MEDICAL INSTRUMENT ELECTRICALLY ENERGIZED USING DRIVE CABLES

[0001] This patent document is related to and incorporates by reference co-filed U.S. patent application No. UNKNOWN, entitled “Four-Cable Wrist with Solid Surface Cable Channels.”

[0002] Minimally invasive medical procedures generally employ small diameter instruments that can be inserted directly or through a cannula in a small incision or natural orifice of a patient. Producing small diameter medical instruments that implement the clinically desired functions for minimally invasive procedures can be challenging. For example, many instruments require a small-diameter wrist mechanism that is able to position and manipulate an end effector at the distal end of the instrument. Such wrist mechanisms commonly employ two cables per rotation axis available in the wrist, so that a wrist mechanism providing pitch, yaw, and grip control commonly uses six cables. All of the cables must be routed through the wrist mechanism and back through a small-diameter tube to a transmission, sometimes referred to herein as a backend mechanism. The backend mechanism moves the drive cables as needed to operate the wrist mechanism. Further, some medical instruments have end effectors that require electrical energy, for example, for clinical functions such as desiccation, hemostasis, cutting, dissection, fulguration, incisions, tissue destruction, cauterizing, and vessel sealing. Accordingly, one or more conductors must be routed to the portion of an end effector to be energized, while other portions of the instrument must be insulated from the electrical energy to avoid unintended burning of the patient or a user of the instrument. Fitting all the components of the wrist mechanism, drive cables, and conductive wires into a small diameter, for example, less than about 10 mm, can be difficult.

[0003] Minimally invasive medical instruments with lower part counts are desired to facilitate miniaturization of the instrument and to reduce instrument costs.

[0004] In accordance with an aspect of the invention, an electrically energized medical instrument uses one or more drive cables both to actuate mechanical components of a wrist mechanism or an end effector and to electrically energize the end effector. Electrical isolation can be achieved using an insulating main tube through which drive cables extend from a backend mechanism to an end effector, an insulating end cover that leaves only the desired portions of the end effector exposed, and one or more seals to prevent electrically conductive liquid from entering the main tube. A reduction in the number of components achieved by some embodiments of the invention can result in a cost savings in a reusable instrument or permit creation of a single-use instrument that is cost competitive with reusable instruments on a per use basis.

[0005] One specific embodiment of the invention is a medical instrument including a main tube, an end effector, a cable, and a backend mechanism. The end effector is attached to a distal end of the main tube and contains an electrically conductive component such as a scissors blade. The cable extends the length of the main tube and is coupled to the end effector so that actuation of the end effector involves movement of the cable. The cable is also electrically conductive. The backend mechanism is coupled to a proximal end of the main tube and includes a mechanical system and an electrical system. The mechanical system is coupled to the cable and is operable to move the cable for the actuation of the end effector. The electrical system is connected to the cable for application of an electrical signal that energizes the electrically conductive component of the end effector. The energized end effector can then be used for a clinical function such as destroying or cauterizing tissue.

[0006] Another embodiment of the invention is a method for operating a medical instrument. The method includes: actuating an end effector on a distal end of a main tube through movement of one or more cables that are attached to the end effector; and electrically energizing the end effector by applying an electrical signal that one or more of the cables conducts through the main tube to the end effector.

[0007] Yet another embodiment of the invention is a medical instrument including a clevis, a pair of pulleys, a pair of jaws, and four drive cables. The clevis and the pulleys are rotatably mounted on a first pin. The jaws are rotatably mounted on a second pin that is in the clevis. A first and a second of the cables attach to one jaw and respectively ride on the first and second pulleys when the clevis is in a first position. A third and a fourth of the cables attach to the other jaw and also ride on the first and second pulleys, respectively, when the clevis is in the first position. Having four cables share two pulleys decreases the part count and the cost of the instrument. The pulleys reduce cable friction because for many motions of the instrument (e.g., change of the pitch angle or closing/opening of the jaws) the rotation of each pulley matches the movement of both cables that ride on the pulley. For other motions of the instrument, a cable may slide or slip on a pulley when the motions of both cables cannot simultaneously be matched to the rotation of the pulley. However, the pulley will generally rotate with whichever of the associated cables exerts greater force on the pulley, e.g., has the larger wrap angle and/or tension, so that the total cable friction can be reduced even when a cable is required to slide against the surface of a pulley.

[0016] Use of the same reference symbols in different figures indicates similar or identical items.

[0017] In accordance with an aspect of the invention, a robotically actuated, electrically energized instrument can use one or more actuating or drive cables for electrical power. One specific embodiment of the invention is a low cost, wristed, electrically energized, scissor instrument that can be actuated using a robotic control system such as the da Vinci system available from Intuitive Surgical, Inc. Using drive cables for electrical energy can reduce the number of component parts, which can result in cost reduction and can facilitate miniaturization of instruments for minimally invasive medical procedures. An additional reduction in the part count and costs can be achieved by routing multiple cables around the same pulley in the wrist of the instrument.

[0018] FIG. 1 shows a configuration for a medical instrument 100 in accordance with an exemplary embodiment of the invention. Medical instrument 100 includes an end effector 200 at a distal end of a main tube 110 that extends from a transmission or backend mechanism 120. During a minimally invasive medical procedure, end effector 200 and the distal end of main tube 110 can be directly inserted or inserted through a cannula or other guide that may be inserted through a small incision or a natural orifice of a patient undergoing the medical procedure. Accordingly, the diameter of end effector 200 and main tube 110 and the length of main tube 110 may be selected according to the size of the cannula with which the instrument will be used. In an exemplary embodiment, end effector 200 and main tube 110 are about 5 mm or about 8 mm in diameter to match the sizes of some existing cannula systems, and the length of main tube 110 can be about 460 mm.

[0019] Main tube 110 is hollow to contain drive cables that run from backend mechanism 120 to end effector 200. In accordance with an aspect of the current invention, main tube 110 is made of an electrically insulating material such as a plastic or polymer material to isolate the drive cables, which may be electrically energized, from the surrounding environment. Main tube 110 may be rigid or flexible. A flexible main tube 100 would be used, for example, for insertion through an endoscope or other guide or cannula that follows a natural lumen or otherwise curved path. However, many common types of minimally invasive medical procedures such as laparoscopic surgery employ straight cannulas for insertion and removal of instruments, permitting use of a rigid main tube 110. A rigid main tube 110 can provide a solid base for use of end effector 200 during a medical procedure. A rigid/straight main tube 110 also permits portions of drive cables extending through main tube 110 to be structures such as rods or tubes (e.g., hypotubes) that may provide better immunity to stretching or be less expensive.

[0020] Backend mechanism 120 can contain an electrical system for energizing end effector 200 and a mechanical system that acts as a transmission and provides a mechanical interface between the drive cables extending through main tube 110 and a control system (not shown). In an exemplary embodiment of the invention, the control system is the da Vinci system available from Intuitive Surgical, Inc. The control system contains drive motors under the control of a processing system, software, and input from a user interface. In general, backend mechanism 120 is shaped to be fitted in a docking port or elsewhere onto the control system so that motor driven axes of the control system can operate end effector 200 to produce desired movements, e.g., changes of the pitch, yaw, and grip of end effector 200.

[0021] FIG. 2A shows an embodiment in which end effector 200 contains scissors 240. Scissors 240 can be electrically energized with an AC signal. For example, the AC signals may use a voltage of 100 volts up to 10,000 volts or more and a frequency above 100 kHz and typically between about 350 kHz and 4 MHz. Such AC signals are known in the art for performing clinical functions such as desiccation, hemostasis, cutting, dissection, fulguration, incisions, tissue destruction, cauterizing, and vessel sealing without shocking a patient. An insulating cover 260 shown in FIG. 2A covers most of end effector 200 so that only the blades of scissors 240 are exposed. During a medical procedure, scissors 240 can be energized with the high voltage AC signal when a contact pad on the patient is grounded or energized with an opposite polarity AC signal. Since only the blades of scissors 240 expose electricity to the patient, an electrical current flows only from the blades through tissue adjacent to the blades when scissors 240 are electrically energized. The concentration of electrical current can be used to destroy tissue and/or cauterize tissue during cutting with or other use of scissors 240. The contact pad on the patient's body is designed to make a wide area electrical connection to spread the current sufficiently to avoid tissue damage or burning at the body contact or anywhere away from the blades of scissors 240.

[0022] Cover 260 can be made of rubber, silicone, or another flexible insulating material and is attached to main tube 110 by a compression clip 262 or alternatively by an elastic ring, a heat shrinkable ring, a rigid ring, or other retaining structure. With a rigid ring, the material of cover 260 under the rigid ring can provide the elasticity needed for assembly of the instrument. Some suitable materials for clip 262 include stainless steel, plastic and nitinol.

[0023] FIG. 2A shows the blades of scissors 240 in the closed position, but a wrist mechanism hidden by cover 260 can open scissors 240 and change the position and orientation of scissors 240 during a medical procedure. FIG. 2B shows end effector 200 with scissors 240 in an open configuration and with cover 260 removed. Scissors 240 include blades 242 and 244 that are pivotally mounted on a distal clevis 230. Blades 242 and 244 are conductive and can be stamped metal blades. Distal clevis 230 is pivotally mounted on a proximal clevis 220, which is attached to the distal end of main tube 110.

[0024] Drive cables are connected to end effector 200 and are used to rotate blades 242 and 244 to change the yaw and grip of end effector 200 and to rotate distal clevis 230 to change the pitch of end effector 200. In one configuration, end effector 200 has only four drive cables that the backend mechanism uses to control the pitch, yaw, and grip motions. Low friction interfaces can be used throughout the instrument to minimize force transmission losses that might otherwise lead to increased cable stretch. In particular, low friction interfaces can be created between the drive cables and the guiding surfaces of proximal and distal devises 220 and 230. Alternatively, pulleys can be provided at the highest friction locations such as where the drive cables apply torque for rotation of distal clevis 230 about a pin in proximal clevis 220. The drive cables can also be swaged to provide smooth, low friction motion. Embodiments of the invention can also be implemented in systems employing more than four drive cables.

[0025] FIGS. 3A and 3B respectively show a partial cut away view of end effector 200 and an exploded view of scissors 240 to better illustrate the operation of an embodiment of the invention using a four-cable wrist mechanism. End effector 200 includes proximal clevis 220, distal clevis 230, and scissors 240 as described above. Drive cables 251, 252, 253, and 254 are attached to scissors 240. More specifically, each blade 242 or 244 as shown in FIG. 3B has a cap 241 or 243 that locks into blade 242 or 244. Caps 241 and 243 slip onto pin 235 and have a notch that traps a crimp 255 or 256. Alternatively, each cap 241 or 243 can be permanently attached to the corresponding blade 242 or 244 (e.g., by swaging). Caps 241 and 243 can be metal, plastic, or other material that provides the desired strength and cost. Crimp 255 is attached to a cable loop having ends that extend back as cables 251 and 252, and crimp 256 is attached to a cable loop having ends that extend back as cables 253 and 254. When assembled into distal clevis 220, caps 241 and 243 hold crimps 255 and 256 in respective notches, so that cables 251 and 252 are attached to blade 242 and cables 253 and 254 are attached to blade 244.

[0026] Cables 251, 252, 253, and 254 are made of a conductive material such as stranded metal cable or metal hypotubes, and may be an assembly with portions made of different materials. For example, portions of cables 251, 252, 253, and 254 in the wrist mechanism can be made of stranded metal cable for flexibility and may be swaged to provide smoother cable surfaces and reduce friction. Portions of cables 251, 252, 253, and 254 extending through main tube 110 may be hypotubes. An electrically insulating coating is not required on any of cables 251, 252, 253, or 254 although one or more of cables 251, 252, 253, or 254 can be used to conduct an electrical signal from the backend mechanism to end effector 240.

[0027] Cables 251, 252, 253, and 254 ride on pulleys 221 and 222, and from there extend back through main tube 110 to a backend mechanism (e.g., backend mechanism 120 of FIG. 1). In the illustrated embodiment cables 251 and 253 ride on pulley 221, and cables 252 and 254 ride on pulley 222. A pin 225 in proximal clevis 220 provides an axel for pulleys 221 and 222. Pin 225 also attaches distal clevis 230 to proximal clevis 220 but allows distal clevis 230 to rotate about a pivot axis sometimes referred to herein as the pitch axis. Pulleys 221 and 222 define a radius about pin 225 at which cables 251 and 252 act when rotating distal clevis 230 about pin 225, i.e., about the pitch axis.

[0028] When changing the pitch angle of end effector 200, the backend mechanism applies a higher tension to one pair of cables 253 and 254 or 251 and 252, and pulleys 221 and 222 and the distal clevis 230 rotate in a direction depending on which pair of cables 253 and 254 or 251 and 252 has higher tension. The low tension pair of cables 251 and 252 or 253 and 254 pay out at the same rate that the high tension cables are pulled in and therefore also rotate with pulleys 221 and 222. There is no relative sliding or slipping of cables 251, 252, 253, and 254 on pulleys 221 and 222 when the pitch of end effector 200 is changed. Rotation of pulleys 221 and 222 about pivot pin 225 results in lower cable friction than if cable 251, 252, 253, and 254 were sliding over an integral sliding surface in distal clevis 230.

