Safety mechanisms for power tools, including kickback detection system with torque sensor

Abstract

Various safety systems for power tools, and in particular table saws include detection systems for detecting a dangerous condition relative to a blade of the power tool, reaction systems for taking mitigation action in response to detection of a dangerous condition. The safety system may detect, prevent, and/or mitigate a dangerous condition associated with the power tool.

What is claimed is: 
     
         1 . A table saw comprising:
 a cutting surface;   a blade for cutting a workpiece on the cutting surface, wherein a portion of the blade is extendable above the cutting surface;   a rotatable shaft positioned below the cutting surface, wherein the blade spins when the shaft rotates;   a motor connected to the rotatable shaft for rotating the rotatable shaft; and   a kickback detection system for detecting kickback of the workpiece during cutting of the workpiece, wherein the kickback detection system comprises:
 a torque sensor connected to the rotatable shaft; and 
 a processor in communication with the torque sensor, wherein the processor is programmed to recognize a condition indicative of kickback of the workpiece during cutting of the workpiece based on input from the torque sensor. 
   
     
     
         2 . The table saw of  claim 1 , further comprising a reaction means in communication with the kickback detection system for taking a mitigating reaction in response to detection of kickback of the workpiece by the kickback detection system during cutting of the workpiece. 
     
     
         3 . The table saw of  claim 2 , wherein the torque sensor comprises a strain gauge torque sensor. 
     
     
         4 . The table saw of  claim 2 , wherein the torque sensor comprises a surface acoustic wave torque sensor. 
     
     
         5 . Table saw of  claim 2 , wherein the blade is mounted to the rotatable shaft. 
     
     
         6 . The table saw of  claim 2 , further comprising:
 a clutch coupled to the rotatable shaft, such that when the clutch is engaged and the motor is running, the blade shaft is rotated; and   wherein the reaction means comprises:
 a brake system for braking the blade; and 
 a motor shut-down circuit connected to the clutch and the brake system, wherein the motor shut-down circuit disengages the clutch and actuates the brake system to brake the blade when the motor is turned off. 
   
     
     
         7 . The table saw of  claim 2 , further comprising a blade-spin detection means 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. 
     
     
         8 . The table saw of  claim 2 , further comprising an electrical generator connected by one or more gears to the rotatable shaft, wherein the electrical generator is further connected to the reaction means and generates electricity when the shaft rotates to power at least one of the reaction means and the detection means. 
     
     
         9 . The table saw of  claims 2 , wherein the blade comprises:
 an outer peripheral portion that comprises a first material; and   an inner portion that comprises a second material that is different from the first material, wherein the first material is denser than the second material.   
     
     
         10 . The table saw of  claims 2 , wherein:
 the table saw further comprises a flywheel that rotates in a direction that is the same as a direction of rotation for the blade, wherein the flywheel is coupled to the rotatable shaft by a clutch; and   the reaction means disengages the clutch when the dangerous condition is detected.   
     
     
         11 . The table saw of  claim 2 , wherein the reaction means comprises a downstream kickback mitigation means that is downstream from the blade for mitigating kickback of the workpiece. 
     
     
         12 . The table saw of  claim 11 , wherein the downstream kickback mitigation means comprises moveable wing members that move to a deployed position parallel to the cutting surface and above the workpiece when triggered by the reaction means. 
     
     
         13 . The table saw of  claim 2 , further comprising a passive downstream safety member for mitigating kickback of the workpiece, wherein the passive downstream safety member is not actuated by the detection means. 
     
     
         14 . The table saw of  claim 13 , wherein the passive downstream safety member comprises angled snells that impede kickback of the workpiece. 
     
     
         15 . The table saw of  claim 2 , further comprising a suction feed assembly that feeds the workpiece to the blade for cutting. 
     
     
         16 . The table saw of  claim 2 , further comprising sensor means connected to the cutting surface for sensing a characteristic of the workpiece during cutting of the workpiece. 
     
     
         17 . The table saw of  claim 2 , further comprising a blade contact sensor means for sensing contact with by a foreign object with the blade, wherein the blade contact sensor is in communication with the reaction means, and wherein the reaction means is for taking the mitigating reaction in response to detection of contact by a foreign object with the blade upon detection by the blade contact sensor means. 
     
     
         18 . The table saw of  claim 17 , wherein:
 the blade comprises:
 a first electrically conductive blade portion; 
 a second electrically conductive blade portion that comprises teeth for cutting the workpiece; and 
 a dielectric between the first and second electrically conductive blade portions, and 
   the blade contact sensor means is connected to the first electrically conductive blade portion and drives the first electrically conductive blade portion with a drive signal, and wherein the blade contact sensor means comprises a processor for detecting contact with the blade by the object based on an electrical signal from the first electrically conductive blade portion.   
     
     
         19 . The table saw of  claim 2 , further comprising a blade proximity sensor means for sensing proximity of a foreign object to the blade, wherein the blade proximity sensor means is in communication with the reaction means, and wherein the reaction means is for taking the mitigating reaction in response to detection of proximity by a foreign object to the blade upon detection by the blade proximity sensor means.