CA2316067A1 - A multi-touch sensor pad input device - 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 (18)

1. A multi-touch sensor input device for detecting the time, location and magnitude of an applied force and converting these to electrical signals comprising:

a) an array of regularly spaced apart transducers, each transducer having a one-to-one correspondence between applied force to said each transducer and an electrical parameter of said each transducer;

b) a contact pad extending over said array operative to extend an applied force over only a plurality of nearby transducers; and c) a sampling and measuring circuit coupled to said array and operative to alternately connect to each transducer of said array and to detect and measure the time, location of application and the magnitude of the applied force to said each transducer.

2. A device according to claim 1, 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.

3. 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.

4. A device according to claim 3, wherein said pylons have a dome-shaped surface where said each pylon makes contact with said one of said transducers.

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

6. A device according to claim 5, wherein conductance changes monotonically with an increase in applied force.

7. A device according to claim 2, 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.

8. A device according to claim 7, 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.

9. A device according to claim 7, 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.

10. A sensing circuit having an array of transducers for sensing an external applied force 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.

11. A sensing circuit according to claim 10, 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.

12. A sensing circuit according to claim 11, 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.

13. A sensing circuit according to claim 12, 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.

14. A sensing circuit according to claim 12, including a force image processing unit coupled to an output of said analog-to-digital converter operative to receive data from said sampling and measuring circuit and compute the magnitude and location of application of the applied force.

15. A sensing circuit according to claim 14, wherein said force image processing unit stores the output of said analog-to-digital converter in a force image array via dynamic memory allocation.

16. A sensing circuit according to claim 15, including a microprocessor operative to compute the magnitude and location of an applied force from information stored in said force image array.

17. 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) 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.

18. 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.