U.S. patent number 3,858,043 [Application Number 05/398,943] was granted by the patent office on 1974-12-31 for light barrier screen.
This patent grant is currently assigned to Erwin Sick Optik-Elektronic. Invention is credited to Ernst Gass, Erwin Sick.
United States Patent |
3,858,043 |
Sick , et al. |
December 31, 1974 |
LIGHT BARRIER SCREEN
Abstract
A light barrier screen having a plurality of sequentially
arranged light sources which emit a light beam occupying a given
predetermined area, and a photosensitive receiver which registers
the intensity of the light beam coming out of the predetermined
area and emits an output signal upon a given decrease in intensity
of one or more light beams, said individual light sources being
introduced through a single energy source in rapid temporal
sequence.
Inventors: |
Sick; Erwin (Icking,
DT), Gass; Ernst (Munich, DT) |
Assignee: |
Erwin Sick Optik-Elektronic
(Waldkirch, DT)
|
Family
ID: |
5857357 |
Appl.
No.: |
05/398,943 |
Filed: |
September 20, 1973 |
Foreign Application Priority Data
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|
|
|
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Sep 26, 1972 [DT] |
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2247053 |
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Current U.S.
Class: |
250/221;
340/555 |
Current CPC
Class: |
F16P
3/144 (20130101); G01V 8/22 (20130101); G08B
13/184 (20130101) |
Current International
Class: |
G08B
13/184 (20060101); F16P 3/00 (20060101); F16P
3/14 (20060101); G01V 8/10 (20060101); G01V
8/22 (20060101); G08B 13/18 (20060101); G06m
007/00 (); G08b 013/00 () |
Field of
Search: |
;250/209,221,222
;317/124 ;340/258B |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lawrence; James W.
Assistant Examiner: Grigsby; T. N.
Claims
While the above described embodiments constitute the presently
preferred modes of practicing the invention, other embodiments or
equivalents are within the scope of the actual invention, which is
claimed as;
1. A light barrier screen having a plurality of sequentially
arranged light sources which emit a light beam occupying a given
predetermined area, said individual light sources being introduced
through a single energy source in rapid temporal sequence, the
light beams coming out of said area being optically unified upon a
single measurement-photoreceiver which registers the intensity of
the light beams coming out of said area and emits an output signal
upon a given decrease in intensity of one or more light beams, and
a single evaluation electronics connected to said
measurement-photoreceiver for the evaluation of electrical signals
actuated by the individual light beams coming out of said area.
2. Light barrier screen in accordance with claim 1, wherein
comparison-beams emitted by each of the light sources are unified
through the same optics as the measurement beams upon a single
comparison-photoreceiver which is hooked up to a comparison circuit
provided in the evaluation-electronic.
Description
FIELD OF THE INVENTION
The present invention concerns a light barrier screen with (1) a
plurality of sequentially arranged light sources which emit a light
beam occupying a predetermined area, and (2) a photosensitive
receiver which registers the intensity of the light beam coming out
of the predetermined area and emits an output signal upon a given
decrease in intensity of one or more light beams. Light barrier
screens of this type are already known (DAS 1,170,286) and are
utilized as guards for relatively large surface areas. They are,
for example, used as safety light curtains in front of the danger
zones of machines such as presses, giving an automatic shut-off
signal when a hand or other body part approaches the danger
zone.
SUMMARY OF THE INVENTION
The aim of the present invention is a light barrier screen of the
above-named type in which the cost of its practical embodiment is
substantially lowered without adversely affecting the high
requirements of reliability and safety which are made upon such
screens. The present screen is also of compact, neat design and
easy to manufacture.
To accomplish this, the present invention provides that the
individual light sources can be introduced through a single energy
source in quick temporal succession. In this manner, a sort of
radius vector (guide beam) principle results, but without the
necessity of using mechanically moving parts such as mirror wheels
or vibrating mirrors. It is an advantage of the present invention
that only a single energy source is called for, which constitutes a
considerable cost reduction. Between the energy source and the
individual light sources is located, in accordance with the present
invention, an electronically operated reverser switch, which
connects the light sources with the energy source in the temporal
sequence mentioned above.
