Design and kinetostatic analysis of a tip-stiffness improved compliant continuum robot using anti-buckling universal joints

Cable-driven compliant continuum robots (CCRs) can reach target areas in constrained spaces due to their elastic bodies being controlled remotely. They have been widely employed to inspect, maintain, or repair industrial machines such as gas turbine engines and oil pipes. However, their performances are usually limited by the low tip stiffness and the stiffness usually decreases with the increase of cable pulling forces. This paper aims to address the above problems by presenting a tip stiffness improved CCR formed by compliant anti-buckling universal joints (ACCR). The normalized nonlinear spatial models of the one-segment CCR and three-segment CCR are proposed and comprehensively verified using commercial nonlinear finite element analysis software. Given cable forces, prescribed cable displacements, tip loads, and gravity, the motion of any points on the CCRs can be analytically obtained. The performance characteristics of the one-segment CCRs and three-segment CCRs are extensively studied under different loading conditions, including the maximum CCR deformation, tip-location accuracy, shape dexterity, and tip stiffness. The results show that the tip stiffness of the ACCR is always much higher than that of the counterpart CCR under the same loading conditions. For example, the one-segment and three-segment ACCRs both have a high in-plane tip stiffness under in-plane actuation, which can increase by 49.0% and 31.3%, respectively; and they both have a high transverse tip stiffness under spatial actuation, which can increase by 48.9% and 31.2%, respectively. It is also confirmed that the ACCRs can increase tip stiffness by increasing cable actuation. Several preliminary planar experimental tests are carried out to validate the fabrication feasibility of the prototype, the accuracy of the analytical model, and/or the above-mentioned stiffness improvement.