Abstract:
A method of performing minimally invasive endoscopic surgery in a body cavity of a patient includes introducing an elongate shaft having a working end into the cavity. The elongate shaft has a proximal end and a shaft axis between the working end and the proximal end. A wrist member pivotally coupled with the working end is rotated relative to the working end. The wrist member has a wrist axis. The method further includes rotating at least one of the elongate shaft around the shaft axis and an end effector pivotally mounted on the wrist member around the wrist axis to position the end effector at a desired location inside the cavity.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a divisional application and claims the benefit of U.S. patent application Ser. No. 10/340,129, filed Jan. 10, 2003 now U.S. Pat. No. 6,685,698, which is a divisional of U.S. patent application Ser. No. 09/626,527, filed Jul. 27, 2000, now U.S. Pat. No. 6,746,443, the entire disclosures of which are incorporated herein by reference. 
     This application is related to the following patents and patent applications, the full disclosures of which are incorporated herein by reference: PCT International Application No. PCT/US98/19508, entitled “Robotic Apparatus”, filed on Sep. 18, 1998, U.S. application Ser. No. 09/418,726, entitled “Surgical Robotic Tools, Data Architecture, and Use”, filed on Oct. 15, 1999; U.S. Application Ser. No. 60/111,711, entitled “Image Shifting for a Telerobotic System”, filed on Dec. 8, 1998; U.S. application Ser. No. 09/378,173, entitled “Stereo Imaging System for Use in Telerobotic System”, filed on Aug. 20, 1999; U.S. application Ser. No. 09/398,507, entitled “Master Having Redundant Degrees of Freedom”, filed on Sep. 17, 1999, U.S. application Ser. No. 09/399,457, entitled “Cooperative Minimally Invasive Telesurgery System”, filed on Sep. 17, 1999; U.S. application Ser. No. 09/373,678, entitled “Camera Referenced Control in a Minimally Invasive Surgical Apparatus”, filed on Aug. 13, 1999, now U.S. Pat. No. 6,424,885; U.S. application Ser. No. 09/398,958, entitled “Surgical Tools for Use in Minimally Invasive Telesurgical Applications”, filed on Sep. 17, 1999, now U.S. Pat. No. 6,394,998; and U.S. Pat. No. 5,808,665, entitled “Endoscopic Surgical Instrument and Method for Use”, issued on Sep. 15, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     Advances in minimally invasive surgical technology could dramatically increase the number of surgeries performed in a minimally invasive manner. Minimally invasive medical techniques are aimed at reducing the amount of extraneous tissue that is damaged during diagnostic or surgical procedures, thereby reducing patient recovery time, discomfort, and deleterious side effects. The average length of a hospital stay for a standard surgery may also be shortened significantly using minimally invasive surgical techniques. Thus, an increased adoption of minimally invasive techniques could save millions of hospital days, and millions of dollars annually in hospital residency costs alone. Patient recovery times, patient discomfort, surgical side effects, and time away from work may also be reduced with minimally invasive surgery. 
     The most common form of minimally invasive surgery may be endoscopy. Probably the most common form of endoscopy is laparoscopy, which is minimally invasive inspection and surgery inside the abdominal cavity. In standard laparoscopic surgery, a patient&#39;s abdomen is insufflated with gas, and cannula sleeves are passed through small (approximately ½ inch) incisions to provide entry ports for laparoscopic surgical instruments. The laparoscopic surgical instruments generally include a laparoscope (for viewing the surgical field) and working tools. The working tools are similar to those used in conventional (open) surgery, except that the working end or end effector of each tool is separated from its handle by an extension tube. As used herein, the term “end effector” means the actual working part of the surgical instrument and can include clamps, graspers, scissors, staplers, and needle holders, for example. To perform surgical procedures, the surgeon passes these working tools or instruments through the cannula sleeves to an internal surgical site and manipulates them from outside the abdomen. The surgeon monitors the procedure by means of a monitor that displays an image of the surgical site taken from the laparoscope. Similar endoscopic techniques are employed in, e.g., arthroscopy, retroperitoneoscopy, pelviscopy, nephroscopy, cystoscopy, cistemoscopy, sinoscopy, hysteroscopy, urethroscopy and the like. 
     There are many disadvantages relating to current minimally invasive surgical (MIS) technology. For example, existing MIS instruments deny the surgeon the flexibility of tool placement found in open surgery. Most current laparoscopic tools have rigid shafts, so that it can be difficult to approach the worksite through the small incision. Additionally, the length and construction of many endoscopic instruments reduces the surgeon&#39;s ability to feel forces exerted by tissues and organs on the end effector of the associated tool. The lack of dexterity and sensitivity of endoscopic tools is a major impediment to the expansion of minimally invasive surgery. 
     Minimally invasive telesurgical robotic systems are being developed to increase a surgeon&#39;s dexterity when working within an internal surgical site, as well as to allow a surgeon to operate on a patient from a remote location. In a telesurgery system, the surgeon is often provided with an image of the surgical site at a computer workstation. While viewing a three-dimensional image of the surgical site on a suitable viewer or display, the surgeon performs the surgical procedures on the patient by manipulating master input or control devices of the workstation. The master controls the motion of a servomechanically operated surgical instrument. During the surgical procedure, the telesurgical system can provide mechanical actuation and control of a variety of surgical instruments or tools having end effectors such as, e.g., tissue graspers, needle drivers, or the like, that perform various functions for the surgeon, e.g., holding or driving a needle, grasping a blood vessel, or dissecting tissue, or the like, in response to manipulation of the master control devices. 
