Patent Publication Number: US-2023149103-A1

Title: Computer-assisted tele-operated surgery systems and methods

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/246,008 filed on Apr. 30, 2021, which is a continuation of U.S. patent application Ser. No. 16/325,978 filed on Feb. 15, 2019 (U.S. Pat. No. 11,020,192), which claims the benefit of International Patent Application No. PCT/US2017/048425 filed on Aug. 24, 2017, which claims the benefit of priority to U.S. Provisional Patent Applications No. 62/379,112 filed Aug. 24, 2016, and 62/379,114 filed Aug. 24, 2016. Each of the foregoing applications are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to devices and methods for minimally invasive computer-assisted tele-operated surgery. For example, this disclosure relates to surgical instruments for computer-assisted tele-operated surgery that are structured to negate the effects of cable stretch. 
     BACKGROUND 
     Teleoperated surgical systems (often called “robotic” surgical systems because of the use of robot technology) and other computer-assisted devices often include one or more instrument manipulators to manipulate instruments for performing a task at a surgical work site and at least one manipulator for supporting an image capturing device which captures images of the surgical work site. A manipulator arm comprises a plurality of links coupled together by one or more actively controlled joints. In many embodiments, a plurality of actively controlled joints may be provided. The robot arm may also include one or more passive joints, which are not actively controlled, but which comply with movement of an actively controlled joint. Such active and passive joints may be various types, including revolute or prismatic joints. The kinematic pose of the manipulator arm and its associated instrument or image capture device may be determined by the positions of the joints and knowledge of the structure and coupling of the links and the application of known kinematic calculations. 
     Minimally invasive telesurgical systems for use in surgery are being developed to increase a surgeon&#39;s dexterity as well as to allow a surgeon to operate on a patient from a remote location. Telesurgery is a general term for surgical systems in which the surgeon uses some form of remote control, e.g., a servomechanism, or the like, to manipulate surgical instrument movements rather than directly holding and moving the instruments by hand. In such a telesurgery system, the surgeon is provided with an image of the surgical site at the remote location. While viewing typically a stereoscopic image of the surgical site that provides the illusion of depth on a suitable viewer or display, the surgeon performs the surgical procedures on the patient by manipulating master control input devices, which in turn control the motion of corresponding teleoperated instruments. The teleoperated surgical instruments can be inserted through small, minimally invasive surgical apertures or natural orifices to treat tissues at surgical sites within the patient, often avoiding the trauma generally associated with accessing a surgical worksite by open surgery techniques. These computer-assisted tele-operated systems can move the working ends (end effectors) of the surgical instruments with sufficient dexterity to perform quite intricate surgical tasks, often by pivoting shafts of the instruments at the minimally invasive aperture, sliding of the shaft axially through the aperture, rotating of the shaft within the aperture, and the like. 
     SUMMARY 
     This disclosure provides devices and methods for minimally invasive robotic surgery using a computer-assisted tele-operated surgery device. For example, this disclosure relates to surgical instruments for computer-assisted tele-operated surgery that are structured to negate the effects of cable stretch. The devices and methods provided herein can be used in conjunction with computer-assisted tele-operated surgery systems (also referred to herein as “robotic surgery systems”) that use either hardware-constrained remote centers of motion or software-constrained remote centers of motion. 
     In one aspect, a medical device includes a surgical instrument and a drive unit for the surgical instrument. A first actuator in the drive unit is in a non-detained engagement with a first engagement member of the instrument, and a second actuator in the drive unit is in a non-detained engagement with a second engagement member of the instrument. The first and second engagement members of the instrument are coupled to the instrument&#39;s end effector, so that the end effector moves as the first and second engagement members move. In a further aspect, the drive unit includes an instrument shaft actuator, the instrument includes a shaft actuator engagement member, and the instrument shaft actuator and the shaft actuator engagement member may be in either a non-detained or a detained engagement. 
     In one aspect, a surgical instrument includes an end effector, a first engagement member coupled to the end effector, and a second engagement member coupled to the end effector. The first and second engagement members are configured to be in a non-detained engagement with corresponding first and second actuators of a drive unit for the surgical instrument. In a further aspect, the instrument includes a shaft actuator engagement member that is configured to be in either a non-detained or a detained engagement with a corresponding instrument shaft actuator of the drive unit. 
     In one aspect, the disclosure is directed to a surgical instrument for a computer-assisted tele-operated surgery system. The surgical instrument includes: a proximal end portion; an instrument shaft extending from the proximal end portion (the instrument shaft including a distal end portion opposite from the proximal end portion); an end effector coupled to the distal end portion (the end effector having at least a first degree of freedom whereby the end effector is movable relative to the instrument shaft); a first tensioning member coupled to the end effector and extending along the instrument shaft; and a second tensioning member coupled to the end effector and extending along the instrument shaft. The second tensioning member terminates at a second actuator engagement member. The second actuator engagement member is movably coupled to the proximal end portion. The instrument shaft defines a longitudinal axis of the surgical instrument. The first tensioning member terminates at a first actuator engagement member. The first actuator engagement member is movably coupled to the proximal end portion. Moving the first actuator engagement member proximally moves the second actuator engagement member distally and moves the end effector in a first manner relative to the instrument shaft. The first manner comprises movement facilitated by the first degree of freedom. Moving the second actuator engagement member proximally moves the first actuator engagement member distally and moves the end effector in a second manner relative to the instrument shaft. The second manner is facilitated by the first degree of freedom and opposes the first manner The first actuator engagement member and the second actuator engagement member are positionable at a same longitudinal location along the longitudinal axis of the surgical instrument. 
     Such a surgical instrument may optionally include one or more of the following features. The proximal end portion may include a handle configured to facilitate manual gripping and manipulation of the surgical instrument. The handle may extend radially from the longitudinal axis in relation to other portions of the proximal end portion. The handle may include an RFID chip for storing information pertaining to the surgical instrument. The handle may include an indicium identifying a type of surgical instrument. The surgical instrument may also include an instrument shaft actuator engagement member coupled to the proximal end portion. The instrument shaft actuator engagement member may include a latch mechanism. The first actuator engagement member and the second actuator engagement member may each be slidably coupled to the proximal end portion. The surgical instrument may also include one or more pre-load tensioning members that tension the first tensioning member and the second tensioning member. The one or more pre-load tensioning members may each comprise a spring. The first tensioning member and the second tensioning member may each comprise a cable. The end effector may have at least a second degree of freedom. The surgical instrument may also include: a third tensioning member coupled to the end effector and extending along the instrument shaft (the third tensioning member may terminate at a third actuator engagement member and may be movably coupled to the proximal end portion); and a fourth tensioning member coupled to the end effector and extending along the instrument shaft (the fourth tensioning member may terminate at a fourth actuator engagement member and may be movably coupled to the proximal end portion). Moving the third actuator engagement member proximally may move the fourth actuator engagement member distally and may move the end effector in a third manner relative to the instrument shaft (the third manner comprising movement facilitated by the second degree of freedom). Moving the fourth actuator engagement member proximally may move the third actuator engagement member distally and may move the end effector in a fourth manner relative to the instrument shaft (the fourth manner facilitated by the second degree of freedom and opposing the third manner). In some embodiments, each of: (i) the first actuator engagement member, (ii) the second actuator engagement member, (iii) the third actuator engagement member, and (iv) the fourth actuator engagement member are positionable at a same longitudinal location along the longitudinal axis of the surgical instrument. The third actuator engagement member and the fourth actuator engagement member may be each slidably coupled to the proximal end portion. 
     In another aspect, the disclosure is directed to a surgical instrument for a computer-assisted tele-operated surgery system. The surgical instrument includes: a proximal end portion; an instrument shaft extending from the proximal end portion (the instrument shaft includes a distal end portion opposite from the proximal end portion and defines a longitudinal axis of the surgical instrument); an end effector coupled to the distal end portion (the end effector has at least a first degree of freedom whereby the end effector is movable relative to the instrument shaft); a first tensioning member coupled to the end effector and extending along the instrument shaft (the first tensioning member terminates at a first actuator engagement member that is movably coupled to the proximal end portion); a second tensioning member coupled to the end effector and extending along the instrument shaft (the second tensioning member terminates at a second actuator engagement member that is movably coupled to the proximal end portion); and an instrument shaft actuator engagement member that is coupled to the proximal end portion. Moving the first actuator engagement member proximally moves the second actuator engagement member distally and moves the end effector in a first manner relative to the instrument shaft. The first manner includes movement facilitated by the first degree of freedom. Moving the second actuator engagement member proximally moves the first actuator engagement member distally and moves the end effector in a second manner relative to the instrument shaft. The second manner is facilitated by the first degree of freedom and opposes the first manner The first actuator engagement member and the second actuator engagement member are each configured for facilitating movements of the end effector in response to receiving a proximally -directed force, and are each not configured for facilitating movements of the end effector in response to receiving a distally -directed force. The instrument shaft actuator engagement member is configured for facilitating movements of the entire surgical instrument distally in response to receiving a distally -directed force. 
     Such a surgical instrument may optionally include one or more of the following features. The proximal end portion may include a handle configured to facilitate manual gripping and manipulation of the surgical instrument. The handle may extend radially from the longitudinal axis in relation to other portions of the proximal end portion. The handle may include an RFID chip for storing information pertaining to the surgical instrument and an indicium identifying a type of surgical instrument. The instrument shaft actuator engagement member may be configured for facilitating movements of the entire surgical instrument proximally in response to receiving a proximally -directed force. The instrument shaft actuator engagement member may include a latch mechanism The first actuator engagement member and the second actuator engagement member may be each slidably coupled to the proximal end portion and may be each positionable at a same longitudinal location along the longitudinal axis of the surgical instrument. The surgical instrument may also include one or more pre-load tensioning members that tension the first tensioning member and the second tensioning member. The one or more pre-load tensioning members may each comprise a spring. The end effector may have at least a second degree of freedom. The surgical instrument may also include: a third tensioning member coupled to the end effector and extending along the instrument shaft (the third tensioning member may terminate at a third actuator engagement member that may be movably coupled to the proximal end portion); and a fourth tensioning member coupled to the end effector and extending along the instrument shaft (the fourth tensioning member may terminate at a fourth actuator engagement member that may be movably coupled to the proximal end portion). Moving the third actuator engagement member proximally may move the fourth actuator engagement member distally and may move the end effector in a third manner relative to the instrument shaft. The third manner may include movement facilitated by the second degree of freedom. Moving the fourth actuator engagement member proximally may move the third actuator engagement member distally and may move the end effector in a fourth manner relative to the instrument shaft. The fourth manner may be facilitated by the second degree of freedom and may oppose the third manner The third actuator engagement member and the fourth actuator engagement member may be each configured to move the end effector in response to receiving a proximally -directed force, and may be each configured to not move the end effector in response to receiving a distally -directed force. In some embodiments, each of: (i) the first actuator engagement member, (ii) the second actuator engagement member, (iii) the third actuator engagement member, and (iv) the fourth actuator engagement member may be positionable at a same longitudinal location along the longitudinal axis of the surgical instrument. 
