This paper presents a robust and low-cost three-degree-of-freedom laser measurement system (3DOFLMS) that can measure both straightness error and roll angular error of long-travel linear stages. A low-cost laser diode is adopted as the laser source. A beam drift compensation module is employed to improve the stability of the 3DOFLMS. The relationships between the sensitivity of detector, the dual-beam parallelism and the measurement distance along the laser propagation direction are theoretical analyzed. Compensation methods are then proposed for eliminating the effects of detector sensitivity variation, beam drift and misalignment on the accuracy of the measurement system. The effectiveness of the compensation methods and the feasibility of the designed measurement system are demonstrated by a series of experiments. With the comparisons between commercial measurement instruments and the proposed measurement system in the measurement distance up to 1 m, the measurement accuracy of straightness errors and roll angular error are within ±1.0 μm and ±1.2 arcsec, respectively. The designed measurement system is very easy to construct both in the laboratory environment and in the actual measurement environment.
A compact diffracting grating based laser wavemeter is constructed in this paper. Wavelength is the length unit of laser interferometers, it must be very accurate and stable during the length measurement. An air sensor, which is employed to correct the air refractive index through an empirical equation, is essential in laser interferometers. However, the empirical equation is suffered from indirect measurement, the correction accuracy is depended on the measurement accuracy of the air sensor. Slow response is other disadvantages of the empirical equation. Additional, the empirical equation is not applicable to correct the laser diode wavelength. Therefore, a direct measurement method of laser diode wavelength, based on the diffraction principle, is proposed and a compact, low-cost and simple wavemeter is constructed in this paper. Laser beam drift is recognized as one of critical error source in laser measurement. Therefore, a novel laser beam drift active compensation method is thus proposed in this study that integrates the functions of automatic type angle turning and PID controlled fine angle motion. After introducing the principles of wavelength measurement and laser beam drift compensation, the effectiveness of the wavemeter in real-time wavelength measurement is well verified by the experimental results.