     Some surgical tools employ a roll-pitch-yaw mechanism for providing three degrees of rotational movement to an end effector around three perpendicular axes. At about 90° pitch, the yaw and roll rotational movements overlap, resulting in the loss of one degree of rotational movement. 
     SUMMARY OF THE INVENTION 
     The present invention is generally directed to robotic surgery methods, devices, and systems. The invention provides a minimally invasive surgical tool which operates with three degrees of rotational movement at about 90° pitch. In particular, the surgical tool employs a roll-pitch-roll configuration in which an elongate shaft is rotatable in proximal roll, a wrist member is pivotally mounted on the working end of the elongate shaft to rotate in pitch, and an end effector is pivotally mounted on the wrist member to rotate in distal roll around the wrist axis of the wrist member. At about 90° pitch, the wrist axis is generally perpendicular to the shaft axis of the elongate shaft. The proximal roll around the shaft axis and the distal roll around the wrist axis do not overlap. In some embodiments, a pulley and cable mechanism is used to rotate and actuate the end effector. 
     In some embodiments, the end effector can be bent back beyond 90° pitch. The mechanism coupling the end effector to the working end of the elongate shaft allows the wrist member and end effector to bend back by an angle θ of more than about 90° from the forward position, desirably by more than about 120°, and more desirably by more than about 135°. The ability to operate the end effector at about 90° pitch and to bend back the end effector renders the wrist mechanism more versatile and adaptable to accessing hard to reach locations, particularly with small entry points such as those involving spinal, neural, or rectal surgical sites. In specific embodiments, a pair of linking arms are pivotally connected between the working end and the wrist member to facilitate bend back pitching while maintaining the size of the tool to a sufficiently small size for minimally invasive surgical applications. 
     In accordance to an aspect of the present invention, a minimally invasive surgical instrument comprises an elongate shaft having a working end and a shaft axis, and at least one linking arm having a proximal end and a distal end. The proximal end is pivotally mounted on the working end of the shaft to rotate around a first pitch axis which is nonparallel to the shaft axis. A wrist member has a proximal portion pivotally connected to the distal end of the linking arm to rotate around a second pitch axis which is nonparallel to the shaft axis. An end effector is pivotally mounted on a distal portion of the wrist member to rotate around a wrist axis of the wrist member. The wrist axis extends between the proximal portion and the distal portion of the wrist member. The elongate shaft is rotatable around the shaft axis. 
     In some embodiments, the first pitch axis and the second pitch axis are parallel, and are perpendicular to the shaft axis. A pair of linking arms are connected between the working end and the wrist member. The end effector includes an end effector support pivotally mounted on the distal portion of the wrist member to rotate around the wrist axis. The end effector includes at least one end effector link pivotally mounted on the end effector support to rotate around a pivot axis which is nonparallel to the wrist axis. The pivot axis may be perpendicular to the wrist axis. The end effector may include a pair of end effector links. The end effector links may be rotatable around the pivot axis to move toward and away from one another. The end effector links may be rotatable around the pivot axis to move together in the same direction. One of the end effector links may be fixed relative to the end effector support. 
     In accordance with another aspect of the invention, a minimally invasive surgical instrument comprises an elongate shaft having a working end and a proximal end. The elongate shaft has a shaft axis between the proximal end and the working end. A wrist member includes a wrist axis between a proximal portion and a distal portion. An end effector is pivotally mounted on the distal portion of the wrist member to rotate around the wrist axis. At least one linking member is rotatably coupled between the working end and the wrist member to permit rotation of the wrist member relative to the working end, from a forward position in which the wrist axis is oriented with the end effector at the distal portion pointing generally away from the proximal end of the elongate shaft, to a backward position in which the wrist axis is oriented with the end effector at the distal portion pointing generally toward the proximal end of the elongate shaft. 
     In accordance with another aspect of the present invention, a method of performing minimally invasive surgery in a body cavity of a patient comprises introducing an elongate shaft having a working end into the cavity. The elongate shaft has a proximal end and a shaft axis between the working end and the proximal end. A wrist member which is pivotally coupled with the working end is rotated relative to the working end. The wrist member having a wrist axis. The method further comprises rotating at least one of the elongate shaft around the shaft axis and an end effector pivotally mounted on the wrist member around the wrist axis to position the end effector at a desired location inside the cavity. 