     In another aspect, the disclosure is directed to a surgical instrument and an instrument drive system configured to be selectively coupled with the surgical instrument by moving the surgical instrument distally along the longitudinal axis into releasable engagement with the instrument drive system. The surgical instrument includes: a proximal end portion; an instrument shaft extending from the proximal end portion (the instrument shaft includes a distal end portion opposite from the proximal end portion and defines a longitudinal axis of the surgical instrument); an end effector mounted to the distal end portion (the end effector has at least a first degree of freedom whereby the end effector is movable relative to the instrument shaft); a first tensioning member coupled to the end effector and extending along the instrument shaft; and a second tensioning member coupled to the end effector and extending along the instrument shaft. The instrument drive system includes: a first actuator for tensioning the first tensioning member with a first tensile force that can move the end effector in a first manner relative to the instrument shaft (the first manner including movement facilitated by the first degree of freedom); a second actuator for tensioning the second tensioning member with a second tensile force that can move the end effector in a second manner relative to the instrument shaft (the second manner facilitated by the first degree of freedom and opposing the first manner); and a shaft actuator for applying a force to the instrument shaft (the force to the instrument shaft being directionally opposite to the first tensile force and to the second tensile force). 
     Such a surgical instrument system may optionally include one or more of the following features. The proximal end portion may include a handle configured to facilitate manual gripping and manipulation of the surgical instrument. The handle may extend radially from the longitudinal axis and may extend farther radially than adjacent portions of the instrument drive system while the surgical instrument is coupled with the instrument drive system. The selective coupling of the instrument drive system and the surgical instrument may be facilitated by the instrument drive system slidably receiving the surgical instrument is moved distally along the longitudinal axis. The surgical instrument may also include an instrument shaft actuator engagement member to which the shaft actuator releasably couples. The instrument shaft actuator engagement member may include a latch mechanism. The latch mechanism may extend radially from the longitudinal axis and may extend farther radially than adjacent portions of the instrument drive system while the surgical instrument is coupled with the instrument drive system. The first tensioning member may terminate at a first actuator engagement member that is slidably coupled to the proximal end portion. The second tensioning member may terminate at a second actuator engagement member that is slidably coupled to the proximal end portion. The first actuator may be selectively coupleable with the first actuator engagement member. The second actuator may be selectively coupleable with the second actuator engagement member. The first tensile force and the second tensile force may be parallel along the instrument shaft and directed toward the proximal end. The force to the instrument shaft may be directed along the instrument shaft toward the distal end portion. The end effector may move in the first manner relative to the instrument shaft when the first tensile force is greater than the second tensile force. The end effector may move in the second manner that may be in opposition to the first manner when the second tensile force is greater than the first tensile force. The instrument shaft may move distally in relation to the instrument drive system when the force to the instrument shaft is greater than a sum of the first tensile force plus the second tensile force. The instrument shaft may move proximally in relation to the instrument drive system when the force to the instrument shaft is less than the sum of the first tensile force plus the second tensile force. The end effector may have at least a second degree of freedom. The surgical instrument may also include: a third tensioning member coupled to the end effector and extending along the instrument shaft; a third actuator for tensioning the third tensioning member with a third tensile force that can move the end effector in a third manner relative to the instrument shaft (the third manner may include movement facilitated by the second degree of freedom); a fourth tensioning member coupled to the end effector and extending along the instrument shaft; and a fourth actuator for tensioning the fourth tensioning member with a fourth tensile force that can move the end effector in a fourth manner relative to the instrument shaft (the fourth manner may be facilitated by the second degree of freedom and may oppose the third manner). The end effector may move in the third manner relative to the instrument shaft when the third tensile force is greater than the fourth tensile force. The end effector may move in the fourth manner that is in opposition to the third manner when the fourth tensile force is greater than the third tensile force. The instrument shaft may move distally in relation to the instrument drive system when the force to the instrument shaft is greater than a sum of the first tensile force plus the second tensile force plus the third tensile force plus the fourth tensile force. The instrument shaft may move proximally in relation to the instrument drive system when the force to the instrument shaft is less than the sum of the first tensile force plus the second tensile force plus the third tensile force plus the fourth tensile force. The surgical instrument system may also include one or more pre-load tensioning members that tension the first tensioning member and the second tensioning member while the first actuator and the second actuator are not tensioning the first tensioning member and the second tensioning member, respectively. The one or more pre-load tensioning members may each comprise a spring. The surgical instrument system may also include: a first force sensor for detecting the first tensile force; a second force sensor for detecting the second tensile force; and an instrument shaft force sensor for detecting the force to the instrument shaft. Each of the first actuator, the second actuator, and the shaft actuator may be linear actuators comprising lead screws. In some embodiments, an entirety of the surgical instrument system is configured to roll about the longitudinal axis. 
     Some or all of the embodiments described herein may provide one or more of the following advantages. In some cases, the tele-operated surgical instruments provided herein are advantageously structured to negate the effects of cable stretch. Cables within conventional tele-operated surgical instruments are pre-tensioned during manufacturing, but the tensions may tend to decrease over time because the cables may stretch as the instruments are used. Such tension decreases can contribute to a lessening in the accuracy of control of the tele-operated surgical instruments in some cases. Additionally, autoclave sterilization of the tele-operated surgical instruments using heat and humidity can exacerbate cable stretch and losses of cable tension. The tele-operated surgical instruments provided herein advantageously compensate for cable stretch without a loss in the accuracy of control of the instruments. In addition, while the tele-operated surgical instruments provided herein are not in use, the tension on the cables is advantageously less than the tension during operation of the instrument. Further, the tele-operated surgical instruments provided herein advantageously compensate for manufacturing tolerances that pertain to cable tension. In result, the manufacturing processes of the instruments can be streamlined and made more cost effective. 
     In addition, the tele-operated surgical instruments provided herein are advantageously structured to interface with an instrument drive system that is compact, and has a relatively low mass and inertia. In addition, the mass distribution is substantially constant such that the inertia is substantially constant and therefore predictable. 
     Still further, in some embodiments the tele-operated surgical instruments provided herein are advantageously structured to interface with an instrument drive system in a manner that is readily detachable. For example, in some embodiments the surgical instrument can be detached from an instrument drive system merely by actuating a latch mechanism and retracting the instrument proximally out of engagement with the drive system. Such a readily detachable interface between the surgical instrument and the instrument drive system can provide advantages such as quick instrument removal in the event of an emergency, and user convenience during general change-outs of one surgical instrument for another. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of an example patient-side unit of a computer-assisted tele-operated surgery system. 
         FIG.  2    is a front view of an example surgeon control unit of a computer-assisted tele-operated surgery system. 
         FIG.  3    is a side view of an example manipulator arm assembly of a computer-assisted tele-operated surgery system. 
         FIG.  4    is a perspective view of another type of patient-side computer-assisted tele-operated surgery system. 
         FIG.  5    is a perspective view of a distal end portion of an example surgical instrument in a first pose. 
         FIG.  6    is a perspective view of the distal end portion of the surgical instrument of  FIG.  5    in a second pose. 
         FIG.  7    is a perspective view of the distal end portion of the surgical instrument of  FIG.  5    in a third pose. 
         FIG.  8    is a simplified schematic diagram of an example tele-operated surgical instrument in accordance with some embodiments. 
         FIG.  9    is a schematic diagram of the tele-operated surgical instrument of  FIG.  8    coupled with an example instrument drive system in accordance with some embodiments. 
         FIG.  10    is a force diagram pertaining to the instrument and drive system of  FIG.  9   . 
         FIG.  11    is a schematic diagram of the instrument and drive system of  FIG.  9    with the end effector oriented in an example pose. 
         FIG.  12    is a schematic diagram of the instrument and drive system of  FIG.  11    with the instrument extended distally in relation to the drive system while the end effector remains oriented in the example pose. 
         FIG.  13    is a schematic diagram of the instrument and drive system of  FIG.  11    with the instrument retracted proximally in relation to the drive system while the end effector remains oriented in the example pose. 
         FIG.  14    is a schematic diagram of a portion of the instrument and drive system of  FIG.  11    showing example locations of force sensors for detecting forces such as cable tension. 
         FIG.  15    is a perspective view of an example surgical instrument that is configured in accordance with the schematic diagram of  FIG.  9   . 
         FIG.  16    is a perspective view of a proximal end portion of the surgical instrument of  FIG.  15   . 
         FIG.  17    is another perspective view of the surgical instrument of  FIG.  15   . 
         FIG.  18    is a proximal end view of the surgical instrument of  FIG.  15   . 
         FIG.  19    depicts how the surgical instrument of  FIG.  15    can be coupled with an example instrument drive system in accordance with some embodiments. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     This description and the accompanying drawings that illustrate inventive aspects, embodiments, implementations, or applications should not be taken as limiting—the claims define the protected invention. 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, or techniques have not been shown or described in detail in order not to obscure the invention. Like numbers in two or more figures represent the same or similar elements. 
     Further, specific words chosen to describe one or more embodiments and optional elements or features are 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 locations (i.e., translational placements) and orientations (i.e., rotational placements) of a device in use or operation in addition to the location and orientation shown in the figures. For example, if a device in the figures is 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 locations and orientations of above and below. A device may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. Likewise, descriptions of movement along (translation) and around (rotation) various axes includes various special device locations and orientations. The combination of a body&#39;s location and orientation define the body&#39;s pose. 
     Similarly, geometric terms, such as “parallel”, “perpendicular”, “round”, or “square”, are not intended to require absolute mathematical precision, unless the context indicates otherwise. Instead, such geometric terms allow for variations due to manufacturing or equivalent functions. For example, if an element is described as “round” or “generally round”, a component that is not precisely circular (e.g., one that is slightly oblong or is a many-sided polygon) is still encompassed by this description. The words “including” or “having” mean including but not limited to. 
