US 3206656 A
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sept. 14, 1965 D. D. MUSGRAVE SAFETY SOLENOID HAVING A PERMANENT MAGNET LATCHING MEANS Filed sept. 24, 196s United States Patent 3,206,656 SAFETY SOLENOID HAVING A PERMANENT MAGNET LATCHING MEANS Daniel D. Musgrave, 8201 Caraway St., Cabin John, Md. Filed Sept. 24, 1963, Ser. No. 311,068 Claims. (Cl. 317-172) -This invention relates to a safety solenoid of the moving plunger type. Such devices are frequently used to effect mechanical actuation from a distant station which is connected to the solenoid by electrical conductors. Because of their low cost, ease of installation, and simplicity, solenoids are widely used in industrial and military equipment. The solenoid may provide direct mechanical actuation or it may be used to control a prime mover. As a result of long usage and development, solenoids can be expected to function properly upon signal when situated in any normal environment.
Equal importance must be placed upon another kind of reliability, that is, assurance that the unit will not function independent of the operators willful signal. This is particularly true when the solenoid arms a weapon system or controls a power plant, for in such applications inadvertent operation might cause a disastrous accident. It is not intended to limit the utility of the present invention by the aforesaid examples, fo-r the safety features of this invention can be used advantageously in other installations. In any system where the end result must be carefully controlled, consideration must be given to safeguards against human error, environmental conditions, and combinations of circumstances which might result in inadvertent actuation.
The hazards associated with electrically actuated devices are diicult to evade completely, particularly because electrical energy is not normally visible and because under some circumstances it can be transmitted without a physical conductor. It is usually necessary to specify a low energy level for intentional actuation in order to avoid excessive time lag between the signal and the actuation. The constantly increasing usage of electric and electronic equipment provides more and more sources from which electrical energy may be unintentionally introduced into a solenoid circuit.
Important sources of extraneous electrical energy which are recognized as particularly dangerous to circuits controlling high-energy devices are lightning, static changes, galvanic `action and radio-frequency energy. Designers also try to make it difficult to accidently introduce electricity from improper connections of conductors. The radio-frequency hazard has recently become severe, particularly because modern emitters, such as radar equipment, transmit in a concentrated beam.
The above discussion pertains to typical hazards but is not exhaustive, nor is it intended to be limiting.
In consideration of the aforesaid circumstances, the principal object of this invention is to provide a safety solenoid which is relatively immune to typical extraneous electricity.
Another object is to provide such a solenoid which does not consume power when standing by in a safe condition.
Another object is to provide a solenoid so designed that inadvertent changing of polarity of conductors will not permit unintentional functioning.
Another object is to provide a safety solenoid having a single circuit for control and actuation, which circuit may be tested for continuity without causing the solenoid to function.
These and other objects of the present invention will be apparent upon reference to the following specification,
3,206,656 Patented Sept. 14, 1965 ice taken in connection with the accompanying drawings, wherein:
FIGURE 1 is a plan View, partly cutaway, of a safety solenoid which embodies the present invention.
FIGURE 2 is a cross-section taken in the plane indicated by numerals 2-2 on FIGURE 1.
FIGURE 3 is a cross-section taken in the plane indicated by numerals 3-3 on FIGURE l.
FIGURE 4 is an external view of a portion of the solenoid shown in FIGURE 1, with an additional element added for an alternate.
FIGURES 5, 6, 7, 8 and 9 are schematic views which illustrate the sequence of events in a typical cycle of operation of the safety solenoid shown in FIGURES 1, 2, vand 3, and the electric input to the coil during each stage of the cycle.
Referring to FIGURES 1, 2, and 3 there is shown a safety solenoid having a frame 1, of iron or some other suitable material. Within frame 1 is positioned a sleeve 3 having discs 5 and 7 encircling it near its ends, to form a bobbin on which is wound a coil 9, of insulated wire. The construction of the typical coil is well-known in the art and need not be detailed here. The conductor leads of the coil (not shown) are connected to a source of electricity (not shown) with a polarity reversing switch (not shown) in the circuit.
Slidable in sleeve 3 is plunger 11 which is fabricated of some material having a high magnetic retentivity. Plunger 11 is a permanent magnet with polarity as indicated. A hole 13 is formed in plunger 11 for attaching linkage (not shown) to a driven or controlled device.
Also formed in plunger 11 is an axial hole 15 into which is inserted an end of a non-magnetic guide rod 17, which projects substantially along the main axis of the plunger. Rod 17 may be aixed in hole 15 by any suitable mechanical means such as by mating threads on the rod and in the hole. Positioned on rod 17 at a point along its length is ring 19 which may be attached to the rod in any convenient manner. Ring 19 should preferably be made of non-magnetic material.
