Vibrating beam accelerometer with velocity change output

• US 4,712,427 A
• Filed: 09/17/1986
• Issued: 12/15/1987
• Est. Priority Date: 10/21/1985
• Status: Expired due to Term

• Current Assignee: Alliedsignal Inc.
• Original Assignee: Sundstrand Data Control, Inc.
• Inventors: Peters, Rex B.
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US06/908,356
• Time in Patent Office: 454 Days
• Field of Search: 73/517 AV, 73/510, 73/DIG. 1, 73/503, 73/862.59, 364/565, 364/566
• US Class Current: 73/514.29
• CPC Class Codes: G01P 15/097 by vibratory elements

Abstract

A dual sensor, frequency output accelerometer that does not require either high sampling rates or mechanical matching of the sensors to achieve high levels of accuracy. In one embodiment, the accelerometer comprises a first sensor (12, 14, 16) that produces an output signal S₁ having a frequency f₁ related to acceleration along the sensitive axis, and a second sensor (18, 20, 22) that produces a second signal S₂ having a frequency f₂ related to acceleration along the sensitive axis, the sensors being arranged such that a given acceleration causes the frequency of one output signal to increase and the frequency of the other output signal to decrease. Velocity change ΔV during time interval T is determined according to:

ΔV=A[Δφ+FT+BΣφ]

where A, F and B are constants, Δφis the difference between the phase changes of the output signals over time interval T, and Σφ is the sum of the phase changes of the output signals over time interval T. Higher order correction terms are also described for very high precision applications. Also disclosed is an accelerometer or measuring velocity change during a time interval that includes a subinterval during which electrical power is unavailable.

Claims

1. An accelerometer for measuring velocity change along a sensitive axis, comprising:

a pair of acceleration sensors, each sensor being operative to produce an output signal having a frequency related to the acceleration along the sensitive axis, the sensors being arranged such that a given acceleration along the sensitive axis causes the frequency of one output signal to increase and the frequency of the other output signal to decrease; and

means for determining the velocity change Δ

V along the sensitive axis during a selected time interval in accordance with the relation;

space="preserve" listing-type="equation">Δ

V=A[Δ

φ

+FT+BΣ

φ

]

where A, F and B are nonzero constants, T is the length of said time interval, Δ

φ

is the difference between the phase changes of the output signals over said time interval and Σ

φ

is the sum of the phase changes of the output signals over said time interval.

2. The accelerometer of claim 1, wherein each sensor comprises a vibrating beam force sensing element, and wherein each force sensing element is connected to a proof mass constrained to have a single degree of freedom defining the sensitive axis.

3. The accelerometer of claim 1, wherein the means for determining the velocity change includes means for determining the relative phase of one output signal with respect to the other output signal at times t_n-1 and t_n that correspond to the beginning and ending of said time interval respectively.

4. The accelerometer of claim 3, wherein the means for determining the relative phase comprises means for determining the time difference between preselected periodic characteristics of the output signals, means for determining the period of said other output signal, and means for determining a ratio value corresponding to the quotient of said time difference divided by said period.

5. The accelerometer of claim 3, wherein the means for determining the velocity change includes means for determining the number of complete cycles of each output signal that occur during said time interval.

6. The accelerometer of claim 5, wherein the means for determining the number of complete cycles of each output signal includes means for producing a series of enable signals after every N₁ complete cycles of one of the output signals, and means for counting the number of full cycles of the other output signal that occur between successive enable signals.

7. An accelerometer for measuring velocity change along a sensitive axis during a time interval from t₁ to t₂ that includes a subinterval during which electrical power is unavailable, comprising:

a pair of acceleration sensors, each sensor being operative to produce an output signal having a frequency related to the acceleration along the sensitive axis, the sensors being arranged such that a given acceleration along the sensitive axis causes the frequency of one output signal to increase and the frequency of the other output signal to decrease; and

means for determining the velocity change Δ

V along the sensitive axis during said time interval, including means for determining and storing a relative phase value corresponding to the relative phase of one of the output signals with respect to the other output signal at each of times t₁ and t₂, and means for determining Δ

V in accordance with the relationship;

space="preserve" listing-type="equation">Δ

V=2π

AΔ

W

where A is a calibration constant and Δ

W is the change in said relative phase between times t₁ and t₂.