     It should be understood that although this description is made to be sufficiently clear, concise, and exact, scrupulous and exhaustive linguistic precision is not always possible or desirable, since the description should be kept to a reasonable length and skilled readers will understand background and associated technology. For example, considering a video signal, a skilled reader will understand that an oscilloscope described as displaying the signal does not display the signal itself but a representation of the signal, and that a video monitor described as displaying the signal does not display the signal itself but video information the signal carries. 
     In addition, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context indicates otherwise. And, the terms “comprises”, “includes”, “has”, 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. And, each of the one or more individual listed items should be considered optional unless otherwise stated, so that various combinations of items are described without an exhaustive list of each possible combination. The auxiliary verb may likewise implies that a feature, step, operation, element, or component is optional. 
     Elements described in detail with reference to one embodiment, implementation, or application optionally may be included, whenever practical, in other embodiments, implementations, or applications in which they are not specifically shown or described. For example, if an element is described in detail with reference to one embodiment and is not described with reference to a second embodiment, the element may nevertheless be claimed as included in the second embodiment. Thus, to avoid unnecessary repetition in the following description, one or more elements shown and described in association with one embodiment, implementation, or application may be incorporated into other embodiments, implementations, or aspects unless specifically described otherwise, unless the one or more elements would make an embodiment or implementation non-functional, or unless two or more of the elements provide conflicting functions. 
     Elements described as coupled may be electrically or mechanically directly coupled, or they may be indirectly coupled via one or more intermediate components. 
     The term “flexible” in association with a part, such as a mechanical structure, component, or component assembly, should be broadly construed. In essence, the term means the part can be repeatedly bent and restored to an original shape without harm to the part. Many “rigid” objects have a slight inherent resilient “bendiness” due to material properties, although such objects are not considered “flexible” as the term is used herein. A flexible part may have infinite degrees of freedom (DOF&#39;s). Examples of such parts include closed, bendable tubes (made from, e.g., NITINOL, polymer, soft rubber, and the like), helical coil springs, etc. that can be bent into various simple or compound curves, often without significant cross-sectional deformation. Other flexible parts may approximate such an infinite-DOF part by using a series of closely spaced components that are similar to a snake-like arrangement of serial “vertebrae.” In such a vertebral arrangement, each component is a short link in a kinematic chain, and movable mechanical constraints (e.g., pin hinge, cup and ball, live hinge, and the like) between each link may allow one (e.g., pitch) or two (e.g., pitch and yaw) DOF&#39;s of relative movement between the links. A short, flexible part may serve as, and be modeled as, a single mechanical constraint (joint) that provides one or more DOF&#39;s between two links in a kinematic chain, even though the flexible part itself may be a kinematic chain made of several coupled links. Knowledgeable persons will understand that a part&#39;s flexibility may be expressed in terms of its stiffness. 
     Unless otherwise stated in this description, a flexible part, such as a mechanical structure, component, or component assembly, may be either actively or passively flexible. An actively flexible part may be bent by using forces inherently associated with the part itself. For example, one or more tendons may be routed lengthwise along the part and offset from the part&#39;s longitudinal axis, so that tension on the one or more tendons causes the part or a portion of the part to bend. Other ways of actively bending an actively flexible part include, without limitation, the use of pneumatic or hydraulic power, gears, electroactive polymer (more generally, “artificial muscle”), and the like. A passively flexible part is bent by using a force external to the part (e.g., an applied mechanical or electromagnetic force). A passively flexible part may remain in its bent shape until bent again, or it may have an inherent characteristic that tends to restore the part to an original shape. An example of a passively flexible part with inherent stiffness is a plastic rod or a resilient rubber tube. An actively flexible part, when not actuated by its inherently associated forces, may be passively flexible. A single part may be made of one or more actively and passively flexible parts in series. 
     An example of a teleoperated surgical system is the da Vinci Surgical System, commercialized by Intuitive Surgical, Inc. of Sunnyvale, California. Inventive aspects are associated with computer-assisted teleoperated surgical systems. Knowledgeable persons will understand that inventive aspects disclosed herein may be embodied and implemented in various ways, including computer-assisted and hybrid combinations of manual and computer-assisted embodiments and implementations. As applicable, inventive aspects may be embodied and implemented in both relatively smaller, hand-held, hand-operated devices and relatively larger systems that have additional mechanical support, as well as in other embodiments of computer-assisted tele-operated medical devices. In addition, inventive aspects are associated with advances in computer-assisted surgical systems that include autonomous rather than teleoperated actions, and so both teleoperated and autonomous surgical systems are included, even though the description concentrates on teleoperated systems. 
     A computer is a machine that follows programmed instructions to perform mathematical or logical functions on input information to produce processed output information. A computer includes a logic unit that performs the mathematical or logical functions, and memory that stores the programmed instructions, the input information, and the output information. The term “computer” and similar terms, such as “processor” or “controller”, encompasses both centralized single-location and distributed implementations. 
     This disclosure provides improved surgical and telesurgical devices, systems, and methods. The inventive concepts are particularly advantageous for use with telesurgical systems in which a plurality of surgical tools or instruments are mounted on and moved by an associated plurality of teleoperated manipulators during a surgical procedure. The teleoperated surgical systems will often comprise tele-robotic, telesurgical, and/or telepresence systems that include processors configured as master-slave controllers. By providing teleoperated surgical systems employing processors appropriately configured to move manipulator assemblies with articulated linkages having relatively large numbers of degrees of freedom, the motion of the linkages can be tailored for work through a minimally invasive access site. The large number of degrees of freedom may also allow a processor to position the manipulators to inhibit interference or collisions between these moving structures, and the like. 
     The manipulator assemblies described herein will often include a teleoperated manipulator and a tool mounted thereon (the tool often comprising a surgical instrument in surgical versions), although the term “manipulator assembly” will also encompass the manipulator without the tool mounted thereon. The term “tool” encompasses both general or industrial robotic tools and specialized robotic surgical instruments, with these later structures often including an end effector that is suitable for manipulation of tissue, treatment of tissue, imaging of tissue, or the like. The tool/manipulator interface will often be a quick disconnect tool holder or coupling, allowing rapid removal and replacement of the tool with an alternate tool. The manipulator assembly will often have a base that is fixed in space during at least a portion of a telesurgical procedure, and the manipulator assembly may include a number of degrees of freedom between the base and an end effector of the tool. Actuation of the end effector (such as opening or closing of the jaws of a gripping device, energizing an electrosurgical paddle, or the like) will often be separate from, and in addition to, these manipulator assembly degrees of freedom. 
     The end effector will typically move in the workspace with between two and six degrees of freedom. As used herein, the term “position” encompasses both location and orientation. Hence, a change in a position of an end effector (for example) may involve a translation of the end effector from a first location to a second location, a rotation of the end effector from a first orientation to a second orientation, or a combination of both. As used herein, the term “end effector” therefore includes but is not limited to the function of changing the orientation or position (e.g., a “wrist” function, a parallel motion function) of its distal-most part or parts (e.g., jaw(s) and the like). 
     When used for minimally invasive teleoperated surgery, movement of the manipulator assembly may be controlled by a processor of the system so that a shaft or intermediate portion of the tool or instrument is constrained to a safe motion through a minimally invasive surgical access site or other aperture. Such motion may include, for example, axial insertion of the shaft through the aperture site, rotation of the shaft about its axis, and pivotal motion of the shaft about a pivot point adjacent the access site, but will often preclude excessive lateral motion of the shaft which might otherwise tear the tissues adjacent the aperture or enlarge the access site inadvertently. Some or all of such constraint on the manipulator motion at the access site may be imposed using mechanical manipulator joint linkages that inhibit improper motions, or may in part or in full be imposed using robotic data processing and control techniques. Hence, such minimally invasive aperture-constrained motion of the manipulator assembly may employ between zero and three degrees of freedom of the manipulator assembly. 
     Many of the exemplary manipulator assemblies described herein will have more degrees of freedom than are needed to position and move an end effector within a surgical site. For example, a surgical end effector that can be positioned with six degrees of freedom at an internal surgical site through a minimally invasive aperture may in some embodiments have nine degrees of freedom (six end effector degrees of freedom—three for location, and three for orientation—plus three degrees of freedom to comply with the access site constraints), but will often have ten or more degrees of freedom. Highly configurable manipulator assemblies having more degrees of freedom than are needed for a given end effector position can be described as having or providing sufficient degrees of freedom to allow a range of joint states for an end effector position in a workspace. For example, for a given end effector position, the manipulator assembly may occupy (and be driven between) any of a range of alternative manipulator linkage positions Similarly, for a given end effector velocity vector, the manipulator assembly may have a range of differing joint movement speeds for the various joints of the manipulator assembly. 
     Referring to  FIGS.  1  and  2   , systems for minimally invasive computer-assisted telesurgery (as referred to herein as “minimally invasive robotic surgery”) can include a patient-side unit  100  and a surgeon control unit  40 . Telesurgery is a general term for surgical systems where the surgeon uses some form of remote control, e.g., a servomechanism, or the like, to manipulate surgical instrument movements by using robot technology rather than directly holding and moving the instruments by hand. The robotically manipulatable surgical instruments can be inserted through small, minimally invasive surgical apertures to treat tissues at surgical sites within the patient, avoiding the trauma associated with accessing for open surgery. These robotic systems can move the working ends of the surgical instruments with sufficient dexterity to perform quite intricate surgical tasks, often by pivoting shafts of the instruments at the minimally invasive aperture, sliding of the shaft axially through the aperture, rotating of the shaft within the aperture, and/or the like. 
     In the depicted embodiment, the patient-side unit  100  includes a base  110 , a first robotic manipulator arm assembly  120 , a second robotic manipulator arm assembly  130 , a third robotic manipulator arm assembly  140 , and a fourth robotic manipulator arm assembly  150 . As shown, the base  110  includes a portion that rests on the floor, a vertical column, and a horizontal boom, and other base configurations to mechanically ground the patient-side unit may optionally be used. Each robotic manipulator arm assembly  120 ,  130 ,  140 , and  150  is pivotably coupled to the base  110 . In some embodiments, fewer than four or more than four robotic manipulator arm assemblies may be included as part of the patient-side unit  100 . While in the depicted embodiment the base  110  includes casters to allow ease of mobility, in some embodiments the patient-side unit  100  is fixedly mounted to a floor, ceiling, operating table, structural framework, or the like. 
