This paper presents the nonlinear dynamics and sliding mode control design for a 1-DOF needle insertion robot. The robot actuator is an MR-compatible pneumatic piston-cylinder. A brief review of the dynamics for this type of actuator is provided. The reaction force of tissue on the needle remains an unknown for which our controller compensates. A sliding mode control law is formulated that relies solely on position and pressure measurements (no force sensor). Experimental implementation of the actuator and controller is described. The mean and maximum steady-state position errors for step reference positions were 0.018 mm and 0.028 mm, respectively.

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