SU1241062A1 - Laser meter of linear shifts of surface - Google Patents

Abstract

The invention relates to a measurement technique and is intended to measure linear movements of a surface. The purpose of the invention is to improve the measurement accuracy by analyzing speckle reflected from the diffuse surface of laser radiation. The meter contains a laser 1 and a collimator 2 located on the platform 9. Passing the diaphragm 3, the radiation branches a semitransparent plate 1 1 into two parts. One part, having passed the plate 4, forms the reference direction 21, the stability of which the second one is supported by the stabilization unit 5. The other part of the radiation is directed towards the controlled surface 20 and is focused on it in the form of a spot having a granular structure called speckle. The largest dimensions of the speckle elements are reached if the surface 20 is located at the focus of the optical system 12. As the spot diameter increases, i.e. during defocusing, the size of the speckle elements decreases and the number of elements increases on microscope lens 14, two streams of radiation are directed with a cube-prism 13: one from the surface 20, the other, the reference one from one of the lateral faces of the cube-prism 13. on the photodiode array 16 an interesting pattern in the form of concentric rings is formed. The control unit 17 conducts the element-by-element interrogation of the matrix, the computing device-. Unit 18 determines the magnitude and direction of the displacement of the surface and provides a signal to the recorder 19. 1 Il. i (L tvD 4;

Description

The invention relates to a measuring technique and can be used in systems for automatic control of a surface profile.

The purpose of the invention is to improve the measurement accuracy by processing the speckled laser radiation signals reflected from the surface.

The drawing shows a functional diagram of a laser meter of surface displacements.

The device contains a laser 1, a collimator 2, a diaphragm 3, a measuring unit 4, a stabilization unit 5., a position-sensitive photo detector 6, a control signal generating unit 7, an electromechanical adjustment unit 8, a platform 9, a fixed base 10, a translucent plate 11, an optical forming system 12, a cube-prism 13, a micro-lens 14, a spatial filter 15, a photodetector matrix 16, a control unit 17, an optical device 18, a recorder 19. Position 20 indicates the measurable surface.

The laser 1 and collimator 2 mounted on platform 9, as well as the diaphragm 3, measuring unit 4 and stabilization unit 5 are installed in series along the laser 1. The measuring unit 4 contains a translucent plate 11 oriented obliquely relative to the axis of the laser 1 emitted by the radiation reflected from the plate 11, which forms the optical system 12 and the cube-prism 13 with two optical outputs, as well as the microscope 14 sequentially installed opposite one of the outputs, the spatial filter 15 and ozitsionno-sensitive photodetector is configured as a photodetector array 16 is connected to the control unit 17 to the synchronization output.

The device works as follows.

The laser radiation 1 is formed by the collimator 2, and the passage of the diaphragm is directed to the measuring unit 4 In the measuring unit 4, the radiation from the semitransparent plate 11 is divided into two light fluxes. One stream is used to irradiate the surface being monitored, and the second to create the reference direction 21.

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As a result of the effect of the environment on the laser radiation 1, it deviates from the reference direction 21, resulting in slow fluctuations. In order to stabilize the reference direction .. 21, stabilization unit 5 is inserted into the meter, which consists of a position-sensitive quadrant photodetector 6 and block 7 of the formation of control signals.

When the laser beam 1 is displaced from the optical axis of the photodetector 6, the outputs of the control signal generating unit 7 generate voltages proportional to the angular mismatch. These voltages are applied to the electromechanical adjustment unit 8, which is mechanically connected to the platinum 9, on which the laser 1 is installed with the collimator 2, and moves the optical axis of the laser 1 in elevation and azimuth to compensate for the error. The position-sensitive photo detector 6 is located on a stationary relative to the measured surface 20 of the base, 10.

The measuring unit 4-1 is designed to quantify the movements of the test surface 20 relative to the reference direction (line) 21.

The translucent plate 11, located in the radiation flux at an angle, reflects part of the radiation, which with the help of the focusing optical system 12 is formed on the measured surface as a spot with dimensions depending on the diameter and focal length of the optical system 12. At By this, the radiation reflected from the surface in a plane parallel to the surface of the object has a granular structure called speckle. The parameters of the speckle structure depend on the diameter of the spot formed on the surface of the object, the wavelength of the radiation, the quality of the surface and a number of other factors.