     In a typical application, two of the robotic manipulator arm assemblies  120 ,  130 ,  140 , or  150  hold surgical instruments and a third holds a stereo endoscope. The remaining robotic manipulator arm assembly is available so that another instrument may be introduced at the work site. Alternatively, the remaining robotic manipulator arm assembly may be used for introducing a second endoscope or another image capturing device, such as an ultrasound transducer, to the work site. 
     Each of the robotic manipulator arm assemblies  120 ,  130 ,  140 , and  150  is conventionally formed of links that are coupled together and manipulated through actuatable joints. Each of the robotic manipulator arm assemblies  120 ,  130 ,  140 , and  150  includes a setup arm and a device manipulator. The setup arm positions its held device so that a pivot point occurs at its entry aperture into the patient. The device manipulator may then manipulate its held device (tool; surgical instrument) so that it may be pivoted about the pivot point, inserted into and retracted out of the entry aperture, and rotated about its shaft axis. 
     In the depicted embodiment, the surgeon console  40  includes a stereo vision display  45  so that the user may view the surgical work site in stereo vision from images captured by the stereoscopic camera of the patient-side cart  100 . Left and right eyepieces  46  and  47  are provided in the stereo vision display  45  so that the user may view left and right display screens inside the display  45  respectively with the user&#39;s left and right eyes. While viewing typically an image of the surgical site on a suitable viewer or display, the surgeon performs the surgical procedures on the patient by manipulating master control input devices, which in turn control the motion of robotic instruments. 
     The surgeon console  40  also includes left and right input devices  41 ,  42  that the user may grasp respectively with his/her left and right hands to manipulate devices (e.g., surgical instruments) being held by the robotic manipulator arm assemblies  120 ,  130 ,  140 , and  150  of the patient-side cart  100  in preferably six degrees-of-freedom (“DOF”). Foot pedals  44  with toe and heel controls are provided on the surgeon console  40  so the user may control movement and/or actuation of devices associated with the foot pedals. Additional input to the system may be made via one or more other inputs, such as buttons, touch pads, voice, and the like, as illustrated by input  49 . 
     A processor  43  is provided in the surgeon console  40  for control and other purposes. The processor  43  performs various functions in the medical robotic system. One function performed by processor  43  is to translate and transfer the mechanical motion of input devices  41 ,  42  to actuate their respective joints in their associated robotic manipulator arm assemblies  120 ,  130 ,  140 , and  150  so that the surgeon can effectively manipulate devices, such as the surgical instruments. Another function of the processor  43  is to implement the methods, cross-coupling control logic, and controllers described herein. 
     Although described as a processor, it is to be appreciated that the processor  43  may be implemented by any combination of hardware, software, and firmware. Also, its functions as described herein may be performed by one unit or divided up among a number of subunits, each of which may be implemented in turn by any combination of hardware, software, and firmware. Further, although being shown as part of or being physically adjacent to the surgeon control unit  40 , the processor  43  may also be distributed as subunits throughout the telesurgery system. Accordingly, control aspects referred to herein are implemented via processor  43  in either a centralized or distributed form. 
     Referring also to  FIG.  3   , the robotic manipulator arm assemblies  120 ,  130 ,  140 , and  150  can manipulate devices such as surgical instruments to perform minimally invasive surgery. For example, in the depicted arrangement the robotic manipulator arm assembly  120  is pivotably coupled to an instrument holder  122 . A cannula  180  and a surgical instrument  200  and are, in turn, releasably coupled to the instrument holder  122 . The cannula  180  is a tubular member that is located at the patient interface site during a surgery. The cannula  180  defines a lumen in which an elongate shaft  220  of the surgical instrument  200  is slidably disposed. As described further below, in some embodiments the cannula  180  includes a distal end portion with a body wall retractor member. 
     The instrument holder  122  is pivotably coupled to a distal end of the robotic manipulator arm assembly  120 . In some embodiments, the pivotable coupling between the instrument holder  122  and the distal end of robotic manipulator arm assembly  120  is a motorized joint that is actuatable from the surgeon console  40  and processor  43 . 
     The instrument holder  122  includes an instrument holder frame  124 , a cannula clamp  126 , and an instrument holder carriage  128 . In the depicted embodiment, the cannula clamp  126  is fixed to a distal end of the instrument holder frame  124 . The cannula clamp  126  can be actuated to couple with, or to uncouple from, the cannula  180 . The instrument holder carriage  128  is movably coupled to the instrument holder frame  124 . More particularly, the instrument holder carriage  128  is linearly translatable along the instrument holder frame  124 . In some embodiments, the movement of the instrument holder carriage  128  along the instrument holder frame  124  is a motorized, translational movement that is actuatable/controllable by the processor  43 . 
     The surgical instrument  200  includes a transmission assembly  210 , the elongate shaft  220 , and an end effector  230 . The transmission assembly  210  is releasably coupleable with the instrument holder carriage  128 . The shaft  220  extends distally from the transmission assembly  210 . The end effector  230  is disposed at a distal end of the shaft  220 . 
     The shaft  220  defines a longitudinal axis  222  that is coincident with a longitudinal axis of the cannula  180 . As the instrument holder carriage  128  translates along the instrument holder frame  124 , the elongate shaft  220  of the surgical instrument  200  is moved along the longitudinal axis  222 . In such a manner, the end effector  230  can be inserted and/or retracted from a surgical workspace within the body of a patient. 
     Also referring to  FIG.  4   , another example patient-side system  160  for minimally invasive computer-assisted tele-operated surgery includes a first robotic manipulator arm assembly  162  and a second robotic manipulator arm assembly  164  that are each mounted to an operating table  10 . In some cases, this configuration of patient-side system  160  can be used as an alternative to the patient-side unit  100  of  FIG.  1   . While only two robotic manipulator arm assemblies  162  and  164  are depicted, it should be understood that more than two (e.g., three, four, five, six, and more than six) can be included in some configurations. 
     In some cases, the operating table  10  may be moved or reconfigured during the surgery. For example, in some cases, the operating table  10  may be tilted about various axes, raised, lowered, pivoted, rotated, and the like. In some cases, by manipulating the orientation of the operating table  10 , the clinicians can utilize the effects of gravity to position internal organs of the patient in positions that facilitate enhanced surgical access. In some cases, such movements of the operating table  10  may be integrated as a part of the computer-assisted tele-operated surgery system, and controlled by the system. 
     Also referring to  FIGS.  5 - 7   , a variety of alternative computer-assisted tele-operated surgical instruments of different types and differing end effectors  230  may be used, with the instruments of at least some of the manipulators being removed and replaced during a surgical procedure. Several of these end effectors, including, for example, DeBakey Forceps  56   i,  microforceps  56   ii,  and Potts scissors  56   iii  include first and second end effector elements  56   a,    56   b  which pivot relative to each other so as to define a pair of end effector jaws. Other end effectors, including scalpels and electrocautery probes, have a single end effector element. For instruments having end effector jaws, the jaws will often be actuated by squeezing the grip members of input devices  41 ,  42 . 
     In some cases, the computer-assisted tele-operated surgical instruments include multiple degrees of freedom such as, but not limited to, roll, pitch, yaw, insertion depth, opening/closing of jaws, actuation of staple delivery, activation of electro-cautery, and the like. At least some of such degrees of freedom can be actuated by an instrument drive system to which the surgical instrument can be selectively coupled. 
     In some embodiments, the computer-assisted tele-operated surgical instruments include end effectors with two individually movable components such as, but not limited to, opposing jaws designed for grasping or shearing. When a first one of the individually movable components is moved as a second one of the individually movable components remains generally stationary or is moved in an opposing manner, the end effector can perform useful motions such as opening and closing for grasping, shearing, releasing, and the like. When the two components are moved synchronously in the same direction, speed and distance, the resulting motion is a type of pitch or yaw movement of the end effector. Hence, in some surgical instrument embodiments that have end effectors with two individually movable components, such as jaws, the arrangement can provide two degrees of freedom (e.g., pitch/yaw movements and opening/closing movements). 
     The elongate shaft  220  allow the end effector  230  and the distal end of the shaft  220  to be inserted distally into a surgical worksite through a minimally invasive aperture (via cannula  180 ), often through a body wall (e.g., abdominal wall) or the like. In some cases, a body wall retractor member on a distal end of the cannula  180  can be used to tent the body wall, thereby increasing the surgical workspace size. In some cases the surgical worksite may be insufflated, and movement of the end effectors  230  within the patient will often be effected, at least in part, by pivoting of the instruments  200  about the location at which the shaft  220  passes through the minimally invasive aperture. In other words, the robotic manipulator arm assemblies  120 ,  130 ,  140 , and  150  will move the transmission assembly  210  outside the patient so that the shaft  220  extends through a minimally invasive aperture location so as to help provide a desired movement of end effector  50 . Hence, the robotic manipulator arm assemblies  120 ,  130 ,  140 , and  150  will often undergo significant movement outside patient during a surgical procedure. 
     Referring to  FIG.  8   , an example surgical instrument  300  that can be used as part of a computer-assisted tele-operated surgery system is schematically depicted. The surgical instrument  300  includes an instrument shaft  302  (similar to shafts  220 ,  640 ) having a proximal (away from the surgical site) end portion  310  and a distal (toward the surgical site) end portion  320  opposite from the proximal end portion  310 . The surgical instrument  300  also includes an end effector  330  (similar to end effectors  230 ,  650 ). In this schematic diagram, the end effector  330  is depicted as having a single degree of freedom in relation to the instrument shaft  302  (i.e., a freedom to yaw the end effector  330  in a rotary or pivoting fashion). It should be understood, however, that the end effectors  330  of the surgical instruments described herein can have more than one degree of freedom (e.g., two, three, four, five, six, or more than six degrees of freedom). Moreover, it should be understood that the concepts described in the context of the single degree of freedom of the end effector  330  can be extended to each degree of freedom of multiple degrees of freedom of the surgical instrument  300  and of other types of surgical instruments for computer-assisted tele-operated surgery systems. 
     Example surgical instrument  300  also includes a first tensioning member  340 , a first actuator engagement member  350 , a second tensioning member  360 , and a second actuator engagement member  370 . The first tensioning member  340  is coupled to the end effector  330  and extends along the instrument shaft  302  where it terminates at the first actuator engagement member  350  Similarly, the second tensioning member  360  is coupled to the end effector  330  and extends along the instrument shaft  302  where it terminates at the second actuator engagement member  370 . The first actuator engagement member  350  and the second actuator engagement member  370  are movably coupled to the proximal end portion  310  of the surgical instrument. In some embodiments, the first actuator engagement member  350  and the second actuator engagement member  370  are slidably coupled to the proximal end portion  310  of the surgical instrument. 
