Note: Descriptions are shown in the official language in which they were submitted.
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1 3 1 0721
t,IGI IT F cr,T~1~ WI'l'~ UTOMl~T:[C
Rl;~GULl~'l'ION O OP'ïICAL TR NSMISSION
l'he present invetltioll relates to a light Eilter having
autolllatic regul.ation of the opticaL transmission.
~ rlle Ei:Lter has a Eilter element adjustable in relation
to vary its optical translllis.sion o.E visible light. ~n
optica:L sensc~r cletectY lncidellt and/or baekground light
transmitted througll the Eilter and is connected to a
regulatiny circuit. Tl-le circu.it produces an electric signal
necessary for the regulation oE the optical transmission oE
the Ei:lter element ciependent 011 the radiation Ealling on the
sensorO Ti~e sensor is arranged behind the filter element in
the radiation emittilly direction.
'I'he invenkioll also contemplates a light Eilter with
autolllatic regulation of the optical transmission which has
two ~ilter elements adjustable in relation to th,eit optieal
trasmlssiorl c~E v.isible light, and an optical sensor which
detects the ineidellt and/or background light anc3 is
connected to a regul,ati.llcJ ci~cuit whicl; produces the
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electric siyna:L nee~e~l ~or the reyulation oE the optical
trans,lllis~ioll oE the Eilter elemellt dependent on the
radlatiorl ~al]iny on the sensor.
Sucll ligl-t Eilters are used, Eor example, as protective
Eilters in tlle pcotective shields or helmets, etc., oE
wek~ers, ln order to protect the person operatiny the
weldlny apparatus Erom the extremely briyht radiation
occurriny during we.ldiny. On tlle other hand, other uses
are also possible, Eor example, in sunglasses, window panes
Eor bulLdings, auto or aircraEt windows etc.
~ slgl-ltllly wirl(low with automatic reyulation of light
translllissioll is knowrl Erom German Laicl-Open Patent
~pplicatiotl No. 2,~42,998 among others. There, a so-called
13(1ukl crystal cell, that i9, a liquid crystal element is
used Eor light screeniny. The amount of light behind the
sight winclow is measured by a photosensor and a signal is
Eecl as a regulating variable to a control circuit which
adjusts the control voltage Eor the crystal ].ayer so that
the amoullt oE :Light allowed to pass through corresponds to
a preselected desired value.
Theoretical].y, sucll an arranyement may Eunction, but it
has beerl Eound that the occurrence oE inErared radiation
can sensitively disturb this regulating mechanislll. But
sincej in weldiny applicatlons, increasinyly and almost
a].ways, a stroncJ inErared radiation occurs, the device
proposed in the above-lnentiond German disclosure has only
_3_ 131~72~
].im;.tecl ll~Se Eor wel~ler's protective shields or l)elmets,
since strollg sullsl)llle, but especia:l.ly tlle work oE a nearby
EeLlo~ weldeL, can badly impair the reyulation, because of
a strong ;.nfrared racl:iation wh:ich can unexpectedly blank
the protective sl~ield or helmet.
Invis.ible ul.traviolet radiation, also present, afEects
littl.e or not all an arrangelllent with a sensor placed
behillcl a liquic3 crystal cell since liquid-crystal cells, as
we know, let throuyll inErared radiation almost unhindered,
but largely screen out the ultraviolet radiation,
especia:l1y wherl yrovided, as usual, with polarizers in
Eront oE and behirld thelll. Moreover, usual yhotosensors,
beslcles their sensitivity in the visible range oE the
spectrum, have little or 110 sensitivity to ultraviolet
radlatlon, but are very sensitive to inEr:ared radiation.
The object of the present invention is to improve a
liyht Eilter of the kind mentiolled so that in its
regulating behavic)r, it responds mainly to visible light
but hardly at all to inErared radiation, which latter is
mucll less harmEul to persons.
