Signal processor for inertial measurement using coriolis force sensing accelerometer arrangements
First Claim
1. A signal processing apparatus for determining the amplitudes of components of an output signal obtained from a pair of accelerometers mounted on a moving body, the pair of accelerometers being mounted in alignment with an axis of a coordinate system associated with said moving body and being cyclically displaced in response to a drive signal, said output signal including a first periodic component having a first amplitude equal to an angular rate associated with the moving body, a second periodic component having a second amplitude, and a third component having a third amplitude representing an unmodulated random value sequence, said signal processing apparatus comprising:
- (a) means for repetitively estimating the first, second and third amplitudes;
(b) means for repetitively producing an estimated signal corresponding to the output signal obtained from said pair of accelerometers using said estimated first, second and third amplitudes;
(c) means for repetitively determining an error signal by subtracting the estimated signal from the output signal obtained from said pair of accelerometers; and
(d) means for repetitively revising the three estimated amplitudes as a function of the error signal,(e) the error signal approaching zero as the estimated amplitudes respectively approach the first, second and third amplitudes of the output signal obtained from said pair of accelerometers, the estimated first amplitude being then equal to the angular rate associated with the moving body.
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Accused Products
Abstract
Disclosed is a method and apparatus for processing signals supplied by accelerometer assemblies in which one or more accelerometers are cyclically displaced in a predetermined manner so that signals representing the specific force experienced by the accelerometers and the angular rate experienced by the accelerometers are produced. The signal processor separately estimates the signal components of the signal being processed and provides an error signal by subtracting the estimated signal components from the signal being processed. The error signal is fed back through circuitry that controls the magnitude of the estimated signal components so that the value of each estimated signal component rapidly converges to the value of the signal components of the signal being processed. In an arrangement for determining the angular rate of one or more pair of cyclically displaced accelerometers, the signal processor includes a signal component that is in-phase with the signal that oscillates the accelerometer pair, a signal component that is in phase quadrature with the signal that displaces the accelerometer pair and a signal component that corresponds to random unmodulated additive noise. In this arrangement, a signal summing unit subtracts estimates of each signal component from the signal being processed to supply an error signal equal to (a1 -a1) Cos ωt+(a2 -a2) Sin ωt+(a3 -a3), where a1, a2, and a3, respectively represent the values of the in-phase, quadrature and random noise components of the signal being processed and a1, a2, and a3 represent estimates of those signal component values. To obtain a3, the error signal is scaled and integrated. To obtain the a1 Cos ωt signal estimate, the error signal is multiplied by Cos ωt, and scaled to obtain a signal representative of the derivative with respect to time of a1. This signal is then integrated and multiplied by Cos ωt. The signal component a2 Sin ωt is obtained in a similar manner by multiplying the error signal by Sin ωt, scaling, integrating and multiplying the integrated signal by Sin ωt. In such an arrangement, angular rate is obtained by scaling the a1 signal estimate. In addition, the signal estimates can be used in an inertial navigation system that employs the invention to eliminate misalignment of the accelerometer pairs and to improve system operation by eliminating phase shift between the signal source that oscillates the accelerometer pairs and the signals provided by the accelerometer pairs.
51 Citations
26 Claims
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1. A signal processing apparatus for determining the amplitudes of components of an output signal obtained from a pair of accelerometers mounted on a moving body, the pair of accelerometers being mounted in alignment with an axis of a coordinate system associated with said moving body and being cyclically displaced in response to a drive signal, said output signal including a first periodic component having a first amplitude equal to an angular rate associated with the moving body, a second periodic component having a second amplitude, and a third component having a third amplitude representing an unmodulated random value sequence, said signal processing apparatus comprising:
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(a) means for repetitively estimating the first, second and third amplitudes; (b) means for repetitively producing an estimated signal corresponding to the output signal obtained from said pair of accelerometers using said estimated first, second and third amplitudes; (c) means for repetitively determining an error signal by subtracting the estimated signal from the output signal obtained from said pair of accelerometers; and (d) means for repetitively revising the three estimated amplitudes as a function of the error signal, (e) the error signal approaching zero as the estimated amplitudes respectively approach the first, second and third amplitudes of the output signal obtained from said pair of accelerometers, the estimated first amplitude being then equal to the angular rate associated with the moving body. - View Dependent Claims (2, 3, 4)