     In some embodiments, the wrist member is rotated around a pitch axis which is perpendicular to at least one of the shaft axis and the wrist axis to change an angle between the wrist axis and the shaft axis. The wrist member is rotated relative to the working end until the wrist axis is approximately perpendicular to the shaft axis. The wrist member may be rotated relative to the working end from a forward position in which the wrist axis is oriented with the end effector pointing generally away from the proximal end of the elongate shaft, to a backward position in which the wrist axis is oriented with the end effector pointing generally toward the proximal end of the elongate shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a robotic arm and surgical instrument assembly according to a preferred embodiment of the invention; 
         FIG. 2  is a perspective view of the robotic arm and surgical instrument assembly of  FIG. 1 ; 
         FIG. 3  is a perspective view of a surgical instrument according to a preferred embodiment of the invention; 
         FIG. 4  is a schematic kinematic diagram corresponding to the side view of the robotic arm shown in  FIG. 1 , and indicates the arm having been displaced from one position into another position; 
         FIG. 5  is a perspective view of a roll-pitch-yaw wrist mechanism; 
         FIG. 6  is a front view of the wrist mechanism of  FIG. 5  along arrow VI; 
         FIG. 7  is a side view of the wrist mechanism of  FIG. 5  along arrow VII; 
         FIG. 8  is a perspective view of the wrist mechanism of  FIG. 5  schematically illustrating the singularity at the 90° pitch position; 
         FIG. 9  is a perspective view of a roll-pitch-roll wrist mechanism according to a preferred embodiment of the present invention; 
         FIG. 10  is a front view of the wrist mechanism of  FIG. 9  along arrow X; 
         FIG. 11  is a side view of the wrist mechanism of  FIG. 9  along arrow XI; 
         FIG. 12  is a perspective view of the wrist mechanism of  FIG. 9  at the 90° pitch position; 
         FIG. 13  is a perspective view of a roll-pitch-roll wrist mechanism according to another preferred embodiment of the present invention; 
         FIG. 14  is a sectional view of the wrist mechanism of  FIG. 13  along XIV—XIV; 
         FIG. 15  is another perspective view of the wrist mechanism of  FIG. 13 ; 
         FIG. 16  is another perspective view of the wrist mechanism of  FIG. 13 ; and 
         FIG. 17  is a perspective view of the wrist mechanism of  FIG. 13  schematically illustrating the bend back feature of the end effector. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 and 2  illustrate a robotic arm and surgical instrument assembly  10 . The assembly  10  includes a robotic arm  12  and a surgical instrument  14 .  FIG. 3  indicates the general appearance of the surgical instrument  14 . 
     The surgical instrument  14  includes an elongate shaft  14 . 1 . A wrist-like mechanism  50  is located at a working end of the shaft  14 . 1 . A housing  53  arranged releasably to couple the instrument  14  to the robotic arm  12  is located at an opposed end of the shaft  14 . 1 . In  FIG. 1 , and when the instrument  14  is coupled or mounted on the robotic arm  12 , the shaft  14 . 1  extends along an axis indicated-at  14 . 2 . The instrument  14  is typically releasably mounted on a carriage  11  which is driven to translate along a linear guide formation  24  in the direction of arrows P. The surgical instrument  14  is described in greater detail herein below. 
     The robotic arm  12  is typically mounted on a base (not shown) by a bracket or mounting plate  16 . The base is typically in the form of a mobile cart or trolley (not shown) which is retained in a stationary position during a surgical procedure. 
     The robotic arm  12  includes a cradle  18 , an upper arm portion  20 , a forearm portion  22 , and the guide formation  24 . The cradle  18  is pivotally mounted on the plate  16  in a gimbaled fashion to permit rocking movement of the cradle in the direction of arrows  26  about a pivot axis  28 , as shown in  FIG. 2 . The upper arm portion  20  includes link members  30 ,  32  and the forearm portion  22  includes link members  34 ,  36 . The link members  30 ,  32  are pivotally mounted on the cradle  18  and are pivotally connected to the link members  34 ,  36 . The link members  34 ,  36  are pivotally connected to the guide formation  24 . The pivotal connections between the link members  30 ,  32 ,  34 ,  36 , the cradle  18 , and the guide formation  24  are arranged to enable the robotic arm to move in a specific manner. 
     The movements of the robotic arm  12  is illustrated schematically in  FIG. 4 . The solid lines schematically indicate one position of the robotic arm and the dashed lines indicate another possible position into which the arm can be displaced from the position indicated in solid lines. 
     It will be understood that in a preferred embodiment, the axis  14 . 2  along which the shaft  14 . 1  of the instrument  14  extends when mounted on the robotic arm  12  pivots about a pivot center or fulcrum  49 . Thus, irrespective of the movement of the robotic arm  12 , the pivot center  49  normally remains in substantially the same position relative to the stationary cart  300  on which the arm  12  is mounted. In use, the pivot center  49  is typically positioned at a port of entry into a patient&#39;s body during an endoscopic procedure when an internal surgical procedure is to be performed. It will be appreciated that the shaft  14 . 1  extends through such a port of entry, the wrist-like mechanism  50  then being positioned inside the patient&#39;s body. Thus, the general position of the mechanism  50  relative to the surgical site in a patient&#39;s body can be changed by movement of the arm  12 . Since the pivot center  49  is coincident with the port of entry, such movement of the arm does not excessively effect the surrounding tissue at the port of entry. It is to be appreciated that the field of application of the invention is not limited to surgical procedures at internal surgical sites only, but can be used on open surgical sites as well. 
