Sensor module, method of correction therefor, and mobile object including the sensor module

• US 7,743,519 B2
• Filed: 10/05/2007
• Issued: 06/29/2010
• Est. Priority Date: 10/06/2006
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Fuse, Akihiro, Kou, Futoyoshi
• Primary Examiner(s): SMITH, RICHARD A
• Application Number:
  US11/868,141
• Publication Number:
  US 20080250661A1
• Time in Patent Office: 998 Days
• Field of Search: 333/56, 701/221, 701/224, 702/92, 702/93, 702/94, 702/95
• US Class Current: 33/356
• CPC Class Codes: G01C 17/28 Electromagnetic compasses with north seeking magnetic elements and having electric pick-offs G01C17/26
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01P 15/0922 of the bending or flexing mode type
• 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

Abstract

A sensor module maintaining high detection accuracy. Correction data of a detected magnetic field is updated only in a case that a fluctuation band acquired from an output signal of an acceleration sensor is less than a threshold value and a difference between an azimuth angle acquired from an output signal of a terrestrial magnetism sensor and an inclination angle acquired from an output signal of acceleration sensor is less than the threshold value. Therefore, the correction data is updated only in a case that a magnetic field at a position of a mobile object is stably detected, and an accuracy of the correction data can be maintained.

Claims

1. A sensor module mounted on a mobile object, comprising:

a magnetic sensor having at least two magnetic field detecting axes and that outputs first azimuth data indicating a first direction that a reference portion in the mobile object faces based on magnetic information;

a motion sensor detecting at least one of an acceleration motion or angular motion of the mobile object and configured to output a second azimuth data indicating a second direction that the reference portion in the mobile object faces based on the acceleration motion or angular motion; and

a processing device that stores correction data to correct the magnetic information used by the magnetic sensor, and that updates that stored correction data when a difference between the first azimuth data and the second azimuth data is less than a first threshold value.

2. The sensor module according to claim 1, wherein:

the magnetic sensor is a terrestrial magnetism sensor.

3. The sensor module according to claim 2, wherein:

the motion sensor is one of an acceleration sensor or a gyro sensor.

4. The sensor module according to claim 3, wherein:

the motion sensor includes the acceleration sensor; and

the second azimuth data is an inclination data to a direction of gravity calculated from an output signal from the acceleration sensor.

5. The sensor module according to claim 3, wherein:

the motion sensor includes a gyro sensor; and

the second azimuth data is calculated from an output signal from the gyro sensor.

6. The sensor module according to claim 4, wherein:

the processing device acquires acceleration information from the acceleration sensor prior to judging whether the difference is less than the first threshold value or not; and

the processing device judges whether the difference is less than the first threshold value or not in a case that a fluctuation band of accelerations is less than a second threshold value.

7. The sensor module according to claim 1, wherein:

the processing device acquires the magnetic information from the magnetic sensor and rotation information from at least the motion sensor prior to judging whether the difference is less than the first threshold value or not; and

the processing device judges whether the difference is less than the first threshold value or not when changing trends of a magnetic field and a rotation angle are the same as each other.

8. The sensor module according to claim 1, wherein:

the processing device acquires the magnetic information from the magnetic sensor and rotation information from at least the motion sensor prior to judging whether the difference is less than the first threshold value or not;

the processing device calculates a declination angle from a parallel direction of a magnetic field at a position of the mobile object based on the magnetic information and rotation information; and

the processing device judges whether the difference is less than the first threshold value or not when a declination angle is less than the third threshold value.

9. The sensor module according to claim 7, wherein:

the magnetic sensor and the motion sensor are monolithic.

10. The sensor module according to claim 8, wherein:

the magnetic sensor and the motion sensor are monolithic.

11. The sensor module according to claim 7, wherein:

the magnetic sensor and the motion sensor are manufactured on a same substrate by an Micro Electro Mechanical System (MEMS) manufacturing process.

12. The sensor module according to claim 8, wherein:

the magnetic sensor and the motion sensor are manufactured on a same substrate by an Micro Electro Mechanical System (MEMS) manufacturing process.

13. The sensor module according to claim 9, wherein:

the magnetic sensor includes a tunneling magnetic resistance effect element or a giant magnetic resistance effect element.

14. The sensor module according to claim 10, wherein:

the magnetic sensor includes a tunneling magnetic resistance effect element or a giant magnetic resistance effect element.

15. The sensor module according to claim 11, wherein:

the magnetic sensor includes a tunneling magnetic resistance effect element or a giant magnetic resistance effect element.

16. The sensor module according to claim 12, wherein:

the magnetic sensor includes a tunneling magnetic resistance effect element or a giant magnetic resistance effect element.

20. A mobile object comprising:

a sensor module according to claim 1.

17. A correction method for correcting magnetic information for a sensor module mounted on a mobile object including a magnetic sensor including at least two magnetic field detecting axes and a motion sensor detecting at least one of an acceleration or angular motion of the mobile object, the method comprising:

calculating a first azimuth data indicating a direction that a reference portion of the mobile object faces based on magnetic information from the magnetic sensor;

calculating a second azimuth data indicating a direction that the reference portion of the mobile object faces based on information from at least the motion sensor;

judging whether a difference between the first azimuth data and the second azimuth data is less than a first threshold value or not;

updating a stored correction data for correcting magnetic data in a case the difference is less than the first threshold value; and

correcting the magnetic information based on the correction data.

18. The correction method according to claim 17, further comprising:

acquiring acceleration information from the acceleration sensor prior to judging whether the difference is less than the first threshold value or not;

obtaining a fluctuation band of accelerations based on the acceleration information; and

judging whether the difference is less than the first threshold value or not when the fluctuation band of accelerations is less than a second threshold value.

19. The correction method according to claim 17, further comprising:

acquiring the magnetic information from the magnetic sensor and rotation information from at least the motion sensor prior to judging whether the difference is less than the first threshold value or not; and

obtaining a first changing trend of magnetic field from the magnetic information;

obtaining a second changing trend of a rotation angle from the rotation information; and

judging whether the difference is less than the first threshold value or not when changing trends of magnetic field and a rotation angle are the same as each other.