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Accuracy vs repeatability; why the difference matters.

cad cam repeatability robot accuracy robotic control robotics

When robots are programmed point to point, it does not matter where the robot thinks it is. The encoders give rotational positions for each axis that are very accurate and allow the robot to return to the position precisely. This ability is called repeatability and usually quoted by robot manufacturers. It is also usually very good- under 0.1mm.

However accuracy is different. If you specify the robot to move from a point, to a position not previously specified, (say 500mm in one direction) the precision with which it does this is the accuracy. This is not often quoted by robot manufacturers.

Robots, due to the compound inaccuracies in the mechanical structure and kinematic model, often have accuracy which is far from ideal. Often 500mm will lead to a error of over 1mm.  This makes programming from CAD data less reliable, meaning robots have to be programmed point to point, or have to have their movement envelope fully measured and offsets made to compensate for inaccuracies.

One of the things that makes the ALLY robot different is that it was designed from the ground up to be programmed using CAD. As a result both the kinematic and the mechanical structure combine to give great accuracy as well as repeatability straight out of the box.


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