8. The accelerometer of claim 7, wherein each sensor comprises a vibrating beam force sensing element, and wherein each force sensing element is connected to a proof mass constrained to have a single degree of freedom defining the sensitive axis.

9. The accelerometer of claim 7, wherein the means for determining and storing the relative phase value comprises means for determining the time difference between preselected periodic characteristics of the output signals, means for determining the period of said other output signal, and means for determining a ratio value corresponding to the quotient of said time difference divided by said period.

10. The accelerometer of claim 7, wherein the means for determining the velocity change includes means for adjusting Δ

W at time t₂ by ±

1 such that Δ

W for said time interval does not exceed ±

0.5.

11. An accelerometer for measuring velocity change along a sensitive axis during a time interval from t_n-1 to t_n that includes a subinterval during which electrical power is unavailable comprising:

a pair of first sensors, each first sensor being operative to produce a first output signal having a frequency related to the acceleration along the sensitive axis, the first sensors being arranged such that a given acceleration along the sensitive axis causes the frequency of one first output signal to increase and the frequency of the other first output signal to decrease;

a pair of second sensors, each second sensor being operative to produce a second output signal having a frequency related to the acceleration along the sensitive axis, the second sensors being arranged such that a given acceleration along the sensitive axis causes the frequency of one second output signal to increase and the frequency of the other second output signal to decrease;

means for determining and storing a first relative phase value corresponding to the relative phase of one of the first output signals with respect to the other first output signals at each of times t_n-1 and t_n ;

means for determining and storing a second relative phase value corresponding to the relative phase of one of the second output signals with respect to the other second output signal at each of times t_n-1 and t_n ;

means for determining values for i and j such that;

space="preserve" listing-type="equation">A.sub.1 (Δ

W.sub.1 +i)=A.sub.2 (Δ

W.sub.2 +j)

where i and j are integers, A₁ and A₂ are scale constants for the first and second pairs of sensors, respectively, and are not integer multiples of one another, Δ

W₁ is the difference between the first relative phase value at time t_n-1 and the first relative phase value at time t_n, and Δ

W₂ is the difference between the second relative phase value at time t_n-1 and the second relative phase value at time t_n, whereby velocity change Δ

V between times t_n-1 and t_n may be determined as;

space="preserve" listing-type="equation">Δ

V=2π

A.sub.1 (Δ

W.sub.1 +i)=2π

A.sub.2 (Δ

W.sub.2 +j).

12. An accelerometer for measuring velocity change along a sensitive axis, comprising:

a pair of acceleration sensors, each sensor being operative to produce an output signal having a frequency related to the acceleration along the sensitive axis, the sensors being arranged such that a given acceleration along the sensitive axis causes the frequency of one output signal to increase and the frequency of the other output signal to decrease; and

means for determining the velocity change Δ

V along the sensitive axis during a selected time interval in accordance with the relation;

space="preserve" listing-type="equation">Δ

V=A.sub.1 [(1-A.sub.2 Σ

φ

)Δ

φ

+A.sub.3 (Δ

φ

).sup.3 +A.sub.4 Σ

φ

+A.sub.5 (Δ

φ

).sup.2 +A.sub.0 ]

where A₀, A₁ and A₄ are nonzero constants, A₂, A₃ and A₅ are constants at least one of which is nonzero, T is the length of said time interval, Δ

φ

is the difference between the phase changes of the output signals over said time interval, and Σ

φ

is the sum of the phase changes of the output signals over said time interval.

13. The accelerometer of claim 12, wherein the means for determining the velocity change includes means for determining the relative phase of one output signal with respect to the other output signal at times t_n-1 and t_n that correspond to the beginning and ending of said time interval respectively.

14. The accelerometer of claim 13, wherein the means for determining the relative phase comprises means for determining the time difference between preselected periodic characteristics of the output signals, means for determining the period of said other output signal, and means for determining a ratio value corresponding to the quotient of said time difference divided by said period.