An artificial limb used by a number of athletes in the Paralympic Games has proved a medal winner. High-activity knee and lower limb joints made by Chas A Blatchford & Sons have proved so successful that American Todd Schaffhauser has won bronze medals for both the 100m and 200m.
Three pairs of NK12/12 H+21+16 needle roller bearings supplied by INA Bearing are used in the joint, each bearing being 12mm long and operating on a nominal 12mm shaft. Initially a 10mm bearing was tried in the prosthesis, but it was found that an athlete running could generate shock loads of 1tonne, which led to premature bearing failure. However, the 12mm bearing proved extremely reliable, largely due to the reduced enveloping circle tolerance, which has been halved from the normal tolerance band to just +21/+16mm to reduce clearance on the shaft.
Although it is unusual for needle roller bearings to be used in a reciprocating arrangement, plain bushes were found to be incapable of handling the loads necessary whilst still giving very low friction operation.
To provide low friction and low stiction, the needle roller bearings are pre-lubricated and sealed for life. Combined with the reduced clearance, this allows the joint to function without any perceptible `play’ during use, which can be a problem with other designs as it leads to a lack of confidence in the assembly from the wearer.
INA Bearing Tel: 0121 351 3833