The term robot comes from the Czechoslovakian wordfor “forced labor,” invented by Karel Capek. Karel Capek used robots in his plays and had them look and behave like people. Today, the word “robot” is harder to define because of new designs and technology. The third edition of Websters’s New International Dictionary defines a robot as “a machine in the form of a human being that performs the mechanical functions of a human being. ” However, today’s robot makers are not interested in giving their creations human forms. Most industrial robots look like lobsters or oversized grasshoppers.
Around 1981, the members of the Robot Institute of America, held a meeting to develop a definition of an industrial robot. Finally after long debate, they came up with the definition: “A reprogrammable, multifunctional manipulator designed to move material, parts, tools or specialized devices, through variable programmable motions, for the performance of a variety of tasks. ” The key wor ds in their definition are “reprogrammable” and “multifunctional. ” By “reprogrammable” they mean that if a robot gets a new assignment, it will need new instructions, but its basic structure will not change (except maybe a new mechanical hand).
By “multifunctional” they mean a robot is the mechanical counter part of a computer that can handle various problems without any major hardware modifications. The only thing that changes when a robot is reassigned is its program of instructions. In modern robots, programmable microprocessors control all the robot’s movements and actions. Robots can be taught by using a teaching mode. An operator moves the robot’s hand through all of the desired motions manually with his own hand. When the robot is activated, it will repeat those same motions over and over again.
Most robots are equipped with one hand and one arm of several articulated joints. Some of these joints swivel in smooth arcs mimicking the behavior of the human shoulder, wrist, and elbow. Other robots move in straight lines similar to a crane. Robots rarely have a pair of arms, and are usually stationary. If a robot moves that is all it does. Examples are delivery robots rolling down halls delivering mail or supplies. The hands and arms of early robots were pneumatically powered (air pressure) or hydraulically powered (fluid pressure). Flexible tubes carried the pressurized substances to the joints.
Now, electric motors located at the joint give the robot greater precision and control, but slow down its movements. All robot manufacturers dream of joints with human-like tendons. Most robots are blind and are insensitive to their surroundings. Some have sensors triggered by light, pressure, or heat that can create a crude picture of what is happening. ROBOTIC ARMS There are four types of robot arms that are used today. Degrees of freedom are the axes around the arm in which it is free to move. The area a robot arm can reach is its work envelope.
Rectangular arms are sometimes called “Cartesian” because the arm’s axes can be described by using the X, Y, and Z coordinate system developed by Descartes. Descartes is a famous French philosopher, scientist, and mathematician. If a pen were attached to the arm, it would draw a rectangle which would be its work envelope. Imagine a graph where X would be side to side, and Y would be in and out on the graph. Up and down would be Z which runs through the graph and describes depth. Z also adds the third dimension. A cylindrical arm also has three degrees of freedom, but it moves linearly only along the Y and Z axes.
Its third degree of freedom is the rotation at its base around the two axes. The work envelope is in the shape of a cylinder. The spherical arm replaces up and down movements along the two axes with a rocking motion of the arm. The spherical arm’s work envelope is a partial sphere which has various length radii. The last and most used design is the jointed-arm. The arm has a trunk, shoulder, upper arm, forearm, and wrist. All joints on the arm can rotate, creating six degrees of freedom. Three are the X, Y, and Z axes. The other three are pitch, yaw, and roll. Pitch is when you move your wrist up and down.
Yaw is when you move your hand left and right. Rotate your entire forearm as if you are drilling a hole. Your arm would rotate around an axis that goes through the center of your wristbone. This motion is called roll. What a robot does is stated in its program. The program tells a microprocessor what to do. The microprocessor sends signals to joint boards, which in turn, send signals to a motor. Then the motor moves the joint the way the program wants it to. Robots can be programmed by a computer. An operator enters the work movements into a computer which tells the robot what to do.
Robots can also be “taught” what to do by having its arm moved. The operator moves the robot’s arm with his own arm through all the movements. The robot preforms the movements over and over again. In factories today, industrial robots perform such tasks as welding, machine loading and unloading, material handling, spray finishing, assembly, and machine applications. In nuclear power plants and other facilities where radiation is hazardous to humans, robotic arms that are partly machine and human controlled are used for maintenance, repair, and waste removal.
Similar arms on diving vehicles facilitate undersea salvage and exploration by navies and offshore oil industry. Industrial robots can perform two kinds of welding operations – spot and arc welding. For spot welding, two metal sheets are welded by laying one sheet on top of the other and fusing them with an electric gun at several points. This is a difficult and unpleasant task for humans because the welding gun is heavy. Also, assembly lines only allow a short time to move the gun, and welds can be placed inconsistently or missed. The parts move on a conveyor belt and as they pass by, the robot welds them.
The robots remember the position of each weld that is to be made, and can recall other programs when a new material appears on the line. In arc welding, metal sheets are pressed together. Then a thin tungsten wire at the tip of and electrode is brought close to the surface. Current is passed through the electrode, creating a spark. The resulting heat, as much as 6,500 degrees Fahrenheit, melts the sheets together. Robots are used instead of humans because of the heat and flying sparks. Also, the robot must hold the electrode at the same height while welding. This is hard for a human to do hour after hour.
