Abstract:
An ultrasonic probe having: an ultrasonic transmission and reception unit provided inside housing; and a drive device provided therein that encases a main sound transmission medium and swings the ultrasonic transmission and reception unit. The ultrasonic probe is characterized by: the drive device being a drive transmission mechanism that converts the rotation of a drive motor to swinging of the ultrasonic transmission and reception unit; all or part of the drive transmission mechanism comprising a gear mechanism; and preventing backlash in a meshing section of at least a pair of gears in the gear mechanism, by elastically impelling and pressing one pair of gears on to the other pair of gears by using compression springs.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a short-axis oscillating ultrasonic probe that transmits and receives ultrasonic waves from a piezoelectric element group which is an ultrasonic transmission and reception unit for a subject (living body) and that takes in three dimensional (3D) data for ultrasonic diagnosis of the subject, and more particularly relates to an ultrasonic probe that prevents backlash occurring during meshing of tooth surfaces of a pair of gears which mechanically oscillate a piezoelectric element group of the ultrasonic probe in a short axis direction. 
       BACKGROUND ART 
       [0002]    An ultrasonic diagnostic device using a mechanical short-axis oscillating ultrasonic probe for taking in three dimensional data generally creates a three dimensional image based on drive signals of a drive motor which is used for oscillating a piezoelectric element group or output signals of an encoder provided at a motor drive mechanism. 
         [0003]    However, in the both cases, the ultrasonic transmission and reception unit (the piezoelectric element group) that is a subject to drive is arranged in a housing (a sealed container) which contains and seals acoustic propagation liquid, e.g., oil. On the other hands, the driving motor and the encoder are arranged outside the housing in order to prevent from directly contacting the acoustic propagation liquid. Therefore, the ultrasonic transmission and reception unit is driven through the driving motor or the encoder by a gear mechanism provided there between, e.g., made of a pair of bevel gears. Such a gear mechanism has a problem that if backlash of gears meshing each other is larger than a prescribed value, the deviation may occur in an ultrasonic image to be created when the ultrasonic transmission and reception unit oscillates. 
         [0004]    That is, ultrasonic images of the subject are taken in both cases that the ultrasonic transmission and reception unit (piezoelectric element group) oscillates in one direction (forward direction) and oscillates in a reverse direction (the other direction). Even though ultrasonic images are created based on drive signals of the drive motor or output signals of the encoder as it is determined that the ultrasonic transmission and reception unit is in the same oscillating angle in a forward direction and a reverse direction, the ultrasonic transmission and reception unit is actually in different oscillating positions (angles) in the forward and reverse directions by backlash of gears meshing each other that forms a gear mechanism for oscillation. In result, the above-described deviation occurs in the ultrasonic image. 
         [0005]    Therefore, conventionally, as shown in  FIGS. 9 ( a ) ( b ) , in the short-axis oscillating probe, a piezoelectric element group  320  arranged in the longitudinal direction which has an acoustic lens on an ultrasonic transmission and reception surface is provided on a rotary holding table  310  contained in a sealed container  300 , and the piezoelectric element group  320  is oscillated in its short-axis direction through a drive shaft  307  and bevel gears  308 ,  309  so as to mechanically scan ultrasonic waves transmitted and received from the ultrasonic transmission and reception surface of the piezoelectric element group  320 . Liquid as acoustic medium L is filled and sealed in the sealed container  320  by covering with a cover  330 . 
         [0006]    Here, backlash of gears  308  and  309  meshing each other is adjusted appropriately by rotating a pair of holding shafts  314  screwed in upper parts of both ends of the rotary holding table  10 , e.g., with a tip of a screw driver to be inserted into an adjusting groove  314   a  (see Patent Document 1). 
         [0007]    For the conventional adjustment of backlash of gears  308 ,  309  meshing each other as described above, an ultrasonic probe having acceptable limit of backlash is prepared as a limit sample, and an operator rotates and oscillates the limit sample of ultrasonic probe by hand and determines by the feel whether backlash is in the acceptable range. 
         [0008]    Further, as other conventional example, as show in  FIGS. 10( a ), ( b ) , an ultrasonic probe has two-divided gears, a driving bevel gear  401  and a driven bevel gear  402 , between an oscillation device and a motor shaft  408  which oscillate the oscillation device and to which the driving bevel gear  401  is fixed. The bevel gears  401  and  402  are supported by the motor shaft  408  so that one of the bevel gears  401  and  402  is rotatable relative to the other and biased to the other in one direction by coil springs  405  attached to pins  403  and  404 . 
