Power tool anti-kickback system with rotational rate sensor

Abstract

A control system is provided for use in a power tool. The control system includes: a rotational rate sensor having a resonating mass and a controller electrically connected to the rotational rate sensor. The rotational rate sensor detects lateral displacement of the resonating mass and generates 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 rotary shaft. Based on the generated signal, the controller initiates a protective operation to avoid further undesirable rotation of the power tool. The controller may opt to reduce the torque applied to shaft to a non-zero value that enables the operator to regain control of the tool.

What is claimed is: 
     
       1. A method for initiating a protective response in a power tool having a rotary shaft, comprising:
 monitoring rotational motion of the power 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 using a controller disposed in the power tool and based on input from the rotational motion sensor;   initiating a protective operation by the controller when an operating condition of the power tool exceeds a threshold and the angular displacement of the power tool falls within a range of angular displacements; and   initiating a protective operation by the controller when the operating condition of the power tool is less than the threshold but the angular displacement of the power tool exceeds the range of angular displacements.   
     
     
       2. The method of  claim 1  further comprises initiating a protective operation when angular velocity of the power tool about the axis exceeds a velocity threshold and the angular displacement of the power tool falls within the range of angular displacements. 
     
     
       3. The method of  claim 1  further comprises initiating a protective operation when angular displacement of the power tool falls within a range of angular displacements and angular acceleration of the power tool about the axis exceeds an acceleration threshold. 
     
     
       4. The method of  claim 1  further comprises arranging the rotational motion sensor at a location in the power tool spatially separated from the rotary shaft. 
     
     
       5. The method of  claim 1  further comprises employing a rotational motion sensor that measures rotational velocity based on Coriolis acceleration. 
     
     
       6. The method of  claim 1  wherein the protective operation when angular displacement of the power tool falls within a range of angular displacements is different than the protective operation when angular displacement of the power tool exceeds the range of angular displacements. 
     
     
       7. The method of  claim 1  wherein the protective operation is selected from the group consisting of pulsing a motor of the power tool, braking the rotary shaft, braking the motor, disengaging the motor from the rotary shaft, discontinuing power delivered to the motor and reducing slip torque of a clutch disposed between the motor and the rotary shaft. 
     
     
       8. A method for initiating a protective response in a power tool having a motor drivably coupled to a rotary shaft to impart rotary motion thereto, comprising:
 monitoring rotational motion of the power tool about a longitudinal axis of the rotary shaft using a rotational motion sensor disposed in the power tool;   determining angular displacement of the power tool about the axis of the rotary shaft from a baseline using a controller disposed in the power tool and based on input from the rotational motion sensor;   initiating a protective operation in the power tool by the controller when a first operating condition of the power tool exceeds a first operating threshold and angular displacement of the power tool falls within a first range of angular displacements; and   initiating a protective operation in the power tool by the controller when a second operating condition of the power tool exceeds a second operating threshold and angular displacement of the power tool falls within a second range of angular displacements, where the second operating condition is different than the first operating condition and the second range of angular displacements is mutually exclusive of the first range of angular displacements.   
     
     
       9. The method of  claim 8  further comprises initiating a protective operation when angular velocity of the power tool about the axis exceeds a velocity threshold and angular displacement of the power tool falls within the first range of angular displacements. 
     
     
       10. The method of  claim 9  further comprises initiating a protective operation when angular velocity of the power tool is less than the velocity threshold and angular displacement of the power tool falls within the second range of angular displacements. 
     
     
       11. The method of  claim 8  further comprises arranging the rotational motion sensor at a location in the power tool spatially separated from the rotary shaft. 
     
     
       12. The method of  claim 8  further comprises employing a rotational motion sensor that measures rotational velocity based on Coriolis acceleration. 
     
     
       13. The method of  claim 8  further comprises periodically resetting the baseline when angular velocity of the power tool about the axis is less than a velocity threshold. 
     
     
       14. The method of claim S wherein the protective operation is selected from the group consisting of pulsing a motor of the power tool, braking the rotary shaft, braking the motor, disengaging the motor from the rotary shaft, discontinuing power delivered to the motor and reducing slip torque of a clutch disposed between the motor and the rotary shaft. 
     
