Digital flexure beam accelerometer

• US 5,305,640 A
• Filed: 05/01/1992
• Issued: 04/26/1994
• Est. Priority Date: 10/12/1990
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Sampsell, Jeffrey B., Boysel, Robert M.
• Primary Examiner(s): Heyman, John S.
• Application Number:
  US07/877,571
• Time in Patent Office: 725 Days
• Field of Search: 377/23, 307/360, 307/361, 73/517 R, 324/162
• US Class Current: 73/514.16
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 3/0002 Arrangements for avoiding sticking of the flexible or moving parts
• CPC Class Codes: B81C 1/00246 Monolithic integration, i.e. micromechanical structure and electronic processing unit are integrated on the same substrate
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/135 by making use of contacts which are actuated by a movable inertial mass

Abstract

Acceleration is measured using an array of micro-machined elements. The array is configured so each successive element is deflected by a higher acceleration. For each acceleration there will be a set of elements that is deflected. By determining the transition point between deflected and undeflected elements, the acceleration can be measured.

Claims

1. A system for detecting and measuring acceleration comprising the following:

a) a circuit for providing electronic pulses;

b) an array of sensor elements capable of altering said electronic pulses and propagating said altered pulses;

c) a holding circuit for receiving and holding said altered pulses;

d) a comparator circuit for receiving and comparing said altered pulses held by said holding circuit; and

e) an encoding circuit for generating a unique digital word based on said comparison.

2. The system of claim 1 wherein said circuit for providing said pulses is a CMOS shift register.

3. The system of claim 1 wherein each one of said array of sensors comprises:

a) a substrate;

b) address circuitry formed in said substrate;

c) a ground plane located upon said substrate;

d) an electrical contact formed upon said address circuitry;

e) a spacer layer defining a well located over said address circuitry and said electrical contact;

f) a thin layer of metal supported by said spacer layer, said thin layer of metal including hinges supported by said spacer layer, said hinges further defining a central portion connected to said hinges; and

g) a thick layer of metal formed upon said thin metal layer, said thick metal layer patterned to cover only said central portion of said thin metal layer.

4. The system of claim 1 wherein said circuit for receiving and holding altered signals is an array of latches.

5. The system of claim 1 wherein said circuit for receiving and comparing signals is a comparator.

6. The system of claim 1 wherein said circuit for receiving and comparing signals contains a means of detecting and resolving errors.

7. The system of claim 1 wherein said circuit for receiving the resulting signals from the comparison and generating a unique digital word is an NMOS decoder array.

8. A system for detecting acceleration comprising:

an array of sensor elements for detecting the acceleration experienced by said array, wherein each of said sensor elements is fabricated to detect a selected level of acceleration such that for a given acceleration a first group of said sensor elements will indicate an acceleration greater than the threshold of the elements in said first group, and a second group will indicate an acceleration less than the threshold of the elements in said second group;

a holding circuit for receiving and holding the outputs of said array;

a comparator circuit for comparing said outputs of said array held by said holding circuit and for determining the level of acceleration experienced by said sensor array; and

an encoding circuit for generating a unique digital word based on said comparison.

9. The system of claim 8 further comprising a shift register for sequentially strobing the elements of said array.

10. The system of claim 8 wherein said array of sensor elements contains at least two elements fabricated to detect the same level of acceleration, said system further comprising an error detection circuit for detecting stuck elements.

11. The system of claim 10 wherein three sensor elements are fabricated to detect the same level of acceleration, said error detection circuit for signalling when any two of said three sensor elements has deflected.

12. The system of claim 8 wherein said comparator circuit has one output corresponding to each of said various levels of acceleration wherein only one output is active to indicate the level of acceleration detected by said array.

13. The system of claim 8 wherein said encoding circuit has one input corresponding to each of said various levels of acceleration, only one of said inputs being active at any time, wherein said encoding circuit outputs a binary representation of the level of acceleration experienced by said sensor array.

14. A method of measuring acceleration comprising:

deflecting at least one of the elements of an array of sensor elements by accelerating said sensor array;

providing an electrical stimulus to said array of sensor elements;

detecting which of said array of sensor elements is deflected;

determining the magnitude of the acceleration from said detection; and

encoding the acceleration magnitude.

15. The method of claim 14 wherein said array comprises redundant sensor elements, said detecting step further comprises detecting if a majority of said redundant sensor elements are deflected.