Compensation technique for environmental and light source power variations applied in a polymer optical fiber curvature sensor for wearable devices

Abstract

Introduction: Polymer optical fibers (POF) are lightweight, present high elastic strain limits, fracture toughness, flexibility in bend, and are not influenced by electromagnetic fields. These characteristics enable the application of POF as curvature sensor and can overcome the limitations of the conventional technologies, especially for wearable and soft robotics devices. Nevertheless, POF based curvature sensors can suffer from environmental and light source power deviations. This paper presents a compensation technique for the environmental and light source power deviations in a POF curvature sensor. Methods: The curvature sensor was submitted to variations of temperature, humidity and light source power to characterize the sensor response and evaluate the proposed compensation technique. In addition, tests with the simultaneous variation of the angle and light source power variation were performed. Results: Results show that temperature and humidity effects do not lead to significative errors on the sensor measurement for wearable devices application, where a hardware-based compact and portable compensation technique of the light source deviation is applied. Moreover, the sensor with the compensation technique developed is compared with a potentiometer for dynamic measurements and the root-mean-square error of about 1° is obtained, which is lower than sensors based on similar operation principle presented in the literature and some commercially available devices. Conclusions: The compensation technique proposed was able to compensate power deviations applied and resulted in a sensor with low errors with the additional advantages of compactness and low-cost, which enable its application as wearable sensors and on the instrumentation of wearable robots.

Polymer Optical Fiber Goniometer: A New Portable, Low Cost and Reliable Sensor for Joint Analysis

“…It should be emphasized that the errors found in this study can be reduced through compensation techniques, as done by Arnaldo et al [4], which can improve the sensor response. These techniques will be implemented in future work.…”

“…The quantitative measurement of articular motion is an important indicator of its functional state and for clinical and pathology diagnoses, and as an indicator of neurodegenerative disorders, which assists in the verification of joint and muscular limitation [1], and to determine the effectiveness of rehabilitation exercises [2]. Joint angle evaluation techniques can also be applied to improve sports performance [3] and provide feedback information for prostheses control [4]. The elbow joint motion has an important role in daily activities, and its amplitude can determine limitations, impairments, and can aid in medical diagnostics.…”

“…The elbow articular motion can be analyzed during flexion–extension movement [5]. This measurement can be assessed through a variety of methods, such as goniometers, video-based techniques, inertial measurement units, and encoders, among others [4]. The most common is by using a goniometer, which can be made up of different types of sensors.…”

“…Although they are compact and lightweight, they present a high sensitivity with magnetic field interferences and can present high errors on the angle measurement [8,9]. A video tracking technique is also implemented, but is very expensive and time consuming [4].…”

Wearable Wrist Movement Monitoring Using Dual Surface-Treated Plastic Optical Fibers

“…where V ref_i is the current output reference voltage and V ref_0 is the original value for the output reference voltage through the optocoupler, acting as a reference directly connected with the coupler, as depicted in Figure 2. Similar compensation method was also previously reported in a POF curvature sensor for wearable devices [30]. In view of the relatively simple differential compensation scheme for the light intensity fluctuations caused by light source instability, a power fluctuation compensation scheme for intensity-based POF sensor via the light reflection [31] could be introduced in the following work, to stabilize the light intensity disturbances for further improving the sensor performance.…”