Patent Publication Number: US-2021170608-A1

Title: Passive joint device, cable guide, and power transmission mechanism

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a passive joint device for connecting arms in a medical robot or the like. 
     Description of the Related Art 
     Laparoscopic surgery is generally performed by a physician who performs incision, excision, and suture of an organ (hereinafter referred to as “surgeon”), by a physician who holds an endoscope (hereinafter referred to as “scopist”), and by a physician who pulls the organ or holds tension during incision in order to deploy the surgeon&#39;s visual field (hereinafter referred to as “assistant”). Some surgical support apparatus (also referred to as surgical support robots) used in laparoscopic surgery attempt to reduce the number of doctors required for surgery by controlling the posture of surgical tools such as forceps, endoscope, and electrocautery by one or more robot arms. 
     Surgical support apparatus used in conventional laparoscopic surgery can be roughly divided into those that perform actions of three persons, i.e., a surgeon, a scopist, and an assistant, and those that hold an endoscope with one arm. Console-type surgery support robots are known to serve as surgeon, scopist, and assistant, and a plurality of robot arms are disposed around a patient or above the patient. 
     As the mechanism of the robot arm, it can be roughly classified into two types: one in which the rotation center on the abdominal wall is mechanically determined, and the other in which the robot itself has a passive joint and it is supported with a degree of freedom with the abdominal wall as a fulcrum, as disclosed in Japanese Patent Laid-Open No. 2018-175863. 
     In a mechanism having a passive joint, there is a problem that the weight of the body on the distal side of the joint is applied to the abdominal wall. The weight on the abdominal wall may be compensated by a counterweight, but a very large mass is required for compactness, which is not practical. Therefore, as disclosed in Japanese Patent Laid-Open No. 2011-115906, a mechanism for compensating the self-weight by a spring has also been proposed, but in such a mechanism, the size of the joint portion becomes a problem. 
     When a passive joint is provided, power cannot be transmitted to the distal end side from the joint. Therefore, as disclosed in Japanese Patent Laid-Open 2018-175863, it was necessary to attach the actuator to the distal end side from the passive joint. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of the above-mentioned problems, and has its object to enable a passive joint used in a medical robot or the like to reduce a downward direction force applied to an arm by a weight of a distal end side while suppressing enlargement of the joint. 
     According to a first aspect of the present invention, there is provided a passive joint device for supporting a rotation-side member rotatably about a horizontal axis in a vertical direction with respect to a fixed-side member, comprising: a cylindrical cam member having a cylindrical surface centered on the horizontal axis and fixed to the fixed-side member, the cam member having a pair of cam surfaces symmetrically arranged on the cylindrical surface about the horizontal axis and formed obliquely along the horizontal axis; a pedestal slidably disposed along the horizontal axis within the horizontal axis fixed to the rotation-side member, the pedestal having a pair of cam followers that contact with each of the pair of cam surfaces; a spring disposed inside the horizontal axis fixed to the rotation-side member, the spring biasing the pedestal toward the fixed-side member along the horizontal axis, wherein the spring force causes the pair of cam followers to come into contact with the pair of cam surfaces, push the pair of cam surfaces, and provide upward rotational force to the rotation-side member to reduce the downward rotational force of the rotation-side member by the weight applied to the rotation-side member. 
     According to a second aspect of the present invention, there is provided a cable guide for guiding a pair of cables one ends of which are fixed to a fixed-side member and the other ends of which are fixed to the rotation-side member, and used in a joint device in which a rotation-side member is rotatably supported about a rotation axis with respect to a fixed-side member, the cable guide comprising: a pipe-shaped member which is rotatably disposed with respect to the rotation axis; and a pair of portions whose envelope has a shape close to arc shape and which are formed to face each other on the outer surface of the pipe-shaped member, a pair of portions slidably guiding each of the pair of cables, wherein the cable guide rotates around the rotation axis while guiding the pair of cables as the pair of cables move in the same direction with each other by relative rotation between the fixed-side member and the rotation-side member. 