     While the depicted embodiment includes sliding actuator engagement members  350  and  370 , in some embodiments one or more other types of actuator engagement members can be included in the surgical instrument  300 . For example, in some embodiments rotatable actuator engagement members are included. Such rotatable actuator engagement members can be coupled to capstans or pulleys that are engaged with the tensioning members  340  and  360 . Rotation of the rotatable actuator engagement members can apply or relieve tension on the corresponding tensioning member  340  and  360 . Accordingly, movements of the end effector  330  and tensioning of the tensioning member  340  and  360  can be controlled via rotatable actuator engagement members. 
     In some embodiments, some or all portions of the first tensioning member  340  and the second tensioning member  360  comprise flexible cables (e.g., without limitation, stranded tungsten cables, stainless steel cables, etc.). In some embodiments, the first tensioning member  340  and the second tensioning member  360  are different portions of a single continuous cable. In some embodiments, the first tensioning member  340  and the second tensioning member  360  are separate cables. The first tensioning member  340  and the second tensioning member  360  may additionally or alternatively include other components such as, but not limited to, hypo-tubes. 
     The first tensioning member  340  and the second tensioning member  360  are each coupled to the end effector  330 . In the depicted embodiment, the first tensioning member  340  and the second tensioning member  360  are each coupled to the end effector  330  via a pulley  332  (which can be a capstan, crank arm, rotary drive member, etc.). Hence, a proximal movement of the first actuator engagement member  350  moves the second actuator engagement member  370  distally, and moves the end effector  330  in a first manner relative to the instrument shaft  302 . Conversely, a proximal movement of the second actuator engagement member  370  moves the first actuator engagement member  350  distally, and moves the end effector  330  in a second manner relative to the instrument shaft  302 . In this fashion, desired movements of the end effector  330  can be facilitated in a controlled manner Moreover, as described further below, while the movements and/or pose of the end effector  330  is being controlled using actuator engagement members  350  and  370 , the tensions in the tensioning members  340  and  360  can be concurrently controlled. In effect, two degrees of freedom (e.g., end effector  330  position and tensioning members  340  and  360  tension) of the surgical instrument  300  can be concurrently controlled in accordance with the devices and methods described herein. 
     The surgical instrument  300  is depicted here as being separated from an instrument drive system. Accordingly, in some embodiments the tension in the first tensioning member  340  and the second tensioning member  360  can be less than the tension used during the operation of the surgical instrument  300 . In some cases, having a relatively low tension in the first tensioning member  340  and the second tensioning member  360  while the surgical instrument  300  is not in use can be advantageous (e.g., to reduce the potential for cable stretch). In some embodiments, pre-load tensioning members (e.g., springs, not shown) may be included in surgical instrument  300  to maintain a minimal tension in the first tensioning member  340  and the second tensioning member  360  while the surgical instrument  300  is separated from an instrument drive system. Such minimal pre-tensioning may help ensure that the first tensioning member  340  and the second tensioning member  360  remain oriented within the surgical instrument  300  as desired. 
     While the surgical instrument  300  is depicted as having a single degree of freedom, it should be understood that this is a simplified schematic diagram and that the surgical instrument  300  can have two or more degrees of freedom. The concepts described herein in reference to the single degree of freedom of surgical instrument  300  (as depicted) can be extrapolated to the two or more degrees of freedom of the surgical instruments provided herein. For example, when the end effector  330  includes two individually movable components, such as opposing jaws designed for grasping or shearing as described above, the arrangement provides two degrees of freedom (e.g., pitch/yaw movements when the components are moved synchronously and opening/closing movements when the components are moved asynchronously or in an opposing manner). Extending the concepts described in reference to the surgical instrument  300  to such an end effector would result in an instrument having four actuator engagement members and four tensioning members to actuate the two degrees of freedom. 
     Referring to  FIG.  9   , the surgical instrument  300  can be selectively coupled with an instrument drive system  400 . That is, the surgical instrument  300  can be coupled with the instrument drive system  400  for operation as part of a computer-assisted tele-operated surgery system. Additionally, the surgical instrument  300  can be uncoupled from the instrument drive system  400  (e.g., for replacement by another type of surgical instrument, for sterilization of the surgical instrument  300 , etc.). 
     In some embodiments, the instrument drive system  400  can be mounted to a manipulator assembly, which can in turn be mounted to another structure or a base. The instrument drive system  400  can be interchangeably mounted to a manipulator assembly in some cases. That is, in some embodiments the instrument drive system  400  is designed for convenient detachment from a manipulator assembly such that it is readily interchangeable with another instrument drive system. Therefore, the instrument drive system  400  may also be referred to as a pod  400 . As used herein, the term “pod” indicates the interchangeable aspects of some instrument drive systems in relation to a manipulator assembly—i.e., one pod may be removed from a manipulator assembly and replaced with a second pod of the same, similar, or different configuration. In some embodiments, the instrument drive system  400  is affixed to a manipulator assembly in such a way that the instrument drive system  400  is not readily detachable or interchangeable. 
     In some embodiments, the surgical instrument  300  is slidably coupleable with the instrument drive system  400 . That is, the surgical instrument  300  can be slidably extended distally and slidably retracted proximally in relation to the instrument drive system  400 . 
     In the depicted embodiment, the instrument drive system  400  includes a first actuator  410 , a second actuator  420 , and a shaft actuator  430 . The first actuator  410  is releasably coupleable with the first actuator engagement member  350 . Hence, the first actuator  410  can induce a tensile force in the first tensioning member  340 . The second actuator  420  is releasably coupleable with the second actuator engagement member  370 . Hence, the second actuator  420  can induce a tensile force in the second tensioning member  360 . The actuators  410 ,  420  are shown in a non-detained engagement with the corresponding actuator engagement members  350 ,  370 . Optionally, the actuators  410 ,  420  are in a detained engagement with the corresponding actuator engagement members  350 ,  370 , such as a latch. In a detained engagement, two objects are fixed together (releasably or otherwise) so that as one object moves, the other object correspondingly moves. In a non-detained engagement, the two objects are not fixed together, so that if one object moves toward the other, the other object moves, but if one object moves away from the other, the other object will not move. 
     In light of the arrangement between the surgical instrument  300  and the first and second actuators  410  and  420  of the instrument drive system  400  as described above, it can be envisioned that concerted modulation of the forces exerted from the first and second actuators  410  and  420  to the first and second actuator engagement members  350  and  370 , respectively, can result in controlled motion of the end effector  330  in its degree of freedom. Moreover, it can also be envisioned (as described further below), that the tensions in the first and second tensioning members  340  and  360  can also be controlled by the concerted modulation of the forces exerted from the first and second actuators  410  and  420  to the first and second actuator engagement members  350  and  370 , respectively. Still further, it can also be envisioned that the tensions in the first and second tensioning members  340  and  360  can be controlled by the concerted modulation of the forces exerted from the first and second actuators  410  and  420  to the first and second actuator engagement members  350  and  370 , respectively, while the concerted modulation of the forces exerted from the first and second actuators  410  and  420  to the first and second actuator engagement members  350  and  370  also concurrently cause desired movements of the end effector  330 . Put more simply, the tensions in the first and second tensioning members  340  and  360  can be controlled to a desired amount of tensile force while movements of the end effector  330  are being made as desired. This concept can be referred to herein as “dynamic tension control” or “dynamic tension and position control.” 
     Still referring to  FIG.  9   , the instrument drive system  400  also includes the shaft actuator  430  that engages with a corresponding shaft actuator engagement member on the surgical instrument in a non-detained or detained engagement. An example of non-detained engagement is engagement with a part of distal end portion  310  that acts as the shaft actuator engagement member, as shown. An example of detained engagement is engagement with a latch, as described below. The shaft actuator  430  releasably couples with the instrument shaft  302  for both detained and non-detained engagement. 
     In some embodiments, the shaft actuator  430  releasably couples with the instrument shaft  302  (or to a structure coupled to the instrument shaft  302 ) using a latch mechanism. Accordingly, in some such embodiments, while the shaft actuator  430  is latched to the instrument  300 , the shaft actuator  430  is able to exert either a distally -directed force or a proximally -directed force to distally extend or proximally retract the instrument  300 , as desired, in relation to the instrument drive system  400 . It should be understood that such a latch mechanism for coupling the shaft actuator  430  to the instrument shaft  302  is not required in all embodiments. Further, in some embodiments the shaft actuator  430  is configured to only exert a distally -directed force to the instrument  300  (i.e., not a proximally -directed force). The dynamic tension and position control concepts described herein can still be performed while the shaft actuator  430  is configured to exert only a distally -directed force to the instrument  300 . 
     The actuators  410 ,  420 , and  430  can be various types of actuators. In some embodiments, the first actuator  410 , a second actuator  420 , and a shaft actuator  430  each comprise electrical motors that are coupled to lead screws that linearly drive nut members on the threads of the lead screw. In some embodiments, the entire assembly of the surgical instrument  300  in combination with the instrument drive system  400  can be driven together to result in a desired motion of the end effector, such as a rolling motion about the longitudinal axis of the surgical instrument  300 . 
     Referring also to  FIG.  10   , a force diagram  500  can be used to further describe the structure and operations of the surgical instrument  300  in combination with the instrument drive system  400 . 
     The body  301  is representative of the surgical instrument  300 . Force f 1  is representative of the force applied by the first actuator  410  to the first engagement member  350 . Forcefi is representative of the force applied by the second actuator  420  to the second engagement member  370 . Force f s  is representative of the force applied by the shaft actuator  430  to the instrument shaft  302 . 
     Force f s  is directionally opposite to forces f 1  and f 2 . Hence, in a static context, force f s  is equal to the sum of forces f 1  and f 2 . In a dynamic context, if force f s  is greater than the sum of forces f 1  and f 2 , then the body  301  will move in the direction of force f s . Conversely, if force f s  is less than the sum of forces f 1  and f 2 , then the body  301  will move in the direction of forces f 1  and f 2 . 
