Detection systems for power equipment

• US 8,498,732 B2
• Filed: 12/19/2011
• Issued: 07/30/2013
• Est. Priority Date: 12/31/2003
• Status: Expired due to Fees

• Current Assignee: Sawstop Holding LLC
• Original Assignee: SD3, LLC
• Inventors: Gass, Stephen F
• Primary Examiner(s): KASENGE, CHARLES R
• Application Number:
  US13/374,288
• Publication Number:
  US 20120186699A1
• Time in Patent Office: 589 Days
• Field of Search: 700/21, 700/79, 700/177, 83/72, 83/76, 144/427, 144/382, 702/65, 318/445
• 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 detect contact between a person and the blade of the saw. 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 for detecting contact between a user and a cutting tool on a piece of woodworking equipment, the method comprising:

inducing an electrical signal on the cutting tool by generating an electrical current between a drive circuit and the cutting tool, wherein the electrical signal induced on the cutting tool has a phase and an amplitude, wherein the cutting tool has an apparent electrical impedance dependent at least in part on whether the cutting tool is in contact with the user, and wherein the electrical current, phase and amplitude are dependent at least in part on the apparent electrical impedance of the cutting tool;

sampling one or more of the current, phase or amplitude a plurality of times at discrete intervals to generate multiple data points;

calculating a value based at least in part on more than one of the data points; and

deciding there has been contact between the user and the cutting tool if the value compares to a threshold in a predetermined way.

2. The method of claim 1, wherein the value is based at least in part on a change in at least one of the data points relative to at least one other of the data points.

3. The method of claim 1, wherein the piece of woodworking equipment includes memory and further comprising storing multiple data points in memory.

4. The method of claim 1, wherein the piece of woodworking equipment includes memory, and further comprising storing a predetermined number of data points in memory and updating the data points stored in memory by adding recent data points and discarding older data points.

5. A method for detecting contact between a user and a cutting tool on a piece of woodworking equipment, the method comprising:

applying an electrical signal to the cutting tool, wherein the cutting tool has an apparent electrical impedance dependent at least in part on whether the cutting tool is in contact with the user, and wherein the electrical signal applied to the cutting tool has an associated measureable characteristic that changes based on the apparent electrical impedance of the cutting tool;

taking multiple measurements of the characteristic over time, wherein each measurement result in a data point;

comparing one or more data points with one or more data points taken at one or more prior times; and

deciding there has been contact between the user and the cutting tool if the data points compare in a predetermined way.

6. The method of claim 5, wherein the associated measureable characteristic is based on one or more of an electrical current associated with the electrical signal, an amplitude of the electrical signal, or a phase of the electrical signal.

7. The method of claim 5, further comprising storing multiple data points.

8. The method of claim 5, wherein comparing one or more data points involves a sum.

9. The method of claim 5, wherein comparing one or more data points involves an average.

10. A method for detecting contact between a user and a cutting tool on a piece of woodworking equipment, The method comprising:

applying an electrical signal to the cutting tool, wherein the cutting tool has an apparent electrical impedance dependent at least in part on whether the cutting tool is in contact with the user, and wherein the electrical signal applied to the cutting tool has one or more associated characteristics that change based on the apparent electrical impedance of the cutting tool; and

a step for performing the function of deciding whether there has been contact between the user and the cutting tool based at least in part on accumulated changes over time of one or more of the associated characteristics.

11. The method of claim 10, wherein the one or more associated characteristics is based on one or more of an electrical current associated with the electrical signal, an amplitude of the electrical signal, or a phase of the electrical signal.