US3549916A - Shock absorbing magnet - Google Patents

Description

fi ige lg lnventor Donald G. Sherwood Monroeville, Pa. Appl. No. 727.407 Filed May 8, 1968 Patented Dec. 22, 1970 Assignee Westinghouse Electric Corporation Pittsburgh, Pa. a corporation of Pennsylvania SHOCK ABSORBING MAGNET 10 Claims, 3 Drawing Figs.

US. Cl 310/14, 310/17: 335/259: 310/30 int. Cl [102k 41/02 Field of Search 3 10/ l 2. -l7, 2224, 30, 33, 34; 318/128. 131. I35; 335/253, 259

[56] References Cited UNlTED STATES PATENTS 2,972,091 2/1961 Clements 335/253 3,344,377 9/1967 Clements... 335/259 3,158,766 11/1964 v Frisch 310/14 2,752,546 6/1956 Frisch..... 3 l0/l4X 1,837,197 12/1931 Barman. 3l0/16X Primary Examiner-Milton O. Hirshfield Assistant Examiner-B. A. Reynolds Attorneys-A. T. Stratton and Z. L. Dermer ABSTRACT: An electromagnet is provided that absorbs shock at the end of its stroke, thereby preventing detrimental effects on the magnet structure and associated apparatus. The shock is absorbed .by magnetically decelerating the magnet plunger to a soft" stop. Instead of dissipating the kinetic energy of the plunger by shock loads in the mechanisms, the kinetic energy is transferred to a magnetic field where it can be used later, that is, for opening the magnet,

PAT ENTEU 05022 I978 SHEET 1 OF 2 WITNESSES FIGJA.

ATTCDRNEY PATENTEU DEEZZIBYB $549,916

SHEEI 2 UF 2 EXCESS (CLOSING RCE PLUNGER CONTACTS FIG. [8.

RESULTANT FORCE ON PLUNGER FWD MAGNET GAP SHOCK ABSORBING MAGNET BACKGROUND; OF THE INVENTION An objection to prior large capacity electromagnets of the solenoid type is the sharp increase in magnet force as the air gap between the stationary pole and the magnet plunger closes. The increased force is not needed and it causes high shock loading when the magnet closes. The high shock loads can have detrimental efiects on the magnet structure and associated apparatus.

An object of this invention is to provide an electromagnet that absorbs shock at the end of its stroke.

Another object of the invention is to shorten the release time of an electromagnet.

Other objects of the invention will be explained fully hereinafter or will be apparent to those skilled in the art.

SUMMARY OF THE INVENTION In accordance with one embodiment of the invention, an electromagnet has a movable shock pole in addition to a relatively stationary pole and a magnet plunder. When the magnet coil is energized, the plunger is raised toward the stationary pole and contacts the shock pole before completing its stroke. The shock pole is raised to create an air gap between the shock pole and the stationary pole as the gap between the stationary pole and the plunger closes, thereby decelerating the plunger before it contacts the stationary pole.

BRIEF DESCRIPTION OF THE DRAWING For a better understanding of the nature and objects of the invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawing in which:

FIGS. 1A and 18, when taken end-to-end, constitute a view, partly in elevation and partly in section, of a magnetically operated linear motion device embodying principal features of the invention, and I FIG. 2 is a graphical view illustrating the principle of operation of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The drawings illustrate the manner in which the present invention can be utilized in a linear motion device of the type described in US. Pat. No. 3,158,766, issued Nov. 24, 1964 to E. Frisch and assigned to the Westinghouse Electric Corporation. The aforesaid device is of a gripper type in which three solenoid coils are utilized to provide incremental linear motion of a linearly movable element. Two of the coils are utilized to provide, when energized, latching of the two gripper assemblies of the linear motion device. The third coil achieves raising or lowering, as the case may be, of the linearly movable element.

As described in the aforesaid patent, the gripper members of the linear motion device may be located in three relative positions with respect to the linear element which is moved thereby. One of the relative positions is defined as the "unlatched" position wherein the gripper is not in position for engagement with the teeth of the linearly movable element. A second relative position is defined as the latched position wherein the gripper is engaged with the linearly movable element and the gripper is subjected to the load or weight of the movable element. The third relative position of the component is defined as the coupled position wherein the gripper is located in its engaged position relative to the linearly movable element, but the gripper is not subjected to the load created thereby. In other words, a clearance exists between the teeth of the linearly movable element and the tip of the gripper member.

