Method and apparatus for storing velocity data
First Claim
1. A method for recovering velocity data for a body from an attached accelerometer following a power disruptive event that interrupts electrical power supplied to the accelerometer, said accelerometer including two acceleration sensors, one of the acceleration sensors being characterized by a periodic output having a frequency that increases and the other by a periodic output having a frequency that decreases in response to an acceleration acting on the body along a sensitive axis of the accelerometer, each acceleration sensor having a scale factor associated with an output signal from it, said method comprising the steps of:
- (a) providing selected different scale factors K1 and K2 to define output signals produced by the two acceleration sensors, said output signals varying as a function of said acceleration;
(b) determining a first phase difference, Δ
Φ
(t1), between a component of the output signals of the two acceleration sensors that changes due to the acceleration, prior to the power disruptive event, at a first time, t1 ;
(c) determining a second phase difference, Δ
Φ
(t2), between said components of the output signals of the two acceleration sensors, after the power disruptive event, at a second time, t2 ; and
(d) following the power disruptive event, determining a change in velocity of the body between times t1 and t2 as a function of the scale factors and the first and second phase differences of the output signals.
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Abstract
A method and apparatus for determining a change in velocity of a body following a power disruptive event. An accelerometer (10, 50) includes quartz crystals (16 and 18, 60 and 62), which produce output signals indicative of the acceleration to which a body connected to the accelerometer is subjected. The acceleration measured is directed along the sensitive axis of the accelerometer. The quartz crystals are selected to have different scale factors, K1 and K2, which define the change in frequency of the quartz crystal from its no-load resonant frequency as a force is applied to it. The quartz crystals are connected between a supporting case (14) and a proof mass (12) so that a given acceleration applied to the proof mass along its sensitive axis causes one of the crystals to experience a tension force and the other to experience a compression force. A processor (86) determines the change in velocity of the body as a function of the change in phase of the signals produced by the quartz crystals at a time, t1, and a subsequent time, t.sub. 2, and further in response to the scale factors, K1 and K2. Since the quartz crystals continue to oscillate during a brief interruption of their driving signal, the change in velocity of the body during a time interval from t1 to t2 can be determined after recovery from a brief power disruptive event that has occurred during that interval.
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Citations
20 Claims
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1. A method for recovering velocity data for a body from an attached accelerometer following a power disruptive event that interrupts electrical power supplied to the accelerometer, said accelerometer including two acceleration sensors, one of the acceleration sensors being characterized by a periodic output having a frequency that increases and the other by a periodic output having a frequency that decreases in response to an acceleration acting on the body along a sensitive axis of the accelerometer, each acceleration sensor having a scale factor associated with an output signal from it, said method comprising the steps of:
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(a) providing selected different scale factors K1 and K2 to define output signals produced by the two acceleration sensors, said output signals varying as a function of said acceleration; (b) determining a first phase difference, Δ
Φ
(t1), between a component of the output signals of the two acceleration sensors that changes due to the acceleration, prior to the power disruptive event, at a first time, t1 ;(c) determining a second phase difference, Δ
Φ
(t2), between said components of the output signals of the two acceleration sensors, after the power disruptive event, at a second time, t2 ; and(d) following the power disruptive event, determining a change in velocity of the body between times t1 and t2 as a function of the scale factors and the first and second phase differences of the output signals. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for determining a change in velocity of a body using a vibrating beam accelerometer that includes opposed piezoelectric crystals arranged such that an acceleration acting on the body and directed along a sensitive axis of the accelerometer subjects one of the piezoelectric crystals to compression and the other to tension, the method comprising the steps of:
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(a) biasing at least one of the piezoelectric crystals so that they have different scale factors, K1 and K2, where the scale factors define the relationship between the acceleration and a component of a periodic output signal produced by each piezoelectric crystal; (b) at successive intervals of time Δ
t, determining phase differences Δ
Φ
(tn) between said components of the periodic output signals produced by the two piezoelectric crystals, where a frequency of the component varies in response to the acceleration acting on the body; and(c) determining the change in velocity of the body, Δ
V, as a function of the change in the phase differences determined at two different points in time, tn-1 and tn, and as a function of the scale factors, K1 and K2. - View Dependent Claims (9, 10, 11, 12)
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13. An accelerometer capable of determining the change in velocity, Δ
- V, of a body to which the accelerometer is attached, from a time tn-1, to a time tn, comprising;
two opposed acceleration sensitive elements, each operative to produce a periodic output signal having a component that varies in frequency as a function of an acceleration directed along a sensitive axis of the accelerometer, as described by a scale factor associated with each acceleration sensitive element, said acceleration causing one of the acceleration sensitive elements to be subjected to a force of compression and the other to be subjected to a force of tension, said acceleration sensitive elements being provided with different scale factors K1 and K2, so that said components of their periodic output signals have a time varying phase relationship; and
processor means for determining a difference in phase Δ
Φ
(tn-1) between said components of output signals from the acceleration sensitive elements at the time tn-1, and a difference in phase Δ
Φ
(tn) of the output signals at the time tn, and for determining the change in velocity Δ
V of the body as a function of both the differences in phase and the scale factors. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
- V, of a body to which the accelerometer is attached, from a time tn-1, to a time tn, comprising;
Specification