Patel A, Kothari M, Webster J G, Tompkins W J, Wertsch J J
Department of Electrical and Computer Engineering, University of Wisconsin, Madison 53706.
J Rehabil Res Dev. 1989 Spring;26(2):55-62.
We are using a Hercules (model #F4-4R, 100 psi) pressure sensor to measure the pressure between the foot and shoe. An interface circuit converts the capacitance change into voltage. Over the pressure range from 0 to 1300 kPa, the capacitance changes from 275 to 580 pF. A 555 timer circuit converts the capacitance into a frequency range from 30 to 63 kHz. A phase-locked loop (PLL) converts this frequency to voltage from 0 to 5 V, which is then filtered using a first-order, low-pass filter, having a corner frequency of 20 Hz to reduce the ripple to 10 mV. The sensor's hysteresis is about 8 percent at 40 degrees Celsius (C) and 12 percent at 20 degrees C. The sensor has a maximal nonlinearity of 8 percent and a worst-case nonrepeatibility of 7 percent. Its temperature coefficient is -0.147 percent per degree C. Its spatial sensitivity decreases nonlinearly from 1 to 0.17 from the center towards the periphery. The sensitivity of the system is 2.77 mV/kPa and the temperature drift is +0.53 percent per degree C. We monitor the pressure at 7 locations under each foot (the rear and the front heel, great toe, and 4 of the 5 metatarsal heads). A portable data-acquisition system permits continuous monitoring for 7 minutes. Test results for pressure distribution for normal walk and run are presented. Results are useful when studying normal and abnormal gait, and for possibly providing feedback (sensory substitution) to diabetic patients with insensate feet in order to help them dynamically adjust pressure distribution under their feet.
我们正在使用一个大力神（型号#F4 - 4R，100 psi）压力传感器来测量足部与鞋子之间的压力。一个接口电路将电容变化转换为电压。在0至1300 kPa的压力范围内，电容从275 pF变化到580 pF。一个555定时器电路将电容转换为30至63 kHz的频率范围。一个锁相环（PLL）将该频率转换为0至5 V的电压，然后使用一个截止频率为20 Hz的一阶低通滤波器进行滤波，以将纹波降低至10 mV。该传感器在40摄氏度（℃）时的滞后约为8%，在20℃时为12%。该传感器的最大非线性度为8%，最坏情况下的不可重复性为7%。其温度系数为每摄氏度-0.147%。其空间灵敏度从中心向周边呈非线性下降，从1降至0.17。该系统的灵敏度为2.77 mV/kPa，温度漂移为每摄氏度+0.53%。我们在每只脚下的7个位置（后跟和前脚跟、大脚趾以及5个跖骨头中的4个）监测压力。一个便携式数据采集系统允许连续监测7分钟。给出了正常行走和跑步时压力分布的测试结果。这些结果在研究正常和异常步态时很有用，并且可能为足部感觉迟钝的糖尿病患者提供反馈（感觉替代），以帮助他们动态调整脚下的压力分布。
