Compact capstan

A compact capstan includes a drum, a coupled hub, a passage extending through the drum and hub, and a shaft extending through the drum and hub. The shaft engages the passage such that the shaft can transmit a torsional force to the drum and the hub which are free to move along the length of the shaft. The drum includes a spiral groove to receive a cable loop wound around the drum. The hub has a thread with substantially the same pitch as the spiral groove to engage a threaded support such that the hub and the drum move laterally along their length relative to the threaded support as the hub and the drum are rotated. The shaft has a length that is substantially greater than the passage such that the shaft extends beyond both ends of the passage.

FIELD

The embodiments of the invention are generally related to robotic surgical systems. More particularly, the embodiments of the invention relate to cable drive systems for robotic surgical arms.

BACKGROUND OF THE INVENTION

Minimally invasive surgery (MIS) provides surgical techniques for operating on a patient through small incisions using a camera and elongate surgical instruments introduced to an internal surgical site, often through trocar sleeves or cannulas. The surgical site often comprises a body cavity, such as the patient's abdomen. The body cavity may optionally be distended using a clear fluid such as an insufflation gas. In traditional minimally invasive surgery, the surgeon manipulates the tissues using end effectors of the elongate surgical instruments by actuating the instrument's handles while viewing the surgical site on a video monitor.

A common form of minimally invasive surgery is endoscopy. Laparoscopy is a type of endoscopy for performing minimally invasive inspection and surgery inside the abdominal cavity. In standard laparoscopic surgery, a patient's abdomen is insufflated with gas, and cannula sleeves are passed through small (generally ½ inch or less) incisions to provide entry ports for laparoscopic surgical instruments. The laparoscopic surgical instruments generally include a laparoscope (for viewing the surgical field) and working tools.

The working tools are similar to those used in conventional (open) surgery, except that the working end or end effector of each tool is separated from its handle by a tool shaft. As used herein, the term “end effector” means the actual working part of the surgical instrument and can include clamps, graspers, scissors, staplers, image capture lenses, and needle holders, for example. To perform surgical procedures, the surgeon passes these working tools or instruments through the cannula sleeves to an internal surgical site and manipulates them from outside the abdomen. The surgeon monitors the procedure by means of a monitor that displays an image of the surgical site taken from the laparoscope. Similar endoscopic techniques are employed in other types of surgeries such as arthroscopy, retroperitoneoscopy, pelviscopy, nephroscopy, cystoscopy, cisternoscopy, sinoscopy, hysteroscopy, urethroscopy, and the like.

Endoscopy may be performed with robotically controlled working tools. Robotic control may provide an improved control interface to the surgeon. Robotically controlled working tools may be driven by servo mechanisms, such as servo motors, that are coupled to the working tool by mechanical cables. Each servo mechanism may be coupled to a cable by a capstan that draws in and pays out the cable wound around the capstan. The cable may be routed to and from the capstan by one or more pulleys. The cable may rotate a driver that is coupled to the robotically controlled working tool to drive and control movement of the tool. As space in the surgical field where robotically controlled working tools are being used is at a premium, it is desirable to have a compact mechanism to drive and control the robotically controlled working tools.

In a typical cable drive system for a robotically controlled working tool, a cable is guided by a pulley and wound onto a capstan that is rigidly fixed to a shaft. The capstan being rigidly fixed to the shaft it can only be rotated with the shaft. As a result, the point at which the cable comes onto the capstan moves along the length of the capstan as the capstan rotates. If the capstan is close to the pulley guiding the cable, a large angle can be created in the cable at a take off point at the capstan. If this angle is too large, the cable may wear excessively, incur physical damage to its cable strands, run off the take off pulley, or run out of a groove in the capstan. By increasing a distance between the capstan and the pulley, the angle at the take off point may be reduced and be acceptable. However, this makes the cable drive system less compact. It is desirable to minimize the angle in the cable at the take off point of the capstan while at the same time providing a compact mechanism to drive and control movement of a robotically controlled working tool.

It will be appreciated that all the drawings of Figures provide for herein are for illustrative purposes only and do not necessarily reflect the actual shape, size, or dimensions of the elements being illustrated.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the embodiments of the invention, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention. However, it will be obvious to one skilled in the art that the embodiments of the invention may be practiced without these specific details. In other instances well known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the embodiments of the invention.

The embodiments of the invention include methods, apparatus, and systems for a compact capstan.

