(Idea)Twin-Stage switches

[SpectreiiI]

So, coming from an industrial design backround, I have quickly fallen head over heels for mechanical keyboards. I have already looked at designing my own caps, layouts, colorways,  and cases.

These are all fun ventures, but the thing that keeps my up at night is switches. I have hashed out a few concepts, and all by one were either overly complex or prohibitively expensive. The one design that seems like it could be worthwhile is a twin-stage switch. It is essentially two linear switches that work in tandem. When the switch is pressed, the upper and lower sliders both move relative to their springs until the actuation point is met. At this point, the upper slider collapses downward and the pressure of it's spring is released, yielding a sharp drop in force. Once the key is released, the lower slider pushes the upper slider back into postion, reloading the upper assembly.

Has anybody ever looked into something like this?

[Joey Quinn]

So would the point be a switch that has 2 actuation points and thus registers 2 different outputs depending on how far you press it?

Or is this just complicated for the sake of being complicated

[Daniel Beardsmore]

Boy, I have to wonder about your "overly complex [and] prohibitively expensive" designs if this is the cheap and simple option!

"Two-stage" (not "twin-stage") is another term for double action, but that's different. You appear to be using this mechanism to only register a single keypress.

Having a slider where the spring can be engaged and disengaged at will sounds possible, but it seems like it's an overly complicated replacement to stacked spring. There are some fiendishly weird switches; Alps SKFF series (vertical plate spring) for example.

If you look through patents, you'll see that there are so many of them for switches we've never come across yet (and may not have all gone into production), and all sorts of strange ideas. I don't recall seeing anything like you've described, though.

With so many things, it's not a case of outright "possible" or "impossible" so much as whether you can achieve the desired level of reliability within an acceptable manufacturing cost. I don't know how you imagine that the inner slider is going to disengage from its spring, considering the size constraints. I'm thinking that it might be more realistic for the inner slider to remain on its spring, and for it to hit a hard stop that causes the outer slider to ratchet past it, causing the inner slider to fly back up to the top. That would give you a click sound, too. The outer slider would need to be able to reliably re-engage the inner slider under very low force (close to the preload, so 30-45 cN).

However, that would give you massive "click hysteresis" where you'd not get another click until they key was fully released. So you'd need some other device to hold the inner slider down so that it can be re-engaged at a deeper point than fully home.

I like how the Romer-G leaves room for central illumination, but that of course comes at a cost of consuming much valuable space within the switch, so you have to consider whether your design would leave room for an LED (be that through-hole monochrome, through-hole RGB, SMD monochrome or SMD RGB). Also, what sort of switch contacts were you envisioning?

[SpectreiiI]

Boy, I have to wonder about your "overly complex [and] prohibitively expensive" designs if this is the cheap and simple option!

"Two-stage" (not "twin-stage") is another term for double action, but that's different. You appear to be using this mechanism to only register a single keypress.

Having a slider where the spring can be engaged and disengaged at will sounds possible, but it seems like it's an overly complicated replacement to stacked spring. There are some fiendishly weird switches; Alps SKFF series (vertical plate spring) for example.

If you look through patents, you'll see that there are so many of them for switches we've never come across yet (and may not have all gone into production), and all sorts of strange ideas. I don't recall seeing anything like you've described, though.

With so many things, it's not a case of outright "possible" or "impossible" so much as whether you can achieve the desired level of reliability within an acceptable manufacturing cost. I don't know how you imagine that the inner slider is going to disengage from its spring, considering the size constraints. I'm thinking that it might be more realistic for the inner slider to remain on its spring, and for it to hit a hard stop that causes the outer slider to ratchet past it, causing the inner slider to fly back up to the top. That would give you a click sound, too. The outer slider would need to be able to reliably re-engage the inner slider under very low force (close to the preload, so 30-45 cN).

However, that would give you massive "click hysteresis" where you'd not get another click until they key was fully released. So you'd need some other device to hold the inner slider down so that it can be re-engaged at a deeper point than fully home.

I like how the Romer-G leaves room for central illumination, but that of course comes at a cost of consuming much valuable space within the switch, so you have to consider whether your design would leave room for an LED (be that through-hole monochrome, through-hole RGB, SMD monochrome or SMD RGB). Also, what sort of switch contacts were you envisioning?

You seem to have the right idea of what I'm envisioning. The upper slider would in fact be a telescoping component to the lower slider, so inner would perhaps be the more accurate way to describe it. In my original concept I had envisioned that the inner slider would release upward, hammering upward for a click event, but I haven't yet been able to come up with a mechanism that could reset the action in a way that would not require significant accommodations for hysteresis management.

Either way, the initial concept uses the inner spring as a contact which is made when the inner slider is released from the outer.  I agree that the force required to reload the inner slider is likely to be one of the principle constraining factors.

The switch was modeled from the get-go with significant central void space to accommodate LED lighting, similar to Logitech's Romer G solution. This is by no means the driving feature of the design, but having designed several miniature cylindrical actuators in the past, I am confident that it could be made practical.

Speaking to the previous poster, I have never produced a product that was not significantly less complex than it's competition.

[Daniel Beardsmore]

I was thinking something vaguely along these lines:

To allow the outer slider to push the inner slider up to the point where it hits the central post, there will be a hard stop to overcome until the connecting prongs are pushed aside. That would give it a strange feel in between Cherry MX Blue and buckling spring, where the force drops off permanently after actuation like buckling spring, but there will also be the temporary bump to clear from MX Blue. The angles of the connecting prongs and their engagement recesses would need to be adjusted for a balance of comfort and reliability.

I've had to juggle the parts so that the outer slider spring stays clear of the connecting prongs (hence running it below, or possibly outside). The same adaptation could be made to the inner slider to allow it to be entirely hollow, for a central LED.

I've made no attempts to fit any switch contacts in anywhere.

[Daniel Beardsmore]

BTW, my rough guess at the force curve:

Blue is buckling spring, and purple is twin-stage, adjusted to have the same lead-out as buckling spring with a roughly 1:1 ratio between the two springs.

[tp4tissue]

I was thinking something vaguely along these lines:

(Attachment Link)

To allow the outer slider to push the inner slider up to the point where it hits the central post, there will be a hard stop to overcome until the connecting prongs are pushed aside. That would give it a strange feel in between Cherry MX Blue and buckling spring, where the force drops off permanently after actuation like buckling spring, but there will also be the temporary bump to clear from MX Blue. The angles of the connecting prongs and their engagement recesses would need to be adjusted for a balance of comfort and reliability.

I've had to juggle the parts so that the outer slider spring stays clear of the connecting prongs (hence running it below, or possibly outside). The same adaptation could be made to the inner slider to allow it to be entirely hollow, for a central LED.

I've made no attempts to fit any switch contacts in anywhere.

This is the same as cherry MX blue.


in cherry mx blue,  your spring one is in spring 2 position ,  and the spring for upper stage is a horizontal leaf spring instead of your spring 1.

[SpectreiiI]

I was thinking something vaguely along these lines:

(Attachment Link)

To allow the outer slider to push the inner slider up to the point where it hits the central post, there will be a hard stop to overcome until the connecting prongs are pushed aside. That would give it a strange feel in between Cherry MX Blue and buckling spring, where the force drops off permanently after actuation like buckling spring, but there will also be the temporary bump to clear from MX Blue. The angles of the connecting prongs and their engagement recesses would need to be adjusted for a balance of comfort and reliability.

I've had to juggle the parts so that the outer slider spring stays clear of the connecting prongs (hence running it below, or possibly outside). The same adaptation could be made to the inner slider to allow it to be entirely hollow, for a central LED.

I've made no attempts to fit any switch contacts in anywhere.

I like where you are going, but if I understand your sketch correctly, the inner slider bottoms out before pushing the leafs apart. If this is the case, the plastic response would increase the force required at actuation, and progressively for the duration of the stroke.

[Daniel Beardsmore]

My reasoning was this: if you let go of the inner slider, you'll have to fully release the key before you can engage it again and that's not viable.

However, I was thinking that you could compromise with this idealised force curve:

That is, the inner slider would have 1 mm travel. For the first 1 mm, you push only the outer slider. Then at 1 mm you engage also the inner slider. At 2 mm, you disengage the inner slider and it is released back to its start point at 1 mm, giving you a drop in force and a click sound.

This would allow for click feedback and total disengagement of the inner slider, and tolerable hysteresis of around 1 mm.

For the sliders, you'd want some kind of semi-ratchet. Having the inner slider travel start at 1 mm down means that the outer slider could push past it on the way up, and re-engage on the way down. However, the ratchet would have to be bidirectional so that you can push past it at allow the inner slider to spring up.

It's not the same as Cherry MX in design, operation or feel, but there is a similarity. The first question is how you synchronise the contacts and inner slider. If the inner slider controls the contacts and it's released upon actuation, then the contacts wouldn't stay closed, so you'd need an additional mechanism for this.

[SpectreiiI]

My reasoning was this: if you let go of the inner slider, you'll have to fully release the key before you can engage it again and that's not viable.

However, I was thinking that you could compromise with this idealised force curve:

(Attachment Link)

That is, the inner slider would have 1 mm travel. For the first 1 mm, you push only the outer slider. Then at 1 mm you engage also the inner slider. At 2 mm, you disengage the inner slider and it is released back to its start point at 1 mm, giving you a drop in force and a click sound.

This would allow for click feedback and total disengagement of the inner slider, and tolerable hysteresis of around 1 mm.

For the sliders, you'd want some kind of semi-ratchet. Having the inner slider travel start at 1 mm down means that the outer slider could push past it on the way up, and re-engage on the way down. However, the ratchet would have to be bidirectional so that you can push past it at allow the inner slider to spring up.

It's not the same as Cherry MX in design, operation or feel, but there is a similarity. The first question is how you synchronise the contacts and inner slider. If the inner slider controls the contacts and it's released upon actuation, then the contacts wouldn't stay closed, so you'd need an additional mechanism for this.

I like the idea of delaying the inner slider loading. I have figured out a way to decouple it from the outer slider using a snap ring mount that is released by a static lobe the could be molded into the lower housing. It would be relatively simple, reliable, and frictionless. I think this may be doable.

[Daniel Beardsmore]

I demand to see teh darwingz!

[orihalcon]

There are a few manufacturers that have "dual action" though not sure that's the correct term.  Alps has two variants, one that looks like a regular alps switch and an alps plate spring variant.  The plate spring one has the slider run into a metal dome tact switch inside of it and the bottom of the key travel.  The dual action regular sized ones are linear at first, then have a tactile bump with additional force.  Instead of a click leaf, there's two sets of contacts on either side of the slider, so in the end, you have 4 contacts to solder on the bottom of the switch.

http://imgur.com/a/ldnlP

I have a couple of these around somewhere if I can find them.  Seems like good photos of them are lacking out in the wild.

[SpectreiiI]

I demand to see teh darwingz!

I tried to do it on paper, but I think I'm going to need to model it to illustrate the concept. I should be able to crank it out tonight. While you are waiting, here is one of my previous actuator designs; very similar in mechanics, though far more complicated than a key switch.

https://imgur.com/gallery/uBaTn

[Daniel Beardsmore]

There are a few manufacturers that have "dual action" though not sure that's the correct term.

See my first reply earlier.

[SpectreiiI]

I demand to see teh darwingz!

Darwingz as requested. Sorry for the delay. It was more work I procrastinated more than I expected.

So grey doozer up top is top of switch. I didn't care to draw a keycap mount. The rest of the case isn't shown for clarity. Gray cylindrical thingamah-bopper is the outer slider. Yellow cylindrical whatsama-hoozer is the inner slider. When switch is pressed down to 1.8mm, the clay-colored dildo looking thingie spreads the legs of the pink ringading which releases the inner slider. when the outer slider travels back up the green roundybout of the bottom prohibits the inner slider from traveling too far upward and the pink legs ease off the dildo and the ringading shuts above the inner slider at precisely the same travel distance as it opened on the downstroke.

The switch has 8 parts total at this point, 6 of which move. This includes the yet to be determined contact method, which I'm assuming will be a leaf.

[Daniel Beardsmore]

I'd been wondering whether it would be possible to have the inner slider be engaged from 0 mm, but only spring up by 1 mm or less when released. My reasoning being is that I'm not convinced that a sharp engagement point of the inner slider would feel good, nor am I certain that a sharp drop in force would be good either. I found it uncomfortable for some time on Cherry MX blue, and I don't know why I've stopped noticing — either I'm used to it, or my switches have worn smooth.

I couldn't think of a way to have an obstacle for the inner slider that would be activated as the switch is pressed and retracted when it's released, but I've just come up with this nightmare:

The side prongs are held in their retracted position by extra lugs on the outer slider, and as that reaches 2 mm, the prongs move into position to catch the inner slider. Edit: note that the red slider is halfway pressed but the black slider is unfortunately not ... Oops.

I don't pretend that this is a good idea though, and I can't even follow your drawing. I do like old-school textbook style though.

The other aspect is spring strength ratio: with the inner slider given a comparatively weak spring, it would make the tactility more subtle and less jarring. You could tune the tactility by simply trying different length springs for the two sliders.

[SpectreiiI]

I'd been wondering whether it would be possible to have the inner slider be engaged from 0 mm, but only spring up by 1 mm or less when released. My reasoning being is that I'm not convinced that a sharp engagement point of the inner slider would feel good, nor am I certain that a sharp drop in force would be good either. I found it uncomfortable for some time on Cherry MX blue, and I don't know why I've stopped noticing — either I'm used to it, or my switches have worn smooth.

I couldn't think of a way to have an obstacle for the inner slider that would be activated as the switch is pressed and retracted when it's released, but I've just come up with this nightmare:

(Attachment Link)

The side prongs are held in their retracted position by extra lugs on the outer slider, and as that reaches 2 mm, the prongs move into position to catch the inner slider. Edit: note that the red slider is halfway pressed but the black slider is unfortunately not ... Oops.

I don't pretend that this is a good idea though, and I can't even follow your drawing. I do like old-school textbook style though.

The other aspect is spring strength ratio: with the inner slider given a comparatively weak spring, it would make the tactility more subtle and less jarring. You could tune the tactility by simply trying different length springs for the two sliders.

So, forgive me for not posting detailed section views of the mechanism. It was quite late by the time I finished the initial model, and I wanted to get to bed. The answer to you first question is yes. The mechanism as it is currently designed already allows for this.  The inner slider travels upward on release as far as the barrel of the outer slider allows it. Making the distance shorter would actually make the packaging as bit easier. There is no need for another mechanism to achieve this. It is inherent in the current design.

Secondly, the height of the tactile event is, in fact, an exercise of adjusting the ratio between the inner and outter spring rates. The severity of the tactile event can be tuned by adjusting the preload compression of the inner spring in relation to the release load'. Furthermore, the spring could be preloaded to the extent that the inner slider is still under load once it reached full actuation, which would smooth out the bottom end of the tactile curve after the event.

The only changes that may need to be made to accomplished these requests would be to adjust the sprint seats on the sliders to allow for more or less preloaded, and, of course, changing spring rates and/or lengths.

I will post those sectional details tonight. Thanks for the feedback.