Patent GB-753678-A (GB)
Title: Improvements in snap-action electric switch
Inventor: SCHELLMAN JOSEPH HENRY
IPC: H01H13/14
Filed: 1954-02-18
Abstract: 753,678. Press-button retractive switches; retractive switches. HETHERINGTON, Inc. Feb. 18, 1954, No. 4816/54. Class 38(5) A switch has two sets of contacts arranged in series such that should one contact set fail to separate when the switch is opened the circuit will he interrupted by the other set. As shown. Figs. 1, 8, a plunger 42 biased by a spring 75 has a portion 46 loosely carrying an insulating contact carrier 47 biased by a spring 52 against a plunger shoulder 50, the other end of the spring 52 abutting a pushbutton 40 attached to the plunger. A hill- and-valley projection 61 on the plunger co-operates with a pair of straight coil springs 66 located on opposite sides of the plunger and held between a U-shape metal plate 62 and an insulating plate 68, the latter being fixed to notched arms 65 of the plate 62, ears 67 on the plate 62 serving to retain the spring ends. The plates 62, 68 are centrally apertured to permit free passage over the projector 61, and a discshaped contact 72. is welded to the upper side of the plate 62. An insulating block 58 carries a pair of fixed contacts 55, 56 which co-operate with a pair of contacts 53. 54 carried by the carrier 47. The metal switch casing 30 has an insulating lining 60. When the button 40 is pressed, the carrier 47 is moved with the plunger 42 by the spring 52 and contacts 53, 54 engage the contacts 55, 56. This movement is not sufficient to move the springs 66 over the projection 61 and the plate arms 65 remain in engagement with the block 58. On further depression of the button the carrier 47 moves relatively tc the plunger 42 and the springs 66 snap over the projection 61 so that the contact 72 bridges contacts 53, 54 and the circuit between contacts 55, 56 is completed. On release of the button, the circuit is first broken by the contact 72 and then the contacts 53...56 separate. Should either the contacts 53, 54 or the contact 72 become welded in the closed position, the circuit will be broken by the unwelded contact or contacts. In a modification, Fig. 10, the insulating carrier 47 has a single contact 53 co-operating with a fixed contact 55<SP>1</SP>, and the insulating block 58<SP>1</SP> carries a number of L-shaped contacts 78 engageable by the contact 72. The plunger 42 is conducting and operates in a terminal 82 whereby the latter is electricallv connected to the contact 72. On depression of the button 40, the contacts 53, 55<SP>1</SP> engage and then the contact 72 snaps over the 'projection 61 to engage the contact 53 and contacts 78. Thus a number of circuits are completed from the contact 55<SP>1</SP> to the terminals connected to the contacts 78 and the terminal 82 connected to the contact 72. In a further modification. Figs. 16, 18-20, in which the circuit may be closed by an auxiliary contact should the contact 72 fail to close, the plunger 42<SP>1</SP> carries a conducting contact carrier 83 of cruciform shape having a pair of diametrically opposite contacts 53<SP>1</SP>, 54<SP>1</SP>, a recess 84<SP>1</SP> in the carrier extending at right-angles to a line through the contacts 53<SP>1</SP>, 54<SP>1</SP> and receiving an auxiliary bridging contact bar 85. The carrier 83 and contact 85 are slidable on the plunger and biased by springs 93, 90, respectively, against a plunger shoulder 48<SP>1</SP>. The hill- and-valley projection 61 is formed on a member slidable on a plunger stem 102, the member being biased in opposite directions by a spring 76<SP>1</SP> and a weaker spring 104 so that, normally, the upper end of the projection 61 is retained against a shoulder 107 of a fixed insulating contactcarrying block 110 through the interposition of a washer 106. The projection 61 co-operates with a ball 98 biased by an annular coil spring 97 into a recess 100 in a ring 95 carrying an annular contact 72. The top of the block 110 carries fixed contacts 111, 114, 117 and the underside carries fixed contacts 116, 121. The contacts 114 and 117 are connected respectively to contacts 116 and 121 by rivets 115 and 122. When the button 40 is pressed the contacts 53<SP>1</SP>, 54<SP>1</SP> engage fixed contacts 111, 114 and spring 104 is compressed. On further movement, spring 93 is compressed and the lost-motion permitted by spring 104 is taken up whereupon the ball 98 rides over the projection 61 and contact 72 bridges fixed contacts 116, 121 whereby a circuit is completed between terminals 112, 118 connected to the contacts 111, 117. On release of the button the circuit is broken by the contact 72 before the contacts 53<SP>1</SP>, 54<SP>1</SP> disengage. Should the contact 72 fail to operate when the button is pressed, the button is pressed further so that contact bar 85 bridges contacts 114, 117 and the circuit is completed between terminals 112, 118. To provide a positive dislodging force for the plunger in the event of it sticking, Fig. 21, two switches 30 (according to Figs. 1, 8) are mouted in a frame 123, their plungers 43 being extended and carrying plug and socket elements 126, 127, respectively. The lost-motion between the elements 126, 127 is such that only one plunger may be depressed at one time whereby should one plunger remain stuck in the depressed position it may be dislodged by depression of the other plunger. In a modification, Fig. 22, two switches 130, 131 according to Figs. 1, 8, have buttons 132 operated alternatively by a rocker 135 fixed to a lever 136, and the plungers have extensions 141 which cooperate with the ends of a. lever 144 pivoted at 145. The lost-motion between the extensions 141 and the lever 144 is such that a stuck plunger will be dislodged by operation of the other plunger. In a further modification, Figs. 25, 27, employing four switches 147, 148, 150, 151, according to Figs. 1, 8, the operating lever 161 is universally mounted on a ball 156 whereby it may be moved in any one of four directions to operate one of the switches. An interlock plate 165 mounted on a universal bearing 164 has forked ends 166 embracing the respective switch plungers and cooperating with the plunger springs 52 whereby when one switch is operated the plate ends 166 move the springs 52 of the unoperated switches upwardly and dislodge any plunger which may have been stuck. Each switch, when closed, completes a circuit from a separate fixed contact 153 to a common central contact 154.