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Robotic Assembly Operation Strategy Investigation Without Force Sensors Through the Research on Contact Point Location and Range of Peg Movement

The assembly operation plays an important role in manufacturing industry. The robotic peg-hole insertion operation, the most widely used assembly model, has been heavily studied due to its widespread application. The purpose of the research in this area is to design techniques that enable the robot to perform assembly operations with high speed, high accuracy and low cost. The key problems of strategy investigation research include: (a) designing a series of sub-goals through which the peg-hole system can achieve the insertion operation from any point in the initial area, (b) calculating the allowable range for the initial area, (c) determining the values and duration of the control inputs and (d) analysing the robustness of the strategy. There are many strategies given to perform the assembly operation with the assistance of specially designed force sensors or flexible wrists. In this paper: 1. The map from the position of the peg in the coordinate frame attached to the hole and the location of the contact point in the frame attached to the peg was analysed. This provided the basis for the identification of the position relationship between the peg and the hole using a force sensor signal. 2. The range of peg movement was analysed and found to be useful in the selection of the sub-goals for the insertion operation. 3. A deficient and yet precise hardware strategy, characterized by not requiring force sensors or flexible wrists, was analysed. 4. The validity of the deficient hardware strategy was demonstrated through experiments with the UMI-RTX robot. The results were further confirmed through simulation. The allowed initial area, the control input design and the robustness of the strategy were analysed in detail. A constant cycle time of 2.5 s was achieved during the ten trials in which the diameters of the pegs were selected from a choice of 29.99, 31.98 or 31.99 mm with a clearance between the hole remaining at 0.02 mm and a common peg legnth of 41 mm.