How can human motion prediction increase transparency?

International audienceA major issue in the field of human-robot interaction for assistance to manipulation is transparency. This basic feature qualifies the capacity for a robot to follow human movements without any human-perceptible resistive forces. In this paper we address the issue of human motion prediction in order to increase the transparency of a robotic manipulator. Our aim is not to predict the motion itself, but to study how this prediction can be used to improve the robot transparency. For this purpose, we have designed a setup for performing basic planar manipulation tasks involving movements that are demanded to the subject and thus easily predictible. Moreover, we have developed a general controller which takes a predicted trajectory (recorded from offline free motion experiments) as an input and feeds the robot motors with a weighted sum of three controllers: torque feedforward, variable stiffness control and force feedback control. Subjects were then asked to perform the same task but with or without the robot assistance (which was not visible to the subject), and with several sets of gains for the controller tuning. First results seems to indicate that when a predictive controller with open loop torque feedforward is used, in conjunction with force-feeback control, the interaction forces are minimized. Therefore, the transparency is increased

Design and acceptability assessment of a new reversible orthosis

International audience— We present a new device aimed at being used for upper limb rehabilitation. Our main focus was to design a robot capable of working in both the passive mode (i.e. the robot shall be strong enough to generate human-like movements while guiding the weak arm of a patient) and the active mode (i.e. the robot shall be able of following the arm without disturbing human natural motion). This greatly challenges the design, since the system shall be reversible and lightweight while providing human compatible strength, workspace and speed. The solution takes the form of an orthotic structure, which allows control of human arm redundancy contrarily to clinically available upper limb rehabilitation robots. It is equipped with an innovative transmission technology, which provides both high gear ratio and fine reversibility. In order to evaluate the device and its therapeutic efficacy, we compared several series of pointing movements in healthy subjects wearing and not wearing the orthotic device. In this way, we could assess any disturbing effect on normal movements. Results show that the main movement characteristics (direction, duration, bell shape profile) are preserved

Workspace boundaries of Complex Robotic Mechanisms

This paper proposed a general method for the determination of the workspace boundaries of complex mechanisms. For that, the mechanism is considered as an arrangement of sub-structures (parallel and serial kinematic chains). Force and motion transmission models are compute in their symbolic form. These models are expressed in terms of screw systems. We make use of geometrical properties between screw axes to determine stationary configurations. Those defining the sub-structure extreme reaches are then extracted using the fact that they define a stable static equilibrium position of the structure. The structural decomposition is applied to obtain the complex mechanism workspace limits. As illustration a macro/mini-manipulation system is studied

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Development of an optomechanical measurement system for dynamic stability analysis

The paper presents the development of a measurement system for dynamic stability analysis. The system is composed of an actuation device, that is a robotic platform with four degrees of freedom, and two measurement systems: a force platform, to measure the position of the centre of pressure (COP), and a vision system, to measure the position of the centre of mass (COM). The purpose of the system is to provide means to identify whether a subject behaves like an inverted pendulum (as the literature predicts for static posturography), when a dynamic perturbation is applied. This can be achieved by generating a movement of the robotic platform and, simultaneously, by measuring COP and COM trajectories and verify their coherence with the inverse pendulum model. © 2015 IEEE

A Reactive Robotized Interface for Lower Limb Rehabilitation: Clinical Results

International audience—This article presents clinical results from the use of MONIMAD, a reactive robotized interface for lower limb Rehabilitation of patients suffering from cerebellar disease. The first problem to be addressed is the postural analysis of sit-to-stand motion. Experiments with healthy subjects were performed for this purpose. Analysis of external forces shows that sit-to-stand transfer can be subdivided into several phases: preaccel-eration, acceleration, start rising, rising. Observation of Center of Pressure, ground forces and horizontal components force on handles yields rules to identify the stability of the patient and to adjust the robotic interface motion to the human voluntary movement. These rules are used in a fuzzy-based controller implementation. The controller is validated on experiments with diseased patients in Bellan Hospital

Elderly people sit to stand transfer experimental analysis

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Two Techniques Of GEOMETRICAL MODELIZATION FOR AN HEXAPOD ROBOT

: this paper presents two techniques of geometric modelization in 3D-space for an hexapod robot. The direct and inverse models involving an alternating tripod walking pattern are described. The strategy of the first method consists in solving the problem in the plane of the body platform and then integrating the solution in the 3D analysis. The second method relies on an analytic approach and appears more mathematical. We test both modelizations thanks to computer simulation and implement them for real with success on our first six-legged machine called RHEA. The modelization assumes that the positions of the leg extremities are known at each time with respect to a stationary reference frame. Several control commands are based on the direct and inverse 3D models and emphasis has been focused on how to smooth the body motion when changing propulsive tripod. 1. Introduction Before implementing control laws on a real robot to make it walk, simulations have to be conducted to verify the ..

Experimental Evaluation of Several Strategies for Human Motion Based Transparency Control

Human interactive robots continue to improve human quality of life with their diverse applications. Their field includes, but is not limited to, haptic devices, force feedback tele-manipulation, surgical co-manipulation, medical rehabilitation, and various multi-degree of freedom robotic devices where the human operator and robot are often required to simultaneously execute tasks and collaborate with a specific share of forces/energy. More than tuning mechanical design, the robot control enhancement with a force sensor, is the key for increasing transparency (i.e the capacity for a robot to follow human movements without any human-perceptible resistive forces). With ail ideal robot control, the interaction between robot and human Would be extremely natural and fluid that the comanipulation of tasks Would seem to be achieved with a transparent aid from the robot. For Such, the classical force feedback control in certain cases still seems insufficient as is often limited by various factors (noise, bandwidth limitation, stability, sensor cost..etc). Our experiments are focused on evaluating the performance increase in terms of transparency of controller by using human motion predictions. We evaluate several ways to use predictive informations in the control to overcome present transparency limitations during a simple comanipulation pointing task