Multi-axis accelerometer comprising a mass suspended by springs above an optical sensor

• US 6,568,268 B1
• Filed: 10/31/2001
• Issued: 05/27/2003
• Est. Priority Date: 10/31/2001
• Status: Active Grant

• Current Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Original Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Inventors: Bennett, George J.
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US10/004,433
• Time in Patent Office: 573 Days
• Field of Search: 735/142.6, 735/142.9, 735/10, 250/231.1, 250/227.21, 250/227.14, 360/78.01, 360/78.04, 360/78.13, 360/77.02, 318/122, 318/127
• US Class Current: 73/514.26
• CPC Class Codes: G01P 15/0888 for indicating angular acceleration
• CPC Class Codes: G01P 15/093 by photoelectric pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G11B 5/5534 Initialisation, calibration, e.g. cylinder "set-up"
• CPC Class Codes: G11B 5/5582 system adaptation for working during or after external perturbation, e.g. in the presence of a mechanical oscillation caused by a shock
• CPC Class Codes: G11B 5/59694 System adaptation for working during or after external perturbation, e.g. in the presence of a mechanical oscillation caused by a shock

Abstract

A multi-axis accelerometer is disclosed comprising at least one optical sensor for generating a sensor signal in response to light illuminating the optical sensor, a mask positioned over the optical sensor for covering a first area of the optical sensor, at least one spring, and a mass suspended above the optical sensor by the spring. The mass comprises at least one mass aperture for allowing the light to pass through the mass aperture and illuminate a second area of the optical sensor not covered by the mask. When the multi-axis accelerometer accelerates causing the mass to move, a corresponding movement of the mass aperture alters the illumination of the optical sensor such that the sensor signal is indicative of the acceleration.

Claims

1. A multi-axis accelerometer comprising:

(a) at least one optical sensor for generating a sensor signal in response to light illuminating the optical sensor;

(b) a mask positioned over the optical sensor for covering a first area of the optical sensor;

(c) at least one spring; and

(d) a mass suspended above the optical sensor by the spring, wherein;

the mass comprises at least one mass aperture for allowing the light to pass through the mass aperture and illuminate a second area of the optical sensor not covered by the mask; and

when the multi-axis accelerometer accelerates causing the mass to move, a corresponding movement of the mass aperture alters the illumination of the optical sensor such that the sensor signal is indicative of the acceleration.

2. The multi-axis accelerometer as recited in claim 1, wherein the optical sensor and the mask are integrally formed.

3. The multi-axis accelerometer as recited in claim 1, wherein:

(a) the at least one mass aperture comprises a plurality of linear apertures; and

(b) the mask comprises a corresponding plurality of opaque lines.

4. The multi-axis accelerometer as recited in claim 1, wherein the at least one spring comprises a vertical wire having a first end connected to the mass and a second end connected to the optical sensor.

5. The multi-axis accelerometer as recited in claim 1, wherein:

(a) the at least one optical sensor comprises an A sensor, a B sensor, a C sensor and a D sensor;

(b) the A sensor generates an A sensor signal, the B sensor generates a B sensor signal, the C sensor generates a C sensor signal, and the D sensor generates a D sensor signal;

(c) a first linear acceleration is detected relative to the A sensor signal and the D sensor signal;

(d) a second linear acceleration is detected relative to the B sensor signal and the C sensor signal; and

(e) a rotational acceleration is detected relative to the A, B, C and D sensor signals.

6. The multi-axis accelerometer as recited in claim 5, wherein:

(a) the first linear acceleration is detected relative to a difference between the A sensor signal and the D sensor signal;

(b) the second linear acceleration is detected relative to a difference between the B sensor signal and the C sensor signal; and

(c) the rotational acceleration is detected relative to;

a first sum generated by summing the A sensor signal and the D sensor signal;

a second sum generated by summing the B sensor signal and the C sensor signal; and

a difference between the first sum and the second sum.

7. The multi-axis accelerometer as recited in claim 1, further comprising:

(a) a housing for creating a compartment between the optical sensor and the mass; and

(b) a fluid within the compartment for providing a damping effect.

8. The multi-axis accelerometer as recited in claim 1, wherein:

(a) the optical sensor and the mass are enclosed in a housing; and

(b) the at least one spring comprises a horizontal wire having a first end connected to the mass and a second end connected to the housing.

9. A method of detecting linear and rotational accelerations, the method comprising the steps of:

(a) positioning a mask over an optical sensor to cover a first area of the optical sensor;

(b) suspending a mass above the optical sensor using springs; and

(c) illuminating the optical sensor with light to generate a sensor signal;

wherein;

the mass comprises at least one mass aperture for allowing the light to pass through the mass aperture and illuminate a second area of the optical sensor not covered by the mask; and

when the multi-axis accelerometer accelerates causing the mass to move, a corresponding movement of the mass aperture alters the illumination of the optical sensor such that the sensor signal is indicative of the acceleration.

10. The method as recited in claim 9, wherein the optical sensor and the mask are integrally formed.

11. The method as recited in claim 9, wherein:

(a) the at least one mass aperture comprises a plurality of linear apertures; and

(b) the mask comprises a corresponding plurality of opaque lines.

12. The method as recited in claim 9, wherein the at least one spring comprises a vertical wire having a first end connected to the mass and a second end connected to the optical sensor.

