Method and device for photoelectric identification of a material web

• US 5,467,194 A
• Filed: 10/12/1993
• Issued: 11/14/1995
• Est. Priority Date: 02/06/1991
• Status: Expired due to Term

• Current Assignee: Valmet Paper Machinery, Inc.
• Original Assignee: Valmet Paper Machinery, Inc.
• Inventors: Ahola, Juhani, Erkkila, Kari, Vahatalo, Harri, Pellinen, Kari, Koiranen, Jukka
• Primary Examiner(s): Rosenberger, Richard A.
• Application Number:
  US08/135,315
• Time in Patent Office: 763 Days
• Field of Search: 356/429, 356/430, 250/561, 250/548, 250/561
• US Class Current: 356/429
• CPC Class Codes: B65H 23/0216 with an element utilising photoelectric effect
• CPC Class Codes: B65H 2557/10 for signal transmission
• CPC Class Codes: B65H 26/025 responsive to web breakage

Abstract

A method and apparatus for identifying a moving web in a paper making machine are disclosed. The method includes of the steps of illuminating the web with the light from a transmitter, reflecting the transmitted light off the web, receiving the reflected light with a light transducer to produce an electrical signal corresponding to the intensity of the received light, and identifying the moving web based on the received signal. The intensity of the transmitted light is adjusted so that the received light signal from the transducer is normalized with respect to an optimum value. The apparatus includes a light transmitter, a light receiver, and a control and identification circuit which identifies the web based on a signal from the light receiver, and which adjusts the intensity of the light transmitter to optimize the reception of the signal from the light receiver in order to minimize the effects of environmental interference.

Claims

1. A method of identifying a state of presence of a web moving on and supported by a wire or felt in a paper making machine, comprising the steps of:

illuminating a portion of the web with a pulse-modulated transmitted beam of light from a light transmitter to produce a reflected beam of light, said modulated beam of light modulating in intensity from an on state to an off state, said reflected beam of light having a first pattern when said web supported by the wire or felt is present and a second pattern when said web is not present and the wire or felt is present, said first and second patterns being different from one another;

detecting said reflected beam of light with a light receiver to produce an electric signal corresponding to the intensity of said reflected beam of light received by said light receiver;

obtaining a background light level from said electric signal corresponding to when said modulated transmitted beam of light is in an off state and said web supported by the wire or felt is present;

obtaining an illuminated light level from said electric signal corresponding to when said modulated transmitted beam of light is in an on state and said web supported by the wire or felt is present and is illuminated by said modulated transmitted beam of light;

processing said electric signals corresponding to said background light level and said illuminated light level by subtracting said electric signal corresponding to said background light level from said electric signal corresponding to said illuminated light level to obtain a calibration signal;

adjusting the intensity of said transmitted beam of light when said web supported by the wire or felt is present so that said calibration signal is normalized; and

analyzing said electric signal produced by said light receiver and determining whether the web supported by the wire or felt is present or whether the web is not present and the wire or felt is present.

2. A method according to claim 1, wherein said light transmitter is a light emitting diode and said adjusting step further comprises adjusting an intensity of a transmitted beam of light from said light emitting diode by adjusting an input voltage to said light emitting diode.

3. A method according to claim 1 wherein said adjusting step further comprises adjusting the intensity of said transmitted beam of light such that between about 10% and about 30% of the available total light capacity of said light transmitter is required to normalize said calibration signal.

4. A method according to claim 1, wherein said analyzing step further comprises filtering said electric signal with a high pass filter, and detecting a break in said web based on the occurrence of a rapid change in the filtered electric signal.

5. A method according to claim 1 further comprising detecting an error condition indicative of device failure, in which an electric signal indicative of an error condition is different from an electric signal indicative of a change of presence of the material web.

6. A method according to claim 1, wherein said transmitted beam of light is visible light having a frequency above the spectrum associated with fluorescent light.

7. A method according to claim 1, wherein said step of obtaining a background light level, said step of obtaining an illuminated light level, said electric signal processing step, and said adjusting step are performed at preset intervals.

8. A photoelectric device for identifying a state of presence of a web moving on and supported by a wire or felt in a paper making machine, comprising:

an adjustable light intensity transmitter for illuminating a portion of the web with a pulse-modulated transmitted beam of light to produce a reflected beam of light, said modulated beam of light modulating in intensity from an on state to an off state, said reflected beam of light having a first pattern when said web supported by the wire or felt is present and a second pattern when said web is not present and the wire or felt is present, said first and second patterns being different from one another;

a light receiver for detecting said reflected beam of light to produce an electric signal corresponding to the intensity of said reflected beam of light received by said light receiver;

control means for adjusting the intensity of light transmitted by said transmitter comprising;

means for obtaining a background light level from said electric signal generated by said light receiver corresponding to when said transmitter is in an off state and said web supported by the wire or felt is present;

means for obtaining an illuminated light level from said electric signal generated by said light receiver corresponding to when said transmitter is in an on state and said web supported by the wire or felt is present and is illuminated by said modulated transmitted beam of light;

calibration means for processing said electric signals generated by said light receiver corresponding to said background light level and said illuminated light level by subtracting said electric signal corresponding to said background light level from said electric signal corresponding to said illuminated light level to obtain a calibration signal;

adjusting means for adjusting the intensity of light transmitted by said transmitter so that said calibration signal is normalized; and

signal processing means for analyzing said electric signal generated by said light receiver and determining whether the web supported by the wire or felt is present or whether the web is not present and the wire or felt is present.

9. A device according to claim 8 wherein said light transmitter transmits and said light receiver receives from a measurement head in proximity to the material web.

10. A device according to claim 9, wherein said light transmitter comprises an adjustable intensity light output source and a fiber optic cable and wherein said light receiver comprises a light detector and a fiber optic cable.

11. A device according to claim 9, wherein said light transmitter is a transmitter for generating visible light having a frequency above a spectrum associated with fluorescent light.

12. A device according to claim 9, wherein said measurement head comprises a protective casing and a cable communicating with said control means and said signal processing means, said measurement head further comprises an electronic circuit and said cable comprises an electronic cable for communicating electrical signals with said control means and said signal processing means.

13. A device according to claim 9, wherein said measurement head comprises a protective casing, a first fiber optic cable transmitting light from said transmitter, a transmit optic for transmitting said transmitted light from said first fiber optic cable to the material web, a receive optic for receiving said reflected light from the material web, a second fiber optic cable receiving light from said receive optic and transmitting it to said light receiver.

14. A device according to claim 9, further comprising a compressed air supply capable of supplying a compressed air stream, wherein said measurement head comprises a protective casing with at least one opening through which light is transmitted, and wherein the compressed air stream from said compressed air supply is applied to said at least one opening to prevent foreign particles from collecting therein.

15. A device according to claim 8, wherein said signal processing means further comprises a high pass filter for passing rapid changes in the electric signal, a transmitted light pulse generating circuit for controlling said pulse of light from said light transmitter, and a sampling control circuit for controlling sampling of said signal at a time when said light transmitter transmits a pulse of light.

16. The device according to claim 8, wherein said control means normalizes said calibration signal at preset intervals.