Fall detection device, magnetic disk drive, and portable electronic apparatus

• US 8,676,532 B2
• Filed: 03/19/2010
• Issued: 03/18/2014
• Est. Priority Date: 09/21/2007
• Status: Active Grant

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation), Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Shibata, Akihiko
• Primary Examiner(s): Kundu, Sujoy
• Assistant Examiner(s): Lee, Paul D
• Application Number:
  US12/727,795
• Publication Number:
  US 20100172052A1
• Time in Patent Office: 1,460 Days
• Field of Search: 702/41, 702/141, 702/152, 702/169
• US Class Current: 702/141
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 5/1117 Fall detection
• CPC Class Codes: G01P 15/0891 with indication of predetermined acceleration values G01P15/135 takes precedence
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G11B 19/043 by detecting a free-fall condition
• CPC Class Codes: G11B 21/12 Raising and lowering; Back-spacing or forward-spacing along track; Returning to starting position otherwise than during transducing operation
• CPC Class Codes: G11B 5/54 with provision for moving the head into or out of its operative position or across tracks

Abstract

A fall detection device that is allowed to reduce the processing load put when making a determination using software, to reliably determine the start of a fall, and to make a fall prediction as necessary, and a magnetic disk drive and a portable electronic apparatus that each include the fall detection device are configured. Accelerations are obtained in three orthogonal axis directions (a_x, a_y, a_z), and an evaluation value is obtained with respect to each of the accelerations (a_x, a_y, a_z) on the basis of an evaluation function, by which an evaluation value is increased as the difference increases between accelerations (a_x0, a_y0, a_z0) at a steady time and accelerations (a_x, a_y, a_z) at a fall determination time, and whether a fall has started is determined on the basis of whether this evaluation value exceeds a predetermined value.

Claims

1. A fall detection device configured to detect a fall on the basis of a signal outputted from an acceleration sensor, the fall detection device comprising:

acceleration detection means that detects accelerations in three orthogonal axis directions; and

fall start determination means that

determines a steady time and accelerations in the three axis directions at the steady time by performing monitoring of an acceleration detected by the acceleration detection means,

obtains an evaluation value with respect to the accelerations in the three axis directions detected by the acceleration detection means on the basis of an evaluation function, by which an evaluation value is increased as a difference increases between the acceleration at the determined steady time and an acceleration at a fall determination time in each of the three axis directions, and

determines the start of a fall on the basis of whether the evaluation value exceeds a first predetermined threshold, wherein

the steady time is a time just before a time when the absolute value of a differential value of an acceleration detected by the acceleration detection means exceeds a second predetermined threshold, and the fall determination time is a time just after a time when the absolute value of a differential value of an acceleration detected by the acceleration detection means falls below a third predetermined threshold.

2. The fall detection device according to claim 1, wherein

if a value of the evaluation function is represented by A, the accelerations in the three axis directions at the steady time are represented by (a_x0, a_y0, a_z0) and the accelerations at the fall determination time are represented by (a_x, a_y, a_z), relations among the A, the (a_x0, a_y0, a_z0), and the (a_x, a_y, a_z) are represented by A=√

{(a_x−

a_x0)²+(a_y−

a_y0)²+(a_z−

a_z0)²}.

3. The fall detection device according to claim 1, wherein

if a value of the evaluation function is represented by A, the accelerations in the three axis directions at the steady time are represented by (a_x0, a_y0, a_z0) and the accelerations at the fall determination time are represented by (a_x, a_y, a_z), relations among the A, the (a_x0, a_y0, a_z0), and the (a_x, a_y, a_z) are represented by A=(a_x−

a_x0)²+(a_y−

a_y0)²+(a_z−

a_z0)².

4. The fall detection device according to claim 1, wherein

if a value of the evaluation function is represented by A, the accelerations in the three axis directions at the steady time are represented by (a_x0, a_y0, a_z0) and the accelerations at the fall determination time are represented by (a_x, a_y, a_z), relations among the A, the (a_x0, a_y0, a_z0), and the (a_x, a_y, a_z) are represented by A=|a_x−

a_x0|+|a_y−

a_y0|+|a_z−

a_z0|.

