Abstract:
An articulated surgical instrument for enhancing the performance of minimally invasive surgical procedures. The instrument has a high degree of dexterity, low friction, low inertia and good force reflection. A unique cable and pulley drive system operates to reduce friction and enhance force reflection. A unique wrist mechanism operates to enhance surgical dexterity compared to standard laparoscopic instruments. The system is optimized to reduce the number of actuators required and thus produce a fully functional articulated surgical instrument of minimum size.

Description:
[0001]     This application is a continuation of, and claims the benefit of priority from, co-pending U.S. patent application Ser. No. 10/076,812, filed Feb. 15, 2002, which is a continuation of Ser. No. 09/340,946, filed Jun. 28, 1999, which is a continuation of U.S. patent application Ser. No. 09/030,661, filed Feb. 25, 1998 (now U.S. Pat. No. 5,976,122), which is a continuation of U.S. patent application Ser. No. 08/857,776, filed May 16, 1997 (now U.S. Pat. No. 5,792,135), which claims priority to U.S. Provisional Application No. 60/017,981, filed May 20, 1996, the full disclosures of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates generally to methods and apparatus for enhancing the performance of minimally invasive surgery. This invention relates particularly to surgical instruments that augment a surgeon&#39;s ability to perform minimally invasive surgical procedures. This invention relates more particularly to a novel articulated surgical instrument for minimally invasive surgery which provides a high degree of dexterity, low friction, low inertia and good force reflection.  
       BACKGROUND OF THE INVENTION  
       [0003]     Minimally invasive medical techniques are aimed at reducing the amount of extraneous tissue which must be damaged during diagnostic or surgical procedures, thereby reducing patient recovery time, discomfort, and deleterious side effects. Approximately 21,000,000 surgeries are now performed each year in the United States. It is estimated that 8,000,000 of these surgeries can potentially be performed in a minimally invasive manner. However, only about 1,000,000 surgeries currently use these techniques due to limitations in minimally invasive surgical instruments and techniques and the additional surgical training required to master them.  
         [0004]     Advances in minimally invasive surgical technology could have a dramatic impact. The average length of a hospital stay for a standard surgery is 8 days, while the average length for the equivalent minimally invasive surgery is 4 days. Thus, the complete adoption of minimally invasive techniques could save 28,000,000 hospital days, and billions of dollars annually in hospital residency costs alone. Patient recovery times, patient discomfort, surgical side effects, and time away from work are also reduced with minimally invasive surgery.  
         [0005]     The most common form of minimally invasive surgery is 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.  
         [0006]     The laparoscopic surgical instruments generally include a laparoscope for viewing the surgical field, and working tools such as clamps, graspers, scissors, staplers, and needle holders. The working tools are similar to those used in conventional (open) surgery, except that the working end of each tool is separated from its handle by an approximately 12-inch long extension tube.  
         [0007]     To perform surgical procedures, the surgeon passes instruments through the cannula and manipulates them inside the abdomen by sliding them in and out through the cannula, rotating them in the cannula, levering (i.e., pivoting) the instruments in the abdominal wall and actuating end effectors on the distal end of the instruments. The instruments pivot around centers of rotation approximately defined by the incisions in the muscles of the abdominal wall. The surgeon monitors the procedure by means of a television monitor which displays the abdominal worksite image provided by the laparoscopic camera.  
         [0008]     Similar endoscopic techniques are employed in arthroscopy, retroperitoneoscopy, pelviscopy, nephroscopy, cystoscopy, cisternoscopy, sinoscopy, hysteroscopy and urethroscopy. The common feature of all of these minimally invasive surgical techniques is that they visualize a worksite within the human body and pass specially designed surgical instruments through natural orifices or small incisions to the worksite to manipulate human tissues and organs thus avoiding the collateral trauma caused to surrounding tissues which would result from creating open surgical access.  
         [0009]     There are many disadvantages of current minimally invasive surgical technology. For example, existing MIS instruments deny the surgeon the flexibility of tool placement found in open surgery. Most laparoscopic tools have rigid shafts and are constrained to approach the worksite from the direction of 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 tool. The lack of dexterity and sensitivity provided by endoscopic tools is a major impediment to the expansion of minimally invasive surgery.  
