US2361238A - Electric switch - Google Patents

Description

Oct. 24, 1944. L, T. RAbER 2,361,238-

ELECTRIC SWITCH Filed June 26, 1943 gg- 1 ull I 'lllllllllllllll PERMANENT 71 MA GNET Inventor: I Louis T Render '3 btor'nq Patented Oct. 24, 1944 ELECTRIC SWITCH Louis T. Rader, Schenectady, N. Y., assignor to General Electric Company, a corporation oi New York Application June 26, 1943, Serial No. 492,431

4 Claims.

My invention relates to electric switches, more particularly to mechanically operated limit switches, and has for its object a simple and reliable magnet snap action mechanism for snapping the movable element of the switch between its two positions.

My invention is especially useful in limit switches of the type described and claimed in Patent 2,175,932, issued on October 10,1935, to Kenneth J. Unwin. The device of this patent is provided with a permanent magnet for effecting a snap action of the movable switch element, this magnet having two pairs of pole faces engaged alternately by mechanically operated armatures. One of the pole faces of each pair is spaced slightly from the armature when in its attracted position to provide an air gap. While this arrangement is perfectly operable, it has been found that in installations requiring operation of the switch many million times, the striking of each armature on the single pole face gradually pounds down the pole face which reduces the length of the air gap between the armature and the other pole face of the same pair, and consequently increases the magnetic holding force applied to the armature. This increased holding force causes increased Wear on various parts of the mechanism with the result that the mechanism wears out quickly.

In accordance with one form of my invention,

I provide as before a single pole for engagement with each of the two armatures, but in placeof an air gap between two other poles of the magnet and the armatures respectively, I extend or position the magnet so that the air gap is formed with relation to the hub of the switch operating member bearing the armatures. Thus the air gap is independent of the position of the armature and the pole faces of the magnet may be hammered down by the impact of the armatures for an indefinite time without affecting the length of the air gap.

, For a more complete understanding of my invention, reference should be had to the accompanying drawing in which Fig. 1 is a plan view of a limit switch embodying my invention; Fig. 2 is a side elevation view of the device shown in Fig. 1; and Fig. 3 is a view partly in section taken along the line 33 of Fig. 1 looking in the direction of the arrows.

Referring to the drawing, in one form of my invention I provide a switch operating shaft which is square for convenience in attaching the various switch parts to it, except at its ends which are cylindrical and rotatably supported on the upright supports II and I2 secured to a metallic base member [3. The operating shaft in is provided with a helical snap spring l4 surrounding a cylindrical hub Ma attached to the shaft and having its ends on opposite sides of two pins l5 and 3 extending lengthwise of the shaft. an armature member ll, rigidly mounted at its lower end on the shaft, and a laterally extending projection 18 which is movable through a-predetermined angle between projections l9 and 20 carried by the armature member H. The projection I8 is mounted in a hollow cylindrical member 20a which forms a bearing for the righthand end of the shaft l0 and is in turn jour nalled in the support I2. In order to give an initial restraining force to effect the snap action, a permanent magnet 2| is mounted in position with its center line passing through the axis of the shaft l0 and perpendicular thereto to restrain the armature member for movement in each direction. The magnet also holds the armature member in each position to which the armature is snapped.

In accordance with my invention, I provide a single pole piece 22 at the lower end of the magnet, which pole-piece extends transversely with respect to the center line of the magnet.2l and is in a predetermined spaced relation with an arcuate section 23 on the armature member. Thus magnetic flux passes from the pole piece 22 through the air gap 22a to the armature member, and thence through one or the other of the two arms Ha and Nb of the armature member and one or the other of the pole pieces 24 or 25 to an upper pole piece 26 on the magnet 2|. It will be noted that each of the two arms together with the arcuate section constitutes an armature.

The permanent magnet 2| preferably is made of a material having a high coercive force and,

a high resistance to change in magnetic properties due to shock. One such material is an alloy of 12 per cent aluminum, 25 per cent nickel, and 5 per cent copper, the balance being mainly iron, such as described and claimed in Patent 1,947,274, issued on February 13, 1934, to William E. Ruder, and Patent 2,027,997, issued on January 14, 1936, to Tokushichi Mishima.

The upper magnet pole piece 26 is provided with two pole faces 26a and 261) at its opposite ends which are bevelled downward and preferably lie'in planes passing throughthe axis of the shaft [0. The armature pole pieces 24 and 25 have pole faces which likewise lie in planes These pins are secured, respectively, to

piece 22 and the armatures, such as the air gap 21 between the side of the pole piece 22 and the left-hand arm of the armature member, is many time greater than the air gap 22a betweenthe end of the pole piece 22 and the portion 23. This air gap 27, furthermore, can be increased if desired and made much greater than shown on the drawing. In any case, it is long enough so that a great amount of pounding down of the faces 26a and 282) can be effected without any effect on the length and function ofthe air gap between the parts 22 and 23. Of course, it will be understood that when the armature member is thrown to its counterclockwise position with the pole piece 25 in engagement with the armature face 261), an air gap similar to the air gap 21 is provided between the right-hand arm of the armature member and the pole piece 22. Preferably, the movable pole pieces 24 and 25 are hardened to reduce the wear and hammering effect on them.

