Position detecting device and corresponding method with compensation for the effects of offset voltage and/or gain variation

• US 5,619,431 A
• Filed: 03/06/1995
• Issued: 04/08/1997
• Est. Priority Date: 03/18/1994
• Status: Expired due to Term

• Current Assignee: Wacom Co Limited (Wacom)
• Original Assignee: Wacom Co Limited (Wacom)
• Inventors: Oda, Yasuo
• Primary Examiner(s): Voeltz, Emanuel T.
• Assistant Examiner(s): Wachsman, Hal D.
• Application Number:
  US08/398,782
• Time in Patent Office: 764 Days
• Field of Search: 364/559, 364/560, 364/709.1, 364/709.11, 178/18-20, 324/207.24, 341/3, 341/15, 367/117, 367/127, 367/128, 367/907, 345/104, 345/173, 345/179, 375/317
• US Class Current: 702/150
• CPC Class Codes: G06F 3/046 by electromagnetic means

Abstract

A position detecting device for calculating coordinates of the position indicator rapidly and accurately to provide data related thereto without using any high sampling rate and high speed arithmetic operation is provided. The position detecting device performs a signal processing for providing coordinates of the pen based upon signals (50) from a sensing unit, which has a large number of loop coils disposed in parallel with respect to one another and generates said signals due to electromagnetic effects between the coils and a position indicator (input pen ) (3) disposed on these coils. Said signal processing includes analog phase detect operations of multiplication and integration using the data of the signals, which include a first pair of phase detect signals orthogonally related to each other and a second pair of phase detect signals being in inverted relation with respect to each of the first pair of phase detect signals, to provide a plurality of values of real and imaginary parts which correspond to an objective frequency component of said signal. Following that processing, it further performs add and subtract operations on the data to eliminate errors due to the offsets and gain variations produced in the analog phase detect portion (70), and performs operations for calculating the amplitude and phase angle of the signal to determine the coordinates using the accurate data thus provided and simple approximate expressions of high accuracy.

Claims

1. A position detecting device for calculating coordinate values of a specified position of a position indicator based upon electromagnetic effects between a sensing unit comprising a large number of loop coils disposed in parallel with respect to one another in the direction of position detection and the position indicator having at least one coil, wherein said position detecting device comprises:

signal processing means for processing a receiving signal from said sensing unit; and

coordinate calculating means for calculating the coordinates of said position indicator;

said signal processing means including;

a phase detect signal generator for generating a plurality of phase detect signals including first phase detect signals orthogonally related to each other, and second phase detect signals, each phase of which is respectively in an inverted phase relationship with each of said first signals;

(ii) a switch for selecting one of said plurality of phase detect signals;

(iii) an analog signal detect portion for performing multiplications and integrations of said plurality of phase detect signals with said receiving signal, and outputting a plurality of values of real or imaginary parts which correspond to one frequency component of said receiving signal;

(iv) an analog to digital converter for converting said values of real or imaginary parts into digital signals; and

(v) a first arithmetic processor for performing predetermined add and/or subtract operations to said plurality of values of real or imaginary parts in order to eliminate offsets and/or gain variations included in said values;

said coordinate calculating means including;

a second arithmetic processor for calculating amplitudes and/or phase angles of any one of said frequency components within said receiving signal using the result of the first arithmetic processor; and

wherein said plurality of phase detect signals in said signal processing means include first and second phase detect signals which are different by 90°

from each other and third and fourth phase detect signals which are different by 180°

, respectively, from the first and second signals;

said analog signal detect portion comprising first and second analog phase detectors, each of which contains a multiplier and an integrator;

said plurality of values of real and imaginary parts respectively comprising;

values of the real part which are outputs from the first and second detectors detecting the first and third signals; and

values of the imaginary part derived from the first and second detectors processing the second and fourth signals; and

said predetermined add and or subtract operations processed within the first arithmetic processor including;

a) adding the difference of the values of the real part of first and third signal outputs by the first detector and the difference of the values of the real parts of the first and third signal outputs by the second detector, adding the difference of the values of the real part of first signal output by the first and second detectors and the difference of the values of the real part of third signal outputs by the first and second detectors, then adding the results of the former two additions;

b) adding the difference of the values of the imaginary part of the second and fourth signal outputs by the first detector and the difference of said values of the imaginary part of the second and fourth signal outputs by the second detector; and

c) adding the difference of the value of the imaginary part of second signal output by the first and second detectors and the difference of the values of the imaginary part of fourth signal outputs by the first and second detectors, then calculating the difference of the result of the former two additions.