         [0010]     Telesurgery systems for use in surgery are being developed to increase a surgeon&#39;s dexterity as well as to allow a surgeon to operate on a patient from a remote location. Telesurgery is a general term for surgical systems where the surgeon uses some form of servomechanism to manipulate the surgical instruments movements rather than directly holding and moving the tools. In a system for telesurgery, the surgeon is provided with an image of the patient&#39;s body at the remote location. While viewing the three-dimensional image, the surgeon performs the surgical procedures on the patient by manipulating a master device which controls the motion of a servomechanism-actuated instrument. The surgeon&#39;s hands and the master device are positioned relative to the image of the operation site in the same orientation as the instrument is positioned relative to the act. During the operation, the instrument provides mechanical actuation and control of a variety of surgical instruments, such as tissue graspers, needle drivers, etc., that each perform various functions for the surgeon, i.e., holding or driving a needle, grasping a blood vessel or dissecting tissue.  
         [0011]     Such telesurgery systems have been proposed for both open and endoscopic procedures. An overview of the state of the art with respect to telesurgery technology can be found in “Computer Integrated Surgery: Technology And Clinical Applications” (MIT Press, 1996). Moreover, prior systems for telesurgery are described in U.S. Pat. Nos. 5,417,210, 5,402,801, 5,397,323, 5,445,166, 5,279,309, 5,299,288.  
         [0012]     However methods of performing telesurgery using telemanipulators still require the development of dexterous surgical instruments capable of transmitting position, force, and tactile sensations from the surgical instrument back to the surgeon&#39;s hands as he/she operates the telesurgery system such that the system the surgeon has the same feeling as if manipulating the surgical instruments directly by hand. A system&#39;s ability to provide force reflection is limited by factors such as friction within the mechanisms, gravity, the inertia of the surgical instrument and forces exerted on the instrument at the surgical incision.  
         [0013]     What is needed, therefore, is a surgical instrument that increases the dexterity with which a surgeon can perform minimally invasive surgical procedures.  
         [0014]     It would also be desirable to provide a dexterous surgical apparatus having a wrist with two degrees-of-freedom.  
         [0015]     It would further be desirable to provide a wrist mechanism that has low friction in order to provide the surgeon with sensitive feedback of forces exerted on the surgical instrument.  
         [0016]     It would still further be desirable to provide a surgical instrument having a wrist mechanism for minimally invasive surgery which is suitable for operation in a telemanipulator mechanism.  
       SUMMARY AND OBJECTS OF THE INVENTION  
       [0017]     Accordingly, it is an object of this invention to provide a surgical instrument that increases the dexterity with which a surgeon can perform minimally invasive surgical procedures.  
         [0018]     It is also an object of this invention to provide a dexterous surgical apparatus having a wrist with two degrees-of-freedom.  
         [0019]     It is a further object of this invention to provide a wrist mechanism that has low friction in order to provide the surgeon with sensitive feedback of forces exerted on the surgical instrument.  
         [0020]     It is a still further object of this invention to provide a surgical instrument having a wrist mechanism for minimally invasive surgery which is suitable for, operation in a telemanipulator mechanism.  
         [0021]     In accordance with the above objects of the invention applicants describe a compact articulated surgical instrument suitable for endoscopic surgery. The instrument has two opposed pivoting jaws and a pivoting wrist member. The instrument is capable of providing force reflection with high sensitivity. The instrument is adapted to be coupled via a servomechanism to a master control operated by a surgeon. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.  
         [0023]      FIG. 1  is a schematic drawing of a servomechanical surgery system including a force-reflecting surgical instrument mounted to a positioning mechanism.  
         [0024]      FIG. 2  is a schematic drawing of a positioning mechanism in forward and rearward positions with the surgical instrument inserted into a patient.  
         [0025]      FIG. 3  is a perspective view of a force-reflecting surgical instrument.  
         [0026]      FIG. 4  is a schematic view of the cable drive actuation of the rotary motion of the force-reflecting surgical instrument.  
         [0027]      FIG. 5  is a perspective view of the distal end of the force-reflecting surgical instrument.  
         [0028]      FIG. 6  is a simplified schematic drawing of the force-reflecting surgical instrument showing the relationship of the cables and pulleys.  
