2 of the present invention, 
         FIGS. 7   a ,  7   b ,  7   c  are external views showing the constitution of the vibration member of Embodiment 2, 
         FIGS. 8   a ,  8   b  are entire schematic views of a friction drive actuator of Modification 1 of Embodiment 2, 
         FIGS. 9   a ,  9   b ,  9   c  are external views showing the constitution of the vibration member of Modification 1 of Embodiment 2, and 
         FIGS. 10   a ,  10   b  are entire schematic views of a conventional friction drive actuator. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the friction drive actuator relating to the present invention will be described with reference to the accompanying drawings. Further, although the present invention will be described on the basis of the embodiments drawn, the present invention is not limited there. 
     Embodiment 1 
     Firstly, the constitution of the friction drive actuator of Embodiment 1 will be described by referring to  FIGS. 1   a ,  1   b .  FIG. 1   a  is a front view showing the outline of the entire constitution of a friction drive actuator  1  and  FIG. 1   b  is a side view thereof. 
     The friction drive actuator  1 , as shown in  FIG. 1   a , includes a vibration member  10 , a sliding member  20 , and a pressing member  30 . 
     In the friction drive actuator  1 , a part of the vibration member  10  is made to move so as to make an elliptical orbit (including a circular orbit), that is, make an elliptical vibration (including a circular vibration) by inputting a drive signal into the vibration member  10  having a piezoelectric displacement element  101 , which will be described later, comprised of an electromechanical energy conversion element so as to permit the vibration member  10  to expand and contract. By doing this, the friction drive actuator permits the vibration member  10  and the sliding member  2  in contact therewith in the pressurized state to make a relative movement by frictional force. 
     The sliding member  20  is permitted to make pressure contact with the vibration member  10  by the pressing member  30  comprised of a coil spring  301 , a roller  302 , and a roller rotary shaft  303 . When the vibration member  10  is driven to make an elliptical vibration, the sliding member  20  is moved by the frictional force. When the rotational direction of the elliptical vibration is clockwise, the sliding member  20  moves to the right, and when it is counterclockwise, the sliding member  20  moves to the left. 
     The sliding member  20  is an elongated part with an almost rectangular cross section and made of a metal such as stainless steel which is inexpensive and easy to process. The surface thereof, to prevent abrasion with the vibration member  10 , is subject to the surface hardening treatment such as tempering or nitriding treatment. Ceramic coating such as CrN or TiCN may be applied. Further, by use of ceramics such as alumina or zirconia, the abrasion resistance can be improved more. Further, to prevent abrasion with the vibration member  10 , it is preferable that the surface of the contact portion of the sliding member  20  is smooth. 
     The constitution of the vibration member  10  is shown in  FIGS. 2   a ,  2   b ,  2   c .  FIG. 2   a  is a front view of the vibration member  10 , and  FIG. 2   b  is a side view thereof, and  FIG. 2   c  is a plan view thereof. 
     The vibration member  10 , as shown in  FIG. 2   a , includes the piezoelectric displacement portion  101  and a contact portion  102 . The piezoelectric displacement portion  101  has a rectangular shape comprised of the electromechanical energy conversion element such as a piezoelectric element and performs a resonance in the primary longitudinal (expansion and contraction) vibration mode and secondary bending vibration mode which will be described later. The piezoelectric displacement portion  101  is comprised of four displacement portions  101   a ,  101   b ,  101   c , and  101   d , and an inner electrode not shown is divided in a predetermined shape for each displacement portion. A predetermined voltage waveform is impressed to these electrodes, thus to hemispherical projections  102   a  and  102   b  formed on the concerned contact portion  102 , an elliptical vibration is excited. 
     Further, the shape of the vibration member  10  and the resonance modes used for driving are not limited to thereto, and an ordinary stationary wave vibration member whose drive force can be taken out from a plurality of places is usable. 
