Geomagnetic sensor for detecting azimuth angle and method thereof

• US 7,200,948 B2
• Filed: 12/08/2005
• Issued: 04/10/2007
• Est. Priority Date: 12/13/2004
• Status: Expired due to Fees

• Current Assignee: Samsung Electro-Mechanics Co., Ltd. (Samsung Group)
• Original Assignee: Samsung Electro-Mechanics Co., Ltd. (Samsung Group)
• Inventors: Choi, Sang-on, Lee, Woo-jong
• Primary Examiner(s): BENNETT, GEORGE B
• Application Number:
  US11/296,345
• Publication Number:
  US 20060123642A1
• Time in Patent Office: 488 Days
• Field of Search: 333/55.R, 333/55.D, 333/56
• US Class Current: 33/356
• CPC Class Codes: G01C 17/30 Earth-inductor compasses

Abstract

A geomagnetic sensor and method are provided. The geomagnetic sensor has a geomagnetic detection module for outputting an electric signal value corresponding to a geomagnetism, a tilt detection module for detecting a tilt angle with reference to a reference plane, a memory for storing a constant for each azimuth angle, and a central processing unit for performing a first azimuth computation using an initial value of the constants, the electric signal value and the tilt angle, and for performing a second azimuth computation by detecting from the memory a constant corresponding to the resultant azimuth of the first azimuth computation and using the detected constant. The method includes outputting an electric signal corresponding to a geomagnetism; normalizing the output electric signal; detecting a tilt angle with respect to a reference plane; performing a first azimuth computation; detecting a constant corresponding to the resultant azimuth; and performing a second azimuth computation.

Claims

1. A geomagnetic sensor, comprising:

a geomagnetic detection module which is configured to output an electric signal value corresponding to a geomagnetism;

a tilt detection module which is configured to detect a tilt angle which indicates a degree of inclination with reference to a reference plane;

a memory which is configured to store a constant for each azimuth angle for consideration of geomagnetic influence by a dip angle; and

a central processing unit which is configured to perform a first azimuth computation using an initial value of the constant, the electric signal value and the tilt angle, and to perform a second azimuth computation by detecting from the memory a constant corresponding to an azimuth of the first azimuth computation and using the detected constant.

2. The geomagnetic sensor of claim 1, wherein the central processing unit updates the initial value of the constant with the detected constant when the second azimuth computation is completed.

3. The geomagnetic sensor of claim 2, wherein the central processing unit performs the first and second azimuth computations using the updated constant each time the electric signal value and the tilt angle are detected from the geomagnetic detection module and the tilt detection module, respectively.

4. The geomagnetic sensor of claim 3, wherein the central processing unit performs the azimuth computations a certain number of times.

5. The geomagnetic sensor of claim 1, wherein the geomagnetic detection module comprises an X-axis fluxgate and a Y-axis fluxgate for respectively outputting the electric signal corresponding to the geomagnetism as induced by a driving signal.

6. The geomagnetic sensor of claim 5, further comprising a normalizing part which is configured to perform a normalizing process to map the electric signal from the X and Y-axis fluxgates to values of a predetermined range;

and

a display part which is configured to indicate the resultant value of the second azimuth computation,

wherein the central processing unit performs the first and the second azimuth computations using the normalized electric signal value from the normalizing part.

7. The geomagnetic sensor of claim 6, wherein the normalizing part performs the normalizing process using the following equations:

${\mathrm{Xf}}_{\mathrm{norm}}=\frac{\left(\mathrm{Xf}-{\mathrm{Xf}}_{\mathrm{bias}}\right)}{{\mathrm{Xf}}_{\mathrm{sf}}}\star <br><br>\mathrm{\alpha <br><br>}$ ${\mathrm{Yf}}_{\mathrm{norm}}=\frac{\left(\mathrm{Yf}-{\mathrm{Yf}}_{\mathrm{bias}}\right)}{{\mathrm{Yf}}_{\mathrm{sf}}}\star <br><br>\mathrm{\alpha <br><br>}$ ${\mathrm{Xf}}_{\mathrm{bias}}=\frac{{\mathrm{Xf}}_{\max }+{\mathrm{Xf}}_{\min }}{2},{\mathrm{Xf}}_{\mathrm{sf}}=\frac{{\mathrm{Xf}}_{\max }-{\mathrm{Xf}}_{\min }}{2}$ ${\mathrm{Yf}}_{\mathrm{bias}}=\frac{{\mathrm{Yf}}_{\max }+{\mathrm{Yf}}_{\min }}{2},{\mathrm{Yf}}_{\mathrm{sf}}<br><br>\frac{{\mathrm{Yf}}_{\max }-{\mathrm{Yf}}_{\min }}{2}$

where, Xf and Yf are output values from the X and Y-axis fluxgates, Xf_norm and Yf_norm are output values from the X and Y-axis fluxgates after the normalizing process, Xf_max and Xf_min are maximum and minimum values of Xf, respectively, Yf_max and Yf_min are maximum and minimum values of Yf, respectively, and α

is a fixed constant.

8. The geomagnetic sensor of claim 1, wherein the tilt detection module comprises:

an X-axis acceleration sensor and a Y-axis acceleration sensor which are disposed in a perpendicular relation with each other, and which output an electric signal corresponding to a deviation with respect to the reference plane;

a tilt normalizing part which is configured to perform a normalizing process to map the electric signal from each of the X and Y-axis acceleration sensors to a certain value; and

a tilt computation part which is configured to compute pitch and roll angles using the value normalized in the tilt normalizing part and to output the pitch and roll angles as the tilt angle.

9. The geomagnetic sensor of claim 8, wherein the tilt computation part computes the pitch and roll angles using the following equations:

$\mathrm{\theta <br><br>}={\sin }^{-1}<br><br>\left({\mathrm{Xt}}_{\mathrm{norm}}\right)$ $\mathrm{\varphi <br><br>}={\sin }^{-1}<br><br>\left(\frac{{\mathrm{Yt}}_{\mathrm{norm}}}{\cos <br><br><br><br>\mathrm{\theta <br><br>}}\right)$

where, θ

is the pitch angle, φ

is the roll angle, and Xt_norm and Yt_norm are output values of the X and Y-axis acceleration sensors, respectively, after the normalizing process.

10. The geomagnetic sensor of claim 1, wherein the central processing unit computes an output value of an imaginary Z-axis fluxgate using one of the following equations and performs first and second azimuth computations using the output value:

${\mathrm{Zf}}_{\mathrm{norm}}=\frac{\left(\mathrm{\beta <br><br>}-{\mathrm{Xf}}_{\mathrm{norm}}\star <br><br>\sin <br><br><br><br>\mathrm{\theta <br><br>}-{\mathrm{Yf}}_{\mathrm{norm}}\star <br><br>\cos <br><br><br><br>\mathrm{\theta <br><br>}\star <br><br>\sin <br><br><br><br>\mathrm{\varphi <br><br>}\right)}{\cos <br><br><br><br>\mathrm{\theta <br><br>}}$ ${\mathrm{Zf}}_{\mathrm{norm}}=\mathrm{\beta <br><br>}-{\mathrm{Xf}}_{\mathrm{norm}}\star <br><br>\sin <br><br><br><br>\mathrm{\theta <br><br>}-{\mathrm{Yf}}_{\mathrm{norm}}\star <br><br>\cos <br><br><br><br>\mathrm{\theta <br><br>}\star <br><br>\sin <br><br><br><br>\mathrm{\varphi <br><br>}$ ${\mathrm{Zf}}_{\mathrm{norm}}=\mathrm{\beta <br><br>}-{\mathrm{Xf}}_{\mathrm{norm}}\star <br><br>\sin <br><br><br><br>\mathrm{\theta <br><br>}$

where, Zf_norm is a normalized output value of the imaginary Z-axis fluxgate, β

is a constant value, θ

is a pitch angle, φ

is a roll angle, and Xf_norm and Yf_norm are the normalized output values of the X and Y-axis fluxgates, respectively.

