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Abstract
Mechanical systems for manufacturing in the past have represented monolithic, dedicated machines which remain expensive and inflexible relative to product changes due to market demands. Computer systems, by contrast, are increasingly modular, easily upgradable, and rapidly reconfigurable to meet customer requirements. Modularity based on a full architecture in the mechanical structure of machines (robots), now makes a universal control system software possible for a very large class of machines. This operating system must be able to support the development of a full manufacturing cell made up of fixtures, handling systems, assembly devices, forming subsystems, etc. Common among these would be actuator modules, end-effectors, link structures, standardized interfaces, communication buses, etc. The operating system software would automatically be configured to meet any combination required to make up the cell. This software must provide for the performance, criteria based maintenance, andfault-tolerance of the cell.
Keywords: Software, Digital Control, Robots, Manufacturing Cells.
Background
Today’s increasingly global trade for manufactured goods requires that those products be of world class quality and responsive to market demands. Over the past 10 years, the U.S. trade deficit in manufacturing goods has averaged $150 biffion per year [63]. Much of this deficit has been due to a weakness in U.S. machine technology, which is, not competitive with the best offered in Central Europe and Japan. With the advent of commercially available, inexpensive, high-performance computing technology, programmable automation has seen unprecedented growth. Nevertheless, tasks associated with dexterous systems (robots, fixturing, positioners, etc.) are usually used for low valued functions which require only the simplest technology far below that now used in our fly-by-wire aircraft. This lack of technical sophistication leads to integration costs (special fixture designs, calibration, etc.) which exceeds the cost of the robot itself by as much as five times
[64].
Modular Robotics
To achieve a revolution in the manufacturing industry it is crucial to draw from the successes of the computer industry. The first lesson to learn from the computer industry is its application of modularity to the design of the personal computer. Surprisingly, an intuitive design issue like modularity, is rarely present in the design of industrial robots. Current industrial robots are monolithic structures that have limited application and almost no upgradability options. On the other hand, a personal computer offers us the best example of modularity and upgradability. Modularity provides us with a system that has standardized interfaces and plug-and-play capability. Also, due to the availability of various modules that maintain standard interfaces, a modular robot may be configured for a particular task and then quickly reconfigured later if the task changes. The University of Texas, Robotics Research Group, has been aggressively pursuing modular robot technology
for over two decades [14]. It is the goal of the Robotics Research Group to design a mechanical architecture that can rapidly evolve in the same fashion as is now feasible for a personal computer. This effort has centered around the design of a family of link, joint, and actuator modules. A prototype has been designed and built for a 2-DOF knuckle module [76]. Furthermore, a modular robotics testbed consisting of 1-DOF joint modules, various link modules, and off-the-shelf
actuators has been designed and built. In addition, a project to design and build a 7-DOF modular robotic system is in its fourth year of development [49].
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