As shown in FIG. 1, typical wave gear devices are constructed of three fundamental components referred to as a circular spline CS (hereinafter also referred to as a “CS”) which is a ring-shaped rigid body having teeth carved into the inner circumference of the ring; a flexspline FS (hereinafter also referred to as an “FS”) which is a thin cup-shaped component having teeth carved into the outer circumference of the open part of the cup; and a wave generator WG (hereinafter also referred to as a “WG”) which is an elliptical cam and a wave generator (Non-patent Document 1). The FS uses a flexible metal, flexibly deforms in accompaniment with the rotation of the WG, and is a special reduction gear in which the meshing position with the CS moves to thereby transmit drive power. Wave gear devices are frequently used in industrial robots or the like because the devices have a high reduction ratio, high torque, no backlash, and other characteristics.
Wave gear devices make use of elastic deformation of metal, and the flexspline FS therefore behaves as a nonlinear spring having hysteresis and has a substantial effect on positioning response performance (Non-patent Document 2). Moreover, an angular transmission error occurs in synchrony with the relative rotation of every constituent part due to machining and assembly errors of the gears, producing steady-state errors of the output shaft and vibrations during transitions (Non-patent Document 3). In addition, it has been pointed out that compensation must be made for nonlinear friction produced in the portions of the device in contact with each other (Non-patent Document 4).
Nonlinear FF compensation based on strict linearization has been proposed in response to problems related to nonlinear elements (Non-patent Document 5, Patent Document 1). In this method, strict linearization is performed without approximation of a nonlinear state equation by expanding a state equation into an equation that includes nonlinear characteristics, and performing linearized feedback and input conversion. However, this method is an FF compensation method that presupposes a model-base, and a problem therefore arises in that modeling errors are directly influenced by compensation accuracy. Non-patent Documents 6 to 11 are art related to the present invention.