Power tool anti-kickback system with rotational rate sensor

• US 20060081386A1
• Filed: 10/19/2005
• Published: 04/20/2006
• 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, Puzio, Daniel, West, Joshua D., Schell, Craig, Deshpande, Uday, Waikar, Shailesh P., Hilsher, William F.
• Granted Patent: US 7,410,006 B2
• Time in Patent Office: Days
• US Class Current: 173/2
• 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

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 control scheme employed by the power tool may initiate different protective operations for different tool conditions.

Claims

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

a rotational rate sensor having a resonating mass, wherein the rotational rate sensor 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 shaft; and

a controller electrically connected to the rotational rate sensor and operable to initiate a protective operation based on the signal.

2. The control system of claim 1 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 rotary shaft.

3. The control system of claim 1 wherein the controller is operable to activate a protective operation when the rotational speed exceeds a predefined threshold.

4. The control system of claim 1 wherein the controller is operable to pulse the motor a plurality of times when the rotational speed exceeds a predefined threshold.

5. The control system of claim 1 wherein the controller is operable to activate a first protective operation when an angular displacement of the tool exceeds a first threshold and to activate a second protective operation when the angular displacement exceeds a second threshold, where the angular displacement is derived from the rotational speed and the first protective operation is different than the second protective operation.

6. The control system of claim 1 wherein the controller is operable to determining rotational energy of experienced by the power tool based on the rotational motion and to activate a protective operation when the rotational energy exceeds a predefined threshold.

7. The control system of claim 1 wherein the controller is operable to activate a protective operation 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.

8. A control scheme for a power tool having a rotary shaft, comprising:

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

determining a condition of the tool based on said rotational motion of the power tool;

initiating a first protective operation upon detecting a first tool condition; and

initiating a second protective operation upon detecting a second tool condition, where the first protective operation is different than the second protective operation.

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

10. The control scheme of claim 8 wherein determining a condition of the tool further comprises determining an angular displacement of the power tool about the axis of the rotary shaft.

11. The control scheme of claim 10 further comprises pulsing a motor of the power tool when the angular displacement exceeds a first threshold and disconnecting power to the motor when the angular displacement exceeds a second threshold which is greater than the first threshold.

12. The control scheme of claim 8 wherein determining a condition of the tool further comprises determining an angular velocity of the power tool about the axis of the rotary shaft.

13. The control scheme of claim 12 further comprises pulsing a motor of the power tool when the angular velocity exceeds a first threshold and disconnecting power to the motor when the angular velocity exceeds a second threshold which is greater than the first threshold.

14. The control scheme of claim 8 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, and reducing slip torque of a clutch disposed between the motor and the rotary shaft.

15. A control scheme for a power tool having a rotary shaft, comprising:

determining rotational motion of the power tool about a longitudinal axis of the rotary shaft;

determining rotational energy of experienced by the power tool based on the rotational motion; and

initiating a protective operation in relation to the power tool when the rotational energy exceeds a threshold.

16. The control scheme of claim 15 wherein monitoring rotational motion further comprises using a rotational acceleration sensor disposed in a handle of the power tool.

17. The control scheme of claim 15 wherein monitoring rotational motion further comprises using a rotational motion sensor that measures rotational velocity based on Coriolis acceleration.

18. The control scheme of claim 15 wherein determining rotational energy is computed in accordance with

E_ω

<sub>—

TOOL</sub>=(I)(ω

_TOOL)²,

where ω

_TOOL is the rotational motion and I is a moment of inertia.

19. The control scheme of claim 15 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, and reducing slip torque of a clutch disposed between the motor and the rotary shaft.