A Simple Accurate Positioning System for an Industrial Robot

The present designs of industrial robots or mechanical handling units generally fall into two categories, the simple pick‐and‐place units with two fixed positions per axis, or the more sophisticated type such as Unimate with a very large number of positions per axis and a large memory. Whilst the latter devices are essential for complex operations such as spot welding, paint spraying or palletising there are many applications where only a small number of positions per axis are required, e.g. press loading, conveyor transferring, assembly operations. This paper describes a positioning system that falls between the above two general categories in that it allows a number of positions on each axis to be selected. A detailed description is given of the positioning system which basically consists of a number of mechanical stops attached to indexable bars such that there are a minimum number of 6 positions per axis. These stops are positioned as required and include a fine positioning adjustment. It is found that this system gives a positioning accuracy far greater than those commonly used with robots. The design of the hydraulic system and the control system for the fast to slow traverse are given together with test results obtained from a prototype system. The method of programming and the advantages and disadvantages are specified in a final discussion. In particular how the system can be used in fairly complex operations such as palletising is discussed.