Power tool anti-kickback system with rotational rate sensor

• US 20070084613A1
• Filed: 09/12/2006
• Published: 04/19/2007
• Est. Priority Date: 10/20/2004
• Status: Active Grant

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Zhang, Qiang, Schell, Craig, Bodine, Thomas, Norona, Joao, Beers, David, Deshpande, Uday, Vanko, John, Leh, Jason
• Granted Patent: US 7,552,781 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. A control scheme for a power tool having a rotary shaft, comprising:

monitoring rotational motion of the tool about a longitudinal axis of the shaft;

detecting a condition of the tool based on the rotational motion of the tool; and

reducing torque imparted to the shaft upon detecting the tool condition, where the torque is set to a non-zero value that enables an operator of the tool to regain control of the tool.

2. The control scheme of claim 1 further comprises determining angular displacement of the tool in relation to a starting angular position and reducing the torque when the angular displacement exceeds a threshold.

3. The control scheme of claim 2 further comprises reducing the torque to said non-zero value when the angular displacement exceeds a first threshold and reducing the torque to zero when the angular displacement exceeds a second threshold which is greater than the first threshold.

4. The control scheme of claim 1 further comprises determining angular velocity of the tool about the longitudinal axis and deriving an angular displacement of the tool from the angular velocity.

5. The control scheme of claim 1 further comprises determining angular velocity of the tool about the longitudinal axis and reducing the torque when the angular velocity exceeds a threshold.

6. The control scheme of claim 1 further comprises:

determining angular displacement of the tool in relation to a starting angular position;

determining angular velocity of the tool about the longitudinal axis; and

reducing the torque when the angular displacement of the tool exceeds a displacement threshold and the angular velocity exceeds a velocity threshold.

7. The control scheme of claim 1 further comprises determining angular acceleration of the tool about the longitudinal axis and reducing the torque when the angular acceleration exceeds a threshold.

8. The control scheme of claim 1 wherein monitoring rotational motion further comprises measuring rotational velocity based on Coriolis acceleration using a rotational motion sensor.

9. The control scheme of claim 1 wherein reducing torque further comprises reducing rotational speed of a motor coupled to the rotary shaft.

10. The control scheme of claim 1 wherein reducing torque further comprises reducing torque of a torque transmitting device interposed between a motor and the rotary shaft.

11. The control scheme of claim 1 wherein detecting a condition of the tool further comprises comparing the rotational motion of the tool to values in a look-up table.

12. A control system suitable for use in a power tool comprising:

a motor drivably coupled to a rotary shaft to impart rotary motion thereto;

a rotational rate sensor disposed within the tool and operable to detect rotational motion of the tool about a longitudinal axis of the shaft; and

a controller electrically connected to the rotational rate sensor, the controller operable to detect a rotational condition of the tool based on the rotational motion detected by the sensor and reduce the torque imparted to the shaft upon detecting the rotational condition of the tool, where the torque is set to a non-zero value that enables an operator of the tool to regain control of the tool.

13. The control system of claim 12 wherein the rotational rate sensor having a resonating mass is operable to detect lateral displacement of the resonating mass and 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 rotary shafts further defined

14. The control system of claim 12 wherein the controller determines angular displacement of the tool in relation to a starting angular position and reduces the torque when the angular displacement exceeds a threshold.

15. The control system of claim 14 wherein the controller reduces the torque to said non-zero value when the angular displacement exceeds a first threshold and reduces the torque to zero when the angular displacement exceeds a second threshold which is greater than the first threshold.

16. The control system of claim 12 wherein the controller determines angular velocity of the tool about the longitudinal axis and reduces the torque when the angular velocity exceeds a threshold.

17. The control system of claim 12 wherein the controller determines angular displacement of the tool in relation to a starting angular position;

determines angular velocity of the tool about the longitudinal axis; and

reduces the torque when the angular displacement of the tool exceeds a displacement threshold and the angular velocity exceeds a velocity threshold.

18. The control system of claim 12 wherein the controller reduces torque by controlling rotational speed of the motor.

19. The control system of claim 12 further comprises a torque transmitting device interposed between the motor and the shaft, wherein the controller reduces torque using the torque transmitting device.

20. A method for calibrating a power tool having a rotational rate sensor configured to detect rotational motion of the tool about an axis, comprising:

mounting the power tool to a test fixture;

rotating the power tool at a known angular velocity about the axis using the test fixture;

comparing an angular velocity as measured by the rotational rate sensor with the known angular velocity; and

determining a difference value between the measured angular velocity and the known angular velocity.

21. The method of claim 20 further comprises measuring output of the rotational rate sensor when the power tool is stationary on the test fixture to obtain an offset calibration value.

22. The method of claim 20 further comprises

rotating the power tool at the known angular velocity about the axis using the test fixture;

adjusting the angular velocity reported by the rotational rate sensor using the difference value; and

comparing the adjusted angular velocity to the known angular velocity to verify calibration of the tool.

23. The method of claim 20 further comprises

rotating the power tool at a known angular velocity in an opposite direction about the axis using the test fixture;

comparing an angular velocity as measured by the rotational rate sensor with the known angular velocity; and

determining another difference value between the measured angular velocity and the known angular velocity.

24. The method of claim 20 further comprises measuring angular velocity based on Coriolis acceleration.

25. The method of claim 20 further comprises

storing the difference values in the power tool;

removing the power tool from the test fixture; and

adjusting the angular velocity reported by the rotational rate sensor using the difference values during operation of the power tool.

26. A method for calibrating a power tool, comprising:

removing a test module from the power tool, the test module containing a rotational rate sensor configured to detect rotational motion of the tool about an axis;

mounting the test module to a test fixture;

rotating the test module at a known angular velocity about the axis using the test fixture;

comparing an angular velocity as measured by the rotational rate sensor with the known angular velocity; and

determining a difference value between the measured angular velocity and the known angular velocity.

27. The method of claim 26 further comprises measuring output of the rotational rate sensor when the test module is stationary on the test fixture to obtain an offset calibration value.

28. The method of claim 26 further comprises

rotating the test module at the known angular velocity about the axis using the test fixture;

adjusting the angular velocity reported by the rotational rate sensor using the difference value; and

comparing the adjusted angular velocity to the known angular velocity to verify calibration of the tool.

29. The method of claim 26 further comprises

rotating the test module at a known angular velocity in an opposite direction about the axis using the test fixture;

comparing an angular velocity as measured by the rotational rate sensor with the known angular velocity; and

determining another difference value between the measured angular velocity and the known angular velocity.

30. The method of claim 26 further comprises measuring angular velocity based on Coriolis acceleration.

31. The method of claim 26 further comprises

storing the difference values in the test module;

removing the test module from the test fixture;

re-installing the test module in the power tool; and

adjusting the angular velocity reported by the rotational rate sensor using the difference values during operation of the power tool.