View source for Buckling spring

{{Short description|Mechanical switch mechanism}}
{{More citations needed|date=March 2023}}
[[File:Unicomp space saver model m. with removed key 3864555240 9a2c6b95da o.jpg|thumb|upright|[[Unicomp]] Model M with removed z key. The exposed buckling spring is visible.]]

A '''buckling spring''' is a type of keyswitch [[Mechanism (technology)|mechanism]], popularized by [[IBM]]'s [[Keyboard technology|keyboards]] for the [[IBM PC|PC]], PC/AT, 5250/3270 terminals, PS/2, and other systems. It was used by IBM's [[Model F keyboard]]s (for instance the [[AT keyboard]]), and the more common [[Model M keyboard|Model M]]. It is described in {{US patent|4118611}} (Model F) and {{US patent|4528431}} (Model M), both now expired. According to the original patent: "A non-teasible, snap action, tactile feedback, key mechanism of extreme mechanical simplicity and high reliability is achieved."<ref>{{Cite patent|number=US4118611A|title=Buckling spring torsional snap actuator|gdate=1978-10-03|invent1=Harris|inventor1-first=Richard Hunter|url=https://patents.google.com/patent/US4118611/en}}</ref>

==Operation==
{{Listen |filename=IBM M2 sound.ogg |title=IBM M2 sound |description=The characteristic sound produced by the buckling-spring mechanisms of a Model M keyboard }}

The [[coil spring]] tensed between the [[keycap]] and a pivoting hammer [[Buckling|buckles]] (i.e. kinks or collapses) at a certain point in its downward traverse, providing auditory and tactile feedback to the keyboard operator. Upon buckling, the hammer is pivoted forward by the spring and strikes an electrical contact which registers the key press. In a Model M, the electrical contact is a membrane sheet similar to that of a modern [[Keyboard technology#Dome-switch keyboard|dome switch keyboard]].

==Image gallery==
<gallery mode="packed" style="text-align:left">
File:Bucklingspring-animation-300ms.gif|Buckling spring on key press and release
File:Bucklingspring1-o.svg|Illustration from the original buckling spring {{US patent|4118611}}, issued to IBM in 1978
File:IBM buckling spring.svg|A drawing included in the patent for the buckling spring mechanism
File:Fig 2 harris keyforce-o.svg|Graph of key force over key travel for a buckling spring key. Visible in graph position 1C the fast force drop when the spring buckles. {{US patent|4118611}}, issued to IBM in 1978.
File:Buckling spring comparison.jpg|IBM Model F (left) and Model M (right) keyboard springs
</gallery>

== See also ==
* [[Euler's critical load]]
* [[List of mechanical keyboards]]
* {{Section link|Switch#Contact bounce}}

== References ==
{{Reflist}}

== External links ==
* [http://deskthority.net/wiki/Buckling_Spring Wiki article on the various buckling spring mechanisms] – From deskthority.net

[[Category:Computer keyboards]]


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