As illustrated in FIGS. 1A and 1B of the drawing, the linear motion device is provided with a tubular outer housing 10, formed from magnetic material of a thickness capable of withstanding relatively high internal pressures. The housing is provided with a plurality of spaced circumferential weld inserts 12 disposed between adjacent axial portions of the housing 10 and formed from nonmagnetic material. The function of the welding inserts i2 is to interrupt a shunting magnetic path which would exist along the housing ill in the axial direction were the housing formed'completely from magnetic material.

The housing 10 is provided with a plurality of annular solenoid coils 14 mounted in an axially spaced array on the outer surface thereof in positions juxtaposed respectively to the nonmagnetic weld inserts 12. In the present structure, three solenoid coils 141 are provided on the housing 10 to form solenoids 36, it and 20 for the linear motion device. The solenoid coils 14 are each provided with a support structure including annular magnetic portions 22, 24 and 26 which form part of a flux path for magnetic flux generated by each of the coils 1 The annuli 22 and 26 are mounted respectively above and below each of the coils M and are formed from magnetic material. Likewise, the annulus 2d is formed from magnetic material and is disposed outwardly of the coil 14 in juxtaposed relationship therewith and bridging the outward edges of the adjacent annuli 22 and 26. The solenoids 16, 1d and 20 are formed to be slid over the outer surface of the housing ill) and are fixedly disposed in positions juxtaposed to the nonmagnetic inserts 12 of the housing lit) by a plurality of spacers.

The lower end of the housing 10 is provided with an outward flange 22 having threads 30 on its outer surface which are positioned to receive a lower housing member 32. The lower housing member 32 is threadly secured to the lower flange 28 and is desirably formed at its lower end (not shown) to be secured in a suitable hermetic manner to a pressurized system with which the linear motion device is utilized. The lower housing 32 is provided with an annular canopy 34 which extends in close proximity with a portion of the flange 28 for the purpose of permitting an annular seal weld 36 between the canopy 34 and the flange 28 for sealing hermetically the housing 10 to the lower housing 32.

The solenoids 16, 18 and 20 are fixedly positioned relative to the nonmagnetic inserts 12 by means of spacing sleeves 38, 40 and 42. The spacing sleeve 38 is disposed between the flange 28 and the lower surface of the annulus 26 of the solenoid 20. The spacing sleeve 40 is disposed between the annuli ,22 and 26 of the solenoids 20 and 18, respectively. Likewise,

the spacing sleeve 42 is disposed between the annuli 22 and 26 of the solenoids 18 and 16, respectively. An additional spacing sleeve 66 may be similarly mounted on the annulus 22 of the upper solenoid 16 for the purpose of providing a fixed mounting arrangement for the solenoid. The upper end of the spacer 56 may be secured to a suitable annulus, such as a locking ring (not shown), which may be threadly mounted on the outer periphery of the housing 10 and disposed to engage the spacer 56 to prevent relative movement of the solenoids 16, 18 and 20 with respect to the housing 10. In this manner the solenoids may be easily assembled to the linear motion devised by merely slipping them over the top of the housing 10 into the positions shown in the drawings and similarly may be removed in the event inspection of the housing lid is desired. The upper end of the housing It) is desirably closed off by a cover (not shown) which may be secured to the housing 10 by suitable means, for example welding, to insure hermetic integrity of the housing It).

The interior of the housing 10 is formed to receive a pair of gripper assemblies 58 and 60 which are mounted for movement within the housing 10 relative to a tooth linearly movable element or lead screw 62. By energizing the solenoid coils l6, l8 and 20 in a predetermined sequence, the gripper assemblies 58 and 60 are movable independently of each other to the latched, coupled an unlatched positions relative to the lead screw 62 in a manner to be described. Movable gripper supports forming a part of the gripper assembly 58 and 60, respectively, are movable relative to the interior of the housing it) and between fixed stop members 62, 66 and 63. The stop members 6 3, as and 68 are fixed in position relative to the housing 10 by means of spacing sleeves 7i) and 72.

