SNAP ACTING MECHANISM

Abstract: A snap acting electrical switch is devised in which a frame (12) carries first, second and third wireform contacts (18, 24, 29) and a plunger (14) movable along a first axis (16). The first and second wireform contacts (18, 24) are biased together along a second axis (23) transverse to the first axis (16), and are also biased against an end (36, 37) of the plunger (14). The first and second wireform contacts (18, 24) together are adapted to be deflected along the second axis (23) by means of a cam surface (13) on the frame(12) as the plunger (14) is depressed. As the second contact(18) is caused to slide off the end (37) of the plunger (14),it snaps against the third wireform contact (29) which is ina fixed position along side the plunger.

Description: The present invention relates to a snap acting mechanism which has particular utility in low cost miniature electrical snap switches. Electrical switches exhibiting snap action are in exceptionally wide use. A large variety of designs are known for such switches, and such switches are available with a large variety of electrical ratings and other performance characteristics. There is considerable competition particularly among manufacturers of low power snap acting switches. As a result, there is great incentive to decrease price while still providing acceptable performance, and there is a continuing search for switch designs which are simple, suitable for miniaturization, require only a few simply built parts, and are easy to manufacture. The present invention departs from an electrical switch as it is known from DE-A-3 145 986. This switch comprises a resilient element to be moved into contact or out of contact with a stationary element,respectively by means of a plunger having an inclined bottom surface. The inclined bottom surface is provided with a catching groove serving to catch the resilient element when it slides along the inclined bottom surface of the plunger. At this known switch the switch actuation can not be reversed. It is, therefore, the object of the present invention to devise a low cost snap acting mechanism which after actuation can be deactivated and which is suitable for miniaturization and easy to manufacture. This object is achieved by the features of the independent claim. Further advantageous embodiments of said mechanism may be taken from the dependent subclaims. The present invention is most basically a snap acting mechanism in which a plunger having a surface with a line of inflection is adapted for reciprocal movement between released and depressed positions. A first resilient element is biased to a position proximate a portion of the surface, and a stationary ramp surface is positioned and configured to deflect the element across the surface of the plunger toward the line of inflection as the plunger is depressed, the element, after reaching the line of inflection, tending spring along the surface away from the line of inflection. A stationary element may be positioned such that it is adjacent the line of inflection of the plunger surface when the plunger is in its released position, and remains in proximity to a portion of the surface on one side of the line of inflection as the plunger is depressed. A second resilient element may also be included, such element having a free end positioned between the ramp surface and the first resilient element. The first and second resilient elements and the stationary element may be electrically conductive and formed of wire segments so as to provide an electrical switch in which the first and second resilient elements comprise normally closed contacts and the first resilient element and the stationary element comprise normally open contacts. Under reference to the attached drawings a snap acting mechanism and in particular an electric switch shall be described in detail, where Figure 1 is a perspective illustration of an electrical switch in accordance with the invention, the switch frame being partially broken away and a plunger omitted; Figure 2 is an enlarged perspective view of a plunger used in the switch of Figure 1; and Figures 3(a) - 3(c) are end views of the switch of Figure 1 showing the interrelationship of the essential elements in sequence during operation. In Figures 1 and 3, reference numeral 10 generally identifes a switch having a frame or housing 11 including a base 12 which may be molded of a suitable plastic material. Frame 11 is configured with a cam or ramp surface 13 whose function will be described hereinafter. Frame 11 is also adapted to support a plunger 14 which is guided in a channel or aperture 15 for reciprocal movement along a first axis 16 between released and depressed positions. A first resilient electrically conductive member or element generally identified by reference numeral 18 is mounted in frame 11. Element 18 includes a fixed end 19 shown molded into base 12, a free end 20 and an intermediate segment 21 joining fixed and free ends 19 and 20. Segment 21 extends generally along a second axis 22 which is perpendicular to axis 16. Axes 16 and 22 are perpendicular