Motor

1. Field of the Invention

The present invention relates to a motor, and more particularly to a motor adapted to be built in a lens barrel to drive a diaphragm vane or lens.

2. Description of the Prior Art

In a conventional stepping motor, an excitation coil and pole teeth can be constructed in a hollow structure and a magnet rotor can also be constructed in a hollow structure. Accordingly, it is suitable to drive a diaphragm vane or lens in a lens barrel.

A structure to drive the diaphragm vane by a drive force of the stepping motor is disclosed in Japanese Patent Application Laid-open 165825/1982.

When the diaphragm vane or the lens is to be driven, a power souce for the motor may be a battery in the lens barrel, a battery in a camera body or a battery separate from the camera body. None of those can store a large capacity of power supply energy. As a result, if a rotation efficiency between the rotor and the stator is low, the power supply energy is wasted and the product value of the lens with a built-in motor is lowered. If the rotation between the stator and the rotor is not smooth, the diaphragm vane and the lens may not be moved or rotated to a position determined by an exposure control system or an auto-focus system and it adversely affects the lens performance.

In the prior art stepping motor, the stator is fixed to an outer ring of a bearing, the magnet rotor is fixed to an inner ring of the bearing, and balls are arranged between the outer ring and the inner ring. Because of such a structure, the friction coefficient is high and the rotation efficiency is low. This manufacturing step is also time-consuming.

It is an object of the present invention to provide a motor having a lubrication member arranged between a rotor and a stator to smoothen the rotation of the rotor.

It is another object of the present invention to provide a motor having the structure of a bearing which is most fitted to the shape of a lens barrel.

Other objects of the present invention will be apparent from the description of a preferred embodiment of the present invention set forth hereinbelow.

FIG. 1 is a lateral sectional view of one embodiment of a motor of the present invention,

FIG. 2 shows a detail of a bearing shown in FIG. 1,

FIG. 3 is a modification of the bearing shown in FIG. 2, and

FIG. 4 shows the motor of FIG. 1 arranged in a lens barrel.

One embodiment of the present invention is now explained with reference to FIG. 1. Numeral 1 denotes a stator which includes coils 1A.sub.1 and 1A.sub.2, pole tooth yokes 1B.sub.1 and 1B.sub.2 and a coil bobin 1C. Numeral 2 denotes a magnet rotor arranged inside the stator 1 through a bearing ring 4, and numeral 6 denotes a hold ring for holding the stator 1, rotor 2 and the bearing ring 4 in union. The shape and structure of the coils, yokes and bobbin of the stator 1 and the magnet rotor have been known in the art and also are disclosed in the above-mentioned patent publication. Therefore, the explanation thereof is omitted here.

The bearing ring 4 is made of a material having a low friction coefficient and a self-lubrication property. It may be Delrin (trademark of DuPont) made of polyacetal resin filled with polyfluorocarbon short fiber, ultra-high molecular polyethylene, or polyphenylene sulphide (PPS).

When the ultra-high molecular polyethylene material is used for the bearing ring 4, an ultra-high molecular polyethylene belt or sheet may be applied to an inner periphery of the bobbin 1c of the stator 1 so that the thickness of the bearing member is reduced.

When an adhesive tape (fluorine resin) (tradename Nitfron in Japan) is used, the tape need not be applied to the entire periphery of the gap between the stator and the rotor but it may be intermittently applied.

FIG. 2 shows a material such as Delrin which can be formed into the bearing member. Two or more ring-shaped projections 4B.sub.1, 4B.sub.2, . . . are formed on an inner periphery of the ring 4A of the bearing 4, and a flange 4C is formed at an axial end of the ring 4A.

A stator is fixed to an outer periphery of the ring 4A of the bearing member 4 shown in FIG. 2. A hold ring 6 is fixed to a side of the stator so that the flange 6A (FIG. 1) extending along the inner periphery of the hold ring 7, the flange 4C of the be bearing and the ring 4A of the bearing define a space, into which the magnet rotor 2 is inserted. The magnet rotor 2 is supported by the ring-shaped projections 4B.sub.1, 4B.sub.2, . . . of the bearing.

FIG. 3 shows a modification of the bearing. It differs from the bearing of FIG. 2 in the area contacting the magnet rotor 2. In FIG. 3, instead of the ring-shaped projections 4B.sub.1, 4B.sub.2, . . . shown in FIG. 2, intermittent projections 4D.sub.1 and 4D.sub.2 are concentrically formed on the inner periphery of the ring 4A. The magnet rotor is rotated while it is supported by the intermittent projections 4D.sub.1, 4D.sub.2, . . . .

The magnet rotor of the above motor is rotated by a rotation torque generated by energizing the coils 1A.sub.1, 1A.sub.2, . . . . Since the contacting surface of the bearing member 4 which contacts the surafce of the rotor has a low friction coefficient and a self-lubrication property, the magnet rotor rotates smoothly.

The stepping motor of the present embodiment does not need a separate bearing member and the movment of inertia of the rotor is reduced and the rotation speed is increased. When a brushless motor is used, the reduction of the moment of inertia improves the controlability.

FIG. 4 shows a diaphragm mechanism of a camera which uses the motor shown in FIG. 1. The hollow motor 10 shown in FIG. 1 is arranged concentrically to a lens barrel (not shown). A pin 21 of the ring-shaped rotor 2 is fitted to a groove 15 of a lever 14 for driving diaphragm vanes mounted on a diaphragm mechanism, and the rotor 2 is rotated by an external signal to drive the lever 14 in one of the directions shown by arrows so that the diaphragm vanes 13 are driven to a desired aperture to control an intensity of light passing therethrough.

In accordance with the present invention, the ring shaped or belt-shaped lubricant member made of a resin material having a low friction coefficient is arranged between the stator and the rotor so that the thickness of the bearing member is significantly reduced. The motor of the present invention is suitable to be built in the lens barrel.