13. The method as recited in claim 9, wherein the at least one optical sensor comprises an A sensor, a B sensor, a C sensor and a D sensor, and the A sensor generates an A sensor signal, the B sensor generates a B sensor signal, the C sensor generates a C sensor signal, and the D sensor generates a D sensor signal, the method further comprises the steps of:

(a) detecting a first linear acceleration relative to the A sensor signal and the D sensor signal;

(b) detecting a second linear acceleration relative to the B sensor signal and the C sensor signal; and

(c) detecting a rotational acceleration relative to the A, B, C and D sensor signals.

14. The method as recited in claim 13, wherein:

(a) the step of detecting the first linear acceleration comprises the step of computing a difference between the A sensor signal and the D sensor signal;

(b) the step of detecting the second linear acceleration comprises the step of computing a difference between the B sensor signal and the C sensor signal; and

(c) the step of computing the rotational acceleration comprises the steps of;

computing a first sum by summing the A sensor signal and the D sensor signal;

computing a second sum by summing the B sensor signal and the C sensor signal; and

computing a difference between the first sum and the second sum.

15. The method as recited in claim 9, wherein:

(a) the optical sensor and the mass are enclosed in a housing to create a compartment between the optical sensor and the mass; and

(b) the compartment is filled with a fluid to provide a damping effect.

16. The method as recited in claim 9, wherein:

(a) the optical sensor and the mass are enclosed in a housing; and

(b) the at least one spring comprises a horizontal wire having a first end connected to the mass and a second end connected to the housing.

17. A disk drive comprising:

(a) a disk;

(b) a head;

(c) an actuator for actuating the head radially over the disk;

(d) a multi-axis accelerometer for generating an acceleration signal representing a vibration affecting the actuator, the acceleration signal for controlling operation of the disk drive, the multi-axis accelerometer comprising;

at least one optical sensor for generating a sensor signal in response to light illuminating the optical sensor;

a mask positioned over the optical sensor for covering a first area of the optical sensor;

at least one spring; and

a mass suspended above the optical sensor by the spring, wherein;

the mass comprises at least one mass aperture for allowing the light to pass through the mass aperture and illuminate a second area of the optical sensor not covered by the mask; and

when the disk drive accelerates causing the mass to move, a corresponding movement of the mass aperture alters the illumination of the optical sensor such that the sensor signal is indicative of the acceleration.

18. The disk drive as recited in claim 17, further comprising a servo controller, responsive to the acceleration signal, for maintaining the head in a desired position relative to the disk during read and write operations.

19. The disk drive as recited in claim 17, wherein a write current applied to the head during write operations is disabled in response to the acceleration signal.

20. The disk drive as recited in claim 17, wherein the head is parked in a parked position in response to the acceleration signal.

21. The disk drive as recited in claim 17, wherein the optical sensor and the mask are integrally formed.

22. The disk drive as recited in claim 17, wherein:

(a) the at least one mass aperture comprises a plurality of linear apertures; and

(b) the mask comprises a corresponding plurality of opaque lines.

23. The disk drive as recited in claim 17, wherein the at least one spring comprises a vertical wire having a first end connected to the mass and a second end connected to the optical sensor.

24. The disk drive as recited in claim 17, wherein:

(a) the at least one optical sensor comprises an A sensor, a B sensor, a C sensor and a D sensor;

(b) the A sensor generates an A sensor signal, the B sensor generates a B sensor signal,

(b) the C sensor generates a C sensor signal, and the D sensor generates a D sensor signal,

(c) a first linear acceleration is detected relative to the A sensor signal and the D sensor signal;

(d) a second linear acceleration is detected relative to the B sensor signal and the C sensor signal; and

(e) a rotational acceleration is detected relative to the A, B, C and D sensor signals.

25. The disk drive as recited in claim 24, wherein:

(a) the first linear acceleration is detected relative to a difference between the A sensor signal and the D sensor signal;

(b) the second linear acceleration is detected relative to a difference between the B sensor signal and the C sensor signal; and

(c) the rotational acceleration is detected relative to;

a first sum signal generated by summing frequencies of the A sensor signal and the D sensor signal;

a second sum signal generated by summing frequencies of the B sensor signal and the C sensor signal; and

a difference between the first sum signal and the second sum signal.

26. The disk drive as recited in claim 25, wherein the multi-axis accelerometer further comprises:

(a) an A variable oscillator (VO) for generating an A oscillating signal in response to the A sensor signal;

(b) a B VO for generating a B oscillating signal in response to the B sensor signal;

(c) a C VO for generating a C oscillating signal in response to the C sensor signal;

(d) a D VO for generating a D oscillating signal in response to the D sensor signal;

(e) a first axis counter comprising an up count input responsive to the A oscillating signal and a down count input responsive to the D oscillating signal, the first axis counter for generating on output signal indicative of the first linear acceleration;

(f) a second axis counter comprising an up count input responsive to the B oscillating signal and a down count input responsive to the C oscillating signal, the second axis counter for generating on output signal indicative of the second linear acceleration; and

(g) a rotation counter comprising an up count input responsive to the A and D oscillating signals and a down count input responsive to the B and C oscillating signals, the rotation counter for generating an output signal indicative of the rotational acceleration.

27. The disk drive as recited in claim 17, further comprising:

(a) a housing for creating a compartment between the optical sensor and the mass; and

(b) a fluid within the compartment for providing a damping effect.

28. The disk drive as recited in claim 17, wherein:

(a) the optical sensor and the mass are enclosed in a housing; and

(b) the at least one spring comprises a horizontal wire having a first end connected to the mass and a second end connected to the housing.