         [0009]    With such structure, tooth surfaces of the driving bevel gear  401 , together with tooth surfaces of the driven bevel gear  402  adjacent to the bevel gear  401 , push both sides of tooth surfaces of a bevel gear  430  of the other end to mesh therewith by the strength of the coil springs  405 , thereby eliminating backlash between tooth surfaces. 
       CITATION LIST 
     Patent Documents 
       [0010]    Patent Document 1: Unexamined Japan Patent Application No. 2012-95256 
         [0011]    Patent Document 2: Unexamined Japan Patent Application No. 1990-177043 
       SUMMARY 
     Technical Problems 
       [0012]    However, such backlash elimination of the drive gear mechanism of the conventional ultrasonic probe, it is conceivable to minimize backlash by adjusting the space of the gear tooth meshing each other but there is a limit to keep eccentricity accuracy of the gear below a specified value. Therefore, even if it is possible to eliminate the backlash at “the certain oscillating position” of the ultrasonic transmission and reception unit (piezoelectric element group), backlash may occur at “other oscillating positions”. Because of this reason, it was technically impossible to eliminate backlash over the entire oscillating range of the drive gear mechanism. Further, since it takes many working steps to adjust backlash, it prevents decrease of manufacturing cost of the ultrasonic probe, which is a problem (in the case of the conventional example in the Patent Document 1). 
         [0013]    Further, there is a problem in the case of conventional example disclosed in the Patent Document 2 that since the bevel gear forming the gear mechanism to be used in the oscillation of the ultrasonic transmission and reception unit is divided in two, the bevel gear becomes large, which hinders downsizing of the ultrasonic probe. 
       Solutions to Problems 
       [0014]    In order to solve the above problems, an ultrasonic probe of the present invention, comprises an ultrasonic transmission and reception unit provided inside a housing, an acoustic transmission medium sealed in the housing, and a drive device for oscillating the ultrasonic transmission and reception unit. The drive device is a drive transmission mechanism for converting rotation of a drive motor to oscillation of the ultrasonic transmission and reception unit. All or a part of the drive transmission mechanism comprises a gear mechanism. In a meshing section of at least one pair of gears in the gear mechanism, one of the pair of gears is elastically biased and pressed to the other of the pair of gears. 
         [0015]    Further, in an ultrasonic probe of the present invention, the one of the pair of gears, together with other member that rotates integrally therewith is elastically biased and pressed to the other of the pair of gears. 
         [0016]    Furthermore, in an ultrasonic probe of the present invention, the pair of gears is bevel gears meshing each other. 
         [0017]    Furthermore, in an ultrasonic probe of the present invention, the other member that rotates integrally with the one of the pair of gears is a drive shaft for transmitting rotational force to the one of the pair of gears, or a rotary shaft of the gear mechanism. 
         [0018]    In an ultrasonic probe of the present invention, a member for merging and pressing the one of the pair of gears to the other of the pair of gears is a compression spring provided around the other member that rotates integrally with the one of the pair of gears. 
       Advantageous Effects of Invention 
       [0019]    According to the present invention, backlash between tooth surfaces of a pair of gears meshing each other is prevented with simple structure, and deviation due to the oscillation of the ultrasonic transmission and reception unit does not occur in ultrasonic images to be created, and assemblability of the ultrasonic probe is superior. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  shows a front view (a) and a side view (b) of an ultrasonic probe of the present invention. 
           [0021]      FIG. 2  shows a cross sectional view of the ultrasonic probe of the present invention, taken along II-II of  FIG. 1 ( b ) . 
           [0022]      FIG. 3  shows a perspective view of an ultrasonic transmission and reception unit and an oscillating unit of the ultrasonic probe shown in  FIG. 1  of the present invention. 
           [0023]      FIG. 4  shows a perspective view of a whole oscillating unit for the ultrasonic transmission and reception unit of the ultrasonic probe of the present invention shown in  FIG. 3 . 
           [0024]      FIG. 5  is an enlarged view of the first embodiment of a gear mechanism of the oscillating unit for the ultrasonic transmission and reception unit shown in  FIG. 4 . 
           [0025]      FIG. 6  is an enlarged view of an area pointed by an arrow A in  FIG. 5   
           [0026]      FIG. 7  is an enlarged view of the second embodiment of a gear mechanism of the oscillating unit for the ultrasonic transmission and reception unit shown in  FIG. 4 . 
           [0027]      FIG. 8  is a cross sectional view of a bearing pointed by an arrow B shown in  FIG. 7  which shows the second embodiment of the gear mechanism of the oscillating unit for the ultrasonic transmission and reception unit shown in  FIG. 4 . 
