Patent Publication Number: US-2007096601-A1

Title: Drive unit

Description:
RELATED APPLICATION  
      This application is based on Japanese Patent Application No. 2005-318145, the content of which is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      The present invention relates to drive units, more particularly, to a drive unit which uses an electromechanical conversion element such as a piezoelectric element and which is suitably used for, for example, lens drive or precision stage drive.  
      Conventionally, there has been known such a drive unit  60  as shown in  FIG. 6 . This drive unit  60  is composed of a cylindrical-shaped weight  62  to be fixed to an immovable part of a device into which the drive unit  60  is to be incorporated, a piezoelectric element (electromechanical conversion element)  64  which is cylindrical-shaped as an example and of which one end in its expansion/contraction direction is fixed to the weight  62 , for example, by adhesion, a drive friction member  66  which is a cylindrical bar-shaped member as an example and which is to be fixed to the other end of the piezoelectric element  64  in its expansion/contraction direction, for example, by adhesion, and a movable member  68  which is to be fitted to the drive friction member  66  by frictional force.  
      The movable member  68  includes a holder  72 , which is a resin molded article, for holding a lens  70  which is an optical member. The holder  72  is so designed that the drive friction member  66  is slidably accepted into a generally V-shaped groove portion  74  formed in its side portion.  
      In the drive friction member  66 , a sliding friction member  76  formed from, for example, an SUS plate is placed in contact at a portion where the drive friction member  66  is accepted into the groove portion  74  of the holder  72 . The sliding friction member  76  is composed of a curved portion  78  curved in close contact along an outer circumferential surface of the drive friction member  66 , and rectangular-shaped protruding portions  80  protrusively provided on both sides of the curved portion  78 , respectively. As the protruding portions  80  fit into recessed portions, respectively, formed on both sides of the holder  72  with the groove portion  74  interposed therebetween, the sliding friction member  76  is positioned with respect to the holder  72 .  
      The sliding friction member  76  is pressed by a leaf spring (press member)  82  bent into an L shape. An end portion of the leaf spring  82  is fixed to the holder  72  by a screw  84 . By biasing force of the leaf spring  82 , the drive friction member  66  is pressed and sandwiched by the groove portion  74  of the holder  72  and the curved portion  78  of the sliding friction member  76 , so that the movable member  68  is frictionally fitted to the drive friction member  66 . It is noted that the means for mounting the leaf spring  82  to the holder  72  is not limited to screwing, and the leaf spring  82  may be fitted and mounted by, for example, snapping.  
      Next, operation of the drive unit  60  having the above-described construction is explained.  
      As a voltage is applied from a drive circuit not shown in figures to the piezoelectric element  64 , the piezoelectric element  64  vibrates in expansion and contraction in the axial direction thereof. For instance, when a pulse voltage having a steep rise and a gentle fall is applied, the piezoelectric element  64  steeply extends and then contracts slowly. This expansion-and-contraction operation is transferred to the drive friction member  66 , by which the drive friction member  66  is steeply moved to return to its original position. When the drive friction member  66  steeply moves, the movable member  68  is inclined to stay in situ by the inertia force of the movable member  68 , giving rise to a slide between the groove portion  74  of the holder  72  and the drive friction member  66 . Then, when the drive friction member  66  returns to the original position slowly, the movable member  68  moves together with the drive friction member  66  without occurrence of the slide. By repetition of such expanding/contracting vibrations, the movable member  68  moves to approach the piezoelectric element  64 .  
      In a principle converse to the above, when a pulse voltage having a gentle rise and a steep fall as an example is applied to the piezoelectric element  64 , the movable member  68  moves to go away from the piezoelectric element  64 .  
      It is to be noted that JP H8-149860 A would be recited as an exemplary prior art document which relates to the present invention.  
      For assembly of the conventional drive unit  60  described above, the leaf spring  82  has to be fixed to the holder  72  by screwing and moreover the sliding friction member  76  needs to be assembled. Thus, the assembly would involve time and labor. It can also occur that the leaf spring  82  is plastically deformed during the assembly. In this case, there would arise variations in frictional force among individual units, lead also a cause of variations in unit performance. Furthermore, there has also been a possibility that component parts might be decomposed and scattered upon a shock of fall.  
     SUMMARY OF THE INVENTION  
      An object of the present invention is to provide a drive unit which makes it possible to achieve a cost reduction by a cut of assembling steps, suppression of variations in drive performance by a reduction of plastic deformation of the leaf spring, and prevention of decomposition and scattering of component parts due to a shock of fall.  