Accordillg to the Eirst embodimellt oE the invention,
this object is achievec] in a liyht Eilter oE the kincd Eirst
mentiollecl by provicling another sensor in an arrangement
with a sincJle llght Ei.lter element which is adjustable in
its optical transllllssion. The anotller sensor i8 arranged
beslde or in Eront oE the Eilter element, in the direction
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c~E racli~tiorl emi~ssi.oll ~ subtraction circuit that Eorms
part c~E ll-~e reyulatilly circuit is provlded. The
subtraction clrcuit subtlacts the signal yenerated by the
other sensor from the siyllal oE the optica]. sensor, or the
siynal oE the optical sensor Erom the signal of the other
sensor, ~so that the output signal oE the regulating circuit
is at :least approxilllately proportional to the amount oE
visible light in ~ront of the Eilter element.
In an arrangemellt witll two light Eilter elernents,
switclled 011 in series and adjustable in their optical
traslnission, the object oE ~he invention is achieved
accordinc3 to c].aim 2, by arranging an opti~cal sensor
functiona:Lly behilld the Eirst Eilter element in the
directioll of radiation ernis.sion and by providing another
sensor whicll is arranged beside or in Eront oE the Eirst
Eilter elerment in the radiation emission direction, and by
providi:ng a subtractlon circuit in the regu:lating cicuit
which subtracts the signal generated by the other sensor ~
Erorn the sigral of the optical sensor, or the signal oL the
opti.cal sensor Erom the signal oE the other sensor, so that
the output signal oE the regulatiny circuit is at least
approximately proportional to the amount of visible lig-ht
in Erollt oE the filter elernent.
In each case, there~ore, it is assured that, throuyl
the suhtraction, the i~nEluence oE inErared radiation is
elimirlated and that the regulatiny circuit Eunctioniny
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deperldq only on the ~moullt oE visible :llght ~s it has
alrea(~ly been melltiolle(l, ultraviolet radiation has on]y a
sliyht inEluerlce, ancl can be Eurther reduced, i~ desired,
by a~rang;llg arl ultravlolet blocking filter in Eront of one
or botll oE the sensors.
Witll a view to sirnpLicity oE constructiorl, it may be
aclvalltayeous iE the optical sensor and the other sensor are
identical. This provides ~ Eurther advantacJe oE their
sensitivity beiny the same. This recluces expenses ~or the
reyulatiny circuit and improves regulation. Witll this
arrangelllellt a neyative or positive control signal is
obtained according to the kind oE circuit. The signal
correspollds to the cli~Eerence between the light actually
present and the Eiltered visible light, that isl to the
amoullt oE visible ligllt behind the light filter element
without the in~rared component.
~ nother solution may consist in that the sensor arranged
behilld the liyt-t Eilter element is sensitive to inErared
racliatioll and visible l;ght, but the other sensor is
sensitive only to inErared radiation. ~ter subtraction,
accordincJ to the circuit, a positive or negative signal is
obtalned, wilich is directly proportional to the visible
liyht component without inErared radiation. The
disadvalltage here is that two diEEerent sensors, possibly
with diEEerent sensitivity, or sensors with difEerent
characteristics, must be usecl. This can be compensated,
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however, by arrang;.llg an adj-lstable arnpliEier after one or
boLI~ sensors. Irhe aclvantage o~ the Eirst mentioned
reyul.ating circuit ls that it is simp]er.
Other embodilnel-ts ancl further Eeatures of the subject
invelltioll are deE:ined in the dependent claims.
Tlle invelltioll wi:Ll be explained in detail below, with
reEerence to the attached drawings, which ~show
schematically several embocl:ilnents:
F;.y. 1 shows a Eirst embodirnent with a single filter
elelnellt;
l~ly. 2 shows a modiEied Eorm oE the Eirst embodiment;
Fig. 3 shows a second embodiment witll two Eilter
elemellts conllected one aEter the other? and
E'iy. 4 shows a modiEied ~orm oE the second embodiment.
