A new method for measuring a large set of poses with a single telescoping ballbar

This paper presents a novel method of measuring a set of more than fifty poses under static conditions, using a single telescoping ballbar and two fixtures, each bearing three equally spaced magnetic cups. The position accuracy of the device is in the ±0.003 mm range, making it suitable for measuring the pose accuracy and repeatability of industrial robots and even calibrating them. The proposed method is an extension of a known approach using a hexapod (a Stewart-Gough platform) comprising telescoping ballbar legs and provides an original solution to the constraint imposed by the limited measurement range of current telescoping ballbars, namely an innovative hexapod geometry capable of assembly in 144 different configurations. An additional advantage of the method is that the pose of one fixture with respect to the other can be obtained for each of these configurations by solving a cascade of three quadratic equations using the six hexapod leg lengths as input. The application of the device and method to measuring numerous poses of an ABB IRB 120 industrial robot is presented.