Alps KFNR Series

KFNR is a series of membrane keyboards from Alps Electric. The series is illustrated in the 1993 and 1994 Alps catalogues with the following diagram, to which colour has been applied according an interpretation of its structure:

The specifications are as follows:

The keyboard was advertised as dust-proof and drip-proof. N-key rollover was offered, with the following descriptions (where the Japanese and English descriptions given in the catalogues are not direct translations of other):

• “抵抗印刷式メンブレン採用により，Nキーロールオーバーが可能です。 / N-key rollover is available using carbone printed membrane.” — 1993 Alps catalogue
• “抵抗印刷方式メンブレン採用により，ロールオーバー対応も可能です。 / With resistance printing membrane feature, roll-over feature is possible.” — 1994 Alps catalogue

The switch uses an inverted buckling rubber sleeve, and thus requires an extra component to apply pressure to the membrane. A design matching this requirement forms the fourth embodiment of US patent 5120923 “Push button switch” filed in September 1990 with priority to a Japanese patent filed in May 1989. This patent was reprised in 1992 as US patent 5201824. The actuator in these keyboards is depicted in the patent as follows:

A central post presses on the membrane; the bottom of the post is stepped such that only one side makes contact. To provide overtravel, the keycap rests on a pair of prongs, that flex once actuation has occurred. Keyboards matching this design are known:

• Toshiba T4600C (uses the compact type for the function keys)
• IBM external numeric keypad

The latter contains no Alps model sticker. The Toshiba keyboard may well have a model sticker inside (as is typical for Toshiba laptops) but this was not documented at the time.

In the examples above, the actuator is typically white (clear) but yellow has been sighted in a more compact version of the switch.