[0029] A pin 235 in distal clevis 230 is perpendicular to pin 225 and defines a pivot axis, sometimes referred to as the yaw axis or grip axis, for scissors 240 as a whole or blades 242 and 244 individually. The yaw axis and the grip axis coincide in end effector 200. The term grip is used herein in a general sense since the action of blades 242 and 244 is generally to cut as blades 242 and 244 close or grip.

[0030] Opening or closing the grip of blades 242 and 244 without changing the yaw angle of end effector 200 requires high tension on cables that are on opposite sides of distal clevis 230. For example, to close jaws 242 and 244, high tension is applied to cables 251 and 254. Equal lengths of cables 251 and 254 are pulled in as the same length of cables 252 and 253 are paid out. As a result, relative to the view of FIG. 3B, pulley 221 rotates counterclockwise, pulley 222 rotates clockwise, and cables 251, 252, 253, and 254 do not slide or slip on pulley 221 or 222 when closing jaws 242 and 244. Opening blades 242 and 244 switches the tension in cables 251, 252, 253, and 254 and reverses the directions of rotation of pulleys 221 and 222 but still avoids sliding on pulleys 221 and 222.

[0031] Some of cables 251, 252, 253, and 254 can slide or slip in the groove of or move relative to the rotation of pulleys 221 or 222 when the yaw angle of blades 242 and 244 is being changed. For example, the yaw of end effector 200 can be changed by pulling in (or paying out) equal lengths of cables 251 and 253 while paying out (or pulling in) the same lengths of cables 252 and 254. When the pitch angle of end effector 200 is zero as shown in FIGS. 3A and 3B, at least one of cables 251 and 253 will slide on pulley 221, and at least one of cables 252 and 254 will slide on pully 222. The sliding friction that resists a cable's movement will then depend on the wrap angle of the cable on its associated pulley 221 or 222 and the component cable tension pulling the cable on to its pulley 221 or 222. With a pitch angle of zero, the wrap angles of cables on pulleys 221 and 222 are relatively small and the sliding friction is relatively small.

[0032] A non-zero pitch angle of end effector 200 will cause cable 251 to have a wrap angle around pulley 221 that differs from the wrap angle of cable 253 around pulley 221 and cause cable 252 to have a wrap angle around pulley 222 that differs from the wrap angle of cable 254 around pulley 222. FIG. 3C illustrates how a large pitch angle of distal clevis 230 causes cable 251 to have a large wrap angle on pulley 221 and lifts cable 253 off of pulley 221. When high tension is applied to cables 251 and 253 to causes blades 242 and 244 to rotate in the same direction, cable 253 slides on solid surfaces of devises 220 and 230, but pulley 221 rotates as cable 251 moves, resulting in lower friction for cable 251 than if cable 251 were sliding over an integral sliding surface in distal clevis 230.

[0033] Both cables 251 and 253 may contact pulley 221 but have different wrap angles when distal clevis 230 has other pitch angles. In these configurations, the cable 251 or 253 exerting greater force on pulley 221 will rotate with pulley 221 during rotation of blades 242 and 244 to change the yaw angle of end effector 200. The other cable 253 or 251 then slides on pulley 221, but that cable has smaller force/wrap angle on pulley 221. Similarly, cables 252 and 254 will generally have different wrap angles on pulley 222, and the cable that exerts the greater force on pulley 222 (and that would therefore experience greater sliding friction) moves with the rotation of pulley 222.

[0034] The use of a single pulley for a pair of cables as in end effector 200 thus usually reduces cable friction when compared to cables riding solely on solid fixed surfaces. Use of one pulley for two cables also conserves space and reduces part count when compared to a traditional pulley system including a pulley for each cable (or four pulleys total for a four cable system). However, alternative embodiments of the invention can employ other pulleys structures to reduce cable friction. Alternatively, to provide lower component count and costs, pulleys 221 and 222 can be eliminated and guide channels such as described in the co-filed patent application entitled, “Four-Cable Wrist with Solid Surface Cable Channels,” which was incorporated by reference above, could be used to guide the drive cables and define the moment arm for torques causing pitch rotations.

[0035] A backend mechanism can change the pitch, yaw, or grip of scissors 240 or any combination of pitch, yaw, and grip through manipulation of cables 251, 252, 253, and 254 as described above. For example, the backend mechanism pulling in the same length of cables 251 and 252 while releasing an equal length of cables 253 and 254 causes clevis 230 to rotate about pin 225, e.g., to pitch downward in FIG. 3B. Similarly, the backend mechanism pulling in the same length of cables 253 and 254 while releasing an equal length of cables 251 and 252 causes clevis 230 to pitch upward in FIG. 3B. Pulling in a length of one cable 251 or 252 while releasing an equal length of the other cable 252 or 251 causes blade 242 to rotate about pin 235. Similarly, pulling in a length of one cable 253 or 254 while releasing an equal length of the other cable 254 or 253 causes blade 244 to rotate about pin 235. The backend mechanism can thus change the yaw of scissors 240 by rotating both blades 242 and 244 in the same direction through the same angle. The grip of scissors 240 can be changed by rotating both blades 242 and 244 in opposite directions through the same angle.