to a third axis 23. A second resilient electrically conductive member or element generally identified by reference numeral 24 is also mounted in frame 11. Member 24 includes a fixed end 25 molded into base 12, a free end including first and second portions 26 and 27, and an intermediate segment 28 joining the fixed end and free ends. As shown in Figure 1, segments 21 and 28 of elements 18 and 24 are substantially parallel. Also mounted in frame 11 is a rigid electrically conductive member or element generally identified by reference numeral 29 which includes a first segment 30 molded into base 12 and a second segment 31 positioned adjacent plunger 14. Segment 31 functions both as an electrical contact and a camming surface as will be more fully described hereinafter. As shown in Figure 3, the fixed ends of resilient elements 18 and 24 and rigid element 29 extend through base 12 to form electrical terminals 32, 33 and 34 respectively of switch 10. As shown in Figure 2, plunger 14 has an end surface generally comprising a first land 36 and a second land 37 which projects from land 36. The switch embodiment illustrated in Figure 1 is configured such that a portion of plunger 14 must be cut away to provide clearance for ramp surface 13. In the perspective view of Figure 2, the cut away portion of plunger 14 is just visible at reference numeral 38. Plunger 14 further has a side surface 40 which joins land 37 at a line of inflection 41. As illustrated, surface 40 is perpendicular to surfaces 36 and 37. Side surface 40 is configured with a clearance recess 42 for accommodating the end of segment 31 of rigid member 29. The operation of switch 10 is apparent from the end view sequence of Figures 3(a)-3(c). As shown in Figure 3(a), plunger 14 is in its released position. It is biased to the released position by resilient elements 18 and 24 of which free end 20 of element 18 rides on land 37 and free end 26, 27 of element 24 rides on land 36. Portion 26 of element 24 extends in a direction parallel with axis 23 generally toward free end 20 of element 18 and substantially perpendicular to intermediate segment 28. Portion 27 of element 24 extends generally along axis 16 and substantially perpendicular to portion 26. Element 24 is biased so that segment 28 rides on ramp surface 13, and element 18 is biased so that free end 20 is urged against portion 27 of element 24. The relationship between lands 36 and 37 insures that free end 20 of element 18 does not slip between portion 26 of element 24 and end surface 36 of plunger 14. Accordingly, free end 20 of element 18 and portion 27 of element 24 form a pair of normally closed electrical contacts between terminals 32 and 33. Similarly, free end 20 of element 18 and second segment 31 of element 29 form a pair of normally open electrical contacts between terminals 32 and 34. In Figure 3(b), plunger 14 is shown partially depressed, and cam surface 13 has moved the free ends of elements 18 and 24 across lands 36 and 37 in a direction parallel with axis 23. Before plunger 14 reaches its fully depressed position, free end 20 is moved past line of inflection 41 at the intersection of side surface 40 and land 37. At that time, free end 20 springs along side surface 40 away from line of inflection 41 and is urged against segment 31 of element 29 so as to open the contact between terminals 32 and 33 and close the contact between terminals 32 and 34. This condition is illustrated in Figure 3(c). As plunger 14 is released, segment 31 of element 29 causes free end 20 of element 21 to slide along surface 40 of plunger 14 back toward line of inflection 41. Concurrently, the free end of element 24 is allowed by ramp surface 13 to slide back across surface 36 of plunger 14 toward its initial position. When free end 20 passes the intersection of plunger surfaces 37 and 40, it springs across surface 37 away from the line of intersection and is urged against portion 27 of element 24. Element 29 is configured to insure desired movement of free end 20 across line of inflection 41. Specifically, element 29 is configured with segment 31 forming an acute angle α with side surface 40. Free end 20 is confined to the acute angle between surface 40 and segment 31 when plunger 14 is depressed, and segment 31. tends to urge free end 20 away from surface 40 as plunger 14 is released. As shown in Figures 3(a) - 3(c), recess 42 in plunger 14 permits the end of segment 31 to extend slightly beyond surface 40 into the plunger. This insures that free end 20 cannot slip past segment 31 between the segment and the plunger. In accordance with the foregoing description, the applicant has provided a snap acting electrical switch design having only a minimum number of simple inexpensive and easily assembled parts, most of which perform dual functions. For example, the plunger is biased to its released position by wire forms which also provide normally closed electrical contacts and electrical terminals for the switch. The other elements are also configured to cooperate in a unique manner to achieve the various functions required for a snap acting switch.

