Patent Publication Number: US-2022233259-A1

Title: Telescoping cannula arm

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/774,240, entitled “TELESCOPING CANNULA ARM” and filed May 7, 2018, which is a U.S. National Stage application of International Patent Application No. PCT/US2016/067694 filed on Dec. 20, 2016, the benefit of which is claimed and claims priority to and the benefit of the filing date of U.S. Provisional Patent Application 62/276,136, entitled “TELESCOPING CANNULA ARM” and filed Jan. 7, 2016, each of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     Field of the Invention 
     The present invention relates generally to cannula arms for computer-assisted surgical system, and more particularly to a telescoping cannula arm for the computer-assisted surgical system. 
     Description of Related Art 
     A sterile surgical drape has been previously used to cover a surgical manipulator and a plurality of instrument manipulators  140  in computer-assisted surgical system  100 . The drapes have taken various forms. In each instance, the manipulator and associated supports links are covered with a sterile surgical drape prior to the start of a surgical procedure. 
     Surgical system  100  is a computer assisted surgical system that includes an endoscopic imaging system  192 , a surgeon&#39;s console  194  (master), and a patient side support system  110  (slave), all interconnected by wired (electrical or optical) or wireless connections  196 . One or more electronic data processors may be variously located in these main components to provide system functionality. Examples are disclosed in U.S. patent application Ser. No. 11/762,165, which issued as U.S. Pat. No. 9,060,678 and is incorporated by reference herein. Arrow  190  shows the distal and proximal directions used in the discussion of  FIG. 1 . 
     Imaging system  192  performs image processing functions on, e.g., captured endoscopic imaging data of the surgical site and/or preoperative or real time image data from other imaging systems external to the patient. Imaging system  192  outputs processed image data (e.g., images of the surgical site, as well as relevant control and patient information) to a surgeon at surgeon&#39;s console  194 . In some aspects, the processed image data is output to an optional external monitor visible to other operating room personnel or to one or more locations remote from the operating room (e.g., a surgeon at another location may monitor the video; live feed video may be used for training; etc.). 
     Surgeon&#39;s console  194  includes multiple degrees-of-freedom (“DOF”) mechanical input devices (“masters”) that allow the surgeon to manipulate the instruments, entry guide(s), and imaging system devices, which are collectively referred to as slaves. These input devices may in some aspects provide haptic feedback from the instruments and surgical device assembly components to the surgeon. Console  194  also includes a stereoscopic video output display positioned such that images on the display are generally focused at a distance that corresponds to the surgeon&#39;s hands working behind/below the display screen. These aspects are discussed more fully in U.S. Pat. No. 6,671,581, which is incorporated by reference herein. 
     Control during insertion of the instruments may be accomplished, for example, by the surgeon moving the instruments presented in the image with one or both of the masters; the surgeon uses the masters to move the instrument in the image side to side and to pull the instrument towards the surgeon. The motion of the masters commands the imaging system and an associated surgical device assembly to steer towards a fixed center point on the output display and to advance inside the patient. 
     In one aspect, the camera control is designed to give the impression that the masters are fixed to the image so that the image moves in the same direction that the master handles are moved. This design causes the masters to be in the correct location to control the instruments when the surgeon exits from camera control, and consequently this design avoids the need to clutch (disengage), move, and declutch (engage) the masters back into position prior to beginning or resuming instrument control. 
     Base  101  of patient side support system  110  supports an arm assembly that includes a passive, uncontrolled setup arm assembly  120  and an actively controlled manipulator arm assembly  130 . Actively controlled manipulator arm assembly  130  is sometimes referred to as entry guide manipulator  130 . 
     In one example, the setup portion includes a first setup link  102  and two passive rotational setup joints  103  and  105 . Rotational setup joints  103  and  105  allow manual positioning of the coupled setup links  104  and  106  if the joint brakes for setup joints  103  and  105  are released. Alternatively, some of these setup joints may be actively controlled, and more or fewer setup joints may be used in various configurations. Setup joints  103  and  105  and setup links  104  and  106  allow a person to place entry guide manipulator  130  at various positions and orientations in Cartesian x, y, z space. A passive prismatic setup joint (not shown) between link  102  of arm assembly  120  and base  101  may be used for large vertical adjustments  112 . 
     A remote center of motion  146  is a location at which yaw, pitch, and roll axes intersect (i.e., the location at which the kinematic chain remains effectively stationary while joints move through their range of motion). Some of these actively controlled joints are manipulators that are associated with controlling DOFs of individual instruments, and others of these actively controlled joints are associated with controlling DOFs of a single assembly of these manipulators. The active joints and links are movable by motors or other actuators and receive movement control signals that are associated with master arm movements at surgeon&#39;s console  194 . 
     As shown in  FIG. 1 , a manipulator assembly yaw joint  111  is coupled between an end of setup link  106  and a first end, e.g., a proximal end, of a first manipulator link  113 . Yaw joint  111  allows first manipulator link  113  to move with reference to link  106  in a motion that may be arbitrarily defined as “yaw” around a manipulator assembly yaw axis  123 . As shown, the rotational axis of yaw joint  111  is aligned with a remote center of motion  146 , which is generally the position at which an instrument enters the patient (e.g., at the umbilicus for abdominal surgery). 
     In one embodiment, setup link  106  is rotatable in a horizontal or x, y plane and yaw joint  111  is configured to allow first manipulator link  113  in entry guide manipulator  130  to rotate about yaw axis  123 . Setup link  106 , yaw joint  111 , and first manipulator link  113  provide a constantly vertical yaw axis  123  for entry guide manipulator  130 , as illustrated by the vertical line through yaw joint  111  to remote center of motion  146 . 
     A distal end of first manipulator link  113  is coupled to a proximal end of a second manipulator link  115  by a first actively controlled rotational joint  114 . A distal end of second manipulator link  115  is coupled to a proximal end of a third manipulator link  117  by a second actively controlled rotational joint  116 . A distal end of third manipulator link  117  is coupled to a distal portion of a fourth manipulator link  119  by a third actively controlled rotational joint  118 . 
     In one embodiment, links  115 ,  117 , and  119  are coupled together to act as a coupled motion mechanism. Coupled motion mechanisms are well known (e.g., such mechanisms are known as parallel motion linkages when input and output link motions are kept parallel to each other). For example, if rotational joint  114  is actively rotated, joints  116  and  118  are also actively rotated so that link  119  moves with a constant relationship to link  115 . Therefore, it can be seen that the rotational axes of joints  114 ,  116 , and  118  are parallel. When these axes are perpendicular to rotational axis  123  of joint  111 , links  115 ,  117 , and  119  move with reference to link  113  in a motion that may be arbitrarily defined as “pitch” around a manipulator assembly pitch axis. The manipulator pitch axis extends into and out of the page in  FIG. 1  at remote center of motion  146 , in this aspect. The motion around the manipulator assembly pitch axis is represented by arrow  121 . Since links  115 ,  117 , and  119  move as a single assembly in this embodiment, first manipulator link  113  may be considered an active proximal manipulator link, and second through fourth manipulator links  115 ,  117 , and  119  may be considered collectively an active distal manipulator link. 
     An entry guide manipulator assembly platform  132 , sometimes referred to as platform  132 , is coupled to a distal end of fourth manipulator link  119 . An entry guide manipulator assembly  133  is rotatably mounted on platform  132 . Entry guide manipulator assembly  133  includes an instrument manipulator positioning system. 
     Entry guide manipulator assembly  133  rotates a plurality of instrument manipulators  140  as a group around axis  125 . Specifically, entry guide manipulator assembly  133  rotates as a single unit with reference to platform  132  in a motion that may be arbitrarily defined as “roll” around an entry guide manipulator assembly roll axis  125 . 
     Each of a plurality of instrument manipulators  140  is coupled to entry guide manipulator assembly  133  by a different insertion assembly  135 . In one aspect, each insertion assembly  135  is a telescoping assembly that moves the corresponding instrument manipulator away from and towards entry guide manipulator assembly  130 . In  FIG. 1 , each of the insertion assemblies is in a fully retracted position. 
     Each of the plurality of instrument manipulator assemblies includes a plurality of motors that drive a plurality of outputs in an output interface of that instrument manipulator. See U.S. Patent Application No. 61/866,115 (filed on 15 Aug. 2013), which is incorporated by reference, for one example of an instrument manipulator and a surgical instrument that can be coupled to the instrument manipulator. 
     In one aspect, a membrane interface that is part of a sterile surgical drape may be placed between the instrument mount interface of an instrument manipulator and the input interface of the transmission unit of a corresponding surgical instrument. See, for example, U.S. Patent Application Publication No. US 2011/0277776 A1 for an example of the membrane interface and sterile surgical drape. In another aspect, a sterile adapter that is part of a sterile surgical drape may be placed between the instrument mount interface of the instrument manipulator and the input interface of the transmission unit of the corresponding surgical instrument. See, for example, U.S. Patent Application Publication No. US 2011/0277775 A1 for an example of a sterile adapter and a sterile surgical drape. 
