High resolution graphic data tablet

• US 3,921,165 A
• Filed: 03/21/1973
• Issued: 11/18/1975
• Est. Priority Date: 03/21/1973
• Status: Expired due to Term

• Current Assignee: Herbert Dym
• Original Assignee: Herbert Dym
• Inventors: Dym, Herbert
• Primary Examiner(s): Miller, Charles D.
• Application Number:
  US05/343,577
• Time in Patent Office: 972 Days
• Field of Search: 178/18,19,20 340/347P,347AD,347NT 33/1M,23J 235/61.6A
• US Class Current: 341/5
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0441 using active external devices, e.g. active pens, for receiving changes in electrical potential transmitted by the digitiser, e.g. tablet driving signals
• CPC Class Codes: H03M 1/52 Input signal integrated with linear return to datum

Abstract

A graphic data tablet of the type which includes at least one voltage divider element from which is developed signals indicative of position points along a coordinate direction. Position points along other coordinate directions are measured using other voltage divider elements. Each voltage divider element is sectionalized to permit the drive potential to be applied across a particular section or across the entire element. Position points are determined by first determining the section within which a position detecting pen is situated and subsequently the position of the pen within the section. Sectionalizing the tablet increases the tablet resolution. By providing overlapping sections, problems associated with nonlinearity at section boundaries are eliminated.

Claims

1. In a position transducing system including a voltage distribution means for producing, in response to a drive voltage, a voltage varying as a function of position along said distribution means, and sensing means for sensing the potential along said distribution means, the improvement comprising;

means for dividing said voltage distribution means into sections, said last-mentioned means comprising a plurality of taps coupled to the ends of said voltage distribution means and at least two other locations along the length of said voltage distribution means, and means for applying said drive voltage across selected sections of said voltage distribution means, said last-mentioned means for applying comprising control logic means producing a section designating signal and decoder means responsive to the section designating signal for activating said section switch means to apply the drive voltage across the pair of taps defining the section designated by the section designating signal, wherein each section of said voltage distribution means includes non-linear regions wherein the produced voltage varying as a function of position is a non-linear function of position, voltage measurements to be made only within the linear region of a section, bounded by what is termed the modified origin and modified full scale points of the section, the actual origin and full scale appliance of a section being bounded by the pair of taps associated therewith, the control logic including means responsive to the position varying voltage, for causing said sensing means to generate a signal representing a zero value of the position varying voltage when the voltage at the modified origin is sensed, wherein said sensing means comprises a dual slope type analog-digital converter, and switch means for applying said position varying voltage to said converter during a sample period and a reference voltage to said converter during a reference period, during which time the voltage stored in the converter during the sample period is decayed, at a rate determined by the value of the reference voltage, the ratio of the position varying voltage to the reference voltage being proportional to the ratio of the time, t, required for the voltage stored in the converter to decay to zero to the sample period T, wherein time t is proportional to the position varying voltage, said control logic including cycle control logic comprising;

a control counter, means for producing a sample period indicating signal indicating a first predetermined count in said control counter, corresponding to said sample period, means for detecting a second predetermined count delta representing an offset count defined as the count required for the voltage stored in the integrator to decay to zero at time T + delta and 2T + delta when the position varying voltage represents the modified origin and the modified full scale points of a section respectively, and means responsive to the delta count detecting means for producing control counter reset signal resetting only those stages of the control counter necessary to store a count corresponding to the time of a sample period T.

2. The transducing system of claim 1 wherein said resetting means comprises first coincidence gate means responsive to said sample period indicatIng means and said delta count detecting means for producing a signal indicating coincidence between a sample period indicating signal and a delta count detection signal, delta latch means, responsive to said coincidence indicating signal, for producing a delta latch set signal and second coincidence gate means, responsive to said delta latch set signal and said coincidence indicating signal for producing said control counter reset signal.

3. The transducing system of claim 1 wherein said cycle control logic further includes means responsive to said reset signal and said sample period indicating means for initiating a clock gate, said sensing means further including zero crossing detector means for ending said clock gate when the position varying voltage stored in said integrator decays to zero.

4. The transducing system of claim 3 wherein said cycle control logic further comprises means for producing an overflow count responsive to said means for producing a sample period indicating signal, for producing a control counter reset signal a predetermined time after time T of a reference period has elapsed.

5. The transducing system of claim 3 further including voltage responsive pen means for applying the position varying voltage to said analog-digital converter means and wherein said control logic further includes section control logic comprising:

an N+n section counter including a number of stages n in excess of the number N required to store a count corresponding to time T, threshold logic means responsive to the distance of the pen means from the voltage distribution means for producing a search mode signal and a sectioned mode signal, means responsive to said search mode signal for applying clock pulses to the N high order stages of the section counter, and means responsive to said sectioned mode signal for applying clock pulses to the N low order stages of the section counter, said section switch means including means responsive to said search mode signal for applying said drive voltage across the entire length of said voltage distribution means.

6. The transducing system of claim 5 wherein said section control logic further includes register means for storing the count in the n high order stages of the section counter, said decoder means being responsive to the count in said register means to cause said section switch means to apply the drive voltage across the section designated by the n high order stages of the section counter, and means responsive to the end of said clock gate for causing the contents of the n high order stages of the section register to be loaded into said register means.

7. The transducing system of claim 6 wherein said section control logic further includes means responsive to said sectioned mode signal for decrementing the count stored in said register means when the count in the low order N stages of the section counter fails to reach a predetermined minimum count during a reference period and for incrementing the count stored in said register means when the count in the low order N stages of the section counter exceeds a predetermined count greater than a count corresponding to time T during a reference period.

8. The transducing system of claim 7 wherein said decrementing means comprises a single shot multivibrator responsive to the initiation of a clock gate, a decrementing flip-flop, the set input thereof being coupled to said single shot, means for resetting said flip-flop when the count in the low order N stages of the section counter exceeds said predetermined minimum count and decrementing coincidence gate means responsive to said sectioned mode signal, the end of said clock gate and said flip-flop for producing a decrement signal when the flip-flop is not reset at the end of the clock gate during the sectioned mode of operation, and said incrementing means comprises an incrementing flip-flop coupled to the N th stage of the low order N stageS of the section counter, and incrementing coincidence gate means coupled to said incrementing flip-flop producing an incrementing signal, when after said incrementing flip-flop detects a count of N in the lower order N stages of the section counter, said predetermined count is detected during the sectioned mode of operation.

9. The transducing system of claim 8 wherein said section switch means comprises a plurality of electronic switch means equal to the number of sections the voltage distribution means is divided into and is responsive to section indicating signals produced by said decoder means for selectively connecting the drive voltage to a selected section, a further electronic switch means responsive to said search mode signal for applying said drive voltage across the entire voltage distribution means and offset voltage compensating means, operable when the drive voltage is applied across the entire length of the voltage distribution means for causing the count in said section counter to store the same count for a common point on said voltage distribution means when operating in either the search mode or the sectioned mode.

10. A position transducing system comprising:

a. a voltage distribution means having end taps and intermediate taps defining adjacent sectional parts of distribution means for producing, in response to a voltage applied to any pair of said taps, a distributed voltage which varies between said pair of taps as a function of position between said pair of taps, b. reference voltage producing means, c. sensor means movable in the vicinity of said voltage distribution means for sensing said distributed voltage most nearly adjacent the instantaneous position of said sensor means, d. mode control means for providing first and second mode control signals designating first and second mode operation, respectively, e. means responsive to said first mode control signal for applying said reference voltage between said end taps, f. section storage means for storing a value therein, g. means responsive to said first mode control signal and to said sensor means for deriving a value representative of the said section of said voltage distribution means which is most nearly adjacent the instantaneous position of said sensor means and for entering said value into said section storage means, and h. means responsive to said second mode control signal and to said section storage means for applying said reference voltage between the pair of said taps which define the said section designated by the value stored in said section storage means.

11. A position transducer as claimed in claim 10 further comprising means responsive to said second mode control signal and to said sensor for deriving a value representative of the position in said section to which said sensor is most nearly adjacent.

12. A position transducer as claimed in claim 11 further comprising means responsive to said second mode control signal and to the movement of said sensor between sections for altering the value stored in said section storage means to accurately represent the section said sensor is most nearly adjacent to during the existence of said second mode control signal.

13. A position transducer as claimed in claim 12 wherein the taps are positioned on said voltage distribution means so that there is a slight overlap between adjacent sections.