CA1276258C - Coordinate detecting method - Google Patents
Coordinate detecting methodInfo
- Publication number
- CA1276258C CA1276258C CA000535271A CA535271A CA1276258C CA 1276258 C CA1276258 C CA 1276258C CA 000535271 A CA000535271 A CA 000535271A CA 535271 A CA535271 A CA 535271A CA 1276258 C CA1276258 C CA 1276258C
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- Prior art keywords
- coordinate
- loop
- loops
- segment
- coarse region
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
- G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
- G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
- G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
- G06F3/046—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means by electromagnetic means
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- General Engineering & Computer Science (AREA)
- Theoretical Computer Science (AREA)
- Electromagnetism (AREA)
- Human Computer Interaction (AREA)
- General Physics & Mathematics (AREA)
- Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
- Position Input By Displaying (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A coordinate detecting method, adapted to a coordinate input device comprising an input plane having a plurality of parallel embedded loops, establishes a plurality of coarse regions while taking as a reference the polarity reversing positions of a magnetic field detected when these loops are scanned in sequence.
The method comprises the steps of specifying one coarse region to be interpolated, interpolating the designation position of a coordinate designating member within the specified coarse region, and calculating the coordinate of the designation position on the basis of the coordi-nate position of the specified coarse region and an interpolation value obtained in the interpolating step.
A coordinate detecting method, adapted to a coordinate input device comprising an input plane having a plurality of parallel embedded loops, establishes a plurality of coarse regions while taking as a reference the polarity reversing positions of a magnetic field detected when these loops are scanned in sequence.
The method comprises the steps of specifying one coarse region to be interpolated, interpolating the designation position of a coordinate designating member within the specified coarse region, and calculating the coordinate of the designation position on the basis of the coordi-nate position of the specified coarse region and an interpolation value obtained in the interpolating step.
Description
~2~6258 COORDINA~E DETECTING METHOD
FIELD OF THE INVENTION
This invention relates to a coordinate detecting method adaptable to a coordinate input device for reading a designated position on an input plane at a high accuracy.
SUMMARY OF THE INVENTION
The present invention has been devised to provide a coordinate detecting method which can detect a coordinate using a comparatively simple algorithm by establishing seg-ments or regions in consideration of the behaviour of shift.
To achieve the above, the present invention provides acoordinate detecting method of detecting a coordinate posi-tion on an input plane, which comprises the steps of:
establishing a plurality of coarse regions while taking as a reference the polarity reversing positions of a magnetic field detected when a scan signal is sent to the input plane equipped with a plurality of main loops made of parallel embedded conductors such that the main loops are driven in sequence by the scan signal, specifying a coarse region to be interpolated, interpolating the designation position of a coordinate designating member within the specified coarse region, and calculating the coordinate of the designation 11695/LCM:jj 1 ^l`~' . I
~.Z7~258 position on the input plane designated by the coordinate designating member on the basis of the coordinate position of the specified coarse region and in interpolation value ob-tained in the interpolating stern.
According to the present process, it is possible to calculate speedily an accurate coordinate position by the use of a comparatively simple algorithm through the steps of establishing segments while taking as a reference the polar-ity reversing positions of a magnetic field detected, enter-ing polarity reversing position data in a ROM table, inter-polating a coordinate designated by a coordinate designating member within a pertinent segment, and adding/subtracting the amount of deviation of the segment to/from an interpolation value obtained in the interpolating step.
In describing the calculation principle, assume that certain loops Ln and Ln,2 are scanned under the condition that the coordinate designating member is standing at a position X. Let a detection voltage owing to loop Ln be Vn and another detection voltage owing to loop Ln,2 be Vn~2. Then, an interpolation value Xp within segment Sn defined by polarity 11695/LCM:jj 2 . ~
~76~;8 reversing positions Xn and Xn~2 is given by n ~1 ) P Vn ~ Vn~2 The X coordinate of the coordinate designating member between loops Ln and Ln,2 is obtained by addition of the amount n f deviation of segment Sn from loop Ln as follows:
X p n (2 In this case, the value of X can easily be obtained if the value of n is previously stored in the ROM table.
BRIEF DE8CRIP~ION OF THE DRAWING8 Figs. 1 through 8 are explanatory of an embodiment of the present invention, in which Fig. 1 is a drawing explanatory of the calculation principle of coordinate detection of the present invention;
Fig. 2 is a drawing illustrative of a segment dis-criminating process;
Fig. 3 is a drawing illustrative of segments and shift directions; and Figs. 4 through 7 are diagrams showing observed errors;
Fig. 8 is a flow chart illustrative of a detection process;
Fig. 9 is a fundamental block diagram of a coordinate input device according to a conventional system which is also applicable to the present embodiment;
11695/LCM:jj 3 ~27~258 Fig~. 10 through 14 are explanatory of conventional systems, in which Fig. 10 is a drawing explanatory of a segment dis-criminating process;
Figq. 11 and 12 are drawings explanatory of the re-lationship between detection voltage and segment; and Figs. 13 and 14 are diagrams showing observed shifts of segments.
One coordinate inputting and detecting technique of reading a designated position on a plane at a high accuracy is configured so as to supply scan signals of the same phase concurrently to at least two conductors out of a plurality of parallel conductors embedded in a tablet, detect a signal generated by the scan signals supplied to the conductors by means of a coordinate designating member, perceive that the polarity of the detected signal has reversed, detect signal levels before and after this reversal of polarity, and calcu late the position the coordinate designating member is desig-nating on the basis of a coarse region on the coordinatewhere the reversal of polarity was perceived and the signal levels detected in the coarse region.
The foregoing coordinate calculating process was proposed supposing that the polarity of a magnetic field 11695/LCM:jj 4 ~"Z7~2~i8 reverses at the middle point between two selected conductors.
Thus, there was a possibility that the reversing position shifts from the middle point owing to the magnetic field generated by a common conductor for supplying a scan current to each conductor, thereby sometimes resulting in the problem of causing a calculation error. Especially, in the case of the configuration wherein the conductors or loops are select-ed and scanned in sequence one at a time, the shift of the reversing position causes a very serious accuracy problem.
This will be described in greater detail hereinafter.
Fig. 11 shows the distribution of detection voltage when the polarity reversing position has no shift. This distribution graph illustrates the interval of lOmm < X < 30mm as an example, wherein the detection voltages owing to the respective loops reversing in polarity at X = 10, 15, 20, 25, and 30mm are designated by Llo, L1s, L20, , and L30, respectively. Although the distribution of magnetic field strength Hz corresponding to each loop, Llo - L30, is positive on the left side in the drawing of the zero point and negative on the right side, the voltage de-tected represents the absolute value of the magnetic field strength Hz. For convenience of explanation, the regions of 11695/LCM:jj 5 :::
~' ~Z76;;~5~3 lOmm _ X < 20mm, 15mm < X < 25mm, 20mm < X < 30mm, are refer-red to as segment 2 (S2), segment 3 ~S3), and segment 4 (S4), respectively.
Consider that a pickup is standing at position T ~X = 21mm) in Fig. 11; hence, Hz < 0 holds up to S4, X = 20mm, whereas H2 > 0 holds at S5, X = 25mm. Thus, a system gets a detection voltage V2 owing to loop L25. Then, the system selects loop L15, i.e., the preceding-but-one loop, S52 = S3, X = 25 - lo = 15mm, and gets a detection voltage V1 owing thereto. Hence, in this exemplary opera-tion, S3 corresponding to the region of 15mm < X _ 25mm is selected as an object segment to be interpolated.
The case wherein the polarity reversing position has shifted will now be described with reference to Fig. 12.
This example is illustrative of the distribution curve of magnetic field strength Hz having shifted in a positive direction of X, wherein the loops and segments are indicated by the same reference symbols as in Fig. 11. It is also assumed that the pickup is standing at position T correspond-ing to X = 21mm.
In the case of Fig. 12, Hz > 0 holds already at S4, 11695/LCM:jj 6 ~2~25a X = 20mm. Thus, the interpolation region is considered ass4-2 = s2, hence, interpolation is going to be performed in the region of lOmm _ X _ 20mm.
Accordingly, it will be appreciated that the inter-polation calculation is performed with respect to that region being different from the region of the inherent segment, thereby resulting in an erroneous operation. In this example of Fig. 12, it is ideal to perform interpolation in S3.
Thus, even if the discrimination of segment were done in error, an improvement of accuracy will be expected if the interpolation segment is set as S4.
To solve the aforementioned problem, the present applicant proposed the process of comparing the absolute values of the detection voltages of a first loop from which the reversal of polarity of the magnetic field has first been detected by the coordinate designating member and a second loop preceding a given number of loops to the first loop in the direction of scanning to thereby determine a coarse region to be interpolated. This second prior proposal ob-tains the comparative ratio between the absolute values ofthe detection voltages of the loops before and after the reversal of polarity has occurred to determine the coarse 11695/LCM:jj 7 - ;
~L2762~8 region which is subjected to interpolation. The principle of the foregoing process will now be described.
Fig. 10 shows the distribution of detection voltage obtained by the pickup, in which each curve is made straight for simplification. In the following description, similarly to the above, each segment is designated by Sn (n: an integer) and the corresponding loop by L5nl the interpolation regions are of lOmm long each, the segments are defined so as to overlap each other by a length of 5mm, and the loops are arranged at 5mm intervals.
