Abstract
The dynamics analysis and control of the upper limb exoskeleton for supporting user movement is done by using the force feedforward control model. Based on a novel combination of Proportional Derivative (PD) force feedforward and Proportional Integral (PI) feedback control model [1], this paper proposes a method to assist the user’s movement for a three degree of freedom exoskeleton structure. When the user exerts force at the handle, the force is measured by a force sensor placed at the handle. These sensed forces are applied to command the actuators to support the human movement and reduce the disturbance effects of the device. This technique is well established approach in haptics for reducing the effects of inertia, damping, friction, centrifugal and Coriolis forces and gravity of haptic device [2]. Simulation result shows the torque controlled by robot to assist human for a desired loading motion.
Highlights
An upper limb exoskeleton (Fig. 1) is an electromechanical system of mechanical structure, sensors, actuators and a digital processing unit which is controlled by a Personal Computer [3, 4] (Fig. 2 and Fig. 4)
This research is motivated by two current projects in Institute of Mechanics (VAST) and Asian Institute of Technology (AIT) where we focus on an arm exoskeleton with force assistant using force feedforward control
The Proportional Integral controller will compare the difference between the desired inputs torque provided by the force feedforward controller, the torque u (i = 1,2,3) following Eq (12) with the output torques generated by electrical motors u (i = 1,2,3) following Eq (17) which is fedback by hall sensors
Summary
An upper limb exoskeleton (Fig. 1) is an electromechanical system of mechanical structure, sensors, actuators and a digital processing unit (dSPACE or DAQ card) which is controlled by a Personal Computer [3, 4] (Fig. 2 and Fig. 4). Upper limb exoskeleton equipped with a force sensor which can sense the force exerted by the user, and can produce necessary torques through joints at wrist, elbow and shoulder for supporting human movement, has been developed [1, 2, 5]. This research is motivated by two current projects in Institute of Mechanics (VAST) and Asian Institute of Technology (AIT) where we focus on an arm exoskeleton with force assistant using force feedforward control These devices contain both hardware and software and are designed and built for rehabilitation purpose. In Step 2, a force feed forward control is used to control motors located at joints to support the current force generated by the user to perform some tasks: moving freely and lifting some objects vertically and horizontally. Simulation results show the performance of force control for a desired loading motion
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