         [0029]      FIG. 7   a  is a perspective view of a cable wrapped around the drive shaft of a drive motor.  
         [0030]      FIG. 7   b  is a schematic drawing showing another preferred method for driving the cables in the present invention.  
         [0031]      FIG. 8  is a top view of the wrist member of another preferred force-reflecting surgical instrument. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]     The surgical instrument in the first embodiment includes an elongate support member having a proximal portion and a distal portion lying along a longitudinal axis. A distal wrist member is rotatably coupled to the distal portion of the support member by a wrist joint. First and second opposed work members are mounted to respective first and second driven capstans. The first and second driven capstans are rotatably mounted to the wrist member by respective first and second capstan joints which preferably have a common axis. First, second, third and fourth intermediate idler pulleys are rotatably mounted to the wrist member about the wrist joint. A cable drive system including first, second, third and fourth cables is provided. Each intermediate idler pulley is engaged by one cable and each driven capstan is drivingly engaged by two cables. The cable drive system is capable of pivoting the wrist member about the wrist joint and pivoting the work members independently of each other about the capstan joints.  
         [0033]     In preferred embodiments, a linear bearing is mounted in sliding engagement with the support member for allowing the distal portion of the support member to be reciprocated along the longitudinal axis relative to the proximal portion of the support member. In such embodiments the cable drive system is capable of translating the support member along the longitudinal axis. In preferred embodiments, the support member may also include a rotary joint separating the proximal and distal portions of the support member for allowing rotation of the distal portion relative to the proximal portion about the longitudinal axis. In such embodiments the first through fourth cables are capable of twisting about the longitudinal axis during rotation of the distal portion and the cable drive system comprises a fifth cable coupled to the rotary joint for rotating the distal portion about the longitudinal axis.  
         [0034]     The present invention also provides a novel system for tensioning the first, second, third and fourth cables. A first proximal idler pulley rotatably engages and tensions the first and second cables. A second proximal idler pulley rotatably engages and tensions the third and fourth cables. Fifth and sixth cables are connected to the first and second proximal idler pulleys for tensioning the first and second proximal idler pulleys. A third more proximal idler pulley is rotatably mounted to a support member for rotatably engaging and tensioning the fifth and sixth cables.  
         [0035]     The surgical instrument further includes a plurality of actuators, each for driving one of the cables of the cable drive system. The instrument preferably comprises one actuator for each degree-of-freedom of the instrument. The actuators are preferably servomotors which are positioned between the intermediate idler pulleys and the proximal idler pulleys. The servomotors are preferably directly coupled to the cables by means of a drive capstan mounted on the drive shaft of the servomotor.  
         [0036]     The surgical instrument is adapted to be a slave device which is controlled by a master device and a controller. Movements of the instrument and the master device as well as forces exerted thereon may be scaled between the instrument and the master device. A positioning mechanism having two degrees-of-freedom may be mounted to the instrument for positioning the instrument over a work site. The positioning mechanism may provide the instrument with redundant degrees-of-freedom for positioning the endpoint. The combination of a positioning mechanism with the applicants articulated surgical instrument is adapted to enable a surgeon operating the master device to feel forces that are experienced by the instrument during positioning and use of the instrument with greater sensitivity than with prior systems.  
         [0037]     Details about the preferred attributes of the surgical system are also described in applicants&#39; copending applications titled “Force-Reflecting Surgical Instrument And Positioning Mechanism For Performing Minimally Invasive Surgery With Enhanced Dexterity And Sensitivity” and “Wrist Mechanism For Surgical Instrument For Performing Minimally Invasive Surgery With Enhanced Dexterity And Sensitivity” filed on even date herewith. The disclosures of these applications are incorporated herein by reference.  
         [0038]     Referring to  FIG. 1 , telesurgery system  10  allows a surgeon at one location to perform surgery on a patient at another location. The surgeon may be in the same operating room as the patient or many miles away. Telesurgery system  10  includes a force-reflecting surgical instrument  12  which is mounted by a bracket  36  to a positioning mechanism  14 . Instrument  12  and positioning mechanism  14  are controlled by a computer  11  and a master device  150  which is manipulated by a surgeon at a remote location. Instrument  12  and positioning mechanism  14  are driven by drive motors M 1 , M 2 , M 3 , M 4 , M 5 , M 6  and M 7  ( FIGS. 3, 4 ,  6  and  7   a - b ) in conjunction with a series of cables and pulleys.  
