Design of a wireless and fully flexible insole using a highly sensitive pressure sensor for gait event detection

Abstract

Gait event detection is a requirement for clinical diagnosis and control strategies for power exoskeletons and rehabilitation robots. Smart insoles are widely used in gait research as they are easy to wear. However, current sensor insoles still have some problems, such as being easily affected by temperature, low sensor sensitivity and discomfort while wearing. To solve these problems, in this work we developed a fully flexible insole based on a high-sensitivity capacitive sensor. High sensitivity was achieved by preparing the dielectric material with a porous structure and full flexibility was obtained by using customized compliant electrodes. The porous structure was produced by mixing xylitol with silicone rubber and the compliant electrode was manufactured by mixing conductive carbon nanotubes into plasticized polyvinyl chloride. The mechanical and sensing properties of the sensor were studied. The results show that our sensor has high sensitivity, a good dynamic response, a fast response time (about 80 ms), a large pressure detection range (0–500 kPa), good durability (>1000 cycles) and is little influenced by temperature. We integrated the sensors into the self-made flexible silicone insole. A wireless data transmission measurement module was developed for ease of use. Finally, we found that the prepared sensor insole is able to detect gait events.

Smart Shoe Insole Based on Polydimethylsiloxane Composite Capacitive Sensors

“…As indicated, the behavior of the template for these loads is close to linear. This result is consistent with the results obtained in preliminary tests of this study, and in the works [ 43 , 44 ]. Regarding work with capacitive plantar insoles, again, the behavior of the sensors in this study coincides with those elaborated in [ 29 , 32 ].…”

“…The three materials most commonly used in the literature as dielectrics in capacitive insoles are: PDMS, PVC and Ecoflex. PDMS is the material with the best pressure measurement range, the best sensitivity and the best durability [ 43 , 44 ]. PDMS is a type of silicon-based material which is transparent.…”

From a biological template model to gait assistance with an exosuit

“…In our experimental setup, we utilized the GRF signal measured by the instrumented treadmill, which is applicable for training and rehabilitation tasks. For measuring GRF in a portable exosuit for overground walking, the common technology is using the insole shoe sensors, which suffer from wear, imprecision, and low sensitivity [71]. New technologies are introduced to measure the GRF using magnetic fields [72,73], or high-sensitivity capacitive sensors [71], which are more robust than the traditional insole force sensor and are more appropriate for our application.…”

Recent progress of flexible pressure sensors: from principle, structure to application characteristics

“…In the preparation process of flexible pressure sensors, materials with good conductivity and mechanical properties are usually selected as electrodes. Electrode materials commonly include metal film [89][90][91][92], conductive ink [93], carbonbased material [94][95][96], ITO [97], and conductive polymer [98].…”