Control system for detecting intrusion of a light curtain

• US 5,404,008 A
• Filed: 07/16/1993
• Issued: 04/04/1995
• Est. Priority Date: 07/16/1993
• Status: Expired due to Fees

• Current Assignee: Meritor Light Vehicle Technology, LLC (Meritor, Inc. (Nevada))
• Original Assignee: Rockwell International Corporation
• Inventors: Kramer, Dennis A., Malinowski, Mark E.
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): Allen, Stephone B.
• Application Number:
  US08/092,844
• Time in Patent Office: 627 Days
• Field of Search: 250/561, 250/222.1, 250/214 B, 250/221, 341/31, 340/555, 340/556, 340/557
• US Class Current: 250/222.1
• CPC Class Codes: G01V 8/20 using multiple transmitters or receivers

Abstract

A light curtain system having a series of light emitting diodes is arranged to produce a beam of light which is modulated at about 40 KHz. The light is broadcast across a physical space in which intrusion detection is desired and received by respectively arranged photo diodes. Each of the light emitting diodes is connected in parallel to a single modulated power supply. Each photo diode produces an electrical signal having a magnitude which is proportional to the amount of light incident thereon. The signal produced by each photo diode is sequentially sampled and then compared to a reference value. If an intrusion in the respective region of the light curtain has occurred, the magnitude of the sampled signal will be less than the reference value providing indicia of an intrusion. Upon such a detection, the light curtain system provides indicia of the intrusion such that consequential remedial action in response thereto may be performed.

Claims

1. A control system adapted to detect intrusion of a control plane by an object;

said control system comprising a plurality of light sources arranged along a first margin of said control plane;

a plurality of light detectors arranged along a second margin of said control plane in generally parallel disposition with respect to said first margin, said light detectors being adapted to receive light emitted from the respective light sources, said light sources being connected in a parallel circuit to a power supply and adapted thereby to broadcast a light curtain across said control plane;

means for sequentially sampling output signals of said light detectors;

said parallel circuit including an oscillator circuit means for powering said light sources with a driving voltage of preselected frequency;

a band pass filter circuit means for establishing an output signal feedback control loop for said sequential sampling means whereby a narrow output signal band frequency near said preselected frequency is established thus reducing extraneous electronic noise and background light effects;

means for establishing and storing a reference output signal value indicative of a calibrated value;

means for comparing said output signals with said calibrated value and for developing a control system signal in response to detection of a predetermine difference between said reference signal and said output signals as a result of an intrusion of said light curtain.

2. The system set forth in claim 1 wherein said light curtain comprises a plurality of light beams developed by said light sources, said oscillator circuit means powering said light sources at a frequency of approximately 40 KHz.

3. The system set forth in claim 1 wherein said light sources comprise light emitting diodes.

4. The system set forth in claim 1 wherein said light detectors are photo diodes.

5. The system set forth in claim 4 wherein said light detectors comprise transistor circuit elements having bases adapted, when energized by said control system signal developing means, to connect said photo diodes to ground.