     Applying the principles described above regarding the force diagram  500  to the analogous arrangement of the surgical instrument  300  in combination with the instrument drive system  400 , the following concepts can be envisioned. While the surgical instrument  300  is in a constant spatial relationship with the instrument drive system  400  (i.e., in a static context), the sum of the forces exerted from the first and second actuators  410  and  420  to the first and second actuator engagement members  350  and  370  equal the force exerted from the shaft actuator  430  to the instrument shaft  302 . In addition, while the sum of the forces exerted from the first and second actuators  410  and  420  to the first and second actuator engagement members  350  and  370  are greater than the force exerted from the shaft actuator  430  to the instrument shaft  302 , the surgical instrument  300  will move proximally in relation to the instrument drive system  400 . Still further, while the sum of the forces exerted from the first and second actuators  410  and  420  to the first and second actuator engagement members  350  and  370  are less than the force exerted from the shaft actuator  430  to the instrument shaft  302 , the surgical instrument  300  will move distally in relation to the instrument drive system  400 . 
     To be clear, the combinations of forces from the actuators  410 ,  420 , and  430  that cause the proximal and distal movements of the surgical instrument  300  in relation to the instrument drive system  400  involve the sum of the forces exerted from the first and second actuators  410  and  420  to the first and second actuator engagement members  350  and  370 . Hence, it can be envisioned that the forces exerted from the first and second actuators  410  and  420  to the first and second actuator engagement members  350  and  370  can be equal to each other, or can differ from each other while the sum is still a total amount that is appropriate to result in a desired distal/proximal movement and/or orientation between the surgical instrument  300  and the instrument drive system  400 . For example, in the case when the forces exerted from the first and second actuators  410  and  420  to the first and second actuator engagement members  350  and  370  differ from each other, a movement of end effector  330  will result, and in the case when the forces exerted from the first and second actuators  410  and  420  to the first and second actuator engagement members  350  and  370  are equal to each other, the end effector  330  will be stationary in relation to the instrument shaft  302 . Again, it should be understood that, using the structure and operational concepts provided herein, distal/proximal movements of the surgical instrument  300  in relation to the instrument drive system  400  can be made concurrently with movements of the end effector  300  in relation to the instrument shaft  302 . Moreover, both such movements can be made concurrently while the tensions in the first tensioning member  340  and the second tensioning member  360  are maintained at a desired level of tensile force (e.g., within a target range of desired tensile force). 
     It should be understood that the force exerted by actuator  430  may be the prime moving force, so that instrument  330  insertion and withdrawal is directly controlled by actuator  430 , and actuators  410 , 420  apply force sufficient to maintain tension in tension elements  340 , 360  and to maintain or change end effector  330 ′s orientation as actuator  430  inserts and withdraws the instrument. And so, in one aspect actuator  430  controls instrument  300 ′s insertion and withdrawal location while actuators  410 , 420  react to control tension on tension elements  340 , 360  as the location changes. For example, when actuator  430  slightly increases force to insert the instrument shaft, the slight tension increase in tension elements  340 , 360  is sensed and so actuators  410 , 420  decrease force to return tension elements  340 , 360  to the desired value. Alternatively, instrument  330  insertion and withdrawal is controlled by actuators  410 , 420 , 430  working in concert to control tension on tension elements  340 , 360  which in turn controls instrument  300 &#39;s insertion and withdrawal location, and at the same time end effector  330 &#39;s orientation is maintained or changed by actuators  410 , 420  working together to control relative tension between tension elements  340 , 360 . For example, when actuator  430  slightly increases force to insert the instrument shaft, actuators  410 , 420  simultaneously decrease force to maintain tension in tension elements  340 , 360  at the desired value. It can be appreciated that these two tension-control aspects apply to a reverse situation in which actuators  410 , 420  act together to apply the prime moving force for insertion/withdrawal, with actuator  430  controlling tension in the tension members. And, it can be appreciated that these tension-control aspects apply to more complicated movements in which the instrument shaft is moved in insertion/withdrawal and the end effector is moved in one or more degrees of freedom. 
     Referring also to  FIGS.  11 - 13   , the concepts described above can be further described by examples using illustrations of the surgical instrument  300  in various positions in relation to the instrument drive system  400 . 
     In a first example, the arrangement of  FIG.  9    can be transitioned to that of  FIG.  11    by temporarily increasing the force exerted by the first actuator  410  to the first actuator engagement member  350  in comparison to the force exerted by the second actuator  420  to the second actuator engagement member  370 , while the sum of the two forces is held equal to the force exerted by the shaft actuator  430  to the instrument shaft  302 . In result, the end effector  330  will move in relation to the instrument shaft  302  while the surgical instrument  300  is maintained in a constant spatial relationship (i.e., no distal and proximal movements) in relation to the instrument drive  400 . Such a movement can be made while the tensions in the first tensioning member  340  and the second tensioning member  360  are maintained at a desired level of tensile force (e.g., within a target range of desired tensile force). 
     In a second example, the arrangement of  FIG.  9    can be transitioned to that of  FIG.  12    by temporarily increasing the force exerted by the first actuator  410  to the first actuator engagement member  350  in comparison to the force exerted by the second actuator  420  to the second actuator engagement member  370 , while the sum of the two forces is temporarily less than the force exerted by the shaft actuator  430  to the instrument shaft  302 . In result, the end effector  330  will move in relation to the instrument shaft  302 , and the surgical instrument  300  will extend distally in relation to the instrument drive  400 . Such movements can be made while the tensions in the first tensioning member  340  and the second tensioning member  360  are maintained at a desired level of tensile force (e.g., within a target range of desired tensile force). 
     In a third example, the arrangement of  FIG.  9    can be transitioned to that of  FIG.  13    by temporarily increasing the force exerted by the first actuator  410  to the first actuator engagement member  350  in comparison to the force exerted by the second actuator  420  to the second actuator engagement member  370 , while the sum of the two forces is temporarily greater than the force exerted by the shaft actuator  430  to the instrument shaft  302 . In result, the end effector  330  will move in relation to the instrument shaft  302 , and the surgical instrument  300  will retract proximally in relation to the instrument drive  400 . Such movements can be made while the tensions in the first tensioning member  340  and the second tensioning member  360  are maintained at a desired level of tensile force (e.g., within a target range of desired tensile force). 
     In a fourth example, the arrangement of  FIG.  12    can be transitioned to that of  FIG.  13    by maintaining equal forces exerted by the first actuator  410  to the first actuator engagement member  350  and by the second actuator  420  exerted to the second actuator engagement member  370 , while the sum of the two forces is temporarily greater than the force exerted by the shaft actuator  430  to the instrument shaft  302 . In result, the end effector  330  will not move in relation to the instrument shaft  302 , and the surgical instrument  300  will retract proximally in relation to the instrument drive  400 . Such a movement can be made while the tensions in the first tensioning member  340  and the second tensioning member  360  are maintained at a desired level of tensile force (e.g., within a target range of desired tensile force). 
     In a fifth example, the arrangement of  FIG.  13    can be transitioned to that of  FIG.  12    by maintaining equal forces exerted by the first actuator  410  to the first actuator engagement member  350  and by the second actuator  420  exerted to the second actuator engagement member  370 , while the sum of the two forces is temporarily less than the force exerted by the shaft actuator  430  to the instrument shaft  302 . In result, the end effector  330  will move in relation to the instrument shaft  302 , and the surgical instrument  300  will extend distally in relation to the instrument drive  400 . Such a movement can be made while the tensions in the first tensioning member  340  and the second tensioning member  360  are maintained at a desired level of tensile force (e.g., within a target range of desired tensile force). 
     Examples so far have illustrated the drive unit&#39;s first and second actuators applying a proximal compressive force against their corresponding first and second actuator engagement members, and the drive unit&#39;s shaft actuator applying a distal compressive force against the instrument shaft. But, in another aspect the orientations of these forces are reversed, so that the drive unit&#39;s first and second actuators apply a distal compressive force against their corresponding first and second actuator engagement members, and the drive unit&#39;s shaft actuator applies a proximal compressive force against the instrument shaft. In this aspect, the tensioning members may be routed over pulleys so that distal movement of an actuator engagement member causes tension in the corresponding tension member and associated end effector movement. Or, the tensioning members may be replaced with compression members, such as push rods coupled to the end effector, so that distal movement of an actuator engagement member causes compression in the corresponding compression member and associated end effector movement. 
     Referring to  FIG.  14   , in some embodiments the forces exerted by the actuators  410 ,  420 , and/or  430  to the surgical instrument  300  can be detected by the use of one or more force detection devices. The output(s) of such force detection devices can be used for controlling the actuators  410 ,  420 , and/or  430  (i.e., to control movements of the surgical instrument  300  and/or to control tensions of the first and second tensioning members  340  and  360 ). 
     In a first non-limiting example, the depicted arrangement includes a load cell  510  type of force sensor disposed at or near the juncture between the first actuator  410  and the first actuator engagement member  350 . In another example, the depicted arrangement includes a load cell  520  type of force sensor disposed near the connection between the first actuator  410  and a structural member  401  of the instrument drive system  400 . In some embodiments, the instrument drive system  400  can be a pod (i.e., readily interchangeable in relation to mounting on a manipulator assembly). 
     In some embodiments, other sensors and/or other devices can be used to detect the forces exerted by the actuators  410 ,  420 , and/or  430  to the surgical instrument  300 . For example, in some embodiments strain gauges can be located on the actuator engagement members, e.g., the first actuator engagement member  350 . In another embodiment, the electrical current drawn by electric motors of the actuators  410 ,  420 , and/or  430  can be measured and used as an indication of the forces exerted by the actuators  410 ,  420 , and/or  430  to the surgical instrument  300 . In some embodiments, a combination of such force detection devices and techniques can be used. 
     Referring to  FIGS.  15 - 18   , an example surgical instrument  600  that can be used as part of a computer-assisted tele-operated surgery system includes a proximal end portion  610 , an instrument shaft  640 , and an end effector  650 . The surgical instrument  600  is an example of a surgical instrument that is configured in accordance with the schematic diagrams (e.g.,  FIGS.  8 ,  9 , and  11 - 14   ) described above. Hence, the surgical instrument  600  can function in accordance with the schematic diagrams described above. 
     The instrument shaft  640  extends distally from the proximal end portion  610 . The instrument shaft  640  includes a distal end portion to which the end effector  650  is coupled. The instrument shaft  640  defines a longitudinal axis  602  of the surgical instrument  600 , along which the instrument is inserted into and withdrawn from the patient. 