     As can best be seen in  FIG. 4 , the robotic arm  12  provides three degrees of freedom of movement to the surgical instrument  14  when mounted thereon. These degrees of freedom of movement are firstly the gimbaled motion indicated by arrows  26 , pivoting or pitching movement as indicated by arrows  27 , and the linear displacement in the direction of arrows P. Movement of the arm as indicated by arrows  26 ,  27  and P is controlled by appropriately positioned actuators, e.g., electrical motors or the like, which respond to inputs from its associated master control to drive the arm  12  to a desired position as dictated by movement of the master control. 
     Roll-Pitch-Yaw Mechanism 
       FIGS. 5 ,  6  and  7  show a roll-pitch-yaw wrist-like mechanism  50 . In  FIG. 5 , the working end of the shaft  14 . 1  is indicated at  14 . 3 . The wrist-like mechanism  50  includes a rigid wrist member  52 . One end portion of the wrist member  52  is pivotally mounted in a clevis  17  on the end  14 . 3  of the shaft  14 . 1  by means of a pivotal connection  54 . As best seen in  FIG. 7 , the wrist member  52  can pitch in the direction of arrows  56  about the pivotal connection  54 . This rotation around the pivotal connection  54  in the direction  56  is referred to as the pivot or pitch of the wrist member  52 . The end  14 . 3  is rotatable with the shaft  14 . 1  around the axis  14 . 2  in the direction H, as shown in  FIGS. 3 and 5 . This rotation around the axis  14 . 2  in the direction H is referred to as the roll of the working end  14 . 3 . 
     An end effector, generally indicated by reference numeral  58 , is pivotally mounted on an opposed end of the wrist member  52 . The end effector  58  is in the form of forceps or graspers for grasping tissue or the like during a surgical procedure. Accordingly, the end effector  58  has two parts  58 . 1 ,  58 . 2  together defining a jaw-like arrangement. The end effector  58  is pivotally mounted in a clevis  19  on an opposed end of the wrist member  52 , by means of a pivotal connection  60 . Free ends  11 ,  13  of the parts  58 . 1 ,  58 . 2  are angularly displaceable about the pivotal connection  60  toward and away from each other as indicated by arrows  62 ,  63  in  FIG. 6 . This movement of the parts  58 . 1 ,  58 . 2  is referred to as the grip of the end effector  58 . The members  58 . 1 ,  58 . 2  can be displaced angularly about the pivotal connection  60  to change the orientation of the end effector  58  as a whole, relative to the wrist member  52 . Thus, each part  58 . 1 ,  58 . 2  is angularly displaceable about the pivotal connection  60  independently of the other, so that the end effector  58  is, as a whole, angularly displaceable about the pivotal connection  60  in the direction  61 , as indicated in dashed lines in  FIG. 6 . This rotation around the pivotal connection  60  in the direction  61  is referred to the yaw of the end effector  58 . The wrist mechanism  50  as illustrated in  FIGS. 5–7  is referred to as a roll-pitch-yaw mechanism having roll in the direction H, pitch in the direction  56 , and yaw in the direction  61 . 
     The parts  58 . 1 ,  58 . 2  each include an elongate finger portion or end effector element  58 . 3  and an end effector mounting formation in the form of, e.g., a pulley portion  58 . 5 . In a preferred embodiment, the finger portion  58 . 3  is integrally formed with the pulley portion  58 . 5 . The pulley portion  58 . 5  defines a circumferentially extending channel  58 . 6  in which an elongate element in the form of, e.g., an activation cable, is carried. A generally circumferentially directed hole  58 . 8  extends through a nape region of the finger portion  58 . 3  and generally in register with the circumferentially extending channel  58 . 6 . The hole  58 . 8  has a first portion  58 . 9  and a second portion  58 . 10  having a diameter greater than the first portion  58 . 9 . In use, the activation cable has a thickened portion along its length which seats in the hole portion  58 . 10 , the rest of the activation cable then extending along the channel  58 . 6  in opposed directions. The thickened portion is crimped in its seated position in the hole portion  58 . 10  so as to anchor the cable in the hole  58 . 8 . It will be appreciated that a greater force is necessary to clamp the free ends together when gripping an object therebetween, than that which is required to open the free ends  11 ,  13 . Thus, the thickened portion of the cable is urged against an annular stepped surface between the hole portion  58 . 9  and the hole portion  58 . 10 , when the free ends  11 ,  13  are urged into a closed condition. 
     As best seen in  FIG. 6 , the wrist member  52  is flanked by two sets of pulleys  64 ,  66  which are coaxially positioned on the pivotal connection  54  and in the clevis  17  at the end  14 . 3  of the shaft  14 . 1 . Two further sets of pulleys  68 ,  70  are rotatably mounted on opposed sides of the wrist member  52 . Each pulley of the set of pulleys  68  on the one side of the wrist member  52  is generally co-planar with an associated pulley of the pulley set  66 . Furthermore, each of the pulleys  68  is positioned such that its circumference is in close proximity to the circumference of its associated pulley of the pulley set  66 . A similar arrangement exists for each pulley of the pulley set  70  on the other side of the wrist member and its associated pulley of the pulley set  64 . Thus, the circumferentially extending channel formation of each pulley of the pulley sets  68 ,  70  and their associated pulleys of the pulley sets  64 ,  66  define between each of them a space  72  through which an activation cable can snugly pass. 
