Patent ID: 8302507

Claim:
A wave gear device, comprising: a rigid circular spline having internal teeth formed on a circular inner circumferential surface thereof; a flexspline disposed inside the circular spline and provided with a cylindrical body capable of bending in a radial direction, a diaphragm having one end contiguous with a rear end of the cylindrical body, a rigid boss formed on another end of the diaphragm, and external teeth formed on an external circumferential part near an open end of the cylindrical body; and a wave generator for bending the cylindrical body of the flexspline into an elliptical shape, causing the external teeth to partially mesh with the internal teeth of the circular spline, causing positions at which both of the sets of teeth are enmeshed to move in a circumferential direction, and generating relative rotation between both of the splines in accordance with a difference in the number of teeth between the two sets of teeth; wherein the amount of bending in a radial direction at a position along a major axis of the elliptical shape in the cylindrical body bent into an elliptical shape by the wave generator gradually increases in a direction from the rear end to the open end; wherein the tooth profile of the external teeth is defined by a first modified tooth profile obtained by modifying a first basic tooth profile, the first basic tooth profile has a bottom land and a top land parallel to each other so that a tooth depth thereof is kept constant, and the first modified tooth profile is provided with a first tapered surface in a top land area near a tooth trace end of the first basic tooth profile located on an open end side of the flexspline so that a tooth depth thereof gradually decreases toward an open end of the flexspline along a tooth trace direction thereof; wherein the tooth profile of the internal teeth is defined by a second modified tooth profile obtained by modifying a second basic tooth profile, the second basic tooth profile has a bottom land and a top land parallel to each other so that a tooth depth thereof is kept constant, and the second modified tooth profile is provided with a second tapered surface in a top land area near a tooth trace end of the second basic tooth profile located on a side of an open end of the flexspline so that a tooth depth thereof gradually decreases toward an open end of the flexspline along a tooth trace direction thereof; and, wherein respective angles of the first and second tapered surfaces formed on the external teeth and the internal teeth, and respective ranges in which the first and second tapered surfaces are formed in the tooth trace direction, are set so that the top land of one set of teeth does not interfere with the bottom land of the other set of teeth in the internal teeth and external teeth that have been brought to an enmeshed state by the wave generator.