Multi-cable medical instrument

A medical instrument includes cable pairs respectively wound around input spindles and connected to actuate degrees of freedom of an instrument shaft structure. The cables may connect so that rotating the input spindles actuates corresponding degrees of freedom. First pulleys in the instrument may receive first cables from the input spindles and redirect the first cables toward the instrument shaft, and second pulleys may receive second cables from the input spindles and redirect the second cables toward the instrument shaft. In one configuration, the first and second pulleys are respectively mounted at first and second levels, and the second pulleys redirect the second cables through the first level. Additionally or alternatively, one level of cables may cross while the other level of cables does not.

BACKGROUND

Robotically controlled instruments such as employed for minimally invasive medical procedures often employ a tool or end effector or other manipulation element at the distal end of an extended instrument shaft. (As used herein, the terms “robot” or “robotically” and the like include teleoperation or telerobotic aspects.) The instrument shaft and the distal tool generally have small diameters, often less than a centimeter, to minimize the size of incisions or natural lumens needed for insertion of the instrument. Accordingly, the distal tools are often remotely operated or actuated via thin drive members (e.g., tendons or rods) that extend between the distal tool and a transmission, sometimes referred to as the backend mechanism of the instrument. The backend mechanism of a replaceable instrument is generally configured to removably couple to actuators (e.g., a motor pack) in a docking port of a robot. The robot can then control the actuators and apply force through the backend mechanism to the drive members and through the drive members to the distal tool of the instrument.

Medical instruments that have many degrees of freedom of movement typically require many drive members, and backend mechanisms that accommodate the transition from the layout of a docking port of a robot to the layout of the drive members in the instrument shaft can be complex and difficult to assemble.

SUMMARY

In accordance with an aspect of the invention, a medical instrument may provide efficient routing of actuation cables and relatively simple assembly process for complex medical instruments.

One specific implementation provides a medical instrument including a chassis, input spindles mounted in the chassis, upper and lower cables wound around the input spindles, and an instrument shaft extending from the chassis and including a mechanical structure providing multiple degrees of freedom of motion. The upper and lower cables may connect to the mechanical structure so that rotations of the input spindles actuate respective degrees of freedom. Lower pulleys may be mounted at a first level to receive the lower cables from the input spindles and to redirect the lower cables toward the instrument shaft. Upper pulleys may be mounted at a second level to receive the upper cables from the input spindles and redirect the upper cables through the first level and toward the instrument shaft.

Another specific implementation is a method for assembling a medical instrument. The method may include: mounting lower pulleys on a first piece of a chassis of the medical instrument; feeding lower cables from an instrument shaft of the medical instrument over the lower pulleys; attaching a second piece of the chassis to the first piece so that at least portions of the lower cables are between the lower pulleys and the second piece; mounting upper pulleys in positions such that the second piece is between the upper pulleys and the lower pulleys; and feeding upper cables from the instrument shaft over the upper pulleys.

Yet another specific implementation is a medical instrument including input spindles, lower cables respectively wound around the input spindles, upper cables respectively wound around the input spindles, and an instrument shaft extending from a chassis in which the input spindles are mounted. A mechanical structure on the instrument shaft has multiple degrees of freedom of motion, and the upper and lower cables connect to the structure such that rotations the input spindles respectively actuate the degrees of freedom. The lower or upper cables may extend between the input spindles and the instrument shaft without crossing, and paths of the other upper or lower cables cross between the input spindles and the instrument shaft. The crossing in one set of cables may allow the upper cable and the lower cable that wrap around the same input spindle to be more efficiently directed toward locations on opposite sides of a central axis of the instrument shaft, which may improve mechanical efficiency of actuation of the mechanical structure.

The drawings illustrate examples for the purpose of explanation and are not of the invention itself. Use of the same reference symbols in different figures indicates similar or identical items.

DETAILED DESCRIPTION

A backend mechanism of a robotically controlled medical instrument routes cables from multiple input spindles to an instrument shaft of the instrument and employs a routing that allows simple assembly using few components. Cables and associated pulleys in an instrument may be particularly grouped by level or height relative to the instrument shaft, and lower cables may be fit on pulleys mounted in a lower chassis piece before a next, higher chassis piece and pulleys for upper cables are attached to the lower chassis piece. A two-level system is particularly effective in a self-antagonistic system in which each input spindle has a pair of two associated cables that are wrapped around the input spindle in opposite directions and at different heights so that one cable pays in in one direction and the other cable pays out in an opposite direction as the spindle rotates. The cable routing leaves space for other components of the backend of a medical instrument, for example, to allow control or actuation of instrument shaft roll, grip drive, electrical connectors, and latching mechanisms that attach the backend mechanism to a robot. The cable routing can also position cables paired in opposition in the instrument shaft, so that the paired cables can efficiently actuate opposite directions of motion of a degree of freedom of the instrument.

