SawStop: The World's Safest Table Saw
Check out the SawStop, the world's safest Tablesaw. The SawStop can detect when a person's finger, or other flesh-like objects, has touched the blade and reacts by shutting down the power and withdrawing the blade into the machine. All within 1/200th of a second. Wow!
The SawStop safety system includes an electronic detection system that detects when a person contacts the blade. The system induces an electrical signal onto the blade and then monitors that signal for changes. The human body has a relatively large inherent electrical capacitance and conductivity which cause the signal to drop when a person contacts the blade. Wood has a relatively small inherent capacitance and conductivity and does not cause the signal to drop.
A fast-acting brake stops the blade when contact is detected. The brake includes a heavy-duty spring to push a block of aluminum, called a brake pawl, into the teeth of the blade to stop the blade from spinning. The spring is held in compression by a fuse wire until contact is detected. When contact is detected, the system sends a surge of electricity through the fuse wire to burn the wire and release the spring. The spring pushes the brake pawl into the teeth of the spinning blade, and the teeth cut into the aluminum and bind, thereby stopping the blade. All this happens in about 3Â5 milliseconds, or 1/200th of a second. At the same time, the angular momentum of the blade causes the blade to retract below the table and the power to the motor is shut off.
Check out the video section to see a couple of demonstrations including a few in slow-motion. What an excellent idea for a product. I personally shiver each time I see people using tablesaws, and mildly dislike using knives in general. Nobody would ever want to loose a finger.
Link (via Sataguini)