       FIGS. 2A and 2B  illustrate perspective views of an example of a movable and/or detachable cannula mount  250  in a retracted position and a deployed position, respectively. Cannula mount  250  includes a linear extension  252 , i.e., a straight arm, which is movably coupled to a link  219  of the manipulator arm, such as an end of fourth manipulator link  119  ( FIG. 1 ). Cannula mount  250  further includes a clamp  254  on a distal end of linear extension  252 . 
     In one implementation, linear extension  252  is coupled to link  219  by a rotational joint  253  that allows linear extension  252  to move between a stowed position adjacent link  219  ( FIG. 2A ) and an operational position ( FIG. 2B ) that holds the cannula in the correct position so that the remote center of motion is located along the cannula. In one implementation, linear extension  252  may be rotated upwards or folded toward link  219 , as shown by arrow C ( FIG. 2B ), to create more space around the patient and/or to more easily drape the cannula mount when draping the manipulator arm. 
     SUMMARY 
     A surgical system includes a link of a manipulator arm and a telescoping cannula mount assembly. The link includes a curved end. The telescoping cannula mount assembly is positioned in the curved end of the link. The telescoping cannula mount assembly includes a curved cannula mount arm. In a first state, the curved cannula mount arm is parked within the curved end of the link. In a second state, the curved cannula mount arm extends from the curved end of the link and is locked in an extended position. The telescoping cannula mount assembly is configured to automatically move the curved cannula mount arm from the extended position to the parked position. 
     The telescoping cannula mount assembly also includes a mechanical arm retraction system. The mechanical arm retraction system couples the curved cannula mount arm to the curved end of the link. The mechanical arm retraction system is configured to automatically move the curved cannula mount arm from the second state to the first state. In one aspect, the curved cannula mount arm includes a bearing assembly that moves linearly along a curved rail that is affixed to the curved end of the link. 
     The mechanical arm retraction system includes a spring, a segment gear, a pinion gear, and a damper. The damper is coupled to the curved end of the link and is coupled to the curved cannula mount arm. The spring is coupled to the curved end of the link and is coupled to the curved cannula mount arm. The segment gear includes a first end and a second end. The first end of the segment gear is connected to the curved end of the link, and the second end of the segment gear is coupled to the spring. The pinion gear is coupled to the curved cannula mount arm. The pinion gear mates with the segment gear. The damper includes a shaft. The damper is connected to the curved cannula mount arm, and the pinion gear is mounted on the shaft of the damper. 
     The telescoping cannula mount assembly also includes a curved tray and a rolling loop electrical cable. The curved tray is connected to the curved end of the link. The rolling loop electrical cable includes a first end and a second end. The first end of the rolling loop electrical cable is connected to the curved cannula mount arm, and the second end of the rolling loop electrical cable is connected to the curved tray. 
     In one aspect, the curved cannula mount arm has a first end and a second end. The second end of the curved cannula mount arm is within the curved end of the link in the first state and in the second state. The telescoping cannula mount assembly also includes a latch and a latching/unlatching system. The latch is on the second end of curved cannula mount arm. When the curved cannula mount arm is in the extended position, the latching/unlatching system engages the latch to lock the curved cannula mount arm in the extended position. 
     The latching/unlatching system includes an electric actuator and a locking assembly connected to the electric actuator. In the extended position, the locking assembly engages the latch to lock the curved cannula mount arm in the extended position. If the electric actuator is activated, the locking assembly disengages from the latch so that the mechanical arm retraction system can automatically retract the curved cannula mount are into the link. 
     The telescoping cannula mount assembly also includes an interlock control system. The interlock control system includes an electric actuator bus, a bus dump circuit, and the electric actuator. The bus dump circuit and the electric actuator are connected between the electric actuator bus and a ground. 
     In one aspect, the curved cannula mount arm includes an arm retraction button and a cannula release button. In this aspect, the curved cannula mount arm has an outer surface and the arm retraction button has a surface. The arm retraction button is mounted in the curved cannula mount arm with the surface of the arm retraction button flush with the outer surface of curved cannula mount arm when the arm retraction button is not depressed. The cannula release button is configured to move linearly into the curved cannula mount arm with respect to the outer surface. 
     The surgical system also includes a cannula mount assembly. The cannula mount assembly includes a cannula docking assembly configured to dock a cannula, a linkage assembly, a cannula release button assembly having a first end and a second end, and a linear motion assembly. The cannula docking assembly is coupled to the first end of the cannula release button assembly by the linkage assembly. The second end of the cannula release button assembly is coupled to the linear motion assembly. The linear motion assembly is configured to constrain the cannula release button assembly to linear motion in first and second directions. 
     A method includes automatically configuring a manipulator arm assembly including a curved cannula mount arm for draping by withdrawing the curved cannula mount arm into a curved end of a link of the manipulator arm assembly by a mechanical arm retraction system in the curved end of the link. 
     Another method includes locking a curved cannula mount arm in an extended position from a curved link of a manipulator arm assembly by engaging a locking assembly coupled to the curved link with a latch on the curved cannula mount arm. This method also includes activating an electrical component coupled to the locking assembly to disengage the locking assembly from the latch. This method further includes inhibiting the activating of the electrical component if a cannula is docked to the curved cannula mount arm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of a prior art computer-assisted surgical system. 
         FIGS. 2A and 2B  illustrate perspective views of an example of a prior art movable and/or detachable cannula mount in a retracted position and a deployed position, respectively. 
         FIG. 3  is an illustration of a patient side support system with a telescoping cannula mount system. 
         FIG. 4A  is a perspective view of the curved distal end portion of a fourth link of the patient side support system of  FIG. 3  with a curved cannula mount arm retracted, e.g., parked, in the curved distal end portion. 
         FIG. 4B  is a perspective view of the curved distal end portion of the fourth link of the patient side support system of  FIG. 3  with the curved cannula mount arm extending from the curved distal end portion and locked in the extended position. 
         FIG. 5A  a perspective cut away view of the curved distal end portion of the fourth link of the patient side support system of  FIG. 3  with the curved cannula mount arm parked to show a cannula mount system that includes a mechanical arm retraction system and a latching/unlatching system. 
         FIG. 5B  a perspective cut away view of the curved distal end portion of the fourth link of the patient side support system of  FIG. 3  with the curved cannula mount arm in the extended position to show the cannula mount system that includes the mechanical arm retraction system and the latching/unlatching system. 
         FIGS. 6A and 6B  are opposing perspective side views of portions of the telescoping cannula mount system. 
         FIG. 7A  is a perspective side view of a portion of the telescoping cannula mount system showing a latching/unlatching system and a latch. 
         FIG. 7B  is a view of the latching/unlatching system and the latch. 
         FIG. 8  is process flow diagram of acts used to control retraction of cannula mount arm in the telescoping cannula mount system. 
         FIG. 9  is a block diagram of an interlock control system that implements an interlock that prevents retraction of the cannula mount arm when a cannula is mounted on the cannula mount arm. 
         FIG. 10  is a cut away perspective view of the cannula mount arm to show a cannula mount assembly. 
         FIG. 11  is a cut away perspective view of the cannula docking assembly of  FIG. 10 . 
         FIG. 12  is a schematic of a patient side support system with a telescoping cannula mount system. 
         FIG. 13  show schematics of example telescoping cannula mount systems that can be used with the patient side support system of  FIG. 12 . 
     
    
    
     In general, in the drawings, the first digit of a three digit reference numeral is the figure number in which the element having that reference numeral first appeared. The first two digits of a four digit reference numeral are the figure number in which the element having that reference numeral first appeared. 
     DETAILED DESCRIPTION 
       FIG. 3  is an illustration of a patient side support system  310  in a computer-assisted surgical system that includes a telescoping cannula mount system  350 , sometimes referred to as cannula mount system  350 , in a curved distal end portion  319 D of a fourth link  319  in a manipulator arm assembly  330 . Telescoping cannula mount system  350  is configured to automatically move a curved cannula mount arm  355  of telescoping cannula mount system  350  from a position extending from fourth link  319  to a parked position within fourth link  319 . 
     Arrow  390  shows the distal and proximal directions used in the discussion of  FIG. 3 . The proximal and distal directions are an example of a first direction and a second direction opposite to the first direction. The computer-assisted surgical system includes a controller, an imaging system and a surgeon&#39;s console—all of which are coupled to patient side support system  310 . 
     In this aspect, some parts of manipulator arm assembly  330  are equivalent to corresponding parts in patient side support system  110  in  FIG. 1 . In particular, links  113 ,  115 ,  117 ,  119 , manipulator arm assembly  130 , and plurality of instrument manipulators  140  are equivalent to links  313 ,  315 ,  317 ,  319 , manipulator arm assembly  330 , and plurality of instrument manipulators  340 , respectively, with the exceptions described in more detail below. In particular, link  319  has a curved distal end portion  319 D that includes a telescoping cannula mount system  350 , described herein. Thus, the description associated with  FIG. 1  is not repeated here for  FIG. 3 , but is incorporated herein by reference. 