FIG. 1shows an example of a medical system100using replaceable medical instruments110. System100, which may, for example, be a da Vinci® Surgical System commercialized by Intuitive Surgical, Inc., may particularly employ multiple surgical instruments110, each of which is removably mounted in a docking port120on a manipulator arm130of a robot140. A sterile barrier (not shown) including a drape and adaptors for instruments110may be between instruments110and robot140, so that robot140, including manipulator arms130and docking ports120, is outside a sterile environment for a patient. Accordingly, robot140may not need to be sterilized between medical procedures. In contrast, instruments110, which may be used in the sterile environment and may contact the patient, are compact and removable so that instruments110may be sterilized or replaced between medical procedures performed using system100.

Instruments110may vary in structure and purpose but may still be interchangeable, so that instruments110mounted in docking ports120of robot140can be selected for a particular medical procedure or changed during a medical procedure to provide the clinical functions needed. Each instrument110generally includes an end effector or distal tool112, an instrument shaft114, and a backend mechanism116. Distal tools112may have different designs to implement many different functions. For example, distal tools112for different instruments110may have many different shapes or sizes and may include forceps, graspers, scalpels, scissors, cautery tools, or needle drivers to name a few possibilities, and instruments110having different distal tools112may be mounted on different arms130of robot140and may work cooperatively in the same work site. An endoscopic camera, for example, a stereoscopic camera, can also be mounted on an arm to provide visual information, particularly images, of the work site in which distal tools112of instruments110may be operating.

Docking ports120may include actuators, such as drive motors, that provide mechanical power for actuation of mechanical structures in instruments110, drive couplings that connect the actuators to inputs of instruments110, and systems for establishing and maintaining a sterile barrier between instruments110and the rest of medical system100. Docking ports120may additionally include an electrical interface to provide power to instruments110or for communication with instruments110, for example, to identify the type of instrument110in a docking port120, to access parameters of instruments110, or to receive information from sensors in instruments110. For example, the electrical interface may convey to robot140measurements such as measurements of the position, orientation, or pose of distal tool112and instrument shaft114of an instrument110. A computer system, which may be connected to or part of robot140and connected to a user interface device (not shown), may receive the measurements from instrument110and receive user commands from a surgeon or other medical personnel and may execute software that controls arms130and drive motors in docking ports120as needed to operate instruments110according to the user commands.

FIGS. 2A and 2Billustrate an example implementation of a medical instrument110.FIG. 2Aparticularly shows a perspective view of an implementation having a tool112at the distal end of instrument shaft114and shows instrument shaft114extending from backend mechanism116. In the illustrated implementation, distal tool112and instrument shaft114have six degrees of freedom of movement relative to backend mechanism116. In particular, the six degrees of freedom correspond to: pitch and yaw rotations of a distal portion of tool112about two respective perpendicular axes201and202associated with a first joint mechanism211(also called “first joint211”); pitch and yaw rotations or movement of jaws213relative to two respective perpendicular axes203and204associated with a second joint mechanism212(also called “second joint212”; the joints211,212are sometimes referred to as “wrists”); opening or closing movement205of jaws213for “grip” actuation; and “roll” rotations of instrument shaft114about its central length axis206. Other instruments may have more, fewer, or different degrees of freedom of movement.

