Sensor fusion

• US 8,289,115 B2
• Filed: 02/28/2011
• Issued: 10/16/2012
• Est. Priority Date: 09/17/2010
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Cretella, Michael A. Jr., Huang, Ronald Keryuan, Moore, Christopher, Mullens, Christopher T., Duggineni, Venu Madhav, Eng, Michael Man-Cheung
• Primary Examiner(s): MUSLEH, MOHAMAD A
• Application Number:
  US13/037,271
• Publication Number:
  US 20120072167A1
• Time in Patent Office: 596 Days
• Field of Search: 335/219, 335/285, 335302-306, 335205-207, 439/38, 439/218, 439/217, 439/39, 243/03, 361/807, 361/679.01, 361/600, 206/45.2, 206/45.23, 206/45.24, 206/305, 206/320, 206/764, 206/765
• US Class Current: 335/219
• CPC Class Codes: G05B 15/02 electric
• CPC Class Codes: G06F 1/1626 with a single-body enclosure integrating a flat display, e.g. Personal Digital Assistants [PDAs]
• CPC Class Codes: G06F 1/1677 for detecting open or closed state or particular intermediate positions assumed by movable parts of the enclosure, e.g. detection of display lid position with respect to main body in a laptop, detection of opening of the cover of battery compartment
• CPC Class Codes: G06F 2200/1633 Protecting arrangement for the entire housing of the computer
• CPC Class Codes: G06F 2200/1634 Integrated protective display lid, e.g. for touch-sensitive display in handheld computer
• CPC Class Codes: G06F 9/00 Arrangements for program control, e.g. control units program control for peripheral devices G06F13/10
• CPC Class Codes: Y10T 24/32 having magnetic fastener

Abstract

Accurate and reliable techniques for determining a current status of an accessory device in relation to an electronic device are described.

Claims

1. A method of continuously monitoring by a tablet device pivotally attached to a cover, a pivot angle of the cover in relation to the tablet device, the cover comprising a magnet, the tablet device comprising a processor coupled to which is a display having a top protective layer, a magnetic sensor configured to detect a magnetic field from the magnet through the top protective layer, and an inertial system configured to determine a spatial orientation of the tablet with respect to an inertial reference frame, in a closed configuration the pivot angle is 0 radians and the magnetic sensor is substantially co-planar with the magnet and separated by a first distance R₀ and detects a first magnetic field value propagating through the top protective layer from the magnet, and in an open configuration, the pivot angle is it radians and the magnetic sensor is substantially coplanar with the sensor and separated by a second distance R₁, and detects a second magnetic field value propagating from the magnet, the second distance R₁ being greater than first distance R₀, the method comprising:

sensing a current magnetic field value from the magnet by the magnetic sensor;

determining a relative magnetic field value by comparing the current magnetic field value to the first and second magnetic field values;

determining a current spatial orientation of the tablet device with respect to the inertial reference frame by the inertial system;

adjusting the relative magnetic field value in accordance with the current spatial orientation; and

providing a current pivot angle in accordance with the adjusted relative magnetic field value.

2. The method as recited in claim 1, wherein the magnetic sensor is a magnetometer.

3. The method as recited in claim 2, the cover further comprising a first magnetic attachment unit.

4. The method as recited in claim 3, the tablet device further comprising a second magnetic attachment unit, the first and second magnetic attachment units configured to generate a mutual magnetic attachment force of sufficient strength to pivotally attach the tablet device and the cover.

5. The method as recited in claim 4, wherein the magnetometer detects a magnetic offset value in accordance with the mutual magnetic attachment force.

6. The method as recited in claim 5, wherein the processor determines that the cover and the tablet device are magnetically attached to each other when the processor receives an indication that the magnetometer has detected the magnetic offset value.

7. The method as recited in claim 2, wherein the magnetometer is a compass.

8. The method as recited in claim 7, further comprising compensating for a moving cover magnetic offset at the compass induced by the magnet as the cover moves.

9. The method as recited in claim 8, wherein the compensating for the moving cover magnetic offset comprises:

determining a horizontal component of an external magnetic field; and

using the horizontal component to estimate a maximum change in a magnetic compass heading induced by the relative change in position of the cover in relation to the tablet device.

10. The method as recited in claim 1, wherein the inertial system is an accelerometer coupled to the processor.

11. The method as recited in claim 1, wherein the inertial system is a gyroscope coupled to the processor.

12. The method as recited in claim 1, wherein the inertial system comprises an accelerometer and a gyroscope each coupled to the processor.