Dual-Parallel-Pixel-Row Decoupling Method for Camera-Based Three-Degree-of-Freedom Interferometers

Camera-based three-degree-of-freedom (3DoF) interferometers can be used to simultaneously measure the displacement, yaw, and pitch. Furthermore, high precision can be achieved in these interferometers with a fairly compact structure. However, they suffer from the problem of the 10-Hz-level frame rate of the used camera sensor, which limits their measurement speed to a micrometer per second. Therefore, this study proposes a dual-parallel-pixel-row decoupling (DPPRD) method. Here, 3DoF results are decoupled using two pixel-rows rather than an entire image. Hence, the DPPRD can overcome the hardware limitations of the area-scan camera; therefore, the frame rate and measurement speed can be further improved. The features introduced by the DPPRD method, particularly the influence of pixel-row interval on pitch angle measurement, are analyzed and simulated. Further, an interferometer prototype is developed and optimized using an industrial area-scan camera to verify the feasibility of the proposed method. Experimental results show that the resolution can achieve 0.8 nm and 0.5 μ rad levels, and the measurement accuracy can reach nanometer and microradian levels. The maximum measurement speed can be substantially improved approximately 44.25 times without modifying the hardware, and for some area-scan cameras, the measurement speed can exceed 1 mm/s.