Abstract:
The present invention provides an ultrasonic motor including a wire having a coiled stator at one end thereof, a vibration generating device disposed at another end of the wire, a moving member that is in contact with the stator, a guide member that guides the rotation of the moving member, and an elastic member that covers the periphery of the wire. Accordingly, the driving efficiency of the ultrasonic motor that has a simple structure and that can be easily downsized can be enhanced and the performance stability thereof can be realized.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a ultrasonic motor using ultrasonic vibrations of an elastic member as a driving source, and a ultrasonic motor that can be mounted on a small electronic device such as a catheter. 
     2. Description of the Related Art 
     The ultrasonic motor using ultrasonic vibrations of an elastic member as a driving source, with various features which an electromagnetic motor does not have, has been increasingly applied to diverse fields such as electronic devices including a driving source of an autofocus mechanism of a camera, and a medical device that is exposed to an electromagnetic environment. Also, since the ultrasonic motor is easily downsized and has a high degree of freedom in shape, new type ultrasonic motors have been actively researched and developed. 
     Among the new type ultrasonic motors, it is expected that an ultrasonic motor of a type that transmits ultrasonic vibrations through an acoustic waveguide to a coiled stator and drives a moving member that is disposed in the vicinity of the stator (WO 2005/114824) is applied to, for example, a catheter that can be inserted into an extremely thin portion such as a blood vessel within a human body since the ultrasonic motor can be downsized, and an energy can be supplied from a remote location. 
     However, the ultrasonic motor of the type which transmits the ultrasonic vibrations to the coiled stator through the acoustic waveguide and drives the moving member that is disposed in the vicinity of the stator cannot efficiently drive the moving member because the ultrasonic vibrations that have been transmitted from the acoustic waveguide are attenuated or affected by reflected waves for the following reasons. 
     1) A wire that is an acoustic waveguide comes in contact with another member to attenuate the vibrations. 
     2) The vibrations that have been transmitted through the acoustic waveguide are reflected on a boundary between the stator (coiled) and the acoustic waveguide. 
     3) The vibration that has been transmitted to the stator is reflected by an end portion of the stator, and is mixed with the vibrations that are transmitted to the stator. 
     Also, the shape of a coil that constitutes the stator is changed during driving, and the output of the ultrasonic motor is not stabilized. 
     An object of the present invention is to provide an ultrasonic motor that is simple in structure and high in output and reliability. 
     SUMMARY OF THE INVENTION 
     To solve the above-mentioned problems, according to the present invention, there is provided an ultrasonic motor, including: a wire having a coiled stator at one end thereof; a vibration generating device disposed at another end of the wire; a moving member that is in contact with the stator; a guide member that guides the rotation of the moving member; and an elastic member that covers the periphery of the wire. 
     With the above structure, the output of the ultrasonic motor is stabilized irrespective of the use state because the attenuation of the vibrations which are transmitted to the stator can be suppressed even if the wire comes in contact with another member. 
     Further, according to the present invention, there is provided an ultrasonic motor including: a wire having a coiled stator at one end thereof; a vibration generating device disposed at another end of the wire; a moving member that is in contact with the stator; a guide member that guides the rotation of the moving member; and a fixing portion that is disposed in the guide member and fixes a part of the wire. 
     With the above structure, the output of the ultrasonic motor is stabilized because the shape of the coil that constitutes the stator during driving remains stable. 
     Still further, according to the present invention, there is provided an ultrasonic motor which may include: a wire having a coiled stator at one end thereof; a vibration generating device disposed at another end of the wire; a moving member that is in contact with the stator; a guide member that guides the rotation of the moving member; and a vibration absorbing member that is disposed on an end of the stator. 
     With the above structure, since the vibrations that have been transmitted to the stator are prevented from being reflected by the end of the stator, the efficiency of the ultrasonic motor may be improved. 
     In the ultrasonic motor of the present invention, the vibration absorbing member may be a movement regulation member. According to the ultrasonic motor of the present invention, the number of parts can be reduced, and a smaller ultrasonic motor can be realized. 
     Yet further, according to the present invention, there is provided an ultrasonic motor, which may include: a wire having a coiled stator at one end thereof; a vibration generating device disposed at another end of the wire; a moving member that is in contact with the stator; a guide member that guides the rotation of the moving member; and a second coil portion that is different in shape from a coil that constitutes the coiled stator, and continuous to the coiled stator. 
     In the ultrasonic motor of the present invention, an outer diameter of the second coil portion may be smaller than an outer diameter of the coiled stator. Also, an outer diameter of the second coil portion may become larger toward the coiled stator. 
