A novel error mapping of bi-directional angular positioning deviation of rotary axes in a SCARA-type robot by “open-loop” tracking interferometer measurement

Abstract

To further extend the application of an industrial robot to e.g. the machining, it is crucial to ensure its three-dimensional (3D) positioning accuracy over its entire workspace. Numerous past works presented numerical compensation based on the robot kinematic model containing position and orientation errors of rotary axes average lines, widely known as Denavit-Hartenberg (D-H) parameters. This paper presents two novel contributions. First, this paper proposes a kinematic model with the angular positioning deviation “error map” of each rotary axis, which is given as a function of command angular positions. Furthermore, to model the backlash influence, it is modelled dependent also on the direction of rotation. The second contribution is on the proposal of the “open-loop” tracking interferometer measurement to indirectly identify the angular positioning deviation of each rotary axis. It measures the distance from the retroreflector, fixed on the table, to the robot's end effector at many points over the entire workspace by using a laser interferometer attached to the robot's end effector. The identified kinematic model's accuracy is experimentally investigated, and is compared to the conventional D-H model.