I am working on a machine design at work that will pick and place to stack a product. It has to be fast and have a large travel (8’ x 12’) with a 12 pound load. This seems to exclude the delta option I am planning on using a core XY design and servo motors to move a vacuum head around. I also need about 1inch of travel in the Z direction and a way to rotate ± 100 degrees. I’m trying to keep the head as light as possible so I have been thinking about ways to get the rotation and the Z up/down robust but light.
So far I am looking at using 4 Z motors to raise and lower the whole frame and possibly rotate the head using something like the core x/y so the rotation motors are in a fixed location.
There are a lot of smart people in this group so I thought I would see what you guys though of.
That is a good goal. But you already are lifting 12lbs, so another one for a rotation axis isn’t going to be that much of a problem, right?
The 1" Z travel is binary, right? You either need it up or down? I wonder if you can work out a passive system with the vacuum. If the vac is on, but not grabbing, a lot of air is moving, so you need to reach down. If no air is moving (because the vac is off or it has a good hold) it needs to go up. So maybe something that turns the air movement into a downward stretch and some springs?
Or if you had an air cavity (I am imagining an accordion shape) above the grabber, the suction would pull it up once it made a good connection. When you release the vac, it would lower the load. You just need a way to lift it out of the way when you aren’t holding anything. The advantage is that you would not need a servo strong enough to lift the part, just push down the grabber. Flip that around, you should use the smaller servo to lift the grabber when not used, so the servo doesn’t have to fight the vac lift when you’re holding a part. Gravity it springs can push it down.
Thanks for the input. I like your creativity and ideas with the Z axis.
I agree the rotation weight is not going to be a deal breaker. I guess I am mainly brainstorming to see if there are other creative solutions to the rotation of the gripper.
As for the Z travel it will be more than either up or down. The pallets we are stacking on have variation and I am using some of the 3d printer tech to my advantage here. I plan to probe the empty pallet when as well as after each layer (because our product is not exact either) is added so the Z axis can place it right where it needs to be.
I learned a little while ago that there are hollow shaft stepper motors. Steven Hawes uses them on his open-source pick-and-place for electronics components the he’s documenting on his YouTube channel. They allow the vacuum to run “through” the shaft to precisely rotate parts to align them with the pads on the circuit boards.
You’ll probably need a bigger one to lift 12 pounds than he uses for surface mount components, but I imagine they are available in a variety of sizes.
Look up cable driven parallel robots. Those can be super fast and extend the idea of keeping motors fixed rather than carrying them along for the ride. They can operate 6 axes of motion and the size can scale big with just longer cables and a big outer frame.
Can’t say if its appropriate for your application, but it’s an interesting idea that might lead to something else.
The parallel cable driven bots are impressive and definitely give me ideas. Thank you for this. This is exactly the kind of suggestions I was hoping to get out of this group. Thank you guys!