Scissor switch
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A scissor switch (also pantograph switch) is a form of stabilised 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.
A typical scissor switch uses a small rubber dome over membranes but many other solutions for return force and sensing exist.
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
A traditional scissor-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.
The exact design of the mechanism varies between manufacturers.
On butterfly-type scissor switches the legs don't extend below past the hinge, and each leg pivots and/or slides against the bottom on its own side. Butterfly switches typically have very low key travel, often below 1 mm.
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
Scissor switch on a Compal notebook
Normal and compact switches from an Apple Aluminium Keyboard
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See also
- Elecom rack and pinion — an alternative approach to scissor switches
- Category:Scissor switches