Backend mechanism116as shown inFIG. 2Bhas six input spindles221to226with engagement features that are shaped and positioned to engage actuators, e.g., drive motors, in a docking port of a robot. In general, each input spindle221to226may be coupled for actuation of a different degree of freedom of movement of the instrument, so that the robot can identify and use the correct actuator or actuators to rotate the spindle or spindles that exercise desired degrees of freedom of motion. The assignment input spindles221to226to corresponding degrees of freedom must be known to the robot but can be otherwise defined by an arbitrary standard or convention. In an exemplary implementation, input spindle226may couple to a roll mechanism that connects to a proximal end of instrument shaft114for rotation of instrument shaft114about its length axis206when input spindle226rotates. Input spindles221to225may couple to drive members (not shown) such as cables or rods extending though instrument shaft114to distal tool112, so that the actuators in the robot can rotate input spindles221to225to control a distal mechanism including joints211and212and jaws213. More specifically, in an exemplary implementation, rotation of input spindle221may control rotation or actuation of a distal portion of tool112about an axis201. Rotation of input spindle222may control rotation about an axis202. Rotation of input spindle223may control rotation about an axis203for yaw actuation of jaws213, and rotation of input spindle224may control rotation about an axis204for pitch actuation of jaws213. In some implementations, rotations of input spindles221to226may correspond to motion that is different from or more complex than simple rotations of structures about axes. For example, input spindle225may be coupled to jaws213through a push-pull rod for actuation of gripping with jaws213. Also, in a particular implementation, the mechanism in tool112may couple a proximal portion of joint212to a distal portion of joint211for parallelogram motion, while the distal portion of joint212may move independently.

FIG. 3shows selected elements within an implementation of the backend mechanism116ofFIGS. 2A and 2Band particularly illustrates a routing in backend mechanism116of cables that run through instrument shaft114and connect to joints211and212. The term “cable” is used herein in a broad sense to include any tendon-like structure. In particular, a length of cable in a medical instrument may include sections of different materials or different characteristics. A cable may include, for example, a stranded section where flexibility in the cable is desired (e.g., where the cable winds around a spindle, capstan, or pulley) and may include a more rigid section (e.g., a tube or rod) to limit stretching where less bending of the cable is needed.FIG. 3does not show elements of backend mechanisms116that may be used for actuation of degrees of freedom associated with rotation of instrument shaft114or for opening and closing of jaws213. Co-filed U.S. Pat. App. No. 62/362,340 (filed Jul. 14, 2016), entitled “GEARED ROLL DRIVE FOR MEDICAL INSTRUMENT”, and U.S. Pat. App. No. 62/362,365 (filed Jul. 14, 2016), entitled “GEARED GRIP ACTUATION FOR MEDICAL INSTRUMENTS”, disclose aspects of particular implementations of such mechanisms and are hereby incorporated by reference in their entirety.

Input spindles221,222,223, and224, as described above, are for actuation of degrees of freedom associated with respective axes201,202,203, and204, and each input spindles221,222,223, and224includes a pair of capstans around which a pair of actuation cables are wrapped. For example, as shown inFIG. 3, an upper capstan231A and a lower capstan231B may be fixed on an axle of input spindle221so that both capstans231A and231B rotate with rotation of input spindle221. (The terms upper and lower are used here to distinguish levels and may only apply literally when instrument shaft114points in a generally downward direction, as illustrated inFIG. 3.) A cable241A wraps in one direction (e.g., clockwise or counterclockwise) around capstan231A, and a cable241B wraps in the opposite direction (e.g., counterclockwise or clockwise) around capstan231B. Cable241A extends from upper capstan231A to an upper pulley251that directs cable241A toward instrument shaft114. Similarly, cable241B extends from lower capstan231B to a lower pulley261that directs cable241B toward instrument shaft114. Cables241A and241B extend from respective pulleys251and261through a guide280, into instrument shaft114, and through instrument shaft114to connect to actuated joint mechanism211, so that pulling cable241A or242B rotates a distal portion of mechanism211(and distal portions of tool112) about axis201. The positions of pulleys251and261and the shape of guide280may position cables241A and241B on opposite sides of the center or length axis206of instrument shaft114, which may allow cable241A to efficiently drive motion of mechanism211in one direction or sense about axis201and also allow cable241B to efficiently drive motion of mechanism211in an opposite direction or sense about axis201.

Each input spindle222,223, or224similarly includes an axle through a pair of capstans232A and232B,233A and233B, or234A and234B around which a pair of cables242A and242B,243A and243B, or244A and244B wrap in opposite directions, and cables242A,242B,243A,243B,244A, and244B pass over respective pulleys252,262,253,263,254, and264and run through guide280and instrument shaft114. In an exemplary implementation, cables242A and242B connect to joint mechanism211, and cables243A,243B,244A, and244B connect to joint mechanism212.