~ ccordlng to liig. 1, the l.lght Eilter according to the
lnvelltion includes, Eor example, a liquid crystal cell l;
that ls, a llquid crysta:L element consisting, in principle,
oE two parallel glass.palles 2 with a liquid crystal layer 3
between theln. 'rhe ylass panes may themselves act as
polarizers, or separate polarizers may be provided Eor the
llqui.d crystal elements. Such elements are known and are
characterized by the Eact that such a filter element, by
applyiny a variable alternating voltage to the liquid
crysta.l layer 3, can be changed Erom a substantially
transparellt cond.itioll to a substantially opaque condition.
Behind the liquid crystal cell 1 is arranged a
photosel-sor 4 which pick5 Up the radlation let through by
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t:he ce:l:L l, and gerlera~e3 an vutput siyndL proportional to
the receive~ intells;ty of the radlation. ~ difEerential
alllpl.i~i.er 5, WhiCIl will be discussed later, transmits the
output signa] o~ the sensor ~1 to a reyulatiny circuit 6,
wh.icl) processes the signa.l. and, in turn, yenerates an
output control signal directed thro~lgll a line 7 to the
].iquid crystal cell 1. '.I'he arranyement is such that the
cel.L :l is blanked when the sensor 4 receives much light,
ancl vice versa; such a device is known and need not be
explained here.
'rhe arrangement showl) in ~ig. 1 includes also anotller
sensor ~, which in the pres.ent case is arranged beside the
cell 1. It might equally well be arranged in Eront of the
cell 1 since it is on.l.y essential that it always receives
the total amount oE existiny radiation without being
inE.luenced by the cell :l. The sensor a generates an output
signa:l dependellt on the received radiation and which is
transmitted to an impedance transEormer 9 the outlet of
~which is connected to the second inlet of the differential
ampliEler 5. Ultraviolet b].oclcing Eiltees miyht be
instalJ.ed in front oE the sensor 4 and/or the sensoe ~ to
filter out any disturbilly ultraviolet radiation.
'rhe circuit Eunctions as Eollows:
lladiation, Erom a we].dinc] spot, for example, and thus
contain.ing a (relative].y strony) infrared componellt, a
vi.s.i.ble liyht componellt and, possibly, an ultraviolet
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1310721
component, also is emitted in the direction Pl as shown by
arrows. 'rhe cell l ;s in an open condition, and the sensor
4 rece;ves almost a:ll the radiation. In any ease, it should
be noted tllat a l;quid crystal cell, ev~n in an open
concli~ion, already acts as an ultraviolet blocking filter,
so that, practically, at Eirs~, the total amount of inrared
racliatlon and visible light is received by the ~sensor 4.
The reyulating circuit 6 is deslyned in the known way, 50
that it de:livers at once an output signal to the cel] 1,
whictl acts witllill mil.Lisecollds, so that the eell 1 is ;~
blanked; that is, its radiation perrnèability is redueed. A
control circuit, which may be provided, permits to ~set the
regulatillg circuit 6 to a certain preseleeted blanked value.
'[he distinction oE sueh arl arrangernent, however, is
that, even with the occurrence oE inErared radiation alone,
OL with a strong compollellt oE radiation oE such wavelengtlls, ~;
a response oE the regulatiny circuit and, thus, blanking oE
visible light takes ylace. I~owever, in many cases, this is
hiyhly undesirable; Eor example, in ease oE a strong
sullligllt or witll an inErared radiation caused by a
neiyhborillg workplace.
Provi~ lg a remedy here is the objeet oE the present
illVellt iOIl. 'l'his takes place, in the Eirst discu~ssed
embodimer-t and shown schematically in Fig. 1, in the
followillg way:
Le~ us assume that the two sensoes nalllely sensors 4 and
8, are identieal; that is, equally senslti.ve to in~rared
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radiati.~ and to v.i.sib.le light. The sensor 4 receives all,
or pl:act.ically al,,l. i.nCrared radiation and a component of
vi~sible ;ligllt when the :L.;quid crystal cell is blanked. The
sensor ~, on the other halld, receives al]. the in~rared
racl;.ation as we:L1 as a:ll the radiation in the visible range
oE tl1e spectrum, since, accordiny to the invention, it is
p].aced in Eront o[ or beslde the liquid crystal cell 1. The
ultraviolet radiation compolleni: i9 practically negligibleO
L,et:
IR = IR radiation component
Sv = component oE visible radiation behilld the
liquid crystal cell
Sk = component oE visible radiation in Eront
oE the liquid crystal cell
Ao1 = ~rop:ortiollality Eactor oE the output
siynal oE the subtraction circuit.
