CN106643743B - A method for measuring the three-axis attitude of a birefringent solar sensor and its carrier - Google Patents

Abstract

The invention discloses a birefringence solar sensor, comprising: a light filtering module, a single-axis crystal lens, an image sensor and a data processing module; the feature is that the light filtering module bundles the light to form a thinner incident light ; The uniaxial crystal lens performs birefringence on the incident light to form two refracted rays; the image sensor images the two refracted rays; the data processing module is used to extract the center of the image point, and according to the two refracted rays Calculate the vector information of the incident light, and thus calculate the three-axis attitude information of the carrier. When the above-mentioned birefringent sun sensor is installed on the carrier, the invention also discloses a method for measuring the three-axis attitude of the carrier, which can enable the spacecraft/unmanned aerial vehicle to realize the three-axis attitude measurement solely relying on the sun measurement. The birefringent sun sensor of the invention can achieve a larger field of view, and can ensure no loss of attitude measurement accuracy.

Description

A method for measuring the three-axis attitude of a birefringent solar sensor and its carrier

technical field

The invention belongs to the field of attitude measurement and determination, in particular to a method for measuring the three-axis attitude of a birefringent sun sensor and its carrier.

Background technique

The sun sensor is an important measurement component in the aerospace attitude control system. It is the most widely used photoelectric sensor in the aerospace field. It can provide angle feedback between the sun vector and a specific axis on the spacecraft. Almost all spacecraft need to be equipped with sun sensors in order to complete the attitude control tasks of the spacecraft at various stages according to the state feedback information provided by the sun sensors.

The conventional sun sensor uses the principle of pinhole imaging to realize the measurement of the sun vector. There is only one ray, and it can only measure the attitude information in the direction of the two perpendicular sensor optical axes, and cannot measure the attitude information around the optical axis of the sensor; in addition , the main indicators to measure whether the solar sensor is good or bad are the field of view and measurement accuracy. Conventional solar sensors are subject to design principles. If you want to improve the measurement accuracy, you must reduce the field of view, and to expand the field of view, you must reduce the measurement accuracy. .

Contents of the invention

The purpose of the present invention is to overcome the defect that the current solar sensor cannot measure the attitude information of the carrier around the optical axis of the sensor, and proposes a birefringent solar sensor, which utilizes the birefringence of a uniaxial crystal Based on the principle, the three-axis attitude measurement of the carrier can be realized by observing the sun alone, and high-precision attitude measurement can be achieved under the condition of ensuring a large field of view, so that the spacecraft/UAV can be realized by relying on the sun measurement alone Three-axis attitude measurement.

In order to achieve the above object, the present invention provides a birefringent solar sensor, comprising: a light filtering module, a single-axis crystal lens, an image sensor and a data processing module; the light filtering module bundles the light to form a finer incident light; the uniaxial crystal lens doubles the incident light to form two refracted rays; the image sensor images the two refracted rays; the data processing module is used to extract the center of the image point, and according to the two refracted The ray calculates the vector information of the incident ray, and thus calculates the three-axis attitude information of the carrier.

In the above technical solution, the material of the uniaxial crystal lens is calcite.

In the above technical solution, the light filtering module is provided with a light transmission hole on the surface of the uniaxial crystal lens; the light transmission hole is placed at the center of the outer surface of the uniaxial crystal lens, and the diameter of the light transmission hole is not greater than 0.1 mm.

In the above technical solution, the light filtering module is provided with a black origin on the single-axis crystal lens; the black origin is placed at the center of the outer surface of the single-axis lens, and the diameter of the black origin is not greater than 0.1mm.

In the above technical solution, the light filtering module is provided with a convex lens sheet in front of the uniaxial crystal lens; focal length.

The above-mentioned birefringent solar sensor is installed on the carrier, and the present invention also provides a method for measuring the three-axis attitude of the carrier, the method comprising:

Step 1) the light filtering module filters the sunlight;

Step 2) The filtered incident light becomes birefringent light through the uniaxial crystal lens: o light and e light;

Step 3) using an image sensor to image the light spots formed by o-light and e-light;

Step 4) extracting the spot centroid of o light and e light;

Step 5) Calculate the vector information of the incident light by using two beams of refracted light;

Step 6) Calculate the three-dimensional pose information of the carrier according to the incident ray and the two refracted rays.

