Measuring foam model shapes with a contact digitizer

Abstract

It is difficult to measure foam model shapes using contact digitizers because the stylus contact tends to get stuck in the soft foam. The aim of this paper is to describe a technique to overcome this challenge and to assess its effect on digitizer error. A controlled laboratory study was conducted. Thirty trans-tibial socket models were measured using a custom mechanical digitizer. Models were coated with a thin layer of resin, and then the resin thickness measured and subtracted from the digitizer data. Error introduced to the measurement from presence of the resin was determined. The technique did not introduce meaningful error to the digitizer data beyond that already present from other sources in the instrument. The total instrument error for the contact digitizer used was 0.1% for model volume and 0.05 mm for mean radii. The root-mean-square error for individual measurement points was 0.08 mm. While resin coating introduced error to the digitizer measurements, the effect on volume, mean radii and interquartile range accuracies was minimal. Accurate model measurements can assist clinical service providers in the identification of problems and the repair of carving equipment. This facilitates the delivery of high quality sockets to practitioners and patients.