Patent Publication Number: US-2011071399-A1

Title: Ultrasonic probe

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to ultrasonic imaging and more particularly to a 3D mechanical scanning probe for medical ultrasonic imaging. 
     SUMMARY OF THE INVENTION 
     Various embodiments of a probe for use in medical ultrasonic imaging are disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an axonometric view of an embodiment of the present disclosure; 
         FIG. 2  is an exploded perspective view of a transducer and a driven wheel; 
         FIG. 3  is an exploded perspective view of a motor and a driving wheel; 
         FIG. 4  is a perspective view of an embodiment of the present disclosure schematically illustrating hiding the base after the probe has been mounted; 
         FIG. 5  is a perspective view of an embodiment of the present disclosure schematically illustrating the connection of the ropes; 
         FIG. 6  is a sectional view of an embodiment of the present disclosure illustrating the probe as it passes through the centre line of the shaft; 
         FIG. 7  is an axonometric drawing of one side of an embodiment of the present disclosure; 
         FIG. 8  is an axonometric drawing of another side relative to  FIG. 7 ; 
         FIG. 9  is an axonometric drawing of an elastic component; 
         FIG. 10  is a perspective view schematically illustrating an embodiment of the present disclosure; 
         FIG. 11  is a perspective view of an embodiment of the present disclosure schematically illustrating the winding of the ropes; 
         FIG. 12  is a perspective view schematically illustrating an embodiment of the present disclosure; 
         FIG. 13  is an axonometric view of an embodiment of the present disclosure; 
         FIG. 14  is a perspective view of an embodiment of the present disclosure schematically illustrating hiding the base; 
         FIG. 15  is a perspective view of an embodiment of the present disclosure schematically illustrating the connection of the ropes; 
         FIG. 16  is a perspective view schematically illustrating an embodiment of the present disclosure; 
         FIG. 17  is a perspective view of an embodiment of the present disclosure schematically illustrating the connection of the ropes; 
         FIG. 18  is an exploded perspective view of an embodiment of the present disclosure illustrating the connection of the ropes; 
         FIG. 19  is a perspective view schematically of an embodiment of the present disclosure illustrating the connection of the ropes; 
         FIG. 20  is an exploded perspective view of an embodiment of the present disclosure illustrating the connection of the ropes; 
         FIG. 21  is a part sectioned view of an embodiment of the present disclosure illustrating the connection between the rope and the driven wheel; 
         FIG. 22  is a perspective view of an embodiment of the present disclosure schematically illustrating the connection of the ropes; 
         FIG. 23  is a perspective view of an embodiment of the present disclosure schematically illustrating the connection of the ropes; 
         FIG. 24  is an exploded perspective view of an embodiment of the present disclosure illustrating the connection of the ropes; and 
         FIG. 25  is a perspective view of an embodiment of the present disclosure schematically illustrating the connection of the ropes. 
     
    
    
     DETAILED DESCRIPTION 
     An ultrasonic probe for a 3D ultrasonic imaging system is generally referred to as a 3D mechanical probe, which internally has a step motor as a driving power source to drive a transducer to swing at a certain angle. At every swing angle, the 3D mechanical probe works like the conventional probe by emitting ultrasound waves and receiving echo information about human tissue. As a result, ultrasonic imaging of human tissues may be obtained at every swing angle without sliding or swinging a probe on a human body by a doctor. 
     The 3D mechanical probe needs to transmit the motion of the step motor to the transducer. The normal method to transmit the motion to the transducer is using ropes. In such a case, the ropes should be tightened. However, the motion of the step motor is not smooth as the speed or direction can have sudden changes when in use, which will create an impact on the rope or on the transducer. Thus it is necessary to cushion the impact. 
     The structure of the rope connecting device in the existing ultrasonic probe is complicated, expensive, and difficult to assemble. Therefore, an easily mounted ultrasonic probe with a simple structure is needed to provide continuous power to keep the rope tight and cushion the impact when in use. 
