Abstract:
A rotation transmitting mechanism comprises: a three-layered coil that has an innermost layer coil portion, a middle layer coil portion and an outermost layer coil portion with alternating winding directions; and at least one elastic band that is fit to an outer peripheral area of said three-layered coil to press said outermost layer coil portion toward an inner peripheral side.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a rotation transmitting mechanism and an optical scanning probe that uses the rotation transmitting mechanism. 
     Obtaining a cross-sectional image of a sample under measurement such as biological tissue without cutting thereinto may be achieved using a method of optical coherence tomography (OCT) measurement. OCT measurement is a kind of optical interferometric measurement using the optical interference that occurs only when the optical path lengths of the measuring light and the reference light, into which the light from the light source is divided, are matched to within the coherence length of the light from the light source. 
     An optical tomographic imaging device that obtains a tomographic image using OCT measurement employs an optical scanning probe that is inserted into the test body so as to scan the sample using measuring light. This OCT optical scanning probe comprises, for example, a mechanism that rotates a flexible shaft so as to rotate a lens, mirror, and optical fiber that are fixed to the flexible shaft via a connecting member, and obtains information on the tomographic image in a body when inserted into a forceps channel of an endoscope and made to perform a lateral scan in the test body. 
     The flexible shaft is a hollow member having flexibility, and the flexible shaft employed generally comprises a two-layered (dual) coil spring with each layer coil wound in a different direction (Refer to JP06-205775A and JP06-090954A). However, with a two-layered coil spring, the rotation followability at the tip is insufficient, sometimes causing an increase in the rotational speed variation of the lens and other components disposed at the tip section of the probe. Further, the two-layered coil spring has rotational torque transmissibility in one direction only, resulting in a significant decrease in torque transmissibility during rotation in the other direction. Conversely, in JP2001-079007A is proposed a design wherein the coil spring is provided with a triple winding so that the rotation and movement operations are transmitted with good followability to the tip area of the flexible shaft. 
     Nevertheless, the inventors of the present invention found that, even with a three-layered coil spring, torque transmissibility is optimally exhibited in one rotational direction, but tends to decrease during rotation in the opposite direction. This is because rotation in the direction opposite the winding direction of the outermost layer coil of the coil spring is considered to be in a direction in which the winding of the outermost layer coil loosens, causing an increase in the diameter of the outermost layer coil and, in turn, contact with the inner surface of the probe sheath, thereby hindering smooth rotation of the flexible shaft. Further, when the outermost layer coil contacts the sheath inner surface, the possibility exists that the sheath inner surface will get scratched. Furthermore, with a conventional two-layered coil spring and three-layered coil spring, the problem arises that, in a case where self-induced vibration caused by rotational vibration occurs, the vibration cannot be suppressed. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to solve the above-described problems of prior art and provide a rotation transmitting mechanism that, during rotation in both directions of a flexible shaft of an OCT probe system, is capable of suppressing or decreasing displacement in the axial direction so as to prevent contact with the sheath inner surface and exhibit good torque transmissibility. 
     Further, it is an object of the present invention to provide an optical scanning probe that employs such a rotation transmitting mechanism. 
     A rotation transmitting mechanism according to the present invention comprises: a three-layered coil that has an innermost layer coil portion, a middle layer coil portion and an outermost layer coil portion with alternating winding directions; and at least one elastic band that is fit to an outer peripheral area of said three-layered coil to press said outermost layer coil portion toward an inner peripheral side. 
     An optical scanning probe according to the present invention comprises: a long sheath having a closed tip; the above-mentioned rotation transmitting mechanism of the invention that is inserted in said sheath so that its distal end is positioned near the tip of said sheath, said rotation transmitting mechanism extending along the longitudinal direction of said sheet to transmit to said distal end a rotational force provided to its proximal end; an optical fiber that passes through the inside of said rotation transmitting mechanism and extends along the longitudinal direction of said rotation transmitting mechanism so that its tip is positioned near the distal end of said rotation transmitting mechanism; and an optical scanning member that is fixed to the distal end of said rotation transmitting mechanism and connected to the tip of said optical fiber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial cross-sectional view illustrating the schematic configuration of an optical scanning probe according to embodiment 1 of the present invention. 