Therl, accordiny to whetller the sensor 4 is connected to
the nollillvertilly inlet, and the sensor 1' to the inverting
inlet oE the diEEerential ampl.LEier 5, or conversely:
(Sv ~ IR) - ~Sk -~ IR) = Sv ~ Sk = -A 1~ or
~(Sv ~ IR) -~ (Sk -~IR) = =Sv ~ Sk = ~A 1~
In both ca~ses, thereEore, a Eactor is obtained,
indepell(1ellt oE the inErared component, whicll is used to
control. the i.iqu.i.d crystal cell 1 and whicll is a].so
inEluellced by the visible light component behind the cell
1, so that it can be used as a regulating variable.
..., ~ ~.
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rlle arranye1nent discus~sed above has the advantage that
two ide11tical sensors (4 and B) can be used, oE w11ic1l the
characteristics may also be equal or very simLlar; however,
tl-e costs o~ evaLuatiny the output signal, Aol or -~ol~
i9 somew11at greater.
In order to avoid these costs, lt i5 posslble to use
two dirEere11t sensors ~ and 8. ~I'he sensor ~, aEter the
cel] l, i9 sensitive to ;.nErared radiation and to visible
light; t11e sen.sor ~, beside or in front oE the cell l, on
the other hand, is sensitive ~y to inErared radiation.
Ther1, based 01l the above deEinitions, dependent, again, on
tlOW the two sensors are connected to the difEerential
ampliEiers:
(Sv ~~ IR = Sv ~o2' or
~(Sv ~ IR) ~ l) = Sv ~02'
11ere again, the output signals ~02 or -~02~ are
Eree oE any inErared componerlt and also directly
proprotional to the amour1t oE visible light received behind
the cell l. Thus, they may be processed simply and
directly, in the reyulatiny circuit.
With this arranyement, two difEerent sensors might be
used as sensors 4 and 8, or, as in Fig. 2, identical sensors
14 and l8 miy11t be used, with an inErared band-pass Eilter
beiny p:Laced in Eront oE the sensor 18. The rest oE the
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3~0721
arrangelllellt, witll a liquicl crystal cel]. 11, consi.stiny oE
two pa~allel gla~ss plate~s 12, a l:iquid crystal layer 13
Lying betweell them, possible separate polari%ers (not
sllowll)~ a ~ilolosellsor 1~ arranyed behirld a diEEerentia:l
amp:LiE;er 15, a regulatlllcJ circuit lG, connected througll a
l.ine 1-1 with the cell l:l, and an impedance transEormer/
amp:LiEier :I9, i.s, ilt pTinciple~ exactly the same. Ilowevee,
it may be recommellde(l here that the .switchillg circuit :L9 be
a~justable in its ampliEication to be able to compensate
any losses oE sensltivity caused by tlle filter 20.
In Fiy. 3 is shown a second embodiment oE the
lnventioll. Unlike the desigM in Fiys. 1 and 2, two liquid
crystal cells 2]a and 21b, connected one after the other,
are usecl here, in order to obtain a stronyer dampiny oE
light whicll ls sometimes desirable. For the rest, these
structures are the same, witll a liquid crystal layer 23a or
23b, betweell two parallel glass plates 22a or 22br in each
case, WlliCIl themselves act as polarizers, or with separate
~o.l.arizers (not shown) located in Eront oE and behind the
cells. The yllotosellsor 24 is arranged aEter tlle Eirst cell
21a b-lt in Eront oE the cell 21b, in the radiation emitting
~lirectioll Pl, so tllat a suEEicient residual amount of light
Ealls on the sensor, Wtl ich is necessary for actuation oE
the regulatiny circuit 26.