2. A position detecting device as claimed in claim 1, wherein

said phase detect signals generated in said phase detect signal generator are polarity switching signals;

said multiplier utilized in said analog phase detectors include;

means of generating polarity inverted and non-inverted signals from said receiving signal, and

a switch controlled by said polarity switching signals for switching synchronously with the cycles of said signals; and

,

said output signals from said multiplier, which includes said inverted and non-inverted signals alternately switched by said switch, are equivalent to the signals obtained as the result of multiplication process of said receiving signal and a bipolar square wave.

3. A position detecting device as claimed in claim 1, wherein

said phase detect signals generated in said phase detect signal generator are analog sinusoidal signals, and

said multiplier utilized in said analog phase detector includes an analog multiplier for multiplying said receiving signal and said analog sinusoidal signals.

4. A position detecting device as claimed in claim 1, wherein

said phase detect signals generated in said phase detect signal generator are digital pseudo-sinusoidal signals, and

said multiplier utilized in said analog phase detectors include a digital to analog converter and an analog calculator.

5. A position detecting device as claimed in claim 1, wherein:

the phase detect signals generated in said phase detect signal generator are digital pseudo sinusoidal signals, and

the multiplier utilized in the analog signal detect portion is realized by inputting said digital pseudo-sinusoidal signals and said receiving signal as a reference signal into a multiplication digital to analog converter.

6. A position detecting device as claimed in claim 1, wherein said coordinate calculating means

calculate the amplitude L_c by using an approximate expression L_c =B+A/2 (the greater of the absolute values of said values of real and imaginary parts is designated as B, the smaller as A), then calculating said coordinates based upon the L_c values obtained from said plurality of loop coils adjoining each other.

7. A position detecting device as claimed in claim 1, wherein said coordinate calculating means

calculate the phase angle θ

using an approximate expression

space="preserve" listing-type="equation">θ

=(1.5A/(B+0.5A))×

K

(the greater of the absolute values of said values of real and imaginary parts is designated as B, the smaller as A, and K as a value which expresses an angle equivalent to 45θ

).

8. A position detecting device for calculating coordinate values of a specified position of a position indicator based upon electromagnetic effects between a sensing unit having a large number of loop coils disposed in parallel with respect to one another in the direction of position detection and a position indicator having at least one coil, wherein said position detecting device comprises:

signal processing means for processing a receiving signal from said sensing unit; and

coordinate calculating means for calculating coordinates of said position indicator;

said signal processing means including;

(i) a phase detect signal generator for generating a first pair of phase detect signals orthogonally related to each other, and a second pair of phase detect signals, each of which is respectively in an inverse relationship with each of the first pair;

(ii) a switch for selecting one of said four phase detect signals in said first and second pairs;

(iii) an analog signal detect portion for performing multiplication and integration by applying said four phase detect signals to said receiving signal and outputting two values of real and imaginary parts respectively, which correspond to the component of any one frequency of said receiving signal;

(iv) an analog to digital converter for converting said two values of the real part or two values of the imaginary part into digital signals; and

(v) a first arithmetic processor for performing predetermined subtract operations to said two values of the real part or the two values of the imaginary part in order to eliminate the value which corresponds to offset included in the values;

wherein said coordinate calculating means includes;

a second arithmetic processor for calculating amplitudes and/or phase angles of any one frequency component within said receiving signal by using the result of said first arithmetic processor;

wherein said four phase detect signals in said signal processing means include first and second phase detect signals which are different by 90°

from each other and third and fourth phase detect signals which are different by 180°

, respectively, from the first and second signals;

said analog signal detect portion including first and second analog phase detectors each of which contains a multiplier and an integrator;

said two real and imaginary values respectively comprising;

a) values of the real part which are outputs of the first detector, detecting the first and third signals, and

b) values of the imaginary part derived from the second detector processing the second and fourth signals; and

said predetermined subtract operations processed within said first arithmetic processor including;

means for calculating the difference of the values of the real part of the first and third signal outputs by the first detector and calculating the difference of the values of the imaginary part of the second and fourth signal outputs.

9. A position detecting device as claimed in claim 8, where said analog phase detect portion includes an analog phase detector which has a first multiplier and an integrator, which sequentially applies one of said four phase detect signals to said receiving signal to provide said values of two real parts and two imaginary parts.

