MOTION PLANE CORRECTION FOR MEMS-BASED INPUT DEVICES

• US 20100042358A1
• Filed: 08/15/2008
• Published: 02/18/2010
• Est. Priority Date: 08/15/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: MOUSSAVI, Farshid
• Granted Patent: US 8,050,886 B2
• Time in Patent Office: Days
• US Class Current: 702/141
• CPC Class Codes: G06F 3/0346 with detection of the device orientation or free movement in a 3D space, e.g. 3D mice, 6-DOF [six degrees of freedom] pointers using gyroscopes, accelerometers or tilt-sensors
• CPC Class Codes: G06F 3/03543 Mice or pucks G06F3/03541 takes precedence
• CPC Class Codes: G06F 3/0383 Signal control means within the pointing device

Abstract

An electronic motion-based input device and method for correcting errors in acceleration due to a deviation from a horizontal plane of motion by correcting for gravitational acceleration components due to the deviation in the plane of motion.

Claims

1. A method for tracking movement of a motion-based electronic input device, the method comprising:

receiving one or more measured acceleration values indicative of the acceleration of an input device moving in plane of motion that is tilted with respect to a horizontal plane;

determining one or more corrected motion values by accounting for the effects of gravity on the measured acceleration values due to the tilted plane of motion; and

calculating a change in position of the input device based on at least one of the one or more corrected motion values.

2. The method of claim 1, wherein determining the one or more corrected motion values further comprises:

calculating one or more acceleration measurement error values based on the an angle of tilt of the tilted plane of motion; and

compensating the measured acceleration values with at least one of the one or more acceleration measurement error values.

3. The method of claim 2, wherein compensating the measured acceleration values comprises subtracting at least one of the one or more acceleration measurement error values from at least one of the measured acceleration values.

4. The method of claim 2, further comprises:

calculating a net acceleration value of the electronic input device based on the following relationship;

a_r′

=√

{square root over (a_x′

²+a_y′

²)}, where a_r′

is the net acceleration, and a_x′ and

a_y′

are acceleration components in the x′ and

y′

dimensions, respectively, of the electronic input device moving the tilted plane of motion.

5. The method of claim 4, wherein calculating the angle of tilt value is based on the following relationship:

$\mathrm{\phi <br><br>}={\cos }^{-1}<br><br>\left(\frac{g^{\mathrm{\prime <br><br>}}}{g}\right),$

where φ

is the angle of tilt, g a measurement of static gravity in the horizontal plane of motion, and g′

is measured value of gravitational acceleration in a dimension normal to the tilted plane of motion.

6. The method of claim 5, wherein the determining the one or more error values further comprises:

calculating a value for a gravity error component, g′

_x, in the x′

dimension based on the following relationship;

$g_x^{\mathrm{\prime <br><br>}}=g*\sin <br><br>\left(\mathrm{\phi <br><br>}\right)*\frac{x^{\mathrm{\prime <br><br>}}}{r^{\mathrm{\prime <br><br>}}};<br><br>\mathrm{and}$

calculating a value for gravity error component, g′

_y, in the y′

dimension based on the following relationship;

$g_y^{\mathrm{\prime <br><br>}}=g*\sin <br><br>\left(\mathrm{\phi <br><br>}\right)*\frac{y^{\mathrm{\prime <br><br>}}}{r^{\mathrm{\prime <br><br>}}}$

7. The method of claim 4, wherein the one or more measured acceleration values comprise a measured acceleration value a_x′

corresponding to the acceleration of the input device in the x′

dimension and a measured acceleration value a_y′

corresponding to the acceleration of the input device in the y′

dimension.

8. The method of claim 7, wherein determining the one or more corrected motion values further comprises:

calculating a corrected tilted plane of motion acceleration value a_xc′

based on a value of a g_x′

gravity error component in the x′

dimension and the measured acceleration value a_x′

; and

calculating a corrected tilted plane of motion acceleration value a_yc′

based on the a value of a g_y′

gravity error component in the y′

dimension and the measured acceleration value a_y′

.

