DRAPE INTERFACE STRUCTURE

A drape interface structure including a frame defining an opening, a membrane spanning the opening of the frame, and a drive transfer element attached to the membrane and adapted to convey motion through the membrane. The membrane is of a material that can deform to form a plastically deformed region in the membrane in response to an initial movement of the drive transfer element relative to the frame, such that subsequent movements of the drive transfer element in the membrane have reduced resistance from the membrane.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to GB Patent Application No. 2213927.3, filed Sep. 23, 2022, which is incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

This invention relates to an interface structure which provides a sterile barrier. In one embodiment, the structure has a thin membrane, retained in a frame and covering an opening defined by the frame. The membrane may be capable of plastically deforming without tearing or detaching from the frame, meaning that a barrier is maintained, and no contaminants can pass through. The interface structure may have at least one drive transfer element retained in the membrane. Each drive transfer element may be adapted to convey motion through the structure.

BACKGROUND

In a surgical environment, it is particularly important that any components that cannot readily be disinfected between procedures are prevented from becoming contaminated during an operation.

Robots have become increasingly prevalent for use in surgical procedures. A surgical robotic assembly comprises a base which supports the robot, an arm and an instrument. The arm extends between the base and instrument. There is an interface between the instrument and the arm; at this interface, various instruments can be releasably connected to the arm and a driving mechanism in the arm can be used to manipulate the distal end of the instrument.

It is typically impractical to sterilise the base and arm of a robotic assembly without damaging the mechanical components and the large size presents further challenges when disinfecting and sterilising. As an alternative to disinfection and sterilisation, covering a surgical robot with a disposable covering is an effective barrier to prevent contamination. A surgical drape is a covering which envelops the base and arm of a surgical robot to separate a sterile field from an operative area where surgery is performed by the instrument.

At the interface between the robotic arm and instrument, the two components can suitably engage with each other so that the instrument is supported and can articulate to perform or assist with a surgical procedure. There is a need for an improved interface structure which can convey motion from the robotic arm to the instrument through a barrier during a surgical procedure while maintaining sterility.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a drape interface structure comprising a frame defining an opening; a membrane spanning the opening of the frame, and a drive transfer element attached to the membrane and adapted to convey motion through the membrane. The membrane is of a material that may deform to form a plastically deformed region in the membrane in response to an initial movement of the drive transfer element relative to the frame, such that subsequent movements of the drive transfer element in the membrane have reduced resistance from the membrane.

The membrane may be substantially taut such that the drive transfer element is held in the membrane

The membrane may deform, in response to the initial movement of the drive transfer element a distance along a drive path, to form the plastically deformed region having a length along the drive path of at least half of the distance moved along the drive path.

The membrane may deform, in response to the initial movement of the drive transfer element along a drive path, to form the plastically deformed region having a width perpendicular to the drive path of at least the width of the drive transfer element.

The membrane may deform, in response to the initial movement of the drive transfer element, to form the plastically deformed region such that the membrane surrounding the plastically deformed region is not plastically deformed.

The membrane may deform such that the subsequent movements of the drive transfer element in the plastically deformed region have substantially no resistance from the membrane.

The membrane may deform such that the subsequent movements of the drive transfer element in the plastically deformed region have reduced resistance from the membrane

A drape interface structure may comprise one or more further drive transfer elements, each further drive transfer element being attached to the membrane and adapted to convey motion through the membrane.

One or more further drive transfer elements may be adapted to convey motion through the membrane along respective drive paths, and the respective drive paths of the drive transfer elements may be parallel to one another.

The membrane may deform to form respective further plastically deformed regions in the membrane in response to an initial movement of each of the further drive transfer elements relative to the frame, such that subsequent movements of each of the further drive transfer elements in the membrane have reduced resistance from the membrane.

The membrane may deform, in response to the initial movement of each of the drive transfer elements, to form the respective plastically deformed regions such that the respective plastically deformed regions do not overlap.

The membrane may deform, in response to the initial movement of each of the drive transfer elements, to form the respective plastically deformed regions such that the respective plastically deformed regions do overlap.

According to a second aspect of the present invention there is provided a drape interface structure comprising a frame defining an opening, a membrane spanning the opening of the frame, and a drive transfer element attached to the membrane and adapted to convey motion along a drive path through the membrane. The membrane may be configured to have a lower resistance on the movement of the drive transfer element in a direction along the drive path and a higher resistance on the movement of the drive transfer element in a direction not along the drive path.

The membrane may comprise a material that is configured to have a lower resistance on the movement of the drive transfer element in a direction along the drive path and a higher resistance on the movement of the drive transfer element in a direction not along the drive path.

The membrane may comprise an anisotropic material.

The membrane may comprise a structure that is configured to have a lower resistance on the movement of the drive transfer element in a direction along the drive path and a higher resistance on the movement of the drive transfer element in a direction not along the drive path.

The membrane may be configured to have a highest resistance on the movement of the drive transfer element in a direction perpendicular to the drive path.

The membrane may be configured to have an increasing resistance on the movement of the drive transfer element with respect to the angle of the direction of the movement of the drive transfer element from the drive path.

The drape interface structure may comprise one or more further drive transfer elements, each further drive transfer element being attached to the membrane and adapted to convey motion through the membrane along a respective drive path.

The respective drive paths of the drive transfer elements may be parallel to one another.

The membrane may be configured to have a lower resistance on the movement of each of the further drive transfer elements in a direction along the respective drive paths and a higher resistance on the movement of each of the further drive transfer elements in a direction not along the respective drive paths.

The drive transfer element may comprise a recess on a first side of the membrane and a protrusion on the second side of the membrane.

The drive transfer element recess may be engageable with an interface protrusion, and the drive transfer element protrusion may be engageable with an interface recess.

The frame may comprise a securing fittings for securing the frame to a robot arm.

The drive path may be linear.

The frame and the drive transfer element may be heat welded to the membrane.

The material of the membrane may be a thermoplastic polymer.

The thermoplastic polymer material of the membrane may comprise one or more of high-density polyethylene or linear low-density polyethylene.

