Control and protection methodologies for a motor control module

• US 7,551,411 B2
• Filed: 10/06/2006
• Issued: 06/23/2009
• Est. Priority Date: 10/12/2005
• Status: Active Grant

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Beers, Daniel R., Woods, Samuel G., Forster, Michael K., Leh, Jason K., Vanko, John C., Gallagher, William F., Usselman, Robert A., Kalbfleisch, William G., Privett, Zollie W.
• Primary Examiner(s): Leykin; Rita
• Application Number:
  US11/543,990
• Publication Number:
  US 20070097566A1
• Time in Patent Office: 991 Days
• Field of Search: 361/33, 361/23, 361/1, 318/434, 388/819, 408/124
• US Class Current: 361/33
• CPC Class Codes: B24B 23/028 Angle tools
• CPC Class Codes: B24B 55/00 Safety devices for grinding or polishing machines; Accessories fitted to grinding or polishing machines for keeping tools or parts of the machine in good working condition of general applicability for machine tools B23Q11/00; in general F16P
• CPC Class Codes: H02H 5/04 responsive to abnormal temperature specially adapted for electric machines H02H7/0852
• CPC Class Codes: H02H 7/08 for dynamo-electric motors
• CPC Class Codes: H02K 11/33 Drive circuits, e.g. power electronics H02K11/38 takes precedence
• CPC Class Codes: H02M 5/2573 with control circuit
• CPC Class Codes: H02P 25/14 Universal motors H02P25/12 takes precedence
• CPC Class Codes: H02P 29/02 Providing protection against overload without automatic interruption of supply protection against faults of stepper motors H02P8/36
• CPC Class Codes: Y10T 408/65 Means to drive tool

Abstract

A motor control module designed to control operation of a plurality of different motors in a plurality of different tools a power tool uses an electronic clutch in the module in conjunction with a mechanical clutch in the tool to protect the tool against an overload event. The module is adapted to implement methods to provide aural and/or tactile feedback to a tool user as a warning of an impending or current fault condition in the tool. The module can prevent power from inadvertently turning on either after an overload event has cleared with the tool plugged in and its power switch on, or after plugging in the tool within the power switch on. The control module is adapted to provide torque control for the power tool, to estimate tool motor temperature and to inform a tool user when a servicing need in the tool is required.

Claims

1. A power tool, comprising:

a tool motor drivably coupled to a rotary shaft,

an electronic clutch interfaced with the tool motor;

a microcontroller configured to detect a fault condition in the power tool and initiate a protective action via the electronic clutch to remove or reduce power to the tool motor in response to the detected fault condition; and

a mechanical clutch disposed between the tool motor and the rotary shaft that operates independently from the microcontroller.

2. The power tool of claim 1, wherein the combination of using the electronic clutch with the mechanical clutch in the tool enables a cycle life of the mechanical clutch to increase by at least a factor of 10 as compared to using the mechanical clutch alone in the tool.

3. The power tool of claim 1, wherein the microcontroller controls firing of a triac in the tool to control voltage to the tool motor and, based on detection of a fault condition by the electronic clutch, is configured to control the triac to fully shut off the tool motor, pulse the tool motor, reduce voltage applied to the tool motor, or to perform at least one of the above protective actions in combination with turning on an indicator such as an LED.

4. The power tool of claim 1, wherein the electronic clutch is a software-based routine iterated by a processor in the microcontroller.

5. The power tool of claim 1, wherein the electronic clutch is configurable in a first mode in which a given parameter is sampled, and a fault condition is detected if the sampled parameter exceeds a first threshold and if a timer count, incremented based on the first threshold being exceeded, exceeds a second threshold.

6. The power tool of claim 5, wherein the given parameter is a current value calculated from digitized current samples of half line-cycle positions or full line-cycle positions of an AC voltage waveform powering the tool.

7. The power tool of claim 6, wherein the calculated current value is one of an instantaneous, average or root mean square (RMS) current value, and the first threshold is based on an average current, RMS current or maximum instantaneous current value.

8. The power tool of claim 5, wherein the given parameter is a motor speed of the tool motor and the threshold is based on tool motor speed.

9. The power tool of claim 1, wherein the electronic clutch is configurable in a second mode in which in which a given parameter is sampled, a difference value is calculated based on the sampled parameter and compared to a first threshold, and a fault condition is detected if the difference value exceeds the first threshold.

10. The power tool of claim 9, wherein, if the difference value is less than or equal to the first threshold, the electronic clutch compares the difference value to a second threshold smaller than the first, and a fault condition is detected if the difference value exceeds the second threshold for at least N consecutive line cycles, where N is ≧

2.

11. The power tool of claim 9, wherein the difference value is a difference between current values calculated for a previous line cycle and a current line cycle from samples of an AC voltage waveform powering the tool.

12. The power tool of claim 9, wherein the difference value is a difference between motor speed values calculated at two different timings.

13. The power tool of claim 1, wherein the tool is prevented from being inadvertently turned on even after the fault condition has been cleared after initiation of the protective action.

14. The power tool of claim 1, further comprising:

an on/off power switch, and

a cord attached to the tool for providing AC line power to the tool,

wherein the tool is prevented from being inadvertently turned on with the tool plugged in and powered, but the tool has reached an overload event that has caused a shutdown while still plugged in, and the overload event has cleared with the power switch still in the on position.

15. In a corded power tool having an on/off power switch and a control module, the control module including a microcontroller for controlling power to a tool motor via a triac, a method of preventing the corded power tool from inadvertently turning on either after an overload event has cleared with the tool plugged in and power switch on, or after plugging in the tool with the power switch on, the method comprising:

performing a series of voltage checks at different phase positions in each line cycle of an AC waveform supplied to the tool to detect the presence of voltage across the triac, and

preventing the triac from firing until a voltage check indicates that there is no voltage in a given line cycle.

16. The method of claim 15, wherein a voltage check indicates no voltage in a given line cycle after the user has cycled the power switch to an off position prior to restarting the power tool.

17. The method of claim 15, wherein the series of voltage checks are performed consecutively to eliminate random noise due to electrical spikes, surges or suppressions causing periods of voltage across the triac.

18. The method of claim 15, wherein performing a series of voltage checks includes:

setting a first checkpoint value based on a given conduction angle of the triac or based on a given time duration, and

commencing checks of voltage across the triac once the first checkpoint has been reached.

19. The method of claim 18, wherein if a voltage check after reaching the first checkpoint indicates no voltage across the triac, the method further comprises:

checking whether at least two consecutive line cycles of the AC voltage waveform have been tested, and if not, checking whether additional checkpoints have been tested.

20. The method of claim 19, wherein a given line cycle has multiple checkpoints.

21. The method of claim 19, wherein if three consecutive line cycles of the AC voltage waveform have been tested, the method further comprises:

determining whether voltage across the triac is high, and if so,

inserting a delay to wait for the power switch to close, wherein if the voltage across the triac is still high after the delay elapses, the power switch closes so that the power tool is turned on for operation.