CA1257917A

CA1257917A - Electro-optical position determining system

Info

Publication number: CA1257917A
Application number: CA000506246A
Authority: CA
Inventors: James M. Lapeyre
Original assignee: Laitram LLC
Current assignee: Laitram LLC
Priority date: 1985-05-10
Filing date: 1986-04-09
Publication date: 1989-07-25
Also published as: EP0202468B1; DE3684722D1; NO177167C; JPS61260322A; NO861636L; US4688933A; NO177167B; EP0202468A1; JPH0490242U; JPH0720761Y2

Abstract

ABSTRACT

A position determining system for providing electrical signals representative of the positions of light source movable within a defined area. The system may be implemented for purposes of data entry or for purposes of object location or surveying. When embodied in a data entry tablet, the invention provides signals representative of the positions of a stylus movable within the area of the tablet and comprising first and second photodetectors spaced along a base line by a predetermined distance, and means associated with each photodetector and operative to provide a movable narrow field of view for each photodetector.
Means are provided for monitoring the angular position of each of the fields of view with respect to the base line and for providing a signal indication of the respective angular positions. A stylus having a light emitter at the tip thereof is movable within the area of the tablet and provides light detectable by each of the photodetectors. Each of the photodetectors provides a respective signal when the field of view of the corresponding photodetector receives light from the emitter.
Means are provided which are operative in response to the signal indication of the angular position of each of the movable means at which light from the emitter is respectively detected to provide a signal representing the position of the emitter within the area of the tablet.

Description

S7~7 D_r IIIE l'~VEN OM, ~ls invention relfltes to position determining ~ystems and more p~rticu!~rly to appsratus for prOYidillg electricsl ~nQls representatlve of the position of an object movable within ~ predetermined are~.

~ _ ENTION

Systems are known for determiniulg the position or location of ~n objec~
within a defirled are~. Such systems find utility for the entry of gr~phic ~nd othe~
information into ~ computer, ~nd sre often embodied into ~ data entry tablet which includes me~ or sens~ng the position of a stylus or other po~nt movsble withi~ adeflned ~rea, snd for providing an electrical sign~l whch is r~presentQti~ of successive stylus pO5itiOrls~ thereby t9 denote lines, curves and flgures drawn by the stylus on thc tablet. Another known use for ~05ition determining systems ~Is forland sur~eying and wherein laeans are provided ~or sensirlg the position o~ rgetmoYable within a deIin~d 0rea, and îor pro~nding a signsl reE~resenta~ive of the~ensed target positions and from which s~ey information ~an b~ deriv~d.
~. related data entry device is ltnown ~s 8 curlsor con~o~ler or "mousen, which is usu~lly in the form of a small housing movable over Q surface asld which pro~rides co~Tesponding movemerlt of a cursor on 8 diSpl13Ly screen. Movement ofthe cursor can b~ employed for data entry ot graphic~! inliorm~tion ~nd csn al~o be ~ced as ~. pointer for identifying Q position on the screen or inform~tion displayed on the ~reen, such as for interactive computer usage. ~ general, mous~

. -2-movernent is provided by a ball that rolls over ~ surf~ce, the b~ll rnovement belng sensed by mechanicQl or optical means. Motion ~n ~Lso be s2nsed via ~L speciQllyprep~red sensible surf~ce over which the mouse is moved~ For ex~mple, a checkerbo~rd p~ttern has been employed on a surf~ce, ~Lnd llght reflected from the surface is detected by a photodetector which pro~ides pulse sign~ls indicstlve of mo~on with respeat to the surfac0 pattern. ~ review o~ sever~l d3fferent types of mouse cursor controllers ~s provided in ar ~rtlcle entitled ~terfacing Mice to C~omputersn, achine Design, January 12,1984, pp. 84 91.
Grapilic lnput devices a~e known uslng palrs of scRnned llght beams, ~3 shown, for example, ln U3. Pstents 3,553,630; 3,613,066; 3,364,389~ and 4,294,5~3.
L~ this type of entry device, flrst and second n~rrow llght be~rns ~re scann~d ~cross a surf~ce and means are provided for sensing the l~ght be~ms at ln~ersecting po{nts w~thin the surface, the ~ngular position of the two be~ms at the d~te~ted lnter~ ions ~epresenting the position within the defined ~rea. Another k~own techniqu~ employ~ orthogonal light beams pro~ded ~cross ~ display surfac~, the irlterruption of selected orthogonal p~ f be9ms pro~iding An Identi~ tion ol~
the data entry poirlt.
Example~ of su~eying ~nd related systems for ~u~m~tlc pos~tion det~rmin-atlon are ~hown In U50 Patents 3~714,657; 3,400,398; 3,437,825; and 3,443,095.
Rang~ m~surlng systems are shown for example in V.S. PRte;1tS 2,830,487;
3,759,614; snd 3,961,851~

The present Invention provides R position determlning syst~em for pro~idirlg electrical sign~ls representative of th~ positioRs of ~ light source movable within a deflned area. The system mQy be implemented for purposes o~ d~ta erltry or for

