APPARATUS AND METHOD OF CAPACITIVELY SENSING OPERATOR PRESENCE FOR A STUMP CUTTER

• US 20090079444A1
• Filed: 07/29/2008
• Published: 03/26/2009
• Est. Priority Date: 07/31/2007
• Status: Active Grant

• Current Assignee: Vermeer Manufacturing Company
• Original Assignee: Vermeer Manufacturing Company
• Inventors: Khapochkin, Yuriy, Kelpe, Hans
• Granted Patent: US 7,999,562 B2
• Time in Patent Office: Days
• US Class Current: 324/688
• CPC Class Codes: H03K 17/962 Capacitive touch switches

Abstract

An operator detection and presence device includes a conductive sensor and a guard electrode. The sensor and electrode are physically located and electrically connected in a manner which helps the detection circuit measure if an operator'"'"'s hand is on the handle or if the change in capacitance is due to water. The sensor and electrode are preferably physically located in the handle spaced apart from one another, where the sensor is located in an area that the operator will touch. The electrode is located in an area that the operator will not generally touch. A detection circuit is connected to the sensor and electrode for measuring whether the capacitance of the sensor has changed. The electrode is used to avoid false detections and/or the ability to detect of operator presence.

Claims

1. A capacitive operator presence detector for an operator control handle, comprising:

(a) a capacitive sensor mounted in the handle, the capacitive sensor arranged and configured to form a capacitor when the handle is touched by an operator;

(b) a guard electrode mounted in the handle, the guard electrode arranged and configured to substantially isolate the capacitive sensor from ground when it is not touched by an operator; and

(c) an operator presence circuit connected to the capacitive sensor and the guard electrode, the circuit having a node where changes in capacitance of the capacitive sensor can be measured as a change in voltage and where the change in voltage is provided to the guard electrode, whereby the voltage at the guard electrode is equal to the voltage at the capacitive sensor and any changes in capacitance due to water on the handle forming capacitance to ground are reduced.

2. The capacitive operator presence detector of claim 1, wherein the capacitive sensor is located on a top portion of the handle.

3. The capacitive operator presence detector of claim 2, wherein the guard electrode is located on a lower portion of the handle.

4. The capacitive operator presence detector of claim 1, wherein the handle is covered by a protective coating.

5. The capacitive operator presence detector of claim 1, wherein the capacitive sensor and the guard electrode are connected to a frequency generator.

6. The capacitive operator presence detector of claim 1, wherein an initial voltage is read and stored to provide a baseline capacitance and a predetermined sensitivity cutoff is established for determining whether a measured voltage is interpreted as operator presence.

7. The capacitive operator presence detector of claim 1, wherein a shielded wire is used to connect the capacitive sensor and the guard electrode to the operator presence circuit.

8. The capacitive operator presence detector of claim 1, wherein the capacitive sensor and the guard electrode include portions that are generally ring shaped and extend proximate a surface of the handle.

9. The capacitive operator presence detector of claim 1, wherein the handle has a longitudinal axis, the capacitive sensor is located in a first portion of the handle, and the guard electrode is physically located inside of the capacitive sensor and in a second portion of the handle where at least a part of the second portion is offset from the first portion.

10. The capacitive operator presence detector of claim 1, wherein the detector is located on a stump cutter.

11. A method of detecting the presence of an operator touching a hydraulic control handle of a stump cutter, comprising:

(a) generating an electrical signal;

(b) connecting a capacitive sensor mounted in the handle to the electrical signal, the capacitive sensor forming a capacitor when the handle is touched by an operator;

(c) connecting a guard electrode mounted in the handle to the electrical signal, the guard electrode substantially isolating the capacitive sensor from ground when it is not touched by an operator; and

(c) connecting the capacitive sensor and the guard electrode to a detection circuit, the detection circuit having a node where changes in capacitance of the capacitive sensor can be measured as a change in voltage and where the change in voltage is provided to the guard electrode, whereby the voltage at the guard electrode is equal to the voltage at the capacitive sensor and any changes in capacitance due to water on the handle forming capacitance to ground are reduced.

12. The method of claim 11, wherein the electrical signal is a sine wave.