Electromagnetic Actuator

The present invention generally relates to an electromagnetic actuator which electrically controlls mechanical force for electromagnetic devices such as electro-magnetic relay, electromagnetic switch, electromagnetic valve, electromagnetic locking means, electromagnetic brake, electromagnetic clutch, electromagnetic vibrator, or the like.

In various field of industrial art, public use and so on, conventionally used electromagnetic actuators are generally composed of a combination of electromagnetic attraction of an electromagnet and spring bias force. For a specific use, it is well known that an electromagnetic actuator with self-supporting ability (latching property) is composed of an electromagnet, a spring, and a permanent magnet as a self-latching means.

Referring to FIGS. 9(a),(b), there is shown a constitution of most commonly used plunger type electromagnetic actuator in the prior art. That is, in the drawing, this plunger type electromagnetic actuator comprises a stationary element consisting of a stationary iron core 1 and a winding element 4 wound round the core 1, a plunger shape movable iron core 2 capable of reciprocating with respect to the iron core 1, and a spring 3 generating a bias force so as to maintain a gap 1a between the stationary iron core 1 and the movable iron core 2 while the winding element 4 is free from an electric current.

FIG. 9(a) shows this OFF-state of this plunger type electromagnetic actuator; that is, the plunger shape movable iron core 2 is present to the iron core 1 under mechanical stable condition on account of the function of the spring 3 which applys the bias force in the direction shown by an arrow 3a to the movable core 2.

When an electric current is flowed through the winding element 4 as shown in FIG. 9(b), a magnetic flux 27 is generated so that a magnetic attractive force will be also caused in the reverse direction of the bias force 3a and the magnetic attractive force is greater than the bias force. Accordingly, the plunger shape movable iron core 2 is forcedly moved towards the stationary iron core 1 and contacted thereto as shown in FIG. 9(b). In this way, an actuating member connected to the movable iron core 2 such as an electric contact piece, a valve rod or like ( not shown ) can be mechanically actuated.

This mechanical actuated state is maintained during the ON-state of the winding element 4. On the other hand, the movable iron core 2 will be returned to the mechanical stable state as shown FIG. 9(a) due to the bias force of the spring 3 if the winding element 4 is switched from the ON-state to the OFF-state.

Referring to FIGS. 10(a)(b), there is shown another conventional electromagnetic actuator which is additionally provided with a permanent magnet for latching. That is, this latching type electromagnetic actuator is so constituted that the magnetomotive force of the permanent magnet 5 is applied in series to the magnetomotive force of the magnetic circuit consisting of the stationary iron core 1, the movable iron core 2 and the gap 1a as shown in FIGS. 9(a),(b).

When the winding element 4 is present in the OFF-state; i.e., an electric current is not flowed therethrough, the magnetic flux 26 caused by the magnetic force of the permanent magnet 5 applys the attractive force to the movable iron core 2 which is always subjected to the bias force in the direction of arrow 3a by means of the spring 3. Since this attractive force by the permanent magnet 5 exists in equilibrium with the bias force of the spring 3, the movabble iron core 2 is isolated from the stationary iron core 1 with a gap 1a therebetween. This state is referred as "first mechanical stable state".

Nextly, when an electric current in a series of pulses is flowed through the winding element 4 in the direction as shown in FIG. 10(a), the magnetic flux 27 is generated and overlapped with the magnetic flux 26 caused by the permanent magnet 5 so that the magnetic attractive force greater than the bias force ( arrow 3a ) of the spring 3 is generated. Thus the movable iron core 2 is attracted and forcedly moved towards the stationary iron core 1. As a result, the movable iron core 2 contacts to the stationary iron core 1. This state is shown in FIG. 10(b) and referred as "second mechanical stable state". In this way, an actuating member connected to the movable iron core 2 such as an electric contact piece, valve rod or the like (not shown ) can be mechanically actuated.

Under this second mechanical stable state, an electric current in a series of pulses is flowed in the direction shown in FIG. 10(b) so that the magnetic flux 27 in the counter direction to the magnetic flux 26 caused by the permanent magnet 5 will be generated. Thus the movable iron core 2 is free from the magnetic attractive force so that the movable iron core 2 will return to the first mechanical stable state by the bias force ( arrow 3a) shown in FIG. 10(a) and will be maintained in this state.

The former mentioned conventional plunger type electromagnetic actuator shown in FIGS. 9(a),(b)however has the following problems.

(a) Ampere turns required for the desired attractive force and desired stroke of actuator becomes greater.

(b) Since it is required to maintain the actuator in ON-state when the actuator is kept in its actuating position, this actuator consumes greater electric energy.

(c) As the electric energy is consumed, the winding element generates heat. In order to control a rise in temperature in the winding element, the size of the electromagnetic actuator will be increased.

Although the latter mentioned conventional electromagnetic actuator having the latching property shown in FIGS. 10(a),(b) has a merit that both mechanical stable states can be easily switched to the other by applying the electric current in a series of pulses in an instant and thus this actuator can be controlled by a small amount of electric energy.

However, since the permanent magnet 5 having a great reluctance is arranged in the magnetic circuit in series which is energized by the winding element 4, this actuator requires the ampere turns for energizing several times as large as the former actuator shown in FIGS. 9(a),(b). So this actuator requires a great capacity of power source for energizing this electromagnetic element and / or to increase the size of winding element. Further, this actuator causes a problem that the required values of ampere turns for switching on and off are remarkable different from each other.

With these problems in mind, it is the primary object of the present invention to provide an improved electromagnetic actuator which is a highly sensitive and saves electric power type actuator capable of controlling with a power source of fine capacity.

Further, it is another object of the present invention to provide a compact, simple and strongly built electromagnetic actuator.

To accomplish the above objects, the electromagnetic actuator according to the present invention can be performed in accordance with the following knowledge.

Referring to FIG. 5 and FIG. 6, they are schematic illustrations showing the operation principles of the actuator according to the present invention and the conventional actuator, respectively. In these drawings, the same numbers designate the same or corresponding elements already mentioned in FIG. 9 and FIG. 10.

First of all, in FIG. 5 the magnetic flux generated by the permanent magnet 5 is flowingly divided into the leftside and rightside flux flows .phi.b and .phi.a at a pole piece 16. The magnetic flux .phi.i is generated as an electric current is flowed through the winding element 4.

In the conventional plunger type electromagnetic actuator shown in FIG. 6, the magnetic flux .phi.io is also generated as an electric current is flowing through the winding element 4.

If the bias force of the spring 3 in the direction shown by the arrow 3a is represented by Fs, the value of proporional constant K is assumed to be equivalent for both actuators, and leaking magnetic flux is ignored, then the attractive force Fa, Fb of the actuators according to the present invention and the conventional electromagnetic actuator will be represented by the following equations.

Further, Fs is eliminated in order to simplify the equations and then the following equations are assumed.

These conditions are substituted into the equations (1) and (2) and they are rearranged in order to obtain the ratio of Fa and Fb, thereby resulting in the following equation.

According to this equation, as is clear from the curve shown in FIG. 7, the actuator accroding to the present invention can easily generate the attractive force several times as great as that of the prior art under the same condition; i.e., the same value of the ampere turns for energizing, in accordance with the value of .alpha..

Nextly, according to the equations (1),(2) and (3), assuming that the value of Fa is equivalent to that of Fb;

then the following equation will be obtained.

According to equation (7), as is clear from the curve shown in FIG. 8 in accordance with the value of .alpha., the actuator of the present invention can easily generate the same value of the attractive force as that of the prior art at the small value of ampere turns in comparison with the prior art.

Although the above assumption has been obtained after no-consideration of the influence of increase of magnetic reluctance caused by the divided magnetic flow material 17 against the magnetic flux .phi.i, the influence can be so minimized as to be neglected in practical manner.

The first and second present inventions have been achieved in accordance with the above assumed knowledge. That is, the electromagnetic actuator according to the first present invention comprises:

A permanent magnet (5); a pole piece (16) having a first pole face secured to a first pole face of the permanent magnet (5); a pair of movable iron cores (2) so arranged that the inner end faces (2a) of the two cores (2) can be moved close to or apart from a pair of second pole faces (16a) of the pole pieces (16) and are connected through a non-magnetic connecting shaft (8); a stationary iron core (1) having first pole faces (1f) facing respectively a side surface (2b) meeting at right angles with the inner end face (2a) each of the movable iron cores (2) through a fine gap (1n) and a second pole face (1f) secured to a second pole face of the permanent magnetic (5); a pair of dividing magnetic paths (17) having a required magnetic reluctance and each dividing magnetic path (17) being fixed to an outer end face (2h) of each of the movable iron cores (2) and a winding element (4) for energizing the magnetic circuit consisting of the stationary iron core (1), the movable iron cores (2), the pole pieces (16), and the dividing magnetic paths (17).