In furtherance of this purpose, the lower stop member 68 is clamped against a shoulder 69 on the housing 11) by a locking ring '71. The locking ring 71 is threadly secured to the interior of the housing adjacent to flange 28 by complementary threads 74. The lower spacing sleeve 70 is secured at its lower end to the lower stop 68 by complementary threads 76. The intermediate stop member 66 is threadly secured to the upper end of the lower spacing sleeve 70 by complementary threads 78. Positioning of the upper stop 64 is achieved by threadly securing the upper spacing sleeve 72 to the intermediate stop 66 at 80 and to the upper stop 64 at 82. The upper stop 64 and the intermediate stop 66 form portions of the magnetic circuit for the solenoids 16 and 13, respectively, and, therefore, must be formed from magnetic material. The lower stop 68 and the spacing sleeves 70 and 72 do not form portions of the magnetic circuit of the linear motion device and may be formed from nonmagnetic material. Each of the stops 6 1, 66 and 611 is of an annular configuration to surround the lead screw 62, thereby permitting the securing of the stop members to the respective spacing sleeve 70 and 72.

As described in the aforesaid patent, the lower gripper assembly 60 is provided with three circumferentially spaced gripper arms 84 preferably formed'frorn a corrosion resistant material. Each arm 8 is provided at the lower end with an inwardly extending tip 86 which is of a size to fit closely between spaced teeth 88 of the element 62. The tips 86 are preferably formed from an extremely hard material, such as Stellite, to permit long operating lives therefor. The tip 86 of each gripper arm 84 is of a size and shape to provide slight clearance spaces when it is disposed in the coupled position in the groove formed between each pair of adjacent teeth 88. Each of the gripper arms 84 is pivotally mounted at two separate places by means of pivot pins 911 and 92. A movable latch support tube 94 extends above the gripper arm 84 and is provided with three axially extending circumferentially spaced cutouts 96 which are coextensive with and receive the gripper arms 84. The pivot pin 90 is received in flanges on opposite sides of the cutout 96 in the latched support tube 194. In this manner, the gripper arms 84 are pivotally movable relative to the latch support tube 94 with the axis of such pivotal movement being the pivot pin 90. Such pivotal movement of the gripper arms 84 permits movement of the tips 86 through openings 89 in the spacer tube 70 toward the element 62. The lower end of each of the gripper arms 84 is provided with a slot 100 therein which receives one end of a link member 102. This end of the link member 102 is provided with an opening therein which receives a pivot pin 92 to permit pivotal movement of the link member 102 about the axis formed by the pivot pin 92. A movable latch operating magnetic pole or support tube 104 of annular configuration is disposed between the inner surface of the housing 10 and the outer surface of the latch support tube 94. The lower end of the latch operating support tube 104 is provided with an inwardly extending groove 106 which receives the adjacent end of the link member 102. This end of the link member 102 is provided with an opening therein disposed in alignment with opposed openings in portions of the pole member 104 adjacent the groove 106. A pivot pin 168 is disposed in the last-mentioned aligned opening and passes through the link member 102.

Movement of the gripper arms 841 into and out of engagement with the lead screw 62 is accomplished by movement of the latch operating magnetic pole 104 relative to the latch support tube 94. For example, movement of the pole 1M downwardly relative to the tube 5 4' causes the link member 102 to pivot relative to both of its pivotal axes. Thus, the pivot pin 108 moves downwardly with the resulting effect being that the pivot pin 92 is moved toward the latch operating pole 1%. This movement of the pivot pin 92 causes the gripper arm 8 to pivot about the pin 91), thereby moving the tip $43 of the gripper arm 84 out of engagement with the teeth of the lead screw 62. The upper gripper structure 5% (FIG. 1A) is illustrated in this last-mentioned position.

With respect to the upper gripper arrangement 58, it is to be noted that the grippers are formed in essentially the same manner as the gripper arms for the lower gripper arrangement 60. Basically, the only differences between the upper and lower gripper arrangements are in the formation of an upper gripper support tube 110 and the formation of a latch operating magnetic pole or support 112 for the upper gripper arrangernent 58. With those exceptions, the construction of the upper gripper arrangement 58 and the operation thereof are the same as that for the lower gripper arrangement 61).

