Synchronous FM digital detector

• US 4,712,426 A
• Filed: 10/21/1985
• Issued: 12/15/1987
• Est. Priority Date: 10/21/1985
• Status: Expired due to Term

• Current Assignee: Alliedsignal Inc. (Honeywell International Inc.)
• Original Assignee: Sundstrand Data Control, Inc. (Rtx Corporation)
• Inventors: Peters, Rex B.
• Primary Examiner(s): Levy, Stewart J.
• Assistant Examiner(s): Chapman, Jr., John E.
• Application Number:
  US06/789,657
• Time in Patent Office: 785 Days
• Field of Search: 73/505, 73/510, 73/517 R, 73/517 AV, 329/107, 329/110, 329/126
• US Class Current: 73/504.04
• CPC Class Codes: G01C 19/5614 Signal processing
• CPC Class Codes: G01C 19/5776 Signal processing not specific to any of the devices covered by groups G01C19/5607 - G01C19/5719

Abstract

A system for determining angular rate of rotation of a body about a rate axis. In one arrangement, the system comprises first (10) and second (12) accelerometers, movement apparatus and processor. The first and second accelerometers have their sensitive axes (16, 18) parallel to a sensing axis that is in turn perpendicular to the rate axis. The first and second accelerometers produce first and second output signals (a₁, a₂), each output signal having a frequency corresponding to the acceleration experienced by the respective accelerometer along its sensitive axis. The movement apparatus includes a generator (68) for producing a periodic movement signal and a mounting system (14) responsive to the movement signal for periodically moving the accelerometers along a movement axis perpendicular to the rate and sensing axes, such that each output signal includes a periodic Coriolis component. The processor includes a device (75) for producing a reference signal that defines one or more first time periods during which the Coriolis components have one polarity and one or more second time periods during which the Coriolis components have the opposite polarity. The first and second time periods together span one or more complete periods of the movement signal. The processor further comprises counters (71, 72) for determining, for each output signal, a phase value representing the difference between the phase change of the output signal during the first time periods and the phase change of the output signal during the second time periods. The processor further includes a microprocessor (80) for determining from the phase values a value representing the angular rate of rotation of the body about the rate axis. In a second arrangement, a single accelerometer is periodically moved along the movement axis.

Claims

1. A system for determining the angular rate of rotation of a body about a rate axis, the system comprising:

first and second accelerometers having their sensitive axes parallel to a sensing axis perpendicular to the rate axis, the first and second accelerometers being adapted to produce respective first and second output signals, each output signal having a frequency corresponding to the acceleration experienced by the respective accelerometer along its sensitive axis;

movement means including means for producing a periodic movement signal and means responsive to the movement signal for periodically moving the accelerometers along a movement axis perpendicular to the rate and sensing axes, whereby each output signal includes a periodic Coriolis component; and

processing means comprising means for producing a reference signal that is operative to define one or more first time periods during which the Coriolis components have one polarity and one or more second time periods during which the Coriolis components have the opposite polarity, the first and second time periods together comprising one or more complete periods of the movement signal, means for determining, for each output signal, a phase value representing the difference between the phase change of the output signal during the first time periods and the phase change of the output signal during the second time periods, means for adding the phase values to one another to determine a phase sum value and for subtracting the phase values from one another to determine a phase difference value, and means for linearly combining the phase sum and phase difference values to determine a value representing the angular rate of rotation of the body about the rate axis.

2. The system of claim 1, wherein the means for determining the phase values comprises first and second counter means connected to receive the first and second output signals respectively, each counter means being operative to determine the difference between the cycles of the respective output signal that occur during the first time periods and the cycles of the respective output signal that occur during the second time periods.

3. The system of claim 1, wherein the means for determining the phase values comprises counter means for counting cycles of each output signal and data processing means for obtaining samples of the contents of the counter means at least twice during said one movement period and for algebraically combining the samples to determine the phase values.

4. The system of claim 1, wherein the processing means comprises frequency multiplication means for multiplying the frequency of each output signal by a predetermined number to thereby improve the resolution of the determination of phase values.