In the case of the distribution of detection voltage shown in Fig. 10, detection voltages Vn 2 and Vn owing to loops Ln2 and Ln are used in performing interpolation using segment Sn2. Let the X coordinate of the intersection point c1 of detection voltages Vn2 and Vn1 be A and the X co-ordinate of the intersection point C2 of detection voltagesVn1 and Vn be B. Then, Vn2 has a smaller value than the other in the region of X < A and Vn has in the region of X > B. In view of the performance of a circuit, it is pre-ferred to employ a larger value than that at the intersectionpoint Cl of Vnl and Vn2 and at the intersection point C2 of Vn and Vn1, hence, it is desirable to perform interpolation 11695/LCM:jj 8 `
7G~8 always within the region of A ~ X < B. That is, where the pickup stands on the right side of X = 5(n-l)mm in Fig. 10, the reversal of polarity is detected for the first time when loop Ln is driven. Accordingly, to meet the foregoing re-quirements, segment Sn2 must be selected when the pickup iswithin the region of 5(n-l)mm < x < B, whereas segment Sn 1 be selected when it is within the region of B < X < 5n mm. As the results of such selection, it is always possible to get detection voltages larger than those at the aforementioned points C1 and C2 and define the optimal region as the inter-polation one.
Accordingly, the algorithm of deducing the optimal segment with respect to the range of A < X < B is as below.
Assume that in the course of driving loops Lo~ L1,...
in sequence, the reversal of polarity of the magnetic field strength H~ has been detected for the first time upon coming to loop Ln. Under this condition, 1. Sn z iS selected when ¦Vn/Vn l ¦ 2 1 (Vn2, Vn are used in interpolation) 2. Snl is selected when ¦Vn/Vnl¦ < l (Vnl, Vn~l are used in interpolation) If so selected as above, the detection voltages for use in interpolation are always within the interpolation region and higher than the voltages at the intersection points C1 and 11695/LCM:jj 9 . .
,, . ~, ~.27~ ;8 c2, hence, it is possible to ensure a certain accuracy on interpolation.
An exemplary process of selecting the segments in accordance with the above algorithm is shown in Figs. 13 and 14. Figs. 13 and 14 show the distribution of detection voltage in the vicinity of Y = lOOmm and the interpolation regions corresponding to the respective distribution curves, in which rectangular blocks illustrated below the X axis represent the aforementioned segments S and it is intended to select one segment for interpolation when the pickup stands within the shaded portion thereof. However, the amount of shift of the field polarity reversing position becomes large in a peripheral portion of the input plane and the positions corresponding to A and B of Fig. 10 also shift such that they tend to come close to the segment boundary or come off a little from the segment concerned. In such a case, the aforementioned conditional equations are changed to 1. Snl is selected when ¦Vn/Vnl¦ < 2 2. Sn2 is selected when ¦Vn/Vnll 2 2 By the use of the algorithm above it becomes possible to select a proper segment.
The foregoing second prior proposal selects a proper segment through obtaining the comparative ratio of the vol-11695/LCM:jj 10 ~7~2~;8 tage values. Although it is necessary to change the refer-ence value of the comparative ratio with respect to the peripheral portion of the input plane, this prior proposal makes it possible to use a proper segment in the vicinity of position A or B of Fig. 10 with respect to the peripheral portion of the input plane. However, this process has a fear that a voltage to be used in interpolation will take a small value and that a coordinate output will become unstable when performing the detection of high accuracy, thereby resulting in a bad effect on the accuracy of detection. Further, since the detection is performed after changing the reference value of the comparative ratio depending upon a segment number, there is an anxiety that the algorithm of detection will become too complicated.
In view of the foregoing, the present applicant pro-posed a coordinate detecting method of performing coordinate detection by the use of a comparatively simple algorithm wherein the segments are offset a preset distance in the shift direction of the field polarity reversing position and 2~ an object segment is selected depending only upon the rela-tive magnitude of Vn, Vn1.
11695/LCM:jj 11 :
~.%~625~3 A coordinate input device disclosed in the foregoing third prior proposal will now be described.
Fig. 9 is a fundamental block diagram of the co-ordinate input device. In this drawing, the device comprises an input plane 2b equipped with main loops 2a and a compen-sating loop 3a, a driver 2 for sending a current of certainamplitude from an oscillator 1 to the main loops 2a, another driver 3 for sending a current to the compensating loop 3a, a pickup 6 including a magnetic field detecting coil and func-tioning as the coordinate detecting member, an amplifiercircuit 7 for amplifying the output of the pickup 6, a polar-ity discriminator circuit 8, a detector circuit 9, sample-hold amplifiers 11 and 12, a multiplexer 13, and A/D con-verter 14, a ROM table 15 functioning as a first memory means storing therein compensation values, another ROM table 16 functioning as a second memory means storing therein correc-tion values for correction of errors of interpolation values, and a control circuit 10. In addition, there are provided an X-direction switching circuit 4 in connection with the X-direction group of main loops 2a and a Y-direction switching circuit 5 in connection with the Y-direction group of main loops 2a.
11695/LCM:jj 12 ~Z76258 The main loops 2a are embedded mutually parallelly in the input plane 2b at 5mm intervals; one end of each loop L
being connected to the switching circuit 4 (or, to the switching circuit 5 in the case of the Y-direction group) with the other end connected to a source line 2s, and are dimensioned so as to form an input plane surface measuring, for example, 200mm x 200mm as a whole. The source line 2s is connected to the driver 2. The Y-direction loops are simi-larly arranged and oriented so as to intersect orthogonally the X-direction loops.
The compensating loop 3a is formed by a conductor independent of the main loops 2a, which is disposed in the vicinity of the source line 2s of the main loops 2a so as to surround all the main loops 2a, one end of this compensating loop 3a being connected to the driver 3 for sending thereto a current of certain amplitude in reverse to the current flow-ing through the source line 2s of the main loops 2a with the other end grounded. In the ROM table 15 functioning as the first memory means storing therein compensation values, there are stored compensation values pertinent to respective loops L and Y-direction (or X-direction) regions.
11695/LCM:jj 13 ~, ~2762~;8 In this ROM table 15 are stored compensation values ISC relating to all the segments Sn and to the respective main loops corresponding to the segments Sn under the condi-tion of the detection height Z = 15mm. In operation, a pertinent compensation value ISC is called up by the control circuit 10 in accordance with the detection results of the control circuit 10 and used to calculate an interpolation value by means of an arithmeti~ means included in the control circuit 10.
The ROM table 16 functioning as the second memory means storing therein correction values is used to obtain an accurate coordinate position from the thus calculated inter-polation value through correction of its error. Specifical-ly, in this table are stored correction values corresponding, for example, to each 0.lmm increment of the interpolation value pertinent to the segment detected.
The pickup 6 includes in its tip portion the magnetic field detecting coil, a voltage produced by this magnetic field detecting coil being sent via the amplifier circuit 7 to the detector circuit 9 and the polarity discriminator circuit 8.
11695/LCM:jj 14 ~276258 The operation of the foregoing coordinate input device will now be described.
The process of detecting the position of the pickup 6 is achieved principally through the three steps of detecting a coarse position or a segment of the pickup 6, performing interpolation or detecting a fine position within the thus detected segment, and combining the segment position and the fine position within the segment.
At the time of segment detection, first, the drivers 2 and 3 are operated by the use of a sinusoidal wave generated by the oscillator 1. As a result, a current is caused by the driver 2 to flow through the loops L in sequence, one speci-fied via the switching circuits 4 and 5 by the control cir-cuit 10 at a time. During the above, a current having an amplitude equal to one-half that of the current flowing through the main loop 2a is caused by the driver 3 to flow through the compensating loop 3a.
As the individual loops L are scanned by the current, the magnetic field generated by the effective loop L is sensed by the pickup 6 and amplified by the amplifier circuit 7 into a signal of desired amplitude. This signal is com-pared in terms of phase with the output of the oscillator 1 11695/LCM:jj 15 ~276~58 by the polarity discriminator (phase comparator) circuit 8.
In other words, the polarity of the magnetic field is detect-ed at this time. Assume that the output of the polarity discriminator circuit 8 was "H" when the loop L on the left-hand side in the drawing of the pickup 6 was driven. Hence, the polarity of the magnetic field detected reverses when the loop L on the right-hand side of the pickup 6 is driven, as a result, the output of the polarity discriminator circuit also reverses and becomes "L".
Therefore, as the loops L are selected and supplied in sequence with the current in the order of X0, X1, X2,... Xn, loop Ln is detected in the vicinity of the pickup 6 by which the output of the polarity discriminator circuit 8 was re-versed. After the perception of this loop Lnl the system detects a voltage Vn owing to this loop Ln and another vol-tage Vn1 owing to the preceding loop Ln1, compares the two voltages Vn and Vn1, and determines in accordance with a given algorithm a region (segment) to be interpolated.
If an object segment (Sn2, for example, in Fig. 10) is determined, the control circuit first selects loop Ln2 located at the left-hand end of that segment Sn2. Then, the signal passed through the pickup 6 and the amplifier circuit 11695/LCM:jj 16 ~.27~258 7 is converted by means of the detector circuit 9 into a dc signal and held in the sample-hold circuit 11 in the form of a dc voltage.