The material of the one or more drive transfer elements may comprise a non-elastomeric material.

The material of the one or more drive transfer elements may comprise polyethylene.

The material of the frame may comprise polyethylene.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art.

FIG.1shows a typical surgical robot100and associated control system106. A base101is shown which supports an arm102and an instrument103. The base provides stability by, for example, being rigidly attached to an operating theatre floor or attached to a trolley. The arm102is articulated by means of multiple flexible joints104along its length, used to position the instrument103in a suitable location for performing surgery. A surgical drape (not shown) may be attached at the interface105between the instrument103and arm100. The surgical instrument103is connected at the distal end of the robot arm102, it may be releasably attached.

The control system106includes a surgeon command interface109where commands are input. The control system106comprises a processor107and a memory108. The control system106is coupled to motors for driving motion of a drive assembly to articulate the instrument103.

A surgical robot arm102interface105is illustrated inFIG.2. The interface105comprises one or more robot arm interface elements201.FIG.2shows three robot arm interface elements201a,201b,201c. However, it will be appreciated that there may be a different number of robot arm interface elements201a,201b,201cdepending on the requirements on the driving structure. For example, the number of degrees of freedom of the instrument103may determine the number of drive inputs required which may in tern determine the number of robot arm interface elements201a,201b,201c.

The robot arm interface elements201a,201b,201care shown to comprise interface features202a,202b,202c. The robot arm interface features202a,202b,202care suitable for engaging with corresponding features in the instrument103.FIG.2shows that the robot arm interface features202a,202b,202ccomprise interface protrusions202a,202b,202c. However, it will be appreciated that the robot arm interface features202a,202b,202cmay additionally or alternatively comprise interface recesses202a,202b,202c. The selection of a protrusion or recess may depend on the requirements of the drive system, and the features present in the instrument103. The robot arm interface features202a,202b,202care located on the robot arm interface elements201a,201b,201c. For example, the robot arm interface features202a,202b,202cmay extend out of, for protrusions, or extend into, for recesses, the robot arm interface elements201a,201b,201c.

InFIG.2, the robot arm interface elements201a,201b,201care driven by respective lead screws203a,203b,203c. The lead screws203a,203b,203cmay rotate along a female threaded elements engaged with the lead screws203a,203b,203c. This causes the female threaded elements to move along the lead screws203a,203b,203c. The result is that the lead screws203a,203b,203cmay provide the robot arm interface elements201a,201b,201cwith linear drive. However, it will be appreciated that there may be different ways of driving the robot arm interface elements201a,201b,201c, which may result in different types of drive. For example, the robot arm interface elements201a,201b,201cmay be provided with rotational or irregular non-linear drive.

A surgical instrument103is illustrated inFIG.3. The instrument103comprises one or more instrument interface elements301.FIG.3shows three instrument elements301a,301b,301c. However, it will be appreciated that there may be a different number of instrument elements301a,301b,301cdepending on the requirements on the driving structure. For example, the number of degrees of freedom of the instrument103may determine the number of drive inputs required which may in tern determine the number of instrument interface elements301a,301b,301c.

The instrument interface elements301a,301b,301care shown to comprise interface features302a,302b,302c. The instrument interface features302a,302b,302care suitable for engaging with corresponding features in the robot arm102.FIG.3shows that the instrument interface features302a,302b,302ccomprise interface protrusions302a,302b,302c. However, it will be appreciated that the instrument interface features302a,302b,302cmay additionally or alternatively comprise interface recesses302a,302b,302c. The selection of a protrusion or recess may depend on the requirements of the drive system, and the features present in the robot arm102. The instrument interface features302a,302b,302care located on the instrument interface elements301a,301b,301c. For example, the instrument interface features302a,302b,302cmay extend out of, for protrusions, or extend into, for recesses, the instrument interface elements301a,301b,301c.

InFIG.3, the instrument interface elements301a,301b,301cdrive instrument cables303a,303b,303c. The instrument interface elements301a,301b,301care connected to the instrument cables303a,303b,303cand slide along straight bars. The result is that the instrument interface elements301a,301b,301cmay provide the instrument cables303a,303b,303cwith linear drive. However, it will be appreciated that there may be different ways of driving the instrument cables303a,303b,303c, which may result in different types of drive. For example, the instrument cables303a,303b,303cmay be provided with rotational or irregular non-linear drive. The instrument cables303a,303b,303care used to control the end effector elements of the instrument103.

A drape interface structure of all embodiments is illustrated inFIGS.4and5.

FIG.4shows the drape interface structure400. The drape interface structure400acomprises a frame401. As shown inFIG.4, the frame401comprises a substantially rectangular profile. However, other shapes for the frame401may be suitable, such as round shapes. Additionally, the edges of the frame401may be chamfered, rounded, or notched. In any event, the frame401preferably is shaped to fit with the structure to which it is attached. The frame401may also be a rigid frame. In other words, the frame401may substantially maintain its shape when under loading during operation. Alternatively, the frame401may not be a rigid frame. For example, the frame401may be provided by a drape surrounding the drape interface structure400.

The frame401may comprise a non-elastomeric material. In this way, the frame401may comprise the rigid structure which may substantially maintain its shape when under loading during operation. In particular, the frame401may comprise a polyolefin material, such as polyethylene or polypropylene. Additionally, the frame401may be made from more than one material. For example, the frame401may be made from high density polyethylene (HDPE) with a styrene-ethylene-butylene-styrene (SEBS) coating.

The outer edge of the frame401(the sides opposing the opening) may be attached to a surgical drape (not shown in the Figures). This surgical drape may be used to cover at least the arm102of the surgical robot100. The drape interface structure400may be retained within the drape or connect to it. In an embodiment, the surgical drape is attached to the drape interface structure400. A technician, surgeon or nurse may position the drape interface structure400between the robotic arm102and robotic instrument103prior to a surgical procedure. The drape interface structure400may be disconnected after a surgical procedure.

