The contribution of this paper comes from a modeling which allows simplify equations compared to the previous study. Depending on the number of channels, we calculate the teleoperation transparency at steady states and discuss conditions to achieve ideal transparency. New experimental results are proposed with the four channel teleoperation system to validate again our simulator. Then results of the calculations are checked by simulation for each type of control laws.

A classical frequency approach in order to tune the closed-loop of each robot for bilateral teleoperation system is studied. The originality of the tuning is done through closed loop of velocity, position and force. Where the resulting equation of the dynamic gives coefficients that can be assimilate to the apparent impedance of each robot. The apparent impedance feel by the operator depending on the number of control channel is studied with the Hannaford method.

International audience

A cascaded force and position control is implemented on each of two robots of a bilateral teleoperation system. The aim is to propose a classical frequency approach in order to tune the closed-loop of each robot for different operating modes. Thus an efficient four channel bilateral teleoperation controller is proposed. It can be decomposed into four different two channel controller variations that can introduce inner virtual flexibility. This virtual flexibility is calculated for each case and can be tuned with the gains of the position control of the robots. An original way to calculate the apparent impedance is provided.

The following topics are dealt with: indoor radio; mobile robots; pedestrians; smart phones; position control; radionavigation; wireless LAN; indoor communication; indoor navigation; Kalman filters.

Actual control of most humanoid robots is based on the 3D linear inverted pendulum and assumes an horizontal displacement of the center of mass of the robot while obviously the center of mass in human walking is characterized by vertical oscillations. The objective of the paper is to show that these oscillations have a crucial role for the high level control of the walk. Based on a controlled length inverted pendulum model of the walker, it will be shown that vertical oscillations induce a self stabilization of the walk while this self stabilization is not observed in the case of a horizontal motion of the center of mass. The results are essentially based on the evolution of the angular momentum throughout the walk. The decrease of the angular momentum during the change of support is determinant to introduce a dependence between the path of the center of mass and the walking velocity. For a large set of walking characteristics (stride, velocity ...) a self synchronization of the motion in the sagittal and frontal planes appears that allows a low level control to produce stable cyclic gaits.

A second order sliding mode controller is utilised to track reference trajectories for all the joints of a fully actuated biped robot. The existing tuning rules for the `twisting' controller are used to guarantee a priori attainment of a prescribed settling time between two successive impacts. The joint torque is modeled as the control input. Smoothing of the discontinuous controller is carried out by introducing a high gain linear controller inside a boundary layer defined by an arbitrarily small region around the origin thereby avoiding numerical errors in the simulations. The overall accuracy of motion control is dictated by the size of this layer leading to practical stability of the closed-loop system. The main contribution of the paper is to provide straightforward and realizable engineering guidelines for the reference trajectory generation and for the tuning of a robust finite time controller for achieving stable gait of a biped in the presence of disturbances in both continuous and impact phases. Numerical simulations of a biped robot are shown to support the theoretical results.

The paper presents an online estimation of parameters of a multi-input renewal Markov process. The underlying model is derived from the physiological generation of intramuscular electromyographic (iEMG) signals, which are recorded by wire electrodes. The iEMG is the sum of several sparse spikes trains and noise. An hidden Markov model, whose parameters express the muscular activity, is developed. The time duration between spikes is modeled with a discrete Weibull distribution, helping us to reduce the complexity of the estimation done with the help of a Bayes filter.

Energetic efficiency and stability are the fundamental criteria which can improve the autonomy and task performance capabilities of humanoid robots. The scope of this paper is to investigate the energetic effects of knee locking and addition of torsional springs to different joints of a seven-link fully actuated planar bipedal robot. The focus is on the reduction of energy consumption during walking. The energetic cost of walking is determined without joint stiffness and knee locking as a baseline for the comparison of results. In the first approach, the gait trajectory is optimized by adding springs to different joints and energetic cost of walk is then calculated at different walking speeds. The second approach presented in this paper is to mechanically lock the support knee and then optimize the gait and calculate the walking cost. The energetic cost of walking determined for the above two cases is then compared to the baseline cost. It is observed that addition of torsional springs at both hips reduce the walking cost up to 50%, support hip up to 85% with spring stiffness as an optimization variable for both cases while mechanically locking the support knee reduces the cost of walking up to 25% with gait and knee locking angle optimized.

This paper deals with a planar biped. The aim of this paper is the estimation, during the imbalance phases of a walking cyclic gait, of its absolute orientation by only using the measurement of the actuated joint variables. The main contribution is the experimental evaluation of an original finite-time convergent-posture observer.

Experimental validation of absolute orientation estimation solutions is displayed for the dynamical stable five-link biped robot Rabbit during a walking gait. The objective is to prove the technical feasibility of posture online software estimation in order to remove sensors. Finally, this paper presents the first experimental results of walking biped robot posture estimation.

A ballistic walking gait is designed for a planar biped with two identical two-link legs, a trunk and two one-link arms. This seven-link biped is controlled via impulsive torques at the instantaneous double support to obtain a cyclic gait. These impulsive torques are applied in six inter-link joints. Then infinity of solutions exists to find the impulsive torques. An energy cost functional of these impulsive torques is calculated to choose a unique solution by its minimization. Numerical results show that for a given time period of the walking gait step and a length of the step, there exists an optimal swinging amplitude of arms. For this optimal motion of the arms, mentioned above cost functional is minimum.

Fast human walking includes a phase where the stance heel rises from the ground and the stance foot rotates about the stance toe. This phase where the biped becomes underactuated is not present during the walk of humanoid robots. The objective of this study is to determine if the introduction of this phase for a 3D biped robot is useful to reduce the energy consumed in the walking. In order to study the efficiency of this new gait, two cyclic gaits are presented. The first cyclic motion is composed of successive single support phases with flat stance foot on the ground. The second cyclic motion includes a sub-phase of rotation of the supporting foot about the toe. For these two gaits, optimal motions are designed by minimizing a functional torques cost. It is shown that for fast motion a foot rotation sub-phase is useful to reduce the functional cost.

The objective of this study is to obtain optimal cyclic gaits for a biped without actuated ankle. For the walking, the gait is composed of successive single support phases and instantaneous double support phases that are modeled by passive impact equations. The legs swap their roles from one single support phase to the next one. During each phase the evolution of the joints variables is assumed to be polynomial functions of a scalar path parameter. The coefficients of the polynomial functions are chosen to optimise a torque criterion and to insure a cyclic motion for the biped. Furthermore, the optimal gait is defined with respect to given performances of actuators. The torques and velocities at the output of the gearbox are bounded. For this study, the physical parameters of a prototype are used. Initial starting motions that are composed of a double support and a transitional single support are also defined.

A step-by-step observer based on second order sliding mode approach is proposed to determine the absolute orientation of a biped robot during a walking cyclic gait. The gait are composed of single support phases and impacts. The biped is underactuated in single support because there is no motor in the ankles. The observer and the control law converge in finite-time. The originality is both: firstly, the observer is based on second-order sliding mode approach and is original in biped robot context Secondly, the estimation of all state variables are derived from only actuated joint variables, which induces a minimization of the sensors number. Numerical tests are proposed to show the robustness of the observer coupled with the control.

The authors propose a nonlinear control law defined to minimize the variation of the performances of the robot whatever the location of the trajectory in the workspace. It takes elastic deflections into account, and minimizes the norm of the difference between the real behavior and the desired behavior of the robot. A method for calculating the gain is proposed, and the results are compared with the linear control laws. The applicability domains on both control laws are considered, and robustness is studied.>