And the electromagnetic actuator according to the second present invention comprises; a permanent magnet (5); a pole piece (16) having a first pole face secured to a first pole face of the permanent magnet (5) and a second pole face at the inner surface of a recessed or penetrated space (16d); a movable iron core (2) so arranged that an end (2i) of the movable iron core (2) can be moved into or out of the recessed or penetrated space (16d); a stationary iron core (1) having a first pole face (1f) facing a side surface (2b) of the movable iron core (2) through a fine gap (1n) and a second pole face (11) secured to a second pole face of the permanent magnet (5); a pair of dividing magnetic paths (17) having a required magnetic reluctance interposed between a third pole face (16b) of the pole piece (16) and a third pole face (1k) of the stationary iron core (1); a winding element (4) for energizing a magnetic circuit consisting of the stationary iron core (1), the movable iron core (2), the pole piece (16), and the dividing magnetic paths (17); and a spring (3) interposed between the movable iron core (2) and the pole piece (16) or the stationary iron core (1) in order to apply mechanical bias force to the movable iron core (2).

As given explanation above, the electromagnetic actuator according to the first and second present inventions can provide the following excellent effects in comparison with the conventional device.

(1) The present invention can generate the magnetic attractive force remarkably greater than that of the conventional device by using the same winding element for generating the equivalent magnetomotive force.

(2) The present invention can generate the magnetic attractive force equivalent to the conventional device by using the winding element for generating the magnetomotive force remarkably smaller than the conventional device.

(3) The present invention can provide the alternative functions of a single stable state operation and a two-stable states operation by the same composition.

(4) The above effects provide further detailed features;

(a) The capacity of power source for operating this device is relatively small;

(b) The highly sensitive and energy saving type device can be achieved;

(c) The compact sized and light weight device can be achieved;

(d) Simple structure with water proof, pressure resistive, and dust proof properties can be easily achieved.

FIG. 1 is a schematic illustration showing a embodiment of an electromagnetic actuator according to the first present invention;

FIG. 2(a) is a schematic illustration showing a embodiment of an electromagnetic actuator according to the second present invention which is present in its first mechanical stable state;

FIG. 4(b) is a schematic illustration showing the second mechanical stable state of the actuator shown in FIG. 4(a);

FIG. 3 is a schematic illustration showing a principle of the electromagnetic actuator according to the first and second present inventions;

FIG. 6 is a schematic illustration showing a principle of a conventional electromagnetic actuator;

FIG. 5 and FIG. 6 are graphs showing characteristics curves of the electromagnetic actuator according to the present invention shown in FIG. 5;

FIG. 9(a) is a schematic illustration showing a conventional electromagnetic actuator in its first mechanical stable state;

FIG. 9(b) is a schematic illustration showing the second mechanical stable state of the conventional actuator shown in FIG. 9(a);

FIG. 10(a) is a schematic illustration showing another conventional electromagnetic actuator in its first mechanical stable state; and

FIG. 10(b) is a schematic illustration showing the second mechanical stable state of the actuator shown in FIG. 10(a).

Referring to FIG. 3, there is shown an embodiment of an electromagnetic actuator according to the first present invention comprising a permanent magnet 5; a pole piece 16 having a first pole face secured to a first pole face of the permanent magnet 5; a pair of movable iron cores 2 so arranged that the inner end faces 2a of both cores 2 can be moved close to or apart from a pair of second pole faces 16a of the pole pieces 16 and are connected through a non-magnetic connecting shaft 8; a stationary iron core 1 having first pole faces 1f facing respectively a side surface 2b meeting at a right angle with the inner end face 2a of each movable iron cores 2 through a fine gap 1n and a second pole face 1l secured to a second pole face of the permanent magnet 5; a pair of dividing magnetic paths 17 having a required magnetic reluctance and each dividing magnetic path 17 being fixed to an outer end face 2h of each of the movable iron cores 2; and a winding element 4 for energizing the magnetic circuit consisting of the stationary iron core 1, the movable iron cores 2, the pole pieces 16, and the dividing magnetic paths 17.

An operation on such constituted embodiment of the electromagnetic actuator will be explained.

FIG. 3 shows a first mechanical stable state.

Under this condition, when an electric current in a series of pulses is flowed through the winding element 4 in the flowing direction as shown in FIG. 3, the magnetic flux .phi. i is overlaps the magnetic flux .phi. b. Thus, the moveable iron core 2 is subjected to the magnetic attractive force so that the movable iron core 2 will be moved toward the right side and maintained in the state; i.e., the second mechanical stable state.

