Alps buckling spring
|This article requires photographic illustration — need photos of the internals|
|Sense method||Hammer over membrane|
|Keycap mount||Alps mount|
This mechanism was patented by Alps in 1989 as the "Push button switch with actuator for applying transverse force to buckling spring", with Takafumi Kato as the inventor. It is commonly associated with the keyboard of the IBM-designed Sega TeraDrive, although it was used in some non-IBM keyboards such as certain C. Itoh terminal keyboards. It is unknown if it was developed by request of IBM, or whether it developed under Alps's own initiative, and later picked by IBM for the Sega TeraDrive design.
According to the patent, the switch was designed to have a lower profile than other buckling spring implementations. As with IBM membrane and Brother designs, Alps buckling spring is a hammer-over-membrane design. However, it differs in that the pivoting hammer has a follower behind the spring which pushes the spring forward during travel. The patent describes this modification as being necessary in a compact buckling spring switch to ensure that a short spring will buckle forward properly. It also noted that a regular buckling spring mechanism needed springs manufactured to very specific tolerances for the spring to buckle properly, which might imply that assisting the buckling of the spring with a follower would allow cheaper springs to be used. This switch uses a shorter spring than other buckling spring implementations, and has notably less key travel. It also has lower force requirements than other buckling spring switches. However, it has been described as a less satisfying switch to type on compared with the more conventional buckling spring mechanisms.
Unusually for a buckling spring mechanism, there is a slider over the spring. This slider is compatible with standard Alps keycaps as used with the Alps SKCL/SKCM series and Plate Spring switch designs.