         FIG. 2  is a cross-sectional view schematically illustrating the rotation transmitting mechanism used in embodiment 1. 
         FIGS. 3A and 3B  are cross-sectional views respectively schematically illustrating the section of the rotation transmitting mechanism of  FIG. 2  that comprises a band. 
         FIG. 4  is a graph illustrating the state of speed variation with respect to frequency caused by a difference in the configuration of the rotation transmitting mechanism. 
         FIG. 5  is a cross-sectional view schematically illustrating the tip section of the endoscope where an optical scanning probe according to embodiment 2 is inserted. 
         FIG. 6  is a cross-sectional view schematically illustrating the rotation transmitting mechanism used in embodiment 2. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A rotation transmitting mechanism and optical scanning probe according to the present invention will now be described in detail based on the preferred embodiments shown in accompanying drawings. 
     Embodiment 1 
       FIG. 1  illustrates the schematic configuration of an optical scanning probe  10  of embodiment 1 used in an OCT system. In  FIG. 1 , the right side of the drawing is the tip side inserted into the test body, and the left side of the drawing is the base side connected to the system main body (not shown).  FIG. 1  shows the section of the tip side of the optical scanning probe  10  only. 
     The optical scanning probe  10  comprises a cylindrical sheath (outer casing)  12 , a cap  14  that covers the end of the sheath  12 , a rotation transmitting mechanism  16  that transmits a rotational force from an externally provided rotation driving source (not shown) to the end of the sheath  12 , a first sleeve  18  installed to the tip of the rotation transmitting mechanism  16 , a second sleeve  20  fit to the first sleeve  18 , a hemispherical lens  22  which is an optical scanning member disposed at the end of the sheath  12  and held by the second sleeve  20 , and an optical fiber  28  inserted through the sheath  12  and connected to the hemispherical lens  22  at the tip. 
     The base area (rod lens section) of the hemispherical lens  22  and the optical fiber  28  are respectively held by a first ferrule  24  and a second ferrule  26 . With the first ferrule  24  and the second ferrule  26  held in contact by the second sleeve  20 , the hemispherical lens  22  and the optical fiber  28  are optically connected. The sections other than the section held by the second ferrule  26  of the optical fiber  28  are covered by a covering material  30 . 
     The rotation transmitting mechanism  16  comprises a three-layered coil and a plurality of bands  38  fit to the outside of the three-layered coil. The three-layered coil is a coil consecutively comprising in layers a first coil spring  32  of the outermost layer, a second coil spring  34  having an outer diameter substantially equivalent to the inner diameter of the first coil spring  32 , and a third coil spring  36  having an outer diameter substantially equivalent to the inner diameter of the second coil spring  34 , with the winding direction of neighboring coil springs differing from each other. The optical fiber  28  passes through the inner peripheral section of the third coil spring  36 . This rotation transmitting mechanism  16  and the optical fiber  28  extend to the sheath  12  and the base area of the optical scanning probe  10 . 
     The base area of the rotation transmitting mechanism  16  is connected to a rotation driving source (not shown). When the base area is rotationally driven by the rotation driving source, that driving force is transmitted to the tip of the rotation transmitting mechanism  16 . When the tip of the rotation transmitting mechanism  16  rotates, the first sleeve  18  fixed to the tip of the rotation transmitting mechanism  16 , the second sleeve  20  fit to the first sleeve  18 , and the hemispherical lens  22  and the optical fiber  28  held by the second sleeve  20  rotate in an integrated manner. 
