FES-370, formerly referred to as “lever action” is a rare discrete mechanical keyboard switch from Fujitsu. It is a metal dome switch, derived from the earlier Fujitsu leaf spring switches, with the dome assembly mounted vertically and operated by a lever actuator instead of the leaf spring. Keyboards with this switch are very rare; it appears to have been used in model FKB2930 (externally identical to FKB4700 “Peerless” keyboards), which is curious as analysis of Fujitsu keyboard series shows FKB2930 to be within the leaf spring series numbering range.
Fujitsu documented this switch in an article titled スーパーエルゴノミクスキーボード/Super Ergonomics Keyboard, in Fujitsu magazine, volume 38, issue 4 (July 1987), pages 274 to 279, written by Hayashi Kazutoshi (林 和敏), Toshiaki Tanaka (田中敏明) and Hideo Takayama (高山秀雄). This article, almost entirely in Japanese, describes the design and operation of the switch. This article, provided by Kiyoto, cannot be posted online.
Numerically, they are one step after FES-360 (discrete leaf spring) and appear to be a way to provide discrete leaf spring switches in a lower-profile form factor.
The images below are preliminary until such time that better images are made available. The two switches below are from Chinese merchant cherry-jade and came from an unspecified keyboard collected from e-waste sent to China.
The return spring appears to be permanently attached to the plunger.
Most of the specifications below are taken directly from the Super Ergonomics Keyboard. The preload and total travel force figures are taken from the force curve.
|Operating force||60±20 g|
|Preload||ca. 25 g (from the force curve)|
|Total travel force||ca. 75 g (from the force curve)|
|Tactile drop||15 g|
|Bounce time||10 ms maximum|
|Rated voltage||24 DC maximum|
|Rated current||50 mA maximum|
|Contact resistance||Maximum 100 Ω at 5 V DC, 1 mA|
|Rated lifetime||20 million cycles|
The following force curve was included in the article. The operating force is shown as 58 g instead of 60 g, and travel as 4 mm instead of 3.8 mm; these inaccuracies are reproduced as-is.
A US patent and a Japanese utility model have been found for this switch; it was introduced some years after leaf spring.
|US 4803316 A||Push button switch using dome spring and switch element thereof||1986-10-16||1989-02-07|
|JP H0615373 Y2||Pushbutton switch||1987-08-11||1994-04-20|