The upper solenoid 16 is formed to provide a generally to roidal path for magnetic flux generated thereby. The toroidal magnetic flux path is illustrated by the arrows 114 which pass through the sleeve 24, member 22, housing 10, a movable shock pole 115, the stop or stationary pole 64, latch operating magnetic pole or plunger 112, housing 11), lower end piece as and returning to the sleeve 24. The flux path indicated by the arrows 114 is forced through the shock pole 115, the stationary pole 6d and the plunger 112 by the nonmagnetic insert 12 juxtaposed to the solenoid coil 14. The function of the shock pole 115 will be described hereinafter.

in FIG. 1A of the drawings the solenoid 16 is shown with its coil 14 deenergized. The solenoid 16 is provided with three poles, two of which are movable and one of which is stationary. The stationary pole comprises the annular stop member 6 1. One movable pole, which is disposed below the stationary pole 64-, comprises the gripper operating pole or plunger 112. The other movable pole, which is disposed above the stationary pole, is the shock pole 115. A relatively thin wear resistant nonmagnetic washer 116 is disposed on top of the plunger 112 and is adapted to move into engagement with the lower surface of the stationary pole 6d. The nonmagnetic washer 116 serves to reduce the decay time of the magnetic flux in the air gap 1118 upon deenergization of the coil 16, thereby speeding up movement of the magnet pole or plunger 112.

In order to reduce the closing shock of the plunger 112, an annular extension 117, composed of magnetic material, is joined to the plunger 112 by a sleeve 119 composed of nonmagnetic material. The function of the nonmagnetic sleeve is to force the flux to turn radially into the pole 64. As shown by the dotted line, some of the flux goes from shock pole 115 to the lift pole extension 117 and then turns radially into pole 64. The remaining flux goes directly from pole 115 to pole 64. All of the flux crosses the air gap 118. The upper edge of the extension 117 is spaced from the shock pole 115 by a distance less than the air gap 113. The flux develops an axial-magnetic force between the lift pole extension 117 and pole 115; between poles 115 and 64; and between poles 112 and 64. The forces between extension 117 and pole 115, and between poles 64 and 112 add and become F,,. The force F, raises pole 112. When the lift pole extension 117 contacts shock pole 115, the magnetic force (F between poles 115 and 64 decreases the resultant force on lift pole 112. Thus, during closing operation of the electromagnet when the coil 14 is energized, the magnet force 1 raises the plunger 112. When the plunger raises a portion of its travel distance, it contacts the shock pole 115 through the extension 117 on the plunger 112. The momentum of the plunger and the magnet force F,, raise the shock pole until the plunger 112 contacts the stationary pole 64 through the washer 116. As the shock pole 115 is raised, an air gap is provided between the shock pole and the stationary pole 64. The magnet force P, which acts on the shock pole 115 decelerates the plunger 112 to a low velocity before the plunger contacts the stationary pole, thereby minimizing shock. The force F, counteracts the force F so that the resultant force acting on the plunger does not build up and cause high shock loading. The shock is still further reduced by means of a Belleviile washer or spring 121 which is disposed on top of the shock pole 115 to contact a stationary stop ring 123 threaded into the upper end of the spacing sleeve 72. The relative spacings between the members of the electromagnet are such as to cause complete closing of the air gap 118 when the coil is energized.

Shock absorption and release time can be adjusted by changing the areas of the lift pole extension 117, lift pole 112,

and shock pole 115, and by changing the thickness of shim 116. Further adjustment can be obtained by selecting various magnetic gaps between the extension 117 and the pole 1 15.

The closing of the air gap 118 is resisted by a spring 120 which is disposed in compression between opposed surfaces of the upper stop 64 and the gripper operating magnetic pole 112. The spring 120, however, is designed of such size as to increase the air gap 118 to a maximum only when the solenoid 16 is deenergized. The magnetic force between the poles 64 and 112 created by the solenoid 60 is of such magnitude as to overcome the spring force of the spring 120.

A ring member 122 is secured to the inner surface of the spacing sleeve 72 and abuts a shoulder 124 formed thereon. Resilient means, such as a spring 126, is disposed between the ring member 122 and the upper end of the latch support tube 111). The spring 126 is desirably under compression and resists upward movement of the latch support tube 110 toward the ring member 122. Accordingly, upon .en'ergization of the solenoid 16, the air gap 118 begins to close. inasmuch as the upper stop 64 is fixedly positioned, closing of the air gap 118 is accomplished solely by upward movement of the gripper operating pole 112 toward the stop 64.