      In order to achieve the above object, the present invention provides a drive unit comprising:  
      an electromechanical conversion element;  
      a drive friction member which is fixed to one end of the electromechanical conversion element; and  
      a movable member which is functionally fitted to the drive friction member, where the movable member is to be moved relative to the drive friction member by making the electromechanical conversion element vibrated in expansion and contraction, wherein  
      a press member for pressing the movable member against the drive friction member is constructed integrally with the movable member.  
      In the drive unit of the present invention, the movable member may include a sliding portion and a sliding friction member which abut on the drive friction member, respectively. The drive friction member may be formed into a cylindrical bar shape in general and the sliding portion of the movable member may be formed as a generally V-shaped groove. Moreover, the drive friction member may be formed into a cylindrical bar shape in general and the sliding friction member may have a curved portion corresponding to an outer circumference of the drive friction member.  
      Also, in the drive unit of the present invention, the press member may press the sliding friction member against the drive friction member. The press member and the sliding friction member may be mechanically positioned with each other.  
      Also, in the drive unit of the present invention, the press member may abut on the drive friction member directly. An abutting portion of the press member may have a curved shape along an outer circumference of the drive friction member. Moreover, the press member may be a leaf spring which is supported in a cantilever manner by the movable member.  
      Also, in the drive unit of the present invention, the movable member may include a holder which is made from a resin material and which holds a driven article, and the press member may be constructed integrally with the holder. The press member may be insert molded with the holder to form an integrated member. Moreover, the movable member may further include a sliding friction member and the holder has a sliding portion, and both of the sliding friction member and the sliding portion which abut on an outer circumference of the drive friction member may be formed from a metal material.  
      Also, in the drive unit of the present invention, the press member may be formed so as to be twistable with respect to an axial direction of the drive friction member that is an axial member. The press member may have at least two arm portions which are spaced from each other in the axial direction and which are generally perpendicular to the axial direction. Moreover, the two arm portions may be formed by cutting ½ or more of a width of the press member in the axial direction of the drive friction member.  
      Also, in the drive unit of the present invention, the press member may have a base portion formed narrower than its contact portion with the drive friction member. The base portion may be formed by cutting ½ or more of a width of the press member in the axial direction of the drive friction member.  
      Furthermore, the present invention provides as another aspect a drive unit comprising:  
      an electromechanical conversion element;  
      a drive friction member which is fixed to one end of the electromechanical conversion element;  
      a movable member which is functionally fitted to the drive friction member, where the movable member is to be moved relative to the drive friction member by making the electromechanical conversion element vibrated in expansion and contraction; and  
      a press member which is constructed integrally with the movable member so as to press the movable member against the drive friction member, wherein  
      the movable member includes a holder which is made from a resin material and which holds a driven article, the press member is constructed integrally with the holder, the holder has a sliding portion made from a metal material which abut on an outer circumference of the drive friction member, and the press member is a leaf spring formed so as to be twistable with respect to an axial direction of the drive friction member that is an axial member.  
      According to the drive unit of the present invention, since the press member is provided integrally with the movable member, for example, by insert molding, the assembling step for the press member can be omitted, allowing a cost reduction to be achieved, and moreover the press member is free from separation from the movable member due to a shock of fall.  
      Further, in the case where the press member is provided so as to abut directly on the drive friction member so that the sliding friction member is omitted, a further cost reduction can be achieved and moreover the assembly becomes easier to carry out. Still more, whereas expanding the press member by hand for assembling of the sliding friction member in the assembly process would cause the press member to be plastically deformed, making a factor of variations in frictional force and unit performance, the omission of the sliding friction member allows such events to be reduced.  
      Furthermore, in the case where the press member is formed so as to be twistable with respect to the axial direction of the drive friction member that is an axial member, even if the press member, when provided integrally with the movable member, has resulted into a skew more or less, generally uniform pressing force can be made to act on the drive friction member in the axial direction so that variations in the frictional force and the drive performance can be reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention will be further described with reference to the accompanying drawings wherein like reference numerals refer to like parts in the several views, and wherein:  
       FIG. 1  is an exploded perspective view of a drive unit;  
       FIGS. 2A and 2B  are views showing a state in which a leaf spring is insert molded in a skew into a holder;  
       FIGS. 3A  to  3 C are views showing a drive unit using a leaf spring having two arm portions;  
       FIG. 4  is a view showing a drive unit in which a thinner portion is provided at a base portion of the leaf spring;  
       FIGS. 5A and 5B  are views showing a drive unit in which metal material is provided at a sliding portion of the holder; and  
       FIG. 6  is a view showing a drive unit according to a prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       FIG. 1  is an exploded perspective view of a drive unit  10  which is an embodiment of the present invention, where an assembled state of the drive unit  10  is nearly identical to that shown in  FIG. 6 .  
