Alps membrane keyboards
Contents
Overview
Alps membrane series names began “KFN”, where “KF” denotes a full keyboard. The third letter in membrane types is “N” (compared to “C” and “F” for the mechanical types and “E” for the elastic contact types).
In their 1993 and 1994 catalogues, Alps listed membrane types both as keyboards and switches. The switch entries provided an illustration of the outside of the switch along with the force curve. The individual switches were listed with “KF” series names instead of “SK”, as the switches cannot be supplied separately. The switch series had four-letter codes (e.g. KFNR) while the keyboard series had six-letter codes (e.g. KFNRBA).
Series
Plate-mounted actuators
Alps produced several designs using plate-mounted actuators. These are discrete modules that contain a plunger, a return spring, and a membrane pressure spring. An Alps Low-Profile Keyboard Switches sample pack of unknown date depicts one such type as series KNB/KFNB. This has a black plunger, and it is not clear from the photographs whether it is a four-slot or two-slot design, and there is certainly no way to determine whether it uses a prong to press on the membrane. The only specified model is KFNBBA, with a rated lifetime of 3 million cycles, a 90 gf “operating force” (total travel force, heavy for Alps), 3.5 mm travel and 400 Ω contact resistance maximum.
Four-slot dual spring
This is known from an unidentified C.Itoh keyboard. A cube-shaped grey plunger holds the membrane pressure spring. The plunger has a central slot to hold the keycap, and four smaller slots around it, in two pairs. A seemingly black plunger version is also known, from an unknown keyboard.
Four-slot prong
This is known only from orihalcon’s 1x Spring over Membrane Linear ALPS Replacement Keyboard Switch … eBay listing, which carries no mention of what keyboard it came from. The actuator shell is almost identical to the dual-spring type, but it has a prong in the centre that presses on the membrane. From the photos, it appears that the return spring is still wide in diameter, suggesting that there must still be a second spring inside to press on the prong.
Two-slot
This is only known from a Yamaha YIS503IIR keyboard that was once listed on eBay. The poor quality of the photograph makes the actuator design hard to make out, but one could observe that either side of the keycap slot in the plunger is two wide slots, instead of the two pairs of slots on other examples, much more like SKEW plungers. There are no details as to whether the membrane is operated by a prong or directly by a spring.
KFNF
This is a design of notebook keyboard using dual spring over membrane. A plastic plate holds the keycaps. The plungers are moulded into the keycaps, very similar to a standard rubber dome keyboard. There is only one known model, UE0200P12 (KFNFBF004A). This may be a cost reduction over KNB/KFNB.
KFNL
KFNL is Alps buckling spring.
KFNM
KFNM is a low-profile design that uses an inverted rubber sleeve in conjuction with an inner membrane pressure spring.
KFNR
KFNR is advertised in the 1993 and 1994 catalogues. It is a low-profile, non-scissor buckling rubber sleeve keyboard (around 10 mm), offering 3 mm travel and N-key rollover using a “carbone printed membrane” [sic]. The design of the actuator is not shown, but it seems to correspond with a particular known style of Alps membrane keyboard.
KFNS
This is advertised in the 1993 catalogue but not the 1994 catalogue. It is a reduced-height version of KFNR, with 2 mm travel and around 7.5 mm tall. Operating force is still 49 cN (50 gf) but the lifetime is only 5 million, versus 10 million of KFNR. KFNS was advertised with the same printed resistor N-key rollover option as KFNR: “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.”
KFNY
KFNY is known only as a keyboard series, advertised in the 1994 catalogue. KFNY features 3.8 mm travel, N-key rollover and a 20 million cycle lifetime. The sole catalogue model is KFNYEA901A.
Dome–plunger 1
This is a plunger-over-dome type with Alps-mount plungers. This can be seen in some AppleDesign Keyboards, such as this example.
Dome–plunger 2
This is a second, visually simpler plunger-over-dome type, also with Alps-mount plungers. This can be seen in the Wang 725-7952.
KFRF
KFRF is known from Alps keyboards marked “Model : KFRF-1 series”. This is a rubber dome type with no plunger. Some AppleDesign Keyboards are also this type.