Most malformed ears of neonates can be treated by mounting a suitably shaped orthosis. However, it needs much experience to make a orthosis that produces adequate corrective force. Especially, excessive force may cause a decubituslike inflammation on the auricle. We are studying computer aided treatment system to support the orthosis design. And we have already developed fundamental design and manufacturing system.This paper describes automatic orthosis shape modification method to prevent the excessive contact force using three dimensional finite element analysis.In each insertion step of incremental method, contact force of every nodal point of the orthosis is calculated.The shape is modified by canceling the insertion of nodal point where excessive contact force is produced.The result of the simulation shows that the maximum contact force was reduced to one third by the modified shape. Orthoses of original shape and the modified shape by the method are manufactured. Also, two types of force sensor systems using silicon tube and strain gage are constructed.They use phenomena that air flow in the tube decreases and the strain gage is deformed when they are pressed.The thickness of tube sensor is 0.5mm and that of strain gage sensor is 0.2mm. Orthoses on which sensors are mounted are inserted into a testee's auricle and the contact force is measured.The results of both sensors showed that the force produced by the orthosis of modified shape was approximately half of original shape.