In the above-mentioned technical scheme, the concrete realization process of described step 5) is:

The plane wave satisfies n ₁ ·r=n ₂ ·r during refraction, r is an arbitrary vector at the interface, n ₁ and n ₂ are the medium refractive index before and after light refraction, and the wave vector is still in the incident plane;

For o-rays, the wave vector direction coincides with the refracted ray, i.e.

θ _o ＝θ ₂ ＝arcsin(n ₁ sinθ ₁ /n _o ) (1)

In the _formula , _θ1 is the incident angle of the incident light, _θo and θ2 are the angles between the refracted light o and the surface normal of the uniaxial crystal lens, and n _o is the refractive index of the o ray in the uniaxial crystal lens;

For e-light, _n2 is expressed as:

θ _kp is the angle between the light wave vector and the optical axis, so:

In the above formula, n _e is the refractive index of e light in the uniaxial crystal lens; θ _k is the angle between the e light wave vector e _k and the normal line of the uniaxial crystal lens surface, and the e light wave vector e _k is still in the incident plane, Expressed as:

e _k =cosθ _k e _z +sinθ _k e _x (4)

Among them, e _z and e _x are three-axis component unit vectors; therefore:

cosθ _kp ＝e _k e _p ＝cosθ _k cosθ _p +sinθ _k sinθ _p cosφ _p (5)

θ _p is the angle between the optical axis of the uniaxial crystal lens and the z-axis, φ _p is the angle between the projection line of the optical axis on the surface of the uniaxial crystal and the x-axis, e _p is the unit vector of the optical axis, and after the e light wave vector is determined, e The angle θ _rp between the light unit vector e _r and the optical axis is determined by the following formula:

Since the e-ray, the e-ray wave vector and the optical axis are in the same plane, it is assumed that the three satisfies:

e _r =αe _k +βe _p (7)

The undetermined coefficients of α and β are obtained through the constraint relationship between the vectors:

And then get:

In this way, by selecting a single-axis crystal lens, use formula (1) to determine the relationship between incident light θ ₁ of o-ray and refracted light, use formula (10) to determine the relationship between e-ray unit vector e _r and θ _p , θ _k , and then The relationship between θ _k and θ ₁ is determined by formula (3), so that the combination of formulas (1), (3) and (10) determines the relationship between the incident light and the two beams of refracted light, and the two beams of refracted light are obtained by measurement ray, the incident ray vector is uniquely determined.

In the above-mentioned technical scheme, the concrete realization process of described step 6) is:

The attitude information of the carrier includes pitch angle, yaw angle and roll angle; directly measure the two-dimensional coordinates (x, y) of the two beams of refracted light on the image sensor, and calculate the pitch angle θ and yaw angle of the two beams of refracted light The information of ψ, specifically:

where f is the focal length of the convex lens;

Determine the pitch angle θ _m and yaw angle ψ _m of the incident light by directly measuring the centroids of the two beams of refracted light spots, and connect the centroids of the two beams of refracted light spots to determine the rotation angle of the incident light, that is, the roll angle The three attitude angles determined at this time are the values in the solar sensor coordinate system, denoted as Through the transformation matrix T _bm of the sensor, the attitude is transformed into the coordinate system of the aircraft body, namely

is the attitude information in the body coordinate system of the carrier.

Since the birefringent solar sensor makes full use of the refraction principle of light, it can achieve a larger field of view. Compared with the conventional solar sensor, the birefringent solar sensor of the present invention has the following advantages:

1. Can measure three-axis attitude

Since the incident light becomes two beams of light after refraction, the attitude information of the carrier around the optical axis of the sensor can be calculated by imaging the two beams of light; Measurement.

2. High accuracy of attitude measurement

The birefringence sun sensor aligns two beams of refracted rays at the same time, and the two beams of refracted rays determine an incident ray at the same time, so the measurement accuracy of the birefringence sun sensor can be increased by an order of magnitude compared with the conventional sun sensor.

