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提供了检测施加在轴上的扭矩的非接触式方法。在这种方案中遇到的一个问题是，由于表面硬化的钢轴不可避免地存在磁性不均匀，所以精度较低。我们的扭矩传感器由感应淬火SNCM钢轴(25 mmφ)和一对嵌入铁氧体磁芯的平面八字形拾取线圈的磁头组成。本研究项目的目的是研究影响扭矩传感器精度的因素，寻找减小这些因素的影响或提高扭矩传感器精度的方法。研究结果总结如下：1.零电平波动的抑制扭矩传感器的零电平波动很大程度上依赖于电感-电阻电桥的平衡，而电感-电阻电桥是扭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。电桥通过连接p…的可变电阻进行调谐更平行于其中一个拾音圈。通过数值仿真，发现这种调谐条件是唯一的，即在均方根误差方面是全局最小的。然而，最小零电平波动的调谐条件通常不满足最小偏移量的条件。我们指出了一种避免这一问题的方法，其中具有有源磁头的平均值的虚拟阻抗分量将在桥接电路的计数器分支中使用。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磁导率的温度变化，发现对温度稳定性最负责的组件是表面硬化的钢轴。这是由于热膨胀引起的轴壳区域压应力的松弛。对于不同的初始偏移量，扭矩传感器的漂移可以在40℃到140℃的温度范围内观察到。结果表明，初始偏移越小，漂移越小。例如，对于归一化于励磁电压的0.047%的初始偏移量，温度漂移为-22%，而对于0.013%的初始偏移量，温度漂移减小到-7.5%。涡流对零位稳定度的影响传感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，零能级扰动在几个旋转周期内发生，当激励频率高于每秒转速的十倍时，这种现象消失。较少

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