Thereafter, the control circuit lo selects loop Ln located at the right-hand end of segment Sn2, and similarly to the above, another dc voltage obtained by the detector circuit 9 is held in the sample-hold circuit 12. Then, the voltages held in the sample-hold circuits 11 and 12 are selected by the multiplexer 13 in accordance with the signal from the control circuit 10 and converted by the A/D con-verter 14 into a digital form to get the voltages Vnz and Vn owing to loops Ln2 and Ln.
Then, the control circuit 10 turns off all the switch-ing circuits 4 and 5. As a result, the aforementioned pre-determined current flows only through the compensating loop 3a. By A/D-converting a detected output it is possible to obtain a voltage Vc pertinent to the compensating loop 3a through the same process as above.
Subsequently, the control circuit 10 calls up from the ROM table 15 a compensation value ISC corresponding to the value (the distance) ~f the segment obtained through segment discrimination in the X-/Y-direction, and causes the arith-11695/LCM:jj 17 ~Z76Z5~3 metic means included in the control circuit 10 to calculate an interpolation value P' by substituting the detected vol-tages vn2, Vn and Vc and the ISC in the following equation (4) involving the compensation value:
Vn 2 -- ISC - Vc pl = (4) Vn-2 + Vn If this interpolation value P' is calculated, the ROM
table 16, in which correction values P for correction of the aforementioned errors are stored, is accessed to obtain a coordinate value which specifies a position within the seg-ment. Then, the positional coordinate (sn x 5.0 + ~) of the segment and the coordinate value P within that segment are combined by the arithmetic means included in the control circuit to calculate the ultimate X coordinate of the desig-nation position of the pickup 6 in accordance with following equation:
X = ~8n x 5.0 + ~) ~ P (mm) where 8n: the segment number P: the correction value obtained by amending the interpolation value ~: the amount of shift of segment S (for example, ~ = -2.5, 0, +2.5, which is preset in accordance with the presence/absence and the direction of the offset of the segment and is adequately selected by a software).
11695/LCM:jj 18 ~,~7~a A similar group of segments is defined with respect to the Y direction, thus, the system can calculate the Y co-ordinate of the designation position through a similar detec-tion operation and deliver the calculated coordinate value via an interface circuit 17 to the side of a host computer.
As described hereinabove, because coordinate detection errors arise due to the shift of the polarity reversing position of the magnetic field, the aforementioned prior proposals intended to reduce errors as far as possible by introducing the compensation value or correction value to interpolate a correct coordinate position between segments, or by selecting a segment providing less errors.
These prior ideas originated from the configuration wherein the segments are defined on the basis of a given spacing between loops. Therefore, because the arrangement of segments was determined from the view-point of hardware without consideration of the amount of shift, the algorithm of calculation became complicated.
11695/LCM:jj 19 ~27~
D~SCRIPTIO~ OF THE PREF~RRED ~ilBODIMEN~
~ n embodiment o~ tre precent inve~tion will now be described with reference to the drawings.
Figs. 2 tnrough 8 are ex~lanatory of the embodiment of the ~resent invention. The cor.fi~uration and circuit of a coordinate input device adapted for the embodiment are substantially identical with those of the conve~tional device, except for the ~OM table 18 storing therein the amount of deviation of segment S; hence, no further descri~tion is given here with respect to the identical portion. Further, an identicæl or similar elemsr.t to th2t of the cor.ventional device is designated by the same reference srmbol as in the conventional device.
Fig. 2 illustrates loops L and voltage distribution c-~rves owing to the magnetic field produc_d when these loops L are scanned. In this drawing, the distance, 5n, in the X direction of loo~s Ln ( n = O - 39 ) disposed at a pitch of 5mm as in the cPse of the conventional device is shown on the horizontal axis and the absolute value of detection voltage on the vertical axis.
Although the conventional sytem defines segment Sn on the basis of the position of loop ~n~ the present invention defines segment Sn on the basis of the polarity reversing position detected of a magnetic field. That is, the start ~ ~7~258 ~oint of the n-th se~ent Sn is def~ned by a spot at which a det~ction voltage Vn becomes zero when the n-tn loo~ Ln is 9canned? whereas the end point is defined by another spot at which 2 detection voltage Vn+2 becomes zero when loop ~n+2 subseauent but one to Ln is ~car~ed.
Accordingly, although adjoinin~ seg~ents S overla~
~artiall~ each other, the field reversing position, i.e.
the spot at which the detection voltage Vn ( n = O - 39 ) becomes zero, is alwa~s taken as the start point or end ~oint even if the amount of shift increases, thus, the ob'ect segment Sn to be interpolated can be selected b~
the use only of the aforementioned conditional equation A (3).
DeQcribing e~em~larily, assume that the pickup 6 is standing at position T in Fig. 2. Her.ce, the field polarity changes for the first time when the (n+2)th loo~ Ln+2 i8 ~canned. Letting a detection voltage owing to loop Ln+2 which is detected by the pichu~ 6 be Vn+2 and another detection voltage owing to loop Ln+l be Vn+l, the two voltages Vn+2 and Vn+l are compared and the conditional eauation ~) is referred to. As a result, the following is given:
¦Vn+2/~ln+l¦ 1 Thus, segment Sn which i9 effective wnen the n-th loop Ln ~ 2 ~
is scanned is judged as the object se~ent S to be inter-nolated. T~ereIore, it is possibl~ to obtain an inter-~olation value Xp from the enuation (~) using detection volt~ge values Vn+2 and Vn.
Error or discrepancy between interpolation value and ideal value is snown in ~ig. 4. S~ecifically, the graph of ~ig. 4 shows errors pertinent to loop ~ of X = 20~m, i.e. segment S5 with the start point X = 22.36mm; loop ~19 of X ~ 95~m, i.e. segment Slg with the start point X _ 95.07~; and loo~ L34 of X = 170~m, i.e. segment S34 with the start point X = 15~.21mm, or errors within the positi~nal range of lO~m measured from eæch start point.
According to Fig. 4, it will be appreciated that in tne area ( X <190mm ) on t'.1e left-hand side of tne center C of the input plane 2b, t'ne error does not exceed substantially 0.5~ even when the aforementioned equation (3) is used as it is, whereas in t'ne area ( X >lOOm~ ) on the right-hand side it increases in excess of the former when the equation (~t) is used.
~ hus, because of the symmetry in arrangement of t'ne loo~s L of the input plane 2a, if the eauation:
X = Vn+2 (5) P Vn + Vn+2 76~5S
is used with respect to the area ( X ~lOOmm ) on the right-hand side o~ the center of ths inpu~ plane 2b and the magnetic field reversing ~osition observed when loo~
Ln+2, which is clos-r to the end point oî seg~ent Sn, is scanned is taken as a reference, the error pertinent to the rignt-side area is ex~ected to be com~atible in magnitude with that OI the left-side area OI the center a calculated b~ tne eauation (~). Thè foregoing process is shown in Fig. 3. That is, while taking the position o~
the center C ( X = lOOmm ) o~ the input ~lane 2b as a reference, the lnter~olation value is calculated in the increasing direction of X with respect to the left-side area ( X~ lO0 mm ), and in the decreasing direction of X
with respect to the right-side area ( X>lOOmm ).
Discrepancy between interpolation value calculated in the manner above and ideal value is shown in Figs. 5 through 7. Specific~lly, Fig. 5 shows errors in the interval of 20mm' X ~ 30mm, Fig. 6 shows errors in the interval of 95mm ~X~ 105mm, and Fig. 7 shows errors in the i~terval of 170mm ~ XC 180mm ( which is s~mmetrical to Fig. 5 about X = lOOmm ) at five points Y = 20, 60, 100, 140, and 180mm, wherein the start poi~t or origin of each graph corresponds to the position ( 5n mm ) of respective loop ~n to be driven shown in Fig. 3.
~27~i2S8 As ~ill be a~arent from these gra~ns, the error inc~easeC ab~lptly after passed over the field polarit~J
reversing positi~n, bu., it falls within the range of + 0.5 in the whole surface of the in~ut plane 2b, exce~t for the above.
~ o calc~late an actual coordinate using the inter-polatlon value X~ detected in the manner above, it i~
necssarJ to store the field ~olarit~ rsversing nosition in the RO~ table 18. In this connection, if the absolute ~osition of the ~olarity reversing position is to be ~OM-tablized as it is, its data volume i9 too large for one byte to accommodate. ~e~ce, in the embodiment, the amount n ( n - O - 39 ) of deviation from the position of loo~
~ is stored in the ~OM table. Accordingly, the ROM table 15 of Fig. 9 becomes unnecessæry. In practice, the amount n-l~ n~ n+l of devi2tion from the ~osition of loop Ln l~ Ln~ Ln+l corresponding to 5(n-l), 5n, 5(n+1)mm shown in Fig. 2 is ROM-tablized and stored in the ~OM
table 18. Subse~uently, letting the segment number be n, the amount of deviation be n mm ( n = O - 40 ), and the interpolation value be Xp, the X coordinate pertinent to the left-side portion of the center C of the in-out plane 2b is calculated in accordance with the following equation:
~27~2~8 X = 5.0 n + n + lO Xp (~) (6) where ~ = V~/( V~ + V~+2 ), ~d the sæme pertine~t t~ the right-side portion of the center C i9 calculated in accordance with the following equation:
X = 5.3 ( n + 2 ) ~ n ~ l~ Xp (mm) wnere X~ = Vn+2/( Vn + Vn+2 )-The Y coordinate can be calculated in accordancewith a similar process to the case of the X coordinate, whereby it is possible to detect both the X- and Y-direction coordinates of the pic~up 6 on the input plane 2b. Incidentally, because both the foregoing eauations (6) and (7) are em~loyed, the symmetr~y in both the X and Y directions with respect to the center C should be taken into consideration deeply.
