Self-adapting signal detector with digital outputs

• US 4,942,531 A
• Filed: 05/16/1988
• Issued: 07/17/1990
• Est. Priority Date: 05/16/1988
• Status: Expired due to Term

• Current Assignee: BBH Incorporated
• Original Assignee: Bell & Howell LLC (Böwe Systec AG)
• Inventors: Spanhak, F. Nicholaas, Hainsworth, Thomas E., Paske, Richard R. Jr.
• Primary Examiner(s): Black, Thomas G.
• Application Number:
  US07/194,337
• Time in Patent Office: 792 Days
• Field of Search: 364/424.2, 364/443, 180/168, 180/169, 250/202, 318/587
• US Class Current: 701/23
• 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
• CPC Class Codes: G05D 1/0255 using acoustic signals, e.g. ultra-sonic singals sonar systems designed for anti-collision purposes G01S15/93

Abstract

A self-adapting signal detector is adapted to be used with a plurality of guidepath sensors for controlling an automatically guided vehicle. The circuitry detects the presence of a valid guidepath signal over a large dynamic range without the need to make threshold or gain adjustments. A background noise signal is detected as well as a signal from each of the guidepath sensors. The background noise signal is substracted from each sensor signal to define a plurality of difference signals. A maximum remainder signal is defined as the maximum difference signal. Each difference signal is then compared with a predetermined percentage of the maximum remainder signal. Those sensors whose signal level exceeds the predetermined percentage of the maximum remainder signal by a predetermined amount are defined to be a valid guide path signal. The maximum remainder signal is also compared with a predetermined percentage of the background noise signal to determine the signal-to-noise ratio. If the signal-to-noise ratio signal falls below a predetermined value, a signal is provided to stop the vehicle. In an alternate embodiment, the lesser of a predetermined percentage of the maximum remainder signal and a predetermined percentage of the background level is selected to define a reference signal. Those sensors whose signals exceeds the reference signal are defined to be a valid guidepath signal.

Claims

1. A system for an automatically guided vehicle for detecting the presence of a fluorescent material defining a guidepath comprising:

means for providing a first signal representative of said fluorescent guidepath including one or more optical sensors disposed on said vehicle, wherein not all of said sensors are located over said guidepath and an ultraviolet light for irradiating the fluorescent material causing it to emit visible light;

means for detecting background noise;

means responsive to said first signal providing means and said background noise detecting means for providing a signal according to a predetermined criteria indicative of a valid guidepath; and

means responsive to said plurality of optical sensors and said background noise detecting means for providing a signal representative of the maximum value of the differences between each of the optical sensor signals and the background noise signal to define a maximum remainder signal.

2. A system as recited in claim 1 further including means responsive to first signal generating means and said maximum remainder signal for comparing the output signals from each optical sensor with a predetermined percentage of said maximum remainder signal and generating a valid guidepath signal for each sensor if said output signal from said sensor exceeds said maximum remainder signal by a predetermined amount.

3. A system as recited in claim 2 wherein said valid guidepath signal is a digital signal.

4. A system as recited in claim 1 wherein said first signal providing means includes four sensors, A, B, C and D.

5. A system as recited in claim 4 wherein only two of the sensors, B and C are located to sense light emitted from said guidepath.

6. A system as recited in claim 5 wherein said predetermined criteria between the output signals from said sensors is given by the following relationship:

space="preserve" listing-type="equation">(B+C)·

(A+D)=1.

7. A vehicle guidance system as recited in claim 1 further including means for determining the signal-to-noise ratio for the signals from said first signal generating means and stopping the vehicle when the signal-to-noise ratio falls below a predetermined value.

8. A method for detecting a guidepath having a detectable characteristic for an automatically guided vehicle comprising the steps of:

detecting first signals representative of a said detectable characteristic with a plurality of sensors;

detecting signals representative of background noise;

subtracting the background noise signal from said first signals for each sensor and selecting the maximum difference signal to define a maximum remainder signal;

comparing the first signal from each sensor with a percentage of the maximum remainder signal;

providing a valid guidepath signal for each sensor whose first signal level exceeds a percentage of the maximum remainder signal; and

generating a valid guidepath signal if a predetermined relationship exists among the first signals from said plurality of sensors.

