Power tool anti-kickback system with rotational rate sensor

• US 20080110653A1
• Filed: 01/14/2008
• Published: 05/15/2008
• Est. Priority Date: 10/20/2004
• Status: Active Grant

• Current Assignee: Craig Schell, David Beers, Jason Leh, Joao Norona, John Vanko, Qiang Zhang, Thomas Bodine, Uday Deshpande
• Original Assignee: Craig Schell, David Beers, Jason Leh, Joao Norona, John Vanko, Qiang Zhang, Thomas Bodine, Uday Deshpande
• Inventors: Vanko, John, Zhang, Qiang, Schell, Craig, Bodine, Thomas, Norona, Joao, Beers, David, Deshpande, Uday, Leh, Jason
• Granted Patent: US 7,681,659 B2
• Time in Patent Office: Days
• US Class Current: 173/1
• CPC Class Codes: B23D 59/001 Measuring or control devices, e.g. for automatic control of work feed pressure on band saw blade measuring in general G01; controlling in general G05
• CPC Class Codes: B25B 21/00 Portable power-driven screw or nut setting or loosening tools; details or components, e.g. casings, bodies, of portable power-driven tools not particularly related to the operation performed B25F5/00; for mounting or dismounting wheels B60B29/006; Attachments for drilling apparatus serving the same purpose machines B23P19/06
• CPC Class Codes: B25F 5/00 Details or components of portable power-driven tools not particularly related to the operations performed and not otherwise provided for
• CPC Class Codes: B25F 5/001 Gearings, speed selectors, clutches or the like specially adapted for rotary tools
• CPC Class Codes: H02H 7/0854 responsive to rate of change of current, couple or speed, e.g. anti-kickback protection H02H7/0851 takes precedence
• CPC Class Codes: H02P 29/032 Preventing damage to the motor, e.g. setting individual current limits for different drive conditions

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.

Claims

1-31. -31. (canceled)

32. 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 based on input from the rotational motion sensor;

initiating a protective operation when a trigger condition is met and angular displacement of the power tool falls within a range of angular displacements; and

initiating a protective operation when the trigger condition is not met but angular displacement of the power tool exceeds the range of angular displacements.

33. The method of claim 32 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.

34. The method of claim 32 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.

35. The method of claim 32 further comprises arranging the rotational motion sensor at a location in the power tool spatially separated from the rotary shaft.

36. The method of claim 32 further comprises employing a rotational motion sensor that measures rotational velocity based on Coriolis acceleration.

37. The method of claim 32 further comprises computing angular displacement of the power tool from a baseline and periodically resetting the baseline when angular velocity of the power tool about the axis is less than a velocity threshold.

38. The method of claim 32 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.

39. The method of claim 32 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.

40. 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 based on input from the rotational motion sensor;

initiating a protective operation in the power tool when a first trigger condition is met and angular displacement of the power tool falls within a first range of angular displacements; and

initiating a protective operation in the power tool when a second trigger condition is met and angular displacement of the power tool falls within a second range of angular displacements, where the second trigger condition is different than the first trigger condition and the second range of angular displacements is different than the first range of angular displacements.

41. The method of claim 40 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.

42. The method of claim 41 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.

43. The method of claim 40 further comprises arranging the rotational motion sensor at a location in the power tool spatially separated from the rotary shaft.

44. The method of claim 40 further comprises employing a rotational motion sensor that measures rotational velocity based on Coriolis acceleration.

45. The method of claim 40 further comprises periodically resetting the baseline when angular velocity of the power tool about the axis is less than a velocity threshold.

46. The method of claim 40 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.

47. 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:

arranging a rotational motion sensor at a location in the power tool spatially separated from the rotary shaft, where the rotational motion sensor measures rotational velocity based on Coriolis acceleration;

determining angular displacement of the power tool about the axis of the rotary shaft from a baseline based on input from the rotational motion sensor;

initiating a protective operation in the power tool when the rotational velocity of the power tool determined by the rotational motion sensor exceeds a velocity threshold and angular displacement of the power tool falls within at range of angular displacements; and

initiating the protective operation in the power tool when the angular displacement of the power tool exceeds the range of angular displacements.