Further, there is another calculation ~rocess wherein in connection with the resolution of i~terpolation, lO~m, for e~am~le, is divided by 256 and the length o~ one fraction, 0.04mm, is treated as a unit. In this case, the data of deviation amount n will also be handled ta~ing the resolution of interpolation as a unit, and the interpolation ~alue Xp obtained through inter~olation calculation and the deviation amount n will be represent-ed each by an integer from 0 to 255. If so digitized, ~76~
the X coordinate value pertinent to the left-side ~ortion o~ the ce~t~r C of the input plane 2b can be calculated in accordance wlth the following ecuation:
X = 50 n + ( Xp + 0~ (10 lmm) (8) p n/( ~n + Vn+2 ) and n = the se~ment number ( O' n' 20 ), and the same pertinent to t~ne right-side ~ortion of the center C of the input plane 2b can be calculated in accordance with the following eauation:
X - 50 ( n + 2 ) - ( X~ ~ n ) 100 (lO~lm~) (9) p n+2/( ~n + Vn+2 ) and n ~ the se~me~t number ( 21~-nC 39 ).
~ ig. 8 shows a coordinate detection process or flowchart of performing calculation in such a ma~ner as above. The operation of a coordinate i~put device embodying the present invention will now be described with reference to the flowchart, but, the d_scription of the steps up to the detection of polarity reversal is omitted because these steps are identical with those of the conventional process.
Upon scanning the loops L, loop Ln is detected which is located in the vicinity of the piclnup 6 and by which the output of the polarity discriminator circuit 8 is reversed. The voltage ~n owing to t'nis loop Ln is compared with the voltag~ ~n 1 owing to tne ~receding loo~ 1n 1' g~ , Sn_2 or S~_l, to be inte~olated is deter~ined in accordance with the ~a~ m i~rr2~resented by the aforementioned eauation (~). .4fter the determination of the seg~ent S ( for e~ample, Sn of ~ig. 2 ), the control circuit 10 selects loop Ln ( the loop at ~ = 5n ) corres~onding to the start po1.nt of that seg~ent. At this time, tne signal passed through the ~ic~up 6 and the amplifier circuit 7 is converted into a dc signal bl~ the dqtector circuit 9 and held in the sample-hold amnlifier 11 in the L or~ of a dc voltage.
Then, the control circuit 10 selec's loon ~n+2 ( the loo~ at ~ = 5(n+2) ) corres~onding to the end point of ~egment Sn, and a similarl~ obtained dc voltage is held in the sample-hold amnlifier 12. ~he voltages held in these samnle-hold amnlifiers 11 and 12 are converted by the multilexer 13 and the A/D converter 14 into digital values, as a result, the voltages Vn and Vn+2 pertinent to loops Ln and Ln+2, respectivel~, are obtained.
~ hen, the interpolation value Xp is calculated by an arithmetic circuit included in the control circuit 10 A in accordance with the aforementioned eauation (~) o~ (5).
After the calculation of the internolation value Xp, the pertinent deviation amount n is taken o~t from the ROM
6%~8 table 18 having the deviation amounts n of the se~me~ts S stored therein corres~onding to the se~ent nwmbers, and the ultimate X coordinate value is obtained using the afore~entioned eauation (8) or (9). ';Vith re~pect to t~e ~r direction, a si~ilar process is perfor~ed to obtain an object Y coordinate. These ~ coordinate and Y coordinate are conbined together, whereby the detection of the position on the ln~ut plane 2b of the picXup 6 is complsted.
As will be apprsciated, the embodiment provides the following effects:
~ Since there is no need of introducing the compensa-tion value in the inter~olation calculation, the calculation is simplified and the com~uting s~eed is enhanced;
~ Since there is no need of detecting the detection voltage Vc owing only to the compensating loop 3a at the tine of the interpolation calculation, a switching means for connecting and disconnecting ths comnensating loop 3a is unnecessar~, thus, the cost is reduced and the computing speed is enhanced because no switching ste~ is required;
~ Since the data of deviation amount n of the field polarit~ reversing ~osition are directl~ related to the ~27~a coo~dinate value, the data can be corrected easily in experiment;
~ No special consideration is necess~r!r to be ~aid for the shift of segment which invclves the deviation æmo~nt of the ~ola-ity reversing ~osition in the ~eri~heral portion of the inptlt ~lane 2b and for the segment discri-~ Iqor~~th~mination &~ori~ relative to the ~eri~hera.l portion, and one ~ind is enough for the segment discrimination ~I'IDr ;1-h~
~lgo~ism, thus, the system becomes simple; and ~ Sincs the ~te~s u~ to the interpolation calculation can be perform3d ~eparætely betl~een the ~ direction and the Y direction, and the system can be designed so as to access the ROM table 18 for the first.time at the step of combining the coordinate values, the com~uting ~rocess becomes simple and the computing s~eed can be enhanced.
As described hereinabove, the present invention detects the designation ~osition on tne input plane of the coordinate designating member by the ste~s of:
establishing the coarse regions on the input plane where the coordinate designating member stands while taking as a reference the polarity reversing ~osition of the magnetic field detected when the scan signal is sent to the conductors embedded in the input plane in seaue~ce, performing interpolation witnin the coarse region, and ~,Z76Z~8 com~osing the design~tion posi~ion of t'ne coordinate designating member on the basis OI tne coordinate ~o~ition of the coarse region and the interpolation value obtained in t'ne interpolation ste~.
Therefore, according to the present invention, the coarse region to be inter~olated can be spQcifiQd ~y the Qlq~r;t~
use of one l~ind of se~ment discrimination ~ , hence, ~ Iqor~thrr~
a program for the~al~o~m becomes sim~le. The inter-polation value can be calculated onll~ from the detection voltages used in se~ment discrimination, hence, for calculation of the ir.ter~olation value there is no need of introduction of the com~ensation value and the like and detection of the voltage from the com?ensating loo~.
Consequentl~y, the com~uting speed can be enhanced and t'ne ~erformznce of this kind of coordinate in~ut device can be im~roved.
FIELD OF THE INVENTION
This invention relates to a coordinate detecting method adaptable to a coordinate input device for reading a designated position on an input plane at a high accuracy.
SUMMARY OF THE INVENTION
The present invention has been devised to provide a coordinate detecting method which can detect a coordinate using a comparatively simple algorithm by establishing seg-ments or regions in consideration of the behaviour of shift.
To achieve the above, the present invention provides acoordinate detecting method of detecting a coordinate posi-tion on an input plane, which comprises the steps of:
establishing a plurality of coarse regions while taking as a reference the polarity reversing positions of a magnetic field detected when a scan signal is sent to the input plane equipped with a plurality of main loops made of parallel embedded conductors such that the main loops are driven in sequence by the scan signal, specifying a coarse region to be interpolated, interpolating the designation position of a coordinate designating member within the specified coarse region, and calculating the coordinate of the designation 11695/LCM:jj 1 ^l`~' . I
~.Z7~258 position on the input plane designated by the coordinate designating member on the basis of the coordinate position of the specified coarse region and in interpolation value ob-tained in the interpolating stern.
According to the present process, it is possible to calculate speedily an accurate coordinate position by the use of a comparatively simple algorithm through the steps of establishing segments while taking as a reference the polar-ity reversing positions of a magnetic field detected, enter-ing polarity reversing position data in a ROM table, inter-polating a coordinate designated by a coordinate designating member within a pertinent segment, and adding/subtracting the amount of deviation of the segment to/from an interpolation value obtained in the interpolating step.
In describing the calculation principle, assume that certain loops Ln and Ln,2 are scanned under the condition that the coordinate designating member is standing at a position X. Let a detection voltage owing to loop Ln be Vn and another detection voltage owing to loop Ln,2 be Vn~2. Then, an interpolation value Xp within segment Sn defined by polarity 11695/LCM:jj 2 . ~
~76~;8 reversing positions Xn and Xn~2 is given by n ~1 ) P Vn ~ Vn~2 The X coordinate of the coordinate designating member between loops Ln and Ln,2 is obtained by addition of the amount n f deviation of segment Sn from loop Ln as follows:
X p n (2 In this case, the value of X can easily be obtained if the value of n is previously stored in the ROM table.
