A novel absolute multi-pole magnetic shaft encoder structure is proposed to improve the resolution of multi-pole shaft encoders

realize absolute detection and to decrease their costs. A novel signal processing method based on calibration is used to eliminate the influences of nonlinear magnetic fields and assemble errors on the measuring precision. Two ring alnicos defined as an index track and a sub-division track are designed. The index track is magnetized according to a novel improved Gray Code

in which the linear Hall sensors are placed around the track evenly to obtain the absolute offset for magnetic region where the rotor belongs.The sub-division track is magnetized according to N-S-N-S

and the number of N-S is determined by the index track. Other three linear Hall sensors are used to translate the magnetic field to voltage signals

and the relative offset in a single N-S can be obtained by a look-up table. The magnetic encoder is calibrated using a higher resolution incremental optical encoder

the pulse output from the optical encoder and Hall signals from the magnetic encoder are sampled and transmitted to a computer at the same time

and the relation between them is obtained and stored in the FLASH of MCU by the look-up table. In the working state

the absolute angle can be obtained by the looking-up table according to Hall signals. A 12-pole magnetic encoder prototype is made and the result shows that its resolution can achieve ±0.72′and accuracy is ±1.2′. Furthermore

results also show that its accuracy can be improved by increasing the number of poles.