Abstract
Linear position sensing systems has played a crucial role in position control and has been widely used in engineering products such as guide rails, pick-and-place robots and several other applications. Two types of linear sensing systems can be found in most products, that is, the optical encoder and the magnetic encoder. While optical sensing systems prove to have higher resolution, its accuracy and stability tends to decrease in unclean environments, where oil, dust, debris, etc. are present, these impurities could greatly affect the performance of optical sensors. The magnetic encoder holds the advantage of maintaining high precision and better performance in hazardous environments over optical encoders and is hence chosen as the main application of this research. In this research, a new method for achieving absolute position information is proposed, a permanent magnet magnetizer for experiment is developed as well. As opposed to the common approach of matching MR sensors to specific pole pitch patterns on medium, this paper validates the possibility of mismatching between the two with fixed element spacing in MR over pole pitch variation from 1.1 to 1.3mm using two-row magnetic patterns. The 1st row is the incremental row, which has the same 1mm pole pitch as the sensor. The 2nd row serves as the absolute row with tweaked pole pitch pattern. As two rows have different pole pitches, there is an offset between each pole before the two different pole pitches reach their common multiple. By plotting the Lissajous curves from both rows, the relation between two rows on each position is unique, and hence can be used as a mean to determine absolute position.