METHOD AND APPARATUS FOR CALCULATING AZIMUTH

• US 20150032409A1
• Filed: 04/02/2014
• Published: 01/29/2015
• Est. Priority Date: 07/24/2013
• Status: Active Application

• Current Assignee: Magnachip Semiconductor Limited (Magnachip Semiconductor)
• Original Assignee: Magnachip Semiconductor Limited (Magnachip Semiconductor)
• Inventors: KIM, Dong Ho, CHO, Ki Seok
• Granted Patent: US 10,267,649 B2
• Time in Patent Office: Days
• US Class Current: 702/151
• CPC Class Codes: G01C 17/28 Electromagnetic compasses with north seeking magnetic elements and having electric pick-offs G01C17/26
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38

Abstract

A method and an apparatus for calculating azimuth, and a method and an apparatus for determining an offset from geomagnetic field are provided. An apparatus for calculating azimuth includes a magnetic sensor configured to sense magnetic field, a data selecting unit configured to select offset data items, an offset calculating unit configured to calculate an offset by a geometrical method that uses the selected offset data items, and an azimuth calculating unit configured to calculate an azimuth by using the calculated offset.

Claims

1. An azimuth calculating apparatus comprising:

a magnetic sensor configured to sense magnetic field;

a data selecting unit configured to select offset data items;

an offset calculating unit configured to calculate an offset by a geometrical method that uses the selected offset data items; and

an azimuth calculating unit configured to calculate an azimuth by using the calculated offset.

2. The apparatus according to claim 1, further comprising a median filter unit configured to remove noise from the magnetic field.

3. The apparatus according to claim 1, wherein the data selecting unit is configured to select at least three or more data items as the selected offset data items.

4. The apparatus according to claim 3, wherein the data selecting unit is configured to use two values, which are a value having the greatest difference in distance between data items in a measured data group and a value having the second greatest difference, as main-calculation data items, and uses at least one data item between the two values as sub-calculation data.

5. The apparatus according to claim 4, wherein the offset calculating unit is configured to set one point that is far away from the sub-calculation data, among intersecting points of two circles having the two main-calculation data items as centers and each having a radius r, as a new offset reference point.

6. The apparatus according to claim 1, further comprising an offset calculation assisting unit configured to, in response to a data presently measured being determined not to correspond to geomagnetic field and previous data being determined to correspond to the geomagnetic field, calculate the offset by subtracting a difference between the presently measured data and the previous data from a previous offset reference point and setting the resultant value as a new offset reference point.

7. The apparatus according to claim 1, further comprising:

an amplifying unit configured to amplify a voltage of the magnetic field sensed by the magnetic sensor;

an analog-to-digital converting unit configured to convert the amplified voltage into a digital value;

a chopping control unit configured to reduce an offset of the voltage;

a magnetic field separating unit configured to separate the voltage into 3-axis magnetic field components in X, Y, and Z axes and to transmit the separated 3-axis magnetic field components to the median filter unit; and

a magnetic field inspecting unit configured to determine whether or not the magnetic field corresponds to the geomagnetic field, to calculate the azimuth without updating a new offset in response to a determination that the magnetic field is the geomagnetic field, and to calculate the offset in response to a determination that the magnetic field is not the geomagnetic field.

8. An azimuth calculating method comprising:

selecting offset data in response to output data not corresponding to geomagnetic field;

calculating an offset by using the selected offset data, determining whether or not the offset is within a range of variation in the offset, and applying the offset in response to the offset being within a range of a preset reference value and not applying the offset in response to the offset being outside the range of the reference value; and

calculating an azimuth by using the calculated offset.

9. The method according to claim 8, wherein, in the selecting of the offset data, two values, which are a value having the greatest difference in distance between data items in a measured data group and a value having the second greatest difference, are used as main-calculation data items, and

at least one data item between the two values is used as sub-calculation data.

10. The method according to claim 9, wherein in the selecting of the offset data, data items that are sequentially input are arranged in order of size, and a middle data item is selected to remove the noise.

11. The method according to claim 9, wherein the selected offset data items are at least three or more data items.

12. The method according to claim 11, wherein the selecting of the three data items comprises:

storing a predetermined number of 2-axis or 3-axis data items;

calculating X_diff and Y_diff by performing an operation of the following equation 1 by using the stored plurality of data items;

selecting two data items having the largest value and the second largest value from among the X_diff and the Y_diff and selecting the two data items as main-calculation data items C and D;

in response to the X_diff being selected, selecting data having an X value closest to X_avg, and in response to the Y_diff is selected, selecting data having a Y value closest to Y_avg; and

selecting the data selected as the data closest to the X_avg or the Y_avg as sub-calculation data E, in accordance with equations;

X_diff=X_max−

X_min,

Y_diff=Y_max−

Y_min,

X_avg=(X_max+X_min)/2,

Y_avg=(Y_max+Y_min)/2,

wherein X_max, X_min, Y_max, and Y_min are output values of a median filter unit, and X_avg and Y_avg are average values.

13. The method according to claim 12, wherein the calculating of the offset by using the selected three data comprises:

calculating distances r between a changed offset reference point B and the main-calculation data item C and between the changed offset reference point B and the main-calculation data item D;

forming a circle having the main-calculation data C as a center and a radius r and a circle having the main-calculation data D as a center and a radius r, and setting one point of intersecting points a1 and a2 of the circles as an offset reference point; and

in response to coordinates of the main-calculation data C being X₁ and Y₁, coordinates of the main-calculation data D are X₂ and Y₂, coordinates of the changed offset reference point B are ⁰X and ⁰Y, and coordinates of the sub-calculation data E are X₃ and Y₃, calculating as an offset a data that is data having a distance father from the sub-calculation data E, of roots a1 and a2 of equations obtained from the following equations;

(X₁−

⁰X)²+(Y₁−

⁰Y)²=r², and

(X²−

⁰X)²+(Y₂−

⁰Y)²=r².

14. The method according to claim 9, further comprising assisting an offset calculation,

wherein, with data that is presently measured being represented as C₁(X_c, Y_c) and data which is previously measured is represented as P₁(X_p, Y_p), in response to a determination that the P1 is the geomagnetic field and the C₁ is not the geomagnetic field, the offset is calculated by subtracting (X_c−

X_p) and (Y_c−

Y_p) from the offset reference point by using the equation (X_c−

X_p)²+(Y_c−

Y^p)²>

a² and then setting the resultant value as a new offset.

15. The method according to claim 9, wherein the output data is obtained by measuring the magnetic field, separating the measured magnetic field into the 3-axis magnetic field of X, Y, and Z axes, and then removing noise from the 3-axis magnetic field.

16. A method of determining an offset from geomagnetic field, the method comprising:

measuring magnetic field with a magnetic sensor;

selecting offset data items for calculating an offset; and

calculating the offset by applying a geometric method to the selected offset data item.

17. The method of claim 16, further comprising:

separating the measured magnetic field into components along two or more axes to obtain a collected data group.

18. The method of claim 16, further comprising:

removing noise from a collected data group of measured magnetic field by selecting a median value or a value substantially in middle in magnitude in the collected data group to form a measured data group.

19. The method of claim 16, wherein the selecting comprises selecting at least three data items, the three data items comprising two values having the greatest difference and the second greatest difference in distance between data items in a measured data group, and a value between the two values.

20. The method of claim 16, further comprising providing the calculated offset to calculate an azimuth from a measured magnetic field.

21. A non-transitory computer recording medium having recorded thereon an instruction to cause a computer to perform the method of claim 16.