Jump to page content

Fujitsu FES-370

Contents

Overview

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 the Fujitsu journal in July 1987. This article, almost entirely in Japanese, describes the design and operation of the switch.

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.

Specifications

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
Travel 3.8±0.5 mm
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.

Patents

A US patent and a Japanese utility model have been found for this switch; it was introduced some years after leaf spring.

Patent/utility model Title Filed Published
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

Documentation

The material from the Fujitsu journal is presented here by kind permission of Fujitsu. The Japanese material was originally obtained by 聖人 (Kiyoto) with whom this research was conducted.