WO2022182318A2

WO2022182318A2 - Triaxial angle measurement device and method

Info

Publication number: WO2022182318A2
Application number: PCT/TR2022/050170
Authority: WO
Inventors: Hüseyin Avni VURAL; Hakan Keski̇n
Original assignee: Roketsan Roket Sanayi̇i̇ Ti̇caret A.Ş.
Priority date: 2021-02-26
Filing date: 2022-02-25
Publication date: 2022-09-01
Also published as: WO2022182318A3

Abstract

The present invention relates to an angle measurement device that allows measuring the variation of the yaw, pitch and rolling angles from three axes of a reflective surface placed at a certain distance.

Description

TRIAXIAL ANGLE MEASUREMENT DEVICE AND METHOD

Technical field of the Invention

State of the Art

Autocollimators are devices by which angle measurements are made automatically for alignment and angle determination in many areas. It is widely used in two-axis angle measurements of optically reflective surfaces such as mirrors and prisms, alignment of laser cavities and similar alignment and measurement processes. Autocollimators are devices that can measure in two axes and are insensitive to rolling angle. The changes in the rolling angle of the reflective surface cannot be measured by autocollimators.

Polarimeters are used in food, aviation, space and military applications. Polarimeters, which are commercial products such as autocollimators and are very widely used, measure the rolling angle of a reflective surface automatically. However, polarimeters cannot measure yaw and pitch angles.

Polarimeters consist of two parts. The part where the light source and the polariser are constitutes the first part, and the part where the analyser and the photodetector are constitutes the second part. Therefore, the surface where the angle measurement is done constitutes a part of the measurement system. While this causes the system to be more complex, it prevents making a measurement independent from the measurement plane.

The application no "TR2009/04618" in the state of the art was reviewed. The invention that is the subject of the application is a laser distance measurement sensor comprising a beam source that sends a laser beam to the object whose distance is to be measured by means of a collimator and the laser diode it contains, an optical receiver that detects the laser beam spot formed on the object, and a processor unit that processes the electrical signal produced by the said optical receiver to obtain distance information.

The application no "CN110672061 A" in the state of the art was reviewed. The invention that is the subject of the application relates to a three-dimensional angle measurement method and a device thereof that can simultaneously measure the three-dimensional angle change of a dynamic target with high precision and high frequency. The three- dimensional angle measuring device provided by the invention can simultaneously measure three-dimensional pitch, yaw and rolling angles, and perform high-frequency measurement, which is suitable for measuring varying targets.

The application no "CN104792268A" in the state of the art was reviewed. The invention that is the subject of the application relates to an optical measurement system and a measurement method for measuring a linear displacement, a pitch angle, a swing angle, a rolling angle and an engine rotation speed.

In the studies carried out in the state of the art, there are systems that can make three- axis measurements. However, by means of the developed optical design, a device that allows measurement in three axes with a single device is needed.

As a result, due to the negativities described above and the inadequacy of the existing solutions on the subject, it was necessary to make a development in the relevant technical field.

The aim of the invention

The most important aim of the invention is to enable measurements to be taken in all three axes from the reflective surface where the measurement is taken.

Another important aim of the invention is to enable the measurement of rolling and pitch angles that autocollimators cannot measure, and yaw and pitch angles that polarimeters cannot measure. Another aim of the invention is to enable the angles measured by autocollimator and polarimeters to be measured by a single device.

The structural and characteristic features of the invention and all its advantages will be understood more clearly by means of the figures given below and the detailed description written with reference to these figures. For this reason, the evaluation should be made by taking these figures and detailed description into consideration.

Description of Drawings

Figure-1 ; is the drawing presenting the view of the measurement device that is the subject of the invention. Reference numbers:

100. Measurement device

110. light source

120. linear polariser

130. Faraday modulator 140. Beam splitter

150. Lens

160. Linear polariser_3 170. Detector

180. Rotating table with encoder 200. Linear polariser_2

300. Reflective surface Description of the Invention

The measurement device (100) that is the subject of the invention comprises light source (110), linear polariser (120), Faraday modulator (130), beam splitter (140), lens (150), linear polariser3 (160), detector (170), rotating table with an encoder (180) and electronic board.