BRIEF DE8CRIP~ION OF THE DRAWING8 Figs. 1 through 8 are explanatory of an embodiment of the present invention, in which Fig. 1 is a drawing explanatory of the calculation principle of coordinate detection of the present invention;
Fig. 2 is a drawing illustrative of a segment dis-criminating process;
Fig. 3 is a drawing illustrative of segments and shift directions; and Figs. 4 through 7 are diagrams showing observed errors;
Fig. 8 is a flow chart illustrative of a detection process;
Fig. 9 is a fundamental block diagram of a coordinate input device according to a conventional system which is also applicable to the present embodiment;
11695/LCM:jj 3 ~27~258 Fig~. 10 through 14 are explanatory of conventional systems, in which Fig. 10 is a drawing explanatory of a segment dis-criminating process;
Figq. 11 and 12 are drawings explanatory of the re-lationship between detection voltage and segment; and Figs. 13 and 14 are diagrams showing observed shifts of segments.
One coordinate inputting and detecting technique of reading a designated position on a plane at a high accuracy is configured so as to supply scan signals of the same phase concurrently to at least two conductors out of a plurality of parallel conductors embedded in a tablet, detect a signal generated by the scan signals supplied to the conductors by means of a coordinate designating member, perceive that the polarity of the detected signal has reversed, detect signal levels before and after this reversal of polarity, and calcu late the position the coordinate designating member is desig-nating on the basis of a coarse region on the coordinatewhere the reversal of polarity was perceived and the signal levels detected in the coarse region.
The foregoing coordinate calculating process was proposed supposing that the polarity of a magnetic field 11695/LCM:jj 4 ~"Z7~2~i8 reverses at the middle point between two selected conductors.
Thus, there was a possibility that the reversing position shifts from the middle point owing to the magnetic field generated by a common conductor for supplying a scan current to each conductor, thereby sometimes resulting in the problem of causing a calculation error. Especially, in the case of the configuration wherein the conductors or loops are select-ed and scanned in sequence one at a time, the shift of the reversing position causes a very serious accuracy problem.
This will be described in greater detail hereinafter.
Fig. 11 shows the distribution of detection voltage when the polarity reversing position has no shift. This distribution graph illustrates the interval of lOmm < X < 30mm as an example, wherein the detection voltages owing to the respective loops reversing in polarity at X = 10, 15, 20, 25, and 30mm are designated by Llo, L1s, L20, , and L30, respectively. Although the distribution of magnetic field strength Hz corresponding to each loop, Llo - L30, is positive on the left side in the drawing of the zero point and negative on the right side, the voltage de-tected represents the absolute value of the magnetic field strength Hz. For convenience of explanation, the regions of 11695/LCM:jj 5 :::
~' ~Z76;;~5~3 lOmm _ X < 20mm, 15mm < X < 25mm, 20mm < X < 30mm, are refer-red to as segment 2 (S2), segment 3 ~S3), and segment 4 (S4), respectively.
Consider that a pickup is standing at position T ~X = 21mm) in Fig. 11; hence, Hz < 0 holds up to S4, X = 20mm, whereas H2 > 0 holds at S5, X = 25mm. Thus, a system gets a detection voltage V2 owing to loop L25. Then, the system selects loop L15, i.e., the preceding-but-one loop, S52 = S3, X = 25 - lo = 15mm, and gets a detection voltage V1 owing thereto. Hence, in this exemplary opera-tion, S3 corresponding to the region of 15mm < X _ 25mm is selected as an object segment to be interpolated.
The case wherein the polarity reversing position has shifted will now be described with reference to Fig. 12.
This example is illustrative of the distribution curve of magnetic field strength Hz having shifted in a positive direction of X, wherein the loops and segments are indicated by the same reference symbols as in Fig. 11. It is also assumed that the pickup is standing at position T correspond-ing to X = 21mm.
In the case of Fig. 12, Hz > 0 holds already at S4, 11695/LCM:jj 6 ~2~25a X = 20mm. Thus, the interpolation region is considered ass4-2 = s2, hence, interpolation is going to be performed in the region of lOmm _ X _ 20mm.
Accordingly, it will be appreciated that the inter-polation calculation is performed with respect to that region being different from the region of the inherent segment, thereby resulting in an erroneous operation. In this example of Fig. 12, it is ideal to perform interpolation in S3.
Thus, even if the discrimination of segment were done in error, an improvement of accuracy will be expected if the interpolation segment is set as S4.
To solve the aforementioned problem, the present applicant proposed the process of comparing the absolute values of the detection voltages of a first loop from which the reversal of polarity of the magnetic field has first been detected by the coordinate designating member and a second loop preceding a given number of loops to the first loop in the direction of scanning to thereby determine a coarse region to be interpolated. This second prior proposal ob-tains the comparative ratio between the absolute values ofthe detection voltages of the loops before and after the reversal of polarity has occurred to determine the coarse 11695/LCM:jj 7 - ;
~L2762~8 region which is subjected to interpolation. The principle of the foregoing process will now be described.
Fig. 10 shows the distribution of detection voltage obtained by the pickup, in which each curve is made straight for simplification. In the following description, similarly to the above, each segment is designated by Sn (n: an integer) and the corresponding loop by L5nl the interpolation regions are of lOmm long each, the segments are defined so as to overlap each other by a length of 5mm, and the loops are arranged at 5mm intervals.
In the case of the distribution of detection voltage shown in Fig. 10, detection voltages Vn 2 and Vn owing to loops Ln2 and Ln are used in performing interpolation using segment Sn2. Let the X coordinate of the intersection point c1 of detection voltages Vn2 and Vn1 be A and the X co-ordinate of the intersection point C2 of detection voltagesVn1 and Vn be B. Then, Vn2 has a smaller value than the other in the region of X < A and Vn has in the region of X > B. In view of the performance of a circuit, it is pre-ferred to employ a larger value than that at the intersectionpoint Cl of Vnl and Vn2 and at the intersection point C2 of Vn and Vn1, hence, it is desirable to perform interpolation 11695/LCM:jj 8 `
7G~8 always within the region of A ~ X < B. That is, where the pickup stands on the right side of X = 5(n-l)mm in Fig. 10, the reversal of polarity is detected for the first time when loop Ln is driven. Accordingly, to meet the foregoing re-quirements, segment Sn2 must be selected when the pickup iswithin the region of 5(n-l)mm < x < B, whereas segment Sn 1 be selected when it is within the region of B < X < 5n mm. As the results of such selection, it is always possible to get detection voltages larger than those at the aforementioned points C1 and C2 and define the optimal region as the inter-polation one.
Accordingly, the algorithm of deducing the optimal segment with respect to the range of A < X < B is as below.
Assume that in the course of driving loops Lo~ L1,...
in sequence, the reversal of polarity of the magnetic field strength H~ has been detected for the first time upon coming to loop Ln. Under this condition, 1. Sn z iS selected when ¦Vn/Vn l ¦ 2 1 (Vn2, Vn are used in interpolation) 2. Snl is selected when ¦Vn/Vnl¦ < l (Vnl, Vn~l are used in interpolation) If so selected as above, the detection voltages for use in interpolation are always within the interpolation region and higher than the voltages at the intersection points C1 and 11695/LCM:jj 9 . .
,, . ~, ~.27~ ;8 c2, hence, it is possible to ensure a certain accuracy on interpolation.
An exemplary process of selecting the segments in accordance with the above algorithm is shown in Figs. 13 and 14. Figs. 13 and 14 show the distribution of detection voltage in the vicinity of Y = lOOmm and the interpolation regions corresponding to the respective distribution curves, in which rectangular blocks illustrated below the X axis represent the aforementioned segments S and it is intended to select one segment for interpolation when the pickup stands within the shaded portion thereof. However, the amount of shift of the field polarity reversing position becomes large in a peripheral portion of the input plane and the positions corresponding to A and B of Fig. 10 also shift such that they tend to come close to the segment boundary or come off a little from the segment concerned. In such a case, the aforementioned conditional equations are changed to 1. Snl is selected when ¦Vn/Vnl¦ < 2 2. Sn2 is selected when ¦Vn/Vnll 2 2 By the use of the algorithm above it becomes possible to select a proper segment.
The foregoing second prior proposal selects a proper segment through obtaining the comparative ratio of the vol-11695/LCM:jj 10 ~7~2~;8 tage values. Although it is necessary to change the refer-ence value of the comparative ratio with respect to the peripheral portion of the input plane, this prior proposal makes it possible to use a proper segment in the vicinity of position A or B of Fig. 10 with respect to the peripheral portion of the input plane. However, this process has a fear that a voltage to be used in interpolation will take a small value and that a coordinate output will become unstable when performing the detection of high accuracy, thereby resulting in a bad effect on the accuracy of detection. Further, since the detection is performed after changing the reference value of the comparative ratio depending upon a segment number, there is an anxiety that the algorithm of detection will become too complicated.
In view of the foregoing, the present applicant pro-posed a coordinate detecting method of performing coordinate detection by the use of a comparatively simple algorithm wherein the segments are offset a preset distance in the shift direction of the field polarity reversing position and 2~ an object segment is selected depending only upon the rela-tive magnitude of Vn, Vn1.
11695/LCM:jj 11 :
~.%~625~3 A coordinate input device disclosed in the foregoing third prior proposal will now be described.