10. A position detecting device for calculating coordinate values of a specified position of a position indicator based upon electromagnetic effects between a sensing unit comprising a large number of loop coils disposed in parallel with respect to one another in the direction of position detection and the position indicator having at least one coil, wherein said position detecting device comprises:

signal processing means for processing a receiving signal from said sensing unit; and

coordinate calculating means for calculating the coordinates of said position indicator;

said signal processing means including;

(i) a phase detect signal generator for generating two phase detect signals which are orthogonally related to each other;

(ii) a switch selecting one of said two phase detect signals;

(iii) an analog signal detect portion for performing multiplication and integration operations by applying said two phase detect signals to said receiving signal and outputting two values of real and imaginary parts, respectively, which correspond to any one frequency component of said receiving signal;

(iv) an analog to digital converter for converting said two values of the real part or two values of the imaginary part into digital signals; and

(v) a first arithmetic processor for performing predetermined addition to said two values of the real part or two values of the imaginary part in order to eliminate the value which corresponds to offset included in the respective values;

said coordinate calculation means including;

a second arithmetic processor for calculating the amplitudes and/or phase angles of any one frequency component within said receiving signal by using the result of the first arithmetic processor;

wherein said two phase detect signals in said signal processing means include first and second phase detect signals 90°

different from each other;

said analog signal detect portion includes first and second analog phase detectors each containing a multiplier and an integrator;

said two values of real and imaginary parts respectively comprising;

(i) values of the real part derived from the first and second detectors detecting first signals, and

(ii) values of the imaginary part derived from the first and second detectors processing second signals;

said predetermined addition processing within said first arithmetic processor including;

calculating the sum of the values of the real part of first signals output by the first and second detectors; and

b) calculating the sum of the values of the imaginary part of second signals output by the first and second detectors.

11. A position detecting device for calculating coordinate values of a specified position of a position indicator based upon electromagnetic effects between a sensing unit where a large number of loop coils are disposed in parallel with respect to each other in the direction of position detection, and the position indicator having at least one coil, wherein said position detecting device comprises:

signal processing means for processing a receiving signal from said sensing unit; and

coordinate calculating means for calculating coordinates of said position indicator;

said signal processing means including;

(i) a phase detect signal generator for generating from said receiving signal, a first detect signal which has the same phase angle as the receiving signal and a second phase detect signal which has an inverse phase angle with respect to said receiving signal;

(ii) a switch for selecting one of said first and second phase detect signals;

(iii) an analog signal detect portion for performing analog multiplication and integration by applying the receiving signal to said first and second phase detect signals to provide two values of the real part which corresponds to the fundamental frequency component of said receiving signal;

(iv) an analog to digital converter for converting said two values of the real part into digital signals; and

(v) a first arithmetic processor for performing predetermined subtraction operations to said two values in order to eliminate the value which corresponds to offset included in said two values;

said coordinate calculating means including;

a second arithmetic processor for calculating the amplitudes of the fundamental frequency component of said receiving signal by using the result of the calculation performed in said first arithmetic processor;

wherein said first and second phase detect signals are polarity switching signals generated from non-inverted and inverted outputs of a comparator to which said receiving signal is provided;

said multiplication utilized in said analog phase detect portion including;

a) means for generating inverted and non-inverted wave signals of said receiving signal; and

b) a switch for alternating the selection thereof synchronously with the polarity inverting cycle of the polarity switching signals which includes said first and second signals;

wherein said output signals from the multiplication, which include said inverted and non-inverted signals alternately switched by said switch, are respectively equivalent to signals obtained as the result of multiplication between said receiving signal and a bipolar square wave.

12. A method for detecting position and calculating coordinate values of a specified position of a position indicator based upon electromagnetic effects between a sensing unit comprising a large number of loop coils disposed in parallel with respect to one another in the direction of position detection and the position indicator having at least one coil, wherein said method of detecting position comprises the following steps:

calculating the coordinates of said position indicator by signal processing based upon a receiving signal received by said sensing unit;

said signal processing including;

(i) generating a plurality of phase detect signals, including first and second phase detect signals which are 90°

different from each other and third and fourth phase detect signals which are different by 180°

, respectively, from the first and second phase detect signals;

(ii) performing analog multiplication and integration by applying said phase detect signals to said receiving signal and providing a plurality of values of real and imaginary parts, which correspond to any one of the frequency components of said receiving signal;

