GB2166831A

GB2166831A - Infra-red guard

Info

Publication number: GB2166831A
Application number: GB08526493A
Authority: GB
Inventors: Christopher Higgins
Original assignee: L C AUTOMATION Ltd
Current assignee: L C AUTOMATION Ltd
Priority date: 1984-11-06
Filing date: 1985-10-28
Publication date: 1986-05-14
Also published as: GB2166831B; GB8526493D0

Abstract

Pulsed infra-red rays from source 26 pass by way of collimating lens 28 and aperture mask 30 to diverging lens 22 from which they pass to partially-reflective window 18 whereat the rays are reflected as a beam onto parabolic mirror 16 which creates a substantially parallel curtain of rays across the space 14 to be monitored to impinge upon prismatic reflector 24. The beam reflected back from reflector 24 is in turn, reflected back by mirror 16 to the window 18 through which at least part of the beam passes to pass by way of an image lens 34 to detector 36 comprising, for instance, an array of photo-sensitive diodes. Should there be an interruption of the curtain in the space 14, for instance as indicated at 40, there is a corresponding interruption at the detector 36 which sends an appropriate signal to reactive equipment (not shown) such as an alarm, fault display, or machine shut- off mechanism. The mirror 16 is not essential, the beam reflected by the window 18 impinging directly on the prismatic reflector 24, (Fig. 2, not shown). <IMAGE>

Description

SPECIFICATION Infra-red guard This invention concerns infra-red guards for use in the protection of operators and machines, for use as an operating safety device for preventing accidents by monitoring dangerous working or like areas, by detecting entry of any matter, for example an operator's hand or part of his body, into the monitored area.

It is already known to provide a guard arrangement which comprises a transmitter column embodying a plurality of individual infrared emitters or projectors, and a receiver column which is spaced away from the transmitter column and embodies a plurality of receivers each for the reception of a respective infra-red beam from the corresponding one of the emitter or projectors, thereby to provide for monitoring the space between the two columns. Such an arrangement is relatively expensive. Moreover, its protective capability is confined to a plurality of bands between the two columns and the entire area between the two columns may not be reliably monitored.

In order to provide for more reliable monitoring, it is known, also, to provide a guard arrangement wherein the one column is a transmitter and receiver column and the other column is a reflector column. An optical transmitter arrangement in the transmitter and receiver column includes an infra-red emitter producing a beam which is directed onto a rotating mirror which in turn reflects the beam onto a parabolic mirror thereby to generate a beam which passes through a window of the transmitter and receiver column to impinge upon the reflector column. From the latter, the beam is reflected back through the window, to the parabolic mirror and the rotating mirror which reflects it through a beam splitter to a photo-electric sensor.In this arrangement, therefore, the beam is caused, by rotation of the rotating mirror, to sweep the area (between the two columns) which is being monitored, so that the risk of inadequate monitoring, due to banding of the beams, is minimised.

This latter arrangement suffers from the disadvantage that it is relatively expensive, involving moving components in the form of the rotating mirror. Provision must necessarily be made for 'fail safe' operation, that is to say the guard must become effective in the event of the mirror ceasing to rotate since otherwise the monitored space between the two columns would be protected only in register with the stationary band(s) produced by the now stationary mirror.

An object of the present invention is to provide an infra-red guard arrangement in which the disadvantages of both the above-described prior proposals are obviated, the arrangement providing protection over a non-banded area or curtain between two columns, without the use of moving or rotating mirrors.

With this object in view, the present invention provides an infra-red guard for monitoring a dangerouse working or like area and to detect the entry into or presence in such area of intruding matter, such as an operator's hand, comprising a transmitter/receiver combination for provision at one side of the area to be monitored and reflector means for provision at the other side of said area, the transmitter/receiver combination comprising a partiallyreflective window for directing at least part of an infra-red beam falling thereon to the reflector means to be reflected back to said window, an infra-red source disposed to direct a infra-red beam onto said window, and an infra-red detector disposed to recieve infra-red rays reflected back from the reflector means, through said window.

With this arrangement, therefore, the partially-reflective window directs a fully-effective infra-red curtain across the area to be monitored to the reflector means. In the absence of any obstruction, substantially the entire curtain is reflected back to the partially-reflective window and is directed onto the detector through said window. If, however, there should be any obstruction to the rays constituting the curtain, there is a corresponding non-irradiated location at the detector, indicative of the presence of the obstruction.

The invention will be described further, by way of example with reference to the accompanying drawing, in which: Fig. 1 is a schematic diagram illustrating a preferred embodiment of the infra-red guard of the invention; and Fig. 2 is a view comparable with Fig. 1, but illustrating a second embodiment.

As shown in Fig. 1, a preferred embodiment of the guard of the invention, which is, for instance, for preventing injury or accidental approach to machinery such as a press or the like, comprise a transmitter/receiver column illustrated very diagramatically at 10, and spaced away from a reflector column which is indicated very diagrammatically at 12 so as to define therebetween a space 14, which may be of any desired practical dimensions, desired to be monitored.

Incorporated into the transmitter/receiver column 10 is a parabolic mirror 16. This is so located, relative to a partially-reflective window in the form of a planar mirror 18, that rays (indicated diagramatically at 20) impinging thereon from a diverging lens 22 are directed substantially parallel to one another across the space 14 to impinge on a prismatic reflector 24 incorporated in the reflector column 12, and are then reflected back across the space 14 again to encounter the parabolic mirror 16.

