US 4,799,385 A · Angular rate sensor with phase shift correction

Abstract

A Coriolis rate sensor comprising first and second accelerometers mounted with their force sensing axes parallel to a common sensing axis. The accelerometers are vibrated along arcs in response to a periodic drive signal at a first frequency, each arc being tangent to a vibration axis normal to the sensing axis. The accelerometer output signals are demodulated to determine angular rate, as well as to detect the phase shift between the drive signal and the periodic compounds of the output signals. In one arrangement, the detected phase shifts are used to drive a phase servo that tends to reduce the bias error caused by interaction between the phase shifts and misalignments of the accelerometers with respect to the sensing axis. In another arrangement, the phase shifts are used to calculate a bias term for correcting the measured angular rate. A single accelerometer embodiment is also described.

A device for generating an angular rate signal representing the angular rate of rotation of a body, the device comprising:

an accelerometer assembly comprising a first accelerometer having a first force sensing axis and including means for producing a first output signal indicative of acceleration along the first force sensing axis, a second accelerator having a second force sensing axis and including means for producing a second output signal indicative of acceleration along the second force sensing axis, means for mounting the first and second accelerometers such that their force sensing axes are both parallel to a common sensing axis and such that the accelerometers can be vibrated along respective arcs each of which is tangent to a vibration axis normal to the sensing axis, and drive means connected to receive a periodic drive signal having a first frequency, the drive means including means for vibrating the accelerometers along the respective arcs at the first frequency, such that each output signal includes a component at a second frequency equal to twice the first frequency;
timing/control means including means for generating a periodic master timing signal, means for generating the drive signal such that the drive signal bears a predetermined phase relationship to the master timing signal, means for generating a first timing signal such that the first timing signal represents a first rate component at the first frequency in quadrature phase with respect to the drive signal and a first phase shift component at the second frequency in phase with the drive signal, means for delaying the first timing signal by a first time delay that is a predetermined function of a first delay signal to thereby produce a delayed first timing signal, and means for generating a second timing signal such that the second timing signal represents a second rate component at the first frequency in quadrature phase with respect to the drive signal and a second phase shift component at the second frequency in phase with the drive signal, and means for delaying the second timing signal by a second time delay that is a predetermined function of a second delay signal to thereby produce a delayed second timing signal;
first demodulation means connected to receive the first output signal and the delayed first timing signal, and including means for demodulating the first output signal using the first rate component to produce a first rate signal, and means for demodulating the first output signal using the first phase shift component to produce a first phase shift signal;
second demodulation means connected to receive the second output signal and the delayed second timing signal, and including means for demodulating the second output signal using the second rate component to produce a second rate signal, and means for demodulating the second output signal using the second phase shift component to produce a second phase shift signal;
rate channel means for receiving the first and second rate signals and for producing the angular rate signal indicating angular rate about an axis normal to the sensitive and vibration axes;
and
delay control means connected to receive the first and second phase shift signals, including means for producing a first offset signal representing the estimated difference, at the second frequency, between the phase shift corresponding to the first time delay and the phase shift between the drive signal and the periodic components of the first output signal, means for comparing the first offset signal to the first phase shift signal to produce a first error signal representing the difference therebetween, means for producing a second offset signal representing the estimated difference, at the second frequency, between the phase shift corresponding to the second time delay and the phase shift between the drive signal and the periodic components of the second output signal, means for comparing the second offset signal to the second phase shift signal to produce a second error signal representing the difference therebetween, and means responsive to the first and second error signals for producing the first and second delay signals such that the difference between the first and second error signals is driven towards a null value.

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Angular rate sensor with phase shift correction

Life of this patent

Angular rate sensor with phase shift correction

Life of this patent

Abstract

Claims19