The frame401defines an opening. As shown inFIG.4, the opening is substantially rectangular. However, other shapes for the frame401may be suitable, such as round shapes. The opening is covered by a membrane403. The membrane403spans the opening of the frame401. In particular, the membrane403spans the full area of the opening such that there is a sterile barrier formed.

The membrane403may be heat welded to the frame401. The membrane403may be chemically bonded to the frame401, for example with adhesive. The membrane403may comprise a thermoplastic polymer. The membrane may comprise polyethylene. The membrane may comprise an aligned polymer film. In particular, the membrane403may comprise high-density polyethylene. Alternatively, or in addition, the membrane403may comprise linear low-density polyethylene. A single material or a combination of materials may be used in the membrane403to give the desired properties.

Thermoplastics are capable of being heated to a softened state and reshaped. Thermoplastic components may be well-suited to repeated processing and thermal attachment to other components. Several versatile manufacturing methods are commonly used to process thermoplastics such as injection moulding, blow moulding, and casting. Thermoplastic sheets are produced industrially by first blending the necessary raw materials, then heating and pressing through an extrusion die, then the extruded plastic is drawn into a sheet by the pressure applied between rollers. Several sets of rollers or multiple passes through rollers may be used to draw the sheet to a specific thickness while the thermoplastic is warm. Finally, the sheet is cooled and can then be cut to a desired size and shape.

Polyethylenes are a group of polymers with the chemical formula (C2H4)nas the repeat unit. The mechanical properties of polyethylene are influenced by the molecular weight and the extent of branching; highly branched polyethylene has a higher density and typically has a higher percentage crystallinity, meaning it is typically more brittle.

HDPE is made up of linear chains with less branching than the short branches in linear low-density polyethylene (LLDPE). Puncture-resistant thin films of LLDPE are readily processed. LLDPE has a structure composed of many short, branched chains, these branches have a low degree of cross linking between the chains so, in response to an applied tensile stress, the chains are free to slide over each other without becoming entangled. LLDPE has a low dispersity (a narrow distribution of molecular weight) so a higher degree of crystallinity can be achieved. LLDPE has similar strength to HDPE but is more flexible. Use of LLDPE for the material of the membrane403may provide good strength and flexibility.

The membrane403may have a thickness of less than 1 mm. The elongation at break of the film may be more than 600%. The density the film at room temperature may be 0.97 g/cm3plus or minus 10%. The elongation at break of the film may be more than 400%. If the film is an aligned film the elongation at break may be 1400% or more in the alignment direction

The frame401comprises securing fittings securing fittings402for securing the frame401to a structure. Preferably, the securing fittings402are capable of securing the frame401to the robot arm102. In particular, the securing fittings402are capable of securing the frame401to the interface105of the robot arm102. The securing fittings402may comprise a click-in lock, magnets, screws, or any other suitable types of securing fittings402. The securing fittings402are capable of engaging with a corresponding feature on the robot arm102. The securing fittings402may be a surface relief. As shown inFIG.4, the securing fittings402are positioned on a fin which extends away from the opening of the frame401. There may be more than one securing fittings402.FIG.4shows two securing fittings402which are located on opposite sides of the frame401. However, the number, and location, of securing fittings402may be varied depending on the force requirements on the securing fittings402. An operator, prior to a procedure, can position the frame401to releasably attach to an arm102and on the opposing side of the frame401releasably attach to an instrument103.

As shown inFIG.4, the drape interface structure400comprises a drive transfer element404. The drive transfer element404is attached to the membrane403. In other words, the drive transfer element404may be a separate component to the membrane403and attached thereto. The drive transfer element404may be heat welded to the membrane403. The drive transfer element404may be chemically bonded to the membrane403, for example with adhesive. The membrane403may be formed from a flat sheet with holes cut out such that the membrane403is attached to the sides of the drive transfer element404. Alternatively, the flat sheet of the membrane403could be bonded to the top or bottom surface of the drive transfer element404. Alternatively, the membrane403may be over moulded to the drive transfer element404. The membrane403may be substantially taut. In this way, the drive transfer element404may be held in the membrane404.

In an alternative embodiment, the membrane403may be joined to the frame401and drive transfer element404by laser welding. In a further alternative embodiment, the membrane403may have a backing film which is adhered to a surface of the membrane403to improve the bonding with the rigid parts and reinforce the membrane403. Lamination of polymer layers may be used to form a membrane403.

The drape interface structure400may further comprise a reinforcement member in the membrane403. The reinforcement member may be adjacent to the drive transfer element404. For example, the reinforcement member may comprise a ring which surrounds the drive transfer element404. The reinforcement member may comprise a different material to the membrane403. The reinforcement member may comprise a stiffer and/or stronger material than the membrane403. The reinforcement member may provide additional strength to the membrane403in the region where the membrane403and the drive transfer element404connect. In a region of the membrane403surrounding the drive transfer element404the shear forces may be higher. In this way, the reinforcement member may reduce the likelihood of tearing of the membrane403in the region surrounding the drive transfer element404.

Polyethylene (PE), which as described herein the membrane403may be manufactured from, is non-polar and may not readily react with solvents, meaning that adhesives and solvents may not be appropriate for joining PE parts to each other. Heat welding of PE parts is a simple and effective method of joining, which involves overlaying the parts to be attached and applying heat to soften the thermoplastic. An infrared emitter may be used to weld the membrane to the frame401and to the drive transfer element404. The thin membrane layer is suited to attachment by heat welding because it transmits heat well and melts to bond to a substrate. The strength of an attachment made by heat welding parts varies with the temperature used and the materials selected. A higher seal initiation temperature is needed for HDPE than LLDPE: HDPE melts in the temperature range 126° C. to 135° C., LLDPE melts in the temperature range 115° C. to 160° C. In this way, an LLDPE membrane403may have a lower seal initiation temperature.

The heat welding process fixes the membrane403to the rigid parts and a barrier to contaminants is produced. The frame401and drive transfer elements404a,404b,404cmay be made of the same material, for example a polymer, metal, or composite. The frame401and drive transfer element404may be made of dissimilar materials. A non-elastomer such as PE may be used to form the rigid parts.