The gripper operating pole 112 is provided with a lower annulus 128 threadly secured thereto at 130 which is formed to receive a pivot pin 132 upon which there is mounted a link member 134. The link member 134 is capable of moving pivotally about the pivot pin 132. Similarly, the link member 134 is pivotally secured to a latch arm 136 of the upper gripper arrangement 58 in a manner similar to that described in connection with the lower gripper arrangement 60. The gripper arm 136 is pivotally mounted on the gripper support tube 116 by a pivot pin 138 which functions similarly to the pivot pin 90 of the lower gripper arrangement 60.

Upon closing of the air gap 118, the pivot pin 132 is moved upwardly into substantial alignment with the pivot pin 135 causing the gripper arrn 136 to pivot about the pivot pin 138 so that its Stellite tip 141) moves through an opening 141 in the spacing tube 72 to a position between adjacent teeth 88 of the lead screw 62. During this portion of the closing of the air gap 118 only the last described movement takes place because the gripper support tube 110 is restrainedfrom corresponding upward movement by the spring 126. It will'be noted, however, that the lower end of the member 128 is provided with an inwardly extending flange 171 which is disposed in vertical alignment with a shoulder 173 of the gripper support tube 110. The distance of travel of the flange 171 until it is in engagement with the shoulder 173 is constructed to be slightly smaller than the air gap 118 so that upon the final closing movement of the air gap 118, the flange 171 moves the gripper support tube 110 upwardly against the force of the spring 126. A particular need for this last mentioned movement of the gripper support tube 110 will be described hereinafter in conjunction with the description of the operation of the linear motion device.

The lower solenoid 26 controls the movement of the lower gripper arrangement 60 between the latched, coupled and unlatched positions. As illustrated in FIG. 1B, the solenoid 211 is energized. The poles of the lower solenoid 20 comprise the latch operating magnetic pole 104 and a lift pole 142, both of which are formed from magnetic material. Thus, when the solenoid 20 is deenergized an air gap exists between the lift pole 142 and the latch operating pole 1114. The length of the last-mentioned air gap is defined by the upper surface 144 of a spring support plunger 146 which is axially aligned with the operating pole 1114. Resilient means, such as a spring 148, is mounted in compression between opposed surfaces of the lift pole 142 and the operating pole 104 to insure the opening of the air gap between the last-mentioned poles upon deenergization of the solenoid 20. A nonmagnetic vwasher 1511 is placed on the upper surface of the latch operating pole 1114 and serves the same function as the washer 116. Upon deenergization of the solenoid 20, the latch operating pole 104 moves downwardly until its lower surface engages the surface 144 of the spring support plunger 146. The pivot pin 1118 also moves downwardly causing the link 102 to pivotally move in a counterclockwise direction about the pivot pin 108 with the resulting effect that the tip 86 of the gripper arm 84 is swung out of engagement with the adjacent tooth 88 of the lead screw 62. Upon completion of this last-mentioned motion, the latch arm 34 is located in the unlatched position similar to that shown for the latch arm 136 in FIG. 1A.

As will be pointed out hereinafter, deenergization of the solenoid 2t) normally would not be permitted while the latch arm 84 is in the latched position. Before deenergization of the solenoid 211 is permitted, the solenoid 16 will be energized so that the gripper arm 136 is in the latched position which will result in the location of the gripper arm 84 in the coupled position. As illustrated in FIG. 1B, the gripper support tube 94 is threadedly mounted on the lift pole 142 at 152. The latch sup port tube 94 is provided at its lower end with an extension 154 disposed below the gripper arms 84 and having a threaded outer side wall 156. Complementary threads are formed on the spring support plunger 146 to permit the securing of the spring support plunger 146 to the extension 154 at the wall 156. The lower end of the spring support plunger 146 is provided with an inwardly extending circumferential flange 158 which extends to a position closely adjacent the outer surface of the spacer sleeve 76. An annular washer 160 is secured against an outwardly extending shoulder 162 formed on the spacer sleeve 70 and disposed between the lower end of the extension 154 and the flange 158. Resilient means, such as a pulldown spring 164, is disposed in compression between the stop washer 160 and the flange 158 to exert a constant downward force on the flange 158 with the last-mentioned downward force also being exerted on the lift pole 142.

