Compact force sensor for catheters
An ablation catheter system configured with a compact force sensor at a distal end for detection of contact forces exerted on an end effector. The force sensor includes fiber optics operatively coupled with reflecting members on a structural member. In one embodiment, the optical fibers and reflecting members cooperate with the deformable structure to provide a variable gap interferometer for sensing deformation of the structural member due to contact force. In another embodiment, a change in the intensity of the reflected light is detected to measure the deformation. The measured deformations are then used to compute a contact force vector. In some embodiments, the force sensor is configured to passively compensate for temperature changes that otherwise lead to erroneous force indications. In other embodiments, the system actively compensates for errant force indications caused by temperature changes by measuring certain local temperatures of the structural member.
1 . A force sensor for use at a distal tip of a catheter, comprising:
a structural member that defines a longitudinal axis and includes a plurality of segments defining one or more slots therebetween;
a plurality of fiber optics operatively coupled with the structural member, each of the plurality of fiber optics having a distal end that is proximate a corresponding reflecting member to define a respective gap therebetween, each of the plurality of fiber optics being oriented to emit light across the respective gap and onto the corresponding reflecting member,
wherein the structural member is configured to produce a change in a dimension of at least one of the respective gaps in response to a force exerted on the distal tip of the catheter;
wherein a rotational displacement of each of the plurality of fiber optics and the corresponding reflecting members relative to a plane of y-y inertial axes is between about 60° and about 90°; and
wherein a sensitivity of each of the respective gaps is optimized with respect to lateral force components.
2 . The force sensor of claim 1 , wherein the distal ends of the plurality of fiber optics are adapted for collection of at least a portion of the light reflected from the corresponding reflecting member.
3 . The force sensor of claim 1 , wherein the structural member further comprises:
a first segment and a second segment that are adjacent each other along the longitudinal axis, the first segment and the second segment defining a first slot therebetween, the first slot being bridged by a first flexure, and
a third segment adjacent the second segment along the longitudinal axis, the second and third segments defining a second slot therebetween, the second slot being bridged by a second flexure.
4 . The force sensor of claim 3 , wherein the first flexure is centered about a first flexural axis that is parallel to the longitudinal axis, the second flexure is centered about a second flexural axis that is parallel to the longitudinal axis, and wherein the first flexural axis, the second flexural axis, and the longitudinal axis are substantially coplanar.
5 . The force sensor of claim 3 , further comprising at least two temperature sensors, each configured to detect a temperature of the structural member, a first of the at least two temperature sensors being centered substantially at an interface of the first flexure and the second segment, and a second of the at least two temperature sensors being centered substantially at an interface of the second flexure and the second segment.
6 . The force sensor of claim 3 , wherein the rotational displacement of the plurality of fiber optics and the corresponding reflecting members is such that each of the plurality of fiber optics and the corresponding reflecting members is either at or close to 90° relative to a plane of inertial axes of the first flexure and the second flexure.
7 . The force sensor of claim 1 , wherein each of the respective gaps is a Fabry-Perot resonator.
8 . The force sensor of claim 1 , wherein the force sensor is configured to passively compensating for changes in the dimensions of the respective gaps that are caused by temperature changes.
9 . The force sensor of claim 1 , wherein the corresponding reflecting members comprise a material having a coefficient of thermal expansion that differs from the plurality of fiber optics.
10 . The force sensor of claim 1 , wherein a material of the corresponding reflecting members is one of metallic doped fiber optic and a sapphire fiber.
11 . A force sensor for use at a distal tip of a catheter, comprising:
a structural member;
a plurality of reflecting members, each affixed to and extending from the structural member; and
a plurality of fiber optics, each paired with a corresponding one of the plurality of reflecting members, each paired fiber optic and reflecting member defining a corresponding gap therebetween,
wherein the plurality of reflecting members each comprises a material having a coefficient of thermal expansion differing from that of the plurality of fiber optics, the coefficient of thermal expansion of the reflecting member being selected for passive compensation of changes in the corresponding gaps between each paired fiber optic and reflecting member that are caused by temperature change,
wherein the structural member is configured to produce a change in a dimension of at least one of the corresponding gaps in response to a force exerted on the distal tip of the catheter,
wherein a rotational displacement of each of the plurality of fiber optics and the corresponding reflecting members relative to a plane of y-y inertial axes is between about 60° and about 90°, and
wherein a sensitivity of each of the corresponding gaps is optimized with respect to lateral force components.
12 . The force sensor of claim 11 , wherein the coefficient of thermal expansion of the reflecting members is different from that of the structural member.
13 . The force sensor of claim 11 , wherein the structural member includes a plurality of segments that define a plurality of slots, and a plurality of the corresponding gaps defined by the paired fiber optics and reflecting members are located within a common one of the plurality of slots.
14 . The force sensor of claim 11 , wherein the structural member includes an outer surface and a plurality of flexures, and wherein each of the flexures defines a portion of the outer surface of the structural member.
15 . The force sensor of claim 11 , wherein at least one of the fiber optics is a spliced with the respective reflecting member, the gap being defined by a cavity defined between the fiber optic and the respective reflecting member.
16 . The force sensor of claim 11 , wherein the structural member includes a plurality of segments that define a plurality of slots, proximal ends of the plurality of reflecting members are all proximate one of the plurality of slots, the one of the plurality of slots being the distal-most or the proximal-most of the plurality of slots.
17 . The force sensor of claim 11 , wherein the plurality of reflecting members and the structural member have the same coefficient of thermal expansion.
18 . The force sensor of claim 11 , wherein the structural member comprises a plurality of segments defining a plurality of slots, the plurality of fiber optics are affixed to a proximal-most of the plurality of segments and extend so that the corresponding gaps of the paired fiber optics and the reflecting members are proximate the proximal-most of the plurality of slots.
19 . A force sensor for use at a distal tip of a catheter, comprising:
a structural member that defines a longitudinal axis and includes
a first segment and a second segment that are adjacent each other along the longitudinal axis, the first and second segments defining a first slot therebetween, the first slot being bridged by a first flexure, and
a third segment adjacent the second segment along the longitudinal axis, the second and third segments defining a second slot therebetween, the second slot being bridged by a second flexure;
a plurality of reflecting members, each affixed to and extending from the third segment of the structural member and each including a reflective surface; and
a plurality of fiber optics, each paired with a corresponding one of the plurality of reflecting members and each oriented and adapted to irradiate the reflective surface of the corresponding one of the plurality of reflecting members and to collect at least a portion of a light reflected from a proximal end of a corresponding reflecting member, each paired fiber optic and reflecting member defining a corresponding gap having a dimension there between, each of the corresponding gaps being disposed proximate the second slot,
wherein the force sensor is configured to compensate for thermally induced changes to each of the dimensions of the corresponding gaps,
wherein a rotational displacement of each of the plurality of fiber optics and the corresponding reflecting members relative to a plane of y-y inertial axes is between about 60° and about 90°, and
wherein a sensitivity of each of the respective gaps is optimized with respect to lateral force components.
20 . The force sensor of claim 19 , wherein the force sensor is configured to passively compensate for thermally induced changes to each of the dimensions of the corresponding gaps.