Apparatus and method for braking electric motors

• US 6,037,729 A
• Filed: 01/28/1998
• Issued: 03/14/2000
• Est. Priority Date: 02/06/1997
• Status: Expired due to Term

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Woods, Samuel G., Spampinato, David M., White, Paul S.
• Primary Examiner(s): MARTIN, DAVID S
• Application Number:
  US09/014,451
• Time in Patent Office: 776 Days
• Field of Search: 318/245, 318/362-382, 318/759-765, 318/778-797, 310/50, 310/210, 310/158
• US Class Current: 318/375
• CPC Class Codes: B27B 5/38 Devices for braking the circular saw blade or the saw spindle; Devices for damping vibrations of the circular saw blade, e.g. silencing B23D47/005 takes precedence
• CPC Class Codes: H01H 21/10 Casing of switch constituted by a handle serving a purpose other than the actuation of the switch
• CPC Class Codes: H01H 21/52 with means for introducing a predetermined time delay
• CPC Class Codes: H01H 2300/002 Application electric motor braking, e.g. pole reversal of rotor, shorting motor coils, also for field discharge
• CPC Class Codes: H01H 9/548 Electromechanical and static switch connected in series
• CPC Class Codes: H02P 1/16 for starting dynamo-electric motors or dynamo-electric converters
• CPC Class Codes: H02P 3/06 for stopping or slowing an individual dynamo-electric motor or dynamo-electric converter
• CPC Class Codes: H02P 3/12 by short-circuit or resistive braking

Abstract

A braking circuit for braking an electric motor having an armature and run and brake windings, which includes a switching circuit disposed between a source of electrical power and the run winding, this circuit being operable to disconnect the run winding from the source of electrical power. The braking circuit further includes a switching mechanism operable to connect the brake winding in order to brake the electric motor. The switching mechanism preferably connects the brake winding after a predetermined period of time has elapsed from the disconnection of the run winding. This braking circuit can be used in a saw for braking the saw'"'"'s blade.

Claims

1. A braking circuit for braking an electric motor comprising an armature, first and second run windings and a first brake winding, the braking circuit comprising:

a first switch disposed between a source of electrical power and the first run winding, the first switch being operable to disconnect the first run winding from the source of electrical power;

a semiconductor device disposed between the source of electrical power and the second run winding;

a second switch connected to the source of electrical power for changing status of the semiconductor device, the second switch changing the status of the semiconductor device after a first predetermined period of time has elapsed from the disconnection of the first run winding; and

a third switch being operable to connect the first brake winding in order to brake the electric motor, wherein the first brake winding is connected after a second predetermined period of time has elapsed from the status change of the semiconductor device.

2. The braking circuit of claim 1, wherein said third switch is disposed between the first brake winding and the armature.

3. The braking circuit of claim 1, wherein the semiconductor device is a thyristor.

4. The braking circuit of claim 1, wherein the first predetermined period of time is between about 10 milliseconds and about 500 milliseconds.

5. The braking circuit of claim 1, wherein the second predetermined period of time is between 0 milliseconds and about 100 milliseconds.

6. A saw comprising:

an electric motor comprising an armature, first and second run windings and a first brake winding;

a first switch disposed between a source of electrical power and the first run winding, the first switch being operable to disconnect the first run winding from the source of electrical power;

a semiconductor device disposed between the source of electrical power and the second run winding;

a second switch connected to the source of electrical power for changing status of the semiconductor device, the second switch changing the status of the semiconductor device after a first predetermined period of time has elapsed from the disconnection of the first run winding; and

a third switch being operable to connect the first brake winding in order to brake the electric motor, wherein the first brake winding is connected after a second predetermined period of time has elapsed from the status change of the semiconductor device.

7. The saw of claim 6, wherein said third switch is disposed between the first brake winding and the armature.

8. The saw of claim 6, wherein the semiconductor device is a thyristor.

9. The saw of claim 6, wherein the first predetermined period of time is between about 10 milliseconds and about 500 milliseconds.

10. The saw of claim 6, wherein the second predetermined period of time is between 0 milliseconds and about 100 milliseconds.

11. The saw of claim 6, further comprising a blade driven by the motor.

12. The saw of claim 6, further comprising a base.

13. The saw of claim 12, wherein the motor is supported by the base.

14. The saw of claim 12, wherein the motor is movably supported by the base.

15. The saw of claim 12, wherein the base further comprises a table.

16. The saw of claim 6, wherein the saw is a miter saw.

17. A starting circuit for starting an electric motor comprising an armature, first and second run windings and a first brake winding, the starting circuit comprising:

a first switch being operable to disconnect the first brake winding;

a second switch disposed between a source of electrical power and the first run winding, the second switch being operable to connect the first run winding to the source of electrical power after the disconnection of the first brake winding;

a semiconductor device disposed between the source of electrical power and the second run winding; and

a third switch connected to the source of electrical power for changing status of the semiconductor device, the third switch changing the status of the semiconductor device after a predetermined period of time has elapsed from the connection of the first run winding.

18. The starting circuit of claim 17, wherein said first switch is disposed between the first brake winding and the armature.

19. The starting circuit of claim 17, wherein the semiconductor device is a thyristor.

20. The starting circuit of claim 17, wherein the predetermined period of time is between 0 milliseconds and about 150 milliseconds.

21. A saw comprising:

an electric motor comprising an armature, first and second run windings and a first brake winding;

a first switch being operable to disconnect the first brake winding;

a second switch disposed between a source of electrical power and the first run winding, the second switch being operable to connect the first run winding to the source of electrical power after the disconnection of the first brake winding;

a semiconductor device disposed between the source of electrical power and the second run winding; and

a third switch connected to the source of electrical power for changing status of the semiconductor device, the third switch changing the status of the semiconductor device after a predetermined period of time has elapsed from the connection of the first run winding.

22. The saw of claim 21, wherein said first switch is disposed between the first brake winding and the armature.

23. The saw of claim 21, wherein the predetermined period of time is between 0 milliseconds and about 150 milliseconds.

24. The saw of claim 21, further comprising a blade driven by the motor.

25. The saw of claim 21, further comprising a base.

26. The saw of claim 25, wherein the motor is supported by the base.

27. The saw of claim 25, wherein the motor is movably supported by the base.

28. The saw of claim 25, wherein the base further comprises a table.

29. The saw of claim 21, wherein the saw is a miter saw.

30. The saw of claim 21, wherein the semiconductor device is a thyristor.