     Curved cannula mount arm  355 , sometimes referred to as arm  355  or as cannula mount arm  355 , is moveably mounted in telescoping cannula mount system  350 . In  FIG. 3 , patient side support system  310  is configured for mounting a sterile surgical drape on plurality of instrument manipulators  340  and manipulator arm assembly  330 . In particular, curved cannula mount arm  355  is retracted into curved distal end portion  319 D of link  319 , e.g., cannula mount arm  355  is parked within link  319 . This is a first state of cannula mount arm  355 , in which cannula mount system  350  has no stored potential energy that can be used to move cannula mount arm  355 . When cannula mount arm  355  is parked, cannula mount arm  355  is said to be in a first state. 
     Manipulator arm assembly  330  is covered with a sterile drape, by sliding the drape over all links, starting with plurality of instrument manipulators  340 , entry guide manipulator assembly  333  and entry guide manipulator assembly platform  332 , and sliding to the proximal end of first manipulator link  313 . With cannula mount arm  355  in the parked position, draping is easier, in particular when passing the drape over links  319 ,  317  and  315 , because the effective width of the system at this point is narrower with cannula mount arm  355  in the parked position. The drape sleeve for cannula mount arm  355  does not have to be positioned about cannula mount arm  355  to enable the complete draping of links  319  to  313 . A cannula mount sterile adapter is mounted on a first end of cannula mount arm  355  that protrudes from a distal face of curved distal end portion  319 D of link  319 . For an example of a cannula sterile adapter suitable for use with cannula mount arm  355 , see PCT International Publication No. PCT/US2015/020916 A1 (published on 24 Sep. 2015 as WO2015/142814; disclosing “Surgical Cannula Mounts and Related Systems and Methods”), which is incorporated herein by reference. 
     With cannula mount arm  355  parked, it allows the person doing the draping to move around curved distal end portion  319 D of link  319  without worrying about snagging the drape on cannula mount arm  355 , and it provides more unencumbered space for that person to work. This is narrower than a system that has a folded linear cannula mount arm during the draping process. (See  FIG. 2B ). Moreover, curved cannula mount arm  355  permits retracting arm  355  further into curved distal end portion  319 D of link  319  than would be possible if the prior art linear arm were retracted into curved distal end portion  319 D of link  319 . 
     In some aspects, to dock a cannula to the first end of cannula mount arm  355 , cannula mount arm  355  must be in an extended and locked position. To extend cannula mount arm  355  from curved distal end portion  319 D of link  319 , a user grasps the first end of cannula mount arm  355  and pulls cannula mount arm  355  from the distal end of link  319 . 
     As cannula mount arm  355  is pulled from the distal end of link  319 , the motion of arm  355  stores energy in an arm retraction system within telescoping cannula mount system  350 . When cannula mount arm  355  locks in the extended position, telescoping cannula mount system  350  stores sufficient potential energy to automatically retract cannula mount arm  355  back to the parked position. 
     In one aspect, telescoping cannula mount system  350  is used to automatically configure manipulator arm assembly  330  for draping by automatically retracting cannula mount arm  355  to the parked position within curved distal end portion  319 D of link  319 . However, as explained more completely below, when cannula mount arm  355  is locked in the extended position and a cannula is docked to cannula mount arm  355 , a controller of telescoping cannula mount system  350  inhibits unlocking of cannula mount arm  355  until cannula mount arm  355  can be safely retracted back into curved distal end portion  319 D of link  319 . 
     The arm retraction system of telescoping cannula mount system  350  does not include an electrical motor to retract cannula mount arm  355 . The arm retraction system provides an automatic smooth controlled retraction of cannula mount arm  355  without extra motors without the extra electronics, and sensors required to safely implement a motorized axis. Thus, there is no possibility that an electrical short, an induced current, or any other source of electrical power can inadvertently cause such an electrical motor to move cannula mount arm  355  during a surgical procedure. The arm retraction system is referred to as a mechanical arm retraction system to indicate that the arm retraction system includes only mechanical components and no electrical components such as a motor, electronics or electrical components. 
     An electrical component, e.g., an electric actuator, in a latching/unlatching system is used to unlatch cannula mount arm  355  so that potential energy in the mechanical arm retraction system automatically retracts cannula mount arm  355 . As indicated above, the mechanism of mechanical arm retraction system is entirely mechanical and so there is no potential for an electrical problem affecting the operation of mechanical arm retraction system. 
     However, if the electrical component in the latching/unlatching system were inadvertently fired during a surgical procedure, the mechanical arm retraction system would retract cannula mount arm  355 . The normal fault recovery logic in a computer-assisted surgical system would not be able to compensate for such an inadvertent firing of the electrical component in the latching/unlatching system. Thus, in one aspect, the power to trigger this electrical component is shorted to ground during a surgical procedure. Consequently, use of the electrical component in the latching/unlatching system is inhibited during a surgical procedure. Any spurious voltage on the power line to the electrical component is also shorted to ground, and this assures that the electrical component cannot be fired during the surgical procedure, and so cannula mount arm  355  cannot be inadvertently retracted from the locked and extended position. 
       FIGS. 4A and 4B  are enlarged illustrations of curved distal end portion  319 D of fourth link  319 . In  FIGS. 4A and 4B , arrow  490  shows the first and second directions used in the discussion of  FIGS. 4A and 4B . The proximal and distal directions are an example of a first direction and a second direction opposite to the first direction. 
     In particular,  FIG. 4A  is a perspective view of curved distal end portion  319 D of fourth link  319 , sometimes referred to as link  319 , with curved cannula mount arm  355  retracted, e.g., parked. In the parked position, telescoping cannula mount system  350  has no stored potential energy that can move cannula mount arm  355 , and so telescoping cannula mount system  350  and cannula mount arm  355  are said to be in a zero energy state, which was referred to as the first state above. When cannula mount arm  355  is parked in curved distal end portion  319 D of fourth link  319 , a portion of a first end  455 - 1  of cannula mount arm  355  extends from a distal face of curved distal end portion  319 D of link  319 . 
     Cannula sterile adapter  460  is shown mounted on first end  455 - 1  of cannula mount arm  355 . In this example, cannula sterile adapter  460  includes an aperture  461  configured to receive an attachment portion  471  of cannula  470 . While it not shown in the drawings, cannula sterile adapter  460  typically is attached to a surgical drape to facilitate forming a boundary between a sterile region and a non-sterile region. 
     In this example, cannula  470  includes a bowl section  473  at a proximal end  474  of cannula  470 . A tube  475  extends in a distal direction from bowl section  473 . Attachment portion  471  is attached to bowl section  473 . Attachment portion  471  may include depressions  472  on opposite sides of attachment portion  471  to assist with mounting cannula  470  to a cannula mount assembly (see  FIGS. 10 and 11 ) in the distal end, first end  455 - 1 , of cannula mount arm  355 . Depressions  472  are configured to facilitate docking of cannula  470  to cannula sterile adapter  460  and the cannula mount assembly. For examples of cannula  470  suitable for use with cannula mount arm  355 , see PCT International Publication No. PCT/US2015/020916 A1. 
     To attach cannula  470  to cannula mount arm  355 , cannula mount arm  355  must first be withdrawn from curved distal end portion  319 D of distal link  319  and locked in an extended position, and then cannula  470  can be docked at the distal end of cannula mount arm  355 . Since telescoping cannula mount system  350  does not include any electrical motors, cannula mount arm  355  must be manually withdrawn from curved distal end portion  319 D. 
     Thus, a person grasps first end  455 - 1  of cannula mount arm  355  and pulls cannula mount arm  355  from curved distal end portion  319 D. The force used to pull cannula mount arm  355  from curved distal end portion  319 D is stored by telescoping cannula mount system  350  as potential energy that can be used later to automatically retract cannula mount arm  355 . When cannula mount arm  355  is fully extended, cannula mount arm is locked in the extended position, as illustrated in  FIG. 4B . When cannula mount arm  355  is locked in the extended position, e.g., locked in a second state of the arm, a cannula arm extended and locked signal is sent to the controller. 
     Cannula mount arm  355  includes a plurality of buttons. In one aspect, the plurality of buttons includes an arm retraction button  451 , a cannula release button  452 , and a clutch button  453 . If cannula  470  is not docked on cannula mount arm  355 , depressing arm retraction button  451  causes cannula mount arm  355  to be automatically retracted into curved distal end portion  319 D of link  319 . 
     The shape of cannula mount arm  355  and the configuration of the plurality of buttons are selected so that when cannula mount arm  355  is retracted into curved distal end portion of link  319  while draped, it unlikely that drape will be snagged or caught on any of the plurality of buttons or any part of cannula mount arm  355 . This prevents a contaminated drape from being pulled inside curved distal end portion  319 D of link  319  and potentially damaged. Thus, the interior of link  319  does not require sterilization before use in another surgical procedure. 
     In this aspect, a portion of cannula mount arm  355  has an oval shape and there are no abrupt changes in shape of cannula mount arm  355  on which a surgical drape could be caught. When it is said the cannula mount arm  355  has an oval shape, it means that in a cross-sectional view, the outer surface of cannula mount arm  355  has an oval shape. 
