Constant Ord upgraded interferometer maintenance and troubleshooting
An instrument made according to the principle of interference of light. The two beams from one source are completely separated, each passing through a different optical path, and then combined to show interference fringes. In spectroscopy, the precise Michelson interferometer or Fabry-Perot interferometer can be used to accurately and detailedly determine the wavelength of a line and its fine structure.
Laser interferometer
The laser has the advantages of high strength, high directivity, spatial coherence, narrow bandwidth and high monochromaticity. At present, interferometers that are commonly used to measure length are mainly based on Michelson interferometers, and use a stabilized 氦氖 laser as a light source to form a measurement system with interference. The laser interferometer can be used with various refractors, mirrors, etc. for linear position, velocity, angle, true flatness, true straightness, parallelism and verticality, and can be used as a calibration tool for precision machine tools or measuring instruments.
English name: laser interferometer
Laser interferometers are available in single frequency and dual frequency. [1]
Single frequency laser interferometer
The beam emitted from the laser is split by the beam splitter and split into two paths by the beam splitter, and reflected from the fixed mirror and the movable mirror respectively to merge with the beam splitter to generate interference fringes. When the movable mirror moves, the change of the intensity of the interference fringes is converted into an electrical pulse signal by the photoelectric conversion element and the electronic circuit in the receiver, and after being shaped and amplified, the input of the reversible counter is used to calculate the total number of pulses, and then the electronic computer is used. According to the formula [356-11], λ is the laser wavelength (N is the total number of electric pulses), and the displacement amount L of the movable mirror is calculated. When using a single-frequency laser interferometer, the surrounding atmosphere is required to be in a stable state, and various air turbulences will cause a change in the DC level and affect the measurement result.
Dual frequency laser interferometer
The laser interferometer is applied to a HeNe laser with an axial magnetic field of approximately 0.03 Tesla. Due to the Zeeman splitting effect and the frequency pulling effect, the laser produces two different frequencies of left and right circularly polarized light of 1 and 2. After 1/4 wave plate, it becomes two mutually perpendicular linearly polarized lights, and then split into two paths through the beam splitter. After passing through the polarizing plate 1, it becomes a reference beam having a frequency of f1 - f2. The other path is divided into two paths by the polarizing beam splitter: one path becomes a beam containing only f1, and the other path becomes a beam containing only f2. When the movable mirror moves, the beam containing f2 is reflected by the movable mirror to become a beam containing f2 ± Δf, and Δf is an additional frequency due to the Doppler effect when the movable mirror moves, and the sign indicates movement. Direction (Doppler effect is proposed by Austrian CJ Doppler, that is, the frequency of the wave changes when the wave source or receiver moves). This light beam and the light beam reflected by the fixed mirror and containing only the light of f1 pass through the polarizing plate 2, and are combined into a measuring beam of f1 - (f2 ± Δf). The measuring beam and the reference beam are subtracted from the respective photoelectric conversion elements, amplifiers, and shapers into a subtractor, and the output becomes an electrical pulse signal containing only ±Δf. After being counted by the reversible counter, the amount of displacement of the movable mirror can be obtained by equivalent conversion (by 1/2 laser wavelength) by an electronic computer. The dual-frequency laser interferometer uses the frequency change to measure the displacement. This displacement information is carried on the frequency difference between f1 and f2, and is insensitive to the change of the DC level caused by the change of the light intensity, so the anti-interference ability is strong. It is often used to verify the coordinate accuracy of length measuring machines, coordinate measuring machines, lithography machines and machining centers, and also as a measuring system for length measuring machines and high-precision coordinate measuring machines. High-precision straightness measurement, flatness measurement and small angle measurement with the corresponding accessories
application
The application of interferometers is extremely extensive, mainly in the following aspects:
Length measurement
In the two-beam interferometer, if the refractive index of the medium is uniform and constant, the movement of the interference fringes is caused by the difference in the geometrical path of the two-coherent light, and the length comparison or absolute measurement can be performed according to the number of movements of the stripe. The Michelson interferometer and the Fabry-Perot interferometer were used to represent the international meter with the wavelength of the cadmium red line.
Refractive index measurement
The geometrical path of the two beams remains the same, and the change in the refractive index of the medium can also cause a change in the optical path difference, causing the fringes to move. A Rayleigh interferometer is a typical interferometer that measures the refractive index by stripe movement. The Mach-Qinte interferometer applied to the wind tunnel was used to observe the change in the refractive index of the airflow in real time.
Folding wavelength measurement
Any method of measuring a standard meter in units of wavelength is a method of measuring the wavelength in units of a standard meter. Using international meters as the standard, the interferometer can accurately measure the wavelength of light waves. The Fabry-Perot interferometer (etalon) was used to determine the primary standard of wavelength (cadmium red line wavelength) and several secondary wavelength standards to determine the wavelength of other spectral lines by comparison.
Troubleshooting
1. The interference ring is not round
the reason:
(1) The layer of the beam splitter film is reversed.
(2) The two groups of exit pupils are misplaced.
(3) The spectroscopic plate, the compensating plate, the moving mirror and the reference mirror have compressive stress.
Inspection method: the film layer of the beam splitter should be the second side of the incident light. If it is mounted on the first surface, the equal-throwing circle ring that is called is a straight elliptical interference ring, which can loosen the three widths of the beam splitter. Head screws, take out the beam splitter, re-load the metal frame in reverse 180°, and screw the three wide head screws to the original pressing force. Please refer to the troubleshooting method for the beam splitter adjustment. The beam splitter, the wide head screw of the compensating plate, the moving mirror and the reference mirror adjust the knurling screw to a large pressing force, so that the lenses are gradually deformed to generate an equal-angle interference ring irregularity, and the loosening of the over-tightening screw can be eliminated.
