Introduction: Universal Gripper - Syringe Powered


The “universal gripper” developed by researchers from Cornell University, the University of Chicago, and iRobot inspired me to create my own version. The YouTube video is quite impressive. The gripper can form around very asymmetrical and smooth shapes and still pick up the object.

I gathered the materials below and decided to create a gripper of my own that could be incorporated into one of my robot designs. Adding a vacuum pump or a powerful air mover seemed difficult and probably unnecessary. So I started to think about vacuums.

I remembered that when they were filming “An American Werewolf in London” that Rick Baker used hypodermic syringes hooked up in a line. When a really big syringe was compressed at the end of the line, the little ones popped up creating the appearance of a spinal column erupting below the skin of the creature’s back.

I decided that the same idea might work with the “universal gripper.”


In addition, I thought that using a funnel could work nicely for balloon support. Playing around with it, I thought that adding a pressure sensor inside of the funnel would allow the Arduino to apply suction when the balloon came into contact with the object to pick up. This lead me to Plusea and her instructables using velostat and flexible materials.

Amazingly, it all seem to work. Follow these steps to see how I did it. You can probably see alterations that would improve the design.

Step 1: Materials

Materials:
  • Good quality latex balloon
  • Aquarium plastic tubing
  • 60 ml veterinarian syringe
  • 11/64” brass tubing
  • zip ties
  • Bond 527 cement
  • Conductive thread
  • Needle
  • Craft foam
  • some #6 bolts and nuts
  • 5 cm of U channel aluminum
  • TowerPro servo MG995
  • flat stock aluminum
  • an Arduino or other microprocessor

Step 2: Prepare the Balloon

I was worried that the latex balloon might have small pin-holes that would affect the rig’s ability to create a good vacuum. I decided to make a test. I inflated the two latex balloons I had purchased and put a clothespin on the bottom. The next morning I found that one balloon had deflated by half. The second balloon was still fully inflated, so I used it.

I filled the balloon with coffee. I chose the cheapest and coarsest coffee in the store. I think that a coarser grind would provide more jagged edges for the coffee granules to lock onto each other when the vacuum is applied. I didn’t test it, so it remains s theory.

I decided to only fill the balloon about ¾ full of coffee. When the vacuum is removed the coffee needs some room to become a flowing powder again.

Next I used a craft pipe cutter to cut off about 5 centimeters of the brass pipe. You can get pipe cutters from hardware and craft stores. You could also use a Dremel tool or even a hacksaw.

The aquarium tubing was pushed onto the brass tubing, and then the tubing was inserted into the balloon neck and locked on with zip ties.

Step 3: Test One

The first test used lung power. I found that I didn’t have to inhale all that much to create a good vacuum. The coffee became rigid, and I was successful in picking up a variety of objects.

However, I found that the coffee grounds also came up through the tube. This did not taste very good!

Step 4: Test Two

I attached the aquarium air hose to the 60 ml syringe. I added a zip tie to keep it pretty airtight.

Watch the video to see how this rig successfully picked up a variety of objects. I found that you did need to put a fair amount of pressure on the balloon so that it would form around the object and not just sit on top of it.



Step 5: Test Three

The next step automates it.

I added a funnel to give the balloon and tubing some structure. I took the small funnel I had and used a hacksaw to cut it off shorter. That way the balloon could hang freely, but have support when it was pressed against the object to be picked up.

I decided to put a fabric pressure sensor in the funnel. That way the Arduino controlling the servo could sense when enough pressure was applied to the balloon. Plusea has a great Instructable describing how to create pressure and bend sensors. These sensors can be very sensitive and also very accurate in reading pressure or bending.


I created mine out of craft foam from a local craft store. It is flexible, but has enough structure that it doesn’t collapse. You need some material that can be compressed, but won’t stay that way after the pressure is removed.

Instead of sewing the edges together, I used Bond 527 multi-purpose cement. It is flexible and also adheres well to the foam. The conductive thread was sewn in in a criss-cross pattern as Plusea describes. The Velostat middle layer was cut smaller than the outer pieces so that the glue did not adhere to it and cause compression. Velostat is available from The EMF Safety Site.

Conductive thread was left sticking out about an inch on both sides to allow connection to a wire running to the Arduino.



