Acceleration measuring apparatus with calibration function

• US 6,810,738 B2
• Filed: 06/09/2003
• Issued: 11/02/2004
• Est. Priority Date: 07/10/2002
• Status: Expired due to Fees

• Current Assignee: Hitachi Metals (Thailand) Ltd.
• Original Assignee: Hitachi Metals (Thailand) Ltd.
• Inventors: Sakaguchi, Isao
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US10/456,832
• Publication Number:
  US 20040007064A1
• Time in Patent Office: 512 Days
• Field of Search: 735/140.1, 735/143.3, 735/142.9, 735/143.6, 735/142.1, 735/142.3, 738/826.34, 735/10, 734/97, 702/141, 338/2, 338/5
• US Class Current: 73/510
• CPC Class Codes: G01P 15/123 by piezo-resistive elements, e.g. semiconductor strain gauges
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/084 the mass being suspended at more than one of its sides, e.g. membrane-type suspension, so as to permit multi-axis movement of the mass
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

An acceleration measuring apparatus capable of calibrating its output with a zero-point in the state of no acceleration applied as well as sensitivity. An acceleration sensor detects each component of an acceleration and creates an output based on each of the detected components in each direction of at least two mutually perpendicular axes of orthogonal coordinates for the acceleration sensor. The acceleration sensor is held at at least two different positions; each of the acceleration sensor axes at one position is at a angle, with the gravitational acceleration direction, that is different from the angle at the other position. A processing circuit develops calibration parameters based on output by each component in the at least two axis directions of the gravitational acceleration measured by the acceleration sensor positioned at each of the at least two different positions and calibrates the output of the acceleration measured by using the calibration parameters to provide a calibrated output.

Claims

1. An acceleration measuring apparatus comprising:

an acceleration sensor that detects components of an acceleration to be measured and produces an output based on each of the detected components in each direction of at least two mutually perpendicular axes of orthogonal coordinates for the acceleration sensor,

a holding means that holds the acceleration sensor at at least two different positions, the acceleration sensor axes at one of said positions each being at an angle, with the gravitational acceleration direction, that is different from that at the other of said positions, and

a processing circuit that develops calibration parameters based on a gravitational output by each component in the at least two axis directions of the gravitational acceleration, measured by the acceleration sensor positioned at each of the at least two different positions, and that calibrates the output, produced by the acceleration sensor based on each of the detected components of the acceleration to be measured in each of the at least two axis directions, by using the calibration parameters to provide a calibrated output.

2. An acceleration measuring apparatus as set forth in claim 1, wherein the acceleration sensor detects each component of the acceleration to be measured in each direction of three mutually perpendicular axes of the orthogonal coordinates for the acceleration sensor, and produces the output based on each of the detected components, and

the holding means holds the acceleration sensor at only two of said different positions,

the acceleration sensor axes at the one position each being at an angle, with the gravitational acceleration direction, that is different from that at the other position.

3. An acceleration measuring apparatus as set forth in claim 2, wherein the calibration parameters include an output per unit magnitude of acceleration (hereinafter called “

sensitivity”

) in each of the three axis directions of the acceleration sensor and an output of the acceleration sensor in each of the three axis directions without applied acceleration (hereinafter called “

zero-point output”

).

4. An acceleration measuring apparatus as set forth in claim 3, wherein the processing circuit further comprises a memory in which the developed calibration parameters are stored, and calibrates the output, produced by the acceleration sensor based on each of the detected components of the acceleration to be measured in each of the three axis directions, by using the stored calibration parameters to provide the calibrated output.

5. An acceleration measuring apparatus as set forth in claim 3, wherein the acceleration sensor held at the one position of the two different positions has an axis, among the three mutually perpendicular axes, which is identical with the gravitational acceleration direction, and, when the acceleration sensor is held at the other position, this axis is at an angle with the gravitational acceleration direction.

6. An acceleration measuring apparatus as set forth in claim 3, wherein the processing circuit calibrates the output produced by the acceleration sensor based on each of the detected components of the acceleration in each of the three axis directions by using the sensitivity and the zero-point output in each of the three axis directions, according to the following equation:

7. An acceleration measuring apparatus as set forth in claim 2, wherein the acceleration measuring apparatus further comprises a means for measuring an ambient temperature, and the processing circuit develops temperature functions of calibration parameters, based on the gravitational output by each component in the three axis directions of the gravitational acceleration measured by the acceleration sensor positioned at each of the two different positions, and calibrates the output, produced by the acceleration sensor based on each of the detected components of the acceleration, by using the calibration parameters obtained with the ambient temperature by the temperature functions of the calibration parameters to provide the calibrated output.

8. An acceleration measuring apparatus as set forth in claim 7, wherein the temperature functions of the calibration parameters include a temperature function of an output per unit magnitude of acceleration (hereinafter called “

temperature function of sensitivity”

) in each of the three axis directions of the acceleration sensor and a temperature function of an output of the acceleration sensor in each of the three axis directions without applied acceleration (hereinafter called “

temperature function of zero-point output”

).

