Dectection systems for power equipment

• US 20050155473A1
• Filed: 12/31/2004
• Published: 07/21/2005
• 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 7,536,238 B2
• Time in Patent Office: Days
• US Class Current: 83/58
• 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 for acquiring data related to the triggering of a system designed to detect and trigger upon dangerous condition between a human and a dangerous portion of a woodworking machine, the method including:

distributing a plurality of such systems;

detecting a trigger of the system;

storing data associated with the trigger in a permanent memory device associated with the system; and

reading the data from the permanent memory device.

2. The method of claim 1, 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 and further including the steps of:

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.

3. The method of claim 1, further including the step of recovering at least a portion of the system, wherein the recovered portion includes the permanent memory device.

4. The method of claim 3, wherein the permanent memory device is housed in a replaceable module and further including the step of providing a free replacement module in exchange for a module that has trigger data stored therein.

5. The method of claim 1, wherein the dangerous portion of the woodworking machine is a saw blade and the dangerous condition is contact between the human and the saw blade, wherein the detection of contact is based at least in part on changes in the electrical impedance of the saw blade and wherein the stored data relates to the changes in electrical impedance preceding the trigger.

6. The method of claim 1 wherein the detection of dangerous condition is based at least in part on a response level of a detection scheme crossing a threshold level, further including the step of adjusting the threshold level based on data read from the permanent memory.

7. The method of claim 1 further including the step of activating a danger mitigation system to reduce the chance of serious injury to the human in response to the detection of the dangerous condition.

8. The method of claim 7, wherein the dangerous portion of the woodworking machine is a saw blade and the danger mitigation system includes a brake to stop the blade.

9. The method of claim 7, wherein the dangerous portion of the woodworking machine is a saw blade and the danger mitigation system moves the blade away from the human.

10. The method of claim 9, where the woodworking machine is a table saw and moving the blade away from the human involves retracting the saw blade below the table.

11. 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.

12. The method of claim 11, 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.

13. 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.

14. The method of claim 13, wherein the integration is done with an analog circuit.

15. The method of claim 14, wherein the integration is carried out over discrete time intervals.

16. The method of claim 13, wherein the property is digitized prior to the step of integrating.

17. The method of claim 13, wherein the property is related to the amplitude of the signal induced on the blade.