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5. Apparatus for determining components of angular rate of a moving body, comprising:
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(a) at least one pair of accelerometers, mounted in alignment with an axis of a coordinate system associated with said moving body, and cyclically displaced in response to a drive signal, producing an output signal of the form a1 f1 (ω
t)+a2 f2 (ω
t)+a3, where f1 (ω
t) is a periodic function of time representative of the cyclic oscillation of said accelerometer pair, f2 (ω
t) is a periodic function of time that is phase quadrature with f1 (ω
t), a1 and a2 respectively denote the amplitudes of said time varying functions f1 (ω
t) and f2 (ω
t), and a3 represents an unmodulated random value sequence;(b) means for reiteratively subtracting a signal form;
af1 (ω
t)+a2 f2 (ω
t)+a3 from said signal of the form a1 f1 (ω
t)+a2 f2 (ω
t)+a3 to provide an error signal where a1, a2, and a3 are signals estimating said amplitude factors a1, a2, and a3, respectively;(c) means for reiteratively multiplying said error signal by k1 f1 (ω
t), where k1 is a predetermined constant, to obtain a signal that is a derivative with respect to time of a1 ;(d) means for reiteratively multiplying said error signal by k2 f2 (ω
t), where k2 is a predetermined constant, to obtain a signal that is a derivative with respect to time of a2 ;(e) means for reiteratively multiplying said error signal by a predetermined constant k3 to obtain a signal that is a derivative with respect to time of a3 ; (f) means for reiteratively integrating said signal that is a derivative with respect to time of a1 to obtain a1 ; (g) means for reiteratively integrating said signal that is a derivative with respect to time of a2 to obtain a2 ; (h) means for reiteratively integrating said signal that is a derivative with respect to time of a3 to obtain a3 ; (i) means for reiteratively multiplying a1 by f1 (ω
t);(j) means for reiteratively multiplying a2 by f2 (ω
t); and(k) means for multiplying the estimated signal a1 by a predetermined scale factor to produce a signal that corresponds to said angular rate of the moving body as the error signal approaches a minimum and estimated signals a1, a2, and a3 approach the values of amplitudes a1, a2 and a3, respectively, with successive iterations by the above-recited means (b) through (j). - View Dependent Claims (6, 7, 8)
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9. An adaptive signal processor for determining an angular rate component of a moving body from an output signal that is obtained from at least one pair of accelerometers that are mounted in alignment with one axis of a coordinate system associated with said moving body, each said pair of accelerometers being cyclically oscillated by a signal source that drives said one or more accelerometer pairs, said output signal obtained from at least one pair of said accelerometers being of the form a1 f1 (ω
- t)+a2 f2 (ω
t)+a3, where f1 (ω
t) is a first periodic function of time representative of the cyclic oscillation each said accelerometer pair, f2 (ω
t) is a second periodic function of time that is in phase quadrature with f1 (ω
t), a1 and a2 respectively denote the amplitudes of said time varying functions f1 (ω
t) and f2 (ω
t) and a3 represents an unmodulated random value sequence said signal processor comprising;a signal summing unit, said signal summing unit including a first input terminal connected for receiving said output signal of the form a1 f1 (ω
t)+a2 f2 (ω
t)+a3, a second input terminal for receiving a signal a1 f1 (ω
t), a third input terminal for receiving a signal a2 f2 (ω
t) and having a fourth input terminal for receiving a signal a3 where a1, a2 and a3 are estimates of said amplitude factors a1, a2 and a3, said signal summing unit being configured and arranged for supplying a first error signal equal to the difference between the output signal applied to said first input terminal and the signals applied to said second, third and fourth input terminals;first and second multiplier circuits, each of said first and second multiplier circuits having an input terminal connected for receiving said first error signal; a first signal source for generating a signal f1 (ω
t), said first signal source being connected for supplying said signal to a second input terminal of said first multiplier circuit;a second signal source for supplying a signal f2 (ω
t), said second signal source being connected for supplying said signal to a second input terminal of said second multiplier;first and second scaling means, said first scaling means being connected for receiving the signal supplied by said first multiplier circuit, said second scaling means being connected for receiving the signal supplied by said second multiplier circuit; first and second integrator circuits, said first integrator circuit being connected for receiving the signal supplied by said first scaling means, and being connected for supplying a signal representative of a1, said second integrator circuit being connected for receiving the signal supplied by said second scaling means and being connected for supplying a signal representative of a2 ; third and fourth multiplier circuits, said third multiplier circuit being connected for receiving said signal a1 from said first integrator circuit and being connected for receiving said signal supplied by said first signal source, said fourth multiplier circuit being connected for receiving said signal a2 from said second integrator circuit and being connected for receiving said signal supplied by said second signal generator, said third and fourth multiplier circuits each having an output terminal, the output terminal of said third multiplier circuit being connected to said second input terminal of said signal summing unit, said output terminal of said fourth multiplier circuit being connected to said third input terminal of said signal summing unit; a third scaling means connected for receiving said first error signal, said third scaling means being operative to amplify said first error signal by a predetermined constant k3 ; a third integrator circuit connected for receiving the signal supplied by said third scaling means and connected for supplying the output signal of said third integrator circuit to said fourth input terminal of said signal summing unit, wherein the signal summing unit reiteratively determines the first error signal, the first error signal approaching a minimum value with successive iterations, the signals a1, a2 and a3 respectively approaching equivalency with amplitude factors a1, a2 and a3. - View Dependent Claims (10, 11, 12, 13, 14)
