Touch sensing display screen signal processing apparatus and method

• US 4,918,262 A
• Filed: 03/14/1989
• Issued: 04/17/1990
• Est. Priority Date: 03/14/1989
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Flowers, Dale R., Rowe, John T. Jr., Vorhees, Kevin H., Goffinet, Kevin P., Miles, Anthony W.
• Primary Examiner(s): SCHREYER, STAFFORD
• Application Number:
  US07/324,778
• Time in Patent Office: 399 Days
• Field of Search: 178/18, 178/19, 340/706, 340/718, 340/720
• US Class Current: 345/173
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/04186 Touch location disambiguation

Abstract

A touch sensing display apparatus having improved electrical signal processing is described. A plurality of signal threshold comparison levels are employed by the electronic signal calculating and processing unit to identify actual touch signals and to exclude extraneous vibration and offset signal components. Static thresholds of comparison are utilized at lower signal levels and a dynamic, signal tracking threshold is utilized at higher signal levels. The apparatus is particularly effective for use in designs employing a suspended CRT display or other display device in which the screen of the display device is directly touched by a user to record selections of information presented or to input graphical or handwritten information.

Claims

1. In a touch sensing display apparatus having a display means, a frame, suspension means supporting said display means in said frame in a manner permitting uniaxial displacement of said display means relative to said frame, a plurality of electrical sensors connected with said suspension means and providing electrical signal outputs in response to displacement of said display means, and an electrical signal processing means connected to receive the electrical signal outputs from said sensors, the improvements comprising:

each of said electrical sensors comprises a plurality of strain sensors electrically connected together in a Wheatstone bridge configuration and supplying electrical signal outputs therefrom; and

differential amplifier means receiving as inputs the output from said Wheatstone bridge and an offset compensation signal, said differential amplifier providing as an output an amplified signal representative of the difference in voltage between its input; and

an analog to digital converter means connected to receive the output of said differential amplifier means, said analog to digital converter means supplying a digital output representative of the signal level received at its input; and

a digital microprocessor connected to receive said digital output representation from said analog to digital converter and for providing digital outputs representing the locus and magnitude of forces imposed on said display means and to provide digital offset compensation signals; and

a digital to analog conversion means connected to said microprocessor to receive said digital offset compensation signals therefrom for conversion into analog offset compensation signals supplied to said differential amplifier means.

2. Apparatus as described in claim 1, wherein:

said digital to analog conversion means comprises a low pass analog filter.

3. Apparatus as described in claim 1, wherein:

groups of said strain sensors are connected to said suspension means at a plurality of locations associated with the dimensions of said display means in orthogonal axes perpendicular to the said axis of uniaxial displacement of said display means; and

the outputs of each group of said groups of strain sensors being connected as separate input signals to said differential amplifier means; and

said differential amplifier means providing separate output signals to said analog to digital converter means corresponding to each of said groups of strain sensors; and

said analog to digital means providing separate digital outputs to said microprocessor means; and

said microprocessor means providing a plurality of separate digital outputs representative of the locus of forces imposed on said display means in said orthogonal axes and of the magnitude of said forces on the axis of uniaxial displacement permitted by said suspension means.

4. Apparatus as described in claim 2, wherein:

groups of said strain sensors are connected to said suspension means at a plurality of locations associated with the dimensions of said display means in orthogonal axes perpendicular to the said axis of uniaxial displacement of said display means; and

the outputs of each group of said groups of strain sensors are connected as separate input signals to said differential amplifier means; and

said differential amplifier means providing separate output signals to said analog to digital converter means corresponding to each of said groups of strain sensors; and

said analog to digital means provides separate digital outputs to said microprocessor means; and

said microprocessor means provides a plurality of separate digital outputs representative of the locus of forces imposed on said display means in said orthogonal axes and of the magnitude of said forces on the axis of uniaxial displacement permitted by said suspension means.

9. Apparatus as described in claim 1 or 2 or 3 or 4 or 5 or 6 or 7 further comprising:

physical orientation sensor means connected to said display means to sense changes in the orientation of said uniaxial axis of said display means and to provide an electrical output signal responsive thereto, said electrical output being connected to said electrical signal processing means.

12. Apparatus as described in claim 9 wherein:

said electrical signal processing means controlling the sensing and forced calibration of said strain sensors.

5. In a touch sensing display apparatus having an electrical signal processing means comprising a digital microprocessor and a display apparatus having a display means, a frame and a suspension means supporting said display apparatus in said frame and permitting uniaxial displacement of said display means relative to said frame and a plurality of electrical sensors providing electrical signal outputs in response to the uniaxial displacement of said display means, the further improvements comprising:

means for forming the sum of forces in said uniaxial axis direction from the outputs of said plurality of sensors; and

means for comparing said sum of forces with a first static threshold value which, if not exceeded, indicates that the sum of forces is an offset signal value to be stored; and

means for comparing said sum of forces with a second static threshold value which, if exceeded by said sum of force values, indicates that an intentional force has been applied to said display means; and

means for comparing said sum of forces with a third static threshold value which, if exceeded by said sum of forces, indicates that a dynamic intentional force has been applied; and

means responsive to said sum of forces exceeding said third threshold value for comparing said sum of forces to a proportion of a recent value of said sum of forces as a dynamic threshold value therefore.

6. Apparatus as described in claim 5 wherein:

said first, second and third threshold values are distinct from one another, have magnitudes arranged in ascending order and are such that said first value is the smallest and said third value is the largest thereof.

7. Apparatus as described in claim 5, wherein:

said microprocessor includes means for repetitively clocking the sampling of input signals to form separate said sums of applied forces for comparison with said threshold values.

8. Apparatus as described in claim 5 or 6 or 7, wherein:

said means for comparison is provided with a plurality of ascending threshold values for comparison against said sum of forces, each threshold, if exceeded, indicating that a quantity or quality of a variable associated with said sum of forces at a given locus on said display means is intended.

10. In a touchsensitive display apparatus having an electrical processing means for analyzing outputs from electrical sensors indicative of touch forces on said display, the improved method of discriminating between actual touch signals and offset or spurious signals, comprising steps of:

storing a first fixed threshold value;

comparing total force signal values with said first fixed threshold value and, if said force value is less than said first fixed threshold value, storing said force value as an offset or spurious signal value;

storing a second fixed threshold value;

comparing the total force signal value with said second fixed threshold value and, if said force value exceeds said second fixed threshold value, identifying said force signal as a touch signal; and

storing a third fixed threshold value;

and comparing the total force signal value with said third fixed threshold value and, if said force value exceeds said third fixed threshold value, calculating a fraction of said force value and storing it as a dynamic threshold value for subsequent comparison against a succeeding force value.

11. The method as described in claim 10, further including a step of:

subtracting said offset value from said total force signal value to yield a corrected force signal for output.