     In particular, edges of indentation  454  are sloped and curved so that the surgical drape slides over the edges of indentation  454  as cannula mount arm  355  is retracted. Similarly, a surface of arm retraction button  451  is flush with the outer surface of cannula mount arm  355 , when not depressed, so that there is no edge of arm retraction button  451  to snag the drape as the drape moves across arm retraction button  451 . 
     Cannula release button  452  has smooth edges and surfaces so that if the drape falls into indentation  454 , the drape moves smoothly around cannula release button  452  as cannula mount arm  355  retracts. The surface and curvature of clutch button  453  is similarly selected so that there are no edges or abrupt surface changes that could snag the drape as cannula mount arm  355  retracts. 
     If cannula  470  is not docketed on cannula mount arm  355 , the controller inhibits entering a following system mode of operation. In the following system mode of operation, sometimes referred to as following, motion of a slave surgical instrument follows motion of a master tool teleoperatively coupled to the slave surgical instrument. 
     To mount cannula  470  on cannula mount arm  355 , both cannula release button  452  and clutch button  453  are depressed simultaneously and held in the depressed position. Manipulator arm assembly  330  is moved, while clutched, to the location of attachment portion  471  of cannula  470 , and then attachment portion  471  is inserted into cannula sterile adapter  460  and into the distal end of cannula mount arm  355 . Then, cannula release button  452  and clutch button  453  are released and cannula  470  is latched to cannula mount arm  355 , which is now no longer clutched, but is now locked in place. In order to facilitate one-person docking, the two buttons  452  and  453  are positioned to allow operation with one hand, while the second hand can be used to hold cannula  470  in the proper orientation for docking. 
     In one aspect, there are sensors in the cannula mounting system that indicate when a cannula is docked to cannula mount arm  355 . When the controller receives a signal that a cannula is docked to cannula mount arm  355 , the controller disables the retraction of cannula mount arm  355 . The retraction of cannula mount arm  355  remains disabled until after cannula  470  is undocked from cannula mount arm  355 . Specifically, depressing arm retraction button  451  after cannula  470  is docked results in no action. Similarly, the controller cannot successfully command retraction of cannula mount arm  355  until after cannula  470  is undocked. 
     As explained more completely below, cannula release button  452  is purely mechanical, and if cannula release button  452  is depressed, cannula  470  will be free to be pulled out of the cannula mount assembly. The same thing is true in docking cannula  470 , if cannula release button  452  is depressed, cannula  470  can be positioned in the cannula mount assembly. Therefore, clutch button  453  does not always have to be pressed to dock cannula  470 —for example, if the cannula mount arm  355  could be clutched to the exact proper location, then cannula  470  could be docked using only cannula release button  452 . However, typically, both buttons  452  and  453  are activated simultaneously, because otherwise, it is hard to tell when cannula  470  and the cannula mount assembly are properly aligned. 
       FIGS. 5A and 5B  are cutaway illustrations of curved distal end portion  319 D of link  319  to show cannula mount system  350  that includes mechanical arm retraction system  540  and a latching/unlatching system  550 . Mechanical arm retraction system  540  includes a constant force spring  543 - 3 , a pinion gear  547  coupled to a rotary damper  648  ( FIG. 6A ), and a curved segment gear  542 . Latching/unlatching system  550  includes a solenoid  545  and a locking assembly  544 . Solenoid  545  is an example of an electric actuator. In view of this disclosure, electric actuators other than a solenoid can be included in latching/unlatching system  550 . 
     When latch  546  is released by latching/unlatching system  550 , constant force spring  543 - 3  pulls cannula mount arm  355  in the second direction (the proximal direction in  FIGS. 5A and 5B ), i.e., automatically retracts cannula mount arm  355  into curved distal end portion  319 D of link  319 . However, the speed of the retraction is limited by rotary damper  648 , sometimes referred to as damper  648 . Pinion gear  547  rides on curved segment gear  542  and is coupled to cannula mount arm  355  by rotary damper  648 . Thus, as cannula mount arm  355  is moved in the second direction, pinion gear  547  rotates, but the speed of the rotation is limited by rotary damper  648 . This limits the speed that pinion gear  547  can move along curved segment gear  542 . Consequently, cannula mount arm  355  is automatically retracted into curved distal end portion  319 D of link  319  in a controlled manner, without use of any electric motor, electronics, or sensors. 
     An anchor bracket  541  is rigidly affixed to the distal end of curved distal end portion  319 D. A first end, e.g., a distal end, of curved segment gear  542  is fixedly attached to anchor bracket  541 . In this example, curved segment gear  542  is a curved rectangular-shaped arm with a first curved surface  542 - 1  and a second curved surface  542 - 2  opposite and removed from first curved surface  542 - 1 . First curved surface  542 - 1  has a smaller radius of curvature than second curved surface  542 - 2 . Second curved surface  542 - 2  includes gear teeth  642  in this example. See  FIGS. 6A and 6B  for a more detailed illustration of curved segment gear  542 . 
     In another aspect, the gear teeth of curved segment gear  542  could be on first curved surface  542 - 1  or on one of the other sides of curved segment gear  542 . Thus, the configuration of curved segment gear  542  in the drawings is optional and is not intended to be limiting to the specific configuration illustrated. 
     A spring assembly  543  includes a spring assembly bracket  543 - 1 , a spool assembly  543 - 2 , and a constant force spring  543 - 3 . A first end, e.g., a distal end, of spring assembly bracket  543 - 1  is fixedly attached to a second end, e.g., a proximal end, of curved segment gear  542 . Spool assembly  543 - 2  is mounted on a second end, e.g., a proximal end, of spring assembly bracket  543 - 1 . Constant force spring  543 - 3 , sometimes referred to as spring  543 - 3 , is a metal spring. A second end of spring  543 - 3  is coiled onto spool assembly  543 - 2  so that spring  543 - 3  winds and unwinds around spool assembly  543 - 2 . A first end of spring  543 - 3  is anchored to a second end  455 - 2 , e.g., a proximal end, of cannula mount arm  355 . Thus, as cannula mount arm  355  is withdrawn from curved distal end portion  319 D, spring  543 - 3  is unwound from spool assembly  543 - 2 , and so stores potential energy. 
     Second end  455 - 2 , e.g., the proximal end, of cannula mount arm  355  includes a latch  546 . In one aspect, latch  546  is mounted on second end  455 - 2  of cannula mount arm  355 . In this aspect, latch  546  includes an inclined ramp that leads to a socket. (See  FIG. 7B ). 
     The electric actuator, e.g., solenoid  545 , in latching/unlatching system  550  is mounted on anchor bracket  541 . In this example, solenoid  545  is mounted on a second end of anchor bracket  541 , where the first end of anchor bracket  541  is attached to curved distal end portion  319 D. The solenoid plunger is connected to a locking assembly  544  in latching/unlatching system  550 . 
     Locking assembly  544  engages latch  546  when cannula mount arm  355  is moved to the fully extended position as illustrated in  FIG. 4B . To disengage locking assembly  544  from latch  546  so that spring  543 - 3  can retract curved cannula mount arm  355  into curved distal end portion  319 D of link, solenoid  545  is activated, e.g., fired. As explained more completely below, when cannula mount arm  355  is locked in the extended position and cannula  470  is docked on cannula mount arm  355 , firing of solenoid  545  is inhibited, and so cannula mount arm  355  cannot be retracted when a cannula is docked to arm  355 . 
       FIGS. 6A and 6B  are opposing perspective side view of portions of telescoping cannula mount system  350 .  FIG. 6A  shows that in this aspect, first end of spring  543 - 3  is fixedly attached to second end  455 - 2  of cannula mount arm  355  at point  643 . Thus,  FIG. 6A  shows the first end of spring  543 - 3  both attached and unattached. 
       FIG. 6A  also shows more clearly gear teeth  642  on second curved surface  542 - 2  of curved segment gear  542 . Curved segment gear  542  is attached to a curved rail  641  ( FIG. 6B ). A plurality of bearing blocks, which are attached to cannula mount arm  355 , ride on curved rail  641 . A curved rail and associated bearing blocks suitable for use in telescoping cannula mount system  350  are commercially available from THK America, Inc., 200 East Commerce Drive, Schaumburg, Ill. 60173 U.S.A. 
     Pinion gear  547  ( FIGS. 5B and 6A ) is attached to a rotating shaft of damper  648  ( FIG. 6A ). The teeth on pinion gear  547  mesh with gear teeth  642  of curved segment gear  542 . Damper  648  is affixed to second end  455 - 2  of cannula mount arm  355 . Damper  648  provides no damping when cannula mount arm  355  is manually withdrawn, i.e., extended, from curved distal end portion  319 D. Damper  648  provides damping as spring  543 - 3  automatically retracts cannula mount arm  355  into curved distal end portion  319 D. The amount of damping is selected so that cannula mount arm does not suddenly snap back into curved distal end portion  319 D, but retracts with a controlled safe speed with low impact at the end of travel. 