The drive transfer element404is adapted to convey motion through the membrane403. The drive transfer element404may move with respect to the frame401in the membrane403. The membrane403may be flexible such that the drive transfer element404may move within the opening of the frame401.

The drive transfer element404may move along a drive path. The drive path may be a linear path. The drive path may be a circular path. The drive path may be irregular with linear and curved sections. In this case of linear drive paths, the drive path may follow a drive axis. The drive path may be determined by the structure that is driving the drive transfer element404.

As shown in more detail inFIG.5, the drive transfer element404may comprise a recess505on a first side of the membrane203. In particular, the drive transfer element recess505may be engageable with an interface protrusion202. The first side of the membrane403may, for example, face the robot arm102. In this case, the interface protrusion202is located on an interfacing element201of the robot arm102. Alternatively, the first side of the membrane403may face the instrument103. In this case, the interface protrusion202is located on an interfacing element201of the instrument103. As shown inFIG.5, the drive transfer element recess505may comprise a concave or semi-circular shape. In 3D this may provide a hemispherical recess. The interface protrusion202may comprise a corresponding shape, for example the convex or semi-circular shape. In 3D this may provide a hemispherical protrusion. This curved shape, or any other form of tapered shape, may provide self-locating when the interface protrusion202is engaged with the drive transfer element recess505. However, it will be appreciated that other shapes may be suitable depending on the locating and loading requirements on the drive structure. For example, the drive transfer element recess505may comprise a pyramid shape, a rectangular shape, or a cylindrical shape. It is preferable that the shape of the drive transfer element recess505and the interface protrusion202correspond to one another. In other words, the interface protrusion202should fit in the drive transfer element recess505. Preferably, the fit between the interface protrusion202and the drive transfer element505should be a snug, or an interference fit.

The drive transfer element404may comprise a protrusion405on a second side of the membrane403. In particular, the drive transfer element protrusion405may be engageable with an interface recess302. The second side of the membrane403may, for example, face the instrument103. In this case, the interface recess302is located on an interfacing element301of the instrument103. Alternatively, the second side of the membrane403may face the robot arm102. In this case, the interface recess302is located on an interfacing element301of the robot arm102. As shown inFIG.5, the drive transfer element protrusion405may comprise a convex or semi-circular shape. In 3D this may provide a hemispherical protrusion. The interface recess302may comprise a corresponding shape, for example the concave or semi-circular shape. In 3D this may provide a hemispherical recess. This curved shape, or any form of tapered shape, may provide self-locating when the drive transfer element protrusion405is engaged with the interface recess302. However, it will be appreciated that other shapes may be suitable depending on the locating and loading requirements on the drive structure. For example, the drive transfer element protrusion405may comprise a pyramid shape, a rectangular shape, or a cylindrical shape. It is preferable that the shape of the interface recess302and the drive transfer element protrusion405correspond to one another. In other words, the drive transfer element protrusion405should fit in the interface recess302. Preferably, the fit between the drive transfer element protrusion405and interface recess302should be a snug, or an interference fit.

In alternative embodiments, the drive transfer element404may comprise a recess505on both sides of the membrane403, or the drive transfer element404may comprise a protrusion405on both sides of the membrane403. In any event, the drive transfer element404may be provided with a suitable number and arrangement of recesses505and protrusions405depending on the structure of the robot arm102and instrument103on either side of the drive transfer element404.

The drive transfer element404may comprise a non-elastomeric material. The material properties of the drive transfer element404may be stiffer than the membrane403. In this way, the drive transfer element404may comprise the rigid structure which may substantially maintain its shape when under loading during operation. In particular, the drive transfer element404may comprise a polyethylene material. The drive transfer element403may comprise more than one material. For example, the drive transfer element403may comprise a stiffer core and a less stiff coating. In this way, the core may provide the rigid structure, and the coating may provide good adhering properties for connecting to other components. The drive transfer element404may be formed by moulding, casting and/or milling. In the case of milling, CNC milling may be used to form the drive transfer element protrusion406and/or drive transfer element recess405.

As shown inFIG.4, the drape interface structure400may comprise more than one drive transfer element404.FIG.4shows three drive transfer elements404a,404b,404c. It will be appreciated that there may be a different number of drive transfer elements404a,404b,404cdepending on the requirements on the driving structure. Each of the drive transfer elements404a,404b,404care attached to the membrane403. Each of the drive transfer elements404a,404b,404cmay be heat welded to the membrane403.

As seen inFIG.4, the opening of the frame defines a window in a notional coordinate system where the opening extends in the x and y directions. The area of the window is relatively larger than the drive transfer elements404a,404b,404c, such that a plurality of drive transfer elements404a,404b,404ccan fit within the window. A section of membrane403cut from a larger sheet has an area at least the size of the window, and may have an excess edge to attach to the frame. In the coordinate system, the motion of the drive transfer elements404a,404b,404cmay be a translation in the x, y, z direction, or some combination of these, the motion may also be a rotation.

Each of the drive transfer elements404a,404b,404care adapted to convey motion through the membrane403. Each of the drive transfer elements404a,404b,404cmay move with respect to the frame401in the membrane403. Each of the drive transfer elements404a,404b,404cmay move independently with respect to one another. The membrane403may be flexible such that each of the drive transfer elements404a,404b,404cmay move within the opening of the frame401.

Each of the drive transfer elements404a,404b,404cmay move along a respective drive path. The respective drive paths may be a linear path. The respective drive paths may be circular paths. The respective drive paths may be irregular with linear and curved sections. In this case of linear drive paths, the drive path may follow a drive axis. The respective drive paths may be next to one another. In the case of linear drive paths, the respective drive paths may be parallel to one another. In the case of curved or non-linear drive paths, the respective drive paths may maintain a constant distance to one another such that they are parallel at any individual point along the path. The respective drive paths may be determined by the structure that is driving each of the drive transfer elements404a,404b,404c.

One embodiment of the invention is illustrated inFIGS.6and7.

