JP2645111B2 - Sun sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a solar sensor mounted on an artificial satellite or the like and measuring a sun direction in order to determine the attitude of the artificial satellite or the like.

(Prior Art) Conventionally, as a sun sensor mounted on an artificial satellite or the like, there is a sun sensor using an aperture mask with a slit and a linear array sensor. First, the optical system of the sun sensor will be described.

FIG. 4 is a perspective view showing the configuration of the optical system, and FIG.
The figure is a sectional view thereof. In FIG. 4, a slit 42 is formed at the center of the light shielding film (aperture mask) 41 at right angles to the longitudinal direction of the light shielding film 41. This slit 42 has a width
It is about 150 μm, and is formed by, for example, processing with a photoresist or mechanical processing.

The light-shielding film 41 is provided on the surface of a prism 43 made of, for example, quartz of a rectangular tablet or optical glass. For example, a CCD (Charge Transfer Element) linear array sensor 45 is provided on the back surface of the prism 43 via a band-pass filter 44. This CCD linear array sensor 45 has its pixel (CC
The arrangement direction of D) is perpendicular to the slits 42, and the half of the overall length l, that is, the center is the slit 4
The detector is arranged to face 2.
Reference numeral 46 denotes a neutral density filter.

As the number of pixels increases, the angular resolution of the CCD Rainier array sensor 45 increases.
Is used. For example, when a CCD linear array sensor having 2048 pixels is used, if the field of view is ± 50 °, the angular resolution per pixel is 0.05 °.

When sunlight S enters the prism 43, dispersion occurs, and a phenomenon occurs in which the refraction angle differs depending on the wavelength. The band-pass filter 44 limits the wavelength of sunlight S incident on the CCD linear array sensor 45 to reduce the influence of the dispersion. Further, the transmission wavelength range of the bandpass filter 44 is desirably set to, for example, around 600 ± 50 nm in consideration of the spectral sensitivity characteristics of the CCD linear array sensor 45.

In the optical system having the above-described configuration, sunlight S passing through the slit 42 is transmitted through the prism 43 and the band-pass filter 44 to the CC.
The light is received by the D linear array sensor 45. The intensity distribution of sunlight incident on the CCD Rainier array sensor 45 is:
The distribution is as shown in FIG. Therefore, CC
In each pixel of the D linear array sensor 45, as shown in FIG. 6 (c), an electric charge corresponding to the intensity of the incident sunlight is accumulated.

The CCD linear array sensor 45 is supplied with a clock signal corresponding to one pixel in one cycle as shown in FIG. 6 (b) from the CCD driving circuit, and the stored electric charges are generated by the clock signal. Output sequentially.

The sun azimuth is obtained by measuring the position of the image shown in FIG. 6 on the CCD linear array sensor. Conventionally, in order to measure the position of the image shown in FIG. 6 (a), the output signal of the CCD linear array sensor is amplified and then compared with a threshold TH as shown in FIG. 6 (c). Based on the comparator output (FIG. 6 (d)), the times t ₁ and t in FIG. 6 (d) were measured, and t ₁ +
t / 2 is the time representing the center of the image shown in FIG. 6A, and the position of the CCD linear array sensor is measured from the relationship with the CCD clock.

However, in the conventional solar sensor as described above,
Complicated digital signal processing is required due to the necessity of performing the operation of t ₁ + t / 2, and as shown in FIG.
There TH 'when the change (or signal intensity changes) as is, FIG. 6 (e) t ₁ is t ₁ as shown in', t is t ', and the calculated output is t _1' + t There is a disadvantage that the error becomes' / 2 and an error occurs.

(Problems to be Solved by the Invention) As described above, the conventional sun sensor requires complicated digital operation, and can obtain only about 1/2 the resolution of the pixel of the linear array sensor. There is a disadvantage that an error is caused by a change in value or a change in signal strength.

Therefore, the present invention has been made to eliminate the above disadvantages, does not require complicated digital operation, and can obtain a resolution of 1/2 or more of the pixels of the linear array sensor,
It is an object of the present invention to provide a sun sensor that can accurately determine the center of an image without causing an error due to a change in a reference value or a change in signal intensity.

[Constitution of the Invention] (Means for Solving the Problems) In order to achieve the above object, a sun sensor according to the present invention has an aperture mask formed with a slit for restricting the luminous flux of sunlight in a predetermined direction, and the aperture mask. A plurality of photoelectric conversion elements are arranged in a direction perpendicular to the direction in which the slits are formed, and a linear array sensor that sequentially reads signals from the photoelectric conversion elements is provided. An AC amplifier that removes a DC component from the output signal of the linear array sensor, an integrator that integrates the output signal of the AC amplifier, and a zero-cross detector that inverts the output each time the output of the integrator passes through a zero level. Measuring the time from the start of one reading operation of the linear array sensor to the inversion of the output of the zero-cross detector. And a time measuring means for obtaining more sunlight azimuth information.After removing the DC component from the output of the linear array sensor using an AC amplifier, the output is integrated by an integrator, and the image center is detected by a zero-cross detector. Then, the sun azimuth is measured.