2$~ purposes of obfect locat~on or survey~ng. WIIen embodled Irl ~ dat~ entry tabl~t, s --3--~l2S~ 7 the ~nvention provides slgn~ls representa~ive of ~he posltions o~ ~ stylus mov~bh withln the ~rea of the tablet and compris~ng first and second photodetectors spQc~d along a base line by a predetermined dlst~mce, and means assocl~ted with e~ch photodetec~or snd oper~tive to provid~ a mov~ble n~rrow fleld of view tor each photodetector. Mesns Qre provided ~or rnonitoring the angulRr positlon of ~ch o~ the fields of view with respect to the base line ~nd or providing Q sig~l ind~catlon of the respxtive angul~r positlons. A st!~lus having Q light emltter At the tip thereo~ is mov~ble within the areQ of the t~blet nnd provides llght detectable by e~ch of the photodetectors. E~ch of the photodetectors pro~ides Q respective signal when th~ fleld of view of the corresponding ~hotodete~tor receiYes l}ght from the emiKer. MeQns ~re provided which is operative in response to the sig~l indlcatlon of the ~ngul~r position of each of the mov~ble means ~t which light from the en~tter 3s respectively detected to provide a sigQal representing the positlon o~
the emitter wi~hln the area of the tablet.
In one prese~a~y preferred embodiment, a rotsting cylinder is provided for each photodetector, the cylinder hav~ng a slit providi~ nar~w fleld o~ v~w or line of sight which is rotah ble at a const~nt and known angul~r veloci~y. 1rhe ~ me of rotation of esch o~ the cylinde~ ~ monitored with respect to a s*~t or reference pcsition su~h that the time eLQpsed between the start position and thetime at which light from the emitter is detected by e~h of the photodetectors ~
known. The elapsed time is a mea~ure of the angular position of the rot~ting cylinder with respect to the detecte~ position of the emitter ~nd rom this ~r information, the posltion of the emitter with respect to the deteetors is r~adUly determined by known geometrical relations. Alternati~ ly, the ~ngul~r po~ition of each of Ule rotst~ng cylinders can be determined by use of respectiYe sh~t ~ngleencoders which provide signal indications of the rotational position of the resp~-ti~e cyl~nders and therefore the respecti~ve fields of view. In this l~tter instan~e, _a_ ~s~

angular position ~3 measured directly, and the rotational velocity of th~ fieId~ of ~ew need not be const~nt or known, The rotatable ~ield of view can be provided by other means such ~ ~n opflque shield rotatably movQble ~round e~ch detector ~nd operatiYe to occlude light from the light source when in the line of sight between the source ~nd thedetector. A timing cycle can be commenced by the sensed change in received llghtupon passage of the le~ding or trailing edge of the shield. The moving field o~ view can ~lso be provide~d by a linearly moYable slit or other view llmlting shield.
In snother embodlment, d single photodete¢to~ is employed and Is rot~tabl~
~bout an aX~Q and operative to detect light from Q source movabl~ within a d~fined Qre~ at each of two predetermined positions ~n the path of rot~tion. The positlon of the light source in relation to the detector positions is then determined.
~n an alternative embodiment, a p~ir of light em~tter~ rovided along a straight e~ge which is movable within the tablet area ~d the p~sltion of eRch ofthe emitters is deterrnin~ in the m~nner described above to provido an indication of the pos~tion of the straight edge within the tablet area. Additional conrm~nds can be pro~ided in con~unction with the position data of the emit~er or emitters to provide d~h correspoDding wlth the position of the sts~lus or str~ight edge at intende~ portions of the eablet area.

The invention will be more fully understood from the followi~g de~iled description t~ken in conjunction with the ~ccompRnying drawings in which:
Fig. 1 i~ A, pietorial repr~sentation of a preferred embodirnent of the invention;

~2~
: Fi~. 2 is a dlac~ammatic representation of a prefered ~odiment of thn invention;
Flg. 3 i~ z diagrs~atic representation o~ one mean~ for sonAlng cyllnder rotatlon;
Flg. 4 1~ ~ dlagrammatlc ~epre~entatlon o~ another ~eA~B ~or se~in8 cylinder rotatlo~;
Fig. 5 i8 a block diagram of the proce4sing loglc;
Flg. 6 is a dlsgra~matic representatlon o~ an alternati~o ` e~bodi~nt;
Fig. 7 is a ti~r~m~atic represo~tatisn oX an ~ltarnati~
embodim~nt o~ tho inv~ntlon;
Fig. 8 is a plctorial representatlo~ o~ A detector snd view llmltlng 6hfeld means employ~t in the embodiment of Fig. 7;
Flg. 9 1~ ~ dlagra~atic represent~tlon of 8 ~urther cm~od~men~
employi~g a ~ie~ iti~g ~hield whlch Is li~early ~o~able;
Flg. 10 18 a diagra~n~ic r2preseneatlo~ of a ro~s~abla mirror employed for directl~g rece~ved llght to an as60ciated detector;
Fig. 11 1~ a d~a8ra~a ic representatloa of un alt~r~ativ~ rotat~og ~lrror arrangement fo~ dl~ectlng receiY~d llgh~ ~o ~n a socia~d photodetector;
~i~. 12 $8 ~ diagrAm~a~tc repre~enta~lo~ of a~ e~boti~e~e o~ th~
invention e~ployl~g flber optic cables for tlrec~ng llght fro~ ~wo ~ensed posltio~s to a 8i~glo pho~odeteceor;
F~g. 13 and Flg. 14 ar~ el~ation and eop ~ie~s, ~espectivoly, of a~oeher e~bodl~ent utlliz~ng a rotatable s~agl~ deteceor and us~ul especlally or land YurVeying purposes.
Fig. 15 i9 a dldgrammaeic representatio~ of a~ e~bodim~ut o~ tho invention e~ploying three li~he reeeiving locaeio~.
. ., i~ -6-~25~ L7 DhT~ILED DF~SCRIPl7IOM OF T~E :tNV~rION
-1 R~ferrln8 eo Flg~, 1 and 2, th~rQ i3 shown a data tablet havlng a defined area 10 wlthin which a stylus 11 is movsble, The ~tylu~ h~s llght emltter 13 such a~ a l~ght emitter diode (LED) on the tip thereof.
It should ba under~tood, however, that the light provlded by omlttor 13 18 not ll~ited to l~ht havlng a fre~uency in thc vl~lble ra~ge, and, In fact may preferab1y have a frequency in th~ lnfrared freque~cy ~ange.
Flrs~ snd s~co~d photodetectors 12 and 14 are providod along an odg~ of the tablet, th2 dctector~ being spaced apart by a predee~r~l~ed ~i3ta~c~
~ which deflnes ~ known b~se lin8. A pair of opaque cylind~r~ 16 ~nd lB
aro providod around respectlve photodetectors 12 and 14, e~ch o~ the cylinders havlng a r2spective slit 20 and 22, axinlly provlded thc~eo~
to provlde a narrow field of vi~w or line of slght.for light recoivsbla b~ eh~ respecti~ photodetector from the emltter 13. Each o~ thfl cylinder3 18 rotatable b~ suitable ~otlve ~e~s such as respectiYo electrlc motors.
The angul~r pO~le~G~ o each o~ thc ro~atl~ cyli~der~ 18 det~rmlned; i~ o~e embodiment, by ~ea~urs~e~t o~ thQ el~p~od tl~ G~
rotstlon o~ each of tha cyli~ders wlth r~p~ct to ~ star~ or zoro reference po31tion. As illustrated in Flg. 3~ a ~tast po8itio~ for each of the cyllndero is defin~d by a fiduclal ~srk 28 o~ the cyli~der a~d wh~h 18 3en~ad by ~enso~ 29 to .produc~ a s~gnal ~hlch eau~es a clock cou~tsr 1~ proc~sing loglc 30 ~F~g. 53 to b~ seartod to pro~id~ ~ co~t reprc~e~eatl~ of the a~gular positlon of the a~socia~ed rot~tl~g cyllnder ~leh respece to ehe Qtart po~itlon. Th~ pro~e3s~n~ logic 30 2S al90 re ei~ ehe ou~puts from phototetectors 12 ~nt 14. The ti~e ~lapsed be~ween tho start positf on and the time ~e which light fro~ th~
, -7-~ZS~ L7 emitter i~ detected by each of the pho-todetectors is determ med by lo~ic 30 by u3e of kno~m geometrical rel~tlo~shlp~ Th~ elapset ~ime ls ~
measure of t~e angular posltlon of the rota~l~g cyllnder~ with re~pect to ehe detected position of thQ e~itter find, fro~ thls ~ngular informQtion, ~ha posltlon o~ the ~ ter ul~h r~pect to thc d¢tec~or~
19 r&3dily deeermined. Tho logic 30 prsvlde3 ~n output ~iB~81 repre~ent~t~vo o~ th~ posielon of th~ e~lttnr wi~h~n tho tablet area, and thls slgnal csn be provided to a display or o~her u~ z~tio~
npparatus.
An alter~atlv~ embodlmant i5 ~llu~tr~ted ln Fig. 4 ir whtch tb~
angular position o~ each of th~ rotating cyllnders is direetly pro~ided.
~eferring co Fig. 4, a ~haft a~gle ercoder ~9 couplet to thQ cylinder 16, the encoder balne operatlve to provldc 8 signal representatlv~ o~
th~ rotstional po61tion of th~ s~sociated cyli~der. Th~ encod~r comprl6es an e~coder di~c 3b, attached to a~d rotaeable ~l~h th~
c~linder, a~d a light sensor 36 operative eo recei~ ht ~ro~ oourco 38 ~hlch 1~ dlrected thro~gh the dlsc 34. ~he sensor 36 pro~ides sig~al~ whlch repre~ent ehe rotaclon of the disc a~d cyl~ndc~ lC. Th~
eDcoder ~lgnals sre employed by logic 30 in as90el~tlo~ ~leh th~
phoeodetect~r 81gn~1~ tO calculat~ the p~ltlon o~ th~ o~it~r 1 rels~lo~ to ehe de~eetor~.
A ~urther embodlme~t i9 Illu.~tra~ed in Fig. 6 ~ ~h~ch ~ pslr of light emit~ers 40 a~d 42 i8 pro~ided ln 3paced relation along a seralgh~
ed~e which 3 mov~ble wlthl~ the t~blee area. rn the illu~traeed embodi~e~, the light emltter~ 40 and 42 are provldod on a ee~pla~e 44 whleh is movable ~ithl~ the tablet area. Th~ p~8ieiOn of esch o~ th~
emiteers ~9 deter~lned 1~ the man~er described above to pro~lde aa . --8--,~, ~25~7 : mdication of the straight ed~e defined by the ~paced emitt~rs wqthin the area of tho tablet. The template can include a stand~rd ~rame lnto which ~arious te~plate she~ts are inser~able, esch prov~dlng sy~bol~ aud forms as de~ired.
It ~ay bQ desirable to distingulsh between the re3pective ~ltt~r~
40 ant l2. Thi3 cln be acco~plished in ~everal different wsy~, lnclutl~g tho empl~ent of dif~erent fre!~uencles o~ llght ¢mi8810~ by the re3pectivo e~lttar~, or by pulslng thQ emltters at d~f~Qrout raee~, If such eotin~ of the light e~i8BionS iB e~ployed, the cl~cu~try a~sociatet with ~he light sa~sor~ will inelude mea~ for dlstiuguishlng between the raspectiYe light e~lssioo~.
In adtltio~ to the entry of the posltlon o~ ~ flt~lus poi~t or ~n edge and thd display o~ ~uch poiot or odge pO~itiO~ff ~ addltlo~al $n~ormAtlasl ean ~ ~ntered for display iu 8~60clatio~ ~eh ehe po~ltio~al tsta or for other as~ociated u6e. For example, oharActer~
such as n~mbers, l~teers and ~mbols 46 can be prov~ded o~ the templat~
44 of Fig. S aDd AUch ltem~ can ~e dl3played l~ assoclatlon with th~
poæltlo~ and orlentatio~ of the defined edge b~ e~try o~ such l te~w O
Such date enery ca~ b~, for exampl~, by mea~s of ~ optical pQn 48 for ~electi~g. characters. Ouce the orie~eatlon of eb~ d~in2t ed~ or orie~t~tlon o the t~mplat~ l~ k~own, in th2 ~a~ner de~cr~bed abo~e~ eh~
posltio~ of ~ach sgmbol~ nu~ber or lette~ ~thi~ t~a to~pl~t2 i~ al~o known a~d r~ b~ reatlly e~tered lneo a daea ~ysto~ for di~pla~ ~uch a~
~y opt~cal pen or oth~r known mes~s.
I~ th~ aboYe e~bodl~ent~, each det~ctor ha~ a rotatlng ~lit t~socla~ed th2rewith ~or de~lnl~g the re~pect~vc ~arrow fleld o~ ~ie~.
A further e~bodimesle is shown in Fig. 7, which dep~ct~ a p~ir of _9_ Q~' '~ S 7 ~ ~L~

detecbQrs 49 each hav mn a trc~nspc~ent cvlinder 50 disposed there3xound uith an opaqu~ ~egmant 52 on the cyllndar. Each o~ th~ detectors can ~e s~m~l~rly e~bodied as illustrated in F~g. 8,. Th~ detector~ rec~lv~
light from the li~ht source 13 ~t ~ll tlme~ ~x~ept when temporatlly occluded by the lnterpo~itlon of the opaque shleld i~ the llghe psth.
rhe line o~ sight between the light source and detector can b~ speclfIed at the leading edge or traIll~g edge of. the noving shieId. Th~ ~rcuat~
length uP the 3hiald caD be o~ any exl:ent lass than 360o Duri~g the interval at whlch the shleld occludes the light, the clock counters CA~
be res~e for the nexe timing cycle. In op~rstion, a ~t~rt ~ig~al can bs pro~ided ~ the leading ed8e of the ~hield enters th~ l~ght path, causlng a changR in the ~ensed lighe, and a timing lneerval com~w ~d for that rotatlonal cycl~ of ehe cyllnter. Alter~tively, the passage of the trailing edge of ~he shleld out oP tha llght path c~n signify eh~
~5 co~encenent of a timing cyclo.
The ~oving field of vi~w can be otherwise coordIAated ~ith thQ
detector a~t ~eed no~ b~ by a rotati~g fielt o~ ~, a~ de~crlbo~
aboYR. In th~ embodiment of Fig. 9, a~ opaque 8hi~1d 54 la pr~ided h~Yi~g ~ slie 56 ~her~in. Tho shleld beine l~arly uo~able I~
reciprocatlng fa~hion pest ~he. assoc~ated dee~ctor. E~ch detoctor includss a ~ilar reciprocati~g shield. The line o~ ~lght beewse~ o~ch detector a~d th2 light source is deeer~lned by tho alig~n~ Of ehe re~pecti~e ~lles wIth the re~pectivo llghe paths.
~ th~ e~bo~ent of Fig. 10, ~ rotat~ng ~rr~r 58 ~ e~plor~d to d~rec~ light ~r~ the light ~ource 13 eo the photodetector 4~ ~pon ~llgn~e~t of tho r~ cti~g ~urf~co 60 o~ tha rotating mlrror wleh thQ
lncite~t li~he, l~.ghe i~ directed to the detector to pecify tho ~ o~

s~

'7~

Si~lt for the positlon determlnin~ ccmru-tation. Another mirror implementaeion 19 showa ln Fig. 11, ln whlch the mirror 62 i~ rotatsbl~
about the axl~, and upon alignment of the reflecting surfa e 64 whlch the incident lightl light i~ reflected eo the detocto~ 49, which in this i lmplementation l~ top mounted ~ueh as on 8 suppor~ rm 66.
A further embodlment 1~ illustrated in Flg. 12 ln whlch ~ singl~
photodetector 4g~ is employed. A pair of ~ib~r optic cables 68 a~e provlded, each couplin~ l~ght from 8 resp6!et~ve senslng positiun to the single detector. Th~ out~r end 70 of each f~ber optlc c~bla 68 i8 dlDpo~ed to receive light from th~ llght ~ource 13 a6 ~electiv~ly provided by th~ moYing ~iqlt of vlew, ~uch as a rotati~g cyli~d~r 72 having a slit thereon9 as in th~ embodimeat o~ Fig. 3 desrribe~ abovz.
Other ~eans can be providet for transmittlng or reflectlDg light recelved from the respecelve llght 3ensing po~ltions to the 8i~glo photodetector, such a8 a mirror or mlrror a~enbly- Tha i~ner end 74 a~
each fiber optic cabl2 ~8 ~ light coupling relatioa to detector 4g~, 1~ ~111 be apprec~at~d thAt the embodiments di~cussed above m~y bo design~d ~or usa ~ lsnd BurVeyi~g but are ~ore sultabl~ for us¢ wit~
data entry tablee~. NoweYer, the embodiment of ehe lnveatlo~ shown i~
Flg~. 13 ant 14 i~ especially sultod or land survey~g. ~ s~QglR
pho~odetec~or 49b 1~ mouated on the ead of a boo~ 80 hsvin~ a couneerwa~ght 82 at ehe oeher end chereo~, thQ ~oo~ being ~ou~ted ~or rota~ion o~ a tripod B4 or other suleable ~upport, a~d ro~a~ed ae ~
k~ow~ Y~loe~ty b~ ~eans of a ~oeor B6. A lighe ~ource 13~ is pro~lded ae th~ pol~t re~ote from ehe deteotor, the lighe from thls 30urca being d~eectable by ch~ sl~gle detector st each of t~o po81t~0n8, AY
Illuserated In Fl~. 14. In the illustrated e~bodl~e~t, th~ po31~o~'8 ~,...................................... .

~s~
are shown at diametrically opposite Fositions of a ro ~ cycle. A
n~rrow fleld o vlew or the detoctor 1~ provided by any convenIen~
means, such 85 a rotating slle as tescribed-above. Ihu9, a .11~ o~
sight between the light source a~d e~ch lighe seniin~ positlo~ of the detector 1~ speelfied, and the posi.eion o the llght sourco then determined. A ~maller version of thls single detector embodi~ent c~
also b~ employed for data eablet o~ other dsta ~ntry purposas.
I~ all the e~bodi~ents disc.ussQd heretofors, it i8 as~u~d th~t there i~ a cleAr ~lins of ~ight" betw~an the llght sourc~ 3n~ th~
two llght rec~lving locatIons. This would w ually b~ the case rlth data cntry tsblets o~ tha type described, where the s~lected area ~8 al~ay~
locatet on one side of the "base lin~" whlch extends between th~ t~o s21~cted light receiYlng locations. However, 1~ applicatlon~ wh~r~ th~
"fielected area" to be monitored completely surrounds the base lIn~
extendi~g becween ~he two light receivlng location0, or where there ma~
not alwaya be a cle~r "line of 9ight" beeween the llght ~o~rce and both of the light receivltlg locse~ons (such a~ ln land surve~iug where the 0~ Big~lt ~ght b~ blocket by a tree or other ~o~ o~ble ob~ects), eompl~t~ ~urvelllanc~ of the s~lected area may no~ be possl~le.
Th~reforo, accortl~g to ~nother ~bodl~ene ~uch a~ tlagra~
ms~lcally illustraeed in Flg. 15, a ~hlrt light rec~iv~ng loeatio~
be providet eo as~ure complet~ ~urvelll~nce oP th~ ares. I~ th~
lllustration o~ Flg. 15, tho~e ele~nt-~ which ar~ the same R8 el~e~t~
~hown in th~ embodim~nt o~ Flg. 2, car~ co~mon ref~rence nu~bor~. As ~ho~n, a flr~t base line Ll ls deflned by light recei~iDg dlod~3 12 snd 14 which scan ~3.ected area 88 extendlng o~ both ides o~ bas~ Lin~ Ll as indlcated by :Llght pen llA and llB on eho ri~ht ~de a~d ligh~ p~n ~.

~2579~7 ! llC on -the left side. ~orn~ally almost all locations in the select area 88 woult satlsfactori~y be scanned by light recel~ing dlodes 12 and 14 sùch ehat the posi~ion of a llght 60urce could readIly be deter~iaed.
However in th~ e.vent an ob~ect 88 whlch is opa~ue to light source 11B
~a~ loca~ed so 88 to block the llne of sight beeween light pen 1IB a~d light re~elving dlode 14 (which llne of ~lght i8 repre~ented by ll~
segment~ 90 ~nd 92). ~he light receiviDg diodo 12 would not hav~ an input to help d~termlne th~ lo~atlon o~ light pe~ 11B, ~nd co~se4uently the loc~tio~ of llght pen 1lB along the lins of 3ight 94 could not b~
d~torml~ed. ~ow~r, accortlng to tho e~bodlme~t of th~ pres~n~
ln~entio~ show in i~ Fig. 15, there i8 al90 ~ncluded ~ third light r~ceiving dlodo 96 whlch 18 located st a know~ position ~d di~tanc~
wlth re~pect to basa lin~ L1. As i~ 8180 clear Ero~ tha lllustration o~
rig. 15, ehr~ ~re 3econdary ba6e lines L2 and L3 e3tabli~hed b~t~en th~ light rocelvi~g d~ode~ 12 and 96, and 14 and 96 re~pectl~el~.
Consequea'Iy, the positlon o~ llght pe~ 11B may readily be d~ten~ined by proccsslng e~æ inform~tio~ fro~ llgh~ recelvi~g d~ot~ 12 an~ 96 wi~h resp~t to b~s~ lln~ L2 in th~ sa~ ~an~r as the ~n~orm~tion ~rom llgh~
rc~elvlng dlode 12 and 14 ~as processed ~ith re~p~t to ba~a lin~
I~ a simil~r ~s~ner, if the ll~e o~ 8~ 8ht betwee~ tho llght source snd llght recelvl~g diode 12 1~ blocked, informatlo~ from lighg r~c~7~g tiod~ 14 a~t light rec~lvi~g tlod~ 96 mAy be used ~eh resp~ct eo ~a line L3 to d~esrmlne th~ position of ~he l~ght ~o~rc~. ~ th~rd li8h~
receiY~ng d~od~ ~ould sl~o be neceasary if ehe light 90urce ~rQ to 11~
along an exten~io~ o~ a base line eæeenting between two ll~ht re~e~ g dlodas ~ven i~ thore was no blockage of light pat~. For e~a~ple a9 ehow~ i~ Flg, lS light pen llA lle8 alo~g a~ ext~nsio~ of L3 and consequently, it is l~po~sibl~ to deeer~in2 ch2 di~ta~cs of eh~

,~ .

~ 2S7917 light source fram elther liqht receiving diode 14 or li~ht receivin~
diode 96. Bo~ever, in this exampl~ the location of light pen llA ~ay readi~y be detsr~ined by proces~ing the ln~or~aeion rece~ved froM llght receivi~g dlode 12 and llght receiving diode 96 wlth r~spect to bsse i line L2.
Llgh~ pen source llC i~ included eo lllustraee thae thc ~urvelllanco a~ea or selectet area completely surround th~ lighe rec~lv lng locat~ons. Furthermore, although the lighe racelvlng d~ode 12, 14 and 96 are arra~8ed lu Flg. 15 90 as to form ~n equilateral tria~gl~ to slmpll~y the prOCe~Bl~g of data or cslculations, the three locatious of the llght rec~i~ing dlode~ could ~or~ a rlght tr~angl~ os ~y oth~
lrr~ular trla~gl~ ~o loag a~ the location a~d d~s~nca o~ oach llKht recelvlng diode ls k~ow~ with respect to every oth~r llg~t rec~i~icg dioda.
Th~s l~v~ntio~ 1~ not ~o be llm1ted by what h~s ~c~
partlcularly a~ow~ a~d described except a~ lsdlcaeed ln th~ appa~dad cl~ims .

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Apparatus for determining the position of at least one light source located and movable within a selected area, comprising:
light detecting means for monitoring light means emitted by said at least one light source at first and second locations, respectively, said first and second locations spaced a first predetermined distance apart along a base line;
said light detecting means suitable for detecting said light means emitted by said at least one light source located within said selected area, and wherein said light detecting means operates independently of said at least one light source;
means for determining a first line of detection between said at least one light source and a first light detecting means, said first line of detection occurring when said light means from said at least one light source is detected by said first light detecting means, and wherein said first line determining means operates independently of movement of said at least one light source;
means for determining a second line of detection between said at least one light source and a second light detecting means, said second line of detection occurring when said light means from said at least one light source is detected by said second light detecting means, and wherein said second line determining means operates independently of movement of said at least one light source;

means for ascertaining a first angle between said base line and said first line of detection, and for ascertaining a second angle between said base line and said second line of detection; and means responsive to said means for ascertaining for determining and providing signals representative of the position of said at least one light source within said selected area.

2. The apparatus of claim 1 wherein said first and second line determining means further include means associated with each said light detecting means for providing at each of said first and second locations a moving field of view which includes a point of reference associated therewith, movement of said field of view being independent of said at least one light source, and wherein said angle-ascertaining means further includes means for ascertaining the position of the moving point of reference with respect to said first location when the point of reference intersects said first line, and means for ascertaining the position of the moving point of reference with respect to said second location when the point of reference intersects said second line.

3. The apparatus of claim 1 or 2 wherein said at least one light source further includes first and second light sources, said second light source spaced apart from said first light source a second predetermined distance, the pair of light sources indicative of a straight edge movable within said selected area; and wherein said light detecting means are adapted to detect light means emitted by said first and second light sources, and said first and second line determining means further include means for determining a third line of detection between said second light source and said first light detecting means, said third line of detection occurring when said lights means from said second light source is detected by said first light detecting means and wherein said third line determining means operates independently of movement of said second light source, and means for determining a fourth line of detection between said second light source and said second light detecting means, said fourth line of detection occurring when said light means from said second light source is detected by said second light detecting means, and wherein said fourth line determining means operates independently of movement of said second light source, said means for ascertaining further including means for ascertaining a third angle between said base line and said third line of detection, and for ascertaining a fourth angle between said base line and said fourth line of detection, and said means for determining and providing signals representative of the position of said second light source within said selected area and the position of said straight edge indicated by said pair of light sources within said selected area.

4. The apparatus of claim 2 wherein said first and second moving fields of view move arcuately around said first and second locations, respectively.

5. The apparatus of claims 1, 2 or 4 wherein said light detecting means comprises a pair of photodetectors positioned one each at said first and second locations.

6. The apparatus of claims 1, 2 or 4 wherein said light detecting means for monitoring further comprises:
means for supporting said light detecting means at a known distance from a pivot point; and means for pivoting said light detecting means around said pivot point such that said light detecting means intersects said first and second locations.

7. The apparatus of claim 2 wherein said light detecting means comprises a pair of photodetectors positioned one each at said first and second locations; and said means for providing a moving field of view comprises a pair of opaque members located one each between said selected area and said pair of photodetectors, each of said opaque members defining a slit for transmitting a narrow beam of light means from said at least one light source therethrough, and means for repetitively moving said opaque member and said slit defined therein along a known path to provide said moving field of view of said selected area.

8. The apparatus of claim 7 wherein said known path is a straight line adjacent each of said first and second locations.

9. The apparatus of claim 7 wherein said known path is a circular path around each of said first and second locations.

10. Apparatus for providing signals representative of one or more positions of at least one light source movable within a selected area, comprising:
first and second photodetecting means spaced at first and second locations, respectively, along a base line by a first predetermined distance;
means associated with each said photodetecting means for providing a moving field of view for each photodetecting means, said moving fields of view moving arcuately around said photodetecting means independently of movement of said at least one light source;
means for monitoring angular positions of each of the arcuately moving fields of view with respect to the base line and providing signal indications thereof;
light means emitted by said at least one light source detectable by each of the photodetecting means;

a first signal generated by said first photodetecting means upon receipt of said light means from said at least one light source through the field of view of the first photodetecting means;
a second signal generated by said second photodetecting means upon receipt of said light means from said at least one light source through the field of view of the second photodetecting means; and means operative in response to said signal indications of the angular position monitoring means when said first and second signals are generated by said first and second photodetecting means, respectively, for providing a signal representing the position of the at least one light source within the selected area.

11. The apparatus of claim 10 wherein said at least one light source further includes first and second light sources, said second light source spaced along a predetermined line from the first light source and emitting light means detectable by each of said photodetecting means, the first and second light sources defining a straight edge movable within the selected area, and wherein the first and second photodetecting means are further operative to provide signals representative of said light means for said second light source when received through said first and second fields of view, and wherein said means for providing a signal representing the position of said first light source is further operative in response to said signal indictions of said angular position monitoring means when said light means from second light source is respectively detected by first and second photodetecting means for providing signals representing the position of said second light source and the position of said straight edge within said selected area.

12. The apparatus of claim 10 wherein said arcuately moving fields of view are rotating fields of view.

13. The apparatus of claim 12 wherein said means for providing a rotating field of view is operative to provide said rotating field of view at a predetermined angular velocity.

14. The apparatus of claim 13 wherein the predetermined angular velocity is constant.

15. The apparatus of claim 1, 2 or 10 wherein said at least one light source is a light emitting diode.

16. The apparatus of claims 2 or 10 wherein said means for providing a moving field of view includes an opaque member moving between said selected area and each of said first and second locations, said opaque member having a slit therein to provide a narrow field of view.

17. The apparatus of claim 10 wherein said arcuately moving fields of view associated with each said first and second locations includes a first and second reference point, respectively.

18. The apparatus of claims 4 or 17 wherein said means for providing said arcuately moving fields of view associated with each of said first and second locations includes at least a portion of an opaque cylinder with an axial slit therein at least partially surrounding each said first and second locations, and wherein each said axial slit represents said first and second reference points, respectively.

19. The apparatus of claims 4 or 17 wherein each said arcuately moving fields of view is provided by opaque shield means having a distinct boundary at least partially surrounding said first and second locations, respectively, said shield means movable with respect to said first and second locations to interrupt said light means traveling from said at least one light source toward said first and second locations, and wherein said distinct boundary on each said opaque shield is said first and second reference point, respectively.

20. The apparatus of claim 11, wherein light means emitted by each of said first and second light sources is respectively coded, and wherein the photodetecting means is operative to distinguish between said first and second light sources.

21. The apparatus of claim 11 and further including:
a template including said straight edge and having a plurality of information characters and symbols thereon;
means for selecting one of said plurality; and means for providing a signal representative of said selected one of said plurality.

22. The apparatus of claims 1, 2 or 10 wherein said selected area is a data entry tablet and said at least one light source is a stylus having a light emitter on the tip thereon, and movable on the surface of the data entry tablet.

23. The apparatus of claim 10 wherein:
said first and second photodetecting means further includes third photodetecting means for monitoring light means of said at least one light source at a third location spaced a second predetermined distance along a second base line from said first location, and wherein a third signal is generated by said third photodetecting means upon receipt of said light means from said at least one light source through the field of view associated with said third photodetecting means, and said means for providing a position signal further includes means operative in response to a signal indication of said angular positioning monitoring means associated with said third photodetecting means when said third signal is generated for providing a signal representing the position of the at least one light source within said area.

24. A data entry system for providing signals representative of one or more positions of a stylus movable within a defined area, comprising:
first and second photodetecting means spaced along a base line and separated by a predetermined distance therebetween, and wherein said first and second photodetecting means are immobile with respect to said stylus;
means associated with each photodetector for providing a uniformly rotating narrow field of view for each said first and second photodetecting means, and wherein rotation of said narrow field of view for said each said first and second photodetecting means is independent of movement of said stylus;
means for monitoring an angular position of each of the narrow fields of view with respect to the base line and providing signal indications thereof;
a light emitter associated with said movable stylus, said light emitter providing light means detectable by each of the first and second photodetecting means;
a first signal generated by said first photodetecting means each time said first photodetecting means, said narrow filed of view associated therewith and said light means are in linear alignment;

a second signal generated by said second photodetecting means each time said second photodetecting, said narrow field of view thereof, and said light means are in linear alignment;
and means operative in response to the signal indications of the angular position monitoring means when said first and second signals are generated by said first and second photodetecting means, respectively, for providing a signal representing the position of the stylus within the defined area.

25. The apparatus of claims 1, 2 or 10 wherein said selected area is a land area to be surveyed, and said at least one light source is a reference pole selectively emitting light means of a predetermined characteristic, said reference pole being movable over said land area.

26. A method for determining a position of a light source movable within a selected area comprising the steps of:
emitting light having selected characteristics from said light source location within said selected area;
uniformly scanning said selected area from first and second locations spaced a predetermined distance apart along a base line, said step of uniformly scanning further comprising;
positioning first and second photodetecting means at said first and second locations, respectively, sequentially exposing incremental segments of each said first and second photodetecting means to said selected area, said sequential exposure occurring independently of movement of said light source, and monitoring said exposed incremental segments of each said first and second photodetecting means with respect to a reference associated therewith;
detecting emitted light from said light source at each said first and second locations, said detecting occurring independently of movement of said light source;
correlating said monitored incremental detection segments of said first and second photodetecting means with said detected light at each said first and second locations, respectively, to determine a first line of sight between said detected light and said first location and a second line of sight between said detected light and said second location, respectively;
determining a first angle between said base line and said first line of sight and a second angle between said base line and said second line of sight; and computing the position of said light source within said selected area from said first and second angles and said predetermined distance.

27. A data entry tablet for providing signals representative of one or more positions of a stylus movable within the area of the table, comprising:

first and second photodetectors spaced along a base line and separated by a predetermined distance therebetween, said first and second photodetectors being immovable with respect to said stylus;
mean associated with each photodetector for providing a rotating narrow field for each photodetector, rotation of said narrow field of view of each photodetector being independent of movement of said stylus;
means for monitoring angular positions of each of the narrow fields of view with respect to the base line and providing signal indications thereof;
a light emitter associated with said movable stylus, said light emitter providing light means detectable by each said first and second photodetectors;
a first signal generated by said first photodetector each time said first photodetector, said narrow field of view associated therewith and said light means are in linear alignment;
a second signal generated by said second photodetector each time said second photodetector, said narrow field of view associated therewith and said light means are in linear alignment; and means operative in response to the signal indications of the angular position monitoring means when said first and second signals are generated by said first and second photodetectors, respectively, for providing a signal representing the position of the emitter within the area of the tablet.

28. The data entry table of claim 27 including:
a light emitter spaced along a predetermined line from the light emitter of the stylus providing a light means detectable by each said first and second photodetectors, the pair of light emitters defining a straight edge movable within the area of the tablet;
the first and second photodetectors being operative to detect said light means from each of the emitters and provide said first and second signals representative thereof, respectively; and said means for providing said signal representing the position of the emitter being operation in response to the signal indications of the angular position of each of the rotating means when said first and second signals are generated to provide a signal representing the position of each said emitter and the straight edge within the area of the tablet.

29. The data entry tablet of claim 27 wherein the means associated with each said first and second photodetectors is operative to provide a rotating field of view at a predetermined angular velocity.

30. The data entry table of claim 29 wherein the predetermined angular velocity is constant.

31. The data entry system tablet of claim 27 wherein the stylus includes the light emitter on a tip of the stylus movable on the surface area of the tablet.

32. The data entry tablet of claim 31 wherein the light emitter is a light emitting diode.

33. The data entry table of claim 27 wherein said means operative to provide a narrow field of view includes for each photodetector:
an opaque housing having a slit herein to provide the narrow field of view for said light means receivable by said first and second photodetectors from the light emitter.

34. The data entry table of claim 33 wherein the opaque housing is a cylinder having an axial slit therein.

35. The data entry table of claim 28 wherein each of the light emitters are respectively coded, and wherein the first and second photodetectors are operative to provide respective first and second coded signals for distinguishing between respective light means.

36. The data entry table of claim 28 further including:
a template including said straight edge and having information characters thereon; and means for reading the information characters.

37. A data entry system for providing signals representative of one or more positions of a stylus movable within a defined area, comprising:
first and second photodetectors spaced along a base line and separated by a predetermined distance therebetween, said first and second photodetectors being immovable with respect to said stylus;
means associated with each photodetector for providing a rotating narrow field of view for each photodetector, rotation of said narrow field of view of each photodetector being independent of movement of said stylus;
means for monitoring an angular position of each of the narrow fields of view with respect to the base line and providing signal indications thereof;
a light emitter associated with said movable stylus, said light emitter providing light means detectable by each of the first and second photodetectors;
a first signal generated by said first photodetector each time the first photodetector, said narrow field of view associated therewith and said light means are in linear alignment;

a second signal generated by said second photodetector each time the second photodetector, said narrow field of view associated therewith and said light means are in linear alignment; and means operative in response to the signal indications of the angular position monitoring means when said first and second signals are generated for providing a signal representing the position of the emitter within the defined area.