As shown inFIGS.4and6, the drive transfer element404is surrounded by the membrane403and held within the membrane403. In this way, the drive transfer element404may be held in an initial position. In the initial position, the drive transfer element404is supported by the tension in the membrane403. The membrane303is in a strained state in which tensile forces from the membrane403hold the drive transfer element404in place. In implementations where the membrane403is planar, this may hold or support the drive transfer element404substantially in the plane of the membrane403. The drive transfer element404preferably moves in the plane of the membrane403, rather than out of the plane of the membrane403. In this way, the tension in the membrane403may be reduced.

Any movement of the drive transfer element404in the membrane403would need to overcome the tension provided by the membrane403. As such, driving the drive transfer element404in the membrane403would need significant force. The tension force from the membrane403can also be inconsistent. High and/or inconsistent tension force from the membrane403can add additional loading on the driving elements and can make it difficult to control the position of the driving elements. The increased loading on the drive transfer elements can also result in less cable tension in the instrument103for a given motor torque. Additionally, increasing the tension in the membrane403can increase the likelihood of tearing of the membrane403. The tension can be particularly high when two drive transfer elements404are at opposite ends of travel, or are both a long way from their respective starting positions. Alternatively, tension can be particularly high in rotary drive when drive transfer elements404turn by a large angle. It can therefore be advantageous to reduce the level of tension in the membrane403.

As described herein, the drive transfer element404can be driven within the membrane403. As the membrane403is constrained by the frame401, movements in the membrane403are movements relative to the frame401. The membrane403can plastically deform in response to the drive transfer element404moving within the membrane403. In particular, an initial movement of the drive transfer element404causes the membrane403to form a plastically deformed region601in the membrane403. The plastically deformed region601is illustrated inFIG.6. The plastically deformed region601may include the part of the membrane403in which the drive transfer element404has initially moved around in. Alternatively, or additionally, the plastically deformed region601may be outside of the part of the membrane403in which the drive transfer element404has initially moved around in. The plastic deformation is a permanent deformation. As such, the plastically deformed region601may only be increased in size, and not decreased by subsequent movements of the drive transfer element400. Notwithstanding that there may be chemical or mechanical processes in which it is possible to reverse the deformation. The deformation may be permanent in such a way that the deformation may not be reversed easily in normal operation, or by the surgical system alone.

In response to the initial movement of the drive transfer element404, the membrane403may provide a reduced resistance on subsequent movements of the drive transfer element404. The plastically deformed region601of the membrane403provides a region of reduced resistance. Any subsequent movements of the drive transfer element404in the membrane403may have a reduced level of resistance. In the case of the plastically deformed region401being formed in the region of initial movements, any subsequent movements of the drive transfer element404in the plastically deformed region601may have a reduced level of resistance. A reduced level of resistance may be interpreted as the plastically deformed region601of the membrane403providing a lower level of resistance on the drive transfer element404than before the plastically deformed region601was formed. The reduced level of resistance may be due to the plastically deformed region601providing a significantly reduced level of tension force on the drive transfer element404.

As illustrated inFIG.6, the plastically deformed region601may surround the initial position of the drive transfer element404. This may be because any initial movement of the drive transfer element404may produce a surrounding plastically deformed region601. The perimeter of the plastically deformed region601may be defined by the maximum distance the drive transfer element404has moved from the initial starting point. In other words, any point in the membrane403to which the drive transfer element404has travelled my fall within the plastically deformed region601.

However, due to tension in the membrane, and/or other factors, the plastically deformed region601may not perfectly match the points to which the drive transfer element404has travelled. The membrane403may more readily deform in regions which are under higher stress during the movement of the drive transfer element404. Correspondingly, the membrane403may less readily deform in regions which are under lower stress during the movement of the drive transfer element404. The plastically deformed region601may be smaller or larger than the points to which the drive transfer element404has travelled. For example, if the drive transfer element404moves towards the edge of the membrane403, then the tension at that point may be high, and the plastically deformed region601may not reach the extreme point of travel. In another example, as the drive transfer element404moves, the plastically deformed region601may be wider that the width of the drive transfer element404. This may be because tension on the membrane403either side of the drive transfer element404may cause the plastically deformed region601to expand sideways.

The membrane403may comprise a homogeneous structure. The deformation regions601of a membrane403with a homogeneous structure may directly correspond to the regions of stress in the membrane during movement of the drive transfer element404. This is because the variation in deformation may only be as a result of the variation in stress across the membrane403. As a result, the plastically deformed region601may not perfectly match the points to which the drive transfer element404has travelled. Alternatively, the membrane403may comprise a non-homogeneous structure. For example, the membrane403may comprise a non-uniform thickness. The membrane403may comprise thicker regions and thinner regions. The thinner regions may be more likely to deform than the thicker regions. The membrane403may preferentially deform in thinner regions than in thicker regions. As another example, the membrane403may comprise a non-uniform deformability. The membrane403may comprise stiffer regions and less stiff regions. The less stiff regions may be more likely to deform than the stiffer regions. The membrane403may preferentially deform in stiffer regions than in less stiff regions. As a result, the deformation regions601of a membrane403with a non-homogeneous structure may not directly correspond to the regions of stress in the membrane during movement of the drive transfer element404. This is because the variation in deformation is not only as a result of the variation in stress across the membrane403and may also be due to the variation in deformability across the membrane403. As a result, the plastically deformed region601may not perfectly match the points to which the drive transfer element404has travelled.

Preferably, the membrane403surrounding the boundary of the plastically deformed region601is not plastically deformed. Plastically deforming the membrane403may cause the membrane403to be made thinner and/or slacker. In this way, the membrane403may be more susceptible to the sterile barrier being broken. It can be advantageous to keep the surround membrane403as not being plastically deformed such that the membrane403maintains the sterile barrier.

As described herein, the drive transfer element404may move along a drive path. The drive path may be a linear path. The drive path may be a circular path. The drive path may be irregular with linear and curved sections. In this case of linear drive paths, the drive path may follow a drive axis. The drive transfer element404may also convey rotational motion through the membrane403. In this example, the drive transfer element404may not move along a drive path. Instead, the drive transfer element404may rotate around the stationary point. In another embodiment, the drive transfer element404may both rotate and travel along a drive path404, such that the point of rotation also moves.

