In order to solve the problem of low precision in calibration and measurement of large size optical measuring instruments, mask, and other two-dimensional grid standards, a large size(1m × 1m) plane coordinate measuring method based on multi-axis laser interferometer is studied. Use a cube-corner prism as a reflector. Using a fixed bridge measuring machine structure, the co-planar motion is disassembled into independent X-axis movable table motion and Y-directional slider motion on the beam. Geometrical error modeling analysis is carried out on the measuring machine, and optical path spectral layout of multi-axis laser interferometry is studied. In order to monitor the deflection of the X-direction moving platform in real time, use two-channel laser interference to measure the length in the X-direction and a single-channel measurement of the Y-direction slider movement. Finally, a laser interferometry model with large plane coordinates is proposed and a motion simulation analysis is carried out for the deviation of X-axis mobile platform around Z axis, to verify the validity and necessity of real-time monitoring compensation error of double optical path for plane coordinates measurement.
In rotating machines, misaligned shafts increase vibrations and friction, which can increase the energy consumption considerably and cause premature bearing and seal damage. Laser-based alignment systems can realize quick shaft alignment with high accuracy, consisting of laser transmitting unit, charge-coupled device (CCD) or position sensitive detector (PSD) receiving unit and display unit. Their resolution can reach 1 μm or higher, and the accuracy can be even up to ± (0.5%|L| + 1 resolution). In the paper, the principle of a laser-based alignment system is presented. In order to calibrate laser-based alignment systems, a set of measurement device is established. The receiving unit is fixed on a high precision one-dimensional linear stage, while the transmitting unit remains stationary. So, the relative displacement between the two units can be measured. A laser interferometer is used as the standard value of the linear stage displacement, which is traceable to the definition of meter. The layout of the calibration system is complied with Abbe's principle, reducing the measurement error. In addition, several key influencing factors for calibration are given. At last, the uncertainty of the calibration result is analyzed. The result indicates that the calibration apparatus is practical and efficient during the routine work.
In order to measure the squareness of large-size workpieces, a method of squareness measurement based on laser alignment system was introduced. The structure and principle of the laser alignment system were presented. The squareness measuring method of the squareness measuring system and the laser alignment system were described respectively. This paper improved the method of squareness measurement based on laser alignment system and made the accuracy satisfied with the requirement of most in-site measurement. The experiments show that the squareness measurement accuracy of the laser alignment system can be improved to 5 μm/500 mm.
A point laser interferometer for measuring aspheric optics is developed in this paper. The proposed laser interferometer will be used as a optical probe in optical coordinate measuring machines. The point optical probe is based on homodyne interferometry with frequency stabilized He-Ne laser to provide traceable measurements. The influences of various aspheric surface factors on the performance of point optical probe are analyzed, such as roughness, reflectivity, material, slope angle etc. A compensation method is applied in the signal processing system to reduce the influences. Experimental results show that the measurement resolution is at the nanometer level under various conditions.
In order to develop an aspheric surface measurement standard device to provide reliable and traceable measurement and
calibration, a high resolution aspheric surface measurement technology based on laser interferometer is proposed in this
paper. A laser interferometer with frequency stabilized He-Ne laser is used to provide traceable measurements. The
standard device would provide calibrations for different kinds of aspheric surface, therefore the interferometer used in
the standard device would be influenced by various factors, such as roughness, reflectivity, material and slope angle. The
influences of reflectivity and roughness are analyzed. A compensation method based on the analysis is applied in the
signal processing system to reduce the influences of reflectivity and roughness. An objective lens is used to collect the
measurement beam reflected from the target. The laser interferometer is set up and tested under different conditions: the
reflectivity is 1%~100%, the surface roughness is 0.012~0.8μm. Experimental results show that the measurement
resolution of the developed interferometer is at the nanometer level.
Cone parts are widely used in advanced manufacturing and precision mechanics, providing air proof, torque transmission and so on. The straightness of generatrix is one of the important parameters, and the required accuracy can be up to submicrometers. In order to realize the rapid and high precision generatrix measurement of smooth surface cone, a laser interferometric method is proposed based on the structure of typical Fizeau interferometer. The high precision optical flat is used for reference standard, and the surface of cone is the measured object. Two cylindrical lenses with different focal lengths realize unidirectional expansion of parallel beam, solving the problem of CCD camera fringe resolution. The interference fringes are curved because of the cone angle, and the peak is the basis for accurate determination of the generatrix. Two fringe processing techniques are described in detail, which are single-frame and phase-shifting methods. Single-frame method includes two steps, i.e. the calculation of integral part and decimal part. The advantage of this method is the simple measurement structure. Phase-shifting method needs piezoelectric transducer (PZT) to generate several steps for phase calculation, with the advantage of high accuracy. The experimental results show that the straightness measurement accuracy can be better than 0.2 μm.
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