Invention of slight lower limbs’ stretching and walking orthosis

Abstract

This paper describes the invention of a light-weight walking brace which can be hidden in a body’s silhouette and worn inside a pair of trousers. A light-weight, three layer sandwich style planetary gear reduction system (100mm in diameter and 30mm in thickness) was invented. The sandwich mechanism consists of two outer layers of complete planetary gear system which is one tooth larger than the inner layer of incomplete planetary gear system. The reduction rate input to output becomes 535:1. The sandwich system becomes the articulator joint itself and needs no any other joint structure parts.

If the joint driving module is used at the hip, knee and ankle joints connecting the femur, crus and pes bar, then it would be a simple leg brace. The joint mechanism is driven by tiny motor and requires high torque up to 70Nm. In the future, this brace could be connected to a walking motion control system in a portable computer, thus making it a walking vehicle.

Tests were done on the prototype brace using a joint module which was under construction for a lighter and thinner module. Results showed that the joint drive created much noise and low transmission efficiency. There was a gear meshing phase offset between the complete and the incomplete planetary gear systems.

The off-set caused an imbalance between the forces of gear transmissions. The planet gear’s carrier supported this imbalance and tended to be eccentric. Also the carrier is supported indirectly by many bearings in cascade. The indirect support will be greatly affected by unbalanced forces and increase the eccentricity.