Safety mechanism for a rotary hammer

• US 20040211573A1
• Filed: 04/22/2004
• Published: 10/28/2004
• Est. Priority Date: 04/24/2003
• Status: Active Grant

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Carrier, David A., Puzio, Daniel, Bradus, Robert
• Granted Patent: US 7,395,871 B2
• Time in Patent Office: Days
• US Class Current: 173/2
• 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: Y10T 408/14 Responsive to condition of Tool or tool-drive

Abstract

An improved method is provided for controlling a power tool having a rotary shaft. The method includes: disposing an inertial mass in a housing of the power tool, such that the inertial mass is freely rotatable about an axis of rotation which is axially aligned with the rotary shaft; monitoring rotational motion of the power tool in relation to the inertial mass during operation of the power tool; and activating a protective operation based on the rotational motion of the power tool in relation to the inertial mass.

Claims

1. A method for controlling a power tool having a rotary shaft, comprising:

disposing an inertial mass in a housing of the power tool, the inertial mass being freely rotatable about an axis of rotation and the axis of rotation being axially aligned with the rotary shaft;

monitoring rotational motion of the power tool in relation to the inertial mass during operation of the power tool; and

activating a protective operation based on the rotational motion of the power tool in relation to the inertial mass.

2. The method of claim 1 wherein the power tool further includes a motor drivably coupled to the rotary shaft to impart rotary motion thereto.

3. The method of claim 2 wherein the step of activating a protective operation further comprises assessing the rotational motion of the housing of the power tool in relation to a predefined threshold which is in part based on speed of the motor.

4. The method of claim 2 wherein the protective operation is selected from the group consisting of braking the rotary shaft, braking the motor, disengaging the motor from the rotary shaft, and reducing slip torque of a clutch disposed between the motor and the rotary shaft.

5. The method of claim 1 wherein the step of monitoring rotational motion further comprises determining angular velocity of the rotational motion;

and determining when the angular velocity of the rotational motion exceeds a predefined velocity threshold indicative of a bit jam condition.

6. The method of claim 5 further comprises activating a protective operation when the angular velocity of the rotational motion exceeds the predefined velocity threshold.

7. The method of claim 5 further comprises monitoring direction of the rotational motion and activating a protective operation when the angular velocity of the rotational motion exceeds the predefined velocity threshold and the direction of the rotational motion does not change within a predefined time period.

8. The method of claim 5 further comprises monitoring rotational displacement and activating a protective operation when the angular velocity of the rotational motion exceeds the predefined velocity threshold and the rotational displacement exceeds a predefined displacement threshold.

9. A method for detecting a bit jam condition in a power tool having a rotary shaft, comprising:

disposing an inertial mass in a housing of the power tool, the inertial mass being freely rotatable about an axis of rotation and the axis of rotation being axially aligned with the rotary shaft;

monitoring rotational motion of the housing of the power tool in relation to the inertial mass; and

determining when angular velocity of the rotational motion exceeds a predefined velocity threshold indicative of a bit jam condition.

10. The method of claim 9 wherein the power tool further includes a motor drivably coupled to the rotary shaft to impart rotary motion thereto, such that the predefined velocity threshold is based on speed of the motor.

11. The method of claim 9 further comprises activating a protective operation when the angular velocity of the rotational motion exceeds the predefined velocity threshold.

12. The method of claim 9 further comprises monitoring direction of the rotational motion and activating a protective operation when the angular velocity of the rotational motion exceeds the predefined velocity threshold and the direction of the rotational motion does not change within a predefined time period.

13. The method of claim 9 further comprises monitoring rotational displacement and activating a protective operation when the angular velocity of the rotational motion exceeds the predefined velocity threshold and the rotational displacement exceeds a predefined displacement threshold.

14. The method of claim 13 wherein the predefined displacement threshold is on the order of 45 degrees.

15. A method for detecting a bit jam condition in a power tool having a rotary shaft, comprising:

disposing an inertial mass in a housing of the power tool, the inertial mass being freely rotatable about an axis of rotation and the axis of rotation being axially aligned with the rotary shaft;

monitoring rotational motion of the housing of the power tool in relation to the inertial mass; and

determining when rotational displacement of the rotational motion exceeds a predefined displacement threshold indicative of a bit jam condition.

16. The method of claim 15 wherein the power tool further includes a motor drivably coupled to the rotary shaft to impart rotary motion thereto, such that the predefined displacement threshold is based on speed of the motor.

17. The method of claim 16 further comprises setting the predefined displacement threshold at low motor speeds to account for friction of the inertial mass.

18. The method of claim 15 further comprises activating a protective operation when the rotational displacement exceeds the predefined displacement threshold.

19. The method of claim 18 further comprises setting the predefined displacement threshold at high motor speeds to account for additional time needed to perform the protective operation.

20. The method of claim 15 further comprises activating a protective operation when the rotational displacement exceeds the predefined displacement threshold within a predefined time period.

21. The method of claim 15 wherein the step of monitoring rotational displacement further comprises aggregating a cumulative amount of rotational displacement and periodically decrementing the cumulative amount of rotational displacement.

22. A control system for a power tool having a motor drivably coupled to a rotary shaft to impart rotary motions thereto, comprising:

an inertial mass disposed in a housing of the power tool, the inertial mass being freely rotatable about an axis of rotation and the axis of rotation being aligned axially with the rotary shaft;

at least one sensing element in fixed relation to the housing of the power tool and configured to detect rotational motion of the housing in relation to the inertial mass; and

a controller electrically connected to the at least one sensing element and operable to initiate a protective operation based on the detected rotational motions of the housing in relation to the inertial mass.

23. The control system of claim 22 wherein said controller is operable to assess the detected rotational motion of the housing in relation to a threshold which is in part based on current motor speed of the power tool.

24. The control system of claim 22 wherein said controller further operable to determine angular velocity of the rotational motion and comparing the angular velocity to a predefined velocity threshold indicative of a bit jam condition.

25. The control system of claim 24 wherein said controller further operable to activate a protective operation when the angular velocity of the rotational motion exceeds the predefined velocity threshold.

26. The control system of claim 24 wherein said controller further operable to monitor direction of the rotational motion and to activate a protective operation when the angular velocity of the rotational motion exceeds the predefined velocity threshold and the direction of the rotational motion does not change within a predefined time period.

27. The control system of claim 24 wherein said controller further operable to monitor rotational displacement and to activate a protective operation when the angular velocity of the rotational motion exceeds the predefined velocity threshold and the rotational displacement exceeds a predefined displacement threshold.

28. The control system of claim 22 wherein said controller further operable to monitor rotational displacement and to activate a protective operation when the rotational displacement exceeds a predefined displacement threshold indicative of a bit jam condition.

29. The control system of claim 22 wherein the protective operation is selected from the group consisting of braking the rotary shaft, braking the motor, disengaging the motor from the rotary shaft, and reducing slip torque of a clutch disposed between the motor and the rotary shaft.