This paper deals with force and impedance control of series elastic actuators for driving the joints of an exoskeleton for lower limbs. Series elastic actuators are devices where elastic components are introduced between the motor’s output and the load. From the deflection of these components, it is possible to measure the force applied to the load and to control it. Also, the mechanical impedance of the actuator/load interface can be regulated to the typical values of joint’s stiffness and damping presented by humans during the walking. Results of force and impedance control applied to an active ankle-foot orthosis driven by a series elastic actuator are presented. Also, a variable impedance control strategy is performed to reproduce the behavior of an actual ankle joint.

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This paper presents the development of a prototype of an active orthosis for lower limbs. The proposed orthosis is an orthopedical device with the main objective of providing walking capacity to people with partial or total loss of limbs movements. In order to design the kinematics, dynamics and the mechanical characteristics of the prototype, the biomechanics of the human body was analized. The orthosis was projected to reproduce the movements of human gait. The movements of the joints of the orthosis are controlled by DC motors equipped with mechanical reductions, whose purpose is to reduce rotational speed and increase the torque, thus generating smooth movements. An embedded electronic system for sensory data acquisition and motor control was projected. The gait movements of the orthosis will be controlled by high level commands from a human-machine interface based on processings of electroencephalogram signals, speech recognition or joystick.

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