A further substantial simplification is achieved in accordance with
the present invention in that for the evaluation of the electric
signals actuated by the individual light beams leaving the guard
area there is only one single evaluation-electronics provided.
In case a photoreceiver is provided for each light source, a
reverser switch is placed between the photoreceiver and the
evaluation-electronics, and the reverser switch is in the same
rhythm on the evaluation-electronics as the photoreceivers on the
light source side.
An advantageous practical embodiment provides that each light
source is set up with a measuring photoreceiver which receives the
light beam out of the guard area and another
comparison-photoreceiver which receives light emitted by the light
source but not traversing the area, and that the outputs of both
measuring and comparison-receivers are hooked up to a comparison
circuit inside the evaluation-electronics. In the comparison
circuit the quotient of the two signals is formed, so that
differences of background brightness of the light sources utilized
as well as age phenomena, temperature influences, etc., are
completely excluded. Thus in simple fashion a device which is not
sensitive to disturbances is obtained.
Yet another substantial simplification is obtained in that all of
the light beams escaping from the guard area are optically unified
on a single measurement-photoreceiver to which the
evaluation-electronics is connected. In this form of embodiment
there is thus required only one measuring photoreceiver for
numerous light sources.
It is further advantageously provided that the comparison rays
emitted by each light source are united by the same optics as the
measurement rays to a single comparison-photoreceiver, which is
hooked up to a comparison circuit provided in the
evaluation-electronics. In the comparison circuit another
quotient-formation takes place. The advantage constituted by the
non-sensitivity to vacillations of background brightness is thus
achieved in this embodiment with the advantage that only a single
comparison photoreceiver is required, while the optics used for the
measurement ray is doubly exploited.
It is especially advantageous if the light sources are
light-emitting diodes, and Ga-AS-Diodes are used to the best
advantage. Diodes of this type are remarkable for their ease of
handling. In accordance with the present invention, they are hooked
up sequentially to the energy source by means of a shifting
register which is available at very reasonable cost on the
present-day market.
When the inventive light screen is utilized as a safety light
curtain in front of a danger zone in a machine such as a press, the
frequency with which the light sources are sequentially hooked up
is so high that in case of the instrusion of a human hand inside
the light curtain the shut-off signal occurs before the danger zone
is reached by the hand. The optimal frequency is in the order of
magnitude of 5kHz.
BRIEF DESCRIPTION OF THE DRAWING
The present invention will now be described by means of drawings
designated hereinafter as FIGS. 1 through 5;
FIG. 1 is a schematic representation of the circuit and of the
light beam paths of a first embodiment of the inventive light
barrier screen;
FIG. 2 is a side view of the topmost optical partial arrangement
indicated in FIG. 1;
FIG. 3 is a schematic view of the optical portion of a particularly
advantageous embodiment of a light barrier screen in accordance
with the present invention;
FIG. 4 is a side view of the object of FIG. 3; and
FIG. 5 is an example of embodiment of an evaluation-electronics for
the inventive light barrier screen.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
In accordance with FIG. 1, six Ga-As Diodes 11, 12, 13, 14, 15, and
16 are sequentially connected in such a way that the light emitted
by them through paired lenses 48, 49, 50, 51, 52 respectively
result in light beams 18, 19, 20, 21, 22, and 23, which are very
close together and substantially parallel. Light beams 18-23 are
reflected by natural dispersion into a triple mirror 54 in such a
way that they fall into the second rank of the paired lenses 48-53
and a reflection on measuring photoreceivers 26, 27, 28, 29, 30,
and 31 results, which may be especially readily seen in FIG. 2. We
are thus dealing with a reflection in accordance with the
autocollimation principle through pupillary division.
Beams 18-23 thus make up a guard area 24. If an obstacle is
introduced into this area, the light stream reaching one of the
measurement photoreceivers 26-31 is correspondingly weakened. This
decrease in intensity is transmitted for evaluation.