3. Under the condition of ensuring accuracy, the birefringent sun sensor of the present invention can achieve a larger field of view, and can ensure that the accuracy of attitude measurement is not lost.

Description of drawings

Fig. 1 is the schematic diagram of birefringent solar sensor of the present invention;

Fig. 2 is the flow chart of the measurement method of carrier three-axis posture;

Figure 3 is a schematic diagram of incident light filtering;

Fig. 4 is a schematic diagram of lens focusing;

Figure 5 is a schematic diagram of the birefringence principle of a uniaxial crystal;

FIG. 6 is a schematic diagram of determining the rotation angle information of the incident light according to the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

The birefringent sun sensor of the present invention is an optical measurement sensor that utilizes the birefringence characteristics of uniaxial crystals to determine the direction vector of incident sunlight. e-ray (extraordinary light), the relationship between birefringent light and incident light can be calculated through the Fresnel theorem in optics, that is, the vector information of incident light can be accurately determined by collecting the vector information of two beams of refracted light.

Since the sun's rays enter the birefringent sun sensor, they are refracted into two beams of light, so not only can the vector information of the incident light be calculated more accurately under the condition of ensuring a large field of view, but also the direction of the incident light along the optical axis of the sun sensor can be determined. Rotation angle, which is impossible for conventional sun sensors. Compared with conventional solar sensors, birefringent solar sensors can measure the three-axis attitude of the carrier at the same time, and have the characteristics of high measurement accuracy and large field of view.

In order to double refract the incident light and form two spots of refracted light, the spot of the incident light cannot be too large, so it is necessary to filter the incident light of the sun. There are three ways to filter light: a) leave a light-transmitting hole on the surface of the uniaxial crystal; b) place a black origin in the middle of the calcite, as shown in Figure 1; c) use a convex lens to condense the incident parallel light to form a narrow beam, as shown in Figure 2.

As shown in Figure 3, a kind of birefringence sun sensor, comprises: light filtering module, uniaxial crystal lens, image sensor and data processing module; The material of described uniaxial crystal lens is calcite,

According to different ways of light filtering, the light filtering module has three forms:

1. Set a light transmission hole on the surface of the single-axis crystal lens; the light transmission hole is placed at the center of the outer surface of the single-axis crystal lens. In order to improve the measurement accuracy of the image sensor for the spot without diffraction of the incident light, the transmission The diameter of the light hole is not greater than 0.1mm.

2. Set the black origin on the single-axis crystal lens; the black origin is placed at the center of the outer surface of the single-axis crystal lens. In order to improve the recognition accuracy of the image sensor for dark spots without light diffraction, the diameter of the black origin is not Greater than 0.1mm.

3. A convex lens sheet is arranged in front of the uniaxial crystal lens; the function of the convex lens sheet is to converge the incident light. The convex lens sheet is arranged in front of the uniaxial crystal lens, and the distance between its center and the front surface of the uniaxial crystal lens is the focal length of the convex lens.

The light filtering module bundles the light to form a thinner incident light; the single-axis crystal lens performs birefringence on the incident light to form two refracted light; the image sensor images the two refracted light; the The data processing module is used to extract the center of the image point, and calculate the vector information of the incident light according to the two refracted rays, thereby calculating the three-axis attitude information of the carrier.

As shown in Figure 4, when the above-mentioned birefringence sensor is installed on the carrier, the present invention also provides a method for measuring the three-axis attitude of the carrier, the method comprising:

Step 1) the light filtering module filters the sunlight;

Step 2) The filtered incident light becomes birefringent light through the uniaxial crystal lens: o light and e light;

In nonlinear optics, light waves of different components must overlap and interact to achieve nonlinear conversion. In nonlinear optical devices, the optical axis of the uniaxial crystal lens is often at a certain angle to the surface, and the incident light is not always normal incidence, but also oblique incidence. When a beam of light is incident from the surface of the uniaxial crystal lens, after refraction, two beams of light will appear, one beam of light is normal refraction, which conforms to the law of refraction, and is called ordinary light (o-ray), and the other beam of light is non- Normal refraction, which does not conform to the law of refraction, is called extraordinary light (e light). As shown in Figure 5. The angle between the optical axis of the uniaxial crystal lens and the coordinate z is θ _p , the angle between the projection of the optical axis on the xy plane and the x axis is φ _p , and the incident angle of the incident light is θ ₁ .

