Dynamic Hysteresis Compensation for Tendon-Sheath Mechanism in Flexible Surgical Robots Without Distal Perception

Abstract

The accurate position transmission of tendon-sheath mechanisms (TSMs) is challenging but of significance to the flexible robot for minimally invasive surgery. The challenges are mainly attributed to the following: first, the tendon-elongation and its caused hysteresis that depend on the route configuration of the TSM and could result in misaligned position transmission; second, realistic surgical scenarios requiring the TSM with arbitrary and even time-varying route configurations; and third the absence of distal sensory feedback due to strict spatial constraints. Existing works are always devoted to tackling the first challenge yet evade the second and third. Here, a route-related tendon-elongation model is formulated to resolve the first challenge, and in response to the second, a route-sensing optical fiber is used. Obeying the third challenge, a feedforward hysteresis compensator is then developed to align the distal position of the tendon with the desired position. Our final contribution gives an application-oriented remedy for the foregoing methodologies. Applying our compensator on the challenging position transmission tasks subject to second and third challenges, the positional accuracy can be still maintained at around 97.50%; guided by the provided remedy, the surgical end-effector achieves submillimeter tip position accuracy. Extensive tests demonstrate that the pending concerns yet of great practical importance in existing related works are well resolved.