Protection from extraneous light for light guided vehicle

• US 4,876,444 A
• Filed: 03/07/1988
• Issued: 10/24/1989
• Est. Priority Date: 03/07/1988
• Status: Expired due to Fees

• Current Assignee: Tennant Company
• Original Assignee: Tennant Company
• Inventors: Field, Bruce F.
• Primary Examiner(s): Westin, Edward P.
• Assistant Examiner(s): Shami, Khaled
• Application Number:
  US07/164,880
• Time in Patent Office: 596 Days
• Field of Search: 250/214 AL, 250/561, 356/141, 356/152, 180/167-169, 901/47, 364/424.02, 318/587
• US Class Current: 250/214.0AL
• CPC Class Codes: G01S 17/04 Systems determining the presence of a target
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G05D 1/0238 using obstacle or wall sensors G05D1/0246 and G05D1/0289 take precedence; lidar systems designed for anti-collision purposes G01S17/93
• CPC Class Codes: G05D 1/0244 using reflecting strips

Abstract

An automated guided vehicle uses a scanning laser unit having a laser transmitter and receiver to transmit laser signals and receive them reflected back from a series of targets. The reflected signals are used to guide the vehicle along a desired path. The laser unit includes a photodetector mounted near the laser receiver such that any extraneous light, such as sunlight, that strikes the laser receiver will also strike the photodetector. The photodetector converts the extraneous light into an electrical signal proportional to the amount of such light. The photodetector signal is compared to a threshold value which generally is slightly below an amount of extraneous light sufficient to confuse the laser unit. If the threshold value is exceeded, the photodetector signal is used to stop the vehicle or take other appropriate action.

Claims

1. A laser beam detecting device for use in conjunction with one or more retroreflective targets, comprising a transmitter for emitting a laser beam, scanning means for traversing said emitted laser beam through a scanning plane, a traversing said emitted laser beam through a scanning plane, a receiver for detecting a laser beam reflected from one of said targets and converting it to an output signal, a photodetector mounted adjacent the receiver such that extraneous light striking the receiver only from a direction parallel to said scanning plane will also strike the photodetector, the photodetector producing a signal indicating the amount of extraneous light striking the device, and comparing means for comparing the photodetector signal to a predetermined threshold and generating an interrupt signal for overriding the output signal of the receiver when the threshold is exceeded.

2. The device of claim 1 further comprising a first timer means which permits the interrupt signal to override the output signal only when the threshold has been exceeded for a predetermined minium length of time.

3. The device of claim 2 further comprising a second timer means which maintains the interrupt signal for a predetermined length of time once the minium of the first timer means has been exceeded.

4. The device of claim 1 further comprising light shields mounted adjacent the photodector and arranged such that only light substantially parallel to the scanning plane of said laser beam is permitted to strike the photodetector.

9. The device of claim 1 wherein the photodetector is a silicon photovoltaic cell.

5. In a laser beam detecting device for use in conjunction with one or more retroreflective targets, and having a transmitter for emitting a laser beam, scanning means for traversing said emitted a laser beam through a scanning plane, and having means for receiving a light beam reflected from one of said targets and converting it into an output signal, a method of preventing false output signals due to extraneous light sources, comprising the steps of:

detecting extraneous light impinging on the device adjacent the means for receiving the light beam only from a direction substantially parallel to said scanning plane;

comparing the amount of light detected with a predetermined threshold; and

overriding the output signal when the threshold is exceeded.

6. The method of claim 5 wherein the light beam is a laser beam.

7. The method of claim 5 wherein the comparing step is further characterized by generating an interrupt signal for overriding the output signal of the receiver when the threshold is exceeded and timing the interrupt signal so as to permit the interrupt signal to override the output signal only when the threshold has been exceeded for a predetermined minimum length of time.

8. The method of claim 7 further characterized by maintaining the interrupt signal for a predetermined length of time once the minimum length of time has been exceeded.