       FIG. 2  is a schematic cross-sectional view of the rotation transmitting mechanism  16 . The band  38  is cylindrical in shape and disposed in a plurality at a predetermined interval. The band  38  is an elastic body formed by an elastic material such as rubber, and presses the outer peripheral surface of the first coil spring  32  to the inner peripheral side. That is, the band  38  exerts a tightening force on the first coil spring  32  toward the inner peripheral surface. 
     The length of the band  38  (the length in the axial direction of the rotation transmitting mechanism  16 ) is preferably about ⅛ times the bending radius of the optical scanning probe  10  at maximum, since an excessively long length makes the rotation transmitting mechanism difficult to turn, possibly causing a reduction in the flexibility of the optical scanning probe  10 . Further, to ensure that the band  38  effectively exhibits the action of pressing the first coil spring  32 , the length of the band  38  is preferably about four times the diameter of the wire of the first coil spring  32  or greater. For example, when the bending radius of the optical scanning probe  10  is 32 mm and the diameter of the wire of the first coil spring  32  is 0.25 mm, a width B of the band  38  is preferably with the range of 1 mm&lt;B&lt;4 mm. 
     The disposed interval of the band  38  may be determined so as to ensure that flexibility with respect to the bending of the rotation transmitting mechanism  16  is not hindered. The band  38  may be provided with a short width and disposed in a plurality at a short interval. While the band  38  exhibits just one effect, the band  38  is preferably disposed in a plurality across the entire length of the rotation transmitting mechanism  16 . 
     Next, the effect of the rotation transmitting mechanism  16  will be described.  FIGS. 3A and 3B  are schematic cross-sectional views of a section of the rotation transmitting mechanism  16  having the band  38 .  FIG. 3A  shows the state when the rotation transmitting mechanism  16  rotates counterclockwise in the figure, and  FIG. 3B  shows the state when the rotation transmitting mechanism  16  rotates clockwise in the figure. 
     In this embodiment 1, the first coil spring  32  and the third coil spring  36  of the rotation transmitting mechanism  16  are coils wound counterclockwise, and the second coil  34  is a coil wound clockwise. Accordingly, as shown in  FIG. 3A , when the rotation transmitting mechanism  16  rotates counterclockwise (CCW), the first coil spring  32  and the third coil spring  36  tend to slightly tighten toward the inside, and the second coil spring  34  tends to slightly loosen toward the outside. As a result, the first coil spring  32  and the second coil spring  34  act so as to tighten each other, thereby transmitting a rotational force with high efficiency and exhibiting rigidity. 
     On the other hand, as shown in  FIG. 3B , when the rotation transmitting mechanism  16  rotates clockwise (CW), the first coil spring  32  and the third coil spring  36  tend to slightly loosen toward the outside, and the second coil spring  34  tends to slightly tighten toward the inside. As a result, the second coil spring  34  and the third coil spring  36  act so as to tighten each other, thereby transmitting a rotational force with high efficiency and exhibiting rigidity. 
     In this manner, the rotation transmitting mechanism  16  is capable of transmitting a rotational force with high efficiency in both the clockwise and counterclockwise directions. Further, in either direction of rotation, with the neighboring two of the three coil springs working to tighten each other, displacement in the axial direction of the rotation transmitting mechanism  16  is suppressed or reduced. 
     However, when in the state shown in  FIG. 3B , the first coil spring  32  has a tendency to loosen toward the outside and, in that state, the possibility exists that the coil diameter will increase, causing contact with the inner surface of the sheath  12 . When the first coil spring  32  contacts the inner wall of the sheath  12 , load variation occurs in response to the rotation of the rotation transmitting mechanism  16 , resulting in a decrease in torque transmissibility. Further, the possibility also exists that the contact will result in scratches on the inner surface of the sheath  12 . 
