RU2327952C2 - Panoramic sensor of angular coordinate of light checkpoint - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: panoramic sensor of angular coordinate of light checkpoint includes multielement receiver of optical radiation consisting of at least three elemental photo receivers, and signal processing device for defining angular coordinate of checkpoint. Elemental photo receivers are set in circle at regular pace. Number of lit elemental photo receivers within a single unit does not depend on the direction of light checkpoint at a given plane in the sensor coordinate system. Angular coordinate of checkpoint is defined either by order numbers of end elemental receivers in the lit group of photo receivers or by correlation of signal size at any two lit photo receivers, possibly adjoining ones.

EFFECT: viewing field extension for sensor angular coordinate of a light checkpoint.

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Description

The sensor is designed to determine the angular coordinate of a luminous landmark, such as the Sun, when used as part of the orientation system of a spacecraft.

Close in technical essence to the claimed sensor is a sensor [1], which includes: optical spectral filter; crevice mask; a multi-element photosensitive detector formed by elementary photodetectors located one after another on a second-order curve, so that the normals to the sensitive areas of each elementary photodetector and the second-order curve lie in the same plane; threshold elements, photodetector register, counter, output register, clock generator.

The principle of operation of the sensor is that radiation from the Sun passing through a spectral filter and a slit mask illuminates a group of several adjacent elementary photodetectors. The angular coordinate of the Sun is determined by the number of the average illuminated elementary photodetector.

Analysis of the sensor design allows us to establish that the number of illuminated elementary photodetectors depends on the size of the slit in the mask, the thickness of the mask, the angular step of the location of elementary photodetectors, and the direction to the Sun in the coordinate system of the sensor. With small deviations of the Sun from the axis of the sensor, the number of illuminated elementary photodetectors is maximum. With an increase in the deviation of the Sun from the axis of the sensor, the number of illuminated elementary photodetectors decreases. In the extreme case, when the angle at which the Sun is visible in the sensor coordinate system approaches 90 ° in magnitude or becomes larger, the radiation cannot penetrate the mask and illuminate elementary photodetectors, as a result of which measurement becomes impossible. Therefore, the field of view of a sensor having such a design cannot have a magnitude greater than or at least equal to 180 ° (± 90 °), which is a disadvantage.

Also known is a wide-angle sensor [2], which is two identical photoresistors in the form of half rings located on a cylindrical surface and forming a ring.

One pair of adjacent terminals of the photoresistors is combined and is the midpoint of the resistive voltage divider, and equal to the magnitude but opposite in sign of voltage voltage is connected to the other adjacent terminals of the photoresistors. With equal illuminated areas of the photoresistors, when the luminous landmark, the position of which is measured, is located on the symmetry plane of the half rings, the resistors of the photoresistors are equal and the signal at the output of the resistive divider is 0 V. When the landmark is removed from the symmetry plane, the illuminated areas of the photoresistors change and, accordingly, The output voltage of the voltage divider deviates from 0 V up or down.

From the principle of operation of this sensor, it follows that when the luminous landmark is located at angles symmetrical (adjusted for the geometry of the central contact and the terminal contacts of the photoresistors) relative to the perpendicular to the coordinate axis, for example, + 10 ° and + 170 °, -20 ° and -140 ° , 0 ° and 180 °, the same signals will be generated at the output, since in the listed cases the illuminated areas of the photoresistors are equal. To avoid such ambiguity of the output signals, the angle between the direction to the landmark and the coordinate axis of the sensor should not exceed ± 90 °. That is, the field of view of such a sensor is also limited, which, as already mentioned, is a disadvantage.

The aim of the invention is to expand the field of view of the sensor of the angular coordinate of the luminous landmark.

This goal is achieved by the fact that the inventive sensor contains a multi-element receiver of optical radiation and a signal processing device. A multi-element optical radiation detector consists of at least three photosensitive elements located at a given pitch on a circle, with each photosensitive element having a serial number

The device of the proposed sensor in the part of the optical radiation receiver is illustrated in Fig. 1, which shows a cross section of the optical radiation receiver in the form of a disk, and in Fig. 2, which shows the cross section of the optical radiation receiver in the form of a plate with a hole. In figure 1 and figure 2 are indicated by numbers: 1 - coordinate axis: 2 - the angular coordinate of the landmark; 3 - direction to the landmark; 4 - part of the receiver of optical radiation in the shade; 5 - illuminated part of the receiver of optical radiation; 6 is a sectional view of the conditionally last photosensitive member; 7 is a section of a conditionally first photosensitive element; 8 - radiation of a luminous landmark; 9 is an angular pitch of the arrangement of photosensitive elements.

