Control circuitry for vehicle guidance mechanism

• US 3,970,840 A
• Filed: 07/16/1974
• Issued: 07/20/1976
• Est. Priority Date: 07/16/1974
• Status: Expired due to Term

• Current Assignee: Lear Siegler, Inc. (LSS Holdings LLC)
• Original Assignee: Lear Siegler, Inc. (LSS Holdings LLC)
• Inventors: De Bruine, Carl
• Primary Examiner(s): La Roche, Eugene
• Application Number:
  US05/488,961
• Time in Patent Office: 735 Days
• Field of Search: 250/202, 250/209, 250/214 AG, 250/214 B, 318/577
• US Class Current: 250/202
• CPC Class Codes: G05D 1/0242 using non-visible light signals, e.g. IR or UV signals
• CPC Class Codes: G05D 1/0244 using reflecting strips

Abstract

A vehicle guidance mechanism for guiding a vehicle along a guide line comprises a radiation source that causes the guide line to reflect or emit a guidance signal; photocell sensors mounted in the vehicle and adapted to sense the guidance signal and produce an error output signal proportional to the variation of vehicle position from a predetermined lateral position with respect to the guide line; and a control device in the vehicle adapted to steer the vehicle in response to the error signal so as to cause the vehicle to follow the guide line. An automatic contrast or gain control circuit eliminates the effect of background illumination in the output signal received from the guide line. Modulation circuitry and appropriate filters reduce the effects of static background illumination and improve the reliability and line detecting ability of the guide system. Line detection circuitry is employed to prevent operation of the automatic control device unless the vehicle is tracking a valid guide line.

Claims

1. In a vehicle guidance means for guiding a vehicle along a guide line, wherein guidance system radiation means causes the guide line to emit or reflect a guidance signal, sensor means senses the guidance signal and produces a differential error output signal representative of the deviation of the vehicle position from the guide line, and control means automatically controls the position of the vehicle in accordance with the error output signal, the improvement comprising:

feedback means for maintaining a generally constant ratio between error output signal strength and displacement of the guide line from a predetermined centerline position, regardless of the strength of background radiation, said feedback means maintaining said ratio generally constant, as long as the vehicle is following the guide line and the guidance signal is stronger than the signal produced by background radiation when the radiation means is switched on;

modulation means for modulating the guidance signal with a predetermined modulation signal, said modulation means modulating the guidance signal by switching the radiation means on and off at synchronized intervals, the modulation means further generating first and second synchronized pulse signals once each cycle, the first synchronized pulse being generated at a first time interval representative of the time when the radiation means is switched on and the second synchronized pulse being generated at a second time interval representative of the time when the radiation means is switched off, each time interval being a relatively small portion of the total time the radiation means is switched on and off each cycle; and

demodulation circuit means for demodulating the error output signal of the sensor means so as to eliminate the effects of static background radiation and the modulation signal from the error output singal, thus limiting the error output signal to the output signal produced by the guidance signal, said demodulation circuit means comprising synchronized demodulation means for measuring the level of the output signal of each sensor means during each first and second time interval and measuring the difference between said signals, said demodulation circuit further comprising sample and hold amplifier means for producing and holding a DC output signal at a level equal to said difference until the value of the difference signal changes in a subsequent cycle.

2. Vehicle guidance means as claimed in claim 1 wherein:

the change in value of the sensor means output signal lags the change in the guidance signal in accordance with the time constant of the sensor means; and

the demodulation means measures the difference between the sensor means output signals just after the radiation means has been switched on and just before the radiation means is switched off.

3. Vehicle guidance means as claimed in claim 1 wherein:

the modulation means generates a first synchronized pulse at a selected time when the radiation means is on and a second synchronized pulse at a selected time when the radiation time is off;

the synchronized demodulation means comprises a first capacitor means connected in series with the output of the sensor means, a grounded first field effect transistor means connected to the output of the first capacitor means, a series-connected second field effect transistor means connected to the output of the first capacitor means and a grounded second capacitor means connected to the output of the second field effect transistor means, both field effect transistor means being normally non-conductive, the first field effect transistor means being rendered temporarily conductive by one synchonized pulse and the second field effect transistor means being rendered temporarily conductive by the other synchronized pulse; and

the sample and hold amplifier means is connected across the second capacitor means and produces a DC output signal representative of the magnitude of the signal across the second capacitor means.

