INTERPOLATION OF POSITION OF A STYLUS IN A TOUCH SENSOR

• US 20130278550A1
• Filed: 03/12/2013
• Published: 10/24/2013
• Est. Priority Date: 04/20/2012
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Westhues, Jonathan
• Granted Patent: US 9,218,071 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06F 3/03545 Pens or stylus
• CPC Class Codes: G06F 3/0383 Signal control means within the pointing device
• CPC Class Codes: G06F 3/0386 for light pen
• CPC Class Codes: G06F 3/0442 using active external devices, e.g. active pens, for transmitting changes in electrical potential to be received by the digitiser
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

Systems and methods for determining interpolation functions for a stylus position on a sensor matrix and estimating such a position are provided. In one disclosed embodiment, a test apparatus comprises a stylus configured to be positioned on a sensor matrix at each location of a set of known locations. One or more processors are configured to access the touch sensor data corresponding to the set of known locations, where the data is produced in response to positioning the stylus on the sensor matrix at the set of known locations. Stylus location data reflecting the set of known locations is accessed. A stylus position interpolation function is then determined by curve fitting based on the touch sensor data corresponding to the set of known locations and the stylus location data reflecting the set of known locations.

Claims

1. A system for determining an interpolation function for a stylus position on a sensor matrix, the sensor matrix including a first array of conductors and a second array of conductors, the sensor matrix configured to sense a stylus in physical proximity to the sensor matrix and to provide touch sensor data for estimating a location of the stylus on the sensor matrix, the system comprising:

a test apparatus comprising the stylus that is configured to be positioned on the sensor matrix to enable the stylus to be automatically positioned at each location of a set of known locations on the sensor matrix; and

one or more processors configured to;

access the touch sensor data corresponding to the set of known locations on the sensor matrix, the touch sensor data produced in response to the test apparatus positioning the stylus on the sensor matrix at the set of known locations;

access stylus location data reflecting the set of known locations; and

determine a stylus position interpolation function by curve fitting based on the touch sensor data corresponding to the set of known locations and the stylus location data reflecting the set of known locations.

2. The system of claim 1, wherein the one or more processors are further configured to evaluate the stylus position interpolation function to produce a reported position of the stylus.

3. The system of claim 1, wherein the touch sensor data comprises measured capacitance data including a maximum observed capacitance, and the one or more processors are further configured to determine the stylus position interpolation function by normalizing the maximum observed capacitance to 1.

4. The system of claim 1, wherein the stylus position interpolation function is a first stylus position interpolation function that is determined for a first axis of the sensor matrix, and the one or more processors are further configured to determine a second stylus position interpolation function for a second axis of the sensor matrix.

5. The system of claim 1, wherein the one or more processors are further configured to:

determine multiple different stylus position interpolation functions for each axis of the sensor matrix to produce multiple different estimates of a position of the stylus along each axis of the sensor matrix; and

combine the multiple different estimates to provide an estimate of a true position of the stylus along each axis of the sensor matrix.

6. The system of claim 1, wherein the stylus position interpolation function does not include a static offset that is dependent upon an angle of the stylus with respect to the sensor matrix.

7. The system of claim 1, wherein the stylus position interpolation function includes a static offset that is dependent upon an angle of the stylus with respect to the sensor matrix.

8. The system of claim 1, wherein the one or more processors are further configured to determine the stylus position interpolation function by adding one or more differential nonlinearity penalties to minimize a quantity proportional to a non-smoothness of the function.

9. The system of claim 1, wherein the one or more processors are further configured to determine the stylus position interpolation function by adding one or more penalties that seek to minimize a sum of squares of partial derivatives of the function with respect to each input variable at each measured point, to thereby decrease noise sensitivity of the function.

10. A method for determining an interpolation function for a stylus position on a sensor matrix, the method comprising:

accessing touch sensor data corresponding to a set of known locations on a sensor matrix, the touch sensor data produced in response to positioning a stylus on the sensor matrix at a known orientation at each location of the set of known locations;

accessing stylus location data reflecting the set of known locations;

accessing stylus angular orientation data reflecting corresponding known angular orientations of the stylus at the known locations; and

determining a stylus position interpolation function by curve fitting based on the touch sensor data corresponding to the set of known locations, the stylus location data reflecting the set of known locations, and the stylus angular orientation data reflecting the corresponding known angular orientations of the stylus at the known locations.

11. The method of claim 10, further comprising evaluating the stylus position interpolation function to produce a reported position of the stylus.

12. The system of claim 10, wherein determining the stylus position interpolation function further comprises adding one or more differential nonlinearity penalties to minimize a quantity proportional to a non-smoothness of the function.

13. The system of claim 10, wherein determining the stylus position interpolation function further comprises adding one or more penalties that seek to minimize a sum of squares of partial derivatives of the function with respect to each input variable at each measured point, to thereby decrease noise sensitivity of the function.

14. The method of claim 10, wherein the stylus position interpolation function is a first stylus position interpolation function that is determined for a first axis of the sensor matrix, and further comprising determining a second stylus position interpolation function for a second axis of the sensor matrix.

15. A method for estimating a position of a stylus on a sensor matrix of a touch-sensitive system using a plurality of stylus position interpolation functions, the method comprising:

accessing touch sensor data produced by a sensor matrix of the touch-sensitive system in response to the stylus engaging the sensor matrix at a first location;

accessing a first stylus position interpolation function;

calculating a first estimate of the first location by evaluating the first interpolation function using at least a first portion of the accessed touch sensor data;

accessing a second stylus position interpolation function that is different from the first stylus position interpolation function;

calculating a second estimate of the first location by evaluating the second interpolation function using at least a second portion of the accessed touch sensor data;

calculating an improved estimate of the first location by mathematically combining the first estimate and the second estimate; and

storing the improved estimate in a data store.

16. The method of claim 15, wherein calculating the first estimate further comprises calculating the first estimate for a current sensor frame, calculating the second estimate further comprises calculating a plurality of second estimates corresponding to a plurality of sensor frames within a window of time, and calculating the improved estimate further comprises mathematically combining the first estimate with an average of the plurality of second estimates.

17. The method of claim 15, wherein:

calculating the first estimate further comprises calculating the first estimate for a current sensor frame, calculating a plurality of other first estimates corresponding to a first plurality of sensor frames within a first window of time, and combining the first estimate with an average of the other first estimates to yield a combined first estimate;

calculating the second estimate further comprises calculating a plurality of second estimates corresponding to a second plurality of sensor frames within a second window of time; and

calculating the improved estimate further comprises mathematically combining the combined first estimate with an average of the plurality of second estimates.

18. The method of claim 15, further comprising:

calculating an estimated static offset; and

adjusting the first estimate by the estimated static offset.

19. The method of claim 15, wherein the second portion and the first portion are a same portion.

20. The method of claim 15, further comprising:

providing a stylus comprising an electrode split into a plurality of pieces;

accessing a stylus angle interpolation function;

calculating an estimate of a stylus angle by evaluating the stylus angle interpolation function using at least a third portion of the accessed touch sensor data; and

utilizing the estimate of the stylus angle in calculating one or more of the first estimate and the second estimate.