(Operation) In the solar sensor having the above configuration, the output of the linear array sensor is amplified by the AC amplifier. This removes the DC component from the signal. In the obtained signal, the area of the positive polarity is equal to the area of the negative polarity. This signal is integrated by an integrator, the time at which the integrated signal passes through a zero level is detected by a zero-cross detector, and the time from the reading start time of the linear array sensor to the time of the zero cross is measured to determine the sun direction. Can be measured.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 shows a configuration in a case where the present invention is applied to a signal processing circuit for obtaining a sunlight azimuth angle from an output signal of a CCD linear array sensor of the optical system shown in FIGS. 4 and 5.

In FIG. 1, the CCD drive timing generation circuit 12
A clock pulse P ₁ for driving the CCD linear array sensor 45, a clock pulse P ₂ for time measurement, and a reset pulse P ₃ for resetting the scaler 17 at the timing of starting reading of the linear array sensor 45 (FIG. 2 ( e)) occurs.

Signals S ₁ shown in FIG. 2, which is outputted from the CCD linear array sensor 45 (a) is input to the AC amplifier 13. The AC amplifier 13 includes a differentiating circuit having a sufficiently low time constant so as to remove a DC component, and as shown in FIG. 2 (b), an AC signal S ₂ having an area of a positive polarity equal to that of a negative polarity. Is output.

The integrator 14 has a finite amplification factor with respect to the direct current component, and a feedback circuit is constructed so that the direct current component of the integrator output becomes 0. The signal S as shown in FIG. _{Get three} . Zero crossing detector 16 when the input signal S ₃ positive "1", so that the negative time "1", using the comparator can be configured, the output S _4, as shown in FIG. 2 (d) Become.

Scaler 17, the reset pulse P ₃ at the start of reading the linear array sensor 45 is reset to 0, continue to count the time measuring clock pulse P _2. When the latch circuit 18 is the output S ₄ of the zero-crossing detector 16 has up standing from "0" to "1", it latches the count value of the scaler 17.

That is, as shown in FIG. 3, a time when the output S ₃ of the integrator 14 when the mode changes to the positive polarity from the negative polarity, i.e. the output S ₄ of the zero-crossing detector 16 is changed from "1" to "0" area of a and B of the image of the output signals S ₁ of the linear array sensor 45 is time (center value of the image) to equal. Therefore, by latching the output of the scaler 17 at that time, as shown in FIG. 2 (e), it is proportional to the time T 'from the start of one reading of the linear array sensor 45 to the center value of the image signal. A value is obtained, from which information on the sun azimuth can be measured.

Incidentally, can be measured by time measuring clock pulse P ₂ is 1 / N of the pixel accuracy of the linear array sensor by N times the linear array sensor 45 driving clock pulses P _1, capable of high precision is there.

Moreover, the use of the AC amplifier 13, not affected by this be contained DC offset in a linear array sensor signals S _1, the integrator 14 from the viewpoint of the removal of a broad noise for a low-pass filter of the S / N Improvement can be expected, and the use of the zero-cross detector 16 indicates that it does not depend on the signal strength. Further, complicated digital signal processing is not required in the circuit configuration, and the analog signal processing circuit may be a simple circuit such as the AC amplifier 13, the integrator 14, and the zero-cross detector 16, so that the size and weight can be reduced.

Therefore, the sun sensor using the signal processing circuit having the above configuration can detect the center of the image with a small and lightweight circuit, and has high accuracy.

[Effects of the Invention] As described above, according to the present invention, the center of an image can be measured with an accuracy equal to or less than the pixel of the linear array sensor without using a complicated digital signal processing circuit, and a method independent of the intensity of the image Therefore, it is possible to provide a small, lightweight, and highly accurate solar sensor.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing an embodiment of a sun sensor according to the present invention, FIGS. 2 and 3 are diagrams showing operation timings of the embodiment, respectively, and FIGS. 4 and 5 are each a diagram showing the present invention. FIG. 6 is a perspective view and a sectional view showing the structure of an optical system to which is applied, and FIG. 6 is an operation timing chart showing a conventional signal processing method. 45 Linear array sensor, 12 CCD drive timing generation circuit, 13 AC amplifier, 14 Integrator, 16 Zero cross detector, 17 Scaler, 18 Latch circuit, P ₁
…… CCD drive pulse, P ₂ …… Time measurement clock pulse, P ₃ …… Reset timing pulse.

Claims (1)

(57) [Claims] 1. An aperture mask having a slit formed therein for restricting a luminous flux of sunlight in a predetermined direction, and a plurality of photoelectric conversion elements provided below the aperture mask and arranged in a direction perpendicular to a direction in which the slit is formed. In a sun sensor having an optical system including a linear array sensor that sequentially reads signals from photoelectric conversion elements, an AC amplifier that removes a DC component from an output signal of the linear array sensor, and an output signal of the AC amplifier. An integrator to integrate,
A zero-cross detector that inverts the output each time the output of the integrator passes through a zero level, and measures the time from the start of one reading of the linear array sensor to the inversion of the output of the zero-cross detector. And a time measuring means for obtaining sunlight azimuth information.