     According to one aspect of the present disclosure, an ultrasonic probe includes a base; a motor fixedly connected to the base; a driving wheel connected to the output of the motor and driven by the motor; a driven wheel rotationally connected to the base with a shaft; a transducer fixedly connected to the driven wheel for emitting and receiving ultrasonic echoes; two ropes, both ends of each rope having a connection end respectively, one connection end on one end of each rope respectively connected to the driving wheel and another connection end on another end of each rope respectively connected to the driven wheel; and at least one elastic part through which the connection end of at least one end of at least one rope is connected to the driving wheel or the driven wheel in a buffering manner, wherein one end of the elastic part is connected to at least one connector on one end of the ropes, and another end of the elastic part is connected to the driving wheel or the driven wheel. 
     Referring generally to  FIGS. 1-6 , an ultrasonic probe may include a base  1 , a transducer  2 , a driven wheel  3 , a support wheel  4 , a transducer base  5 , a shaft  6 , a motor  11 , a motor support  12 , a driving wheel  14 , two ropes  17 ,  18 , and two springs  16   a - b.    
     As shown in  FIG. 3 , the base  1  may be embodied as a hollow receptacle, within which there is a screw hole  1   a  and another screw hole on the symmetrical side of the screw hole  1   a  (the screw hole is not shown at the position corresponding to la on the dotted line corresponded to screw  13   b  in  FIG. 3 , which is numbered as  1   b ). In one embodiment, two fixing flats respectively stretched out of both sides of the motor support  12 , on which mounting holes  12   a  and  12   b  are formed. To fix the motor support  12  on the base  1 , the screw  13   a  matches the screw hole  1  a through the mounting hole  12   a,  and the screw  13   b  matches the screw hole  1  b through the mounting hole  12   b.  With four screws  122 , the motor  11  is installed and fixed to a mounting plate  121  stretched out of the motor support. 
     In one embodiment, the location of the motor  11  and the motor support  12  may be adjusted in a certain range in the vertical direction shown in the  FIG. 3  by turning the screws  13   a  and  13   b.  As the locations of the driven wheel  3 , the shaft  6  and the transducer  2  are above those of the driving wheel  14 , the motor support  12  and the motor  11  when mounted (the vertical direction shown in  FIG. 3 ), the distance between the driving wheel  14  and the driven wheel  3  in a small range may be adjusted by turning the screws  13   a  and  13   b  and the tightness of the rope may be adjusted thereby. 
     The driving wheel connected to the output of the motor can make the motor turn the driving wheel in one embodiment, wherein the driving wheel connected to the output of the motor is not only the driving wheel connected to the output of the motor directly, but also the driving wheel indirectly connected to the output of the motor via other components, which can make the motor drive the driving wheel. For example, the driving wheel may be directly fixed on the output of the motor, or the driving wheel may be connected to the output of the motor via a driving belt. In the illustrated embodiment, the driving wheel is directly fixed on the output of the motor. As shown in the  FIG. 3 , the output shaft  11  b of the motor  11  extends through a round hole on the mounting plate  121 , penetrates the mounting hole  14   a  of the driving wheel  14 , and fixes the driving wheel  14  with a fastening screw  15 . The motor  11  drives the driving wheel  14  by the output shaft  11   b  thereby. 
     As shown in  FIG. 1  and  FIG. 3 , two extending panels  101   a  and  101   b  are extended upward along both sides of the base  1  respectively. An axle hole  102   a  is formed on the extending panel  101   a  and another axle hole  102   b  on the panel  101   b.  The inside of each axle hole has a bearing (not shown). A revolute pair is made by one end of the shaft  6  rotationally connected to the extending panel  101   a  with the bearing of the axle hole  102   a,  and another revolute pair is made by another end of the extending panel  101  b with the bearing of the hole  102   b.    
     As shown in the  FIG. 2 , the shaft  6  passes through a mounting hole  301  on the rotating axis of the driven wheel  3  and a mounting hole  401  on the rotating axis of the support wheel  4 . The fastening screw  7   b  screws in the fastening screw hole  9   b  formed on the driven wheel  3  and its one end against the shaft  6  tightly to make the driven wheel  3  fix on the shaft  6 . The fastening screw  7   a  screws in the fastening screw hole  9   a  formed on the support wheel  4  and its one end against the shaft  6  tightly to make the support wheel  4  fix on the shaft  6 . 
