Fujitsu Leaf Spring

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Fujitsu
Leaf Spring Switch
(1st Gen)
FLS-1stGen-SwitchActuation.png
Manufacturer Fujitsu
Inventor Seisuke Kamei
Hideo Nabetani
Ryohei Kinoshita
Switch type Linear
Sense method Metal dome
Peak force 80 g
Patents US4370533
Fujitsu
Leaf Spring Switch
(2nd/3rd Gen)
FLS-2nd3rdGen-SwitchActuation.png
FLS-2nd3rdGen-LinearForceCurve.png
Manufacturer Fujitsu
Inventor Seisuke Kamei
Toshiaki Tanaka
Kazutoshi Hayashi
Akira Tanaka
Ryohei Kinoshita
Switch type Linear
Clicky (Rare)
Sense method Metal dome
Peak force 40 g, 45 g
Patents US4529849

History

The Fujitsu Leaf Spring switch seems to have been developed in the late 1970's as a way to reduce manufacturing costs for contact-based keyboard switch mechanisms (as opposed to sense-based mechanisms such as Hall Effect). The first iteration of the switch design used individual housings, and could be used individually, provided the switch is inserted into a stabilizing plate. The second design still used individual barrels for the switches, but it relied on the plate to suspend them over the leaf spring, similar to how IBM Model F capacitive buckling spring keyboards were designed. There is one confirmed keyboard that uses a one piece slider assembly, similar to the way the IBM Model M keyboard is designed.[Citation needed]

There is also a known tactile version of the 3rd generation of the Fujitsu Leaf Spring switch. Though due to the design (the mechanism is inside the slider barrel), this newer design could be used in 2nd generation housings. Unfortunately, keyboards with this tactile switch are much more rare than the linear variants.

These switches are most famously used in the FM Towns line of keyboards as well as the Tandy 1000 keyboards.

1st Generation

Individually housed leaf spring with corresponding button spring for actuation in each switch. Could be used individually. It used a cruciform slider with part of the leaf spring mechanism embedded into the slider, going through it and poking of the top of the cross.

The keycap mount dimensions are a fraction of a millimetre too large to fit Cherry keycaps; keycap insertion is very stiff. Testing with a modern Signature Keycaps novelty keycap yielded borderline success, while testing with a 2009 Filco keycap resulted in what appeared to be whitening of the plastic from stretching. Attempting to use Cherry MX mount keycaps is liable to lead to split keycap stems.

Key feel

Linear, extremely smooth (even when dirty). Much heavier than the later generation switches. One of the best examples of well designed linear switches.

Keycaps

All known keycaps are spherical double-shot, some nearly solid plastic. It uses a cruciform slider, as do many of the switches from the late 1970's through the 1980's.

Linear switch module

The following switch is NOS purchased through AliExpress.

2nd Generation

Individual barrels attached to a metal plate. Leaf spring and button spring attached to PCB below the plate. The slider is separate from the barrel and the keycap. It uses rubber gaskets/stoppers at the bottom of keys to slow the keys down in case the user is bottoming out.

Key feel

Very smooth linear actuation, with a rubber stopper at the bottom of each key.

Keycaps

All known keycaps are spherical double-shots, some double shots also have filled engravings. They fit directly onto the slider, similar to how the legends fit onto the two piece IBM buckling spring keycaps. Thick plastic is used. Keycaps are not compatible with the 1st Generation.

3rd Generation

Individual barrels attached to a metal plate. Leaf spring and button spring attached to PCB below the plate. The slider is separate from the barrel and the keycap. It does not use rubber gaskets/stoppers in the switches. Linear and clicky versions of the switch exist; the clicky version uses a mechanism within the slider, while the rest of the switch remains identical to the linear variety. The FMV77AV keyboard is known to use a single piece housing for all of the sliders, similar to the IBM Model M keyboard.

Key feel

Linear

Very smooth linear actuation.

Clicky

Weak tactile event, and a quiet clicking sound.

There is no known patent, a measured force curve is available elsewhere.[1]

Keycaps

All known keycaps are cylindrical double shots, with a slightly unusual shape bearing no texture on the top. Keycaps are made of thick plastic and they are compatible with the 2nd Generation.

Keyboards

It is believed that production of keyboards with these switches stopped in the late 1990s or perhaps early 2000s. Fujitsu later pushed its Peerless switch.

1st Generation keyboards

  • DK'tronics ZX Spectrum keyboard[5]

3rd Generation keyboards

  • Epson Q503A[6]

References

  1. Atelier Silencium — Force curves for various 3rd Generation keyboards Last updated 2010-02-20. Retrieved 2015-07-25.
  2. MouseFan — FUJITSU テンキーボード FMR30KB501 JAPAN — Uses 3rd Generation switches. Retrieved 2015-07-25.
  3. MouseFan — FUJITSU オアシス OAKB-406 JAPAN — Uses 3rd Generation switches, click variant. Retrieved 2015-07-25.
  4. jpspace — FM77AV keyboard — Uses 3rd Generation switches with diodes and has the single piece housing variant. Retrieved 2015-07-25.
  5. Nightfall Blog — Dk’tronics Keyboard for Sinclair ZX Spectrum
  6. Geekhack — Espson Q503A Keyboard Posted 2013-12-09. Retrieved 2015-07-25.