5. The fall detection device according to claim 1, further comprising:

fall-in-progress detection means that detects whether the fall detection device is placed in a fall-in-progress state, the fall-in-progress state being a state in which a low-gravity state continues for a predetermined time or more, the low-gravity state being a state in which an absolute value of the acceleration falls below a fourth predetermined threshold within a predetermined time or falls within a predetermined range lower than a steady state after the fall start determination means considers that the fall detection device has been put into a fall start state.

6. A magnetic disk drive comprising:

the fall detection device according to claim 5;

a head that records data into a magnetic disk or reads data from the magnetic disk; and

head evacuation means that evacuates the head to an evacuation area when the fall detection device detects the fall-in-progress state.

7. A portable electronic apparatus including the fall detection device according to claim 5 and a device that is allowed to undergo a shock-proof process, the portable electronic apparatus comprising:

shock-proof process means that performs the shock-proof process on the device when the fall detection device detects the fall-in-progress state.

8. The fall detection device according to claim 1, further comprising:

fall-in-progress detection means that detects whether the fall detection device is placed in a fall-in-progress state, the fall-in-progress state being a state in which a low-gravity state continues for a predetermined time or more, the low-gravity state being a state in which a differential value of an absolute value of the acceleration exceeds a fifth predetermined threshold within a predetermined time or falls within a predetermined range near 0 after the fall start determination means considers that the fall detection device has been put into a fall start state.

9. A magnetic disk drive comprising:

the fall detection device according to claim 8;

a head that records data into a magnetic disk or reads data from the magnetic disk; and

head evacuation means that evacuates the head to an evacuation area when the fall detection device detects the fall-in-progress state.

10. A portable electronic apparatus including the fall detection device according to claim 8 and a device that is allowed to undergo a shock-proof process, the portable electronic apparatus comprising:

shock-proof process means that performs the shock-proof process on the device when the fall detection device detects the fall-in-progress state.

11. The fall detection device according to claim 1, further comprising:

fall-in-progress detection means that detects whether the fall detection device is placed in a fall-in-progress state, the fall-in-progress state being a state in which a low-gravity state continues for a predetermined time or more, the low-gravity state being a state in which an absolute value of a differential value of the acceleration falls below a sixth predetermined threshold within a predetermined time or falls within a predetermined range near 0 after the fall start determination means considers that the fall detection device has been put into a fall start state.

12. A magnetic disk drive comprising:

the fall detection device according to claim 11;

a head that records data into a magnetic disk or reads data from the magnetic disk; and

head evacuation means that evacuates the head to an evacuation area when the fall detection device detects the fall-in-progress state.

13. A portable electronic apparatus including the fall detection device according to claim 11 and a device that is allowed to undergo a shock-proof process, the portable electronic apparatus comprising:

shock-proof process means that performs the shock-proof process on the device when the fall detection device detects the fall-in-progress state.

14. A magnetic disk drive comprising:

the fall detection device according to claim 1;

a head that records data into a magnetic disk or reads data from the magnetic disk; and

head evacuation means that evacuates the head to an evacuation area when the fall detection device detects the fall start state.

15. A portable electronic apparatus including the fall detection device according to claim 1 and a device that is allowed to undergo a shock-proof process, the portable electronic apparatus comprising:

shock-proof process means that performs the shock-proof process on the device when the fall detection device detects the fall start state.

16. The fall detection device according to claim 1, wherein the fall start determination means determines the fall determination time by performing first and second monitoring of an acceleration detected by the acceleration detection;

and the first monitoring and the second monitoring are sequentially performed.

17. The fall detection device according to claim 1, wherein the fall start determination means determines the steady time and the accelerations in the three axis directions at the steady time by determining whether or not the absolute value of a differential value of the acceleration exceeds the second predetermined threshold.