     In addition, in the ultrasonic motor of the present invention, a coil pitch the second coil portion may be larger than a coil pitch of the coiled stator. Also, a coil pitch of the second coil portion may become smaller toward the coiled stator. 
     In the ultrasonic motor of the present invention, when the second coil portion is disposed between the stator and the vibration generating device, the vibrations that are transmitted from the vibration generating device can be smoothly transmitted to the stator without being attenuated at the end of the stator. Also, when the second coil portion is disposed at the other end of the stator (opposite to the vibration generating device), it is possible to prevent the reflection at the end of the stator because the vibrations that have been transmitted to the stator from the vibration generating device can be attenuated at the second coil portion. 
     According to the present invention, the ultrasonic motor that is extremely small in size and high in output can be obtained with a simple structure, and the performance stability of the ultrasonic motor can be improved. As a result, the present invention can be applied to electronic devices that are extremely small in the size and require the high reliability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIGS. 1A and 1B  are diagrams showing the structure of an ultrasonic motor according to a first embodiment of the present invention; 
         FIGS. 2A and 2B  are diagrams showing a relationship between a moving member and a stator in an ultrasonic motor according to a second embodiment of the present invention; 
         FIGS. 3A and 3B  are diagrams showing a relationship between a moving member and a stator in an ultrasonic motor according to a third embodiment of the present invention; and 
         FIG. 4  is a diagram showing the structure of a catheter using an ultrasonic motor according to a fourth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a description will be given of embodiments of the present invention with reference to the accompanying drawings. 
     First Embodiment 
     The structure and driving principle of an ultrasonic motor  100  according to a first embodiment of the present invention will be described with reference to  FIGS. 1A and 1B . The ultrasonic motor  100  of the present invention includes a wire  1  having a coiled stator  1   a  at one end, a vibration generating device  6  that is disposed at the other end of the wire  1  and functions as a vibration source, a moving or movable member  2  of substantially cylindrical shape which is disposed around the outer periphery of the stator  1   a , a guide member  4  that guides the rotation of the moving member  2 , a movement regulation member S that is disposed at the end of the guide member  4 , and an output member  3  that extracts the rotation output of the moving member  2 . 
     When the vibration wave is input to the wire  1  from the vibration generating device  6 , the vibration wave is transmitted to the coiled stator  1   a . The surface of the stator  1   a  is elliptically moved by the transmission of the vibration wave. Because the direction of the elliptic motion is opposite to the advancing direction of the vibration waves, the moving member  2  rotates in that direction. Projections  2   a  are disposed on the entire outer circumference of the moving member  2  in the circumferential direction, and rotatably guided in the inner circumference of the guide member  4 . The leading end of the moving member  2  is fixed with the output member  3  and rotated together with the moving member  2 . The movement of the moving member  2  in the rotation center axial direction is conducted by a regulation portion  4   a  that is disposed at one end of the guide member  4  and a convex portion  5   a  of the movement regulation member  5  which is fixed to the other end of the guide member  4 . 
     As long as the elliptic motion can occur on the surface of the stator  1   a , the structure of the vibration generating device  6  is not limited. However, it is preferable to use vertical vibrations that are excited by a Langevin vibrator that can output a large output. 
       FIG. 1B  is a diagram showing an arranging method when a Langevin vibrator  200  is used as the vibration generating device  6 . A wire  1  is fixed to the leading end of the Langevin vibrator  200  (horn  20   a ) by welding, and the vertical vibrations are transmitted to the longitudinal direction of the wire  1 , that is, the direction of the stator  1   a . The Langevin vibrator  200  includes cylindrical blocks  20   b  and  20   c  that are so arranged as to sandwich two disk piezoelectric elements  21  and  22  and constitute a vibration body  20  made of metal such as duralumin, and a horn  20   a  that is fixed to the cylindrical block  20   b  by means of a bolt not shown, welding, or the like. The horn  20   a  is thinned toward the leading end (joint portion with the wire  1 ), and enlarges the vibrations. The piezoelectric elements  21  and  22  are disposed between the cylindrical blocks  20   b  and  20   c , and the cylindrical blocks  20   b  and  20   c  are fastened to each other by a bolt not shown, and fixed in a state where the compression force is applied. Electrodes not shown are disposed on the overall front and rear surfaces of the piezoelectric elements  21  and  22 , and the electrodes are rendered conductive to the external by means of the lead wires  23 ,  24 , and  25 . The polarization of the piezoelectric elements  21  and  22  are made in the thickness direction, and the polarization directions are opposite to each other. The lead wire  23  is grounded, and an AC signal of the resonance frequency of the Langevin vibrator  200  is applied to the lead wires  24  and  25 , to thereby excite the vertical vibrations in the vibration body  20 . When the vertical vibrations that are propagated on the wire  1  are input to the stator  1   a , the curved vibration wave is induced due to the presence of the curve of the wire that constitutes the stator  1   a  (coil), which generates the elliptic motion. In this way, because the vertical vibrations are transmitted to the wire  1 , it is difficult to attenuate the vibrations when the wire  1  comes in contact with another member, and even if the wire is made longer, the vibration waves can be efficiently transmitted from the vibration generating device  6  to the stator  1   a.    