In one embodiment of the invention, a method of controlling a cable loop is provided using a slideable capstan. The method includes guiding a first portion of a cable loop to a slideable capstan using a first takeoff pulley and guiding a second portion of the cable loop to the slideable capstan using a second takeoff pulley; coupling the rotation of a shaft to the slideable capstan to rotate the slideable capstan; rotating the shaft in a first direction to draw in the first portion of the cable loop and feed out the second portion of the cable loop; and in response to the rotation of the capstan, moving the slideable capstan along the shaft to substantially maintain the positions of the first takeoff point and the second takeoff point relative to the first takeoff pulley and the second takeoff pulley, respectively.

In another embodiment of the invention, a capstan drive is provided that includes a cable receiving means to receive a cable loop; a moving means to move a take off point of the cable receiving means laterally as the cable receiving means is rotated; and a transmitting means to transmit a torsional force to rotate the cable receiving means. As the cable receiving means is rotated it is free to move laterally with respect to the transmitting means.

In another embodiment of the invention, a compact capstan drive is provided including a capstan support, a motor coupled to the capstan support, and a capstan coupled to the threaded portion of the capstan support. The capstan support has a threaded portion to receive a hub of the capstan. The motor has a drive shaft with an axis of rotation to rotate the capstan. The capstan includes a drum, a hub coupled to the drum, and a shaft coupled to the drive shaft of the motor. The drum of the capstan has a spiral groove on a cylindrical surface to receive a cable loop wound around the drum. The hub has a thread to engage the threaded portion of the capstan support. As the hub and the drum are rotated together, they move laterally along their length relative to the threaded support. The shaft of the capstan engages the drum and the hub to transmit a torsional force to rotate the drum and the hub. As they rotate, the drum and the hub are free to move along the length of the shaft.

In another embodiment of the invention, a compact capstan is provided including a drum, a threaded hub, and a shaft rotatably supported in a fixed relationship to a threaded support. The drum has a cylindrical surface, a first end, and an opposite second end. The cylindrical surface of the drum has a spiral or helical groove to receive a cable loop that is wound around the drum. The threaded hub is coupled to the first end of the drum and engages the threaded support. The threaded hub and the drum move together laterally along their length relative to the threaded support in response to their being rotated. The shaft engages the drum and the hub to transmit a torsional force to rotate the drum and the hub. The drum and the hub are free to move along the length of the shaft as they are rotated.

The detailed description describes the invention as it may be used in a laparoscopic surgery. It is to be understood that this is merely one example of the types of surgeries in which the invention may be used. The invention is not limited to laparoscopy nor to the particular structural configurations shown which are merely examples to aid in the understanding of the invention. Traditional minimally invasive surgery requires a high degree of surgical skill because the surgeon's hand movements are controlling a surgical tool at a substantial distance from the surgeon's hands, often requiring unnatural and non-intuitive hand motions. In robotically assisted surgery, a surgeon may operate a master controller to control the motion of surgical instruments at the surgical site. Servo mechanisms may move and articulate the surgical instrument based on the surgeon's manipulation of the hand input devices. The robotic assistance may allow the surgeon to control the motion of surgical instruments more easily and with greater precision.

FIG. 1shows a schematic plan view of a surgical suite in which the invention may be used. A patient110is shown on an operating table112undergoing robotically assisted laparoscopic surgery. A surgeon120may use a master controller122to view a video image of the internal surgical site and control one or more surgical instruments and a laparoscopic camera by means of robotic servo mechanisms. The master controller122will typically include one or more hand input devices (such as joysticks, exoskeletal gloves, or the like) which are coupled by a servo mechanism to a surgical instrument. One or more robotic surgical arms100,102may be used to support and move surgical instruments104at the surgical site during robotically assisted surgery.

FIG. 2shows a robotic surgical arm102supporting a surgical instrument104. The surgical instrument104may include a head end200coupled to an end effector204by a tool shaft202. The end effector204may be inserted into a surgical site through a cannula206that is supported by the robotic surgical arm102. The end effector204at an internal end of the tool shaft202may provide any of a variety of surgical tools which may be actuated by servo mechanisms210which may be supported by the robotic surgical arm102. The end effector204is coupled to a head end200of the surgical instrument104through the tool shaft202. The head end200may include one or more drivers that control the movement of the end effector204. Rotation of the drivers may be used to control the movement of the end effector204.