The diameter of the spot has the most significant effect on the size of speckle elements. With decreasing spot diameter, the size of the section of speckle elements increases, and, conversely, with increasing spot diameter, the size of speckle elements decreases and the number of elements increases. The largest dimensions of the elements reach, if the surface is located in the focus of the optical system. Therefore, the displacement of the measured surface from the point of focus leads to a decrease in the size of speckle elements. At the same time, within the speckle element, the radiation retains a sufficient degree of coherence in order to effect its homodyne transformation with the reference beam. This transformation is possible only when matching the edges of two or more interacting signals. If one of the signals is accepted as a supporting one, and the parameters of the other are changed, then these changes are converted into changes in the resulting signal. in the plane of interacting fronts. To create a reference signal and match its fronts with the signal reflected from the measured surface, a cube-prism 13 is inserted into the generated radiation flux. It is made so that its diagonal face is translucent. This allows, as a reference signal, to use the radiation reflected by one of the lateral faces of the cube-prism in the direction of the micro-lens 14, which is located perpendicular to the optical axis. The radiation reflected from the object 20 by the cube-prism 13 is also directed toward the micro-lens 14. When the reference radiation and the radiation reflected from the surface 20 pass through the spatial filter 15, the fronts in the focal plane of the micro-lens 14 are aligned, and on the surface of the photodiode array 16, located behind the spatial filter 15, an interference pattern is formed in the form of concentric rings with a maximum or minimum of radiation in the center. The size of the central zone depends on the position of the surface relative to the focus of the optical system 12, and the change in intensity towards the maximum

or minimum from the direction of its displacement.

The elemental polling of the photodiode array is carried out from the control unit 17. The computing device 18, based on the information received about the size of the central zone of the interference pattern and the distance between the rings, as well as the intensity of radiation at its center, determines the magnitude and direction of the surface displacement and carries the corresponding signal to the recorder.

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Application in the analysis meter

The granular structure (speckle) of the focused laser radiation reflected from the diffusion surface realizes the high spatial characteristics of the latter and thus improves the measurement accuracy.

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5 claims

A laser surface linear displacement meter containing a platform, a successive laser and collimator, an aperture installed on the platform, a measuring unit and a stabilization unit, a measuring unit made in the form of a carriage mounted to move parallel to the laser radiation axis, and fixed on the carriage of a translucent plate, oriented towards the axis of radiation, and a position-sensitive photodetector mounted during the radiation reflected from the semi-transparent plate, the stabilization unit is made in the form of successively connected position-sensitive photodetectors mounted on a fixed base, a shaping unit, control signals and an electromechanical adjustment unit, the output of which is mechanically connected to the platform, characterized in that measurement accuracy, it is provided placed between the translucent plate and the position-sensitive photo detector of the measuring unit and installed on the carriage of the measuring unit forming an optical system, a cube-prism made with two optical outputs, one of which is designed to communicate with a controlled surface, a microscope located opposite the second output of the cube-prism, a spatial filter and a computing device, form the optical system relative to the controlled surface at a distance of the cube-prism is oriented so that its diagonal face is located relative to the optical axes of the focusing optical system themes and microobjects at angles at which the light fluxes are matched by fronts, position-chuv. . 51241062ft;

a detector for measuring the output of the control loop, and the outputs

the block is made in the form of a photomatrix; connected to the first input of the calculation of the control unit from the synchronization device, the second input

control outputs, photo control inputs connected to the sync

The matrices are connected to the corresponding output of the control unit.

Claims (1)

Claim A laser linear surface displacement meter containing a platform, a sequentially located laser and a collimator mounted on the platform, a diaphragm, a measuring unit and a stabilization unit, the measuring unit is made in the form of a carriage mounted to move parallel to the laser radiation axis, and mounted on the carriage of a translucent plate, oriented obliquely relative to the radiation axis, and a position-sensitive photodetector installed during radiation reflected from a translucent plates, the stabilization unit is made in the form of a series-connected positionally sensitive photodetector mounted on a fixed base, a formation unit, control signals and an electromechanical adjustment unit, the output of which is mechanically connected to the platform, characterized in that, in order to increase the accuracy of measurements, it is equipped placed between the translucent plate and the position-sensitive photodetector of the measuring unit and · mounted on the carriage of the measuring unit of the forming optical a cube-prism system made with two optical outputs, one of which is designed for communication with a controlled surface, a micro lens located opposite the second cube-prism output, a spatial filter and a computing device, the forming optical system is installed at a distance from the controlled surface equal to its focal length, the cube prism is oriented so that its diagonal face is located relative to the optical axes of the focusing optical system and lens at an angle at which the light fluxes aligned edges, ^position-5 and void Chuv dotektor measuring unit is designed as a photomatrix and output to the synchronization control unit photomatrixes control inputs connected to respective 1241062 6 outputs of the control unit, and the outputs are connected to the first input of the computing device, the second input 5 connected to the synchronizing output of the control unit.