Method of measuring the amplitude and frequency of an acceleration

• US 5,610,337 A
• Filed: 03/09/1995
• Issued: 03/11/1997
• Est. Priority Date: 04/30/1992
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Nelson, William E.
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): Ashraf, Nashmiya
• Application Number:
  US08/401,668
• Time in Patent Office: 733 Days
• Field of Search: 73/517 R, 73/517 A, 73/651, 73/661, 73/514.29, 73/514.02, 340/669, 200/61.45 R, 200/61.46, 200/61.48, 200/61.49, 200/61.51, 377/23, 307/121, 307/117
• US Class Current: 73/651
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/0888 for indicating angular acceleration
• CPC Class Codes: G01P 15/135 by making use of contacts which are actuated by a movable inertial mass
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends

Abstract

A digital accelerometer manufactured from arrays 11a-11e of micro-mechanical sensing elements 12. The sensing elements 12 of different arrays 11a-11e are designed for detecting acceleration in a particular rotational or translational direction, such that their response to acceleration in other directions is minimized. Further, the sensing elements 12 have size and proof mass parameters that may be adjusted to vary their frequency response and sensitivity to amplitude of acceleration. Arrays 11a-11e of sensing elements 12 provide detection of a range of frequency levels and amplitudes at each frequency. At an appropriate frequency and amplitude of an applied acceleration, a sensing element 12 moves to contact an electrode 126, producing an electrical signal, which may be stored as a data bit. The sensing elements, when used in combination with memory 15 and processing devices 16, results in an intelligent accelerometer whose fabrication techniques are compatible with those used for the digital processing devices.

Claims

1. A method of measuring the amplitude and frequency of a rotational acceleration comprising the steps of:

subjecting an array of micro-mechanical sensing elements to a rotational acceleration event, said micro-mechanical sensing elements each comprising a deflectable member and a corresponding contact electrode, said deflectable members of said micro-mechanical sensing elements deflecting to contact said corresponding contact electrodes in response to a rotational acceleration having a predetermined frequency and amplitude;

generating an electrical signal to indicate which of said deflectable members in said array are in contact with said corresponding contact electrodes; and

detecting said electrical signal to determine the frequency and amplitude of said rotational acceleration event.

2. The method of claim 1, wherein said step of generating comprises generating a data bit from each micro-mechanical sensing element in a row of said array wherein each micro-mechanical sensing element in said row has a different resonant frequency, and generating a data bit from each micro-mechanical sensing element in a column of said array wherein each micro-mechanical sensing element in said column has a different sensitivity to amplitude of acceleration.

3. The method of claim 1, further comprising the step of comparing said electrical signal with a previously stored electrical signal to determine whether a given acceleration has occurred.

4. The method of claim 1, wherein said micro-mechanical sensing elements in said array are torsion beam sensing elements for detecting rotational acceleration about a horizontal axis, each of said torsion beam sensing elements comprised of two torsion hinges, and a beam attached to said torsion hinges, wherein said micro-mechanical sensing elements in said array differ from one another by at least one parameter from the group consisting of hinge length, hinge thickness, hinge width, beam length, beam width, and beam thickness, such that each micro-mechanical sensing element in said array responds to a rotational acceleration having a unique combination of frequency and amplitude.

5. The method of claim 1, wherein said micro-mechanical sensing elements in said array are torsion beam sensing elements for detecting rotational acceleration about a horizontal axis, each of said torsion beam sensing elements comprised of two torsion hinges, a beam having two ends, said beam attached to said torsion hinges, and a mass attached to each end of said beam, wherein said micro-mechanical sensing elements in said array differ from one another by at least one parameter from the group consisting of hinge length, hinge thickness, hinge width, beam length, beam width, beam thickness, mass length, mass width, mass thickness, and mass density, such that each micro-mechanical sensing element in said array responds to a rotational acceleration having a unique combination of frequency and amplitude.

6. A method of measuring the amplitude and frequency of a rotational acceleration comprising the steps of:

providing at least two accelerometer arrays, each of said accelerometer arrays comprising sensing elements arranged as a sensing element array, each of said accelerometer arrays further comprising contact electrodes, each of said sensing elements able to deflect in response to a rotational acceleration having a unique frequency and amplitude and to contact at least one of said contact electrodes, each of said at least two accelerometer arrays configured for detecting rotational acceleration about a unique axis;

subjecting said at least two accelerometer arrays to a rotational acceleration force, said acceleration force causing certain of said sensing elements in said at least two accelerometer arrays to deflect and to contact at least one contact electrode in said at least two accelerometer arrays;

generating an electrical signal indicating which of said sensing elements in said at least two accelerometer arrays is in contact with at least one contact electrode in said at least two accelerometer arrays; and

detecting said electrical signal to determine the frequency and amplitude of said rotational acceleration force.

7. A method of measuring the amplitude and frequency of a rotational acceleration comprising the steps of:

providing an accelerometer array comprised of;

micro-mechanical sensing elements arranged as a sensing element array, each of said micro-mechanical sensing elements having a resonant frequency and an amplitude threshold;

contact electrodes positioned such that when one of said micro-mechanical sensing elements is subjected to a rotational acceleration having a frequency and amplitude sufficient to deflect said one micro-mechanical sensing element, said one micro-mechanical sensing element deflects and contacts one of said contact electrodes; and

memory cells arranged as a memory array for storing data indicating which of said micro-mechanical sensing elements are in contact with one of said contact electrodes;

deflecting a subset of said micro-mechanical sensing elements in response to a rotational acceleration event; and

reading said data stored in said memory cells from at least a portion of said memory array to determine the amplitude and frequency of said acceleration event.

