System and method for measuring straightness of knife-edge-shaped ruler

Abstract

The invention discloses a knife-edge-shaped ruler straightness measurement system and method, and the method comprises the steps: carrying out the beam expansion of a laser beam through a beam expansion collimating lens group, forming parallel light, employing the working surface of a long optical flat as a reference plane, enabling the laser to be diffracted at a slit formed by the working edge of a knife-edge-shaped ruler and the long optical flat, receiving a diffraction image through a photoelectric sensor, and carrying out the measurement of the straightness of the knife-edge-shaped ruler through a photoelectric sensor. A relative light intensity distribution diagram is formed after computer processing, and the straightness of the working edge of the knife-edge-shaped ruler is finally obtained through an image processing algorithm. According to the invention, quantitative and accurate detection of the straightness of the working edge of the knife-edge-shaped ruler is realized, and the test error of human eye estimation and reading is greatly reduced; the flatness error of the long optical flat is smaller, and errors caused by a traditional grinding surface leveling ruler are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of precision measurement, and in particular to a knife-edge ruler straightness measurement system and method. Background Art

[0002] In order to ensure high sealing, wear resistance, stability and other characteristics, machined parts need to be tested for flatness or straightness. Usually, a knife-edge ruler is used to test the straightness or flatness of the surface of machined parts. The straightness of the working edge of the knife-edge ruler directly affects the measurement results of the parts. Therefore, the straightness of the working edge of the knife-edge ruler must be tested before work. The detection method is generally carried out in accordance with the verification procedures, using a ground flat ruler with an effective length not less than the length of the working edge of the knife-edge ruler, and measuring the straightness of the working edge of the knife-edge ruler by the light gap method. However, this method has problems such as large light gap errors observed by the human eye and the inability to quantify the measured values.

[0003] In view of the above problems, the present invention provides a knife-edge ruler straightness measurement system and method based on single-slit Fraunhofer diffraction theory, which solves the problem that the straightness of the working edge of a traditional knife-edge ruler relies on human eye estimation and cannot be accurately measured. Summary of the invention

[0004] The invention provides a knife-edge ruler straightness measurement system and method based on single-slit Fraunhofer diffraction theory, which solves the problem that the straightness of the working edge of a traditional knife-edge ruler depends on human eye estimation and cannot be accurately measured.

[0005] The object of the present invention is to provide a knife-edge ruler straightness measurement system, comprising a laser, a beam expansion collimator lens group, a knife-edge ruler, a long flat crystal, a knife-edge ruler bracket, a photoelectric sensor and a computer, the optical axes of the laser and the beam expansion collimator lens group coincide, the light gap formed by the knife-edge ruler and the long flat crystal is in the same straight line as the optical axis, the working surface of the photoelectric sensor is perpendicular to the optical axis, and the knife-edge ruler is installed on the knife-edge ruler bracket.

[0006] Furthermore, the laser adopts He-Ne laser, and the photoelectric sensor adopts silicon photocell.

[0007] Furthermore, the knife-edge ruler bracket is a gantry-shaped adjustable bracket, including a main beam, legs and a hanger. The hanger hangs the knife-edge ruler at 2 / 9 of the length from both ends of the knife-edge ruler and can move on the main beam.

[0008] A method for measuring the straightness of a knife-edge ruler, the specific steps of the method are as follows:

[0009] Step 1: The light beam emitted by the laser passes through a beam expander and collimator lens group to become a parallel line laser beam;

[0010] Step 2, the parallel line laser beam is incident on the light gap formed by the knife-edge ruler and the long flat crystal and diffracted. The diffracted light is received by the photoelectric sensor and enters the computer diffraction light intensity recording system to obtain a single slit diffraction relative light intensity distribution diagram;

[0011] Step 3, processing the relative light intensity distribution diagram to obtain the straightness of the working edge of the knife-edge ruler;

[0012] Furthermore, the specific steps of step 3 are as follows:

[0013] Step 31, collecting the light intensity distribution on the observation screen for multiple times, adding them up to obtain an average value, and then smoothing the obtained image data;

[0014] Step 32, using the least square method to fit the measured data near the centers of the two first-order diffraction dark fringes to obtain the first-order dark fringes spacing;

[0015] Step 32: According to the single-slit Fraunhofer diffraction theory, the light gap width h formed by the knife-edge ruler and the long flat crystal is calculated by the following formula:

[0016]

[0017] Among them, k is the kth level dark fringe, λ is the laser wavelength, and x k The distance from the kth dark fringe to the optical axis, L is the distance from the photoelectric sensor to the slit;

[0018] Step 33, obtain the slit width value, that is, the straightness of the working edge of the knife-edge ruler, by calculation. If the knife-edge ruler is long, multiple segmented measurements are required, and the maximum value of the multiple measurement results is taken as the straightness value of the working edge of the knife-edge ruler.

[0019] The present invention has the following advantages: the present invention realizes quantitative and accurate detection of the straightness of the working edge of the knife-edge ruler, greatly reducing the test error of human eye estimation; the flatness error of the long flat crystal is smaller, reducing the error introduced by the traditional grinding surface flat ruler. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of the present invention;

[0021] Figure 2 It is a schematic diagram of the structure of the knife edge ruler support of the present invention.

[0022] In the figure: 1. Laser; 2. Beam expansion and collimation lens assembly; 3. Knife-edge ruler; 4. Long flat crystal; 5. Knife-edge ruler bracket; 6. Photoelectric sensor; 7. Computer; 8. Main beam; 9. Hoist; 10. Outrigger. DETAILED DESCRIPTION

[0023] The present invention provides a knife-edge ruler straightness measurement system, comprising a laser 1, a beam expansion collimator lens group 2, a knife-edge ruler 3, a long flat crystal 4, a knife-edge ruler bracket 5, a photoelectric sensor 6 and a computer 7. The optical axes of the laser 1 and the beam expansion collimator lens group 2 coincide, the light gap formed by the knife-edge ruler 3 and the long flat crystal 4 is in the same straight line as the optical axis, the working surface of the photoelectric sensor 6 is perpendicular to the optical axis, and the knife-edge ruler 3 is installed on the knife-edge ruler bracket 5.

[0024] In this embodiment, the laser 1 is a He-Ne laser 1 and the photoelectric sensor 6 is a silicon photocell.

[0025] In this embodiment, the knife-edge ruler bracket 5 is a gantry-shaped adjustable bracket, including a main beam 8, supporting legs 9 and a hanger 10. The hanger 10 hangs the knife-edge ruler 3 at 2 / 9 of the length from both ends of the knife-edge ruler 3 and can move on the main beam 8.

[0026] A method for measuring the straightness of a knife-edge ruler, the specific steps of the method are as follows:

[0027] Step 1, the light beam emitted by the laser 1 passes through the beam expansion collimator group 2 to become a parallel line laser beam;

[0028] Step 2, the parallel line laser beam is incident on the light gap formed by the knife-edge ruler 3 and the long flat crystal 4 and diffracted. The diffracted light is received by the photoelectric sensor 6 and enters the diffracted light intensity recording system of the computer 7 to obtain a single slit diffraction relative light intensity distribution diagram;

[0029] Step 3, processing the relative light intensity distribution diagram to obtain the straightness of the working edge of the knife-edge ruler 3;

[0030] In this embodiment, the specific steps of step 3 are as follows:

[0031] Step 31, collecting the light intensity distribution on the observation screen for multiple times, adding them up to obtain an average value, and then smoothing the obtained image data;

[0032] Step 32, using the least square method to fit the measured data near the centers of the two first-order diffraction dark fringes to obtain the first-order dark fringes spacing;

[0033] Step 32: According to the single-slit Fraunhofer diffraction theory, the light gap width h formed by the knife-edge ruler 3 and the long flat crystal 4 is calculated by the following formula:

