Time Warp Table Saw called SawStop
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Uploaded on Aug 4, 2009
SawStop saws are equipped with a safety
system to stop the blade within 5 milliseconds of
detecting contact with skin. SawStop saws detect contact with skin.
The blade carries a small electrical signal, which the safety system continually monitors.
When skin contacts the blade, the signal changes because the human body is conductive.
The change to the signal activates the safety system.
A heavy-duty aluminum brake stops the blade.
The blade stops within milliseconds of detecting contact, quicker than a car airbag deploys.
During this time three things happen:
1.An aluminum brake springs into the spinning blade, to stop the blade.
2.The blades angular momentum drives the blade beneath the table, removing the risk of subsequent contact.
3.Power to the motor is shut off.
Resetting the saw is easy. It takes about five minutes to replace the $69 single-use brake cartridge and blade.
SawStop® table saws are the most advanced saws in the world, setting the standard for table saw safety.
SawStop saws are equipped with a safety system that detects when someone accidentally contacts the spinning saw blade, and then stops the blade in milliseconds. In most cases, such an accident would result in just a nick on a SawStop saw, instead of the devastating injury which would likely occur on an ordinary table saw.
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.
This drawing shows the changes in the electrical signal when a finger touched the teeth of a spinning saw blade during an actual test.
The line represents the electrical signal, which dropped quickly when the blade touched the finger. The dips in the signal line illustrate the changes in the electrical signal that were detected as two successive teeth touched the finger. When the detection system sees dips like these, it knows a person has touched the blade.
In order to stop the saw, 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 35 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.
The brake mechanism is shown in the drawing to the right. The arrow shows how the aluminum brake pawl pivots into the teeth of the blade. The brake pawl is part of a replaceable cartridge that includes the spring, fuse wire and electronics necessary to burn the fuse wire. An optional dado cartridge provides the same protection for dado cuts.
The standard and dado brake cartridges are single-use components that must be changed if the brake is ever activated. Changing a brake cartridge is fast and easy, no more complicated than changing the blade.
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