The intermediate or lift solenoid 18 provides a flux path similar to the flux path 114 of the solenoid 16. The poles of the lift solenoid 18 comprise the central stop or stationary pole 66, the lift pole or plunger 142 and a movable shock pole 165 disposed above the stationary pole 66. The air gap for the lift solenoid 18 is disposed between the adjacent surfaces of the poles 66 and 142. In the drawing, the lift solenoid 18 is shown in its energized condition with the air gap between the poles 66 and 142 being closed. A nonmagnetic washer 166 is mounted between the opposed surfaces of these poles. A magnetic extension 167 is joined to pole 142 by a nonmagnetic sleeve 169. The extension 167 contacts the shock pole 165 to raise the shock pole during closing of the air gap between the stationary pole 66 and the plunger 142 in the manner hereinbefore described with reference to the extension 117 and the shock pole 115. The magnetic action is similar to that described with reference to solenoid 16. Deenergization of the lift coil 18 would result in the opening of the air gap between the poles 66 and 142. The opening of this air gap would be assisted by the pulldown spring 164. The size of the air gap would be defined by the distancebetween the lower surface 161% of the plunger 146 and the upper surface of the lower stop 66.

Two or more washers may be provided on the upper surface of the lower stop 68 to dampen the shock when surface 168 of the plunger 146 contacts the washers. Fluid trapped between the washers will be squeezed out at high velocity and absorb some of the kinetic energy before a solid stop is achieved. Desirably, the gap for the lift solenoid 16 is constructed to be exactly equal to the thread pitch of the lead screw 62 for a purpose hereinafter described.

The sequence of energization of the solenoids 16, 18 and 20 together with the resulting movement of the upper and lower provide incremental upward movement of the lead screw 62, it will be assumed that the linear motion device is in the operating state illustrated in FIG. 1A and 18, that is, the solenoid 16 is deenergized and the solenoids 18 and 20 are energized and the solenoids 18 and 20 are energized.

Upward incremental movement of the lead screw 62 will begin by energizing the upper solenoid 16. Such energization of the upper solenoid 16 will establish a magnetic field in the gap 118 tending to close the latter. As a result, magnetic pole 112 moves toward the stop 64 and the latch arms 136 are driven toward the lead screw 62 by pivotal movement of the links 134 until the tips 140 of the latch arms 136 assume a position in which a clearance exists between the adjacent teeth 88 and the tips 140. During the last mentioned movement, the tips 140 of the latch arms 136 do not come into contact with the teeth 88 of the lead screw 62 and the arms 136 are in the coupled position. Theaxial position of the latch arms 136 remains unchanged during this period since the latch support tube 110 is held in its original position by the spring 126. At this point of the travel the flange 171 at the lower end of the extension 128 engages the shoulder 173 adjacent the lower end of the support tube 110 with the consequence that the support tube 110, and with it the latch arms 136, are forced upwardly during the last part of the magnet travel until the air gap 118 is completely closed. This last one-sixteenths on an inch of travel takes up the clearance of one thirtyseconds of an inch placing the arms 136 in their latched position and moves the lead screw upwardly through an increment of one thirty-seconds of an inch, thereby transferring the load created by the weight of the lead screw 62 from the lower latch arms 84 to the upper latch arms 136. A clearance of one thirty-seconds of an inch will now exist between the tips 86 of the lower latch arms 84 and the adjacent teeth 88 with the arms 84 are now in the coupled position.