The angular coordinate - α of the luminous landmark is determined as follows:

α = [(n2 + n1) / 2] γ, n1 <n2;

α = [(n1 + n2 + N) / 2] γ, n1> n2 and (n1 + n2 + N) / 2 <N;

α = [(n1 + n2-N) / 2] γ, n1> n2 and (n1 + n2 + N) / 2≥N,

where γ is the angular step of the arrangement of photosensitive elements; n1 is the serial number of the first photosensitive element in the group of illuminated photosensitive elements when counting from the coordinate axis, the signal of which exceeds a predetermined threshold; n2 is the serial number of the last photosensitive element in the group of illuminated photosensitive elements when counting from the coordinate axis, the signal of which exceeds a predetermined threshold; N is the total number of photosensitive elements.

The signal processing device in this case contains threshold devices, N - a bit circular register (N = 2 ^k ), a k-bit pulse counter, k-bit output register, a clock generator.

The sensor works as follows: the landmark illuminates the optical radiation receiver. The signal from each illuminated elementary photodetector arrives at a threshold device for conversion into a digital signal, which takes, for example, the value of a logical unit if the signal exceeds a predetermined threshold and a logical zero if the signal is less than a predetermined threshold. The output signals of the threshold devices are fixed in a circular register. At the command, the data in the ring register begin to cyclically shift with the clock frequency, and the counter begins to count pulses following with the clock frequency. As soon as a signal changes from a logical zero to a logical unit in a ring register discharge corresponding to the first elementary photodetector, the counter will start counting pulses with a frequency 2 times lower than the clock frequency. After that, as soon as the signal changes from a logical unit to a logical zero in the ring register discharge corresponding to the first elementary photodetector, the counter stops counting, and the code received at the counter is stored in the output register. The code fixed in the output register is the desired angular coordinate.

It is possible to more accurately determine the angular coordinate of the landmark - α by finding the centroid [3]:

, при условии n1<n2

provided n1 <n2

, при условии n1>n2 и

, при условии n1>n2 и

provided n1> n2 and

provided n1> n2 and

where γ is the angular step of the arrangement of photosensitive elements: n1 is the sequence number of the first photosensitive element in the group of illuminated photosensitive elements when counting from the coordinate axis, the signal of which exceeds a predetermined threshold; n2 is the serial number of the last photosensitive element in the group of illuminated photosensitive elements when counting from the coordinate axis, the signal of which exceeds a predetermined threshold; A (k) is the signal value of the k-th photosensitive element in the group of illuminated photosensitive elements; N is the total number of photosensitive elements.

To implement such a method for determining the angular coordinate, the signal processing device comprises: an analog-to-digital converter for converting the signals of the photosensitive elements into digital form; a storage device for storing source data, intermediate calculation results and the final result; microprocessor to execute the centroid calculation algorithm.

As follows from Figure 1 and Figure 2, as well as the above-described methods for determining the angular coordinate of the proposed sensor allows you to measure the angles between the direction of the luminous landmark and the axis of the sensor in the range from 0 ° to 360 °. That is, the field of view of the inventive sensor has no restrictions, in contrast to the field of view of the prototypes, and is 360 ° in magnitude.

Expanding the field of view of the sensor to 360 ° allows you to create, for example, an orientation system for spacecraft with a spherical field of view of only 3 sensors, which increases the reliability of the system, reduces its power consumption and weight. In addition, a sensor with a field of view of 360 ° can be used as a small angle-code converter.

It should also be noted that the inventive sensor has another useful property.

It is known that such a physical phenomenon as the photoelectric effect consists in the appearance of free charged particles during the interaction of photons with matter. Moreover, the number of charged particles that appear is directly proportional to the number of photons interacting with the substance. Therefore, the magnitude of the signal generated by the photodetector, the principle of which is based on the photoelectric effect, will also be directly proportional to the number of photons incident on the sensitive surface of the photodetector. Obviously, the number of incident photons is determined by the radiation intensity, the dimensions of the sensitive surface of the photodetector and its angular orientation relative to the front of the radiation wave.

