The present invention relates to electromagnetic solenoid actuators; more particularly, to electromagnet actuators having a magnet contained within the armature; and most particularly, to an actuator having a permanent magnet, preferably a rare earth magnet, contained within a non-magnetic armature, wherein the magnet is shorter than the non-magnetic armature, and wherein the magnet may be selectively positioned at or near the longitudinal center of the armature for double-acting utility, or biased in position toward one end or the other to configure the actuator to be either a pull-type or push-type, without a need for a biasing spring.
A standard prior art electromagnetic actuator, hereinafter referred to as a “solenoid”, typically comprises an electrical coil wound on a hollow bobbin. A ferromagnetic pole piece and an armature are disposed within or proximate the bobbin, and the magnetic field generated by the coil when energized causes the armature to move axially of the coil toward the pole piece. The armature and solenoid housing are then specially configured for either push or pull solenoids. The position of the armature with respect to the pole piece when the solenoid is de-energized is provided by a biasing spring that drives the armature away from the pole piece.
A “push” solenoid includes a plunger portion extending from the armature (“plunger”) through the pole piece and terminating at a point outside the pole piece end of the solenoid. When the coil is energized, the armature moves toward the pole piece and the plunger pushes outwardly of the solenoid housing. A bias spring moves the armature away from the pole piece when the coil is de-energized, causing the plunger to retract. A “pull” solenoid on the other hand is closed at the pole piece end. An opening at the opposite end allows a plunger portion to extend outwardly from the solenoid housing. When the coil is energized, the armature moves toward the pole piece and the plunger is pulled inwardly of the solenoid housing. The bias spring moves the armature away from the pole piece when the coil is de-energized thereby causing the plunger to re-extend, outwardly.
In the solenoid art, it is known to employ a permanent magnet within an armature to bias the armature in one direction or the other, depending upon the polarity of the magnet, to enhance the pull force of the armature in the solenoid and to negate the need for a bias spring; see, for example, in U.S. Pat. No. 3,218,523.
It is also known to employ neodymium as the magnetic material in a solenoid armature; see, for example, U.S. Pat. No. 6,932,317.
What is needed in the art is a solenoid having an armature incorporating a permanent magnet, preferably made of a rare earth material such as neodymium, wherein the magnet may be selectively positioned within the length of the armature to pre-select between a push-type, a pull-type or a dual acting solenoid thereby readily converting the functionality of the solenoid.
Briefly described, a solenoid body is combined with a non-magnetic armature tube which contains a permanent magnet having a length shorter than the length of the armature tube. A pole piece formed of a ferromagnetic material is disposed at each end of the solenoid body. Typically one pole piece (a “stop”) is disposed at a closed end of the body and the other pole piece (a “collar”) is disposed at an open end of the body through which a plunger connected to the armature tube projects and acts on a device controlled by the solenoid. The magnet may be positioned along the length of the armature tube in any one of a plurality of positions depending on the solenoid function desired. When the magnet's position is biased toward the open end of the solenoid body and its polarity arranged to move the armature away from the open end when the solenoid coil is energized, the solenoid functions as a pull-type solenoid. In this configuration, when the solenoid is de-energized, the plunger is held in an extended position by the magnetic attraction of the permanent magnet to the ferromagnetic collar. When the solenoid coil is energized, the force and polarity of the magnetic field causes the magnet and armature tube to move away from the collar and toward the ferromagnetic stop, thereby retracting the plunger. When the solenoid is again de-energized, and the magnetic force field generated by the coil collapses, the plunger re-extends as a result of the magnetic attraction of the permanent magnet to the collar. By reversing the polarity of the magnet (or reversing the direction of current flow through the coil), and by biasing the position of the magnet toward the closed end of the solenoid, the solenoid may be easily converted to function as a push-type solenoid.
If the magnet position is biased toward the ferromagnetic stop, the solenoid functions as a push-type solenoid. In this configuration, when the solenoid is de-energized, the plunger is held in the retracted position by the magnetic attraction from the permanent magnet to the ferromagnetic stop. When the solenoid coil is energized, the force and polarity of the magnetic field causes the magnet and armature tube to move away from the stop and toward the ferromagnetic collar, thereby extending the plunger. When the solenoid is again de-energized, the plunger retracts as a result of the magnetic attraction of the permanent magnet to the ferromagnetic stop.
In either configuration, no spring is required to return the armature to its de-energized position. Since the magnetic force attracting the magnet toward its de-energized position is greater than the magnetic attraction to the opposite pole piece, the armature tube containing the magnet will automatically return to whichever de-energized position has been pre-selected during manufacture or field setting of the solenoid.
