Analysis of gait pattern of individuals is a very useful tool for the identification of locomotive motor anomalies, which can lead to early diagnosis and adequate treatment of patients with motor disorders. The knees are the lower limb joints exposed to major tension during human locomotion, presenting higher risk of a wider range of possible disorders. The devices used to monitor human joints should be comfortable and not restrain patients’ movement, while maintaining their resolution and accuracy. Most of current measurement techniques are based on electronic devices, which are often not adequate for demanding environments, such as the context of physical rehabilitation. We propose an e-Health sensing solution to dynamically monitor human knee angles during gait, using low-cost intrinsic Fabry-Perot interferometers optical fiber sensors (FPI-OFS). To the best of our knowledge, no previous efforts have reported the use of FPI sensors for such dynamic monitoring. The overall sensor consists of an optical fiber containing the FPI microcavity, which is embedded along the longitudinal direction of a kinesio tape (K-Tape), and placed along the knee rotation axis. Since the K-Tape has great adhesion to the skin, the FPI sensor is kept at the knee rotation axis, without restricting the user’s movements. During the knee flexion/extension, the K-Tape extends/compresses accordingly, resulting in the modulation of the reflected spectrum by the FPI-OFS. Several calibration and performance tests have been performed. Their results show the reliability and accuracy of the proposed solution, with sensibilities values of 53.8±2.4 pm/°.
This work consists on the design and implementation of a compact and accurate biaxial optical fiber sensor (OFS) based on two in-line fiber Bragg gratings (FBGs) for the simultaneous measurement of shear and vertical forces. The two FBGs were inscribed in the same optical fiber and placed individually in two adjacent cavities. In the calibration and performance tests, the response from the optical fiber cells was compared with the values given by a three-axial electronic force sensor. Sensitivity values obtained for the FBG1 are K1V= (14.15±0.10) pm/N (vertical force) and K1S= (-26.02±0.08) pm/N (shear force) and for the FBG2 are K2V= (7.35±0.02) pm/N and K2S= (-24.29±0.08) pm/N. The conversion of the Bragg wavelength shift, given by the optical fiber sensors, into the shear and vertical force values is also presented along with its comparison to the values retrieved by an electronic sensor, yielding to low RMSE values, which shows the high accuracy of the algorithm applied. This work stands out from the others with optical fiber by the simplicity of its structure. The proposed solution represents a compact and reliable device for simultaneous measurement of shear and vertical forces, useful in several areas, such as: incorporation into insoles for plantar pressure and shear force measurement; electronic skin technologies; smart rehabilitation robotic exoskeletons; or even biomimetic prosthesis.
In an era of unprecedented progress in technology and increase in population age, continuous and close monitoring of elder citizens and patients is becoming more of a necessity than a luxury. Contributing toward this field and enhancing the life quality of elder citizens and patients with disabilities, this work presents the design and implementation of a noninvasive platform and insole fiber Bragg grating sensors network to monitor the vertical ground reaction forces distribution induced in the foot plantar surface during gait and body center of mass displacements. The acquired measurements are a reliable indication of the accuracy and consistency of the proposed solution in monitoring and mapping the vertical forces active on the foot plantar sole, with a sensitivity up to 11.06 pm/N. The acquired measurements can be used to infer the foot structure and health condition, in addition to anomalies related to spine function and other pathologies (e.g., related to diabetes); also its application in rehabilitation robotics field can dramatically reduce the computational burden of exoskeletons’ control strategy. The proposed technology has the advantages of optical fiber sensing (robustness, noninvasiveness, accuracy, and electromagnetic insensitivity) to surpass all drawbacks verified in traditionally used sensing systems (fragility, instability, and inconsistent feedback).