[0036] Scissors 240 are designed such that the constraining surfaces that maintain blade cutting forces are all metal. In particular, pin 235 has an expanded head portion and an, opposite end cap that constrain blades 242 and 244 from separating during cutting. This ensures consistent closing force of blades 242 and 244 throughout their life while making for a low friction interface when pivoting in distal clevis 230. Further, distal clevis 230 can be made of plastic or other insulating material and does not require the strength/rigidity to prevent blades 242 and 244 from being pushed apart during cutting.

[0037] The use of metal cables 251, 252, 253, and 254 attached to metal blades 242 and 244 for actuation also permits use of cables 251, 252, 253, and 254 to electrically energize blades 242 and 244. This avoids the need for additional conductors in main tube 110 and for additional electrical connectors in end effector 200. In an embodiment used for monopolar scissors, all metal parts in end effector 200 are electrically energized with the same signal at the same time, e.g., whenever a cauterizing function of scissors 240 is activated. As mentioned above, main tube 110 can be made of insulating material and a cover 260, which is held on main tube 100 using compression ring 262, can encapsulate cables 251, 252, 253, and 254 and most of the components of end effector 200, leaving blades 242 and 244 as the only electrically energized components that are exposed and able to contact the patient. Additionally, insulating plastic components can be used throughout the instrument where strength requirements permit, for example, proximal clevis 220 and distal clevis 230 can be made of plastic or other insulating material. Plastic components may also reduce friction where cables ride on solid surfaces.

[0038] Seals may be employed at the end of main tube 200 to isolate electrically energized cables from conductive fluids that may be in contact with the instrument during a medical procedure. The partial cutaway view of end effector 200 in FIG. 3A shows how proximal clevis 220 can extend into main tube 110 and how multiple seals 270 and 275 can be used to prevent fluid flow. Limiting contact to conductive fluids is desired because liquid in contact with energized cables can directly conduct the full working voltage from the cables to the patient and cause alternate site burns. The seals create a barrier to break that the direct conductive path. Additionally, the signal conducted through main tube 110 has a capacitive coupling to the surrounding environment outside main tube 110. This capacitive coupling can cause currents in surrounding liquids, and those currents waste power, lower the working voltage on blades 242 and 244, and could cause alternate site burns. The strength of the capacitive coupling and the magnitude of the capacitive leakage currents depend on factors such as the diameter and length of conductor (e.g., cable 251, 252, 253, or 254), the insulating properties of main tube 110, and the separation between the conductor within main tube 110 and the external environment. If main tube 110 were to fill with conductive fluid, the effective distance between the conductor portion inside main tube 110 and the external environment would be smaller and capacitive coupled current leaked to the patient would be greater.

[0039] An embodiment of end seal 270 is illustrated in FIG. 4. Seal 270 as shown has a diameter that fits tightly inside main tube 110 and four projections 410 through which cables 251, 252, 253, and 254 extend. Seal 270 can be made of silicon or a similar flexible material capable of sealing against main tube 110 and cables 251, 252, 253, and 254 and flexing when cables 251, 252, 253, and 254 move for actuation of scissors 240.

[0040] A variety of multi-seal systems could be employed to isolate a patient or user of the instrument from electrical burn hazards. FIG. 3A shows one example where end effector 200 employs cover 260 and seals 270 and 275 in main tube 110 for these purposes. More generally, seals can be used around the cables and between the proximal clevis and the main tube to limit fluid flow into main tube, which could flow out the back end of the instrument. A rib seal can be used between the proximal clevis and the tip cover to obstruct fluid flow from the inside to the outside of the tip cover, which is important because fluid from the inside of the tip cover would be at full cautery voltage and could cause alternate site burns in a patient. Redundant seals can also be used to improve reliability.

