Fine Motion Strategies for Robotic Peg-Hole Insertion

The robotic assembly operation has a prominent role in industry due to the fact that (a) it accounts for a substantial proportion of production cycle times and (b) it requires high precision. The peg-hole insertion operation, which is a simplified industrial application model, has special prominence. In terms of the hardware, various complex six-component force sensors, passive compliance and vibration systems have been designed for this purpose alone. In the control area, the disturbance filter and real-time control have been applied to the system to enhance performance. Techniques using geometric concepts such as pre-images and back-projections, models of the contact configurations, pattern recognition and fine motion analysis have been studied. The objective of this paper is to illustrate a method that combines these ideas together to solve practical problems. In this paper: 1. General contact configurations and contact motions between the peg and hole are presented. 2. An important problem in the identification of the contact configuration according to the force sensors is studied. It is concluded that the complete identification of the contact configuration should depend not only on the signals from the force sensors but also on the knowledge about the range of the initial state of the peg and clever utilization of the environment. 3. Various strategies with and without force sensors are proposed. Motion and model analysis is used to study the general identification and motion problems in the peg-hole insertion system. Pre-image and back-projection concepts are employed to enable practical implementation of the method which used Petri nets. Selecting the configuration parameters that can be (a) easily measured and (b) used to decide the incremental motion steps through the procedure were found to be complex and critical tasks that enabled success. These strategies have been verified through experimental trials. It is apparent that the fine motion strategy has a wide application in the robotic peg-hole insertion operation.

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