Electricity: motive power systems – Braking – Dynamic braking
Patent
1996-01-11
1998-05-26
Wysocki, Jonathan
Electricity: motive power systems
Braking
Dynamic braking
318113, 318248, 318245, H02D 300
Patent
active
057571546
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to braking a series/Universal motor having a field winding for normal operation and a separate field winding for braking in addition to the armature winding.
BACKGROUND ART
Regulations pertaining to certain motor-operated implements such as hedge trimmers, which require two handed operation are changing to require a structure that will assist in braking of the motor. More specifically, these regulations require that both gripping surfaces contain a switch which must be actuated to operate the implement. These switches are interconnected such that releasing the grip on either handle disconnects the motor from the power supply circuit.
Additionally, the regulations typically specify a maximum stopping time--the time it takes the blades or cutting devices to stop after one of the grips is released. This maximum stopping time is usually less than the normal coasting time of the motor and drive mechanism. These regulations seek to prevent undesirable contact of the hand with the blade. Additionally, the regulations seek to prevent the cutting of power supply cords, and other objects not meant to be cut, when the hedge trimmer is set down with the blade still coasting.
Today, there are commercially available products that comply with this requirement. In these products, there are three general methods of compliance. In the first method, two switch braking is accomplished by interrupting the power supply circuit with a switch in each handle and activating a mechanical braking mechanism, such as a hand brake. Another method is to use an electrical dynamic brake on one switch and a mechanical braking mechanism activated by the other switch. The third method utilizes two switches with electrical braking in conjunction with a permanent magnet motor.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide improved braking in a motor-operated implement having two switches for operating the motor such that when either of the two switches are released, the cutting blade will stop quickly.
In a preferred construction, the hedge trimmer would have one switch located in each handle, thereby insuring that both hands are properly positioned on the normal gripping surfaces before the unit can be operated. Releasing the hand from either handle would disconnect the power supply from the motor and activate the braking action. The switches could be single-pole, double-pole or a combination of both. More specifically, during normal operation, actuation of both switches is required to provide power to the main field coil which is connected in series with the armature winding. Deactuating either switch disconnects the motor from the power supply and connects the braking coil across the armature winding, thereby braking the motor.
In carrying out the above object and other objects and features of the present invention, there is provided a motor braking circuit arrangement, for use with a series/universal motor and a power supply for supplying power to the motor, the motor having a stator and an armature for rotating relative to the stator. The circuit arrangement comprises a field winding wound about the stator, the field winding electrically connected in series with an armature winding wound about the armature. The circuit also comprises a separate brake winding wound about the stator, and two series-connected single-pole switches, each switch being capable of assuming a first position associated with normal motor operation and a second position associated with motor braking. The switches are electrically interconnected with the power supply, the armature and the brake winding such that the motor is energized by the power supply when both switches are in said first position, and such that when either of the switches is in the second position, the motor is disconnected from the power supply and the brake winding is electrically connected in parallel with the armature so as to effect motor braking.
In alternative embodiments, the switches are double-pole switches
REFERENCES:
patent: 3593085 (1971-07-01), Decker
patent: 4096423 (1978-06-01), Bailey et al.
patent: 4217532 (1980-08-01), Alfieri et al.
patent: 4794273 (1988-12-01), McCullough et al.
patent: 5517093 (1996-05-01), Augustyniak et al.
Ryobi Motor Products Corp.
Wysocki Jonathan
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