A pneumatic linear actuator is presented and evaluated. Designed to operate in demanding environments such as MRI, it is developed to be used with two motion control modes: 1) a step-by-step mode with tooth-based gripping to ensure precision, 2) a continuous mode available locally for fine positioning. The actuator can also be disengaged to enable direct handling by an operator, for example for comanipulation. The design is presented. A prototype, developed in the medical context, is implemented and characterized. A specific step-by-step control sequence is then elaborated based on its characterization. Testing of the dual-mode actuation is finally described. The complementarity between the two motion modes and possible adaptations of the original design are discussed.

Non-rigidly foldable origamis are of great interest to build robotic components, as they are light, offer large deployability and can also be multistable. In this paper, we consider the Kresling tower, and propose an original way to actively modulate its kinetostatic properties. Actuated stiffening mechanisms are embedded on some folds of the origami. By adjusting the axial stiffness of the folds, modulation of the axial stiffness and the force required to switch between stable configurations are demonstrated. This adjustment can in addition be performed independently from the height of the stable configurations, which makes it simple to use. The interest of fold stiffening is outlined experimentally. Three actuation strategies are considered and implemented. Impact on Kresling tower properties are shown, with complementary performances of pneumatic, SMA-based and DC motor actuation.

In this paper, an active compliant revolute joint actuated by hydraulic energy is developed. The joint is made of polymer for integration in medical robotic systems, even in a challenging environment such as Magnetic Resonance Imaging (MRI). The use of multimaterial additive manufacturing allows us to develop two original aspects. First, a new seal design is proposed to build miniature hydraulic cylinders embedded in the active joint, with low level of friction. Second, a rack-and-pinion mechanism is being integrated to a compliant revolute joint to obtain a high level of compactness. Design and experimental assessment of the hydraulic cylinder and the compliant joint with embedded rack-and-pinion are presented, as well as an illustration in the context of needle manipulation with passive teleoperation.

In this paper, a new multifunctional compliant joint is introduced for the design of unibody robotic mechanisms. Developed in the demanding context of interventional MRI, the compliant joint integrates kinematic, actuation, braking and sensing functions. Such integration is performed thanks to multimaterial additive manufacturing. Design and experimental behavior of the component are presented. A robotic assistant built with the proposed component and made of a single element is then introduced. It offers interesting performances while being compact and MR-compatible.

Multi-Material Rapid Prototyping (MM-RP) is a promising fabrication process for compliant mechanisms, for instance when compactness is a concern. The Pseudo-Rigid Body Model (PRBM) approach is well-known for the synthesis of compliant mechanisms. It is usually based on the use of compliant joints to provide the mechanism mobilities. In this paper, we propose the HSC joint as a new type of revolute compliant joint that is well adapted to MM-RP, and that offers interesting properties in terms of stiffness and range of motion. Based on the HSC joint, a new compliant mechanism, suitable for interventional MRI, is introduced with assessment of a first prototype that is entirely made out of a single polymer part. The interest is twofold. First, the device constitutes a promising solution in this medical context. Second, the impact of the use of MM-RP in combination with PRBM can be evaluated, and their use is discussed as a conclusion.