Olivetti snap action
|This article requires additional photographic illustration|
|Sense method||Metal contact|
|Switch mount||Plate mount|
Olivetti snap action switches feature a plate spring similar to Alps plate spring, above which is placed a helical spring. When the key is pressed, pressure in the helical spring increases, causing the plate spring to snap into its unstable state, conducting current between two exposed gold-plated PCB pads: one at the corner of the switch that makes permanent contact with the plate spring, and one in the centre. This snap action releases pressure on the helical spring, which lowers the switch force, giving a tactile event and overtravel. The force graph shown in the patent indicates that this design also provides hysteresis, as the reduction in pressure required to release the plate spring involves lifting your finger to a higher point than where the make action occurred.
As the plate spring snaps between its stable and unstable states, a loud click is emitted.
The design is similar to not just Alps plate spring, but also to the Futaba clicky switch which also uses a plate spring. The patent depicts a second version of the switch where a single key can trigger two switches at different travel distances, giving a double-action switch.
Olivetti dome with slider is a revision of the switch that appears to be cost reduction by using a rubber dome instead of the plate spring. The operation of the switch remains otherwise unchanged.
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