Fig. 9 is a fundamental block diagram of the co-ordinate input device. In this drawing, the device comprises an input plane 2b equipped with main loops 2a and a compen-sating loop 3a, a driver 2 for sending a current of certainamplitude from an oscillator 1 to the main loops 2a, another driver 3 for sending a current to the compensating loop 3a, a pickup 6 including a magnetic field detecting coil and func-tioning as the coordinate detecting member, an amplifiercircuit 7 for amplifying the output of the pickup 6, a polar-ity discriminator circuit 8, a detector circuit 9, sample-hold amplifiers 11 and 12, a multiplexer 13, and A/D con-verter 14, a ROM table 15 functioning as a first memory means storing therein compensation values, another ROM table 16 functioning as a second memory means storing therein correc-tion values for correction of errors of interpolation values, and a control circuit 10. In addition, there are provided an X-direction switching circuit 4 in connection with the X-direction group of main loops 2a and a Y-direction switching circuit 5 in connection with the Y-direction group of main loops 2a.
11695/LCM:jj 12 ~Z76258 The main loops 2a are embedded mutually parallelly in the input plane 2b at 5mm intervals; one end of each loop L
being connected to the switching circuit 4 (or, to the switching circuit 5 in the case of the Y-direction group) with the other end connected to a source line 2s, and are dimensioned so as to form an input plane surface measuring, for example, 200mm x 200mm as a whole. The source line 2s is connected to the driver 2. The Y-direction loops are simi-larly arranged and oriented so as to intersect orthogonally the X-direction loops.
The compensating loop 3a is formed by a conductor independent of the main loops 2a, which is disposed in the vicinity of the source line 2s of the main loops 2a so as to surround all the main loops 2a, one end of this compensating loop 3a being connected to the driver 3 for sending thereto a current of certain amplitude in reverse to the current flow-ing through the source line 2s of the main loops 2a with the other end grounded. In the ROM table 15 functioning as the first memory means storing therein compensation values, there are stored compensation values pertinent to respective loops L and Y-direction (or X-direction) regions.
11695/LCM:jj 13 ~, ~2762~;8 In this ROM table 15 are stored compensation values ISC relating to all the segments Sn and to the respective main loops corresponding to the segments Sn under the condi-tion of the detection height Z = 15mm. In operation, a pertinent compensation value ISC is called up by the control circuit 10 in accordance with the detection results of the control circuit 10 and used to calculate an interpolation value by means of an arithmeti~ means included in the control circuit 10.
The ROM table 16 functioning as the second memory means storing therein correction values is used to obtain an accurate coordinate position from the thus calculated inter-polation value through correction of its error. Specifical-ly, in this table are stored correction values corresponding, for example, to each 0.lmm increment of the interpolation value pertinent to the segment detected.
The pickup 6 includes in its tip portion the magnetic field detecting coil, a voltage produced by this magnetic field detecting coil being sent via the amplifier circuit 7 to the detector circuit 9 and the polarity discriminator circuit 8.
11695/LCM:jj 14 ~276258 The operation of the foregoing coordinate input device will now be described.
The process of detecting the position of the pickup 6 is achieved principally through the three steps of detecting a coarse position or a segment of the pickup 6, performing interpolation or detecting a fine position within the thus detected segment, and combining the segment position and the fine position within the segment.
At the time of segment detection, first, the drivers 2 and 3 are operated by the use of a sinusoidal wave generated by the oscillator 1. As a result, a current is caused by the driver 2 to flow through the loops L in sequence, one speci-fied via the switching circuits 4 and 5 by the control cir-cuit 10 at a time. During the above, a current having an amplitude equal to one-half that of the current flowing through the main loop 2a is caused by the driver 3 to flow through the compensating loop 3a.
As the individual loops L are scanned by the current, the magnetic field generated by the effective loop L is sensed by the pickup 6 and amplified by the amplifier circuit 7 into a signal of desired amplitude. This signal is com-pared in terms of phase with the output of the oscillator 1 11695/LCM:jj 15 ~276~58 by the polarity discriminator (phase comparator) circuit 8.
In other words, the polarity of the magnetic field is detect-ed at this time. Assume that the output of the polarity discriminator circuit 8 was "H" when the loop L on the left-hand side in the drawing of the pickup 6 was driven. Hence, the polarity of the magnetic field detected reverses when the loop L on the right-hand side of the pickup 6 is driven, as a result, the output of the polarity discriminator circuit also reverses and becomes "L".
Therefore, as the loops L are selected and supplied in sequence with the current in the order of X0, X1, X2,... Xn, loop Ln is detected in the vicinity of the pickup 6 by which the output of the polarity discriminator circuit 8 was re-versed. After the perception of this loop Lnl the system detects a voltage Vn owing to this loop Ln and another vol-tage Vn1 owing to the preceding loop Ln1, compares the two voltages Vn and Vn1, and determines in accordance with a given algorithm a region (segment) to be interpolated.
If an object segment (Sn2, for example, in Fig. 10) is determined, the control circuit first selects loop Ln2 located at the left-hand end of that segment Sn2. Then, the signal passed through the pickup 6 and the amplifier circuit 11695/LCM:jj 16 ~.27~258 7 is converted by means of the detector circuit 9 into a dc signal and held in the sample-hold circuit 11 in the form of a dc voltage.
Thereafter, the control circuit lo selects loop Ln located at the right-hand end of segment Sn2, and similarly to the above, another dc voltage obtained by the detector circuit 9 is held in the sample-hold circuit 12. Then, the voltages held in the sample-hold circuits 11 and 12 are selected by the multiplexer 13 in accordance with the signal from the control circuit 10 and converted by the A/D con-verter 14 into a digital form to get the voltages Vnz and Vn owing to loops Ln2 and Ln.
Then, the control circuit 10 turns off all the switch-ing circuits 4 and 5. As a result, the aforementioned pre-determined current flows only through the compensating loop 3a. By A/D-converting a detected output it is possible to obtain a voltage Vc pertinent to the compensating loop 3a through the same process as above.
Subsequently, the control circuit 10 calls up from the ROM table 15 a compensation value ISC corresponding to the value (the distance) ~f the segment obtained through segment discrimination in the X-/Y-direction, and causes the arith-11695/LCM:jj 17 ~Z76Z5~3 metic means included in the control circuit 10 to calculate an interpolation value P' by substituting the detected vol-tages vn2, Vn and Vc and the ISC in the following equation (4) involving the compensation value:
Vn 2 -- ISC - Vc pl = (4) Vn-2 + Vn If this interpolation value P' is calculated, the ROM
table 16, in which correction values P for correction of the aforementioned errors are stored, is accessed to obtain a coordinate value which specifies a position within the seg-ment. Then, the positional coordinate (sn x 5.0 + ~) of the segment and the coordinate value P within that segment are combined by the arithmetic means included in the control circuit to calculate the ultimate X coordinate of the desig-nation position of the pickup 6 in accordance with following equation:
X = ~8n x 5.0 + ~) ~ P (mm) where 8n: the segment number P: the correction value obtained by amending the interpolation value ~: the amount of shift of segment S (for example, ~ = -2.5, 0, +2.5, which is preset in accordance with the presence/absence and the direction of the offset of the segment and is adequately selected by a software).
11695/LCM:jj 18 ~,~7~a A similar group of segments is defined with respect to the Y direction, thus, the system can calculate the Y co-ordinate of the designation position through a similar detec-tion operation and deliver the calculated coordinate value via an interface circuit 17 to the side of a host computer.
As described hereinabove, because coordinate detection errors arise due to the shift of the polarity reversing position of the magnetic field, the aforementioned prior proposals intended to reduce errors as far as possible by introducing the compensation value or correction value to interpolate a correct coordinate position between segments, or by selecting a segment providing less errors.
These prior ideas originated from the configuration wherein the segments are defined on the basis of a given spacing between loops. Therefore, because the arrangement of segments was determined from the view-point of hardware without consideration of the amount of shift, the algorithm of calculation became complicated.
11695/LCM:jj 19 ~27~
D~SCRIPTIO~ OF THE PREF~RRED ~ilBODIMEN~
~ n embodiment o~ tre precent inve~tion will now be described with reference to the drawings.
Figs. 2 tnrough 8 are ex~lanatory of the embodiment of the ~resent invention. The cor.fi~uration and circuit of a coordinate input device adapted for the embodiment are substantially identical with those of the conve~tional device, except for the ~OM table 18 storing therein the amount of deviation of segment S; hence, no further descri~tion is given here with respect to the identical portion. Further, an identicæl or similar elemsr.t to th2t of the cor.ventional device is designated by the same reference srmbol as in the conventional device.
Fig. 2 illustrates loops L and voltage distribution c-~rves owing to the magnetic field produc_d when these loops L are scanned. In this drawing, the distance, 5n, in the X direction of loo~s Ln ( n = O - 39 ) disposed at a pitch of 5mm as in the cPse of the conventional device is shown on the horizontal axis and the absolute value of detection voltage on the vertical axis.
Although the conventional sytem defines segment Sn on the basis of the position of loop ~n~ the present invention defines segment Sn on the basis of the polarity reversing position detected of a magnetic field. That is, the start ~ ~7~258 ~oint of the n-th se~ent Sn is def~ned by a spot at which a det~ction voltage Vn becomes zero when the n-tn loo~ Ln is 9canned? whereas the end point is defined by another spot at which 2 detection voltage Vn+2 becomes zero when loop ~n+2 subseauent but one to Ln is ~car~ed.
Accordingly, although adjoinin~ seg~ents S overla~
~artiall~ each other, the field reversing position, i.e.
the spot at which the detection voltage Vn ( n = O - 39 ) becomes zero, is alwa~s taken as the start point or end ~oint even if the amount of shift increases, thus, the ob'ect segment Sn to be interpolated can be selected b~
the use only of the aforementioned conditional equation A (3).
