Optical sensor arrangement for presence detection with variable pulse repetition frequency

• US 5,416,316 A
• Filed: 01/10/1994
• Issued: 05/16/1995
• Est. Priority Date: 12/14/1992
• Status: Expired due to Fees

• Current Assignee: Erwin SICK GmbH Optik-Elektronik
• Original Assignee: Erwin SICK GmbH Optik-Elektronik
• Inventors: Kappeler, Otmar
• Primary Examiner(s): Nelms, David C.
• Application Number:
  US08/179,298
• Time in Patent Office: 491 Days
• Field of Search: 250/214 B, 250/221, 250/222.1, 250/214 R, 250/223 R, 307/311, 340/555, 340/556, 340/557
• US Class Current: 250/221
• CPC Class Codes: G01V 8/12 using one transmitter and one receiver

Abstract

The invention relates to a method of operating an optical sensor arrangement for detecting articles present in a monitored region by means of a light transmitter and a light receiver. The light transmitter emits light signals which respectively comprise a number of pulses which follow each other at a determined pulse repetition frequency.

Claims

1. The method of operating an optical sensor arrangement for detecting articles present in a monitored region, said method comprising the steps of:

emitting a plurality of light signals from a light transmitter into said monitored region, each of said light signals comprising a number of pulses, forming a pulse sequence, which follow each other at a pulse repetition frequency;

varying said pulse repetition frequency between any two successive emitted light signals;

receiving said light signals at a light receiver as received light signals;

processing said received light signals in a received signal processing stage, said received signal processing stage comprising a filter arrangement permeable to frequency components of the pulse sequence;

producing an article detection signal when said received light signals indicates the presence of an article in said monitored region.

2. The method of operating an optical sensor arrangement of claim 1, further comprising:

testing for receipt of disturbing signals induced by disturbing light signals and electromagnetic signals unrelated to said light signals unrelated to said light signals emitted from said light transmitter, and producing disturbing signal information.

3. The method of operating an optical sensor arrangement of claim 2, wherein said testing step is further limited as follows:

testing for receipt of disturbing signals and producing disturbing signal information, until said disturbing signals have a sufficiently low magnitude.

4. The method of operating an optical sensor arrangement of claim 2, wherein said producing step is further limited as follows:

producing an article detection signal when said received light signal indicates the presence of an article in said monitored region, only when said disturbing signals are sufficiently low.

5. The method of operating an optical sensor arrangement of claim 2, further comprising:

from said disturbing signal information approximating the evolution of said disturbing signal during the emission of light signals and extracting a useful signal from the received total light signal composed of said useful signal and said disturbing signal.

6. An apparatus for detecting articles present in a monitored region, said apparatus comprising:

an oscillator, generating an oscillation signal;

a pulse repetition generator, receiving as input said oscillation signal for producing groups of pulses which follow each other at a pulse repetition frequency and for varying the pulse repetition frequency from one group of pulses to a next group of pulses;

a light transmitter, receiving as input said pulses and emitting light signals comprising a group of light pulses generated in response to input pulses, with said pulse repetition frequency varying from one light signal to the next light signal;

a light receiver, receiving as input said light signals and producing electrical signals; and

a filter arrangement, receiving as inputs said electrical signals and said oscillation signal, and generating an output indicating the detection of articles in said monitored region;

wherein;

the fundamental frequency of said oscillation signal equals said pulse repetition frequency of said emitted light signals; and

said filter arrangement is permeable to frequency components of pulse sequences.

7. The apparatus of claim 6, wherein:

said filter arrangement comprises;

a high-pass filter receiving as input said electrical signals and generating a high-pass filter output signal; and

a multiplier, receiving as inputs said high-pass filter output signal and said oscillation signal, and producing a multiplier output.

8. The apparatus of claim 6, wherein:

said filter arrangement comprises;

a high-pass filter, receiving as input said electrical signals and generating a high-pass filter output signal;

a preamplifier, receiving as input said high-pass filter output signal and producing a preamplified output signal; and

a multiplier, receiving as inputs said preamplified output signal and said oscillation signal, and producing a multiplier output.

9. The apparatus of claim 6, wherein:

said oscillator generates an oscillation signal which is sinusoidal.

10. The apparatus of claim 6, wherein:

said oscillator generates an oscillation signal which is rectangular.

11. The apparatus of claim 6, wherein:

said pulse repetition generator produces pulses which are sinusoidal.

12. The apparatus of claim 6, wherein:

said pulse repetition generator produces pulses which are rectangular.

13. The apparatus of claim 6, wherein:

said filter arrangement comprises;

a high-pass filter, receiving as input said electrical signals and generating a high-pass filter output signal;

a multiplier, receiving as inputs both said high-pass filter output signal and an oscillation signal, and producing a multiplier output; and

a low-pass filter, receiving as input said multiplier output and producing a low-pass filter output.

14. The apparatus of claim 13, wherein said filter arrangement further comprises:

a demodulator, receiving as input said low-pass filter output signal and generating a demodulated output signal.

15. The apparatus of claim 14 wherein said demodulator further comprises:

a delay circuit, receiving as input said low-pass filter output signal and producing a delayed output signal, for delaying the demodulation of said low-pass filter output signal for a time sufficient to compensate for the transit of said multiplier output through said low-pass filter.

16. The apparatus of claim 14, wherein:

said demodulator comprises an integrator.

17. The apparatus of claim 16, wherein:

said demodulator comprises an integrator where said integrator short-circuits when no light signal is emitted.

18. The apparatus of claim 6, further comprising:

a first multiplier, receiving as input said electrical signals and said oscillation signal, and producing a first multiplier output signal; and

a second multiplier, receiving as input said electrical signals and said oscillation signal with a 90°

phase shift, and producing a second multiplier output signal.

19. The apparatus of claim 18, further comprising:

a first low-pass filter, receiving as input said first multiplier output signal and producing a first low-pass filter output signal;

a second low-pass filter, receiving as input said second multiplier output signal and producing a second low-pass filter output signal; and

an adder, receiving as input said first low-pass filter output signal and said second low-pass filter output signal and producing an adder output signal.