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Robot Welding

The essential guide

Absolute accuracy and repeatability
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Absolute accuracy is the ability of an industrial robot to position its tool centre point (TCP), coming from a specified direction, to a point in space specified in Cartesian coordinates within a tolerance range given by the radius of a sphere.

The absolute accuracy thus describes the mean deviation, in all degrees of freedom, of the tool centre point and its orientation from a specified point in the workspace and a specified orientation (DIN EN ISO 9283).

Repeatability describes the ability of an industrial robot to position its tool centre point reproducibly to a programmed point in the workspace within a tolerance range given by the radius of a sphere, with a defined orientation and under defined conditions (DIN EN ISO 9283). The absolute accuracy is generally significantly poorer than the repeatability.

h:                      Frequency distribution
AP:                   Absolute accuracy
RP:                   Repeatability
P
TCP_IST
:        Actual position of the TCP
P TCP_SOLL:  Command position of the TCP

The absolute accuracy defines the position of the mean value of the numerical actual positions, e.g. programmed textually or offline, relative to the command position.

The repeatability defines the deviation of the individual actual positions from the mean value of the actual positions (cf. diameter and centre of sphere).

 
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