DeQcribing e~em~larily, assume that the pickup 6 is standing at position T in Fig. 2. Her.ce, the field polarity changes for the first time when the (n+2)th loo~ Ln+2 i8 ~canned. Letting a detection voltage owing to loop Ln+2 which is detected by the pichu~ 6 be Vn+2 and another detection voltage owing to loop Ln+l be Vn+l, the two voltages Vn+2 and Vn+l are compared and the conditional eauation ~) is referred to. As a result, the following is given:
¦Vn+2/~ln+l¦ 1 Thus, segment Sn which i9 effective wnen the n-th loop Ln ~ 2 ~
is scanned is judged as the object se~ent S to be inter-nolated. T~ereIore, it is possibl~ to obtain an inter-~olation value Xp from the enuation (~) using detection volt~ge values Vn+2 and Vn.
Error or discrepancy between interpolation value and ideal value is snown in ~ig. 4. S~ecifically, the graph of ~ig. 4 shows errors pertinent to loop ~ of X = 20~m, i.e. segment S5 with the start point X = 22.36mm; loop ~19 of X ~ 95~m, i.e. segment Slg with the start point X _ 95.07~; and loo~ L34 of X = 170~m, i.e. segment S34 with the start point X = 15~.21mm, or errors within the positi~nal range of lO~m measured from eæch start point.
According to Fig. 4, it will be appreciated that in tne area ( X <190mm ) on t'.1e left-hand side of tne center C of the input plane 2b, t'ne error does not exceed substantially 0.5~ even when the aforementioned equation (3) is used as it is, whereas in t'ne area ( X >lOOm~ ) on the right-hand side it increases in excess of the former when the equation (~t) is used.
~ hus, because of the symmetry in arrangement of t'ne loo~s L of the input plane 2a, if the eauation:
X = Vn+2 (5) P Vn + Vn+2 76~5S
is used with respect to the area ( X ~lOOmm ) on the right-hand side o~ the center of ths inpu~ plane 2b and the magnetic field reversing ~osition observed when loo~
Ln+2, which is clos-r to the end point oî seg~ent Sn, is scanned is taken as a reference, the error pertinent to the rignt-side area is ex~ected to be com~atible in magnitude with that OI the left-side area OI the center a calculated b~ tne eauation (~). Thè foregoing process is shown in Fig. 3. That is, while taking the position o~
the center C ( X = lOOmm ) o~ the input ~lane 2b as a reference, the lnter~olation value is calculated in the increasing direction of X with respect to the left-side area ( X~ lO0 mm ), and in the decreasing direction of X
with respect to the right-side area ( X>lOOmm ).
Discrepancy between interpolation value calculated in the manner above and ideal value is shown in Figs. 5 through 7. Specific~lly, Fig. 5 shows errors in the interval of 20mm' X ~ 30mm, Fig. 6 shows errors in the interval of 95mm ~X~ 105mm, and Fig. 7 shows errors in the i~terval of 170mm ~ XC 180mm ( which is s~mmetrical to Fig. 5 about X = lOOmm ) at five points Y = 20, 60, 100, 140, and 180mm, wherein the start poi~t or origin of each graph corresponds to the position ( 5n mm ) of respective loop ~n to be driven shown in Fig. 3.
~27~i2S8 As ~ill be a~arent from these gra~ns, the error inc~easeC ab~lptly after passed over the field polarit~J
reversing positi~n, bu., it falls within the range of + 0.5 in the whole surface of the in~ut plane 2b, exce~t for the above.
~ o calc~late an actual coordinate using the inter-polatlon value X~ detected in the manner above, it i~
necssarJ to store the field ~olarit~ rsversing nosition in the RO~ table 18. In this connection, if the absolute ~osition of the ~olarity reversing position is to be ~OM-tablized as it is, its data volume i9 too large for one byte to accommodate. ~e~ce, in the embodiment, the amount n ( n - O - 39 ) of deviation from the position of loo~
~ is stored in the ~OM table. Accordingly, the ROM table 15 of Fig. 9 becomes unnecessæry. In practice, the amount n-l~ n~ n+l of devi2tion from the ~osition of loop Ln l~ Ln~ Ln+l corresponding to 5(n-l), 5n, 5(n+1)mm shown in Fig. 2 is ROM-tablized and stored in the ~OM
table 18. Subse~uently, letting the segment number be n, the amount of deviation be n mm ( n = O - 40 ), and the interpolation value be Xp, the X coordinate pertinent to the left-side portion of the center C of the in-out plane 2b is calculated in accordance with the following equation:
~27~2~8 X = 5.0 n + n + lO Xp (~) (6) where ~ = V~/( V~ + V~+2 ), ~d the sæme pertine~t t~ the right-side portion of the center C i9 calculated in accordance with the following equation:
X = 5.3 ( n + 2 ) ~ n ~ l~ Xp (mm) wnere X~ = Vn+2/( Vn + Vn+2 )-The Y coordinate can be calculated in accordancewith a similar process to the case of the X coordinate, whereby it is possible to detect both the X- and Y-direction coordinates of the pic~up 6 on the input plane 2b. Incidentally, because both the foregoing eauations (6) and (7) are em~loyed, the symmetr~y in both the X and Y directions with respect to the center C should be taken into consideration deeply.
Further, there is another calculation ~rocess wherein in connection with the resolution of i~terpolation, lO~m, for e~am~le, is divided by 256 and the length o~ one fraction, 0.04mm, is treated as a unit. In this case, the data of deviation amount n will also be handled ta~ing the resolution of interpolation as a unit, and the interpolation ~alue Xp obtained through inter~olation calculation and the deviation amount n will be represent-ed each by an integer from 0 to 255. If so digitized, ~76~
the X coordinate value pertinent to the left-side ~ortion o~ the ce~t~r C of the input plane 2b can be calculated in accordance wlth the following ecuation:
X = 50 n + ( Xp + 0~ (10 lmm) (8) p n/( ~n + Vn+2 ) and n = the se~ment number ( O' n' 20 ), and the same pertinent to t~ne right-side ~ortion of the center C of the input plane 2b can be calculated in accordance with the following eauation:
X - 50 ( n + 2 ) - ( X~ ~ n ) 100 (lO~lm~) (9) p n+2/( ~n + Vn+2 ) and n ~ the se~me~t number ( 21~-nC 39 ).
~ ig. 8 shows a coordinate detection process or flowchart of performing calculation in such a ma~ner as above. The operation of a coordinate i~put device embodying the present invention will now be described with reference to the flowchart, but, the d_scription of the steps up to the detection of polarity reversal is omitted because these steps are identical with those of the conventional process.
Upon scanning the loops L, loop Ln is detected which is located in the vicinity of the piclnup 6 and by which the output of the polarity discriminator circuit 8 is reversed. The voltage ~n owing to t'nis loop Ln is compared with the voltag~ ~n 1 owing to tne ~receding loo~ 1n 1' g~ , Sn_2 or S~_l, to be inte~olated is deter~ined in accordance with the ~a~ m i~rr2~resented by the aforementioned eauation (~). .4fter the determination of the seg~ent S ( for e~ample, Sn of ~ig. 2 ), the control circuit 10 selects loop Ln ( the loop at ~ = 5n ) corres~onding to the start po1.nt of that seg~ent. At this time, tne signal passed through the ~ic~up 6 and the amplifier circuit 7 is converted into a dc signal bl~ the dqtector circuit 9 and held in the sample-hold amnlifier 11 in the L or~ of a dc voltage.
Then, the control circuit 10 selec's loon ~n+2 ( the loo~ at ~ = 5(n+2) ) corres~onding to the end point of ~egment Sn, and a similarl~ obtained dc voltage is held in the sample-hold amnlifier 12. ~he voltages held in these samnle-hold amnlifiers 11 and 12 are converted by the multilexer 13 and the A/D converter 14 into digital values, as a result, the voltages Vn and Vn+2 pertinent to loops Ln and Ln+2, respectivel~, are obtained.
~ hen, the interpolation value Xp is calculated by an arithmetic circuit included in the control circuit 10 A in accordance with the aforementioned eauation (~) o~ (5).
After the calculation of the internolation value Xp, the pertinent deviation amount n is taken o~t from the ROM
6%~8 table 18 having the deviation amounts n of the se~me~ts S stored therein corres~onding to the se~ent nwmbers, and the ultimate X coordinate value is obtained using the afore~entioned eauation (8) or (9). ';Vith re~pect to t~e ~r direction, a si~ilar process is perfor~ed to obtain an object Y coordinate. These ~ coordinate and Y coordinate are conbined together, whereby the detection of the position on the ln~ut plane 2b of the picXup 6 is complsted.