The light source (110) provides lightening around it. Laser or LED can be used as the light source (110), depending on the desired sensitivity and the target application. The wavelength of the light source (110) is selected according to the characteristics of the detector (170) used and the crystal (MR3-2 crystal glass) in the Faraday modulator (130). In the preferred embodiment of the invention, a diode laser with a wavelength of 808 nm and 1 W average power is used as the light source (110).

The linear polariser (120) ensures that the non-polarised light emanating from the light source (110) is polarised in the x-axis.

The Faraday modulator (130) provides modulation with a certain frequency of the light passing through the linear polariser (120) by changing its polarisation direction according to the applied current. The Faraday modulator (130) consists of a coil wound around materials such as Lithium Niobate, MR3-2 glass, which has birefringence. The Faraday modulator (130), modulation frequency can be selected between 1 KFIz - 5 KHz.

The beam splitter (140) delivers the light coming from the Faraday modulator (130) to the lens (150) by directing it 90 degrees in the direction of the lens (150).

The lens (150) provides refraction of the beams incident upon it. The lens (150) provides collimation of the beam coming from the beam separator (140).

The detector (170) provides the conversion of optical power to electrical power. In one embodiment of the invention, the detector (170) is used silicon-based for the 808 nm wavelength light source (110). In one embodiment of the invention, the detector (170) can be used as a CCD (charge coupled device), CMOS (Complementary Metal Oxide Semiconductor) or four-section. In an embodiment of the invention, a photodetector is used as a detector (170).

The polarisation direction of the linear polariser3 (160) and the directions of the linear polariser (120) and the linear polariser2 (200) are placed perpendicularly in such away to prevent the light from falling on the detector (170). Linear polariser2 (200) and reflective surface (300) are connected to the equipment or test set-up that is required to be measured. The polarisation direction is indicated on the linear polariser2 (200) and the reflective surface (300). The connection direction will be made according to this polarisation direction. By this way, the polarisation direction of the rotating light and the direction of the linear polariser3 (160) on the rotary table with encoder (180) will cross each other perpendicularly. Because of the Faraday modulator (130), which is used only as a polarisation modulator and changes the polarisation direction of the light at a certain frequency, light will come on the detector (170) at a certain frequency.

The rotating table with encoder (180) provides precise positioning of the linear polariser3 (160) and the detector (170) on it. The rotating table with encoder (180) enables the linear polariser3 (160) to be rotated in small intervals (1 angle second). By this way, the rotating table with encoder (180), the linear polariser3 (160), the linear polariser (120) on the reflective surface (300) and the linear polariser2 (200) ensure that the angle between them is exactly 90 degrees (90 degrees 0 angle minutes 0 angle seconds). The angle accuracy of the rotating table with encoder (180) directly affects the measurement. In the preferred embodiment of the invention, a rotary table with encoder (180) with a precision of 3.6 angle seconds is used and the rolling angle precision of the linear polariser3 (160) and the reflective surface (300) is 3.6 angle seconds.

The linear polariser2 (200) is positioned where the angle measurement is desired and provides polarisation of the beams transmitted from the lens (150) and the reflective surface (300).

The reflective surface (300) is positioned where the angle measurement is desired and provides the reflection of the light incident on it. In the preferred embodiment of the invention, the reflective surface (300) is positioned at a distance of 0-2 meters from the lens (150). The beam reflected from the reflective surface (300) passes through the linear polariser2 (200), the lens (150) and the beam splitter (140) and reaches the linear polariser3 (160) placed on the rotating table with encoder (180) and the detector (170) behind it.

