Rubber dome pretravel — myth?

[Daniel Beardsmore]

It's widely claimed that rubber dome keys have to fully depressed to register, but does anyone have evidence of this being true?

All the force curves I've seen for rubber dome over membrane give the actuation as occurring before full travel.

For example:

wiki/File:Cherry_The_keyboard_pros!_Catalog_06-07.pdf

[002]

I reckon it is just a myth and it's probably come about as a product of people trying to explain why mechanical switches are better than dome. Like you, I've never seen a force graph for a rubber dome board where the operating point is right at the end. With some designs (e.g. Topre conductive dome + membrane) it is quite obvious that there will be travel after the operating point.

[Findecanor]

You have to (well, I have to) bottom out even to actuate a Topre 45g switch that has the actuation threshold near 2 mm above the bottom. It is not about where the threshold/point is but because the shape of the tactile bump (in the force graph) encourages you to press harder you will practically always overshoot and reach the bottom.

On a regular rubber dome with a rubber foot (or rubber foot on inner dome), you will reach the mushy bottom at speed when you actuate. You don't have to press the mushy bottom all the way down but you will definitely have to feel it.

[codemonkeymike]

Have you considered that the travel after key registering is just displacing the rubber of the dome. As in the sense pad contact(thing) is on the PCB/membrane but the rubber still can be compressed from there. I think the actual travel is measured on how far the sense pad contact(thing) is above the PCB/membrane. This is under the assumption that the dome is being pushed down directly in the middle and the rubber is collapsing around the middle outwards.

[Daniel Beardsmore]

Have you considered that the travel after key registering is just displacing the rubber of the dome.

Are there any alternatives?