Custom-made force sensing resistors embedded in insole applied for measuring plantar pressure

Accurate and consistent measurement of plantar pressure and gait analysis holds significant importance in guiding gait training for neurologically injured patients and others undergoing gait rehabilitation at home. In this paper, the fabrication of cost-effective force sensing resistors (FSRs) using rattan as a substrate and aluminum foil for sensing purposes is shown. A total of six unique combinations were generated by combining two types of rattan surfaces and three dissimilar materials (Kapton, blue cotton fabric, and white cotton fabric) for printing the carbon layer to create FSRs to print the carbon layer by an unconventional subtractive xurographic technique using a conductive layer of aluminum (foil). The sensitivity of all types of sensors was determined and compared using a compression test. All produced sensors showed the same characteristic diagram of the FSRs dependence resistance as commercial sensors. Two FSRs were selected to measure the pressure applied at the first metatarsal heads and the heel during the gait test. The test involved five subjects of different ages taking a hundred steps and wearing a custom insole created using the 3D printing fused deposition modeling (FDM) technique. The sensors successfully detected the force during the subjects’ walking and were not damaged even after the tests.