Energy source monitoring and control system for power tools

• US 20080059089A1
• Filed: 09/06/2006
• Published: 03/06/2008
• Est. Priority Date: 09/06/2006
• Status: Active Grant

• Current Assignee: Eastway Fair Company Limited
• Original Assignee: Eastway Fair Company Limited
• Inventors: Soultanian, Daniel, Hornick, George Michael, Minalga, Philip F.
• Granted Patent: US 7,496,460 B2
• Time in Patent Office: Days
• US Class Current: 702/63
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence
• CPC Class Codes: H02J 7/0063 with circuits adapted for supplying loads from the battery
• CPC Class Codes: H02J 7/007182 in response to battery voltage

Abstract

An energy source monitoring system evaluates the state of an energy source and responsively controls a power tool or other device. The energy source may be, for example, a power tool battery pack that includes multiple individual battery packs connected in series. The energy source monitoring system may be incorporated into a power tool, screwdriver, flashlight, audio and/or video player, or any other device. The energy source monitoring system intelligently exercises control over the power applied to the device (e.g., to the motor in the device). In one implementation, the energy source monitoring system detects when voltages in the energy source have fallen below a cutoff level, yet allows the device to continue running until the operator finishes the current device operation (e.g. a miter saw cut, or playback of a song).

Claims

1. A power tool energy source monitoring and control system comprising:

a main power switch operable to connect series connected voltages V1 and V2 to a power tool motor voltage input;

a switch state control input coupled to the main power switch;

voltage measurement logic operable to determine V1 and V2;

comparison logic operable to determine a cutoff condition when V1, V2, or both V1 and V2 fade below a cutoff threshold for disconnecting the voltages V1 and V2 from the power tool; and

switch control logic operable to use the switch state control input to hold the main power switch in an ‘

ON’

state for an extension time despite determination of the cutoff condition.

2. The power tool energy source monitoring and control system of claim 1, where:

the extension time is a completion time of an existing power tool operation.

3. The power tool energy source monitoring and control system of claim 2, further comprising:

a trigger switch which initiates power tool operation, and where;

the tool operation completion time ends when the trigger switch state changes from ‘

ON’

to ‘

OFF’

.

4. The power tool energy source monitoring and control system of claim 3, where the switch control logic is operable to use the switch state control input to change the main power switch to an ‘

OFF’

state after the trigger switch state changes to ‘

OFF’

, and is further operable to prevent reconnection of V1 and V2 for power tool restart until V1 and V2 rise above an operation threshold for allowing the power tool to start.

5. The power tool energy source monitoring and control system of claim 4, where the voltage measurement logic comprises a first voltage divider across both V1 and V2 in series and a second voltage divider across V2.

6. The power tool energy source monitoring and control system of claim 1, where the cutoff threshold comprises a predetermined percentage of a nominal energy source voltage for disconnecting the voltages V1 and V2 from the power tool.

7. The power tool energy source monitoring and control system of claim 4, where the operation threshold comprises a predetermined percentage of a nominal energy source voltage for allowing the power tool to start.

8. The power tool energy source monitoring and control system of claim 1, comprising a controller which implements the voltage measurement logic, the comparison logic, and the switch control logic.

9. A method for power tool energy source monitoring and control, the method comprising:

providing a switch state control input coupled to switch control logic and to a main power switch which connects series connected voltages V1 and V2 to a power tool motor voltage input;

measuring V1;

measuring V2;

determining a cutoff condition when V1, V2, or both V1 and V2 fade below a cutoff threshold for disconnecting V1 and V2 from the power tool motor voltage input; and

holding the main power switch in an ‘

ON’

state using the switch state control input for an extension time despite the cutoff condition, then releasing the main power switch to the ‘

OFF’

state.

10. The method of claim 9, where holding comprises:

holding the power switch in the ‘

ON’

state until a trigger switch is released.

11. The method of claim 9, where holding comprises:

maintaining a main power dropout switch in an ‘

ON’

state.

12. The method of claim 9, further comprising:

illuminating a warning indicator when V1, V2, or both V1 and V2 have faded below the cutoff threshold.

13. The method of claim 9, further comprising:

preventing reconnection of V1 and V2 until V1 and V2 rise above an operation threshold.

14. The method of claim 9, further comprising:

determining when V1, V2, or both V1 and V2 fade below a fading threshold, and responsively illuminating a warning indicator.

15. A power tool energy source monitoring and control system comprising:

a energy source input that accepts series connected voltages V1 and V2;

a first voltage measurement point coupled to the energy source input;

a second voltage measurement point coupled to the energy source input;

a main power switch coupled to the energy source input and comprising a switch state control input; and

a controller coupled to the first and second voltage measurement points and the main power switch;

a memory coupled to the controller, the memory comprising;

a cutoff threshold for disconnecting the series connected voltages V1 and V2 for stopping power tool operation;

an operation threshold for connecting the series connected voltages V1 and V2 to allow power tool startup;

a fading threshold for determining when voltages V1 and V2 are fading; and

an energy source monitoring program operable to;

measure the series connected voltage V1;

measure the series connected voltage V2;

determine when both V1 and V2 exceed the operation threshold and responsively hold the main power switch in an ‘

ON’

state using the switch state control input;

determine when V1, V2, or both V1 and V2 fade below the fading threshold and responsively illuminate a warning indicator; and

determine when V1, V2, or both V1 and V2 fade below the cutoff threshold for disconnecting V1 and V2 to stop power tool operation, and responsively hold the main power switch in an ‘

ON’

state for an extension time using the switch state control input.

16. The power tool energy source monitoring and control system of claim 15, where the extension time persists while a trigger switch is in an ‘

ON’

state.

17. The power tool energy source monitoring and control system of claim 16, where the energy source monitoring program is further operable to:

prevent reconnection of V1 and V2 to prevent tool restart until V1 and V2 rise above the operation threshold.

18. The power tool energy source monitoring and control system of claim 15, where the cutoff threshold comprises a predetermined percentage of a nominal energy source voltage for determining when to disconnect the voltages V1 and V2.

19. The power tool energy source monitoring and control system of claim 15, where the operational threshold comprises a predetermined percentage of a nominal energy source voltage for determining when to allow power tool startup.

20. The power tool energy source monitoring and control system of claim 15, where the fading threshold comprises a predetermined percentage of a nominal energy source voltage for determining when to illuminate the warning indicator.

21. The power tool energy source monitoring and control system of claim 15, where the main power switch is a dropout switch.

22. A method for power tool control, comprising:

identifying activation of a trigger switch for motor activation;

despite activation of the trigger switch, limiting maximum motor speed to less than a final motor speed;

detecting a state transition of the power tool;

in response to the state transition, advancing the motor speed to the final motor speed.

23. The method of claim 22, where detecting comprises:

determining a change in an arm state by monitoring a power tool arm switch.

24. The method of claim 22, where limiting maximum motor speed comprises:

generating Pulse Width Modulated (PWM) control signals that limit maximum motor speed to approximately 50% of the final motor speed.

25. The method of claim 22, where detecting comprises:

determining a first change in arm state by monitoring a power tool arm switch; and

further comprising;

determining completion of a power tool operation;

determining a second change in arm state, and in response, limiting motor maximum motor speed to less than a final motor speed.