Patent ID: 12186047

DETAILED DESCRIPTION

The embodiments described herein can advantageously be used in a wide variety of grasping, cutting, and manipulating operations. In particular, the inverted flexure designs described herein can allow a single compliant segment (or compliant segment assembly) to deflect to produce both gripping motion and wrist motion of an end effector tool with respect to a mounting shaft. As described herein, the flexures are inverted so that the loads on the flexure are in tension and bending rather than in compression, thus avoiding buckling. The embodiments described herein include joints having an end effector tool (e.g., shears or grasper) with two degrees of freedom that minimizes or reduces friction. The embodiments described herein have mechanisms providing relatively low friction. The embodiments described herein include at least a two-degree-of-freedom tool at small scales, and that has a minimum or reduced number of parts. In other embodiments, however, a tool, a joint assembly, or both, has only one degree-of-freedom.

In some embodiments, an apparatus includes a shaft, a tool member, and a flexure. The shaft has a distal end portion and a proximal end portion, and defines a longitudinal axis therebetween. The distal end portion of the shaft includes a ground portion. The tool member has an engagement portion and an actuation portion. The engagement portion is disposed distally from the actuation portion, and can exert an engagement force on a target structure. The actuation portion receives an actuation force. The flexure has a first end portion and a second end portion. The first end portion is coupled to the ground portion of the shaft, and the second end portion is coupled to the tool member. The flexure is configured to deform elastically when the actuation force is exerted on the actuation portion of the tool member such that the tool member rotates relative to the shaft.

In some embodiments, an apparatus includes a shaft, a tool member, and a flexure. The shaft has a distal end portion and a proximal end portion, and defines a longitudinal axis therebetween. The distal end portion of the shaft includes a ground portion. The tool member has an engagement portion and an actuation portion. The engagement portion is configured to exert an engagement force on a target structure, and the actuation portion is configured to receive an actuation force at an attachment point. The flexure is coupled to the ground portion of the shaft and the tool member. The flexure is configured to deform elastically when the actuation force is exerted on the actuation portion of the tool member such that the tool member rotates relative to the shaft about a pivot axis. The actuation portion is configured such that the attachment point is spaced apart from the pivot axis in a direction normal to the longitudinal axis by a moment distance. The moment distance varies by less than about ten percent through an angular range of motion of the tool member.

In some embodiments, an apparatus includes a shaft, a first tool member, a second tool member and a flexure assembly. The shaft has a distal end portion and a proximal end portion, and defines a longitudinal axis therebetween. The distal end portion of the shaft includes a ground portion. The first tool member has a first engagement portion and a first actuation portion, the first actuation portion being configured to receive a first actuation force. The second tool member has a second engagement portion and a second actuation portion, the second actuation portion being configured to receive a second actuation force. The flexure assembly is coupled to the ground portion of the shaft and is disposed between a proximal-most surface of the first actuation portion and the first engagement portion, the first tool member, and the second tool member. A first portion of the flexure assembly is configured to deform elastically when the first actuation force is exerted on the first actuation portion of the tool member such that the first tool member rotates relative to the shaft. A second portion of the flexure assembly is configured to deform elastically when the second actuation force is exerted on the second actuation portion of the tool member such that the second tool member rotates relative to the shaft.

Methods of using a joint assembly are also described herein. In some embodiments, a method includes moving a shaft of a medical device such that an engagement portion of a tool member is placed in a delivery position relative to a target structure. The shaft defines a longitudinal axis. The tool member is coupled to a ground portion of the shaft via a flexure that is disposed between the engagement portion and a proximal-most surface of an actuation portion of the tool member. An actuation force is exerted on the actuation portion, and causes the flexure to deform elastically such that the tool member rotates relative to the shaft. The engagement portion of the tool member exerts an engagement force on the target structure when the tool member is rotated.

As used herein, the term “about” when used in connection with a referenced numeric indication means the referenced numeric indication plus or minus up to 10% of that referenced numeric indication. For example, the language “about 50” covers the range of 45 to 55. Similarly, the language “about 5” covers the range of 4.5 to 5.5.

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. Certain flexible components can also be resilient. For example, a component (e.g. a flexure) is said to be resilient if possesses the ability to absorb energy when it is deformed elastically, and then release the stored energy upon unloading (i.e., returning to its original state). 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's).

Flexibility is an extensive property of the object being described, and thus is dependent upon the material from which the object is formed as well as certain physical characteristics of the object (e.g., cross-sectional shape, length, boundary conditions, etc.). For example, the flexibility of an object can be increased or decreased by selectively including in the object a material having a desired modulus of elasticity, flexural modulus and/or hardness. The modulus of elasticity is an intensive property of (i.e., is intrinsic to) the constituent material and describes an object's tendency to elastically (i.e., non-permanently) deform in response to an applied force. A material having a high modulus of elasticity will not deflect as much as a material having a low modulus of elasticity in the presence of an equally applied stress. Thus, the flexibility of the object can be decreased, for example, by introducing into the object and/or constructing the object of a material having a relatively high modulus of elasticity. 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) DOFs of relative movement between the links. A short, flexible part may serve as, and be modeled as, a single mechanical constraint (a joint) that provides one or more DOF's between two links in a kinematic chain, even though the flexible part itself may be a kinematic chain made of several coupled links.

As used in this specification and the appended claims, the words “proximal” and “distal” refer to direction closer to and away from, respectively, an operator (or controller) of the surgical device. Thus, for example, the end of a joint assembly that is farthest away from the user (and that is closest to the target tissue) would be the distal end of the joint assembly, while the end opposite the distal end (i.e., the end manipulated by the user or coupled to the actuation shaft) would be the proximal end of the joint assembly.

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 the relationship of one element or feature to another element or feature as illustrated in the figures. These spatially relative terms are intended to encompass different positions (i.e., translational placements) and orientations (i.e., rotational placements) of a device in use or operation in addition to the position 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 term “below” can encompass both positions 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 spatial device positions and orientations. The combination of a body's position and orientation define the body'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.

In addition, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context indicates otherwise. The terms “comprises”, “includes”, “has”, and the like specify the presence of stated features, steps, operations, elements, components, etc. but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, or groups.

Unless indicated otherwise, the terms apparatus, joint mechanism, joint assembly, and variants thereof, can be interchangeably used.

Aspects of the invention are described primarily in terms of an implementation using a surgical system, such as, for example, the da Vinci® Surgical System, commercialized by Intuitive Surgical, Inc. of Sunnyvale, California Examples of such surgical systems are the da Vinci® Xi™ Surgical System (Model IS4000) and the da Vinci® Si™ HD™ Surgical System (Model IS3000). Knowledgeable persons will understand, however, that inventive aspects disclosed herein may be embodied and implemented in various ways, including computer-assisted, non-computer-assisted, and hybrid combinations of manual and computer-assisted embodiments and implementations. Implementations on da Vinci® Surgical Systems (e.g., the Model IS4000, the Model IS3000, the Model IS2000, the Model IS1200), or any other surgical assemblies, are merely presented as examples, and they are not to be considered as limiting the scope of the inventive aspects disclosed herein. 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.

FIGS.1and2are schematic illustrations of a compliant joint assembly100, according to an embodiment. The joint assembly100includes a shaft102, a tool member120, and a flexure171. The joint assembly100, and any of the joint assemblies described herein, can be used in any suitable surgical device or system as described herein. For example, the tool member120and the flexure171are optionally parts of an end effector, such as a gripper, shears, or the like. The shaft102can be coupled to the distal end of a surgical instrument shaft, either directly or via a wrist assembly that allows the end effector to change orientation (e.g., one or more of roll, pitch, and yaw) with reference to the shaft.

The shaft102has a proximal end portion112and a distal end portion113. The shaft102defines a longitudinal axis AL, along which the distal and proximal directions are defined (see, e.g., the arrow indicating the distal direction). The distal end portion113of the shaft102includes a ground portion110. The ground portion110is a part of, or fixedly coupled to, the shaft102, and serves as a point of attachment for the tool member120(via the flexure171).

