Material-Handling Robots for Programmable Automation

Abstract

This paper deals with the requirements, present development, and research issues concerning advanced material-handling systems based on programmable manipulators that are commonly called industrial robots.Industrial robots are becoming increasingly important as part of programmable automation systems being developed for the production of batch-produced discrete part goods. As contrasted with hard or fixed automation, programmable systems are designed for flexibility, that is, for ease of set-up for new or changing products in small or variable lot sizes, and adaptively responsive to a variable environment.Material handling entails the controlled manipulation of raw materials, workpieces, assemblies and finished products. Together with inspection and assembly, these functions represent essential parts of the total manufacturing process that are still highly labor-intensive.The great majority of present industrial robots (first generation) are performing relatively simple repetitive material handling tasks in highly constrained or structured environments. They are also increasingly used in spot-welding and paint-spraying operations. Second generation robots which incorporate computer processors or minicomputers have begun to appear in factories, considerably extending rudimentary pick-and-place operations. More advanced robots are being developed which incorporate visual and tactile sensing, all under computer control. These integrated systems begin to emulate human capabilities in coping with relatively unstructured environments.There are two major requirements for advanced material handling systems. The first requirement is for a programmed robot to be able to acquire randomly-positioned and un-oriented workpieces, subassemblies or assemblies from stationery bins or from moving conveyors, in a predetermined manner, and to convey them via a predetermined path, safely, to some desired position and orientation.The second requirement is for the robots to be able to place the acquired workpiece or assembly with a desired orientation in a position with a specified precision.These two requirements share the need for sensor-controlled manipulation to varying degrees. Tactile sensing may be sufficient for a simple task in which the workpieces are already oriented and require crude end-positioning at the destination such as in a palletizing operation. Visual sensing may be required when the workpieces are unoriented originally, are in motion, or when the final position is not precisely determined. In some instances, both tactile and visual sensing would be the most effective method, as when packing an unoriented container with workpieces in a desired order. Finally, in automated assembly processes, visual and/or tactile sensing may be required to bring parts together in fitting operations, or for insertions of shafts or bolts in holes. In the latter cases, the precision requirements for a passive accomodation system, together with the completeness of jigging or fixturing would govern how much sensor control was necessary.The major issues thus are the relative costs of orienting parts, of fixturing to preserve position and orientation, of high-performance robots (speed and precision) and on the trade-off attainable by the use of sensor control to reduce the cost of the other alternatives.