Each pair of cables242A and242B,243A and243B, and244A and244B as described above includes one cable wound in one direction (e.g., clockwise) about an input spindle221,222,223, or224and another cable wound in the other direction (e.g., counterclockwise) around the input spindle221,222,223, or224, so that rotation of an input spindle221,222,223, or224pulls in one cable while paying out another cable. Accordingly, instrument110may employ self-antagonistic actuation in which each pair of cables241A and2416,242A and242B,243A and243B, or244A and244B controls a corresponding degree of freedom of movement, e.g., rotations about axes201,202,203, or204, of the instrument. Non-antagonistic cable actuation may be used in some embodiments (e.g., one cable per spindle).

In the illustrated system, mechanisms211and212are wrists or joints that each provide two degrees of freedom of movement. Many other mechanisms can provide one or more degrees of freedom of movement and may be connected so that one or more pairs of cables can respectively actuate the one or more degrees of freedom. An actuated mechanism may, for example, include a mechanical linkage with a link that is rotatable about a pivot, and a pair of cables may be connected to rotate the link in opposite directions relative to the pivot. Alternatively, actuated mechanisms may be any structure, e.g., a linkage, a slide, or a flexure, capable of being moved/actuated in opposite directions. For each pair of cables, pulling one cable may drive actuation of the corresponding degree of freedom in one direction or sense, and pulling the other cable in the pair may drive actuation of the corresponding degree of freedom in an opposite direction or sense.

Routing of cables241A,242A,243A, and244A employs upper pulleys251,252,253, and254to receive cables241A,242A,243A, and244A from upper capstans231A,232A,233A, and234A and employs lower pulleys261,262,263, and264to receive cables241B,242B,243B, and244B from respective lower capstans231B,232B,2336, and234B. Upper pulleys251,252,253, and254may all be positioned at about the same common height, while lower pulleys261,262,263, and264may all be positioned at about another common height that differs from the common height of upper pulleys251,252,253, and254. This allows the pulleys to be captured in stacked blocks or chassis pieces as described further below.

The arrangement of upper pulleys251,252,253, and254and lower pulleys261,262,263, and264may also be simplified by pairing pulleys to independently spin on shared axles. Using pulleys that share an axle may allow faster assembly, because multiple pulleys can be added to a structure by attaching a single axle. In the implementation ofFIG. 3, input spindles221,222,223and224are arranged in a rectangular array, e.g., in rows and columns, and paths of cables from input spindles in the same row to locations over instrument shaft114are roughly parallel. Accordingly, pulleys251and253, which guide cables241A and243A running at the same height and substantially the same direction from input spindles221and223, can be mounted on a common axle271. Similarly, upper pulleys252and254, which guide cables242A and244A that emerge from input spindles222and224with substantially the same height and direction, can be mounted on a shared axle272. Lower pulleys262and264, which guide cables242B and244B that emerge from input spindles222and224with substantially the same height and direction, can be mounted on another shared axle (not visible inFIG. 3), and lower pulleys261and263, which guide cables241B and243B that emerge from input spindles222and224with substantially the same path and direction can be mounted on yet another shared axle274.

Pulley axles271to274may also be angled according to exit directions of the cables from the input spindles221to224and relative to the central axis206of instrument shaft114. For example, axle271may be turned about a first axis (e.g., an axis parallel to the axles of input spindles221to224) to minimize the fleet angles at pulleys251and253of cables241A and243A from input spindles221and223. Axle271may be turned about a second axis (e.g., an axis approximately parallel to the portion of cables241A and243A between pulleys251and253and capstans231A and233A) so that the portion of cables241A and243A between pulleys251and253and guide280converge toward guide280and instrument shaft114. The angling of axles271to274may reduce the average fleet angle for entry and exit of the cables from the upper and lower pulleys and thereby reduce friction and wear.

Axles271to274may further be positioned relative to input spindles221to224and instrument shaft114to minimize wrap angles across sliding surfaces on the pulleys. The positions of the pulleys may be further refined according to the desired cable paths exiting guide280. In particular, redirection of any cable passing through guide280should only cause rubbing on the resilient surface (e.g., a metal portion) of guide280and not a softer surface (e.g., a plastic portion) of guide280. The wrap angle across guide280should also be small so that the friction and sawing action any cable against guide280is small. The cable path should further be relatively direct so that length of stranded cable does not negatively affect the overall stiffness of the drive train between the corresponding input spindle and the actuated mechanism. In general, the stranded sections of cables tend to stretch more than the rigid hypotube sections used in some embodiments.