The tool member120includes an engagement portion122and an actuation portion132. As shown inFIG.2, the engagement portion122is disposed distally from the actuation portion132, and is configured to exert an engagement force FENG on a target structure (not shown). The engagement portion122can include an engagement surface that forms an angle α. The engagement angle α is defined between the engagement surface and the longitudinal axis AL when the tool member120is in the resting (or undeflected) configuration. As described in more detail herein, in some embodiments, the angle α of the engagement surface can be selected so that the engagement surface remains flush with another structure (e.g., a second tool member, a fixed surface, a target structure or the like) throughout the range of angular motion of the tool member120. In some embodiments, for example, the tool member120can move relative to a fixed portion of a jaw (not shown) that is coupled to the shaft102. In other embodiments, the compliant joint assembly100can include multiple moving tool members (not shown) that cooperatively perform gripping or shearing functions.

The target structure can be internal or external tissue within a patient that is manipulated by the tool member. For example, a target tissue can be cancer cells, tumor cells, lesions, vascular occlusions, thrombosis, calculi, uterine fibroids, bone metastases, adenomyosis, or any other bodily tissue. Furthermore, the presented examples of target structures are not an exhaustive list. Moreover, a target structure can also include an artificial substance (or non-tissue) within or associated with a body, such as for example, a stent, a portion of an artificial tube, a fastener within the body or the like. The engagement portion122can be, for example, a gripping portion, a shear, or the like.

The actuation portion132is configured to receive an actuation force FACT to actuate the tool member120, as shown inFIG.2. The actuation force FACT can be exerted on the actuation portion132in any suitable manner and at any location. For example, although the actuation portion132is shown as receiving the actuation force FACT at a single point, in other embodiments, the actuation portion132can include multiple points of contact upon which an actuation force can be exerted. In some embodiments, the actuation force FACT can be exerted on the actuation portion132via a flexible cable, a rigid linkage (e.g., a push/pull rod) or any other suitable force-transmitting member (not shown inFIGS.1and2).

The tool member120is coupled to the ground portion110of the shaft102via the flexure171. More specifically, the flexure171has a first end portion173and a second end portion174. The first end portion173is coupled to the ground portion110of the shaft102, and the second end portion174is coupled to the tool member120. As shown inFIG.2, the flexure171is configured to deform elastically when the actuation force FACT is exerted on the actuation portion132of the tool member120such that the tool member120rotates relative to the shaft102, as shown by the arrow AA. Thus, the flexure171is a resilient member that stores energy from the actuation force FACT and releases the energy when the actuation force FACT is removed, thus allowing the tool member to repeatedly rotate relative to the shaft102. This arrangement results in a mechanism with low part count, reduced friction, and the ability to scale the device to smaller sizes, as compared to a traditional pin joint.

The flexure171and any of the flexures described herein can have any suitable shape and can be constructed from any suitable material to produce the desired flexibility, resilience, and durability during operation. For example, in some embodiments, the flexure171(and any of the flexures shown herein) can be a small rod-shaped member having a circular cross-sectional shape. In other embodiments, the flexure171(and any of the flexures shown herein) can be a thin, flat member having a rectangular cross-sectional shape. Moreover, in some embodiments, the flexure171(and any of the flexures shown herein) can be constructed from stainless steel, titanium, metallic glass, and the nickel titanium alloy Nitinol. Nitinol (also referred to as NiTi) includes nearly equal atomic percentages of nickel and titanium. NiTi can exhibit the superelastic effect and is therefore suitable for use in the compliant mechanisms described herein due to the large strains that it can undergo before yielding. Flexures constructed from NiTi can reach strains of between about 6% and about 8% with very small material set. Conversely, steels generally reach strains on the order of less than 1% before yielding.

As shown inFIGS.1and2, the tool member120is coupled to shaft102in a manner that produces an inverted configuration. Similarly stated, the tool member120is coupled to the shaft102in a manner such that the flexure171is placed in tension when the actuation force FACT is exerted on the actuation portion132of the tool member120during normal use. This arrangement eliminates the likelihood that the flexure171will be exposed to a buckling load, thereby improving the performance of the compliant mechanism. In some embodiments the inverted configuration is achieved by having the flexure171disposed between the engagement portion122and a proximal-most surface131of the actuation portion132, as shown inFIGS.1and2. In other embodiments, the tool member120is coupled to the shaft102such that the ground portion110of the shaft102is disposed between the engagement portion122and the proximal-most surface131of the actuation portion132. In yet other embodiments, the engagement portion122of the tool member120includes an engagement surface disposed distally from each of the actuation portion132, the ground portion110, and the flexure171.

Thus, the tool member120, flexure171and ground portion110are arranged to accommodate application of a tensile actuation force FACT. Although the actuation force FACT is shown as being parallel to the longitudinal axis AL and being solely in the proximal direction, in other embodiments, only a component of the actuation force FACT has a proximal direction. Said another way, the actuation force FACT (and any of the actuation forces described herein) can form a non-zero angle with the longitudinal axis AL.

As shown inFIG.2, during use the flexure171deforms to allow angular rotation of the tool member120relative to the shaft102. The range of motion of the flexure171, and therefore the tool member120can be modeled using a pseudo-rigid-body model. This is shown inFIGS.3and4, which are schematic illustrations of a compliant joint mechanism200according to an embodiment, that is represented as a pseudo-rigid-body model. The joint mechanism200is shown in a first configuration (FIG.3) and a second configuration (FIG.4). The joint mechanism200includes a shaft (not shown) having a ground portion210, a tool member220, and a flexure271. The joint assembly200, and any of the joint assemblies described herein, can be used in any suitable surgical device or system as described herein.

The shaft defines a longitudinal axis AL, along which the distal and proximal directions are defined (see, e.g., the arrow indicating the distal direction). The ground portion210is a part of, or fixedly coupled to, the shaft, and serves as a point of attachment for the tool member220(via the flexure271). The tool member220can be similar to the tool member120described above, and includes an engagement portion222and an actuation portion232. As shown inFIG.4, the engagement portion222is disposed distally from the actuation portion232, and is configured to exert an engagement force FOUT on a target structure (not shown). The engagement portion222can be, for example, a gripping portion, a shear, or the like.

The actuation portion232is configured to receive the actuation forces F1and F2to actuate the tool member220, as shown inFIG.4. The actuation forces F1and F2can be exerted on the actuation portion232in any suitable manner and at any location. For example, as shown inFIG.4, the actuation portion232includes a first connection point236at which the first actuation force F1is exerted. The actuation portion232includes a second connection point237at which the second actuation force F2is exerted. The actuation forces F1and F2can be exerted on the actuation portion232via a flexible cable, a rigid linkage (e.g., a push/pull rod) or any other suitable force-transmitting member (not shown inFIGS.3and4).

The tool member220is coupled to the ground portion210via the flexure271. More specifically, the flexure271has a first end portion273and a second end portion274. The first end portion273is coupled to the ground portion210, and the second end portion274is coupled to the tool member220. In this manner, the tool member220is coupled to shaft in a manner that produces an inverted configuration. Similarly stated, the tool member220is coupled to the shaft in a manner such that the flexure271is placed in tension when the actuation forces F1and F2are exerted on the actuation portion232of the tool member220during normal use. As shown, the inverted configuration is achieved by having the flexure271disposed between the engagement portion222and a proximal-most surface of the actuation portion232. Similarly, the tool member220is coupled to the shaft such that the ground portion210is disposed between the engagement portion222and the proximal-most surface of the actuation portion232. In some embodiments, the engagement portion222of the tool member220includes an engagement surface disposed distally from each of the actuation portion232, the ground portion210, and the flexure271.

In the pseudo-rigid-body model (PRBM), the motion can be approximated as that of a pin joint that rotates about a single point P with a torsional spring278. The pivot point P is referred to as the characteristic pivot, and is located half the distance of the flexure length from its fixed point (at the ground210). As shown inFIG.3, when the tool member220is in the undeflected position, the actuation forces F1and F2are exerted at the same position along the longitudinal axis AL as the characteristic pivot P. This arrangement minimizes the amount of cable stretch or cable slack in those embodiments in which the cable is attached to the same actuating spool (see, e.g.,FIG.17). In other embodiments, however, either the first connection point236or the second connection point237(or both) can be at any suitable position along the longitudinal axis AL. For example, in some embodiments, either the first connection point236or the second connection point237(or both) can be located distally from the characteristic pivot point P. In other embodiments, either the first connection point236or the second connection point237(or both) can be located proximally from the characteristic pivot point P.

As shown inFIG.4, the flexure271is configured to deform elastically when the actuation forces F1and F2are exerted on the actuation portion232of the tool member220such that the tool member220rotates relative to the shaft202, as shown by the arrow BB. This is modeled using the PRBM as the second end portion274of the flexure271rotating about the characteristic pivot P by an angle of 0.

Although the joint assemblies100and200are shown as including only a single tool member, in other embodiments, a joint assembly can include any number of tool members. For example,FIG.5is a schematic illustration of a joint mechanism300(also called “joint assembly300”) according to an embodiment. The joint mechanism300may be comprise a compliant mechanism. The joint mechanism300includes a shaft (not shown) having a ground portion310, a first tool member320, a second tool member340, and a flexure assembly370. The first tool member320and the second tool member340can be a portion of an end effector304for a surgical instrument. The joint mechanism300, and any of the joint assemblies described herein, can be used in any suitable surgical device or system as described herein.

The shaft defines a longitudinal axis AL, along which the distal and proximal directions are defined. The ground portion310is a part of, or fixedly coupled to, the shaft, and serves as a point of attachment for the first tool member320and the second tool member340(via the flexure assembly370). The first tool member320includes an engagement portion322and an actuation portion332. As shown inFIG.5, the engagement portion322is disposed distally from the actuation portion332, and is configured to exert an engagement force (not shown, similar to the force FOUT) on a target structure (not shown). Specifically, the engagement portion322includes an engagement surface323. Moreover, as shown inFIGS.7and8, the engagement portion322defines several characteristic points of contact, including the point P1(also identified as point324), the point P2(also identified as point325), and the point P3(also identified as point326, seeFIG.8).

The actuation portion332of the first tool member320is configured to receive the actuation forces (not shown, but similar to the forces F1and F2described above) to actuate the first tool member320. The actuation forces can be exerted on the actuation portion332in any suitable manner and at any location. For example, in some embodiments, the actuation forces can be exerted at a first actuation point336and a second actuation point337(seeFIG.9). Moreover, the actuation forces can be exerted on the actuation portion332via a flexible cable, a rigid linkage (e.g., a push/pull rod) or any other suitable force-transmitting member (not shown inFIG.5).

The second tool member340includes an engagement portion342and an actuation portion352. As shown inFIG.5, the engagement portion342is disposed distally from the actuation portion352, and is configured to exert an engagement force (not shown, similar to the force FOUT) on a target structure (not shown). Thus, the first tool member320and the second tool member340can together (or collectively) exert an engagement force on the target structure that is located between the engagement portion322and the engagement portion342. Specifically, the engagement portion342includes an engagement surface343. Moreover, the engagement portion342of the second tool member340can define several characteristic points of contact similar to the point P1, the point P2, and the point P3defined for the first tool member320. The actuation portion352of the second tool member340is configured to receive the actuation forces (not shown, but similar to the forces F1and F2described above) to actuate the second tool member340. The actuation forces can be exerted on the actuation portion352in any suitable manner and at any location. Moreover, the actuation forces can be exerted on the actuation portion352via a flexible cable, a rigid linkage (e.g., a push/pull rod) or any other suitable force-transmitting member (not shown inFIG.5).

The first tool member320and the second tool member340are coupled to the ground portion310via the flexure assembly370. The flexure assembly370includes a first flexure371and a second flexure (not shown inFIG.5). The first flexure371has a first end portion373and a second end portion374. The first end portion373is coupled to the ground portion310, and the second end portion374is coupled to the first tool member320. In this manner, the tool member320is coupled to the shaft in a manner that produces an inverted configuration, as described above.

As described above with reference to the joint mechanism200, the first flexure371is configured to deform elastically when the actuation forces are exerted on the actuation portion332of the first tool member320such that the first tool member320rotates relative to the shaft. This is modeled using the PRBM as the second end portion374of the first flexure371rotating about a characteristic pivot P.

In some embodiments, the engagement surface323and the engagement surface343are designed (or have an orientation) such that they close at upon each other throughout the entire range of motion of the joint mechanism300. In some embodiments, the engagement surface323and the engagement surface343are each planar, and are configured to be parallel to (“flush with”) each other when the first tool member320and the second tool member340close upon each other throughout the range of motion. In other embodiments, it may be desired for the tips of the engagement portions322,342to meet slightly ahead of the base of the engagement portions322,342, as shown inFIG.5(with contact occurring at or near point P2). In some instances, however, it can be undesirable for the base of the engagement portions322,342to meet prior to the tips of the engagement portions322,342meeting. To facilitate design of the first tool member320and the second tool member340to ensure that the engagement surfaces322,342contact as desired, the following kinematic analysis can be applied to the joint mechanism300.

As discussed above,FIGS.6and7identify three key points: the origin O (which is coincident with the characteristic pivot point P), and two points on the engagement surface323, point P1and point P2. In some embodiments, these three points can be collinear. Said another way, in some embodiments, the engagement surface323defines an engagement plane that intersects the pivot axis P. Moreover, the engagement plane can intersect the pivot axis P over the entire range of angular motion of the first tool member320. The range of motion for the first tool member320(and any of the tool members shown and described herein) can be within ±30 degrees, ±45 degrees, ±60 degrees, ±75 degrees, or ±90 degrees.

Based on the pseudo-rigid body model, the first tool member320and the second tool member340will each pivot about the characteristic pivot P, which is the same location as the origin O. Because the first tool member320and the second tool member340both pivot about this common point, the requirement of collinearity will ensure that the surfaces of the jaws always meet. Vectors from the origin O can be used to define points P1and P2. For the undeflected position, these vectors are defined as:
P1=(−x1)î+(1)ĵEq. (1):
P2=P1+[−(x2−x1)î+(2−1)ĵ]Eq. (2):
=(−x2)î+(2)jEq. (3):

With the assumption of collinearity, P2can be defined as P1multiplied by a scalar, c, as in:
P2=cP1Eq. (4):
(−x2)î+(2)ĵ=c[(−x1)î+(1)j]  Eq. (5):

Decomposing Eq. 5 into its I and J components yields the following constraints:
−x2=−cx1Eq. (6):
2=c1Eq. (7):

Substituting Eq. 6 into Eq. 7 will yield an equation which, if satisfied, ensures that the engagement surface323and the engagement surface343(also referred to as the faces of the two jaws) meet flush at any given angle of motion (within the bounds that will be discussed later). This equation is given as:

x1y1=x2y2Eq.⁢(8)

As discussed above, in other embodiments, it may be acceptable for the tips of the engagement portions322,342to meet slightly ahead of the base of the engagement portions322,342, as shown inFIG.5(with contact occurring at or near point P2). In such embodiments, the engagement plane does not intersect the pivot axis P. In some embodiments, for example, the engagement plane can define an angle α (seeFIG.7) with respect to the longitudinal axis AL that is greater than about 5 degrees.

Moreover, in some embodiments, the joint mechanism300(and any of the joint mechanisms described herein) can be modeled to define a third point, P3. The third point P3can be defined at some point near point P2but slightly offset from the engagement surface323, as shown inFIGS.7and8. Two more vectors can be used to define point P3—a vector from the origin to P3and a vector from P2to P3(P2,3). For simplicity, P2,3can be defined orthogonal to P2as in Eqs. 9 and 10 below. Furthermore, the offset distance, or magnitude of P2,3, can be defined as a fraction of the length of the tool member320(or jaw). For example, if djaw is used as a scalar, Eq. 11 can be used to determine the offset distance.
P2,3⊥P2Eq. (9):
P2·P2,3=0  Eq. (10):
∥P2,3∥=djaw∥P2−P1∥  Eq. (11):

To solve for P2,3, Eq. 10 can be expanded as shown in Eq. 12 where x23and y23represent the I and J components of P2,3, respectively. This provides one equation, but two unknown values. The expanded form of Eq. 11 can serve as a second equation and is shown in Eq. 13.
[(−x2)î+(2)ĵ]·[x23î+23ĵ]=0  Eq. (12):
√{square root over ((x23)2+(23)2)}=djaw√{square root over ((x1−x2)2+(2−1)2)}  Eq. (13):

These two equations can be solved simultaneously for x23and y23which results in the following equations:

x23=y2x1[djaw2(y2x1)2+1⁡[(x1-x2)2+(y2-y1)2]]12Eq.⁢(14)y23=[djaw2(y2x1)2+1⁡[(x1-x2)2+(y2-y1)2]]12Eq.⁢(15)

Once these points are calculated, the tool member (or jaw) can be designed to extend from P1to P3rather than from P1to P2. The derivation of these equations is based on the assumption that the small length flexural pivots of the two tool members320,340act purely as a pin joint.

