Design characteristics of Robots:
Some of the advanced capabilities being designed into robots in addition to their basic reprogram ability and manipulative skills are virtually all the human senses â€“ vision, tactile sensing, and hand-to-hand coordination. In addition, some robots can be â€œtaughtâ€ a sequence of motions in a three dimensional pattern by moving the end of the arm through the required positions and manipulations. The robot records the pattern in its computer memory and will repeat them on command.
The motions that robots can reproduce seem to duplicate all those that human arms and hands can perform. For example, the jointed arm, spherical motions in both planes, cylindrical rotation and even complex wrist motions are duplicated in current designs.
There are some unique applications of robots, such as assembling high-explosive shells in government arsenals, picking up hot steel ingots and placing them in presses, handling radioactive rods in nuclear power plants, and other nuclear applications where human safety requires remote mechanical handling. But by all odds, the dominant applications have been in ordinary manufacturing operations, such as spot welding and material handling.
The auto industry has been the dominant user, though other industries are rapidly installing robots too, such as electrical machinery, fabricated metals, electronics and heavy machinery.
Economics of Robots
Robots are already economically justified in many situations. Assuming an average original cost of $100,000, they cost in the range of $9 to $12 per hour to operate, including capital and operating costs. Compared to the average steel workerâ€™s wage per hour including benefits or the average autoworkerâ€™s wage, the costs worked out have shown the robot is obviously a bargain. While robots have been available for many years, it is only recently that it has become attractive to replace humans with robots because of technological breakthrough and high labor costs.
The accuracy and consistency of operations is greatly improved with robots, reducing rejection rates and the need for further quality checks. For example, at the Fort Worth General Dynamics plant, the computerized Milicron T-3, drills a set of holes to a tolerance of Â±0.005 inch and shapes the outer edges of 250 types of parts at a rate of 24 to 30 parts per shift with no defects. A human worker can produce only 6 parts per shift with a 10% rejection rate. The robot costs $120,000, but can save $90,000 in the first year.
Numerically Controlled (NC) Machines:
When the positions or paths of cutter tools are under the control of a digital computer, we have numerical control. Te feedback control paths emanate from the basic positioning controls of the tools or work tables that determine the position of the cutters relative to the work. These feedback control loops continually compare the actual position with the programmed position and apply correction when necessary.
When two dimensions are controlled, we have position control, illustrated by the drilling of holes that must be positioned accurately. The drill tool can be moved in two dimensions to achieve the desired position, after which the tool does the work to produce the hole. Such a system can be programmed to drill a series of accurately positioned holes.
When position control is carried one step further, by controlling three dimensions, we have contour control, controlling the actual path of the cutter. Contour control involves a much more complex programming problem because curves and surfaces must often be specified. Contour control systems have great flexibility in terms of the part shapes that can be produced as well as in the change of shapes from job to job. Instead of the part being processed through a sequence of machines or machine centers, it is often possible all the required operations with a single set-up because the cutter can be programmed to make cuts along any path needed to produce the required configuration. Very complex parts can be produced with a single set-up. One of the great advantages of numerically controlled systems is that the machine tool is not tied up for long periods during set-up because practically all the preparation time is in programming, which does not involve the actual machine tool. In addition, repeat orders require virtually no set-up time. Thus, the field of applicability includes parts that are produced in low volumes. Therefore, through numerically controlled processes, automation is having an important impact on process technology for both high-volume, standardized types of products and low-volume products (even custom designs).