Cable-driven restrained Z-motion

Hi, I was thinking of ways to lift/descend the Z axis with no linear rails/etc and since all the spectra-driven printers ranging from corexy, corexz, deltas and so on, I noticed that there is not much focus on using the cable tension principle for the Z axis. The large scale cable driven parallel robots are a good start to look into. I was wondering if there is any such experimental z lifting method in the reprap community.

I think this picture is a good representation of what could be achieved:


The bad thing in the design above is the small platform that can be actuated by cable tensioning but I think the platform can be increased if the cables go up to the opposite corners pf the platform instead of the closest one to the point of pulling. Also I am thinking a single loop could be used so that it can be actuated by a single motor.

I'd love to hear your thoughts regarding this. Also if you know about any such approach.

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RepRap Lander concept on Concept Forge
RepRap Lander concept on RepRap Forums
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Unless you tensioned the lines far more than they would support, I don't think you'd get anywhere near the stability you'd need. Any type of movement of the printer would cause oscillations of varying degree depending on the vertical position of the bed.

You've taken something fairly simple with linear rods and made it extremely complex with positioning of 7 (or more) lines. What you'd save on not having rails/rods you more than pay in motors, controllers, and electronics.

The build volume seems heavily intersected by the lower cables. Good for printing pyramids? Interesting idea though - it's good to keep the mind open to different approaches.

There have been many attempts for a cable driven parallel robot even in the reprap area, starting with the skydelta and then there is this Mini Cable Robot from Fraunhofer that shows it can take some force, then there are heavy lifting parallel robots that move pallets and stuff... cable sure has potential, and if they use some sorts of steel cable for their heavy lifting application sure thing a kevlar or dyneema or other type of string can take the load of a typical 3d printer that prints in plastic.

I am thinking of this application for both the platform bed lifting and also the end effector. I've seen the platform rocking in a solidoodle while infill printing short segments I was afraid the part is going to pop off the bed but it didn't.

@cdru: we are still thinking Z-only, so one motor would suffice for that, and one string loop too. At least this is what I am imagining that can be achieved. Like you say, the challenge here is properly tensioning the string to pull the platform/effector from all sides with the same force that would be enough to compensate for any rocking/oscillation. I don't see (maybe I am wrong here) a problem with a properly dimensioned kevlar/dyneema string. One can test or calculate what kind of string they need... and scale it up accordingly. I rather see an issue with the reduction mechanism needed so that a nema17(?) can keep the motion.

@JamesK: the drawing is just an example. Of course the more steep the angles the better stabilization but there must be a sweetspot so I think the platform in the image above can be larger.

One other disadvantage of such a design, besides the already mentioned ones is that spectra/kevlar can't be enclosed in a high temp chamber as they loose their properties (spectra at above 80C i guess and Kevlar at above 150?).

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RepRap Lander concept on Concept Forge
RepRap Lander concept on RepRap Forums
My Things, mostly experimental stuff