To assess the accuracy of the kinematic modeling, a comparison between the pseudo-rigid body model and a finite element model was performed. The comparison was based on the joint mechanism300shown inFIGS.5-9. In particular,FIG.9shows the tool member320and the flexure371, but represents the flexure371as a solid member, rather than using the two-piece model with the characteristic pivot point P that is shown inFIGS.5-7. Additionally, the tool member320shown inFIG.9defines four points: one point at the bottom of the second end portion of the flexure371, one point at each of the input force locations on the actuation portion332(identified as points336and337), and one point at the distal-most tip of the engagement portion322(point P2,325). For the purpose of modeling, the dimensions for the tool member320were as shown in Table 1, below.

TABLE 1Geometric Design Boundary ConditionsParameterReference FIG.ValueL1FIG. 31.30mmL2FIG. 31.30mmL3FIG. 36.35mmαFIGS. 1, 2, 712.5degreeslFIG. 12.00mmwSee FIG. 1; width is normal to0.50mmt and ltFIG. 10.080mm

The plot shown inFIG.10shows the motion paths that each selected point follows as the tool member320is actuated to rotate from the undeflected configuration of 0 degrees to 45 degrees (shown by the arrow CC inFIG.10). As shown, the pseudo-rigid-body calculations and the finite element models agree closely with one another. Although the calculations and modeling above are described for the joint mechanism300with the boundary conditions as provided in Table 1, the general results are applicable to any of the joints shown and described herein, including all compliant joints described.

The joint mechanism300(and any of the other joint or compliant mechanisms described herein) can be configured to produce the desired mechanical advantage over the range of motion of the tool member. The mechanical advantage is defined as the ratio of the output force Fout (seeFIG.4) to the force input at the ends of the actuation portion332(see, e.g., the two actuation forces F1and F2inFIG.4). For example, in some embodiments, the mechanical advantage can be greater than 1. In other embodiments, however, the mechanical advantage can be less than 1, less than 0.8, less than 0.6, less than 0.4, less than 0.2, and any range therebetween.

Although the magnitude the two actuation forces F1and F2varies depending on the desired direction of actuation, if the actuating cables (not shown inFIGS.5-9) attached at the attachment points336,337are connected to a common spool, then as a force is applied to one cable, the force in the opposite cable goes to zero. For example, under this assumption if F1equals 2 N then F2is zero. This assumption is used in the derivation of the equations to calculate the mechanical advantage. Thus, the case where F1≥0 and F2=0 will be used to help illustrate the use of the derivations. As such, Fin is equal to F1. However, the derivations are also suited for the case where F2≥0 and F1=0. Mechanical advantage can be calculated using the principle of virtual work. This method provides an equation for F1as a function of output force Fout and rotation angle θ. After F1is calculated, the mechanical advantage is given by the ratio of Fout to F1. The first step in calculating the virtual work in the system is choosing a generalized coordinate. The most convenient variable in this case is the rotation angle θ. Next, each of the applied forces (F1and Fout) are written in vector form. In the derivations that follow, the rotation angle θ is defined to be positive in the counter-clockwise direction (seeFIG.4).
F1=−F1ĵEq. (16):
Fout=Fout(−cos(θ+α)î−sin(θ+α)ĵ)  Eq. (17):

Next, position vectors are written from the origin to the placement of the applied forces. As shown inFIG.7, the origin O is located at the characteristic pivot P, which is half the distance of the flexure length from the fixed point of the flexure.
Z1=L1cos(θ)î+L1sin(θ)ĵEq. (18):
Zout=(−L2cos θ−L3sin θ)î+(−L2sin θ+L3cos θ)ĵEq. (19):

The virtual displacement of the tool member320can now be calculated by differentiating the position vectors with respect to the generalized coordinate.
δZ1=(−L1sin θî+L1cos θĵ)δθ  Eq. (20):
δZout=[(L2sin θ−L3cos θ)î+(−L2cos θ−L3sin θ)ĵ]δθEq. (21):

The virtual work, δW, is calculated by taking the dot product of the force vectors from Eqs. 16 and 17 and the virtual displacement vectors from Eqs. 20 and 21.
δW1=(−F1L1cos θ)δθ  Eq. (22):
δWout=FoutL2[cos(θ)sin(θ+α)−sin(θ)cos(θ+α)]δθ+FoutL0[cos(θ)cos(θ+α)+sin(θ)sin(θ+α)]δθ  Eq. (23):

The virtual work due to the compliance of the flexure must also be accounted for. This is done by first determining the potential energy of the torsional spring (see, e.g., spring278in the model for the tool member220) that is used in the pseudo-rigid-body model.
V=½K(θ−θo)2Eq. (24):

In this equation θo is zero and the torsional spring constant, K, is defined as EI/l. Next, the virtual work is calculated by differentiating the potential energy with respect to the generalized coordinate and multiplying by −δθ.
δWspring=−KθδθEq. (25):

The total virtual work in the system is calculated by summing each component of virtual work from Eqs. 22, 23, and 25. Lastly, once the total virtual work is calculated, the principle of virtual work states that if the system is in equilibrium then the virtual work is equal to zero. This can be used to determine F1.

δ⁢⁢W=⁢(-F1⁢L1⁢cos⁢⁢θ)⁢δ⁢⁢θ+Fout⁢L2[cos⁡(θ)⁢sin⁡(θ+α)-sin⁡(θ)⁢cos⁢(θ+α)]⁢δ⁢⁢θ+Fout⁢L3⁡[cos⁡(θ)⁢cos⁡(θ+α)+sin⁡(θ)⁢sin⁡(θ+α)]⁢δ⁢⁢θ-EI⁢⁢θl⁢δ⁢⁢θ=⁢0Eq.⁢(26)⁢F1=Fout⁡(L2⁢sin⁢⁢α+L3⁢cos⁢⁢α)-EI⁢⁢θlL1⁢cos⁢⁢θEq.⁢(27)

In some embodiments, the actuation forces can include a preload (or nonzero forces applied at the first point336and the second point337). In this manner, the amount of backlash in the compliant mechanism can be reduced, thereby allowing improved control over the motion of the first tool member320and/or the second tool member340. In considering the calculations for the mechanical advantage, if an equal preload force is applied to both sides of the mechanism (i.e., equal preload in both actuation cables) then the input force term, F1, in Eq. 26 is replaced by (F1+Fp) where Fp is the preload force. The virtual work calculations would also need to account for the force at the point of F2where F2=Fp. This results in a slightly different expression for F1given by:

F1=Fout⁡(L2⁢sin⁢⁢α+L3⁢cos⁢⁢α)-EI⁢⁢θl+(L2-L1)⁢Fp⁢cos⁢⁢θL1⁢cos⁢⁢θEq.⁢(28)

Because Eqs. 27 and 28 include both geometric boundary conditions and material properties (e.g., Young's Modulus), to calculate the mechanical advantage of the joint mechanism300, material properties must also be selected. Table 2 includes an example set of material properties used to illustrate the mechanical advantage of a complaint mechanism, such as the joint mechanism300.

TABLE 2Material Property Design Boundary ConditionsParameterValueNotesDesired Fout0.5NE (Young's Modulus)95 GPaMetallic glass materialSy (Yield Strength)1800 MPaMetallic glass material

FIG.11is a plot showing the mechanical advantage for the compliant mechanism300as the tool member320is actuated to rotate from the undeflected configuration of 0 degrees to 45 degrees.FIG.12shows a 3-D “surface” plot of the required input force for a range of output forces from 0 to 2.0 N and a range of rotation of 0 degrees to 45 degrees. Although the calculations and modeling above are described for the joint mechanism300with the boundary conditions as provided in Table 1 and the material properties in Table 2, the general results are applicable to any of the compliant joints shown and described herein.

Although Table 1 includes geometric dimensions for one embodiment, in other embodiments, the size and the ratio of various components can be within any suitable range. For example, in some embodiments, the flexure371(and any of the flexures shown and described herein) can have any suitable length, width, and thickness to provide the desired resiliency and durability. Specifically, the largest stress within the joint mechanism300(or any of the mechanisms described herein) will occur in the flexure371. The stress in the flexure371is a combined result of bending and tension. To determine the desired dimensions and material properties, the magnitude and locations of the maximum stress can be modeled using finite element analysis. Specifically, the joint mechanism300having geometric dimensions as set forth in Table 1 and material properties as set forth in Table 2 was modeled using the ANSYS software package.

FIG.13is a plot of a finite element analysis showing the calculated stress of the tool member320shown inFIG.9when deflected at an angle of 45 degrees, and having an output force of 0.3 N.

Stress on the flexure371(or any of the flexures described herein) can also be calculated using the pseudo-rigid-body model, as described above. Specifically, the combined loading (moment and force) of the flexure is shown in a pseudo-rigid-body model inFIGS.14and15. Specifically,FIG.14shows a portion of a mechanism400having a flexure471that is coupled to a ground410. The mechanism400and the flexure471can be similar to any of the mechanisms and flexures, respectively, described herein. As shown inFIG.14, Mtot is the applied moment and Ftot is the total axial force applied to the flexure471.FIG.15shows the pseudo-rigid-body model of the flexure471, and shows a spring478and pivot point P. To model the deflection, the second end portion473of the flexure pivots about the pivot point P, as shown.

The stress within the flexure471can be calculated at any spatial location by summing the component of stress due to bending and the component due to axial tension, as shown in Eq. 29:

σ=Mtot⁢cI+FtotAEq.⁢(29)

where Mtot is the applied moment, c is the distance from the neutral axis to the point of interest, I is the second moment of area about the neutral axis, Ftot is the total axial force, and A is the cross-sectional area of the flexure471. The total force and moment can be determined by drawing a free-body diagram from the fixed point to the end of the flexure, as shown inFIG.15. Thus, the total force and moment are given by Eqs. 30 and 31:

Ftot=F1+F2+Fout⁢sin⁡(θ+α)Eq.(30)Mtot=F2⁢L2⁢cos⁢θ-F1⁢L1⁢cos⁢θ+Fout[L2⁢sin⁢α+(L3+l2)⁢cos⁢α]Eq.(31)

Using these equations, the maximum stress within the flexure471can be calculated when there is no output force applied. For this example, the dimensions for the flexure471(and associated tool member) are the same as those in Table 1. For a particular angle of rotation, for example, θ=−20 degrees, the input force, F1is calculated from Eq. 27 as 0.290 N. Substituting this value into Eqs. 30 and 31 gives the forces and moments associated with the stress calculations.

Ftot=0.290⁢⁢NEq.⁢(32)Mtot=⁢-0.290⁢(1.30⁢⁢cos-20)=⁢-0.354⁢⁢N·mm=⁢0.000354⁢⁢N·mEq.⁢(33)

These values can be substituted into Eq. 34 to calculate the maximum stress in the flexure471.

σmax=⁢(-0.354)⁢(-0.080⁢⁢mm2)(0.50⁢⁢mm)⁢(0.080⁢⁢mm)312+0.290(0.50⁢⁢mm)⁢(0.080⁢⁢mm)=⁢671⁢⁢MPaEq.⁢(34)

FIG.16is a graph showing the calculated stress, based on this modeling, over a range of motion of the tool member shown inFIGS.14and15. Although the calculations and modeling above are described for the compliant mechanism400with the boundary conditions as provided in Table 1, the general results are applicable to any of the compliant joints shown and described herein

Any of the compliant mechanisms described herein can be used in any suitable surgical assembly or instrument. For example,FIG.17shows a schematic illustration of a surgical instrument500according to an embodiment. The surgical instrument500includes an actuator assembly560, a shaft502and an end effector504. The actuator assembly560includes a series of actuation spools567about which a first cable561and a second cable562are disposed. As described herein, rotational motion of the spools567produces actuation forces (e.g., similar to the forces F1and F2described above) to actuate the end effector504.

The shaft502has a proximal end portion512and a distal end portion513. The shaft502defines a longitudinal axis, along which the distal and proximal directions are defined (see, e.g., the arrows indicating the proximal and the distal direction). The distal end portion513of the shaft502includes a ground portion510. The ground portion510is a part of, or fixedly coupled to, the shaft502, and serves as a point of attachment for the first tool member520and the second tool member540(via the flexure assembly570).

The end effector504includes a first tool member520, a second tool member540, and a flexure assembly570. The instrument500or the end effector504, and any of the joint assemblies described herein, can be used in any suitable surgical device or system as described herein. The first tool member520includes an engagement portion522and an actuation portion532. As shown inFIG.17, the engagement portion522is disposed distally from the actuation portion532, and is configured to exert an engagement force (not shown, similar to the force FOUT) on a target structure (not shown). The actuation portion532of the first tool member520is configured to receive the actuation forces (not shown, but similar to the forces F1and F2described above) to actuate the first tool member520. The actuation forces can be exerted on the actuation portion532via the cable562.

The second tool member540includes an engagement portion542and an actuation portion552. As shown inFIG.17, the engagement portion542is disposed distally from the actuation portion552, and is configured to exert an engagement force (not shown, similar to the force FOUT) on a target structure (not shown). The actuation portion552of the second tool member540is configured to receive the actuation forces (not shown, but similar to the forces F1and F2described above) to actuate the second tool member540. The actuation forces can be exerted on the actuation portion552via the cable561.

The first tool member520and the second tool member540are coupled to the ground portion510via the flexure assembly570. The flexure assembly570can include any suitable flexure or assembly of flexures to facilitate movement of the first tool member520and the second tool member540as described herein with respect to any of the compliant mechanisms shown. As shown, the flexure assembly570is positioned such that the first tool member520and the second tool member540are each coupled to the shaft502in a manner that produces an inverted configuration.

In use, the surgical instrument500can be used in any number of scenarios. For example,FIG.18shows a portion of the instrument500approaching a target structure T within a long, narrow lumen.FIG.19shows a pair of instruments500approaching a target structure T within a wider lumen that has restricted access at the bottom of the lumen.

Although the joint mechanism300and the modeling thereof was described for a range of motion of between ±45 degrees, in some embodiments, a compliant joint mechanism can have any suitable range of motion. Moreover, although the joint mechanism300is shown as having a decreasing mechanical advantage as the angle of rotation increases (see, e.g.,FIG.11), in other embodiments, a compliant joint mechanism can have a substantially constant mechanical advantage of its range of motion. For example, in some embodiments, a compliant joint mechanism can be configured such that the mechanical advantage varies by less than 20 percent over its range of motion (e.g. of 90 degrees). This arrangement permits a wider operating range through which grasping, cutting, and manipulating can be performed. Moreover, in some embodiments, a tool member can include an actuation portion that receives an actuation force in a manner that maintains a substantially constant moment arm throughout the range of motion. By maintaining a substantially constant moment arm, the actuation force can remain effective to rotate the tool member throughout a wide angular range.

For example,FIGS.20-31are various views of a compliant joint mechanism600(also “joint mechanism600” or “compliant mechanism600”) according to an embodiment. The joint mechanism600includes a shaft602having a ground member610, a first tool member620, a second tool member640, and a first flexure assembly670, and a second flexure assembly680. The first tool member620and the second tool member640can be a portion of an end effector604for a surgical instrument, such as the instrument500. The joint mechanism600can be used in any suitable surgical device or system as described herein.

The shaft defines a longitudinal axis along which the distal and proximal directions are defined. The distal end portion of the shaft602defines an opening (slot)615that allows the tool member to rotate through the desired range of motion. The distal end portion of the shaft602also includes a mounting portion614to which the ground member610is fixedly coupled. As shown inFIGS.22and23, the mounting portion614defines a pair of slots606that receive the ground member610.

