OT:Pick and place motion design

This is similar to what I have done in the past and have the need to do again, it works ok, just not great

I think the pic shows a lot, anyone have a better concept? the new one is going to be short 3m travel aprox, I have them up to 12m the belt is the issue with that length, I have to have it banjo tight.

I have Baldor, SEW and Danfoss drives and other suggestion on drives?

I think I will be getting some from another plant, if so they will have motors but no drives, they also have small servos on the suction cups to run them in and out, my others are manual, but this means it could be up to six axis EDIT: the six come from 2 heads one to pick and the other to place 3axis per head

Thanks

In the second pic you can see the idler, must of been off in the first

What type of speeds & positioning do you need? You could go with a screw of some type unless you need the speed. Is that 8020 that you are using for the frame? One of my local sales guys had a guy from Robotunits in a few weeks ago. They have what looks like a good system for doing this type of work. You may not want to change but it could give you a few ideas.

www.robotunits.com

Interesting, a servo motor system with a mass between two springs.

Why didn't it work great? Was it the compliance of the cables? What keeps the tension?

A mass between two springs is more difficult to control than normal systems. What makes this even more difficult is that the spring lengths change as the mass moves back and forth.

Hydraulic systems are similar.

You may not need the precision of it, but most precision linear systems of lenght I have seen are rack and pinion. The rack is securely mounted to the machine frame and the gearbox and pinion are mounted to the sliding part of the machine.


Alpha Gear has a system you can read about here:

http://www.alphagetriebe.de/pdf/rack_and_pinionde1006.pdf

The up side is, like Peter said, there are no "springs" in the system. The down side, besides cost, is that the motor is mounted on the slide so there is a cable track to design into the system.
Danaher also has some belt drive units that get to 12m. A premade unit might have a better chance of getting the belt tightened than what you have.

http://www.danahermotion.com/documents/index.php?product_cat_id=984#

Other people make similar items these are just the ones I'm familiar with since we sell them.

Yes its 8020, trying to reduce the weight, the product that I am moving weighs (aprox) 40lbs

I think the reason they have not worked great was (I think) due to a large part failure on the mechanical design, if you go over X rpm’s you get a bad chatter and jerking, the very good example of ‘bad motion’

The belts are 100mm wide and steel reinforced, they have tensioned pulleys and the motors/end pulleys are moveable

I have several ball and screw systems but these are vertical, the only horizontal screw design was a failure due to the weight cantilevered past the support bearings, that was a tray design, 300lbs + cantilevered 1m, this was too much weight for the support bearings and failed after 3 months, we ended up going with 2 THK rails and a rod less cylinder

Right now my cycle time just needs to me less then 7sec, that should not be a issue with any system, but we are also considering another pick and place to insert a separator product, therefore my cycle time needs to be less the 3.5 on both system (plus the need more factor)

I think one of the issues is inertia after we start moving the mass its hard to stop, the placement (accuracy) is not a factor within 10-20mm

Cycle time is defined by, picking up/moving/placing and getting out of the way

I have a couple of rack and pinion 2 axis punch machines, they work good but they are loud (relative) I think due to the straight gear design, they move very smooth and fast but I did not know how that type of system would hold up against the inertia

Thanks for the links and input

At my previous job, we had numerous belt driven motion applications very similar to your picture. They were very low maintenance when compared to other ballscrew and rack and pinion applications.

There was no worry about contaminating the product with lube and our belts seem to last indefinitely as long as we kept them aligned. One particularly interesting line used a round disc shear driven by a 50Hp DC motor controlled by an AB S-Class controller/8720 spindle drive.

The cutter assembly was probably about 300 pounds moving about 20 feet and back 14 times per minute on THK bearings (we started out with another brand that could not handle the job...)

They were a little more difficult to tune but that was eased by using steel reinforced belting which was not so "springy".

I would go pneumatic on the picker/placer if you only need 2 or 3 vertical positions. Air lines are easier to route through flexible wireway than servo cables...

How much does the carriage weigh and how fast must it operate?