(iii) converting said plurality of values into digital signals; and

(iv) performing predetermined add and/or subtract operations to said plurality of values in order to eliminate offsets and/or gain variations included in said values of said real and imaginary parts;

said calculating the coordinates step including;

calculating the amplitudes and/or phase angles of any one of the frequency components of said receiving signal by using the results of said add and/or subtract operations;

wherein the plurality of values of real and imaginary parts respectively comprise;

a) values of the real part which are outputs from first and second detectors detecting the first and third signals; and

b) values of the imaginary part derived from the first and second detectors processing the second and fourth signals;

wherein said predetermined add and/or subtract operations include;

(i) adding the difference of the values of the real part of first and third signal outputs of the first detector and the difference of the values of the real parts of the first and third signal outputs of the second detector, adding the difference of the values of the real part of first signal output of the first and second detectors and the difference of the values of the real part of third signal outputs of the first and second detectors, and then adding the results of the former two additions, and

(ii) adding the difference of the values of the imaginary part of the second and fourth signal outputs of the first detector and the difference of said values of the imaginary part of the second and fourth signal outputs of the second detector; and

(iii) adding the difference of the value of the imaginary part of second signal output by the first and second detectors and the difference of the values of the imaginary part of fourth signal outputs of the first and second detectors, then calculating the difference of the result of the former two addition.

13. A method for detecting position as claimed in claim 12, further comprising step of converting said plurality of values of real and imaginary parts into digital signals after performing the predetermined add and/or subtract operations.

14. A method of detecting position as claimed in claim 12 wherein the step for calculating said coordinate comprises:

calculating the amplitude L_c by applying an approximate equation L_c =B+A/2, and calculating said coordinates based upon a plurality of L_c values transmitted from said plurality of loop coils adjoining each other, wherein for the absolute values of said values of real and imaginary parts, the larger value, the smaller value, and an amplitude to be calculated respectively are designated A, B and L_c.

15. A method for detecting position as claimed in claim 12, wherein said step for calculating said coordinate comprises:

calculating the phase angle θ

by applying an approximate equation

space="preserve" listing-type="equation">θ

={1.5A/(B+0.5A)}×

K,

wherein for the absolute values of said values of real and imaginary parts, A, B and θ

respectively designated for the larger value, the smaller value and the phase angle to be calculated, and K is a value which expresses an angle equivalent to 45°

.

16. A method for detecting position and calculating coordinate values of a position including the specified position of a position indicator based upon electromagnetic effects between a sensing unit where a large number of loop coils are disposed in parallel with respect to one another in the direction of position detection and the position indicator having at least one coil, wherein said method of detecting position comprises following steps:

calculating the coordinates of said position indicator by signal processing based upon a receiving signal transmitted from said sensing unit;

said signal processing including;

(i) generating a first pair of phase detect signals which are orthogonally related to each other and a second pair of phase detect signals each of which is in an inverted phase relationship with respect to each of the first pair;

(ii) said first pair of phase detect signals including first and second phase detect signal which are different by 90°

from each other and said second pair includes third and fourth phase detect signals which are different by 180°

, respectively, from the first and second phase detect signals;

(iii) switching said four signals;

(iv) performing analog multiplication and integration by applying said four signals to said receiving signal;

(v) outputting two values of real parts and two values of imaginary parts which correspond to any one frequency component of the receiving signal;

(vi) converting said two values into digital signals; and

(vii) performing predetermined subtraction operations to said two values in order to eliminate the value which corresponds to offset included in said two values of real parts and said two values of imaginary parts;

said calculating step of said coordinates including;

calculating the amplitudes and/or phase angles of any one of the frequency components of said receiving signal by using the result of above subtract operations;

wherein said two real and imaginary values respectively comprise;

a) values of the real part which are outputs of the first and third signals, and

b) values of the imaginary part derived from the second and fourth signals;

wherein said predetermined subtraction operations include;

calculating the difference of the values of the real part of the first and third signal outputs and calculating the difference of the values of the imaginary part of the second and fourth signal outputs.

17. A method of detecting position as claimed in claim 16, further comprising a step for converting said two respective values into digital signals after performing the predetermined subtract operations.