         [0039]     Instrument  12  has low friction, low inertia and high bandwidth but a small range of motion. Positioning mechanism  14  has a large range of motion but typically has a higher inertia and a lower bandwidth than the instrument. The combination of instrument  12  and positioning mechanism  14  in a macro/micro actuation scheme results in a system with increased dynamic range compared to either of its individual components. Positioning mechanism  14  provides telesurgery system  10  with redundant degrees-of-freedom and helps positions instrument  12  at a surgical worksite so that instrument  12  is generally in the proper location for performing the necessary surgery. Thus, by mounting instrument  12  on positioning mechanism  14 , telesurgery system  10  is provided with high quality force control through the use of instrument  12  while at the same time having a large range of motion due to positioning mechanism  14 . Instrument  12  is mounted on positioning mechanism by means of mounting bracket  36 . Preferably, the Instrument  12  is releasably attached to positioning mechanism  14  using any suitable releasable attachment means such as screws, bolts, clamps.  
         [0040]     Instrument  12  has a proximal portion  28   a  which is rotatably coupled to a distal portion  28   b  by a rotary joint  26 . Proximal portion  28   a  is slidably coupled to a sliding bracket  96  which forms a sliding joint  30 . Sliding bracket  96  is fixed to bracket  36 . Bracket  36  is a mounting bracket which releasably connects instrument  12  to positioning mechanism  14 . Distal portion  28   b  of instrument  12  includes a wrist member which is rotatably coupled to a tubular support member  24  by a wrist joint  16 . Two opposed work members  20   a  and  20   b  are fixed to respective driven capstans  18   a  and  18   b  which are rotatably coupled to wrist member  22  about capstan joints  19   a  and  19   b . The work members  20   a  and  20   b  can be the operative end of standard surgical instruments such as scissors, retractors, needle drivers and electrocautery instruments.  
         [0041]     Instrument  12  has five degrees-of-freedom with sliding joint  30  providing linear motion along longitudinal axis C-C, rotary joint  26  providing rotational motion about axis C-C, wrist joint  16  providing rotational motion about axis B-B and capstan joints  19   a  and  19   b  providing rotational motion about axis A-A for work members  20   a  and  20   b . Instrument  12  provides master device  150  with four degrees of force reflection so that the surgeon can have tactile feedback of surgical procedures. These degrees of force reflection include x, y and z forces exerted on the work members  20   a  and  20   b , as well as the holding force between work members  20   a  and  20   b . However, force reflection can be provided on more or fewer motion axes as required in any particular embodiment.  
         [0042]     Positioning mechanism  14  is a two degree-of-freedom linkage which is preferably a four bar linkage which rotates about an axis E-E. Positioning mechanism  14  has a series of rigid members  36 ,  40 ,  42 ,  60  and  62  which are joined together by joints  34 ,  38 ,  48 ,  50 ,  52 ,  54 ,  56 . Positioning mechanism  14  also includes a base  68  having ears  58  which engage shafts  64  and  66  to form a joint  57  for pivoting about axis E-E. Joint  56  allows link  62  to rotate about axis D-D which is orthogonal to axis E-E. The four bar linkage of rigid members  36 ,  40 ,  42 ,  60  and  62  transmits this rotation to instrument  12  via bracket  36  causing instrument  12  to rotate about axis E-E and axis D′-D′ (axis D′-D′ is parallel to axis D-D and intersects axis E-E orthogonally). Thus the four bar linkage operates to move point P.sub.s of instrument  12  about the surface of a sphere having its center at a remote center  111 . Although a four bar linkage has been shown, the articulated surgical instrument of the present invention can be supported by any suitable positioning mechanism. To be suitable for minimally invasive surgery the positioning mechanism must pivot the surgical instrument about axes that intersect at the orifice through which the instrument is inserted into the patient.  
