Three-step precise robotic peg-hole insertion operation with symmetric regular polyhedral objects

Robotic peg-hole insertion operation, the most widely used assembly model, has been extensively investigated. The objective is to design strategies, o r hardware, in order to enable a robot to achieve the assembly operation wi th: (1) higher accuracy than that obtainable directly from the resolution o f the robot, (2) a cost lower than manual labour prices and, (3) an operati on time in the range from 1.0 to 2.5secs. There are many strategies provide d through the use of specially designed hardware, for example, force sensor s and robotic flexible wrists. However, it is difficult to achieve robotic peg-hole insertion with high accuracy, low cost and high speed. In previous work, strategies were designed to achieve the assembly operations without using force sensors or RCC (H. Qiao, B. H. Dalay, J. A. G. Knight, 1996, Ro botic assembly operation strategy investigation without force sensors throu gh the research on contact point location and range of peg movement. Procee dings of the IMechE, Journal of Engineering Manufacturing, Vol. 210, pp. 28 9-307). The strategy development in our work is based on the back-projectio n concept and the analysis of the allowable range of the peg system, which is constrained by the geometry of the hole system. The allowable range of t he peg in the peg-hole system has been established, and features of this al lowable range have been studied in detail. Compared with our previous strat egies, this paper provides a strategy where the number of the required oper ational steps is reduced and the assembly process is simplified. The validi ty of this new method and the allowable initial range of the strategy are a lso studied. The key point in this paper are as follows: (a) establishing t he general allowable range for the peg-hole system with symmetrical regular polyhedral objects, rather than for the round peg-hole system only, (b) st udying the characteristics about this allowable range in more detail and fi nding out simplified strategies by their utilization, and finding out the a llowable initial range for the peg-hole system in the new strategy. This st rategy only includes three steps with the peg: (i) first rotated around an axis normal to its axis, (ii) then pushed towards the hole, (iii) then rota ted back and inserted into the hole. This paper develops a particular strat egy with the following characteristics: (1) it can perform the assembly ope ration fast. reliably and precisely, (2) there is no need to use force sens ors or flexible wrists (3) the operation is simplified through the use of c ontact fords between the peg and the hole. There are three steps involved i n the operation process. This method has been successfully applied to the c ylindrical peg-hole insertion operation based on a 29.99 mm diameter peg an d a hole with a diameter clearance of 0.02 mrl. The operational time averag es 1.5 sec. The strategy has been further verified through the simulation p rocess. In addition, other issues about the strategy investigation, which m ay lead to new strategies, have been discussed.