The head end200of the surgical instrument104may be coupled to a tool carriage220on the robotic surgical arm102. This may facilitate exchange of the surgical instrument104during the course of a surgical procedure. The tool carriage220may be slidingly supported by a spar222that is supported by the robotic surgical arm102. The tool carriage220may be moved along the spar222to change the depth of insertion of the end effector204by moving the entire surgical instrument104.

Referring toFIGS. 1 and 2, the robotic surgical arm102may include one or more servo motors210to move the surgical instrument104and/or the end effector204on the surgical instrument. One or more control wires124may provide signals between the computer123in the master controller122and the servo motors210on the robotic surgical arm102. The master controller122may include a computer123to provide signals that control the servo mechanisms210of the surgical instrument104based on the surgeon's input and received feedback from the servo mechanisms.

FIG. 3shows the spar222, the tool carriage220, and the servo motors210removed from the robotic surgical arm. The servo motors210may move the tool carriage220laterally along the spar222. Movement of the tool carriage220along the spar222controls the depth of insertion of the surgical instrument that is connected to the tool carriage. The servo motors210may further move the end effector204.

The end effector204may be moved by rotating receiving elements provided in the head end200of the surgical instrument104. Each receiving element of the surgical instrument104may be coupled to a rotatable driver324provided on the tool carriage220. The end effector204may be arranged such that approximately one revolution or less of the rotatable driver324moves the controlled motion of the end effector204through its full range. Thus, one or more servo motors210may be coupled to the surgical instrument104to control a motion of the end effector204or a rotation of the tool shaft202.

FIG. 4shows a schematic of a cable loop400that may be used to provide the lateral motion of the tool carriage220along the spar222. For the purposes of this invention, a cable loop is used to describe a mechanical power transmission by means of a long flexible “cable”, such as a wire or fiber cable or a thin flexible belt or band, that is driven such that one part of the cable is drawn in by the driving mechanism while an equal amount of the cable is fed out. This results in a motion of the cable comparable to the motion of a continuous loop of cable. However, for the purposes of this invention, the “cable loop” need not physically be in the form of a continuous loop of cable. The cable may also be tubing that transports fluids or gases to or from the surgical tool.

As shown inFIG. 4, the “cable loop”400may advantageously be provided by one or more cable segments402,404that are coupled to provide the motion of a continuous loop of cable. In the schematic cable loop400ofFIG. 4, the cable loop is provided by two cable segments402,404each of which has an end406,408that is coupled to the tool carriage220. As a first end410of the cable is drawn in, a second end412of the cable is fed out and passed around an outboard pulley414. This arrangement provides a controlled lateral movement of the tool carriage220.

FIG. 5shows a schematic of a cable loop500that may be used to provide the rotary motion of a rotatable driver324. A single cable segment is shown with each of the two ends502,504coupled to one of two coupled driver pulleys such that the pulleys are rotated as a first portion508of the cable500is drawn in while a second portion510of the cable is fed out and passed around an outboard pulley514. It will be appreciated that two or more cable segments could be used to control the rotation of the rotatable driver324in an arrangement similar to that shown inFIG. 4. Likewise, a single cable segment in the arrangement shown inFIG. 5could be used to control lateral movement of the tool carriage220.

FIG. 6shows a schematic of a cable loop600that may be used to provide a lateral movement of the tool carriage220. The first602and second604ends of the cable loop600are wound around a capstan606and secured thereto. The capstan606provides a positive drive for drawing in a first portion608of the cable loop600while feeding out a second portion609of the cable at the same rate. The capstan606further provides spooling of the cable loop600as it is drawn in and unspooling of the cable as it is fed out. Two take off pulleys610,612may be provided adjacent the capstan606to provide a stable path for the cable loop600as it passes to the outboard pulley614and to the tool carriage220. Each end602,604of the cable loop600may make one or more turns around the capstan606and then pass around one of the take off pulleys610,612adjacent the capstan. Additional pulleys (not shown) may be provided between the take off pulleys610,612and the tool carriage220to direct the cable loop600as required.

FIG. 7shows a side elevation of the capstan606and a portion of the cable loop600. The portions of the cable608,609that extend to the take off pulleys610,612have been shown as extending to the sides so that the point of take off616from the capstan606can be more easily seen. The point at which one end604of the cable may be secured to the capstan606is visible while the other end602of the cable may be secured to the capstan at the opposite end and on the opposite side such that it is not visible in this elevation. Alternatively, the cable may be attached at different places on the capstan or may not be attached to the capstan.

