A new experimental platform permits us to study a novel variety of issues of human motor control, particularly full 3-D movements involving the major seven degrees-of-freedom (DOF) of the human arm. We incorporate a seven DOF robot exoskeleton, and minimize weight and inertia through gravity, Coriolis, and inertia compensation, such that subjects’ arm movements are largely unaffected by the manipulandum. Torque perturbations can be individually applied to any or all seven joints of the human arm, thus creating novel dynamic environments, or force fields, for subjects to respond and adapt to. Our first study investigates a joint space force field where the shoulder velocity drives a disturbing force in the elbow joint. Results demonstrate that subjects learn to compensate for the force field within about 100 trials, and, from the strong presence of aftereffects when removing the field in some randomized catch trials, that an inverse dynamics, or internal model, of the force field is formed by the nervous system. Interestingly, while after learning, hand trajectories return to baseline, joint space trajectories remained changed in response to the field, indicating that, besides learning a model of the force field, the nervous system also chose to exploit the null space to minimize the effects of the force field on the realization of the endpoint trajectory plan. We discuss applications of these results in the light of current theories of robotic control, including inverse kinematics and optimal control.

(далее…)

Категория: Научные статьи | Нет комментариев »

In this paper an embedded control system for a powered orthosis is presented. The orthosis is used to support the thigh muscles during flexion and extension of the knee while performing common motions like getting up from a chair, walking, or climbing stairs. The user interface of the control system is implemented by evaluating EMG signals from significant thigh muscles to find out the intended motion of the subject. The intended motion is executed with a linear actuator to support the subject’s own muscle force. Results from two experiments are presented. During the trials the torque support from the actuator illustrates the performance of the system.

(далее…)

Категория: Научные статьи | Нет комментариев »

We have developed a feedback controller for a walking simulator composed of a treadmill and a rear projection screen, that keeps the subject centered and visual extent consistent across subjects and time while allowing them to set their own walking pace.

(далее…)

Категория: Научные статьи | Нет комментариев »

This paper presents a gait-pattern adaptation algorithm for exoske-letons based on the Zero Moment Point criterion. The proposed exoskeleton is developed for lower limbs and based on a commercially available orthosis. The step length and duration are considered as the adaptation parameters, they are computed through minimization based on inverse dynamics and considering the orthosis-patient interaction forces. Also, a robust controller based on the H method is designed to attenuate the effects of external disturbances and parametric uncertainties in the trajectory tracking errors. The dynamic model of the actual exoskeleton, with interaction forces included, is used to generate simulation results.

(далее…)

Категория: Научные статьи | Нет комментариев »

This chapter discusses the advantages and feasibility of using compliant actuators in exoskeletons. We designed compliant actuation for use in a gait rehabilitation robot. In such a gait rehabilitation robot large forces are required to support the patient. In case of poststroke pa-tients only the affected leg has to be supported while the movement of the unaffected leg should not be hindered. Not hindering the motions of one of the legs means that mechanical impedance of the robot should be minimal. The combination of large support forces and minimal impedances can be realised by impedance or admittance control. We chose for impedance control. The consequence of this choice is that the mass of the exoskeleton including its actuation should be minimized and sufficient high force bandwidth of the actu-ation is required. Compliant actuation has advantages compared to non compliant actuation in case both high forces and a high force tracking bandwidth are required. Series elastic actuation and pneumatics are well known examples of compliant actuators. Both types of compliant actuators are described with a general model of compliant actuation. They are compared in terms of this general model and also experimentally. Series elastic actuation appears to perform slightly better than pneumatic actuation and is much simpler to control. In an alternative design the motors were removed from the exoskeleton to further minimize the mass of the exoskeleton. These motors drove an elastic joint using flexible Bowden cables. The force bandwidth and the minimal impedance of this distributed series elastic joint actuation were within the requirements for a gait rehabilitation robot.

(далее…)

Категория: Научные статьи | Нет комментариев »