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.

Robotization of medical acts often requires the evaluation of contacts between a robotic system and a patient, for safety or efficiency reasons. When contact occurs with a stiff environment, instabilities and vibrations can appear and a passive compliance is therefore needed. In this paper, we propose to embed compliance in a force sensor and to develop a novel force sensor with large compliance, i.e. a zero stiffness at contact transition to ease robot control. To get at the same time a satisfying measurement range and low off-axis sensitivity, an optical measurement process based on an optical line generated thanks to additive manufacturing is exploited. A compliant sensor body allowing the desired stiffness profile is presented and the specific optical measurement technique is developed. Finally, a prototype of the proposed force sensor is evaluated experimentally.

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, we describe the use of calibration techniques to help improving prediction accuracy of models for soft actuators. A finite-difference model considering anisotropy of soft actuator flexible chamber is combined with experimental identification to assess actuator motion. Identifiability conditions are exploited to determine suitable experimental conditions, taking into account the manufacturing process capabilities, multimaterial additive manufacturing in this context. As a second contribution, a soft actuator with Wren mechanism for reinforcement is being developed. It is considered for rotary actuation, with the description of a proof of concept. The interest of the calibration technique and the actuator design are finally discussed.

In this paper, we propose to take advantage of concentric tube robots (CTR) properties to design a robotic system for optical biopsies with fiber-based imaging modalities. Follow-the-leader (FTL) deployment, with CTR body following its tip, is being integrated as a design constraint in order to minimize the device invasiveness. A design procedure is proposed and developed in the context of olfactory cell inspection. Stability issues of CTR are considered with theoretical validation of FTL deployment. Finally, an experimental assessment in lab conditions is being conducted that includes the device deployment and the reproduction of scanning task for imaging. The whole surface to be inspected can be accessed, and 20 μm resolution of the CTR tip is observed.

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, 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.

An active needle is proposed for the development of magnetic resonance imaging (MRI)-guided percutaneous procedures. The needle uses a low-transition-temperature shape memory alloy (LT SMA) wire actuator to produce bending in the distal section of the needle. Actuation is achieved with internal optical heating using laser light transported via optical fibers and side coupled to the LT SMA. A prototype, with a size equivalent to a standard 16-gauge biopsy needle, exhibits significant bending, with a tip deflection of more than 14° in air and 5° in hard tissue. A single-ended optical sensor with a gold-coated tip is developed to measure the curvature independently of temperature. The experimental results in tissue phantoms show that human tissue causes fast heat dissipation from the wire actuator; however, the active needle can compensate for typical targeting errors during prostate biopsy.

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.

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.

A side optical actuation method is presented for a slender MR-compatible active needle. The needle includes an active region with a shape memory alloy (SMA) wire actuator, where the wire generates a contraction force when optically heated by a laser delivered though optical fibers, producing needle tip bending. A prototype, with multiple side heating spots, demonstrates twice as fast an initial response compared to fiber tip heating when 0.8 W of optical power is applied. A single-ended optical sensor with a gold reflector is also presented to measure the curvature as a function of optical transmission loss. Preliminary tests with the sensor prototype demonstrate approximately linear response and a repeatable signal, independent of the bending history.

An active needle is proposed for the development of MRI guided percutaneous procedures. The needle uses internal laser heating, conducted via optical fibers, of a shape memory alloy (SMA) actuator to produce bending in the distal section of the needle. Active bending of the needle as it is inserted allows it to reach small targets while overcoming the effects of interactions with surrounding tissue, which can otherwise deflect the needle away from its ideal path. The active section is designed to bend preferentially in one direction under actuation, and is also made from SMA for its combination of MR and bio-compatibility and its superelastic bending properties. A prototype, with a size equivalent to standard 16G biopsy needle, exhibits significant bending with a tip rotation of more than 10°. A numerical analysis and experiments provide information concerning the required amount of heating and guidance for design of efficient optical heating systems.

In this paper, control strategies for an active stabilizer dedicated to beating heart coronary artery bypass grafting are investigated. The active stabilizer, which consists of a piezoactuated compliant mechanism, has to be controlled to compensate for the displacements induced by the beating heart in order to provide the surgeon with a locally motionless myocardium surface. Three controllers, including different levels of prior knowledge about the heart motion, are presented. Their performance with respect to modeling uncertainties, arising unknown interactions of the stabilizer with its positioning mechanism, and the heart, is studied through simulations, as well as laboratory and in vivo experiments. Finally, the selection of the most adequate control scheme and the performance of the device from a clinical point of view are discussed.

Low-cost piezoresistive sensors can be of great interest in robotic applications due not only to their advantageous cost but to their dimension as well, which enables an advanced mechanical integration. In this paper, a comparison of two commercial piezoresistive sensors based on different technologies is performed in the case of a medical robotics application. The existence of significant nonlinearities in their dynamic behavior is demonstrated, and a nonlinear modeling is proposed. A compensation scheme is developed for the sensor with the largest nonlinearities before discussing the selection of a sensor for dynamic applications. It is shown that force control is achievable with these kinds of sensors, in spite of their drawbacks. Experiments with both types of sensors are presented, including force control with a medical robot.

In this paper, the design of a new active cardiac stabilizer, Cardiolock2, is presented. Following the proof of concept Cardiolock [7], this device allows an active stabilization of the surface of a beating heart in two directions, which is considered sufficient for a complete stabilization. Piezoelectric actuation is combined with a compliant architecture to obtain high dynamics and accuracy. A remote center of motion is obtained with a serial architecture, and parallel mechanisms in configurations close to singularity are used to increase the workspace. A kinematic analysis is first presented, before detailing the main properties of the device and the current development of the prototype.

