Digitizer for position sensing
First Claim
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1. A method for determining the positional coordinates of a pointer movable relative to a planar pad having spaced conductors arranged along orthogonal axes thereof, said spaced conductors and pointer being energized to produce responses which form a response curve dependent upon the distance between said pointer and said energized spaced conductors, said method comprising the steps of:
- (a) storing information functionally related to the characteristic shape of said response curve;
(b) measuring said responses produced when said pointer is at an unknown positional coordinate relative to said planar pad; and
(c) mathematically fitting said measured responses to a functional expression which represents said characteristics shape of said response curve to determine said positional coordinates of said pointer.
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Accused Products
Abstract
Apparatus and method for determining position, tilt and offset of a pointer with respect to a grid of parallel conductors with which it is coupled by obtaining measured responses between each of a group conductors and the pointer and fitting an expression for the response to said measured responses.
37 Citations
40 Claims
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1. A method for determining the positional coordinates of a pointer movable relative to a planar pad having spaced conductors arranged along orthogonal axes thereof, said spaced conductors and pointer being energized to produce responses which form a response curve dependent upon the distance between said pointer and said energized spaced conductors, said method comprising the steps of:
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(a) storing information functionally related to the characteristic shape of said response curve; (b) measuring said responses produced when said pointer is at an unknown positional coordinate relative to said planar pad; and (c) mathematically fitting said measured responses to a functional expression which represents said characteristics shape of said response curve to determine said positional coordinates of said pointer. - View Dependent Claims (2, 3, 4)
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5. A method for determining the positional coordinates of a pointer movable relative to a planar pad having spaced conductors arranged along orthogonal axes thereof, said spaced conductors and pointer being energized to produce responses which form a response curve dependent upon the distance between said pointer and said energized spaced conductors, said method, for each axis comprising the steps of:
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(a) measuring said responses at a plurality of predetermined positional coordinates to obtain a plurality of calibration values; (b) mathematically fitting said plurality of calibration values to a polynomial to obtain therefrom a plurality of polynomial coefficients for said polynomial which define a polynomial response function representing said characteristic shape of said response curve; (c) measuring responses produced when said pointer is at an unknown positional coordinate relative to said planar pad; and (d) mathematically fitting said measured responses to said polynomial response function to determine therefrom said unknown positional coordinate of said pointer. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12)
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9. The method of claim 8 wherein segments of f(x) and g(x) are approximated by a series of parabolas to represent said characteristic shape of said response curve.
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10. The method of claim 9 wherein said series of parabolas are mathematically fitted to said plurality of calibration values by a least-squares technique to obtain polynomial coefficients thereof which determine said polynomial response function.
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11. The method of claim 8 wherein said measured responses are fitted to said function by a least-squares technique which minimizes the squared differences between said measured response and said function with respect to C1, C2, C3 and C4 to thereby obtain values of C1, C2, C3 and C4, determining therefrom the positional coordinate of said pointer by combining the value of C2 so obtained with a previously determined coordinate of said spaced conductor which is nearest said pointer.
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12. The method of claim 9 wherein said measured responses are fitted to a series of parabolas which approximate different segments of said function by minimizing the squared differences between said measured responses and said series of parabolas with respect to C1, C2, C3 and C4 to obtain values of C1, C2, C3 and C4 , determining therefrom the positional coordinate of said pointer by combining the values of C2 so obtained with a previously determined coordinate of said spaced conductor which is nearest said pointer.
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13. A method for making an initial coarse determination of the position of a pointer relative to a planar pad having spaced conductors arranged along orthogonal axes thereof, said spaced conductors and pointer being energized to produce responses which form a response curve dependent upon the distance between said pointer and said energized spaced conductors, said method, for each axis, comprising the steps of:
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(a) selecting a group of said spaced conductors located at one edge of said grid; (b) measuring the responses for each conductor of said group; (c) mathematically fitting the measured responses to a functional expression of the form
space="preserve" listing-type="equation">Y.sub.i =C.sub.1 f(x.sub.i +C.sub.2)+C.sub.4 g(x.sub.i +C.sub.2 )+C.sub.3which represents the response Yi for a conductor at coordinate xi, where f(x) is an amplitude term having a gain coefficient C1, g(x) is a tilt term having a tilt coefficient C4, C2 is the distance along said planar pad from said pointer to the nearest of said spaced conductors, and C3 represents an offset term, said fitting being performed by a least-squares technique to determine the values of C1, C2, C3 and C4 which fit said measured responses for said group; (d) storing the value of C1 and the location of said group of conductors; (e) successively selecting next groups of conductors each spatially offset from the previously selected group of conductors by one conductor spacing and determining and storing for each of said next groups the value of C1 and the location of said group in accordance with the above steps (b), (c) and (d), for each of said successively selected groups of conductors comparing the value of C1 to the previously stored value of C1, retaining the greater of the two values of C1 and the corresponding location of said group of conductors associated with said greater value until all the conductors along said axis have been so selected to determine therefrom which of said group of conductors corresponds to a maximum value of C1 ; and (f) determining the coordinate of said conductor nearest said pointer from the location of said group of conductors corresponding to said maximum value of C1, which coordinate defines the coarse location of said pointer along each of said axes.
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14. A method for determining the fine position of a pointer movable relative to a planar pad having sets of spaced conductors arranged along orthogonal axes thereof, said fine position being the distance along said planar pad of said pointer from a conductor previously determined to be nearest said pointer, said spaced conductor and pointer being energized to produce responses which form a response curve dependent upon the distance between said pointer and said energized spaced conductors, said method, for each axis, comprising the steps of:
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(a) selecting a group of said spaced conductors including said conductor nearest said pointer; (b) measuring the responses for each conductor of said group; (c) mathematically fitting the measured responses to a function of the form
space="preserve" listing-type="equation">Y.sub.i =C.sub.1 f(x.sub.i +C.sub.2)+C.sub.4 g(x.sub.i +C.sub.2)+C.sub.3which represents the response Yi for a conductor at coordinate xi, where f(x) is an amplitude term having a gain coefficient C1, g(x) is a tilt term having a tilt coefficient C4, C2 is said fine position, and C3 represents an offset term, said fitting being performed by a least-squares technique to determine values of C1, C2, C3 and C4 which fit said measured responses for said group, said value of C2 determined therefrom corresponding to the fine position of said pointer along each of said axes. - View Dependent Claims (15, 16, 17)
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18. An apparatus comprising:
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(a) a planner pad having spaced conductors arranged along orthogonal axes thereof to form a grid; (b) a pointer capable of being moved along said planar pad; (c) energizing means to produce responses dependent upon the distance between said pointer and said energized spaced conductors which form a response curve; and (d) a control system including a microprocessor having means for controlling said energizing means and means for determining the positional coordinates of said pointer along each axis as it is moved relative to said planar pad, by the steps of; (i) storing information functionally related to the characteristic shape of said response curve; (ii) measuring the responses produced when said pointer is at unknown positional coordinate; and (iii) mathematically fitting said measured response to a functional expression which represents said characteristic shape of said response curve to determine therefrom said unknown positional coordinate of said pointer. - View Dependent Claims (19, 20, 21)
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22. An apparatus comprising:
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(a) a planner pad having spaced conductors arranged along orthogonal axes thereof; (b) a pointer capable of being moved relative to said planar pad; (c) energizing means to produce responses which form a response curve dependent upon the distance between said pointer and said spaced conductors; and (d) a control system including a microprocessor having means for controlling said energizing means, and means for determining positional coordinates of said pointer along each axis as it is moved relative to said planar pad by the steps of; (i) measuring said responses at a plurality of predetermined positional coordinates to obtain a plurality of calibration values which are stored therein; (ii) mathematically fitting said plurality of calibration values to a polynomial to obtain therefrom a plurality of polynomial coefficients which are stored therein to define the characteristic shape of said response curve; (iii) measuring said responses corresponding to an unknown positional coordinate of said pointer along said axis; and (iv) mathematically fitting said measured responses to said polynomial to obtain therefrom said positional coordinate of said pointer along said axis. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29)
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26. The apparatus in accordance with claim 25 wherein said microprocessor stores information to represent segments of f(x) and g(x) by parabolas.
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27. The apparatus in accordance with claim 26 wherein said microprocessor stores information to mathematically fit said series of parabolas to said plurality of calibration values by a least-squares technique to obtain said stored polynomial coefficients which represent the characteristic shape of said response curve.
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28. The apparatus in accordance with claim 25 wherein said microprocessor stores information to fit said measured responses to said function by a least-squares technique which minimizes the squared differences between said measured responses and said function with respect to C1, C2, C3 and C4 to obtain values of C1, C2, C3 and C4, determining therefrom the positional coordinate of said pointer by combining the value of C2 so obtained with a previously determined coordinate corresponding to said spaced conductor which is nearest said pointer.
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29. The apparatus in accordance with claim 26 wherein said microprocessor stores information to fit said measured responses to a series of parabolas which approximate different segments of said function by minimizing the squared differences between said measured responses and said series of parabolas with respect to C1, C2, C3 and C4 to obtain values of C1, C2, C3 and C4, determining therefrom the positional coordinate of said pointer by combining the value of C2 so obtained with a previously determined coordinate of said spaced conductor which is nearest said pointer.
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30. An apparatus comprising
(a) a planner pad having spaced conductors arranged along orthogonal axes thereof; -
(b) a pointer capable of being moved relative to said planar pad; (c) energizing means to produce responses which form a response curve dependent upon the distance between said pointer and said spaced conductors; and (d) a control system including a microprocessor having means for controlling said energizing means and means for determining an initial coarse position along each axis when said pointer if first placed onto said planar pad by the steps of; (i) selecting a group of said spaced conductors located at one edge of said grid; (ii) measuring the responses for each conductor of said group; (iii) fitting the measured responses to a function of the form
space="preserve" listing-type="equation">Y.sub.i =C.sub.1 f(x.sub.i +C.sub.2)+C.sub.4 g(x.sub.i +C.sub.2)+C.sub.3representing the response Yi for a conductor at coordinate xi, where f(x) is an amplitude term having a gain coefficient C1, g(x) is a tilt term having a tilt coefficient C4, C2 the distance along said planar pad from said pointer to the nearest of said spaced conductors, and C3 represents an offset term, said fitting being performed by a least-squares technique to determine the values of C1, C2, C3 and C4 which fit said measured responses for said group; (iv) storing the value of C1 and the location of said group of conductors; (v) successively selecting next groups of conductors each spatially offset from the previously selected group of conductors by one conductor spacing and determining and storing for each of said next groups the value of C1 and the location of the group in accordance with the above steps (ii) (iii), and (iv) for each of said successively selected groups of conductors comparing the value of C1 to the previously stored value of C1, retaining the greater of these two values of C1 and the corresponding location of said group of conductors associated with said greater value until all the conductors along said axis have been so selected to determine therefrom which of said group of conductors corresponds to a maximum value of C1 ; (vi) determining the coordinate of said conductor nearest said pointer from the location of said group of conductors corresponding to said maximum value of C1, which coordinate defines the coarse location of said pointer.
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31. An apparatus comprising:
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(a) a planar pad having spaced conductors arranged along orthogonal axes thereof; (b) a pointer capable of being moved along said planar pad; (c) energizing means to produce responses which form a response curve dependent upon the distance between said pointer and said spaced conductors; and (d) a control system including a microprocessor having means for controlling said energizing means and means for determining the distance of said pointer from a conductor previously determined to be nearest said pointer by performing, for each axis, the steps of; (i) selecting a group of said spaced conductors including said conductor nearest said pointer; (ii) measuring the responses for each conductor of said group; (iii) mathematically fitting the measured responses to a function of the form
space="preserve" listing-type="equation">Y.sub.i =C.sub.1 f(x.sub.i +C.sub.2)+C.sub.4 g(x.sub.i +C.sub.2)+C.sub.3which represents the response Yi for a conductor at coordinate xi, where f(x) is an amplitude term for said pointer having a gain coefficient C1, g(x) is a tilt term having a tilt coefficient C4, C2 is the distance from said pointer to said nearest of said spaced conductors and C3 represents an offset term, said fitting being performed by a least-squares technique to determine values of C1, C2, C3 and C4 which fit said measured responses for said group, said value of C2 determined thereby corresponding to the distance of said pointer from said nearest conductor. - View Dependent Claims (32, 33, 34)
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35. A method for determining the tilt angle of a pointer positioned on and movable over a planar pad having spaced conductors arranged along orthogonal axes thereof, said spaced conductors and pointer being energized to produce responses which form a response curve dependent upon the tilt angle and distance between said pointer and said energized spaced conductors, said method comprising the steps of:
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(a) storing information functionally related to the characteristic shape of said response curve; (b) measuring responses produced when said pointer is at an unknown position and tilt angle relative to said planar pad; and (c) mathematically fitting said measured responses to a functional expression which represents said characteristic shape of said response curve to determine therefrom said tilt angle and position of said pointer. - View Dependent Claims (36, 37, 38)
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38. The method in accordance with claim 37, wherein said measured responses are fitted to said functional expression by minimizing the squared differences between said measured responses and said functional expression with respect to C1, C2, C3 and C4, determining thereby a value of C2 which corresponds to said position of said pointer and a value of C4 which corresponds to the tilt angle at said position of said pointer.
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39. A method for determining the positional coordinate and tilt angle of a pointer movable relative to a planar pad having spaced conductors arranged along orthogonal axes thereof, said spaced conductors and pointer being energized to produce responses which form a response curve dependent upon the tilt angle and distance between said pointer and said energized spaced conductors, said method comprising the steps of:
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(a) storing information functionally related to the characteristic shape of said response curve; (b) measuring responses produced when said pointer is at an unknown positional coordinate and tilt angle relative to said planar pad; (c) mathematically fitting said measured responses to a functional expression which includes parameters representing said positional coordinate and tilt angle to determine therefrom values for said parameters.
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40. An apparatus comprising:
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(a) a planar pad having spaced conductors arranged along orthogonal axes thereof; (b) a pointer movable relative to said planar pad; (c) energizing means to produce responses which form a response curve dependent upon the tilt angle and distance between said pointer and said spaced conductors; and (d) a control system including a microprocessor having means for controlling said energizing means, and means for determining said positional coordinate and tilt angle of said pointer, for each axis as it is moved along said planar pad, by the steps of; (i) storing information functionally related to the characteristic shape of said response curve; (ii) measuring responses produced when said pointer is at an unknown positional coordinate and tilt angle relative to said planar pad; (iii) mathematically fitting said measured responses to a functional expression which includes parameters representing said positional coordinate and tilt angle to determine therefrom values for said parameters.
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Specification