The electronic board enables having a processor in it that provides the execution of the algorithms. The measurement device (100) provides the rolling angle to be found with the reflective surface (300) and linear polariser2 (200) placed on an outer surface. For polarimeter-based measurement, a linear polariser2 (200) and reflective surface (300) component is placed outside the device where angle measurement is desired. The non-polarised light coming out of the light source (110) passes through the linear polariser (120) and is polarised in the x-axis. The polarisation directions of linear polarisers are indicated on the polarisers. The direction of linear polariser (120) and linear polariser3 (160) is the same; the polarisation of the light is maintained while passing through these two polarisers. The polarisation direction of the linear polariser2 (200) is perpendicular to each other with the linear polariser (120) and the linear polariser3 (160); in this case the light can pass to the detector (170) only as much as the polarisation damping ratio. However, the Faraday modulator (130) changes the polarisation direction of the light at a certain angle at the frequency amplitude applied to it. When linear polariser2 (200) and linear polariser3 (160) are perfectly perpendicular to each other (90 degrees 0 angle minutes 0 angles seconds), a sine wave, the frequency of which is twice the frequency applied to the Faraday modulator (130), is formed on the detector (170). The rotating table with encoder (180) used behind the detector (170) converts the linear polariser3 (160) by taking Fast Fourier Transform (FFT) at certain angles. During this process, it is tried to find the angle at which the frequency applied to the Faraday modulator (130) is twice the signal frequency obtained by the detector (170). By subtracting the angle found from the angle in the initial state, the rolling angle of linear polariser2 (200) is determined.

The measurement device (100) enables the yaw and pitch angles to be found with the reflective surface (300) and linear polariser2 (200) placed on an outer surface. For autocollimator-based measurement, a linear polariser2 (200) and reflective surface (300) component is placed outside the device where angle measurement is desired. The beam splitter (140) first delivers the light coming from the light source (110) to the lens (150) by directing it 90 degrees. After the lens (150), the collimated light is reflected from a reflective surface (300) positioned somewhere between 0-2 meters and reaches the detector (170) passing through the lens and the beam separator again. The distances between the light source (110)- the beam splitter (140)- the lens (150) and the lens (150)- the beam splitter (140)- the rotating table with encoder (180) are equal and are equal to the focal length of the lens. Since the light emanating from the light source (110) advances as far as the focal length of the lens (150) when it reaches the lens (150), it advances and hits the reflective surface (300) in a collimated form. When it reflects from the reflective surface (300) and re-enters inside, it advances as far as the focal length again and reaches the detector (170) in a focused form. By algorithm finding the weighted average of the power of the light coming to the detector (170), the place of the light falling on the detector (170) is determined. The yaw and pitch angles of linear polariser2 (200) are determined by finding the distance between the designated place and the centre of the detector (170) according to the axis set.

It is an autocollimator-based measurement method of the angle measurement system, comprising the following steps;

• placing the linear polariser2 (200) and the reflective surface (300) component to the surface where the angle measurement is desired,

• the beam splitter (140) delivering the light coming from the light source (110) to the lens (150) by directing it 90 degrees,

• the reflective surface (300) delivering the light collimated after the lens (150) to the detector (170) by reflecting and passing through the lens (150) and the beam separator (140) again,

• the light emanating from the light source (110) advancing and hitting the reflective surface (300) in a collimated form since it advances as far as the focal length of the lens (150) when it reaches the lens (150),

• the reflective surface (300) delivering it to the detector (170) in a focused form by advancing it as far as the focal length when it reflects and re enters the measurement device (100),

• the algorithm executed in the processor on the electronic card determining the location of the light falling on the detector (170) by finding the weighted average of the power of the light coming to the detector (170),

• finding the distance between the location determined by the algorithm executed in the processor on the electronic card and the centre of the detector (170) according to the axis set and determining the yaw and pitch angles of linear polariser2 (200).

It is a polarimeter-based measurement method of the angle measurement system, comprising the following steps;

• placing the linear polariser2 (200) and the reflective surface (300) component outside the device where angle measurement is desired

• the non-polarised light coming out of the light source (110) being polarised by the polariser (120),

• by including polarisation direction perpendicular to the linear polariser (120) and the linear polariser3 (160), the linear polariser2 (200) ensuring that the light can pass to the photodetector (170) as much as the polarisation damping ratio,

• the Faraday modulator (130) changing the polarisation direction of the light at a certain angle at the frequency amplitude applied to it,

• linear polariser2 (200) and linear polariser3 (160) being perfectly perpendicular to each other between, the frequency on the photodetector (170) forming a sine wave, the frequency of which is twice the frequency applied to the Faraday modulator (130),

• with the rotating table with encoder (180) used behind the photodetector (170) converting the linear polariser3 (160) by taking Fast Fourier Transform (FFT) at certain angles, finding the angle in which the frequency applied to the Faraday modulator (130) is twice the signal frequency obtained by the photodetector (170), by the algorithm in the processor running on the electronic board,

• by the algorithm in the processor running on the electronic card, subtracting the angle at which the signal frequency obtained by the photodetector (170) is twice the frequency applied to the Faraday modulator (130), from the angle of the rotating table with encoder (180) in the initial state taken before the measurement and thereby determining the rolling angle of linear polariser2 (200).