     
       15. A method for initiating a protective response in a power tool having a rotary shaft, comprising:
 monitoring rotational motion of the power 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 from a baseline using a controller disposed in the power tool and based on input from the rotational motion sensor;   periodically resetting the baseline when angular velocity of the power tool about the axis is less than a velocity threshold;   initiating a protective operation by the controller when an operating condition of the power tool exceeds a threshold and the angular displacement of the power tool falls within a range of angular displacements; and   initiating a protective operation by the controller when the operating condition of the power tool is less than the threshold but the angular displacement of the power tool exceeds the range of angular displacements.   
     
     
       16. A method for controlling operation of a power tool having a rotary shaft, comprising:
 monitoring rotational motion of the power 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   driving the rotary shaft at a given rotational speed, where the given rotational speed is set to a non-zero value based on the angular displacement of the power tool.   
     
     
       17. The method of claim 16 wherein the computing angular displacement further comprises determining the angular displacement of the power tool in relation to a reference position and driving the rotary shaft at the given rotational speed when the angular displacement from the reference position exceeds a displacement threshold. 
     
     
       18. The method of claim 16 wherein the computing angular displacement further comprises determining the angular displacement of the power tool in relation to a reference position and lowering rotational speed of the rotary shaft to a non-zero value when the angular displacement from the reference position exceeds a displacement threshold. 
     
     
       19. The method of claim 16 further comprises arranging the rotational motion sensor at a location in the power tool spatially separated from the rotary shaft. 
     
     
       20. A method for controlling operation of a power tool having a rotary shaft, comprising:
 monitoring rotational motion of the power 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;   driving the rotary shaft at a first rotational speed when the angular displacement is less than a displacement threshold; and   driving the rotary shaft at a second rotational speed having a non-zero value when the angular displacement is greater than the displacement threshold, where the second rotational speed differs from the first rotational speed.   
     
     
       21. The method of claim 20 wherein the computing angular displacement further comprises determining the angular displacement of the power tool in relation to a reference position and driving the rotary shaft at the given rotational speed when the angular displacement from the reference position exceeds a displacement threshold. 
     
     
       22. The method of claim 20 wherein the computing angular displacement further comprises determining the angular displacement of the power tool in relation to a reference position and lowering rotational speed of the rotary shaft to a non-zero value when the angular displacement from the reference position exceeds a displacement threshold. 
     
     
       23. The method of claim 20 further comprises arranging the rotational motion sensor at a location in the power tool spatially separated from the rotary shaft. 
     
     
       24. A control system for a power tool having an output shaft, comprising:
 a motor disposed in the power tool and drivably connected to the output shaft to impart rotary motion thereto;   a rotational motion sensor disposed in the power tool and operable to detect rotational motion of the tool about a longitudinal axis of the output shaft; and   a controller configured to receive a signal indicative of rotational motion of the tool from the rotational motion sensor and operable to determine angular displacement of the power tool about the axis of the output shaft from the signal, the controller electrically connected to the motor and operable to set rotational speed of the motor to a non-zero value based on the angular displacement of the power tool.   
     
     
       25. The control system of 24 wherein the controller determines the angular displacement of the power tool in relation to a reference position and sets the rotational speed of the motor to a non-zero value when the angular displacement from the reference position exceeds a displacement threshold. 
     
     
       26. The control system of claim 24 wherein the controller determines the angular displacement of the power tool in relation to a reference position and lowers rotational speed of the motor to a non-zero value when the angular displacement from the reference position exceeds a displacement threshold. 
     
     
       27. The control system of claim 24 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. 
     
     
       28. The control system of claim 27 wherein the resonating motion of the mass and the lateral movement of the mass occur in a plane which is orientated perpendicular to the rotational axis of the output shaft. 
     
     
       29. The control system of claim 24 wherein the rotational motion sensor is further defined as a gyroscope. 
     
     
       30. 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;   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 set rotational speed of the motor to a non-zero value when the angular displacement from the reference position exceeds a displacement threshold.