Rapid 3D Shape Measurement using Sine Pattern in Phase-Shifting Projection Method

The accuracy and speed of measurement are very important in a 3D measurement system using a DLP projector and a camera. In order to increase the accuracy, the measurement area is divided as small as possible by using a gray code. When the width of the pattern becomes narrower, the square pattern appears as a sine wave, making further division difficult. The sine wave shown here can be subdivided into a range of 2π using the phase-shifting method. This method is the most widely used measurement method called the SBM so far. It is a simple method to increase the accuracy by using gray codes with a short pitch, but there is a problem that the measuring time is lengthened due to an increase in the number of camera shots. In order to reduce the number, it is necessary to use fewer gray codes by using a long-period sine wave in the phase-shifting method. However, if the sine pattern is directly projected, an ideal sine wave cannot be obtained due to the gamma effect, so it is necessary to appropriately modify the fringe pattern and redesign. In this paper, we propose a method to compensate for the gamma effect in a sine pattern and show that an ideal sine wave can be generated even with a long periodic phase-shifting method. When the measuring speed and accuracy of the proposed method were compared with the SBM, it was confirmed through experiments that the measuring speed was increased by 25% at the same accuracy and the accuracy of the reference plane was improved by 7 times at the same speed.