In a number of respects, robots are like numerically controlled automated machine tools,wire cutting, die casting, etc. Cnc machining such as an automated lathe, since they are both reprogrammable to produce a number of different objects. What distinguishes robots is their flexibility regarding both range of tasks and motion. In one typical manufacturing application, robots move parts in their various stages of completion from one automated machine tool to the next,the system of robots and machine tools making up a flexible manufacturing workcell. Robots are classified as soft automata, whereas automated machine tools are classified as hard automata. The Japanese Industrial Robot Association also classifies manually operated manipulators and nonreprogrammable, single-function manipulators as robots, and one must bear this in mind when comparing data on robot use between Japan and the United States.
Since robots are defined by their capacity to move objects or tools through space, key issues in robotic control are location and movement, referred to in the industry as kinematics and dynamics. Cnc machining The position of an object in a three-dimensional space can be defined relative to a fixed point with three parameters via the Cartesian coordinate system, indicating placement along x, y, and z axes. The orientation of an object requires three additional parameters, indicating rotation on these axes. These parameters are referred to as degrees of freedom. Together these six parameters and the movement among them make up the data of kinematic control equations.
Robots carrying out simpler tasks may operate with fewer than six degrees of freedom, but robots may also operate with more than six, which is referred to as redundancy. Redundancy gives a robot greater mobility, enabling it to more readily work around obstructions and to choose among a set of joint positions to reach a given target in less time.
Two types of joints are commonly used in robots, the prismatic or sliding joint, resembling a slide rule, and the re volute joint, a hinge. The simplest type of robot to control is one made up of three sliding joints, each determining placement along a Cartesian axis. Robots made solely of revolute joints are more complex to control, in that the relation of joint position to control parameters is less direct. Other robots use both types of joints. Among these, a common type uses a large sliding joint for vertical placement of an arm made of revolute joints. The vertical rigidity and horizontal flexibility of such robots make them ideal for heavy assembly work (this configuration is referred to as SCARA for Selectively Compliant Arm for Robot Assembly). Robots may also be made of a system of arms each with restricted movement (i.e., with relatively few degrees of freedom) but which together can perform complex tasks. These are referred to as distributed robots. Such robots have the advantage of high speed and precision, but the disadvantage of restricted range of movement.
Robots are activated by hydraulic, pneumatic, and electrical power. Electric motors have become increasingly small with high power-to-weight ratios, enabling them to become the dominant means by which robots are powered. The hand of a robot is referred to in the industry as an end effector. End effectors may be specialized tools, such as spot welders or spray guns, or more general-purpose grippers. Common grippers include fingered and vacuum types.
One of the central elements of robotics control technology involves sensors. It is through sensors that a robotic system receives knowledge of its environment, to which subsequent actions of the robot can be adjusted. Sensors are used to enable a robot to adjust to variations in the position of objects to be picked up, to inspect objects, and to monitor proper operation. Among the most important types are visual, force and torque, speed and acceleration, tactile, and distance sensors. The majority of industrial robots use simple binary sensing, analogous to an on/off switch. This does not permit sophisticated feedback to the robot about how successfully an operation was performed. Lack of adequate feedback also often requires the use of guides and fixtures to constrain the motions of a robot through an operation, which implies substantial inflexibility in changing operations.
Robots may also be able to adjust to variations in object placement without the use of sensors. This is enabled by arm or end effector flexibility and is referred to as compliance. Robots with sensors may also make use of compliance.
Robots are programmed either by guiding or by off-line programming. Most industrial robots are programmed by the former method. This involves manually guiding a robot from point to point through the phases of an operation, with each point stored in the robotic control system. With off-line programming, the points of an operation are defined through computer commands. This is referred to as manipulator level off-line programming. An important area of research is the development of off-line programming that makes use of higher-level languages, in which robotic actions are defined by tasks or objectives. Cnc machining Robots may be programmed to move through a specified continuous path instead of from point to point. Continuous path control is necessary for operations such as spray painting or arc welding a curved joint.
Programming also requires that a robot be synchronized with the automated machine tools or other robots with which it is working. Thus robot control systems are generally interfaced with a more centralized control system.