     The end effectors (e.g., end effector  650 ) of the surgical instruments described herein can be any type of surgical end effector (e.g., graspers, cutters, cautery instruments, staplers, forceps, cameras, etc.). The end effectors (e.g., end effector  650 ) of the surgical instruments described herein can have one or multiple degrees of freedom (e.g., two, three, four, five, six, seven, eight, or more than eight degrees of freedom). Moreover, it should be understood that the concepts described herein in the context of a single degree of freedom of the end effectors can be extended to each degree of freedom of multiple degrees of freedom of the surgical instrument  600 , and of other types of surgical instruments for computer-assisted tele-operated surgery systems. 
     In the depicted embodiment, the proximal end portion  610  includes a handle  612 , a plurality of actuator engagement members (depicted here disposed in a grouping  630  at a same longitudinal location along the longitudinal axis  602 ), and an instrument shaft actuator engagement member  620 . The plurality of actuator engagement members  630  are movably coupled to the proximal end portion  610 . In the depicted embodiment, the plurality of actuator engagement members  630  are slidably coupled to the proximal end portion  610  such that the plurality of actuator engagement members  630  can translate parallel to the longitudinal axis  602 . The instrument shaft actuator engagement member  620  is coupled to the proximal end portion  610 . In the depicted embodiment, instrument shaft actuator engagement member  620  is pivotably coupled to the proximal end portion  610 . 
     The handle  612  extends radially from the longitudinal axis  602 . In the depicted embodiment, the handle  612  is the portion of proximal end portion  610  and of the entire surgical instrument  600  that radially extends the farthest. The handle  612  is configured to facilitate manual gripping and manipulation of the surgical instrument  600 . 
     In some embodiments, the handle  612  includes an indicium that identifies the type of the surgical instrument  600 . For example, in the depicted embodiment the handle  612  includes a visible indicium that is an icon  614  that depicts that the surgical instrument  600  is a grasper device. In some embodiments, the handle  612  includes a machine-readable indicium, such as an RFID chip or NFC tag that can be used to store and communicate information pertaining to the surgical instrument  600 . For example, such information pertaining to the surgical instrument  600  can include, but is not limited to, a unique identification or serial number, the type of instrument, the number of times the instrument has been used for one or more surgical procedures, and the like. 
     In some embodiments, the handle  612  optionally includes one or more magnets that an instrument drive system can use to sense the presence of the surgical instrument  600  mounted in the instrument drive system. 
     The proximal end portion  610  includes the plurality of actuator engagement members. As depicted the actuator engagement members are disposed in a grouping  630  at a common longitudinal location along the longitudinal axis  602 . Optionally they may be at two or more longitudinal locations along longitudinal axis  602  so that a first coupled pair of actuator engagement members is at a first longitudinal location and a second coupled pair of actuator engagement members is at a second longitudinal location, or each actuator engagement member of a coupled pair is at a different longitudinal location. The actuator engagement members are configured to releasably engage with actuators which drive the actuator engagement members and corresponding movements of the end effector  650  as described above in reference to  FIGS.  8 - 14   . As shown, each individual actuator engagement member slides longitudinally in a corresponding individual longitudinal slot in proximal end portion  610 . In other optional aspects, however, an individual actuator engagement member may have a different configuration (e.g., a lever, a rotating piece such as a disk or gear, a cam surface, and the like). As shown, all individual actuator engagement members extend radially outward slightly beyond the outer perimeter of proximal end portion  610  so that the associated actuators to not extend into proximal end portion  610 . Alternatively, one or more individual actuator engagement members may not extend to or beyond the outer perimeter of proximal end portion (e.g., they are positioned slightly inside proximal end portion  610 ) so they are less prone to damage or do not snag on an object. In this alternative configuration, the associated actuators extend slightly into proximal end portion  610  to engage the instrument&#39;s actuator engagement members. All actuator engagement members may have the same configuration, or two or more actuator engagement member configurations may be used in a single instrument, as long as the actuator engagement members comply with the principles of operation described with reference to  FIGS.  8 - 14   . In the depicted embodiment the following example actuator engagement members are included:  632   a,    632   b,    634   a,    634   b,    636   a,    636   b,  and  638 . More or fewer actuator engagement members may be included in some embodiments. 
     The actuator engagement members, e.g., actuator engagement members  632   a,    632   b,    634   a ,  634   b,    636   a,    636   b,  and  638 , are coupled to tensioning members (e.g., comprising flexible cables that can be routed over small radius pulleys (e.g., 2-10 mm scale), semi-flexible cables that cannot be routed over small radius pulleys, rigid hypo-tubes, pull rods, etc.) that extend along the instrument shaft  640  and that are movably coupled to the end effector  650 . Hence, movements of the actuator engagement members result in movements of the end effector  650 . 
     In some cases, the actuator engagement members are paired (e.g., actuator engagement members  632   a  and  632   b,  actuator engagement members  634   a  and  634   b,  and actuator engagement members  636   a  and  636   b ) such that moving one actuator engagement member of the pair proximally results in a corresponding distal movement of the other actuator engagement member of the pair. For example, moving actuator engagement member  632   a  proximally results in a corresponding distal movement of actuator engagement member  632   b,  and moving actuator engagement member  632   b  proximally results in a corresponding distal movement of actuator engagement member  632   a.  In other words, actuator engagement member pairs move in opposition to each other. 
     When the structure of the surgical instrument  600  includes actuator engagement members (e.g., actuator engagement members  632   a,    632   b,    634   a,    634   b,    636   a,    636   b,  and  638 ) that are coupled to flexible tensioning cables, it can be envisioned that distal movements of the actuator engagement members without a corresponding proximal movement of a paired actuator engagement member will not move the end effector  650 . Rather, the flexible tensioning cable attached to the actuator engagement member being moved distally would simply become flaccid (due to the limited column strength/rigidity of a flexible tensioning cable). Hence, it can be said that, in some embodiments, the actuator engagement members  632   a,    632   b,    634   a,    634   b,    636   a,    636   b,  and  638  are configured to move the end effector  650  in response to receiving a proximally -directed force, and are configured to not move the end effector  650  in response to receiving a distally -directed force. However, in some embodiments one or more of the actuator engagement members (e.g., the actuator engagement member  638  which is not paired with another actuator engagement member) are configured to move the end effector  650  both ways (proximally and distally). That is, such actuator engagement members optionally drive a flexible or semi-flexible member in a manner similar to Bowdin cable operation, or drive a rigid member in a manner similar to push/pull rod operation. For example, in some embodiments the actuator engagement member  638  may be configured to operate a blade of the end effector  650  or a clamp in the case that the end effector  650  includes a stapler. In the example of the blade, the actuator engagement member  638  works opposite to a spring (cut under drive, spring back). In the example of the stapler, the actuator engagement member  638  moves distally to drive the firing sequence, while the grip-open actuation returns the actuator engagement member  638  proximally. 
     Still referring to  FIGS.  15 - 18   , in the depicted arrangement of surgical instrument  600 , the actuator engagement members  632   a,    632   b,    634   a,    634   b,    636   a,    636   b,  and  638  are all positioned at the same longitudinal location along the longitudinal axis  602  of the surgical instrument. However, during use of the surgical instrument  600 , the actuator engagement members  632   a,    632   b,    634   a,    634   b,    636   a ,  636   b,  and  638  are moved to various longitudinal locations along the longitudinal axis  602  of the surgical instrument. This is described further by the following example 
     When the surgical instrument  600  is coupled with an instrument drive system, actuators of the instrument drive system will releasably couple with the actuator engagement members  632   a,    632   b ,  634   a,    634   b,    636   a,    636   b,  and  638 . For example, the actuators will engage the actuator engagement members by moving proximally until a reaction force that indicates engagement is sensed. For paired actuator engagement members  632   a  and  632   b,  a first actuator moves proximally until actuator engagement member  632   a  is engaged, and a second actuator moves proximally until actuator engagement member  632   b  is engaged. The first and second actuators may then adjust the longitudinal position of the corresponding actuator engagement members  632   a  and  632   b  to set a desired tension in corresponding paired tension members coupled to the distal end component so that all slack or backlash is removed from the drive train between the actuator engagement members and the corresponding distal end component and so that movement of the actuator engagement members results in immediate movement of the corresponding distal end component. That is, one or more instrument drive system actuators engage the corresponding one or more instrument actuator engagement members and set a dynamic preload tension (which may be in addition to the static preload tension described below) in the one or more instrument tension members between the one or more actuator engagement members and the corresponding instrument distal end component (e.g., wrist or end effector component). 
     Then, in response to input (such as from surgeon console  40  of  FIG.  2   ), the actuators of the instrument drive system correspondingly move some or all of the actuator engagement members (e.g., the actuator engagement members  632   a,    632   b,    634   a,    634   b,    636   a,  and/or  636   b ) proximally to initiate desired movements of the end effector  650  or other distal end component. For example, for paired actuator engagement members  632   a  and  632   b,  a first actuator of the instrument drive system may move actuator engagement member  632   a  proximally. In concert with that proximal movement of actuator engagement member  632   a,  a second actuator of the instrument drive system may resist distal movement of actuator engagement member  632   b,  thus keeping tension on actuator engagement member  632   b &#39;s corresponding tension member, but still allows actuator engagement member  632   b  to move distally. The second actuator&#39;s resistance to actuator engagement member  632   b &#39;s distal movement is modulated to maintain a desired tension in the tensioning members that correspond to the actuator engagement members  632   a  and  632   b.  This operation is performed in accordance with the dynamic tensioning concepts described above in reference to  FIGS.  8 - 14   . 
     In one aspect, the control system controls the tension in each of the paired tension members to be equal as the tension members move the corresponding end effector. In another aspect, however, the control system controls the tension in the tension members to cause a required load force in the loaded tension member and to maintain a minimum tension on the non-loaded tension member. 
     To explain this differential force aspect by example, consider paired actuator engagement members  632   a  and  632   b.  When their associated end effector is at a neutral position (e.g., centered on the instrument&#39;s longitudinal axis and not engaged with another object), not moving, and not experiencing a load, the control system may cause an equal force to be applied to actuator engagement members  632   a  and  632   b.  This equal force is at or above a minimum force required to remove backlash from the tension member connections between the end effector and the actuator engagement members for effective control. But, the equal force is kept low in order to reduce friction and tension loads that result in mechanical wear. 