       FIG. 6B  shows locking assembly  544  in more detail. A circuit board  680  ( FIG. 6B ) is attached to second end  455 - 2  of cannula mount arm  355 . Circuit board  680  is coupled to a latch sensor that is described below (see latch sensor  748  ( FIG. 7A )), and to all other sensors and switches on cannula mount arm  355 . To provide power to the latch sensor and to transfer signals from the circuit board  680  back to the controller, ribbon cables  681  are connected to circuit board  680 . Ribbon cables  681  are an example of a rolling loop electrical cable. The use of more than one ribbon cable is optional. In some applications, a single ribbon cable could be used. 
     In this aspect, ribbon cables  681  are stacked beneath a cross-curve spring, i.e., are coupled to a spring. The cross-curve spring prevents ribbon cables  681  from buckling as the rolling loop formed by ribbon cables  681  deploys when cannula mount arm  355  moves into and out of curved distal end portion  319 D. Thus, the electrical cable is coupled to a spring to prevent the electrical cable from buckling as the rolling loop formed by the electrical cable deploys The rolling loop formed by ribbon cables  681  is placed between two concentric trays  685  and  686 . 
     In one aspect, ribbon cables  681  include a first plurality of ribbon cables and a second plurality of ribbon cables. The first plurality of ribbon cables carry signals to and from cannula mount system  350  and provide power to cannula mount system  350 . The second plurality of ribbon cables form a ground bond between cannula mount arm  355  and link  319 . 
     First ends of the first plurality of ribbon cables are attached to first connectors  682  that mate with first circuit board  680  of cannula mount arm  355 . Second ends of the first plurality of ribbon cables are attached to a second circuit board within link  319  (the second circuit board is not shown). In one aspect, the second plurality of ribbon cables, e.g., two ribbon cables, is stacked beneath the first plurality of ribbons cables. The second plurality of ribbon cables is used as a ground bond between stationary link  319  and moving cannula mount arm  355 . The second plurality of ribbon cables runs between connectors  683  and  684 . Connector  683  is connected to cannula mount arm  355  and connector  684  is connected of second curved tray  685 . Curved tray  685  is coupled to anchor bracket  541 , and so is coupled to curved distal end portion  319 D of link  319 . 
     Thus, telescoping cannula mount system  350  includes a first curved tray  686  and a second curved tray  685 . Second curved tray  685  is connected to the curved distal end portion  319 D of link  319 . First curved tray  686  is connected to the proximal end of cannula mount arm  355 . 
     Rolling loop ribbon cables  681  are anchored between a first end  685 - 1 —a distal end—of second curved tray  685  and a first end—a distal end—of first curved tray  686 . A first portion of ribbon cables  681 , e.g., a first leg, follows the curve of first curved tray  686  and then ribbon cables  681  have a shape resembling a letter “U” on its side. The U-shape forms a transition to a second portion of ribbon cables  681 , e.g., a second leg that follows the curve of second curved tray  685 . Thus, ribbon cables  681  form an open loop with both legs of the loop being curved and the length of each leg changing as cannula mount arm  355  is withdrawn and as cannula mount arm  355  is retracted. 
       FIGS. 7A and 7B  are more detailed illustrations of locking assembly  544  and latch  546 . In this aspect, locking assembly  544  includes a first link  744 - 1 , a second link  744 - 2 , a latch link  744 - 3 , a spring  744 - 4 , a cam follower  744 - 6 , and a latch flag  744 - 5 . 
     First link  744 - 1  has a Y-shaped body. A second end of first link  744 - 1 , which forms the base leg of the Y-shape, is rotatably mounted on a first pin  701  extending from anchor bracket  541 . Thus, first link  744 - 1  is grounded to anchor bracket  541 . A pin  702  extends between two legs at a first end of first link  744 - 1 —the two legs forming the uprights of the Y-shape. 
     A plunger  745 - 1  of solenoid  545  is connected to pin  702 . In this aspect, solenoid  545  is a linear motion solenoid, and plunger has a slot in one end. The slot rides on pin  702 . A spring  745 - 2  around plunger  745 - 1  returns plunger  745 - 1  to the extended position after solenoid  545  is activated and then deactivated. Spring  745 - 2  and spring  744 - 4  work in the same direction, thus the forces of these two springs are additive. 
     A second end of second link  744 - 2  is rotatably mounted on pin  702 , i.e., second link  744 - 2  is rotatably connected to first link  744 - 1 . A first end of second link  744 - 2  is rotatably connected to a second end  744 - 32  of latch link  744 - 3 . 
     Latch link  744 - 3  is mounted on a second pin  703  that extends from anchor bracket  541  between first end  744 - 31  and second end  744 - 32 . Second pin  703  functions as a fulcrum (pivot point) for latch link  744 - 3 . Latch link  744 - 3  is grounded to anchor bracket  541  by second pin  703 . Cam follower  744 - 6  is affixed to a first side of a first end  744 - 31  of latch link  744 - 3 . Latch flag  744 - 5  is affixed to a second side of the first end  744 - 31  of latch link  744 - 3 . In this aspect, the first side and the second side of latch link  744 - 3  intersect to form one edge of latch link  744 - 3  that extends from the first end to the second end. 
     Thus, in this aspect, latch link  744 - 3  is implemented as a V-shaped lever with a first leg that extends from the pivot point to first end  744 - 31  and a second leg that extends from the pivot point to second end  744 - 32 . The first leg is longer than the second leg in this aspect. 
     In this example, latch link  744 - 3  is a Class 1 lever because the fulcrum is between the effort (the force supplied by solenoid  545 ) and the load (cam follower  744 - 6  and latch flag  744 - 5 ). While in this example, latch link  744 - 3  is implemented as a Class 1 lever, this is illustrative only and is not intended to be limiting. In other aspects, a Class 2 lever or a Class 3 lever could be used. For a Class 2 lever, the load is between the fulcrum and the effort, and for a Class 3 lever, the effort is between the fulcrum and the load. 
     A first end of spring  744 - 4  is connected to latch link  744 - 3  between first end  744 - 31  and the pivot point. A second end of spring  744 - 4  is connected to a third pin  704  extending from anchor bracket  541 . Spring  744 - 4  provides a force on the first leg of latch link  744 - 3  that pulls cam follower  744 - 6  into latch socket  746 - 2 . 
     For the configuration illustrated in  FIG. 7A , cannula mount arm  355  is fully extended and latched in the extended position, as shown in  FIGS. 4B and 5B . To arrive at this position, cam follower  744 - 6  moves up inclined ramp  746 - 1  ( FIG. 7B ) of latch  746  as cannula mount arm  355  is withdrawn. 
     The forces on the first leg of latch link  744 - 3  provided by springs  744 - 4  and  745 - 2  maintains cam follower  744 - 6  on inclined ramp  746 - 1 . When cam follower  744 - 6  reaches the high end of inclined ramp  746 - 1  and cannula mount arm  355  is withdrawn further, springs  744 - 4  and  745 - 2  pull and hold cam follower  744 - 6  in socket  746 - 2  of latch  546 . As cam follower  744 - 6  is pulled into socket  746 - 2 , latch flag  744 - 5  is positioned in latch sensor  748 . In this aspect, latch sensor  748  includes a pair of photo-interrupt switches so that if latch flag  744 - 5  is positioned in latch sensor  748 , a light beam in each of the pair of photo-interrupt switches is broken. Breaking the light beams changes the state of the photo-interrupt switches, which is used to determine when cannula mount arm  355  is latched in the extended position. In this aspect, the pair of photo-interrupt switches is used for safety redundancy. If such redundancy is not needed, a single photo-interrupt switch could be used. 
     The use of a pair of photo-interrupt switches as a latch sensor is illustrative only and is not intended to be limiting. In other aspects, a capacitance switch or an inductive switch could be used. Alternatively, the latch mechanism could depress a switch that provides the cannula arm extended and locked signal. 
     When cannula mount arm  355  is locked in the extended position, to retract cannula mount arm  355  into curved distal end portion  391 D, solenoid  545  is activated, sometime referred as being fired, either by depressing button  451  ( FIG. 4B ) or by the controller issuing a retract cannula mount arm command. When solenoid  545  is activated, solenoid  545  pulls plunger  745 - 1  linearly into the solenoid body, e.g., plunger  745 - 1  is moved proximally by activation of solenoid  545 . The force from a linear solenoid is highly non-uniform, with the greatest force being applied at the fully retracted (most proximal) and the force dropping off rapidly as the plunger extends (in the distal direction). The geometry of links  744 - 1 ,  744 - 1 ,  744 - 2 , and  744 - 3  is designed to compensate for this non-linearity of force, and to allow the solenoid to effectively lift cam follower  744 - 6  clear of latch  546 . 
