International audience

Haptic interfaces aim at realistically simulating physical interactions within a Virtual Environment (VE) through the sense of touch. Therefore, they should display both a negligible impedance in free space and high forces and stiffness in contact. These constraints are however difficult to meet simultaneously. While compromises can usually be found when interacting through a handle grasped in hand, this is much more difficult when considering dexterous interactions with manual interfaces or exoskeletons due to the high number of degrees of freedom and limited space available. To ease their design, the authors previously made an analysis of the hand contact areas of interest for the simulation of the majority of interactions in a VE. It was shown that tracking and providing force feedback only on the five fingertips and the side of the index allows interacting naturally within a VE more than 50% of the time. This paper goes a step further and analyses in which directions these forces are applied on each hand area. A new result is that forces are required on the 6 areas of interest only normal to the skin, while tangential forces can be limited to 4 and even 1 area(s) depending on the direction.

Encounter-type devices have been introduced to solve one of the main drawbacks of common haptic interfaces i.e. their limited transparency in free space and their restricted ability to render realistic transitions between free space and contact. Advantageously, encounter-type interfaces collide with fingers and display interaction forces only if a contact occurs in the virtual environment. In free space, their end-effectors are mechanically detached from the operator and closely track his fingers, allowing for a perfect transparency. This paper introduces a control scheme that handles the transition between tracking and force display modes in a smooth way. Experimental results using a custom encounter-type interface are also given. The obtained results show the efficiency of the proposed control law when compared to the conventional switch-based control usually found in the literature.

Haptic interfaces are purposed for the simulation of physical interactions with a virtual environment in a realistic way. Their design is often based on a compromise between the interaction capabilities and mechanical design complexity. This paper is aimed at providing a methodology that helps tuning this trade-off. A survey of both manipulation and exploration taxonomies allows the identification of elementary hand contact areas with their associated frequency of use. The relative importance of these areas is illustrated by the building of an interaction map for the hand. Some combinations of these elementary areas, with their frequency of use, are then organised into a graphical tree as a function of their complexity. This tree allows to review some existing devices and to propose some guidelines for improved designs.

Assistance to walking is a key point in improving autonomy during daily living activities of elderly and disabled people. Despite the significant number of active robotized walkers and canes proposed in the literature, only few studies focused on the mechanical influence of assistive devices on the gait generation process. A deeper analysis of assisted walking dynamics is very likely to help improving the design and the adequacy of the robotized assistants. In this paper a simulation framework of impaired and cane assisted gaits is developed. Simulations of common passive cane assistance allow a deeper analysis of its contributions to the locomotion. The behaviour of an active cane and its beneficial impact on the energetics of impaired gaits are exposed.

Supplementary visual, audio and tactile inputs have been shown to enhance postural control. In particular the light touch on a stable surface has been proven to significantly increase postural stability. Furthermore, it has been reported that the Center of Pressure (CoP) can be sinusoidally driven thanks to somatosensory inputs. In this paper, these results are extended to improve balance control. A closed loop control of the CoP position based on somatosensory feedback is developed. This control strategy allows both setpoint tracking and path following of the CoP. The effectiveness of the proposed somatosensory feedback is assessed through experiments involving 11 naive subjects.

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.

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.

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.

Robotized ultrasound examination offers on one hand more accuracy for the medical diagnostic and on the other hand a suitable assistance to radiologists. In the literature, very few researches deal with ultrasound image-based control of a medical robot holding the ultrasound probe. This paper presents a new visual servoing approach allowing the automatic guidance of the ultrasound probe. This technique is based on the modeling of the coupling between the ultrasound probe and egg shaped objects. The robotic task consists in reaching a desired image from an arbitrary initial position. The aim of this task is to assist the radiologist diagnostic by automatically moving the ultrasound probe in order to find the ultrasound image view of a tumour cross-section registered in a previous date. This work presents simulation results of the proposed ultrasound vision-based control scheme