The next step in the sequence of operation is to deenergize the lower solenoid 20. This permits the lower latch operating magnetic pole to drop underthe impetus of the Spring 148 to move the gripper arms 84 from a coupled position to the unlatched position with the upper gripper arms 136 remaining in the latched position. it is to be noted that the movement of the gripper arms 84 to the unlatched position is permitted without making contact with the teeth 88 of the lead screw 62, thereby preventing wear on these parts. The lift solenoid 18 is now deenergized and the entire lift magnetic assembly including the lift pole 142, the latch operating magnetic pole 104 and the spring support plunger 146 moves downwardly to its bottorn position by impetus of the spring 164 until the lower surface 168 engages the damping washers 170. Energization of the lower solenoid 20 moves the latch operating pole 104 into engagement with the lower end of the lift pole 142, thereby moving the latch arms 84 from the unlatched position to the coupled position, so that the tips 86 of latch arms 84 are not in actual contact with the teeth 88. The upper solenoid 16 is now deenergized causing the opening of the gap 11% and a downward movement of the latch operating pole 112 and gripper support tube 110 under the impetus of the springs 120 and 126, respectively, it is to be noted that the speed of the downward movement of the gripper support tube 116 is limited by the speed of movement downwardly of the flange 171. The force exerted by the spring 126 is of such a magnitude as to permit more rapid lowering of the gripper support tube 110 than the speed of lowering of the magnetic pole piece 112. On this basis, for the first one-sixteenth of an inch of travel of the latch support tube 110 carrying with it the gripper arms 136, the flange 171 defines the upper limit of the speed of downward movement of the gripper support tube 110. During the first one-sixteenthof an inch of travel the gripper support tube 110 and the pole piece 112 move substantially as a unit. When the gripper support tube 110 has moved the first one-sixteenth of an inch, the lower end 130 thereof engages a stop ring 172 and prevents further downward movement of the support tube 110. The first one thirty-seconds of an inch of downward movement also moves the lead screw 62 downwardly to absorb the clearance between the lead screw teeth and the tip 86 of the lower gripper arm 84 placing the lower gripper arm in the latched position. The second one thirty-seconds of an inch of movement completes the freeing of the tips of the upper gripper arms 136 from contact with the lead screw 62. During the latter part of the travel of the pole 112 the tips 140 are withdrawn from the grooves between the lead screw teeth moving the grippers 136 to the unlatched position. Incrementa! movement of the lead screw 62 upwardly is completed by energizing the lift solenoid 1% until the air gap between the pole 66 and the pole 142 is closed.

As explained hereinbefore, the raising of the plunger 142 to close the air gap between the plunger and the stationary pole 66 causes the rim 167 on the washer 166 to raise the shock pole and create an air gap between this pole and the stationary pole 66, thereby decelerating the upward movement of the plunger 1412 and the lead screw 62. Cushioning of the closing shock is also effected by means of a Belleville spring or washer disposed between the shock pole 165 and the stop ring 172 which is fixed in the spacing sleeve '72.

To continue incremental movement in the upward direction the whole cycle as described above is merely repeated.

The deceleration of the plungers of the electromagnets magnetically may be understood by a discussion of the transfer of energy. As shown by the curve in FIG. 2, the Resultant Force on Plunger" decreases suddenly when Plunger Contacts Shock Pole. Then the "Resultant Force on Plunger" increases gradually until the magnet is closed. When the plunger contacts the shock pole, it has kinetic energy which is equivalent to the work done on the plunger by the force F,,. Neglecting friction losses, the work done is represented by the shaded area in FIG.2. When the plunger contacts the stationary pole, the above kinetic energy appears as magnetic field energy in the gap between the shock pole and the stationary pole. Ordinarily, the kinetic energy is dissipated by the shock loads in the mechanism. in the shock absorbing magnet herein described, the kinetic energy is transferred to a magnetic field where it can be used later, that is, for opening the magnet.

in a prior mechanism, which is utilized as an example, the moving parts attained 633 in-lbs. of kinetic energy during a lift stroke. When the magnet closes, the parts are decelerated to a zero velocity. The kinetic energy is dissipated mainly as strain energy in the parts. Permanent deformation of control rod locking parts can occur.

In the magnet disclosed herein, the moving parts attain kinetic energy of only 400 in-lbs. This energy is then transferred to the magnet field between the stationary pole and the shock pole, instead of being dissipated as strain energy in the mechanism parts. Theoretically, shock loads can be eliminated by this invention. Practically, they can be reduced to an insignificant amount.

Another benefit of the shock absorbing magnet is that the magnet release time is shortened. This is due to the lower resultant force acting on the plunger. Again theoretically, the release time can be made almost instantaneous by constructing for a low resultant force on the plunger. Then the slightest flux reduction would release the plunger. Practically, this invention permits the construction of large control rod mechanisms with scram delay time in the order of 0.040 seconds versus existing 0.150 seconds scram delay time.

