Patent GB-916524-A (GB)
Title: Improvements in or relating to electric switching devices
Inventor: MYATT EDWARD RONALD
IPC: H04M1/23
Filed: 1960-11-23
Abstract: 916,524. Press-button retractive switches; keyboard switches. STANDARD TELEPHONES & CABLES Ltd. Nov. 23, 1960, No. 40324/60. Class 38 (5). [Also in Group XXXIX] Depression of the buttons of a key sender is given a " snap action " by causing the buttons to separate an armature from a magnet at the start of depression, additional resistance to depression and restoration of a button being effected by a spring. The contacts associated with a button are operated by a separate spring coupled to the button with lost motion so that the contacts are operated with a uniform pressure and for a predetermined time. The unoperated and operated states of a single button are shown in Figs. 1 and 2 where the button 16 is guided between a base-board 1 and a cover 14 with its movement limited by collars 17 and 22. The button is held up by a cantilever spring 12 which also supports a contact operating card 5, shown in Fig. 3, against the action of a weaker cantilever spring 9. Spring 9 engages a notch 8 in the top of card 5 while spring 12 passes through an aperture 11. The underneath side of baseboard 1 has printed circuit connections between a contact bar 4 and two contact wires 2 mounted on its upper side for the purpose of switching two-out-of-five frequencies. The wires 2 pass through holes 6 in the card 5 and when the button is depressed are driven downwards by spring 9 on to contact bar 4, the spring 12 leaving the top edge of aperture 11 in card 5 when the contacts are made so that there is lost motion between the button and operating card. The contacts are not broken until the spring 12 collects the card 5 as the button restores. The card is guided by a pin 7 working through the base-board 1. The bottom of the button shaft normally rests on an armature 21 adhering to a magnet 23, the initial pressure necessary to operate the button having to separate the armature which pivots along one edge of the magnet and is limited by a stop 24. The armature is attracted back to the magnet on release of the button. As difficulty can arise in threading the contact wires 2 through the holes 6 in card 5, the wires may be pinched in the larger holes 38 in the two-card arrangement of Figs. 8 and 9, where one card is pressed down by spring 9 and the other is held up by spring 12 to grip the wires in shear. A tenbutton keysender arrayed in two rows of five is shown in Figs. 4, 5 and 7, where the spring 12 are offset from the line of the buttons which are set side-by-side. The springs are mounted between spacers raised on U-shaped side members 26 on the base-board 1 and end-pieces 25 carry stops 24 for a common armature 21 which adheres to magnets 23 placed at each end. Side flaps 31 on the end pieces 25 hold the armature in place laterally. Secured to the under-surface of the armature 21 are insulating blocks 35 carrying off-normal contact strips 34 which normally bridge contact-pins 33 mounted in baseboard 1 into the printed circuit on which they are connected. According to which row a button belongs its operation will tilt the armature about one or the other edge of the permanent magnets 23 and separate the contact strips 34 from one or other of the sets of pins 33.