In the operation of this switch the operating shaft I is operatedby mechanical engagement of a part carried by the member 200. with an operating member secured to the moving part of the machine being controlled, such as paper planer, milling machine, lathe, etc., as described in the aforesaid Unwin patent. Thus, as the part of the machine operating the switch moves back and forth, it turns the member 2Ga through a small angle sufficient to throw the switch from one position to another and thereby effect a control operation, such as the reversal of the driving motor for the machine. Thus to move the shaft l 0 counterclockwise, as viewed in Fig. 3, the operating member 20a, which is journalled on the outer cylindrical end of the shaft ID and in turn mounted for rotation in the support I2, is turned in a counterclockwise direction, as seen in Fig. 3, whereby the pin l6 engages and moves the lefthand end of the spring [4 toward the left, the other end of the spring bearing on the pin Hi. This end bearing on the pin applies a counterclockwise force to the armature member I! which tends to overcome the force of the magnet. In any case, as the member 28 is turned, the projection l3 engages the projection l9 and forcibly disengages the armature member from the magnet whereupon the spring [4 snaps the armature member counterclockwise to its opposite position.

It is believed that the reverse operation to the position shown in Fig. 3 will be obvious from the preceding description.

As described and claimed in the aforesaid Unwin patent, I also provide a helical over-center snap spring 29 whose function is to turn the operating member a still farther in its operating direction after the armature member has snapped to its other position. This additional movement of the operating member turns it out of the path of the part of the machine which operated it,

thus providin for free movement of the-machine.

Any suitable switching means can be secured to the shaft l0. As shown, I have provided four supports 30, 31, 32 and 33 mounted in two pairs .ate portion between said arms on opposite sides of the shaft. These supports are made of a suitable electrically insulating material, such as a molded phenolic resin roduct. Each is provided with two stationary contacts 34 and 35 mounted on electrically conducting U- shaped pieces whose outer ends are provided with quickly detachable screw 36 for the connection of electrical conductors thereto. Mounted on the shaft are two electrically insulating supports 31 and 38, each being provided with a pair of bridging contacts 39 and 40 mounted on opposite sides in position to engage the corresponding pair of stationary contacts. A terminal connection member 41, also made of an electrically insulating material, is mounted on a projection 42 on the support ll. These various parts are secured to the supports II and [3 by suitable screws, as shown in the drawing.

As shown, the magnet 2| is supported on the upper pole piece 26 which in turn is secured to the upper end of a rectangular plate support 43. The support 43 is in turn secured at its lower end by screws 44 and 45 to the upper end of the support 12. A non-magnetic screw 46 secures the magnet 2| and lower pole piece 22 to the upper pole piece 26. Although the screw 46 may be made of magnetic material and still make the device operable, it is essential for best performance that this screw be of non-magnetic material. Otherwise it will tend to short-circuit the useful working flux.

It will be understood that under certain conditions requiring the magnet to hold the armature in only one position, only one armature pole piece 24 or 25 may be provided and only one magnet pole face 26a or 25b.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made, and I therefore contemplate by the appended claims to cover any such modifications as fallwithin the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A switch comprising an operating shaft, a permanent bar magnet mounted in a fixed position with relation to said shaft and provided on one end with oppositely disposed pole faces, an armature member secured to said shaft having a pair of arms on opposite sides of said magnet provided with pole pieces for engagement alternately with said magnet pole faces, a rotata, bly mounted operatingmember, a loose connection between said operating member and said armature for disengaging said armature from said pole faces, a spring for snapping said armature to its other. position after such disengagement, said armature being provided with an arcuin closely spaced air gap relation with the other end of said magnet, thereby to maintain a predetermined air gap irrespective of the final attracted position of said armature.

2. A switch comprising an operating shaft, a permanent bar magnet mounted in afixed position with relation to said shaft and provided on one end with oppositely disposedpole faces, an armature member secured to said shaft having a pair of arms on opposite sides of said magnet provided with pole pieces for engagement alternately with said magnet pole faces, an operating member rotatably mounted on one end of said shaft, a laterally extending projection on.said

operating member, a pair of pins extending lengthwise of said shaft mounted respectively on said armature and said projection, a helical snap spring surrounding'said operating member and having its ends extending laterally away from said shaft on opposite sides of said pins, said armature being provided with an arcuate portion between said arms in closely spaced air gap relation with the other end of said magnet, and projections on said armature spaced apart on opposite sides of said first projection and engageable by said first projection upon turning movement of said operating member thereby forcibly to move said armature against the pull of one or the other of said oppositely disposed pole faces whereupon said armature is snapped by said spring into engagement with the other of said magnet pole faces.

3. The combination in a snap action device, of a permanent magnet mounted in a fixed position and provided with a first pole face at one end and a second pole face at its other end extending transversely with respect to said first pole face, an armature pivotally mounted for moverange of movement of said armature, and means ment about an axis substantially parallel with i said first pole face and provided with an arcuate i engagement with said second pole face and to an unattracted position in spaced relation with said second pole face, said arcuate portion being coextensive with the angular movement of said armature between said positions so that the surface of said arcuate portion is a predetermined distance from said first pole face throughout the for operating said armature with a snap action into engagement with said second pole face.

4. A switch comprising a permanent bar magnet mounted in a fixed position and provided with oppositely disposed pole faces at one end, an armature member mounted for limited rotation and having a pair of spaced apart arms on opposite sides of said magnet provided with pole pieces for engagement alternately with said magnet pole faces when said armature is rotated between two positions, an operating member for said armature member, a snap spring between said operating member and said armature member for rotating said armature member with a snap action between said two positions, said armature member being provided with an arcuate portion between said arms coextensive with the angular movement of said armature between said positions, and a third pole face on the other end of said bar magnet having its face in a predetermined spaced relation with said arcuate portion throughout the entire movement of said armature between said positions.

LOUIS T. RADER.

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