         [0043]     Haptic master device  150  suitable to control instrument  12  is a seven degree-of-freedom input device. During use the master  150  is fixed in place to a console or cart or similar stationary support such that the mount provides a fixed reference point. During use, the surgeon manipulates the position and orientation of the master mechanism relative to its stationary support. Linkages, motors and encoders of the master detect the surgeon&#39;s movements and transmit them to the computer. The motors of the master preferably also provide force feedback to the surgeon. This controls motions of instrument  12  and positioning mechanism  14  and thus controls the position of the distal end of instrument  12  relative to the surgical site.  
         [0044]     One apparatus suitable for use as a master in the presently described system is described in U.S. Pat. No. 5,587,937, titled Force Reflecting Haptic Interface the contents of which are incorporated by reference herein. Another suitable master device is described in U.S. Pat. No. 5,576,727, titled Electromechanical Human-Computer Interface With Force-Feedback the contents of which are incorporated by reference herein. The haptic master apparatus disclosed in the above references would require the addition of a further powered degree-of-freedom to provide force reflection from gripping the work members. For example, finger grippers may be attached to a motor and encoder on a separate mechanism for operation by the other hand of the surgeon. Alternatively, finger grippers may be attached to a motor and encoder on the same device for operation by the surgeon.  
         [0045]     When employing telesurgery system  10  for laparoscopic surgery, positioning mechanism  14  is mounted to a manually-operated setup joint (not shown). After the setup joint has been used to position the tool and lock the tool in place, the surgeon then manipulates master device  150  to move instrument  12  through a cannula  113  inserted through small incision  112  in the abdominal wall  110  of the patient. In response to manipulation of master device  150 , the distal portion  28   b  of the instrument  12  is translated downwardly relative to positioning mechanism  14  along sliding joint  30  for insertion through cannula  113  and abdominal wall  110 .  
         [0046]     Once within the abdomen, the distal portion  28   b  of instrument  12  is further positioned over the desired surgical site.  FIG. 2  depicts motion of mechanism  14  pivoted about axis D-D in forward and rearward positions for making large position movements. Positioning mechanism  14  pivots about axes D-D and E-E to perform large movements of telesurgery system  10  while precise movements are made by the joints of instrument  12 . Point  111  on instrument  12  is a remote point of rotation from positioning mechanism  14  which coincides with entry wound  112 . When positioning mechanism  14  is pivoted about axes D and E, instrument  12  pivots about point  111 . Note that point  111  adjacent incision  112  remains stationary as the instrument  12  is pivoted within the patient. As a result, incision  112  only needs to be large enough to accept instrument  12 .  
         [0047]     As positioning mechanism  14  pivots, if wrist member  22  or work members  20   a / 20   b  engage tissue causing rotation about joints  16  or  19   a / 19   b , instrument  12  will reorient itself so that instrument  12  is maintained relative to positioning mechanism  14  in the middle of its workspace. If necessary, positioning mechanism  14  can slow down as instrument  12  is reorienting itself.  
         [0048]     Once instrument  12  is in the proper position, by further manipulating master device  150 , the surgeon can perform the necessary surgical procedures on the patient with instrument  12 . Forces experienced by instrument  12  are reflected back to the surgeon by master device  150 . The reflected forces may be scaled up in order to allow the surgeon to better “feel” the surgical procedures. As a result, the surgeon can feel instrument  12  engaging types of tissue that do not provide much resistance. In addition, movements of master device  150  relative to instrument  12  may be scaled down so that the precision and dexterity of instrument  12  can be increased.  
         [0049]     Positioning mechanism  14 , because it is optimized to have a large range of motion, is likely to have higher inertia, higher friction and lower resolution than instrument  12 . Moreover, friction forces in cannula  113  and disturbance forces at incision  112  may be applied to the positioning mechanism.  
         [0050]     However, in applicants&#39; preferred embodiment, primarily the surgical instrument detects forces for force reflection. Therefore, the higher inertia and friction of the positioning mechanism and the extraneous forces acting on it are excluded from the force reflection system. Thus, the quality of the force reflection between the tip of the instrument  12  and the master device is greatly improved.  