      The drive unit  10  is composed of a cylindrical-shaped weight  12  to be fixed to an immovable part of a device into which the drive unit  10  is to be incorporated, a piezoelectric element (electromechanical conversion element)  64  which is cylindrical-shaped as an example and of which one end in its expansion/contraction direction is fixed to the weight  12 , for example, by adhesion, a drive friction member  16  which is a cylindrical bar-shaped member as an example and which is to be fixed to the other end of the piezoelectric element  14  in its expansion/contraction direction, for example, by adhesion, and a movable member  18  which is to be fitted to the drive friction member  16  by frictional force. The cylindrical bar shape of the drive friction member  16  allows the drive friction member  16  to be easily produced with high dimensional accuracy.  
      The movable member  18  includes a holder  22 , which is a resin (e.g., PPS (Polyphenylene Sulfide), liquid crystal polymer) molded article, for holding a lens  20  which is an optical member. The holder  22  is so designed that the drive friction member  16  is slidably accepted into a generally V-shaped groove portion  24  formed in its side portion. Forming the holder  22  with the resin material is effective to reduce the weight and production cost of the movable member  18 .  
      In the drive friction member  16 , a sliding friction member  26  formed from, for example, an SUS plate is placed in contact at a portion where the drive friction member  16  is accepted into the groove portion  24  of the holder  22 . The sliding friction member  26  is composed of a curved portion  28  curved in close contact along an outer circumferential surface of the drive friction member  16 , and rectangular-shaped protruding portions  30  protrusively provided on both sides of the curved portion  28 , respectively. As the protruding portions  30  fit into recessed portions, respectively, formed on both sides of the holder  22  with the groove portion  24  interposed therebetween, the sliding friction member  26  is positioned with respect to the holder  22 . The curved shape of the sliding friction member  26  allows the sliding friction member  26  to easily accept the drive friction member  16  during the assembly of the drive unit  10 .  
      The sliding friction member  26  is pressed by a leaf spring (press member)  32  bent into an L shape. The leaf spring  32  formed from a metal plate is provided integrally with the holder  22 , which is a resin molded article, by insert molding. The leaf spring  32  is supported in the cantilever manner by the holder  22 , so that the leaf spring  32  facilitates an adjustment of biasing force thereof and has high tolerance to the twist from an original posture with respect to the holder  22 , in comparison with those in the leaf spring both ends of which are fixed to the holder  22 . By biasing force of the leaf spring  32 , the drive friction member  16  is pressed and sandwiched by the groove portion  24  of the holder  22  and the curved portion  28  of the sliding friction member  26 , so that the movable member  18  is frictionally fitted to the drive friction member  16 .  
      A small protrusion  27  is formed on the surface of the sliding friction member  26 , and a small hole  33  is formed in the leaf spring  32 . As these protrusion  27  and the hole  33  are fitted to each other, the sliding friction member  26  is positioned with respect to the leaf spring  32 , thereby omitting positioning adjustment of the sliding friction member  26  relative to the leaf spring to in turn make the assembly of the drive unit  10  easy.  
      Operation of the drive unit  10  having the above-described construction is absolutely similar to that of drive unit  60  described as a prior art example, and so its description is omitted here.  
      According to the drive unit  10  of this embodiment, since the leaf spring  32  is provided integrally with the movable member  18  by insert molding, the assembling step for the leaf spring  32  can be omitted, allowing a cost reduction to be achieved, and moreover the leaf spring  32  is free from separation from the movable member  18  due to a shock of fall.  
      In the drive unit  10  shown above, the drive friction member  16  is pressed by the leaf spring  32  via the sliding friction member  26 . However, it is also possible that with the sliding friction member  26  omitted, the leaf spring  32  is set in direct contact with the drive friction member  16  so that the leaf spring  32  serves also as the sliding friction member. In this case, the sliding friction member  26  can be omitted, so that a further cost reduction can be achieved and moreover the assembly becomes easier to carry out. Still more, whereas expanding the leaf spring  32  by hand for assembling of the sliding friction member  26  in the assembly process would cause the leaf spring  32  to be plastically deformed, making a factor of variations in frictional force and drive performance, the omission of the sliding friction member  26  allows such events to be reduced.  