     To move the associated end effector, the control system moves the actuator engagement members  632   a  and  632   b  in opposite directions. The end effector movement caused by the proximal motion of actuator engagement member  632   a  may be unresisted (e.g., the end effector moves freely) or resisted (e.g., the end effector moves against tissue or another part of the end effector, such as a jaw moving against another jaw in grip). Friction in the drive train may also cause a load that requires a higher force be applied to actuator engagement member  632   a  than is required to keep the end effector under effective control at a neutral position. Thus, the actuator associated with actuator engagement member  632   a  must increase its force against actuator engagement member  632  to either continue to move the corresponding end effector or to maintain the corresponding end effector&#39;s force against the resistance. In this situation, however, there is no need for the actuator associated with the paired actuator engagement member  632   b  to exert a force on actuator engagement member  632   b  that is the same as the force exerted on actuator engagement member  632   a.  What is required is that the force exerted on actuator engagement member  632   b  be at or above a minimum threshold necessary to keep the associated tension member from going slack or deviating from its path, such as by leaving a pulley. 
     As a further illustration, if the control system causes actuator engagement member  632   a  to receive a maximum allowable force from its associated drive unit actuator in order to produce a maximum force at the corresponding end effector (e.g., to produce a maximum possible end effector grip force), then the control system may cause actuator engagement member  632   b  to receive only a minimum force required to ensure that its associated tension member does not go slack and does not disengage from its proper routing, or to receive a force between this minimum force and the force applied to actuator engagement member  632   a.  And, although this aspect applies for maximum force applied to actuator engagement member  632   a,  it also applies when lower forces are applied so that again the conflicting tension caused by the force against actuator engagement member  632   b  is minimized It should be understood that if the end effector is then to be moved in the opposite direction, the required load force is applied against actuator engagement member  632   b,  and the required tension-maintaining force is applied against actuator engagement member  632   a.  It should also be understood that this differential force aspect applies if compression is used to move an end effector instead of tension, so that any unnecessary compression force is reduced or minimized. 
     In some embodiments of surgical instrument  600 , pre-load tensioning members (e.g., springs  633 ) may be included to maintain a minimal tension in the tensioning members while the surgical instrument  600  is separated from an instrument drive system—a static preload tension. Such minimal pre-tensioning may help ensure that the tensioning members remain oriented and routed within the surgical instrument  600  as desired. In the depicted embodiment, compression springs  633  apply a proximally -directed force to the actuator engagement members  632   a,    632   b,    634   a,    634   b,    636   a,    636   b , and  638  to maintain a minimal tension in the tensioning members while the surgical instrument  600  is separated from an instrument drive system. In some embodiments, other types of pre-load tensioning members may be used such as, but not limited to, flexures created as part of shaft  640  or proximal end portion  610 , extension springs, torsion springs, leaf springs, and the like. Further, in embodiments that incorporate compression members in place of tensioning members, pre-load compression members similar to these pre-load tensioning members may be used to eliminate mechanical backlash in the drive trains between actuator engagement members and the end effector. 
     Still referring to  FIGS.  15 - 18   , proximal end portion  610  includes the instrument shaft actuator engagement member  620 . The instrument shaft actuator engagement member  620  is used for releasably coupling the proximal end portion  610  to an actuator of an instrument drive system. Since the instrument shaft  640  is rigidly coupled to the proximal end portion  610 , the instrument shaft actuator engagement member  620  also releasably couples the instrument shaft  640  to an actuator of an instrument drive system. This concept of using the instrument shaft actuator engagement member  620  to couple an actuator to the proximal end portion  610  and the instrument shaft  640  was introduced above by the schematic diagrams and the descriptions thereof (e.g., by  FIG.  9    which includes the shaft actuator  430  that can releasably couple with the instrument shaft  302 ). Hence, the instrument shaft actuator engagement member  620 , when coupled with an actuator of an instrument drive system, is used for moving the entire surgical instrument  600  proximally and/or distally in relation to the instrument drive system. In addition (as described in reference to the force diagram of  FIG.  10   ), the instrument shaft actuator engagement member  620 , when coupled with an actuator of an instrument drive system, is used for balancing proximally directed forces applied by actuators to the actuator engagement members  632   a,    632   b,    634   a,    634   b,    636   a,    636   b,  and  638 . 
     In the depicted embodiment, the actuator engagement members  632   a,    632   b,    634   a,    634   b,    636   a ,  636   b,  and  638  are configured to receive proximally -directed forces from the actuators of an instrument drive system but are not configured to receive distally -directed forces from the actuators of an instrument drive system. In other words, the actuator engagement members  632   a,    632   b,    634   a ,  634   b,    636   a,    636   b,  and  638  are not detained (not immovably coupled with; a non-detained engagement) to the actuators of an instrument drive system. Stated differently, the actuator engagement members  632   a,    632   b,    634   a,    634   b,    636   a,    636   b,  and  638  are each configured for directly facilitating (causing) movement the end effector  650  in response to receiving a proximally -directed force from a corresponding actuator, and are each not configured for directly facilitating movement the end effector  650  in response to receiving a distally -directed force from a corresponding actuator. In contrast, in the depicted embodiment the instrument shaft actuator engagement member  620  is configured to directly facilitate movement of the entire surgical instrument  600  proximally in response to receiving a proximally -directed force, and is configured to directly facilitate movement of the entire surgical instrument  600  distally in response to receiving a distally -directed force. That is the case because the instrument shaft actuator engagement member  620  is configured to be releasably detained to an actuator of an instrument drive system. For example, in the depicted embodiment the instrument shaft actuator engagement member  620  is a latch mechanism that can be used to releasably detain the proximal end portion  610  and the instrument shaft  640  to an actuator of an instrument drive system. It should be understood that the use of a latch mechanism for the instrument shaft actuator engagement member  620  is not required in all embodiments, and other suitable coupling mechanisms at various locations on the instrument may be used. 
     Further, in some embodiments the instrument shaft actuator engagement member  620  is configured such that the instrument drive system only exerts distally -directed forces to the surgical instrument  600  (i.e., not proximally -directed forces). The dynamic tension and position control concepts described herein can still be performed in such a case where the instrument shaft actuator engagement member  620  is configured to receive only a distally -directed force from the instrument drive system. In this aspect, distally -directed force on the instrument&#39;s shaft actuator engagement member is balanced with proximally -directed forces on the instrument&#39;s actuator engagement members. 
     Referring particularly to  FIG.  18   , in some embodiments the surgical instrument  600  is configured with one or more connectors or contacts for inputting energy to the end effector  650  (e.g., energy for cauterization). For example, in some embodiments the surgical instrument may be configured to use monopolar RF, bi-polar RF, or another energy form. In such a case, in some embodiments the one or more connectors are located on a proximal area  613  of the handle  612 . Such a location can allow the one or more connectors to be readily accessible for connection with one or more cables that supply the energy. Such a location can also allow the connections to be made and/or disconnected while the surgical instrument  600  is coupled with an instrument drive system. 
     Referring to  FIG.  19   , the surgical instrument  600  can be selectively coupled with a compatible instrument drive system  700  (also referred to as pod  700 ) that defines a longitudinal axis  702  of a space configured to receive the surgical instrument  600 . In accordance with a typical implementation for computer-assisted tele-operated surgery, the instrument drive system  700  can be coupled to a manipulator assembly  800  with multiple degrees of freedom. In some embodiments, the pod  700  is readily detachable from the manipulator assembly  800  such that the pod  700  can be conveniently interchanged with another pod. The manipulator assembly  800  can be attached to a supporting structure of various types (e.g., refer to  FIGS.  3  and  4   ). The instrument shaft  640  can slidably extend through a cannula  740  that is optionally releasably mounted to the manipulator assembly  800  or to the instrument drive system  700 . 
     In the depicted embodiment, the surgical instrument  600  can be releasably coupled with the instrument drive system  700  by moving the surgical instrument  600  distally into an opening at the proximal end  704  of the instrument drive system  700 . In particular, the longitudinal axis  602  of the surgical instrument  600  can first be aligned with the longitudinal axis  702  of the instrument drive system  700 . Then the surgical instrument  600  can be slid distally in relation to the instrument drive system  700  until the instrument shaft engagement member  620  couples with the instrument drive system  700 . 
     At least portions of the handle  612  and the instrument shaft engagement member  620  extend farther radially than adjacent portions of the instrument drive system  700  while the surgical instrument is coupled with the instrument drive system, so that handle  612  protrudes out of pod  700 . Accordingly, the handle  612  and instrument shaft engagement member  620  are accessible to the hands of a user. Such accessibility can advantageously facilitate ready decoupling of the surgical instrument  600  from the instrument drive system  700 . 
     Although not visible, the instrument drive system  700  includes multiple actuators (schematically depicted in  FIGS.  9  and  11 - 14   ) that releasably couple with the actuator engagement members  632   a,    632   b,    634   a,    634   b,    636   a,    636   b,  and  638  while the surgical instrument  600  is coupled with the instrument drive system  700 . In some embodiments, the actuators are linear actuators that include lead screws and lead screw nut members, and other suitable linear actuators (e.g., chain, belt, hydraulic, pneumatic, electromagnetic, and the like) may be used. In some embodiments, non-linear actuators such as rotary actuators, or combinations of linear and non-linear actuators, may be used to produce the antagonistic force aspects as described. In some embodiments, one or more force sensors are included in the instrument drive system  700  by which forces applied to the actuator engagement members  632   a,    632   b,    634   a,    634   b,    636   a,    636   b,  and/or  638  can be determined and fed back to the processor  43  ( FIG.  2   ). 
     In some embodiments, the entirety of the surgical instrument  600  coupled to the instrument drive system  700  can be rotated or rolled about the longitudinal axes  602  and  702  as a single unit. The instrument actuator engagement member  620 , when coupled to pod  700  either via an instrument shaft insertion/withdrawal actuator or directly to pod  700 , is used to secure the instrument shaft during roll around longitudinal axis  602  as pod  700  rotates around its longitudinal axis  702 . In addition, handle  612  may provide extra support against pod  700  for roll. A motor at the distal end of pod  700 , either inside pod  700  or part of manipulator  800 , rotates the assembly of pod  700  and instrument  600 . Thus the instrument shaft, and the distal end effector, may be simultaneously inserted/withdrawn and rolled. 
     While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described herein as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system modules and components in the embodiments described herein should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single product or packaged into multiple products. 
     Particular embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In certain implementations, multitasking and parallel processing may be advantageous.