A method for measuring the apex angle of an optical triangular prism

Abstract

The present invention discloses a method for measuring the apex angle of an optical triangular prism, belonging to the field of optical measurement. Technical solution: The measurement method involved is formed by combining a laser, a triangular prism to be measured, a rotary table, two plane mirrors and a camera. A beam of laser is incident on the triangular prism to be measured, and the light emerging from the inclined surface of the triangular prism is reflected back and forth between the two mirrors and then converges onto the camera target surface to form a light spot; the rotary table is deflected by a known small angle, at this time the light spot on the camera target surface is shifted, the shift amount of the light spot is calculated, and the apex angle of the triangular prism to be measured can be obtained by combining the corresponding formula. The triangular prism is placed at the center of rotation of the rotary table, the two mirrors are in a parallel state, and the selection range of the small angle by which the rotary table is deflected is from 0.04° to 0.4°. In the present invention, the greater the distance between the two mirrors, the more times the laser beam is reflected between the mirrors, and the smaller the pixel of the camera target surface, the higher the final measurement accuracy.

Description

Technical Field

[0001] The present invention belongs to the field of optical measurement, and particularly relates to a method for measuring the apex angle of an optical triangular prism. Background Art

[0002] Currently, the measurement of an optical prism usually relies on the principle of a spectrometer. The light emitted by a light source forms a parallel light beam through a slit and a focusing lens, and after being reflected or refracted by each surface of the prism, it enters the objective lens of a telescope and forms an image on the focal plane of the telescope. It is observed through an eyepiece, and the angle of light deflection is measured in combination with an angle scale, and finally the apex angle of the prism is calculated. However, the field of view of the telescope in the spectrometer is less than 2", the adjustment difficulty is high, and the reading by the human eye through the eyepiece is prone to accidental errors, affecting the accuracy. In order to improve the method for measuring an optical prism, the invention patent CN107941469A discloses "a method for measuring the apex angle deviation of an equilateral triangular prism", which uses an angle mirror fixed at 60° in combination with an interferometer to achieve, but this method is not applicable to the measurement of triangular prisms with arbitrary apex angles. Another example is the invention patent CN202020310283.0, which discloses "a prism angle measuring instrument", using an optoelectronic autocollimator and a reflector to replace the telescope, but the distance between the reflector and the sensor is short, and the measurement accuracy needs to be further improved. Summary of the Invention

[0003] The object of the present invention is to provide a method for measuring the apex angle of an optical triangular prism, which compresses the optical path with two reflectors and combines the relative displacement generated by a laser on the camera target surface to achieve high-precision measurement of the apex angle of the triangular prism. Not only is the system easy to build, but also the measurement degree of freedom is high.

[0004] The technical solution for achieving the object of the present invention is as follows:

[0005] The device involved is formed by combining a laser (S1), a triangular prism to be measured (S3), a rotary table (S2), a plane mirror (S4), a plane mirror (S5) and a camera (S6); the process of realizing the measurement method is that the laser emitted by the laser is vertically incident on the triangular prism to be measured, and the light emerging from the inclined surface of the triangular prism is reflected back and forth between the two reflectors and then converges on the camera target surface to form a light spot (S7); the rotary table is deflected by a known small angle β, at this time the light spot on the camera target surface is offset to form a light spot (S8), the offset amount Δl of the light spot (S7) and the light spot (S8) is calculated, and the apex angle α of the triangular prism to be measured can be obtained by combining the formula between the offset amount Δl and the apex angle α of the triangular prism to be measured;

[0006] The laser emitted by the described laser is initially incident vertically on the bottom surface of the triangular prism; the described triangular prism is placed at the center of rotation of the rotating table, and its bottom surface is parallel to the plane mirror (S5) before rotation; the two mirrors are in a parallel state; the camera target surface, the plane mirror (S5), and the bottom surface of the triangular prism are at the same height; the selected range of the small angle β by which the rotating table deflects is from 0.04° to 0.4°;

[0007] The formula for the offset Δl and the apex angle α is as follows:

[0008] (4)

[0009] (5)

[0010] (6)

[0011] Where n is the number of reflections of the laser on the plane mirror (S4), d is the distance between the two mirrors, θ and θ' are the angles of incidence of the laser on the mirror (S4) before and after the rotation of the triangular prism respectively, and n1 is the refractive index of the triangular prism.