A coupled device, such as the tool carriage220or the rotatable driver324, may be moved by rotating the capstan606to cause one portion608of the cable loop600to be drawn in and wound onto the capstan while unwinding and feeding out a second portion609of the cable loop. The capstan606may include a spiral or helical groove having a shape that receives the cable as it is wound onto the capstan. The spiral or helical groove may have a pitch, longitudinal spacing of adjacent sections of the groove, that allows the cable to be wound onto the capstan without overlaying adjacent turns of the cable. It will be appreciated that the take off point616for the cable loop600will move laterally along the capstan606as the cable is wound onto and around the capstan.

FIG. 8shows a pictorial view of the spar222, the tool carriage220, and the servo motors210with the supporting structure removed so that capstans800which are driven by the servo motors may be seen. The capstans800are illustrated facing upward for clarity but they would typically face downward toward the patient in use.FIG. 9shows a closer view of just the portion with the capstans800. Five servo motors are shown driving five capstans. Two take off pulleys are provided for each capstan. Additional pulleys are provided to guide the cable through the spar.

Referring toFIG. 8, each of the servo motors210may provide a rotary motion that is coupled to the tool carriage220by a cable loop830. For example, the cable loop830may pass over a pulley832at the end of the spar222remote from the servo motors210. One of the instrument drivers324(seeFIG. 3) on the tool carriage220may be coupled to the cable loop830such that movement of the cable loop by one of the servo motors210rotates the instrument driver. Additional cable loops (not shown) may be coupled to the remaining instrument drivers324on the tool carriage and to the tool carriage220itself such that movement of the additional cable loops by the associated servo motors210rotates the remaining drivers and moves the tool carriage along the spar222.

Each servo motor210may drive one of the capstans800, possibly through a gearbox (not shown). It may be appreciated fromFIG. 8, which shows five servo motors210with their associated capstans and take off pulleys and additional pulleys for guiding the cables, that space is at a premium.

Referring toFIG. 9, it will be seen that the cables are directed from the capstans toward the spar (not shown) which is located toward the left inFIG. 9. Two of the capstans904,906are adjacent the spar, two capstans908,910are remote from the spar, and a fifth capstan902is between the other four capstans. For a capstan908that is remote from the spar, the take off pulleys912,914may be a substantial distance from the capstan.

As shown inFIG. 21, the lateral shift in the take off point2106of the cable loop2100from the capstan908as the cable loop is wound and unwound from the capstan creates only an acceptably small angle2104between the portion of the cable loop extending to the take off pulley914and the plane2102of the take off pulley, even when the cable is at the extremes of its travel on the capstan. A small angle2104between the cable2100and the plane2102of the take off pulley914is acceptable. An angle of approximately five degrees may be acceptable for a typical configuration.

In contrast, the remaining three capstans902,904,906are close to their take off pulleys916,918,920,922,1024,1026that receive the cable loops from these capstans.

FIG. 10shows these three capstans and their take off pulleys.FIG. 11is a plan view of these three capstans and their take off pulleys which shows the short distance between the capstan and the take off pulleys. The distance between each capstan and its associated take off pulleys may be comparable to the distance between the take off points when the cable is at the extremes of its travel on the capstan.

FIG. 12is a side elevation of a capstan904that is close to its take off pulley922. This creates a relatively large angle1204between the cable1200and the plane1202of the take off pulley922when the cable is at the extremes of its travel on the capstan904. It will be appreciated that a large angle1204between the cable1200and the plane1202of the take off pulley922causes unbalanced forces on the take off pulley that can increase friction and cause wear in the system. The size of angle1204between the cable1200and the plane1202of the take off pulley922that becomes unacceptable depends on a variety of factors, such as the load on the cable and configuration of the pulleys. The cable1200may run off the capstan groove or the take off pulley922if the angle between the cable and the plane of the take off pulley1202is too great. An angle1204between the cable1200and the plane1202of the take off pulley922increases the length of the cable loop, which may require some form of tension compensating device. The capstan904and take off pulley922configuration shown may be unworkable if the cable1200is allowed to form the angle1204shown to the plane1202of the take off pulley922.

FIGS. 13 through 15show a compact capstan1300withFIG. 13being an end view,FIG. 14being a side view, andFIG. 15being a sectioned view from the side. The compact capstan1300includes a drum1310that is generally in the form of a cylinder having a cylindrical surface1302, a first end1304, and an opposite second end1306. A spiral or helical groove1308is provided in the cylindrical surface1302of the drum into which a cable loop may be wound. The cable loop may be discontinuous with two ends of segments of the cable loop being secured to opposite ends1312,1318of the spiral or helical groove1308. This configuration of the cable loop may permit the two segments of the cable loop to take off from the capstan at approximately the same lateral position along the length of the drum as may be seen inFIG. 10.

