Acceleration measuring apparatus with calibration function

• US 20040007064A1
• Filed: 06/09/2003
• Published: 01/15/2004
• Est. Priority Date: 07/10/2002
• Status: Active Grant

• Current Assignee: Hitachi Metals (Thailand) Ltd.
• Original Assignee: Hitachi Metals (Thailand) Ltd.
• Inventors: Sakaguchi, Isao
• Granted Patent: US 6,810,738 B2
• Time in Patent Office: Days
• US Class Current: 73/488
• 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 is disclosed. An acceleration measuring apparatus an acceleration sensor that detects each component of an acceleration and creates an output based on each of the detected component in each direction of at least two mutually perpendicular axes of orthogonal coordinates for acceleration sensor; a holding means that holds the acceleration sensor at at least two different positions, in which the acceleration sensor axes at one position each is at a different angle with the gravitational acceleration direction from the other; and a processing circuit. The 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 calibrated output.

Claims

1. An acceleration measuring apparatus comprising:

an acceleration sensor that detects each component of an acceleration and causes an output based on each of the detected component 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 position each being at a different angle with the gravitational acceleration direction from the other, and

a processing circuit that 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 created by the acceleration sensor based on each of the detected component of the acceleration in each of the at least two axis directions by using the calibration parameters to provide calibrated output.

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

the holding means holds the acceleration sensor at two different positions,

the acceleration sensor axes at one position each being at a different angle with the gravitational acceleration direction from the other.

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, stores the obtained calibration parameters in the memory, and calibrates the output created by the acceleration sensor based on each of the detected component of the acceleration 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 one position of the two different positions has an axis among the three mutually perpendicular axes identical with the gravitational acceleration direction, and the acceleration sensor when held at the other position has 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 created by the acceleration sensor based on each of the detected component 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:

Calibrated output=(the output based on each of the detected component of the acceleration−

the zero-point output)/the sensitivity.

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 parameter, based on the 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 created by the acceleration sensor based on each of the detected component of the acceleration by using the calibration parameters obtained with the ambient temperature by the temperature functions of calibration parameter to provide the calibrated output.

8. An acceleration measuring apparatus as set forth in claim 7, wherein the temperature functions of calibration parameter include a temperature function of 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 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, stores the obtained temperature functions of calibration parameter in the memory, and calibrates the output created by the acceleration sensor based on each of the detected component of the acceleration 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 one position of the two different positions has an axis among the three mutually perpendicular axes identical with the gravitational acceleration direction, and the acceleration sensor when held at the other position has 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 created by the acceleration sensor based on each of the detected component of the acceleration 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:

Calibrated output=(the output based on each of the detected component of the acceleration−

the zero-point output)/the sensitivity.