         [0051]     Referring to  FIGS. 3, 4  and  5 , instrument  12  is now described in greater detail. Tubular support member  24  of distal portion lies along axis C-C and houses a series of cables C 1 , C 2 , C 3  and C 4  which travel the length of tubular support member  24 . Cables C 1 , C 2 , C 3  and C 4  control the rotation of joints  19   a ,  19   b  and  16  for controlling the operation of work members  20   a  and  20   b  and the orientation of wrist member  22 . Wrist member  22  includes two opposed distal ears  21   a  and  21   b  forming a clevis for supporting driven capstans  18   a  and  18   b  at respective capstan joints  19   a  and  19   b  which lie along axis A-A. Wrist member  22  also includes two opposed proximal ears  23   a  and  23   b  forming a clevis for supporting intermediate idler pulleys  70  and  72  which lie along axis B-B between ear  23   a  and tongue  24   a  at wrist joint  16 . Intermediate idler pulleys  74  and  76  are supported between ear  23   b  and tongue  24   a . Cables C 1 , C 2 , C 3  and C 4  engage driven capstans  18   a / 18   b  as well as intermediate idler pulleys  70 ,  72 ,  74  and  76  as described later in greater detail.  
         [0052]     Work members  20   a  and  20   b  may be removably fixed to respective driven capstans  18   a  and  18   b . Although work members  20   a  and  20   b  are depicted in the figures as being grippers, work members  20   a  and  20   b  can be replaced with other types of work members such as scissors, cutters, graspers, forceps or needle holders for stitching sutures. Typically, the work members are fixed to driven capstans  18   a  and  18   b  by a screw, clip or other suitable fastener. However, the work members may also be permanently affixed to the driven capstans by soldering or welding or the like or may be formed in one piece with the driven capstans.  
         [0053]     Work members  20   a  and  20   b  together comprise one form of surgical end effector. Other surgical end effectors may be used in the surgical instrument of the present invention. End effectors simply may comprise standard surgical or endoscopic instruments with their handles removed including, for example, retractors, electrocautery instruments, microforceps, microneedle holders, dissecting scissors, blades, irrigators, and sutures. The end effectors will typically comprise one or two work members.  
         [0054]     Proximal portion  28   a  of instrument  12  includes support brackets  98  and  102  which are connected together by a support rod  100  as well as two guide rails  104  and  106 . A rotary bearing  91  forming rotary joint  26  is housed within support bracket  98  for supporting tubular support member  24 . Sliding bracket  96  is slidably mounted to guide rails  104  and  106  along linear bearings. As shown in  FIG. 1 , sliding bracket  96  is connected by bracket  36  to positioning mechanism  14 . Sliding bracket  96  preferably has about 8 inches of travel for surgical applications.  
         [0055]     Drive motors M 1 , M 2 , M 3 , M 4  and M 5  are mounted to sliding bracket  96  and drive respective cables C 1  C 2 , C 3  and C 4  and C 5 . Sliding bracket  96  supports each of the drive motors. During operation sliding bracket  96  is connected to positioning mechanism  14  by mounting bracket  36 . When instrument  12  is mounted on positioning mechanism  14 , the drive motors operate to move distal portion  28   b  relative to sliding bracket  96 . Sliding bracket  96  thus forms the support bracket of the surgical instrument. Each drive motor M 1 , M 2 , M 3 , M 4  and M 5  includes a respective encoder E 1 , E 2 , E 3 , E 4  and E 5  for providing computer  11  with the rotational position of their respective drive shafts.  
         [0056]     As shown in  FIG. 4 , drive motor M 5  has a drive shaft capstan  93  which engages a cable drive loop consisting of Cable C 5 . The cable passes around rear tensioning pulley  83 . The cable passes around idler pulleys  84  and  85  and around drive capstan  90  which forms the proximal end of tubular support member  24 . Thus rotation of actuation of motor M 5  can be used to rotate tubular support member  24  and the end effector it supports.  
         [0057]     Referring to  FIG. 6 , the cable drive system of instrument  12  is now described in greater detail. Work members  20   a  and  20   b , wrist member  22  and the translation of instrument  12  along longitudinal axis C-C are driven by cables C 1 , C 2 , C 3  and C 4  which are arranged in an N+1 actuation scheme. The N+1 actuation scheme allows the actuation of a three degree-of-freedom wrist using four cables. Four cables is the theoretical minimum possible number of tension elements required to drive three degrees-of-freedom and thus allows the instrument to be of minimum size and weight. Alternative actuation schemes using more cables may be desirable in situations where the forces required for actuation of different motions differ greatly in magnitude. The disadvantage of using more cables is an increase in weight, complexity and minimum size.  