It can be seen from Fig. 5 that for the ordinary light o-ray, the refracted light and the light wave vector are in the same direction, but for the extraordinary light e-ray, the refracted light and the light wave vector are not in the same direction.

In this way, the light passing through the uniaxial crystal lens is refracted into two beams of light: ordinary light (o light) and extraordinary light (e light).

Step 3) using an image sensor to image the light spots formed by o-light and e-light;

This step can reduce the power consumption of the sensor and prepare for the extraction of the spot centroid.

Step 4) extracting the spot centroid of o light and e light;

After extracting all the pixel positions of each spot, the center of mass of each spot is calculated using the centroid positioning algorithm, and the position accuracy of the center of mass of the spot calculated by this algorithm can reach the sub-pixel level.

Step 5) Calculate the vector information of the incident light by using two beams of refracted light;

The plane wave satisfies n ₁ ·r=n ₂ ·r during refraction, r is an arbitrary vector at the interface, n ₁ and n ₂ are the medium refractive index before and after light refraction, the wave vector is still in the incident plane, and n ₁ sinθ ₁ = n ₂ sinθ ₂ , the angle here is the angle between the wave vector and the normal of the crystal surface, not the angle of refraction (the angle between the light and the normal of the crystal surface).

For o-rays, the wave vector direction coincides with the refracted ray, i.e.

θ _o ＝θ ₂ ＝arcsin(n ₁ sinθ ₁ /n _o ) (1)

In the _formula , _θ1 is the incident angle of the incident light, _θo and θ2 are the angles between the refracted light o and the surface normal of the uniaxial crystal lens, and n _o is the refractive index of the o ray in the uniaxial crystal lens;

For e-light, _n2 is expressed as:

In the above formula, n _e is the refractive index of e light in the uniaxial crystal lens; θ _kp is the angle between e light wave vector e _k and the optical axis, so:

θ _k is the angle between e light wave vector e _k and the surface normal of the uniaxial crystal lens, e light wave vector e _k is still in the incident plane, expressed as:

e _k =cosθ _k e _z +sinθ _k e _x (4)

e _z , e _x are three-axis component unit vectors (as shown in Figure 5); so it can be obtained

cosθ _kp ＝e _k e _p ＝cosθ _k cosθ _p +sinθ _k sinθ _p cosφ _p (5)

θ _p is the angle between the optical axis of the uniaxial crystal lens and the z-axis, φ _p is the angle between the projection line of the optical axis on the xy plane (the surface of the uniaxial crystal lens) and the x-axis (as shown in Figure 5), and e _p is After the optical axis unit vector and e light wave vector are determined, the angle θ _rp between the e light unit vector e _r and the optical axis can be determined by the following formula:

Since the e-ray, the e-ray wave vector and the optical axis are in the same plane, it is assumed that the three satisfies:

e _r =αe _k +βe _p (7)

The undetermined coefficients of α and β can be obtained through the constraint relationship between the vectors:

Furthermore, one can get

In this way, by selecting a single-axis crystal lens, the relationship between the incident light and refracted light of o-ray can be determined by using formula (1) (θ ₁ is the incident angle of incident light), and the unit vector e _r of e-ray can be determined by using formula (10). The relationship between θ _p (the angle between the optical axis of the uniaxial crystal and the z-axis, which is determined when the uniaxial crystal lens is selected), θ _k (the angle between the e light wave vector and the normal of the crystal), and then by the formula (3) Determine the relationship between θ _k and θ ₁ , so that the joint formulas (1), (3) and (10) stipulate the relationship between the incident light and the two beams of refracted light, and the two beams of refracted light are obtained through measurement, then the incident light The vector is uniquely determined.