The ground member610is fixedly coupled to the shaft602, and serves as a point of attachment for the first tool member620and the second tool member640(via the first flexure assembly670and the second flexure assembly680, respectively). The ground member610includes a first end portion616, a second end portion618, and a central portion617therebetween. Each of the first end portion616and the second end portion618are disposed within their respective mounting slot606. The central portion617is raised from the first end portion616and the second end portion618(i.e., the ground member610has an offset shape). As shown inFIG.23, the central portion617defines a series of openings619that mount the first flexure assembly670and the second flexure assembly680to the ground member610.

The first tool member620includes an engagement portion622and an actuation portion632. The engagement portion622is disposed distally from the actuation portion632, and is configured to exert an engagement force (not shown, similar to the force FOUT shown inFIG.4) on a target structure (not shown). Specifically, the engagement portion622includes an engagement surface623. Moreover, as shown inFIG.28, the engagement surface623defines an engagement plane (indicated by the dashed line inFIG.28). As described herein, the engagement plane intersects the characteristic pivot point (identified as CoR inFIG.28). Moreover, the engagement plane can intersect the pivot point over the entire range of angular motion of the first tool member620. This arrangement allows the engagement surface623and the engagement surface643to remain parallel to (“flush with”) each other when the first tool member620and the second tool member640close upon each other throughout the range of motion.

The actuation portion632of the first tool member620is configured to receive the actuation forces (see the forces F1and F2inFIG.28) to actuate the first tool member620. The actuation portion632includes a longitudinal portion (or arm)633, a lateral portion (or arm)635, and a spool638(also referred to as a pulley). The longitudinal arm633is substantially parallel to the longitudinal axis of the shaft602when the first tool member620is in the undeflected configuration (seeFIG.25). The longitudinal arm633defines a slot634through which the cable661passes. The lateral arm635is substantially normal to the longitudinal axis of the shaft602when the first tool member620is in the undeflected configuration (seeFIG.25). Although the lateral arm635is normal to the longitudinal arm633, in other embodiments, the lateral arm635can form any angle with the longitudinal arm633. The lateral arm635defines two openings605that mount the first flexure assembly670to the first tool member620.

The actuation forces can be exerted on the actuation portion632by the cable661shown inFIG.21. Specifically, the actuation forces can be exerted along the tangent points to the spool638. As shown inFIG.28, the spool638is a circular shaped member having a radius R. In use, the cable661exerts the actuation forces F1and F2at a first attachment point636and a second attachment point637, respectively. Because the actuation forces are exerted along the surface of the circular spool638, as the first tool member620rotates, the moment distance remains substantially constant. Similarly stated, because the actuation forces are not exerted at a fixed location on the actuation portion632, the attachment points remain spaced apart from the pivot point (in a direction normal to the longitudinal axis of the shaft602) by a substantially constant moment distance. This arrangement allows the mechanical advantage to remain substantially constant throughout the angular range of motion of the first tool member620.

Although the moment distance between the attachment points636,637and the pivot point CoR is described as being substantially constant throughout the angular range of motion of the first tool member620, in other embodiments, the moment distance can vary by less than ten percent. In other embodiments, the moment distance can vary by less than twenty percent.

The second tool member640includes an engagement portion642and an actuation portion652. The engagement portion642is disposed distally from the actuation portion652, and is configured to exert an engagement force (not shown, similar to the force FOUT shown inFIG.4) on a target structure (not shown). Thus, the first tool member620and the second tool member640can together (or collectively) exert an engagement force on the target structure that is located between the engagement portion622and the engagement portion642. Specifically, the engagement portion642includes an engagement surface643. Moreover, as shown inFIG.28with respect to the engagement surface623, the engagement surface643also defines an engagement plane that intersects the characteristic pivot point (identified as CoR inFIG.28). Moreover, the engagement surface643can intersect the pivot point over the entire range of angular motion of the second tool member640. This arrangement allows the engagement surface623and the engagement surface643to remain parallel to (“flush with”) each other when the first tool member620and the second tool member640close upon each other throughout the range of motion (see e.g.,FIG.31).

The actuation portion652of the second tool member640is configured to receive the actuation forces (see the forces F1and F2inFIG.28) to actuate the second tool member640. The actuation portion652includes a longitudinal portion (or arm)653, a lateral portion (or arm)655, and a spool658(also referred to as a pulley). The longitudinal arm653is substantially parallel to the longitudinal axis of the shaft602when the second tool member640is in the undeflected configuration (seeFIG.25). The longitudinal arm653defines a slot654through which the cable662passes. The lateral arm655is substantially normal to the longitudinal axis of the shaft602when the second tool member640is in the undeflected configuration (seeFIG.25). Although the lateral arm655is normal to the longitudinal arm653, in other embodiments, the lateral arm655can form any angle with the longitudinal arm653. The lateral arm655defines two openings651that mount the second flexure assembly680to the second tool member640. The actuation forces can be exerted on the actuation portion652by the cable662shown inFIG.21.

The actuation forces can be exerted on the actuation portion652by the cable662shown inFIG.21. Specifically, the actuation forces can be exerted along the tangent points to the spool658. As shown inFIG.28with respect to the first tool member620, the spool658is also a circular shaped member having a radius R. In use, the cable662exerts the actuation forces at attachment points that are along the surface of the circular spool658. Thus, as described above, when the second tool member640rotates, the moment distance remains substantially constant. Similarly stated, because the actuation forces are not exerted at a fixed location on the actuation portion652, the attachment points remain spaced apart from the pivot point (in a direction normal to the longitudinal axis of the shaft602) by a substantially constant moment distance. This arrangement allows the mechanical advantage to remain substantially constant throughout the angular range of motion of the second tool member640.

The first tool member620and the second tool member640are coupled to the ground portion610via the first flexure assembly670and the second flexure assembly680, respectively. The first flexure assembly670includes a pair of flexures671. Each of the flexures671has a first end portion that is coupled within a respective opening619defined by the ground member610. Each of the flexures671has a second end portion that is coupled within a respective opening605defined by the lateral arm635. In this manner, the first tool member620is coupled to the shaft602in a manner that produces an inverted configuration, as described above. As shown, the first flexure assembly670is disposed between the engagement portion622and a proximal-most surface of the actuation portion632. Moreover, the first tool member620is coupled to the shaft602such that the ground member610is disposed between the engagement portion622and the proximal-most surface of the actuation portion632.

The second flexure assembly680includes a pair of flexures681. Each of the flexures681has a first end portion that is coupled within a respective opening619defined by the ground member610. Each of the flexures681has a second end portion that is coupled within a respective opening651defined by the lateral arm655. In this manner, the first tool member620is coupled to the shaft602in a manner that produces an inverted configuration, as described above. As shown, the second flexure assembly680is disposed between the engagement portion642and a proximal-most surface of the actuation portion652. Moreover, the second tool member640is coupled to the shaft602such that the ground member610is disposed between the engagement portion642and the proximal-most surface of the actuation portion652.

As described above with reference to the joint mechanisms200and300, the flexures671are configured to deform elastically when the actuation forces are exerted on the actuation portion632of the first tool member620such that the first tool member620rotates relative to the shaft. This rotation is shown by the arrow DD inFIGS.25and29. The rotational motion can be modeled using the PRBM, which, as described above, models the flexures671as a pin joint rotating about a characteristic pivot. Referring toFIG.28, the characteristic pivot is identified as CoR. The characteristic pivot is also coaxial with a central axis629(also referred to as the axis of rotation) of the spool638(see e.g.,FIG.24). Thus, when the first tool member620is actuated, it rotates about the characteristic pivot CoR and the central axis629. Moreover, as described above, the spool638and the spool658are configured to produce a substantially constant moment distance through the angular range of motion of the first tool member620and the second tool member640, respectively. The range of motion for the first tool member620and the second tool member640can be within ±30 degrees, ±45 degrees, ±60 degrees, ±75 degrees, ±90 degrees, or greater than ±90 degrees.

FIGS.25,29-31show the joint mechanism600in a first configuration, second configuration, third configuration, and fourth configuration respectively. As shown, the first tool member620and the second tool member640can rotate about the shaft602independently of each other. Thus, the compliant joint mechanism600has two degrees of freedom (both wrist motion and gripping motion). Moreover, the range of motion for the first tool member620and the second tool member640can be within ±30 degrees, ±45 degrees, ±60 degrees, ±75 degrees, ±90 degrees, or greater than ±90 degrees. Specifically, because the actuation cables661and662are confined with the grooves of the spool638and the spool658, respectively, the moment distance throughout the entire range of motion remains substantially constant. Thus, the mechanical advantage (and therefore the performance) of the compliant joint mechanism600is consistent throughout the entire range of motion.

