A new phase error compensation method of 3-D shape measurement system using DMD projector

Structured light system using a digital micro-mirror device (DMD) projector is increasingly used for a 3-D shape measurement because of its digital nature. When the DMD projector is used in phase measuring profilometer (PMP), the precision of profile measurement will increase with the precision of phase-shift increasing. But the non-sinusoidal nature of the projected fringe patterns causes significant phase measurement error and consequent shape measurement error. In the reality, we find that the non-sinusoidal effect is never caused by only one factor. A real measurement shows that it is a combination of influences by all effects, e.g., the object independent irradiance function, the nonlinear gamma curve of the projector, the spatio-temporal characteristic of DMD, etc. In view of the above factors, a comprehensive compensation method is proposed to compensate these factors for the 3D measurement. If the compensation is well accomplished, the measurement error can be reduced average 6 times. The experiment is carried out to demonstrate the validity of this technique.