Safety mechanisms for power tools

A table saw comprising:

• a cutting surface;
• a motor-driven, rotatable blade for cutting a workpiece on the cutting surface, wherein a portion of the blade is extendable above the cutting surface;
• detection means for detecting a dangerous condition relative to the blade;
• reaction means in communication with the detection means for taking a reaction in response to detection of the dangerous condition by the detection system;
• and
• a blade-spin detection system for detecting whether the blade is rotating based on energy from the blade, wherein the blade-spin detection system is in communication with the reaction means and provides an output to arm the reaction means when the blade-spin detection system detects that the blade is spinning.

A table saw comprising:

• a cutting surface;
• a motor-driven, rotatable blade that is partially extendable above the cutting surface for cutting a workpiece positioned on the cutting surface;
• and
• a sensor connected to the cutting surface for sensing a characteristic of the workpiece during cutting of the workpiece.

A table saw comprising:

• a cutting surface;
• a motor-driven, rotatable blade for cutting a workpiece on the cutting surface, wherein a portion of the blade is extendable above the cutting surface;
• a contact detection system for detecting contact with the blade by an object other than the workpiece;
• and
• reaction means in communication with the contact detection system for taking a mitigating reaction in response to detection of contact with the blade by the object,
• wherein the blade comprises:
• a first electrically conductive blade portion;
• a second electrically conductive blade portion;
• and
• a dielectric between the first and second electrically conductive blade portions, and
• wherein the contact detection system is connected to the first electrically conductive blade portion and drives the first electrically conductive blade portion with a drive signal, and wherein the contact detection system comprises a processor for detecting contact with the blade by the object based on an electrical signal from the first electrically conductive blade portion.

A table saw comprising:

• a cutting surface;
• a motor-driven rotatable shaft positioned below the cutting surface;
• a blade for cutting a workpiece on the cutting surface, wherein the blade is mounted on the shaft, and wherein a portion of the blade is extendable above the cutting surface;
• a detection system for detecting a dangerous condition relative to the blade;
• a reaction system in communication with the detection system for taking a reaction in response to detection of the dangerous condition, wherein the reaction system comprises a magnetorheological rotary brake connected to the shaft that brakes the shaft to thereby brake the blade in response to detection of the dangerous condition by the detection system.