- t)+a2 f2 (ω
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15. An inertial measurement unit for measuring specific force and angular rate components of a moving body, said inertial measurement unit comprising:
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an accelerometer assembly including at least three pairs of accelerometers, each of said pairs of accelerometers being mounted for measuring specific force along one axis of a Cartesian coordinate system that is fixed to said moving body and being mounted for cyclic displacement of the form f1 (ω
t);accelerometer drive means connected to said accelerometer assembly for cyclically dispacing each of said three pairs of accelerometers; a preprocessor unit connected for receiving said signal supplied by each of said accelerometers, said preprocessor unit including means for adding the signals supplied by each said pair of accelerometers and means for subtracting the signals supplied by each said pair of accelerometers to generate first, second and third signals representative of the specific force along each coordinate axis of said coordinate system and to generate first, second and third angular rate signals of the form a1 f1 (ω
t)+a2 f2 (ω
t)+a3, where f2 (ω
t) is a periodic signal that is in phase quadrature with said signal f1 (ω
t), and where a1 and a2 denote the amplitudes of said periodic signals f1 (ω
t) and f2 (ω
t) respectively and a3 represents an unmodulated random value sequence with the amplitude a1 of each of said signals being representative of the angular rate associated with a separate axis of said coordinate system of said moving body; andfirst, second and third signal processing circuits, said first, second and third signal processing circuits being connected for receiving a different one of said angular rate signals supplied by said preprocessor unit and for supplying a signal representative of the angular rate for a different one of said axes of said coordinate system, each of said first, second and third signal processing circuits including (a) a signal summing unit, said signal summing unit including a first input terminal connected for receiving said signal of the form a1 f1 (ω
t)+a2 f2 (ω
t)+a3, a second input terminal for receiving a signal a1 f1 (ω
t), a third input terminal for receiving a signal a2 f2 (ω
t) and having a fourth input terminal for receiving a signal a3 where a1, a2 and a3 are estimates of said amplitudes a1, a2 and a3, said signal summing unit being configured and arranged for supplying a first error signal equal to the difference between the signal applied to said first input terminal and the signals applied to said second, third and fourth input terminals;(b) first and second multiplier circuits, each of said first and second multiplier circuits having an input terminal connected for receiving said first error signal; (c) a first signal source for generating a signal f1 (ω
t), said first signal source being connected for supplying said signal to a second input terminal of said first multiplier circuit;(d) a second signal source for supplying a signal f2 (ω
t), said second signal source being connected for supplying said signal to a second input terminal of said second multiplier;(e) first and second scaling means, said first scaling means being connected for receiving the signal supplied by said first multiplier circuit, said second scaling means being connected for receiving the signal supplied by said second multiplier circuit; (f) first and second integrator circuits, said first integrator circuit being connected for receiving the signal supplied by said first scaling means, and being connected for supplying a signal representative of a1, said second integrator circuit being connected for receiving the signal supplied by said second scaling means and being connected for supplying a signal representative of a2 ; (g) third and fourth multiplier circuits, said third multiplier circuit being connected for receiving said signal a1 from said first integrator circuit and being connected for receiving said signal supplied by said first signal source, said fourth multiplier circuit being connected for receiving said signal a2 from said second integrator circuit and being connected for receiving said signal supplied by said second signal generator, said third and fourth multiplier circuits each having an output terminal, the output terminal of said third multiplier circuit being connected to said second input terminal of said summing unit, said output terminal of said fourth multiplier circuit being connected to said third input terminal of said signal summing unit; (h) a third scaling means connected for receiving said first error signal, said third scaling means for amplifying said first error signal by a predetermined constant k3 ; and (i) a third integrator circuit connected for receiving the signal supplied by said third scaling unit and connected for supplying the output signal of said integrator circuit to said fourth input terminal of said summing unit. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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Specification