Alternate Z-axis designs

[chuckknigh]

We've all seen countless designs for the Z axis of our machines, and they all seem to work quite well. Stepper motors driving it, usually with screw drives, just like X and Y.

My question is simple -- is there any other way to design it, that makes sense?

I've had, stuck in my head, the idea of a cam...attached to a servo or a stepper. Considering the relatively short range of travel (1-2 inches from what I've seen on this forum) that's required, there are a number of ways to design this thing.

You can control the height with a cam, and have the simplest possible mechanism, as I see it. Just turn the cam until the router is at the desired height -- springs on either side could negate its weight, and make everything easier to turn.

Is there any reason why a cam is not used in this application? It seems the simplest solution, unless there is a limitation of some sort, that I've not yet spotted.

-- Chuck Knight

[JOE65]

VERY interesting idea!

Just off the top of my head I Think you would have positioning trouble because the cam is not liner. IE) four steps at the start of the cam are not equal in height to four steps at top of cam.(are they?) This and all other problems can be overcome with much beer drinking and heated discussion

[balsaman]

You would need a gearbox. One revolution of the cam would make the head move it's whole travel so unless you use a gearbox your resolution would be poor. With a screw you would have much better resolution. Gearboxes add complexity and backlash.

IMHO a screw can't be beat for simplicity/accuracy.

eric

[chuckknigh]

VERY interesting idea!

Thank you...I learned years ago to never just "accept" the norm, but to always question it. Sometimes coming from a problem from a different direction yields a different, sometimes better (often worse) solution.

One revolution of the cam would make the head move it's whole travel so unless you use a gearbox your resolution would be poor.

Again, I guess it depends on your intentions. If it's not to implement a 3D function, but only to implement "pen up" or "pen down," then the cam might be the simplest possible solution.

Just off the top of my head I Think you would have positioning trouble because the cam is not liner.

You're right...the cam would not have a linear response. It would be controlled by a formula that I'm not in the mood to integrate... My calculus is rusty.

As to having a linear response, if the cam was designed right, it could be made linear. The "lifter" (can't really call it a cam anymore) would have to be a spiral form, rather than an offset disc, but still quite simple to make. Basically just an inclined plane wrapped around a central axis.

Another way to do it would be to implement it in software, but since resolution is a fixed value dependent on the hardware itself, that's probably not the best solution.

Yet another way would be to use some sort of optical feedback, probably scrounged from a modern optical mouse, but now we're adding real complexity. The idea was to keep it as simple as is possible. KISS.

-- Chuck Knight

[tsalaf]

"Basically just an inclined plane wrapped around a central axis."

Isn't this what a screw is?

If all you want is "up and down" movement, it seems to me that the simplest solution is a pneumatic cylinder.

Sometimes it's not worth while to reinvent the wheel.