         [0058]     In  FIG. 6 , the rotational motion of joint  26  about axis C-C is omitted in order to more easily show cables C 1 -C 4 . Such rotation results only in twisting of the cables C 1 -C 4  between motors M 1 -M 4  and pulleys  70 ,  72 ,  74  and  76 . The cables are however arranged in tubular support member  24  such that this twisting does not significantly change the length of the cable path. Care should however be taken to prevent over-rotation of the instrument which would cause the cables to twist into contact with each other and create friction between the cables.  
         [0059]     As shown in  FIG. 6 , cables C 1  and C 2  form two sides of a continuous cable loop  44 . Cable C 1  of loop  44  engages a proximal idler pulley  80 , the drive shaft of motor M 1 , intermediate idler pulley  70  and driven capstan  18   a . Cable loop  44  returns from driven capstan  18   a  as cable C 2  and engages intermediate idler pulley  76 , the drive shaft of motor M 2  and proximal idler pulley  80 .  
         [0060]     As shown in  FIG. 6 , cables C 3  and C 4  form two sides of a continuous loop of cable  46 . Cable C 3  of cable loop  46  engages proximal idler pulley  78 , the drive shaft of motor M 3 , intermediate idler pulley  72  and driven capstan  18   b . Cable loop  46  returns from driven capstan  18   b  as cable C 4  and engages intermediate idler pulley  74 , the drive shaft of motor M 4  and proximal idler pulley  78 .  
         [0061]     As shown in  FIG. 6 , proximal idler pulleys  78  and  80  are tensioned by cables C 7  and C 6  which are fixed to the center of proximal idler pulleys  78  and  80 . Cables C 7  and C 6  form two sides of a single cable  45  which engages proximal idler pulley  82  which is rotatably mounted to support bracket  102  by shaft  82   a . Shaft  82   a  is preferably movably mounted to support bracket  102  by a mechanism such as a lead screw. The lead screw may then be adjusted to appropriately tension cables C 7  and C 6 . The tension is also applied via idler pulleys  78  and  80  to cables C 1 , C 2 , C 3  and C 4 . A similar lead screw tensioning scheme can be used to tension cable C 5  by longitudinal movement of idler pulley  83 . It may be required for idler pulleys  82  and  83  to be mounted on separately adjustable shafts for these purpose instead of single shaft  82   a  illustrated in  FIG. 3 .  
         [0062]     Driven capstans  18   a  and  18   b  may have different diameters in order to allow cables C 1  through C 4  to suitably engage their respective intermediate idler pulleys. Cables C 1  and C 2  engage the outer intermediate idler pulleys  70  and  76  while cables C 3  and C 4  engage the inner intermediate idler pulleys  72  and  74 . Proximal idler pulleys  78  and  80  are sized such that pulley  80  is larger than pulley  78  to keep the cables straight.  
         [0063]     Drive motors M 1 , M 2 , M 3  and M 4  control rotation of wrist member  22  about axis B-B, translation of instrument  12  longitudinally along axis C-C and rotation of work members  22   a  and  22   b  independent of each other about axis A-A by driving cables C 1 , C 2 , C 3  and C 4 . Drive motors M 1  and M 2  drive cables C 1 /C 2  in unison in opposition to cables C 3 /C 4  driven by drive motors M 3  and M 4  in order to rotate wrist member  22  about axis B-B. Drive motor M 1  drives cable C 1  in opposition to cable C 2  driven by drive motor M 2  to rotate capstan  18   a  and attached work member  20   a  about axis A-A. In addition, drive motor M 3  drives cable C 3  in opposition to cable C 4  driven by drive motor M 4  to rotate capstan  18   b  and attached work member  20   b  about axis A-A. All four drive motors M 1 , M 2 , M 3  and M 4  drive cables C 1 , C 2 , C 3  and C 4  simultaneously to translate instrument  12  along longitudinal axis C-C.  