The separations between input spindles221to224may be considerably larger than the diameter of instrument shaft114into which the cables need to be directed. Accordingly, the paths of the cables need to converge between input spindles221to225and instrument shaft114. The cables also should not rub against each other or against any other structures in backend mechanism116. To avoid cable interference, the winding directions of cables241A,241B,242A,242B,243A,243B,244A, and244B around the input spindles in the illustrated implementation are chosen so that cables at one level (e.g., lower cables241B,242B,243B and244B) emerge from inside the array of input spindles221to224, and cables at other levels(e.g., upper cables241A,242A,243A and244A) emerge from an outer edge of the array of input spindles. Lower cables241B,242B,243B and244B, which emerge from inside an area of the input spindle array, can directly converge at a relatively small angles toward instrument shaft114without interfering with each other or rubbing against other structures, such as input spindles223or224. Upper cables241A,242A,243A and244A, which emerge from the outer edge of input spindles221to224, have crossing paths, which increases the angle of convergence. In particular, upper cables241A and243A, which emerge from input spindles221and223, cross over upper cables242A and244A, which emerge from input spindles222and224. For the crossing pattern, upper pulleys251and253, which are within the same level group as upper pulleys252and254, although having a generally common height may be staggered in height (e.g., so that cables241A and243A can cross over cables242A and244A without rubbing). The larger angle of convergence provided by the crossing pattern allows cables241A and242A to pass from outer edges of input spindles221and222through the gap between input spindles223and224. The crossing pattern also allows pulleys251and253, which receive cables241A and243A, to be farther from pulleys252and254, which receive cables242A and244A, than pulleys261and263are from pulleys262and264. The wider spacing of upper pulleys251to254allows routing cables241A to244A toward instrument shaft114without interference from lower pulleys261to264or cables241B to244B. Crossing one level of cables in this fashion also allows positioning of cables that wrap about the same input spindle and that are therefore paired for actuation of the same degree of freedom in opposition in instrument shaft114, which may permit efficient connection of the pair of cables to an actuated mechanism.

The cable routing in the implementation ofFIG. 3may provide several advantages. In particular, the difference in the horizontal separation of upper pulleys251to254from the horizontal separation of lower pulleys261to264, may allow upper pulleys251to254to be vertically positioned closer to lower pulleys261to264, e.g., at a vertical separation that is less than the diameter of pulleys251to254and261to264. Also, upper pulleys251to254and lower pulleys261to264may be at the same distance from the closest input spindles223and224. Since one group of pulleys is not required to be closer to the input spindles, all of the pulleys can be at a relatively long distance from the input spindles, which may minimize the splay angles for the actuation cables. A crossing cable pattern may further reduce the space needed to accommodate the required splay. The cable routing can position pulleys so that the cables do not rub on each other or on neighboring input spindles and do not require additional intermediary idler pulleys.

FIG. 4shows a cross-sectional view of internal structure in an example implementation of a backend mechanism116. As illustrated, backend mechanism116may include a chassis500with a central support structure410that extends between rows of input spindles221,222,223, and224. The routing of cables241A to244A or241B to244B allows use of central support structure410to strengthen chassis500without interfering with cables241A to244A or241B to244B. The cable routing also causes cables241A to244A or241B to244B to converge sufficiently to pass between input spindles225and226, through an opening in a linkage420for actuation of jaws213, and through an opening in a linkage430used for actuation of rotation about instrument shaft axis206. This configuration with support structure410in the center of backend mechanism116opens up access to input spindles221,222,223, and224from around the perimeter of chassis500, for example, to attach and wrap cables241A to244A or241B to244B on capstans231A to234A and231B to234B and to tighten capstan clamping screws during assembly of backend mechanism116. Once input spindles221,222,223, and224are mounted in chassis500and capstans231A to234A and231B to234B are wrapped and clamped, the space around input spindles221,222,223, and224is available for other structures, such as a structure440, for latching backend mechanism to a docking port on a robot.

FIG. 5shows an expanded view of some of the components in an implementation of a medical instrument with a multi-piece chassis500for a backend mechanism116. Chassis500includes pieces510,520,530,540,550and560that may be snapped together during an assembly process. During the assembly process, a proximal end of instrument shaft114may be inserted in a bearing system in chassis piece510, at which point cables, e.g., cables241A to244A and241B to244B, which are attached to the distal tool of the instrument extend from instrument shaft114. The cables may then be fed through desired locations in guide280, and chassis piece520may be attached to chassis piece510so that guide280is captured between chassis pieces510and520. All or portions of grip or roll gears or mechanisms that couple to input spindles225or226may also be assembled on chassis pieces510and520before chassis pieces510and520are snapped together and may be held in place by chassis pieces510and520. An upper portion of chassis piece520further includes central support structure410, which is described above and includes features524shaped to hold lower capstans231B to234B which will be mounted on input spindles221to224.

