APS based integrated sun sensor

• US 7,552,026 B2
• Filed: 03/16/2007
• Issued: 06/23/2009
• Est. Priority Date: 08/01/2006
• Status: Expired due to Fees

• Current Assignee: Beihang University
• Original Assignee: Beihang University
• Inventors: Jiang, Jie, Fan, Qiaoyun, Zhang, Guangjun
• Primary Examiner(s): Feliciano; Eliseo Ramos
• Assistant Examiner(s): Suarez; Felix E
• Application Number:
  US11/687,333
• Publication Number:
  US 20080029652A1
• Time in Patent Office: 830 Days
• Field of Search: 702/19, 702/152, 702/156, 702/158, 702188-190, 702/150, 702/154, 702/155, 702/159, 332/68, 250/208.1, 701/13, 348113-120, 348/207.99, 348/227.1, 348/229.1, 348/362, 348/366
• US Class Current: 702/154
• CPC Class Codes: B64G 1/363 using sun sensors

Abstract

The disclosure relates to an APS based integrated sun sensor comprising: a diaphragm unit, a detection unit, a processing electronics unit and an interface unit. The diaphragm unit is operatively connected with the detection unit for forming a sunspots image. The detection unit is configured for outputting a gray value of each pixel. The processing electronics unit is operatively connected with the detector unit and the interface unit respectively, for evaluating an attitude angle on the basis of the gray value and coordinate of each pixel. The interface unit is operatively connected with a host computer, for transferring the attitude angle to the host computer. This disclosure has such merits as high accuracy, wide FOV (Field of View), low power consumption, low weight, small size and high update rate.

Claims

1. An active pixel sensor based integrated sun sensor comprising:

a diaphragm unit;

a detection unit;

a processing electronics unit; and

an interface unit;

wherein the diaphragm unit is operatively connected with the detection unit for forming a sunspots image; and

wherein the detection unit is configured for outputting a gray value of each pixel of the sunspots image;

wherein the processing electronics unit is operatively connected with the detector unit and the interface unit respectively for evaluating an attitude angle on the basis of the gray value and a coordinate of each pixel of the sunspots image;

the processing electronics unit includes an absence detection and identification of a sunspot module configured to detect an absence of a specific sunspot in the sunspots image detected by the detection unit according to sunspots included in the sunspots image; and

wherein the interface unit is operatively connected with a host computer for transferring an attitude angle to the host computer.

2. The active pixel sensor based integrated sun sensor according to claim 1, wherein the diaphragm unit is a mask fabricated from 300 micron thick silicon wafers, wherein one side of the mask is gold coated with an apertures array.

3. The active pixel sensor based integrated sun sensor according to claim 2, wherein the detection unit comprises a complementary metal oxide semiconductor active pixel image sensor.

4. The active pixel sensor based integrated sun sensor according to claim 3, wherein the processing electronics unit is based on a field programmable gate array (FPGA) for realizing all logic control and functionality thereof, and the processing electronics unit further includes a detector drive module, a centroid calculation module, an attitude evaluation module and an interface protocol module.

5. The active pixel sensor based integrated sun sensor according to claim 4, wherein the interface unit includes an RS422 transceiver.

6. The active pixel sensor based integrated sun sensor according to claim 1, wherein the processing electronics unit further includes a centroid calculation module configured to calculate a centroid coordinate of each sunspot in the sunspots image according to the gray value of each pixel of the sunspots image, and the absence detection and identification of sunspot module detects and identifies sunspots image based on the centroid coordinate of each sunspot in the sunspots image.

7. The active pixel sensor based integrated sun sensor according to claim 1, wherein the diaphragm unit has an apertures array having a plurality of apertures;

sunlight incident on the detection unit through the plurality of apertures forms sunspots in a plurality of rows of the sunspots images;

the processing electronics unit further includes an attitude evaluation module configured to perform an attitude evaluation; and

when the absence detection and identification of sunspot module detects a sunspot absence in a specific row of the sunspots image, each sunspot in the specific row of the sunspots image is excluded from the attitude evaluation.

8. An attitude measurement method of an active pixel sensor based integrated sun sensor comprising the following steps:

exposing sunlight on a detection unit such that the sunlight is incident on the detection unit through a diaphragm unit to form a sunspots image on the detection unit;

outputting a gray value of each pixel by the detection unit;

evaluating an attitude angle by a processing electronics unit on the basis of the gray value and a coordinate of each pixel; and

transferring an attitude angle to a host computer by an interface unit;

wherein the step of evaluating attitude angle by the processing electronics unit comprises;

(1) the step of the centroid calculation module reading the gray value and coordinate value of each pixel row by row, and marking the pixels of which the gray value exceeds the threshold; and

according to the marks, distinguishing each sunspot of the sunspots image; and

calculating a centroid coordinate value of each sunspot utilizing a first-moment centroid algorithm, then saving those centroid coordinate values in an Xc/Yc memory;

(2) the step of the absent detection and identification of sunspot module reading the centroid coordinate value from the Xc/Yc memory and identifying a row index and column index of each sunspot of the sunspots image; and

in accordance with the identified row and column indices, calibrating parameters x<sub>0—

nm</sub>, y<sub>0—

nm</sub>, sin φ

_nm, cos φ

_nm, F′

_nm, α

<sub>0—

nm</sub>, β

<sub>0—

nm</sub> for each aperture of the diaphragm unit are selected;

then the calibrated parameters together with the centroid coordinate value are transferred to an attitude evaluation module; and

(3) based on a coordinate rotation digital computer algorithm, the attitude evaluation module of the processing electronics unit next calculates a sunlight incident angle for each sunspot;

after all the sunlight incident angles have been calculated, the attitude evaluation module obtains the final attitude angles by averaging the values of the sunlight incident angles for each sunspot.

9. The attitude measurement method of an active pixel sensor based integrated sun sensor according to claim 8, wherein the diaphragm unit forms a sunspots image through a silicon wafer mask with an apertures array.

10. The attitude measurement method of an active pixel sensor based integrated sun sensor according to claim 8, wherein the detection unit which is driven by a detector drive module of the processing electronics unit, outputs the gray value of each pixel row by row.

11. The attitude measurement method of an active pixel sensor based integrated sun sensor according to claim 8, wherein the attitude evaluation considers installation error between the diaphragm unit and the detection unit, and the sun incident angle for a sunspot is calculated as:

$\mathrm{\alpha <br><br>}=\arctan <br><br>\left[\frac{\left(X_c-x_0\right)<br><br>\cos <br><br><br><br>\mathrm{\phi <br><br>}+\left(Y_c-y_0\right)<br><br>\sin <br><br><br><br>\mathrm{\phi <br><br>}}{F^{\mathrm{\prime <br><br>}}}\right]+{\mathrm{\alpha <br><br>}}_0$ $\mathrm{\beta <br><br>}=\arctan [\frac{\left(X_c-x_0\right)<br><br>\sin <br><br><br><br>\mathrm{\phi <br><br>}-\left(Y_c-y_0\right)<br><br>\cos <br><br><br><br>\mathrm{\phi <br><br>}}{\sqrt{F^{\mathrm{\prime <br><br>2}}+{\left[\left(X_c-x_0\right)<br><br>\cos <br><br><br><br>\mathrm{\phi <br><br>}+\left(Y_c-y_0\right)<br><br>\sin <br><br><br><br>\mathrm{\phi <br><br>}\right]}^2}}+{\mathrm{\beta <br><br>}}_0$

Where (Xc, Yc) is centroid coordinate value and F′

, x₀, y₀, α

₀, β

₀, φ

are calibrated parameters for (n,m) aperture.