The most widely accepted definition of an industrial robot is: "a reprogrammable multi-functional manipulator designed to move material, parts, tools or specialised devices through variable programmed motions to accomplish a variety of tasks". Robot is a mechanical machine that is programmable, which means that a sequence of moves can be preset to be repeated time after time, then reset again to perform another set of moves. Robots replace humans for some very heavy, dirty, dangerous, or unpleasant tasks where the job is very routine (monotonous) in nature. The art of selecting robots for various applications - and deciding when to use them - is called robotics. Although industrial robots may vary widely from one to another, they are all made up of three basic components - a manipulator, power supply, and control system. These components may be assembled in one integral unit or separated into individual components connected by pneumatic, hydraulic or electrical connections. Another definition of "robot" is: a programmable manipulator arm with grippers that move and position material, parts, tools or other objects in a CAM system.
The simplest types are pick and place robots typically used in performing material handling functions in which something is picked from one spot and placed at another. This type of robot typically moves only in two or three directions such as in and out, right and left, and up and down. Programming may be done physically with various configurations of electrical wiring or pneumatic connections. The most common type in industry is the servo robot with servo mechanisms that may alter the direction of the arm or gripper in midair. This gives the robot arm joints far greater articulated movement in five to seven directions. The robot may be connected to a programmable controller and programmed in a so called teach mode in which an operator physically leads the arm through the required steps of an operation. This type of manual teaching is one of the most widely used robot programming techniques; although it is time consuming, error-prone and changes in the program usually require the entire sequence of tasks to be taught. The most sophisticated robots are connected to a computer from which instructions are produced and transmitted electronically. These so called smart robots do not have to be given detailed instructions for performing tasks. Rather, the robot program automatically determines grip points and motion paths from application specifications.
Robots can manipulate objects weighing from a few grams to over a tonne and are being used extensively in industry to perform a variety of tasks. Most of these final applications involve tasks that are too tedious or dangerous for human workers. Typical examples include loading and unloading stamping machines and handling toxic material. Among the more common applications of robots are loading and unloading machine tools, painting and spot welding - especially in the automotive and appliance industries. The primary advantage of robots over human workers is that their performance never varies. Quality levels are maintained without distraction or fatigue. Reliability is often greater. Reprogrammable robots can perform a variety of specialised tasks sequences to precise specifications and they require less plant space than do alternative production processes. As robots are refined, however, the advantage of using them to perform other tasks becomes apparent. Robots are now used in a wide range of applications including parts assembly, forging, sheet metal fabrication, and material handling. In these and other applications, the use of robots results in increased productivity, lower costs, and improved quality.
The robots cost heavily. Yet because of tremendously high productivity, payback periods are generally less than two years. Usually, a robot can do the work of many human workers. On an average, their hourly operating cost is one fourth the hourly labour cost in advanced economies. As a result, tenfold reductions in costs are often possible with robots. The following example shows how a robot can be economical for the tasks that it can perform.
A robot installed will cost Rs 5 lakhs for an unpleasant job involving stacking full cans of paints in a paint factory. The robot can be used 20 hours a day, on an average, 7 days/-week. The robot should last 7 to 10 years under such usage with but a few major repairs. An employee is paid Rs 30/hour and Rs 20/hour in fringe benefits. To recover only the initial investment, the robot needs work
Hours to work = (Rs 500000 / Rs 50/hour) = (10000 hours)
The plant operates only two shifts, a total of 16 hours/day for 6 days a week and 52 weeks/year. The total hours a robot would be used per year would be Hours/year plant operation = 16x6x52 = 4992, say 5000 hours. The payback period would be : Payback (years) = (10000 hours) / (5000 hr/yr) = 2 years. Therefore, in two years the robot would recover its initial outlay. The rapid recovery of the initial investment is indeed quite attractive. Although the operating costs for the robot have been ignored in the simplified example, we see that a robot can offer attractive financial returns to the firm.
Robot loaders are also used for work handling for turning/ machining centres. Dedicated robots represent the major trend in automated work handling for turning and machining centres. The robots with four to six axes, body, arm, wrist and grippers sell from US $ 30,000 (appr IR 1300000) and up, and with a buffer table of storage, parts may be able to be machined relatively untended for four to five hours. Most models can handle 5 to 40 kg parts maximum, although larger units handling up to 1000 kg are available. Figure 2 shows a typical robot application in the machine tool industry, that of loading and unloading several machines in sequence and handling conveyor parts.
Industrial applications: an overview
The automotive industry is presently one of the largest users of robots, mostly for spot welding. The author has seen 20,000 bodies of refrigerator compressors being arc welded in a day by robots at NECCHI, Italy in1984. The MNCs like General Motors Corporation, have hundreds of robot welders at various works in the United States and abroad. Toyota, Volvo and Chrysler have made heavy investments in robots. In body framing system, over 200 robots make 98% of all spot welds on some models of cars. Maruti Udyog has been using robots for spray painting of car bodies from day one of its work after incorporation in India. The development of the process is as under: First a sensor is attached to the hand or better the spray gun of a person manually spray painting the car bodies. The sensor traces the movement of the spray gun in various axes including rotations. The path is fed into a computer. A number of readings are taken striking some balance between the accuracy of the results required and the time expended. Just like the "line of best fit", the path of best fit is found out. The robot is programmed to follow this path. The success of the robots in automotive work has also prompted their increasing use in general industry including producers of home appliances. Companies invest millions of dollars on robotics and some of them are likely to have around 1000 of them in operation at present. Companies are continually looking for areas to apply robots, which they find pay for themselves in cost saving in about two years. In some applications robots spray paint on refrigerator liners and porcelain enamel on dish-washer liners, load and unload a press that makes refrigerator liners, and spray refrigerator cabinet interiors with adhesives.
Robots in advanced economies are being used increasingly in the fabrication of aircraft and as far back as 1978 to drill mounting holes in skinpanels for F-16 fighter wings. The productivity has reportedly doubled. Robots being used for drilling aluminium fuselage panels are said to have increased productivity by 400%. Worker reaction in developed countries to these so called "steel collar workers" has generally been favourable although some experts predict that million of industrial jobs around the world could be replaced by robots. For the most part, robots usually create through increased productivity more jobs than they eliminate. Many operators unions have sup-ported robotics. These unions have viewed such technological progress as inevitable and essential for continuous economic growth. The feeling is that the resulting economic growth more that offsets temporary job losses. Robot capabilities continue to be refined and extended, and experts agree that robots used in combination with NC machine tools are the key elements to future automated factories.