Corresporldillgly, anotller sensor 28 is arranged beside
or in Eront oE tlle Eirst cell 21a, which, as it was already
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1310721
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melltlolle(3, receives eitl-ler the who:le radiation spectrum or
onl.y the inrrared colllpollerlt, alld conduct6 its output signal
throllcJIl a posslbly adjus~ab]e impedance transformer-
amp]iEier 29 to a diEEerential ampliEier 25. The output oE
the reglllatiny circuit 26 i.5 conducted through a line 27 to
the two cell.s 21a and 2:Lb, conllected one aEter ~he other,
wlli:le rneans (not shown) may possibly be provided Eor the
opposite-pllase ac~uation oE the ce.l.ls.
~ 5 to the spectruln sensitivity oE the cells 24 and 2B,
or the Eilters (not shown), arrancJed in Eront oE them in
all cases, what has beer- said above applies in principle.
t~, Eor physical reasons or Erom commercial
consicleratiorls, it is impossible to pIace the sensor 24
between the cells 2Ja and 21b, a solution according to Fig.
4 may be considered. Eleee, two liquid crystal cells 31a
and 31b, arranyed more c].osely to each other and arranged
one behilld tl-e other in ~he licJht-emittillg direction Pl,
are providecl. ~ach ce].:l CollSiSts oE two parallel glass
plates 32a arld 32b ancl a liquid crystal layer 33a or 33b
between them. As to polarizers, what has been saicd beEore
app].Les.
The pllotosensor 34 can be mounted behind the Eirst cell
31a, brlt can be arranyed, pllysically, aEter the second
cell, the second cell 31b is provided with an opening 40,
whicll always remains openso that no changes in optical
transmission behavior occur even whell tlle cell 31b is
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blanked. This is advantayeous whenever the two liquid
crysl.al cells 31a ar-l 3]1 unlilce the schematic
reLrese~ atlon in tlle drawillg are very narrow or must be
placecZ very close to each other. The small opening 4~ at
tl~e etlcJe oE the ce:Ll 31b hardly di.sturbs the behavior and
eEEect oE the tota] arranc~ement or not at all. For the
re~st the str~lcture oE the arrangement with another sensor
3~ the impelallce trallsEormer-ampliEier 39 the
diEferential ampliEier 35 and the reyulating circuit 36
connected to tlle cel.:l.s 3:La and 31b througll the line 37 are
the same as described beEore.
Natural].yr in the arrangelllellt accordinc3 to Fig. 3 and
Fi.g. 4 respectively the sensors 24 and 34 on the one
hand and 2~ and 3~ on tlle ottler hand are oE the same
type possibly wlth band-pass Eilter (not shown) beEore the
sellsor 2~ or 38. ~lternat:ively dieEerent types may be
uscl; that ls sensor 24 or 34 may be sensitive to inrared
an(l to vlsible liglt and sensor 28 or 3~3 on the other
hanc3 may be sensltive only to inErared component. What
has been sai3 beEore as to the adjus-table ampllEication Oe
the impedallce transEormer-arrlpliEier 25 or 35 also applies
ill pr.illcip] e.
J.ina.lly it should be melltioned that polari~ation
f.ilters must be located in Eront oE and behind the llquid
crystal cell.s Eor eYample as Icnown in the state oE the
art Çor example Eroln U.S. Patent 4 039 354.
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~310721
",
lt :is importarlt accorcling to tl)e invention that the
inEluence oL inErared radiatioll on the regulating circuit
be elimll-latecl, and tllat an .inErared blockiny Eilter be
e:lectrica:LLy si~ lated. ln thls way, an eEfective,
rel.iabl.e regulation oE the li.ght permeability of tlle light
Eilter, whetller it consists oE one cell or oE two cells
located one behil-ld the other, is always assured, even when
strony inErared radiatio1l prevails in the backyround, since
tile reyulatiny circuit now responds only to visible light.
rhe u]traviolet racliati.on, also present, harclly interferes,
since most photosellsors, as already mentioned, hardly
respollcl to this, and since a liquid crystal cell is in
itselE already a good ultraviolet blocking filter.
