POSITION SENSING DEVICE AND METHOD USING SELF-CAPACITANCE

• US 20150268790A1
• Filed: 03/20/2015
• Published: 09/24/2015
• Est. Priority Date: 03/21/2014
• Status: Active Grant

• Current Assignee: Melius SA
• Original Assignee: Advanced Sensor Technology Limited
• Inventors: Meyer, Hans U.
• Granted Patent: US 9,939,932 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01D 5/2415 adapted for encoders
• 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: H03K 17/955 using a capacitive detector

Abstract

A capacitive position sensing system has a pickup electrode, a shield electrode partially enclosing the pickup electrode, and an essentially grounded relatively movable target near the pickup electrodes; a capacitance-to-digital converter, and switching means for connecting each electrode in turn to the converter input or to ground. A capacitive position sensing method in the system includes measuring a first capacitance C1 of at least one pickup electrode set with the shield electrode set grounded, measuring a second capacitance C2 of at least one shield electrode set with the pickup electrode set grounded, and measuring a third capacitance C3 of the pickup electrode set and the shield electrode set connected together; and calculating a first result indicating a position of a target using the first capacitance C1, the second capacitance C2 and the third capacitance C3.

Claims

1. A capacitive position sensing method in a measurement system having a pickup electrode set, one shield electrode set;

and an essentially grounded relatively movable target near the pickup electrodes, the method comprising

measuring a first capacitance C1 of at least one pickup electrode set with the shield electrode set grounded,

measuring a second capacitance C2 of at least one shield electrode set with the pickup electrode set grounded, and

measuring a third capacitance C3 of the pickup electrode set and the shield electrode set connected together; and

calculating a first result indicating a position of a target using the first capacitance C1, the second capacitance C2 and the third capacitance C3.

2. The capacitive position sensing method of claim 1 wherein the pickup electrode set comprises a pickup electrode or a plurality of pickup electrodes connected together, and the shield electrode set comprises a shield electrode with the pickup electrodes connected to the shield electrode.

3. The capacitive position sensing method of claim 1 wherein calculating the first result comprises subtracting the second capacitance C2 from the first capacitance C1 to obtain an intermediate result and adding the intermediate result and the third capacitance C3 (C1−

C2+C3).

4. The capacitive position sensing method of claim 1 further including calculating a second result indicating a degree of contamination comprises adding the second capacitance C2 to the first capacitance C1 to obtain an second intermediate result and subtracting the third capacitance C3 fro the second intermediate result (C1+C2−

C3).

5. The capacitive position sensing method of claim 1 wherein a linear or curvilinear pickup electrode array defines a track along which a target in the shape of a screen is movable at an essentially constant gap.

6. The capacitive position sensing method of claim 1 wherein the first result is calculated for the pickup electrode set.

7. The capacitive position sensing device of claim 4 wherein the second result is calculated from the pickup electrode set.

8. The capacitive position sensing method of claim 1 further comprising using an incremental position sensing device scale as a target, thereby enabling an absolute position determination over a range larger than the incremental sensor'"'"'s pitch.

9. A capacitive position sensing system including

a pickup electrode,

a shield electrode partially enclosing the pickup electrode, and

an essentially grounded relatively movable target near the pickup electrodes;

a capacitance-to-digital converter, and

switching means for connecting each electrode in turn to the converter input or to ground.

10. The capacitive position sensing system of claim 9 further comprising a linear or curvilinear pickup electrode array defining a track along which a target in the shape of a screen is movable at an essentially constant gap.

11. The capacitive position sensing system of claim 10 further comprising an incremental position sensing device scale, the incremental position sensing device scale defining a target thereby enabling an absolute position determination over a range larger than the incremental sensor'"'"'s pitch.

12. The capacitive position sensing system of claim 11, wherein the incremental position sensing device is capacitive or inductive.

13. The capacitive position sensing system of claim 9, wherein the pickup electrode array faces an edge of the incremental position sensing device scale.

14. The capacitive position sensing system of claim 9, wherein a common printed circuit board is shared with the incremental position sensing device.