A grating beam splitter, angle measurement device and method

Abstract

The application discloses a grating beam splitter, an angle measuring device and a method. The lens body of the grating beam splitter has a front surface and a rear surface, an included angle between the front surface and the rear surface is not zero, and the front surface and the rear surface are both grating planes. The application utilizes the grating beam splitter to realize lateral shearing of an incident light beam, two light beams emitted on a light signal collecting unit form an interference image, the interference image is related to the angle of the grating beam splitter relative to the incident light beam, and the measurement of the rotating angle of the grating beam splitter can be realized by demodulating the interference image. The application can realize the precise measurement of the rotation of the element without a reference light beam or a reference benchmark, has a simple structure, is easy to realize, has small error and high precision.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of diffraction grating and optical device, in particular to a grating beam splitter, an angle measuring device and method. BACKGROUND

[0002] Precise small angle measurement is the basis and important component of geometric measurement detection, and has wide application in the fields of precise machining, precise equipment manufacturing and calibration, machining and assembly of large-scale equipment in national defense industry, mechanical deformation of large-scale building and metrology testing. With the continuous development of related fields, the requirements for the measurement accuracy and stability of angle are also improved.

[0003] With the rapid development of optical technology, optical measurement technology has been developed accordingly. Grating ruler sensor, referred to as grating ruler, is a typical optical measuring instrument, which is widely used in the measurement of mechanical angular displacement or linear displacement. Generally, the grating ruler has two gratings, namely an indicating grating and a scale grating, which are fixed on two opposite moving mechanical parts. When the mechanical parts move, the indicating grating and the scale grating are driven to move relatively. Moire fringes are generated by the interference and diffraction of light on the two gratings. The Moire fringes are converted into a sinusoidal varying electrical signal by a photosensitive element, and the relative position information is obtained after processing by a data circuit. The scale grating is a whole grating, and the technical constraints in production make the length of the engraved scale grating not ideal, resulting in complex manufacturing process and high production cost of the grating ruler displacement sensor, and there is also the problem of relatively large volume of the grating ruler. SUMMARY

[0004] In order to overcome the above-mentioned defects of the existing grating angle measuring device, the present application provides a grating beam splitter, an angle measuring device and method.

[0005] The technical scheme adopted by the present application is as follows: a grating beam splitter, comprising a lens body, the lens body has a front surface and a rear surface, there is a non-zero included angle between the front surface and the rear surface, and the front surface and the rear surface are both grating planes.

[0006] Preferably, the included angle between the front surface and the rear surface is 0-90°.

[0007] Preferably, the front surface is made of a grating with a certain line density, allowing the collimated incident light beam to be directly transmitted, and being divided into zero-order transmitted light beam and first-order diffracted light beam.

[0008] Preferably, the rear surface is made of a grating with a certain line density, allowing the zero-order transmitted light beam to be directly transmitted as a zero-order exit light beam, and the first-order diffracted light beam to be diffracted and transmitted as a first-order exit light beam.

[0009] An angle measuring device, comprising: a light source for emitting a collimated incident light beam; a grating beam splitter arranged in the path of the incident light beam to form a zero-order exit light beam and a first-order exit light beam; a light signal collection unit for receiving and recording a light image after interference between the zero-order exit light beam and the first-order exit light beam; the grating beam splitter and the light source are respectively fixed on relatively rotating parts.

[0010] Preferably, the wavelength of the incident light beam is stable, and the spectral width supports the formation of an interference image on the light signal collection unit.

[0011] Preferably, the light signal collection unit is a photosensitive paper or a photosensitive element.

[0012] An angle measuring method, comprising the following steps:

[0013] Step 1: the light source emits a collimated incident light beam to the grating beam splitter;

[0014] Step 2: after the incident light beam passes through the front surface of the grating beam splitter, it is divided into two beams into the lens body of the grating beam splitter, one of which is a zero-order transmitted light beam, and the other is a first-order diffracted light beam;

[0015] Step 3: the zero-order transmitted light beam is transmitted to the rear surface of the grating beam splitter and directly transmitted as a zero-order exit light beam, and the first-order diffracted light beam is transmitted to the rear surface of the grating beam splitter and diffracted and transmitted as a first-order exit light beam;

[0016] Step 4: the zero-order exit light beam and the first-order exit light beam interfere on the light signal collection unit, and the light signal collection unit records the interference fringes;

[0017] Step 5: the relative rotation angle between the grating beam splitter and the light source is calculated according to the density change of the interference fringes and the translation of the fringe strong area.