[0034] Wherein, k is the kth level dark fringe, λ is the laser wavelength, is the distance from the kth level dark fringe to the optical axis, and L is the distance from the photoelectric sensor 6 to the slit;

[0035] Step 33, obtain the slit width value, that is, the straightness of the working edge of the knife-edge ruler 3, by calculation. If the knife-edge ruler 3 is long, multiple segmented measurements are required, and the maximum value of the multiple measurement results is taken as the straightness value of the working edge of the knife-edge ruler 3.

[0036] In this embodiment, the laser beam is expanded by the beam expansion collimator set 2 to form parallel light. The working surface of the long flat crystal 4 is used as a reference plane, and the laser is diffracted at the slit formed by the working edge of the knife-edge ruler 3 and the long flat crystal 4. The diffraction image is received by the photoelectric sensor 6, and is processed by the computer 7 to form a relative light intensity distribution diagram. After the image processing algorithm, the straightness of the working edge of the knife-edge ruler 3 is finally obtained.

[0037] Although the specific embodiments of the present invention are described in detail in conjunction with the accompanying drawings, it should not be understood as limiting the scope of protection of the present invention. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still belong to the scope of protection of the present invention.

Claims

1. A knife-edge ruler straightness measurement system, comprising a laser, a beam expansion collimator, a knife-edge ruler, a long flat crystal, a knife-edge ruler bracket, a photoelectric sensor and a computer, characterized in that: The optical axes of the laser and the beam expander collimator lens group coincide, the light gap formed by the knife-edge ruler and the long flat crystal is in the same straight line as the optical axis, the working surface of the photoelectric sensor is perpendicular to the optical axis, and the knife-edge ruler is installed on a knife-edge ruler bracket.

2. A knife-edge ruler straightness measurement system as claimed in claim 1, characterized in that: The laser is a He-Ne laser, and the photoelectric sensor is a silicon photocell.

3. A knife-edge ruler straightness measurement system as claimed in claim 1, characterized in that: The knife-edge ruler bracket is a gantry-shaped adjustable bracket, comprising a main beam, legs and a hanger. The hanger hangs the knife-edge ruler at 2 / 9 of the length of both ends of the knife-edge ruler and can move on the main beam.

4. A method for measuring straightness of a knife-edge ruler, characterized in that: The specific steps of the method are as follows: Step 1: The light beam emitted by the laser passes through a beam expander and collimator lens group to become a parallel line laser beam; Step 2, the parallel line laser beam is incident on the light gap formed by the knife-edge ruler and the long flat crystal and diffracted. The diffracted light is received by the photoelectric sensor and enters the computer diffraction light intensity recording system to obtain a single slit diffraction relative light intensity distribution diagram; Step 3: Process the relative light intensity distribution diagram to obtain the straightness of the working edge of the knife-edge ruler.

5. A method for measuring straightness of a knife-edge ruler as claimed in claim 4, characterized in that: The specific steps of step 3 are as follows: Step 31, collecting the light intensity distribution on the observation screen for multiple times, adding them up to obtain an average value, and then smoothing the obtained image data; Step 32, using the least square method to fit the measured data near the centers of the two first-order diffraction dark fringes to obtain the first-order dark fringes spacing; Step 32: According to the single-slit Fraunhofer diffraction theory, the light gap width h formed by the knife-edge ruler and the long flat crystal is calculated by the following formula: Among them, k is the kth level dark fringe, λ is the laser wavelength, and x k The distance from the kth dark fringe to the optical axis, L is the distance from the photoelectric sensor to the slit; Step 33, obtain the slit width value, that is, the straightness of the working edge of the knife-edge ruler, by calculation. If the knife-edge ruler is long, multiple segmented measurements are required, and the maximum value of the multiple measurement results is taken as the straightness value of the working edge of the knife-edge ruler.

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