In accordance with the present invention all six light-emitting
diodes 11-16 are connected to an energy source 17 via a reverser
17a. The reverser guarantees that only one diode at one time is
charged with voltage and that in rapid sequence all diodes are
cyclically charged, while this operation is constantly repeated. If
this operation occurs with a sufficiently high frequency in the
order of magnitude of 1 through 10 kHz, a light curtain which is
for all practical purposes uninterrupted is generated in guard area
24.
Measurement photoreceivers 26-31 are hooked up to an
evaluation-electronics 25, which delivers a signal at its output 55
as soon as the intensity of the light reaching any of the
measurement photoreceivers falls beneath a given predetermined
value.
Differences in background brightness of the light-emitting diodes
being used, as well as of other disturbances influencing diode
brightness, can be excluded in that each of the diodes 11-16 is
arranged in front of guard area 24 but next to the plane mirrors
42, 43, 44, 45, and 46 which are arranged for the measurement of
ray paths, said plane mirrors connecting one portion of the light
emitted by the relevant diode to comparison-photoreceivers 32, 33,
34, 35, 36, and 37 respectively.
Also, comparison-photoreceivers 32 through 37 are hooked up to the
evaluation electronics 25 in which a comparison circuit is located,
in which the quotient from the electric signals of each
measurement-comparison-photoreceiver pair is formed. In this
fashion differing background brightnesses of the light sources
being used are of as little significance in the evaluation as aging
phenomena or temperature influences on the light sources.
In the embodiment illustrated by FIGS. 3 and 4, the light rays
escaping from guard area 24 are reflected (instead of through
lenses) through a wedge 62 arranged as in the drawing and a concave
mirror 40 together upon a single measurement-photoreceiver 38 which
is hooked up to the evaluation-electronic 25 shown in FIG. 4.
To each of the diodes 11-16 a small plane mirror (42-47) is
connected (said mirrors having been appropriately arranged relative
to the measurement beam path). Each of the said mirrors throws
light escaping from the light source arranged relative to it onto a
concave mirror 40, which unifies the light coming from all the
mirrors onto a single comparison-photoreceiver 41. As may be seen
from FIG. 4, plane mirrors 42-47 are arranged relative to paired
lenses 48-53 in such a way that light is used for comparison-beam
39 which otherwise would not enter the measurement beam path.
FIG. 5 shows a circuit for evaluation of the signals emitted by
photoreceivers 38 and 41. These are first boosted in boosters 56
and 57 and then applied to both entrances of a trigger 58. In
accordance with the present invention, the output of the trigger is
zero as long as the signal transmitted from diode 38 is smaller
than the signal from reference diode 41. The output of the trigger
is however L, if the signal from diode 38 is greater than the
signal coming from diode 41.
At the output of booster 57 a differentiation step 59 is connected
which emits an output only for the positive side of an impulse
reaching 41. Also at the output of trigger 58 a differentiation
step 60 is connected, which however emits an output impulse only
upon the presence of the negative side of an impulse appearing at
trigger 58.
The two differentiation steps are applied at the inputs of a
settable flip-flop 61.
During normal operation, output impulses appear in regular sequence
at the output of trigger 58, so that at the output of flip-flop 61
an alternating current appears. If, however, the signal at receiver
diode 38 sinks beneath a given predetermined value in consequence
of the introduction of an obstacle inside of guard area 24, at
least one of the impulses at the output of trigger 58 disappears
and flip-flop 61 remains slightly longer in the position determined
by differentiation step 59. In the output of flip-flop 61 there is
applied in accordance with the present invention, a very rapid
automatic circuit like a relay which is responsive to every single
impulse, and if a single impulse of the series is missing it
immediately actuates a warning signal or a switch-off mechanism to
stop the machine. The circuit in accordance with FIG. 5 is also
intrinsically safe and reliable, because if any of the circuit
factors is missing the same effect is obtained as by introducing an
obstacle in guard area 24.
* * * * *