Fujitsu FKB4690 Series
Fujitsu FKB4690 Series is a spring-over-membrane custom mechanical keyboard series intended for Point of Sale (POS) applications.
The switch is very broadly linear. In addition to the membrane actuator spring, there are buckling rubber sleeves described as “防塵ゴム”, meaning “dustproof rubber”. The implication is that the rubber is there only to keep out dust, but there is no other component that looks like it would function as a return spring.
The plunger is labelled “スライダー”, meaning “slider”, which is interesting in being the first documented example of “slider” being an official manufacturer term. (This term may have originated from Japanese Alps keyboard enthusiasts; the origin of the term has been lost.)
The specifications below cover the individual switch units. The data below is taken from the datasheet.
|Total travel||3.8±0.5 mm|
|Operating force||44±24 cN|
|Lifetime||10 million times|
|Contact resistance||1 kΩ or less|
|Bounce time||10 ms or less|
- FKB4690 Series datasheet (fujitsu.com; 2001-10-03, modified 2004-07-22)