Patent GB-1418222-A (GB)
Title: Magnetic actuator mechanism
IPC: G06F3/02
Filed: 1973-06-04
Abstract: 1418222 Permanent magnets; magnetic retaining devices; magnetic switches INTERNATIONAL BUSINESS MACHINES CORP 4 June 1973 [19 June 1972] 26541/73 Headings H1P and H1N A snap action magnetic key actuator providing a predetermined tactile force-displacement characteristic for the operator is mounted on a printed circuit board 11 (Fig. 2) of an assembly and comprises a press button 13 attached to a reciprocating plunger in which plastic shaft 15 has interconnected upper and lower bearings 16, 17 and is upwardly biased by, e.g. a cylindrical permanent magnet interposed between the bearings surrounded externally by a further annular permanent magnet 20 of opposed polarity externally of the plastic housing of the device. The bearings of the plunger are reciprocable within chamber 21 of the housing and limited by stop rim 22 and flange 23 respectively engaging the upper bearing 16 and edge 24 of the housing. At the upper position, the magnetic axis 25 of magnet 19 is displaced a critical distance below the magnetic axis of magnet 20 so that a constant magnetic force biases the plunger upwardly. The bearing 17 carries on its bottom surface a cylindrical disc permanent magnet 27 and annular permanent magnet 28 is carried on the upper end of a plastic cup member 30 slidable in chamber 31 of the housing; the magnets being axially magnetized in similar polarities; a reciprocable movement of magnet 27 relative to magnet 28 by vertical movement of button 13 moving magnet 28 and cup 30 with snap action; the limits of movement being set by rims 32 and 33. A switching means is operatively attached to cup 30 to activate or deactivate a circuit of board 11 on reciprocation of the plunger; and may comprise a disc permanent magnet 35 with a soft iron keeper 36 concentrating flux in a magnetic, e.g. Hall effect sensor (not shown) mounted on part of an integrated semi-conductor chip on the upper surface of the printed circuit board; as described in Specification 1,418,221. Alternative switches operable by cup 30 may be capacitative or mechanical. The permanent magnets may be, e.g. of barium ferrite particles in a synthetic rubber matrix. Multiple key actuators may be assembled in a single monolithic housing with plural chambers. In a modification (Fig. 3) the button 42 is integral with the shaft 41 and a coil spring 40 is mounted between the underside thereof and a recess 43 of the housing. A recess 45 of the shaft carries a cylindrical permanent actuator magnet 46 and a slidable cup 47 in recess 48 of the housing carries a permanent annular magnet 49, while rim 50 of chamber 48 engages flange 51 to limit upward displacement of the shaft. A switch mechanism on cup 47 contacts a circuit element of the printed circuit board. In a further modification (Fig. 5, not shown) an actuating annular magnet is incorporated with a cylindrical plunger sliding externally of the housing and a housing spring is inserted between the upper end of the housing and the plunger, while a coaxial cylindrical magnet reciprocates in snap action with an internal vented chamber of the housing with a switch element attached thereto by an axial pin. A base supporting the housing encloses the switch element, which operates a capacitative or resistive sensitive circuit of a printed circuit board. Details of the sequential operations of the device are explained (Figs. 6, 7, not shown) and constructional dimensions are given.