     The transducer  2  may be fixed on the transducer base  5  using various conventional methods not discussed in detail here. Two grooves are respectively formed on the upper side of the driven wheel  3  and that of the support wheel  4 . The transducer  2  and the transducer base  5  may be engaged with the grooves of the driven wheel  3  and the support wheel  4  respectively. Two holding sheets  302  and  304  of the driven wheel  3 , which are respectively perpendicular to the surface of the wheel, are extended out of the two opposite sides of the groove. Two mounting holes  303  and  305  are respectively formed on the holding sheet  302  and  304 . A screw hole  10   a  is formed on one side of the transducer base  5  and another screw hole on the symmetrical position of another side (not shown in the figure). In one embodiment, the fastening screw  8   a  screws in the screw hole  10   a  of the transducer base  5  through the mounting hole  305  of the holding sheet  304 , and the fastening screw  8   b  screws in the screw hole of the transducer base  5  (the screw hole not shown in the figure) through the mounting hole  303  of the holding sheet  302 . In this way, the transducer base  5  and the transducer  2  may be fixedly connected to the driven wheel  3  with the fastening screw  8   a  and  8   b,  so that the transducer base  5  and transducer  2  may be swung around the shaft  6  with the driven wheel  3 . 
     The springs or ropes are connected to the driving wheel with a joint structure provided by the driving wheel. The joint structure may be any suitable structure as long as the springs may be connected thereto, such as pin, hook, bolt, groove, slot, etc. The pin is used as the joint structure in the embodiment. As shown from  FIG. 4  to  FIG. 6 , a pin  14   c  is fixedly attached to the lateral surface  141  of the driving wheel  14  and another pin  14   d  fixedly attached to another lateral surface  142 . A concave groove  144  is formed on the circum surface  143  of the driving wheel  14  along the circumferential direction. A gap  14   a  formed on one side of the lateral surface  141  connects the lateral surface  141  to the concave groove  144 , and another gap  14   b  formed on another side of the lateral surface  142  corresponded to the gap  14   a  connects the lateral surface  142  to the concave groove  144 . 
     In one embodiment, the springs or ropes are connected to the driven wheel with joint structures provided by the driven wheel. The joint structures may be any suitable structure as long as the springs may be connected thereto, such as pin, hook, bolt, groove, slot, etc. The groove is used as the joint structures in the illustrated embodiment. As shown in  FIG. 5 , a concave groove  307  is formed on the circum surface  306  of the driven wheel  3  along the circumferential direction. Two joint structures  3   a  and  3   b  are arranged on the upper of the two sides of the concave groove  307 . A slot  309  which is formed on the joint structure  3   a  connects the concave groove  307  to the joint structure  3   a,  and another slot  308  which is formed on the joint structure  3   b  connects the concave groove  307  to the joint structure  3   b.    
     Two hooks are respectively formed at the two ends of the spring  16   a,  wherein one hook at one end hooks the pin  14   c,  and another hook at another end hooks the connection end  17   b  of one end of the rope  17 . (In the illustrated embodiment, the connection end  17   b  of the rope  17  is a ring.) The rope  17  passes the gap  14   a  into the concave groove  144 , winds the driving wheel  14  along the concave groove for a certain distance, enters the concave groove  307  of the driven wheel  3 , winds along the concave groove  307  for a certain distance, and enters the joint structure  3   a  through the gap  309 . Another connection end  17   a  on another end of the rope  17  is clamped to the joint structure  3   a  (the connection end  17   a  is a knot in the embodiment). 
     Similarly, two hooks are respectively formed at the two ends of the spring  16   b,  wherein one hook at one end hooks the pin  14   d,  and another hook hooks the connection end  18   b  of one end of the rope  18  (the connection end  18   b  of the rope  18  is a ring in the embodiment). The rope  18  passes the gap  14   b  into the concave groove  144 , winds the driving wheel  14  along the concave groove for a certain distance, enters the concave groove  307  of the driven wheel  3 , winds along the concave groove  307  for a certain distance, and enters the joint structure  3   b  through the gap  308 . Another connection end  18   a  on another end of the rope  18  is clamped to the joint structure  3   b  (the connector  18   b  is a knot in this embodiment). The winding direction of the rope  18  is opposite to that of the rope  17  in the concave groove  144  of the driving wheel  14  and the groove  307  of the driven wheel  3 . 
     When the probe works, the motor  11  turns, thus driving the driving wheel  14 . The driving wheel  14  transmits the motion to the driven wheel  3  with the rope  17  and  18 , thus driving the driven wheel  3  and the shaft  6 . The transducer  2  is fixedly connected to the shaft  6 , thus driving the transducer  2  thereby. The rotation direction of the motor  11  changed repeatedly can realize the transducer  2  swing within a certain range. 
     The springs  16   a  and  16   b  may keep the ropes tight continuously and perform a shock absorption function in case the impact to the ropes and the driven wheel caused by the motor  11  changes the rotation direction. In addition, with the spring, the demand for the accuracy of rope length may be reduced. The ropes may be wire rope, or may be made of other materials suitable materials. The connection ends of the ropes may be processed with conventional methods, such as die casting, or directly twisted by wire rope manufacturers. The connection ends may be knots, rings or other similar joint parts according to requirements. To reduce the damage to the ropes, the gaps  14   a  and  14   b  may be rounded off. 
       FIG. 6  is a sectional view of one embodiment. The position of the ropes  17  and  18  winding on the driving wheel  14  is  14   e,  which is a cylindrical surface herein. The position of the ropes  17  and  18  winding on the driven wheel  3  is  3   c,  which is a part of the cylindrical surface. Tangency point of the ropes and  3   c  on the cylindrical surface can ensure the ratio of the angle the driving wheel  14  rotated to the angle the driven wheel  3  rotated equal to the diameter ratio of the two cylindrical surfaces. 
     The ropes on the driving wheel and driven wheel which are kept away from sliding to avoid the rotation angle error caused by the ropes sliding. After the ropes  17  and  18  are connected to and wound around the driving wheel  14  and the driven wheel  3 , turning the screws  13   a  and  13   b  can enlarge the distance between the driving wheel  14  and the driven wheel  3  to make the ropes tight. Thus no other forms of strength needed to make the springs out of shape. 
     The springs  16   a  and  16   b  may be replaced with other elastic parts in the illustrated embodiment. As shown in  FIG. 7  to  FIG. 9 , the springs may be replaced with elastic slices. As shown in  FIG. 7  and  FIG. 8 , two bosses  241  and  242  are formed on the two lateral surfaces of the driving wheel  14  respectively. An elastic slice  34  is fastened to the boss  241  of the driving wheel  14  with the screws  35   a  and  35   b.  As shown in  FIG. 9 , a joint structure  34   a  is formed on the elastic slice  34  forms. The rope  17 , with the connection end  17   b  (which is a knot in the depicted embodiment) at its one end clamped at the joint structure  34   a  of the elastic slice  34 , passes the gap  14   a  into the concave groove  144 , winds the driving wheel  14  along the concave groove for a certain distance, enters the concave groove  307  of the driven wheel  3 , winds along the groove  307  for a certain distance, and enters the joint structure  3   a  through the gap  309 . Another connection end  17   a  (which is a knot in the depicted embodiment) on another end of the rope  17  is clamped to the joint structure  3   a.  That is, the winding of the rope  17  and the connection end  17   a  connected to the driven wheel  3  as described above. 
