Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – With magneto-mechanical motive device
Reexamination Certificate
2002-12-09
2003-10-28
Barrera, Ramon M. (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
With magneto-mechanical motive device
C335S229000
Reexamination Certificate
active
06639496
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of electromagnetic mechanical actuators and more particularly it relates to an actuator that provides an usually long powered stroke for toggling between two unpowered but positively stabilized stroke-end positions, suitable for locking movable components in place by remote control as frequently required in defense ordnance including missiles and other aerospace craft as well as in ground vehicles, marine vessels and in many kinds of buildings such as residential, industrial, and commercial.
BACKGROUND OF THE INVENTION
Usage of electromagnetic actuators has continuously expanded as part of the overall technological advancement of communications, electronics, aerospace and defense ordnance of all kinds including missiles. Such actuators play a key role in a wide variety of present day equipment, especially remotely controllable mechanisms in vehicles, spacecraft, aircraft, missiles, boats, ground equipment, public, commercial and residential buildings, garages or parking areas, etc.
The class of electrically powered actuators that are addressed in the field of the present invention are structured coaxially with a central moving core, sometimes referred to as an armature or plunger, mechanically linked to a load: in the present instance the moving armature is extended at one end to form a retractable locking pin. Typically the unit is powered by D.C. e.g. from a 12 volt battery. The unit must be capable of actuation in two opposite directions, and, at either end of the stroke, must remain substantially constrained without consuming any holding power, since locks or locking devices are often left unattended for very long period of time.
Basic electrical actuators without permanent magnets, such as solenoids and relays, whether powered by AC or DC, operate on the principle of physical attraction between cores magnetized by a coil, and are thus inherently monostable, i.e. limited to a unidirectional power stroke, i.e. in a solenoid from an offset position of the armature (in either direction) to the centered position, and in a relay, from a spring-biased open position to an electrically-powered closed position that holds only as long as sufficient current is maintained in the coil.
It is important to note that it is generally inherent in conventional solenoids and relay type actuators there is a working magnetic flux path set up in an air gap between movable magnetic pole pieces, such that throughout the power stroke both the length of the air gap and the flux density vary substantially from a large gap and low flux density at the “open” end position to small or even zero air gap and maximum flux density at the “closed” end position, and the magnitude of this air gap variation determines length of stroke available, generally limiting the stroke length to only a small fraction of the overall size of the actuator and thus limiting the device to a relatively short stroke.
For use in demanding fields such as in aerospace, missiles and other defense products, as addressed by the present invention, the actuator must provide
(1) uniform bidirectional drive power delivering a high transfer force against a substantial load in both directions over a relatively long stroke and
(2) positive bistable hold at both stroke-end positions under adverse ambient conditions including high acceleration; there can be no holding power consumption at either stroke end, since there are long periods of time involved in which any power consumption would be unacceptable.
Even when a conventional solenoid or relay structure is modified to make it bistable by departing from the simple structure, e.g. by adding springs, a second coil, and/or permanent magnet(s) to obtain bidirectional actuation, the basic principle of depending on attraction between magnetized pole pieces with variable gap and flux density inherently limits the stroke to an unacceptably short length.
Further background information can be found in allowed U.S. patent application Ser. No. 09/843,478, which is incorporated herein by reference.
DISCUSSION OF KNOWN ART
Practically all known art in this field operates on the magnetic-keeper-attraction principle of electromagnetic operation of solenoids or relays in which the inherent electrical drive is unidirectional and end-holding is monostable, so that these properties must be modified mechanically; e.g. stroke-end holding force in conventional vehicular locks is often implemented by some form of mechanical force, usually from metallic springs in coiled or other form.
Patents showing mono-stable lock actuators utilizing a single solenoid with spring bias are exemplified by U.S. Pat. Nos. 3,576,119, 4,917,419, 4,907429 and 4,679,834.
U.S. Pat. Nos. 5,199,288 and 4,703,637 exemplify actuators that obtain bistable stroke-end positions for locking and unlocking purposes through the use of a rotary electric motor typically utilizing a worm gear engaging a threaded shaft or pinion.
U.S. Pat. No. 5,231,336, by the present inventor, discloses a mono-stable electromagnetic actuator for active vibration control. The magnetic armature of this actuator operates in the voice coil mode to create a linear vibratory motion under the influence of a sinusoidal current through the surrounding coils. A positive current in the coils drives the armature in one direction while a negative current drives the armature in the opposite direction. Removing the current returns the armature to its stable central rest position under influence of the magnetic field and internal springs. This construction is inherently monostable at the center position: it would require radical redesign to provide a stable unpowered armature position on each end of the stroke.
U.S. Pat. No. 4,829,947 by Lequesne for variable lift operation of a bistable electro-mechanical poppet valve actuator discloses an automotive valve actuating device whereby a valve, with attached armature is spring-biased toward a neutral central position but held in a full open or a closed position by permanent magnets having associated coils. Activation of a coil can fully cancel the field of the associated magnet to allow the spring to move the valve to the other position.
U.S. Pat. No. 4,533,890 to Patel discloses a PERMANENT MAGNET BISTABLE ACTUATOR for automotive valves, having a pair of solenoid coils acting on a common central core which requires two coaxial permanent magnets to provide bi-stability.
For actuators in the field of the present invention, two basic parameters are the stroke length and the housing size, which for simplicity can be expressed as the average of the housing diameter and its length. The ratio of stroke length/housing size provides a non-dimensional figure of merit for relative stroke length.
Actuators of known art, whether of the solenoid or other moving armature type that depend on a single mode of electromagnetic actuation for the entire stroke, typically those involving a highly variable air gap, are inherently short stroke actuators with a stroke length under 10% of the average of the housing length and diameter in practical designs.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide an actuator, suitable for locking purposes in missiles, aerospace craft and the like, that is bi-powered and bistable, i.e. providing electrically powered drive force in both directions over a predominant central portion of the stroke, and stable unpowered holding conditions at both stroke-ends, positively stabilized by design-controllable force to withstand designated axial acceleration loading.
It is a further object of the present invention to make the actuator simple and inexpensive and in a basic coaxial form that utilizes a minimum quantity of coils and permanent magnets, preferably only one of each.
It is a further object to provide a long stroke actuator wherein the stroke length exceeds 50% of the housing size defined by the average of the housing length and diameter.
SUMMARY OF THE INVENTION
The aforementioned objectives have been accomplished in the present
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