Three- point capacitor trackpoint

• US 6,271,830 B1
• Filed: 09/24/1998
• Issued: 08/07/2001
• Est. Priority Date: 09/24/1998
• Status: Expired due to Term

• Current Assignee: Lenovo PC International Limited (Lenovo Group Ltd.)
• Original Assignee: International Business Machines Corporation
• Inventors: Berstis, Viktors
• Primary Examiner(s): Liang, Regina
• Application Number:
  US09/159,960
• Time in Patent Office: 1,048 Days
• Field of Search: 345/157-161, 345/163, 345/167, 345/173, 341/33, 341/20, 200/6.A
• US Class Current: 345/157
• CPC Class Codes: G06F 2203/0384 Wireless input, i.e. hardware and software details of wireless interface arrangements for pointing devices
• CPC Class Codes: G06F 3/0338 with detection of limited linear or angular displacement of an operating part of the device from a neutral position, e.g. isotonic or isometric joysticks
• CPC Class Codes: G06F 3/038 Control and interface arrangements therefor, e.g. drivers or device-embedded control circuitry

Abstract

A capacitive trackpoint device employs three capacitive sensors rather than four to increase sensitivity while reducing power consumption. Use of capacitive rather than resistive sensors provides a more sensitive and consistent signal with respect to pressure and a greater dynamic range than can be obtained from a resistive or strain gauge sensor, while use of larger area capacitive sensors for a given total area reduces the power requirements for reading the sensors both by having fewer capacitive sensors to read and by reducing the oscillating frequency. Because a more sensitive sensor is utilized, sampling of the signal may be made for a shorter time during periods of inactivity. The overall reduction in power consumption is particularly important for battery operated, hand-held input devices. Use of three sensors rather than four allows sampling of only two in a power-saving mode during periods of inactivity. Normalized force signals measured from the sensing electrodes are translated into displacement-type signals in at least two independent directions through simple trigonometric computations, with the normalized, translated signals being transformed to conventional displacement signals for a pointing device. The reduced power consumption is especially significant for infrared remote control devices of the type employed to control a set-top box, in which battery life is an important consideration.

Claims

1. A method of operating an input device for a data processing system, comprising:

measuring an oscillation frequency for at least two of three variable capacitances within the input device;

translating the oscillation frequency for the at least two variable capacitances into predetermined signals corresponding to displacement in any of at least two independent directions by;

calculating normalized gain signals for three oscillators each including one of the variable capacitances;

calculating a first signal corresponding to displacement along a first axis from a normalized gain signal for an oscillator including a first of the three variable capacitances minus a normalized gain signal for an oscillator including a second of the three variable capacitances; and

calculating a second signal corresponding to displacement along a second axis from a normalized gain signal for an oscillator including the first of the three variable capacitances plus a normalized gain signal for an oscillator including the second of the three variable capacitances minus a normalized gain signal for an oscillator including a third of the variable capacitances; and

transforming the predetermined signals into displacement signals for a cursor within a graphical user interface in the data processing system.

2. The method of claim 1, wherein the step of measuring an oscillation frequency for at least two of three variable capacitances within the input device further comprises:

selecting one of the at least two variable capacitances for a period;

counting oscillations of an oscillator including the selected variable capacitance during the period; and

repeating the selecting and counting steps for each of the remaining variable capacitances.

3. The method of claim 1, wherein the step of translating the oscillation frequency for the at least two variable capacitances into predetermined signals corresponding to displacement in any of at least two independent directions further comprises:

calculating normalized gain signals for at least two oscillators each including one of the variable capacitances; and

calculating signals corresponding to displacement in the at least two independent directions.

4. The method of claim 1, wherein the step of translating the oscillation frequency for the at least two variable capacitances into predetermined signals corresponding to displacement in any of at least two independent directions further comprises:

calculating normalized gain signals for three oscillators each including one of the variable capacitances; and

calculating two signals corresponding to displacement along two independent axes.

5. The method of claim 1, wherein the step of translating the oscillation frequency for the at least two variable capacitances into predetermined signals corresponding to displacement in any of at least two independent directions further comprises:

computing zeroing and scaling parameters.

6. A method of operating an input device for a data processing system, comprising:

measuring an oscillation frequency for at least two of three variable capacitances within the input device;

translating the oscillation frequency for the at least two variable capacitances into predetermined signals corresponding to displacement in any of at least two independent directions by;

calculating normalized gain signals for three oscillators each including one of the variable capacitances;

calculating a first signal corresponding to displacement along a first axis from a normalized gain signal for an oscillator including a first of the three variable capacitances minus a normalized gain signal for an oscillator including a second of the three variable capacitances; and

calculating a second signal corresponding to displacement along a second axis from a normalized gain signal for an oscillator including the first of the three variable capacitances plus a normalized gain signal for an oscillator including the second of the three variable capacitances; and

transforming the predetermined signals into displacement signals for a cursor within a graphical user interface in the data processing system.

7. A computer program product in a computer readable medium, comprising:

instructions for measuring an oscillation frequency for each of three variable capacitances within an input device;

instructions for translating the oscillation frequency for each of three variable capacitances into predetermined signals corresponding to displacement in any of at least two independent directions by;

calculating normalized gain signals for three oscillators each including one of the variable capacitances;

calculating a first signal corresponding to displacement along a first axis from a normalized gain signal for an oscillator including a first of the three variables capacitances minus a normalized gain signal for an oscillator including a second of the three variable capacitances; and

calculating a second signal corresponding to displacement along a second axis from a normalized gain signal for an oscillator including the first of the three variable capacitances plus a normalized gain signal for an oscillator including the second of the three variable capacitances minus a normalized gain signal for an oscillator including a third of the variable capacitances; and

instructions for transforming the predetermined signals into displacement signals for a cursor within a graphical user interface in the data processing system.

8. The computer program product of claim 7, wherein the instructions comprise a input device driver for the input device.

9. The computer program product of claim 7, wherein the instructions are contained in a microcontroller within the input device for a data processing system.

10. The computer program product of claim 7, wherein the instructions form a portion of an operating system for a data processing system.

11. A computer program product in a computer readable medium, comprising:

instructions for measuring an oscillation frequency for at least two of three variable capacitances within the input device;

instructions for translating the oscillation frequency for the at least two variable capacitances into predetermined signals corresponding to displacement in any of at least two independent directions by;

calculating normalized gain signals for three oscillators each including one of the variable capacitances;

calculating a first signal corresponding to displacement along a first axis from a normalized gain signal for an oscillator including a first of the three variables capacitances minus a normalized gain signal for an oscillator including a second of the three variable capacitances; and

calculating a second signal corresponding to displacement along a second axis from a normalized gain for an oscillator including the first of the three variables capacitances plus a normalized gain signal for an oscillator including the second of the three variable capacitances; and

instructions for transforming the predetermined signals into displacement signals for a cursor within a graphical user interface in the processing system.