Claims

1. A rolling angle measurement system enabling the measuring of the rolling, yaw and pitch angle of a surface, comprising a measurement device (100) that comprises at least one light source (110), the wavelength of which is selected according to the characteristic features of the Detector (170) used and the Faraday modulator (130), and which lightens around it, at least one linear polariser (120) that provides polarising the non polarised light emanating from the light source (110), at least one Faraday modulator (130), consisting of a coil wrapped around materials with birefringence, which allows the light passing through the linear polariser (120) to be modulated with a certain frequency by changing the polarisation direction according to the applied current, at least one beam splitter (140) that directs the light coming from the Faraday modulator (130) 90 degrees in the direction of the lens (150) to reach the lens (150), at least one lens (150), which provides refraction of the beams coming on it, at least one linear polariser3 (160) which enables the light to be polarised, at least one detector (170) that converts optical power to electrical power, at least one rotating table with encoder (180), on which the linear polarisser3 (160) and the detector (170) are positioned, at least one linear polariser2 (200) having polarisation direction on it, positioned where the angle measurement is desired and polarising the beams transmitted from the lens (150) and the reflective surface (300), at least one reflective surface (300) having polarisation direction on it, positioned where the angle measurement is desired and reflecting the light coming on it, at least one electronic board having the processor that enables the execution of the algorithms therein.

2. Autocollimator-based measurement method of the angle measurement system, comprising the process steps of;

• Finding the distance between the location determined by the algorithm executed in the processor on the electronic card and the centre of the detector (170) according to the axis set and determining the yaw and pitch angles of the linear polarise2 (200).

3. Polarimeter-based measurement method of the angle measurement system according to Claim 1 , comprising the steps of;

4. Rolling, yaw, and pitch angle measurement system according to Claim 1 , comprising the Faraday modulator (130) that enables the modulation frequency to be chosen between 1 KFIz - 5 KFIz.

5. Rolling, yaw, and pitch angle measurement system according to Claim 1 , comprising the light source (110) the wavelength of which is selected according to characteristics of the detector (170) and the Verdet constant and working wavelength of the crystal in the Faraday modulator (130).

6. Rolling, yaw and pitch angle measurement system according to Claim 1 , wherein the materials with birefringence feature are Lithium, Niobate and MR3- 2 glass.

7. Rolling, yaw, and pitch angle measurement system according to Claim 1 , comprising at least one lens (150) that enables the light coming from the beam splitter (140) to be collimated.

8. Rolling, yaw, and pitch angle measurement system according to Claims 1 or 4, comprising Faraday modulator (130) that changes the polarisation direction of the light coming on the detector (170) at a certain angle and enabling the light to come at a certain frequency.

9. Rolling, yaw, and pitch angle measurement system according to Claim 1 , comprising rotating table with encoder (180) enabling the linear polariser3 (160) to rotate with intervals for the angle between the linear polariser (120) and linear polariser2 (200) to be exactly 90 degrees.

10. Rolling, yaw, and pitch angle measurement system according to Claim 1 , comprising linear polariser3 (160) enabling the maintaining the polarisation of the light by selecting its polarisation direction the same with that of linear polariser (120).

11. Rolling, yaw, and pitch angle measurement system according to Claim 1 , comprising linear polariser2 (200) enabling the light to pass to the photodetector (170) as much as the polarisation damping ratio by being in a polarisation direction perpendicular to the polarisation direction of linear polariser (120) and linear polariser3 (300).

12. An angle measurement system operating method that enables autocollimator- based measurement according to Claim 2, wherein the distance between the light source (110)-beam splitter (140)- lens (150) and the lens (150)-beam splitter (140)- rotating table with encoder (180) are the same and equal to the focal length of the lens (150).