Abstract
A parallel mechanism’s pose is usually obtained indirectly from the active joints’ coordinates by solving the direct kinematics problem. Its accuracy mainly depends on the accuracy of the measured active joints’ coordinates, the tolerances in the active and passive joints, possible backlash, axes misalignment, limb deformations due to stress or temperature, the initial pose estimate that is used for the numerical method, and the accuracy of the kinematic model itself. Backlash and temperature deformations in the active joints especially hinder high-precision applications as they usually cannot be observed. By implementing a camera module on the base platform and an array of fiducial tags on the moveable manipulator platform of a parallel mechanism, a highly accurate, direct, and absolute pose measurement system can be obtained that can overcome those limitations. In this paper, such a measurement system is proposed, designed, and its accuracy is investigated on a state-of-the-art H-811.I2 6-axis miniature hexapod by Physik Instrumente (PI) GmbH & Co. KG.
Highlights
Sensing for Parallel Mechanisms.Parallel mechanisms are famous for their higher position accuracy compared to serial mechanisms due to the higher stiffness and the parallel arrangement of their limbs that connect the fixed base platform with the moveable manipulator platform
In this paper, such a measurement system is proposed, designed, and its accuracy is investigated on a state-of-the-art H-811.I2 6-axis miniature hexapod by Physik Instrumente (PI) GmbH & Co
The Stewart–Gough platform is especially widely used for high-precision applications due to its parallel kinematic structure, six degrees of freedom, and simple kinematic architecture
Summary
Parallel mechanisms are famous for their higher position accuracy compared to serial mechanisms due to the higher stiffness and the parallel arrangement of their limbs that connect the fixed base platform with the moveable manipulator platform. They offer lower moving masses, smaller overall machine sizes, lower inertial forces, and faster processing velocities. The Stewart–Gough platform, named after its inventors Gough [6] and Stewart [7], has three translational and three rotational degrees of freedom and consists of six identical limbs that connect the fixed base platform with the moveable manipulator platform. The underlined joint indicates that this joint is active and actuated while the other joints are passive and align according to the closure constraints of the mechanism
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