Ground speed sensor
First Claim
Patent Images
1. A velocity sensor for sensing the velocity of a vehicle moving over a terrain, the velocity sensor comprising:
- a transmitter for transmitting a signal with a certain constant transmit frequency toward the terrain;
a receiver for receiving a signal reflected from the transmitter to the receiver by the terrain, the reflected signal having a variable reflected frequency dependent upon the speed and direction of the motion of the vehicle with respect to the terrain, the receiver also receiving a cross talk component signal having the same frequency as the transmit frequency, the receiver generating a combined signal having variable reflected frequency and constant transmit frequency components;
means for converting the transmit signal to an attenuated, phase-shifted signal;
a summing circuit having a first input receiving the combined signal, a second input receiving the attenuated, phase-shifted signal, the summing circuit operating to cancel the transmit frequency component of the combined signal, the summing circuit thereby providing at an output thereof a modified signal with a substantially pure reflected frequency;
a first circuit for converting the modified signal to a first voltage having a magnitude proportional to the frequency of the modified signal;
a second circuit for converting the transmit signal to a second voltage having a magnitude proportional to the transmit frequency; and
a difference circuit receiving the first and second voltages and generating a third voltage representing a difference between the first and second voltages, the first and second circuits having similar components so that the third voltage is substantially uneffected by component drift.
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Abstract
An ultrasonic ground speed sensor has a vehicle-mounted transmitter and a receiver for receiving signals reflected from the transmitter to the receiver by terrain over which the vehicle travels. An attenuated and phase-shifted transmit frequency is superimposed upon an output of the receiver to cancel cross talk, thus providing a substantially pure reflected frequency. A phase-locked loop converts the reflected frequency to a voltage which represents the direction and speed of the vehicle.
31 Citations
7 Claims
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1. A velocity sensor for sensing the velocity of a vehicle moving over a terrain, the velocity sensor comprising:
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a transmitter for transmitting a signal with a certain constant transmit frequency toward the terrain; a receiver for receiving a signal reflected from the transmitter to the receiver by the terrain, the reflected signal having a variable reflected frequency dependent upon the speed and direction of the motion of the vehicle with respect to the terrain, the receiver also receiving a cross talk component signal having the same frequency as the transmit frequency, the receiver generating a combined signal having variable reflected frequency and constant transmit frequency components; means for converting the transmit signal to an attenuated, phase-shifted signal; a summing circuit having a first input receiving the combined signal, a second input receiving the attenuated, phase-shifted signal, the summing circuit operating to cancel the transmit frequency component of the combined signal, the summing circuit thereby providing at an output thereof a modified signal with a substantially pure reflected frequency; a first circuit for converting the modified signal to a first voltage having a magnitude proportional to the frequency of the modified signal; a second circuit for converting the transmit signal to a second voltage having a magnitude proportional to the transmit frequency; and a difference circuit receiving the first and second voltages and generating a third voltage representing a difference between the first and second voltages, the first and second circuits having similar components so that the third voltage is substantially uneffected by component drift. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A velocity sensor for sensing the velocity of a vehicle moving over terrain, the velocity sensor comprising:
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a transmitter for transmitting an ultrasonic signal with a constant transmit frequency toward the terrain; a receiver for receiving an ultrasonic signal reflected from the transmitter for the receiver by the terrain, the reflected signal having a reflected frequency dependent upon the speed and direction of the motion of the vehicle with respect to the terrain, the receiver also receiving a cross talk component signal having the same frequency as the transmit frequency, the receiver generating a combined signal having reflected frequency and transmit frequency components; means for converting the transmitted signal to an attenuated, phase-shifted signal; a summing circuit having a first input receiving the combined signal, a second input receiving the attenuated, phase-shifted signal, the summing circuit operating to cancel the transmit frequency component of the combined signal, the summing circuit thereby providing at an output thereof a modified signal with a substantially pure reflected frequency; a first circuit for converting the modified signal to a first voltage having a magnitude proportional to the frequency of the modified signal; a second circuit for converting the transmit signal to a second voltage having a magnitude proportional to the transmit frequency; and a difference circuit receiving the first and second voltages and generating a third voltage representing a difference between the first and second voltages, the first and second circuits having similar components so that the third voltage is substantially uneffected by component drift.
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Specification