Membrane keyboard

摘要

In order to make it possible to replace the markings and nevertheless to screen the regions of the switches from environmental influences, a protective membrane (6) is arranged between the replaceable strips (5) and the region of the switches (8), which protective membrane (6) is firmly bonded together without any interruption and to adjacent layers (4, 7), and all the switch regions are insulated from the unfavourable environmental influences in an industrial concern. The switches are designed as switches with snap-action discs (8). In order to prevent defects which may be caused by rotation of the snap-action discs (8), either a fixing part is attached which engages in a recess in the contact chamber (7') and thus blocks the rotation, or an essentially centrally symmetrical arrangement, running over the entire circumference, of the outer contact is used, so that any rotation of the snap-action disc (8) cannot cause a defect. When this circuit is operated, the operator senses the switching movement with his or her finger and at the same time hears the snap-action disc (8) snapping over. The design is very simple and reliable even in the case of severe environmental influences, that is to say dust and gaseous and liquid media as well as vibration. <IMAGE>