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This investigation develops a laser encoder system based on a heterodyne laser interferometer. For eliminating geometric errors, the optical structure of the proposed encoder system was carried out with the internal zero-point method. The designed structure can eliminate the geometric errors, including positioning error, straightness error, squaren...
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Context 1
... laser source has orthogonally polarized beams with different angular frequencies (ω 1 , ω 2 ). The basic structure of the heterodyne interferometer is shown in Figure 3 [26]. The movement of the measuring mirror will induce a phase shift (∆ω 1 ). ...
Citations
... The common initial resolutions of the laser interferometers are about 0.32 µm or 0.16 µm, depending on the optical structure [2] (Table S1, Supplementary Material). The initial resolution of the laser interferometer is several times higher than that of a grating-based encoder system [3], and laser interferometers also have the feature of error reduction [4][5][6]. Therefore, the interferometry−based encoders have high potential in precision positioning. ...
... Furthermore, in the multi-axis positioning task, the homodyne interferometer requires more optical elements and detectors to fit the differential signaling [19]. On the contrary, the heterodyne interferometer can share the reference signal, eliminating the need to arrange the reference signal for every positioning axis [6]. This characteristic is advantageous in the positioning application, especially for the multi-axis positioning systems [20,21]. ...
... The common heterodyne signal processing is based on LIA technology [22,23], and is wildly used in interferometer signaling [6,24]. The block diagram of the LIA method is shown in Figure 4. ...
Laser interferometer technology is used in the precision positioning stage as an encoder. For better resolution, laser interferometers usually work with interpolation devices. According to the interpolation factor, these devices can convert an orthogonal sinusoidal signal into several square-wave signals via digital processing. The bandwidth of the processing will be the limitation of the moving speed of the positioning stage. Therefore, the user needs to make a trade-off between the interpolation factor and the moving speed. In this investigation, a novel analog interpolation method for a heterodyne laser interferometer has been proposed. This method is based on the principle of the lock-in amplifier (LIA). By using the proposed interpolation method, the bandwidth of the laser encoder system can be independent of the interpolation factor. This will be a significant benefit for the ultra-high resolution encoder system and the laser interferometers. The concept, design, and experiment are revealed in this manuscript. The experimental results show that the proposed interpolation method can reach nanometer resolution with a heterodyne laser interferometer, and the bandwidth of the signal is independent of the resolution.
... To meet the process and performance requirements of chip manufacture, the measurement accuracy of the lithography machine's displacement system must reach the subnanometer level [1]. At present, the measurement tools used in the field of ultraprecision displacement measurement mainly include heterodyne laser and grating interferometers [2][3][4][5][6]. ...
In this study, a subnanometer heterodyne interference signal processing algorithm with a dynamic filter is proposed. The algorithm can effectively reduce the measurement error caused by the noise introduced in the optical path and circuit. Because of the low signal−to−noise ratio of the measurement signal, a dynamic filter with variable coefficients is designed. The role of the bi−quadrature lock−in amplifier algorithm in the problem of different amplitudes among the measurement signal, reference signal, and uncertainty of the frequency difference of the dual−frequency laser is analyzed. With the aid of the heterodyne interferometry platform, the error in the solution results of the proposed algorithm and the conventional algorithm is compared. The results indicate that the maximum deviation of the phase increment of the algorithm does not exceed 6 mrad, the single−cycle phase difference can be subdivided by 1024, and the system resolution reaches 0.15 nm.