     In response, the rotation transmitting mechanism  16  comprises the band  38  that presses against the outer peripheral surface of the first coil spring  32 . The band  38  biases the entire circumference of the first coil spring  32  substantially equally toward the inside due to its own elasticity. Thus, even if the first coil spring  32  tends to spread to the outside as shown in  FIG. 3B , the spread is suppressed by the band  38 . In other words, the band  38  has a function of preventing contact with the sheath  12 , which is caused by the spread of the first coil spring  32  toward the outer peripheral side. With this arrangement, the rotation transmitting mechanism  16  is capable of smoothly rotating and exhibiting good torque transmissibility in either direction of rotation without the first coil spring  32  of the outermost layer contacting the inner surface of the rotation transmitting mechanism  16 . 
     The band  38  also has a function of improving the smoothness with the inner surface of the sheath  12  by employing an outer peripheral surface that has a small friction coefficient with the inner surface of the sheath  12 . With an optical scanning probe of prior art, the coil spring sometimes comes in contact with the inner surface of the sheath, especially at the section where the sheath curves. With the optical scanning probe  10  of the present invention, however, the band  38  rather than the first coil spring  32  comes in contact with the sheath  12 , thereby improving the smoothness between the rotation transmitting mechanism  16  and the sheath  12 . 
     Further, the band  38  is made of an elastic material such as rubber and therefore is capable of damping any self-induced vibration that may occur as a result of the rotation vibration of the rotation transmitting mechanism  16 , that is, of functioning as a damping mechanism. 
       FIG. 4  is a graph illustrating the state of speed variation with respect to frequency caused by a difference in the configuration of the rotation transmitting mechanism. In a frequency range of 10 Hz to 20 Hz, which corresponds to the rotational speed range of the rotation transmitting frequency mechanism of the optical scanning probe, a rotation transmitting mechanism that employs a three-layered coil spring has less speed variation than a rotation transmitting mechanism that employs a two-layered coil spring. However, in a case where the rotation transmitting mechanism comprises a three-layered coil spring and bands similar to the above-described rotation transmitting mechanism  16 , the rotation transmitting mechanism is found to suppress speed variation to an even higher degree than in a case where the rotation transmitting mechanism has a three-layered coil spring only and no bands. 
     Furthermore, even in a case where the coil spring that constitutes the rotation transmitting mechanism  16  comprises one layer, two layers, or four layers or more, providing the band  38  makes it possible to suppress the spread in the radial direction of the coil spring even during rotation in the direction opposite the winding direction of the coil spring of the outermost layer, thereby improving the transmissibility of the rotational torque to a higher degree than in a case where the band  38  is not provided. 
     Further, even in a case where the coil spring is provided with four layers or more, similar to the case of three layers described above, the coil spring is capable of suppressing or reducing the displacement in the axial direction of the rotation transmitting mechanism  16 , and smoothly rotating in either direction of rotation without the first coil spring  32  of the outermost layer contacting the inner surface of the rotation transmitting mechanism  16 , making it possible to exhibit good torque transmissibility. However, in a case where there are four layers or more, the reduction in flexibility that is associated with the increase in the number of layers needs to be taken into consideration. 
     Embodiment 2 
     Next, embodiment 2 of the present invention will be described. 
     In the aforementioned embodiment 1, the rotation transmitting mechanism  16  was constructed using a three-layered coil spring in order to reduce the speed variation of the tip section of the optical scanning probe  10 . However, the optical scanning probe  10  is extremely small when its diameter is about 3 mm or less, causing the diameter of the rotation transmitting mechanism  16  loaded inside the sheath  12  to be extremely small, and each coil of the three-layered coil spring to weaken in coil spring bending rigidity where the wire is fine. As a result, when the rotation transmitting mechanism  16  is rotated, the tip section sometimes vibrates. Here, in this embodiment 2, a three-layered coil spring is used to suppress the rotational speed variation caused by the two-layered coil spring of prior art, and the tip section is designed as a two-layered coil spring having a thicker coil wire diameter, thereby increasing the rigidity of the coil spring and suppressing the tip vibration that occurs due to a decrease in bending rigidity. 