     The motion of plunger  745 - 1  causes second link  744 - 2  to exert a force in a first direction—downward—on second end  744 - 32  of latch link  744 - 3 . The force in the first direction on second end  744 - 32  of latch link  744 - 3  causes latch link  744 - 3  to pivot about pin  703 , which moves first end  744 - 31  of latch link  744 - 3  in a second direction, opposite to the first direction—upward—and extends spring  744 - 4 . The motion of first end  744 - 31  of latch link  744 - 3  moves cam follower  744 - 6  out of socket  746 - 2  and above the highest point on inclined ramp  746 - 1 . Similarly, latch flag  744 - 5  is moved out of latch sensor  748 . Since cam follower  744 - 6  is no longer seated in latch  546 , spring  543 - 3  automatically retracts cannula mount arm  355  into curved distal end portion  319 D. The speed of the retraction is controlled by damper  648  as pinion gear  547  moves along gear teeth  642  on curved segment gear  542 . 
       FIG. 8  is process flow diagram of acts used to control retraction of cannula mount arm  355 . The linear flow in  FIG. 8  is used for ease of understanding only and is not intended to be limiting. The various processes in  FIG. 8  might be performed in an order other than that illustrated by the linear flow, and could be perform simultaneously rather than sequentially. 
     Initially, a user accesses a user interface that includes a CONFIGURE FOR DRAPING  801  option. The user interface is generated by a controller in the computer-assisted surgical system that includes patient side support system  310 . It should be appreciated that the controller can be made up of one unit, or multiple different units. When the controller is divided up among different units, the units may be centralized in one location or distributed across the computer assisted surgical system. Also, the different units of the controller may be given names that characterize the acts controlled by that unit of the controller. 
     When the user selects CONFIGURE FOR DRAPING  801  option, the controller configures patient side support system  310  to facilitate draping patient side support system  310 . Here, only the acts related to controlling cannula mount arm  355  are considered in the configuring patient side support system  310  for draping. 
     In an ARM RETRACTED check process  802 , the controller determines whether cannula mount arm  355  is parked within curved distal end portion  319 D of link  319 . If the signal from latch sensor  748  indicates cannula mount arm  355  is retracted in curved distal end portion  319 D of link  319 , ARM RETRACTED check process  802  transfers to an INHIBIT FOLLOWING process  804 . Conversely, if the signal from latch sensor  748  indicates cannula mount arm  355  is not retracted in curved distal end portion  319 D of link  319 , ARM RETRACTED check process  802  transfers to a RETRACT ARM process  803 . Note that a surgical system including patient side support system  310  typically has several features that are monitored to determine whether following is permitted or is inhibited. In  FIG. 8 , only the actions associated with cannula mount system  350  are considered with respect to the inhibiting and permitting of following. 
     In RETRACT ARM process  803 , the controller first enables solenoid  545  and then activates solenoid  545 . As described above, when activated, solenoid  545  causes locking assembly  544  to lift cam follower  744 - 6  out of latch  546 , and consequently spring  543 - 3  automatically retracts cannula mount arm  355  into curved distal end portion  319 D of link  319 . RETRACT ARM process  803  transfers to INHIBIT FOLLOWING process  804 . Thus, in this aspect, mechanical arm retraction system  540  is used to automatically change the shape of manipulator arm assembly  330  for draping. 
     When cannula mount arm  355  is parked in curved distal end portion  319 D of link  319 , cannula  470  is not docked on cannula mount arm  355 . When cannula  470  is not docked, following is inhibited. Thus, in INHIBIT FOLLOWING process  804  following is inhibited based on a cannula not being docked. INHIBIT FOLLOWING process  804  transfers to ARM EXTENDED AND LOCKED check process  805 . 
     ARM EXTENDED AND LOCKED check process  805  determines whether cannula mount arm  355  has been withdrawn from curved distal end portion  319 D of link  319  and is locked in the extended position. If the signal from latch sensor  748  indicates cannula mount arm  355  is not latched in the extended position, ARM EXTENDED AND LOCKED check process  805  takes no action. Conversely, if the signal from latch sensor  748  indicates cannula mount arm  355  is latched in the extended position, ARM EXTENDED AND LOCKED check process  805  transfers to a CANNULA DOCKED check process  806 . ARM EXTENDED AND LOCKED check process  805  should not be interpreted as requiring polling to determine whether cannula mount arm  355  is latched in the extended position. In one aspect, an event handler is used to detect an event that is fired when the signal from latch sensor  748  indicates cannula mount arm  355  is latched in the extended position. 
     Once cannula mount arm  355  is latched in the extended position, two events are of interest—a cannula is docked or a command to retract cannula mount arm  355  is issued. Thus, CANNULA DOCKED check process  806  determines whether a cannula has been mounted on extended cannula mount arm  355 . If a signal is not received that a cannula is docked on cannula mount arm  355 , CANNULA DOCKED check process  806  transfers to RETRACT ARM COMMAND check process  807 . Conversely, if a signal is received that a cannula is docked on cannula mount arm  355 , CANNULA DOCKED check process  806  transfers to FOLLOWING INHIBITED check process  808 . 
     RETRACT ARM COMMAND check process  807  determines whether a command to retract cannula mount arm  355  into curved distal end portion  319 D has been received. A command to retract cannula mount arm  355  can be generated by the user depressing arm retraction button  451  or by the controller issuing the command. As indicated above, cannula mount arm  355  can only be automatically retracted when a cannula is not docked on cannula mount arm  355 . This condition is satisfied when processing transfers to RETRACT ARM COMMAND check process  807 . Thus, if RETRACT ARM COMMAND check process  807  receives a command to retract cannula mount arm  355 , RETRACT ARM COMMAND check process  807  transfers to RETRACT ARM process  803 , and otherwise returns to CANNULA DOCKED check process  806 . 
     The loop between RETRACT ARM process  803  and CANNULA DOCKED check process  806  should not be interpreted as requiring polling to determine whether a cannula was docked and whether a command to retract cannula mount arm  355  was received. In one aspect, an event handler is used to detect the appropriate conditions and to fire an appropriate event indicating the conditions detected. 
     After a cannula is first docked to cannula mount arm  355 , the inhibition of following due to a cannula not being docked is removed, and then the next event of interest is undocking of the cannula. As described previously, cannula mount arm  355  cannot be retracted so long as cannula  470  is docked on arm  355 . 
     Thus, FOLLOWING INHIBITED check process  808  determines whether following is inhibited because a cannula is not docked on cannula mount arm  355 . If a cannula is docked on cannula mount arm  355 , FOLLOWING INHIBITED check process  808  transfers to PERMIT FOLLOWING process  809 , which removes the inhabitation of following by cannula mount system  350 . If there is no cannula docked on cannula mount arm  355 , FOLLOWING INHIBITED check process  808  returns to CANNULA DOCKED check process  806 . 
     Note that even if cannula mount system  350  permits following, the controller may still inhibit following due to other conditions in the surgical system. PERMIT FOLLOWING process  809  considers only the state of cannula mount system  350  in determining whether to permit following and does not consider other factors that may be used to determine when the surgical system is actually permitted to enter following by the controller. 
     The loop between CANNULA DOCKED check process  806  and FOLLOWING INHIBITED check process  808  also should not be interpreted as requiring polling to determine whether a cannula was docked. In one aspect, an event handler is used to detect the appropriate conditions and to fire an appropriate event indicating the conditions detected. 
     Note that as long as a cannula is docked, a retract arm command is not acted upon, and so cannula mount arm  355  cannot be inadvertently retracted. During a surgical procedure, parts of one or more surgical instruments extend through cannula  470  into a patient. If cannula mount arm  355  were retracted while a cannula was docked, the inadvertent motion of the surgical instruments might harm the patient, and so the interlock on retraction is used to prevent retraction so long as a cannula is docked to arm  355 . 
       FIG. 9  is a block diagram of an interlock control system  900  that implements an interlock that prevents retraction of cannula mount arm  355  when a cannula is mounted on cannula mount arm  355 . An arm retraction controller  910 , sometimes referred to as controller  910  receives system status information  909  that includes whether a cannula is docked on cannula mount arm  355 . A voltage control line  911  is connected between arm retraction controller  910  and a solenoid driver  930 . A switch with current limiter circuit  920  is positioned between a supply voltage V+ (48 volts in one aspect) and solenoid driver  930 . Solenoid driver  930  is an example of an electric actuator driver. A solenoid bus  935  connects solenoid driver  930  to solenoid  545  and to a bus dump circuit  940 . Solenoid bus  935  is an example of an electric actuator bus. Both solenoid  545  and bus dump circuit  940  are also connected to ground. An enable/disable line  912  connects arm retraction controller  910  to bus dump circuit  940 . 
     When status information  909  indicates that a cannula is not mounted on cannula mount arm  355  and includes an arm retraction command, arm retraction controller  910  first generates a disable signal on enable/disable line  912  to bus dump circuit  940 . The disable signal causes bus dump circuit  940  to open a connection, in bus dump circuit  940 , between solenoid bus  935  and ground. Thus, when the disable signal is on enable/disable line  912 , bus dump circuit  940  does not connect solenoid bus  935  to ground. 
