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; it is the switch type used in all modern laptop computers to allow for laptops to have ultra-thin keyboards. For reasons of both familiarity and preference, scissor switch keyboards are becoming increasingly common in desktop keyboards, and all current Apple desktop keyboards use scissor switches.

Because of the size of the scissor mechanism itself, scissor switches with key travel higher than 2 mm are uncommon.

Internals

The switch has two plastic 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:

  • US4433225 (General Instrument, filed in 1983) — keycap levelling mechanism patent, that appears to be a forerunner of the scissor switch
  • US5894117 (SMK, filed in 1997)
  • EP1164463 (SMK, filed in 1999)
  • US6312176 (Alps, filed in 1999)
  • US6297461 (SMK, filed in 2000)
  • US7238907 (Alps, filed in 2003)

Gallery