Motion detecting system for use in a safety system for power equipment

• US 7,359,174 B2
• Filed: 08/18/2006
• Issued: 04/15/2008
• Est. Priority Date: 08/14/2000
• Status: Expired due to Term

• Current Assignee: Sawstop Holding LLC
• Original Assignee: SD3, LLC
• Inventors: Gass, Stephen F.
• Primary Examiner(s): Donovan; Lincoln
• Assistant Examiner(s): PAUL, ANTONY M
• Application Number:
  US11/506,260
• Publication Number:
  US 20060272463A1
• Time in Patent Office: 606 Days
• Field of Search: 83/58, 834/772, 361/143
• US Class Current: 361/143
• 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: B26D 7/24 arranged to disable the operating means for the cutting member
• CPC Class Codes: B27G 19/00 Safety guards or devices specially adapted for wood saws; Auxiliary devices facilitating proper operation of wood saws
• CPC Class Codes: B27G 21/00 Safety guards or devices specially designed for other wood-working machines auxiliary devices facilitating proper operation of said wood-working machines
• 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: F16P 3/148 using capacitive technology
• CPC Class Codes: Y10T 83/081 With randomly actuated stopping means
• CPC Class Codes: Y10T 83/773 Work-support includes passageway for tool [e.g., slotted table]

Abstract

A woodworking machine including a detection system adapted to detect a dangerous condition between a person and a working portion of the machine is disclosed. The machine includes a reaction system associated with the detection system to cause a predetermined action to take place relative to the working portion upon detection of the dangerous condition. A motion detection system is adapted to detect motion of the working portion and to disable the reaction system when the working portion is not moving. The motion detection system may sense whether motion in a machine has stopped by monitoring the back emf produced on the motor leads as the motor coasts to a stop. The woodworking machine may take the form of a saw, the working portion may be a blade adapted to cut when spinning, and the dangerous condition may be a person contacting the blade.

Claims

1. A woodworking machine comprising:

a cutter;

a motor adapted to drive the cutter;

a detection system adapted to detect a dangerous condition between a user and the cutter;

a reaction system adapted to perform a specified action to mitigate the dangerous condition upon detection of the dangerous condition by the detection system; and

a control system adapted to detect back emf produced by the motor as the motor as the motor coasts down after power has been removed from the motor, and where the control system is further adapted to permit the reaction system to perform the specified action during coast down of the motor only if back emf is detected.

2. The woodworking machine of claim 1, where the motor has leads and where the control system is connected to the leads.

3. The woodworking machine of claim 1, where the control system is adapted to employ zero-cross detection to detect back emf.

4. The woodworking machine of claim 1, where the control system includes circuitry to detect zero crossings of back emf.

5. The woodworking machine of claim 1, where the control system includes circuitry to detect when the back emf from the motor changes signs.

6. The woodworking machine of claim 5, where the control system is adapted to detect when the back emf from the motor changes signs by at least 10 mV.

7. The woodworking machine of claim 5, where the control system is adapted to detect when the back emf from the motor changes signs by 10 mV to 100 mV.

8. A woodworking machine comprising:

a cutter;

a motor adapted to drive the cutter;

a detection system adapted to detect a dangerous condition between a user and the cutter;

a reaction system adapted to perform a specified action to mitigate the dangerous condition upon detection of the dangerous condition by the detection system; and

a control system adapted to determine whether the cutter is moving by detecting back emf produced by the motor as the motor coasts down after power has been removed from the motor, and further adapted to deactivate the detection and/or reaction system if the cutter is not moving.

9. The woodworking machine of claim 8, where the control system includes circuitry to detect back emf.

10. The woodworking machine of claim 9, where the circuitry is configured to detect zero crossings of back emf.

11. The woodworking machine of claim 9, where the circuitry provides an amount of hysteresis.

12. The woodworking machine of claim 11, where the control system determines the cutter is not moving when the back emf is insufficient to overcome the hysteresis.

13. The woodworking machine of claim 8, where the cutter is a circular blade and where the control system is adapted to determine that the cutter is not moving when the cutter has coasted down to a rate of around 0.2 to 5 rotations per minute.

14. The woodworking machine of claim 8, where a delay period is incorporated into the control system to cause the control system to wait a predetermined interval after no more back emf is detected to deactivate the detection and/or reaction systems.

15. A woodworking machine comprising:

a cutter;

a motor adapted to drive the cutter;

a detection system adapted to detect a dangerous condition between a user and the cutter;

a reaction system adapted to perform a specified action to mitigate the dangerous condition upon detection of the dangerous condition by the detection system; and

control means for detecting back emf produced by the motor as the motor coasts down after power has been removed from the motor, and for triggering the reaction system only if a dangerous condition is detected when a predetermined level of back emf is also detected.

16. The woodworking machine of claim 15, where the machine is a table saw.

17. The woodworking machine of claim 15, where the cutter is a circular blade.

18. The woodworking machine of claim 15, where the control means includes circuit means for detecting zero crossings of back emf.

19. The woodworking machine of claim 15, where the control means includes circuit means for detecting sign changes of back emf.