绝对式多极磁电轴角编码器的设计

为了实现多对极磁电式轴角编码器的高分辨率绝对式检测并降低其成本,基于改进格雷码构建了一种新型多极磁电轴角编码器模型,提出一种基于校准查表的信号处理方式,以消除磁场非线性和装配误差对测量精度的影响。设计了两个由永磁体磁环构成的码道:粗码道,根据改进格雷码生成N和S极充磁顺序,采用圆周均匀分布的线性霍尔元件得到转子所处磁极区域的绝对偏移量;细分码道,N和S极等距间隔排列,定子上3个线性霍尔元件将磁信号转换为电信号,查表得到转子于所处信号周期内的相对偏移量。在离线状态下,用高分辨率的增量式光电轴角编码器进行校准,对其A/B相脉冲输出和磁电式轴角编码器的霍尔信号同时采样并上传到计算机进行高精度信号重构,得到标准角位移和霍尔信号映射关系,通过单片机的自编程技术将数据存储于主控芯片中固定地址以供查表;角位移检测状态下,根据霍尔信号查表得到绝对角位移。根据上述原理研制出12极磁电式轴角编码器样机,实现了分辨率为±0.72′,精度达±1.2′以下的单圈绝对位置检测。该编码器通过增加磁极数还可进一步提高测量精度。

Design of absolute multi-pole shaft encoders

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.