CA2355434A1 - Multi-point touch pad - Google Patents

Abstract

This invention relates to an input device for computers and other electronic equipment that can detect the presence, location and force of multiple contacts applied to the active surface of the input device. The invention comprises a multi-touch sensor pad input device that includes an array of regularly spaced apart transducers, a contact pad extending over this array, and a sampling and measuring circuit to detect and measure the time, location of application and magnitude of the applied force to each transducer.

Claims (24)

1. A multi-touch sensor input device for detecting the time, location, magnitude, and width of an applied force and converting these to electrical signals with a sampling and measuring circuit, comprising:
a) an array of spaced apart transducers, each transducer having a one-to-one correspondence between force applied to said each transducer region and an electrical parameter of said each transducer;
b) a flexible pad extending over said array operative to extend said force applied over a plurality of nearby transducers.

2. A device according to claim 1, wherein said sampling and measuring circuit is coupled to said array and is operative to alternately connect to each transducer region of said array and to detect and measure the time, location of application, the magnitude and width of the applied force to said each transducer.

3. A device according to claim 2, including a force image processing unit coupled to said sampling and measuring circuit operative to receive data from said sampling and measuring circuit and compute the magnitude, and location of application of the applied force.

4. A device according to claim 1, wherein the pad includes a semi-rigid layer and an array of pylons affixed to said semi-rigid layer, each pylon aligned with a corresponding one of said transducers.

5. A device according to claim 4, wherein said pylons each makes contact with said one of said transducers.

6. A device according to claim 1, wherein said transducers change conductance in response to changes in applied force.

7. A device according to claim 6, wherein conductance changes monotonically with an increase in applied force.

8. A device according to claim 3, wherein said force image processing unit contains a force-to-conductance approximation function for each of said transducers for converting conductance readings from said sampling and measuring circuit to applied force.

9. A device according to claim 8, wherein said force image processing unit locates local maxima, defines regions around respective local maxima, distributes forces among overlapping ones of said regions in accordance with a squared distance from each maxima, and computes the magnitude of applied force from the sum of forces in said one region, the location of said applied force from the two-dimensional centroid of said forces around said each maxima, and the width of contact of the applied force from the second moments of said forces.

10. A device according to claim 8, wherein said force image processing unit locates local maxima, defines a region around each said maxima, fits a curve of predefined shape to each said maxima, and extracts parameters such as magnitude of force, location of applied force, time and half-width.

11. A multiple-touch sensor device for detecting the time location, magnitude, and width of one or more applied forces when used in conjunction with a sampling and measuring circuit, said sensor device, comprising:
(a) a substrate;
(b) an array of electrically conductive row pads formed on said substrate interconnected in a series of spaced apart rows;
(c) a flexible sheet dimensioned to overlay said array of pads and operative to extend an applied force over a plurality of nearby pads;
(d) an array of electrically conductive column pads deposited on said flexible sheet interconnected in a series of spaced-apart columns;
(e) an array of pressure sensitive polymer pads deposited on said column pads;
(f) an array of spacer material deposited on one of said substrate and said flexible sheet in a position to form a gap between said row pads and corresponding ones of said pressure sensitive polymer pads;
(g) an array of adhesive spots deposited on one of said substrate and flexible film operative to releasably bond said flexible film to said substrate; and (h) means for connecting each of said rows and columns to an external circuit.

12. A sensor device according to claim 11, wherein said substrate is a printed circuit board.

13. A sensor device according to claim 11, wherein said spacer material is a dielectric and is deposited around a periphery of each of said pads of pressure sensitive polymer.

14. A sensor device according to claim 11, wherein said electrically conductive column pads are of conductive polymer.

15. A sensor device according to claim 11, wherein said adhesive is deposited onto said substrate and releasably bonds said flexible film.

16. A sensing circuit having an array of transducers for sensing an external applied force, said transducers interconnected by column traces and row traces, comprising:
a) a column switch in each of said column traces operative when activated to alternately connect each transducer in said column traces to ground;
b) a row switch in each of said row traces operative, when activated, to alternately connect each transducer in said row traces to a sampling circuit; and c) an array control circuit coupled to said column switches and to said row switches operative to activate said column switches and said row switches such that each transducer in said array is alternately connected to ground and to said sampling circuit and wherein said sampling circuit maintains current through said each transducer and also measures output from said each transducer.

17. A sensing circuit. according to claim 16, wherein said row switches connect to an output of a follower circuit whose input is connected to a reference voltage and to an input of an amplifier connected to said reference voltage and having an output connected to an input of an analog-to-digital converter.

18. A sensing circuit according to claim 17, including an analog-to-digital converter coupled to said array amplifier output wherein said array amplifier has a feedback resistor selected so that an input to said analog-to-digital converter produces an output occupying a full range of said analog-to-digital converter output.

19. A sensing circuit according to claim 18, wherein said control circuit is coupled to said analog-to-digital converter and senses completion of a sample so that a next column and row switch can be activated.

20. A sensing circuit, comprising:
(a) a sampling and measuring circuit coupled to a sensor array that provides signals corresponding to time, location and applied force, said sampling and measuring circuit providing a digital output corresponding to said signals;
(a) a force image processing unit coupled to an output of said sampling and measuring circuit operative to receive data from said sampling and measuring circuit and compute the magnitude and location of application of the applied force.

21. A sensing circuit according to claim 20, wherein said force image processing unit stores the output of said analog-to-digital converter in a force image array via dynamic memory allocation.

22. A sensing circuit according to claim 21, including a microprocessor operative to compute the magnitude and location of an applied force from information stored in said force image array.

23. A method of estimating time, location, magnitude, and width of applied forces on a multi-touch sensor input device, comprising:
a) scanning a force image array and marking values which are local maxima;
b) defining neighbourhoods of n-by-n values around each marked value;
c) distributing forces from elements of said force image array to overlapping regions of said neighbourhoods according to squared distance from and value of said local maxima;
d) calculating the two-dimensional moments on said neighbourhoods to estimate time, location and magnitude of said applied forces; and e) storing final vectors representing time, location and magnitude of said applied forces in memory.

24. A method of estimating time, location and magnitude of applied forces on a multi-touch sensor input device, comprising:
a) scanning a force image array and marking values which are local maxima;
b) defining neighbourhoods of n-by-n values around each marked value;

c) performing a non-linear optimization on said neighbourhoods using a characteristic function to estimate time, location and magnitude of said applied forces; and d) storing final vectors representing time, location and magnitude of said applied forces in memory.