Alps plate spring
|Sense method||Metal leaf|
|Peak force||60 cN|
|Total travel||4 mm|
|Keycap mount||Alps mount|
The Alps plate spring or leaf spring is a stacked spring switch patented by Alps in 1974 as the Nodally Operated Push-Button Switch, with Taneo Murata as the inventor. It is only known to have been used in a small number of IBM Japan keyboard designs, with the PS/2 P70/P75 keyboard being the only one available outside of Japan.
The switch could be described in some ways as a simplified beam spring switch, as it uses a flat spring to generate tactility and actuate the contact mechanism. The return spring is held captive inside the slider by a block that clips into the primary slider from below. When the slider is removed, the return spring remains inside the slider. This slider/spring/block arrangement presses down onto the plate spring. The helical–plate spring pairing provides hysteresis and pretravel.
Total travel is 4 mm. Attempts to measure the plate spring snap and release points with callipers yields a snap point between 2.2 and 2.5 mm, and a release point between 1.3 and 1.6 mm, with the exact points varying from stroke to stroke. The perceptual hysteresis seems to be somewhere in the region of 1 mm, but this is hard to determine with callipers as, even using the thumbwheel to increment the switch travel and release, the kick from the plate spring is enough to cause a significant misreading. Testing with a multimeter shows however that the click and tactile feel does not directly correspond with contact operation. The actuation feedback does correspond with the actuation itself, but the contact hysteresis is much lower than the perceived hysteresis. After actuating the switch, releasing the slider a small amount will allow the switch to be "teased" (generating a resistance proportional to slider position in either direction), and after a short release distance the contacts will fully disengage. The slider can then be released significantly further before the plate spring snaps back, at which point a second click is heard. As the tests was performed on a used switch, and no documentation for the switches has been found, it is not known whether this discrepancy is due to the design or due to wear within the switch.
The slider is compatible with the same keycaps as Alps SKCL/SKCM series switches.
The mechanism provides an action that is described as particularly pleasant compared with more common switches made by Alps, Cherry and others. However, there are some reports of the mechanism getting mushy with age.
- Apls 5576003 mov.gif
Plate spring animation
- US Patent 3899648, Taneo Murata, "Nodally Operated Push-Button Switch", filed Mar 13 1974, issued Aug 12 1975.
- Sandy — P70 keyboard
- Deskthority — IBM PS/2 P70/P75 keyboard (ALPS Plate Springs)
- Qwerters Clinic — Dissection of an Alps plate spring switch