     Further, as an electromechanical energy conversion element (hereinafter, may be referred to as a displacement element), a laminated piezoelectric element made by alternately laminating a plurality of ceramic thin plates, such as a PZT, showing the piezoelectric characteristic and inner electrodes may be used, or a combination of a single layer of piezoelectric element and a metallic elastic body may be used. In the former case, by adding the displacement of each ceramic thin plate (a piezoelectric element of a single layer), the displacement of whole the displacement element is increased. In the latter case, by resonating the elastic body using the piezoelectric element as a drive source, a large displacement can be obtained. 
     As a material of the contact portion  102 , a preferable material is an ultra hard material which is made of tungsten carbide (WC) as a main material and has a high stable friction coefficient and an excellent abrasion resistance. Further, hard ceramics such as alumina or zirconia may be used, or a ferrous material the surface of which is hardened by the surface treatment such as heat treatment or nitriding treatment may be used. 
     Here, the elliptical vibration excited in the vibration member  10  having such a constitution will be described by referring to  FIGS. 3   a ,  3   b ,  3   c . The vibration member  10  is resonantly driven.  FIGS. 3   a ,  3   b ,  3   c  show the appearance of the deformation of the vibration member  10  in the intrinsic mode used for the resonance drive, and  FIG. 3   a  is a drawing showing the appearance of the vibration member  10  when not driven, and  FIG. 3   b  is a drawing showing the appearance of the deformation in the primary longitudinal (expansion and contraction) vibration mode, and  FIG. 3   c  is a drawing showing the appearance of the deformation in the secondary bending vibration mode. 
     In the primary longitudinal vibration mode, as shown in  FIG. 3   b , an expansion and contraction vibration is performed with a central part F 1  of the vibration member  10  as a node, and the projections  102   a  and  102   b  are displaced in the Y direction (longitudinal direction). In the secondary bending vibration mode, as shown in  FIG. 3   c , a secondary bending modification is performed with F 2  as a node, and the ends of the projections  102   a  and  102   b  are displaced in the P direction. Further, the appearance of the deformation of the vibration member  10  shown in  FIGS. 3   b  and  3   c  are exaggeratedly drawn in displacement amount for the purpose of explanation in the respective modes. 
     The primary longitudinal vibration mode is driven by impressing drive signals in the same phase at their resonance frequencies to the four displacement portions  101   a ,  101   b ,  101   c , and  101   d . The secondary bending vibration mode is drive by impressing a drive signal  1  in the same phase to the displacement portions  101   a  and  101   d  and by impressing a drive signal  2  having a predetermined phase difference from the phase of the drive signal  1  to the displacement portions  101   b  and  101   c  at their resonance frequencies. The shape of the vibration member  10  is formed so as to set both the resonance frequencies in the primary longitudinal vibration mode and secondary bending vibration mode within a predetermined range, and the vibration member  10  is driven with the two modes almost synchronized with each other, and an elliptical vibration D is thus excited in the projections  102   a  and  102   b , as shown in  FIG. 3   a . When the projections  102   a  and  102   b  are driven so as to make an elliptical orbit, the projections  102   a  and  102   b  make contact with the sliding member  20  in a certain range, and the sliding member  20  is driven in a predetermined direction by the frictional force acting between the projections  102   a  and  102   b  and the sliding member  20 . Further, when the phase shift direction of the drive signals is reversed, the rotational direction of the elliptical orbit of the projections  102   a  and  102   b  is reversed, and the moving direction of the sliding member  20  is reversed. 
     In the friction drive actuator  1  of this embodiment having such a constitution, the change in the relative position between the vibration member  10  and the sliding member  20  is controlled so as to uniquely set the relative position in a direction except a predetermined relative movement direction which is the first direction of the present invention. Hereinafter, the details will be explained. 