      In the meantime, in the case where the leaf spring  32  is provided integrally with the movable member  18  by insert molding, there can occur a case where the leaf spring  32  is fixed in a skewed state with respect to the movable member  18  during the insert molding as shown in  FIG. 2A . In such a case, after the assembly, the leaf spring  32  comes to be in one-side contact with the drive friction member  16  (or the sliding friction member  26  if it is present) as shown in  FIG. 2B , resulting in unstable pressing force of the leaf spring  32 . As a result, the frictional force of the movable member  18  against the drive friction member  16  is varied among individual units, causing the drive performance to be varied.  
      Thus, in order to prevent the event that the leaf spring  32  is fixed in a skew to make the pressing force unstable, it is also possible that the leaf spring  32  is formed so as to be twistable with respect to the axial direction of the drive friction member  16 , which is an axial member.  
      More specifically, as shown in  FIG. 3A , the leaf spring  32  has two arm portions  32   a  which are spaced from each other in the axial direction of the drive friction member  16  and which are generally perpendicular to the axial direction. These arm portions  32   a  each have a central portion bent in a generally V-shape substantially along the outer circumferential surface of the drive friction member  16 . With the two arm portions  32   a  provided in the leaf spring  32  as shown above, even in the case where the leaf spring  32  is fixed in a skew with respect to the holder  22  as shown in  FIG. 2B , when the leaf spring  32  is assembled to the drive friction member  16 , there arises a twist between the two arm portions  32   a  with respect to the axial direction of the drive friction member  16 , so that the arm portions  32   a  are both brought into close contact with the drive friction member  16  as shown in  FIG. 3B , thus allowing the active pressing force to be generally uniform. Thus, variations in the frictional force and the drive performance among individual units can be reduced. Alternatively, the arm portions  32   a  may be provided three or more in number without being limited to two.  
      It is still along possible that, as shown in  FIG. 4 , a narrow portion  32   b  thinner than the contact portion with the drive friction member  16  is formed at a base portion of the leaf spring  32 , so that the leaf spring  32  is allowed to twist at the narrowed portion  32   b  with respect to the axial direction of the drive friction member  16 . In this case also, the portion of the leaf spring  32  that makes contact with the drive friction member  16  is bent in a generally V-shape substantially so as to extend along the outer circumferential surface of the drive friction member  16 . As a result of this also, even in the case where the leaf spring  32  is fixed in a skew with respect to the holder  22 , when the leaf spring  32  is assembled to the drive friction member  16 , the leaf spring  32  is twisted at the narrowed portion  32   b  with respect to the axial direction of the drive friction member  16 , so that the leaf spring  32  are brought into close contact with the drive friction member  16 , allowing the active pressing force to be generally uniform. Thus, variations in the frictional force and the unit performance among individual units can be reduced.  
      Preferably, the two arm portions  32   a  of the leaf spring  32  shown in  FIG. 3  and the narrowed portion  32   b  of the leaf spring  32  shown in  FIG. 4  are formed by cutting out ½ or more of the width of the leaf spring  32  in the axial direction of the drive friction member  16  in order to provide the above-described successful twist function of the leaf spring  32 .  
      In the above-described drive unit  10 , since the holder  22  is molded with a resin material, the inner surface of the groove portion  24  to make contact with the drive friction member  16  is formed also with resin. However, as shown in  FIGS. 5A and 5B , the inner surface of the groove portion  24  in the holder  22 , which serves as the sliding portion against the drive friction member  16 , may be formed from a metal material  34 . This metal material  34  may be provided integrally with by insertion during the molding of the holder  22 , or provided by other means (adhesion, plating etc.). In the case where the sliding portion against the drive friction member  16  is formed from a metal material of higher rigidity than resin material as shown above, the drive performance can be improved and the durability of the movable member  18  against friction with the drive friction member  16  can be enhanced.  
      In addition, in the case where the arm portions  32   a  or the narrow portion  32   b  is formed in the leaf spring  32 , it has been described that the leaf spring  32  serves also as the sliding friction member. However, such a leaf spring  32  may be used in combination with the sliding friction member  26 .  
      Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the spirit and the scope of the present invention, they should be construed as being included therein.  
     Attachment A  
      John C. Freeman (34,483)  
      John G. Rauch (37,218)  
      Andrew D. Stover (38,629)  
      Tadashi Horie (40,437)  
      Joseph F. Hetz (41,070)  
      James L. Katz (42,711)  
      James A. Collins (43,557)  
      Vincent J. Gnoffo (44,714)