Claims: A snap acting mechanism, in particular a snap switch comprising a plunger (14) adapted for reciprocal movement between released and depressed positions within a housing (12), said plunger (14) having intersecting end and side surfaces (37,40), a first resilient element (18) having a fixed end (19) and having a free end (20) biased to a position proximate the end surface (37) of said plunger (14), a stationary element (29) to be contacted by said first resilient element (18) and a ramp surface (13) positioned and configured to move the free end (20) of said first resilient element (18) across the end surface (37) of said plunger (14) as said plunger is depressed, characterized in that said ramp surface (13) is a stationary part of the housing (12) moving the free end (20) of said first resilient element (18) over the intersection (41) of the end and side surfaces (37,40) so that it springs along the side surface (40) away from the end surface (37) to achieve the contact with the stationary element (29) when said plunger (14) is depressed. Mechanism according to claim 1, characterized in that said stationary element (29) has a first end (31) positioned proximate the intersection (41) of the side and end surfaces (40, 37) of said plunger (14) when said plunger is in its released position, the first end (31) remaining proximate the side surface (40) as said plunger (14) is depressed, whereby as said plunger (14) is released said stationary element (29) allows the free end (20) of said first resilient element (18)to move past the intersection (41) of the end and side surfaces (37, 40), permitting the free end (20) to spring across the end surface (37) away from the intersection (41). Mechanism according to claim 2, characterized by a second resilient element (24) having a fixed end (25), and having a free end (26, 27) located between said ramp surface (13) and the free end (20) of said first resilient element (18), the free end (26, 27) of said second resilient element (24)being biased toward the end surface (36) of said plunger (14). Mechanism according to claim 3, characterized in that said first resilient element (18) and at least one of said second resilient element (24) and said stationary element (29) are electrically conductive so as to provide electrical continuity therebetween when the free end (20) of said first resilient element (18) and said at least one of said second resilient element (24) and said stationary element (29) are in contact. Mechanism according to claim 4, characterized in that : said first and second resilient elements (18, 24) and said stationary element (29) are electrically conductive; and the free end (20) of said first resilient element (18) is biased toward the free end (26, 27) of said second resilient element (24) so as to provide a single pole, double throw switch. Mechanism according to claim 5, characterized in that: said plunger (14) is adapted for reciprocal movement along a first axis (16); said ramp surface (13) and the end surface (36) of said plunger (14) are adapted to move the free ends (20, 26, 27) of said first and second resilient elements (18, 24) in a direction substantially parallel with a second axis (23) perpendicular to the first axis (16); said first and second resilient elements (18, 24) each include an intermediate segment (21, 28) connecting the fixed and free ends (19, 25; 20, 26, 27), the intermediate segments (21, 28) extending substantially perpendicular to the first and second axes (16, 23); and the first end (31) of said stationary element (29) is configured to form an acute angle with the side surface (40) of said plunger (14) when said plunger (14) is in its depressed position. Mechanism according to claim 6, characterized in that: the end surface of said plunger (14) includes a first land (36) and a second land (37) which projects from the first land (36); the free end (26, 27) of said second resilient element (24) includes a first portion (26) which rides on the first land (36) and extends along the second axis (23) toward the free end (20) of said first resilient element (18) and a second portion (27) adjacent the second land (37) which extends substantially parallel with the first axis (16) by an amount greater than the projection of the second land (37); and the free end (20) of said first resilient element (18) rides on the second land (37), extends substantially perpendicular to the first and second axes (16, 23), and is biased in a direction to contact the second portion (27) of said second resilient element (24).

Inventors: REID, BRUCE E.
Applicants: HONEYWELL INC.
Application year: 1985
Main classification: H01H13
IPC codes: H01H13, H01H1