A threaded hub1314is coupled to the first end1304of the drum1310. The threaded hub1314may include a synchronization thread with substantially the same pitch as the spiral or helical groove1308. In the configuration shown, the thread is an external thread but an internal thread may be used in other configurations. The thread may be a sixty degree Unified National thread, a metric thread, an Acme thread, or other form of screw thread.

As shown inFIGS. 18A and 18B, the threaded hub1314engages a threaded support1800. As the threaded hub1314and the drum1310are rotated, they move laterally along their length relative to the threaded support1800. As discussed further below, this may maintain a substantially constant angle between the cable and the plane of the take off pulley.

A splined passage1500extends through the drum1310and threaded hub1314from an end1306of the drum to an opposing end1316of the hub. A splined shaft1330has a length that is greater than a length of the splined passage1500. The splined shaft1330passes through the splined passage1500extend. The splined shaft1330extends beyond both ends1206,1316of the splined passage1500. The splined shaft1330transmits a torsional force to the drum1310and the threaded hub1314which remain free to move laterally along the splined shaft.

The splined shaft1330may provide one or more grooves1832or projections that extend along the length of the splined shaft. The splined passage1500may provide one or more projections or grooves that mate with the respective grooves or projections of the splined shaft1330to provide positive transmission of torsional forces to the drum1310and the threaded hub1314.

A particularly advantageous form of splined shaft and passage for use in the present invention is a ball spline assembly. As may be seen inFIG. 15, a ball spline assembly may include a splined shaft1330and a ball spline nut1502. The ball spline nut may include a number of recirculating balls1500as the projections that mate with a groove1832in the splined shaft1330. Ball spline assemblies provide nearly friction-free linear motion while simultaneously transmitting torsional loads. The spline nut1502may be preloaded to decrease the radial play in the ball spline assembly and provide low backlash.

FIG. 15is a section view of the side elevation of the compact capstan assembly1300. A portion1504of the splined passage1500that is within the drum1310may be enlarged to receive the spline nut1502, which may have a diameter that is similar to the diameter of the hub portion1314. The spline nut1502may be fixed within the splined passage1500by any of a variety of means, such as a set screw. The spline nut1502may move in unison with the drum1310. The portion of the splined passage1500within the threaded hub1314may have a diameter that is only sufficient to receive the splined shaft1330.

FIG. 16shows an end view of a hub1600that includes a conventional splined passage1602.FIG. 17shows an end view of a hub1700that includes a hexagonal shaped passage1702. It will be appreciated that the shaft and passage can take any of a variety of forms. The passage will engage the shaft such that the shaft can transmit a torsional force to the drum and the hub which are free to move along the length of the shaft.

FIGS. 18A and 18Bshow a compact capstan assembly1300in a threaded support structure1800. The threaded support structure1800provides a threaded passageway1806to receive the threaded hub1314of the capstan assembly1300. The threaded support structure1800may also support a motor assembly210, two take off pulleys1802,1804, and the end1334of the splined shaft1330that emerges from the drum end1306of the capstan assembly1300. The portion of the threaded support structure1800providing the threaded passageway1806and the support and coupling1810of the motor assembly210are shown in cross-section along the diameter of the threaded passageway and the remainder of the elements are shown in full elevations.

The motor assembly210may include a gear box such that the shaft that emerges from the assembly provides a higher torque and a slower rotational speed than the shaft of the motor itself. The splined shaft1330is fixedly coupled to a shaft of the motor assembly210such that the splined shaft is an extension of the motor assembly shaft. It may be appreciated that the threaded support structure1800may hold all the components in a fixed relationship to one another except for the compact capstan assembly1300.

As may be seen inFIGS. 18A and 18Bthe threaded hub1314and drum1310move laterally along the length of the splined shaft1330as the capstan assembly1300is rotated. This is because the threads of the hub1314couple to the threaded passageway1806of the threaded support structure1800.FIGS. 18A and 18Bmay represent the two extremes of travel of the threaded hub1314and drum1310with respect to the support structure.

