Measurement system for 3-D foot shapes under different loads

A measurement system for 3-D foot shapes under different loads is described, which can automatically extract foot parameters such as foot length, ball width, heel width, ball girth, toe height, instep height, arch height, ankle height, arch curve and footprint. The information on how the foot shape changes with loads is important for shoe designing, plantar stresses analysis and orthopaedic treatment. The measurement system consists of a motion unit driven by a servo motor, a load measurement unit, a vision sensor unit and a synchronous multi-channel image capturing unit. The measurement system is developed based on the laser line-scanning triangulation method, including four groups of vision sensors for foot image acquisition, realizing a full range of 360 degree profile coverage from foot heel to toe. The load measurement unit composed of pressure sensors can measure and display foot loads in-time. A global calibration method based on scanning the inclined planes in four different orientations combined with a space mapping is employed to reduce the nonlinearity of the system. In image processing, Two-Step method is put forward for the laser stripe sub-pixel detection and the Dilation-Thinning method is adopted for the assembly of stripes from all CCD cameras. The system is verified through the measurement of the foot loads and foot shapes for 4 persons. The results are presented.