[0018] The present application has the following beneficial effects:

[0019] 1. The device realizes beam splitting by using a specially designed single grating beam splitter, which is used for shearing interference instead of two gratings, thereby simplifying the structure of the angle measuring device;

[0020] 2. The grating beam splitter has stable structure, and the angle rotation will cause changes in the phase and inclination angle of the exit light beam, and the angle rotation information can be obtained through interference image demodulation, the interference image is less affected by the environment, the system error is small, and the measurement precision is high. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The optical path principle diagram of the embodiment of the present application.

[0022] In the figure: 1-Grate beam splitter; 101-Front surface; 102-Rear surface; 103-Lens body; 2-Light source; 3-Image recording unit; 401-Incident beam; 4021-Zero-order transmitted beam; 4022-First-order diffracted beam; 4031-Zero-order exit beam; 4032-First-order exit beam. Detailed Implementation

[0023] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0024] like Figure 1 As shown, a grating beam splitter 1 includes a lens body 103. The lens body 103 has a front surface 101 and a rear surface 102, with a non-zero angle between the front surface 101 and the rear surface 102. Both the front surface 101 and the rear surface 102 are grating planes. Specifically, there is an angle of 0~90° between the front surface 101 and the rear surface 102. The front surface 101 is fabricated with a grating of a certain scribe density, allowing a collimated incident beam 401 to be directly transmitted, resulting in a zero-order transmitted beam 4021 and a first-order diffracted beam 4022. The rear surface 102 is fabricated with a grating of a certain scribe density, allowing the zero-order transmitted beam 4021 to be directly transmitted as a zero-order output beam 4031, and the first-order diffracted beam 4022 to be diffracted and transmitted as a first-order output beam 4032.

[0025] like Figure 1 The diagram illustrates an angle measurement device based on the aforementioned grating beam splitter 1, comprising: a light source 2 for emitting a collimated incident beam 401; a grating beam splitter 1 disposed in the path of the incident beam 401 to form a zero-order outgoing beam 4031 and a first-order outgoing beam 4032; and an illumination signal collection unit 3 for receiving and recording the illumination image after interference between the zero-order outgoing beam 4031 and the first-order outgoing beam 4032. The grating beam splitter 1 and the light source 2 are respectively fixed on components that rotate relative to each other. The wavelength of the incident beam 401 is stable, and its spectral width supports the formation of an interference image on the illumination signal collection unit 3. The illumination signal collection unit 3 is photosensitive paper or a photosensitive element such as a CCD.

[0026] like Figure 1 The figure shows an angle measurement method based on the above-mentioned angle measuring device, and the steps are as follows:

[0027] Step 1: The collimated incident beam 401 emitted by the light source 2 is directed to the grating beam splitter 1;

[0028] Step 2: After the incident beam 401 passes through the front surface 101 of the grating beam splitter 1, it is split into two beams and enters the lens body 103 of the grating beam splitter 1. One beam is the zero-order transmitted beam 4021, and the other beam is the first-order diffracted beam 4022.

[0029] Step 3, the zero-order transmission light beam 4021 is transmitted to the rear surface 102 of the grating beam splitter 1, and is directly transmitted as a zero-order exit light beam 4031; the first-order diffracted light beam 4022 is transmitted to the rear surface 102 of the grating beam splitter 1, and is diffractively transmitted as a first-order exit light beam 4032;

[0030] Step 4, the zero-order exit light beam 4031 and the first-order exit light beam 4032 interfere on the light signal collection unit 3, and the light signal collection unit 3 records interference fringes;

[0031] Step 5, the relative rotation angle between the grating beam splitter 1 and the light source 2 is calculated according to the density change of the interference fringes and the translation of the fringe strong area.

[0032] In the embodiment, as shown in the figure, Figure 1 the light source 2 emits an incident light beam 401 with a diameter of D 0=20mm, the central wavelength of the light beam is Lambda =632.8nm, and the line width is Delta v =1MHz.

[0033] (1) The angle of the incident light beam 401 incident to the front surface is α , which is the included angle between the incident light beam 401 and the normal line of the front surface 201; the zero-order diffractive transmission angle is β 1, which is the included angle between the zero-order transmission light beam 4021 and the normal line of the front surface 201; the first-order diffractive transmission angle is β 2, which is the included angle between the first-order diffracted light beam 4022 and the normal line of the front surface 201; the refractive index of the grating beam splitter to the incident light beam 401 is n , and the grating constant of the front surface 101 is d . According to Snell's law and the grating diffraction formula, the following relationship is obtained:

[0034]

[0035]

[0036] The angle between the front surface 101 and the rear surface 102 is Theta , which is a small angle; the zero-order transmission light beam 4021 is incident to the rear surface 102 after a distance at an angle β 1- Theta , and is emitted in the direction of the zero-order exit light beam 4031 with an exit angle of Gamma 1; the first-order diffracted light beam 4022 is incident to the rear surface 102 after a distance at an angle β 2+ Theta , and is emitted in the direction of the first-order exit light beam 4032 with an exit angle of Gamma 2; the grating constant of the rear surface 102 is dAccording to Snell's law and grating diffraction formula, the following relationship is obtained:

[0037]

[0038]

[0039] The included angle of the zero-order emergent light beam 4031 and the first-order emergent light beam 4032 can be expressed as:

[0040]

[0041] When the incident angle changes, the change amount is:

[0042]

[0043] That is, when the angle of the grating beam splitter 1 changes, the included angle of the two light beams will change, and the change of the fringe density on the interference fringes can be observed.