     As shown in  FIGS. 1   a  and  1   b , the vibration member  10  is engaged to a shaft  40   a  provided on a fixing stand  40  corresponding to the base of the present invention through a hole  101   h  formed in the neighborhood of the node F 2  of the secondary bending vibration and is positioned and fixed in the XY plane of the fixing stand  40 . The shaft  40   a  is preferably engaged to the hole  101   h  by close fit to eliminate backlash. Further, to prevent the vibration member  40  from vibrating laterally (in the X direction) of the fixing stand  40 , the vibration member  10  is engaged to a support member  40   b  provided on the fixing stand  40  for supporting the neighborhood of both ends of the node F 1  of the vibration member  10  in the primary longitudinal vibration mode. Further, although there needs to be a gap between the vibration member  10  and fixing stand  40  when they get engaged to each other, they are fixed by an adhesive to eliminate backlash due to the gap. Further, when the adhesion is difficult, the vibration member  10  is pressed by a plate spring  41  against the fixing stand  40  to eliminate backlash also in the Z direction. Further, the fixing of the vibration member  10  is preferably executed in the neighborhood of the node of the vibration as mentioned above so as to prevent the vibration member  10  from disturbing the vibration. Further, power is supplied to the vibration member  10  by using a flexible printed circuit board or a lead wire. 
     As shown in  FIGS. 1   a  and  1   b , the sliding member  20  is an elongated part having an almost rectangular cross section, and a groove portion  20   c  including a V-shaped elongated groove  20   a  is formed in the X direction (a predetermined relative movement direction) on the opposite surface to the vibration member  10 . The two hemispherical projections  102   a , which are provided on the contact portion  102  of the vibration member  10  and correspond to the projections of the present invention, make contact with the V-shaped elongated groove  20   a . The angle of the V-shaped portion of the V-shaped elongated groove  20   a  is preferably 90°, though it is not limited to it and is preferably from 60° to 120° or so. When the angle of the V-shaped portion is excessively small, the engagement of the V-shaped elongated groove  20   a  to the projections  102   a  becomes shallow, and the V-shaped elongated groove  20   a  makes contact with the projections  102   a  in the neighborhood of the edge thereof, thus the engagement is easy to be disengaged. On the other hand, when the angle of the V-shaped portion is excessively large, the contacts of the side wall of the V-shaped elongated groove  20   a  with the projections  102   a  get close each other, and the angle holding the contacts becomes smaller, so that the effect of positioning is lowered. 
     Further, on the surface of the sliding member  20  where the V-shaped elongated groove  20   a  is formed, a belt-shaped flat stripe portion such as a flat stripe portion  20   b  for controlling the swing of the sliding member  20  around the X-axis is provided in a belt shape in parallel to the V-shaped elongated groove  20   a . The projection  102   b  which is provided on the contact portion  102  of the vibration member  10  and corresponds to the projection of the present invention makes contact with the flat stripe portion  20   b.    
     It is preferable that the surfaces of the V-shaped elongated groove  20   a  and flat stripe portion  20   b  have smooth surfaces having small surface roughness, and the flatness thereof is highly precise. Further, as the distance between the V-shaped elongated groove  20   a  and the flat stripe portion  20   b  becomes longer, the control effect for the swing of the sliding member  20  around the X-axis is increased. Further, the projections  102   a  and  102   b , V-shaped elongated groove  20   a , and flat stripe portion  20   b  correspond to the control member of the present invention. 
     To keep the sliding member  20  and vibration member  10  in the prescribed contact state, the pressing member  30  permits the sliding member  20  and vibration member  10  to be in pressure contact with each other. The pressing force of the pressing member  30  is transferred by the roller  302 , and the coil spring  301  is provided between the roller rotary shaft  303  for bearing the roller  302  and a fixing member  50 . The working point of the pressing member  30  to the sliding member  20  is the contact portion between the roller  302  and the sliding member  20 , and it is preferable that this contact portion is located almost at the central part of the area, viewed in the Y direction, surrounded by all the contact points between the sliding member  20  and the vibration member  10 , that is, the projections  102   a  and  102   b , V-shaped elongated groove  20   a , and flat stripe portion  20   b . When the working point is outside the concerned area, the posture of the contact portion is easy to change due to a disturbance. 