The influence of the angular orientation of the photodetector relative to the plane front of the radiation wave on the signal magnitude is illustrated in FIG. 3, in which the number 1 indicates the cross section of the photodetector, the sensitive surface of which is parallel to the wavefront; 2 is a cross section of a photodetector, the sensitive surface of which is located at an angle γ to the wave front; 3 - section of the wavefront of the radiation; 4 is a cross-sectional view of the projection onto the wavefront of the photodetector, the sensitive surface of which is parallel to the wavefront; 5 is a sectional view of the projection onto the wavefront of the photodetector, the sensitive surface of which is located at an angle γ to the wavefront.

On the segment corresponding to section 1, photons fall through the segment corresponding to section 4, and on the segment corresponding to section 2 photons pass through the segment corresponding to section 5. The length of the segment corresponding to section 1 is equal to the length of the segment corresponding to section 4, and is equal to the length of the segment corresponding to section 2. The ratio of the length of the segment corresponding to section 5 to the length of the segment corresponding to section 2 is equal to the ratio of the leg to the hypotenuse in a right triangle and is equal to the braid of the angle between them γ. Thus, photons 1 / cosγ times smaller than the segment corresponding to section 1 of the photodetector parallel to the wavefront fall on the segment corresponding to section 2 of the photodetector turned relative to the wavefront.

In the general case, the angular orientation of the photodetector relative to the wavefront is specified by two angles, for example, γ and δ. Therefore, the photodetector, whose sensitive surface is rotated relative to the wave front, receives photons 1 / cosγcosδ times smaller than the photodetector, whose sensitive surface is parallel to the wave front.

Therefore, in relation to the claimed sensor, the sensitive elements of which are located on a circle and the radiation of the landmark has a flat wave front, for the nth photosensitive element its signal - U (n) can be defined as:

U (n) = Acosnγcosδ,

where δ is the angle between the normal to the flat face of the sensor and the wavefront of the landmark radiation; γ is the angular step of the arrangement of photosensitive elements; n is the number of angular steps between the photosensitive element, the signal of which is determined by the photosensitive element, the signal of which has a maximum value; And - the maximum possible value of the signal.

The graph of the dependence of the signal - U (n) of the nth photosensitive element from its angular position on a plane parallel to the faces of the sensor, and depending on the position of the landmark relative to the coordinate axis of the sensor is shown in Figure 4, where: 1 - axis of angular coordinates; 2 - reference point in the coordinate system of the sensor; 3 - signal value U (n) of the nth illuminated photosensitive element; 4 - signal value of the U (n + 1) (n + 1) -th illuminated photosensitive element: 5 - reference point in the landmark coordinate system; 6 - distribution of signal values in a group of illuminated photosensitive elements; 7 - signal value of the U (n + k-1) (n + k-1) -th illuminated photosensitive element; 8 - signal value of the U (n + k) (n + k) th illuminated photosensitive element.

From figure 4 it follows that:

U (n) = Acosnγcosδ = Acos (-φ) cosδ,

U (n + 1) = Acos (nγ + γ) cosδ = Acos (-φ + γ) cosδ,

Taking into account the parity of the cosine function, the signal value of the (n + 1) -th illuminated photosensitive element can be determined differently by expanding the cosine of the difference of two angles according to the well-known formula:

U (n + 1) = Acos (φ-γ) cosδ = [Acosφcosγ + Asinφsinγ] cosδ,

The ratio of the signal values of the (n + 1) th and n th illuminated photosensitive elements:

U (n + 1) / U (n) = (Acosφcosγ + Asinφsinγ) / Acosφ = cosγ + tgφsinγ,

From the ratio of signal values, one can find an expression for the angle φ:

tgφ = U (n + 1) / U (n) sinγ-ctgγ,

since no more than half of the photosensitive elements of the radiation receiver can be illuminated, as can be seen from FIG. 1 and FIG. 2, the angle φ is limited to a range from −π / 2 to π / 2, and therefore

φ = arctan [U (n + 1) / U (n) sinγ-ctgγ]

The angular distance α between the coordinate axis of the sensor and the coordinate axis of the landmark, as can be seen from Figure 4:

α = nγ + φ,

or after substitution:

α = nγ + arctg [U (n + 1) / U (n) sinγ-ctgγ], provided that U (n) <U (n + 1)