Downward movement of the lead screw 62 is achieved by sequentially energizing and deenergizing the solenoid coils 16, 18 and 20 in the following manner.

With the linear motion device in the position shown in FIGS. 1A and 1B, the first step to obtain downward incremental movement is to deenergize the lift coil 18 causing the lower gripper arms 64 and the lead screw 62 to move downwardly until the surface 165*; of the plunger M6 engages the washers 170. Next, the solenoid coil 16 is energized, moving the tips of the gripper arms 136 to the coupled position between adjacent teeth of the lead screw until the flange 171 engages the shoulder 173, and then lifting the lead screw 62 and the gripper arms 136 for an additional one-sixteenth of an inch to move the tips Mil from the coupled position to the latched position and whereupon the tips 86 of the lower gripper arms 84 are placed in the coupled position. The lower solenoid 20 is deenergized moving the gripper arms M from the coupled position to the unlatched position. The lift coil 18 is then energized moving the lift pole M2} into engagement with the stop as with the lift pole 142 also moving the gripper arms 84 upwardly for a distance equal to one tooth pitch. The lower solenoid 20 is then energized moving the gripper arms M from the unlatched position to the coupled position. Finally, the cycle is completed by deenergizing the solenoid 16 which accomplishes the movement of the upper gripper arms 136 to the coupled position, thereby placing the gripper arms 84in a latched position and then moving the gripper arms 136 to the unlatched position. The cycle is then repeated to obtain further incremental downward movement of the lead screw It is to be noted that at all times during the operation of the linear motion device, the gripper arms 84 and 136 are moved to the unlatched position from the coupled position and not from the latched position. in this manner there is no direct frictional engagement between the teeth of the lead screw 62 and the tips of the gripper arms. Thus, substantially no wear on the engaging parts of the gripper arms and the lead screw takes place during operation of the linear motion device.

Further, the shock absorbing magnet herein described which functions to absorb the closing shock magnetically, thereby decelerating the magnet plunger and the load carried by the plunger to a soft" stop, reduces the detrimental effects on the magnet and associated apparatus heretofore experienced in electromagnetically operated mechanisms. This permits the construction of linear motion devices and other electromagnetically operated mechanisms having long life operation and requiring only a small amount of maintenance or service.

Since numerous changes may be made in the abovedescribed construction and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all subject matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

lclaim:

H. An electromagnet comprising a coil, a relatively stationalid ry pole formed from magnetic material, a movable magnetic plunger disposed for movement toward and away from said stationary pole and being spaced from said stationary pole when the coil is deen'ergized, a movable shock pole of magnetic material, and means actuated by the plunger for contacting the shock pole to move it away from said stationary pole prior to the contacting said stationary pole by the plunger when the coil is energized.

2. The electromagnet defined in claim ll, wherein the plunger and the shock pole are disposed at opposite sides of the stationary pole.

3. The electromagnet defined in claim 2, wherein the stationary pole and the plunger and the shock pole and the contacting means constitute part of the path for magnetic flux generated by the coil.

4. The electromagnet defined in claim 2, wherein the shock pole is moved to provide agap between it and the stationary pole as the gap between the plunger and the stationary pole is closed.

5. The elecuomagnet defined in claim 1, wherein said contacting means is spaced from the shock pole by a distance less than the space between said plunger and said stationary pole when the coil is deenergized.

6. The electromagnet defined in claim 1, wherein the contacting means is composed of magnetic material and is joined to the plunger by a sleeve composed of nonmagnetic material. 7. In a linear motion dev1ce,m combination, a generally tubular housing, a linearly movable element disposed in said housing, said linearly movable element having a plurality of spaced teeth thereon, a gripper member for engaging said teeth, electromagnetic means for lifting said element through said gripper member, said electromagnetic means comprising a stationary pole fixed in the housing, a movable plunger attached to the gripper member below the stationary pole, a shock pole movably disposed above the stationary pole, a coil mounted outside the housing, and means actuated by the plunger for raising the shock pole together with the plunger when the coil is energized.

8. The combination defined in claim 7, wherein said actuated means is spaced from the shock pole a predetermined distance when the coil is deenergized.

9. The combination defined in claim 7, including stop means in the housing for limiting upward movement of the shock pole.

10. The combination defined in claim 9, including resilient means disposed between the stop means and the shock pole.

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