     The connection of the rope  18  may be identical to that of the rope  17 . As shown in  FIG. 8 , an elastic slice  36 , whose shape is same to the elastic slice  34 , is fastened to the boss  242  of the driving wheel  14  with the screw  37   a  and  37   b.  The rope  18 , with the connection end  18   b  (which may be a knot) at its one end clamped at the joint structure of the elastic slice  36 , passes the gap  14   b  into the concave groove  144 , winds the driving wheel  14  along the groove for a certain distance, enters the concave groove  307  of the driven wheel  3 , winds along the groove  307  for a certain distance, and enters the joint structure  3   b  through the gap  308 . Another connection end  18   a  (which may be a knot) on another end of the rope  18  is clamped to the joint structure  3   b.  That is, the winding of the rope  18  and the connection end  18   a  connected to the driven wheel  3  is identical to those described above. 
     In the illustrated embodiment, the elastic slice  34  may keep the ropes tight continuously and perform a shock absorption function in case the impact on the ropes and the driven wheel caused by the motor  11  changes the rotation direction. In addition, with the elastic slice, the demand for the accuracy of rope length may be reduced. Furthermore, the elastic slice may be easily manufactured. 
     In various embodiments, two elastic parts (springs or elastic slices), each of which is respectively connected to a rope, may be used. An elastic part connected to a rope and another rope directly connected to driving wheel without any elastic parts is allowed. 
     Various embodiments of the present disclosure are shown in  FIG. 10  to  FIG. 12 . In one embodiment, as shown in  FIG. 10  and  FIG. 11 , the driving wheel  14  is provided with a screw  19 . The rope  18 , with its connection end  18   b  attached to the screw  19 , winds at the position  14   e  on the driving wheel  14  and the position  3   c  on the driven wheel  3 . The winding in this embodiment is similar to that in the aforesaid embodiments. The rest of the parts in this embodiment are identical to the aforesaid embodiments. In the illustrated embodiment, the two ropes may be tightened by using one spring. 
     Similarly,  FIG. 12  shows an embodiment of the present disclosure, whose structure is mostly as same as the last embodiment. The difference is that, instead of spring being used, an elastic slice, whose construction is identical to the elastic slice described above, is used. 
     Another embodiment of the present disclosure is shown in  FIG. 13  to  FIG. 15 . As illustrated, the motor  11  is fastened to the base  1  by the motor support  12 . A driving timing pulley  23  and a driving wheel  24  may be used (in the present disclosure, the wheel, which directly drives the driven wheel connected to the transducer, is regarded as a driving wheel; in the illustrated embodiment, though the wheel  24  is driven by the driving timing pulley  23 , it is still referred to as “driving wheel” for it directly drives the driven wheel  3 ). The driving timing pulley  23 , which is fixedly connected with the output shaft of the motor, drives the driving wheel  24  through the timing belt  25 ; that is, the driving wheel  24  is connected to the output of the motor  11  by the timing belt  25 . 
     The driving wheel  24  may include a driven timing pulley  249  and a revolving shaft  26 . The driven timing pulley  249  is fixedly connected with one end of the revolving shaft  26 . The timing belt  25  wraps around the driven timing pulley. The revolving shaft  26  is rotationally connected with the base  1  through a bearing (such as the bearing  28 ) and may be rotated freely relative to the base  1 . 
     As shown in  FIG. 15 , a winding area  260  for ropes wound, whose surface shape may be a cylindrical or other curved surface to meet practical requirements, is arranged on the middle part of the revolving shaft  26 . A king pin  29  and a link pin  30  are respectively arranged at the two sides of the winding area; a link pin  28  is arranged near the end of the revolving shaft  26 . The king pin  29  is located between the link pin  28  and the link pin  30 , and further, the distance the king pin  29  to the end of the revolving shaft  26  is larger than that the link pin  28  to the end. The rope  17 , whose connection end  17   a  (which may be a knot) is clamped to the joint structure  3   a  of the driven wheel  3  through the gap  309 , winds the driven wheel  3  for a certain distance, winds the winding area  260  of the revolving shaft  26  for a certain distance, and bypasses the king pin  29  fixedly connected with the revolving shaft  26 , and connects to the spring  27  with the connection end  17   b  (which may be a ring) clamped to the hook ring at one end of the spring  27 . Another hook ring at another end of the spring  27  hooks to the link pin  28  fixedly connected with the revolving shaft  26 . 
