This invention relates to electric motors and in particular, to a PMDC motor with a speed sensor.
Known speed sensors for PMDC motors use a coil to pick up electromagnetic signals emitted by the motor as the rotor turns. Known arrangements generally mount the sensor coil in the field magnet or in the space between adjacent magnets, resulting in a complex structure or assembly.
The present invention provides a PMDC motor with a speed sensor in which the coil is conveniently located.
Accordingly, the present invention provides a PMDC motor comprising: a shaft; a rotor core mounted on the shaft; a commutator mounted on the shaft adjacent the rotor core; windings wound about the rotor core and terminated on the commutator; a permanent magnet stator having at least one magnet confronting the rotor core; a housing supporting the stator; an end cap fixed to the housing and supporting: motor terminals; brush gear in sliding contact with the commutator for transferring electrical power from the motor terminals to the windings; and a speed sensor, wherein the speed sensor comprises a sensor coil fixed to the base plate and sensor terminals fixed to the end cap for connecting the sensor coil to external lead wires.
Preferred and/or optimal features are defined in the dependent claims.
One preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Referring to
Located on an inner surface of the end cap 16 is a speed sensor 20. In
The sensor 20 is more clearly shown in FIG. 2.
Referring to
The coil 22 may be any suitable coil with or without a core, including a chip-type coil. However, the preferred coil is a helical coil of enamel insulated single strand copper wire wound about a steel pin core and varnished for strength and integrity. The steel pin core concentrates and thus amplifies the electromagnetic signals picked up by the coil. Thus it may be useful in applications where the strength of the monitored signal is very low.
The thus described motor incorporates a speed sensor which is conveniently located, easy to install and provides a good pick up of the electromagnetic emissions from the armature windings.
The embodiment described above is given by way of example only and various modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined in the appended claims. For example, the coil may be located about a post on the brush plate or the steel pin may be directly mounted to the brush plate. Also, the connector could be formed as an integral part of the brush plate and the brush holders, while described as separate items, may be formed integrally with the motor terminals.
Number | Date | Country | Kind |
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0130147 | Dec 2001 | GB | national |
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Number | Date | Country | |
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20030111919 A1 | Jun 2003 | US |