Amperage control for protection of battery over current in power tools

• US 7,276,878 B2
• Filed: 09/29/2006
• Issued: 10/02/2007
• Est. Priority Date: 02/18/2003
• Status: Expired due to Fees

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Phillips, Alan, Jones, Julie L.
• Primary Examiner(s): DUDA, RINA I
• Application Number:
  US11/529,304
• Publication Number:
  US 20070019933A1
• Time in Patent Office: 368 Days
• Field of Search: 318/811, 318/432, 318/599, 388/811, 388/815, 388/907.5, 388/937
• US Class Current: 318/811
• 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: Y10S 388/937 Hand tool

Abstract

Amperage control of a power tool motor is provided by pulse width modulation of current from a power supply. The pulse width modulation may be varied according to the determined motor current and measured power supply voltage. The power supply may include a battery such as lithium ion or nickel cadmium.

Claims

1. A power tool, comprising:

a housing;

a motor disposed within the housing and providing torque to the power tool;

a power supply disposed within the housing and including a plurality of lithium ion batteries providing a direct voltage between 30 and 40 volts to the motor; and

a pulse width modulation controller within the housing for varying the pulse width of voltage pulses supplied to the motor based on a comparison of the motor current to one of a plurality of different thresholds.

2. The power tool of claim 1, wherein the pulse width modulation controller changes the pulse width based on a comparison of the motor current to one of at least three different thresholds.

3. The power tool of claim 1, wherein the pulse width modulation controller changes the pulse width from an initial pulse width to one of zero, a first alternative pulse width and a second alternative pulse width based on the comparison to a given threshold.

4. The power tool of claim 1, wherein the lithium ion batteries are rechargeable.

5. The power tool of claim 1, wherein the pulse modulation controller includes a switch that supplies current to the motor when the switch is turned on.

6. The power tool of claim 5, wherein the pulse modulation controller further includes a microprocessor that turns the switch on and off.

7. The power tool of claim 5, wherein the pulse modulation controller further includes voltage measuring circuitry to determine a turn on time for the switch.

8. The power tool of claim 7, wherein the voltage measuring circuitry measures battery voltage and motor voltage.

9. The power tool of claim 8, further comprising potentiometer for speed control of the motor, wherein the voltage measuring circuitry measures a voltage across the potentiometer.

10. The power tool of claim 8, wherein the pulse width modulation controller further includes a ramp generator that provides a ramp signal and a comparator that compares the ramp signal to a measured motor voltage to determine the pulse width modulation waveform.

11. An apparatus for limiting current to a load, comprising:

a motor for providing torque to a load;

a power supply including a plurality of lithium ion batteries providing a direct voltage between 30 and 40 volts to the motor;

a controller for determining an amount of motor current supplied to the motor; and

a pulse width modulated (PWM) switch that supplies motor current to the motor under control of the controller, wherein a duty cycle of pulse width modulation of the switch is varied by the controller based on a comparison of the motor current to one of a plurality of different thresholds.

12. The apparatus of claim 11, wherein the controller changes the pulse width based on a comparison of the motor current to one of at least three different thresholds.

13. The apparatus of claim 11, wherein the controller changes the pulse width from an initial pulse width to one of zero, a first alternative pulse width and a second alternative pulse width based on the comparison to a given threshold.