Braking and control circuit for electric power tools

• US 6,236,177 B1
• Filed: 06/04/1999
• Issued: 05/22/2001
• Est. Priority Date: 06/05/1998
• Status: Expired due to Term

• Current Assignee: Milwaukee Electric Tool Corporation (Techtronic Industries Company Limited)
• Original Assignee: Milwaukee Electric Tool Corporation (Techtronic Industries Company Limited)
• Inventors: Zick, Jonathan A., Willhide, Joseph W.
• Primary Examiner(s): Martin, David
• Assistant Examiner(s): Leykin, Rita
• Application Number:
  US09/326,028
• Time in Patent Office: 718 Days
• Field of Search: 318/362-374, 318/375-381, 318/493, 318/757, 318/17, 408/9
• US Class Current: 318/362
• 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: B25H 1/0071 by magnetic means
• 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: 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
• CPC Class Codes: H02P 3/14 by regenerative braking

Abstract

A power tool including a braking and control circuit. The braking and control circuit includes a microcontroller-based control means circuit. The microcontroller assures control of switch means, such as triacs, switches and relays, and ensures that braking is effectuated regardless of the phase in the power cycle of the alternating current. Also, the microcontroller is programmable so that the braking and control circuit accommodates different braking conditions for different power tools and accommodates combinations of braking conditions for the same power tool. Further, the microcontroller is programmable to configure the braking and control circuit so that the braking force applied to the motor and the stopping time of the motor are regulated and adjustable. This may be accomplished by outputting a control signal so that the switch means skips cycles in the alternating current or by otherwise adjusting the operation of the switch means.

Claims

1. A braking and control circuit for an electric motor, the motor including a housing, a stator supported by the housing, and a shaft rotatably supported by the housing, wherein the stator is selectively connected with an alternating current power source to rotatably drive the shaft, said braking and control circuit comprising:

a first switch for selectively disconnecting the motor from the power source;

a second switch electrically connected across the motor; and

a control circuit electrically connected with the power source, said control circuit receiving a current signal representing the alternating current and including a microcontroller electrically connected with at least one of said first switch and said second switch, said microcontroller being operable to output a control signal to control said at least one of said first switch and said second switch to brake the motor, said microcontroller being programmable to optimize braking of the motor and to select a braking start point corresponding to a start point phase angle of the alternating current, and said microcontroller outputting the control signal when the alternating current is in the start point phase angle.

2. The braking and control circuit as set forth in claim 1 wherein the alternating current has a plurality of cycles, and wherein said microcontroller is programmable to select a braking end point corresponding to an end point phase angle of the alternating current, the end point phase angle being a selected number of cycles after the start point phase angle, said microcontroller ceasing to output the control signal when the alternating current is in the end point phase angle.

3. The braking and control circuit as set forth in claim 1 wherein the alternating current has a plurality of cycles, and wherein said microcontroller outputs the control signal on selected ones of the plurality of cycles to control said at least one of said first switch and said second switch on the selected ones of the plurality of cycles to brake the motor.

4. A drill press comprising:

a housing;

a base connected with said housing and supporting said drill press on a workpiece, said base being selectively connected with the workpiece;

an electric motor supported by said housing and operable to drive a tool element, said motor including a stator supported by said housing, and a shaft rotatably supported by said housing, said motor being connectable with a power source;

a spindle connected with said shaft for rotation with said shaft, said spindle supporting a tool bit engageable with the workpiece;

braking and control means for controlling and braking said motor, said braking and control means including

switch means electrically connected with said motor, and

control means electrically connected with said switch means and operable to output a control signal to control said switch means to brake the motor; and

breakaway sensing means electrically connected with said control means and operable to output a breakaway signal to said control means if said base brakes away from the workpiece so that said control means outputs the control signal to said switch means to brake said motor.

5. A power tool comprising:

a housing;

an electric motor supported by said housing and operable to drive a tool element, said motor including a stator supported by said housing, and a shaft rotatably supported by said housing, said motor being connectable with a power source;

a spindle connected with said shaft for rotation with said shaft, said spindle supporting a tool element engageable with a workpiece;

braking and control means for controlling and braking said motor, said braking and control means including

switch means electrically connected with said motor, and

control means electrically connected with said switch means and operable to output a control signal to control said switch means to brake the motor; and

binding sensing means electrically connected with said control means and operable to output a binding signal to said control means if the tool element binds on the workpiece so that said control means outputs the control signal to said switch means to brake said motor.