In response to an initial movement of the drive transfer element404along the drive path, the membrane403may form a plastically deformed region601which has a length of at least half of the distance moved along the drive path. In other words, if the drive transfer element404moves 20 mm along the drive path, then the plastically deformed region601will be at least 10 mm long. It will be appreciated that the dimensions are arbitrary, and are not necessarily representative of the drape interface structure400size. Preferably, the length of the deformed region601is as close as possible to the distance moved by the drive transfer element404. In this way, the region of reduced resistance may be larger. In some embodiments, the deformed region601may cover the entire membrane403. In this way, any subsequent movement of the drive transfer element404may have reduced resistance.

In response to an initial movement of the drive transfer element404along the drive path, the membrane403may form a plastically deformed region601which has a width of at least the width of the drive transfer element404. In other words, if the drive transfer element404is 5 mm wide, then the plastically deformed region601will be at least 5 mm wide. It will be appreciated that the dimensions are arbitrary, and are not necessarily representative of the drape interface structure400or drive transfer element size. Preferably, the width of the deformed region601is significantly wider the width of the drive transfer element404. In this way, the region of reduced resistance may be larger.

As described herein the plastically deformed region601is formed in response to an initial movement of the drive transfer element404. The plastically deformed region601may be expanded by means of subsequent movements of the drive transfer element404. For example, if, in a subsequent movement, the drive transfer element404moves beyond the boundary of the plastically deformed region601, the plastically deformed region601may further increase in size. In this way, the region of reduced resistance may be increased. This may be advantageous if the normal operating drive path is due to increase.

As described herein the plastically deformed region601may provide a region of reduced resistance when compared to the resistance before the membrane403was plastically deformed. Preferably, the plastically deformed region601provides a region of significantly reduced resistance on the drive transfer element404. For example, the level of resistance may be reduced by 50%. More preferably, the plastically deformed region601provides a region of substantially no resistance on the drive transfer element404. This may be interpreted as an insignificant level of resistance when compared to the resistance before the membrane403was plastically deformed, or when compared to the forces used in driving the drive transfer elements404.

The level of resistance on the drive transfer element404may not be constant over the plastically deformed region601. For example, the level of resistance may be higher at or near the perimeter of the plastically deformed region601. As such, it may be advantageous to carry out subsequent movements of the drive transfer element404within a subregion of the plastically deformed region601. Put another way, it may be advantageous to make the plastically deformed region601slightly larger than the region in which the drive transfer element404will subsequently move.

A method for operating the surgical robot100to form the plastically deformed region601is included below. The control system106of the surgical robot100is configured to initially drive the drive transfer element404in the membrane403relative to the frame401. The initial movement may be performed as part of a start up of the surgical robot100. Alternatively, the initial movement may be performed in response to a new instrument103being attached to the robot arm102. For example, this may be the first instrument103being attached during surgery. Moving the drive transfer element404may cause the membrane403to form a plastically deformed region601in the membrane403. The plastically deformed region401may provide a region of reduced resistance on the drive transfer element404. The control system106is configured to subsequently drive the drive transfer element404within the plastically deformed region601. The control system106may drive the drive transfer element404by means of an interface element201on the robot arm102. Additionally, the control system106may be configured to detect when the plastically deformed region601has been formed. For example, the control system106may comprise a sensor configured to monitor the resistance on the driving elements.

As described herein with reference toFIG.4, the drape interface structure400may comprise more than one drive transfer element404.FIG.4shows three drive transfer elements404a,404b,404c. The membrane403is configured to plastically deform in response to each of the drive transfer elements404a,404b,404cmoving within the membrane403. In particular, an initial movement of each of the drive transfer elements404a,404b,404ccauses the membrane403to form respective plastically deformed regions601a,601b,601cin the membrane403. The respective plastically deformed regions601a,601b,601care illustrated inFIG.6. The respective plastically deformed regions601a,601b,601cmay include the parts of the membrane403in which each of the drive transfer elements404a,404b,404cinitially moved around in.

In response to the initial movement of each of the drive transfer elements404a,404b,404c, the membrane403may provide a reduced resistance on subsequent movements of each of the drive transfer elements404a,404b,404c. The respective plastically deformed regions601a,601b,601cof the membrane403provide respective regions of reduced resistance. Any subsequent movements of each of the drive transfer elements404a,404b,404cin the respective plastically deformed regions601a,601b,601cmay have a reduced level of resistance.

In some situations, it may be suitable for the respective plastically deformed regions601a,601b,601cto not overlap. In this case, there may be a region which has not plastically deformed between each of the respective plastically deformed regions601a,601b,601c. This may provide a stronger sterile barrier in between each of the drive transfer elements404a,404b,404c. Alternatively, in other situations, it may be suitable for the respective plastically deformed regions601a,601b,601cto overlap. In this case, the respective plastically deformed regions601a,601b,601cmay form a continuous plastically deformed region601. A continuous plastically deformed region may provide reduced tension from the membrane403between the each of the drive transfer elements404a,404b,404c. This may be advantageous when each of the drive transfer elements404a,404b,404care being driven independently, and possibly in different directions at different times.

FIGS.7aand7bshow a side profile view of the structure seen inFIG.6.FIG.7ashows an initial position where the membrane403has not been plastically deformed and supports three drive transfer elements404a,404b,404c.FIG.7bshows a second position showing that the membrane403has been plastically deformed by the conveyed motion of at least one of the drive transfer elements404a,404b,404c.

FIG.7ashows two opposing sides of the frame401and the membrane403spanning between the sides. The drive transfer elements404a,404b,404care shown to have sides that are bonded to the membrane403. The membrane403is shown to be substantially thinner than the side of the drive transfer elements404a,404b,404c. As shown inFIG.7b, once the membrane403has been plastically deformed, it may no longer provide tension to support the drive transfer elements404a,404b,404c.

