CA2124181A1 - Acoustic digitizing system - Google Patents
Acoustic digitizing systemInfo
- Publication number
- CA2124181A1 CA2124181A1 CA002124181A CA2124181A CA2124181A1 CA 2124181 A1 CA2124181 A1 CA 2124181A1 CA 002124181 A CA002124181 A CA 002124181A CA 2124181 A CA2124181 A CA 2124181A CA 2124181 A1 CA2124181 A1 CA 2124181A1
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- acoustic
- receivers
- indicator
- point
- receiver
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- Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)
Abstract
ABSTRACT
An acoustic position sensing apparatus is described which determines the position of an indicator in relation to a datum surface or volume. The apparatus comprises an acoustic point source transmission device mounted on the indicator for transmitting a sequence of periodic acoustic oscillations, and a plurality of acoustic point receivers positioned about the datum surface for receiving the acoustic oscillations. Comparators are connected to each acoustic receiver for converting the received acoustic oscillations to square waves having logical up and down levels. A register or other time determining circuit is coupled to each comparator and receives at least a leading portion of a square wave and provides an output if it determines that the portion exhibits one of the aforesaid logical levels for a predetermined time duration. A processor is responsive to the outputs from the registers to find the position of the indicator.
The acoustic point source transmission device is configured both as a linear stylus and as a planar "puck", both having at least a pair of acoustic transmitters. The apparatus employs, for two dimensional position detection, at least three acoustic receivers arranged in a non-linear fashion. A three dimensional position detector system is described which employs four receivers, three of which are oriented in one plane and a fourth in another plane.
An acoustic position sensing apparatus is described which determines the position of an indicator in relation to a datum surface or volume. The apparatus comprises an acoustic point source transmission device mounted on the indicator for transmitting a sequence of periodic acoustic oscillations, and a plurality of acoustic point receivers positioned about the datum surface for receiving the acoustic oscillations. Comparators are connected to each acoustic receiver for converting the received acoustic oscillations to square waves having logical up and down levels. A register or other time determining circuit is coupled to each comparator and receives at least a leading portion of a square wave and provides an output if it determines that the portion exhibits one of the aforesaid logical levels for a predetermined time duration. A processor is responsive to the outputs from the registers to find the position of the indicator.
The acoustic point source transmission device is configured both as a linear stylus and as a planar "puck", both having at least a pair of acoustic transmitters. The apparatus employs, for two dimensional position detection, at least three acoustic receivers arranged in a non-linear fashion. A three dimensional position detector system is described which employs four receivers, three of which are oriented in one plane and a fourth in another plane.
Description
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.~.".,i ~ I. GILCHRIST 212 ~
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,~`,, ~i; ACOUSTIC DIGITIZING SYSTEM
''!~'~ The present application ls a Division of Canadian ~ Application Serial No. 2 ! 024 ! 527 filed September 4, ,~:i ! 19 9 0 .
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FIELD_OF THE INVENTION
~;~`' This invention relates to an apparatus for locatinq a " , j point in either two dimensional or three dimensional space and, more particularly to an acoustic position ~
~ 5 sensinq apparatus.
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,~ ., ,~, BACKGRO~ND OF THE INVENTION
Acoustic position locatinq systems are well known in ; the prior art. Some systems employ a Pointer havinq ~A a sparX qap incorporated into its structure. The spark qap ~enerates an acoustic siqnal which is ` propagated to orthoqonally oriented, linear microphones. The arrival of the spark acoustic signal at a microphone is detected by an amplitude discrimination circuit and then passed to a timin~
circuit which compares the time of arrival of the r.~
' siqnal with the time of the siqnal's qeneration, to thereby achieve a ranqe determination. SPark-acoustic ~' position determininq systems are disclosed in U.S.
:,."j Patents 3 ! 838 ! 212 to Whetstone et al.; 4 ! 012,588 to , 20 Davis et al.; 3,821,469 to Whetstone et al.; 4,357!672 to Howells et al.; and 3,731,273 to Hunt.
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Spark-based acoustic ranging systems exhlbit a number of disadvantages. The generated spark creates both possible shock and fire hazard, makes an audible noise ~-1$ which is, a~ times disconcerting, and creates S electromagnetic interference. Further, since the spark generates a shock acoustic wave, its detect~on ls dependent upon the accurate sensing o~ the leading edge of ~he wavefront. Due to changes in amplitude as the ,'3 spark source is moved relative to the microphones, and 0 further, due to the wavefro~t's non-linear rise time, accurate 6ensing is difficult to ~mplement reliably.
In fact, systems which employ spark gap ranging exhibit a limited distanca resolution specifically due to the detection problems which arise fro~ the use of a shock acoustic wave.
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A further class of acoustic wave position determining systems employ emitted, p~riodic, acoustic signals for i,;.l~
ranging purposes. For lnstance, in U.S. Patent 3,504,334 to Turnage, Jr., microphone receivers of the ~ bar type are oriented along X and Y axes, and measure `,~ the propagation time o~ an acoustic signal from a measuriny point to the respective receivers. Th~
mea~ured times are converted to mlnimum dis~a~es between the mea~uring point and the respective receivers, thereby enabl~ng the coordinates o~ the ~,~ ~ea~uri~g point to bQ de~ermined. Bar-type microphones, (used by the Turnage, Jr.) are both expensi~e and are di~icult to apply to limited-size ~'' 3 30 position determining ~y~tems (e.g. desk top size).
;~ Furthermore, the accuracY of systems which employ ,~ 3, bar-type microphones depends on the uniformity of the ~ e~itted acoustlc wave~ront, and iP there is any ., .
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.~.".,i ~ I. GILCHRIST 212 ~
~.
.;
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,~`,, ~i; ACOUSTIC DIGITIZING SYSTEM
''!~'~ The present application ls a Division of Canadian ~ Application Serial No. 2 ! 024 ! 527 filed September 4, ,~:i ! 19 9 0 .
,,;
FIELD_OF THE INVENTION
~;~`' This invention relates to an apparatus for locatinq a " , j point in either two dimensional or three dimensional space and, more particularly to an acoustic position ~
~ 5 sensinq apparatus.
!, .
,~ ., ,~, BACKGRO~ND OF THE INVENTION
Acoustic position locatinq systems are well known in ; the prior art. Some systems employ a Pointer havinq ~A a sparX qap incorporated into its structure. The spark qap ~enerates an acoustic siqnal which is ` propagated to orthoqonally oriented, linear microphones. The arrival of the spark acoustic signal at a microphone is detected by an amplitude discrimination circuit and then passed to a timin~
circuit which compares the time of arrival of the r.~
' siqnal with the time of the siqnal's qeneration, to thereby achieve a ranqe determination. SPark-acoustic ~' position determininq systems are disclosed in U.S.
:,."j Patents 3 ! 838 ! 212 to Whetstone et al.; 4 ! 012,588 to , 20 Davis et al.; 3,821,469 to Whetstone et al.; 4,357!672 to Howells et al.; and 3,731,273 to Hunt.
:
.
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~!
- ` 2 ~
s, .
Spark-based acoustic ranging systems exhlbit a number of disadvantages. The generated spark creates both possible shock and fire hazard, makes an audible noise ~-1$ which is, a~ times disconcerting, and creates S electromagnetic interference. Further, since the spark generates a shock acoustic wave, its detect~on ls dependent upon the accurate sensing o~ the leading edge of ~he wavefront. Due to changes in amplitude as the ,'3 spark source is moved relative to the microphones, and 0 further, due to the wavefro~t's non-linear rise time, accurate 6ensing is difficult to ~mplement reliably.
In fact, systems which employ spark gap ranging exhibit a limited distanca resolution specifically due to the detection problems which arise fro~ the use of a shock acoustic wave.
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A further class of acoustic wave position determining systems employ emitted, p~riodic, acoustic signals for i,;.l~
ranging purposes. For lnstance, in U.S. Patent 3,504,334 to Turnage, Jr., microphone receivers of the ~ bar type are oriented along X and Y axes, and measure `,~ the propagation time o~ an acoustic signal from a measuriny point to the respective receivers. Th~
mea~ured times are converted to mlnimum dis~a~es between the mea~uring point and the respective receivers, thereby enabl~ng the coordinates o~ the ~,~ ~ea~uri~g point to bQ de~ermined. Bar-type microphones, (used by the Turnage, Jr.) are both expensi~e and are di~icult to apply to limited-size ~'' 3 30 position determining ~y~tems (e.g. desk top size).
;~ Furthermore, the accuracY of systems which employ ,~ 3, bar-type microphones depends on the uniformity of the ~ e~itted acoustlc wave~ront, and iP there is any ., .
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t~ aberration in the wavefront, inaccurate range measurementS result.
Another pa~ent which employs bar-type microphones is 4,246,439 of Romein. Romei~ employs a pair o~ acoustic ~1 transmit~ers mounted on a stylus, which transducers enable the precise posi.tion of the stylus tip to be determined.
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Others have attemp~ed to overcome the above-stated problems by employing discrete point miorophone ~i receivers. In U.S. Patent 3,924,450 of Uchiya~ et al., a three dimensional acoustic range determining system is broadly described and includes three microphones placed about a ~urface to ~e digitized. A
stylus having two acoustic sources is used to point to various points on the 3-D ~ur~ace. Signals from the stylus are received by the microp~ones and analyzed to determine the digital position of the sur~ace point.
2~ Little detail is given o~ the measurement method employed by Uchiyama et al.
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,~1 Another ac:oustic point digitizer employing a wireless . stylus or puck is desc:ribed by ~errl n~ton et a~. ' in U. S . Patent 4, 654, 648 . In that system, a stylus emits acoustic signals and a linear array o~ micropholles ., receive~i the signal~ and determines the position o~ the ~;tylus ~y hyperbolic triangulation. Herrington et al.
. 1 uses point sourca acoustic transmitters which enable 3 o urli~orm transmi~;~ioll patterns to be achleved . The ~i ~easure~ent t~chniqu~ employed by H~rrington Qt al.
~;~ t~at 1~Q ou~put ~rom tha ~nsiny ~icrophone~ be ctivaly ~witchad to ~e~d intQ a det~tor circuit, which circui~ in addition to including a zero crossi~g , ~ ' ~ 2~2~
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~, 4 detector, also sample~ and holds the value of peak amplitudes of each cycle. This data is used to ~ determine range in~ormat:ion and from that, to obtain ?~t`~ positional triangulation o~ the aooustic transmit~er.
Whi~e the Herring~on et alO system overcomes many prior art problems, its use of a linear array o~ microphones;
:;, the switching o~ the microphones; ~nd the sampling of the input signals to determine instantaneous amplitudes si;!; all present proble~s which lead to an unnecessarily complex and expensive system.
Accordingly, it is an object of this i~vention to provide an acoustic position determining system whiGh provides lmproved posltion accuracy and detection.
It i~ another object of this inYention to provide an acoustic .position digitizing system which is not ~:i dependant upon the amplitude of a received acoustic signal.
It is still another object of this invention to provide ~;7 an acoustic position determining system which enables c,;' arbitrAry positioning of acoustic receiving units.
~'. 25 It is another object o~ this invention to provide an acoustic po6ition determining system which is easily calibrated.
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It is a further object o~ this invention to provide an acoustic position d~gitizin~ sy5tem which employ~ an open-loop signal proce~sing elem~nt ~or determi~ing the ~: time o~ arrlv~l o~ an acoust~c signal~
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~ SUMMARY OF THE INVENTION
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. An acoustic posi~ion sensin~ apparatus is described ' which de~ermines ~he position of an indicator in relation to a datum surface or volume. The apparatus comprises an acoustic point source transmission device ii mounted on the indicator for transmitting a sequence o~
periodic acoustic oscillations, and a plurality of acoustic point receivers positioned about the datum surface for receiving the acoustic oscillations.
Comparators are connected to each acoustic receiver ~or converting the received acoustic oscillations to square waves having logic 1 up and down levels. A registex or other time determining circuit is coupled to each comparakor and receives at least a le~ding portion of a square wave and proYides an output if it determines that the.portion e~hibits one of the a~oresaid logical ~ levels ~or a predetermined time duration. A processor .`.~,, is responsive ~o the outputs ~rom the registers to find the position of the indicator.
The acoustic poin~ source transmission device is configured both as a linear 5tylu~ and as a planar ~` "puck", both having at least a pair of acoustic transmitters. Th~ apparatus employsl for two ` `:t `;. dimensional position detection,.at least three acoustic ~,~ recei~ers arranged in a non-llnear fashion. A three ~' dimensional position detector system ls described which `~ employs four receivers, three of which are oriented in one plane and a~ourth in another plane.
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i.~ RIEF DEScRIPTION OF THE DRAWINGS
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Fig. 1 ls a schematic diagram of the invention as it is employed to d~termin~ th~ posltion of a point in a two ,~ 5 dimensional space.
3, Fig. 2 is a schematic diagram of the invention employed to determlne the position of a point in a three dimensional space.
~! Fig. 3 is a diagram indicating how the acoustic ~;, receivers, shown schematically in Fiy. 2, mav be positioned to properly receive the emitted acoustic signal~ from a stylus or puck.
Fig. 4 is a section view o~ an acousti~ point source transmitter.
. Flg~ S is a front view of the transmitter of Fig, 4.
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'I Flg. 6 is an acoustic diagram helpful in understanding . the operation of the acoustic transmitter of Fig. 4.
i Fig. 7 is an exploded view of an acoustic receiver ::. 25 employed by the in~ention.
., .. Fig. 8 is a plan view o~ a puck with a pair of acoustic ~ transmit~ers mounted thereonO
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Fig. 9 1:; a block diagram of the position detection p c:ircultry used by the invention.
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~'' ii~; Fig. 10 is a schematiC hlock diagram o~ a pre~erred '! si~nal de~ector ~or sensing the "~ront porch" o~ a received acoustic signal.
! ~1 Fig. 11 is a schematic block diagram o~ another signal correlation detection circuit which is more resistant to noise ~han the circuit of Fig. lO.
,G ,.~,, Fig. 12 defines the p~ints used in the two dimensional position determina~ion mathematics.
Fig. 13 shows an arrangement for calibration of the ~;j invention.
. j J 15 Fig. 14 defines the points used in the three dimensional position determination mathematics.
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~;, Fig. 15 shows the placemenk o~ an additional scaling transmitter used for measurement correction.
DETAILED DESCRIPTION OP Tl{E ;rNVENTION
~ ( Referring now to Fig. 1, a rectangular two dimensional workspace lO is is de~ined by lts X and Y bounda~i~s.
Work space lO may contain a drawing, a planar constxuct or ~o~e other planar axrangement whose points are to be ~, dlgitized, ~or either di~play on a computer terminal or or ~torage in a computers memot~. Three acoustic ~l receiYers 12, 14, and 16 are arrayed about the '~ 30 perimater o~ wor~5pac~ 109 with each belng co~nected to a two di.mensional pos~tion detection circuit 18. Whil~
acoustic receivers 12, 1~, and 16 may be placed ~`1 arbitrar~ly about work~pac~ 10, th~ one cons~rain~ is ",, : :, . ~d' . .
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that they should not be placed along a single line.
The reason for this will become apparent hereinbelow A stylus 20 is adapted t:o be moved by a user so that its pointed end 22 touches a point in workspace 10 to ~e digitized. A pair o~ acoustic point source , 5, transmltters 24 and 26 are mounted on stylus 20 and are oriented along a line 2a which also intersects pointed ., end 22. Stylus 20 is connected to 2-D position ~.
- lO detection circuit 18 via conductor 30.
,i, Broadly stated, the operation of the system of Fig. l ~9 iS similar to the prior art in that acoustic point source transmitters 24 and 26 emit bursts of periodic `b~ 15 acoustic oscillations which are sensed by acoustic . receivers 12, 14, and 16. By determining the time of ~, arrival of the acoustic signals, the 2-D position -~j d tector l8 is able to det~rmine the position in . workspace 10 at which point end 22 of stylus 20 is ; 20 pointed. Furthermore, hy properly analyzing these signals, the orientation of stylus 20 can be .~ determined.
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As afore~tated, two dimensional position detection,h~s ~` 25 been accompllshed hereto~ore, in its most simple f~rm, by employing a pair of acoustic receivers. This :~ geometry has led to a number of dlsadvantages. First, the Y coordinate value was subject to larger error deviations than the X coordinate value ~ecause the Y
coordinate value was calculated from a combination of a slant range and the X coordinate value. Any errors associated with the X coordinate value thus combined with errors arisin~ f rom the measurement of the slant range. Furthermore, a squa~e root ~unctlon, ~eeded t3 ' t.
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In Fig. 2, the acoustic position digitizing system is shown, as modified for three dimensional point determination. In this case, workspace 32 is three ~'! dimensional and i5 bounded hy X, Y, and Z coordinates.
;s 10 The stylus employed is identical to that shown in Fig.
~; l; however in this case, four acoustic receivers 34, 36, 38, and 40 are arrayed around workspace 32. Each ~' ~ rec~iver is arranged so that it is capable of receiving ;~l acoustic signal emanations ~rom either of point source 15 transmitters 24 or 26. Acoustic receivers 34, 36, and 38 are arrayed in one plane whereas acoustic receiver 40 is positioned in a different plane. Ou~puts ~ro~
"`' each of the aforestated receivers are ~ed to three j dimenslonal posi~ion detection circuit 42.
; 20 In Fig. 3, a preferred mounting arrangement ~or each of -i acoustic receivers 34, 36, 38, and 40 is shown. All of ;;~ the receivers are supported by head 44 which is, in turn, mounted at an end o~ cantilever beam 4~. Ea~h'of 25 the receivers is attached to a connecting post 48 which provides bsth mechanical support and electrical connection to the position detection circuitry.
Receivars 34, 36, and 38, are arrayed in plane SO while receiver 40 is displaced there~rom. This enables the ~0 receive:r array to be arbttrarily located without degradation o~ calculated coordinate values due to slant range distance ~rom the array plane. This arrangement also avoids the problems which were ~ inheren~ in previous three dimensional acoustic array ;3 ~3 ..;,~
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~, sensing systems which employed only three receivers.
( In those systems, the Z coordinate was susceptible to ;~ larger error deviations than the X and Y coordLnate '~ values as it was calculated ~rom a slant range a~d the .
X and Y coordinate values. Any errors associated with - the X and Y coordinate~ added to errors due to the measurement of the slant range and thereby contributed to less ~han desirable accuracy. Sensors ~, 36, 3B, ~;' and ~0 pro~ide independent X, Y, and Z coordinate-`~ 10 measurements so that errors do not aceumulate for the Z
i~ coordinate.
, j Re~erring now to Figs. 4 and 5, the structure o~ an ~'~'`! acoustic point source transmitter is shown. Each acoustic transmitter comprises a conical resonator 60 which is mounted on a piezoelectric actuator 62. Both resonator 60 and piezcelectric actuator 62 are mounted on a pedes~al 6~ and the actuatDr i5 connected to pins , ~
-' 66 and 68 via conductors 70 and 72 and thence to pulse '`~l 20 source 770 The ~ransmitter structure is mounted in a housing 74 which i~ provided with a ~aceplate 76 (see Fig. 5). An opening 78 i6i centrally locate~ in ~ faceplate 76 and pro~id~s a "point ~ource'l effect for ;,,l the acoustic e~anatiOn~ produced by piezoelect~ic actuator 62 and r~sonator 600 Th~ diameter d of opening 78 involve~ a trada o~ betw~en emitted power and wa~e front beam widtho As can ~e seen from Fig. 6, when piezoelectric actuator 62 i~ en~rgized~ it creates an acou5tic wave~ront 80.
'~ When wavefront 80 pai~es through opening 78, assuming opening 7~ i5 ~u~fic~ently 5~all, the txan~mitted ~ wavefc~n a~sume~ an omnid~rectional wave~ront 82 due to i~ diffracl:ion beam-widt~ ~o~mation. How2ver, if opening ", ~
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78 is made ~oo small, ~he power of the transmitted acoustic signal is greatly constrained. On the other -i hand, if it is made too l~rge, wave~ront 82 is distorted with poor side lobe beam patkerns~ From the system standpoint, it i8 most desirable that wavefront 82 be as close to omnidixectional as possible so the .~ diameter d o~ opening 78 is made as small as possible.
i 0 ovPrcome the power reduction created by a minimum ~i 10 diameter opening 7~, it has been found that .'. piezoelectric actuator 62 can be p~lsed with high `j voltage pulses while still remaining within the ~Jl allowable power dissipation limits of the actuator.
.j 031e piezoelectric actuator which is commercially . 15 available from the Panasonic Corporation, when ~:. energized, provides a 40 kHz output ~requency. Its specifications call for a maximum voltage rating of 20 ~ volts for continuous operation. It has been ~ound that .~ by app~ying a 300 volt pulse for lOo microseconds, at a 2 0 repetition rate o~ one pulsç~ every iEi~re miliseconds, "; :, that the ou~put ~ransmitted acoustic energy can be ~`~ substantially inc:reaE;ed without: c:reat:ing daraage t:o actuator 62. P'urthermore, the application of t:his ~'"! extremely high energlzing potential creates a bett'er i~ ~ 25 omnidirectional ~eam pattern and improved amplitude signal levels. It ha~; been fc1und t:hat: lf the applied voltage pulse level to actuator 62 i~ reduced, the beam pattern degrade~ and the amplitude o~ the transmitted ` acoustlc: si~nal drop~. Thus~ it is preferred that the level o~ the appli~d voltage pu15~ and it5 duty cycle be such that it not exceed the ~aximum power rating of the actuator, but that the voltage ~e such that it ~ substant:ially exceeds the applied Voltage rating of the ,; device. It ~hould be understood that the above~noted : ~ `
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'-S values are merely exe:mplary and that the values .. ~ employed with actuatorS having dif~erlng specifications will vary in accordance with the above teachings.
.i Re~erring now ~o Fig. 7, an exploded view of an ~: acoustic receiver is shown. The acoustic receiver ,~~
. comprises an electret membrane 90 mounted on an electrode ring ~2. A rear electrode plate 94 is mounted behind ~he front electrode ring and the entire ~ 10 structure is contained within housing 96. While not ;j~ shown, a field effect transistor is connected to one of the el~ctrode plates to ampli~y the signal created by . the movement of membrane 90 in response to a received -¢-~: acoustic signal. A fac~ plate 98 having an opening lO0 ~`^?~ 15 is positioned over the receiving structure. As with the aooustic transmitters, opening 100 pro~ld~s a "point source" receptio~ capability. The operation of the receiver is conventional and will not be ~urther descri~ed.
Referring now to Fig~ 8, an alternative positiDn encoder is shown in lieu of 5tylus 20 (see Fig. 1).
Position encoder lO1 thereina~ter called a "puck") comprises a housing 102 which ha5 an aperture 1~4 in , 25 which a pair of crosshairs lU6 and 108 are positioned.
Crossha.irs 106 and 108 may be e~edded in a transparent glass or poly~tyrene that e~ables a user to see the underlying workspace and to precisely position crossha:ir point 110. A pair of acoustic transmitters ~ 30 112 and 118 are~centered along a llne coincident with !`'','''i crosshalr 106 and are equidi~tant from crosshair point llO. A depressible selection bar 120 enables a user to provide an output pul~ on line 30 w~en crosshair point 110 is positioned over a sux~ace point to be digitized.
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; As is well known, the puck 101 is placed ~lat on a `, workspace (e.g. workspace 10 ln Fig. l) and is moved thereabout to position the crosshair point llo over a sur~ace point to be digitized, at which time, the user -~........ 5 depresses bar 120 and causes the transmitters 112 and ~ïj 118 to emit pulses o~ acoustic energy to receivers -j.' positioned about the workspace.
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:i, In Fig~ 9, a block diagram is shown o:~ the circuitry ~ -:J
i~; 10 employed to determine the range ~rom one or more .`-'', acoustic transmitters to the acoustic recei~ers and to then process that range information to arrive at a digitization o~ a point in the workspace. All circuitry ~hown in Fig. 9 is under control of microprocessor 200, however the control lines have ~een i~ omitked to avoid unnecessarily compllcating the diagram. The circuitry of Fig. 9 implements the 3-D
position deteckor 42 shown in Fig. 2.
Acoustic point source transmitters 24 and 26 are alternately pulsed to generate periodic acoustic signals which are transmitted towards acoustic . receivers 34, 36, 38, and 40. Each acoustic receiver feeds an independent circuit which compri~es a ~rdnt ~f rJ , 25 end receiver/comparator 202, a signal detector 204, and ~ a counter and latch 206. Whila these independent `!'i: signal chains are not shown separately on Fig. 9, it is to be understood ~hat ~ront-end recei~er~comparators 202 contains ~our separate ~ront-end receivers, comparators, signal detectors, et~.
' ` ' Thus, a received acoustic signal ~s passed rom its~ acoustic recsiver (e.g. 34) to an associated front end ., receiver 202 where it is ampli~iad and applied ko a .
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~, . 14 ~ . , -~.~ comparator. The comparator (also sometimes called a ., .
,. zero crossing detector) is an analog circuit which ~ outputs a high logical level when its analog input -i~ traverses in a positive going direction past a :: 5 reference voltage and it outputs a down level when its analog input traverses :Ln a negatlve going direction ~- past the reference voltaye. In essence, therefore, the -~ comparator is a wave shaper which converts an analog - burst of period acoustic oscillations to a series of square waves whose positive and negative going ~1 transitions are coincident with the positive and negative going transitions of the analog signal.
Signal detector 204 receives the square wave output ~'~ 15 from the comparator and both detects the leading edge of the first square wave (or a subsequent one) and determines that it is, in fact, a portion of a cycle fro~ a received acoustic signal. Assuming that the signal is identified as an acoustic sig~al by detector 204, a stop pulse is generated to a counter and latch circuit 206. Previously, microprocessor 200, via multiplexer 203 and transmitter drivers 210 caused acoustic transmitter 24 to emit an acoustic signal~ At the same time, a clock signal wa~ applied from c~o~k 212 to a counter in count~rs a~d latches 206. When that counter receives a pulse " top'l signal ~rom signal ~,, deteGtor 204, it stops the count and ~nters it into a latch whose output is, in turn, fed to microprocessor 200. That count is then used by microprocessor ~02 to v~ 30 determine the slant range o~ acoustic transmitter 24 rom acoustic receiver 34. The range circ~its associated with each of acoustic receivers 36, 38, and .: 40 act identically to that above described.
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Multiplexer 208 causes transmitter drivers 210 to `~ alternately apply energizing pulses to transmitters 24 ~` and 26 so tha~ the slant range to those transducers can 3' be alternately detected and calculated. Additionally, ":l 5 a correction transducer 212 is provided which, prior to each range measuremen~, ~ends out an acoustic signal ~, which is sensed by acoustic receivers 34, 36, 38, and .~ 40 and is subsequently processed to determine the slant - range to the correckion transmitter. The position of transmitter 212 i5 fixed so that microprocessor 200 is ~,~i, able to derive a correction factor f rom that range measurement. Thiat correction factor is used to alter a ;1 subsequent measurement to take into account any .. ~ atmospherically lnduced changes in the transmitted signal's transit time.
. f ., ' ` . ,j Re~erring now to Flg. 10, a pre~erred slgnal detector circuit is illustrated. The circuit in Fig. 10 is designed to detect the "front porch" of the ~irst ~3 20 positive going hal~ cycle of a received ~ignal from receiver/comparator circuit 202. The detector circuit comprise~ a serial shift register 250, each o~ whose ~tages has an output which ~eeds into a multiple input NAND gate 252 . The output o* NAND gate 252 re~lec~s'an .. j, . .
~p level on line 254 at all t~mes except wh~n there i5 .:. a "one" bit in each ~tage o~ ~hi~t register 250, at "~, which time i~s output on line 254 falls. A shifk clock ~,~, " i5 applied via conductor 256 to ~hi~t register 250 and s~eps input signals appearing on line 2~8 in~o the . . - ~:, .
ragist~r~ ~
it i6 as~u~ed that wave~orm 260 evidences the ~ initlall.y trans~ltt~d ~lr~t hal~ cycle ~rom stylus 20, ,~ and th~t: a resul~ing recei~ed signal 262 is impressed .~ .
~ :' . . ~ , ~. , .
~: i ;
2~2~
.
-. 16 I
,. .
-. on line 258, it can be seen that the ~oltage levels `; shifted into ~hift register 250 will represent wavePorm 262. Assuming that th~re are su~cient stages 1~
: shift r~gister 250 to hold only a portion of a halP
cycle o~ wave~orm 262, a:Ll stages thereof will re~lect ; the "one" state, a determined number of shift clock pulses after the arrival o~ the high state 263 ~f .~ waveform 262. When all stage~s o~ shi~t register 250 evidence the "one" level, NAND gate 252 drops its .,.!~ 10 output. That drop ln output causes a counter in counters and latches 206 to cease counting, with the count indicative, after processing, of the time of transmission of a transmitted signal between an acoustic transmitter and recelver.
If the number of stages in ~ihift r~gister 250 is suf~icient to handle a full half cycle of waveform 262, then stop pulse 264 on line 254 will be a~ shown, with its duration equal to the duration of one shift clock pulse. If the capacity shift register 250 is less ~han the duration of hal~ cycle of lnput signal 262, then stop pul8e 264 will exhibit a down level until the flrst zero appears in ~hi~t register 250. In eikher case, it i8 the leading edge of stop pulse 264 whlch ;! 25 causes the associa~ed counter to cease its count.
;. ;~
; Microprocessor 200, knowing the number o~ shift pulses required ko ~ill shift xegister 250, converts that number t:o a ~ime and subtracks it ~ro~ the ti~e i~dicated by th~ counter and thus obtains a direct indication o~ the time o~ s~nal transmisi~iDn between ~!.i ,; the acoustic receiver and tran~itter. The clrcuit o~
: Fig. 10 th~re~ore, d~tects the hal~ cycle wave~orm 262 ` :!
.: ` '~`
: i, "~"S ~ . ' , ' ``':, ' .
'', i i . , ' - ' . , ' , : ~ .
2 ~ 2 ~
., ~,; .
. and determines that it is, in fact, a signal from an `! acoustic transmi~ter.
While the signal detector in Fig. 10 i5 implemented with a shift register, it is to be understood that any ~; circuit which is capable of determining the presence of 1 a return signal from incoming noise may be employed, ' assuming that it is reasonably economical to implement.
,; For instance, a counter can be ~ubstituted ~or shift ~ 10 register 250, wlth the input signal t 5 "front porch"
~! being used to gate stepping pulses into the counter.
When the predetermlned count is reached, the presence of a return signal ls confirmed and a "stop" pulse generated.
If a noise signal is received, and its duration is equal to or longer than the duration o~ shift register 250, an erroneous range output will occur. Thus if the ~, .i. invention is to be operated ln a noi~y environment, a ~ 20 somewhat ~ore costly, less noise ~usceptible circuit ;~ for noise detection i8 dQsirable and is shown ln Fig~
11.
,.,~,'1} ,.
~, In Fig. 11, serial shift register 300 has, for ex~mple 25 any purposes, a suf~lcient number o~ 6tages to contain an entire ~ull cycle o~ a received acoustic signal when it is clocked by shi~t clock over line 302. The system . o~ Fig. 11 will also function i~ ~hift register 300 ~, includes enough stages to contain either less than or 1 30 more than one cycle o~ a received acoustic signal.
.~
3 A r~ceived signal is i~pressed upon input lins 304 and :~; it~ levels are shl~ted into 5hi~t r~gi ter 300 as ~hey ~` are receivQd ~rom the receiver/comparator circuit 202.
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. 1~
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A repllca o~ ~he transm~tted (re~erence) siynal is - permanent~.y fix~d in reference register 306, with :~ register 306 having an identical number of stages as shift register ~00. At each shift interval, the levels S in the corresponding stages of serial shi~t register 300 and re~erence register 306 are compared in a mod 2 adder circuit. For instance, the level in stage 308 is fed via line 310 to mod 2 adder 312 and the level from re~erence register stage 314 fed via ~ine 311 to mod 2 adder 312. There is one mod 2 adder ~or each pair of register stages and, at each shift time, their outputs are collectively ~ed to a chain o~ accumulators 316, which accumula~ors provide a sum o~ the resultant signals ko peak detector 318.
Those skilled in the art will recognize that the circuit shown in Fig. 11 bears a resemblance to a correlation circ-llt which correlates the wa~e shape of a received signal on li~e 3Q4 to the wave shape of a re~erence ~ignal Rtored in register 306. As the received ~ignal begins to shi~t into ~hift regist~r 300, the ~um ~alue from accumulators 316 starts to increase as shown by wa~e~orm 320. When the received ~ signal is fully pre~e~t in shift register 300 ~in ph~se . 25 with the signal level~ in reference register 306), the level ~rom accumulators 316 reaches a peak 322 ; (waveform 320) and then begins to decrease as the received signal shi~ts ~urther through register 300.
Peak 322 is detect~d by peak detector 313 which 30 provides a ~top puls~ ~o a count&r in count~r~ and -:i latche~ 206.
. . .
~ ~s w~th the circuit o~ Fig. 9, mic:roprocesSor 200 .`. subtract~ the tlme r quired to insert the received : .;
:, . .
.... ~ :-2 1 2 ~
., 1 9 i~
~, ~'` signal in~o shi~t regi~ter 300 ~rom the time indicated .i by the counter cloc~ circuit to thereby derive the .~' actual time o~ transmission of the acoustic signal.
~ The circuit o~ Fig. 11 is highly speci~ic to the ... ~ 5 transmitted frequency ancl is able to dif~erentiate that signal from all others and provides a high noise-immune detection circuit.
. '`!
!
,;. Microprocessor 200, in response to determining the i. ~
,!,.,. 10 slant ranges between transmitters 24 and 26 and ~;'.i receives 24, 26, 38, and 40 per~orms a num~er of j,~`,~3 additional calculations to derive the position in the workspace of the stylu~ point or puck crosshair. These calculations ar~ ~escribed herein below.
TWO DIMENSIONAL MATHEMATICS~ CALIBRATION AND AL~GO ITHM
The measured slant ranges must be trans~ormed to x and !';`~ 20 Y coordinate values. The ~et-up and location o~ the ~, receivers plays an important role in overall system accuracy.
This section discusses a geometry that uses ~h~ee :-. , 25 receivers to det~rmin~ the x and y coordinates. The . geomet~y allows arbitrary receiver location ~or workspace placement. The three receivers pro~ide independent x and y coordinate measurements so that errsrs do not accumulate wlth the y coordinate. The 30 three receivers also allow t:he calculation oî stylus .. ori~ntat~on so t~at o~et errors to the a~tual digitized point can be corrected ~or. Finally, ~ the r~celver array i8 calibrat~d with r~pect to known calibrat~on point location5, the acou~t~c scale ~actor .. ..
`: 2 ~
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.;
`' 20 ~i will be less sensitive to offset errors, and the final accuracy of the system will be based primarily on the known calibra~ion poin~ location accuracy.
Figure 12 shows the 2-D geometry. The receiver locations are defined for receivers A, B, and C. The range distances between the receivers and transmitter (a, b, and c) ~re measured with the acoustic hardware, and stored ~or each receiver. The xeceivers are all located in the same plane, and the receivers can be located arbitrarily so long as they do not form a straight line.
.~ .1 Slmultaneous equations can be set up for the slant ranges with respect to the coordinate position o~ a transmitter and the coordinate positions of the receivers.as follows:
a2 _ (x X~) + (Y YA)2 r.'ii 20 2 B 2 B 2 ~ c = (x -- XC) + (Y ~ YC) ~; The complete ~olution ~or the above equations can be ~-' shown to be:
x - (allbll ~ al2b21 .. :..
:,:
y a ~a~2~b~ 22b21) ;, whe:re ~ 30 ~ D = (XA - Xc)(Yg ~ Yc~(xB Xc)(~A YC) ;., e ~ l :~5 2D
. j . , , ~ `
~ ~ 2 ~
.`;, ", , ~
:1 a _ y _ y a12 = YC ~ YA
21 = XC ~ XB~ a22 = XA ~ XC
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~ ... ' ~, 5 ., bll = R A ~ R2C + c2 _ a2 21 R B ~ R2C + c2 - b2 ~i . J
.,j 10 A z coordinate can be calculated based on a slant ......
~ range~ and the x, y coordinate values. However, two `~ restriotions are needed- first the transmitter must not approach the receiver plane since z accuracy deteriorates quickly with small slant range ^~ 15 differences/ and secondly the value is calculated with ~, a square root function so that the ~ign o~ the ~, coordlnat~ cannot be determined. Both o~ these -jf restrictio~ ara eli~inated with th~ 3-D geometry using ~our ~ecei~ers (dlscussed below). The z coordinate ~^f 20 value i~
`~
d æ ~
' TWO DIMENSION~L CALIBRATION
.. 25 :~ Calibration o~ the receiver array is important to the : .:
~, accuracy o~ the 6ystem. There are several pref~rred :`1 ways to calibrate the system.
., :.
The first method requires precisely mounting the ~^i, rec~ivers at known distances so that their Cartesian ! coordinates are known ~or initializing the geometry.
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Usually, placement o~ the receivers alo~g symmetrical axe~ will reduce the complexity o~ the geometry, such that in the extreme ca~e, only the di.stance between them is required. The receivers can be mounted with respect to the workspace coordinate ~ystem, or they can be mounted on a separate base and referenced only to itself. The rinal allgnment of receiver coordinates and workspace coordinates can be ~ound by rotation and ,1' ~ ' . translation.
A preferred method is to set a piece of grid paper on the worXspace surface, and arbitrarily set the receivers in convenient locations as shown in the Fig.
', ....
: 13. (An ~rror analysis indicates the best accuracy is obtained i~ ~he receivers are approximately placed at right angles, and separated by a reasonable distance.) ~hree known points can be digitized on the grid paper, :i and by reversing the geometry equations (i.e. the three ;.i digitized point~ be~ome the receiver positions in the original geometry and a single receiver location becomes the transmitter location in the original .;; geometry), the receiver coordinate locations can be ~,;,.~
mapped. Now the recelver coordinate system is completely referenced to the workspace coord~n~te system, and rotation and translatlon is not required to `.. align the two coordinate zystems.
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~ TWO DIM~ ~ S
.~, ... s~3 The complete procedurQ ~or determlning a 2-D posi~ion .~ wikh three recei~er i~ outlined below In A-E.
'`i 5 (See Fig. 12 for de~:Lnitlon3 of transmikter and `,;,?~ recelver location5-) ~ "^, -p~ame~$
~m~um~m ~nt~ a~ow~(~ ~) ~l s ~ ~ e~ fi~m ~c~ o~n~
: 10 bc ~d~yb~(~) c ~ "~ 2 y 2 ~ a ~ Y J ~ l y 2 A~AC--RA--RC f2;c ~ R c . . , . d, 15~ ~A e:xyJ
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3 2 0 ~ ~ C X J ~ ~ ~ A ~Z g ~'.~'''. .
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(d~ b,), bSs $?!~ CI~ b") b~ z ~ ca _ ~, b~ 3 ~ ~ + ~;?a b ~:~i3 x = ~ b~l + a~ab~
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T~ansla~e to wor~ c~rdhla~ sys~a ~by Xtn y3~ equ~d: ;
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212~81 THR~E DIMENSIONAL MAT~EMATIcs~ CALIERATION AND ALGORITHM
~1 The measured slant ranges must be transformed to x, y, and z coordlnate values~ The set-up and location of the receivers plays an important role in the overall system accuracy.
The following sections discuss a geometry that uses four receivers to determlne the x, y, and z coordlnates. The `'3'~' 10 geometry allows arbitrary receiver location for easier workspace placementO The four receivers provide ~, independent x, y, and z coordinate measurement so that errors do no~ accumulate with the z coordinate. If the receiver array is calibrated with respect to known ~, 15 calibration point lo~ations, intrinsic ~unctions are not required to rotate the coordinate system to workspace .3 coordlnates. Finally, if the recei~er array is ! callbrated with respect to krLown callbration point 7 locations, the scale ~actor will be less sensitive to of~set errors, and the final accuracy of the system will be based primarily on the known calibration point location accuracy.
,; T~REE DIMENSION~L SLANT~RANGE CONVERSION ' ' ; Four recelver~ are used tQ dete~mine the x, y, and z ~,~ Cartesian coordinate~. The ~our receiv rs also allow the use of the two transmltter ~tylus for accurate projection o~ the coordlnate value to the tip of the stylus for minimal o~et error. Fig. 14 shows the 3-D geometry.
~' The receiver locàtions are shown ~or receivers A, B, C, . and D. The range dlstances between the receivers and .i( transmitt:er (a, b, ct and d) are measured and stored ~or each receivex. Three o~ khe receivers are located in ~he ..~ ,.
"....... . . . .
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~ . .i .~ ! :'., : .1 2 5 ,..
~ jl ~3ame plane and the ~ourth i8 o~ et ~rom this plane~ The receivers can be located arbitrarily as long as they are ~, not all in the same plane.
$ :",i 5 ~$ ~ Simultaneous equa~ion~ ~or the ~lant ranges can be set: up wlth respect to the coordlnatQ position o~ a tran~mitter .. ~ and the coordinatQ po~;itlons o~ the receiver a~3 ~ollows:
- 10 a = (x - XA)2 ~ (y ~ yp,) 2 + ( _ z )2 ~: ' b2 (x X~) 2 + (Y ~ Yg) 2 + (Z ~ ZB) -- (x Xc) + (Y YC) + tZ C) d = (x -- XD) ~ (Y ~ ~D) ~ (Z ~ ZD) .~ The above equatlons can b~ ~hown to lead to the ~oll~wirlg 801utions:
(ql b~ b~ ~ a~
., Y - t~,~ b~ ~ ~ ba ~ a~, b,;) ~
. ~s 20 s =(a~b~ a~a"b~,~)c ~ X -- .~ y; 3 j~ rD ~ I A ZO
.. ; ~ XB_ XD ~ Yaa ~0 YD ~ ~a~ Z~ ~ Z~
: 25 X ~ X X ~'a ' YC rO . ~ ZC ZO
, ,,, ~ 2D
,~ D ~ X~y~ + ~ y,s~ + x~,y~ sY~I ~ xly~ 2YI~J
a~3y~ y~z~ aU~3Y Z --y ~ 4~3y~S3--a2t~x~sJ,~ J, ~ X~S~~X Z j a2~ st-x a~ Ya . ~ 3 X~yl ~ Ya ~ Y~~ ~ Y
~ ~ ~ .
c bll ~ R A - R D + d - ~
. 35 b~RaJ-R~+d'_~3 , ~. b~l ~ R c ~ R D ~ d - c J
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~ 212~181 ~,ji .~
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THREE DIME~S :~C)NAI~ Cl~
~i The calibration o~ tho three dlmension sy~tem ls much the ~ame aa ~or the two di:mensional ~ystem. Three known ~.~' 5 locations on a grld paper can b~ digitized to establlsh ' receiver coordinate po~itions. An addltional techni~ue makeç lt pos~ible to extend the concept o~ digitizing ~nown locatlons o~ a grid paper. A r~erence array o~
;~, precl~ely fixed transmitter po~ition~ can he located at a ~`~?~' 10 convenlent position in the workspace~ I~ the reference . transmitter array i8 not moved, the receiver array can be relocated at any time by Eimply re initializi~g the 'î sy~tem with the fixed reference array~
~,d 15 THREE DIMENSIONAL AIJGORII~S
3~ ~he complete procedureç ~or de~ermining a 3-D position ~l with four receiYers i8 outlined in tA-D) b~çlowO
(S~e Fig. 14 for d~çfinitions o~ transmitter and receiver locatlon~.) i,;, ., :., j 2", .'~
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~ 2 5 ; . . -, ~p2~rametes$
r~,L ~~ t ~nge ~llowod (~unts) s ~ scale fac~ ~om ~i~ c~rrec~n CuJcolmt) ; i ~ O ~s ~ d~lay bia~2 ~D~i~nt (~o?m~) "~ RC 5 X3 t y~ ~ za R~ a ~ Y~ ~I Z3 ~', 35 R 2- ~'A~-~'n~ R~ 0 . . ~ ~ . . .
2 ~
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.' ............... x~ = X"--X~,,, y = Y --Y ~ I ~I Zo D ~ Y~ ~ YD ~ ~Z, ZD
C XD ~ Y3 ~c D ~ ~ C D
., D = ~IY~z~ YlZa~ x~y~zl--x~y~ xly~zl--xaylZ3 : c - -, ,1, a~lt = Y,~,--Y~l . a~ Y~ZI YlZ, . 4J~ Y~Za--0 all a ac~za - X~ Z9, az~ = X1Z~ ~ ~y ~1 a~ = xa~- xiz 1 a" = x~y~ Ya a3a--.X~YI--;CIY9 ' ~ Y~t--~aY~
~:; B F~ thc nitIer:
- '; Read ~arîg~ a b c'~ d' ~co~
1 5 ~ Yalid tb~ r~ th~ fi~ the~ em~ a~d ~ s~ep~
:.'5'~
3 Sub~ct delay (co~ d ~1~ mea~ sl~s ~ange~ ches):
= s(d--be)s b~ s fl~
`;:'~ C=S(~ )9 ~1 zs(d' b,~) ~ 20 .,,~ ~ ,, ... ;s 2 5 ~ b b~ 5e R ~ a bla ~ bs~.) e 3 o Y ~ æ b:~ + a~
i .
~ D T3;l~lslate ~ woAcspæe couid~natc ~ystem (b~ yO7 z~
i ~ x = x ~ x~, t 2 ~
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RATIO SCALING CORRECTION
; ~
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- Range measurement accuracy is affected by the acoustic ;i~ medium in the workspace~ Factors such as temperature, ~ S humidity, and air ~low a~ect the speed of sound, and ,!~`,., there~ore measurement accuracy. If temperature is used !.' to correct the speed of sou~d constant, then the ~ correction factor at 70 F is , ." ;
i. 10 V = 13,574 inches/sPcond.
. :. ,.
If the digitizer counters run at lOMHz, the length per ~,i count is:
13,574 in./sec- z 001357 inches/cou~t-10 x 106 counts/sec.
. .
Prior art units correct for the speed of sound with a temperature probe. The problem with temperature compensation by a probe is that the probe and circuitry have to be extremely accurate and not susceptible to bias or drift. ~dditionally, te~perature is only one of the ~actors that affect the speed o~ sound. , , ,i 25 This invention uses a method of measuring the reference range with each coordinate measurement, and correcting with a xatio scale factor. ~he speed of sound constant is not :required, and scaling ratios provide the systems acoustlc correction.
A reference correction transmitter 400 (see Fig. 15) is permanently mounted at a precisely Xnown location with respect to a receiver, and fired periodically so that the 212~
, ~
~`. 29 range values can be rescaled for temperature and other ~-~ environmental conditions. The ~ollowing approach 15 used -~, ;. for range scaling~
~ .,.
;~. 5 rererence dist~nce (inch~s) i~ r;~ efinches~ x m~n~uredr~n~e(counls) ` '~ me3~ure~r~fer~ncer~n~coun~sJ
. .
~'; or in mathematical ~orm, ~. 1 0 r' = actual reference range distance r = measured reference range corresponding to r' c = constant delay bias of circuitry .,; ~
`~ 15 r' C
Correct the range measurement for each receiver:
.. ~ a=s(a-bc~
s b=s(b-b~) C=5 ( C-bC ) :~ d=s (d-bC) ~ ' .
This invention u~e~ ~ ~ethod o~ ~ea~uæing th2 refer~nce ~' range w~th each coordinate measurement, and correcting -~ with a ratio scal~ ~actor. The speed o~ sound constant .i, is not required, and scaling ratios provida the systems :~ acoustlc correction.
:~ The ~teps for sy~tem calibration are afi follows:
~ ~x ~ 1. Place the grid paper on the workspaoe (flat ~able top) .
,', ":. ' ` ' " ' ' : : ` ' '.~.'... ' ` ' ~ ` , `' ~ : , 2 ~
;~
.
.
, 30 , 2. Place the receiver array anywhere to one side of the . workspace 3. Digitize the calihration points on the grid paper.
.. 4. The scaling transmitter mounted on the array base is ~ired for a ref~rencle range~
. The computer calibration and scallng procedure employs the above derived data as ~ollows:
, ,, .i lO 1. The systems consta~ts are initialized.
:., ~ 2. For each poi~t measured above, the ranges are scaled !j'`;'' and two range values (from two transmitters on the puck) are used to calculate the ranges to the center of the crosshair ~or each calibration point.
3. The measured range values ~rom above are stored: 3 :~ digitized points, and 4 receiver.qi for a total of 12 , rangesO
~. ' ' ~`;! 3 '~' 1 ,.~."-~
t~ aberration in the wavefront, inaccurate range measurementS result.
Another pa~ent which employs bar-type microphones is 4,246,439 of Romein. Romei~ employs a pair o~ acoustic ~1 transmit~ers mounted on a stylus, which transducers enable the precise posi.tion of the stylus tip to be determined.
. -:"
.;. ,- :.
Others have attemp~ed to overcome the above-stated problems by employing discrete point miorophone ~i receivers. In U.S. Patent 3,924,450 of Uchiya~ et al., a three dimensional acoustic range determining system is broadly described and includes three microphones placed about a ~urface to ~e digitized. A
stylus having two acoustic sources is used to point to various points on the 3-D ~ur~ace. Signals from the stylus are received by the microp~ones and analyzed to determine the digital position of the sur~ace point.
2~ Little detail is given o~ the measurement method employed by Uchiyama et al.
! ' ~
,~1 Another ac:oustic point digitizer employing a wireless . stylus or puck is desc:ribed by ~errl n~ton et a~. ' in U. S . Patent 4, 654, 648 . In that system, a stylus emits acoustic signals and a linear array o~ micropholles ., receive~i the signal~ and determines the position o~ the ~;tylus ~y hyperbolic triangulation. Herrington et al.
. 1 uses point sourca acoustic transmitters which enable 3 o urli~orm transmi~;~ioll patterns to be achleved . The ~i ~easure~ent t~chniqu~ employed by H~rrington Qt al.
~;~ t~at 1~Q ou~put ~rom tha ~nsiny ~icrophone~ be ctivaly ~witchad to ~e~d intQ a det~tor circuit, which circui~ in addition to including a zero crossi~g , ~ ' ~ 2~2~
~ ',', , r ~ ~
~, 4 detector, also sample~ and holds the value of peak amplitudes of each cycle. This data is used to ~ determine range in~ormat:ion and from that, to obtain ?~t`~ positional triangulation o~ the aooustic transmit~er.
Whi~e the Herring~on et alO system overcomes many prior art problems, its use of a linear array o~ microphones;
:;, the switching o~ the microphones; ~nd the sampling of the input signals to determine instantaneous amplitudes si;!; all present proble~s which lead to an unnecessarily complex and expensive system.
Accordingly, it is an object of this i~vention to provide an acoustic position determining system whiGh provides lmproved posltion accuracy and detection.
It i~ another object of this inYention to provide an acoustic .position digitizing system which is not ~:i dependant upon the amplitude of a received acoustic signal.
It is still another object of this invention to provide ~;7 an acoustic position determining system which enables c,;' arbitrAry positioning of acoustic receiving units.
~'. 25 It is another object o~ this invention to provide an acoustic po6ition determining system which is easily calibrated.
.~:
, ~, ;
It is a further object o~ this invention to provide an acoustic position d~gitizin~ sy5tem which employ~ an open-loop signal proce~sing elem~nt ~or determi~ing the ~: time o~ arrlv~l o~ an acoust~c signal~
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~`; 21241~1 ..:
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~ SUMMARY OF THE INVENTION
,, .
. An acoustic posi~ion sensin~ apparatus is described ' which de~ermines ~he position of an indicator in relation to a datum surface or volume. The apparatus comprises an acoustic point source transmission device ii mounted on the indicator for transmitting a sequence o~
periodic acoustic oscillations, and a plurality of acoustic point receivers positioned about the datum surface for receiving the acoustic oscillations.
Comparators are connected to each acoustic receiver ~or converting the received acoustic oscillations to square waves having logic 1 up and down levels. A registex or other time determining circuit is coupled to each comparakor and receives at least a le~ding portion of a square wave and proYides an output if it determines that the.portion e~hibits one of the a~oresaid logical ~ levels ~or a predetermined time duration. A processor .`.~,, is responsive ~o the outputs ~rom the registers to find the position of the indicator.
The acoustic poin~ source transmission device is configured both as a linear 5tylu~ and as a planar ~` "puck", both having at least a pair of acoustic transmitters. Th~ apparatus employsl for two ` `:t `;. dimensional position detection,.at least three acoustic ~,~ recei~ers arranged in a non-llnear fashion. A three ~' dimensional position detector system ls described which `~ employs four receivers, three of which are oriented in one plane and a~ourth in another plane.
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i.~ RIEF DEScRIPTION OF THE DRAWINGS
....
Fig. 1 ls a schematic diagram of the invention as it is employed to d~termin~ th~ posltion of a point in a two ,~ 5 dimensional space.
3, Fig. 2 is a schematic diagram of the invention employed to determlne the position of a point in a three dimensional space.
~! Fig. 3 is a diagram indicating how the acoustic ~;, receivers, shown schematically in Fiy. 2, mav be positioned to properly receive the emitted acoustic signal~ from a stylus or puck.
Fig. 4 is a section view o~ an acousti~ point source transmitter.
. Flg~ S is a front view of the transmitter of Fig, 4.
~l{
'I Flg. 6 is an acoustic diagram helpful in understanding . the operation of the acoustic transmitter of Fig. 4.
i Fig. 7 is an exploded view of an acoustic receiver ::. 25 employed by the in~ention.
., .. Fig. 8 is a plan view o~ a puck with a pair of acoustic ~ transmit~ers mounted thereonO
'.'~
Fig. 9 1:; a block diagram of the position detection p c:ircultry used by the invention.
~ . 1 ., ~ .
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~'' ii~; Fig. 10 is a schematiC hlock diagram o~ a pre~erred '! si~nal de~ector ~or sensing the "~ront porch" o~ a received acoustic signal.
! ~1 Fig. 11 is a schematic block diagram o~ another signal correlation detection circuit which is more resistant to noise ~han the circuit of Fig. lO.
,G ,.~,, Fig. 12 defines the p~ints used in the two dimensional position determina~ion mathematics.
Fig. 13 shows an arrangement for calibration of the ~;j invention.
. j J 15 Fig. 14 defines the points used in the three dimensional position determination mathematics.
`!
~;, Fig. 15 shows the placemenk o~ an additional scaling transmitter used for measurement correction.
DETAILED DESCRIPTION OP Tl{E ;rNVENTION
~ ( Referring now to Fig. 1, a rectangular two dimensional workspace lO is is de~ined by lts X and Y bounda~i~s.
Work space lO may contain a drawing, a planar constxuct or ~o~e other planar axrangement whose points are to be ~, dlgitized, ~or either di~play on a computer terminal or or ~torage in a computers memot~. Three acoustic ~l receiYers 12, 14, and 16 are arrayed about the '~ 30 perimater o~ wor~5pac~ 109 with each belng co~nected to a two di.mensional pos~tion detection circuit 18. Whil~
acoustic receivers 12, 1~, and 16 may be placed ~`1 arbitrar~ly about work~pac~ 10, th~ one cons~rain~ is ",, : :, . ~d' . .
~ ' ~i 2 1 2 ~
....
that they should not be placed along a single line.
The reason for this will become apparent hereinbelow A stylus 20 is adapted t:o be moved by a user so that its pointed end 22 touches a point in workspace 10 to ~e digitized. A pair o~ acoustic point source , 5, transmltters 24 and 26 are mounted on stylus 20 and are oriented along a line 2a which also intersects pointed ., end 22. Stylus 20 is connected to 2-D position ~.
- lO detection circuit 18 via conductor 30.
,i, Broadly stated, the operation of the system of Fig. l ~9 iS similar to the prior art in that acoustic point source transmitters 24 and 26 emit bursts of periodic `b~ 15 acoustic oscillations which are sensed by acoustic . receivers 12, 14, and 16. By determining the time of ~, arrival of the acoustic signals, the 2-D position -~j d tector l8 is able to det~rmine the position in . workspace 10 at which point end 22 of stylus 20 is ; 20 pointed. Furthermore, hy properly analyzing these signals, the orientation of stylus 20 can be .~ determined.
. . .
As afore~tated, two dimensional position detection,h~s ~` 25 been accompllshed hereto~ore, in its most simple f~rm, by employing a pair of acoustic receivers. This :~ geometry has led to a number of dlsadvantages. First, the Y coordinate value was subject to larger error deviations than the X coordinate value ~ecause the Y
coordinate value was calculated from a combination of a slant range and the X coordinate value. Any errors associated with the X coordinate value thus combined with errors arisin~ f rom the measurement of the slant range. Furthermore, a squa~e root ~unctlon, ~eeded t3 ' t.
212~
g ..~, ~'' ! , detennine the Y coordinate, did not allow ~or its sign ~o be detennined. As will be understood below, the use o~ three acoustic receivers completely avoids the afores~ated problems.
In Fig. 2, the acoustic position digitizing system is shown, as modified for three dimensional point determination. In this case, workspace 32 is three ~'! dimensional and i5 bounded hy X, Y, and Z coordinates.
;s 10 The stylus employed is identical to that shown in Fig.
~; l; however in this case, four acoustic receivers 34, 36, 38, and 40 are arrayed around workspace 32. Each ~' ~ rec~iver is arranged so that it is capable of receiving ;~l acoustic signal emanations ~rom either of point source 15 transmitters 24 or 26. Acoustic receivers 34, 36, and 38 are arrayed in one plane whereas acoustic receiver 40 is positioned in a different plane. Ou~puts ~ro~
"`' each of the aforestated receivers are ~ed to three j dimenslonal posi~ion detection circuit 42.
; 20 In Fig. 3, a preferred mounting arrangement ~or each of -i acoustic receivers 34, 36, 38, and 40 is shown. All of ;;~ the receivers are supported by head 44 which is, in turn, mounted at an end o~ cantilever beam 4~. Ea~h'of 25 the receivers is attached to a connecting post 48 which provides bsth mechanical support and electrical connection to the position detection circuitry.
Receivars 34, 36, and 38, are arrayed in plane SO while receiver 40 is displaced there~rom. This enables the ~0 receive:r array to be arbttrarily located without degradation o~ calculated coordinate values due to slant range distance ~rom the array plane. This arrangement also avoids the problems which were ~ inheren~ in previous three dimensional acoustic array ;3 ~3 ..;,~
; ~''1 , ~ .
21241~1 .-.i ..,.~
J, ':.-'1 .,!
~, sensing systems which employed only three receivers.
( In those systems, the Z coordinate was susceptible to ;~ larger error deviations than the X and Y coordLnate '~ values as it was calculated ~rom a slant range a~d the .
X and Y coordinate values. Any errors associated with - the X and Y coordinate~ added to errors due to the measurement of the slant range and thereby contributed to less ~han desirable accuracy. Sensors ~, 36, 3B, ~;' and ~0 pro~ide independent X, Y, and Z coordinate-`~ 10 measurements so that errors do not aceumulate for the Z
i~ coordinate.
, j Re~erring now to Figs. 4 and 5, the structure o~ an ~'~'`! acoustic point source transmitter is shown. Each acoustic transmitter comprises a conical resonator 60 which is mounted on a piezoelectric actuator 62. Both resonator 60 and piezcelectric actuator 62 are mounted on a pedes~al 6~ and the actuatDr i5 connected to pins , ~
-' 66 and 68 via conductors 70 and 72 and thence to pulse '`~l 20 source 770 The ~ransmitter structure is mounted in a housing 74 which i~ provided with a ~aceplate 76 (see Fig. 5). An opening 78 i6i centrally locate~ in ~ faceplate 76 and pro~id~s a "point ~ource'l effect for ;,,l the acoustic e~anatiOn~ produced by piezoelect~ic actuator 62 and r~sonator 600 Th~ diameter d of opening 78 involve~ a trada o~ betw~en emitted power and wa~e front beam widtho As can ~e seen from Fig. 6, when piezoelectric actuator 62 i~ en~rgized~ it creates an acou5tic wave~ront 80.
'~ When wavefront 80 pai~es through opening 78, assuming opening 7~ i5 ~u~fic~ently 5~all, the txan~mitted ~ wavefc~n a~sume~ an omnid~rectional wave~ront 82 due to i~ diffracl:ion beam-widt~ ~o~mation. How2ver, if opening ", ~
' i'~' . . .
:
212~
i;,., ~
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78 is made ~oo small, ~he power of the transmitted acoustic signal is greatly constrained. On the other -i hand, if it is made too l~rge, wave~ront 82 is distorted with poor side lobe beam patkerns~ From the system standpoint, it i8 most desirable that wavefront 82 be as close to omnidixectional as possible so the .~ diameter d o~ opening 78 is made as small as possible.
i 0 ovPrcome the power reduction created by a minimum ~i 10 diameter opening 7~, it has been found that .'. piezoelectric actuator 62 can be p~lsed with high `j voltage pulses while still remaining within the ~Jl allowable power dissipation limits of the actuator.
.j 031e piezoelectric actuator which is commercially . 15 available from the Panasonic Corporation, when ~:. energized, provides a 40 kHz output ~requency. Its specifications call for a maximum voltage rating of 20 ~ volts for continuous operation. It has been ~ound that .~ by app~ying a 300 volt pulse for lOo microseconds, at a 2 0 repetition rate o~ one pulsç~ every iEi~re miliseconds, "; :, that the ou~put ~ransmitted acoustic energy can be ~`~ substantially inc:reaE;ed without: c:reat:ing daraage t:o actuator 62. P'urthermore, the application of t:his ~'"! extremely high energlzing potential creates a bett'er i~ ~ 25 omnidirectional ~eam pattern and improved amplitude signal levels. It ha~; been fc1und t:hat: lf the applied voltage pulse level to actuator 62 i~ reduced, the beam pattern degrade~ and the amplitude o~ the transmitted ` acoustlc: si~nal drop~. Thus~ it is preferred that the level o~ the appli~d voltage pu15~ and it5 duty cycle be such that it not exceed the ~aximum power rating of the actuator, but that the voltage ~e such that it ~ substant:ially exceeds the applied Voltage rating of the ,; device. It ~hould be understood that the above~noted : ~ `
`` 21241~
. .
, .~.., . ..i -.` 12 ..~:
'-S values are merely exe:mplary and that the values .. ~ employed with actuatorS having dif~erlng specifications will vary in accordance with the above teachings.
.i Re~erring now ~o Fig. 7, an exploded view of an ~: acoustic receiver is shown. The acoustic receiver ,~~
. comprises an electret membrane 90 mounted on an electrode ring ~2. A rear electrode plate 94 is mounted behind ~he front electrode ring and the entire ~ 10 structure is contained within housing 96. While not ;j~ shown, a field effect transistor is connected to one of the el~ctrode plates to ampli~y the signal created by . the movement of membrane 90 in response to a received -¢-~: acoustic signal. A fac~ plate 98 having an opening lO0 ~`^?~ 15 is positioned over the receiving structure. As with the aooustic transmitters, opening 100 pro~ld~s a "point source" receptio~ capability. The operation of the receiver is conventional and will not be ~urther descri~ed.
Referring now to Fig~ 8, an alternative positiDn encoder is shown in lieu of 5tylus 20 (see Fig. 1).
Position encoder lO1 thereina~ter called a "puck") comprises a housing 102 which ha5 an aperture 1~4 in , 25 which a pair of crosshairs lU6 and 108 are positioned.
Crossha.irs 106 and 108 may be e~edded in a transparent glass or poly~tyrene that e~ables a user to see the underlying workspace and to precisely position crossha:ir point 110. A pair of acoustic transmitters ~ 30 112 and 118 are~centered along a llne coincident with !`'','''i crosshalr 106 and are equidi~tant from crosshair point llO. A depressible selection bar 120 enables a user to provide an output pul~ on line 30 w~en crosshair point 110 is positioned over a sux~ace point to be digitized.
. .
....
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2i241~1 :.~ 13 : ,~
; As is well known, the puck 101 is placed ~lat on a `, workspace (e.g. workspace 10 ln Fig. l) and is moved thereabout to position the crosshair point llo over a sur~ace point to be digitized, at which time, the user -~........ 5 depresses bar 120 and causes the transmitters 112 and ~ïj 118 to emit pulses o~ acoustic energy to receivers -j.' positioned about the workspace.
,~,.1~
:i, In Fig~ 9, a block diagram is shown o:~ the circuitry ~ -:J
i~; 10 employed to determine the range ~rom one or more .`-'', acoustic transmitters to the acoustic recei~ers and to then process that range information to arrive at a digitization o~ a point in the workspace. All circuitry ~hown in Fig. 9 is under control of microprocessor 200, however the control lines have ~een i~ omitked to avoid unnecessarily compllcating the diagram. The circuitry of Fig. 9 implements the 3-D
position deteckor 42 shown in Fig. 2.
Acoustic point source transmitters 24 and 26 are alternately pulsed to generate periodic acoustic signals which are transmitted towards acoustic . receivers 34, 36, 38, and 40. Each acoustic receiver feeds an independent circuit which compri~es a ~rdnt ~f rJ , 25 end receiver/comparator 202, a signal detector 204, and ~ a counter and latch 206. Whila these independent `!'i: signal chains are not shown separately on Fig. 9, it is to be understood ~hat ~ront-end recei~er~comparators 202 contains ~our separate ~ront-end receivers, comparators, signal detectors, et~.
' ` ' Thus, a received acoustic signal ~s passed rom its~ acoustic recsiver (e.g. 34) to an associated front end ., receiver 202 where it is ampli~iad and applied ko a .
:
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~ ;- 2~24~ 1 ;~, i`
!;' '1;~';
""';
~, . 14 ~ . , -~.~ comparator. The comparator (also sometimes called a ., .
,. zero crossing detector) is an analog circuit which ~ outputs a high logical level when its analog input -i~ traverses in a positive going direction past a :: 5 reference voltage and it outputs a down level when its analog input traverses :Ln a negatlve going direction ~- past the reference voltaye. In essence, therefore, the -~ comparator is a wave shaper which converts an analog - burst of period acoustic oscillations to a series of square waves whose positive and negative going ~1 transitions are coincident with the positive and negative going transitions of the analog signal.
Signal detector 204 receives the square wave output ~'~ 15 from the comparator and both detects the leading edge of the first square wave (or a subsequent one) and determines that it is, in fact, a portion of a cycle fro~ a received acoustic signal. Assuming that the signal is identified as an acoustic sig~al by detector 204, a stop pulse is generated to a counter and latch circuit 206. Previously, microprocessor 200, via multiplexer 203 and transmitter drivers 210 caused acoustic transmitter 24 to emit an acoustic signal~ At the same time, a clock signal wa~ applied from c~o~k 212 to a counter in count~rs a~d latches 206. When that counter receives a pulse " top'l signal ~rom signal ~,, deteGtor 204, it stops the count and ~nters it into a latch whose output is, in turn, fed to microprocessor 200. That count is then used by microprocessor ~02 to v~ 30 determine the slant range o~ acoustic transmitter 24 rom acoustic receiver 34. The range circ~its associated with each of acoustic receivers 36, 38, and .: 40 act identically to that above described.
. , ;
.;~.! ~
: .,' .~. ----`.
` `;
~` 21~181 .
~ . .
Multiplexer 208 causes transmitter drivers 210 to `~ alternately apply energizing pulses to transmitters 24 ~` and 26 so tha~ the slant range to those transducers can 3' be alternately detected and calculated. Additionally, ":l 5 a correction transducer 212 is provided which, prior to each range measuremen~, ~ends out an acoustic signal ~, which is sensed by acoustic receivers 34, 36, 38, and .~ 40 and is subsequently processed to determine the slant - range to the correckion transmitter. The position of transmitter 212 i5 fixed so that microprocessor 200 is ~,~i, able to derive a correction factor f rom that range measurement. Thiat correction factor is used to alter a ;1 subsequent measurement to take into account any .. ~ atmospherically lnduced changes in the transmitted signal's transit time.
. f ., ' ` . ,j Re~erring now to Flg. 10, a pre~erred slgnal detector circuit is illustrated. The circuit in Fig. 10 is designed to detect the "front porch" of the ~irst ~3 20 positive going hal~ cycle of a received ~ignal from receiver/comparator circuit 202. The detector circuit comprise~ a serial shift register 250, each o~ whose ~tages has an output which ~eeds into a multiple input NAND gate 252 . The output o* NAND gate 252 re~lec~s'an .. j, . .
~p level on line 254 at all t~mes except wh~n there i5 .:. a "one" bit in each ~tage o~ ~hi~t register 250, at "~, which time i~s output on line 254 falls. A shifk clock ~,~, " i5 applied via conductor 256 to ~hi~t register 250 and s~eps input signals appearing on line 2~8 in~o the . . - ~:, .
ragist~r~ ~
it i6 as~u~ed that wave~orm 260 evidences the ~ initlall.y trans~ltt~d ~lr~t hal~ cycle ~rom stylus 20, ,~ and th~t: a resul~ing recei~ed signal 262 is impressed .~ .
~ :' . . ~ , ~. , .
~: i ;
2~2~
.
-. 16 I
,. .
-. on line 258, it can be seen that the ~oltage levels `; shifted into ~hift register 250 will represent wavePorm 262. Assuming that th~re are su~cient stages 1~
: shift r~gister 250 to hold only a portion of a halP
cycle o~ wave~orm 262, a:Ll stages thereof will re~lect ; the "one" state, a determined number of shift clock pulses after the arrival o~ the high state 263 ~f .~ waveform 262. When all stage~s o~ shi~t register 250 evidence the "one" level, NAND gate 252 drops its .,.!~ 10 output. That drop ln output causes a counter in counters and latches 206 to cease counting, with the count indicative, after processing, of the time of transmission of a transmitted signal between an acoustic transmitter and recelver.
If the number of stages in ~ihift r~gister 250 is suf~icient to handle a full half cycle of waveform 262, then stop pulse 264 on line 254 will be a~ shown, with its duration equal to the duration of one shift clock pulse. If the capacity shift register 250 is less ~han the duration of hal~ cycle of lnput signal 262, then stop pul8e 264 will exhibit a down level until the flrst zero appears in ~hi~t register 250. In eikher case, it i8 the leading edge of stop pulse 264 whlch ;! 25 causes the associa~ed counter to cease its count.
;. ;~
; Microprocessor 200, knowing the number o~ shift pulses required ko ~ill shift xegister 250, converts that number t:o a ~ime and subtracks it ~ro~ the ti~e i~dicated by th~ counter and thus obtains a direct indication o~ the time o~ s~nal transmisi~iDn between ~!.i ,; the acoustic receiver and tran~itter. The clrcuit o~
: Fig. 10 th~re~ore, d~tects the hal~ cycle wave~orm 262 ` :!
.: ` '~`
: i, "~"S ~ . ' , ' ``':, ' .
'', i i . , ' - ' . , ' , : ~ .
2 ~ 2 ~
., ~,; .
. and determines that it is, in fact, a signal from an `! acoustic transmi~ter.
While the signal detector in Fig. 10 i5 implemented with a shift register, it is to be understood that any ~; circuit which is capable of determining the presence of 1 a return signal from incoming noise may be employed, ' assuming that it is reasonably economical to implement.
,; For instance, a counter can be ~ubstituted ~or shift ~ 10 register 250, wlth the input signal t 5 "front porch"
~! being used to gate stepping pulses into the counter.
When the predetermlned count is reached, the presence of a return signal ls confirmed and a "stop" pulse generated.
If a noise signal is received, and its duration is equal to or longer than the duration o~ shift register 250, an erroneous range output will occur. Thus if the ~, .i. invention is to be operated ln a noi~y environment, a ~ 20 somewhat ~ore costly, less noise ~usceptible circuit ;~ for noise detection i8 dQsirable and is shown ln Fig~
11.
,.,~,'1} ,.
~, In Fig. 11, serial shift register 300 has, for ex~mple 25 any purposes, a suf~lcient number o~ 6tages to contain an entire ~ull cycle o~ a received acoustic signal when it is clocked by shi~t clock over line 302. The system . o~ Fig. 11 will also function i~ ~hift register 300 ~, includes enough stages to contain either less than or 1 30 more than one cycle o~ a received acoustic signal.
.~
3 A r~ceived signal is i~pressed upon input lins 304 and :~; it~ levels are shl~ted into 5hi~t r~gi ter 300 as ~hey ~` are receivQd ~rom the receiver/comparator circuit 202.
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. 1~
` .~
~!:
'`
A repllca o~ ~he transm~tted (re~erence) siynal is - permanent~.y fix~d in reference register 306, with :~ register 306 having an identical number of stages as shift register ~00. At each shift interval, the levels S in the corresponding stages of serial shi~t register 300 and re~erence register 306 are compared in a mod 2 adder circuit. For instance, the level in stage 308 is fed via line 310 to mod 2 adder 312 and the level from re~erence register stage 314 fed via ~ine 311 to mod 2 adder 312. There is one mod 2 adder ~or each pair of register stages and, at each shift time, their outputs are collectively ~ed to a chain o~ accumulators 316, which accumula~ors provide a sum o~ the resultant signals ko peak detector 318.
Those skilled in the art will recognize that the circuit shown in Fig. 11 bears a resemblance to a correlation circ-llt which correlates the wa~e shape of a received signal on li~e 3Q4 to the wave shape of a re~erence ~ignal Rtored in register 306. As the received ~ignal begins to shi~t into ~hift regist~r 300, the ~um ~alue from accumulators 316 starts to increase as shown by wa~e~orm 320. When the received ~ signal is fully pre~e~t in shift register 300 ~in ph~se . 25 with the signal level~ in reference register 306), the level ~rom accumulators 316 reaches a peak 322 ; (waveform 320) and then begins to decrease as the received signal shi~ts ~urther through register 300.
Peak 322 is detect~d by peak detector 313 which 30 provides a ~top puls~ ~o a count&r in count~r~ and -:i latche~ 206.
. . .
~ ~s w~th the circuit o~ Fig. 9, mic:roprocesSor 200 .`. subtract~ the tlme r quired to insert the received : .;
:, . .
.... ~ :-2 1 2 ~
., 1 9 i~
~, ~'` signal in~o shi~t regi~ter 300 ~rom the time indicated .i by the counter cloc~ circuit to thereby derive the .~' actual time o~ transmission of the acoustic signal.
~ The circuit o~ Fig. 11 is highly speci~ic to the ... ~ 5 transmitted frequency ancl is able to dif~erentiate that signal from all others and provides a high noise-immune detection circuit.
. '`!
!
,;. Microprocessor 200, in response to determining the i. ~
,!,.,. 10 slant ranges between transmitters 24 and 26 and ~;'.i receives 24, 26, 38, and 40 per~orms a num~er of j,~`,~3 additional calculations to derive the position in the workspace of the stylu~ point or puck crosshair. These calculations ar~ ~escribed herein below.
TWO DIMENSIONAL MATHEMATICS~ CALIBRATION AND AL~GO ITHM
The measured slant ranges must be trans~ormed to x and !';`~ 20 Y coordinate values. The ~et-up and location o~ the ~, receivers plays an important role in overall system accuracy.
This section discusses a geometry that uses ~h~ee :-. , 25 receivers to det~rmin~ the x and y coordinates. The . geomet~y allows arbitrary receiver location ~or workspace placement. The three receivers pro~ide independent x and y coordinate measurements so that errsrs do not accumulate wlth the y coordinate. The 30 three receivers also allow t:he calculation oî stylus .. ori~ntat~on so t~at o~et errors to the a~tual digitized point can be corrected ~or. Finally, ~ the r~celver array i8 calibrat~d with r~pect to known calibrat~on point location5, the acou~t~c scale ~actor .. ..
`: 2 ~
` ~
.;
`' 20 ~i will be less sensitive to offset errors, and the final accuracy of the system will be based primarily on the known calibra~ion poin~ location accuracy.
Figure 12 shows the 2-D geometry. The receiver locations are defined for receivers A, B, and C. The range distances between the receivers and transmitter (a, b, and c) ~re measured with the acoustic hardware, and stored ~or each receiver. The xeceivers are all located in the same plane, and the receivers can be located arbitrarily so long as they do not form a straight line.
.~ .1 Slmultaneous equations can be set up for the slant ranges with respect to the coordinate position o~ a transmitter and the coordinate positions of the receivers.as follows:
a2 _ (x X~) + (Y YA)2 r.'ii 20 2 B 2 B 2 ~ c = (x -- XC) + (Y ~ YC) ~; The complete ~olution ~or the above equations can be ~-' shown to be:
x - (allbll ~ al2b21 .. :..
:,:
y a ~a~2~b~ 22b21) ;, whe:re ~ 30 ~ D = (XA - Xc)(Yg ~ Yc~(xB Xc)(~A YC) ;., e ~ l :~5 2D
. j . , , ~ `
~ ~ 2 ~
.`;, ", , ~
:1 a _ y _ y a12 = YC ~ YA
21 = XC ~ XB~ a22 = XA ~ XC
`.:,J
~ ... ' ~, 5 ., bll = R A ~ R2C + c2 _ a2 21 R B ~ R2C + c2 - b2 ~i . J
.,j 10 A z coordinate can be calculated based on a slant ......
~ range~ and the x, y coordinate values. However, two `~ restriotions are needed- first the transmitter must not approach the receiver plane since z accuracy deteriorates quickly with small slant range ^~ 15 differences/ and secondly the value is calculated with ~, a square root function so that the ~ign o~ the ~, coordlnat~ cannot be determined. Both o~ these -jf restrictio~ ara eli~inated with th~ 3-D geometry using ~our ~ecei~ers (dlscussed below). The z coordinate ~^f 20 value i~
`~
d æ ~
' TWO DIMENSION~L CALIBRATION
.. 25 :~ Calibration o~ the receiver array is important to the : .:
~, accuracy o~ the 6ystem. There are several pref~rred :`1 ways to calibrate the system.
., :.
The first method requires precisely mounting the ~^i, rec~ivers at known distances so that their Cartesian ! coordinates are known ~or initializing the geometry.
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Usually, placement o~ the receivers alo~g symmetrical axe~ will reduce the complexity o~ the geometry, such that in the extreme ca~e, only the di.stance between them is required. The receivers can be mounted with respect to the workspace coordinate ~ystem, or they can be mounted on a separate base and referenced only to itself. The rinal allgnment of receiver coordinates and workspace coordinates can be ~ound by rotation and ,1' ~ ' . translation.
A preferred method is to set a piece of grid paper on the worXspace surface, and arbitrarily set the receivers in convenient locations as shown in the Fig.
', ....
: 13. (An ~rror analysis indicates the best accuracy is obtained i~ ~he receivers are approximately placed at right angles, and separated by a reasonable distance.) ~hree known points can be digitized on the grid paper, :i and by reversing the geometry equations (i.e. the three ;.i digitized point~ be~ome the receiver positions in the original geometry and a single receiver location becomes the transmitter location in the original .;; geometry), the receiver coordinate locations can be ~,;,.~
mapped. Now the recelver coordinate system is completely referenced to the workspace coord~n~te system, and rotation and translatlon is not required to `.. align the two coordinate zystems.
: ..
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~ TWO DIM~ ~ S
.~, ... s~3 The complete procedurQ ~or determlning a 2-D posi~ion .~ wikh three recei~er i~ outlined below In A-E.
'`i 5 (See Fig. 12 for de~:Lnitlon3 of transmikter and `,;,?~ recelver location5-) ~ "^, -p~ame~$
~m~um~m ~nt~ a~ow~(~ ~) ~l s ~ ~ e~ fi~m ~c~ o~n~
: 10 bc ~d~yb~(~) c ~ "~ 2 y 2 ~ a ~ Y J ~ l y 2 A~AC--RA--RC f2;c ~ R c . . , . d, 15~ ~A e:xyJ
e~
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3 2 0 ~ ~ C X J ~ ~ ~ A ~Z g ~'.~'''. .
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(d~ b,), bSs $?!~ CI~ b") b~ z ~ ca _ ~, b~ 3 ~ ~ + ~;?a b ~:~i3 x = ~ b~l + a~ab~
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T~ansla~e to wor~ c~rdhla~ sys~a ~by Xtn y3~ equ~d: ;
:~: `?
212~81 THR~E DIMENSIONAL MAT~EMATIcs~ CALIERATION AND ALGORITHM
~1 The measured slant ranges must be transformed to x, y, and z coordlnate values~ The set-up and location of the receivers plays an important role in the overall system accuracy.
The following sections discuss a geometry that uses four receivers to determlne the x, y, and z coordlnates. The `'3'~' 10 geometry allows arbitrary receiver location for easier workspace placementO The four receivers provide ~, independent x, y, and z coordinate measurement so that errors do no~ accumulate with the z coordinate. If the receiver array is calibrated with respect to known ~, 15 calibration point lo~ations, intrinsic ~unctions are not required to rotate the coordinate system to workspace .3 coordlnates. Finally, if the recei~er array is ! callbrated with respect to krLown callbration point 7 locations, the scale ~actor will be less sensitive to of~set errors, and the final accuracy of the system will be based primarily on the known calibration point location accuracy.
,; T~REE DIMENSION~L SLANT~RANGE CONVERSION ' ' ; Four recelver~ are used tQ dete~mine the x, y, and z ~,~ Cartesian coordinate~. The ~our receiv rs also allow the use of the two transmltter ~tylus for accurate projection o~ the coordlnate value to the tip of the stylus for minimal o~et error. Fig. 14 shows the 3-D geometry.
~' The receiver locàtions are shown ~or receivers A, B, C, . and D. The range dlstances between the receivers and .i( transmitt:er (a, b, ct and d) are measured and stored ~or each receivex. Three o~ khe receivers are located in ~he ..~ ,.
"....... . . . .
2 1 ~
~ . .i .~ ! :'., : .1 2 5 ,..
~ jl ~3ame plane and the ~ourth i8 o~ et ~rom this plane~ The receivers can be located arbitrarily as long as they are ~, not all in the same plane.
$ :",i 5 ~$ ~ Simultaneous equa~ion~ ~or the ~lant ranges can be set: up wlth respect to the coordlnatQ position o~ a tran~mitter .. ~ and the coordinatQ po~;itlons o~ the receiver a~3 ~ollows:
- 10 a = (x - XA)2 ~ (y ~ yp,) 2 + ( _ z )2 ~: ' b2 (x X~) 2 + (Y ~ Yg) 2 + (Z ~ ZB) -- (x Xc) + (Y YC) + tZ C) d = (x -- XD) ~ (Y ~ ~D) ~ (Z ~ ZD) .~ The above equatlons can b~ ~hown to lead to the ~oll~wirlg 801utions:
(ql b~ b~ ~ a~
., Y - t~,~ b~ ~ ~ ba ~ a~, b,;) ~
. ~s 20 s =(a~b~ a~a"b~,~)c ~ X -- .~ y; 3 j~ rD ~ I A ZO
.. ; ~ XB_ XD ~ Yaa ~0 YD ~ ~a~ Z~ ~ Z~
: 25 X ~ X X ~'a ' YC rO . ~ ZC ZO
, ,,, ~ 2D
,~ D ~ X~y~ + ~ y,s~ + x~,y~ sY~I ~ xly~ 2YI~J
a~3y~ y~z~ aU~3Y Z --y ~ 4~3y~S3--a2t~x~sJ,~ J, ~ X~S~~X Z j a2~ st-x a~ Ya . ~ 3 X~yl ~ Ya ~ Y~~ ~ Y
~ ~ ~ .
c bll ~ R A - R D + d - ~
. 35 b~RaJ-R~+d'_~3 , ~. b~l ~ R c ~ R D ~ d - c J
t' iÇ "
~ 212~181 ~,ji .~
~,, ~;., 2 6 ir~`
THREE DIME~S :~C)NAI~ Cl~
~i The calibration o~ tho three dlmension sy~tem ls much the ~ame aa ~or the two di:mensional ~ystem. Three known ~.~' 5 locations on a grld paper can b~ digitized to establlsh ' receiver coordinate po~itions. An addltional techni~ue makeç lt pos~ible to extend the concept o~ digitizing ~nown locatlons o~ a grid paper. A r~erence array o~
;~, precl~ely fixed transmitter po~ition~ can he located at a ~`~?~' 10 convenlent position in the workspace~ I~ the reference . transmitter array i8 not moved, the receiver array can be relocated at any time by Eimply re initializi~g the 'î sy~tem with the fixed reference array~
~,d 15 THREE DIMENSIONAL AIJGORII~S
3~ ~he complete procedureç ~or de~ermining a 3-D position ~l with four receiYers i8 outlined in tA-D) b~çlowO
(S~e Fig. 14 for d~çfinitions o~ transmitter and receiver locatlon~.) i,;, ., :., j 2", .'~
. '.:;:.
'' /
~ 2 5 ; . . -, ~p2~rametes$
r~,L ~~ t ~nge ~llowod (~unts) s ~ scale fac~ ~om ~i~ c~rrec~n CuJcolmt) ; i ~ O ~s ~ d~lay bia~2 ~D~i~nt (~o?m~) "~ RC 5 X3 t y~ ~ za R~ a ~ Y~ ~I Z3 ~', 35 R 2- ~'A~-~'n~ R~ 0 . . ~ ~ . . .
2 ~
,;
. i ;i ~r 2 7 i ~
.' ............... x~ = X"--X~,,, y = Y --Y ~ I ~I Zo D ~ Y~ ~ YD ~ ~Z, ZD
C XD ~ Y3 ~c D ~ ~ C D
., D = ~IY~z~ YlZa~ x~y~zl--x~y~ xly~zl--xaylZ3 : c - -, ,1, a~lt = Y,~,--Y~l . a~ Y~ZI YlZ, . 4J~ Y~Za--0 all a ac~za - X~ Z9, az~ = X1Z~ ~ ~y ~1 a~ = xa~- xiz 1 a" = x~y~ Ya a3a--.X~YI--;CIY9 ' ~ Y~t--~aY~
~:; B F~ thc nitIer:
- '; Read ~arîg~ a b c'~ d' ~co~
1 5 ~ Yalid tb~ r~ th~ fi~ the~ em~ a~d ~ s~ep~
:.'5'~
3 Sub~ct delay (co~ d ~1~ mea~ sl~s ~ange~ ches):
= s(d--be)s b~ s fl~
`;:'~ C=S(~ )9 ~1 zs(d' b,~) ~ 20 .,,~ ~ ,, ... ;s 2 5 ~ b b~ 5e R ~ a bla ~ bs~.) e 3 o Y ~ æ b:~ + a~
i .
~ D T3;l~lslate ~ woAcspæe couid~natc ~ystem (b~ yO7 z~
i ~ x = x ~ x~, t 2 ~
.". ~.
RATIO SCALING CORRECTION
; ~
, ~ .
- Range measurement accuracy is affected by the acoustic ;i~ medium in the workspace~ Factors such as temperature, ~ S humidity, and air ~low a~ect the speed of sound, and ,!~`,., there~ore measurement accuracy. If temperature is used !.' to correct the speed of sou~d constant, then the ~ correction factor at 70 F is , ." ;
i. 10 V = 13,574 inches/sPcond.
. :. ,.
If the digitizer counters run at lOMHz, the length per ~,i count is:
13,574 in./sec- z 001357 inches/cou~t-10 x 106 counts/sec.
. .
Prior art units correct for the speed of sound with a temperature probe. The problem with temperature compensation by a probe is that the probe and circuitry have to be extremely accurate and not susceptible to bias or drift. ~dditionally, te~perature is only one of the ~actors that affect the speed o~ sound. , , ,i 25 This invention uses a method of measuring the reference range with each coordinate measurement, and correcting with a xatio scale factor. ~he speed of sound constant is not :required, and scaling ratios provide the systems acoustlc correction.
A reference correction transmitter 400 (see Fig. 15) is permanently mounted at a precisely Xnown location with respect to a receiver, and fired periodically so that the 212~
, ~
~`. 29 range values can be rescaled for temperature and other ~-~ environmental conditions. The ~ollowing approach 15 used -~, ;. for range scaling~
~ .,.
;~. 5 rererence dist~nce (inch~s) i~ r;~ efinches~ x m~n~uredr~n~e(counls) ` '~ me3~ure~r~fer~ncer~n~coun~sJ
. .
~'; or in mathematical ~orm, ~. 1 0 r' = actual reference range distance r = measured reference range corresponding to r' c = constant delay bias of circuitry .,; ~
`~ 15 r' C
Correct the range measurement for each receiver:
.. ~ a=s(a-bc~
s b=s(b-b~) C=5 ( C-bC ) :~ d=s (d-bC) ~ ' .
This invention u~e~ ~ ~ethod o~ ~ea~uæing th2 refer~nce ~' range w~th each coordinate measurement, and correcting -~ with a ratio scal~ ~actor. The speed o~ sound constant .i, is not required, and scaling ratios provida the systems :~ acoustlc correction.
:~ The ~teps for sy~tem calibration are afi follows:
~ ~x ~ 1. Place the grid paper on the workspaoe (flat ~able top) .
,', ":. ' ` ' " ' ' : : ` ' '.~.'... ' ` ' ~ ` , `' ~ : , 2 ~
;~
.
.
, 30 , 2. Place the receiver array anywhere to one side of the . workspace 3. Digitize the calihration points on the grid paper.
.. 4. The scaling transmitter mounted on the array base is ~ired for a ref~rencle range~
. The computer calibration and scallng procedure employs the above derived data as ~ollows:
, ,, .i lO 1. The systems consta~ts are initialized.
:., ~ 2. For each poi~t measured above, the ranges are scaled !j'`;'' and two range values (from two transmitters on the puck) are used to calculate the ranges to the center of the crosshair ~or each calibration point.
3. The measured range values ~rom above are stored: 3 :~ digitized points, and 4 receiver.qi for a total of 12 , rangesO
4. The x, y, z coordinate ~or each receiver is '.~7 calculated.
5. Based on ~he receiver coordinates, matrix ;. coe~icients are calculated (t~ese coefficients are used in the ~inal solution for normal digitizing).
Now the user can digitize any point in the workspace, and get an x, y, z coordinate ~alue (and ~tylus orientation ,l.. , , 25 if required~. Th~ user ~imply place3 the stylus tip on the point to be digitizedO The steps below outline what ;~ the computer 60ftware doe~ to convert a~d scale the `.~ coordinate values:
i,,, ^~ 30 lo The computer polls the stylus and waits ~or lt to be activated te~g. by the user pressing a switch on the stylus).
.,j , :' :3 , 1-;,,~;i ~
i `:
2 1 2 ~
~.'-:~ 31 . .
.: ~
2. When ready to digitize, a ~irst transmitter on the . 3stylu~ is fired and the ~our range distances to the receivers are ~tored.
~3 3. A ~econd ~ransmitter on the stylus is ~lred, and the four range di~tances to the receivers are stored.
4. The reference tran,smitker on the base of the . receiver array i8 ~ired, and the range distance to . the receiver is ~tored.
5. The actual reference range is divided by the scale ~, 10 range measurement f3rom the reference transmitter on ~ the recei~er base to ~30rm the ~inal scale correction .~1 factor. The range values are multiplied by the .3 scale ~actor to provide the corrected range values.
6n Range measurement~ ~rom the transmitters on the stylus are used to calculate the x, y, z coordinates at the stylus tip, and ~tylus orientation angl~s.
",.,.,~
It is to ~e noted that $hQ speed o~ sound conskant is never ~sed in this procedure, only scaling ratios.
SCALE RATIO ALGORIT~M
~- i . ,.
D below ~how the algorithms which allow the conversion :-~ o~ a binary range n~mber to inches while scali~g~khe , . . .
.; 25 range to correct ~or environmental changes that e~3ect ~::
~ the sp2ed of sound.
:,,.;~
~ . ., ~
~ ' ., ~' .
. ,~;
2~2~
. .
:
. .
.,.;;lii, :
......
. ., ~ ~ SQDiC Ca~On.
':, ?! R~ angc r (16 bit c~t) ~! 5 IEr ~r~ ~peatabo~es~:ps :-.,: i , j,; .
......
10 ,~ 8i r b `;''i: ~ W~i ',~' 2 r ~ ~e~d C~ c~d~ or ~m~
b~ ~ sonst~td~y W~ o~iky (c~u~ts) ~j; ..;
;~ ,,~
, .
~ ~ 2 0 ~d ~ ~ t ~ ? ~ d~ (16 b~ ~
" - , ~;
2 5 D 5ubtract thc delay (~t~ d æale tho d~ san~s (~hcs):
a-i ~ (a b"3 b i s(~ ~ b,) s \ c~i 3 (c ~ "j) ~ s (d b~,) `` 2 ~`2 :...
. ~
'''~'' ; It should be understood that the foregoing description is only illus~rative of the invention. Various alternatives and modifications can be devised by those skilled in the i:~ art without departin~ from the invention. For instance, ~ 5 while the acoustic transmitters have been shown as parts ; j~ , of a stylus or puck, they could ~e attached to any moving ~ body in the work space, e.g., to a human's arm, for `;i~l instance, when it is desired to study the arm's movements , , .I under predetermined conditions. With one acoustic transmitter, single point coordinates can be determined a, for three coordinate space tracking of point or object positions. With two acoustic transmitters, the invention is able to determine position, pitch and yaw. If a third acoustic transmitter is added, roll can ~e determined, so long as the third transmitter is not located in the same line as the other two transmitters. Additionally, while a single set o~ acoustic receivers has been described, .. added sets of receiver ~roups may be positioned about the work space (1) to accommodate barriers which may block the signals to one group o~ receivers, and not another or (2) to accommodate too great attenuation of received signals due to the distance between receivers and transmitters. ~ccordingly, the present invention is ;~i intended to embrace all such alternatives, modific~t~ons .. ;-.i 25 an ~ariances which fall within the scope of the appended ~ claims.
.
:
~, .
: ~
....:~
Now the user can digitize any point in the workspace, and get an x, y, z coordinate ~alue (and ~tylus orientation ,l.. , , 25 if required~. Th~ user ~imply place3 the stylus tip on the point to be digitizedO The steps below outline what ;~ the computer 60ftware doe~ to convert a~d scale the `.~ coordinate values:
i,,, ^~ 30 lo The computer polls the stylus and waits ~or lt to be activated te~g. by the user pressing a switch on the stylus).
.,j , :' :3 , 1-;,,~;i ~
i `:
2 1 2 ~
~.'-:~ 31 . .
.: ~
2. When ready to digitize, a ~irst transmitter on the . 3stylu~ is fired and the ~our range distances to the receivers are ~tored.
~3 3. A ~econd ~ransmitter on the stylus is ~lred, and the four range di~tances to the receivers are stored.
4. The reference tran,smitker on the base of the . receiver array i8 ~ired, and the range distance to . the receiver is ~tored.
5. The actual reference range is divided by the scale ~, 10 range measurement f3rom the reference transmitter on ~ the recei~er base to ~30rm the ~inal scale correction .~1 factor. The range values are multiplied by the .3 scale ~actor to provide the corrected range values.
6n Range measurement~ ~rom the transmitters on the stylus are used to calculate the x, y, z coordinates at the stylus tip, and ~tylus orientation angl~s.
",.,.,~
It is to ~e noted that $hQ speed o~ sound conskant is never ~sed in this procedure, only scaling ratios.
SCALE RATIO ALGORIT~M
~- i . ,.
D below ~how the algorithms which allow the conversion :-~ o~ a binary range n~mber to inches while scali~g~khe , . . .
.; 25 range to correct ~or environmental changes that e~3ect ~::
~ the sp2ed of sound.
:,,.;~
~ . ., ~
~ ' ., ~' .
. ,~;
2~2~
. .
:
. .
.,.;;lii, :
......
. ., ~ ~ SQDiC Ca~On.
':, ?! R~ angc r (16 bit c~t) ~! 5 IEr ~r~ ~peatabo~es~:ps :-.,: i , j,; .
......
10 ,~ 8i r b `;''i: ~ W~i ',~' 2 r ~ ~e~d C~ c~d~ or ~m~
b~ ~ sonst~td~y W~ o~iky (c~u~ts) ~j; ..;
;~ ,,~
, .
~ ~ 2 0 ~d ~ ~ t ~ ? ~ d~ (16 b~ ~
" - , ~;
2 5 D 5ubtract thc delay (~t~ d æale tho d~ san~s (~hcs):
a-i ~ (a b"3 b i s(~ ~ b,) s \ c~i 3 (c ~ "j) ~ s (d b~,) `` 2 ~`2 :...
. ~
'''~'' ; It should be understood that the foregoing description is only illus~rative of the invention. Various alternatives and modifications can be devised by those skilled in the i:~ art without departin~ from the invention. For instance, ~ 5 while the acoustic transmitters have been shown as parts ; j~ , of a stylus or puck, they could ~e attached to any moving ~ body in the work space, e.g., to a human's arm, for `;i~l instance, when it is desired to study the arm's movements , , .I under predetermined conditions. With one acoustic transmitter, single point coordinates can be determined a, for three coordinate space tracking of point or object positions. With two acoustic transmitters, the invention is able to determine position, pitch and yaw. If a third acoustic transmitter is added, roll can ~e determined, so long as the third transmitter is not located in the same line as the other two transmitters. Additionally, while a single set o~ acoustic receivers has been described, .. added sets of receiver ~roups may be positioned about the work space (1) to accommodate barriers which may block the signals to one group o~ receivers, and not another or (2) to accommodate too great attenuation of received signals due to the distance between receivers and transmitters. ~ccordingly, the present invention is ;~i intended to embrace all such alternatives, modific~t~ons .. ;-.i 25 an ~ariances which fall within the scope of the appended ~ claims.
.
:
~, .
: ~
....:~
Claims (2)
1. An acoustic position sensing apparatus for determining the position of an indicator in relation to a datum surface, said apparatus including acoustic point source transmission means on said indicator for transmitting a sequence of periodic acoustic oscillations, said transmission means comprising:
a pair of point source acoustic transducers;
means for supporting said transducers in a spaced apart relationship along a common line, said supporting means further having indicator means located on said line, said supporting means further being movable by hand across said datum surface to indicate a point on said surface, said supporting means being substantially planar in shape, and said indicator means being positioned between said transducers.
a pair of point source acoustic transducers;
means for supporting said transducers in a spaced apart relationship along a common line, said supporting means further having indicator means located on said line, said supporting means further being movable by hand across said datum surface to indicate a point on said surface, said supporting means being substantially planar in shape, and said indicator means being positioned between said transducers.
2. The invention as defined in Claim 1, wherein said indicator means is positioned along a straight line between said transducers and said indicator means comprises an opening in said supporting means with crosshairs mounted therein, a point of intersection of said crosshairs positioned on said line.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/412,885 US4991148A (en) | 1989-09-26 | 1989-09-26 | Acoustic digitizing system |
| US07/412,885 | 1989-09-26 | ||
| CA002024527A CA2024527C (en) | 1989-09-26 | 1990-09-04 | Acoustic digitizing system |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002024527A Division CA2024527C (en) | 1989-09-26 | 1990-09-04 | Acoustic digitizing system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2124181A1 true CA2124181A1 (en) | 1991-03-27 |
Family
ID=25674287
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002124181A Abandoned CA2124181A1 (en) | 1989-09-26 | 1990-09-04 | Acoustic digitizing system |
| CA002124180A Abandoned CA2124180A1 (en) | 1989-09-26 | 1990-09-04 | Acoustic digitizing system |
Family Applications After (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002124180A Abandoned CA2124180A1 (en) | 1989-09-26 | 1990-09-04 | Acoustic digitizing system |
Country Status (1)
| Country | Link |
|---|---|
| CA (2) | CA2124181A1 (en) |
-
1990
- 1990-09-04 CA CA002124181A patent/CA2124181A1/en not_active Abandoned
- 1990-09-04 CA CA002124180A patent/CA2124180A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| CA2124180A1 (en) | 1991-03-27 |
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