           [0028]      FIG. 9  shows a conventional probe; (a) shows a perspective view of the ultrasonic probe with a cover removed, seen from the above; (b) shows a cross sectional view of the ultrasonic probe in which acoustic propagation liquid is contained and sealed with a cover. 
           [0029]      FIG. 10  shows an oscillating mechanism of an oscillating device of another conventional ultrasonic probe; (a) shows a cross sectional view thereof; (b) shows a plan view thereof seen from the above. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       [0030]    The first embodiment of an ultrasonic probe of the present invention will be described with accompanying drawings in the following. 
         [0031]    As shown in  FIGS. 1 and 2 , in an ultrasonic probe for medical diagnosis of the present invention, a housing is formed by a cap  30  of plastic material and a base  50  inserted in the cap  30 , and an ultrasonic transmission and reception unit (piezoelectric element group)  20  with an acoustic lens is rotatably provided on a pair of rotary shafts  14  which are provided at a table  10  of a base  50  opposing to the other in a longitudinal direction of the ultrasonic probe. And liquid functioning as acoustic medium L, e.g., oil, is placed in the housing and sealed by covering the housing with a grip case  40  which is an exterior member made of the plastic material. 
         [0032]    Then, a drive motor  1  provided in the grip case  40  is driven by supplying power from a power supply cable  60  so that the ultrasonic transmission and reception unit (piezoelectric element group)  20  oscillates, and ultrasonic waves transmitted and received from the ultrasonic transmission and reception surface of the ultrasonic transmission and reception unit  20  is mechanically scanned in a short-axis of the ultrasonic transmission and reception unit (piezoelectric element group)  20 , thereby taking in three dimensional data for ultrasonic diagnosis of a subject. 
         [0033]    Here, an oscillating mechanism of the ultrasonic transmission and reception unit (piezoelectric element group) of the ultrasonic probe of the present invention will be described with reference to  FIGS. 2, 3 and 4 . 
         [0034]    As shown in  FIG. 2  and  FIG. 3 , it is constituted that the drive motor  1  is provided vertically at the upper surface of the base  50  constituting a part of the housing of the ultrasonic probe of the present invention, and that driving power of a motor pulley  2  fitted in a drive shaft extending from the lower end of the drive motor  1  is transmitted to a drive shaft pulley  4  fitted in a drive shaft  7  vertically and rotatably provided on the upper surface of the base  50 , through a timing belt  3 . 
         [0035]    Further, a small bevel gear  8  is fitted in the drive shaft  7  at the lower end which is an output side of the ultrasonic probe, and a large bevel gear  9  meshing with the small bevel gear  8  is fitted in one of the rotary shafts  14  provided at the base plate  10 , so that the rotation of the small bevel gear  8  is transmitted to the large bevel gear  9  to reduce the rotation of the drive shaft  7  and to change the rotating direction, thereby oscillating the ultrasonic transmission and reception unit (piezoelectric element group)  20 . 
         [0036]    Here, a reflector  5  is fitted in the upper end of the drive shaft  7 , and a reflection type photo sensor  6  provided and fixed above the reflector  5  detects reference position of the ultrasonic transmission and reception unit (piezoelectric element group)  20 . 
         [0037]    Further, the oscillating operation of the ultrasonic transmission and reception unit (piezoelectric element group)  20  as shown in  FIG. 4  is controlled by the drive motor  1  itself, but may be controlled by a stepping motor which is controlled by open loop. Alternatively, it can be controlled by a DC motor or an AC motor, which is controlled by closed loop. In this case, for closed loop control, an encoder not shown here is provided. 
         [0038]    As shown in  FIG. 5 , a solid oil seal may be provided between an inner hollow part of the drive shaft pulley  4  and an outside surface of the drive shaft  7 . 
         [0039]    In particular, in the oscillating mechanism of the ultrasonic transmission and reception unit (piezoelectric element group) of the ultrasonic probe of the present invention, as shown in  FIG. 6 , the large bevel gear  9  oscillated by the rotation of the small bevel gear  8  is fixed at the rotary shaft  14 , and the distal end portion of the rotary shaft  14  is rotatably supported to the base  50  by a ball bearing  13 . 
         [0040]    Further, a coiled compression spring  11  is arranged between the base plate  10  and a collar  12  which is slidably fitted in the rotary shaft  14  and pressed against the base plate  10  so as to generate pressing force to the base plate  10 . Thus, since the compression spring  11  is regulated to move to a right direction in  FIG. 6  by the base  50  through the collar  12  and the ball bearing  13 , the compression spring  11  presses (F) the whole of the ultrasonic transmission and reception unit  20  to a left direction in  FIG. 6  through the base plate  10 . 