[0044] (II) The optical path difference of the zero-order emergent light beam 4031 and the first-order emergent light beam 4032 can be expressed as:

[0045]

[0046] wherein l is the distance experienced by the zero-order diffraction light beam inside the grating mirror.

[0047] When the incident angle changes, the change amount is:

[0048]

[0049] That is, when the angle of the grating beam splitter 1 changes, the optical path difference of the two light beams will change, and the translation of the fringe intensity region on the interference fringes can be observed.

[0050] Therefore, the embodiment utilizes the grating beam splitter 1 to realize the lateral shearing of the incident light beam 401, and the two emergent light beams form an interference image on the light signal collection unit. The interference image is related to the angle of the grating beam splitter relative to the incident light beam, and the measurement of the rotation angle of the grating beam splitter can be realized by demodulating the interference image. The precise measurement of the rotation of the element can be realized without a reference light beam or a reference benchmark. The structure is simple and easy to realize, has small error and high precision.

[0051] In specific applications, the grating beam splitter 1 can be placed on a linear guide to measure the straightness of the guide; or placed on the surface of a vacuum device to measure the deformation of the surface when vacuumizing; or placed on the surface of a workpiece, when the workpiece is deformed under force, the attitude of the grating beam splitter 1 changes, and then the deformation of the workpiece is evaluated.

[0052] Obviously, the above embodiments of the present application are only examples for illustrating the present application, and are not intended to limit the embodiments of the present application. Other obvious changes or modifications derived from the spirit of the present application still belong to the protection scope of the present application.

Claims

1. An angle measuring device, characterized in that The application relates to a light source (2) for emitting a collimated incident light beam (401); a grating beam splitter (1) arranged in the path of the incident light beam (401) to form a zero-order exit light beam (4031) and a first-order exit light beam (4032); and a light signal collection unit (3) for receiving and recording a light image after interference between the zero-order exit light beam (4031) and the first-order exit light beam (4032). The grating beam splitter (1) comprises a lens body (103) having a front surface (101) and a rear surface (102), the front surface (101) and the rear surface (102) form a non-zero angle, and the front surface (101) and the rear surface (102) are both grating planes; the front surface (101) is provided with a grating with a certain grating line density, allowing the collimated incident light beam (401) to be directly transmitted and divided into a zero-order transmitted light beam (4021) and a first-order diffracted light beam (4022); the rear surface (102) is provided with a grating with a certain grating line density, allowing the zero-order transmitted light beam (4021) to be directly transmitted as the zero-order exit light beam (4031), and allowing the first-order diffracted light beam (4022) to be diffractively transmitted as the first-order exit light beam (4032). The grating beam splitter (1) and the light source (2) are respectively fixed on relatively rotating parts, the wavelength of the incident light beam (401) is stable, the spectral width supports the formation of an interference image on the light signal collection unit (3), and the light signal collection unit (3) is photosensitive paper or a photosensitive element. The steps are as follows: Step 1: the collimated incident light beam (401) emitted by the light source (2) is incident on the grating beam splitter (1); Step 2: after the incident light beam (401) passes through the front surface (101) of the grating beam splitter (1), it is divided into two beams entering the lens body (103) of the grating beam splitter (1), one of which is a zero-order transmitted light beam (4021) and the other of which is a first-order diffracted light beam (4022); Step 3: the zero-order transmitted light beam (4021) is transmitted to the rear surface (102) of the grating beam splitter (1) and directly transmitted as a zero-order exit light beam (4031), and the first-order diffracted light beam (4022) is transmitted to the rear surface (102) of the grating beam splitter (1) and diffractively transmitted as a first-order exit light beam (4032); 2. An angle measurement method based on the angle measurement device according to claim 1, characterized in that Step 4: the zero-order exit light beam (4031) and the first-order exit light beam (4032) interfere on the light signal collection unit (3), and the light signal collection unit (3) records interference fringes; Step 5: the interference fringes are demodulated to image, and the relative rotation angle between the grating beam splitter (1) and the light source (2) is calculated according to the density change and the translation of the fringe strong area. ​ ​ ​ ​

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