     As mentioned above, the relative position between the sliding member  20  and the vibration member  10  is controlled by the four contact points between the V-shaped elongated groove  20   a  of the sliding member  20  and the two projections  102   a  of the vibration member  10 , so that the changes in the Y direction and Z direction, except the movement in the X direction (the first direction of the invention, or predetermined relative movement direction), are controlled. Further, the pressing force by the pressing member  30  permits the projection  102   b  of the vibration member  10  and the flat stripe portion  20   b  of the sliding member  20  to make pressure contact with each other, so that the swing of the sliding member  20  around the X-axis is controlled. As a result, the relative position between the sliding member  20  and the vibration member  10  is set uniquely except the movement in the X direction (the first direction, or predetermined relative movement direction). 
     As mentioned above, in the friction drive actuator  1  of Embodiment 1 of the present invention, by the pressing member  30  and control member (the two projections  102   a  and  102   b , groove portion  20   c , flat stripe portion  20   b ), the relative position between the vibration member  10  and the sliding member  20  is set uniquely except the predetermined relative movement direction. Since the relative position between the vibration member  10  and the sliding member  20  is set uniquely, the vibration member  10  is positioned, for example, to the cabinet of frame of the apparatus via the fixing stand  40 , thus the position of the sliding member  20  is set also at a predetermined position. As a result, a driven member such as the recording/reproducing head to be attached to the sliding member  20  can be positioned with high precision. 
     Further, there is no backlash at the contact position between the vibration member  10  and the sliding member  20 , so that from immediately after start of driving, the sliding member  20  is moved in a desired direction, and a drive mechanism having a rapid start response can be structured. Further, the conventional bearing members are not necessary, and the members concerned in driving are decreased, so that the designs intrinsic to the vibration drive such as keeping the resonance frequencies of these members away from the drive frequency are decreased, thus the apparatus can be designed easily. Further, since the bearing members are not necessary, enlargement and complication of the device are not caused, and the rigidity of the friction drive actuator  1  can be improved. Therefore, the frequency band under the servo control can be shifted toward the high frequency side, and the controllability can be enhanced. 
     Further, the contact points of by the control member between the vibration member  10  and the sliding member  20  all transfer the drive force, so that even if the friction coefficient at one contact point is changed due to local changes in the surface condition, the friction coefficients including the other contact points are averaged, thus stable driving force can be obtained. 
     Further, compared with the conventional friction drive actuator, the number of components is decreased, so that the device can be miniaturized. 
     Modification 1 of Embodiment 1 
     The constitution of the friction drive actuator  1  according to Modification 1 of Embodiment 1 is shown in FIGS.  4   a ,  4   b .  FIG. 4   a  is a front view showing the outline of the entire constitution of the friction drive actuator  1  and  FIG. 4   b  is a side view thereof. 
     In the friction drive actuator  1  according to Modification 1, as shown in  FIGS. 4   a  and  4   b , two semicylindrical convex rails  21   a  and  21   b  corresponding to the convex rails of the present invention are provided in parallel in the X direction (the first direction, or the predetermined relative movement direction) on the surface, of a sliding member  21 , opposite to a vibration member  11 . 
     On the other hand, in the vibration member  11 , a groove portion  112   c  having two V-shaped grooves  112   a  in contact with the convex rail  21   a  are provided with a predetermined interval in the X direction (the first direction, or the predetermined relative movement direction) Further, a flat stripe portion  112   b  in contact with the convex rail  21   b  is provided in a belt shape in parallel with the direction connecting the two V-shaped grooves  112   a.    