6. In a power tool, a method for braking and controlling an electric motor, the motor including a housing, a stator supported by the housing, and a shaft rotatably supported by the housing, the motor being selectively connected with an alternating current power source to rotatably drive the shaft, said method comprising:

(a) providing a braking and control circuit including a first switch for selectively connecting the motor to the power source, a second switch electrically connected in parallel with the motor, and a control circuit including a microcontroller electrically connected with at least one of the first switch and the second switch;

(b) outputting a control signal from the microcontroller to control at least one of the first switch and the second switch to brake the motor said outputting act including outputting the control signal when the alternating current is in a start point phase angle;

(c) programming the microcontroller to optimize braking of the motor, said programming act including programming the microcontroller to select the braking start point corresponding to a start point phase angle of the alternating current; and

(d) providing to the control circuit a current signal representing the alternating current.

7. The method as set forth in claim 6 wherein (c) includes programming the microcontroller to select a braking end point corresponding to an end point phase angle of the alternating current, the end point phase angle being a selected number of cycles after the start point phase angle, and wherein said method further comprises:

(e) ceasing to output the control signal when the alternating current is in the end point phase angle.

8. The method as set forth in claim 6 wherein the alternating current has a plurality of cycles, and wherein (b) includes outputting the control signal on selected ones of the plurality of cycles to control the at least one of the first switch and the second switch on the selected ones of the plurality of cycles to brake the motor.

9. A software program for controlling the braking of a motor in a power tool, said software program controlling the motor by:

receiving a signal representing an alternating current supplied to the motor from a power source;

receiving a trigger signal to trigger braking of the motor;

evaluating the alternating current signal to determine a phase angle of the alternating current; and

outputting a control signal to control a switch to brake the motor when the current signal represents a selected brake start point phase angle.

10. The software program as set forth in claim 9 wherein said outputting act includes outputting a first control signal to a first switch to brake the motor, and outputting a second control signal to a second switch to brake the motor.

11. A braking and control circuit for an electric motor, the motor including a housing, a stator supported by the housing, and a shaft rotatably supported by the housing, wherein the stator is selectively connected with a power source to rotatably drive the shaft, said braking and control circuit comprising:

a first switch for selectively disconnecting the motor from the power source;

a second switch electrically connected across the motor; and

a control circuit electrically connected with said first switch and said second switch and operable to output a first control signal to said first switch and a second control signal to said second switch to brake the motor;

wherein said control circuit includes a microcontroller electrically connected with said first switch and said second switch, said microcontroller being operable to output the first control signal and the second control signal, wherein said microcontroller is programmable to optimize braking of the motor;

wherein the motor is braked in a stopping time, and wherein said microcontroller is programmable to change the stopping time of the motor.

12. A braking and control circuit for an electric motor, the motor including a housing, a stator supported by the housing, and a shaft rotatably supported by the housing, wherein the stator is selectively connected with a power source to rotatably drive the shaft, said braking and control circuit comprising:

a first switch for selectively disconnecting the motor from the power source;

a second switch electrically connected across the motor; and

a control circuit electrically connected with said first switch and said second switch and operable to output a first control signal to said first switch and a second control signal to said second switch to brake the motor;

wherein said control circuit includes a microcontroller electrically connected with said first switch and said second switch, said microcontroller being operable to output the first control signal and the second control signal, wherein said microcontroller is programmable to optimize braking of the motor;

wherein the motor is braked with a braking force, and wherein said microcontroller is programmable to change the braking force applied to the motor.

13. A braking and control circuit for an electric motor, the motor including a housing, a stator supported by the housing, and a shaft rotatably supported by the housing, wherein the stator is selectively connected with a power source to rotatably drive the shaft, said braking and control circuit comprising:

a first switch for selectively disconnecting the motor from the power source;

a second switch electrically connected across the motor; and

a control circuit electrically connected with said first switch and said second switch and operable to output a first control signal to said first switch and a second control signal to said second switch to brake the motor;

wherein said control circuit includes a microcontroller electrically connected with said first switch and said second switch, said microcontroller being operable to output the first control signal and the second control signal, wherein said microcontroller is programmable to optimize braking of the motor;

wherein the power source is an alternating current power source, wherein said control circuit receives a current signal representing a voltage of the alternating current, and wherein said microcontroller is programmable to output at least one of the first control signal and the second control signal at a point in the alternating current so that a desired voltage is supplied to brake the motor.