8. The method of claim 7 further comprising the step of:

comparing data stored in said memory cells with previously stored data to determine whether a given rotational acceleration has occurred.

9. A digital accelerometer for detecting rotational acceleration about a first axis, comprising:

a first array of sensing elements for detecting rotational acceleration around said first axis, wherein each of said sensing elements has a tilting beam attached to at least one corresponding torsion hinge, wherein each said tilting beam is in a plane parallel to said first axis and is operable to tilt toward an underlying contact electrode when each said sensing element is subjected to acceleration about said first axis, and wherein said first array has rows and columns of said sensing elements, said sensing elements adjusted so that said first array detects a range of frequency levels and a range of amplitudes of acceleration at each of said frequency levels;

wherein said tilting beams and said contact electrodes of said first array are generally in parallel planes, and wherein each of said tilting beams has two tilted states and an untilted state, depending on whether said tilting beam has been tilted counterclockwise, clockwise, or not tilted.

10. The accelerometer of claim 9, wherein each said tilting beam is centered over and supported by each said corresponding torsion hinge, which permits each said tilting beam to tilt in either of two directions toward each said underlying contact electrode.

11. The accelerometer of claim 9, wherein each said tilting beam is suspended between two torsion hinges, one hinge at each opposing end of each said tilting beam, which permits each said tilting beam to tilt in either of two directions toward each said underlying contact electrode.

12. The accelerometer of claim 9, and further comprising a second array of sensing elements similar in structure to said first array, said second army of sensing elements aligned orthogonally to said first array for detecting rotational acceleration around a second axis.

13. The accelerometer of claim 9, and further comprising a pair of reset electrodes associated with each of said sensing elements for restoring each said tilting beam to an untilted position.

14. The accelerometer of claim 9, and further comprising at least one memory cell associated with each sensing element, said at least one memory cell for storing an electrical signal from said contact electrodes.

15. The accelerometer of claim 9 further comprising at least one reset electrode underlying each said tilting beam, each said reset electrode for freeing each said tilting beam should each said tilting beam become stuck to each said contact electrode.

16. The accelerometer of claim 9 further comprising at least one test electrode underlying each said tilting beam, each .said test electrode for deflecting each said tilting beam in response to a voltage signal applied to each said test electrode.

17. An accelerometer for measuring rotational acceleration about an axis, said accelerometer comprising:

a first array of sensing elements fabricated on a substrate, each of said sensing elements comprising;

at least one torsion hinge, said torsion hinge for generating a restoring torque;

a tilting beam attached to and suspended away from said substrate by said torsion hinge, said tilting beam having a length from a first end to a second, opposite end, said tilting beam having a moment of inertia, said tilting beam operable for tilting toward said substrate in response to a rotational acceleration of a predetermined frequency and amplitude;

at least one contact electrode on said substrate proximate said tilting beam, said contact electrode for contacting said tilting beam when said tilting beam is tilted toward said substrate;

at least one reset electrode fabricated on said substrate proximate said tilting beam, said reset electrode for freeing said tilting beam should said tilting beam become stuck to said contact electrode; and

wherein said sensing elements in said array of sensing elements are responsive unique combinations of frequency and magnitude such that a given acceleration event deflects a first portion of said sensing elements m said array of said sensing elements and does not deflect a second portion of said sensing elements in said first array of said sensing elements.

18. The accelerometer of claim 17, having each said tilting beam supported by two of said torsion hinges such that each said tilting beam can tilt in either of two directions toward one of two said contact electrodes.

19. The accelerometer of claim 17 further comprising:

a second array of said sensing elements fabricated on said substrate, said second array of sensing elements aligned orthogonally to said first array of sensing elements for detecting rotational acceleration about an orthogonal axis.

20. The accelerometer of claim 17 further comprising:

at least one memory cell associated with each said sensing element for storing an electrical signal from said contact electrodes.

21. An accelerometer for measuring rotational acceleration about an axis, said accelerometer comprising:

a first array of sensing elements fabricated on a substrate, each of said sensing elements comprising;

at least one torsion hinge, said torsion hinge for generating a restoring torque;

a tilting beam attached to and suspended away from said substrate by said torsion hinge, said tilting beam having a length from a first end to a second, opposite end, said tilting beam having a moment of inertia, said tilting beam operable for tilting toward said substrate in response to a rotational acceleration of a predetermined frequency and amplitude;

at least one contact electrode on said substrate proximate said tilting beam, said contact electrode for contacting said tilting beam when said tilting beam is tilted toward said substrate;

at least one test electrode fabricated on said substrate proximate said tilting beam, said test electrode operable to deflect said tilting beam such that said tilting beam contacts said contact electrode when a test voltage is applied to said test electrode; and

wherein said sensing elements in said first array of sensing elements are responsive unique combinations of frequency and magnitude such that a given acceleration event deflects a first portion of said sensing elements in said array of said sensing elements and does not deflect a second portion of said sensing elements in said array of said sensing elements.

22. The accelerometer of claim 21, having each said tilting beam supported by two of said torsion hinges such that each said tilting beam can tilt in either of two directions toward one of two said contact electrodes.

23. The accelerometer of claim 21 further comprising:

a second array of said sensing elements fabricated on said substrate, said second array of sensing elements aligned orthogonally to said first array of sensing elements for detecting rotational acceleration about an orthogonal axis.

24. The accelerometer of claim 21 further comprising:

at least one memory cell associated with each said sensing element for storing an electrical signal from said contact electrodes.