     Further, the length of the V-shaped grooves  112   a  in the X direction (the first direction, or the predetermined relative movement direction) is preferably shorter. When the length is longer, each contact between the V-shaped grooves  112   a  and the convex rail enter the line contact state, so that the relative movement of the sliding member  21  in the X direction (the first direction, the predetermined relative movement direction) may be affected depending on the processing precision. 
     The relative position between the sliding member  21  and the vibration member  11  is controlled at the four contact points between the convex rail  21   a  of the sliding member  21  and the two V-shaped grooves  112   a  of the vibration member  11 , so that the changes in the Y direction and Z direction except the movement in the X direction (the predetermined relative movement direction) are controlled. Further, the pressing force by the pressing member  30  permits the convex rail  21   b  of the sliding member  21  and the flat stripe portion  112   b  of the vibration member  11  to make pressure contact with each other, so that the swing of the sliding member  21  around the X-axis is controlled. As a result, the relative position between the sliding member  21  and the vibration member  11  is set uniquely except the movement in the X direction (the first direction, or the predetermined relative movement direction) and the same effect as that of Embodiment 1 can be obtained. 
     Modification 2 of Embodiment 1 
     The constitution of the friction drive actuator  1  according to Modification 2 of Embodiment 1 is shown in  FIGS. 5   a ,  5   b .  FIG. 5   a  is a front view showing the outline of the entire constitution of the friction drive actuator  1 , and  FIG. 5   b  is a side view thereof. 
     The friction drive actuator  1  according to Modification 2, as shown in  FIGS. 5   a  and  5   b , has two vibration members similar to the vibration member  10  of Embodiment 1 which is described by referring to  FIGS. 1   a ,  1   b  (vibration members  10 - 1  and  10 - 2 ). 
     One vibration member  10 - 1  is positioned, similarly to Embodiment 1, for example, on the cabinet or frame of the device via a fixing stand  40 - 1 . 
     A pressing member  31 , in replacement of the roller  302  of Embodiment 1, has the other vibration member  10 - 2  and permits the sliding member  20  to make pressure contact with the vibration member  10 - 1  by using the concerned vibration member  10 - 2 . 
     In the friction drive actuator  1  having such a constitution, the two vibration members (the vibration members  10 - 1  and  10 - 2 ) are caused to perform an elliptical vibration, thus driving force two times that of Embodiment 1 can be obtained. Further, it is a preferable constitution that the fixed vibration member  10 - 1  controls the relative position to the sliding member  20 , and the vibration member  10 - 2  performs only driving and pressurization but does not control the relative position. 
     Embodiment 2 
     The constitution of the friction drive actuator  1  according to Embodiment 2 will be explained by referring to  FIGS. 6   a ,  6   b ,  6   c .  FIG. 6   a  is a front view showing the outline of the entire constitution of the friction drive actuator  1 , and  FIG. 6   b  is a cross sectional view along the line A-A′ shown in  FIG. 6   a , and  FIG. 6   c  is a cross sectional view along the line A-B shown in  FIG. 6   a.    
     The friction drive actuator  1 , as shown in  FIG. 6   a , includes a vibration member  12 , a sliding member  22 , and the pressing member  30 . 
     In the friction drive actuator  1  according to Embodiment 1, the vibration member  10  and sliding member  20  make a straight relative movement, while in Embodiment 2, the circular ring-shaped sliding member  22  and the vibration member  12  arranged therein make a relative rotation. 
     The sliding member  22 , as shown in  FIG. 6   a , is formed in a circular ring shape, and as shown in  FIGS. 6   b  and  6   c , a groove portion  22   c  having a V-shaped elongated groove  22   a  is formed in a ring shape in a swing direction Q (a first direction of the present invention, or a predetermined relative movement direction) on the surface thereof facing the vibration member  12 . Further, on the surface where the V-shaped elongated groove  22   a  of the sliding member  22  is formed, a flat stripe portion  22   b  for controlling the swing of the sliding member  22  around the X-axis is provided in a belt shape in parallel with the V-shaped elongated groove  22   a.    
     On the other hand, the surface of the vibration member  12  facing the sliding member  22 , as shown in  FIGS. 7   a ,  7   b ,  7   c , is formed in a circular arc shape along the inner peripheral surface of the sliding member  22 . On the vibration member  12 , two hemispherical projections  122   a  in contact with the V-shaped elongated groove  22   a  are provided with a predetermined interval in the swing direction Q (the predetermined relative movement direction) Further, a projection  122   b  is provided in contact with the flat stripe portion  20   b . Further, it should be noted that  FIG. 7   a  is a front view of the vibration member  12 , and  FIG. 7   b  is a side view thereof, and  FIG. 7   c  is a plan view thereof. 
     The relative position between the sliding member  22  and the vibration member  12  is controlled by the four contact points between the V-shaped elongated groove  22   a  of the sliding member  22  and the two projections  122   a  of the vibration member  12 , so that the changes in the Y direction and Z direction are controlled except the movement in the rotating direction Q (the first direction, or the predetermined relative movement direction). Further, the pressing force by the pressing member  30  causes the projection  122   b  of the vibration member  12  and the flat stripe portion  22   b  of the sliding member  22  to make pressure contact with each other, so that the rotation of the sliding member  22  around the X-axis is controlled. As a result, the relative position between the sliding member  22  and the vibration member  12  is set uniquely except the movement in the rotating direction Q (the first direction, or the predetermined relative movement direction) and the same effect as that of Embodiment 1 can be obtained. 
     Modification 1 of Embodiment 2 
     The constitution of the friction drive actuator  1  according to Modification 1 of Embodiment 2 is shown in  FIGS. 8   a ,  8   b .  FIG. 8   a  is a front view showing the outline of the entire constitution of the friction drive actuator  1 , and  FIG. 8   b  is a cross sectional view along the line A-B shown in  FIG. 8   a.    
     The friction drive actuator  1  according to Modification 1, as shown in  FIG. 8   a , includes a vibration member  12  and sliding member  22 , and similarly to Embodiment 2, the circular ring-shaped sliding member  22  rotates relative to the vibration member  12  arranged therein. 
     In the friction drive actuator  1  according to Modification 1, the sliding member  22  itself has a pressing function instead of having a pressing member  30  comprised of a coil spring  301 , roller  302 , and roller rotary shaft  303  which are equipped in Embodiment 2. 
     In the sliding member  22 , before assembly with the vibration member  12 , the diameter (inside diameter) thereof is set smaller than the length of the vibration member  12 , and when it is assembled with the vibration member  12 , the sliding member  22  is deformed by the vibration member  12  so that the diameter thereof is increased (in an elliptical shape), and on each contact portion between the vibration member  12  and the sliding member  22 , the restoring force due to the elastic deformation of the sliding member  22  acts as pressing force. By the pressing force, the movement in the radial direction of the sliding member  22  with respect to the vibration member  12  is controlled without any backlash. 
     Further, the contact between the sliding member  22  and the vibration member  12  is limited at three portions, instead of all the circumferential area, so as to provide non-contact portions free of restriction by the vibration member  12 . Compared with the case that all the circumferential area is in contact with the vibration member  12 , the elastic deformation of the sliding member  22  is easy, so that the sliding member  22  is charged by the contact portions and the spring constant, when assuming the pressing force as one caused by the spring, is made smaller, compared with the case that all the circumferential area is in contact. In this arrangement, even if there are manufacturing errors in the dimensions of the vibration member  12  or sliding member  22 , changes in the pressing force with respect to the error amounts is limited small. Further, due to temperature changes, even if dimensional changes are caused in the vibration member  12  and sliding member  22 , changes in the pressing force is limited small, since the spring constant is small, thus the pressing force is stabilized. This arrangement reduces the error sensitivity of the pressing force with respect to the change of dimension, consequently, the drive performance is stabilized. 