Step 6) Calculate the three-dimensional attitude information of the carrier according to the incident ray and the two refracted rays;

It can be seen from Figure 5 that since the refracted light is two beams, namely o-ray and e-ray, connecting the centroids of the two beams of refracted light can uniquely determine the rotational attitude of the incident light around the optical axis of the sensor. In this way, the three-dimensional vector information of the incident light is realized by combining the above measurement results. Combining the installation matrix of the birefringence sensor and the spacecraft/UAV, the three-dimensional attitude information of the carrier can be measured.

The attitude information of the carrier includes pitch angle, yaw angle and roll angle. Directly measure the two-dimensional coordinates (x, y) of the two beams of refracted light on the image sensor. After calculation, the information of the pitch angle θ and yaw angle ψ of the two beams of refracted light can be obtained, specifically:

where f is the focal length of the convex lens.

According to the formula in step 5), the pitch angle and yaw angle information of the incident light can be obtained, so that the two-dimensional attitude information of the incident light can be determined by directly measuring the center of mass of the two refracted light spots. And because one beam of refracted light is determined by two beams of refracted light, compared with conventional solar sensors, the determination accuracy of incident light can be increased by more than 50%.

When the incident light rotates (equivalent to the rotation of the sun sensor around the incident light), the two beams of refracted light (o light and e light) will also rotate on the image sensor, as shown in Figure 6, the center of mass of the o light spot and the e light By connecting the centroids of the light spots, the rotation angle of the incident light can be determined, that is, the rotation angle information of the incident light can be determined. In this way, the pitch angle and yaw angle of the incident light can be determined by directly measuring the centroids of the two beams of refracted light spots, and the rotation angle of the incident light, that is, the roll angle, can be determined by connecting the centroids of the two beams of refracted light spots. The three attitude angles determined at this time are the values in the solar sensor coordinate system, denoted as Through the transformation matrix T _bm (3×3) of the sensor, the attitude can be transformed into the coordinate system of the aircraft body, namely

It is the attitude information in the carrier body coordinate system, so the three-axis attitude measurement of the aircraft is realized by using the birefringent sun sensor.

Using two beams of refracted rays to determine the vector information of the incident rays is the core and key of the sun sensor. Using nonlinear optics theory to deduce the constraint relationship between the two beams of refracted rays and the incident rays in detail, so that the vector information of the two beams of refracted rays can be uniquely determined The 2D vector information of the incident ray. The attitude rotation angle of the incident light around the optical axis of the sensor is calculated by using the positional relationship of the two beams of refracted light. In this way, the three-dimensional vector information of the incident light is obtained by combining the two-dimensional vector information of the incident light determined above.

The innovation of the present invention is: for the first time, a birefringent solar sensor is developed by using a uniaxial crystal with birefringence characteristics as the optical lens of the solar sensor, so that the solar sensor has the ability to measure three-axis attitude, and has the characteristics of high precision and wide field of view .

Claims (8)

