Linear actuators

[GTS]

Hi all - first post so go easy on me!

Have a project that requires me to source really long (for me) linear actuators - basically two units that are 8 meters long and to be driven together via servo drive. preferably the drive motor is external to the gantry (e.g. no omega drives etc).

The application is not CNC, though there is force opposing motion outside of friction/mass/etc. These will move a gantry of some 30kg mass. Accuracy (+/-0.1mm) and repeatability are important. speed isn't really so - 0.5m/s (around 1200ipm) would be great though i'd be happy with 300ipm.

Our local linear motion suppliers are having minor heart attacks over this, so I thought I'd canvas the project here first. I know that they'll need to be belt driven units and that tension is going to be a challenge (as is a relaiable position feedback source).

Has anyone out there built their own? Any comments/thoughts/references?
Success stories/failures?

Keen to hear your feedback (and hope I've posted this in the right forum...)

[Al_The_Man]

Not suprised you are having a problem with linear actuators that length.
I Have made my own with large Item Products extrusions, with Breco endless Timing belt transport, the extrusion allows the use of Chrome steel rod to be embedded on either side to allow a wheeled transport carriage or truck to be ran along the Rails, The timing belt runs inside the extrusion for one length and lays supported on the top to return.
I am not sure if this extrusion comes in the length you want, but you may have to construct some similar arrangement.
The belt has a precision gear reduction drive on one end with an encoder on the motor.
I have also used a commercial made linear actuator that goes to the length you want, The make escapes me, I would have to look it up, this was a project about 15yrs ago.

Ballscrew of that length would be expensive, you would have to contain the nut between a track of some sort to prevent whip.
Al.

[GTS]

Hi Al;

Have the Item catalogue here actually and have spoken to the local distributors. Lengths so long are not impossible (just not off shelf either!) I hadn't considered the Breco product. They've got a very nice product - well detailed website - just very little local representation (in Australia). Keen to get away from using Item for the motion components as once landed in Australia it seems expensive for what it is.

I'm a bit concerned using a rotary encoder off the back of a motor as the rotary motion won't reflect changing belt tension. I've seen a few interesting arrangements using multiple sources to calculate feedback, though I agree a linear transducer is simplest, easiest and most reliable. Just not the most inexpensive.

The only long-ish linear displacement transducers I'm aware of are MTS Temposonics - I'm sure there are others though that's just what I've used on other projects - unfortuantely they cost almost as much as a linear actuator 8m long. Any other options here?

This is a long shot Al but do you have any photos of the work?

Anyone else?

[Al_The_Man]

Originally Posted by GTS This is a long shot Al but do you have any photos of the work?

The pre-made units are long gone, unless I can get the plant to take a couple of pic's, I think I have some of the Item one somewhere, i will see if I can dig it out.
Al.

[GTS]

Thanks again Al;

Basically we've got Item and a few other makes down here to choose from it'd seem (Maytec, etc) regards the profile system bits. Would seem to be a bit of research required into belts and hardware given the application.

We are looking at our options regards rolling hardware - I'll keep you posted with how we go.

Still a bit lost regards "cost-effective" foolproof position feedback - thoughts anyone?

Of interest, what's a linear displacement sensor over 8m worth in the US?