Inspection method: first adjust the top block gap, the slide body looses the top block screw under working condition, the left thumb pushes the carriage body toward the reading head, the middle finger compresses the top block, and then tightens the top block screw. If the requirements are still not met, adjust the gap between the baffle and the guide rail to 0.02mm, and then adjust the two screws on the drive nut (four old products).
3. The carriage will not go when turning the rough handwheel.
the reason:
(1) After the instrument is subjected to strong impact, the screw rod is disengaged in the direction of the tailstock, causing the reading head to mesh with the gear.
(2) The drive pinion tightening nut is loose, causing the drive pinion and the lead screw to slip.
(3) The compression nut of the large gear and the coarse handwheel is loose.
Inspection method: first check the coarse hand wheel compression nut, and then check whether the precision screw rod is pulled out in the direction of the tailstock. If it has been pulled out, loosen the three screws of the tailstock and push the screw to the reading head while slowly turning coarse. Turn the handwheel and finally tighten the three screws of the tailstock. If the pinion tightening nut and the large gear tightening nut are loose, first remove the transmission box cover, then remove the door frame, tighten the nut, and reassemble in order. .
4. When the micro-handwheel is turned, the carriage will not go.
the reason:
(1) The transmission pinion compression nut is loose, so that the basin-shaped spring piece has no pressing force, causing the worm wheel to idle.
(2) The interferometer with coarse and slight motion and the disengagement mechanism, the worm compression spring piece fails.
(3) The micro-acting handwheel compression nut is loose.
Inspection method: first check the compression nut of the micro-handle. Then open the transmission box cover, remove the door frame, tighten the transmission pinion compression nut, and make the basin-shaped spring piece compact the worm wheel. At this time, the rotating worm wheel should drive the precision screw rod, and then install the removed parts in turn. If it is a disengagement mechanism, check if the worm carriage has been crushed. If it is crushed to death, the left and right clamps can be removed, and the oil can be cleaned and reassembled (7101 grease). If the worm carriage is loose, the spring pressure of the worm carriage is reduced. (1) The spring can be removed. Small R increases elasticity. (2) Change the spring piece.
5. When turning the coarse handwheel, the equal-pitch interference ring drifts outward from the center.
Cause: The incident light source is not perpendicular to the moving mirror.
Inspection method: This phenomenon is not an instrument failure. The main reason is that the incident light source is not perpendicular to the moving mirror. Because most of the misunderstandings are caused by the poor linearity of the guide rail, it is also explained here. First adjust the three foot leveling screws of the interferometer, so that the instrument is basically pressed horizontally, then adjust the light source, make the beam expander laser fill the fixed mirror, adjust the moving mirror to near zero path, turn the coarse hand wheel to adjust the straight stripes. , indicating that the beam expander laser is substantially perpendicular to the moving mirror, and the interference ring that rotates the coarse hand wheel will not drift.
maintain
1. The instrument should be properly placed in a dry, clean room to prevent vibration. When the instrument is moved, the base should be supported to prevent deformation of the guide rail.
2. When the optical parts are not in use, they should be stored in a clean drying basin to prevent mold. Mirrors and beamsplitters are generally not allowed to be wiped. When necessary, the dust must be carefully removed with a spare brush, and then wiped with a mixture of alcohol and ether with a degreased cotton ball.
3. The transmission components should have good lubrication. In particular, the guide rail, screw, nut and shaft hole parts are lubricated with T5 precision instrument oil.
4. When using, the force of each adjustment part should be appropriate, not strong rotation or hard pull.
5. The screw on the surface of the guide rail should be protected from scratches and rust. After use, it will remain oil-free.
6. The screws on the precisely adjusted instrument parts are painted with red paint and should not be rotated.
This paragraph application
(1) Geometric accuracy detection can be used to detect straightness, verticality, pitch and yaw, flatness, parallelism, and so on.
(2) The detection of positional accuracy and its automatic compensation can detect the positioning accuracy, repeat positioning accuracy and micro-displacement precision of CNC machine tools. The Renishaw ML10 laser interferometer not only automatically measures machine errors, but also automatically compensates for linear errors via the RS232 interface, saving a lot of time compared to the usual compensation methods and avoiding manual calculations and manual CNC typing. The operator error is caused, and the compensation points on the measured axis can be selected to the maximum extent, so that the machine can achieve the best precision. In addition, the operator does not need to have knowledge of machine parameters and compensation methods.
Currently available compensation software is Fanuc, Siemens 800 Series, UNM, Mazak, Mitsubishi, Cincinnati Acramatic, Heidenhain, Bosch, Allen-Bradley.
(3) Detection of the indexing accuracy of the CNC rotary table and its automatic compensation Now, the automatic measurement of the rotary axis can be performed by using the ML10 laser interferometer plus the RX10 turntable reference. It can automatically measure at any angular position for any angular position with an accuracy of ±1. This new technology has been recommended for new international standards. It not only saves a lot of measurement time, but also obtains a complete rotary axis accuracy curve, knows every detail of its accuracy, and gives statistical results processed according to relevant standards.
(4) Detection of double-axis positioning accuracy and its automatic compensation The Renishaw dual-laser interferometer system can simultaneously measure large-scale gantry mobile CNC machine tools, which can drive the positioning accuracy of an axial movement by dual servos, and can also pass the RS232 interface. , automatically compensate for the two-axis linearity error.
(5) Dynamic performance testing of CNC machine tools Using RENISHAW dynamic characteristic measurement and evaluation software, laser interferometer can be used for machine vibration test and analysis (FFT), dynamic analysis of ball screw, response characteristics analysis of servo drive system, dynamics of guide rails Characteristics (low speed crawling) analysis, etc.
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