To allow for the deformation, the material of the membrane403has a high percentage strain-to-failure and low yield strength so the membrane403be elongated and permanently deformed while remaining as a continuous sheet between the rigid elements (frame401and the drive transfer elements404a,404b,404c). Additionally, the material of the membrane403may have a low maximum tensile strength beyond the yield point. In this way, the resistance is reduced during the period of plastic deformation. The membrane403is also relatively thinner than either the frame401or the drive transfer elements404a,404b,404cand provides minimal resistance to future motions conveyed by the drive transfer elements404a,404b,404c.

To further reduce the resistance on the drive transfer elements404a,404b,404cfrom the membrane403, the length of the drive paths, compared to distance between adjacent drive paths may be minimized. Preferably, the length of each of the adjacent drive paths is less than five times the distance between the adjacent drive paths. Similarly, to further reduce the resistance on the drive transfer elements404a,404b,404cfrom the membrane403, the length of the drive paths, compared to distance between the frame401and the adjacent drive transfer element may be minimized. Preferably, the length of each of the adjacent drive paths is less than five times the distance between the frame401and the adjacent drive path. As a result of both options, there may be a larger area of membrane403which is able to stretch between the drive transfer element404and the adjacent component (the adjacent drive transfer element404or the frame401) to which the drive transfer element404is moving relative. This may reduce the resistance on the drive transfer element404.

Another embodiment of the invention is illustrated inFIG.8.

As shown inFIGS.4and8, the drive transfer element404is surrounded by the membrane403and held within the membrane403. In this way, the drive transfer element404may be held in an initial position. In the initial position, the drive transfer element404is supported by the tension in the membrane403. The membrane303is in a strained state in which tensile forces from the membrane403hold the drive transfer element404in place. In implementations where the membrane403is planar, this may hold or support the drive transfer element404substantially in the plane of the membrane403.

Any movement of the drive transfer element404in the membrane403would need to overcome the tension provided by the membrane403. As such, driving the drive transfer element404in the membrane403would need significant force. The tension force from the membrane403can also be inconsistent. High and/or inconsistent tension force from the membrane403can add additional loading on the driving elements and can make it difficult to control the position of the driving elements. The increased loading on the drive transfer elements can also result in less cable tension in the instrument103for a given motor torque. Additionally, increasing the tension in the membrane403can increase the likelihood of tearing of the membrane403. The tension can be particularly high when two drive transfer elements404are at opposite ends of travel, or are both a long way from their respective starting positions. Alternatively, tension can be particularly high in rotary drive when drive transfer elements404turn by a large angle. It can therefore be advantageous to reduce the level of tension in the membrane403.

As described herein, the drive transfer element404can be driven within the membrane403. As the membrane403is constrained by the frame401, movements in the membrane403are movements relative to the frame401. The membrane403is configured to have a lower resistance on the movement of the drive transfer element404in a direction along the drive path. The membrane403is also configured to have a higher resistance on the movement of the drive transfer element404in a direction not along the drive path. This is illustrated by the lines in the membrane403inFIG.8. As a result, when the drive transfer element404is driven along the drive path, then the resistance from the membrane403is less than if the drive transfer element404were to be driven in a different direction which is not along the drive path. It is possible that the membrane403may be configured to have other directions in which resistance is at a lower level. For example, the resistance in directions close to the drive path may have similarly low resistance levels. However, the resistance in the direction of the drive path is lower than the resistance in at least one direction not in the direction of the drive path.

Preferably, the resistance on the movement of the drive transfer element404in the direction along the drive path is the lowest level of resistance of all of the directions within the membrane403. For example, once the angle of the direction of the drive transfer element404moves away from the drive path, then the level of resistance may increase. In particular, membrane403may be configured to have increasing resistance on the movement of the drive transfer element404with respect to the angle of the direction of movement of the drive transfer element404from the drive path. Merely by way of example, if the angle of the direction of movement of the drive transfer element404is 0° then it may have a lower resistance than 15°, which may in turn have a lower resistance than 30°. The increase in resistance with respect to angle of the direction of movement of the drive transfer element404from the drive path may increase linearly. Alternatively, increase in resistance with respect to angle of the direction of movement of the drive transfer element404from the drive path may increase non-linearly, for example as defined by function of angle. The relation between the resistance and the angle of the direction of movement of the drive transfer element404from the drive path may depend on the configuration of the membrane403.

Preferably, the membrane403is configured to have the highest level of resistance on the movement of the drive transfer element404in a direction perpendicular to the drive path. In other words, if the drive transfer element404is moved in a direction significantly from the drive path, then the resistance will be significantly higher. As described herein, as the level of resistance may increase with the angle of the direction of movement of the drive transfer element404from the drive path, the level of resistance may be a maximum in a direction 90° from the drive path. The level of resistance may increase with angle of the direction of movement of the drive transfer element404from the drive path between 0° and 90°. The level of resistance may decrease with angle of the direction of movement of the drive transfer element404from the drive path between 90° and 180°.

Although the level of resistance may be higher in directions which angle away from the direction of movement of the drive transfer element404, it can be preferable that the level of resistance in all directions is substantially lower that the force available to drive the drive transfer elements404. In this way, any movement of the drive transfer element404should not be significantly resisted by the membrane403.

As shown inFIGS.7aand7b, and as described herein, the membrane403may comprise a thin-skinned structure. Preferably, the drive transfer element404is configured to be driven in the plane of the thin-skinned membrane403. As such, the variation of the resistance with angle of the direction of movement of the drive transfer element404from the drive path may be in the plane of the membrane403. For example, a movement perpendicular to the drive path would be in the plane of the membrane403at 90° from the drive path. However, in embodiments where the membrane403is not thin-skinned and/or planar, the resistance may also vary with angle of the direction of movement of the drive transfer element404from the drive path, in which the angle is with respect to the plane of the drive path. For example, the resistance may increase if the drive transfer element404moves above or below the membrane403.

