Picking soft objects like a stack of magazines or books

Sebastien

Hi Pros, anyone has some tips and tricks or seen some designs that would allow a robot to pick stacks of magazines or other similar soft parts? The application we are looking at contains books and magazines that are different in weight and size. Picking from the side with a Robotiq 2F gripper would be nice but books can weigh up to 15lbs so over the specs of the gripper. Any suggestions?

mikebeauchemin

@Sebastien thanks for sending some parts our way, it is always nice to be able to test our gripping solution on real industrial applications. I even took a video of my testing (see at the end of the post). Here are the steps that I did to evaluate your application:

1. Some books are rigid and others are just like a stack of paper which is quite soft. However, all books or stack of paper are sealed in a weak plastic shell. Suction cup is not an option because the plastic is too weak. It would just break apart when lifting.

2. Manipulating hardcover books seems no problem. When manipulating soft ones, the trick is to grab the pile with a wide and strong grip.

3. So I first decided to try with one 2F85 gripper, which is the strongest Robotiq 2F gripper and added some wide custom fingertips (See below). This works very good. The control that we have on the gripper’s positioning and force allows us to manipulate the pile just like a human would do. However, some stacks were too heavy for the single gripper.

4. Second option I looked at is using dual gripper mounted in parallel on the robot (See below). I used 2x 2F85 grippers but with the 2F140 fingertips because they are longer and would help get a stronger grip on the pile. For the real application I would consider manufacturing custom fingertips that would be long and wide to get a steady grip on a soft pile with both grippers. This setup worked very well. Again the control allows us to really mimic human grasp. 

Here are a couple of tips to watch out for in the real application:

The fit of the books in the box is quite tight. So you need to place the box accurately each time to make sure that positions are repeatable and that you are able to correctly place the books in the box. Once the book dropped in the box, you can close the gripper and move the robot to push against the book until it is correctly placed in the box. Using the UR force function at this point could be useful. Another key point would be the position where you pick the book from. The way I am thinking of doing this would be to activate 2 cylinder that would push the book in place such that it is always positioned the same and that the robot has access to pick the book from the side. Also note that I used the path recording function with the FT300 to program the path as the book is being placed in the box. This was the easiest and fastest way to program this trajectory that contains linear motion and some rotations as you lay the book against the bottom of the box. 

https://youtu.be/Xcjp-5Js2AU

Sebastien

@mikebeauchemin
Really nice. The only issue now being that we do not have access to the side of the book. The books are staked on a pallet such that they lay flat on top of on another. So the concept that we are thinking about is having a system that would first push down on the book and then have a plastic pallet to slide underneath. Then closing the gripper and picking up the book. So that would require a custom gripping solution. Have you seen something similar elsewhere? Here is the video showing this concept by hand. 
https://www.youtube.com/watch?v=CE_N3Dbg5E8&feature=em-upload_owner

matthewd92

@Sebastien Could you use vacuum?

Sebastien

@matthewd92
Not really. Some books have hard covers, others are soft like a piece of paper. Vacuum can be part of the solution but we would need some other mechanical devices to prevent the top page from opening under vacuum. We will be working on a prototype later in the fall.

matthewd92

Ok, so these aren't wrapped books. Do you know if you will always pick up in the spline side or will that vary?

Sebastien

@matthewd92
we can always pick from the spline side. We have some concepts in mind but still have to spend some time on design and testing.

matthewd92

The thought that I had would be to use a large stroke pneumatic gripper, I'd have a cutout in the conveyor feeding the books so that the gripper could get to the parts from the end of the conveyor and grasp them with wide, long fingers similar to what was shown above.

I think the issue you may face is the weight of the gripper, the fingers and gripper and mounting plate would have to be less than 3.5kg to stay within the UR10  payload and handle your possible 15 pound payload of the book.  Schunk has a gripper with a 120mm total stroke that weighs in at 1.9kg but only has a payload in the 2kg range, PHL-G 25-060.  You can increase that payload by slowing down the robot so there is not too much acceleration and using high friction gripper fingers.  Here is how they are calculating the payload capacity



Obviously, if you are using another brand robot the weight of the gripper is less of a concern.

rrobert

Hi @Sebastien,

Working on a similar problem - picking from stacks of paper manuals and having trouble finding proof of concept on the picking part. We have a possibility to pick from the back of the manual so a pneumatic gripper for first lift of the edge and then sliding in gripping fingers underneath for full contact is one way we thought could work.

Would be interested seeing how you solved your issue and how your prototype worked out for you?

Sebastien

@rrobert turns out that the project never moved forward so we have stopped our design process on this.

PauloLobo

I have also a project that needs that, but the books are not with plastic, also in the same project i have books with no covers in the book, and for example 5000 sheets that i need to take some from there and insert in a machine...