         [0041]    Therefore, since the large bevel gear  9  is pressed toward the tooth surface of the small bevel gear  8  meshing with the large bevel gear  9 , backlash does not occur between tooth surfaces of the bevel gears  8  and  9  even the ultrasonic transmission and reception unit  20  is in any oscillating position. In result, the work for adjusting backlash by hand is not needed. 
         [0042]    Further, since the elastic force of the compression spring  11  acts between the base plate  10  and the base  50  through the ball bearing  13 , it can reduce increase of frictional load during the oscillation of the ultrasonic transmission and reception unit  20 . 
         [0043]    In other words, the collar  12  is freely rotated and moved in an axial direction relative to the rotary shaft  14 , and one end of the collar  12  is in contact with the compression spring  11  and the other end is in contact with an inner ring  13   a  of the ball bearing  13 , and the inner ring  13   a  is freely rotated by a ball  13   c  relative to an outer ring  13   b  but the axial movement of the inner ring  13   a  is fixed, and further, a flange  13   d  of the outer ring  13   c  is engaged and fixed with the base  50 . Here, the rotary shaft  14  is fixed to the base  10  while being freely moved in the axial direction relative to the inner ring  13   a.    
         [0044]    Further, an outer diameter that the inner ring  13   c  of the ball bearing  13  is fitted in the distal end portion of the rotary shaft  14  is larger than an outer diameter that the collar  12  is slidably fitted in the rotary shaft  14 . Furthermore, since the outer portion that the collar  12  is slidably fitted in the rotary shaft  14  extends in the axial direction of the rotary shaft  14  and fixed at the base plate  10  with a predetermined length, the rotary shaft  14  is supported by the base plate  10  and the base  50  without axial shift. 
         [0045]    Therefore, during assembly operation of the ultrasonic probe, it can be prevented that the collar  12  is discretely sprung by elastic force of the compression spring  11 , and thus, assemblability of the ultrasonic probe is improved. 
       Second Embodiment 
       [0046]    In the second embodiment of the ultrasonic probe of the present invention, as shown in  FIG. 7 , a holding frame  101 , e.g., having a cylindrical shape is bridged above the upper end of the drive shaft  7  which rotates a small bevel gear  8 , a compression spring  102  is held in a hole portion having a circular cross section formed in the holding frame  101 , and a piece  103  is held in the hole portion  101   a  so as to freely move in the axial direction. 
         [0047]    Here, a tip portion of the piece  103  is formed in a tapered shape or a spherical shape, so that the piece  103  presses the axial center of the upper end portion of the drive shaft  7  in point contact. 
         [0048]    Because of this shape, even the pressing and elastic force of the compression spring  102  acts on the upper end of the drive shaft  7 , the frictional force that prevents rotation of the drive shaft  7  does not occur. 
         [0049]    In the second embodiment of the ultrasonic probe of the present invention, the drive shaft  7  which rotates the small bevel gear  8  is rotatably supported by a ball bearing  104  at the upper end portion and a ball bearing  105  at the lower end portion. 
         [0050]    In particular, in the second embodiment of the ultrasonic probe of the present invention, as shown in  FIG. 8  showing the enlarged cross sectional view pointed by an arrow B of  FIG. 7 , there is a gap g formed so that a stepped portion of the drive shaft  7  does not abut against the end surfaces of the inner ring and the outer ring of the ball bearing  105 , and thus, the biasing and pressing force of the compression spring  102  acting on the drive shaft  7  is effectively transferred to the small bevel gear  8 , and the tooth surface of the small bevel gear Bis constantly biased toward the tooth surface of the large bevel gear  9  meshing with the small bevel gear  8 . 
         [0051]    As a result, backlash between the tooth surfaces of the bevel gear  8  and  9  is eliminated. 
       DESCRIPTION OF THE REFERENCE NUMERALS 
       [0000]    
       
         
           
               1  drive motor 
               2  motor pulley 
               3  timing belt 
               4  drive shaft pulley 
               5  reflector 
               6  reflection type photo sensor 
               7  drive shaft 
               8  small bevel gear 
               9  large bevel gear 
               10  base plate 
               11  compression spring 
               12  collar 
               13  ball bearing 
               14  rotary shaft 
               20  ultrasonic transmission and reception section 
               30  cap 
               40  grip case 
               50  base 
               60  power supply cable