     In the ultrasonic motor  100  according to the present invention, the surface of the wire  1  is covered with an elastic member  7  such as silicon rubber or urethane resin, which has extremely smaller elasticity than the wire  1 . According to this configuration, even if the wire  1  comes in contact with another member while the ultrasonic motor  100  is being driven, the attenuation of the vibrations that are transmitted to the stator  1   a  can be suppressed. As a result, the output of the ultrasonic motor  100  is stabilized not depending on the use state. 
     Also, a part of the wire  1  (close to the boundary with the stator  1   a ) is fixed to a fixing portion  5   b  that disposed in the guide member  4 . The fixing portion  5   b  includes a hole through which the wire  1  is inserted. The hole is filled with an adhesive  8  such as silicon rubber or urethane resin, or an elastic member such as silicon rubber to fix the wire  1 . With the above configuration, the wire  1  can be fixed without attenuating the vibrations. With this structure, because the leading end of the stator  1   a  does not come in contact with the output member  3 , and the shape of the coil that constitutes the stator  1   a  during driving is stabilized, the output of the ultrasonic motor is stabilized. Incidentally, this structure is required when the movement regulation member  5  is made of plastic or metal. However, when the movement regulation member  5  per se is formed of an elastic member such as silicon rubber or urethane resin, the adhesive  8  is not required, and the wire  1  is fixed by pressure by the movement regulation member  5  per se. 
     Also, the wire  1   b  that extends from the end of the stator  1   a  is bent toward the vibration generating device  6  side, and fixedly inserted into the movement regulation member  5 . The movement regulation member  5  is formed of the elastic member such as silicon rubber or urethane resin. However, when the movement regulation member  5  is made of a hard plastic or metal, an adhesive that is low in the hardness such as silicon rubber is filled between the wire  1   b  and the movement regulation member  5 . With this structure, since the vibrations that are transmitted to the stator  2  can be prevented from being reflected by the end of the stator  1 , the efficiency of the ultrasonic motor is improved. Also, when the movement regulation member  5  per se is formed of a vibration absorbing member, it is possible to reduce the number of parts, and the smaller ultrasonic motor can be realized. 
     Second Embodiment 
     A second embodiment of the present invention will be described with reference to  FIGS. 2A and 2B . In this embodiment, because the basic structure of the ultrasonic motor is identical with that shown in the first embodiment, its description will be omitted, and the only configurations of the wire  1  and the moving member  2  will be described. 
     The coiled stator  1   a  is placed in the inner diameter portion of the moving member  2 . The stator  1   a  and the inner diameter portion of the moving member  2  come in pressure contact with each other, and the moving member  2  is frictionally driven by the vibration waves that are generated by the stator  1   a.    
     Referring to  FIG. 2A , a second coil portion  1   c  that is continuous to the stator  1   a  and different in the pitch of the coil from the stator  1   a  is disposed at a side of the vibration generating device  6  not shown rather than the stator  1   a.    
     The pitch P 2  of the second coil portion  1   c  is larger than the pitch P 1  of the coil of the stator  1   a . With the above configuration, it is possible to smoothly transmit the vibration waves that are transmitted from the vibration generating device  6  to the stator  1   a  without attenuation at the end of the stator  1   a . Also, the above effect is larger in the case where the second coil portion  1   c  is replaced with a second coil portion  1   d  in which pitches are gradually increased to P 3  and P 4  (both pitches are larger than the pitch P 1 ), as shown in  FIG. 2B . 
     Note that, the description has been made of the structure in which the stator  1   a  is placed in the inner diameter portion of the moving member  2 . Similarly, this embodiment can be applied to an ultrasonic motor having a structure in which the moving member  2  is placed in the inner diameter portion of the stator  1   a.    