     The rope  18 , whose connection end  18   a  (which may be a knot) is clamped to the joint structure  3   b  of the driven wheel  3  through the gap  308  of the driven wheel  3 , winds the driven wheel  3  for a certain distance, winds the winding area  260  of the revolving shaft  26  for a certain distance and connects to the revolving shaft  26  by the connection end  18   b  (which may be a ring) clamped to the link pin  30  which is fixedly connected with the revolving shaft  26 . In this way, when the motor  11  turns, it drives the driving timing pulley  23 . The revolving shaft  26  of the driving wheel  24 , which is turned by the driving timing pulley  23 , turns the driven wheel  3  through the ropes  17  and  18 . 
     In the illustrated embodiment, the two ropes are tightened continuously by the tension offered by the spring  27 . Furthermore, as one end of the spring  27  is connected with the rope  17  which bypasses the king pin  29 , and another end of the spring is connected to the link pin  28  which is located at one side of the king pin  29  along the axis of the revolving shaft  26 , the spring  27  is located along the axis of the shaft  26  after installed. Take the axis of the revolving shaft  26  in the probe as the radial direction of the probe and the direction along the transducer  2  to the motor  11  as the axial direction of the probe, the structure in the illustrated embodiment takes up a small space along the axial direction, and meets the requirement of taking up a small space along the axial direction in the probe. 
     As shown  FIG. 16 , the spring may be replaced with other elastic parts. For example, an elastic slice  31 , which is almost L-shape and provided with a joint structure  31   a,  may be arranged near one end of the shaft  26 . The elastic slice  31  is fixedly connected to the revolving shaft  26  of the driving wheel  24  through a screw  262 . The connection end  17   a  of the rope  17  is clamped in the joint structure  3   a  of the driven wheel  3 , and the connection end  17   c  is clamped in the joint structure  31   a  of the elastic slice  31 . 
     Two springs, which are respectively connected to a rope in a buffering manner, may be used in the aforesaid embodiments. One spring is connected to the driving wheel in a buffering manner and another spring to the driven wheel in a buffering manner. In this way, the two ropes may be tighten continuously. 
     As shown in  FIG. 17  and  FIG. 18 , an accommodating groove  70  is formed at the upper side of the driven wheel along the rim; a spring  38  is arranged in the accommodating groove  70 ; and a joint structure is arranged at the upper side of the accommodating groove  70 . In the depicted embodiment, the joint structure comprises a pin  39 , which is fixedly connected to the driven wheel  3  through the hole  3   e  and  3   d  on the sidewall of the accommodating groove  70 . The hook ring on one end of the spring  38  hooks the pin  39 , and another hook ring on another end hooks the connection end  18   c  of the rope  18  (which may be a ring). The rope  18  winds the driven wheel  3  for a certain distance, and winds the winding area  260  of the revolving shaft  26  for a certain distance. Another connection end  18   b  (which may be a ring) is clamped to the king pin  30  which is fixedly connected with the revolving shaft  26 . The other parts may be identical or similar to corresponding parts of the aforesaid embodiments and shall not be repeated here. 
     In the depicted embodiment, two springs are used to tighten the ropes, which makes the force provided by each spring may be small. Thus the deformation of the springs may be reduced, which makes assembly easy. Additionally, the springs may be housed in the accommodating groove of the driven wheel and no extra space is occupied. 
     As shown in  FIG. 19  to  FIG. 21 , the joint structure  3   a  and  3   b  of the driven wheel  3  may be accommodating grooves. A connection block  20  is housed in and matched with the joint structure  3   a,  and another connection block  36  is housed in and matched with the joint structure  3   b.  The connection block  20  may be cylindrical, cuboid or other shapes. As shown in  FIG. 21 , the connection block  20  comprises a hollow interior as a housing cavity  701 . An opening is formed on one side of the connection block  20 . A spring  22   a  may be housed in the housing cavity  701  through the opening. Take the side having the opening as the top side of the connection block  20  (that is, the housing cavity  701  is formed concavely at the tope side) and the side opposite to the top side as the bottom side. A hole  702 , which is formed at the bottom side of the connection block  20 , is connected with the housing cavity  701 . Further, the diameter of the hole  702  is smaller than that of the spring  22   a;  thus, one end of the spring  22   a  may be propped against the bottom side of the connection block  20 . 