To assess the impact of the spool638,658on the mechanical advantage of the joint mechanism600over its range of angular motion, a mechanical advantage analysis was completed. The analysis compared the mechanical advantage profile of a tool member without a spool (similar to the tool member220) against the mechanical advantage profile of a tool member including a spool (similar to the tool member620). Specifically,FIGS.32A and32Bshow a tool member220′ (which has a fixed attachment point) andFIGS.33A and33Bshow a tool member620″ (which includes a spool638″).

Referring toFIGS.32A and32B, the tool member220′ includes an engagement portion222′ and an actuation portion232′. The engagement portion222′ is disposed distally from the actuation portion232′, and is configured to exert an engagement force FOUT on a target structure (not shown). The actuation portion232′ is configured to receive the actuation force FIN to actuate the first tool member220′. The actuation portion232′ includes a longitudinal portion (or arm)233′, a lateral portion (or arm)235′, and includes a connection point237′ at which the actuation force FIN is applied. The lateral arm235′ is coupled to a flexure271′ that is, in turn, coupled to a ground210′. The flexure271′ is configured to deform elastically when the actuation force FIN is exerted on the actuation portion232′ such that the tool member220′ rotates relative to the ground210′, as shown by the arrow XX. This is modeled using the PRBM as showing the tool member220′ rotating about the characteristic pivot P by an angle of θ.

For the L-Arm without a spool (as shown inFIGS.32A and32B), the mechanical advantage calculations are described below. First, the sum of the moments about the approximate center of rotation is:

Fin(lin⁢cos⁡(θ)-l2⁢sin⁡(θ))=T+Fout⁢loutEq.(35)

Where FINis the input force, lin is the perpendicular distance from the flexure271′ to the point at which the input force is applied (the connection point237′), θ is the angular deflection from the nominal (undeflected) state, T is the torque due to the modeled torsional spring at the center (pivot point P) of the flexure271′, FOUTis the output force at the tip of the jaw (or engagement portion222′), and lout is the perpendicular distance from center of rotation (P) to the output force FOUT. For this analysis lin is equal to the radius of the pulley, R, used in the analysis of the L-Arm mechanism with an integrated spool (seeFIGS.33A and33B). Using the pseudo-rigid-body model, the SFLP assumption the flexure is modeled as a pin joint with a torsional spring at the mid-length of the flexure271′. The torque, T, due to the torsional spring is defined as:

T=EIl⁢θEq.⁢(36)

Where E is the modulus of elasticity of the flexure, I is the second moment of area, and l is the flexure length. Substituting Eq. 36 into Eq. 35 and solving for the mechanical advantage, FOUT/FIN, results in the following:

MAnp=(1lin⁢cos⁡(θ)-l2⁢sin⁡(θ)⁢(EI⁢⁢θFout⁢l+lout))-1Eq.⁢(37)

Where MAnp is the mechanical advantage of the L-Arm mechanism without the integrated spool.

Referring toFIGS.33A and33B, the tool member620″ includes an engagement portion622″ and an actuation portion632″. The engagement portion622″ is disposed distally from the actuation portion632″, and is configured to exert an engagement force FOUT on a target structure (not shown). The actuation portion632″ is configured to receive the actuation force FIN to actuate the first tool member620″. The actuation portion632″ includes spool638′, which defines a connection point637″ at which the actuation force FIN is applied. The actuation portion632″ is coupled to a flexure671″ that is, in turn, coupled to a ground610″. The flexure671″ is configured to deform elastically when the actuation force FIN is exerted on the actuation portion632″ such that the tool member620″ rotates relative to the ground610″, as shown by the arrow YY. This is modeled using the PRBM as showing the tool member620″ rotating about the characteristic pivot P by an angle of θ.

For the tool member620″, the sum of the torques about the approximate center of rotation P is:
FinR=T+FoutloutEq. (38):

Where R is the radius of the spool638′. Solving for the mechanical advantage, FOUT/FIN, results in the following

MAp=(TFout⁢R+loutR)-1Eq.⁢(39)

Where MAnp is the mechanical advantage of the tool member620″ with the integrated spool638″. Substituting Eq. 36 into Eq. 39 results in the following:

MAp=(EI⁢⁢θFout⁢Rl+loutR)-1Eq.⁢(40)

Using the values in Table 3, below, the mechanical advantage for the L-Arm with and without the integrated spool was calculated as a function of angular deflection.FIG.34shows the mechanical advantage for a 3 mm L-Arm with the spool (e.g., tool member620″) and without the spool (e.g., tool member220′). Titanium was used for simplicity in the model. The material modulus of elasticity will only affect the shape of the curve, not the point at which the mechanical advantage becomes negative (for the L-Arm without a spool). The point at which the curve crosses zero is dictated by the effective moment arm for the input force, Fin. The plot also shows that the mechanical advantage of the L-Arm design with a spool has less variation compared to the L-Arm without a spool, and it never becomes negative. In some embodiments, a tool member (e.g., the tool member220or220′) without a spool can be actuated via cables up to 65 degrees before the mechanical advantage reaches zero. In contrast, in some embodiments, a tool member (e.g., the tool member620or620″) with a spool can be actuated over the desired range of motion, e.g., 90 degrees. Although the mechanical advantage is less than 1 for both designs shown, in some embodiments, electric motors can develop the torques necessary to obtain the desired output force at the tip of the instrument.

In some embodiments, the flexure671(and any of the flexures shown and described herein) can have any suitable length, width, and thickness to provide the desired resiliency and durability. Specifically, the largest stress within the compliant mechanism600(or any of the mechanisms described herein) will occur in the flexure671. The stress in the flexure671is a combined result of bending and tension. To determine the desired dimensions and material properties, the magnitude and locations of the maximum stress can be modeled using finite element analysis. Specifically, the compliant mechanism600having geometric dimensions and material properties as set forth in Table 3 was modeled using the ANSYS software package.

TABLE 3Geometric and Material Property Design Boundary ConditionsParameterValuePropertyValueFlexure length1.25 mmE (Young's Modulus)44.0 GPaFlexure thickness0.102 mmμ0.3Flexure width0.25 mmσASs440 MPaσASf472 MPaσSAs218 MPaσSAf206 MPaεL0.045α0

For the purposes of modeling, and for the fabrication of prototype versions of the compliant joint mechanism600, NiTi was selected for the flexure671. Although superelastic NiTi is commercially available in form factors including wire, rod, tubing, strip and sheet, a NiTi strip of 0.102˜mm (the smallest thickness available) and was used in the modeling described herein. Referring to Table 3, E is the modulus of elasticity of the NiTi in the austenite phase, μ is Poisson's ratio, σASs is the starting stress value of the forward phase transformation, σASf is the final stress value of the forward phase transformation, σSAs is the starting stress value of the reverse phase transformation, σSAf is the final stress value of the reverse phase transformation, εL is the maximum residual strain, and a is the material response ratio between tension and compression.

FIG.35is a schematic illustration of a portion of a flexure671′ of a compliant joint mechanism600′ that was used to model the flexure671of the actual compliant joint mechanism600. The modeled flexure671′ is coupled to a base610′, and the moment arm was modeled such that it is rigid in comparison to the flexure. A follower force was applied to the end of the moment arm to deflect the flexure671′. The mesh was refined in the flexure volume and approximately 30,000 elements were used.FIGS.36and37are plots of the finite element analysis showing the calculated stress of the flexure671(modeled as flexure671′). As shown, the modeling predicts that the flexure671can undergo angular deflections over ˜90 degrees before yielding occurs. Specifically,FIGS.36and37show the calculated stress of the flexure671(modeled as flexure671′) when deflected at an angle of about 88.6 degrees. At this deflection, the flexure has a total von Mises strain of 6.3%. For this strain level the flexure has an expected fatigue life of approximately 1000 cycles.

FIGS.38and39are photographs of a prototype compliant mechanism700. The compliant mechanism700was fabricated based on the design of the compliant mechanism600shown and described above.