     A plurality of elongate elements, e.g., cables, are used to effect movement of the wrist mechanism  50  and end effector  58 . As seen in  FIG. 7 , two cables C 1 , C 2  are anchored on the parts  58 . 1 ,  58 . 2 , respectively, to effect movement of the parts  58 . 1 ,  58 . 2  independently in directions  62 ,  63  or as a whole ( FIG. 6 ). 
     Cable C 1  rides over an outer pulley of the pulley set  64 , an outer pulley of the pulley set  70 , over part of circumferential channel  58 . 6  of the pulley portion  58 . 5  of the part  58 . 2  of the end effector  58 , through the hole  58 . 8 , again along part of the circumferential channel  58 . 6  of the pulley portion  58 . 5 , over an outer pulley of the pulley set  68  and over an outer pulley of the pulley set  66 . Similarly, cable C 2  rides over an inner pulley of the pulley set  64 , over an inner pulley of the pulley set  70 , along the circumferential channel  58 . 6  of the part  58 . 1  of the end effector  58 , through the hole  58 . 8  of the part  58 . 1 , again along the circumferential channel  58 . 6  of the pulley portion  58 . 5 , over an inner pulley of the pulley set  68  and over an inner pulley of the pulley set  66 . The cables C 1 , C 2  pass from the wrist mechanism  50  through appropriately positioned holes  47  in the base region of the clevis  17  ( FIG. 5 ), and internally along the shaft, toward the housing  53  ( FIG. 3 ). The housing  53  includes driving members, e.g., in the form of spool assemblies for manipulating the cables. Additional details of the spool assemblies and the grip mechanism for manipulating the finger portions  58 . 1 ,  58 . 2  to achieve gripping as well as description of various surgical tools can be found in U.S. application Ser. No. 09/398,958, entitled “Surgical Tools for Use in Minimally Invasive Telesurgical Applications”, filed on Sep. 17, 1999. 
     When the end effector  58  is oriented forward, the roll, pitch, and yaw provide rotational movements relative to three generally perpendicular axes.  FIG. 8  shows the position of the end effector  58  after rotation in pitch in the direction  56  of the wrist member  52  around the pivotal connection  54  by about 90°. In this position, the yaw in the direction  61  around the pivotal connection  60  overlaps with the roll H of the working end  14 . 3 . The overlap or redundancy results in the loss of one degree of freedom of movement of the end effector  58  at or near this position of singularity. In some applications, the end effector  58  may be used primarily at this position of about 90° pitch. It is desirable to provide a wrist mechanism that does not operate at a singularity in this position. 
     Roll-Pitch-Roll Mechanism 
       FIGS. 9–11  show a roll-pitch-roll wrist-like mechanism  500 . In  FIG. 9 , the working end of the tool shaft is indicated at  502 , and includes a pair of extensions  506 . The wrist-like mechanism  500  includes a rigid wrist member  504 . One end portion of the wrist member  504  forms a clevis  508  in which the extensions  506  of the working end  502  of the tool shaft is pivotally mounted by means of a pivotal connection  510 . As best seen in  FIG. 10 , the wrist member  504  can pitch in the direction of arrows  512  about the pivotal connection  510 . This rotation around the pivotal connection  510  in the direction  512  is referred to as the pivot or pitch of the wrist member  504 . The end  502  is rotatable with the tool shaft around the shaft axis in the direction  516 . This rotation around the shaft axis in the direction  516  is referred to as the roll of the working end  502 . 
     An end effector, generally indicated by reference numeral  514 , is supported on an end effector support base  518  which is pivotally mounted on an opposed end of the wrist member  504  to rotate around its axis in the direction  520  as shown in  FIG. 9 . In the embodiment shown, the axis of the base  518  coincides with the axis of the wrist member  504 . The rotation in the direction  520  is referred to the distal roll of the end effector  514 . This distal roll of the end effector  514  in the direction  520  is differentiated from the proximal roll of the working end  502  in the direction  516 . In the position of the wrist mechanism  500  as shown in  FIGS. 9–11 , the distal roll  520  of the end effector  514  overlaps with the proximal roll  516  of the working end  502 . Because the rotation of the wrist member  504  around the pivotal connection  510  provides pitch  512  of the end effector  514 , the distal roll  520  generally will not coincide with the proximal roll  516 . The wrist mechanism  500  as illustrated in  FIGS. 9–11  is referred to as a roll-pitch-roll mechanism. 