It will be seen that the take off point1808A,1808B for the cable moves along the length of the drum1310as the drum rotates between the two extremes of travel. It will further be seen that the drum1310moves laterally at a similar rate as the take off point1808A,1808B for the cable moves because the threaded hub1314has substantially the same pitch as the spiral or helical grove1308on the drum1310in which the cable is wound. As a result, the take off point1808A,1808B for the cable remains at substantially the same lateral position relative to the threaded support structure1800and more particularly relative to the take off pulleys1802,1804. This permits the take off pulleys1802,1804to be placed a short distance away from the capstan1300because rotation of the capstan will not result in a large angle between the cable and the plane of the take off pulleys. Moreover the angle between the cable and the plane of the take off pulleys may be essentially constant over the entire range of motion of the compact capstan1300.

The take off pulleys1802,1804and the splined shaft1330are coupled to the threaded support structure1800so they are free to rotate while being constrained against lateral movement. It will be appreciated that only the threaded hub1314, drum1310, and spline nut1502can move laterally relative to the threaded support structure1800. This may simplify the connection between the motor assembly210and the capstan assembly1300because the motor assembly may be coupled to the splined shaft1330and supported by the threaded support structure1800. This is possible because there is no lateral motion of the splined shaft1330relative to the motor assembly210or the threaded support structure1800.

FIG. 19shows an end view of a capstan and shaft assembly1900that provides another form of coupling between the capstan1902and the shaft1904. A disk-like flexure1906is attached to the capstan at the outside diameter of the flexure. The shaft1904passes through a central hole in the flexure1906and is attached to the flexure along the edge of the central hole. The flexure1906has a series of spokes that join the inner and outer portions of the flexure. The spokes make the flexure1906compliant along the axis of the shaft1904while maintaining a high torsional stiffness. Thus the shaft1904can transmit a torsional force to the drum and the hub of the capstan1902which is free to move along the length of the shaft within the limits of the flexure's1906axial compliance.

The flexure1906may provide a limited range of axial motion as compared to configurations that use a splined shaft. Configurations employing a flexure1906to couple the capstan1902to the shaft1904may only provide a moderate shifting of the capstan. In some configurations the hub may have a smaller pitch than the groove in the hub. Thus the capstan will slide to reduce some but not all of the angle between the cable and the plane of the take off pulley. This may maintain the angle within an acceptable range. An angle of approximately five degrees may be acceptable for a typical configuration.

Two flexures1906, spaced some distance apart, may couple the capstan1902to the shaft1904. This may provide radial support for the capstan1902.

In another configuration, a single flexure1906may couple the capstan1902to the shaft1904at one end of the capstan1902. The capstan1902may include a passage with a slip fit on the shaft that enables axial sliding and provides radial support.

FIG. 20shows another compact capstan assembly2000in a threaded support structure2050. The threaded support structure2050provides a threaded post2014that engages a threaded passageway of the capstan assembly2000. The threaded support structure2050may also support a motor assembly2060, and two take off pulleys2002,2004.

In comparison to the threaded support structure1800shown inFIGS. 18A and 18B, the threaded post2014in the configuration shown inFIG. 20is on the opposite side of the support structure2050from the motor assembly2060.

In the configuration shown, the shaft2020of the motor assembly2060is coupled to the capstan2000by a bellows2030. The bellows can transmit a torsional force to the drum and the hub of the capstan2000which is free to move along an axis defined by the motor shaft2020within the limits of the bellows' extension.

It may be appreciated that the threaded support structure2050may hold all the components in a fixed relationship to one another except for the compact capstan assembly2000. The capstan2010moves laterally along the length of threaded post2014as the capstan assembly2000is rotated. As in the previous configuration, the take off point2008for the cable remains at substantially the same lateral position relative to the threaded support structure2050and, more particularly, relative to the take off pulleys2002,2004. Only the capstan assembly2000moves laterally relative to the threaded support structure2050.

In another configuration (not shown), the threaded support structure provides a threaded passageway rather than a threaded post on the opposite side of the support structure from the motor assembly. The compact capstan assembly in this configuration may be similar to the compact capstan assembly1800shown inFIGS. 18A and 18B. However, the threaded passageway supports the threaded hub that, in turn, supports the outboard end of the splined shaft. This may eliminate the need for an outboard bearing to support the outboard end of the splined shaft.

While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention. For example, while an externally threaded hub is shown coupled to an internally threaded passage in the support structure, the capstan may provide an internally threaded hub that is coupled to a threaded post on the support structure. This invention is not limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.