Characterisation of 1D opto-electronic sensors and their application to angular self-centring probes for machine-tool verification

In this paper the application of position sensitive detectors (PSD) as measuring systems for self-centring probes is explained. Self-centring probes are part of a new technique to perform machine-tools (MT) geometrical verification in a faster way than the traditional one (laser interferometry). These probes were initially designed, developed and manufactured using optical sensors (linear encoders) as internal measuring system. This kind of sensors provided a high resolution and accuracy and very good results in the calibrations of the probes and in their final use. However, they made the size and the cost of the probes too high. In order to improve these characteristics, a low-cost LED + PSD combination has been studied as an alternative measuring system. The results of these studies are presented in this paper, including studies of repeatability and characterisation of the LED + PSD system. The influence of the light spot size and form, the distance between LED and PSD and their relative orientation in linear and angular measuring have been analysed. Different calibration techniques have been developed and applied to these sensors in order to optimise their accuracy in linear and angular measurements. Some possible configurations of the measuring system inside the probe have been studied. Finally, the system has been mounted inside a self-centring probe. A final calibration of the system has been carried out and several correction techniques have been applied. The behaviour of the probe has been tested mounting both measuring systems: linear encoders and LED + PSD.