Vision vibration measurement based on coded illumination in a single frame

Abstract

A vision-based mechanical vibration measurement method is presented and verified by experiments in this paper. The coded illumination is projected on the objects by a digital light processing projector with a digital micromirror device in it. The projection patterns are designed to be concentric. In one integration time of the camera, the projector is exposed several times, which embeds temporal information in the images. A single frame can be divided into subframes by separating the coded concentric patterns. The centroids of the coded concentric patterns are fitted, and the centroids are treated as virtual feature points with vibration information. The acquisition devices are common low-speed cameras, and they record the vibration whose frequency exceeds the camera frame rate. The temporal resolution is increased by 10 times, corresponding to the 400 Hz sampling frequency in the experiment. We can measure the vibration of multiple points with different sampling frequencies. The frequency measurement accuracy is in the subhertz level in low-frequency measurement, relative error is always slightly greater than 0.01 in high-frequency measurement, and the amplitude resolution is 130 µm.