Fixed in sleeve 3, with one of its ends contacting frame 1 is iron plug 21. Plug 21 is bored axially to permit rod 17 to slide freely in it. Plug 21 is also counterbored to receive the hollow cylindrical end 23 of a ball retainer 25 which is inserted through a suitable hole formed in frame 1. Retainer 25 has a shoulder 27 which is in contact with frame 1. Suitable mechanical means are provided to rmly fix end 23 in plug 21.
Retainer 25 is bored longitudinally to permit rod 17 to slide therein. That portion of retainer 25 which extends outward from frame 1 is bored to a greater diameter to accommodate ring 19 as it moves with rod 17. The counterbore in retainer 25 is indicated by numeral 29.
Retainer 25 also has a pair of lateral holes 31 and 33 which extend from its counterbore 29 to its exterior surface 35. Holes 31 and 33 are tapered and have their smallest diameter near surface 35.
Loosely positioned within holes 31 and 33 are balls 37 and 39, respectively. The diameter of balls 37 and 39 is so chosen relative to the several diameters of holes 31 and 33 that the balls may be inserted in holes 31 and 33 via counterbore 29 but cannot .pass completely through the holes, and may protrude slightly outside surface 35. When the balls thus protrude the distance between them, at their exterior surfaces, they define a diameter slightly greater than the diameter of ring 19. When the balls do not thus protrude, but are situated completely within their respective holes, the distance between them at their exterior surfaces is slightly greater than the diameter of rod 17.
Slideable on exterior surface 35 of retainer 25 is hollow cylindrical permanent magnet 41 the poles of which :are -oriented oppositely to those of plunger 11. (Expressed in a different way, the poles of magnet 41 and plunger 11 which are nearest to one another are of like polarity, in the disclosed embodiment this being S.) The interior bore of magnet 41 is of such a diameter that it can slide on the exterior surface 35 of retainer 25, thereby covering or uncovering holes 31 and 33 according to its position. To prevent it from sliding completely off, retainer 35 has flange 43 at its outer end to act as a limit stop.
FIGURE 4 shows an alternate arrangement in which a spring 45 is interposed between magnet 41 and flange 43.
OPERATION The solenoid shown in FIGURE l is mechanically latched against operation, which would consist of movement of plunger 11 toward plug 21. The plunger cannot travel toward the plug because ring 19 on rod 17 is engaged with balls 37 and 39, portions of which are in the path of travel of the ring. If the ring is thrust against the balls as by push of rod 17 caused by an attempt of plunger 11 to move toward plug 21, a camming effect results, and the balls tend to diverge. In FIGURE l balls 37 and 39 are restrained from diverging by magnet 41 which is overriding holes 31 and 33. So long as the balls are prevented from diverging, the solenoid remains latched.
It will be assumed that the windings of the coil are such that current in one direction, such as that depicted in FIGURE 5, produces a field tending to move plunger 11 and magnet 41 into the field, while current in the other direction, such as that depicted in FIGURE 6, produces a field tending to move plunger 11 and magnet 41 out of the field. The physical principles involved are wellknown and need not be detailed here. For convenience, we will refer to the current producing a field tending to draw the plunger and magnet into the field as a negative current, and that tending to repel the plunger and magnet out of the field as a positive current.
The control station of the solenoid and the circuit connecting it to the coil are not shown. The operator at the control station would be provided with a source of electric current and means to impress it on coil 9 in the manner hereinafter described. The control station and circuit could use various devices well-known in the art and need not be described in detail. As mentioned hereinbefore, a pole-changing switch can be employed.
FIGURE 5 represents schematically the same situation shown in FIGURE l, but coil 9 is energized and the arrows on plunger 11 and below magnet 41 show the direction each is tending to move due to the magnetic field around coil 9. The operator at the control station may check circuit continuity to coil 9 by impressing a current pulse as depicted in FIGURE 5 on the coil. The flow of current around the circuit may be observed by metering, or otherwise.
When the operator decides to deliberately cause the solenoid to operate, he first unlatches the solenoid by impressing a positive current on coil 9 as depicted in FIGURE 6. The magnetic field produced around the coil will repel both plunger 11 and magnet 41, but the plunger is prevented from traveling any appreciable distance by ring 19 on rod 17 which can move only to the inner end of counterbore 29.
Magnet 41 can move until it strikes flange 43, which is the position it is shown at in FIGURE 6. It will be noted that in this position the magnet no longer covers holes 31 and 33, and therefore balls 37 and 39 are not restrained against divergence.