     After the disable signal is activated on enable/disable line  912 , arm retraction controller  910  provides a pulse width modulation duty cycle signal on voltage control line  911  to solenoid driver  930 . The switch in switch with current limiter circuit  920  is normally closed and so supply voltage V+ is provided to solenoid driver  930 . In response to the pulse width modulation duty cycle on voltage control line  911 , solenoid driver  930  drives a series of pulses on solenoid bus  935 , which activates solenoid  545 . As described above, when solenoid  545  is activated, mechanical arm retraction system  540  is enabled and automatically retracts cannula mount arm  355 . 
     After a brief time (less than the watchdog time, but long enough to unlatch cannula mount arm  355 ) controller  910  removes the pulse width modulation duty cycle signal on voltage control line  911  to solenoid driver  930 . In response, solenoid driver  930  stops driving pulses on solenoid bus  935 , which deactivates solenoid  545 . 
     When a disable signal is generated on enable/disable line  912  by arm retraction controller  910 , watchdog timer  915  is started. When watchdog timer  915  times out, the disable signal on enable/disable line to bus dump circuit  940  is changed to an enable signal. The enable signal causes bus dump circuit  940  to close a connection between solenoid bus  935  and ground in bus dump circuit  940 . Thus, when the enable signal is on enable/disable line  912 , bus dump circuit  940  connects solenoid bus  935  to ground. 
     Hence, bus dump circuit  940  operates as switch between solenoid bus  935  and ground, and the state of the switch—open or closed—is controlled by the signal on enable/disable line  912 . Normally, bus dump circuit  940  is always shorting solenoid bus  935  to ground so that solenoid  545  cannot be fired. This only changes when both a cannula not mounted signal and an arm retraction command are present at the same time in status information  909 . 
     As shown in  FIG. 9 , bus dump circuit  940  and solenoid  545  are connected in parallel between solenoid bus  935  and ground. The resistance in bus dump circuit  940  between solenoid bus  935  and ground is significantly lower than the resistance in solenoid  545  between solenoid bus  935  and ground. Thus, when bus dump circuit  940  is enabled, a large majority of the current flows from solenoid bus  935  through bus dump circuit  940  to ground. The remaining current that flows through solenoid  545  is insufficient to fire solenoid  545 . Consequently, any voltage on solenoid bus  935  does not fire solenoid  545  when bus dump circuit  940  is enabled. 
     The logic in arm retraction controller  910  permits arm retraction controller  910  to generate a command on voltage control line  911  to fire solenoid  545  when both a cannula not mounted signal and an arm retraction command are present in status information  909 , as just described. However, it is possible that arm retraction controller  910  generates a spurious command on voltage control line  911  to fire solenoid  545 , or that there is a short between a power source—either in solenoid driver  930  or in the cabling—and solenoid bus  935 . In each of these cases, bus dump circuit  940  is configured to connect solenoid bus  935  to ground, and so the spurious voltage does not fire solenoid  545 . 
     If solenoid driver  930  unintentionally drives a voltage on solenoid bus  935  and thereby creates a large current through solenoid driver  930  and bus dump circuit  940 , the current limiter circuit in switch with current limiter circuit  920  automatically opens the switch in circuit  920 . Thus, when switch with current limiter circuit  920  detects an abnormal current draw, switch with current limiter circuit  920  disconnects the power to solenoid driver  930 . This assures that the power supply, the circuitry in solenoid driver  930 , and the circuitry in bus dump circuit  940  are not damaged by an excessive current draw. 
     If the switch in switch with current limiter circuit  920  fails open, solenoid  945  cannot be fired. This is a safe condition. If the switch in switch with current limiter circuit  920  fails closed, e.g., is shorted, this could defeat the safety system. Thus, each time the computer-assisted surgical system is powered on, the switch in switch with current limiter circuit  920  is tested to assure that the switch is not shorted. 
     If the switch in bus dump circuit  940  fails closed, e.g., shorted, this is a safe condition. If the switch in bus dump circuit  940  fails open, this could defeat the safety system. Thus, each time computer-assisted surgical system is powered on, the switch bus dump circuit  940  is tested to assure that the switch has not failed open. 
     In the event bus dump circuit  940  receives neither an enable command nor a disable command (possibly because of a broken connection on enable/disable line  912  or a failure in controller  910 ), bus dump circuit  940  automatically enables itself. This is another safeguard to insure that cannula mount arm  355  cannot be inadvertently retracted. 
     In one aspect, arm retraction controller  910  is implemented using a field programmable gate array circuit. In this aspect, bus dump circuit  940  is implemented using a metal-oxide-semiconductor field-effect transistor with the gate connected to enable/disable line  912 . 
       FIG. 10  is a cut away drawing of first end  455 - 1  of cannula mount arm  355  to show a cannula mount assembly. The cannula mount assembly includes a cannula docking assembly  1030 , a linkage assembly  1040 , a cannula release button assembly  1050 , and a linear motion assembly  1060 . This cannula mount assembly can be implemented in cannula mount arms other than those illustrated in the drawings. 
     Cannula docking assembly  1030  is coupled to a first end of cannula release button assembly  1050  by linkage assembly  1040 . A second end of cannula release button assembly  1050  is coupled to linear motion assembly  1060 . Linear motion assembly  1060  constrains cannula release button assembly  1050  to linear motion in third and fourth directions—down and up with respect to the outer surface of first end  455 - 1  of cannula mount arm  355 —as represented by arrow  1091 . The range of motion of cannula release button assembly  1050  along linear motion assembly  1060  in the third direction is limited by a portion of cannula release button assembly  1050  contacting a first hard stop within the housing of first end  455 - 1  of cannula mount arm  355 . 
     When a force is applied on cannula release button  452 , i.e., cannula release button  452  is depressed, cannula release button assembly  1050  moves linearly in the third direction—down in this example—along linear motion assembly  1060 . Linkage assembly  1040  converts the linear motion of cannula release button assembly  1050  in the third direction to linear motion, in the second direction, e.g., in the proximal direction, of a moveable block  1154  ( FIG. 11 ) within cannula docking assembly  1030 , and in so doing compresses a spring  1160  in moveable block  1154 . In one aspect, spring  1160  is implemented using two springs. 
     Here, the second direction—in this example, in the proximal direction—is a direction that is different from the fourth direction that is opposite the third direction, e.g., the up direction is different from the proximal direction. In  FIG. 10  the third direction is a down direction and the fourth direction is an up direction as represented by arrow  1091 . The first direction is a distal direction and the second direction is a proximal direction as represent by arrow  1090 . Thus, as stated, the second direction is different from the fourth direction that is opposite to the third direction and is different from the third direction. 
     Similarly, when the downward force on cannula release button  452  is released, spring  1160  in cannula docking assembly  1030  moves moveable block  1154  linearly in the first direction—in the distal direction in this example—to a position where spring  1160  has a minimum potential energy. Linkage assembly  1040  coverts the linear motion of moveable block  1154  in the first direction to linear motion of cannula release button assembly  1050  in the fourth direction. Here, the first direction is in a direction that is different from the direction opposite the fourth direction. As pointed out above, the fourth direction is up in  FIG. 10 , and the direction opposite the fourth direction is the third direction (down), which is different from the first direction (distal direction). Cannula release button assembly  1050  is moved in the fourth direction by the force of spring  1160  and held in a location such that cannula release button  452  is in its undepressed position, as illustrated in  FIGS. 10, 4B, and 5B . 
     Cannula release button assembly  1050  includes a frame  1051 , cannula release button  452 , and rail  1053 . Frame  1051  includes a first end  1051 - 1  and a second end  1051 - 2 . A linear slide  1061  of linear motion assembly  1060  is affixed to second end  1051 - 2  of frame  1051 . Linear slide  1061  is constrained to slide along rail  1062  of linear motion assembly  1060 . Rail  1053  is mounted in first end  1051 - 1  of frame  1051 . Cannula release button  452  is mounted on frame  1051  adjacent linear slide  1061 . 
     Linkage assembly  1040  includes a first link  1041 , a second link  1042 , and a cam follower  1043 . A first end  1042 - 1  of second link  1042  is rotatably mounted on a pin extending from a housing  1031  of cannula docking assembly  1030 . Thus, second link  1042  is grounded to housing  1031  of cannula docking assembly  1030 . Cam follower  1043  is mounted on a second end  1042 - 2  of second link  1042 . Cam follower  1043  rides within rail  1053  in first end  1051 - 1  of frame  1051  of cannula release button assembly  1050 . Cam follower  1043  is constrained within rail  1053  so that cam follower  1043  can move in the first and second directions, but not in the third and fourth directions. 
     A second end  1041 - 2  of first link  1041  is rotatably connected to a pin mounted in second link  1042 . The pin is located between first end  1042 - 1  of second link  1042  and second end  1042 - 2  of second link  1042 . A first end  1041 - 1  of first link  1041  is rotatably connected to a pin in moveable block  1154  ( FIG. 11 ). 
     When cannula release button  452  is depressed, second link  1042  functions as a lever with a fulcrum provided by the pin extending from housing  1031 . The effort is applied to second end  1042 - 2  and the load is located between the fulcrum and second end  1042 - 2 . In this example, when cannula release button  452  is depressed, second link  1042  is a Class 2 lever because the load is between the fulcrum and the effort. 
