A robotic arm is a type of mechanical arm, usually programmable, with similar functions to a human arm; the arm may be the sum total of the mechanism or may be part of a more complex robot. The links of such a manipulator are connected by joints allowing either rotational motion (such as in an articulated robot) or translational (linear) displacement. The links of the manipulator can be considered to form a kinematic chain. The terminus of the kinematic chain of the manipulator is called the end effector and it is analogous to the human hand.
The end effector, or robotic hand, can be designed to perform any desired task such as welding, gripping, spinning etc., depending on the application. For example, robot arms in automotive assembly lines perform a variety of tasks such as welding and parts rotation and placement during assembly. In some circumstances, close emulation of the human hand is desired, as in robots designed to conduct bomb disarmament and disposal.
Cartesian robot / Gantry robot: Used for pick and place work, application of sealant, assembly operations, handling machine tools and arc welding. It’s a robot whose arm has three prismatic joints, whose axes are coincident with a Cartesian coordinator.
Cylindrical robot: Used for assembly operations, handling at machine tools, spot welding, and handling at diecasting machines. It’s a robot whose axes form a cylindrical coordinate system.
Spherical robot / Polar robot Used for handling machine tools, spot welding, diecasting, fettling machines, gas welding and arc welding. It’s a robot whose axes form a polar coordinate system.
SCARA robot: Used for pick and place work, application of sealant, assembly operations and handling machine tools. This robot features two parallel rotary joints to provide compliance in a plane.
Articulated robot: Used for assembly operations, diecasting, fettling machines, gas welding, arc welding and spray painting. It’s a robot whose arm has at least three rotary joints.
Parallel robot: One use is a mobile platform handling cockpit flight simulators. It’s a robot whose arms have concurrent prismatic or rotary joints.
Anthropomorphic robot: It is shaped in a way that resembles a human hand, i.e. with independent fingers and thumbs.
Notable robotic arms
In space, the Space Shuttle Remote Manipulator System also known as Canadarm or SRMS and its successor Canadarm2 are examples of multi degree of freedom robotic arms. These robotic arms have been used to perform a variety of tasks such as inspection of the Space Shuttle using a specially deployed boom with cameras and sensors attached at the end effector, and also satellite deployment and retrieval manoeuvres from the cargo bay of the Space Shuttle.
The Curiosity rover on the planet Mars also uses a robotic arm.
Low-cost robotic arms
In the decade of 2010 the availability of low-cost robotic arms increased substantially. Although such robotic arms are mostly marketed as hobby or educational devices, applications in laboratory automation have been proposed, like their use as autosamplers.
An articulated robot is a robot with rotary joints (e.g. a legged robot or an industrial robot). Articulated robots can range from simple two-jointed structures to systems with 10 or more interacting joints. They are powered by a variety of means, including electric motors.
Some types of robots, such as robotic arms, can be articulated or non-articulated.
Articulated Robot: See Figure. An articulated robot uses all the three revolute joints to access its work space. Usually the joints are arranged in a “chain”, so that one joint supports another further in the chain.
Continuous Path: A control scheme whereby the inputs or commands specify every point along a desired path of motion. The path is controlled by the coordinated motion of the manipulator joints.
Degrees Of Freedom (DOF): The number of independent motions in which the end effector can move, defined by the number of axes of motion of the manipulator.
Gripper: A device for grasping or holding, attached to the free end of the last manipulator link; also called the robot’s hand or end-effector.
Payload: The maximum payload is the amount of weight carried by the robot manipulator at reduced speed while maintaining rated precision. Nominal payload is measured at maximum speed while maintaining rated precision. These ratings are highly dependent on the size and shape of the payload.
Pick And Place Cycle: See Figure. Pick and place Cycle is the time, in seconds, to execute the following motion sequence: Move down one inch, grasp a rated payload; move up one inch; move across twelve inches; move down one inch; ungrasp; move up one inch; and return to start location.
Reach: The maximum horizontal distance from the center of the robot base to the end of its wrist.
Accuracy: See Figure. The difference between the point that a robot is trying to achieve and the actual resultant position. Absolute accuracy is the difference between a point instructed by the robot control system and the point actually achieved by the manipulator arm, while repeatability is the cycle-to-cycle variation of the manipulator arm when aimed at the same point.
Repeatability: See Figure. The ability of a system or mechanism to repeat the same motion or achieve the same points when presented with the same control signals. The cycle-to-cycle error of a system when trying to perform a specific task
Resolution: See Figure. The smallest increment of motion or distance that can be detected or controlled by the control system of a mechanism. The resolution of any joint is a function of encoder pulses per revolution and drive ratio, and dependent on the distance between the tool center point and the joint axis.
Robot Program: A robot communication program for IBM and compatible personal computers. Provides terminal emulation and utility functions. This program can record all of the user memory, and some of the system memory to disk files.
Maximum Speed: The compounded maximum speed of the tip of a robot moving at full extension with all joints moving simultaneously in complimentary directions. This speed is the theoretical maximum and should under no circumstances be used to estimate cycle time for a particular application. A better measure of real world speed is the standard twelve inch pick and place cycle time. For critical applications, the best indicator of achievable cycle time is a physical simulation.
Servo Controlled: Controlled by a driving signal which is determined by the error between the mechanism’s present position and the desired output position.
Via Point: A point through which the robot’s tool should pass without stopping; via points are programmed in order to move beyond obstacles or to bring the arm into a lower inertia posture for part of the motion.
Work Envelope: A three-dimensional shape that defines the boundaries that the robot manipulator can reach; also known as reach envelope.
Source from Wikipedia