Patent Publication Number: US-4225837-A

Title: Armature for a proximity switch

Description:
BACKGROUND OF THE INVENTION 
     Magnetically actuated proximity switches have been used to sense the relative movement between two member, one carrying the switch and the other being a magnetically permeable member, usually iron or steel. A major problem in the design of magnetically actuated proximity switches is to get adequate pressure between the electrical contacts of the device at reasonable sensing distances. This invention relates to an improvement in a magnetically actuated switch such as that shown in FIG. 5 of U.S. Pat. No. 3,176,096, issued to Charles R. Marcum. Specifically the control member or armature is improved to increase the sensitivity and the contact pressure between the contacts of the device in response to a given diversion of flux from the armature of the device. 
     In a proximity switch according to the invention the control member or armature, which carries the movable contacts, is provided at its ends with magnetically permeable lips extending toward the marginal area of the pole faces of the permanent magnets with which the armature cooperates. 
     A preferred form of the invention is illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a longitudinal section showing a preferred form of the invention. 
     FIG. 2 is a pictorial view of the improved armature. 
     These specific figures and the accompanying description are intended to illustrate the invention but not to impose limitations on the claims. 
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     A magnetically actuated proximity switch constructed according to the invention comprises a pair of permanent magnets 1, 2 mounted in a spaced parallel arrangement within a case 3. An armature 4 is pivotally mounted on a pedestal 5 erected from a partition 6 located at one end of the magnets 1, 2. A pair of contacts 7, 8 are resiliently mounted on the partition 6 and are connected, by means not shown, to suitable terminals in the case 3. 
     The armature 4 includes a pair of contacts 9, 10 that cooperate with the contacts 7 and 8. A suitable flexible connection, not shown, electrically connects the armature to a suitable terminal in the case 3. 
     The armature 4 includes a pair of lips 11, 12 projecting generally normal to the plane of the armature. It thus differs from the flat armatures used in relays and in the proximity switch shown in the Marcum patent. The lips extend the full width of the armature thus forming a shallow U-shaped member. In the mounted position the lips are directed toward the adjacent ends of the magnets 1 and 2. 
     In a practical embodiment of the invention the armature 4 is approximately one and one fourth inches long, three fourths of an inch wide and a sixteenth of an inch thick. The lips extend about an eighth to three sixteenths of an inch normal to the plane of the body of the armature. 
     As may be noted from FIG. 1, the permanent magnet 2 is separated from the partition 6 about a sixteenth of an inch more than the magnet 1. Thus the air gap between the magnet 2 and the armature lip 12 is slightly greater than the gap between the magnet 1 and the lip 11. The shorter air gap provides greater pull so that, without an exterior operator, the armature is biased to the position shown, i.e. with the contacts 7 and 9 in contact. 
     Upon the entry of a body 13 of ferromagnetic material into the space adjacent the gap between magnet 1 and armature lip 11, the approximate boundary of which space is indicated by dotted line 14, magnetic flux is diverted from the gap and the magnetic pull weakened. Thereupon the armature moves in response to the now stronger pull between magnet 2 and lip 12. 
     When compared with a switch using a flat armature, as shown in Marcum Pat. No. 3,176,096, the new arrangement and armature shape provides an increase in contact pressure in the order of 50%. Conversely, if a given contact pressure is required the improved armature provides a substantial increase in sensing distance, i.e. the distance from the case 3 at which a given ferromagnetic body 13 causes a movement of the armature 4.