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Fujitsu FES-301

Overview

FES-301 is Fujitsu’s full-travel leaf spring switch type. FKB2500 Series keyboards currently use FES-301E according to Fujitsu, where “E” denotes “ergonomic” to indicate DIN compliance. This would make FES-301 the original full-travel design (commonly referred to as “second-generation leaf spring”, and FES-301E the lower-profile type (commonly referred to as “third-generation leaf spring”).

FES-301 is a development of FES-300 sheet keyboard switches. The sheet keyboards were introduced in the Fujitsu journal in November 1979. The Fujitsu Scientific & Technical Journal covered both the sheet and “typewriter” keyboards in September 1980, based on a manuscript received in March 1980. The series names of the switches were not given in either article, but a diagram in the Fujitsu journal in June 1985 names the two series and appears to indicate that FES-301 followed FES-300.

FES-301 is given as the switch type for FKB 2831 Series and FKB 3140 Series in Electronic Design’s Gold Book, Volume 2 1987, based on what little information can be observed on Google Books.

Design

The contact assembly is virtually identical to that of FES-300. The significant difference is that the actuator leaf spring is significantly longer, providing much higher leverage. This may be what accounts for the difference in operating force between the two types. The need for high leverage led to two different approaches. The fully-discrete FES-360 switches used a second leaf spring embedded into the plunger. Keyboards with FES-301 switches simply offset the plungers further so that they are still above the end of the longer leaf spring.

The structure of the original FES-301–based keyboard design is roughly as follows (production keyboards appear to have deviated from the drawing in Fujitu’s utility model):

FES-301E–based keyboards follow the same principle, but have a lower-profile plunger assembly.

A Victor 108816-44 keyboard has been found with plungers similar to those of FES-370 and “Peerless” switches, and a case almost identical to that of FKB4700 Series.

FES-301S

Confusingly, FKB3000 keypads offer a choice of FES-301S and FES-310, where FES-301S appears to be a derivative of the low-profile FES-300 sheet keyboard switches. The reason for putting sheet keyboard switches into FES-301 series remains unexplained.

Keyboards

Documentation

The material from the Fujitsu Scientific & Technical Journal is presented here by kind permission of Fujitsu.

References