A buckling spring switch, commonly abbreviated "BS", is a type of spring-based switch where the spring buckles outwards instead of compressing. The advantage of such a mechanism is that buckling of the spring provides tactility and auditory feedback, and this guarantees that feedback occurs at the same time as actuation. Buckling spring switches typically rely on membranes for actuation, but the original IBM design was capacitive.
IBM buckling spring
While numerous keyboard switch designs from various companies were based around a buckling spring, the term is almost exclusively used to refer to the mechanism designed by IBM engineer Richard Hunter Harris in the 1970s, and later variations upon it. Harris's design used the movement of the spring before and after buckling to pivot a hammer, which in turn actuated a contact mechanism. There are a number of variations upon this basic design, however, the best known is a membrane-based variant designed for use in IBM's Model M keyboards, which continues to be manufactured to the present day in keyboards made by Unicomp.
Alps buckling spring
Alps buckling spring is a membrane buckling spring switch with a lower profile and reduced travel compared to IBM's design.
Brother buckling spring
In the late 1980s, IBM Japan moved from using Alps Plate Spring switches in their keyboards to a buckling spring design. The buckling spring mechanism used was designed and manufactured for IBM Japan by Brother Industries, and thus is referred to by Japanese collectors as the Brother switch. The first keyboard to use this switch was the 5576-003. The only other known keyboard to use it was the more common 5576-A01.
AT&T made their own buckling spring keyboards which appear to have been based on the membrane buckling spring mechanism, but may have been subtly different. They had a patent for a silenced buckling spring which used a foam dampener inserted into the spring, but it's not known if it was ever manufactured.
Can Technology buckling spring
Can Technology manufactured buckling spring keyboards in China.
- US patent 4859820, Casimer Gotfryd et. al., "Quiet key switch", filed Mar 31 1988, issued Aug 22 1989.