We proposed a wireless measurement system of 3-axis stress distribution at a human sole by using small and thin 3-axis force sensors. The sensor chips 2mm square made by using MEMS (Micro Electro Mechanical Systems) technologies were mounted on the flexible printed circuit board, wire-bonded and buried in silicone rubber by injection molding to fabricate 3-axis force sensors. After the calibration for crosstalk compensation, these sensors were placed on the insole at the heel, thenar and hypothenar. The 3-axis stress distribution was measured in going up and down stairs. The output signals from sensors were amplified 100 times with Wheatstone bridges and differential amplifiers, converted to digital signals and wirelessly transmitted to PC with a Bluetooth module on the CPU board. Measured data which comprised pressure, shear stress of front-back direction and shear stress of lateral direction were compared with the data in level walking, and were consistent with the somatic sensation of the human subject.