[0041] Electrical connection to at least one of cables 251, 252, 253, or 254 can be made in the backend mechanism that manipulates cables 251, 252, 253, or 254. FIG. 5A shows an exploded view of a portion of a backend mechanism 500 in accordance with an embodiment of the invention predominantly employing gears and levers to control movement of a wrist mechanism or end effector. The illustrated portion of backend mechanism 500 couples to four drive cables 571, 572, 573, and 574 and includes a chassis 510, three drive shafts 512, 513, and 514, three toothed components 520, 530, and 540, and two levers 550 and 560. The components 510, 520, 530, 540, and 550 and 560 can be made of any suitably durable material such as molded or machined plastic or metal depending on the required loads and tolerances of the individual components. However, components such as chassis 510 and drive gears 512, 513, and 514 which are externally accessible are preferably made of plastic or another insulating material. As described further below, cables 571, 572, 573, and 574 can correspond to cables 251, 252, 253, and 254 and connect to an end effector of the type described above with reference to FIGS. 2A, 2B, 3A, and 3B. However, backend mechanism 500 can more generally be used in any instrument that can be electrically energized by drive cables and uses connections of four drive cables to three motor driven axes.

[0042] Chassis 510 may have a footprint chosen for connection to a robotic control system containing motors that operate drive shafts 512, 513, and 514. In particular, chassis 510 may be shaped such that drive shafts 512, 513, and 514 when fit into chassis 510 are positioned to be engaged and rotated by a robotic control such as the da Vinci system available from Intuitive Surgical, Inc.

[0043] Drive shaft 512 acts as a pinion that engages a rack portion of toothed component 520. Toothed component 520 is attached to cable 572 and moves in a straight line to pull in or release a length of cable 572 as gear 512 turns. Toothed component 520 also includes an arm containing an adjustment screw 522 that contacts lever 550. In particular, adjustment screw 522 contacts lever 550 at an end opposite to where cable 571 attaches to lever 550. A pivot point or fulcrum for lever 550 is on toothed component 540, which acts as a rocker arm as described further below. In operation, as toothed component 520 moves, adjustment screw 522 causes or permits rotation of lever 550 about the pivot point so that lever 550 can pull in or release cable 571. The connection of cable 571 to lever 550 and the contact point of adjustment screw 522 on lever 550 can be made equidistant from the pivot point of lever 550, so that when toothed component 520 pulls in (or releases) a length of cable 572, lever 550 releases (or pulls in) the same length of cable 571. Adjustment screw 522 permits adjustment of the tension in cable assembly 571 and 572 by controlling the orientation of lever 550 relative to the position of toothed component 520.

[0044] Drive shaft 513 similarly acts as a pinion that engages a rack portion of toothed component 530. Toothed component 530 is attached to drive cable 573 and moves in a straight line to pull in or release a length of cable 573 as gear 513 turns. Toothed component 520 also includes an arm containing an adjustment screw 532 that contacts lever 560 at an end opposite to where cable 574 attaches to lever 560. A pivot point or fulcrum for lever 560 is on rocker arm 540 as described further below, and the distance of the connection of cable 574 from the pivot point of lever 560 can be made the same as the distance from the pivot point of lever 560 to the contact point of adjustment screw 532 on lever 560. As a result, when toothed component 550 pulls in (or releases) a length of cable 573, lever 560 releases (or pulls in) the same length of cable 574. Adjustment screw 532 permits adjustment of the tension in cable assembly 573 and 574 by controlling the orientation of lever 560 relative to the position of toothed component 530.

[0045] Drive shafts 512 and 513 can be operated to change the yaw angle or the grip of a wrist mechanism using the processes described above. For example, when cables 571, 572, 573, and 574 respectively correspond to cables 251, 252, 253, and 254 of FIG. 3B, turning gears 512 and 513 at the same speed in the same direction or in opposite directions will change the grip or yaw of scissors 240.

[0046] Drive shaft 514 engages an internal sector gear portion of rocker arm 540. Rocker arm 540 has a pivot 542 attached to chassis 510, so that as drive shaft 514 turns, rocker arm 540 rotates about pivot 542. Rocker arm 540 also includes protrusions (not visible in FIG. 5A) that act as pivot points for levers 550 and 560. These protrusions can be located equidistant from pivot 542, so that as rocker arm 540 rotates, one pivot moves closer to the end effector and the other pivot moves further from the end effector by an equal amount. If toothed components 520 and 530 are moved at the appropriate speeds and directions to maintain the orientations of levers 550 and 560, rotation of rocker arm 540 will pull in (or release) equal lengths of cables 571 and 572 and release (or pull in) the same lengths of cables 573 and 574. Backend mechanism 500 can thus be used to perform a pitch change as described above with reference to FIG. 3B when cables 571, 572, 573, and 574 respectively correspond to cables 251, 252, 253, and 254, but the pitch change requires coordinated rotations of all three drive shafts 512, 513, and 514. Such coordinated rotations can be implemented in software of a robotic control system.

