As the title implies this is really no more than an idea right now. But it's something I've been thinking about and I thought I would share.
Here's a crappy diagram of what I have in mind:
The actuation method is about the simplest, dumbest thing imaginable. There are two contacts near the bottom of the housing and a plate near the bottom of the slider that's either made out of or coated with something conductive, so when it hits the contacts it completes the circuit. Now ordinarily this would be a dumb way to do things because then you're actuating when you bottom out, but bear with me for a minute.
What I have in mind is that the bottom plate is not fixed. Instead it can move independently from the rest of the slider. There is a second outer spring that normally keeps it pressed down (that is supposed to be one spring that wraps around the slider, think of the diagram as like a cross-section) and a small lip on the bottom part of the slider to keep it in place.
I hope you can see from this how since the bottom plate can move you're not actually actuating on bottom out anymore, as you can continue to push the slider forward. But make this transition from pressing on one spring to two springs, which will produce a kinked force curve like:
Where the kink happens exactly at actuation, since before that you're only pushing on one spring.
This funny-looking force curve was actually my true objective in this design. I'm looking for a tactile switch where the force actually increases at/post actuation. In most approaches to tactile or clicky switches there is a bump in the force curve prior to actuation and then a sudden drop around actuation. This makes it easy to overshoot the actuation point and bottom out. Indeed there are a lot of switches where the peak of the tactile bump is close to bottom-out force.
I want some tactility so you know by feel where the actuation point is, but I want to strongly discourage bottoming out at all. My experience with Halo True switches has convinced me that this is a good idea. Indeed they're very close to what I'm looking for. But I still wish they had sharper tactility, so the actuation point was instantly recognizable.
Which can be achieved here by preloading the outer spring. See in the above force curve I assumed that the outer spring's rest position is naturally the distance between the two plates. The result is fairly subtle, a change in the slope of the force curve but no distinct bump. But what if the outer spring was already partially compressed? So there's already a force on it but it's held in place by the lip on the slider. Well once it hits the contacts you have to first exceed that existing force before you can move it any further, leading to a clear bump in the force curve:
That's just the general idea. The exact shape of the force curve can be altered significantly by adjusting the weight of the two springs and the amount of preload. A very light outer spring with no preload would feel almost linear, with just a subtle change in slope at actuation. A heavy outer spring would produce really heavy bottom out forces without necessarily requiring any more force for actuation. And of course the amount of preload would affect the size of the jump in the force curve at actuation, though I suspect this wouldn't need to be large at all to be noticeable.
But this is all academic at this point because I'm no switch manufacturer. I do wonder how difficult it would be to build a switch like this. Of course the whole dual spring and slider on top of slider thing sounds like it would significantly complicate things, but on the other hand you do with a fair bit by having such a dead simple actuation mechanism. And while the design is quite different I don't see any fundamental reason you couldn't fit this inside a MX housing for compatibility.
Thoughts?
