Basic study on a Self-tuning method for obtaining highly stable, general-purpose shaft torque sensors

钢轴固有的磁致伸缩效应为检测施加在轴上的扭矩提供了非接触的手段。在此方案中遇到的一个问题是由于淬火钢轴不可避免的磁不均匀性而导致精度低。我们的扭矩传感器由感应硬化SNCM钢轴（25 mmφ）和磁头组成，磁头带有一对嵌在铁氧体磁芯中的平面八字拾取线圈。本研究项目的目的是研究影响扭矩传感器精度的因素，并寻找降低这些因素影响或提高扭矩传感器精度的方法。结果总结如下：1。减小零电平波动力矩传感器的零电平波动很大程度上依赖于电感-电阻桥的平衡，而电感-电阻桥是力矩传感器的主要组成部分。当电桥不平衡时，零电平波动增强。一个电桥通过一个可变电阻进行调谐，该可变电阻与其中一个拾取线圈更平行。通过数值模拟，发现该调谐条件是唯一的，即在均方根误差方面全局最小。然而，最小零电平波动的调谐条件通常不满足最小偏移的条件。我们提出了一种避免这一问题的方法，即在桥电路的计数器支路中使用具有有源磁头平均值的虚拟阻抗分量。由于环境温度引起的漂移观察扭矩传感器中使用的每个组件的渗透率的温度变化，发现对温度稳定性最负责任的组件是淬火钢轴。这是由于热膨胀使轴的壳体区域的压应力松弛。在40℃至140℃的温度范围内，对不同的初始偏移量，观察了扭矩传感器的漂移。发现初始偏移量越小，漂移越小。例如，当初始偏移量为0.047%时，温度漂移为-22%，当初始偏移量为0.013%时，温度漂移降至-7.5%。涡流对零电平稳定性的影响感应线圈在钢轴表面产生涡流。以励磁频率为参数，研究了涡流对零电平稳定性的影响。我们发现，当激励频率较低时，在几个旋转周期内存在零电平扰动，当激励频率高于每秒转速的十倍时，这种现象消失。少

Magnetostrictive effect inherent in the steel shaft provides noncontacting means of detecting torque applied to the shaft. A problem encountered in this scheme is low accuracy due to magnetic inhomogeneities being inevitable for the case-hardened steel shaft. Our torque sensor consists of induction hardened SNCM steel shaft (25 mmφ) and a magnetic head with a pair of planar figure-of-eight pickup coils embedded in a ferrite core. The objective of this research project is to study factors affecting the accuracy of the torque sensor and to find methods of reducing influence of the factors or to improve accuracy of the torque sensor. Results are summarized below :1. Reduction of zero-level-fluctuationZero-level-fluctuation of the torque sensor is strongly dependent on the balance of the inductance-resistance bridge, which is a main building block of the torque sensor. When the bridge is unbalanced, zero-level-fluctuation is enhanced. A bridge was tuned with a variable resistor connected p … More arallel to one of the pickup coils. With numerical simulation, this tuning condition is found to be unique, that is, global minimum in terms of the root mean square error. However, the tuning condition for a minimum zero-level-fluctuation does not meet, in general, the condition for a minimum offset. We indicated a method to avoid this problems, in which dummy impedance components having averaged values of those of active heads are to be used in the counter branch of the bridge circuit.2. Drift due to ambient temperatureObserving temperature variation of the permeability of each component used in the torque sensor, the most responsible component for the temperature stability is found to be casehardened steel shaft. This is due to the relaxation of compressive stresses in the case region of the shaft due to thermal expansion. Drifts of the torque sensor are observed in a temperature range from 40℃ to 140℃ for various initial offsets. It is found that the drift becomes smaller for smaller initial offset. As an example, temperature drift was -22% for an initial offset of 0.047% normalized to the excitation voltage and was reduced to -7.5% for an initial offset of 0.013%.3. Eddy currents effect on the zero-level stabilitySensing coils induce eddy currents on the surface of the steel shaft. We investigated the influence of the eddy currents on the zero-level stability taking the excitation frequency as a parameter. We found that zero-level perturbs over several period of revolution when the excitation frequency is low and that this phenomenon disappears when the excitation frequency is higher than ten times of the rate of revolution per second. Less