11. The geomagnetic sensor of claim 10, wherein the central processing unit performs the first and the second azimuth computations by substituting the output values from the Z-axis fluxgate into the equation:

$\mathrm{\psi <br><br>}={\tan }^{-1}<br><br>\left(\frac{\left({\mathrm{Zf}}_{\mathrm{norm}}\star <br><br>\sin <br><br><br><br>\mathrm{\varphi <br><br>}-{\mathrm{Yf}}_{\mathrm{norm}}\star <br><br>\cos <br><br><br><br>\mathrm{\varphi <br><br>}\right)}{\left({\mathrm{Xf}}_{\mathrm{norm}}\star <br><br>\cos <br><br><br><br>\mathrm{\theta <br><br>}+{\mathrm{Yf}}_{\mathrm{norm}}\star <br><br>\sin <br><br><br><br>\mathrm{\theta <br><br>}\star <br><br>\sin <br><br><br><br>\mathrm{\varphi <br><br>}+{\mathrm{Zf}}_{\mathrm{norm}}\star <br><br>\sin <br><br><br><br>\mathrm{\theta <br><br>}<br><br><br><br>\cos <br><br><br><br>\mathrm{\varphi <br><br>}\right)}\right)$

where, ψ

is an azimuth angle, Xf_norm and Yf_norm are the normalized output values of the X and Y-axis fluxgates, respectively, Zf_norm is the normalized output value of the imaginary Z-axis fluxgate, θ

is pitch angle, and φ

is roll angle.

12. A method of measuring an azimuth angle of a geomagnetic sensor having a memory storing a constant for each azimuth angle for consideration of a geomagnetic influence by a dip angle, the method comprising:

outputting an electric signal corresponding to a geomagnetism;

normalizing the output electric signal by mapping the electric signal to a predetermined range;

detecting a tilt angle which indicates a degree of deviation of a geomagnetic sensor with respect to a reference plane;

performing a first azimuth computation using an initial value of the constant, the normalized electric signal value and the tilt angle;

detecting from the memory a constant corresponding to an azimuth of the first azimuth computation; and

performing a second azimuth computation using the detected constant, the normalized electric signal value and the tilt angle.

13. The method of claim 12, further comprising, after completion of the second azimuth computation, updating the initial value of the constant with the detected constant.

14. The method of claim 13, further comprising, performing the first and the second azimuth computations using the updated constant, each time the electric signal value and the tilt angle are detected.

15. The method of claim 14, wherein the detecting the constant and the performing the second azimuth computation are repeated a certain number of times.

16. The method of claim 12, wherein outputting the electric signal further comprises:

supplying a driving signal to an X-axis fluxgate and a Y-axis fluxgate which are fabricated in a perpendicular relation with each other; and

detecting an electric signal value corresponding to a geomagnetism induced at each of the X and Y-axis fluxgates by the driving signal.

17. The method of claim 16, wherein the normalizing process is performed using the following equations:

${\mathrm{Xf}}_{\mathrm{norm}}=\frac{\left(\mathrm{Xf}-{\mathrm{Xf}}_{\mathrm{bias}}\right)}{{\mathrm{Xf}}_{\mathrm{sf}}}\star <br><br>\mathrm{\alpha <br><br>}$ ${\mathrm{Yf}}_{\mathrm{norm}}=\frac{\left(\mathrm{Yf}-{\mathrm{Yf}}_{\mathrm{bias}}\right)}{{\mathrm{Yf}}_{\mathrm{sf}}}\star <br><br>\mathrm{\alpha <br><br>}$ ${\mathrm{Xf}}_{\mathrm{bias}}=\frac{{\mathrm{Xf}}_{\max }+{\mathrm{Xf}}_{\min }}{2},{\mathrm{Xf}}_{\mathrm{sf}}=\frac{{\mathrm{Xf}}_{\max }-{\mathrm{Xf}}_{\min }}{2}$ ${\mathrm{Yf}}_{\mathrm{bias}}=\frac{{\mathrm{Yf}}_{\max }+{\mathrm{Yf}}_{\min }}{2},{\mathrm{Yf}}_{\mathrm{sf}}<br><br>\frac{{\mathrm{Yf}}_{\max }-{\mathrm{Yf}}_{\min }}{2}$

where, Xf and Yf are output values from the X and Y-axis fluxgates, respectively, Xf_norm and Yf_norm are output values from the X and Y-axis fluxgates, respectively, after the normalizing process, Xf_max and Xf_min are maximum and minimum values of Xf respectively, Yf_max and Yf_min are maximum and minimum values of Yf, respectively, and α

is a fixed constant.