[0047] A connector 590 and a wire 592 can be used to connect an external power supply or generator (not shown) to one or more of cables 571, 572, 573, and 574. The power supply can be of the same type currently known in monopolar cauterizing instruments, and connector 590 can be of any desired type required for connection to the particular power supply. Alternatively, connector 590 can be a standard connector type such as a banana jack that connects to the power supply through an adapter cable (not shown).

[0048] FIG. 5B shows a cross-sectional view of backend mechanism 500 when assembled with additional components not shown in FIG. 5A. As illustrated, backend mechanism 500 includes drive shafts 512, 513, and 514 that respectively engage toothed components 520, 530, and 540, and a robotic control system coupled to backend 500 can rotate drive shafts 512, 513, and 514 to control the pitch, yaw, and grip of a wrist mechanism or end effector (not shown). Cables 571, 572, 573, and 574 extend from the end effector at a distal end of a main tube 110, through main tube 110 and into backend mechanism 500. In the illustrated embodiment, wire 592 makes electrical connection to cable 573 at toothed component 530. Accordingly, wire 592 must provide sufficient slack to accommodate the range of motion of toothed component 530. Alternatively, wire 592 may be connected to any one or more of cables 571, 572, 573, and 574.

[0049] Main tube 110 is attached in backend mechanism 500 to a helical gear 580, which is coupled to a drive shaft 511 through an intervening helical gear 582. When a control system rotates drive gear 511, helical gears 582 and 580 rotate main tube 110 and thereby change the roll angle of the end effector at the distal end of main tube 110.

[0050] FIG. 5B also shows a circuit board 594, which may be included in backend mechanism 500. Circuit board 594 can provide an interface for connection to a robotic control system. Circuit board 594 would typically store information about the instrument such as an identifier identifying the type of instrument and operating parameters of the instrument such as a count of the number of uses of the instrument. In the case of a single use instrument, the control system would check and change the count of the number of uses when the instrument is used. The control system can disable uses of a single-use instrument when the use count indicates the instrument has already been used.

[0051] Backend mechanism 500 as illustrated in FIG. 5B also includes a cover 516 to enclose mechanical and electrical systems in backend mechanism 500. Cover 516 can thus isolate electrically charged cables from unintended contact. A latch system 518 can be used to lock backend mechanism in a docking port of a control system.

[0052] Pulleys and capstans can be used in a backend mechanism in place of some toothed components of FIGS. 5A and 5B. FIG. 6A shows a backend mechanism 600 in accordance with an embodiment of the invention employing cables, pulleys, and capstans. Backend mechanism 600 includes a chassis 610, four drive shafts 611, 612, 613, and 614, a pair of capstans 620 and 630, a rocker arm 640 on which pulleys 642 and 643 are mounted, helical gears 580 and 582, and electrical components 590, 592, and 594. Four drive cables 671, 672, 673, and 674, which are connected to an end effector (not shown), extend through main tube 110 into backend mechanism 600. Cables 671, 672, 673, and 674 can respectively correspond to cables 251, 252, 253, and 254, which are connected to end effector 200 of FIGS. 3A and 3B. However, backend mechanism 600 can more generally be used in any instrument for which an electrically energized drive cable and connection of four cables to three motor driven axes is desired.

[0053] The shape of chassis 610 is generally selected to have a footprint corresponding to a mounting or docking port on a robotic control system. Backend mechanism 600 may thus be fitted to a control system so that drive shafts 611, 612, 613, and 614 are mechanically coupled to motors in the control system. The control system is then able to rotate drive shafts 611, 612, 613, and 614 through precise angles that may be selected by software to achieve the desired operation or movement of the instrument.

[0054] Cables 671 and 672 pass from main tube 110, around one or more pulleys 642, and wrap around capstan 620. The wrapping of cables 671 and 672 around capstan 620 is such that when capstan 620 turns, a length of one cable 671 or 672 is pulled in and an equal length of the other cable 672 or 671 is fed out. Similarly, cables 673 and 674 pass from main tube 110, around one or more pulleys 643, and are wrapped around capstan 630, so that when capstan 630 turns, a length of one cable 673 or 674 is pulled in and an equal length of the other cable 674 or 673 fed out. Drive shafts 612 and 613 are respectively coupled to turn capstan 620 and 630. A control system can thus turn drive shafts 612 and 613 to change the yaw angle or the grip of an end effector using the processes described above. For example, when cables 671, 672, 673, and 674 respectively correspond to cables 251, 252, 253, and 254 of FIG. 3B, turning drive shafts 612 and 613 at the same speed in the same direction or in opposite directions will open, close, or change the yaw of scissors 240.