5. A system for determining the angular rate of rotation of a body about a rate axis, the system comprising:

one or more accelerometers having their sensitive axes parallel to a sensing axis perpendicular to the rate axis, each accelerometer including means for producing an output signal having a frequency corresponding to the acceleration experienced by the accelerometer along its sensitive axis;

movement means including means for producing a periodic movement signal and means responsive to the movement signal for periodically moving the accelerometers along a movement axis perpendicular to the rate and sensing axes, whereby each output signal includes a periodic Coriolis component; and

processing means comprising means for producing a reference signal that is operative to define one or more first time periods during which the Coriolis components have one polarity and one or more second time periods during which the Coriolis components have the opposite polarity, the first and second time periods together comprising one or more complete periods of the movement signal, means for determining, for each output signal, a phase value representing the difference between the phase change of the output signal during the first time periods and the phase change of the output signal during the second time periods, means for generating a high frequency clock signal, counter means for counting cycles of the clock signal during fractions of a cycle of an output signal which overlaps the first and second time periods, to thereby improve the resolution of the determination of phase values, and means for determining from the phase values a value representing the angular rate of rotation of the body about the rate axis.

6. A system for determining the angular rate of rotation of a body about a rate axis, the system comprising:

first and second accelerometers having their sensitive axes parallel to a sensing axis perpendicular to the rate axis, each accelerometer including means for producing an output signal having a frequency corresponding to the acceleration experienced by the accelerometer along its sensitive axis;

movement means including a parallelogram mechanism including a first support member secured to the first accelerometer, a second support member secured to the second accelerometer, a linkage mechanism attached to the first and second support members and secured to the body such that the first and second support members are parallel to the movement axis and such that the sensitive axes of the first and second accelerometers are parallel to the sensing axis, means for producing a sinusoidal movement signal and means responsive to the movement signal for vibrating the parallelogram mechanism such that the accelerometers are sinusoidally vibrated along a movement axis perpendicular to the rate and sensing axes, whereby each output signal includes a sinusoidal Coriolis component; and

processing means comprising means for producing a reference signal that is operative to define one or more first time periods during which the Coriolis components have one polarity and one or more second time periods during which the Coriolis components have the opposite polarity, the first and second time periods together comprising one or more complete periods of the movement signal, means for determining, for each output signal, a phase value representing the difference between the phase change of the output signal during the first time periods and the phase change of the output signal during the second time periods, means for adding the phase values to one another to determine a phase sum value and for subtracting the phase values from one another to determine a phase difference value, and means for linearly combining the phase sum and phase difference values to determine a value representing the angular rate of rotation of the body about the rate axis.

7. The system of claim 6, wherein the sensitive axes of the first and second accelerometers are oriented in opposite directions from one another.

8. The system of claim 7, wherein the processing means includes means for adding the phase values to one another to determine a phase sum value and for subtracting the phase values from one another to determine a phase difference value, and means for linearly combining the phase sum and phase difference value to determine said value representing angular rate.

9. A system for determining the angular rate of rotation of a body about a rate axis and the linear acceleration of the body along a sensing axis perpendicular to the rate axis, the system comprising:

first and second accelerometers having their sensitive axes parallel to the sensing axis, the first and second accelerometers being adapted to produce respective first and second output signals, each output signal having a frequency corresponding to the acceleration experienced by the respective accelerometer along its sensitive axis;

movement means including means for producing a periodic movement signal and means responsive to the movement signal for periodically moving the accelerometers along a movement axis perpendicular to the rate and sensing axes, whereby each output signal includes a periodic Coriolis component;

processing means comprising means for producing a reference signal that is operative to define one or more first time periods during which the Coriolis components have one polarity and one or more second time periods during which the Coriolis components have the opposite polarity, the first and second time periods together comprising one or more complete periods of the movement signal, means for determining, for each output signal, a first phase value representing the difference between the phase change of the output signal during the first time periods and the phase change of the output signal during the second time periods, and a second phase value representing the phase change of the output signal during the complete period of the movement signal, and means for determining from the phase values a first output value representing the angular rate of rotation of the body about the rate axis, and a second output value representing the linear acceleration of the body along the sensing axis.