In this paper, the design of a novel MRI-compatible torque sensor is proposed. The sensor is based on an optical measurement, with a particular architecture to provide a very low cross-sensitivity. Its structure allows to simultaneously tune the sensor stiffness and the measurement amplitude of the optical sensor. To do so, kinematic singularities of parallel structures are used as well as the principles of dissociated metrology structure. The design of the sensor is first introduced by a kinematic analysis, before detailing its behavior using Finite Element Analysis. A prototype is finally introduced with first experimental results.

In this paper, nonlinear modeling of low cost force sensors is considered for force control applications in robotic or biomechanical applications. Commercial force sensors are often expensive, with a limited use in severe conditions such as the presence of a strong magnetic field. On the contrary, thin film piezoresistive sensors such as the Tekscan Flexiforce and the Interlink FSR sensors are of low cost and can be considered in such an environment. Only a few information is however available on their dynamic properties. We therefore provide an experimental study of their dynamic behavior, showing nonlinear properties. Identification is then achieved, and a compensation model is proposed. A force control experiment is finally presented to evaluate the compensation scheme.

Off-pump coronary artery bypass grafting (CABG) is probably an important milestone in the cardiac surgery history. This technique is currently made possible thanks to the use of mechanical stabilizers. Nevertheless, the available stabilizers are not fully satisfying. Indeed, they have been demonstrated to exhibit significant residual motion. In this paper we propose a novel piezo-actuated compliant stabilizer, whose architecture is compatible with a minimally invasive surgery context. This active stabilizer is controlled using high speed visual feedback in order to compensate in real time for the residual cardiac motion. In vivo experimental results using the developed prototype are given to demonstrate the efficiency of the adopted approach.

In this paper, a vision-based measuring device is proposed and experimentally demonstrated to be an accurate, flexible, and low-cost tool for the kinematic calibration of parallel mechanisms. The accuracy and ease of use of the proposed vision sensor are outlined, with the suppression of the need for an accurate calibration target, and adequacy to the kinematic calibration process is investigated. In particular, identifiability conditions with the use of such an exteroceptive sensor are derived, considering the calibration with inverse or implicit models. Extensive results are given, with the evaluation of the measuring device and the calibration of an H4 robot. Using the full-pose measurement, an experimental analysis of the optimal calibration model is achieved, with study of the kinematic behavior of the mechanism. The efficiency of the provided method is thus evaluated, and the applicability of vision-based measuring devices to the context of kinematic calibration of parallel mechanisms is discussed.

In this paper, a novel approach is proposed for the kinematic calibration of parallel mechanisms with linear actuators at the base. The originality of the approach lies in the observation of the mechanism legs with a camera, without any mechanism modification. The calibration can hence be achieved online, as no calibration device is linked to the end-effector, on any mechanism since no additional proprioceptive sensor installation is necessary. Because of the conditions of leg observability, several camera locations may be needed during the experimentation. The associated calibration method does not however require any accurate knowledge of the successive camera positions. The experimental procedure is therefore easy to perform. The method is developed theoretically in the context of mechanisms with legs linearly actuated at the base, giving the necessary conditions of identifiability. Application to an I4 mechanism is achieved with experimental results.

In this paper, an original approach is proposed for the kinematic calibration of parallel mechanisms. The originality lies in the use of vision to get information on all parts of the mechanism, i.e. its end-effector as well as its legs. Metrological redundancy is therefore maximized to improve the calibration efficiency. The approach is implemented for the calibration of the I4 parallel mechanism, with the use of the Jacobian matrix. No accurate camera location is needed so that the experimental procedure is easy to achieve. The calibration algorithm is detailed and experimentally demonstrated more efficient than other calibration methods based on legs observation or end-effector observation.

In this article, a robot formation control strategy based on a vision-based follow-the-leader scenario is proposed, with emphasize on its reliability. On the one hand, perception is enhanced by the control of a motorized zoom. On the other hand, bidirectional and non-oblivious (Suzuki, I and Yamashita, M, 1996) control is implemented, with an odometry-based fault detection of vision-based information and a leader path-planning strategy to improve its visibility. After introduction of the control strategy, extensive experimental results are presented.

In this article, we present the kinematic calibration of H4 parallel robot using vision-based measuring device. Calibration is performed according to the inverse kinematic model method, using first the design model then a model developed for calibration purpose. With a precision of the order of magnitude of 0.2 mm and 0.03/spl deg/, our vision system allowed us to obtain a final positioning accuracy of the end-effector lower than 0.5 mm. Conclusions are given for the calibration of this class of mechanisms.

In this paper, a new pose selection criterion for the kinematic calibration of parallel mechanisms is proposed. It enables one to take into account the measurement noise amplification that may occur for parallel mechanisms, as well as the variation of amplitude and anisotropy of the measuring device accuracy. This new criterion is applied to vision-based calibration of an Orthoglide mechanism, both in simulation, with comparison to existing criteria, and experimentally.

In this article, an evaluation of a vision-based measuring system for parallel machine-tool calibration is performed. Simultaneous measurement of the 6 pose components enables one to perform calibration using the efficient inverse kinematic method. The system is composed of a single camera and a calibration board generated on a LCD monitor. Calibration board size can be adapted to the camera field of view, and specific points of interest can be generated, in order to improve pose measurement. Based on a single industrial camera, the measuring system is low-cost and easy-to-use. An experimental evaluation of the system is performed on a machine-tool axis. Measurement bias and precision are estimated by comparison with laser interferometry, and the influence of focal length and sensor resolution is examined.