The rays 20 lie in the infra-red range and are received by the diverging lens 22 from a solid-state pulsed light source 26 by way of a collimating lens 28 and an aperture mask 30 which together serve to direct a narrow bundle or pencil 32 of rays on the diverging lens 22.

The partially-reflective mirror 18 is so formed, with a regular pattern of adjacent silvered and non-silvered areas, that substantially 50% of the rays falling thereon simply pass through the mirror 18 and the other 50% is reflected. Thus, it will be understood that 50% of the rays from the source 26 are reflected by the planar mirror 18 back to the parabolic mirror 16 where it passes across the space 14 to meet the prismatic reflector 24 in the reflector column 12. They are then reflected back again to the parabolic mirror 16 whereby they are reflected onto the planar mirror 18.Since the latter is only partly-reflective as already described, approximately 50% of the returning rays from the parabolic mirror 16 pass through the mirror 18 and encounter an image lens 34 which appropriately concentrates such rays upon a photo-diode array 36 the area of which is such as to correspond with the beam spread obtained from the ray curtain across the space 14. The photo-diode array 36 may be connected to any suitable reactive equipment (not shown), such as an alarm or fault display, and/or means for shutting off the equipment with which the guard is being used.

The manner of operation of the guard will readily be understood from the foregoing description. So long as there is no obstruction in the space 14 between the two columns 10 and 12, which space 14 is, for instance, the space in front of a piece of machinery such as a press (not shown), the photo-diode array 36 merely provides a substantially constant signal to the reactive equipment (which may, of course, be adapted to compensate for gradual and insignificant changes arising from environmental changes, ageing of components and so on), and no alarm or fault is indicated.Should, however, there be an interruption of the curtain, or part thereof, for instance as indicated at 40 in the figure, this will result in a corresponding interruption of the rays falling upon the photo-diode array 36 as indicated diagrammatically at 42, appropriate to cause the photo-diode array 36 to supply a fault signal to the reactive equipment and, for instance, sound an alarm and simultaneously shut off the machine with which the guard is being used.

The arrangement of the invention accordingly provides, in a very simple manner, and without the need for moving parts, for overall monitoring of the space between the two columns 10 and 12, which will operate reliably and continuously with the minimum of maintenance.

Naturally the invention is not confined to the precise details of the foregoing example and variations may be made thereto. Thus, for ease of illustration the transmitter/receiver column 10 has been shown to be of an irregular configuration, but of course with appropriate dimensioning and positioning of the components thereof, this column 10 could simply be substantially rectangular in configuration with one sidewall formed as a window for the egress and return of the rays, which window may be open or may embody a transparent panel as described. Other modifications are, of course, possible.

For example, since the purpose of the parabolic mirror 16 is merely to convert the diverging beam 20, 20 into a substantially parallel beam, the parabolic mirror 16 may be omitted. An example of such an arrangement is illustrated in Fig. 2 of the drawings in which similar reference numerals have been allocated to those parts which are similar to those already described with reference to Fig. 1. In this embodiment, the curtain of rays impinging upon the prismatic reflector 24 is of diverging configuration. The reflector 24, being of prismatic form, reflects substantially all of the rays impinging thereon back from whence they came. Fifty percent of these reflected rays pass through the partially-reflective window 18 and again result in a corresponding interruption 42 at the photo-diode array 36 which produces an alarm or other signal as described above with reference to the Fig. 1 embodiment.

Claims

1. An infra-red guard for monitoring a dangerous working or like area and to detect the entry into or presence in such area of intruding matter, such as an operator's hand, comprising a transmitter/receiver combination for provision at one side of the area to be monitored and reflector means for provision at the other side of said area, the transmitter/received combination comprising a partiallyreflective window for directing at least part of an infra-red beam falling thereon to the reflector means to be reflected back to said window, an infra-red source disposed to direct an infra-red beam onto said window, and an infra-red detector disposed to receive infra-red rays reflected back from the reflector means, through said window.

2. An infra-red guard as claimed in claim 1 wherein the transmitter/receiver combination includes a parabolic mirror which serves to convert a diverging beam directed by the window towards the reflector means into a substantially parallel beam.

3. An infra-red guard as claimed in claim 1 or 2 wherein the reflector means comprises a prismatic reflector.

4. An infra-red guard as claimed in claim 1, 2 or 3 wherein the infra-red source comprises a solid state pulsed light source.

5. An infra-red guard as claimed in any preceding claim wherein the infra-red beam supplied by the infra-red source is directed by way of a collimating lens, an aperture mask and a diverging lens onto the window.

6. An infra-red guard as claimed in any preceding claim wherein an image lens is provided between the window and the infra-red detector, for concentrating the rays which pass through the window onto the detector.

7. An infra-red guard as claimed in any preceding claim wherein the detector is a photo-diode array.

8. An infra-red guard as claimed in any preceding claim wherein the detector serves to actuate reactive equipment such as an alarm or fault display, or means for switching off equiptment with which the guard is used.

9. An infra-red guard substantially as hereinbefore described with reference to and so illustrated in Fig. 1 or Fig. 2 of the accompanying drawings.