9. The method of claim 8, wherein calculating a change in position of the input device is based on calculating the corrected tilted plane of motion acceleration value a_xc′

and the corrected tilted plane of motion acceleration value a_yc′

.

10. An electronic input device, comprising:

one or more motion sensors operable to generate one or more signals indicative of a measured acceleration of the input device moving in a tilted plane of motion;

a processing element coupled to the one or more motion sensors and operable to;

receive the one or more signals; and

based at least in part on the one or more signals, calculate one or more corrected motion values indicative of the actual motion of the input device; and

an external interface operable to send one or more signals indicative of the corrected motion values to a receiving device.

11. The device of claim 10, wherein the motion sensing element comprises a MEMS-based accelerometer.

12. The device of claim 10, wherein the processing element is further operable to calculate one or more error values corresponding to an effect of gravity on the input device, wherein the processor additionally bases the calculation of the one or more corrected motion values on the one or more error values.

13. The device of claim 10, wherein the processing element is further operable to calculate an angle of tilt of the tilted plane of motion with respect to a horizontal plane.

14. The device of claim 10, wherein the processing element is further operable to calculate an x′

gravity error component and y′

gravity error component and wherein the one or more corrected motion values are additionally based on the x′

gravity error component and the y′

gravity error component.

15. A computer-readable medium for compensating for a tilted plane of motion for a motion-based input device, the program code for:

calculating an angle of tilt of the tilted plane of motion;

estimating an error in a measured acceleration of the electronic input device in the tilted plane of motion due to the angle of tilt; and

determining a corrected acceleration value based at least in part on the estimated error.

16. The computer readable medium of claim 15, wherein estimating the error further comprises estimating a gravitational component of with the measured acceleration.

17. The computer-readable medium of claim 15, further comprising program code for calculating a total acceleration of the electronic input device based on the following relationship:

a_r′

=√

{square root over (a_x′

²+a_y′

²)}, where a_x′ and

a_y′

acceleration values in the x′ and

y′

dimensions of the tilted plane of motion, respectively.

18. The computer-readable medium of claim 15, further comprising program code for calculating the angle of tilt based on the following relationship:

$\mathrm{\phi <br><br>}={\cos }^{-1}<br><br>\left(\frac{g^{\mathrm{\prime <br><br>}}}{g}\right),$

where φ

is the angle of tilt, g is a measured acceleration value for static gravity in a horizontal plane of motion, and g′

is a measured acceleration value along the z′

dimension in the tilted plane of motion.

19. The computer-readable medium of claim 15, further comprising program code for:

calculating a value for a g_x′

gravity error component based on the following relationship;

$g_x^{\mathrm{\prime <br><br>}}=g*\sin <br><br>\left(\mathrm{\phi <br><br>}\right)*\frac{x^{\mathrm{\prime <br><br>}}}{r^{\mathrm{\prime <br><br>}}};<br><br>$

calculating a value for a g′

_y gravity error component based on the following relationship;

$g_y^{\mathrm{\prime <br><br>}}=g*\sin <br><br>\left(\mathrm{\phi <br><br>}\right)*\frac{y^{\mathrm{\prime <br><br>}}}{r^{\mathrm{\prime <br><br>}}},$

where φ

is the angle of tilt, g is a measured acceleration value of gravity in the horizontal plane, a_x′ and

a_y′

are x′ and

y′

dimension acceleration values, respectively, for the input device in moving in the tilted plane of motion, a_r′

is a value for the net acceleration of the input device in the titled plane of motion, and g_x′

and g_y′

are values for gravitational components of acceleration in the x′ and

y′

dimensions, respectively, in the tilted plane of motion.

20. The computer-readable medium of claim 19, wherein determining the corrected acceleration value comprises subtracting the value for the g_x′

gravity error and the value for the g_y′

gravity error from the value for the a_x′

acceleration and the value for the a_y′

acceleration, respectively.

21. The computer-readable medium of claim 16, further comprising program code for determining an estimated position of the input device based at least in part on the corrected acceleration value.