Control Scheme For Detecting And Preventing Torque Conditions In A Power Tool

Abstract

A control scheme is provided for a power tool having a rotary shaft. The control scheme includes: monitoring rotational motion of the tool generally about a longitudinal axis of the shaft; detecting a condition of the tool based on the rotational motion of the tool; and controlling torque imparted to the shaft upon detecting the tool condition, where the torque is inversely related to an angular displacement of the tool about the longitudinal axis of the shaft.

1 - 24 . (canceled) 
     
     
         25 . A method for controlling operation of a power tool having a motor drivably coupled to a rotary shaft, comprising:
 monitoring rotational motion of the tool about a longitudinal axis of the rotary shaft using a rotational motion sensor disposed in the power tool;   detecting rotational motion of the tool with respect to the longitudinal axis of the rotary shaft based on input from the rotational motion sensor and using a controller disposed in the power tool; and   pulsing, in response to detecting rotational motion, torque imparted by the motor to the shaft.   
     
     
         26 . The method of  claim 25  further comprises pulsing torque such that time between pulses enables the operator to regain control of the tool. 
     
     
         27 . The method of  claim 25  further comprises pulsing the torque imparted by the motor so that time between pulses is in a range of 0.1 to 1 second. 
     
     
         28 . The method of  claim 25  further comprises pulsing the torque imparted by the motor by pulsing electric power applied to the motor. 
     
     
         29 . The method of  claim 25  further comprises pulsing the torque through a clutch interposed between the motor and the rotary shaft. 
     
     
         30 . The method of  claim 25  wherein monitoring rotational motion of the tool further comprises determining angular displacement of the rotational motion sensor in relation to a starting angular position and pulsing the torque imparted to the shaft when the angular displacement exceeds a threshold. 
     
     
         31 . The method of  claim 25  wherein monitoring rotational motion of the tool further comprises determining rotational speed of the rotational motion sensor about the longitudinal axis of the shaft and detecting the rotational motion based in part of the rotational speed of the rotational motion sensor. 
     
     
         32 . The method of  claim 25  wherein monitoring rotational motion of the tool further comprises determining rotational speed of the rotational motion sensor about the longitudinal axis of the shaft and deriving the angular displacement of the tool from the rotational speed of the tool. 
     
     
         33 . The method of  claim 32  wherein detecting rotational motion further comprises comparing angular displacement of the rotational sensor to a displacement threshold and comparing rotational speed of the rotational motion sensor to a velocity threshold. 
     
     
         34 . A method for controlling operation of a power tool having a motor drivably coupled to a rotary shaft, comprising:
 monitoring rotational motion of the tool about a longitudinal axis of the rotary shaft using a rotational motion sensor disposed in the power tool;   computing angular displacement of the power tool about the axis of the rotary shaft based on input from the rotational motion sensor and using a controller disposed in the power tool; and   pulsing torque imparted by the motor to the shaft when the angular displacement of the power tool exceeds a threshold, such that time between pulses enables the operator to regain control of the tool.   
     
     
         35 . The method of  claim 34  further comprises pulsing the torque imparted by the motor so that time between pulses is in a range of 0.1 to 1 second. 
     
     
         36 . The method of  claim 34  further comprises pulsing the torque imparted by the motor by pulsing electric power applied to the motor. 
     
     
         37 . The method of  claim 34  further comprises pulsing the torque through a clutch interposed between the motor and the rotary shaft. 
     
     
         38 . A power tool comprising:
 a housing;   an output shaft at least partially contained in the housing and configured to rotate about a longitudinal axis;   a motor contained in the housing and drivably connected to the output shaft to impart rotary motion thereto;   a rotational motion sensor arranged in the housing at a location spatially separated from the output shaft and operable to detect rotational motion of the housing about the longitudinal axis of the output shaft; and   a controller configured in the housing to receive a signal indicative of rotational motion from the rotational motion sensor and operable to determine angular displacement of the housing in relation to a reference position from the signal, the controller electrically connected to the motor and operable to pulse torque imparted by the motor to the output shaft when the angular displacement of the housing exceeds a displacement threshold.   
     
     
         39 . The power tool of  claim 38  wherein the controller pulses the torque imparted by the motor so that time between pulses is in a range of 0.1 to 1 second. 
     
     
         40 . The power tool of  claim 38  wherein the controller pulses the torque imparted by the motor by pulsing electric power applied to the motor. 
     
     
         41 . The power tool of  claim 38  wherein the controller pulses the torque through a clutch interposed between the motor and the rotary shaft. 
     
     
         42 . The power tool of  claim 38  wherein the rotational motion sensor is further defined as an accelerometer. 
     
     
         43 . The power tool of  claim 38  wherein the rotational motion sensor having a resonating mass and being operable to detect lateral displacement of the resonating mass, the rotational motion sensor is further operable to generate a signal indicative of the detected lateral displacement, such that the lateral displacement is directly proportional to a rotational speed at which the power tool rotates about an axis of the output shaft.