A third function can be achieved by locating the permanent magnet at or near the middle of the length of the armature tube (the “neutral position”) such that neither the solenoid stop nor the solenoid collar controls the position of the armature when the magnet is in the neutral (centered) position. Instead, the armature is balanced magnetically between the two solenoid ends. A positive pulse to the solenoid coil will move the armature in the direction of a first end of the solenoid, while a negative pulse will move the armature toward a second and opposite end. Through magnetic attraction of the permanent magnet to one of the pole pieces, the armature will remain at the end of the solenoid body to which it was directed until another pulse of opposite polarity is provided through the solenoid coil. Thus, this configuration functions as a dual acting solenoid that requires no continuous power, only magnetic attraction, to hold it in a deactivated position after pulsing.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate currently preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring to
It is important to note that, in these two prior art solenoids, many components are not interchangeable. For example, an armature used in a pull-type solenoid cannot be used in a push-type solenoid. The pole piece used in a pull-type solenoid cannot be used in a push-type solenoid. Thus, inventory costs increase and assembly procedures are more complicated. Moreover, once a solenoid is assembled as either a push or a pull-type solenoid, it cannot be readily and inexpensively changed to the other type. These issues and others are alleviated by the embodiments of the invention now described.
Referring to
In
In configuration 110b, magnet 116 is disposed nearer to solenoid collar 114 such that, in the absence of a solenoid-coil magnetic field, armature 110b is attracted toward the collar.
In configuration 110c, a magnet 116 is disposed nearer to solenoid stop 112 such that, in the absence of a solenoid-coil magnetic field, armature 110c is attracted toward the stop.
In
Referring to
As described above and shown in
Conversely, as described above and shown in
It is an important advantage of the present invention that a push-type solenoid can be converted to a pull-type solenoid (or vice-versa) by repositioning the magnet along the longitudinal length of the armature tube and changing the polar orientation of the magnet relative to the direction of current flow such as, for example, by either reversing the polar orientation of the magnet or by reversing the direction of the flow of current through the solenoid coil.
It is a further advantage of the present invention that in either the push or pull case, no spring is required to return the armature to one extreme or the other when the solenoid coil is de-energized; the armature tube containing the magnet will automatically return to its de-energized position because of the pre-positioning of the magnet within the armature tube.
It is also important to note that, since magnet 116 is disposed within armatures 110a, 110b so that an end of the armature extends slightly beyond magnet 116, a slight air gap 117 may be maintained between the magnet 116 and solenoid stop 112b and solenoid collar 114b when the coils are in their respective de-energized modes (see
As described above, a third function can be achieved by locating the permanent magnet 16 at or about the middle of armature 110a. In this position, neither the solenoid stop 112 nor the solenoid collar 114 repeatedly controls the position of the armature. Instead, armature 110a is balanced magnetically between the two solenoid ends at a starting point. Referring to
Note that the operating mode of the solenoid (push, pull, or double-acting) may be selected prior to use by simply positioning or repositioning the magnet within the armature to any of several positions generally shown in
Referring to
It has been found that these stop/collar configurations, either separately or in combination, influence the magnetic lines of force and may be manipulated to enhance the magnetic attraction between magnet 116 and stop 112′ and between magnet 116 and collar 114. In
The electromagnet actuator in accordance with the invention is specifically adaptable to an electric door latching mechanism. As known in the art, an electric solenoid may be used in conjunction with an electric strike to either block a strike keeper from movement in a first plunger position, thereby securing a latch to the strike, or unblock the strike keeper in a second plunger position, thereby allowing the keeper to rotate and release the latch from the strike. In such applications, the plunger acts directly on a blocker to move it between a blocking position and an unblocking position. The aforementioned electric strikes are provided as either a fail-safe strike wherein when the solenoid coil is de-energized, the keeper is unblocked and the latch is released, or a fail-secure strike wherein when the solenoid coil is de-energized, the keeper is blocked and the latch is secured. Referring to
In the several configurations shown (
In the prior art, it was necessary to either fabricate an electric strike mechanism to be specifically a fail-safe or fail-secure strike or to incorporate elaborate adjustable features into the mechanics of the strike to be able to convert a strike from a fail-safe to fail-secure strike, or vice-versa. As can be seen by the instant invention, a single strike can be readily converted from a fail-secure to a fail-safe, or vice-versa, by simply repositioning the permanent magnet in the tubular armature and changing the direction of current flow through the coil, or inverting the polarity of the permanent magnet as needed.
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
This application claims the benefit of U.S. Provisional Application No. 61/612,590, filed Mar. 19, 2012.
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