Objective  Phase shifting profilometry (PSP) is one of the most commonly used techniques in 3D measurement, which has the advantages of high accuracy and robustness to ambient light and reflectivity variation. During the reconstruction of PSP, at least three sinusoidal fringe patterns with phase shift are projected onto the surface of the object; the camera captures the ones reflected from the object. Because of the height of the object, the fringe patterns on the object surface will have distortions. The phase information existing in the fringe pattern is employed to analyze the deformation of the fringe patterns. At last, the object is reconstructed based on the phase information and system parameters. Because of multiple fringe patterns are used, the traditional PSP requires the object must be kept stationary during the reconstruction process. Errors will occur if the object moves during the fringe projecting and capture process. However it is difficult to meet this requirement in dynamic scenes. Therefore, it is important to improve the reconstruction accuracy of moving object. For this purpose, a new method with high frame rate and accuracy is proposed based on PSP.

  Methods  This paper proposes a new method to reduce the measurement error caused by moving objects at dense frame rate. First of all, trigger control equipment is added to the camera and projector. The equipment ensures that, for each projection, two consecutive images are captured before the next projection (Fig.1). Then, the phase retrieval algorithm is proposed. As there is no fringe pattern shift among the captured two images of the same projection, the phase shift is introduced by the object motion. By analyzing the phase variation caused by the motion, the reconstruction model describing the fringe patterns with motion is given. At last, the object is reconstructed based on the phase information and system parameters. The proposed algorithm can achieve high frame rate for the reconstruction of object with motion (Fig.2).

  Results and Discussions   The experiments are implemented to verify the performance of the proposed method. The moving object is captured twice in one projecting period (Fig.5). Then, the phase information is retrieved by the proposed method (Fig.6(a)). At last, the object is reconstructed successfully (Fig.6(b)). In order to compare the performance, the same fringe patterns are reconstructed by the traditional PSP and the result is shown in Fig.7. It is apparent that errors have been introduced. By using the data obtained with the static object as true value, the RMS error and mean error are calculated (Tab.1). With the traditional PSP, the RMS error and mean error are 4.918 6 mm and −0.085 1 mm. With the proposed method, the RMS error and mean error are 0.001 9 mm and 0.003 6 mm.

  Conclusions  This article proposes a dual sampling method for reconstructing moving objects based on phase-shifting profilometry. Under the condition of limited device frame rate, the reconstruction frame rate of moving objects can be effectively improved. Firstly, by controlling the synchronization signal between the camera and projector, it is possible to capture the same projected fringe pattern twice to obtain more object motion information. Then, the stripe description of the moving object was analyzed and the phase information under mixed phase shift was extracted; Finally, utilizing stripe multiplexing improved the frame rate of motion object reconstruction.