         [0064]     Locating drive motors M 1 , M 2 , M 3 , M 4  and M 5  on sliding bracket  96  makes the distal portion  28   b  of instrument  12  have a small moving mass since the motors themselves remain stationary during actuation of the instrument. Although the motors are moved by positioning mechanism  14 , the weight and inertia of the motors do not affect force reflection. This is because, as stated above, in the preferred embodiment, only the instrument is used to reflect forces to the master. In addition, employing cables instead of gears to control instrument  12  minimizes the amount of friction and backlash within instrument  12 . The combination of small moving masses and low friction enables instrument  12  to provide force reflection to master device  150  with high sensitivity.  
         [0065]     Certain possible changes to the configuration of pulleys, cables and motors described above will be apparent to those of skill in the art. Although cables C 1 /C 2 , C 3 /C 4 , C 5  and C 7 /C 6  have been depicted to be sides of the same cables, cables C 1 -C 7  alternatively can each be individual cables which are fixed to driven capstans  18   a  and  18   b , and proximal idler pulleys  78 ,  80  and  82 . Moreover, although drive motors M 1 , M 2 , M 3  and M 4  have been depicted to drive cables C 1 , C 2 , C 3  and C 4  respectively, alternatively, some drive motors can be relocated from cables C 1 -C 4  onto cables C 7  and C 6  for driving cables C 7  and C 6 . The choice of the particular drive scheme employed in a particular embodiment will depend on the constraints of the forces required to be exerted by the instrument and the need to reduce the inertia and friction of the parts of the instrument that move during its actuation.  
         [0066]     The surgical instrument of the present invention has been illustrated as using drive motors M 1 , M 2 , M 3 , M 4  and M 5 . This drive motors may be standard servo motors having position encoders as shown in  FIG. 3 . However, other actuators may be used, such as hydraulic actuators and piezoelectric motors. To be used as an actuator in the present surgical instrument a drive mechanism should be able to provide variable and controllable force and position control.  
         [0067]     Cables C 1 , C 2 , C 3 , C 4 , C 7 , C 8  and C 9  are driven by being wrapped about the drive shaft of their respective drive motors M 1 , M 2 , M 3 , M 4 , M 5 , M 6  and M 7 . This cable drive method and an alternative cable drive method are illustrated in more detail in  FIGS. 7   a  and  7   b . For example, in  FIG. 7   a , cable C 4  of cable loop  46  is wrapped around the drive shaft of motor M 4 . Cable C 4  is preferably wrapped two times around the drive shaft to provide enough friction between the cable C 4  and the drive shaft to prevent slippage. In order to further prevent slippage the cable may be fixed to the drive shaft at one point by soldering, welding or mechanical fixing means. However, in such an embodiment the range of motion of the cable is limited by the length of cable wrapped around the drive shaft or capstan thus several turns of cable are usually required.  
         [0068]      FIG. 7   b  depicts another preferred method for driving cables. For example, motor M 4  includes a drive wheel  43   a  and a idler wheel  43   b  for frictionally driving an elongate member  47  therebetween. Cable C 4  consists of two halves,  46   a  and  46   b  which are fixed to opposite ends of member  47 .  
         [0069]      FIG. 8  depicts the distal end and wrist member  116  of another preferred instrument  117 . Instrument  117  differs from instrument  12  in that instrument  117  includes eight intermediate idler pulleys instead of four. Instrument  117  includes intermediate idler pulleys  76 ,  74 ,  72  and  70  at wrist joint  16  but also includes intermediate idler pulleys  76   a ,  74   a ,  72   a  and  70   a  which are positioned adjacent to idler pulleys  76 ,  74 ,  72  and  70  on tongue  24   a  along shaft  118 . Cables C 1 , C 2 , C 3  and C 4  do not make a complete wrap around each intermediate idler pulley but instead contacts a variable amount of the of the surface of each pulley varying in a range between 0.degree. and 180.degree. over the range of motion of the wrist about axis  16 . This prevents the cables from crossing each other and rubbing together which prevents friction and noise.  
         [0070]     Although the present invention has been described for performing laparoscopic surgery, it may also be used for other forms of endoscopic surgery as well as open surgery. The present manipulator could also be employed for any suitable remote controlled application requiring a dexterous manipulator with high quality force feedback. Moreover, while this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.