1. A birefringent solar sensor, comprising: a light filter module, a uniaxial crystal lens, an image sensor and a data processing module; it is characterized in that, the light filter module bundles the light to form a thinner incident light; The single-axis crystal lens performs birefringence on the incident light to form two refracted rays; the image sensor images the two refracted rays; the data processing module is used to extract the center of the image point, and calculate the incident light according to the two refracted rays The vector information of the light is used to calculate the three-axis attitude information of the carrier. Specifically, the pitch angle and yaw angle of the incident light are determined by directly measuring the center of mass of the spot of the two beams of refracted light, and the center of mass of the spot of the two beams of refracted light is connected. Determines the angle of rotation of the incident light, known as the roll angle. 2. The birefringent solar sensor according to claim 1, wherein the material of the uniaxial crystal lens is calcite. 3. The birefringent solar sensor according to claim 1 or 2, wherein the light filtering module is provided with a light transmission hole on the surface of the uniaxial crystal lens; the light transmission hole is placed in the uniaxial crystal lens At the central position of the outer surface, the diameter of the light-transmitting hole is not greater than 0.1 mm. 4. The birefringent solar sensor according to claim 1 or 2, wherein the light filtering module is to set a black origin on the uniaxial crystal lens; the black origin is placed on the outer surface of the uniaxial crystal lens At the central position, the diameter of the black origin is not greater than 0.1mm. 5. The birefringent solar sensor according to claim 1 or 2, characterized in that, the light filter module is provided with a convex lens sheet before the uniaxial crystal lens; the convex lens sheet is arranged before the uniaxial crystal lens, and its The distance between the center and the front surface of the uniaxial crystal lens is the focal length of the convex lens sheet. 6. A method for measuring the three-axis attitude of a carrier, realized by installing the birefringent solar sensor described in one of claims 1-5 on the carrier, the method comprising: Step 1) the light filtering module filters the sunlight; Step 2) The filtered incident light becomes birefringent light through the uniaxial crystal lens: o light and e light; Step 3) using an image sensor to image the light spots formed by o-light and e-light; Step 4) extracting the spot centroid of o light and e light; Step 5) Calculate the vector information of the incident light by using two beams of refracted light; Step 6) Calculate the three-dimensional pose information of the carrier according to the incident ray and the two refracted rays. 7. the measuring method of carrier three-axis posture according to claim 6, is characterized in that, the specific realization process of described step 5) is: The plane wave satisfies n ₁ ·r=n ₂ ·r during refraction, r is an arbitrary vector at the interface, n ₁ and n ₂ are the medium refractive index before and after light refraction, and the wave vector is still in the incident plane; For o-rays, the wave vector direction coincides with the refracted ray, i.e. θ _o ＝θ ₂ ＝arcsin(n ₁ sinθ ₁ /n _o ) (1) In the formula, θ ₁ is the incident angle of the incident light, θ _o and θ ₂ are the angles between the refracted light o and the surface normal of the uniaxial crystal lens; n _o is the refractive index of the o ray in the uniaxial crystal lens; For e-light, _n2 is expressed as: n _e is the refractive index of e light in the uniaxial crystal lens, θ _kp is the angle between the light wave vector and the optical axis, so: θ _k is the angle between e light wave vector e _k and the surface normal of the uniaxial crystal lens, e light wave vector e _k is still in the incident plane, expressed as: e _k =cosθ _k e _z +sinθ _k e _x (4) Among them, e _z and e _x are three-axis component unit vectors; therefore: cosθ _kp ＝e _k e _p ＝cosθ _k cosθ _p +sinθ _k sinθ _p cosφ _p (5) θ _p is the angle between the optical axis of the uniaxial crystal lens and the z-axis, φ _p is the angle between the projection line of the optical axis on the surface of the uniaxial crystal and the x-axis, e _p is the unit vector of the optical axis, and after the e light wave vector is determined, e The angle θ _rp between the light unit vector e _r and the optical axis is determined by the following formula: Since the e-ray, the e-wave vector and the optical axis are in the same plane, it is assumed that the three satisfies: e _r =αe _k +βe _p (7) α and β are undetermined coefficients, which are obtained through the constraint relationship between the vectors: And then get: By selecting a uniaxial crystal lens, use the formula (1) to determine the relationship between the incident light θ ₁ of the o-ray and the refracted light, and use the formula (10) to determine the relationship between the unit vector e _r of the e-ray and θ _p , θ _k , and then by Formula (3) determines the relationship between θ _k and θ ₁ , so the combination of formulas (1), (3) and (10) determines the relationship between the incident light and the two beams of refracted light, and the two beams of refracted light are obtained by measurement , then the incident ray vector is uniquely determined. 8. the measuring method of carrier three-axis posture according to claim 7, is characterized in that, the specific realization process of described step 6) is: The attitude information of the carrier includes pitch angle, yaw angle and roll angle; directly measure the two-dimensional coordinates (x, y) of the two beams of refracted light on the image sensor, and calculate the pitch angle θ and yaw angle of the two beams of refracted light The information of ψ, specifically: where f is the focal length of the convex lens; Determine the pitch angle θ _m and yaw angle ψ _m of the incident light by directly measuring the centroids of the two beams of refracted light spots, and connect the centroids of the two beams of refracted light spots to determine the rotation angle of the incident light, that is, the roll angle The three attitude angles determined at this time are the values in the solar sensor coordinate system, denoted as Through the transformation matrix T _bm of the sensor, the attitude is transformed into the coordinate system of the aircraft body, namely is the attitude information in the body coordinate system of the carrier.