     According to a third aspect of the present invention, there is provided a power transmission mechanism used in a passive joint device in which a rotation-side member is rotatably supported about a rotation axis with respect to a fixed-side member and transmitting power from the fixed-side member to the rotation-side member, the power transmission mechanism comprising: a rotation driving source disposed on the fixed-side member; a rotation shaft coaxial with the rotation axis that is transmitted a rotational force from the rotation driving source; a worm gear disposed on the rotation shaft; a worm wheel engaging with the worm gear; and a rotation operation member fixed to the worm wheel, and rotating about an axis perpendicular to the rotation axis. 
     According to a fourth aspect of the present invention, there is provided a power transmission mechanism used in a passive joint device in which a rotation-side member is rotatably supported about a rotation axis with respect to a fixed-side member and transmitting power from the fixed-side member to the rotation-side member, the power transmission mechanism comprising: a rotation driving source disposed on the fixed-side member; a first rotation shaft coaxial with the rotation axis that is transmitted a rotational force from the rotation driving source; a second rotation shaft that is transmitted a rotational force from the first rotation shaft, a worm gear disposed on the second rotation shaft, a worm wheel engaging with the worm gear, a rotation operation member fixed to the worm wheel, and rotating about an axis perpendicular to the rotation axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a configuration of a surgical support apparatus according to an embodiment of the present invention; 
         FIG. 2  is a diagram showing a configuration of a self-weight compensation mechanism according to an embodiment. 
         FIG. 3  is a view of a second passive joint viewed from the front. 
         FIG. 4  is a view showing a state in which the cable guide member is attached to the second passive joint. 
         FIGS. 5A-5D  are diagrams showing examples of how cables are routed. 
         FIGS. 6A and 6B  are diagrams showing a modification of the guide portion of the cable. 
         FIG. 7  is a diagram showing an example of a mechanism for transmitting power to a portion ahead of the passive joint. 
         FIG. 8  is a diagram showing a structure for guiding the movement of the rotation-side member. 
         FIG. 9  is a diagram showing a power transmission mechanism obtained by offsetting the shaft. 
         FIG. 10  is a diagram showing an example of the attachment/detachment mechanism of the surgical tool. 
         FIG. 11  is a diagram showing the arrangement of drapes. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, an embodiment in which the present invention is applied to a medical surgical support apparatus will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a diagram illustrating a configuration of a surgical support apparatus according to an embodiment of the present invention. 
     The surgical support apparatus  10  according to the present embodiment includes a robot arm  12  for controlling the posture of a surgical tool or an end effector inserted through a cannula  13  into a body cavity  11  of a patient. The surgical support apparatus  10  measures an insertion angle and an insertion depth of a surgical tool  14  that is inserted into the body cavity  11  by a surgeon and actually used for surgery (hereinafter, also referred to as a hand-carry medical tool). The robot arm  12  for controlling the posture of the surgical tool  14  or the end effector (hereinafter, also referred to as a robotic medical tool) is configured to be controlled in accordance with the measurement result. 
     More specifically, the robot arm  12  includes a first arm  18  which rotates around the rotation axis  16  in the vertical direction, an active joint  20  for actively rotating the first arm  18  in the direction of arrow A in the horizontal plane, a second arm  24  which rotates around the rotation axis  22  in the vertical direction of the tip of the first arm  18 , and an active joint  26  for actively rotating the second arn  24  in the direction of arrow B in the horizontal plane. Further, robot arm  12  has a third arm  30  which rotates around the rotation axis  28  in the vertical direction of the tip of the second arm  24 , and an active joint  32  for actively rotating the third arm  30  in the direction of arrow C in the horizontal plane. 
     On the distal end of the third arm  30 , a first passive joint  37  for passively rotating the fixed-side member  34  in the direction of arrow D about the rotation axis  36  in the vertical direction is disposed. At the lower end of the fixed member  34 , a second passive joint  42  is disposed which allows the rotation-side member  38  to be passively rotated about a horizontal axis (rotation axis)  40 , which is a horizontal rotation axis, in the direction of arrow E (vertical direction). 