[0055] Pulleys 642 and 643 could have deep grooves, and a keeper 690 as shown in FIG. 6B could be attached to the pivot pins of pulleys 642 and 643 to help prevent electrified cables from jumping off of pulleys 642 or 643. Keeper 690 can also keep pulleys 642 and 643 from coming off their respective pins when a cable goes slack or the instrument is upside down. Pulleys 642 and 643 are mounted on rocker arm 640. Rocker arm 640 has a sector gear portion that engages drive shaft 614 and is coupled to chassis 610 to rotate about a pivot axis when drive shaft 614 turns. The sector gear portion and pivot of rocker arm 640 are designed so that rotation of rocker arm 640 primarily causes one pulley 642 or 643 to move toward its associated capstan 620 or 630 and the other pulley 643 or 642 to move away from its associated capstan 630 or 620. This effectively pulls in lengths of one pair of cables 671 and 672 or 673 and 674 and releases an equal length of the other pair of cables 673 and 674 or 671 and 672. Backend mechanism 600 simply through rotation of drive shaft 614 can thus change the pitch in an end effector as described above with reference to FIG. 3B when cables 671, 672, 673, and 674 respectively correspond to cables 251, 252, 253, and 254.

[0056] Backend mechanism 600 can control the roll angle of a wrist mechanism at the distal end of main tube 110 using drive shaft 611 to turn helical gears 582 and 580, which are coupled to main tube 110 in the same manner as described above.

[0057] Cables 671, 672, 673, and 674 in backend mechanism 600 wind or wrap around pulleys 642 and 643 and capstans 620 and 630 and must be able to flex when capstans 620 and 630 rotate. Accordingly, portions of cables 671, 672, 673, and 674 in backend mechanism 600 require flexibility and may be, for example, stranded metal cable that can be flexed repeatedly around relatively sharp turns without damage. Accordingly, each cable 671, 672, 673, and 674 may include three portions, a stranded cable portion at the end effector, a more rigid portion (e.g., a hypotube) extending through the straight portion of main tube 110, and a second stranded cable portion in backend mechanism 600. For comparison, backend mechanism 500 of FIG. 5B moves cables 571, 572, 573, and 574 in nearly linear motions and does not require significant flexing of cables 571, 572, 573, and 574 around pulleys or other sharp bends. Accordingly, the portions of cables 571, 572, 573, and 574 in backend mechanism 500 can be relatively rigid structures such as hypotubes.

[0058] Wire 592 and electrical connector 590, which can be used for connection of a power supply or generator as described above, is connected to the hub or pivot pin of pulleys 642 in the illustrated embodiment of FIG. 6A. Alternatively, electrical connections to the pivot pins of pulleys 642 and 643 can be made through keeper 690 which contacts the pivot pins. Pulleys 642 and 643 and the pivot pins can be made of an electrically conductive material such as metal, so that one or more the metal cables 671, 672, 673, and 674 are electrically energized when wire 592 is electrically energized. Since pulleys 642 and 643 and keeper 690 move when rocker arm 640 rotates, wire 592 requires sufficient slack to accommodate the range of motion. Backend mechanism 600 of FIG. 6A or 6B like backend mechanism 500 of FIG. 5B also includes a circuit board 594 with circuits and connectors for electrical systems that may be employed in a medical instrument that connects to a robotic control system.

[0059] Embodiments of the invention as described above can reduce the number of components in an electrified medical instrument and thereby reduce costs through use of drive cables as electrical conductors. Reduction of the cost has obvious benefits, but also enables the creation of single-use instruments that are cost competitive (per case) when compared to existing reusable instruments. A single-use instrument has further benefits of eliminating reprocessing and sterilization at the hospital and allows further cost savings during manufacture of the instruments because components do not need to be designed and verified to enable reprocessing. Additionally, disposable scissors will ensure the cutting blades are new and sharp.

[0060] Although the invention has been described with reference to particular embodiments, the description is only an example of the invention's application and should not be taken as a limitation. In particular, although the above description concentrated on embodiments of the invention that are monopolar scissors, aspects of the invention can be employed in other electrically energized medical instruments such as instruments having non-gripping end effectors such as wire loops or scalpels or having general electrodes with hook shapes, spatula shapes, ball-end shapes, needle shapes, or other shapes. A gripping end effector such as forceps could also be energized to provide an instrument that is usable to grasp tissue and/or apply monopolar cautery energy. Various other adaptations and combinations of features of the embodiments disclosed are within the scope of the invention as defined by the following claims.