The assembly process can then connect chassis piece530to chassis piece520. Chassis pieces530and520are separate to allow for the assembly of linkage420that couples to input spindle525and is employed for grip actuation in the exemplary implementation.

Chassis piece530has an upper portion shaped to hold axles273and274for lower pulleys that guide the actuation cables and redirect the actuation cables toward the instrument shaft. As shown inFIG. 6A, lower pulleys263and261on axle273may be mounted in slots formed in chassis piece530. Similarly, lower pulleys262and264on axle274are mounted in another set of slots in chassis piece530. Lower cables241B,242B,243B, and244B, which extend from instrument shaft114, may be seated in grooves on respective lower pulleys261,262,263, and264and threaded through openings in chassis piece530so that proximal ends of lower cables241B,242B,243B, and244B are near features524where input spindles221to224will reside.

The assembly process can next connect a chassis piece540to chassis piece530as shown inFIG. 6B. Chassis piece530and540may be shaped to provide a close fit between chassis piece540and pulleys261to264so that cables241B,242B,243B, and244B are not easily derailed. Upper pulleys251and253on axle272and upper pulleys252and254on axle271may be mounted in slots created by the combination of chassis pieces530and540. The slot into which axle271fits may be at slightly different level from the slot into which axle272fits so that the upper cables can cross as described above. Upper cables241A,242A,243A, and244A may be seated on respective upper pulleys251,252,253, and254and threaded through openings in chassis500so that proximal ends of upper cables241A,242A,243A, and244A are also near features524. A chassis piece550connects to chassis pieces530and540as shown inFIG. 6Cand may be shaped to provide a close fit to upper pulleys251to254so that upper cables241A,242A,243A, and244A are not easily derailed.FIG. 6Dparticularly shows a cross-sectional view illustrating how chassis piece550when mounted on pieces530and540may be close fit to pulley251so that a gap545between chassis piece550and pulley251is narrower than the thickness of cable241A on pulley251. As a result, cable241A fits into the grove in pulley251and cannot slip through gap545.

Returning toFIG. 5, a chassis piece560snaps onto or otherwise connects to one or more of chassis pieces520,530, and550. The top of chassis piece560is shaped to fit a docking port of a robot and includes features564that are shaped and located to hold the engagement features of input spindles221to224of the instrument. When chassis piece560attaches to the assembly including pieces510,520,530,540, and550, chassis500may capture input spindles221to224between features564on chassis piece560and features524on chassis piece520. Each input spindle may include an axle and a pair of capstans, e.g., upper capstans231A to234A and lower capstans231B to234B, which are initially free to rotate relative to each other. The loose proximal ends of the actuation cables near features524may be attached to the corresponding one of capstans231A to234A or231B to234B. Each capstan can then be independently rotated to wind the attached cable in the desired direction and to take up slack and provide a desired pre-tension in the attached cable. Once both cables wrapped around an input spindle have the desired cable tensioning, the capstans can be clamped or locked in place on the axle of the input spindle, e.g., by tightening a clamping screw. Other structures such as release levers comprising structure440ofFIG. 4may wrap around the outside of the actuation structure and cables and may be installed after assembly of the input spindles and routing of cables. Co-filed U.S. Pat. App. No. 62/362,454 (filed Jul. 14, 2016), entitled “INSTRUMENT RELEASE”, describes structures such as release levers comprising structure440in more detail and is hereby incorporated by reference in its entirety.

The instrument assembly and cable routing process illustrated byFIGS. 5 and 6A to 6Dmay be relatively simple when compared to the complexity of the instrument. In particular, achieving the desired cable routing does not require simultaneous threading of cables through and around a complex sequence of structures from which the cables may slip. Instead, assembly can proceed in a series of simple steps with the cables being in a secure configuration after each step. Further, the shape of the chassis provides good access to input spindles for cable connections.

Although particular implementations have been disclosed, these implementations are only examples and should not be taken as limitations. Various adaptations and combinations of features of the implementations disclosed are within the scope of the following claims. For example, although embodiments that employ rotating spindles have been described, other means of controlling cable motion may be used. These means include, for example, sliding tabs, levers, gimbals, and the like.