Capacitive position sensor

• US 20050052429A1
• Filed: 08/12/2004
• Published: 03/10/2005
• Est. Priority Date: 08/21/2003
• Status: Active Grant

• Current Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Original Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Inventors: Philipp, Harald
• Granted Patent: US 8,217,915 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G06F 2203/0339 Touch strips, e.g. orthogonal touch strips to control cursor movement or scrolling; single touch strip to adjust parameter or to implement a row of soft keys
• CPC Class Codes: G06F 3/03547 Touch pads, in which fingers can move on a surface
• CPC Class Codes: G06F 3/0362 with detection of 1D translations or rotations of an operating part of the device, e.g. scroll wheels, sliders, knobs, rollers or belts
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2217/94073 with capacitive detection
• CPC Class Codes: H03K 2217/96066 Thumbwheel, potentiometer, scrollbar or slider simulation by touch switch

Abstract

A capacitive position sensor for detecting the position of an object, typically an operator'"'"'s finger, relative to a resistive sensing element, wherein the sensing element comprises a sensing path that has terminals connected along it that subdivide the sensing path into multiple sections. Each terminal is coupled to its own sensing channel, each of which generates a signal that is sensitive to the capacitance between its terminal and a system ground. The signals are fed to a processor for analysis. The processor determines over which section the object is positioned by comparing the signals from the sensing channels, and determines the position of the object within that section by comparing the signals from the terminals spanning that section. In this way, the sensing path can be formed in a closed loop, such as a circle for a scroll dial, in which the operator'"'"'s finger position and movement can be uniquely determined in a straightforward manner.

Claims

1. A capacitive position sensor for detecting a position of an object comprising:

(a) a sensing element comprising a sensing path;

(b) a plurality of at least three terminals connected to the sensing element at different locations along the sensing path to subdivide it into a plurality of sections;

(c) a plurality of sensing channels connected to respective ones of the terminals, wherein each sensing channel is operable to generate a signal indicative of capacitance between its terminal and a system ground; and

(d) a processor operable to determine over which section the object is positioned by comparing the signals from the sensing channels, and to determine the position of the object within that section by comparing at least the signals from the terminals spanning that section.

2. A capacitive position sensor according to claim 1, wherein the sensing path forms a closed loop.

3. A capacitive position sensor according to claim 1, wherein the sensing path forms a U-shape.

4. A capacitive position sensor according to claim 1, wherein the sensing path is formed by a single resistor.

5. A capacitive position sensor according to claim 1, wherein the sensing path is formed by a plurality of resistors.

6. A capacitive position sensor according to claim 5, wherein the plurality of resistors are alternately connected in series with a plurality of conducting sense plates.

7. A capacitive position sensor according to claim 1, wherein the sensing path has a substantially constant resistance per unit length.

8. A capacitive position sensor according to claim 1, wherein the sensing path comprises a plurality of at least three tapering strips of conductive material extending adjacent to each other with a gap therebetween and connected to respective ones of the terminals.

9. A capacitive position sensor according to claim 1, wherein each of the sensing channels comprises a sampling capacitor connected in series between its terminal and the system ground such that in use each sampling capacitor is supplied with an amount of charge which depends on the capacitance between its terminal and the system ground.

10. A capacitive position sensor according to claim 1, wherein the processor is operable to determine over which section the object is positioned by comparing magnitude of the signals.

11. A capacitive position sensor according claim 1, wherein the processor is operable to determine the position of the object within the determined section by a ratiometric analysis of signals taken from the terminals spanning the determined section.

12. A capacitive position sensor according claim 11, wherein the processor is operable to subtract a signal taken from a further terminal from each of the signals taken from the terminals spanning the determined section prior to performing the ratiometric analysis.

13. A capacitive position sensor according to claim 1, wherein the processor is operable to provide a position output signal

14. A capacitive position sensor according to claim 13, wherein the position output signal is provided conditional on the signals from the sensing channels exceeding a threshold.

15. A capacitive position sensor according to claim 1, wherein the processor is operable to provide a status output signal indicative of whether the signals exceed a threshold.

16. A capacitive position sensor according to claim 1, wherein the processor is operable to repeatedly determine position of the object and provide a motion output signal indicative of how the object has moved over the sensing element.

17. A capacitive position sensor according to claim 1, further comprising a wiper that is arranged adjacent to the sensing element, wherein the wiper can be manually actuated to move relative to the sensing path so as to constitute the object to be detected.

18. A control panel incorporating a capacitive position sensor for detecting a position of an object comprising:

(a) a sensing element comprising a sensing path;

(b) a plurality of at least three terminals connected to the sensing element at different locations along the sensing path to subdivide it into a plurality of sections;

(c) a plurality of sensing channels connected to respective ones of the terminals, wherein each sensing channel is operable to generate a signal indicative of capacitance between its terminal and a system ground; and

(d) a processor operable to determine over which section the object is positioned by comparing the signals from the sensing channels, and to determine the position of the object within that section by comparing at least the signals from the terminals spanning that section.

19. An apparatus having a control panel incorporating a capacitive position sensor for detecting a position of an object comprising:

(a) a sensing element comprising a sensing path;

(b) a plurality of at least three terminals connected to the sensing element at different locations along the sensing path to subdivide it into a plurality of sections;

(c) a plurality of sensing channels connected to respective ones of the terminals, wherein each sensing channel is operable to generate a signal indicative of capacitance between its terminal and a system ground; and

(d) a processor operable to determine over which section the object is positioned by comparing the signals from the sensing channels, and to determine the position of the object within that section by comparing at least the signals from the terminals spanning that section.