A novel absolute magnetic encoder based on pseudorandom code

In order to improve resolution of multi-pole encoder and realize absolute output, a novel absolute multi-pole encoder structure based on calibration was proposed. Two ring alnicos, defined as look-up table track and index track were used as magnetic source. Look-up table track was magnetized to 8 N-S, three linear evenly placed Hall ICs which air gap is 2 mm are used to translate magnetic field to voltage signals, the relative offset in a single N-S can be get by look-up table. The index track was magnetized according the sequence that get by pseudorandom code, three Hall ICs were used to change N, S to 1 or 0 for getting the absolute offset of the signal period that the shaft belongs to. The magnetic encoder is calibrated using a higher resolution incremental optical encoder, the pulse output from optical encoder and Hall signals from magnetic encoder are sampled at the same time and transmitted to PC, the relation between them can be get, and stored in the ROM of MCU for look up. While in the working state, the absolute angle can be get by looking-up table according to Hall signals. Its structure is very simple and cost is low.