14. The braking and control circuit as set forth in claim 13 wherein the alternating current has a first cycle and a second cycle, and wherein said microcontroller is programmable to output at least one of the control signals at a point in the first cycle so that a first voltage is supplied to brake the motor and to output at least one of the control signals at a point in the second cycle so that a second voltage is supplied to brake the motor.

15. The braking and control circuit as set forth in claim 14 wherein the second voltage is greater than the first voltage.

16. In a power tool, a method for braking and controlling an electric motor, the motor including a housing, a stator supported by the housing, and a shaft rotatably supported by the housing, the motor being selectively connected with a power source to rotatably drive the shaft, said method comprising:

(a) providing a braking and control circuit including a first switch for selectively connecting the motor to the power source, a second switch electrically connected in parallel with the motor, and a control circuit electrically connected with the first switch and the second switch; and

(b) outputting a first control signal from the control circuit to control the first switch and a second control signal from the control circuit to control the second switch to brake the motor; and

wherein the control circuit includes a microcontroller electrically connected with the first switch and the second switch, wherein (b) includes outputting the first control signal and the second control signal from the microcontroller, wherein said method further comprises;

(c) programming the microcontroller to optimize braking of the motor;

wherein the motor is braked in a stopping time, and wherein (c) includes programming the microcontroller to change the stopping time of the motor.

17. In a power tool, a method for braking and controlling an electric motor, the motor including a housing, a stator supported by the housing, and a shaft rotatably supported by the housing, the motor being selectively connected with a power source to rotatably drive the shaft, said method comprising:

(a) providing a braking and control circuit including a first switch for selectively connecting the motor to the power source, a second switch electrically connected in parallel with the motor, and a control circuit electrically connected with the first switch and the second switch; and

(b) outputting a first control signal from the control circuit to control the first switch and a second control signal from the control circuit to control the second switch to brake the motor; and

wherein the control circuit includes a microcontroller electrically connected with the first switch and the second switch, wherein (b) includes outputting the first control signal and the second control signal from the microcontroller, wherein said method further comprises;

(c) programming the microcontroller to optimize braking of the motor;

wherein the motor is braked in a stopping time, and wherein (c) includes programming the microcontroller to change the braking force applied to the motor.

18. In a power tool, a method for braking and controlling an electric motor, the motor including a housing, a stator supported by the housing, and a shaft rotatably supported by the housing, the motor being selectively connected with a power source to rotatably drive the shaft, said method comprising:

(a) providing a braking and control circuit including a first switch for selectively connecting the motor to the power source, a second switch electrically connected in parallel with the motor, and a control circuit electrically connected with the first switch and the second switch; and

(b) outputting a first control signal from the control circuit to control the first switch and a second control signal from the control circuit to control the second switch to brake the motor;

wherein the control circuit includes a microcontroller electrically connected with the first switch and the second switch, wherein (b) includes outputting the first control signal and the second control signal from the microcontroller, wherein said method further comprises the act of;

(c) programming the microcontroller to optimize braking of the motor;

wherein the power source is an alternating current power source, and wherein said method further comprises the act of;

(d) providing to the control circuit a current signal representing a voltage of the alternating current; and

wherein (c) includes programming the microcontroller to output at least one of the first control signal and the second control signal at a point in the alternating current so that a desired voltage is supplied to brake the motor.

19. The method as set forth in claim 18 wherein the alternating current has a first cycle and a second cycle, and wherein act (c) includes programming the microcontroller to output the control signal at a point in the first cycle so that a first voltage is supplied to brake the motor and to output at least one of the control signals at a point in the second cycle so that a second voltage is supplied to brake the motor.

20. The method as set forth in claim 19 wherein the second voltage is greater than the first voltage.

21. A software program for controlling the braking of a motor in a power tool, said software program controlling the motor by:

(a) receiving a signal;

(b) outputting a first control signal to control a first switch to brake the motor; and

(c) outputting a second control signal to a second switch to brake the motor;

wherein the received signal is a signal representing an alternating current supplied to the motor from a power source, wherein said software program further controls the motor by, before (b);

(d) receiving a trigger signal to trigger braking of the motor; and

(e) evaluating the alternating current signal to determine the phase angle of the alternating current;

wherein (b) includes outputting the control signal when the current signal represents a selected brake start point phase angle.