4. Vehicle guidance means for guiding a vehicle along a guide line comprising:

guidance system radiation means for causing the guide line to emit or reflect a guidance signal;

sensor means for sensing the guidance signal and producing a differential error output signal representative of the deviation of the vehicle position from the guide line, the sensor means producing separate output signals representative of guidance signal intensity at at least three different positions with respect to the guide line, said positions being on the left and right sides of the guide line and a center position over the guide line when the guide line is centered with respect to the sensor means, the sensor means being positioned in the vehicle such that approximately the same amount of background radiation is received at all three positions when the guide line is centered with respect to the sensor means;

control means for automatically controlling the position of the vehicle in accordance with the error output signal;

feedback means for maintaining a generally constant ratio between error output signal strength and displacement of the guide line from a predetermined centerline position, regardless of the strength of background radiation, said feedback means maintaining said generally constant ratio as long as the vehicle is following the guide line and the guidance signal is stronger than the signal produced by background radiation when the radiation means is switched on, said feedback means maintaining said constant ratio by maintaining a constant difference between the output signal from the center position and the output signal from the average of the output signals from the other positions when the guide line is centered with respect ot the sensor means, said feedback means including means for modifying the output signal from the center position by adding to it the absolute value of the difference between the left and right position output signals, the difference between this modified center position output signal and the average of the left and right position output signals being the difference signal maintained at a substantially constant level by said feedback means.

5. Vehicle guidance means as claimed in claim 4 wherein:

the radiation means is adapted to cause the guide line to emit or reflect a guidance signal in the form of radiation capable of being sensed by a photocell; and

the sensor means comprises separate left, right and center line photocells positioned respectively at the left, right and center positions with respect to the guide line.

6. Vehicle guidance means for guiding a vehicle along a guide line comprising:

guidance system radiation means for causing the guide line to emit or reflect a guidance signal;

sensor means for sensing the guidance signal and producing a differential error output signal representative of the deviation of the vehicle position from the guide line, the sensor means being adapted to produce separate output signals representative of guidance signal intensity at at least three different positions with respect to the guide line, said positions being on the left and right sides of the guide line and a center position over the guide line when the guide line is centered with respect to the sensor means, the sensor means being positioned in the vehicle such that approximately the same amount of background radiation is received at all three positions when the guide line is centered with respect to the sensor means;

control means for automatically controlling the position of the vehicle in accordance with the error output signal;

feedback means for maintaining a generally constant ratio between error output signal strength and displacement of the guide line from a predetermined centerline position, regardless of the strength of background radiation, said feedback means maintaining said generally constant ratio as long as the vehicle is following the guide line and the guidance signal is stronger than the signal produced by background radiation when the radiation means is switched on, said feedback means maintaining said generally constant ratio by producing a feedback signal to the senor means that maintains a constant difference between the output signal from the center position and the output signal from at lest one or the average of the other positions when the guide line is centered with respect to the sensor means; and

line detection means for preventing the operation of the vehicle guidance means whenever the feedback signal exceeds a predetermined level.

7. Vehicle guidance means as claimed in claim 6 wherein the line detection means is further adapted to prevent operation of the vehicle guidance means if the absolute difference between the sensor means output signals at the left and right positions exceeds a predetermined value.

8. Vehicle guidance means for guiding a vehicle along a guide line comprising:

guidance system radiation means for causing the guide line to emit or reflect a guidance signal;

sensor means for sensing the guidance signal and producing a differential error output signal representative of the deviation of the vehicle position from the guide line, the senor means being adapted to produce discreet output signals representative of guidance intensity at at least three positions with respect to the guide line, two of said positions being to the left and right of the guide line and the third position being such that a predetermined relationship exists between the output signals representative of the third position and at least one of the other positions when the vehicle guidance means is positioned over the guide line, the sensor means being positioned in the vehicle such that approximately the same amount of background radiation is received at all three positions when the guide line is centered with respect to the sensor means;

control means for automatically controlling the position of the vehicle in accordance with the error output signal;

feedback means for maintaining a generally constant ratio between error output signal strength and displacement of the guide line from a predetermined centerline position, regardless of the strength of background radiation, said feedback means maintaining said generally constant ratio as long as the vehicle is following the guide line and the guidance signal is stronger than the signal produced by background radiation when the radiation means is switched on, said feedback means maintaining said generally constant ratio by maintaining a predetermined relationship between the sensor means output from the third position and at least one or a combination of the other positions at least when the guide line is centered with respect to the sensor means, said feedback means receiving an error signal from the sensor means that is representative of the existing relationship between the sensor means output and generating a feedback signal to the sensor means to correct the relationship to the extent necessary to maintain said predetermined relationship, at least one of said error and feedback signals increasing to a predetermined level when the vehicle is not following a guide line or the guidance signal is not stronger than the signal produced by background radiation when the radiation means is switched on; and

line detection means for preventing the operation of the vehicle guidance means whenever at least one of said error and feedback signals increases to said predetermined level.