     Third Embodiment 
     A description will be given of a third embodiment of the present invention with reference to  FIGS. 3A and 3B . In this embodiment, because the basic structure of the ultrasonic motor is identical with that in the first and second embodiments, its description will be omitted, and only the configurations of the wire  1  and the moving member  2  will be described. 
     Referring to  FIG. 3A , a second coil portion  1   e  that is continuous to the stator  1   a  and gradually increases the outer diameter as compared with the stator  1   a  is disposed at a side of the vibration generating device  6  not shown rather than the stator  1   a.    
     With the above structure, it is possible to smoothly transmit the vibration waves that are transmitted from the vibration generating device  6  to the stator  1   a  without attenuation at the end of the stator  1   a . Also, the second coil portion  1   e  can be replaced with a second coil portion that is smaller in outer diameter than the stator  1   a  and constant in outer diameter. 
     Also, when the second coil portion  1   f  is disposed at the end surface opposite to the vibration generating device  6  of the stator, the vibration waves that are transmitted from the vibration generating device  6  to the stator  1   a  can be attenuated at the second coil portion  1   f . As a result, it is possible to prevent the reflection of the vibration waves at the end of the stator. The second coil portion  1   f  has the outer diameter gradually reduced as shown in  FIG. 3B . However, the second coil portion  1   f  can be formed of a second coil portion entirely having an outer diameter smaller than the outer diameter of the stator  1   a , or can be formed of a second coil portion having a larger pitch than the pitch of the stator  1   a  (the coil portion may entirely have the same pitches or gradually increase the pitches). 
     Fourth Embodiment 
     Subsequently, a description will be given of an ultrasonic endoscope  300  as a representative of the catheter which is the electronic device using the ultrasonic motor of the present invention.  FIG. 4  is a diagram showing a section of the catheter. The catheter  300  includes a coiled stator  1   a , a moving or movable member  11  that is disposed around the outer periphery of the stator  1   a , a guide member  18  that guides the rotation of the moving member  11 , a movement regulation member  19  that fixes the guide member  18  as well as a vibrator that is disposed inside of the stator  1   a , and regulates the movement of the moving member  11  in the rotational axial direction. As illustrated in  FIG. 4 , the movable or moving member  11  has a hollow cylindrical shape having inner and outer surfaces and encircles the coiled stator  1   a  with the inner surface in contact with the surface of the coiled stator. The catheter  300  also includes a lead wire  15  for inputting an electric signal to the vibrator  14  from the outside and obtaining the electric signal that is output from the vibrator  14 , a reflector  16  that is fixed to the leading end of the moving member  11 , an adhesive  12  that is filled in the hole of the movement regulation member  19  and fixes the wire  1 , a vibration absorbing member in the form of an acoustic absorbent  13  that is fixed to the end of the stator  1   a  and made of silicon rubber, and a cover  17  that entirely covers the above parts. 
     When the ultrasonic waves are radiated from the vibrator  14  that is formed of piezoelectric elements (arrow R 1 ), the ultrasonic waves are reflected by the reflector  16 , changed in a direction indicated by an arrow R 2 , radiated, and impinge on the inner wall of the blood vessel. Further, after the ultrasonic waves (R 3 ) that have been reflected by the inner wall are again input to the mirror and reflected, the ultrasonic waves are input to the vibrator  14  (R 4 ). The operation is conducted while the reflector  16  that is fixed to the moving member  11  is rotated, and the output signal of the vibrator  14  is analyzed, thereby making it possible to obtain the information on the entire periphery of the blood vessel inner wall. The interior of the case  17  is filled with a solution close to the acoustic impedance within the blood vessel, and even under the environments, the ultrasonic motor of the present invention is stably operated. 
     Also, the ultrasonic motor of the present invention does not supply an energy to the stator by the supply of an electric power by a lead wire, but conducts the ultrasonic vibrations through a wire. Accordingly, when the vibration source  6  is disposed outside the body, there is no influence of temperature rising due to the electric power on the body interior, and there is no fear that a current flows into the body interior. Accordingly, the vibration source can be used within the body at ease. 
     In this embodiment, the description has been made of the example in which the acoustic absorbent  13  is disposed at the end of the stator  1   a  among the ultrasonic motor shown in the above embodiment. Alternatively, the structure of the ultrasonic motor according to another embodiment may be applied. 
     The ultrasonic motor according to the present invention supplies the energy to the stator by inputting not the electric power but the ultrasonic vibration per se, and can supply the energy from a remote location. Therefore, it is possible to apply the ultrasonic motor to, for example, a catheter that is inserted into the blood vessel of the human body. Also, because the structure is simple and the size is small, the present invention is applicable to the driving source of another small electronic device.