Active phase-setting twin-frequency grating for 3D shape measurement based on an absolute phase unwrapping algorithm

An active phase-setting twin-frequency grating based on an absolute phase unwrapping algorithm is proposed to measure the object with a complex shape. Two sinusoidal components with a spacial period ratio are combined into a twin-frequency grating, and two different initial phases are preset in two sinusoidal components, one of which is constant in a low-frequency component and the other is related to the ratio of two periods in a high-frequency component. Using the active phase-setting twin-frequency grating, two wrapped phases can be obtained from nine frames of distorted patterns by a regular phase shifting. Thus, the high-quality wrapped phase of a high-frequency component can be unwrapped by using an absolute phase unwrapping algorithm. Compared with a previous study based on a non-integral twin-frequency grating, the proposed grating needs a less number of patterns and the absolute phase unwrapping algorithm is easier to implement, so the proposed method is time-saving. The experimental results demonstrate that these achievements saved 90 percent of time approximately.