Scissor switch

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Scissor switch on an RM notebook

A scissor switch (also pantograph switch) is a form of stabilised rubber dome switch. The scissor mechanism functions like a pair of opposed stabilisers joined by a hinge. The scissor mechanism allows for a stable key with a low profile.

Key travel is usually in the 1.0-2.5 mm range. In the upper range, the Mitsumi KGL Type has 2.5-3.0 mm and the original Logitech PerfectStroke had 3.2 mm key travel.

Scissor switch keyboards were likely introduced for the constrained dimensions of notebook computers. For reasons of familiarity and preference, scissor switch keyboards are becoming increasingly common in desktop keyboards. For instance, all current Apple desktop keyboards use scissor switches.

Internals

The switch has two cross-arms, one of which pivots on the baseplate, the other pivoting on the keycap. The opposite ends of each cross-arm slide within guides. The cross-arm mechanism replaces the need for an upper shell with guide shafts for sliders, reducing both the height and weight of the board. The flat base of the keycap rests directly on the rubber dome.

Scissor switch mechanism.svg

The exact design of the mechanism varies between manufacturers.

History

The origin of scissor switches has yet to be identified. In 1983, General Instrument filed a patent (US4433225 "Keytop levelling mechanism") for a scissor-like mechanism for stabilising L-shaped keycaps. A narrow scissor arrangement occupies the side of the keycap opposite to the switch. Comparing the patents it cites, with the patents citing it, it would not be a stretch for this design to be the origin of the scissor mechanism.

Patents

There are a great many patents relating to scissor switches from many different manufacturers; examples:

Manufacturer Patent Filed Notes
General Instrument US 4433225 1983 Keycap levelling mechanism patent, that appears to be a forerunner of the scissor switch
SMK US 5894117 1997
SMK EP 1164463 1999
Alps Electric US 6312176 1999
SMK US 6297461 2000
Alps Electric US 7238907 2003
Mitsumi EP 1458000 2004
Mitsumi US 7199320 2006

Gallery

See also

References