     That is, the robot arm  30  includes at least three-axis active joints  20 ,  26 , and  32  having actuators, and first and second passive joints  37  and  42  having at least two axes, and holds the rod-shaped surgical tool  14  on the distal end side from the second passive joint  42 . Generally, the axes of the first and second passive joints  37  and  42  are orthogonal to each other and intersect at one point, but the mechanism of the present embodiment can be realized even if the axes are not orthogonal to each other or do not intersect at one point. 
     The three-axis active joint may be any mechanism as long as the position and posture of the passive joint are uniquely determined, and is not limited to the configuration shown in  FIG. 1 . In each of the active joints  20 ,  26 ,  32  and the first and second passive joints  37 ,  42 , an encoder for measuring the joint angle is disposed, and the position and orientation of the end effector can be uniquely determined by feeding back the position information. 
     Here, generally, in the configuration as shown in  FIG. 1 , there is a mass of the surgical tool  14  or the like at distal-side from the horizontal axis  40  of the second passive joint  42 , by this mass, a downward force is applied to the abdominal wall  15 . This places a burden on the patient. In order to prevent this, in the present embodiment, the second passive joint  42  is provided with the self-weight compensating mechanism  100 . 
     Hereinafter, the self-weight compensating mechanism  100  will be described.  FIG. 2  is a diagram showing a configuration of the self-weight compensating mechanism  100  according to the present embodiment. 
     Self-weight compensating mechanism  100  disposed in the passive joint  42 , as shown in  FIG. 2 , is mainly provided with a fixed-side member  102 , a horizontal shaft bearing  104 , a cylindrical cam member  106 , a horizontal shaft  40 , a horizontal shaft fixing member  108 , a pair of cam followers  110 , a pair of sliding bearings  112 , a spring pedestal  114 , a spring  116  and a rotation-side member  118 . A pair of cylindrical cam surfaces  106   a  are formed on the cylindrical surface of the cylindrical cam member  106  so as to be symmetrical about the horizontal shaft  40 . The cylindrical cam surfaces  106   a  in contact with the pair of cam followers are formed so as to be inclined along the direction of the horizontal shaft  40 . The horizontal shaft  40  is fixed with respect to the rotation-side member  118 , and is relatively rotatably supported with respect to the fixed-side member  102  by the horizontal bearing  104  and the horizontal shaft fixing member  108 . Note that the cable guide described later is not included in this figure. 
     As shown in  FIG. 2 , a pair of cam followers  110 , a pair of sliding bearings  112  are mounted symmetrically about the horizontal axis  40  on both sides of the spring pedestal  114 , and biasing force of the spring  116  is applied to the spring pedestal  114  toward the fixed side member  102 . Sliding bearing  112  is a bearing which is rotatable independently of the spring pedestal  114  and the cam follower  110 , and rotates on the slide surface  40   a  of the horizontal shaft  40 . That is, the cam followers  110 , the spring pedestal  114 , the slide bearings  112  follows the rotation of the horizontal shaft  40 , receives a restraining force from the cylindrical cam surface  106   a  resisting the biasing force of the spring  116 , and move along the horizontal shaft  40 , and the rotation-side member  118  receives a force for rotating upward about the horizontal shaft  40 . In other words, the rotation-side member  118  receives a rotational moment in the direction of the arrow G due to the weight of its tip, but the cam followers  110  contacting the cylindrical cam surface  106   a  receive a reaction force in the direction of the arrow F from the cylindrical cam surface  106   a  due to the biasing force of the spring  116 . Therefore, on the rotation-side member  118 , the rotational moment of the arrow H direction occurs, and the rotational moment due to the dead weight of the rotation-side member  118  is reduced, or canceled. 