18. The method of claim 12, wherein detecting the tilt angle comprises:

detecting from an X-axis acceleration sensor and a Y-axis acceleration sensor, an electric signal corresponding to a degree of deviation with respect to a reference plane, the X and Y-axis acceleration sensors being fabricated in a perpendicular relation with each other;

normalizing, by mapping the electric signal detected from each of the X and Y-axis acceleration sensors to a predetermined range;

computing a pitch angle and a roll angle by substituting the normalized values in the following equations

$\mathrm{\theta <br><br>}={\sin }^{-1}<br><br>\left({\mathrm{Xt}}_{\mathrm{norm}}\right)$ $\mathrm{\varphi <br><br>}={\sin }^{-1}<br><br>\left(\frac{{\mathrm{Yt}}_{\mathrm{norm}}}{\cos <br><br><br><br>\mathrm{\theta <br><br>}}\right)$

where, θ

is the pitch angle, φ

is the roll angle, and Xt_norm and Yt_norm are output values of the X and Y-axis acceleration sensors after the normalizing process; and

outputting the computed pitch angle and roll angle as the tilt angle.

19. The method of claim 12, wherein the first and second azimuth computations further comprise computing an output value of an imaginary Z-axis fluxgate by using one of the following equations:

${\mathrm{Zf}}_{\mathrm{norm}}=\frac{\left(\mathrm{\beta <br><br>}-{\mathrm{Xf}}_{\mathrm{norm}}*\sin <br><br><br><br>\mathrm{\theta <br><br>}-{\mathrm{Yf}}_{\mathrm{norm}}*\cos <br><br><br><br>\mathrm{\theta <br><br>}*\sin <br><br><br><br>\mathrm{\varphi <br><br>}\right)}{\cos <br><br><br><br>\mathrm{\theta <br><br>}}$ ${\mathrm{Zf}}_{\mathrm{norm}}=\mathrm{\beta <br><br>}-{\mathrm{Xf}}_{\mathrm{norm}}*\sin <br><br><br><br>\mathrm{\theta <br><br>}-{\mathrm{Yf}}_{\mathrm{norm}}*\cos <br><br><br><br>\mathrm{\theta <br><br>}*\sin <br><br><br><br>\mathrm{\varphi <br><br>}$ ${\mathrm{Zf}}_{\mathrm{norm}}=\mathrm{\beta <br><br>}-{\mathrm{Xf}}_{\mathrm{norm}}*\sin <br><br><br><br>\mathrm{\theta <br><br>}$

where, Zf_norm is a normalized output value of the imaginary Z-axis fluxgate, β

is a constant value, θ

is a pitch angle, φ

is a roll angle, and Xf_norm and Yf_norm are the normalized output values of the X and Y-axis fluxgates, respectively.

20. The method of claim 19, wherein the first and second azimuth computations further comprise computing the azimuth angle by substituting the output value of the Z-axis fluxgate in the following equation:

$\mathrm{\psi <br><br>}={\tan }^{-1}<br><br>\left(\frac{\left({\mathrm{Zf}}_{\mathrm{norm}}*\sin <br><br><br><br>\mathrm{\varphi <br><br>}-{\mathrm{Yf}}_{\mathrm{norm}}*\cos <br><br><br><br>\mathrm{\varphi <br><br>}\right)}{\left({\mathrm{Xf}}_{\mathrm{norm}}*\cos <br><br><br><br>\mathrm{\theta <br><br>}+{\mathrm{Yf}}_{\mathrm{norm}}*\sin <br><br><br><br>\mathrm{\theta <br><br>}*\sin <br><br><br><br>\mathrm{\varphi <br><br>}+{\mathrm{Zf}}_{\mathrm{norm}}*\sin <br><br><br><br>\mathrm{\theta <br><br>}<br><br><br><br>\cos <br><br><br><br>\mathrm{\varphi <br><br>}\right)}\right)$

where, ψ

is the azimuth angle, Xf_norm and Yf_norm are the normalized output values of the X and Y-axis fluxgates, respectively, Zf_norm is the normalized output value of the imaginary Z-axis fluxgate, θ

is the pitch angle, and φ

is the roll angle.