The solenoid is ready for the actuation stroke depicted in FIGURE 7. The operator now suddenly reverses the polarity of the current through coil 9. The polarity of the magnetic field associated with the coil is thereby reversed, and both plunger 11 and magnet 41 are attracted toward the coil. In so moving, magnet 41 will tend to again cover holes 31 and 33 but it must travel an appreciable distance to do so. Before it can move this distance plunger 11 has moved rod 17, thereby causing ring 19 to cam balls 37 and 39 apart. Plunger 11 continues its stroke until it contacts plug 21.
As magnet 41 continues to move toward frame 1 it may cam balls 37 and 39 together but this will not afiect the operation of the solenoid as ring 19 will have already passed the balls. The electrical input to the coil may now be permitted to fall to Zero as shown by the dashed line on the input chart of FIGURE 7. Plunger 11 will remain in contact with plug 21, and magnet 41 will remain in contact with frame 1.
When the operator desires to return the solenoid to the status shown in FIGURE l, he impresses a positive current on coil 9 thereby repelling both plunger 11 and magnet 41 to their limits of travel, previously explained. This condition is shown in FIGURE 8. The current is permitted to fall to zero and magnet 41, being a permanent magnet, is attracted to and .adheres to, frame 1. In so doing, it forces ball-s 37 and 39 together, and the balls engage ring 19, thus restoring the solenoid to the mechanically latched condition.
If it is desired to assure relatching under all conceivable conditions a spring 45 may be interposed between magnet 41 and flange 43 as shown in FIGURE 4. Energy stored in the spring can assist magnet 41 in its movement back to the latched position.
If an extraneous electrical current passes through the coil the effect will depend on the polarity and other characteristics of the current. A direct current, if of the proper polarity might cause unlatching, but it will, at the same time, prevent movement of the plunger into the coil.
An extraneous alternating current might cause chattering of magnet 41 against frame 1 but the half-cycle time of typical alternating currents is too brief to permit unlatching.
There is thus disclosed a safety solenoid which requires predetermined electrical inputs in a definite sequence to bring about functioning. It is not intended to limit the invention to any specific purpose for it will be of utility in a broad range of industrial, military and communications devices.
It will be apparent to those skilled in the art that frame 1 may serve as a return for the magnetic field of the solenoid and that plug 21 may serve as a core for the solenoid. It will also be apparent that ring 19 can act as a detent surface to cooperate with balls 37 and 39 which are adapted to function as detents, and that magnet 41 is adapted to function as a latch to restrain movement of balls 37 and 39.
1. A safety solenoid comprising: an electromagnet having a core and metallic magnetic field return means; a permanently magnetized plunger slideable relative to said core and normally retained by releasable detent means at a position away from said core; and a permanently magnetized latch having a magnetic axis substantially coincidental with the magnetic axis of said plunger and having poles oriented oppositely to the poles of said plunger, and normally juxtaposed and adhering to said field return means at a latched position whereat said latch is positionally adapted for preventing release of said detent means; whereby a current in a predetermined direction through said electromagnet will cause said field return means to repel said latch from said latched position thereby releasing said detent means whereupon said plunger is no longer retained by said detent means at said position away from said core, and whereafter a current through said electromagnet in a direction opposite to said predetermined direction will cause said electromagnet to attract said plunger toward said core.
2. A safety solenoid comprising: an electromagnet having a core and metallic magnetic eld return means; a permanently magnetized plunger slideable relative to said core and normally at a position away from said core; a guide axed to said plunger and having a detent surface thereon; movable detent means on said eld return means adapted at a rst position for engagement with said detent surface thereby retaining said plunger at said position away from said core and adapted at a second position for disengagement from said detent surface; and a permanently magnetized latch having a magnetic axis substantially coincidental with the magnetic axis of said plunger and having poles oriented oppositely to the poles of said plunger, and normally juxtaposed and adhering to said eld return means at a latched position whereat said latch is positionally adapted for blocking movement of said detent means from said lirst position to said second position and movable to an unlatched position whereat said latch is not blocking said movement of said detent means.
3. The safety solenoid set forth in claim 1 further References Cited bythe Examiner UNITED STATES PATENTS 3,040,217 6/62 Conrad 317-191 X 3,126,501 3/64 Flora 317-171 X OTHER REFERENCES Schiebl, German application 1,035,771, printed Aug. 7, 1958.
BERNARD A. GILHANEY, Primary Examiner.
JOHN F. BURNS, Examiner.