System identification: theory for the user
System identification: theory for the user
A highly backdrivable, lightweight knee actuator for investigating gait in stroke
IEEE Transactions on Robotics - Special issue on rehabilitation robotics
Optimized passive dynamics improve transparency of haptic devices
ICRA'09 Proceedings of the 2009 IEEE international conference on Robotics and Automation
ROBIO'09 Proceedings of the 2009 international conference on Robotics and biomimetics
Modeling of transmission characteristics across a cable- conduit system
IEEE Transactions on Robotics
Compliant robot actuation by feedforward controlled emulated spring stiffness
SIMPAR'10 Proceedings of the Second international conference on Simulation, modeling, and programming for autonomous robots
Control of a robotic orthosis for gait rehabilitation
Robotics and Autonomous Systems
Applied Bionics and Biomechanics
Bio-inspired control of an arm exoskeleton joint with active-compliant actuation system
Applied Bionics and Biomechanics
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Within the context of impedance controlled exoskeletons, common actuators have important drawbacks. Either the actuators are heavy, have a complex structure or are poor torque sources, due to gearing or heavy nonlinearity. Considering our application, an impedance controlled gait rehabilitation robot for treadmill-training, we designed an actuation system that might avoid these drawbacks. It combines a lightweight joint and a simple structure with adequate torque source quality. It consists of a servomotor, a flexible Bowden cable transmission, and a force feedback loop based on a series elastic element. A basic model was developed that is shown to describe the basic dynamics of the actuator well enough for design purpose.Further measurements show that performance is sufficient for use in a gait rehabilitation robot. The demanded force tracking bandwidths were met: 11 Hz bandwidth for the full force range (demanded 4 Hz) and 20 Hz bandwidth for smaller force range (demanded 12 Hz). The mechanical output impedance of the actuator could be reduced to hardly perceptible level. Maxima of about 0.7 Nm peaks for 4 Hz imposed motions appeared, corresponding to less than 2.5% of the maximal force output. These peaks were caused by the stick friction in the Bowden cables.Spring stiffness variation showed that both a too stiff and a too compliant spring can worsen performance. A stiff spring reduces the maximum allowable controller gain. The relatively low control gain then causes a larger effect of stick in the force output, resulting in a less smooth output in general. Low spring stiffness, on the other side, decreases the performance of the system, because saturation will occur sooner.