       FIG. 5  is a schematic cross-sectional view of the tip section of an endoscope  54  where an optical scanning probe  40  according to embodiment 2 is inserted.  FIG. 5  shows the state in which a lid  58  of a forceps channel  56  of an endoscope  54  is open, and the tip of the optical scanning probe  40  is projected from the forceps channel  56 . The tip section of the endoscope  54  is provided with an imaging unit  60  comprising an objective lens, CCD, etc, an air/water supply nozzle (not shown), and a light guide (not shown) in addition to the forceps channel  56 . 
     The optical scanning probe  40  comprises a hemispherical lens  44  disposed inside the end of a sheath  42 , and a rotation transmitting mechanism  46  that transmits the rotational force from a rotation driving source (not shown) so as to rotate the hemispherical lens  44 . In this optical scanning probe  40 , the configuration of the rotation transmitting mechanism  46  differs from that of the rotation transmitting mechanism  16  of the optical scanning probe  10  of embodiment 1, but the configuration of all other components is the same as that of the aforementioned optical scanning probe  10 . 
     The rotation transmitting mechanism  46  comprises a three-layered coil  48 , a two-layered coil  50 , and a connecting unit  52  that connects the three-layered coil  48  and the two-layered coil  50 . The two-layered coil  50  is arranged at the tip side of the three-layered coil  48 , up to the position of length L from the tip of the optical scanning probe  40 . This length L may be set to substantially the same value as the protrusion amount of the optical scanning probe  40  from the endoscope  54  at the time the optical scanning probe  40  is used, such as to L=30 to 50 mm, for example. 
       FIG. 6  is a schematic cross-sectional view of the rotation transmitting mechanism  46 . The three-layered coil  48 , which is the main section of the rotation transmitting mechanism  46 , is the same as the three-layered coil of the rotation transmitting mechanism  16  of embodiment 1, and the first coil spring  32 , the second coil spring  34 , and the third coil spring  36  are combined sequentially from the outside, with the winding directions of neighboring springs differing from each other. Further, the band  38  is fit at an interval to the outside of the first coil spring  32 . 
     On the other hand, the two-layered coil  50  on the tip side of the three-layered coil  48  comprises an outer coil spring  62  and an inner coil spring  64 , which are two coil springs having different winding directions, and the band  38  fit to the outside of the outer coil spring  62 . The outer coil spring  62  and the inner coil spring  64  employed have a larger wire diameter than each of the coil springs of the first to third coil springs  32  to  36  of the three-layered coil  48 . Further, the outer diameter of the outer coil spring  62  is substantially equal to the outer diameter of the first coil spring  32 , making it possible to use bands having the same dimensions for each of the bands  88  fit to that outside. 
     The band  38  is the same as the band  38  of the rotation transmitting mechanism  16  of embodiment 1, and presses the first coil spring  32  or the outer coil spring  62  to the inner peripheral side. The connecting unit  52  connects the three-layered coil  48  and the two-layered coil  50  in a fixed manner by YAG welding or the like, and the rotational force of the three-layered coil  48  is transmitted as is to the two-layered coil  50 , thereby rotating the two in an integrated manner as the rotation transmitting mechanism  46 . 
     Thus, in embodiment 2, owing to a configuration comprising a three-layered coil spring and bands similar to the aforementioned embodiment 1, displacement in the axial direction can be suppressed or reduced and variation in the rotational direction can be decreased. Further, with the tip section of the rotation transmitting mechanism  46  designed as the two-layered coil  50  and each of the coil springs  62  and  64  having a large wire diameter, the bending rigidity of the tip section of the rotation transmitting mechanism  46  can be increased, thereby suppressing tip vibration. 
     Furthermore, with the band  38  fit to the two-layered coil  50  as well, as described with reference to  FIG. 4 , it is possible to decrease speed variation and transmit rotational torque relatively efficiently during rotation in the direction opposite the winding direction of the outer coil spring  62  as well. 
     Note that while a precision rotation transmitting mechanism and optical scanning probe of the present invention has been described in detail above, the present invention is not limited to the aforementioned embodiments, and various modifications may be made without departing from the spirit and scope of the invention.