This paper introduces a 2-DOF spatial remote center of motion (RCM) tensegrity mechanism, based on a double parallelogram system, dedicated for percutaneous needle insertion. The originality of this mechanism is its ability to be reconfigured and its capacity to perform a decoupled modulation of its stiffness in an asynchronous way. To do so, an analytical stiffness model of the robot is established, and a control methodology is proposed. A prototype of the robot is developed and assessed experimentally. The position tracking is evaluated using a 6-DOF magnetic tracker sensor showing a root mean square error less than 0.8° in both directions of the needle guide.

In this paper, the design of a new variable stiffness spherical joint for MR-compatible robotics is presented. It is based on the use of prestressed cable-driven mechanisms in singular configurations to provide large stiffness variation ranges, including zero stiffness configuration as required by the medical context. An original implementation is proposed, with a prestress adjustment system using pneumatic energy and taking advantage of multimaterial additive manufacturing. The proposed component combines compactness, MR-compatibility and is lightweight. The system is evaluated on a dedicated experimental setup with validation of the expected behavior, with in particular a very large achievable range of stiffnesses. The approach is effective for the design of such device and constitutes a novel solution for the design of variable stiffness devices with complex motions.

In this paper, we focus on the technology issues to be solved to develop a cable-driven robot compatible with Magnetic Resonance Imaging constraints. This study is based on the design of a new compact cable-driven manipulator with remote actuators, initially developed for prostate interventions. One of the originalities of the system is to use an instrumented structure to evaluate the cable tensions and lengths in order to perform an adequate control. The sensors assessment has been experimentally achieved and the necessity to introduce a new control strategy using the developed sensors has been demonstrated.