9. A method for detecting a guidepath as in claim 8 wherein four sensors A, B, C and D, are used and wherein only two of the sensors, B and C, are located to detect the guidepath and two of the sensors are adapted to detect areas contiguous to the guidepath.

10. A method for detecting a guidepath as recited in claim 9 wherein said predetermined relationship between the output signals from said sensors is given by the logical expression:

space="preserve" listing-type="equation">(B+C)·

(A+D)=1.

11. A system for an automatically guided vehicle for detecting the presence of a fluorescent material defining a guidepath comprising:

an ultraviolet light for irradiating the fluorescent material causing it to emit visible light;

a plurality of photodetectors for detecting the light emitted from said fluorescent material;

a photodetector for providing a signal representative of the background light;

means for subtracting said signal representative of the background light from the signals from each of said photodetectors defining a plurality of difference signals;

means for selecting the maximum difference signal to define a maximum remainder signal; and

means for comparing the signal from each photodetector with a percentage of said maximum remainder signal and providing a valid guidepath signal for each photodetector whose signal exceeds a percentage of said maximum remainder signal.

12. A guidance system as recited in claim 11 further including means for comparing the background noise signal and said maximum remainder signal for providing a signal representative of the signal-to-noise ratio.

13. A guidance system as recited in claim 12 further including means responsive to said signal representative of the signal-to-noise ratio for stopping the vehicle if the signal-to-noise ratio is below a predetermined value.

14. A system for an automatically guided vehicle for detecting the presence of a guidepath having a detectable characteristic comprising:

a plurality of sensors for providing a first signal representative of said detectable characteristic;

a sensor for providing a signal representative of the background noise;

means for subtracting the signal representative of the background noise from each of the sensor signals defining a plurality of difference signals;

means for selecting the maximum difference signal to define a maximum remainder signal;

means for comparing said maximum remainder signal with said background noise signal to define a signal representative of exceeding a minimum the signal-to-noise ratio; and

means responsive to said signal-to-noise ratio representative signal to stop the vehicle if the signal-to-noise ratio representative signal is less than a predetermined amount.

15. A method for detecting a guidepath having a detectable characteristic for an automatically guided vehicle comprising the steps of:

detecting first signals representative of said detectable characteristic with a plurality of sensors;

detecting signals representative of background noise;

subtracting the background noise signal from each of said first signals and selecting the maximum difference signal to define a maximum remainder signal;

selecting the lesser of a predetermined percentage of the maximum remainder signal and a predetermined percentage of the background noise signal to define a reference signal; and

providing a valid guidepath signal for each first signal level that exceeds the reference signal.

16. A guidance system for an automatically guided vehicle for detecting the presence of a fluorescent guidepath comprising:

an ultraviolet light for irradiating the fluorescent material causing it to emit visible light;

a plurality of photodetectors for providing a signal when light emitted from said fluorescent material is detected;

a photodetector for providing a signal representative of the background light;

means for subtracting said signal representative of the background light from each of said photodetector signals to define a plurality of difference signals;

means for selecting the maximum difference signal to define a maximum remainder signal;

means for selecting the lesser of a predetermined percentage of said maximum remainder signal and the background noise signal to define a reference signal; and

means for comparing the signals from each of said photodetectors with said reference signal and providing a valid guidepath signal for each photodetector whose signal exceeds said reference signal.

17. A system for an automatically guided vehicle for detecting the presence of a guidepath having a detectable characteristic comprising:

a plurality of sensors for providing a first signal representative of said detectable characteristic;

a sensor for providing a signal representative of the background noise;

means for subtracting the signal representative of the background noise from each of the sensor signals defining a plurality of difference signals;

means for selecting the maximum difference signal to define a maximum remainder signal;

means for selecting the lesser value of a predetermined percentage of the maximum remainder signal and a predetermined percentage of said background noise signal to define a reference signal; and

means for comparing the reference signal with said sensor signals to provide a valid guidepath signal for those sensors whose signal exceeds said reference signal.