It may be advantageous to provide a lower resistance in the direction along the drive path and a higher resistance in a direction not along the drive path. For example, a lower resistance along the drive path may reduce the resistance on the drive transfer element404during operation, i.e. when the drive transfer element404is being driven along its operating path. This may reduce the loading on the driving elements which may also make it easier and more accurate to control the position of the driving element. Additionally, a higher resistance in a direction not along the drive path may force the drive transfer element404to be pushed back to its operating path, i.e. if the drive transfer element404has been displaced from the drive path. The increased loading on the driving elements from the increase resistance may also provide feedback to the control system106that the drive transfer element404is not on the operating path.

The membrane403may comprise a material that is configured to have a lower resistance on the movement of the drive transfer element404in a direction along the drive path. The material may also be configured to have a higher resistance on the movement of the drive transfer element404in a direction not along the drive path. In other words, the variation in the resistance with respect to angle of the direction of movement of the drive transfer element404from the drive path may be due to the material of the membrane403. To achieve this, the properties of the material may be varied in different directions. For example, the material may be configured to have higher elasticity in the direction of the drive path, and a have lower elasticity in directions not in the direction of the drive path.

In particular, the material may have anisotropic properties. As an example, the material may comprise a laminated structure. For example, a polymer and/or composite structure. The laminated structure may be layered up in such a way that the more flexible structures run in the direction of the drive path, and the stiffer structures run in the direction perpendicular to the drive path. For example, the laminated structure may be layered up in such a way that the fibres of the material run in the direction perpendicular to the drive path, so that the fibres may be pulled apart in the direction of the drive path, which may result in lower resistance. In particular, the membrane403may comprise a substrate layer, adhesive layer, and a capping layer sandwiched together. Further layers of each type of layer may be used to build up the thickness and/or alter the properties of the membrane403. It will be appreciated that there may be other techniques for providing anisotropic properties to a material.

The membrane403may comprise a structure that is configured to have a lower resistance on the movement of the drive transfer element404in a direction along the drive path. The structure may also be configured to have a higher resistance on the movement of the drive transfer element404in a direction not along the drive path. In other words, the variation in the resistance with respect to angle of the direction of movement of the drive transfer element404from the drive path may be due to the structure of the membrane403. To achieve this, the arrangement of the structure may be varied in different directions. For example, the structure may be configured to have higher elasticity in the direction of the drive path, and a have lower elasticity in directions not in the direction of the drive path.

As an example, the membrane403may comprise corrugations running in the direction perpendicular to the drive path. This may be illustrated by the lines inFIG.8. In this way, the membrane403may be configured to fold up when the drive transfer element404is driven along the drive path. The folding of the membrane403may provide significantly lower resistance than stretching the membrane403material itself. As such, if the drive transfer element404were to move perpendicular the drive path, then the resistance would be significantly higher.

The membrane403may comprise a material and a structure that is configured to have a lower resistance on the movement of the drive transfer element404in a direction along the drive path. The material and the structure may also be configured to have a higher resistance on the movement of the drive transfer element404in a direction not along the drive path. In other words, the variation in the resistance with respect to angle of the direction of movement of the drive transfer element404from the drive path may be due to the material and the structure of the membrane403. To achieve this, the properties of the material and the arrangement of the structure may be varied in different directions. For example, the material and the structure may be configured to have higher elasticity in the direction of the drive path, and a have lower elasticity in directions not in the direction of the drive path. As a result of varying both the material and the structure of the membrane403, there may be further scope for fine tuning the resistance with respect to angle of the direction of movement of the drive transfer element404from the drive path.

As described herein with reference toFIG.4, the drape interface structure400may comprise more than one drive transfer element404.FIG.4shows three drive transfer elements404a,404b,404c. The membrane403is configured to have a lower resistance on the movement of each of the drive transfer elements404a,404b,404cin a direction along the respective drive paths. The membrane403is also configured to have a higher resistance on the movement of each of the drive transfer elements404a,404b,404cin a direction not along the respective drive paths. This is illustrated by the lines in the membrane403inFIG.6. As a result, when each of the drive transfer elements404a,404b,404care driven along their respective drive paths, then the resistance from the membrane403is less than if each of the drive transfer elements404a,404b,404cwere to be driven in a different direction which is not along their respective drive path.

As described herein, the each of the drive transfer elements404a,404b,404cmay move along a respective drive path. In the case of parallel drive paths, the membrane403may be configured to have a lower resistance in the direction of all the drive paths. In this way, each of the drive transfer elements404a,404b,404cmay be provided with the lower resistance. However, in embodiments in which the respective drive paths are not parallel, the direction of lower resistance may only align with one or more of the drive paths. For example, if there are three the drive transfer elements404a,404b,404ceach with drive paths in different directions, then the direction of lower resistance may be aligned with one of the drive transfer elements404a,404b,404c. Preferably, the drive transfer element404a,404b,404cselected to have the lowest resistance from the membrane403may be the drive transfer element404a,404b,404cwith the longest range of travel, or highest amount of operational use. Alternatively, the membrane403may be configured such that, even if the drive paths are not parallel, the membrane403still has a low level of resistance for each of the drive transfer elements404a,404b,404c. For example, the membrane403may comprise regions for each of the drive transfer elements404a,404b,404cin which the resistance on the individual drive transfer element404a,404b,404cin the direction of movement is lower and the resistance on the individual drive transfer element404a,404b,404cnot in the direction of movement is higher.

To further reduce the resistance on the drive transfer elements404a,404b,404cfrom the membrane403, the length of the drive paths, compared to distance between adjacent drive paths may be minimized. Preferably, the length of each of the adjacent drive paths is less than five times the distance between the adjacent drive paths. Similarly, to further reduce the resistance on the drive transfer elements404a,404b,404cfrom the membrane403, the length of the drive paths, compared to distance between the frame401and the adjacent drive transfer element may be minimized. Preferably, the length of each of the adjacent drive paths is less than five times the distance between the frame401and the adjacent drive path. As a result of both options, there may be a larger area of membrane403which is able to stretch between the drive transfer element404and the adjacent component (the adjacent drive transfer element404or the frame401) to which the drive transfer element404is moving relative. This may reduce the resistance on the drive transfer element404.

The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.