Editing IBM buckling spring (section)

==Original IBM patent==
[[File:origbuck1.jpg|100px|thumb|right|Basic design]]
The original IBM buckling spring mechanism was patented by IBM in 1971 as the 
'''"Catastrophically buckling compression column switch and actuator"'''<ref name="_PAT_3699296" /> with Richard Hunter Harris as the inventor.  It was never used in any known production keyboard, and does not have a lot in common with the later buckling spring mechanisms that were actually used, but is noteworthy to show why the later mechanisms were designed like they were.

[[File:origbuck3.jpg|100px|thumb|right|First variation]]
The patent described three related mechanisms based around a spring located in a sealed housing (barrel) tensed between the keycap and a fixed point directly underneath.  In the first design, the spring was electrified. The barrel surrounding the spring was conductive, and hooked up to a circuit. Depressing the key would cause the spring to buckle, and it would make contact with one of the sides (in such a simple mechanism, the spring could buckle any way) and thus completing a circuit. This mechanism would be very simple to implement, but the electrical contact mechanism proposed would be prone to bounce issues.

[[File:origbuck2.jpg|100px|thumb|right|Second variation]]
Consequently, the two subsequent variations proposed more sophisticated electrical contact mechanisms.  In the first variation, at either side of the spring, the barrel was closed to prevent the spring buckling sideways, and a wedge was positioned behind the spring to prevent it buckling backwards, and to push it slightly forwards in the intended direction of travel. In addition, the wedge was conductive, so that the electrified spring made contact with it to form a circuit.  When the spring was buckled by the depression of the keycap, it made contact with another conductive surface, making yet another circuit. Thus there was a circuit for when the key had been pressed, and another for when it was depressed, and this would have provided a more desirable electrical switch at the expense of complicating the mechanism.

The second variation was similar to the first in terms of the fact that it ensured the spring buckled forwards, but it did away with the electrification of the spring. Instead, when the spring hit the appropriate section of the barrel it actuated some sort of sensor. A number of suggestions are provided in the patent for what should be used, including a [[piezoelectric transducer|piezoelectric sensor]], a photosensitive sensor, and most notably a capacitive sensor - which was what was ultimately used in the refined buckling spring mechanism patented six years later. It is interesting to note that if the capacitive sensor was based around detecting the distance between itself and the spring, it is somewhat similar to the operation of the [[Topre switch|Topre capacitive mechanism]].

The patent promised a simplified switch design which would combine the tactility, actuation, pre-travel and travel return into the one spring, but ultimately it seems the means of actuating the circuit was difficult due to the unpredictability of which way the spring would buckle, and mechanisms to control the direction of the buckling added complication and potential unreliability to the design.