Patent Publication Number: US-5153394-A

Title: Tilt-actuated switch

Description:
Cross-references to related applications, assigned to the assignee of the present application, the disclosures of which are hereby incorporated by reference: 
     U.S. Ser. No. 07/701,781, BANTIEN, filed May 17, 1991, based on German Application P 40 16 471.3 of May 22, 1990; 
     U.S. Ser. No. 07/701,880, BANTIEN &amp; FINDLER, filed May 17, 1991, based on German Application P 40 16 472.1 of May 22, 1990; 
     U.S. Ser. No. 07/701,210, KIPPELT et al., filed May 16, 1991, based on German Application P 40 16 032.7 of May 18, 1990. 
     FIELD OF THE INVENTION 
     The present invention relates generally to tilt switches having a movable contact element which bridges two other fixed contacts and, more particularly, to a solid movable contact element which flips decisively when tilted beyond a predetermined angle. 
     BACKGROUND 
     There is a known tilt switch, in which the movable contact element, upon tilting of the switch housing beyond a predetermined angle, moves from a stable first position into another position in which it bridges two fixed contact elements. However, this known tilt switch has the defect that, when the tilt angle increases only slowly, the movable contact element is applied to the fixed contact elements with minimal contact force, so that reliable and continuously electrical contact cannot be assured. Such reliable contact is highly desirable in tilt switches for applications such as a &#34;dead-man switch&#34; used for a mobile radio transceiver carried in the hand or on one&#39;s person. In this application, it is necessary to consistently achieve a reliable electrical contact and, connected therewith, reliable generation of an alarm signal. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a primary object of the present invention to improve the known tilt switch, so that passage of a predetermined critical angle leads to a reliable electrical contact with sufficient contact force. 
     Briefly, this object is achieved by so shaping and dimensioning the movable contact, and the chamber within which it is received, that passage through the critical angle causes the movable contact to flip from a stable first position through an unstable intermediate position into a stable second position where good contact is assured. 
     This has the advantage that, as soon as the movable element passes through the unstable intermediate position or range of positions, it lands in the second stable position in which substantial contact force is present to assure the electrical connection between the fixed contact elements, thus closing the switch. A preferred application for this tilt switch is a mobile radio transceiver, adapted to be carried in the hand or on one&#39;s person, for example by a guard or an industrial plant operator. 
    
    
     BRIEF FIGURE DESCRIPTION 
     FIG. 1 is a cross-sectional view of a first embodiment of the tilt switch of the present invention, in a first stable (switch open) position; 
     FIG. 2 is a cross-sectional view thereof, in an intermediate unstable position; 
     FIG. 3 is a cross-sectional view thereof, in a second, stable, electrical-contact-forming (switch closed) position; 
     FIG. 4 is a cross-sectional view thereof, rotated 180° with respect to said first stable position; 
     FIG. 5 illustrates a second embodiment of the movable contact element. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1-3 illustrate a tilt switch 10 having a housing 11, preferably cylindrical, of electrically conductive material. Housing 11 is formed with an interior chamber 12 of frusto-conical configuration, tapering in toward the bottom. Chamber 12 has a floor 13, on which there rests a base surface 15 of a conical contact element 14. The cone has a point 16, preferably rounded off, which extends, with play, into a central recess 17 of a plate 18 of electrically conductive material. Plate 18 and housing 11 form, respectively, a first and a second stationary contact element. The contact elements are electrically separated by an annular insulating layer or ring 19. Plate 18 and housing 11 each have their own respective electrical terminal 20,21. 
     OPERATION 
     In the rest position (FIG. 1) of the tilt switch, in which its longitudinal axis is vertically oriented, the switch is open because the movable contact element 14 is in its first stable position, and conical point 16 does not make contact with plate 18. If, as shown in FIG. 2, tilt switch 10 is rotated by an angle alpha with respect to the axis of symmetry S passing through center of gravity P, the pivot edge or point of the movable contact 14 migrates down around the lower corner of this contact element and across the lower edge of interior chamber 12. The movable element assumes an unstable position. If the tilt switch is then tilted slightly more, see angle alpha prime in FIG. 3, then the movable contact element flips through a hysteresis angle beta (FIG. 3) into its second stable position. 
     The hysteresis angle beta is the angle between the longitudinal symmetry axis LN of tilt switch 10 and the longitudinal symmetry axis LB of movable element 14. Due to the flipping of movable element 14, its conical point 16 strikes or presses with sufficient contact force against rim or edge 22 of recess 17. 
     The value of hysteresis angle beta determines the distribution of gravitational force of movable element 14 on two contact positions 23 and 24. The greater the hysteresis angle beta chosen, the greater the contact forces applied to contact position 23 become. The distribution of gravitational force of the movable contact element between the two contact positions is thus improved in the region adjacent to tilt angle alpha, to the benefit of contact position 23. 
     Due to the hysteresis phenomenon, the movable contact element 14 will fall back into its first stable position (FIG. 1) upon tilting by less than the tilting necessary to flip the movable contact element from the first stable position into the second stable position. 
     Angle alpha depends upon the dimensions of base surface 15 and the location of center of mass P of movable contact element 14. 
     In order for the contact element 14 of tilt switch 14 to also flip in a 180° rotated orientation and to make contact, the base surface is to be kept small relative to the base surface of contact element 14; compare conical point 16 in FIG. 4. 
     FIG. 5 illustrates an alternate embodiment, in which a movable contact element 30 has a cylindrical portion 31 from which a conical portion 32 extends upwardly and from which a downwardly broadening frusto-conical portion 34 extends downwardly. 
     The relatively large base surface 35 of the frustrum keeps the movable element 30 from flipping until a relatively large tilt angle alpha is reached. Due to the changed shape of movable contact element 30, it has a greater mass than that of the examples in FIGS. 1-4. 
     Various changes and modifications are possible within the scope of the inventive concept.