Detection systems for power equipment

• US 20100023137A1
• Filed: 05/18/2009
• Published: 01/28/2010
• Est. Priority Date: 12/31/2003
• Status: Active Grant

• Current Assignee: Sawstop Holding LLC
• Original Assignee: SD3, LLC
• Inventors: Gass, Stephen F.
• Granted Patent: US 7,991,503 B2
• Time in Patent Office: Days
• US Class Current: 700/21
• CPC Class Codes: B23D 59/001 Measuring or control devices, e.g. for automatic control of work feed pressure on band saw blade measuring in general G01; controlling in general G05
• CPC Class Codes: F16P 3/12 with means, e.g. feelers, which in case of the presence of a body part of a person in or near the danger zone influence the control or operation of the machine F16P3/08 takes precedence
• CPC Class Codes: Y10T 83/081 With randomly actuated stopping means
• CPC Class Codes: Y10T 83/089 Responsive to tool characteristic
• CPC Class Codes: Y10T 83/091 Responsive to work sensing means
• CPC Class Codes: Y10T 83/178 Responsive to work
• CPC Class Codes: Y10T 83/7726 By movement of the tool
• CPC Class Codes: Y10T 83/773 Work-support includes passageway for tool [e.g., slotted table]

Abstract

Improved methods to detect when a human body contacts a predetermined portion of a machine are disclosed. The methods distinguish contact with a person from contact with other materials. The methods are particularly applicable in woodworking equipment such as table saws to distinguish contact between a person and the blade of the saw from contact between the blade and wet or green wood.

Claims

1. A method of reducing the chance of a false detection of a dangerous condition in a system designed to detect a dangerous condition between a user and a dangerous element of a machine comprising:

providing a system configured to detect a dangerous condition between a user and a dangerous element of a machine, wherein the detection is based on the response of at least one detection scheme that has a response level that crosses a first threshold level when a dangerous condition is present, and wherein some events other than a dangerous condition can cause a response level in the detection scheme spanning the first threshold level for a dangerous condition, whereby such other events may cause the detection system to falsely detect a dangerous condition when no such dangerous condition is present;

providing a response-system configured to react to the detection of a dangerous condition, where the reaction involves emergency activation of a danger mitigation device outside the scope of the normal operation of the machine other than when a dangerous condition is detected;

monitoring the response level while operating the machine; and

stopping the machine without emergency activation of the danger mitigation device if the monitored response level crosses a second threshold that lies between a nominal response level of the detection system when no dangerous condition or other response level affecting events are present and the first threshold level.

2. The method of claim 1, where in the response level changes in response to the dangerous condition on a first time scale and the step of monitoring the response level measures the characteristic level of the response over a time scale longer than the first time scale.

3. A method for detecting contact between a user and a cutter on a piece of woodworking equipment, comprising:

applying an electrical signal to the blade;

integrating a property of the electrical signal applied to the blade, where the property is related to the electrical impedance of the blade.

4. The method of claim 3, wherein the integration is done with an analog circuit.

5. The method of claim 4, wherein the integration is carried out over discrete time intervals.

6. The method of claim 3, wherein the property is digitized prior to the step of integrating.

7. The method of claim 3, wherein the property is related to the amplitude of the signal induced on the blade.