دانلود رایگان مقاله انگلیسی فیبر نوری پلیمری برای سنجش زاویه و گشتاور یک سری الاستیسه جریان فعال کننده - IEEE 2018

Abstract

Series elastic actuators (SEAs) can provide low output impedance, bandwidth close to the human movement and direct measurement of torque through the spring deflection. These advantages enable the application of SEAs in human active orthosis and exoskeletons. However, conventional technologies to measure the spring deflection are bulky, inhibit natural pattern of movement or are sensitive to misalignments. This paper presents the application of polymer optical fiber (POF) as a sensor to measure the spring deflection to overcome some of the issues of conventional technologies, since it is compact, lightweight and have electromagnetic immunity. Furthermore, the spring is employed to validate a torque sensor based on POF stress-optic effects. Results show high linearity of both sensors and mean squared errors below the encoder resolution employed as reference on dynamic measurements.

V. CONCLUSIONS

This paper presents the application of POF sensors on the spring of a rotary SEA for active knee orthosis. Two different methods were developed for obtaining spring’s deflection and torque.

The spring deflection was obtained by means of the correlation line between the sensor output voltage and the spring deflection. The correlation equation is obtained on the calibration procedure, which comprises of positioning the spring on predefined angular positions and acquire the sensor output power in each position. Considering that POFs present viscoelastic response with the consequent time-varying component on its stress or strain response, a reliable deflection response is obtained through the viscoelastic effects compensation made with creep recovery or stress relaxation experiments. This compensation successfully isolates the static response from the time-varying response.

Since the sensor response presented the effect of a viscoelastic material under stress and the sensor does not present the characteristic saturation trend in angles higher than 90°, it was made the assumption that all the variation of the output power is due to the variation of the refractive index induced by the stress-optical effect. This assumption enables the application of the POF to measure the torque on the spring.