Detection systems for power equipment

• US 20090236012A1
• Filed: 12/31/2008
• Published: 09/24/2009
• Est. Priority Date: 12/31/2007
• Status: Active Grant

• Current Assignee: Sawstop Holding LLC
• Original Assignee: SD3, LLC
• Inventors: Gass, Stephen F., Slamka, Louis R.
• Granted Patent: US 7,971,613 B2
• Time in Patent Office: Days
• US Class Current: 144/427
• CPC Class Codes: B23Q 11/0092 actuating braking or stopping means
• CPC Class Codes: Y10T 83/088 Responsive to tool detector or work-feed-means detector
• 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 83/162 With control means responsive to replaceable or selectable information program

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 table saws to distinguish contact between a person and the blade of the saw from contact between the blade and wet or green wood. The methods and woodworking equipment may include predictive blade stop algorithms that prevent unnecessary activations of a safety brake during coast down of a blade and continued protection in the event a main power switch is turned off.

Claims

1. A woodworking machine, comprising:

a motor configured to operate a cutter;

a safety system configured to detect a dangerous condition, where the safety system includes a controller; and

a motor control system configured to selectively turn the motor on and off;

where the motor control system is controlled by the safety system, and where the controller in the safety system signals the motor control system to turn the motor off upon detection of a dangerous condition;

where the motor control system includes a motor control circuit adapted with at least one control input, and where the motor control circuit is configured to turn the motor on only upon receipt of a non-constant signal from the controller on the control input; and

where the controller is located remotely from the motor control system and operatively coupled to the motor control system by a cable.

2. The woodworking machine of claim 1, wherein the motor control system includes a solid state switching mechanism and a mechanical switching mechanism, each independently wired in parallel to control the motor and wherein the motor control circuit is adapted to turn on the solid state switching mechanism upon receipt of a first non-constant signal and to turn on the mechanical switching mechanism upon receipt of a second non-constant signal different from the first non-constant signal.

3. The woodworking machine of claim 2, wherein the controller is adapted to output the first non-constant signal for a first interval of time upon turning on the motor and then outputting the second non-constant signal.

4. The woodworking machine of claim 3, wherein the first and second non-constant signals are pulse width modulated signals and the pulse width modulation is different for the first and second non-constant signals.

5. The woodworking machine of claim 2, wherein the controller is adapted to output the second non-constant signal while the motor is operating and to output the first non-constant signal for a period of time prior to turn off of the motor.

6. The woodworking machine of claim 1, where the motor control system includes a motor power switching mechanism to selectively switch power to the motor and a shunt switching mechanism configured to selectively provide a low resistance path in parallel with the motor, wherein the motor control input is configured to select the shunt switching mechanism when the motor control circuit is receiving a constant signal on the motor control input.

7. The woodworking machine of claim 1, including a main power switch configured to selectively supply power to the safety system and a main power bypass circuit configured to prevent the main power switch from disconnecting power to the safety system when the motor is running.

8. The woodworking machine of claim 7, further including a rotation sensing system configured to sense rotation of the cutter, where the rotation sensing system receives discontinuous indications of rotation and is configured to predict the time the cutter stops spinning by extrapolation of the discontinuous indications of rotation, further wherein the rotation sensing system is coupled to the controller to prevent the main power switch from disconnecting power to the safety system when the cutter is spinning

9. A woodworking machine comprising:

a motor configured to operate a cutter;

a safety system configured to detect a dangerous condition;

a motor control circuit adapted to selectively power the motor;

a DC power supply configured to provide power to at least a portion of the safety system;

a main power switch configured to control delivery of power to the power supply and at least a portion of the motor control circuit;

a start/stop switch operatively coupled to the motor control circuit to allow the user to selectively turn the motor on and off;

an interface system coupling the start/stop switch and the main power switch to at least partially prevent the user from interrupting input power to the power supply while the motor is on.

10. The machine of claim 9, further including a rotation sensing system to detect when the motor is spinning and wherein the interface system is configured to at least partially prevent the user from interrupting power to the power supply with the main power switch while the motor is still spinning.

11. The machine of claim 9, further including a rotation sensing system to detect when the cutter is moving and wherein the interface system is configured to at least partially prevent the user from interrupting power to the power supply with the main power switch while the cutter is still moving.

12. A woodworking machine comprising:

a motor configured to spin a cutter;

a safety system configured to detect a dangerous condition between the user and the cutter;

a reaction system configured to take some action to protect the user upon detection of the dangerous condition, where the action taken by the reaction system involves an irreversible change to at least a part of the machine; and

a rotation sensing system configured to sense rotation of the cutter, where the rotation sensing system receives discontinuous indications of rotation and is coupled to send a signal to the safety system to prevent action by the reaction system when the cutter stops spinning, where the rotation sensing system is configured to predict the time the cutter stops spinning by extrapolation of the discontinuous indications of rotation.

13. The woodworking machine of claim 12, wherein the discontinuous indications of rotation are electrical pulses occurring a small integral number of times per rotation of the cutter.

14. The woodworking machine of claim 12, wherein the cutter is mounted to an arbor and the arbor includes a magnet, wherein the discontinuous indications of rotation are electrical pulses from a Hall effect sensor located adjacent to the arbor and the Hall effect sensor is configured to detect rotation by periodic passage of the magnet.