     As shown in  FIG. 21 , the spring  22   a  is housed in the housing cavity  701  through the opening of the connection block  20 . An end of the rope  17  passes through the hole  702  at the bottom side of the connection block into the housing cavity  701 , and passes the spring  22   a  in the housing cavity. The connection end  17   a  (which may be a knot) at the end of the rope  17  is pressed at the end of the spring  22   a,  which is far away from the bottom side of the connection block  20 . 
     As shown in  FIG. 20 , two pins  21   a  and  21   b  are formed on the driving wheel  14 . Another end of the rope  17  passes through the groove  703  formed on the upper side of the joint structure  3   a  of the driven wheel  3  to the wheel surface of the driven wheel. The rope  17  winds the driven wheel for a certain distance and winds the driving wheel  14  for a certain distance. The connection end  17   b  is clamped to the pin  21   a,  which is fixedly connected to the driving wheel  14 . In addition, as shown in  FIG. 21 , to reduce the damage to the rope, the corner  3   c  of the driven wheel  3  and the corner  20   a  of the connection block  20  may be rounded off. 
     The structure of the connection block  36  may be identical to that of the connection block  20  and the connection of the rope  18  may be identical to that of the rope  17 . The connection block  36  may be housed in and matched with the joint structure  3   b,  and the spring  22   b  is housed in the housing cavity of the connection block  36 . The rope, whose connection end  18   a  is pressed to an end of the spring  22   b,  passes through the spring  22   b  and the hole on the bottom side of the connection block  36 , and winds the driven wheel  3  and the driving wheel  14  for a certain distance respectively. The connection end  18   b  on another end of the rope is clamped to the pin  21   b  which is fixedly connected to the driving wheel  14 . 
     The springs  22   a  and  22   b  are compression springs in the depicted embodiment. One end of a compression spring is against to the bottom side of the connection block and another end is pressed by the connection end of a rope. Thus the force to tighten the rope may be offered by the elastic force of the compressed spring. Furthermore, in the illustrated embodiment, the connection block, in which the spring is housed, is housed in the driving wheel, thus the space occupied by the spring and the connection block is contained within the space occupied by the driven wheel. No extra space is needed. In this way the space occupied by the probe may be reduced. 
     In the depicted embodiment, only one spring may be used. As shown in  FIG. 21 , a similar structure may be used except that the connection block  36  and spring  22   b  are not used herein and the connection end  18   a  of the rope  18  is directly connected to the joint structure  3   b  of the driven wheel  3 . In this embodiment, the rope may be tightened continuously by adopting only one spring. 
     In other embodiments, the springs may be replaced with other elastic parts, such as elastic slices, as shown in  FIG. 23  to  FIG. 25 . Referring to  FIG. 23  and  FIG. 24 , the joint structure  3   a  has a spring piece  32  instead of link block and spring. Instead of connection blocks and springs, an elastic slice  32  is arranged on the joint structure  3   a.  A connection end  320  is arranged on one end of the elastic slice  32 . The connection end  320  extends into the groove of the joint structure  3   a,  while another end of the elastic slice  32  is fixedly connected to the driven wheel  3  through the screw  33 . The connection end  17   a  of the rope  17  passes through the groove  703  at the upper side of the joint structure  3   a  of the driven wheel  3 , enters the groove of the joint structure  3   a,  and is connected to the connection end  320  of the elastic slice  32 . The other parts and the winding of the rope in the embodiment are identical to those in the last embodiment. 
     As shown in  FIG. 25 , the connection blocks and springs at the joint structures  3   a  and  3   b  are replaced with the elastic slices. The other parts in the embodiment are identical to those described above and shall not be repeated here. 
     Though the above embodiments describe the invention in detail, the invention is not limited by these specific embodiments. It will be understood by those having skill in the art that many changes may be made to the details of the aforesaid embodiments without departing from the underlying principles of the invention.