The objective of this study is to obtain optimal cyclic gaits for a biped robot without actuated ankles. Two types of motion are studied: walking and running. For walking, the gait is composed uniquely of successive single support phases and instantaneous double support phases that are modelled by passive impact equations. The legs swap their roles from one single support phase to the next one. For running, the gait is composed of stance phases and flight phases. A passive impact with the ground exists at the end of flight. During each phase the evolution of m joints variables is assumed to be polynomial functions, m is the number of actuators. The evolution of the other variables is deduced from the dynamic model of the biped. The coefficients of the polynomial functions are chosen to optimise criteria and to insure cyclic motion of the biped. The chosen criteria are: maximal advance velocity, minimal torque, and minimal energy. Furthermore, the optimal gait is defined with respect to given performances of actuators: The torques and velocities at the output of the gear box are bounded. For this study, the physical parameters of a prototype, which is under construction, are used. Optimal walking and running are defined. The running is more efficient for high velocities than the walking with respect to the studied criteria.

Multichannel intramuscular EMG (iEMG) recordings provide information on motor neuron behaviour, muscle fiber (MF) innervation geometry and, recently, have been proposed as means for establishing human-machine interfaces. Objective: in order to provide a reliable benchmark for computational methods applied to such recordings, we propose a simulation model for iEMG signals acquired by intramuscular multi-channel electrodes. Methods: we propose a simulation model for iEMG simulation methods, such as farthest point sampling for more uniform motor unit innervation centers distribution in the muscle cross-section, accurate fiber-neuron assignment algorithm, motor neuron action potential propagation delay modelling and a linear model for multichannel recordings simulation. The proposed approach is also extended to gradually shifting (scanning) electrodes. Results: we provide representative applications of this model to the validation of methods for the estimation of motor unit territories, and for iEMG decomposition. Moreover, we extend this model to a full multichannel iEMG simulator using classical linear EMG modelling and existing approaches to the generation of motor neuron discharge sequences. Conclusions: the obtained simulation model provides physiologically accurate MUAPs across entire motor unit territories and for various electrode configurations. Significance: it can be used for the development and evaluation of mathematical methods for multichannel iEMG processing and analysis.

It is well known that the homogeneous differentiator strategies reduce the chattering in the implementation of sliding-mode algorithms and the recent implicit framework based projector provides very interesting properties when associated with homogeneous design. In this article, it is proposed to evaluate different strategies of homogeneous differentiators based on Euler explicit and promising Euler semi-implicit strategies, for which discrete implementations have been realized on a pneumatic actuator. Experimental results highlight the benefit of a Euler semi-implicit-based structure using a projector.