A silhouetting shape sensor for the residual limb of a below-knee amputee

A shape sensor based on silhouette imaging techniques was developed to accurately and quickly measure the external geometry of the residual limb of a below-knee amputee. The sensor represents an improvement over previous residual limb imaging methods in that the resolution was higher, the scan-time was shorter, no ionizing radiation was used, and the technique was less sensitive to hair on the residual limb. The sensor will be used for investigative research of long-term (maturation) and short-term (diurnal) residual limb shape changes-information of critical importance to prosthetic fitting because of the effects of shape changes on stress distributions between the residual limb and prosthetic socket. The shape sensor uses a charged-coupled device video camera mounted to one end of an aluminum beam which is fixed at its other end to the shaft of a stepping motor, forming a simply supported cantilever. The motor accelerates the camera around the residual limb up to a constant angular velocity of 202.3°/s. During 216° of the constant-velocity portion of rotation, 17 images are captured at intervals of 13.5° and stored electronically to a computer. The images of the residual limb are then processed to produce silhouette contour outlines which are then used to reconstruct the three-dimensional residual limb shape. Using this silhouette imaging method, the sensor could measure the geometry of residual-limb areas susceptible to shape change with a radial resolution of 0.5 mm in a scan-time of 1.07 s