     When cannula release button is released, second link  1042  still functions as a lever with a fulcrum provided by the pin extending from housing  1031 . The load is at the second end  1042 - 2  and the effort is located between the fulcrum and second end  1042 - 2 . In this example, when cannula release button  452  is released, second link  1042  is a Class 3 lever because the effort is between the fulcrum and the load. Thus, second link  1042  functions as both a Class 2 lever and a Class 3 lever. The class of lever is dependent on the direction that cannula release button  452  moves. 
     Thus, a force supplied by a user to depress cannula button  452  moves frame  1051 , and consequently linear slide  1061  moves along rail  1062 . As frame  1051  moves down, cam follower  1043  moves in the second direction. As second end  1042 - 2  of link  1042  moves in the second direction, link  1042  pivots about the pin in housing  1031 . This motion moves first link  1041  in the second direction and in third direction. The motion of link  1041  moves moveable block  1154  in the second direction, which compresses spring  1160  in cannula docking assembly  1030 , which releases a pair of clamping arms  1150  in cannula docking assembly  1030  so that pair of clamping arms  1150  can be opened. 
     When the force on cannula button  452  is released, spring  1160  expands and moves moveable block  1154  in the first direction, which closes the pair of clamping arms  1150 . As moveable block  1154  moves in the first direction, first end  1041 - 1  of first link  1041  is moved in the first direction. The motion of first link  1041  in the first direction causes second link  1042  to pivot about the pin in housing  1031 . Hence, second end  1042 - 2  of second link  1042  moves in the first direction and in the fourth direction as a result of moveable block  1154  moving in the first direction. The motion of second end  1042 - 2  of link  1042  is transferred to frame  1051  of assembly  1050 , which linearly moves cannula release button  452  in the fourth direction until the motion of slide  1061  is stopped by a second hard stop within the housing of first end  455 - 1  of cannula mount arm  355 . 
     The parts of cannula docking assembly  1030  needed to understand the operation of cannula release button  452  are shown in more detail in  FIG. 11 . Cannula docking assembly  1030  includes a pair of clamping arms  1150  to engage cannula  470 . For example, when attachment portion  471  of cannula  450  is inserted into aperture  1132  of cannula docking assembly  1030 , tips of clamping arms  1150  latch to depressions of cannula sterile adapter  460  that in turn are compressed by clamping arms  1150  into depressions  572  of attachment portion  471  to dock cannula  470  to cannula docking assembly  1030 . 
     While it is not shown in  FIGS. 10 and 11 , each of clamping arms  1150  pivots about a pin to facilitate mounting and releasing cannula  470 . Clamping arms  1150  are actuated by moveable block  1154  that engages and moves clamping arms  1150  into a closed (latched) position to dock cannula  470 . For example, moveable block  1154  includes a cam surface that engages each of clamping arms  1150  to cause clamping arms  1150  to pivot to the closed position. 
     Spring  1160  biases moveable block  1154  to the position that closes each of clamping arms  1150 . Spring  1160  is positioned between a mounting block  1162  and moveable block  1154 . 
     Cannula docking assembly  1030  includes a sensor to detect the position of moveable block  1154  to infer whether clamping arms  1150  are in a locked or released position, as determined by the position of the cam surface on block  1154  relative to clamping arms  1150 . The sensor, for example, may be a switch that moveable block  1154  contacts as moveable block  1154  is actuated back and forth to actuate clamping arms  1150 . Output from the sensor is transmitted to the controller of the computer-assisted surgical system to provide feedback, for example, whether clamping arms  1150  are in a locked or released position. More details on a moveable block, clamping arms, and springs suitable for use in cannula docking assembly  1030  are presented in PCT International Publication No. WO2015/142814 A1, which was previously incorporated by reference. 
     Much of the previous discussion, including discussion associated with  FIGS. 3, 4A -B,  5 A-B,  6 A-B, etc. refer to a patient side support system  310  with a manipulator arm assembly  330  having four links  313 ,  315 ,  317 ,  319  coupled by rotary joints. A telescoping cannula mount system  350  comprises a curved cannula mount arm  355  that can be extended from or parked within a curved distal end portion  319 D of the fourth link  319 . 
     Other designs of patient side support systems, manipulator arm assemblies, and shapes of telescoping cannula arm systems are contemplated and can be utilized in various embodiments. As some specific examples,  FIG. 12  shows a schematic of a patient side support system  1210  that may be implemented with any appropriate number of links and active or passive joints (seven links  1202 ,  1204 ,  1206 ,  1213 ,  1215 ,  1217 ,  1219 , six rotary joints  1203 ,  1205 ,  1207 ,  1214 ,  1216 ,  1218 , and no prismatic joints are shown in  FIG. 12 ). A telescoping cannula mount system  1250  comprises a cannula mount arm  1255  that can be extended from or parked within a distal end portion  1219 D of the link  1219 . A cannula  1270  can be mounted to the cannula mount arm  1255 , and an instrument can be  1280  extended through the cannula  1270  to perform operations, as shown in  FIG. 12 . 
     Parts of patient side support system  1210  are analogous to corresponding parts in patient side support systems  110  and  310 . For example, in various embodiments, links  1213 ,  1215 ,  1217 ,  1219  are analogous to links  113 ,  115 ,  117 ,  119  of patient side support systems  110  and links  313 ,  315 ,  317 ,  319  patient side support systems  310 . Thus, the description associated with the earlier figures is not repeated here for  FIG. 1 × 2 . 
     The cannula mount system  1250  is shown as curved in  FIG. 12  for convenience, and can be any appropriate shape with any number of linear and nonlinear segments in various embodiments.  FIG. 13  shows some example telescoping cannula mount systems with different linear shapes that can be used with the patient side support system of  FIG. 12 . Cannula mount arm  1355  extends and retracts along the main axis of the link  1219 , as shown by the dotted-line arrow  1356 . Cannula mount arm  1357  extends and retracts along an axis perpendicular to the main axis of  1219 , as shown by the dotted-line arrow  1358 . Cannula mount arm  1359  extends and retracts along an axis angled with respect to the main axis of link  1219 , as shown by the dotted-line arrow  1360 . 
     Although a controller is described above, it is to be appreciated that such a controller may be implemented in practice by any number of modules and each module may include any combination of components. Each module and each component may include hardware, software that is executed on a processor, and firmware, or any combination of the three. Also, the functions and acts of controller, as described herein, may be performed by one module, or divided up among different modules or even among different components of a module. When divided up among different modules or components, the modules or components may be centralized in one location or distributed across the computer-assisted surgical system for distributed processing purposes. Thus, references to the controller should not be interpreted as requiring a single physical entity as in some aspects the controller is distributed across the computer-assisted surgical system. 
     As used herein, “first,” “second,” “third,” etc. are adjectives used to distinguish between different components or elements. Thus, “first,” “second,” and “third” are not intended to imply any ordering of the components or elements or to imply any total number of components or elements. 
     The above description and the accompanying drawings that illustrate aspects and embodiments of the present inventions should not be taken as limiting—the claims define the protected inventions. Various mechanical, compositional, structural, electrical, and operational changes may be made without departing from the spirit and scope of this description and the claims. In some instances, well-known circuits, structures, and techniques have not been shown or described in detail to avoid obscuring the invention. 
     Further, this description&#39;s terminology is not intended to limit the invention. For example, spatially relative terms—such as “beneath”, “below”, “lower”, “above”, “upper”, “proximal”, “distal”, and the like—may be used to describe one element&#39;s or feature&#39;s relationship to another element or feature as illustrated in the figures. These spatially relative terms are intended to encompass different positions (i.e., locations) and orientations (i.e., rotational placements) of the device in use or operation in addition to the position and orientation shown in the figures. For example, if the device in the figures were turned over, elements described as “below” or “beneath” other elements or features would then be “above” or “over” the other elements or features. Thus, the exemplary term “below” can encompass both positions and orientations of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. Likewise, descriptions of movement along and around various axes include various special device positions and orientations. 
     The singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context indicates otherwise. The terms “comprises”, “comprising”, “includes”, and the like specify the presence of stated features, steps, operations, elements, and/or components but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups. Components described as coupled may be electrically or mechanically directly coupled, or they may be indirectly coupled via one or more intermediate components. 
     All examples and illustrative references are non-limiting and should not be used to limit the claims to specific implementations and embodiments described herein and their equivalents. Any headings are solely for formatting and should not be used to limit the subject matter in any way, because text under one heading may cross reference or apply to text under one or more headings. Finally, in view of this disclosure, particular features described in relation to one aspect or embodiment may be applied to other disclosed aspects or embodiments of the invention, even though not specifically shown in the drawings or described in the text. 
     Embodiments described above illustrate but do not limit the disclosure. It should also be understood that numerous modifications and variations are possible in accordance with the principles of the present disclosure. For example, in many aspects the devices described herein are used as single-port devices; i.e., all components necessary to complete a surgical procedure enter the body via a single entry port. In some aspects, however, multiple devices and ports may be used.