FIG. 7 illustrates a motion and a l

FIG. 7 illustrates a motion and a locus of one of teeth of a cup-shaped external gear when moving with respect to a tooth groove of a rigid internal gear, showing the motion and locus at a central section of rotation of tooth trace of the cup-shaped flexible external gear.FIG. 8 illustrates a motion and a locus of one of teeth of a cup-shaped external gear when moving with respect to a tooth groove of a rigid internal gear, showing the motion and locus at a section of rotation of tooth trace on an end portion of the diaphragm of the external gear.FIG. 9 is a composite curve by which a continuous contacting tooth profile of the present invention is defined.FIG. 10 illustrates a moving locus of one of teeth of a cup-shaped flexible external gear with respect to a tooth groove of a rigid internal gear, the moving locus being used to form the envelope of the composite curve of FIG. 9.FIG. 11 shows how to introduce the tooth profiles of the present invention based on the composite curve of FIG. 9.FIG. 12 illustrates a motion and a locus of one of teeth of a cup-shaped external gear having tooth profiles defined by the composite curve of FIG. 9 when moving with respect to a tooth groove of a rigid internal gear, showing the motion and locus at a section of rotation on an opening of the cup-shaped flexible external gear (a section of non deviation)