Real-time compensation for interpolation error of moiré fringes signal

Lacking effective error compensation method is one important reason that limits the measurement precision of optical grating. A real-time compensation method for eliminating the interpolation error of moiré fringes signal is proposed. The interpolation error is caused by zero offset; nonorthogonal phase and unequal amplitude of two signals. The principle is introduced as follows: first, tracking eight characteristic points on a grating signal period. The zero offset of sine signal is separated from amplitude of characteristic points, so it can be compensated; then tracking the compensative signal, and the zero offset of cosine signal can also be separated and compensated. Tracking the compensative signal continually, the unequal amplitude of two signals and the nonorthogonal phase can be separated and compensated respectively. The three above errors can be totally compensated in no more than three grating signal periods. Through experiments the effect of this method is proved. © 2009 SPIE.