Self-Calibrating Optical Displacement Sensor

Commercially available reflective optical sensors can be used as displacement sensors which in turn can be used in vibration monitoring, positioning, force-measurement and other applications. The sensor output depends in all cases on the distance between the component and a suitable reflective surface. In this paper a sensor system applicable to vibration measurement (e.g. monitoring a vibration-generating machine mounted on elastic isolation mountings) is presented where a special mechanism enables the controlled adjustment of the reflective surface's position. This feature allows continuous operating point adjustment while the sensor measures vibration. On the other hand, during the intervals when the vibration measurement is not active (e.g. the machine is not in use), the system can be used to automatically calibrate the sensor, i.e. to measure the dependence of the optical sensor output from the distance to the reflective surface. This allows accurate measurements under various circumstances: temperature change, optical component replacement, staining of the reflective surface, ingress of dirt etc. The reflective surface adjustment system is controlled by an embedded digital system which also controls the calibration procedure. Range depends largely on the type of reflective sensor. In case of the component TCRT1000 used in the experiments, range is up to 4 mm.