Norm-Optimal Iterative Learning Control for a Pneumatic Parallel Robot
Iterative learning control is a popular method for accurate trajectory tracking of systems that repeat the same motion many times. This paper presents a norm-optimal iterative learning control scheme for a fast two-degree-of-freedom parallel robot driven
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Norm-Optimal Iterative Learning Control for a Pneumatic Parallel Robot Dominik Schindele and Harald Aschemann
Abstract Iterative learning control is a popular method for accurate trajectory tracking of systems that repeat the same motion many times. This paper presents a norm-optimal iterative learning control scheme for a fast two-degree-of-freedom parallel robot driven by two pairs of pneumatic muscle actuators. The robot consists of a light-weight closed-chain structure with four moving links connected by revolute joints. The two base joints are active and driven by pairs of pneumatic muscles by means of toothed belt and pulley. The proposed control has a cascade structure. The internal pressure of each pneumatic muscle is controlled by a fast underlying control loop. Hence, the control design for the outer control loop can be simplified by considering these controlled muscle pressures as ideal control inputs. The angles of the active joints as well as the corresponding angular velocities represent the controlled variables of the outer loop. The implemented ILC algorithm takes advantage of actual state information as well as of data from previous trials. Experimental results from an implementation on a test rig show an excellent control performance.
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Introduction
Pneumatic muscles are innovative tensile actuators consisting of a fibre-reinforced vulcanised rubber tubing with appropriate connectors at both ends. The working principle is based on a rhombical fibre structure that leads to a muscle contraction in longitudinal direction when the pneumatic muscle is filled with compressed air. This contraction can be used for actuation purposes. Pneumatic muscles are low cost actuators and offer several further advantages in comparison to classical pneumatic cylinders: significantly less weight, no stick–slip effects, insensitivity
D. Schindele (*) • H. Aschemann University of Rostock, Rostock 18059, Germany e-mail: [email protected]; [email protected] H. Gattringer and J. Gerstmayr (eds.), Multibody System Dynamics, Robotics and Control, DOI 10.1007/978-3-7091-1289-2_7, # Springer-Verlag Wien 2013
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Fig. 7.1 Test rig of the parallel robot
to dirty working environment, and a higher force-to-weight ratio. A major advantage of pneumatic drives as compared to electrical drives is their capability of providing large maximum forces for a longer period of time. In this case electrical drives are in risk of overheating and may result in increasing errors due to thermal expansion. Different kinematics actuated by pneumatic muscles have been investigated by the authors so far, such as a high-speed linear axis [5] or a delta parallel robot [13]. Applications with pneumatic muscles of other researchers are presented e.g. in [17], where a proxy-based sliding mode control for a 2-dof serial manipulator has been proposed, or in [18], where an adaptive control structure for a platform connected by a spherical joint to the base with three pneumatic muscles
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