Adaptive tracking approach of flexible cable conduit-actuated NOTES systems for early gastric cancer treatments

To control robotic arms mounted on a flexible endoscope in NaturalOrifice Transluminal Endoscopic Surgery (NOTES) procedure, Cable-ConduitMechanisms (CCMs) are often used. Although the CCMs offer simplicity, safety, and easy transmission, nonlinear friction and backlash-like hysteresis between the cable and the conduit introduce some difficulties in the motion control of the NOTES system. It is challenging to achieve the precise position of robotic arms and force feedback information when the slave manipulator is inside the humans body. This paper presents the dynamic transmission characteristics of CCMs and control strategies to compensate for achieving precise position tracking of the robotic arms. The cable-conduit tension and position transmission are analysed and discussed for both sliding and presliding regimes. Unlike current approaches in the literature, position transmission of the CCM is modelled by an approximation of backlash-like hysteresis profile for both loading and unloading phases. In addition, nonlinear adaptive control algorithm is also used to enhance the tracking performance for a pair of CCMs regardless of the change of cable-conduit configuration during the operation. The backlash-like hysteresis parameters are online estimated under an assumption of presence of output feedback and unknown bound of nonlinear parameters. To validate the proposed approach, a prototype of single-DOF-flexible robotic system, which consists of a motion control device, a telesurgical workstation, and a slave manipulator, is also developed. The proposed compensation scheme is experimentally validated using the designed system. The results show that the proposed control scheme improves the tracking performances significantly regardless of the change of endoscope configuration.