     Here, in the present embodiment, since the cylindrical cam surfaces  106   a  are disposed symmetrically about the horizontal axis  40 , the forces applied to the cam followers  110  are also symmetrical with respect to the axis, and a linear motion guide for accurately sliding the spring pedestal  114  is not necessary. 
       FIG. 3  is a view of the second passive joint  42  viewed from the front. The cam follower  110  is pressed against the cylindrical cam surface  106   a  by the force of the spring  116 . Therefore, the inclination of the cylindrical cam surface  106   a  converts the force of the spring  116  into a moment that rotates upward about the horizontal shaft  40 . This makes it possible to reduce the downward rotational force of the rotation-side member  118  due to the weight of distal side from the horizontal shaft  40 , as described above. This reduces the burden on the patient during surgery. 
     Generally, a spring having a linear characteristic in which displacement and load are proportional is used as the spring  116 , but if the cam curve of the cam surface  106   a  is appropriately designed, the same effect can be obtained by a spring having characteristics such as constant load and non-linearity. 
     Next, a method of passing the cable in the present embodiment will be described. 
     In a drive device used in a robot, a cable is often passed through the joint, but in the present embodiment, since the self-weight compensating mechanism  100  is provided in the second passive joint  42 , the inside of the horizontal shaft  40  is occupied by a mechanism component, and the cable or the like cannot be passed therethrough. Therefore, a routing method of the cable for reducing the load on the cable as much as possible in the configuration of the present embodiment will be described below. 
       FIG. 4  is a view showing a state in which the cable guide member  202  is attached to the second passive joint  42  in the present embodiment. 
     Cable guide member  202  is a pipe-shaped member that can be freely rotated coaxially with the horizontal shaft  40  without affected by any of the horizontal shaft  40 , the fixed-side member  102 , and the rotation-side member  118  in  FIG. 2 . Further, on the outer peripheral surface of the cable guide member  202 , as shown in  FIG. 4 , the guide portion A 204  and the guide portion B 206  having an arcuate portion are disposed. The cables slide over the arcuate surfaces  204   a .  206   a  of the guide portions A 204 , B 206 . Here, in  FIG. 4 , the guide portion A 204  and the guide portion B 206  differ in shape. This is a contrivance for avoiding other components, and it is possible to perform the same function with any shape as long as it has at least a surface for guiding the cable. 
       FIGS. 5A-5D  are diagrams showing an example of how cables are routed. Note that, the technique shown here is applicable not only to electrical cables, but is also applicable to cable-like members, such as a fluid tube or an optical fiber. The cable A 210  and the cable B 212  are disposed while bending three-dimensionally around the cable guide member  202 , and relative movement occurs between the cable guide member  202 . 
       FIGS. 5A and 5B  are diagrams showing the state of the cable A 210 , the cable B 212  and the cable guide  202  when the horizontal shaft  40  is at an angle. There are two types of cable A 210  and cable B 212 , but only one is a cable that is routed distally, and the other may be a mechanical wire. 
     One end and the other end of each cable are fixed by a cable fixing member  214  to the fixed-side member  102  and the rotation-side member  118 , and enter the region of the cable guide member  202  so as to be wound around the shaft. Note that, for convenience of illustration, although the cable fixing member  214  of the fixed-side member  102  is not drawn for the cable A 210 , it is fixed to the fixed-side member  102  similarly to the cable B 212 . 
     Here, consider the case where the rotational angle of the horizontal shaft  40  is changed so that the state of  FIGS. 5A and 5B  changes to the state of  FIGS. 5A and 5B . There is no relative sliding with respect to the cable in both regions of fixed-side member  102  and the rotation-side member  118 , and there is only a simple winding operation. On the other hand, in the region of the cable guide member  202 , either cable slides relative to the cable guide member  202 . As indicated by the positions of the marks  210   a  and  210   b , the cable A 210  and the cable B 212  move in opposite directions, respectively. Further, at this time, the cable guide member  202 , since it is pulled by the cable B 212 , rotates around the horizontal shaft  40 , and the position when viewed from the fixed-side member  102  is changed. 
     Next, consider the case where the rotational angle of the horizontal shaft  40  is changed so that the state of  FIGS. 5C and 5D  changes to the state of  FIGS. 5A and 5B . At this time, since the cable A 210  performs an operation to pull the cable guide member  202 , the cable guide member  202  rotates in the opposite direction and returns to the state shown in  FIGS. 5A and 5B . Since the cable for wiring is also used to drive the cable guide member  202 , the cable can pass through the joint portion without changing the cable length while maintaining a reasonable radius of curvature with respect to the cable. 
     In the example shown here, by arranging the cable A 210  and the cable B 212  to face each other, the cable guide member  202  is driven in the opposite direction, but it is not limited to this method as long as a similar effect can be obtained. For example, a method of providing a torsion spring such as moment is always applied in a certain direction to the cable guide member, or a method of driving the cable guide member by a gear or the like interlocked with the angle of the horizontal shaft is also conceivable. In such a manner, either the cable A 210  or the cable B 212  path alone can behave in a similar manner. 
     In the above explanation, the guide surfaces of the guide portion A 204  and the guide portion B 206  are described as arc-shaped, but the present invention is not limited to the arc-shaped shape. For example, the guide surface does not need to have a true circle shape even if arcuate, but the guide portion may have shape whose envelope has a shape close to the arc shape, such as polygonal shape close to arc shape as shown in  FIG. 6A  or the shape in which pins and balls are arrayed close to the arc shape as shown in  FIG. 6B . 
     Next, a method of transmitting power to a portion ahead of the passive joint  42  will be described. In the section on the related art, it was described that when a passive joint is provided, since power cannot be transmitted to the distal side of the joint, it is necessary to attach an actuator to the distal side of the passive joint. However, in the case of a simple operation, it may be easier to mechanically transmit power without providing an actuator to the distal side of the passive joint. Here, the mechanism will be described. 
       FIG. 7  is a diagram showing an example of a mechanism for transmitting power to a portion ahead of the passive joint. Since the first passive joint  37  and the second passive joint  42  are passive joints having no actuator, the fixed-side member  34  can freely rotate about the vertical rotation axis  36 , and the rotation-side member  38  can freely rotate about the horizontal shaft  40 . In general, the horizontal shaft  40  and the vertical axis  36  intersect at one point orthogonally, but this is not necessary. 
     In  FIG. 7 , the rotational force of the rotation driving source  302  made of a motor or the like is transmitted to the worm shaft  308  through the pulley  304  and the belt  306 . Here, the worm shaft  308  and the horizontal shaft  40  is coaxial, and each axis can be rotated independently. When the worm shaft  308  is supported and rotated by the worm bearing  309 , power is transmitted through the worm gear  310  to the worm wheel  312 . Thus, the rotation operation member  314  that is a driven body is rotated around the rotation axis  316  perpendicular to the paper surface. The surgical tool  14  is mounted on the rotation operation member  314 . 
     Note that, in  FIG. 7 , the worm wheel  312  is not provided on entire circumference, but there are teeth only in a portion. If it is required to rotate one rotation of the rotation operation member  314 , the worm wheel  312  is provided on the entire circumference. If there can be a limitation in the rotation angle, it may only be provided in a portion as shown in  FIG. 7 . 
     Here, the rotation operation member  314  must move while being restrained in a curved shape. An example of a structure enabling this is shown in  FIG. 8 . 
     In  FIG. 8 , the rolling bearing  324  such as a bearing moves in the groove  322  formed in the rotation-side member  38 , and the rotation operation member  314  can be moved while being restrained in a curved shape. However, since only the rolling bearing  324  cannot support movement in all directions, the rotation operation member  314  is slidably supported by the side surface  326  and the R guide surface (sliding surface) of the rotation-side member  328 . 
     Returning to  FIG. 7 , the power generated by the rotation driving source  302  is transmitted to the worm wheel  312  through the pulley  304 , the belt  306 , and the worm gear  310 , and the rotation operation member  314  is driven to rotate. At this time, if the worm wheel  312  is locked, or if the load is very large, the torque for rotating the worm shaft  308  becomes a torque for rotating the horizontal shaft  40 . However, since the reduction ratio by the worm gear is generally very large, it is slight even if the torque to rotate the horizontal shaft is generated. 
     Generally, a surgical tool  14  in the shape of a long shaft such as a forceps or an endoscope is mounted on the rotation operation member  314 , and is supported by the outer cannula  13 . Therefore, even when a slight torque is generated in the horizontal shaft  40 , the rotation operation member  314  is not rotated around the horizontal shaft  40 . It can also be solved by adding a friction force generating mechanism (brake or damper) that does not affect the passive rotation of the horizontal shaft  40 . 
     In the mechanism shown in  FIG. 7 , although the horizontal shaft  40  and the rotation axis  316  of the rotation operation member  314  do not intersect, the vertical axis  36 , the horizontal shaft  40  and the rotation axis  316  can intersect at one point as shown in  FIG. 9  by offsetting the axis by the second belt  332 . 
     Further, in the above example, it has been described that power is transmitted from the rotation driving source  302  by the belt  306 , but it may be via a gear or similar transmission mechanism. 
     Next, a mechanism for attaching and detaching the surgical tool  14  to and from the rotation operation member  314  will be described. 
     Generally, surgical tools are attached to distal side of the passive joints and are frequently removed for replacement. Here, a mechanism that enables attachment and detachment of the surgical tool  14  to and from the rotation operation member  314  described above will be described. 
       FIG. 10  is a view showing an example of the attachment/detachment mechanism of the surgical tool  14 . As shown in  FIG. 9 , the rotation operation member  314  is provided with a fixing projection  342 , and the fixing adapter  344  is attached so as to engage with the fixing projection  342 . A fixing screw  345  or the like is used for the mounting, but the fixing method is not limited thereto. 
     A medical tool adapter  346  is detachably mounted to the fixing adapter  344 . The medical tool adapter  346  is an adapter for attaching the surgical tool  14  to the fixing adapter  344 , and may have several types according to the shape of the surgical tool  14  to be attached. A fixing claw  348  biased by a spring (not shown) is disposed on the fixing adaptor  344 , and the medical tool adaptor  346  is engaged with the fixing claw  348  and attached to the fixing adaptor  344 . The medical tool adapter  346  can also be removed from the fixing adapter  344  by pushing on the release lever  350 . 
     Next.  FIG. 11  is a diagram showing an arrangement of drapes. Generally, since a robot cannot be cleaned or sterilized, the robot is covered by a bag-like covering  352  called as a drape to separate a clean portion and a non-clean portion. In this embodiment, as shown in  FIG. 11 , a hole is provided in a part of the cover  352  to expose the fixing projection  342 , and the fixing adapter  344  is attached. 
     Since the fixing projection  342  is a non-clean portion, it must be exposed as little as possible. In the structure of the present embodiment, since the medical tool adapter  346  can be removed without removing the fixing adapter  344 , it is possible to attach and detach the device without touching the exposed non-clean portion. 
     As described above, according to the above embodiment, by providing the passive joint with the self-weight compensation mechanism by the spring, it is possible to reduce the downward rotational force applied to the rotation-side member by the weight of the tip side while suppressing the enlargement of the joint. 
     Further, by placing a pipe-shaped cable guide member having arcuate cable guide surface and being rotatable around the horizontal axis on the second passive joint, even when providing the self-weight compensation mechanism to the passive joint, it is possible to perform routing of the cable without putting a burden on the cable. 
     Further, by providing the power transmission mechanism as described above in the passive joint, it is possible to transmit power to a portion ahead of the passive joint with a simple configuration. 
     This application claims the benefit of Japanese Patent Application No. 2019-220499, filed Dec. 5, 2019, which is hereby incorporated by reference herein in its entirety.