18. A method for detecting position and calculating coordinate values of a position including the specified position of a position indicator based upon electromagnetic effects between a sensing unit where a large number of loop coils are disposed in parallel with respect to one another in the direction of position detection and the position indicator having at least one coil, wherein said method of detecting position comprises the following steps:

calculating the coordinates of said position indicator by signal processing upon a receiving signal transmitted from said sensing unit;

said signal processing step including;

(i) generating two phase detect signals 90°

different from each other;

(ii) switching said two phase detect signals;

(iii) performing analog multiplication and integration by applying said two phase detect signals to said receiving signal;

(iv) providing two respective values of real and imaginary parts which correspond to any one of frequency components of said receiving signal;

wherein said two values of real and imaginary parts respectively comprise;

a) values of the real part derived from first and second detectors detecting first signals, and

b) values of the imaginary part derived from the first and second detectors processing second signals;

(v) converting said two respective values into digital signals; and

(vi) performing predetermined addition to said two respective values in order to eliminate gains included in said two respective values;

said predetermined addition including;

calculating the sum of the values of the real part of first signals output by the first and second detectors and calculating the sum of the values of the imaginary part of second signals output by the first and second detectors;

wherein said calculating step of said coordinates includes;

calculating the amplitudes and/or phase angles of any one component of frequency within said receiving signal by using the result of said sum calculations.

19. A method for detecting position as claimed in claim 18, further comprising a step for converting said two respective values into digital signals after performing the predetermined addition.

20. A method for detecting position for calculating coordinate values of a position including the specified position of a position indicator based upon electromagnetic effects between a sensing unit where a large number of loop coils are disposed in parallel with respect to one another in the direction of position detection, and the position indicator having at least one coil, wherein said method for detecting position comprises the following steps:

calculating the coordinates of said position indicator by processing signals based upon a receiving signal transmitted from said sensing unit;

said signal processing step including;

(i) producing four phase detect signals including first and second phase detect signals which are different by 90°

from each other and third and fourth phase detect signals which are different by 180°

, respectively, from the first and second phase detect signals;

(ii) switching said phase detect signals;

(iii) performing analog multiplication and integration by applying said phase detect signals to said receiving signal, and outputting two values of the real part which corresponds to the fundamental frequency component of said receiving signal;

(iv) said two real and imaginary values respectively comprising;

values of the real part which are outputs of a first detector, detecting the first and third signals, and

values of the imaginary part derived from a second detector processing the second and fourth signals;

(v) converting the values into digital signals; and

(vi) performing predetermined subtract operations to said values of said real parts in order to eliminate the value which corresponds to offset included in said two values;

said predetermined subtract operations including;

calculating the difference of the values of the real part of the first and third signals and calculating the difference of the values of the imaginary part of the second and fourth signal outputs; and

wherein said step for calculating said coordinates comprises;

calculating the amplitudes and/or phase angles of any one of the frequency components of said receiving signal by using the result of said subtract operations.

21. A method for detecting position as claimed in claim 20, further comprising step for converting said two values of said real parts into digital signals after performing the predetermined subtract operations.

22. A position detecting device for calculating coordinate values of a specified position of a position indicator relative to a sensing unit, the position detecting device comprising:

signal processing means including a phase detect signal generator for generating four phase detect signals including first and second phase detect signals which are different by 90°

from one another and third and fourth phase detect signals which are different by 180°

, respectively, from the first and second signals, wherein said first and second signals are generated by taking out from non-inverted and inverted outputs from an arithmetic processing amplifier to which a receiving signal from said sensing unit is provided;

an analog signal detect portion for performing multiplication and integration by applying said four phase detect signals to said receiving signal and outputting two values of real and imaginary parts, respectively, which correspond to the component of any one frequency of said receiving signal, said analog signal detect portion including first and second analog phase detectors each containing a multiplier and an integrator, said multipliers being analog multipliers which multiply the receiving signal with the appropriate phase detect signals;

said two real and imaginary values, respectively, including values of the real part which are outputs of the first detector detecting the first and third signals, and values of the imaginary part derived from the second detector processing the second and fourth signals;

means for performing predetermined subtraction operations to said two values of the real part or the two values of the imaginary part in order to eliminate the value which corresponds to offset included in said values, said subtraction operations including calculating the difference of the values of the real part of the first and third signal outputs by the first detector and calculating the difference of the values of the imaginary part of the second and fourth signal outputs by the first detector; and

means for calculating the amplitude and/or phase angles of any one of the frequency components within the receiving signal based upon the result of said predetermined subtraction operations.