As will be apprsciated, the embodiment provides the following effects:
~ Since there is no need of introducing the compensa-tion value in the inter~olation calculation, the calculation is simplified and the com~uting s~eed is enhanced;
~ Since there is no need of detecting the detection voltage Vc owing only to the compensating loop 3a at the tine of the interpolation calculation, a switching means for connecting and disconnecting ths comnensating loop 3a is unnecessar~, thus, the cost is reduced and the computing speed is enhanced because no switching ste~ is required;
~ Since the data of deviation amount n of the field polarit~ reversing ~osition are directl~ related to the ~27~a coo~dinate value, the data can be corrected easily in experiment;
~ No special consideration is necess~r!r to be ~aid for the shift of segment which invclves the deviation æmo~nt of the ~ola-ity reversing ~osition in the ~eri~heral portion of the inptlt ~lane 2b and for the segment discri-~ Iqor~~th~mination &~ori~ relative to the ~eri~hera.l portion, and one ~ind is enough for the segment discrimination ~I'IDr ;1-h~
~lgo~ism, thus, the system becomes simple; and ~ Sincs the ~te~s u~ to the interpolation calculation can be perform3d ~eparætely betl~een the ~ direction and the Y direction, and the system can be designed so as to access the ROM table 18 for the first.time at the step of combining the coordinate values, the com~uting ~rocess becomes simple and the computing s~eed can be enhanced.
As described hereinabove, the present invention detects the designation ~osition on tne input plane of the coordinate designating member by the ste~s of:
establishing the coarse regions on the input plane where the coordinate designating member stands while taking as a reference the polarity reversing ~osition of the magnetic field detected when the scan signal is sent to the conductors embedded in the input plane in seaue~ce, performing interpolation witnin the coarse region, and ~,Z76Z~8 com~osing the design~tion posi~ion of t'ne coordinate designating member on the basis OI tne coordinate ~o~ition of the coarse region and the interpolation value obtained in t'ne interpolation ste~.
Therefore, according to the present invention, the coarse region to be inter~olated can be spQcifiQd ~y the Qlq~r;t~
use of one l~ind of se~ment discrimination ~ , hence, ~ Iqor~thrr~
a program for the~al~o~m becomes sim~le. The inter-polation value can be calculated onll~ from the detection voltages used in se~ment discrimination, hence, for calculation of the ir.ter~olation value there is no need of introduction of the com~ensation value and the like and detection of the voltage from the com?ensating loo~.
Consequentl~y, the com~uting speed can be enhanced and t'ne ~erformznce of this kind of coordinate in~ut device can be im~roved.
Claims (5)
1. A coordinate detecting method comprising the steps of:
establishing a plurality of coarse regions while taking as a reference the polarity reversing positions of a magnetic field detected when a scan signal is sent to an input plane equipped with a plurality of main loops made of parallel embedded conductors such that the main loops are driven in sequence by the scan signal, specifying one coarse region to be interpolated, interpolating the designation position of a coordinate designating member within the specified coarse region, and calculating the coordinate of the designation position on the input plane designated by the coordinate designating member on the basis of the coordinate position of the specified coarse region and an interpolation value obtained in the interpolating step.
establishing a plurality of coarse regions while taking as a reference the polarity reversing positions of a magnetic field detected when a scan signal is sent to an input plane equipped with a plurality of main loops made of parallel embedded conductors such that the main loops are driven in sequence by the scan signal, specifying one coarse region to be interpolated, interpolating the designation position of a coordinate designating member within the specified coarse region, and calculating the coordinate of the designation position on the input plane designated by the coordinate designating member on the basis of the coordinate position of the specified coarse region and an interpolation value obtained in the interpolating step.
2. A coordinate detecting method according to claim 1, wherein the coordinate position of the specified coarse region is obtained by accessing a ROM table storing therein the deviation amount ( On, n = an integer ) between the coordinate position of each loop ( Ln ) and the coordinate position of the start point of the corresponding coarse region ( Sn ) to get a pertinent deviation amount and by adding the coordinate position of the corresponding loon ( Ln ).
3. A coordinate detecting method according to claim 1, wherein each coarse region ( Sn, n = an integer ) is established as starting at the point where a detection voltage ( Vn ) owing to the corresponding loop ( Ln ) is zero and ending at the point where a detection voltage ( Vn+2 ) owing to the loop ( Ln+2) succeeding but one to that loop ( Ln ) is zero.
4. A coordinate detecting method according to claim 3, wherein the coarse region to be interpolated is determined as Sn if ¦Vn+2/Vn+l¦?1 when the magnetic field polarity detected by the coordinate designating member reverses for the first time upon scanning the loop Ln+2, otherwise is determined as Sn+1, where Vn+2 and Vn+1 are the detection voltages owing to loops Ln+2 and Ln+1, respectively.
5. A coordinate detecting method according to claim 3, wherein the interpolation value Xp pertinent to the coarse region Sn specified is calculated in accordance with either of the following equations:
where Vn and Vn+2 are the detection voltages owing to loops Ln and Ln+2, respectively.
where Vn and Vn+2 are the detection voltages owing to loops Ln and Ln+2, respectively.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61162933A JPH0654460B2 (en) | 1986-07-12 | 1986-07-12 | Coordinate detection method |
| JP162933/86 | 1986-07-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1276258C true CA1276258C (en) | 1990-11-13 |
Family
ID=15763996
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000535271A Expired - Lifetime CA1276258C (en) | 1986-07-12 | 1987-04-22 | Coordinate detecting method |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US4758690A (en) |
| JP (1) | JPH0654460B2 (en) |
| CA (1) | CA1276258C (en) |
| DE (1) | DE3717272A1 (en) |
Families Citing this family (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS62143120A (en) * | 1985-12-18 | 1987-06-26 | Alps Electric Co Ltd | Input device for coordinate |
| US4928256A (en) * | 1988-03-16 | 1990-05-22 | Ametek, Inc. | Digitizer for position sensing |
| US5148600A (en) * | 1991-09-17 | 1992-09-22 | Advanced Robotics (A.R.L.) Ltd. | Precision measuring apparatus |
| US6028271A (en) * | 1992-06-08 | 2000-02-22 | Synaptics, Inc. | Object position detector with edge motion feature and gesture recognition |
| DE69324067T2 (en) | 1992-06-08 | 1999-07-15 | Synaptics Inc | Object position detector |
| US6239389B1 (en) | 1992-06-08 | 2001-05-29 | Synaptics, Inc. | Object position detection system and method |
| US5861583A (en) * | 1992-06-08 | 1999-01-19 | Synaptics, Incorporated | Object position detector |
| US5889236A (en) * | 1992-06-08 | 1999-03-30 | Synaptics Incorporated | Pressure sensitive scrollbar feature |
| US5880411A (en) | 1992-06-08 | 1999-03-09 | Synaptics, Incorporated | Object position detector with edge motion feature and gesture recognition |
| US5554827A (en) * | 1993-02-22 | 1996-09-10 | Wacom Co., Ltd. | Method of and apparatus for determining whether a digitizer coordinate detecting tablet is properly operating and/or writing adjustment data into a memory associated with the tablet |
| JP3368627B2 (en) * | 1993-08-31 | 2003-01-20 | 双葉電子工業株式会社 | Display integrated tablet |
| US6380929B1 (en) | 1996-09-20 | 2002-04-30 | Synaptics, Incorporated | Pen drawing computer input device |
| US5854625A (en) * | 1996-11-06 | 1998-12-29 | Synaptics, Incorporated | Force sensing touchpad |
| JP2001134382A (en) | 1999-11-04 | 2001-05-18 | Sony Corp | Graphic processor |
| US8050876B2 (en) * | 2005-07-18 | 2011-11-01 | Analog Devices, Inc. | Automatic environmental compensation of capacitance based proximity sensors |
| JP5526898B2 (en) * | 2010-03-19 | 2014-06-18 | カシオ計算機株式会社 | Position detecting device and display device with position detecting function |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IT1061979B (en) * | 1975-05-23 | 1983-04-30 | Seiko Instr & Electronics | AUTOMATIC DEVICE FOR DETERMINING THE COORDINATES OF A POSITION ON A FLAT SURFACE |
| US3999012A (en) * | 1975-07-07 | 1976-12-21 | Ibm Corporation | Graphic entry tablet with improved addressing |
| SE406642B (en) * | 1977-02-16 | 1979-02-19 | Aga Ab | ELECTROMECHANICAL DOCTOR |
| JPS5935069B2 (en) * | 1979-01-19 | 1984-08-27 | セイコーインスツルメンツ株式会社 | Interpolation method of coordinate reading device |
| JPS5920156B2 (en) * | 1980-07-10 | 1984-05-11 | セイコーインスツルメンツ株式会社 | coordinate reading device |
| JPS6077226A (en) * | 1983-10-04 | 1985-05-01 | Matsushita Electric Ind Co Ltd | Input device of coordinate |
| JPS60181816A (en) * | 1984-02-29 | 1985-09-17 | Pentel Kk | Signal detecting position deciding method of graphic input device |
-
1986
- 1986-07-12 JP JP61162933A patent/JPH0654460B2/en not_active Expired - Lifetime
-
1987
- 1987-03-03 US US07/021,148 patent/US4758690A/en not_active Expired - Lifetime
- 1987-04-22 CA CA000535271A patent/CA1276258C/en not_active Expired - Lifetime
- 1987-05-22 DE DE19873717272 patent/DE3717272A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| US4758690A (en) | 1988-07-19 |
| JPH0654460B2 (en) | 1994-07-20 |
| DE3717272C2 (en) | 1989-06-01 |
| DE3717272A1 (en) | 1988-01-21 |
| JPS6319030A (en) | 1988-01-26 |
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