Light barrier apparatus

Light barrier apparatus generally features a light transmitter for projecting light across a region to be monitored to a light receiver. The light transmitter and receiver units can either be separate or can be combined in a single housing and used in conjunction with a retro-reflector for returning light from the sender to the receiver. In any of these arrangements the light transmitter and/or sender units incorporate photoelectric converter components 11, 12 and optical projection components 13, 14 together with electronic processing elements which enable interruption of the light barrier to be detected. The present arrangement features a housing 17 including at least one sealed chamber 15, 15', 15" containing solely the optical and photoelectric converter elements. These chambers are thus sealed against the ingress of contamination and moisture. The remaining elements of the electronic processing circuit are housed separately in a further chamber 16. The housing together with the fixed walls 18, 18', 18" of the sealed chambers 15, 15', 15" is usefully injection molded in one piece and preferably together with sighting aids 22.

The present invention relates to light barrier apparatus and has particular 
reference to a housing incorporating at least one of the light transmitter 
and light receiver for the light barrier. 
Known light barrier apparatus suffers from the problem that the optical 
components easily become contaminated or dirtied or their operating 
efficiency is deleteriously affected by the formation of condensation. In 
addition difficulties are experienced in aligning the optical axes of the 
sender and receiver, or, in an autocollimation device in aligning the 
optical axes of the sender and receiver units with the separate reflector. 
In addition it is important to maintain a precise relationship between the 
effective optical axis of the apparatus and the axis or a reference line 
or reference surface of the housing. 
Satisfying these requirements is particularly difficult with modern light 
barriers which operate with light in the invisable part of the spectrum. 
For these types of light barrier it is generally only possible to ensure 
the troublefree alignment of the light barrier housing in a simple manner 
using sighting aids located on the housing. 
It is thus a principal object of the present invention to provide light 
barrier apparatus with a housing which is of simple construction and which 
can be very economically manufactured, in which the optical components 
which come into contact with the light beam are completely protected 
against contamination and the formation of condensation and which 
guarantees at the stage of manufacture that a troublefree association 
exists between the axis of the housing and the optical axis. 
This object is preferably accomplished in accordance with the invention by 
the provision of light barrier apparatus having a housing incorporating 
photoelectric converter means, said means comprising at least one of a 
photoelectric transmitter for generating a beam of light for subsequent 
propagation across a region to be monitored by the light barrier apparatus 
and a photoelectric receiver for receiving light returned from the 
monitored region, optical elements on which the light beam is incident and 
electronic processing elements, the apparatus being characterized in that 
the housing includes as an integral part at least one sealed chamber 
housing said photoelectric converter means and said optical elements and 
at least one further chamber containing said electronic processing 
elements, said sealed chamber being divided by fixed wall means of the 
housing from said further chamber. 
The fixed wall means defining said sealed chamber preferably form an 
optical tube integrated into the housing. This optical tube preferably 
extends into the housing from a window provided in a sidewall thereof. 
This window, depending on whether the apparatus is basically a light 
barrier transmitter, a light barrier receiver or a combined unit defines 
the light exit and/or the light entry surface for the beam of the light 
barrier. The window is in any case sealingly closed by an optical element 
such as an objective lens, a cover plate or a filter. At its end remote 
from the window the tube is usually arranged to carry the associated 
photoelectric transmitter and/or receiver. 
The photoelectric transmitter and/or receiver can themselves usefully be 
used to seal the inner end of the optical tube remote from the window. 
The optical tube advantageously diverges conically outwardly from the 
associated photoelectric converter means. 
In light barrier apparatus incorporating only a photoelectric transmitter 
or a photoelectric receiver the invention envisages only the use of a 
single optical tube extending from a window provided in one of the narrow 
sidewalls of the housing. If however a light transmitter and receiver are 
united into a single housing then two optical tubes are conveniently 
arranged alongside one another with both optical tubes extending away from 
a window or windows. Preferably only a single window is provided and is 
sealingly closed by a single optical element, such as one of the 
afore-mentioned objective lens, cover plate, or filter. 
Thus in accordance with the present teaching there is provided a separate 
optical space which is hermetically sealed from the atmosphere and from 
the remaining interior space of the housing. This optical space which can 
be manufactured without difficulty or expense thus remains absolutely free 
from contamination and condensation throughout its entire surface life. 
As the optical tube or tubes can conveniently be manufactured in one with 
the housing, for example by injection molding techniques, it can be 
ensured that a fixed association is present between the alignment of the 
optoelectronic components and the housing. The alignment of the optical 
axis with the axis of the housing is ensured, reproducably and without 
problem, by arranging for the optical tube to simultaneously centre the 
objective lens. The decisive factor in ensuring an exact relationship 
between the optical axis and the axis of the housing is the quality of the 
tools that are used for manufacturing the housing. 
A further advantage of the present construction is that the optical space 
or chamber remains tightly sealed even when it is necessary to open the 
housing for example to effect cable connections or to carry out 
adjustments. Moreover during manufacture it is possible to firstly finish 
the optical chamber with all its associated elements so that it is 
protected against the entry of contamination or moisture and then to 
arrange the other elements of the electronic processing circuit in the 
housing.

Turning first of all to FIGS. 1 and 2 there can be seen a general 
illustration of an item of light barrier apparatus which can be either a 
light transmitter or a light receiver. It will be understood that two 
similar units namely one light transmitter and one light receiver would be 
arranged at opposite ends of a region to be monitored so that a light beam 
projected from the light transmitter is directed towards the light 
receiver. 
As seen in the illustrations the light barrier unit comprises a housing 
generally indicated at 17 which is of generally rectangular shallow 
box-like form. An integral optical tube 18 extends into the interior of 
the housing from a window 14 formed in one narrow side of the housing. As 
can be seen more clearly from FIG. 2 the optical tube 18 has a generally 
rectangular cross-section and tapers in conical fashion from the narrow 
sidewall 19 to its inner end. This inner end of the optical tube is 
located approximately half way inside the housing 17. The inner end 20 of 
the optical tube 18 which is closed on all sides by fixed walls houses in 
a sealed arrangement a photoelectric converter in the form of either a 
photoelectric transmitter or a photoelectric receiver depending on whether 
the unit is a transmitter or receiver unit. The outer end of the optical 
tube 18 is closed by a window in the form of a cover plate. This cover 
plate can alternatively be replaced with a filter or an objective lens. In 
any case the window defined by the cover plate, filter or objective lens 
is also arranged in sealed fashion in the housing 17. 
As a result of this construction a sealed optical chamber or space 15 is 
present within the optical tube 18 which is hermetically sealed from 
atmosphere and from the further chamber defined by the remaining inner 
space 16. The optical chamber 15 is thus sealed against the ingress of 
contamination or moisture. The electronic processing elements which are 
associated with the light transmitter or receiver but which do not come 
into contact with the light beam are housed within the further chamber 16. 
These electronic processing elements are not shown because they do not 
form part of the detail of the present invention. Full details of suitable 
electronic processing circuits and components can be found by referring to 
any one of a large number of published patent specifications. As the 
chamber 15 is divided by fixed wall means of the housing from the further 
chamber 16 it remains sealed even when the housing must be opened in order 
to allow assembly, repair, installation or adjustment of the electronic 
processing elements. The sealed optical chamber 15 is thus protected for 
the entire service life of the light barrier unit against contamination 
and the formation of condensation. 
One particular advantage of the above described construction is that the 
optical axis 21 of the optical part is exactly aligned to the walls of the 
housing 17 as a result of the optical tube 18 being injection molded 
together with the housing 17 in one manufacturing step. As a result it is 
possible to simultaneously injection mold a sighting aid 22 with the 
housing so that even when operating with light outside of the visable 
spectrum the light barrier unit can be accurately aligned with the unit at 
the other end of the monitoring region, i.e. a light transmitting unit, a 
light receiver unit or a reflector. As can be seen from FIGS. 1 and 2 the 
sighting aid 22 conveniently has the form of a pair of spaced apart lugs 
each having a sighting aperture with the two sighting apertures aligned 
with the optical axis 21 of the unit. 
Turning to FIGS. 3 and 4 there can be seen an embodiment of the invention 
which is particularly useful for an autocollimation light barrier, i.e. a 
light barrier in which the light transmitter and receiver are arranged in 
one unit. In this arrangement two optical tubes 18', 18" are arranged 
alongside each other and in particular one above each other in the housing 
17. These optical tubes are likewise made in one piece together with the 
remaining parts of the housing (apart of course from a cover plate 
member). The front openings of the two sealed optical chambers 15', 15" 
which are defined by the two tubes 18', 18" respectively are closed by a 
window in the form of a one piece double lens 13. A photoelectric 
transmitter 11 and a photoelectric receiver 12 are located at the far ends 
of the optical tubes 18', 18" respectively and are each associated with 
one of the lenses of the double lens 13. For this embodiment a 
retro-reflector (not shown) is provided at the opposite end of the 
monitoring region and reflects the light received from the light 
transmitter 11 via one part of the double lens 13 back to the receiver 12 
via the other lens of the double lens 13. 
As in the previous embodiment the optical chambers 15', 15" are 
hermetically sealed relative to the atmosphere and relative to the further 
internal chamber 16 of the housing 17 so that neither contamination nor 
moisture can enter the optical tubes 18', 18". 
Thus, in accordance with the present teaching, the accurate construction of 
the mountings for the optical and optoelectronic components in the optical 
tube (or tubes) thus stems from the initial manufacture of the housing and 
the optical tube (or tubes) as a unitary component. In this way the 
optical accuracy is predetermined from the outset. 
The housing 17 can easily be closed by a suitably designed cover plate, 
this cover plate does not however play any roll in sealing the sealed 
optical chamber 15 because this chamber is defined by fixed wall means of 
the housing. 
It will be apparent to those skilled in the art that detailed modifications 
may be made to the arrangements herein described without departing from 
the spirit of the present teaching.