Although the tool member620is shown as including an actuation portion632having centrally-located, fully circular spool630, and that defines a slot634through which the cables (e.g., cable661) can be wrapped about the spool638, in other embodiments a tool member can include any suitable spool design. For example, in some embodiments, a tool member can include any suitable spool (or pulley) design. For example, in some embodiments, a tool member can include a spool that is not fully circular (i.e., that is not a fully-enclosed circle). In some embodiments, for example, a spool can extend about 270 degrees about its center point, thus leaving the proximal portion open. In other embodiments, a spool can extend about 180 degrees about its center point.

Moreover, in some embodiments, a tool member can include a spool or pulley that is offset from a central axis (also referred to as the axis of rotation) of the actuation portion. For example,FIG.40shows a perspective view of a tool member820that can be used in any of the compliant mechanisms, end effectors, or surgical instruments described herein. The tool member820includes an engagement portion822and an actuation portion832. The engagement portion822is disposed distally from the actuation portion832, and is configured to exert an engagement force (not shown, similar to the force FOUT shown inFIG.4) on a target structure (not shown). Specifically, the engagement portion822includes an engagement surface823.

The actuation portion832of the first tool member820is configured to receive actuation forces (similar to the forces F1and F2shown and described with reference toFIG.28) to actuate the tool member820. The actuation portion832includes a longitudinal portion (or arm)833, a lateral portion (or arm)835, and a spool838(also referred to as a pulley). The longitudinal arm833is substantially normal to the lateral arm835. In contrast to the tool member620described above, the longitudinal arm833is devoid of any slot or “pass through” for cables. Instead, the spool838is offset from a centerline of the longitudinal arm833. As shown, the lateral arm835defines two openings805that mount the flexure assembly (not shown) to the tool member820.

Although the first flexure assembly670is shown as including two cylindrical flexures871, in other embodiments, a flexure assembly or any of the flexures described herein can include any suitable flexure. For example, any of the flexures described herein can be constructed from any suitable material and can have any suitable geometric shape to provide the desired resilience, durability, and the like. For example, in some embodiments, a flexure can be a thin, planar strip of material.FIGS.41-44show a compliant joint mechanism900according to an embodiment. The joint mechanism900includes a shaft902having a ground member910, a first tool member920, a second tool member940, and a first flexure971, and a second flexure972. The first tool member920and the second tool member940can be a portion of an end effector904for a surgical instrument, such as the instrument500. The joint assembly900can be used in any suitable surgical device or system as described herein.

The shaft defines a longitudinal axis along which the distal and proximal directions are defined. The distal end portion of the shaft902defines an opening (slot)915that allows the tool members to rotate through the desired range of motion. The distal end portion of the shaft902also includes a mounting portion914to which the ground member910is fixedly coupled. As shown inFIG.42, the mounting portion914defines a pair of slots that receive the ground member910.

The ground member910is fixedly coupled to the shaft902, and serves as a point of attachment for the first tool member920and the second tool member940(via the first flexure971and the second flexure972, respectively). The ground member910includes a first end portion, a second end portion, and a central portion therebetween. Each of the first end portion and the second end portion are disposed within their respective mounting slot906. The central portion917defines two openings919that receive the first flexure971and the second flexure972. In the case shown, the openings919are in the form of slots.

The first tool member920includes an engagement portion922and an actuation portion932. The engagement portion922is disposed distally from the actuation portion932, and is configured to exert an engagement force (not shown, similar to the force FOUT shown inFIG.4) on a target structure (not shown). The actuation portion932of the first tool member920is configured to receive the actuation forces (not shown, similar to the forces F1and F2inFIG.28) to actuate the first tool member920. The actuation portion932includes a spool938(also referred to as a pulley), and defines a slot934through which a cable (not shown) passes. In inner portion of the spool938defines an opening905within which the first flexure971is received to mount the first flexure971to the first tool member920. In the case shown, the opening905is in the form of a slot.

The second tool member940includes an engagement portion942and an actuation portion952. The engagement portion942is disposed distally from the actuation portion952, and is configured to exert an engagement force (not shown, similar to the force FOUT shown inFIG.4) on a target structure (not shown). The actuation portion952of the first tool member940is configured to receive the actuation forces (not shown, similar to the forces F1and F2inFIG.28) to actuate the second tool member940. The actuation portion952includes a spool958(also referred to as a pulley), and defines a slot954through which a cable (not shown) passes. In inner portion of the spool958defines an opening951within which the second flexure972is received to mount the second flexure972to the second tool member940. In the case shown, the opening951is in the form of a slot.

The first tool member920and the second tool member940are coupled to the ground portion910via the first flexure971and the second flexure972, respectively. Each of the first flexure971and the second flexure972have a first end portion that is coupled within a respective opening919defined by the ground member910. Each of the first flexure971and the second flexure972have a second end portion that is coupled within a respective opening905,951. In this manner, the first tool member920and the second tool member940are each coupled to the shaft902in a manner that produces an inverted configuration, as described above.

Although shown as being circular, in other embodiments, the spool638(or any other spool shown herein) can be any suitable shape. For example, in some embodiments, a spool can be elliptical shaped. For example,FIG.45shows a tool member1020having an elliptical shaped spool1038. The joint mechanism also includes a thin, planar flexure1071, similar to the flexure971described above.

In some embodiments, a joint assembly can include guide structures to guide the deflection of the flexures during use. For example, in some embodiments, a joint assembly can include guide structures on the shaft, ground portion, or any other suitable portion, that contact a portion of the flexure during use to guide the shape of deflection. For example,FIG.46shows a joint assembly1100that includes a tool member1120and a flexure1171. The flexure is coupled to a ground member1110, which also includes guide (or cam) surfaces1176. The guide surfaces1176can constrain the radius of curvature of the flexure and therefore limit the stress to a predetermined value. This arrangement can increase the angular rotation of the mechanism for a given geometry. The guide surfaces1176may also constrain the flexure in a way that decreases the variation in the center of rotation of the mechanism, therefore decreasing misalignment of the jaws when they are deflected.

FIG.47is a flow chart of a method10of manipulating an instrument, according to an embodiment. The method10can be performed using any of the devices, joint assemblies, or components thereof described herein. The method10includes moving a shaft of a medical device such that an engagement portion of a tool member is placed in a delivery position relative to a target structure, at12. The shaft defines a longitudinal axis, and the tool member is coupled to a ground portion of the shaft via a flexure that is disposed between the engagement portion and a proximal-most surface of an actuation portion of the tool member. The method further includes exerting an actuation force on the actuation portion, at16. The actuation force causes the flexure to deform elastically such that the tool member rotates relative to the shaft. In response, the engagement portion of the tool member exerts an engagement force on the target structure when the tool member is rotated.

While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Where methods and/or schematics described above indicate certain events and/or flow patterns occurring in certain order, the ordering of certain events and/or operations may be modified. While the embodiments have been particularly shown and described, it will be understood that various changes in form and details may be made.

For example, any of the tool members can be constructed from any material, such as medical grade stainless steel, nickel alloys, titanium alloys or the like. Further, any of the tool members, such as the tool member620, can be constructed from multiple pieces that are later joined together. For example, in some embodiments, a tool member can be constructed by joining together separately constructed components (e.g., the lateral arm, the spool, the longitudinal arm). In other embodiments, however, a tool member can be monolithically constructed. Similarly, in some embodiments a tool member can include an actuation portion, an engagement portion, and a spool that are monolithically constructed.

Although many of the joint mechanisms have been described herein as including a shaft having a ground portion (see, e.g., ground portion110and ground portion310) or a ground member (see, e.g., ground member610), in other embodiments, the ground portion or ground member of any of the joint mechanisms described herein can be coupled to any suitable portion of a medical device. For example, in some embodiments, a medical device can include a shaft, one or more wrist mechanisms, and one or more inverted joint mechanisms (of the types shown and described herein). In such embodiments, the ground portion (or member) of the inverted joint mechanism(s) can be coupled to a distal portion of a wrist mechanism, rather than being coupled directly to the shaft.

Although various embodiments have been described as having particular features and/or combinations of components, other embodiments are possible having a combination of any features and/or components from any of embodiments as discussed above. Aspects have been described in the general context of medical devices, and more specifically surgical instruments, but inventive aspects are not necessarily limited to use in medical devices.