Common Robot Terminology


This refers to linear movement in the X, Y or Z direction. The term is sometimes used to describe the linear offset distance of a rotational or revolute joint.


Perfect accuracy is unattainable and so some dimensional tolerence must be applied. The repeatability is a measure of how close a Robot arm can return to a previously held position. The repeatability must be defined in terms of X, Y and Z coordinates. This is usually done by specifying the diameter of the smallest sphere within which a point on the end effector will return to. A typical repeatability specification for an industrial Robot would be + or - 0.2 mm. The repeatability depends on Robot configuration and the size and mass of the end effector.


The task of picking up an object and changing its position and orientation in space. The manipulation in Robotics often takes the form of a human ( anthropomorphic) arm.


Closed loop control tends to make for more accurate performance, since the negative feedback is continually trying to reduce any error. However under certain conditions this corrctive reaction can lead to instability. Instability is the tendency of the system to oscillate about a desired position. A Robot arm travelling at high speed may have too much inertia to stop when it reaches the desired position and as a result it will overshoot its target and feedback an error signal. This will cause the arm to try again to reach the desired position, if this time it undershoots the proceedure will be repeated and so on. This condition is called Hunting.


The response time is the time lag between the application of the input signal and the arm reaching its desired position. Response time is always a compromise between minimal lag time and stability of the system.