Motor that reduces magnetic interference

A motor includes a housing formed of a first shell and a second shell, a stator, which is formed of a first yoke, a second yoke, a connecting device and two coils. The first yoke and the second yoke each comprise a terminal holder mounting portion, a race and a plurality of pole pawls respectively extended from the race. The race of the first yoke has the race of the first yoke kept apart from the race of the second yoke at a distance to reduce magnetic interference, the connecting device having a terminal holder fastened to terminal holder mounting portions of the first yoke and second yoke of the stator and a plurality of metal terminals installed in the terminal holder, the coils respectively set between the first yoke and the first shell and between the second yoke and the second shell and respectively electrically connected to the metal terminals, and a rotor formed of a transmission shaft and magnets and inserted through the first yoke and the second yoke and rotatable relative to the stator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motor structure and more particularly, to a motor that reduces magnetic interference.

2. Description of the Related Art

A conventional motor, for example, a step motor generally comprises a housing, a rotor and a stator. The housing is comprised of an end cover, a bottom cover and other related component parts, such as axle bearing or bracket. The rotor is comprised of a permanent magnet and a transmission shaft. The stator comprises a coil holder, and a coil formed of an enameled wire and wound round the coil holder. By means of controlling the supply of electric current through the coil, an electromagnetic force is controlled to rotate the motor.

The aforesaid conventional motor design is functional, however it still has drawbacks. The yoke of the stator is formed of a stack of steel plates. Stacking the steel plates into a stack increases magnetic interference. To reduce this magnetic interference problem, a complicated interference preventive structure may be used, complicating the fabrication. Therefore, an improvement in this regard is necessary.

SUMMARY OF THE INVENTION

The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide a motor, which has the races of the two yokes of the stator thereof kept part from each other at a predetermined distance to reduce interference between the two adjacent magnetic fields, improving stepping precision. It is another object of the present invention to provide a motor, which the electrical connecting device thereof separately made and then bonded to the terminal holder mounting portions of the yokes of the stator, simplifying the fabrication and lowering magnetic resistance.

To achieve these and other objects of the present invention, the motor comprises a housing, a stator and a rotor. The housing is comprised of a first shell and a second shell, defining an accommodation space and an escape hole. The stator comprises a first yoke, a second yoke, a connecting device and two coils. The first yoke and the second yoke are hollow metal plates made of a magnetic conductive material and stacked together. The first yoke and the second yoke each comprise a terminal holder mounting portion, a race and a plurality of pole pawls respectively extended from the race. The race of the first yoke and the race of the second yoke are kept apart at a distance. The connecting device comprises a terminal holder fastened to the terminal holder mounting portions of the first yoke and second yoke of the stator, and a plurality of metal terminals installed in the terminal holder. The coils are respectively set between the first yoke and the first shell and between the second yoke and the second shell, each having respective lead wires respectively electrically connected to the metal terminals. The rotor is inserted through the first yoke and the second yoke, and rotatable relative to the stator, comprising a transmission shaft and a magnet mounted on the transmission shaft corresponding to the coils.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIGS. 1˜4, a motor in accordance with the present invention is shown comprising a housing10, a stator30and a rotor50.

The housing10is formed of a first shell11and a second shell12, defining therein an accommodation space. The first shell11has two opposing locating notches111and112, an escape hole113, and a plurality of pole claws115. The second shell12has two opposing locating notches121and122disposed at one side, namely, the front side, an escape hole123, a plurality of pole pawls125and an axial center axle bearing15. Further, the other side, namely, the bottom side of the second shell12is covered with a bottom plate17.

Further, a bracket20may be connected to the free end of the first shell11, forming a screw rod type motor set.

The stator30is comprised of a first yoke31, a second yoke32, a connecting device33, and two coils35. The first yoke31and the second yoke32are hollow plate members made of a magnetically conducting metal material, each comprising a first locating portion311or321, a second locating portion312or322, a terminal holder mounting portion313or323, a race314or324, and a plurality of pole pawls315or325respectively protruded from the race314or324. The first yoke31and the second yoke32are stacked together, defining a gap D between the race314of the first yoke31and the race324of the second yoke32. When the first yoke31and the second yoke32are stacked together, the first locating portions311and321are set in between the locating notches111and121of the housing10, and the second locating portions312and322are set in between the locating notches112and122of the housing10. The connecting device33comprises a terminal holder331, which has a mounting hole332fastened to the terminal holder mounting portions313and323of the first yoke31and second yoke32of the stator30, and a plurality of metal terminals333installed in the terminal holder331. The two coils35are respectively mounted in between the first yoke31and second yoke32and the first shell11and second shell12of the housing10, and respectively sleeved onto the pole pawls315and325of the first yoke31and second yoke32and the pole pawls115and125of the housing10, and then the lead wires of the coils35are respectively electrically connected to the metal terminals333of the connecting device33by a soldering technique.

The rotor50is comprised of two magnets51and a transmission shaft53. The magnets51are mounted on the transmission shaft53. The rotor50is inserted through the first yoke31and the second yoke32, and the transmission shaft53is supported in the axle bearing15. Thus, the rotor50is rotatable relative to the stator30.

The functioning and other features of the motor constructed subject to the aforesaid arrangement are described hereinafter.

At first, a gap D is defined between the races314and324of the first yoke31and second yoke32of the stator30, reducing interference between the two adjacent magnetic fields, and therefore the invention improves the stepping precision of the motor.

Further, the connecting device33is separately made by means of an injection molding technique and then bonded to the terminal holder mounting portions313and323of the first yoke31and second yoke32of the stator30, simplifying the fabrication and lowering magnetic resistance.

Further, the coils35are made by means of a thermal wire fusion technique, eliminating a coil holder, and therefore the invention provides much coin-coil space without increasing the motor size. Further, the first yoke31and the second yoke32are treated through a vacuum evaporation process, reducing defective insulation between the coils35and the yokes31and32.

In general, the invention has the following advantages:

1. The motor of the present invention has a gap D defined between the races314and324of the first yoke31and the second yoke32, reducing interference between the two adjacent magnetic fields, and therefore the motor has excellent stepping precision.

2. The connecting device33of the motor is separately made and then bonded to the terminal holder mounting portions313and323of the first yoke31and second yoke32of the stator30, simplifying the fabrication and lowering magnetic resistance.