The Design and Manufacture of Symptom and Sport Specific Insoles

Abstract

The development of prescription methods and evaluation of biomechanical performance of bespoke orthoses has been a source of research for the last 40 years. What started as anecdotal and experience–led knowledge has evolved into a more quantifiable paradigm utilising state of the art technologies commonly found in other high-precision industries. The manufacturing challenges associated with such customised products have been driven by the requirement to produce small (often one-off) batches, bespoke for the end user. The introduction of precise scanning equipment and CAD/CAM systems to the podiatry community is enabling the accurate and repeatable manufacture of orthoses that were previously predominantly hand crafted and shaped. Although these traditional production methods are still in use today, the advantages that scanning and CAD/CAM provide mean they are rapidly being adopted. Today, CNC machining and additive manufacture provide state of the art manufacturing methods for bespoke insoles prescribed and modelled in a CAD environment. However, the limitations of both these manufacturing methods relate to the materials that can be processed, which becomes problematic when manufacturing soft or semi-rigid orthoses. Hence an opportunity exists to develop a new and innovative method for processing foamed polymer materials that are typically vacuum formed today. This research explores the prescription and analysis methods attributed to insole design for sporting applications using specific sports shoes. The insole designs encompass material selection to deliver a product that provides control and function whilst also providing a degree of impact attenuation, recognising the dynamic and high-impact nature of the sportsspecific movements. Consideration is also given to the types of activities that function with the device. This research analyses characteristic plantar pressures experienced whilst undertaking sports-specific movements to aid in the prescription of bespoke insoles for the chosen sport. A design methodology encompassing state of the art scanning technologies and anthropometric measurements provides a repeatable and accurate means to produce the required geometry for a bespoke sport and symptom-specific insole. The research also presents the concept of cryogenic machining, a novel manufacturing method for the CNC machining of foamed polymers. The materials are cooled with the use of a liquid cryogen to below their glass transition temperature at which point relative motion at a molecular level is significantly reduced, providing a rigid and machineable form. This, along with a bespoke cryogenic facility encompassing a vertical 3 axis CNC machining centre, a pressurised liquid nitrogen dewar connected to a bespoke-designed fixture by a vacuum jacketed pipe, enables the dual-sided machining of an amorphous material, something which is not possible with conventional processes. The major contributions of this work are the design methodology to prescribe a sport and symptom-specific insole using state of the art scanning and CAM methods, the design and manufacture of a fixture to facilitate the dual-sided machining of a customised insole and the subsequent testing of the designs in a laboratory environment. In addition the research utilises motion analysis, force plate data and pressure measurement to explore the effects of the insoles on the kinetics, kinematics and peak plantar pressures at discrete anatomical regions during sport-specific manoeuvres.

Date of Award	27 Feb 2013
Original language	English
Awarding Institution	University of Bath
Supervisor	Martin Ansell (Supervisor) & Stephen Newman (Supervisor)