University of Twente Student Theses


Reducing motion inaccuracies due to cogging in a redundantly actuated 3-DOF manipulator

LI, Yingying (2023) Reducing motion inaccuracies due to cogging in a redundantly actuated 3-DOF manipulator.

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Abstract:PKM are widely used in different fields owing to their advantages of high stiffness, low inertia, and high acceleration. In order to address the singularity problem of the parallel manipulator, RA-PKM has been developed. Previously, a 3DOF RA-PKM with compliant joints and redundant actuation was designed, constructed, and tested. However, the utilization of direct drive brushless actuators resulted in significant motion inaccuracies due to cogging behavior. Because of the magnetic attraction between the rotor’s permanent magnet and the stator, cogging torque occurs. The cogging torque causes periodic variations that can lead to irregularities, hitches, or jerks in motion, ultimately impacting position control and performance accuracy. This thesis focuses on developing a model to mitigate the cogging effect on the dynamic motion of the RA-PKM system. To start with, the kinematic and dynamic motion characteristics of the RA-PKM system have been thoroughly studied. Subsequently, the cogging torque data from the motors operating under diverse conditions were collected by a series of experiments. Based on the cogging torque data, the cogging torque equation was successfully derived by employing a parameter identification method. Meanwhile, the influence of the cogging torque on the dynamic motion of the manipulator was analyzed. In order to mitigate the cogging effect, two control methods, namely feedforward compensation method and feedback compensation method, were developed based on meticulous analyses as well as the application of control theory principles. The efficacy of both control methods was assessed through a combination of simulation and experimental studies, encompassing both single-arm system and the complete system. Here, the feedback control method demonstrated superior performance in enhancing the motion accuracy within the context of single arm system. From the complete system, both methods appear no significant difference in improving the system performance. This is due to the inherent redundancy of the complete system.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:52 mechanical engineering
Programme:Systems and Control MSc (60359)
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