This paper discusses two ways to estimate the interaction force at the end-effector of a robot. The first approach that is presented combines filtered dynamic equations with a recursive least squares estimation algorithm to provide a smoothened force signal, which is useful in the (common) case of noisy torque measurements. The second approach, which uses a generalized momentum based disturbance observer, is mainly discussed to compare it to the first approach. Although very different in appearance, it is shown that a close connection exists between both approaches. Simulation results for both algorithms are shown, and experimental results derived from a sensorless admittance controller that was implemented using the algorithms are presented.

Research in robotic gait rehabilitation still faces many challenges regarding ankle assistance, body weight support and human-robot interaction. This paper reports on the development, focusing on these challenges, of a gait rehabilitation exoskeleton powered by pleated pneumatic artificial muscles. The first prototype is intended as a platform for the evaluation of design and control concepts. The mechanical design procedure is explained with the emphasis on optimization. A proxy-based sliding mode control approach is proposed and evaluated by means of simulation. Simulation results indicate good tracking performance and safe system behavior, encouraging experimental validation on the prototype.

In the biped Lucy pleated pneumatic artificial muscles are used instead of electrical motors to power the joints, because in an antagonistic set-up both the torque and the compliance are controllable. The muscles have also a high power to weight ratio and they can reduce impact effects. Interesting characteristics that can be exploited for legged robots. In this paper a control strategy is discussed where a torque control unit tracks a predefined trajectory and a compliance controller is used to reduce control efforts and energy consumption by fitting the compliance of the actuator to the natural compliance of the desired trajectory. The first part of this paper focusses on the torque control unit for the biped. The proposed control architecture consists of the joint trajectory generator and the joint trajectory tracking controller. The trajectory generator calculates trajectories represented by polynomials based on objective locomotion parameters, which are average forward speed, step length, step height and intermediate foot lift. The joint trajectory tracking controller is divided in three parts: a computed torque module, a delta-p unit and a bang-bang pressure controller. Results of the incorporation of this control architecture in the real biped Lucy are given. Several essential graphs showing tracking performance and pressure regulation are given and the effectiveness of the control algorithm is discussed. A second part of the paper focusses on the compliance controller which is experimentally tested on a one DOF pendulum. A mathematical formulation to exploit the natural dynamics with respect to different walking patterns for this purpose is explained. The experimental results show the effectiveness and importance of the adaptation strategy