Modeling and control of cable actuated surgical robotic systems
Abstract
Many surgical robots as well as other devices like robotic hands and exoskeletons use cable-conduit pairs in pull-pull configuration to actuate the remote instruments. Cable-conduits provide a unique combination of dexterous yet simple and cost-effective design. However, cable compliance and friction between the cable and the conduit makes the system nonlinear and accounts for major losses in tension transmission across the cable. These nonlinearities have prevented wider adoption of cable-conduit actuation despite its potential of simple, dexterous and power dense designs. The objective of this research is to model and control the transmission characteristics in such cable-conduit actuated systems. A continuous domain analytical model has been developed for the transmission characteristics in cable-conduit actuation, and has been discretized to simulate the cable motion. The simulations predict backlash, cable slacking, and other nonlinear behaviors well. The model has also been extended to MR compatible viscoelastic systems using polymeric cables. The simulations results are verified by experiments for both elastic (steel) cables and viscoelastic cables (nylon cables in PEEK tubing), on a setup emulating a typical surgical robot. In surgical devices, traditional sensors like optical encoders cannot be used due to various size and safety constraints and the generally available alternatives have relatively lower sampling rate and accuracy. Therefore, while intermediate state (actuator position) feedback is present, output feedback is limited and the system controller has to be designed utilizing these different types of feedbacks. To fully utilize the available feedback, multi-loop control has been designed with actuator control in the inner loop and compensation of cable dynamics in the slower outer loop. The performance improvements have been presented for a Laprotek robot arm and a motorized gastroscope. Finally, to demonstrate the true potential of cable-conduit actuation, a novel MRI compatible device has been designed and a prototype has been developed using polymeric cable-conduits. The device has been shown to have no image distortation or magnetic effects in MR room, while still avoiding the substantial additional complexity introduced in other MRI compatible counterparts. The device has also been shown to achieve good tracking performance under controller implementation.
Degree
Ph.D.
Advisors
Peine, Purdue University.
Subject Area
Mechanical engineering|Robotics
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