     The end effector  514  is in the form of forceps or graspers for grasping tissue or the like during a surgical procedure. Accordingly, the end effector  514  has two parts  522 . 1 ,  522 . 2  together defining a jaw-like arrangement. The two parts  522 . 1 ,  522 . 2  are pivotally mounted in a clevis  524  on the base  518 , by means of a pivotal connection  526 . Free ends  528 . 1 ,  528 . 2  of the parts  522 . 1 ,  522 . 2  are angularly displaceable about the pivotal connection  526  toward and away from each other as indicated by arrows  530 ,  532  in  FIG. 10 . This movement is referred to as the grip of the end effector  514 . The members  522 . 1 ,  522 . 2  can be displaced angularly about the pivotal connection  526  to change the orientation of the end effector  514  as a whole, relative to the wrist member  504 . Thus, each part  522 . 1 ,  522 . 2  is angularly displaceable about the pivotal connection  526  independently of the other, so that the end effector  514  is, as a whole, angularly displaceable about the pivotal connection  526  in the direction  534 , as shown in  FIG. 10 . This rotation around the pivotal connection  526  is referred to the yaw of the end effector  514 . In the position of the wrist mechanism  500  as shown in  FIGS. 9–11 , the yaw  534  of the end effector  514  overlaps with the pitch  512  of the wrist member  504 . Because the rotation of the base  518  provides distal roll  520  of the end effector  514 , the yaw  534  generally will not coincide with the pitch  512 . With the additional degree of freedom in yaw in the specific embodiment shown, the wrist mechanism  500  as illustrated in  FIGS. 9–11  may be referred to as a roll-pitch-roll-yaw mechanism. 
     The parts  522 . 1 ,  522 . 2  each include an elongate finger portion or end effector element  536  and an end effector mounting formation in the form of, e.g., a pulley portion  538 . The finger portion  536  may be integrally formed with the pulley portion  538 . The pulley portion  538  defines a circumferentially extending channel for receiving an activation cable in a manner similar to the pulley portion  58 . 5  in the end effector  58  of  FIGS. 5–7 . Two elongate members such as cables C 1 , C 2  are used to effect movement of the parts  522 . 1 ,  522 . 2  in yaw  534  and grip  530 ,  532 . The cables C 1 , C 2  pass from the wrist mechanism  500  internally through the shaft toward the housing  53  ( FIG. 3 ). For simplicity, details of the pulley portion  538  in the end effector  514  of  FIGS. 9–11  are omitted. The configuration and operation of the parts  522 . 1 ,  522 . 2  are similar to those of the parts  58 . 1 ,  58 . 2  in  FIGS. 5–7 . 
     In an alternate embodiment, the end effector  514  does not include the additional degree of freedom in yaw  534  but is still configured to perform the grip function. The parts  522 . 1 ,  522 . 2  perform gripping and does not move as a whole in yaw. For example, one part  522 . 1  may be substantially fixed with respect to the support base  518 , while the other part  522 . 2  is rotatable relative to the pivotal connection  526  to move away from and toward the fixed part  522 . 1  in grip  530 ,  532 . In that case, only one cable C 2  is needed to manipulate the part  522 . 2  to effect the grip movement thereof (C 1  is no longer needed). This alternate roll-pitch-roll mechanism with grip capability is simpler in structure and operation than the roll-pitch-roll-yaw mechanism with grip. 
     As best seen in  FIG. 11 , the pair of working end extensions  506  are flanked by two pulleys  540 ,  542  which are coaxially positioned on the pivotal connection  510  and in the clevis  508  at the proximal end of the wrist member  504 . A tangent pulley  544  which is associated with the pulley  540  is attached to the bottom of the end effector support base  518 . Another tangent pulley  546  which is associated with the pulley  542  is also attached to the bottom of the base  518 . The tangent pulleys  544 ,  546  in the specific embodiment shown are generally perpendicular to the pair of pulleys  540 ,  542 , and move together with the base  518 . The circumference of each tangent pulley  544  or  546  is in close proximity to the circumference of its associated pulley  540  or  542 . In a specific embodiment, the tangent pulleys are integrally formed with the bottom of the base  518 . 
     Two elongate elements such as cables C 3 , C 4  are used to effect movement of the end effector  514  and support base  518  in distal roll  520 . As best seen in  FIG. 11 , two cables C 3 , C 4  are anchored on the tangent pulleys  544 ,  546 , respectively, to effect distal roll  520  of the base  518  attached to the tangent pulleys  544 ,  546 . Cable C 3  wraps around a portion of the tangent pulley  544 , rides over the pulley  540  and extends through the shaft  14 . 1  to the housing  53 , while cable C 4  wraps around a portion of the tangent pulley  546 , rides over the pulley  542  and extends through the shaft  14 . 1  to the housing  53  ( FIG. 3 ). The circumference of each tangent pulley  544  or  546  is in sufficiently close proximity to the circumference of its associated pulley  540  or  542  to allow the corresponding cable C 3  or C 4  to slide in the pulley channels securely through the approximately 90° change in orientation from one pulley to the other. In a preferred embodiment, cables C 3 , C 4  are connected in the housing  53  and form a single cable. The single cable substantially does not change in length during distal roll  520  so that no tensioning spring or similar member is needed. 
