US 5,847,522 A · Locking devices and control circuitry for permanent magnet electric motors

Abstract

A positive locking device is provided in order to prevent a motor from rotating after power has been removed. The positive locking device has a plate mounted on the motor which engages a disk or hub on the shaft of the motor. In another aspect of the invention, solid state circuitry for switching a permanent magnet motor and providing dynamic braking thereto is provided. The circuitry allows the back EMF generated by the armature coils of a permanent magnet motor to cause a current to flow through the motor when power is removed. This back EMF may be used to help produce smooth engagement of the locking device. In another aspect of the invention, a dynamic braking circuit for a dual armature permanent magnet motor is provided. By applying current to one or the other of two oppositely wound armature coils the motor is made to rotate in either direction. When power is removed from the active armature, this armature is short-circuited through a diode. The same diode is used to dynamically brake the motor when power is removed from the other armature. In both cases the spinning rotor will quickly slow down to facilitate smooth engagement of the positive locking device.

Claims20

Dependent claims

A locking mechanism for selectively locking the rotor of an electric motor against rotation relative to a stationary part of the motor when power has been removed from the motor and the motor has consequently slowed down to a speed which is relatively slow compared to its speed when power is being applied to the motor, said locking mechanism comprising:

a first member which rotates with said rotor;
a second member which is fixed relative to the stationary part of said motor, said first and second members being movable relative to one another substantially parallel to an axis about which said rotor rotates, said first and second members having respective first and second parts which can interfit with one another to substantially prevent rotation of said first member relative to said second member when said first and second members are in a first position relative to one another substantially parallel to said axis, said first and second parts not interfitting with one another and thus permitting said first member to rotate relative to said second member when said first and second members are in a second position relative to one another substantially parallel to said axis;
a spring for resiliently urging said first and second members to move from said second position to said first position relative to one another substantially parallel to said axis;
and
an electromagnet for selectively overcoming the urging of said spring and holding said first and second members in said second position relative to one another substantially parallel to said axis when said electromagnet is energized, said first and second parts being sized and shaped and the urging of said spring being sufficiently weak so that said first and second parts do not enter into interfitting relationship when said electromagnet is de-energized until said motor has slowed down to said relatively slow speed.

2 more elements

For use with a motor having a rotatable shaft which defines a shaft axis, said motor causing said shaft to rotate when electrical power is applied to said motor, a positive locking device comprising:

a plate which is fixedly mounted on said motor with respect to rotation about said shaft axis and movably mounted on said motor with respect to motion substantially parallel to said shaft axis;
a disk which is fixedly mounted on said shaft, said disk being located proximate said plate, said disk and said plate being adapted to engage one another so as to prevent said shaft from rotating;
a coil fixedly attached to said motor and located proximate said plate so that said plate is positioned between said coil and said disk;
a plurality of guide screws which are fixedly attached to said plate and slidably attached to said motor so as to attach said plate to said motor;
and
at least one spring for urging said plate away from said coil and toward said disk, wherein:
when electrical power is applied to said motor, electrical current flows through said coil and causes said coil to produce a magnetic field which urges said plate toward said coil and away from said disk so as to allow said disk to rotate freely;
and
when electrical power is removed from said motor and electrical current substantially ceases to flow through said coil, said spring urges said plate toward said disk so as to allow said plate to engage said disk in order to provide positive locking of said motor.

6 more elements

Dependencies are inferred from the claim text.

Locking devices and control circuitry for permanent magnet electric motors

Life of this patent

Locking devices and control circuitry for permanent magnet electric motors

Life of this patent

Abstract

Claims20