     Further, the pressing force is generated by the elastic deformation of the sliding member  22  itself, so that an external pressing mechanism is not necessary, and it can contribute to simplification and miniaturization of the mechanism. Further, the adjustment step for the pressing force is not necessary, thus the productivity is improved. 
     As shown in  FIG. 8   a , the sliding member  22  is formed in a circular ring shape, and on the surface thereof opposite to the vibration member  12 , the V-shaped elongated groove  22   a  is formed in a ring shape in the swing direction Q (the first direction, or the predetermined relative movement direction) as shown in  FIG. 8   b.    
     On the other hand, the end face of the vibration member  12  opposite to the sliding member  22  is formed in a circular arc shape along the inner peripheral surface of the sliding member  22  as shown in  FIG. 9   a . On the side of one of the short sides of the vibration member  12 , the two hemispherical projections  122   a  are installed in contact with the V-shaped elongated groove  22   a  with a predetermined interval in the swing direction Q (the first direction, or the predetermined relative movement direction). Further, at the center of the other end face, one hemispherical projection  122   a  is installed in contact with the V-shaped elongated groove  22   a . Further,  FIG. 9   a  is a front view of the vibration member  12 , and  FIG. 9   b  is a side view thereof, and  FIG. 9   c  is a plan view thereof. 
     The relative position between the sliding member  22  and the vibration member  12  is controlled at the six contact points between the V-shaped elongated groove  22   a  provided in a groove portion  22   c  of the sliding member  22  and the three projections  122   a  of the vibration member  12 , so that the relative position is uniquely set, except the movement in the swing direction Q (the predetermined relative movement direction), and the same effect as that of Embodiment 1 can be obtained. 
     Further, in this embodiment, the V-shaped elongated groove  22   a  is installed in the sliding member  22 , and the three hemispherical projections  122   a  are installed on the vibration member  12  in contact with the V-shaped elongated groove  22   a , though they may be configured such that three V-shaped grooves are provided on the vibration member  12  and semicircular semicylindrical convex rails are installed on the sliding member  22  in contact with the three V-shaped grooves. 
     Further, the shape of the vibration member  12  is not limited to the rectangle, and it may be configured triangular so as to be in pressure contact with the sliding member  22  at the three apexes of the triangle. Also in this case, the same effect as that of Embodiment 1 can be obtained. 
     According to the embodiments of the present invention, the constitution is made such that there is provided a control member at each of a plurality of contact portions between the vibration member and the sliding member for controlling the relative movement between the vibration member and the sliding member in the direction perpendicular to a desired movement direction when the vibration member and sliding member are in pressure contact with each other by the pressing member. Namely, by the pressing member and the control member, the relative position between the vibration member and the sliding member is uniquely set except in the desired movement direction. Since the relative position between the vibration member and the sliding member can be uniquely set, the position of the sliding member is set at the predetermined position by positioning the vibration member on, for example, the cabinet or frame of the apparatus. As a result, a driven member to be attached to the sliding member such as the recording/reproducing head can be positioned with high precision. 
     Further, in the case of a circular ring shaped sliding member, the constitution is made such that there is provided a control member on each of a plurality of contact portions between the vibration member and the sliding member for controlling the relative movement between the vibration member and the sliding member in the direction perpendicular to a desired movement direction in the state that the circular ring-shaped sliding member is deformed elastically and the inner peripheral surface thereof is in pressure contact with the vibration member. Namely, the sliding member makes pressure contact with the vibration member due to the restoring force of the sliding member which is formed in a circular ring shape and is deformed in the radial direction. The pressing force is generated from the elastic deformation of the sliding member itself, so that an external pressing mechanism is not necessary and it can contribute to simplification and miniaturization of the mechanism. Further, the adjustment step for the pressing force is not necessary, thus the productivity can be improved.