Vibration Behaviour Analysis of Optical Linear Encoders Based on Different Scanning Methods

摘要

Optical linear encoders are high precision positioning sensors based on the interference patterns produced by the relative movement between two gratings. One of the gratings is impressed on a scale and the other one is located in what is known as the scanning head. The rest of the main components are a light source, collimating lens and a set of photocells. The arrangement of these components is mainly conditioned by the scanning method chosen, resulting in a different encoder mechanical design and therefore in dissimilar dynamic behaviour if transmission, reflection or projection is selected. In transmission methods, single-field scanning encoders represent the ultimate state of the art regarding to insensitivity to contamination, but there is a lack of information concerning their behaviour under vibrations in relation to conventional transmission methods or to reflection reading heads. In this work a performance comparison under vibration of the above mentioned scanning methods used in optical linear encoders is presented. The proposed scheme aims on to assess the loss of accuracy of the sensor due to vibration, resulting in a final diagram of error versus frequency that allows comparing the selected encoders.