Detection systems for power equipment

• US 8,489,223 B2
• Filed: 12/23/2011
• Issued: 07/16/2013
• Est. Priority Date: 12/31/2003
• Status: Active Grant

• Current Assignee: Sawstop Holding LLC
• Original Assignee: SD3, LLC
• Inventors: Gass, Stephen F.
• Primary Examiner(s): KASENGE, CHARLES R
• Application Number:
  US13/374,373
• Publication Number:
  US 20120168032A1
• Time in Patent Office: 571 Days
• Field of Search: 700/21, 700/79, 700/177, 83/72, 83/79, 702/65, 702/187, 318/445, 144/382, 144/383, 144/427, 173/1
• US Class Current: 700/177
• CPC Class Codes: B23D 45/067 the saw blade being adjustable according to depth or angle of cut
• CPC Class Codes: B23D 47/025 of tables
• CPC Class Codes: B23D 47/08 of devices for bringing the circular saw blade to the workpiece or removing same therefrom
• 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: B23D 59/006 for removing or collecting chips
• CPC Class Codes: B27B 13/14 Braking devices specially designed for band sawing machines, e.g. acting after damage of the band saw blade
• CPC Class Codes: B27B 5/38 Devices for braking the circular saw blade or the saw spindle; Devices for damping vibrations of the circular saw blade, e.g. silencing B23D47/005 takes precedence
• CPC Class Codes: B27G 19/02 for circular saws
• CPC Class Codes: B27G 19/06 for band or strap saws
• CPC Class Codes: B27G 19/08 Accessories for keeping open the saw kerf, e.g. riving knives or wedge plates
• CPC Class Codes: Y10S 83/01 Safety devices
• 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 83/141 With means to monitor and control operation [e.g., self-regulating means]
• CPC Class Codes: Y10T 83/704 With work-support and means to vary relationship between tool and work support
• CPC Class Codes: Y10T 83/7688 Plural tool elements successively actuated at same station
• CPC Class Codes: Y10T 83/7693 Tool moved relative to work-support during cutting
• CPC Class Codes: Y10T 83/7697 Tool angularly adjustable relative to work-support
• CPC Class Codes: Y10T 83/7705 Adjustable angular relationship
• 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]
• CPC Class Codes: Y10T 83/7793 : Means to rotate or oscillate tool
• CPC Class Codes: Y10T 83/8773 : Bevel or miter cut

Abstract

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 power saws to distinguish contact between a person and the blade of the saw from contact between the blade and wet or green wood. Woodworking machines and memory devices for use in woodworking machines having safety systems designed to detect a dangerous condition between a human and a dangerous portion of the woodworking machine and to trigger some action to mitigate the dangerous condition are also disclosed.

Claims

1. A method of detecting contact between a user and an operative element of a power tool at start up of the power tool, the method comprising:

providing a detection system adapted to detect contact between a user and the operative element of a power tool, where the detection is at least partially dependent on changes in the value of an electrical property sensed by the detection system;

calibrating the detection system by establishing a nominal value for the electrical property when no contact is present;

determining a current value of the electrical property during power up of the power tool when the operative element of the power tool is not operating;

comparing the current value to the nominal value; and

blocking operation of the operative element of the power tool if the current value is outside a predetermined range relative to the nominal value.

2. The method of claim 1, further comprising the steps of repeating the step of determining a current value and adjusting the value of the nominal value based at least in part on the determined current values.

3. The method of claim 2, where the step of adjusting is asymmetric relative to the determined current values.

4. A method of operating a system designed to detect a dangerous condition between a user and a dangerous element of a power tool, the method comprising:

providing a system configured to detect a dangerous condition between a user and a dangerous element of power tool, 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 detect such other events as a dangerous condition;

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 the normal operation of the power tool other than when a dangerous condition is detected;

monitoring the response level while operating the power tool; and

stopping the power tool 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.

5. The method of claim 4, 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.