     Another pulley  550  is disposed adjacent the pulley  540  and is coaxially positioned with the pulleys  540 ,  542  on the pivotal connection  510  and in the clevis  508  at the proximal end of the wrist member  504 . An elongate element such as cable C 5  is used to effect movement of the wrist member  504  in pitch  512 . As seen in  FIGS. 9–11 , cable C 5  is anchored on the pulley  550 , rides over the pulley  540 , and extends through the shaft  14 . 1  to the housing  53  ( FIG. 3 ). In an alternate embodiment, another pulley is coaxially positioned adjacent the pulley  542  opposite from the pulley  550  on the other side of the pair of working end extensions  506 , and the opposite end of cable C 5  is anchored on that pulley. In the alternate embodiment, cable C 5  substantially does not change in length during pitch  512  of the wrist member  504  so that no tensioning spring or similar member is needed. 
       FIG. 12  shows the position of the end effector  514  after rotation in pitch  512  of the wrist member  504  around the pivotal connection  510  by about 90°. In this position, there is no overlap among the proximal roll  516 , pitch  512 , and distal roll  520 , which are oriented around axes that are generally perpendicular to each other, making the wrist mechanism  500  more suitable to operate in the 90° pitch position than the wrist mechanism  50  of  FIGS. 5–8 . In addition, the two parts  522 . 1 ,  522 . 2  of the end effector  514  are movable in yaw  524  and in grip  530 ,  532  in the specific embodiment shown. In the forward position of the end effector  514  as shown in  FIGS. 9–11 , the distal roll  520  coincides with the proximal roll  516 , which presents a singularity. The addition of the yaw  524  of the end effector  514  in conjunction with the distal roll  520  in a preferred embodiment essentially eliminates the singularity by providing roll  516 , pitch  512 , and yaw  534  oriented around axes that are nonparallel and may be generally perpendicular to each other. 
     Bend Back Roll-Pitch-Roll Mechanism 
       FIGS. 13–17  show a roll-pitch-roll wrist-like mechanism  560  including a bend back feature in the pitch direction to increase the versatility of the mechanism  560 . In  FIG. 13 , the working end of the tool shaft is indicated at  562 . The end  562  is rotatable with the tool shaft around the shaft axis in the proximal roll  563 . The wrist-like mechanism  560  includes a rigid wrist member  564 . The working end  562  forms a working end clevis  566 , and one end portion of the wrist member  564  forms a wrist member clevis  568  facing the clevis  566 . The working end  562  includes a central extension  570 . Disposed in the working end clevis  566  are a first pair of pitch or knee pulleys  572 ,  574  on opposite sides of the central extension  570 . The pulleys  572 ,  574  are coaxially positioned on a pivotal connection  575 . A central extension  576  is located in the wrist member clevis  568 . Disposed in the wrist member clevis  568  are a second pair of pitch or knee pulleys  578 ,  580  on opposite sides of the central extension  576 . The pulleys  578 ,  580  are coaxially positioned on a pivotal connection  581 . The second pair of pitch pulleys  578 ,  580  in the wrist member clevis  568  are coplanar with the first pair of pitch pulleys  572 ,  574  in the working end clevis  566 , respectively. 
     As best seen in  FIGS. 13 and 14 , a first pair of distal roll pulleys  584 ,  586  are disposed in the working end clevis  566  on opposite sides of the central extension  570 . The pulleys  584 ,  586  are coaxially positioned on the pivotal connection  575 . A second pair of distal roll pulleys  588 ,  590  are disposed in the wrist member clevis  568  on opposite sides of the central extension  576 . The pulleys  588 ,  590  are coaxially positioned on the pivotal connection  581 . The second pair of distal roll pulleys  588 ,  590  in the wrist member clevis  568  are coplanar with the first pair of distal roll pulleys  584 ,  586  in the working end clevis  566 , respectively. 
     A pair of bend back pulley arms or lining arms  592 ,  594  extend between the working end clevis  566  and the wrist member clevis  568 , and are disposed on opposite sides of the central extensions  570 ,  576 . Each pulley arm  592 ,  594  has an end coaxially positioned on the pivotal connection  575  of the working end  562  and another end coaxially positioned on the pivotal connection  581  of the wrist member  564 . Rotation of the bend back pulley arms  592 ,  594  relative to the working end  562  around the pivotal connection  575  in the direction  596  provides proximal pitch, while rotation of the wrist member  564  relative to the bend back pulley arms  592 ,  594  around the pivotal connection  581  in the direction  598  provides distal pitch. The proximal pitch  596  and distal pitch  598  allow the wrist member  564  to be bent back in pitch by more than 90° as discussed in more detail below. 
     The central extension  576  in the wrist member clevis  568  is connected to a support base  602  for an end effector, generally indicated by reference numeral  600 . The central extension  576  may be integrally formed with the base  602 . The support base  602  is pivotally mounted on an opposed end of the wrist member  564  to rotate around its axis in the direction  604 , as shown in  FIG. 13 . In the embodiment shown, the axis of the base  602  coincides with the wrist axis of the wrist member  564 . The rotation in the direction  604  is referred to the distal roll of the end effector  600 . This distal roll of the end effector  600  in the direction  604  is differentiated from the proximal roll of the working end  562  in the direction  563 . In the position of the wrist mechanism  560  as shown in  FIGS. 13-16 , the distal roll  604  of the end effector  600  coincides with the proximal roll  563  of the working end  562 . Because the rotation of the wrist member  564  around the pivotal connections  575 ,  581  provides compound pitch  596 ,  598  of the end effector  600 , the distal roll  604  generally will not coincide with the proximal roll  563 . The wrist mechanism  560  as illustrated in  FIGS. 13–17  is referred to as a bend back roll-pitch-roll mechanism. 
     The end effector  600  is in the form of forceps or graspers for grasping tissue or the like during a surgical procedure. Accordingly, the end effector  600  has two parts  608 . 1 ,  608 . 2  together defining a jaw-like arrangement. The two parts  608 . 1 ,  608 . 2  are pivotally mounted in a clevis  610  on the base  602 , by means of a pivotal connection  612 . Although free ends  614 . 1 ,  614 . 2  of the parts  608 . 1 ,  608 . 2  may be angularly displaceable about the pivotal connection  612  toward and away from each other in some embodiments, the specific embodiment shown in  FIGS. 13–17  permits rotation of only the part  608 . 2  relative to the pivotal connection  612 . The other part  608 . 1  is fixed relative to the base  602 . The movable part  608 . 2  is movable toward and away from the fixed part  608 . 1  as indicated by arrows  616 ,  618  in  FIG. 16 . This movement is referred to as the grip of the end effector  600 . 
     The movable part  608 . 2  includes a mounting formation in the form of, e.g., a pulley portion  620 . The pulley portion  620  defines a circumferentially extending channel for receiving an elongate member such as an activation cable C 1  which is anchored to the pulley portion  620 , as best seen in  FIGS. 13 and 14 . The cable C 1  pass through the central extensions  576 ,  570  and the shaft toward the housing  53  ( FIG. 3 ). In a preferred embodiment, the cable C 1  forms a continuous loop between the pulley portion  620  and the housing  53  and does not change in length during grip  616 ,  618  of the end effector  600 , so that no tensioning spring is needed. 
     Two elongate elements such as cables C 3 , C 4  are used to effect movement of the end effector  600  and support base  602  in distal roll  604 . As best seen in  FIG. 14 , two cables C 3 , C 4  are anchored on the tangent surface  624  of the central extension  576  of the base  602  to effect distal roll  604  of the base  602  ( FIG. 13 ). Cable C 3  wraps around a portion of the tangent surface  624 , while cable C 4  wraps around another portion of the tangent surface  624 . Cable C 3  rides over the roll pulleys  588 ,  584  and extends through the shaft  14 . 1  to the housing  53 , while cable C 4  rides over the roll pulleys  590 ,  586  and extends through the shaft  14 . 1  to the housing  53  ( FIG. 3 ). The circumference of the tangent surface  624  is in sufficiently close proximity to the circumferences of the two roll pulleys  588 ,  590  to allow the corresponding cables C 3 , C 4 , respectively, to slide in the pulley channels securely through the approximately 90° change in orientation from the roll pulleys  588 ,  590  to the tangent surface  624 . In a preferred embodiment, cables C 3 , C 4  are connected in the housing  53  and form a single cable. The single cable substantially does not change in length during distal roll  604  so that no tensioning spring or similar member is needed. For clarity, cables C 3 , C 4  are not shown in FIGS.  13  and  15 – 17 . In an alternate embodiment, the tangent surface  624  may include a pair of circumferential channels for receiving the cables C 3 , C 4  such as those for the tangent pulleys  544 ,  546  shown in  FIG. 11  for the wrist mechanism  500 . 
     As best seen in  FIG. 14 , two cables C 5 , C 6  are provided for activating roll  596 ,  598  of the wrist member  564 . Cable C 5  is anchored on the pulley  578 , rides over the pulleys  578 ,  572 , and extends through the shaft  14 . 1  to the housing  53  ( FIG. 3 ). Cable C 6  is anchored on the pulley  580 , rides over the pulleys  580 ,  574 , and extends through the shaft  14 . 1  to the housing  53 . In a preferred embodiment, the two cables C 5 , C 6  are connected to form a single cable that substantially does not change in length during pitch  596 ,  598  of the wrist member  564  so that no tensioning spring is needed. 
       FIG. 17  illustrates the bend back feature of the wrist mechanism  560 . The compound pitch  596 ,  598  around pivotal connections  575 ,  581  allows the wrist member  564  and end effector  600  to bend back by an angle θ of more than about 90° from the forward position of  FIGS. 13–16 , desirably by more than about 120°, and more desirably by more than about 135°. Thus, the angle between the shaft axis and the wrist axis is about 180° when the end effector  600  is in the forward position, and is less than 90° in the bent back position, and may be down to less than about 60° or less than about 45°. The ability to bend back the end effector  600  renders the wrist mechanism  560  more versatile and adaptable to accessing hard to reach locations, particularly with small entry points such as those involving spinal, neural, or rectal surgical sites. The use of the linking arms  592 ,  594  provides this capability while maintaining the size of the tool  560  to a sufficiently small size for minimally invasive surgical applications. 
     The above-described arrangements of apparatus and methods are merely illustrative of applications of the principles of this invention and many other embodiments and modifications may be made without departing from the spirit and scope of the invention as defined in the claims. For instance, the linking arms may have other configurations. Different actuation mechanisms other than activating cables may be used to manipulate the wrist member and end effector. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.