In this second mechanical stable state, when the electric current in a series of pulses is flowed through the winding element 4 in the reverse direction as shown in FIG. 3, the reverse magnetic flux of the magnetic flux .phi. i is generated so that the movable iron core 2 is finally positioned in the first mechanically stable state shown in FIG. 3.

That is, a pair of movable iron cages 2 is connected through a non-magnetic connecting rod 8 and is so arranged that an inner end face 2a of each of the movable iron cores 2 can be moved close to or apart from a second pole face 16a of a pole piece 16. Further, a stationary iron core 1 has a pair of first pole faces 1f facing to the side surface 2b meeting at a right angle with the inner end face 2a of the movable iron core 2 through a fine gap 1n and a second pole face 11 secured to a second pole face of a permanent magnet 5. A pair of dividing magnetic paths 17 having required magnetic reluctance is fixed to the outer end faces 2h of the movable iron cores 2.

According to this constituted actuator, any one of the movable iron cores 2 and the dividing magnetic paths 17 can be operated alternatively as an electric current is flowed through the winding element 4. As a result, there is no means for generating mechanical bias force such as a spring.

Next, referring to FIGS. 4(a) and 4(b), there is shown an embodiment of the electromagnetic actuator according to the second present invention comprising a permanent magnet 5; a pole piece 16 having a first pole face secured to a first pole face of the permanent magnet 5 and a second pole face at the inner surface of a recessed or penetrated space 16d; a movable iron core 2 so arranged that an end 2i of the movable iron core 2 can be moved into or out of the recessed or penetrated space 16d; a stationary iron core 1 having a first pole face 1f facing to a side surface 2b of the movable iron core 2 through a fine gap 1n and a second pole face 1l secured to a second pole face of the permanent magnet 5; a dividing magnetic path 17 having a required magnetic reluctance interposed between a third pole face 16b of the pole piece 16 and a third pole face 1k of the stationary iron core 1; a winding element 4 for energizing a magnetic circuit consisting of the stationary iron core 1, the movable iron core 2, the pole piece 16, and the dividing magnetic path 17; and a spring 3 interposed between the movable iron core 2 and the pole piece 16 or the stationary iron core 1 in order to apply mechanical bias force to the movable iron core 2.

An operation of this embodiment will be discussed as follows:

FIG. 4(a) shows a first mechanical stable state where an electric current is not flowed through the winding element 4. That is, the bias force 3a caused by the spring 3 exists in equilibrium with the attractive force of the magnetic flux .phi. a and .phi. b owing to the magnetomotive force of the permanent magnet 5 so that the movable iron core 2 is maintained at the position where a required space is defined between the end 2i of the movable iron core 2 and the recess 16d of the pole piece 16.

Under this condition, when an electric current in a series of pulses is flowed through the winding element 4 in the flowing direction as shown in FIG. 4(a), the magnetic flux .phi. i in the directio represented by the arrow represented in solid line is generated, and cancelled against the magnetic flux .phi. a and overlapped with the magnetic flux .phi. b. Thus, the movable iron core 2 is subjected to the magnetic attractive force greater than the bias force 3a of the spring 3. Then the movable iron core 2 contacts the pole piece 16 and is maintained in this state as shown in FIG. 4(b). This state is a second mechanical stable state.

In this second mechanical stable state, when the electric current in a series of pulses is flowed through the winding element 4 in the direction as shown in FIG. 4(b), the magnetic flux .phi. i2, in the direction shown in FIG. 4(b); i.e., the reverse direction of magnetic flux .phi. i in FIG. 4(a); is generated. Thus, this magnetic flux .phi. i2 is cancelled against the magnetic flux .phi. b and overlapped with the magnetic flux .phi. a so that the magnetic attractive force is decreased. The movable iron core 2 is separated from the pole piece 16 owing to the bias force of the spring 3 and finally positioned in the first mechanical stable state shown in FIG. 4(a).

A pole piece 16 is formed with a recess 16d as shown in the drawing. A movable iron core 2 is so arranged that an end 2i of the movable iron core 2 can be inserted in or drawn from the recess 16d. The recess 16d in the pole piece 16 may be formed as a penetrated hole.

An operation on the embodiment is designed that the maximum attractive force exhibits at the initial state of attracting motion and it is possible to provide a device with compact, light and low impact noise generated when the movable iron core 2 is contacted with the pole piece 16.

The devices according to the present first and second invention can be utilized for various commonly used devices such as electromagnetic relay, electromagnetic valve, electric locking device, electromagnetic sieve, and so on which are compact, high sensitive, light and low-energy consumed devices capable of working by a tiny power source such as a solar battery, a dry cell or the like.