[0012] In the above technical solution: the surface accuracy and flatness of the two mirrors should be high, and their parallel state can be adjusted by the autocollimation method. The size of the distance d depends on the length and width of the experimental platform. The larger d is, the higher the measurement accuracy.

[0013] The above description is only an overview of the method of the present invention. In order to be able to more clearly understand the technical means of the present invention, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable, the following specific preferred embodiments are given and described in detail in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the triangular prism to be measured;

[0015] Figure 2 It is a schematic diagram of the measuring device provided by the embodiment of the present invention;

[0016] Figure 3 It is a schematic diagram of the light spot on the camera target surface before rotation provided by the embodiment of the present invention;

[0017] Figure 4 It is a schematic diagram of the light spot on the camera target surface after rotation provided by the embodiment of the present invention;

[0018] Figure 2 Marking description: S1, laser; S2, rotating table; S3, triangular prism to be measured; S4, plane mirror; S5, plane mirror; S6, camera; S7, light spot on the camera target surface before rotation; S8, light spot on the camera target surface after rotation; Detailed implementation mode

[0019] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0020] See the attached Figure 1 and the attached Figure 2 The material of the triangular prism is K9, the standard value of the apex angle is 30.02°, the refractive index n1 = 1.51635, the distance d between the two mirrors is 100 mm, the number of reflections n = 3, and the pixel of the camera target surface is 4.5 um. The triangular prism is placed at the center of rotation of the rotary table, and its bottom surface is parallel to the mirror (S5) before rotation. The heights of the camera target surface, the mirror S5 and the bottom surface of the triangular prism are adjusted to be the same, and the two plane mirrors are adjusted to be parallel by the autocollimation method.

[0021] When the laser emitted by the laser is initially vertically incident on the bottom surface of the triangular prism, that is, when the rotary table does not rotate,

[0022] See the attached Figure 3 a light spot is formed on the camera target surface. At this time, the position of the light spot center in the horizontal direction of the target surface can be directly obtained, which is 834 pixels; see the attached Figure 4 When the rotation angle β of the rotary table is equal to 0.1°, the position of the light spot center becomes 921 pixels at this time, then Δl = (921 - 834) * 4.5 = 0.3915 mm. Substitute Δl into the above formula to calculate the apex angle of the triangular prism to be measured is 29.981°.

[0023] See Table 1. At different rotation angles β, the apex angle α value of the triangular prism is measured multiple times, and the percentage deviation from the standard value is calculated. When the rotation angle β is in the range of 0.1 - 0.2°, the error between the measured value and the standard value does not exceed 0.2%.

[0024] / ° Δ α / ° Standard value / ° Error percentage / % 0.10 0.3915 29.981 0.13 0.18 0.6809 30.011 0.03 0.2 0.7564 29.997 30.02 0.08 0.26 0.9842 30.079 0.20 0.3 1.1369 30.175 0.52

Claims

1. A method for measuring the apex angle of an optical triangular prism, characterized in that : The device involved in the described measurement method is formed by combining a laser (S1), a triangular prism to be measured (S3), a rotary table (S2), a plane mirror (S4), a plane mirror (S5), and a camera (S6); the process of realizing the measurement method is that the laser emitted by the laser is vertically incident on the triangular prism to be measured, and the light emitted from the inclined surface of the triangular prism is reflected back and forth between the two mirrors and then converges on the camera target surface to form a light spot (S7); the rotary table is deflected by a known small angle β, at this time the light spot on the camera target surface is offset to form a light spot (S8), the offset Δl of the light spot (S7) and the light spot (S8) is calculated, and the apex angle α of the triangular prism to be measured can be obtained by combining the formula between the offset Δl and the apex angle α of the triangular prism to be measured; The laser emitted by the described laser is initially vertically incident on the bottom surface of the triangular prism; the triangular prism is placed at the center of rotation of the rotary table, and its bottom surface is parallel to the mirror (S5) before rotation; the two mirrors are both plane and in a parallel state; the camera target surface, the mirror (S5), and the bottom surface of the triangular prism are at the same height; the selection range of the small angle β by which the rotary table is deflected is 0.04° to 0.4°; The formula between the offset Δl and the apex angle α is as follows: (1) (2) (3) where n is the number of reflections of the laser on the plane mirror (S4), d is the distance between the two mirrors, θ and θ' are the incident angles of the laser on the mirror (S4) before and after the rotation of the triangular prism respectively, and n1 is the refractive index of the triangular prism.

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