Design and Modelling of A Spring-Like Continuum Joint with Variable Pitch for Endoluminal Surgery

Abstract

In endoluminal surgery, the miniature instruments shall be of high accuracy and flexibility for minimal invasive diagnosis and surgical intervention. To this end, continuum robots with flexible joints have been proposed as the mechanism of endoscopic instruments. The compliance and deformability of the continuum joints enable access into the curved lumen. However, the manufacturing tolerances are normally not considered in the design procedure, and led to inaccuracy in the robotic control. To improve the control accuracy and flexibility of endoluminal surgical robots, we propose a novel design of a metal printed continuum joint in this paper, which incorporates a variable pitch design into the spring-like structure. The design can reduce the position errors accumulated on the distal tip of the joint, especially at large bending angles. The specification of variable pitch is investigated and determined with a friction model. In addition, to eliminate the distortion of the joint induced during the metal printing process, an extensive experiment was conducted to access the effect of the variables in the design (pitch, thickness, width and number of coils), with the aim of determining optimal parameters for reducing discrepancy caused by manufacturing variations. The final results indicated that the bending error of a single joint can be reduced from 18.10% to 4.63%, and a multi-segment prototype was developed to verify its effectiveness for potential surgical applications.