Shape Tracking of a Dexterous Continuum Manipulator Utilizing Two Large Deflection Shape Sensors

Abstract

Dexterous continuum manipulators (DCMs) can largely increase the reachable region and steerability for minimally and less invasive surgery. Many such procedures require the DCM to be capable of producing large deflections. The real-time control of the DCM shape requires sensors that accurately detect and report large deflections. We propose a novel, large deflection, shape sensor to track the shape of a 35 mm DCM designed for a less invasive treatment of osteolysis. Two shape sensors, each with three fiber Bragg grating sensing nodes is embedded within the DCM, and the sensors' distal ends fixed to the DCM. The DCM centerline is computed using the centerlines of each sensor curve. An experimental platform was built and different groups of experiments were carried out, including free bending and three cases of bending with obstacles. For each experiment, the DCM drive cable was pulled with a precise linear slide stage, the DCM centerline was calculated, and a 2D camera image was captured for verification. The reconstructed shape created with the shape sensors is compared with the ground truth generated by executing a 2D-3D registration between the camera image and 3D DCM model. Results show that the distal tip tracking accuracy is 0.40 ± 0.30 mm for the free bending and 0.61 ± 0.15 mm, 0.93 ± 0.05 mm and 0.23 ± 0.10 mm for three cases of bending with obstacles. The data suggest FBG arrays can accurately characterize the shape of large-deflection DCMs.

Keywords: Fiber Bragg grating; dexterous continuum manipulator; large curvature; obstacle; shape tracking.

Fig. 1

The (a) osteolysis and (b) DCM with a tool through screw hole on acetabular cup.

Fig. 2

The configuration of large curvature detection sensor.

Fig. 3

(a) Assembly of shape sensors to the DCM [22]. (b) Arrangement of FBG sensing nodes.

Fig. 4

Schematic diagram for the shape reconstruction method. (a) SS1 -Shape sensor 1. (b) SS2 - Shape sensor 2. (c) N11, N12 and N13 - Three FBG sensing nodes along SS1. (d) N21, N22 and N23 - Three FBG sensing nodes along SS2. (e) ΣD - Distal coordinates system. (f) ΣP - Proximal coordinates system.

Fig. 5

(a) Overall view. (b) Partial enlarged view for experimental platform.

Fig. 6

Obstacle setup to be (a) near the distal tip (case I), (b) in the middle of bending segment (case II) and (c) near the proximal end (case III).

Fig. 7

(a) The reconstructed DCM for 4mm pulling cable displacement. (b) Overlapping of reconstructed and image extracted DCM under different driven cable displacements.

Fig. 8

The (a) centerlines and (b) tip tracks of both shape reconstruction and image extraction.

Fig. 9

Centerline’s curvature comparison for shape reconstruction and image extraction.

Fig. 10

The overlay of shape reconstructed for obstacle case: (a) I, (b) II and (c) III.

Fig. 11

Comparisons between the curvatures reconstructed from sensors and extracted from image for case: (a) I, (b) II and (c) III.