Measurement of 3D forces at the foot-shoe interface during locomotor activity
The origin of this project was the problem of foot ulceration in the diabetic patient. Whilst the principal cause of the susceptibility to foot ulceration in patients with this pathology, and others such as leprosy, is abnormal physiology, there is no doubt the mechanical forces that are applied to the foot surface are a major factor. Currently several devices are available to measure the perpendicular forces at the foot-shoe interface (ie. the "pressure" distribution). However the full assessment of tri-axial forces at this interface has largely eluded quantification despite the fact that it has been demonstrated that shear forces may be of equal significance to those of direct pressure. The purpose of this study was to develop a transducer for the assessment of the three dimensional forces experienced, over a very localised area, at the foot-shoe interface during normal functional locomotor activity. The application of such a device in the clinical setting will provide valuable information for the medical and orthotic professions and thereby assist them in the treatment of many patients who are at risk of foot ulceration. The principle for a transducer to be embedded in an insole and utilising electromagnetic induction between air-cored coils was proposed. Coil winding techniques were developed to enable manufacture of coils within constrained sizes. Examination of the inductive coupling possible between the coils and its variation with displacement in space was carried out using a purpose built testing rig. Transducer electronics were designed and manufactured and a data logging system implemented. Various approaches to the derivation of 3D interpretation from the system were implemented in software. An examination of the accuracy of the approach was made. A prototype design and manufacturing method was suggested utilising a specific grade of silicone rubber. The results indicated that the design proposed could be implemented effectively in a size suited to in-shoe application. The design offers a relatively low cost method which could be adapted for use in many applications requiring three dimensional displacement or force measurements.