For another pair of signal values:

U (n + k) = Acos (n + k) γ = Acosψ,

U (n + k-1) = Acos ((n + k) γ-γ) = Acos (ψ-γ),

After the expansion of the cosine of the difference of two angles according to the well-known formula:

U (n + k-1) = Acos (ψ-γ) = Acosψcosγ + Asinψsinγ,

The ratio of the values of the signals of the (n + k-1) th and (n + k) th illuminated photosensitive elements:

U (n + k-1) / U (n + k) = (Acosψcosγ + Asinψsinγ) / Acosψ = cosγ + tgψsinγ,

From the ratio of signal values, one can find an expression for the angle ψ:

tgψ = U (n + k-1) / U (n + k) sinγ-ctgγ,

in this way:

ψ = arctan [U (n + k-1) / U (n + k) sinγ-ctgγ]

Figure 4 shows that the angular distance between the coordinate axes of the sensor and the landmark:

α = (n + k) γ-ψ,

or after substitution:

α = (n + k) γ-arctan [U (n + k-1) / U (n + k) sinγ-ctgγ], provided that U (n + k) <U (n + k-1)

In a generalized form, you can write:

α = nγ + arctg [U (n + 1) / U (n) sinγ-ctgγ], U (n) <U (n + 1)

α = nγ-arctg [U (n) / U (n + 1) sinγ-ctgγ], U (n)> U (n + 1)

Using the above method, you can express the angular coordinate of the landmark - and through the magnitude of the signals of any pair of illuminated photosensitive elements, not necessarily adjacent. That is, to determine the angular coordinate of the landmark using the proposed sensor, it is enough to know the magnitude of the signals of only two elementary photodetectors in the illuminated group. Consequently:

a) you can increase the accuracy of measuring the angular coordinate - (luminous landmark, if you use averaging:

, U(n+m-1)<U(n+m)

, U (n + m-1) <U (n + m)

, U(n+m-1)>U(n+m)

, U (n + m-1)> U (n + m)

where U (n + m-1) and U (n + m) are the signal values of any two adjacent photosensitive elements in the group of illuminated photosensitive elements, n is the sequence number of the photosensitive element in the group of illuminated photosensitive elements when counting from the coordinate axis, γ is the angular the location step of the photosensitive elements, M is the number of photosensitive elements over which averaging is performed.

b) it is possible to increase the noise immunity of measuring the angular coordinate - α of a luminous landmark, for example, by accumulating α values calculated from the signals of different pairs of photosensitive elements if they differ from each other by a certain amount no more than a given value and ignoring those pairs of photosensitive elements signals for which the difference the calculated value of α from the average, exceeds some predetermined value.

c) the reliability and survivability of the sensor are increased, since even if some photosensitive elements malfunction, the sensor retains the ability to determine the coordinates of a landmark.

Improving the accuracy, noise immunity, reliability makes it possible to create on the basis of the inventive sensor spacecraft orientation systems with improved performance.

A multi-element optical radiation receiver can be manufactured according to planar technology from known semiconductor materials. Obtaining photosensitive elements lying on a circle is done by creating grooves of a given profile in the semiconductor wafer using a laser or etching.

Information sources

1. Patent for the invention of the Russian Federation No. 2244263, MKI G01C 21/24, G01J 1/20, 2003.

2. US patent No. 3875404, NKI 250/211 R, 1975.

3. Brian F. Alexander; Kim Chew Ng. Elimination of systematic error in subpilxel accuracy centroid estimation. Optical Engineering (ISSN 0091-3286), vol. 30, Sept. 1991, p.1320-1331.

Claims (1)

A panoramic sensor for the angular coordinate of a luminous landmark, containing a multi-element optical radiation detector, which consists of at least three elementary photodetectors, and a signal processing device for determining the angular coordinate of the landmark, characterized in that the elementary photodetectors are arranged with a given circle pitch, the number of illuminated elementary photodetectors up to one, it does not depend on the direction of the luminous landmark in the coordinate system of the sensor in the plane of the specified circle Thus, the angular coordinate of the landmark is determined by the serial numbers of elementary photodetectors that start and end the group of illuminated photodetectors, or the angular coordinate of the landmark is determined by the ratio of the signal values of any two, in particular adjacent, elementary photodetectors in the group of illuminated.

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