9. An acceleration measuring apparatus as set forth in claim 8, wherein the processing circuit further comprises a memory in which the developed temperature functions of calibration parameters are stored, and calibrates the output produced by the acceleration sensor based on each of the detected components of the acceleration to be measured in each of the three axis directions by using calibration parameters at the ambient temperature obtained with the ambient temperature by the stored temperature functions of calibration parameter to provide the calibrated output.

10. An acceleration measuring apparatus as set forth in claim 8, wherein the acceleration sensor, held at the one position of the two different positions, has an axis among the three mutually perpendicular axes which is identical with the gravitational acceleration direction, and, when the acceleration sensor is held at the other position, this axis is at an angle with the gravitational acceleration direction.

11. An acceleration measuring apparatus as set forth in claim 8, wherein the processing circuit calibrates the output produced by the acceleration sensor based on each of the detected components of the acceleration to be measured in each of the three axis directions by using the sensitivity and the zero-point output at the ambient temperature calculated with the ambient temperature by the temperature functions of sensitivity and the temperature functions of zero-point output, respectively, according to the following equation:

12. A method of measuring acceleration, comprising the steps of:

holding an acceleration sensor at at least two different positions, the acceleration sensor axes at one of said positions each being at an angle, with the gravitational acceleration direction, that is different from that at the other of said positions;

developing calibration parameters based on a gravitational output by each component of the gravitational acceleration, in at least two axis directions of at least two mutually perpendicular axes of orthogonal coordinates for the acceleration sensor, which is measured by the acceleration sensor positioned at each of the at least two different positions;

detecting each component of an acceleration to be measured and producing an output based on each of the detected components in each direction of the at least two mutually perpendicular axes of the orthogonal coordinates for the acceleration sensor; and

calibrating the output produced by the acceleration sensor based on each of the detected components of the acceleration to be measured in each of the at least two axis directions by using the calibration parameters to provide a calibrated output.

13. The method as set forth in claim 12, wherein

the acceleration sensor is held at only two of said different positions, the acceleration sensor axes at one of said positions each being at an angle, with the gravitational acceleration direction, that is different from that at the other of said positions, and

the acceleration sensor detects each component of the acceleration to be measured in each direction of three mutually perpendicular axes of the orthogonal coordinates for the acceleration sensor, and produces the output based on each of the detected components.

14. The method as set forth in claim 13, wherein

the calibration parameters include an output per unit magnitude of acceleration (hereinafter called “

sensitivity”

) in each of the three axis directions of the acceleration sensor and an output of the acceleration sensor in each of the three axis directions without applied acceleration (hereinafter called “

zero-point output”

).

15. The method as set forth in claim 14, further comprising the step of storing the developed calibration parameters, and

wherein, in the step of calibrating the output, the output produced by the acceleration sensor based on each of the detected components of the acceleration to be measured in each of the three axis directions is calibrated by using the stored calibration parameters to provide the calibrated output.

16. The method as set forth in claim 14, wherein the acceleration sensor held at the one position of the two different positions has an axis, among the three mutually perpendicular axes, which is identical with the gravitational acceleration direction, and when the acceleration sensor is held at the other position, this axis is at an angle with the gravitational acceleration direction.

17. The method as set forth in claim 14, wherein, in the step of calibrating the output, the output produced by the acceleration sensor based on each of the detected components of the acceleration to be measured in each of the three axis directions is calibrated by using the sensitivity and the zero-point output in each of the three axis directions, according to the following equation:

18. The method as set forth in claim 13, wherein the method further comprises the step of measuring an ambient temperature, and

wherein, in the step of developing calibration parameters, temperature functions of calibration parameters are developed, based on the gravitational output by each component in the three axis directions of the gravitational acceleration measured by the acceleration sensor positioned at each of the two different positions, and

in the step of calibrating the output, the output produced by the acceleration sensor based on each of the detected components of the acceleration to be measured is calibrated by using the calibration parameters obtained with the ambient temperature by the temperature functions of calibration parameters to provide the calibrated output.

19. The method as set forth in claim 18, wherein the temperature functions of calibration parameters include a temperature function of an output per unit magnitude of acceleration (hereinafter called “

temperature function of sensitivity”

) in each of the three axis directions of the acceleration sensor and a temperature function of an output of the acceleration sensor in each of the three axis directions without applied acceleration (hereinafter called “

temperature function of zero-point output”

).

20. The method as set forth in claim 19, further comprising the step of storing the developed temperature functions of calibration parameters, and

wherein, in the step of calibrating the output, the output produced by the acceleration sensor based on each of the detected components of the acceleration to be measured in each of the three axis directions is calibrated by using calibration parameters at the ambient temperature obtained with the ambient temperature by the stored temperature functions of calibration parameters to provide the calibrated output.

21. The method as set forth in claim 19, wherein the acceleration sensor, held at the one position of the two different positions, has an axis among the three mutually perpendicular axes which is identical with the gravitational acceleration direction, and when the acceleration sensor is held at the other position, this axis is at an angle with the gravitational acceleration direction.

22. The method as set forth in claim 19, wherein, in the step of calibrating the output, the output produced by the acceleration sensor based on each of the detected components of the acceleration to be measured in each of the three axis directions is calibrated by using the sensitivity and the zero-point output at the ambient temperature calculated with the ambient temperature by the temperature functions of sensitivity and the temperature functions of zero-point output, respectively, according to the following equation: