CA2176529A1 - Position and orientation measuring system having anti-distortion source configuration - Google Patents
Position and orientation measuring system having anti-distortion source configurationInfo
- Publication number
- CA2176529A1 CA2176529A1 CA002176529A CA2176529A CA2176529A1 CA 2176529 A1 CA2176529 A1 CA 2176529A1 CA 002176529 A CA002176529 A CA 002176529A CA 2176529 A CA2176529 A CA 2176529A CA 2176529 A1 CA2176529 A1 CA 2176529A1
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- Canada
- Prior art keywords
- source
- conductor
- planar coil
- spiral
- coil
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/004—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring coordinates of points
Abstract
A method and apparatus for determining the position and orientation of a remote object relative to a reference coordinate frame includes providing a source having a plurality of field-generating elements, wherein the field-generating elements generate electromagnetic fields and have spatially independent components defining a source reference coordinate frame. A driver applies signals to the source to generate a plurality of electromagnetic fields which are distinguishable from one another and a remote sensor has a plurality of field-sensing elements which sense each of the generated electromagnetic fields. A processor processes the output of the sensor in a remote object position and orientation relative to the source reference coordinate frame. At least one of the field-generating elements of the source has at least one electrically conductive sheet and a planar coil including a plurality of coplanar concentric rings above the conductive sheet. The planar coil is configured in a manner that a signal applied to that coil will cause a current density at each ring that is inversely proportional to the square of the radius of that ring. The planar coil may be made from a conductor formed as a simple or foliated spiral. The planar coil and the electrically conductive sheet may be formed from printed circuit board stock. A dihedral source may be made from a pair of orthogonal electrically conductive sheets each having a planar coil above the sheet. A trihedral source may be made from three electrically conducting sheets each having a planar coil above the sheet.
Description
POSITION AND ORIENTATION MEASURING SYSTEM
HAVING ANTI-DISTORTION SOURCE CONFIGURATION
BACKGROUND OF THE INVENTION
This invention relates to position and orientation measuring systems (POS) which5 determine remote object position and orientation and, more particularly, to anelectrom~gnPtic POS having a source which produces a plurality of electrom~gnPtic fields which are distinguishable from one another, a remote sensor which senses the gel~el~led electrom~gnP-tic fields and a processor which processes the output of the sensor into remote object position and orientation relative to a reference coordinate frame of the 10 source. More particularly, the invention relates to an improved source for an electrom~gnPtic position and orientation measuring system.
Remote object position and orientation measuring systems employing electrom~gnP-tic coupling are disclosed in United States Patent No. 3,868,565 issued to Jack Kuipers for an OBJECT TRACKING AND ORIENTATION DETERMINING
15 MEANS, SYSTEM AND PROCESS and United States Patent No. 4,054~881 issued to Frederick Raab for a REMOTE OBJECT POSITION LOCATOR. Such systems traditionally have a source assembly that includes a plurality, typically three, of concentrically positioned, orthogonal field-generating antennas for generating a plurality of electrom~gnPtil~ fields. Signals are applied to the field-generating antennas that are 20 multiplexed so that the resulting electrom~gnPtic fields are distinguishable from one another. Located at the remote object is a sensor having a plurality, also typically three, of concentrically positioned, orthogonal receiving antennas for receiving the electrom~gnP-tic fields generated by the tr~n.smitting antenna and producing signals corresponding to the received electrom~gnPtic fields. A processor resolves the signals 25 produced by the receiving antennas into remote object position and orientation in the elellce coordinate frame of the source.
One application for such position and orientation measuring system (POS) is as athree-dimensional digitizer for determining and ~ligiti7ing the coordinates of a three-dimensional object. In such a digitizer, the source may be embedded in a table having an 30 integral work surface, or ~ligiti7ing tablet, upon which the object to be (iigiti7e~1 is placed.
A hand-held stylus is used for tracing and determining points of interest on the surface of the object. The remote sensor is disposed in the stylus and the stylus is provided with a projection for defining a point of contact between the stylus and the surface of the object 2 1 7 652~
of interest. Since the point of contact of the stylus and the remote sensor are provided with a known relationship, the coordinates of the surface of the three-dimensional object touched by the stylus may be determined from the position and orientation of the sensor in the coordinate frame of the work surface.
One difficulty with a digitizer utili~ing an electrom~gn~tic POS is that the work surface, or ~ligiti~ing tablet, carmot be located on a table including a substantial amount of electrically conductive or fellu~Agn~tic metal. The electrom~gn~ti~ fields generated by the source of the appaldlus induce eddy ~;ullcllL~ in the metal. The eddy ~;ullellls produce an electrom~gn~tic field which distorts the field generated by the source, inducing error in the measured fields and, hence, the calculated position and orientation of the remote object. Various methods exist to map distortion and to compensate for the distortion in the POS processor. However, if the distortion is too severe, such mapping may not adequately compensate for the distortion.
It may be desirable to be able to place a conventional digitizer source on an electrically conductive or ferrom~gnPtic metal plate. Other applications for which it may be desirable to use an electrom~gn~tic POS may also result in severe magnetic-field distortion with a conventional POS source. For example, it may be desirable to place the digitizer source on a metal table adjacent to a metal wall. It may also be desirable to position a POS source at the corner of a metal-walled rectangular room in order to locate 20 one or more remote objects within the room. In all such applications, the ability to compensate magnetic-field distortions would be nil.
SUMMARY OF THE INVENTION
The present invention provides an electrom~gn~tir position and orientation measuring system having a novel source configuration which produces low distortion 25 m~n~tic fields in one portion of a three-dimensional space nolwill~ ling the presence of electrically conductive or ferrom~gn~tic metal in another portion of the electromagnetic space. This is accomplished by positioning a conductive sheet in order to divide the space into two portions and producing an electrom~gn~tir field on one side of the sheet.
The electromagnetic field that is produced has a dipole moment that is normal, or 30 orthogonal, to the sheet. A constant m~gn~tic dipole moment in a low distortion m~gn~tic field is produced in the space portion on the one side of the sheet.
A source configured according to the invention includes an electrically conductive sheet and a planar coil mounted parallel to and near the sheet. The planar coil includes a 2 i 7652~
plurality of substantially coplanar concentric rings. The coil is configured in a manner that a signal applied to the coil will have a current density at each ring that is inversely proportional to the square of the radius of that ring. Such source configuration produces quasi-static magnetic fields which do not .~ignific~ntly penetrate the electrically conducting 5 sheet. It is believed that this is a result of the normal component of the m~gnPtic field at the surface of the electrically conductive sheet being substantially time-invariant. The electrically con~ cting sheet functions as a mirror for orthogonal antennas of the source which produce dipole moments parallel to the electrically conductive sheet.
The present invention finds applications where it is desired to measure the position 10 and orientation of a remote object in the coordinate reference frame of a three-dimensional space, but wherein the remote object is restricted for movement within a portion of the space. In this manner, the presence of even very large quantities of electrically conductive or ferrom~gn~ti~ metals in other portions of the space, where the remote object is not positioned, will have no substantial effect upon the accurate 15 determination of position and orientation of the remote object.
These and other objects, advantages, and fedLul~s of this invention will become apparent upon review of the following specification in conju,l~ion with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram illustrating a position and orientation measuring system 20 useful with the invention;
Fig. 2 is a perspective view of a source, according to the invention;
Fig. 3 is a perspective view of an alternative embodiment of the invention;
Fig. 4 is a perspective view of another alternative embodiment of the invention;Fig. 5 is an enlargement of the portion illustrated at V in Fig. 4; and Fig. 6 is a sectional view taken along the lines VI-VI in Fig. 5.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now specifically to the drawings, and the illustrated embodiments depicted therein, a position and orientation measuring system (POS) is embodied in a three-dimensional digitizer 12 (Fig. 1). The digitizer includes an electronic comyu~ g unit, or processor, 14, an object table 16, a source 18 of electromagnetic fields, a stylus 20, including a sensor 22 having a plurality of receiving all~el~nas, and a foot switch 24.
The output of processor 14 is typically provided to a host colllyuLel 26 where various software packages can be used to transform the ~ligiti~e~l coordinates of the object traced ~1 7652~
-on object table 16 into useful information, such as layout drawings, perspective views, material lists, or a database for graphic image generation. Typically, the output of host co~ ul~l 26 is inputted to a visual display, such as a monitor 28. Source 18 is composed of three independent loop antennas which each define a m~gn~tic dipole field. The loops 5 of the three ~ntenn~ are oriented such that three orthogonal dipole m~gn~tic fields are created, one of the fields being identified with one of the X, Y, and Z axes of the work surface of object table 16 such that the electromagnetic fields define a refelellce coordinate frame. Processor 14 includes a driver connected to source 18 by linesschematically illustrated at 30 for applying to the three loop antennas electrical signals 10 which genelate the three dipole m~gnrtir fields associated with the X, Y, and Z
directions, respectively. The electrical signals applied to the three loop antennas are multiplexed so that the reslllting dipole m~gnrtic fields are distinguishable from one another. A variety of alternative multiplexing techniques include time division,frequency, and phase-multiplexing. Sensor 22 includes a plurality of receiving antel~llas 15 for receiving components of the electromagnetic fields tr~n~mitted by source 18.
Preferably, the receiving antennas also are composed of three loop antennas. The three loop antennas defining sensor 22 are oriented in mlltll~lly orthogonal directions so that the antennas define a sensor coordinate frame Xl, Yl, Zl. The output of the antenna triad defining sensor 22 is connrcte~l to processor 14 by lines schematically illustrated at 32.
20 Digitizer 12 is disclosed in more detail in commonly ~signr.d United States Patent 4,613,866 issued September 23, 1986, for a THREE-DIMENSIONAL DIC~ K
WITH ELECTROMAGNETIC COUPLING.
Although the POS illustrated in Fig. 1 is embodied in a digitizer 12, many otherapplications are possible. In other applications, the sensor can be associated with a 25 particular body part for the purpose of con~ cting biomedical studies or for manipulating three-dimensional images displayed on a design colll~ulel. In an important military application, the sensor is associated with the helmet-~ighting reticle of the pilot of a military aircraft for d~te"llinil~g the line of sight of the pilot to a target and, thereafter, initi~li7ing ordnance which is directed along the line of sight to the target. In the field of 30 head motion sensing, generally, the system can be employed as an input to a virtual reality system in order to drive a displayed image to coincide with the user's head position. Still another application involves the monitoring of the body movements of an invalid for the purpose of creating a non-verbal communication system or providing a 21 7652~
technique for remote-controlling various devices with non-verbal coll~"~llnic~tive body motion.
Source 18, according to the invention, includes an electrically con-lucting sheet 34 positioned at the Z = 0 plane of the source lerelellce coordinate system (Fig. 2). A
planar coil 36 is positioned close to electrically conducting sheet 34. In the illustrated embodiment, planar coil 36 is mounted to a thin in~ul~ting sheet 38 which separates the coil from the electrically conductive sheet. Planar coil 36 is made up of a plurality of essentially coplanar concentric rings 40 all positioned in a plane parallel to electrically conductive sheet 34. In the illustrative embodiment, concentric rings 40 are made from an electrical conductor 41 formed into a simple spiral. Conductor 41 has a first ~ linal 42 positioned at the outer perimeter of the coil and a second terminal 44 positioned at the center of concentric rings 40. Planar coil 36 is constructed such that, when an electrical signal is applied across terminals 42, 44, the density of the current influced in each ring 40 is inversely proportional to the square of the radius of that ring. Such current density may be accomplished as follows.
Electrically conductive sheet 34, planar coil 36, and insulating sheet 38 may bemade from printed circuit board stock. Current density may be established at thedesirable level by making the width of the copper track inversely proportional to the square of the radius of the center of the track. Planar coil 36 may be etched from one of the conductive sheets on one side of in~ ting sheet 38 by providing only a minim~l-width spiral line of a copper-free insulating surface between the windings. In this manner, the con~lucting copper track is of minim~l width close to the center of the coil and widens progressively oulw~rdly. The result is that the current density may be controlled by the geographic layout of planar coil 36.
In a spiral:
r. THETA = constant (1) where r is the radius of the point on the spiral and THETA is the angle measured from the X axis. In the illustrated embodiment, THETA varies from 40*pi at the outside to 800*pi at the inside, resulting in 380 turns in the spiral. At the outside, the radius is 20 inches and the turns of the insulating spiral are one inch apart center-to-center. At the inside, the radius of the ring is one inch and the turns of the in~ ted spiral are 1/400 inch apart, center-to-center. Because the thickness of the track is equal at all points, the width is proportional to the cross-sectional area. As the track gets wider, the current density gets smaller. The product of current density and track cross-sectioned area is equal to the total current in the track.
In an alternative embodiment, a second spiral (not shown) is formed on printed circuit board 39 on the opposite side of in~ ting sheet 38. If such additional coil is 5 formed, then a separate electrically conductive sheet 34 is lltili~ed The second inslll~ting spiral on the opposite side of printed circuit board 39 spirals in the same direction as planar coil 36. Current flows ouLw~ld on one side and inward on the other side so that the two sides generate m~gnPtic field in the same direction. In this alternativeembodiment, a large number of plated-through holes are placed ul~irollnly around the 10 periphery of printed circuit board 39 in order to preserve a uniform current distribution around the periphery.
Planar coil 36 positioned at Z = 0 produces Z-dipole m~gnPtic fields. A
conventional coil assembly 46 is provided at the center of printed circuit board 39 in order to produce X-dipole and Y-dipole m~gnPtic fields. Coil assembly 46 includes a Y
15 coil 48 for producing Y-dipole magnetic fields and an X coil 50 for producing X-dipole magnetic fields. Although not shown, a discrete Z coil may be included with coilassembly 46 and connPcted in series with planar coil 36 in order to increase the turns-density at the center of the coil.
In the illustrated embodiment, a simple spiral is disclosed. The simple spiral has 20 closely spaced turns near the center, but widely spaced turns near the outer edge. These widely spaced turns may cause localized field distortions close to the plane of the spiral at the edge. Such local distortions may be difficult to map and compensate for. In order to overcome such difficulties, a foliated spiral may be l~tili~P,d A foliated spiral is constructed by a repeated subdividing of the current paths into parallel tracks as the 25 conductor defining the coil spirals outwardly. Starting at the center of the spiral, the track has ~ center-to-center turn spacing. As the conductor spirals oulwardly, the spacing increases. When the spacing reaches twice the mini~ center-to-center spacing, a new spiral is started halfway between the turns of the existing conductor by splitting the conductor into two tracks. At such radius, two spiral tracks are present, 30 each carrying half the current. The spacing between adjacent turns is at the mi~i........
center-to-center spacing. Both tracks spiMl oulwaldly until the spacing reaches twice the .lli~-il..lllll. Each track is then split into two tracks for a total of four tracks. This pattern is repeated oulw~ldly for the entire coil. The foliated spiral reduces local distortions by 2 1 7 652~
limiting m~ximllm turn spacing. In order to cause the current in all of the tracks around the outer edge to be equal, series ballast resistors or active current drivers may be used to adjust the current. If active drivers are used, each driver provides a fraction of the current. This makes individual drivers simple and smaller than a single driver for a 5 simple spiral.
Electrically contlucting plane 34 acts as a mirror for m~gn~tic fields wherein the magnetic field at any point above the plane is the sum of the field generated by the sources in that space and the field generated by eddy ~;ullellls from the con(luçting plane.
By placing the source coils near the con(luctin~ plane, with the conducting plane 10 positioned at Z = 0 cooldhlat~s, the X-dipole moment is parallel to and in front of the plane. The X dipole generates an image-dipole moment parallel to and behind the plane.
The image-dipole moment is the same strength as, and in the same direction as, the X-dipole moment. Therefore, the image-dipole moment and the X-dipole moment becomecollocated creating one dipole moment of twice the strength of the original X-dipole 15 moment. The same applies to the Y-dipole moment. The Y-dipole m~gn~tic field is substantially undistorted and double the strength of the Y-dipole m~gn~.tic field when the source is in free space.
As will be described in more detail below, coil 36 which is positioned at Z = 0 produces a constant magnetic dipole moment which is normal to con-lucting plane 34. In 20 practice, the Z-dipole field is somewhat distorted close to the con(luçting plate, the lines of flux curve inward towards the plate rather than being normal to the plate. However, the gellelaled electrom~gn~tic fields are sufficiently non-distorted farther from the plate in order to produce accurate results.
The invention is based upon the ability to generate a quasi-static dipole m~gn~tic 25 field with the dipole moment normal to a con~luçting plane or plate. By placing an actively forced current sheet, in the form of the concentric rings, close to the con-lucting plane, m~gnPtic fields are produced which do not behave according to normal boundary conditions of a con-lucting plane. By forcing the current density in each ring to be inversely proportional to the square of the radius of the ring, the product of the current 30 density in a ring times the area enclosed by that ring is a constant. The constant is 2m where m is the m~gn~tic dipole moment. As will be set forth in more detail below, the magnetic vector potential, and, hence, the m~gn~tic field, is that of a dipole with 6m~gn~tic moment equal to m, normal to the con-lucting plane. If the m~gn~tic fields are 21 ~ 6529 .
generated by slowly varying ~;ullcn~s, the source is operating near-field and radiation effects can be ignored. Such quasi-static magnetic fields do not penetrate the conductive sheet because the normal component of the magnetic field at the surface of the sheet is substantially time-variant.
The vector potential of a finite-sized circular current loop in free space in the Z =
0 plane, centered on the Z axis, may be represented by:
Ao = 11 I ¦ a cos (~) d~ (2) 2~ ~,=o [a2 +p2 + Z2 -2 a p COS (~$\) ] 1/2 where:
~ , Z) are cylin-lri~l coordinates, ,u = permeability of free space, a = loop radius, and I = current in the loop By symmetry, the vector potential has only a ~ component, Ao~ For an infinite array of 15 coplanar concentric circular rings, the current density in each ring is represented by:
I = m/(2 7r a2) (3) The ~ component of the vector potential is:
Al 4 7~2 ¦~I~=o la_o a [a2 +p2 +Z2 -2 a p COS ((1!,) ] 1/2 da d~ (4) The ~ component is integrated over a, as illustrated in equation 5:
A~ log ~1+ P ~ ~ d~ (5) 4 ~2 ~=o (p2 + Z2) 1/2 ~ (p2 + Z2) 1/2) + ,~ m limit [ log ( 2 (p2 + Z2) 1/2) J~ cos (~, d~]
The second term of equation 5 is zero. Equation 5, therefore, becomes:
( 6 ) 4 ~p (p2 + Z2) 1/2 When an array of current carrying conductors is placed extremely close to a con-lucting 5 plane, the vector potential is the negative of the Z-gradient of the vector potential of the array alone. Thus, the ~ component of the vector potential of the array of coplanar rings placed near to a contlucting sheet is:
d z By combining equations 6 and 7:
A = ,u m p ( 8 ) Equation 8 may be converted to spherical coo~inales where p = r sin(e) and Z = r A llmsin (~) (9) 4 ~ r2 cOS(e):
Equation 9 illustrates the vector potential of an ideal dipole in free space with the dipole 15 m~gnPtic moment m normal to the plane. Therefore, an array of coplanar concentric current rings, with the current density inversely proportional to the square of the ring - 21 7652q Mdius, placed near to a conducting plane, produces a dipole m~gnPtic field with dipole moment normal to the plane.
Although planar coil 36 is illustrated as a circular coil, particular applications may be better suited with a rectangular-shaped coil. This may be accomplished in several 5 ways. A spiral coil may be constructed that is large enough to cover the entire rectangular area with parts of the spiral extending beyond the boundaries of the rectangle.
These extraneous parts may be folded under the rem~ining portions of the spiral so that they lie within the rectangle and at the same time are very close to the conductive plate.
The result is that the current still has a path to flow, but the folded parts of the spiral 10 produce little m~gnPti~ field because they are close to the magnetic plate. This may additionally be accomplished by placing the extraneous parts of the spiral close to but under the plate.
Another technique for producing a rectangular coil is to produce a modified elliptical spiral, which fills most of the rectangle. Any distortion in the field will have 15 smooth gradients. Therefore, compensation algo~ ls will readily correct for any such distortion. This may be accomplished by stretching one axis, such as the X axis, by a scale factor greater than 1. To convert any point (X, Y) on the circular spiral to the corresponding point (U, V) on the "rectangular" spiral, the (X, Y) coordinates are converted to polar coordinates (r, THETA). For each value of r, THETA is calculated as 20 follows:
THETA = ARCTAN(Y/X) (10) By choosing values of THETA that put (r, THETA) in the same quadrant as (X, Y), the program (11), which is in fortran, will calculate the corresponding points (U, V) on the rectangular spiral.
CTPTU = COS(THETA) (11) STPTU = SIN(THETA) MODIFY R TO CONVERT CIRCLE TO SQUARE
USING PIET HEIN'S SUPEREGG EQUATION
RORMX = R / RMAX
ALP = 0.5 + 1.5 * EXP(4.0*LOG(2)*RORMX*RORMX) ABSCO = ABS(CTPTU) + 0.000001 ABSSI = ABS(STPTU) + 0.000001 XRMOD = EXP(LOG(ABSCO) *ALP) + EXP(LOG(ABSSI) *ALP) ~1 ~652~
YRMOD = 1.0 / RMOD
R = R * YRMOD
CONVERT FROM POLAR TO CARTESIAN COORDINATES
SCALE X TO CONVERT SQUARE TO RECTANGLE
XSCLF = (SCF - 1) * RORMX * RORMX + 1 U = R * CTPTU * XSCLF
V = R * STPTU
The description of the pler~lled embodiment, so far, pertains to a source which generates a set of three orthogonal dipole magnetic fields on a flat plate of electrically conrlllcting material. A dihedral source 52, provided according to the invention, allows the invention to be utilized in an environment having orthogonal distortion-causing metal surfaces, such as a metal tabletop adjacent to a metal wall (Fig. 3). Dihedral source 52 includes electrically conductive sheets 54 and 56, which are ml1tll~lly orthogonal and positioned on the X, Y and Y, Z planes. A simple or foliated half-spiral 58 is spaced just above conductive sheet 54 with the center of the spiral at the junction between plates 54 and 56. A simple or foliated half-spiral 60 is located near the electrically conductive sheet 56 with its center adjacent to the center of half-spiMl 58. A current in half-spiral 58 produces an X-dipole m~gn~tic field. A current in half-spiral 60 produces a Z-dipole m~gn~tic field. A discrete coil 62 is placed close to the center of half spirals 58 and 60 with the axis of coil 62 in the Y direction. A current in coil 62 produces a Y-dipole m~gnPtic field. In this manner, dihedral source 52 produces three orthogonal dipole m~gn~ti~ fields in the portion of space bounded by orthogonal conductive sheets 54 and 5 56.
A trihedral source 64 is capable of use in an environment where three distortingmetal sheets are oriented in orthogonal directions (Fig. 4). Such an environment may include a corner of a metal-walled rectangular room. Trihedral source 64 includes electrically conductive sheets 66, 68, and 70, which are mlltll~lly perpendicular and form 30 a trihedral angle. The conductive sheets are placed so that all three sheets intersect at a common vertex 71 of the source forming a corner. A simple or foliated quarter-spiral coil 72 is positioned near conductive sheet 66 with the center of the quarter-spiral placed at vertex 71 of the source. Current in quarter-spiral 72 produces an X-dipole magnetic field. A simple or foliated quarter-spiral 74 is located close to conductive sheet 68 with 35 the center of the quarter spiral placed at vertex 71. Current in quarter spiral 74 produces 21 16~29 a Z-dipole m~gn~tic field. A simple or foliated quarter spiral 76 is located near conductive sheet 70 with the center of the quarter spiral placed at vertex 71. A current in quarter-spiral 76 produces a Y-dipole magnetic field. The three quarter-spirals produce the required three orthogonal dipole m~gn~tic fields.
As illustrated in Figs. 5 and 6, return tracks 78 for each of the quarter rings in quarter spirals 72, 74, and 76 may be provided close to the respective conductive sheet 66, 68, 70 in order to complete the current circuit. A similar configuration for return tracks may be utilized for each of the half-spirals 58, 60 in dihedral source 52.
A source, according to the invention, would preferably operate with a planar coil that is infinitely close to an electrically conrlucting sheet that is a perfect conductor.
While such conditions cannot be met, a plefelled embodiment is provided by forming the conductive sheet or sheets from a supercon(lucting material. In the illustrated embodiment, the signal applied to each of the coils of the source is selected to be in the range of between 8 kHz and 20 kHz, although lower or higher frequencies may be utili7:e~1 In the illustrated embodiment, a 120 Hz update rate is provided. A unique source, according to the invention, has been built and successfully operated in combination with a FASTRAK electronics unit m~nllf~(~.tmed by Applicant's assignee, Polhemus Inc. of Colchester, Vermont. OpeMtion of the unit has been satisfactory in all respects.
Changes and modifications in the specifically described embodiments can be carried out without departing from the principles of the invention, which is intended to be limited only by the scope of the appended claims, as hllel~let~d according to the principles of patent law including the doctrine of equivalents.
HAVING ANTI-DISTORTION SOURCE CONFIGURATION
BACKGROUND OF THE INVENTION
This invention relates to position and orientation measuring systems (POS) which5 determine remote object position and orientation and, more particularly, to anelectrom~gnPtic POS having a source which produces a plurality of electrom~gnPtic fields which are distinguishable from one another, a remote sensor which senses the gel~el~led electrom~gnP-tic fields and a processor which processes the output of the sensor into remote object position and orientation relative to a reference coordinate frame of the 10 source. More particularly, the invention relates to an improved source for an electrom~gnPtic position and orientation measuring system.
Remote object position and orientation measuring systems employing electrom~gnP-tic coupling are disclosed in United States Patent No. 3,868,565 issued to Jack Kuipers for an OBJECT TRACKING AND ORIENTATION DETERMINING
15 MEANS, SYSTEM AND PROCESS and United States Patent No. 4,054~881 issued to Frederick Raab for a REMOTE OBJECT POSITION LOCATOR. Such systems traditionally have a source assembly that includes a plurality, typically three, of concentrically positioned, orthogonal field-generating antennas for generating a plurality of electrom~gnPtil~ fields. Signals are applied to the field-generating antennas that are 20 multiplexed so that the resulting electrom~gnPtic fields are distinguishable from one another. Located at the remote object is a sensor having a plurality, also typically three, of concentrically positioned, orthogonal receiving antennas for receiving the electrom~gnP-tic fields generated by the tr~n.smitting antenna and producing signals corresponding to the received electrom~gnPtic fields. A processor resolves the signals 25 produced by the receiving antennas into remote object position and orientation in the elellce coordinate frame of the source.
One application for such position and orientation measuring system (POS) is as athree-dimensional digitizer for determining and ~ligiti7ing the coordinates of a three-dimensional object. In such a digitizer, the source may be embedded in a table having an 30 integral work surface, or ~ligiti7ing tablet, upon which the object to be (iigiti7e~1 is placed.
A hand-held stylus is used for tracing and determining points of interest on the surface of the object. The remote sensor is disposed in the stylus and the stylus is provided with a projection for defining a point of contact between the stylus and the surface of the object 2 1 7 652~
of interest. Since the point of contact of the stylus and the remote sensor are provided with a known relationship, the coordinates of the surface of the three-dimensional object touched by the stylus may be determined from the position and orientation of the sensor in the coordinate frame of the work surface.
One difficulty with a digitizer utili~ing an electrom~gn~tic POS is that the work surface, or ~ligiti~ing tablet, carmot be located on a table including a substantial amount of electrically conductive or fellu~Agn~tic metal. The electrom~gn~ti~ fields generated by the source of the appaldlus induce eddy ~;ullcllL~ in the metal. The eddy ~;ullellls produce an electrom~gn~tic field which distorts the field generated by the source, inducing error in the measured fields and, hence, the calculated position and orientation of the remote object. Various methods exist to map distortion and to compensate for the distortion in the POS processor. However, if the distortion is too severe, such mapping may not adequately compensate for the distortion.
It may be desirable to be able to place a conventional digitizer source on an electrically conductive or ferrom~gnPtic metal plate. Other applications for which it may be desirable to use an electrom~gn~tic POS may also result in severe magnetic-field distortion with a conventional POS source. For example, it may be desirable to place the digitizer source on a metal table adjacent to a metal wall. It may also be desirable to position a POS source at the corner of a metal-walled rectangular room in order to locate 20 one or more remote objects within the room. In all such applications, the ability to compensate magnetic-field distortions would be nil.
SUMMARY OF THE INVENTION
The present invention provides an electrom~gn~tir position and orientation measuring system having a novel source configuration which produces low distortion 25 m~n~tic fields in one portion of a three-dimensional space nolwill~ ling the presence of electrically conductive or ferrom~gn~tic metal in another portion of the electromagnetic space. This is accomplished by positioning a conductive sheet in order to divide the space into two portions and producing an electrom~gn~tir field on one side of the sheet.
The electromagnetic field that is produced has a dipole moment that is normal, or 30 orthogonal, to the sheet. A constant m~gn~tic dipole moment in a low distortion m~gn~tic field is produced in the space portion on the one side of the sheet.
A source configured according to the invention includes an electrically conductive sheet and a planar coil mounted parallel to and near the sheet. The planar coil includes a 2 i 7652~
plurality of substantially coplanar concentric rings. The coil is configured in a manner that a signal applied to the coil will have a current density at each ring that is inversely proportional to the square of the radius of that ring. Such source configuration produces quasi-static magnetic fields which do not .~ignific~ntly penetrate the electrically conducting 5 sheet. It is believed that this is a result of the normal component of the m~gnPtic field at the surface of the electrically conductive sheet being substantially time-invariant. The electrically con~ cting sheet functions as a mirror for orthogonal antennas of the source which produce dipole moments parallel to the electrically conductive sheet.
The present invention finds applications where it is desired to measure the position 10 and orientation of a remote object in the coordinate reference frame of a three-dimensional space, but wherein the remote object is restricted for movement within a portion of the space. In this manner, the presence of even very large quantities of electrically conductive or ferrom~gn~ti~ metals in other portions of the space, where the remote object is not positioned, will have no substantial effect upon the accurate 15 determination of position and orientation of the remote object.
These and other objects, advantages, and fedLul~s of this invention will become apparent upon review of the following specification in conju,l~ion with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram illustrating a position and orientation measuring system 20 useful with the invention;
Fig. 2 is a perspective view of a source, according to the invention;
Fig. 3 is a perspective view of an alternative embodiment of the invention;
Fig. 4 is a perspective view of another alternative embodiment of the invention;Fig. 5 is an enlargement of the portion illustrated at V in Fig. 4; and Fig. 6 is a sectional view taken along the lines VI-VI in Fig. 5.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now specifically to the drawings, and the illustrated embodiments depicted therein, a position and orientation measuring system (POS) is embodied in a three-dimensional digitizer 12 (Fig. 1). The digitizer includes an electronic comyu~ g unit, or processor, 14, an object table 16, a source 18 of electromagnetic fields, a stylus 20, including a sensor 22 having a plurality of receiving all~el~nas, and a foot switch 24.
The output of processor 14 is typically provided to a host colllyuLel 26 where various software packages can be used to transform the ~ligiti~e~l coordinates of the object traced ~1 7652~
-on object table 16 into useful information, such as layout drawings, perspective views, material lists, or a database for graphic image generation. Typically, the output of host co~ ul~l 26 is inputted to a visual display, such as a monitor 28. Source 18 is composed of three independent loop antennas which each define a m~gn~tic dipole field. The loops 5 of the three ~ntenn~ are oriented such that three orthogonal dipole m~gn~tic fields are created, one of the fields being identified with one of the X, Y, and Z axes of the work surface of object table 16 such that the electromagnetic fields define a refelellce coordinate frame. Processor 14 includes a driver connected to source 18 by linesschematically illustrated at 30 for applying to the three loop antennas electrical signals 10 which genelate the three dipole m~gnrtir fields associated with the X, Y, and Z
directions, respectively. The electrical signals applied to the three loop antennas are multiplexed so that the reslllting dipole m~gnrtic fields are distinguishable from one another. A variety of alternative multiplexing techniques include time division,frequency, and phase-multiplexing. Sensor 22 includes a plurality of receiving antel~llas 15 for receiving components of the electromagnetic fields tr~n~mitted by source 18.
Preferably, the receiving antennas also are composed of three loop antennas. The three loop antennas defining sensor 22 are oriented in mlltll~lly orthogonal directions so that the antennas define a sensor coordinate frame Xl, Yl, Zl. The output of the antenna triad defining sensor 22 is connrcte~l to processor 14 by lines schematically illustrated at 32.
20 Digitizer 12 is disclosed in more detail in commonly ~signr.d United States Patent 4,613,866 issued September 23, 1986, for a THREE-DIMENSIONAL DIC~ K
WITH ELECTROMAGNETIC COUPLING.
Although the POS illustrated in Fig. 1 is embodied in a digitizer 12, many otherapplications are possible. In other applications, the sensor can be associated with a 25 particular body part for the purpose of con~ cting biomedical studies or for manipulating three-dimensional images displayed on a design colll~ulel. In an important military application, the sensor is associated with the helmet-~ighting reticle of the pilot of a military aircraft for d~te"llinil~g the line of sight of the pilot to a target and, thereafter, initi~li7ing ordnance which is directed along the line of sight to the target. In the field of 30 head motion sensing, generally, the system can be employed as an input to a virtual reality system in order to drive a displayed image to coincide with the user's head position. Still another application involves the monitoring of the body movements of an invalid for the purpose of creating a non-verbal communication system or providing a 21 7652~
technique for remote-controlling various devices with non-verbal coll~"~llnic~tive body motion.
Source 18, according to the invention, includes an electrically con-lucting sheet 34 positioned at the Z = 0 plane of the source lerelellce coordinate system (Fig. 2). A
planar coil 36 is positioned close to electrically conducting sheet 34. In the illustrated embodiment, planar coil 36 is mounted to a thin in~ul~ting sheet 38 which separates the coil from the electrically conductive sheet. Planar coil 36 is made up of a plurality of essentially coplanar concentric rings 40 all positioned in a plane parallel to electrically conductive sheet 34. In the illustrative embodiment, concentric rings 40 are made from an electrical conductor 41 formed into a simple spiral. Conductor 41 has a first ~ linal 42 positioned at the outer perimeter of the coil and a second terminal 44 positioned at the center of concentric rings 40. Planar coil 36 is constructed such that, when an electrical signal is applied across terminals 42, 44, the density of the current influced in each ring 40 is inversely proportional to the square of the radius of that ring. Such current density may be accomplished as follows.
Electrically conductive sheet 34, planar coil 36, and insulating sheet 38 may bemade from printed circuit board stock. Current density may be established at thedesirable level by making the width of the copper track inversely proportional to the square of the radius of the center of the track. Planar coil 36 may be etched from one of the conductive sheets on one side of in~ ting sheet 38 by providing only a minim~l-width spiral line of a copper-free insulating surface between the windings. In this manner, the con~lucting copper track is of minim~l width close to the center of the coil and widens progressively oulw~rdly. The result is that the current density may be controlled by the geographic layout of planar coil 36.
In a spiral:
r. THETA = constant (1) where r is the radius of the point on the spiral and THETA is the angle measured from the X axis. In the illustrated embodiment, THETA varies from 40*pi at the outside to 800*pi at the inside, resulting in 380 turns in the spiral. At the outside, the radius is 20 inches and the turns of the insulating spiral are one inch apart center-to-center. At the inside, the radius of the ring is one inch and the turns of the in~ ted spiral are 1/400 inch apart, center-to-center. Because the thickness of the track is equal at all points, the width is proportional to the cross-sectional area. As the track gets wider, the current density gets smaller. The product of current density and track cross-sectioned area is equal to the total current in the track.
In an alternative embodiment, a second spiral (not shown) is formed on printed circuit board 39 on the opposite side of in~ ting sheet 38. If such additional coil is 5 formed, then a separate electrically conductive sheet 34 is lltili~ed The second inslll~ting spiral on the opposite side of printed circuit board 39 spirals in the same direction as planar coil 36. Current flows ouLw~ld on one side and inward on the other side so that the two sides generate m~gnPtic field in the same direction. In this alternativeembodiment, a large number of plated-through holes are placed ul~irollnly around the 10 periphery of printed circuit board 39 in order to preserve a uniform current distribution around the periphery.
Planar coil 36 positioned at Z = 0 produces Z-dipole m~gnPtic fields. A
conventional coil assembly 46 is provided at the center of printed circuit board 39 in order to produce X-dipole and Y-dipole m~gnPtic fields. Coil assembly 46 includes a Y
15 coil 48 for producing Y-dipole magnetic fields and an X coil 50 for producing X-dipole magnetic fields. Although not shown, a discrete Z coil may be included with coilassembly 46 and connPcted in series with planar coil 36 in order to increase the turns-density at the center of the coil.
In the illustrated embodiment, a simple spiral is disclosed. The simple spiral has 20 closely spaced turns near the center, but widely spaced turns near the outer edge. These widely spaced turns may cause localized field distortions close to the plane of the spiral at the edge. Such local distortions may be difficult to map and compensate for. In order to overcome such difficulties, a foliated spiral may be l~tili~P,d A foliated spiral is constructed by a repeated subdividing of the current paths into parallel tracks as the 25 conductor defining the coil spirals outwardly. Starting at the center of the spiral, the track has ~ center-to-center turn spacing. As the conductor spirals oulwardly, the spacing increases. When the spacing reaches twice the mini~ center-to-center spacing, a new spiral is started halfway between the turns of the existing conductor by splitting the conductor into two tracks. At such radius, two spiral tracks are present, 30 each carrying half the current. The spacing between adjacent turns is at the mi~i........
center-to-center spacing. Both tracks spiMl oulwaldly until the spacing reaches twice the .lli~-il..lllll. Each track is then split into two tracks for a total of four tracks. This pattern is repeated oulw~ldly for the entire coil. The foliated spiral reduces local distortions by 2 1 7 652~
limiting m~ximllm turn spacing. In order to cause the current in all of the tracks around the outer edge to be equal, series ballast resistors or active current drivers may be used to adjust the current. If active drivers are used, each driver provides a fraction of the current. This makes individual drivers simple and smaller than a single driver for a 5 simple spiral.
Electrically contlucting plane 34 acts as a mirror for m~gn~tic fields wherein the magnetic field at any point above the plane is the sum of the field generated by the sources in that space and the field generated by eddy ~;ullellls from the con(luçting plane.
By placing the source coils near the con(luctin~ plane, with the conducting plane 10 positioned at Z = 0 cooldhlat~s, the X-dipole moment is parallel to and in front of the plane. The X dipole generates an image-dipole moment parallel to and behind the plane.
The image-dipole moment is the same strength as, and in the same direction as, the X-dipole moment. Therefore, the image-dipole moment and the X-dipole moment becomecollocated creating one dipole moment of twice the strength of the original X-dipole 15 moment. The same applies to the Y-dipole moment. The Y-dipole m~gn~tic field is substantially undistorted and double the strength of the Y-dipole m~gn~.tic field when the source is in free space.
As will be described in more detail below, coil 36 which is positioned at Z = 0 produces a constant magnetic dipole moment which is normal to con-lucting plane 34. In 20 practice, the Z-dipole field is somewhat distorted close to the con(luçting plate, the lines of flux curve inward towards the plate rather than being normal to the plate. However, the gellelaled electrom~gn~tic fields are sufficiently non-distorted farther from the plate in order to produce accurate results.
The invention is based upon the ability to generate a quasi-static dipole m~gn~tic 25 field with the dipole moment normal to a con~luçting plane or plate. By placing an actively forced current sheet, in the form of the concentric rings, close to the con-lucting plane, m~gnPtic fields are produced which do not behave according to normal boundary conditions of a con-lucting plane. By forcing the current density in each ring to be inversely proportional to the square of the radius of the ring, the product of the current 30 density in a ring times the area enclosed by that ring is a constant. The constant is 2m where m is the m~gn~tic dipole moment. As will be set forth in more detail below, the magnetic vector potential, and, hence, the m~gn~tic field, is that of a dipole with 6m~gn~tic moment equal to m, normal to the con-lucting plane. If the m~gn~tic fields are 21 ~ 6529 .
generated by slowly varying ~;ullcn~s, the source is operating near-field and radiation effects can be ignored. Such quasi-static magnetic fields do not penetrate the conductive sheet because the normal component of the magnetic field at the surface of the sheet is substantially time-variant.
The vector potential of a finite-sized circular current loop in free space in the Z =
0 plane, centered on the Z axis, may be represented by:
Ao = 11 I ¦ a cos (~) d~ (2) 2~ ~,=o [a2 +p2 + Z2 -2 a p COS (~$\) ] 1/2 where:
~ , Z) are cylin-lri~l coordinates, ,u = permeability of free space, a = loop radius, and I = current in the loop By symmetry, the vector potential has only a ~ component, Ao~ For an infinite array of 15 coplanar concentric circular rings, the current density in each ring is represented by:
I = m/(2 7r a2) (3) The ~ component of the vector potential is:
Al 4 7~2 ¦~I~=o la_o a [a2 +p2 +Z2 -2 a p COS ((1!,) ] 1/2 da d~ (4) The ~ component is integrated over a, as illustrated in equation 5:
A~ log ~1+ P ~ ~ d~ (5) 4 ~2 ~=o (p2 + Z2) 1/2 ~ (p2 + Z2) 1/2) + ,~ m limit [ log ( 2 (p2 + Z2) 1/2) J~ cos (~, d~]
The second term of equation 5 is zero. Equation 5, therefore, becomes:
( 6 ) 4 ~p (p2 + Z2) 1/2 When an array of current carrying conductors is placed extremely close to a con-lucting 5 plane, the vector potential is the negative of the Z-gradient of the vector potential of the array alone. Thus, the ~ component of the vector potential of the array of coplanar rings placed near to a contlucting sheet is:
d z By combining equations 6 and 7:
A = ,u m p ( 8 ) Equation 8 may be converted to spherical coo~inales where p = r sin(e) and Z = r A llmsin (~) (9) 4 ~ r2 cOS(e):
Equation 9 illustrates the vector potential of an ideal dipole in free space with the dipole 15 m~gnPtic moment m normal to the plane. Therefore, an array of coplanar concentric current rings, with the current density inversely proportional to the square of the ring - 21 7652q Mdius, placed near to a conducting plane, produces a dipole m~gnPtic field with dipole moment normal to the plane.
Although planar coil 36 is illustrated as a circular coil, particular applications may be better suited with a rectangular-shaped coil. This may be accomplished in several 5 ways. A spiral coil may be constructed that is large enough to cover the entire rectangular area with parts of the spiral extending beyond the boundaries of the rectangle.
These extraneous parts may be folded under the rem~ining portions of the spiral so that they lie within the rectangle and at the same time are very close to the conductive plate.
The result is that the current still has a path to flow, but the folded parts of the spiral 10 produce little m~gnPti~ field because they are close to the magnetic plate. This may additionally be accomplished by placing the extraneous parts of the spiral close to but under the plate.
Another technique for producing a rectangular coil is to produce a modified elliptical spiral, which fills most of the rectangle. Any distortion in the field will have 15 smooth gradients. Therefore, compensation algo~ ls will readily correct for any such distortion. This may be accomplished by stretching one axis, such as the X axis, by a scale factor greater than 1. To convert any point (X, Y) on the circular spiral to the corresponding point (U, V) on the "rectangular" spiral, the (X, Y) coordinates are converted to polar coordinates (r, THETA). For each value of r, THETA is calculated as 20 follows:
THETA = ARCTAN(Y/X) (10) By choosing values of THETA that put (r, THETA) in the same quadrant as (X, Y), the program (11), which is in fortran, will calculate the corresponding points (U, V) on the rectangular spiral.
CTPTU = COS(THETA) (11) STPTU = SIN(THETA) MODIFY R TO CONVERT CIRCLE TO SQUARE
USING PIET HEIN'S SUPEREGG EQUATION
RORMX = R / RMAX
ALP = 0.5 + 1.5 * EXP(4.0*LOG(2)*RORMX*RORMX) ABSCO = ABS(CTPTU) + 0.000001 ABSSI = ABS(STPTU) + 0.000001 XRMOD = EXP(LOG(ABSCO) *ALP) + EXP(LOG(ABSSI) *ALP) ~1 ~652~
YRMOD = 1.0 / RMOD
R = R * YRMOD
CONVERT FROM POLAR TO CARTESIAN COORDINATES
SCALE X TO CONVERT SQUARE TO RECTANGLE
XSCLF = (SCF - 1) * RORMX * RORMX + 1 U = R * CTPTU * XSCLF
V = R * STPTU
The description of the pler~lled embodiment, so far, pertains to a source which generates a set of three orthogonal dipole magnetic fields on a flat plate of electrically conrlllcting material. A dihedral source 52, provided according to the invention, allows the invention to be utilized in an environment having orthogonal distortion-causing metal surfaces, such as a metal tabletop adjacent to a metal wall (Fig. 3). Dihedral source 52 includes electrically conductive sheets 54 and 56, which are ml1tll~lly orthogonal and positioned on the X, Y and Y, Z planes. A simple or foliated half-spiral 58 is spaced just above conductive sheet 54 with the center of the spiral at the junction between plates 54 and 56. A simple or foliated half-spiral 60 is located near the electrically conductive sheet 56 with its center adjacent to the center of half-spiMl 58. A current in half-spiral 58 produces an X-dipole m~gn~tic field. A current in half-spiral 60 produces a Z-dipole m~gn~tic field. A discrete coil 62 is placed close to the center of half spirals 58 and 60 with the axis of coil 62 in the Y direction. A current in coil 62 produces a Y-dipole m~gnPtic field. In this manner, dihedral source 52 produces three orthogonal dipole m~gn~ti~ fields in the portion of space bounded by orthogonal conductive sheets 54 and 5 56.
A trihedral source 64 is capable of use in an environment where three distortingmetal sheets are oriented in orthogonal directions (Fig. 4). Such an environment may include a corner of a metal-walled rectangular room. Trihedral source 64 includes electrically conductive sheets 66, 68, and 70, which are mlltll~lly perpendicular and form 30 a trihedral angle. The conductive sheets are placed so that all three sheets intersect at a common vertex 71 of the source forming a corner. A simple or foliated quarter-spiral coil 72 is positioned near conductive sheet 66 with the center of the quarter-spiral placed at vertex 71 of the source. Current in quarter-spiral 72 produces an X-dipole magnetic field. A simple or foliated quarter-spiral 74 is located close to conductive sheet 68 with 35 the center of the quarter spiral placed at vertex 71. Current in quarter spiral 74 produces 21 16~29 a Z-dipole m~gn~tic field. A simple or foliated quarter spiral 76 is located near conductive sheet 70 with the center of the quarter spiral placed at vertex 71. A current in quarter-spiral 76 produces a Y-dipole magnetic field. The three quarter-spirals produce the required three orthogonal dipole m~gn~tic fields.
As illustrated in Figs. 5 and 6, return tracks 78 for each of the quarter rings in quarter spirals 72, 74, and 76 may be provided close to the respective conductive sheet 66, 68, 70 in order to complete the current circuit. A similar configuration for return tracks may be utilized for each of the half-spirals 58, 60 in dihedral source 52.
A source, according to the invention, would preferably operate with a planar coil that is infinitely close to an electrically conrlucting sheet that is a perfect conductor.
While such conditions cannot be met, a plefelled embodiment is provided by forming the conductive sheet or sheets from a supercon(lucting material. In the illustrated embodiment, the signal applied to each of the coils of the source is selected to be in the range of between 8 kHz and 20 kHz, although lower or higher frequencies may be utili7:e~1 In the illustrated embodiment, a 120 Hz update rate is provided. A unique source, according to the invention, has been built and successfully operated in combination with a FASTRAK electronics unit m~nllf~(~.tmed by Applicant's assignee, Polhemus Inc. of Colchester, Vermont. OpeMtion of the unit has been satisfactory in all respects.
Changes and modifications in the specifically described embodiments can be carried out without departing from the principles of the invention, which is intended to be limited only by the scope of the appended claims, as hllel~let~d according to the principles of patent law including the doctrine of equivalents.
Claims (46)
1. A source for a position and orientation measuring system having a driver which applies signals to said source to generate a plurality of electromagnetic fields which are distinguishable from one another, a remote sensor which senses the generated electromagnetic fields and a processor which processes an output of said sensor into remote object position and orientation relative to a reference coordinate frame of said source, comprising:
an electrically conducting sheet; and a planar coil including a plurality of substantially coplanar concentric rings above said sheet.
an electrically conducting sheet; and a planar coil including a plurality of substantially coplanar concentric rings above said sheet.
2. The source in claim 1 wherein said coil is configured in a manner that a signal applied to said coil will produce a current density at each ring inversely proportional to the square of the radius of that ring.
3. The source in claim 1 further including a discrete coil at the center of saidconcentric rings oriented the same as said planar coil and electrically connected serially with said planar coil.
4. The source in claim 1 including at least one discrete coil at the center of said concentric rings and oriented orthogonal to said planar coil.
5. The source in claim 3 including two mutually orthogonal discrete coils at thecenter of said concentric rings and both orthogonal to said planar coil.
6. The source in claim 2 wherein said planar coil includes a conductor formed as a spiral.
7. The source in claim 6 wherein said conductor is formed as a simple spiral.
8. The source in claim 6 wherein said conductor is formed as a foliated spiral.
9. The source in claim 6 wherein said conductor has a cross-sectional area that varies inversely proportional to the square of the radius of the center of the conductor at substantially any place along the conductor.
10. The source in claim 9 wherein said conductor is formed from at least one conductive layer of a printed circuit board.
11. The source in claim 10 wherein said conductor spirals outwardly from the center of said coil on one conductive layer of said printed circuit board, crosses over to another conductive layer of said printed circuit board and spirals inwardly toward said center on said another conductive layer.
12. The source in claim 1 wherein said concentric rings are formed from at least one conductive layer of a printed circuit board.
13. The source in claim 12 wherein said concentric rings are formed as a spiral.
14. The source in claim 13 wherein said concentric rings are formed as a simple spiral.
15. The source in claim 13 wherein said concentric rings are formed as a foliated spiral.
16. The source in claim 1 wherein said electrically conductive sheet is a superconductor .
17. A method of determining the position and orientation of a remote object located on one side of a plane relative to the reference coordinate system of said plane in a manner that is substantially unaffected by eddy current induced field distortion on an opposite side of said plane, including:
positioning a conductive sheet relative to said plane;
producing an electromagnetic field on said one side of said conductive sheet, said electromagnetic field having a dipole moment substantially normal to said conductive sheet;
sensing said electromagnetic field with a remote sensor; and processing the output of said remote sensor into remote position and orientationrelative to said plane.
positioning a conductive sheet relative to said plane;
producing an electromagnetic field on said one side of said conductive sheet, said electromagnetic field having a dipole moment substantially normal to said conductive sheet;
sensing said electromagnetic field with a remote sensor; and processing the output of said remote sensor into remote position and orientationrelative to said plane.
18. The method of claim 17 wherein said producing an electromagnetic field includes providing an array of substantially coplanar concentric rings adjacent said conductive sheet and inducing a current in each of the rings having a current density inversely proportional to the square of the radius of that ring.
19. The method of claim 18 wherein said providing an array of rings includes providing a conductor formed as a spiral.
20. The method of claim 19 wherein said conductor is formed as a simple spiral.
21. The method of claim 19 wherein said conductor is formed as a foliated spiral.
22. The method of claim 17 wherein said positioning a conductive sheet includes providing a sheet of superconductor material.
23. The method of claim 17 wherein said producing an electromagnetic field also includes producing at least one other electromagnetic field that is distinguishable from said electromagnetic field having a dipole moment substantially normal to said conductive sheet, said at least one other electromagnetic field having a dipole moment parallel to said plane.
24. The method of claim 23 wherein said producing at least one other electromagnetic field includes positioning another conductive sheet orthogonal to said plane, producing another electromagnetic field on one side of said another sheet, said another electromagnetic field having a dipole moment normal to said another sheet.
25. The method of claim 23 wherein said producing at least one other electromagnetic field includes positioning at least two mutually orthogonal conductive sheets orthogonal to said plane, producing another electromagnetic field on one side of each of said mutually orthogonal sheets, each said another electromagnetic field having a dipole moment normal to one of said mutually orthogonal sheets.
26. A source for a position and orientation measuring system having a driver which applies signals to said source to generate a plurality of electromagnetic fields which are distinguishable from one another, a remote sensor which senses the generated electromagnetic fields and a processor which processes an output of said sensor into remote object position and orientation relative to a reference coordinate frame of said source, comprising:
at least two mutually orthogonal electrically conducting sheets; and a planar coil above each of said sheets, each said coil including a plurality ofsubstantially coplanar concentric rings.
at least two mutually orthogonal electrically conducting sheets; and a planar coil above each of said sheets, each said coil including a plurality ofsubstantially coplanar concentric rings.
27. The source in claim 26 wherein each said planar coil is configured in a manner that a current applied to that planar coil will have a density at each ring inversely proportional to the square of the radius of that ring.
28. The source in claim 26 including at least one discrete coil at the center of said concentric rings and oriented orthogonal to each said planar coil.
29. The source in claim 27 wherein each said planar coil includes a conductor formed as a spiral.
30. The source in claim 29 wherein said conductor is formed as a simple spiral.
31. The source in claim 29 wherein said conductor is formed as a foliated spiral.
32. The source in claim 29 wherein said conductor has a cross-sectional area that varies inversely proportional to the square of the radius of the center of the conductor at substantially any place along the conductor.
33. The source in claim 32 wherein said conductor is formed from at least one conductive layer of a printed circuit board.
34. The source in claim 26 wherein each said electrically conductive sheet is a superconductor .
35. The source of claim 26 wherein said at least two electrically conductive sheets includes three mutually orthogonal conductive sheets.
36. An apparatus for determining the position and orientation of a remote objectrelative to a reference coordinate frame, comprising:
a source having a plurality of field-generating elements, wherein said field-generating elements generate electromagnetic fields and have spatially independent components defining a source reference coordinate frame, at least one of said field-generating elements having at least one electrically conducting sheet and a planar coil including a plurality of substantially coplanar concentric rings above said at least one conductive sheet configured in a manner that a signal applied to that coil will cause a current density at each ring inversely proportional to the square of the radius of that ring;
a driver which applies signals to said source to generate a plurality of electromagnetic fields which are distinguishable from one another;
a remote sensor having a plurality of field sensing elements, wherein said fieldsensing elements sense each of said generated electromagnetic fields and have spatially independent components; and a processor which processes the output of said sensor into remote object position and orientation relative to said source reference coordinate frame.
a source having a plurality of field-generating elements, wherein said field-generating elements generate electromagnetic fields and have spatially independent components defining a source reference coordinate frame, at least one of said field-generating elements having at least one electrically conducting sheet and a planar coil including a plurality of substantially coplanar concentric rings above said at least one conductive sheet configured in a manner that a signal applied to that coil will cause a current density at each ring inversely proportional to the square of the radius of that ring;
a driver which applies signals to said source to generate a plurality of electromagnetic fields which are distinguishable from one another;
a remote sensor having a plurality of field sensing elements, wherein said fieldsensing elements sense each of said generated electromagnetic fields and have spatially independent components; and a processor which processes the output of said sensor into remote object position and orientation relative to said source reference coordinate frame.
37. The apparatus in claim 36 wherein said at least one of said field-generatingelements further includes a discrete coil at the center of said concentric rings oriented the same as said planar coil and electrically connected serially with said planar coil.
38. The apparatus in claim 36 wherein another of said field-generating elements includes at least one discrete coil at the center of said concentric rings and oriented orthogonal to said planar coil.
39. The apparatus in claim 38 wherein two other of said field-generating elements include two mutually orthogonal discrete coils at the center of said concentric rings and both orthogonal to said planar coil.
40. The apparatus in claim 36 wherein said planar coil includes a conductor formed as a spiral.
41. The apparatus in claim 40 wherein said conductor is formed as a simple spiral.
42. The apparatus in claim 40 wherein said conductor is formed as a foliated spiral.
43. The apparatus in claim 40 wherein said conductor has a cross-sectional area that varies inversely proportional to the square of the radius of the center of the conductor at substantially any place along the conductor.
44. The apparatus in claim 43 wherein said conductor is formed from at least oneconductive layer of a printed circuit board.
45. The apparatus in claim 36 wherein said at least one electrically conductive sheet includes a pair of orthogonal electrically conductive sheets and including a said planar coil above each of said conductive sheets.
46. The apparatus in claim 36 wherein said at least one electrically conducting sheet includes three orthogonal electrically conductive sheets and including a planar coil above each of said conductive sheets.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/464,304 | 1995-06-05 | ||
| US08/464,304 US5640170A (en) | 1995-06-05 | 1995-06-05 | Position and orientation measuring system having anti-distortion source configuration |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2176529A1 true CA2176529A1 (en) | 1996-12-06 |
Family
ID=23843378
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002176529A Abandoned CA2176529A1 (en) | 1995-06-05 | 1996-05-14 | Position and orientation measuring system having anti-distortion source configuration |
Country Status (4)
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|---|---|
| US (1) | US5640170A (en) |
| EP (1) | EP0747662A1 (en) |
| JP (1) | JPH08338703A (en) |
| CA (1) | CA2176529A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2652928B1 (en) | 1989-10-05 | 1994-07-29 | Diadix Sa | INTERACTIVE LOCAL INTERVENTION SYSTEM WITHIN A AREA OF A NON-HOMOGENEOUS STRUCTURE. |
| US5603318A (en) | 1992-04-21 | 1997-02-18 | University Of Utah Research Foundation | Apparatus and method for photogrammetric surgical localization |
| WO1994004938A1 (en) | 1992-08-14 | 1994-03-03 | British Telecommunications Public Limited Company | Position location system |
| US5803089A (en) | 1994-09-15 | 1998-09-08 | Visualization Technology, Inc. | Position tracking and imaging system for use in medical applications |
| US5829444A (en) | 1994-09-15 | 1998-11-03 | Visualization Technology, Inc. | Position tracking and imaging system for use in medical applications |
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-
1996
- 1996-05-14 CA CA002176529A patent/CA2176529A1/en not_active Abandoned
- 1996-06-05 JP JP14300096A patent/JPH08338703A/en active Pending
- 1996-06-05 EP EP96304154A patent/EP0747662A1/en not_active Ceased
Also Published As
| Publication number | Publication date |
|---|---|
| EP0747662A1 (en) | 1996-12-11 |
| JPH08338703A (en) | 1996-12-24 |
| US5640170A (en) | 1997-06-17 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |