Toward a Variable Stiffness Surgical Manipulator Based on Fiber Jamming Transition

Abstract

Soft robots have proved to represent a new frontier for the development of intelligent machines able to show new capabilities that can complement those currently performed by robots based on rigid materials. One of the main application areas where this shift is promising an impact is minimally invasive surgery. In previous works, the STFF-FLOP soft manipulator has been introduced as a new concept of using soft materials to develop endoscopic tools. In this paper, we present a novel kind of stiffening system based on fiber jamming transition that can be embedded in the manipulator to widen its applicability by increasing its stability and with the possibility to produce and transmit higher forces. The STIFF-FLOP original module has been re-designed in two new versions to incorporate the variable stiffness mechanism. The two designs have been evaluated in terms of dexterity and variable stiffness capability and, despite a general optimization rule did not clearly emerge, the study confirmed that fiber jamming transition can be considered an effective technological approach for obtaining variable stiffness in slender soft structures.

Keywords: jamming transition; minimally invasive surgery; soft robotics; surgical manipulator; variable stiffness system.

Figure 1

Representation of the two-module STIFF-FLOP manipulator attached to a rigid shaft used as support. The proximal module has been redesigned to lodge a variable stiffness system that can become rigid on demand and provide stability to the distal module (unvaried with respect to the original version).

Figure 2

Design and section view of (A) Module A and (B) Module B.

Figure 3

CAD model for the (A) BT and (B) CT joint.

Figure 4

(a–f) Modules manufacturing steps.

Figure 5

Setup for testing variable stiffness at rest position (Module A is reported as example).

Figure 6

Setup for testing variable stiffness in bent configuration (Module A is reported as example).

Figure 7

(A) Test setup used for workspace and shape locking evaluation (Module A is reported as an example) and (B) bending angle (α) evaluation method.

Figure 8

Experimental results for the angular workspace obtained through the activation of a single pair of chambers of (A) Module A and (B) Module B.

Figure 9

Module features: for each module architecture, weight, the presence of the inner free lumen (i.e., working channel), the number of MPs, the integration of a variable stiffness mechanism and the performance in terms of stability and flexibility are reported.