Step 6: Put It All Together

Build the Syringe Mechanism:

I tested the syringe and found that I only needed to pull the plunger back to 30ml in order to get a good vacuum. So I used a hacksaw to cut off the barrel of the syringe.

I also cut the plunger off about 3cm longer than the barrel.

I drilled a hold in the servo arm and also through the plunger. A #6 bolt with washers and nuts holds the plunger pretty stable as the servo pulls it back and pushes it forward.

I had some aluminum U channel and cut a piece about 20 cm long. I don’t know the technical name, but I had a plastic piece used to mount servos that I got in a box of servos from eBay. I attached the servo to the plastic mount and then bolted the mount to the U channel aluminum.



A piece of flat bar aluminum made the syringe support. The support has to rotate when the plunger is moved, so I put one #6 bolt to hold the barrel, and another bolt into the U channel. The U channel bolt was not tightened so that the whole assembly can rotate.

Wires from the pressure sensor go to the Arduino. I used the same setup as for a photoresistor on the Arduino site.

Some code reads the pressure sensor, and when enough pressure is applied the servo is activated. The Arduino waits 2 seconds and then pushes the plunger back into the barrel removing the vacuum.

I don’t have a robot arm (yet), but this could be really fun to put on one. Its strength is that it can pick up very irregular or smooth objects easily. Using the syringe, there is no need for vacuum pumps or vacuum reservoirs. The system seems pretty robust and reliable.

Let me know if you experiment and come up with improvements!

Step 7: Programming


The attached file is my Arduino code.

Comments

author
arath2 (author)2015-12-16

a very nice instructable sir, indeed it is a very easy DIY version of cornell university gripper. also i like the idea of using the pressure sensor to deter the pressure created to pic up object, are there any ways other than the depicted one to make a cheap pressure sensor???

author
techiebot (author)arath22016-01-03

Yikes - I have been traveling for a while and didn't see your question. I have had good luck with Plusea's pressure sensors. She has a couple of different designs. Here is one:
https://www.instructables.com/id/Conductive-Thread-Pressure-Sensor/

The nice thing is that you can have a foam or fabric structure, so it could work with the gripper's surface and flex.

author
don.zimbelman (author)2015-03-31

Brilliant!!! I have been wanting to mock up something like this but didn't really want to fool around with pumps etc...as you state power consumption is always an issue!!!

author
ramyaas (author)2015-01-07

Hi. I had a doubt. I am trying to make a similar prototype, but my idea is to automate the whole process by constructing the robotic arm. So I was wondering if there is a way in which we could confirm if the gripper has actually held on to the object or not? This is because as soon as the balloon presses either on the surface or around the object, it is bound to diverge and so a signal would be sent, so what if the gripper didnt make contact at all with the object? or maybe the gripper did make a contact but while lifting the object fell, the how do we check?

author
yaly (author)2013-10-27

can it pick a glass of water like on youtube ?

author
AJMansfield (author)2013-03-24

The more jagged edges you have, the more finely the grit is actually able to compact on itself, at least by one theory. Finer grit would be better, I think. The only thing it really has to have is sheer thickening (think cornstarch and water).

author
techiebot (author)AJMansfield2013-04-03

If you read the article, the researchers discuss the optimum material that is fine but not smooth so that the particles grip onto each other. Their conclusion was that coffee grounds make an ideal material, and they are very light. I think your cement idea is interesting, but the material needs to be easily deformed so that when the balloon is pressed onto an object the material inside the balloon can "flow" around the object.

author
AJMansfield (author)techiebot2013-04-04

Portland cement powder actually flows extremely well; when completely dry, it behaves very much like a liquid, actually. It will even splash up if you drop an item into it (it's far cheaper than coffee grounds, too: $5 gives you around 50lbs of it, which will fill 1-2 cubic feet of space). Plus, you can mix it with gravel, sand, and water to make concrete (if you want to be really fireproof, mix powdered fireclay with it).

author
AJMansfield (author)2013-03-24

I'd probably use something like Portland cement for the fill material, because its much finer than coffee grounds, sand, and most other types of grit materials.

author
Kiteman (author)2011-08-30

Very cool, but is it my imagination that the gripper currently lets go as soon as the pressure is off?

author
techiebot (author)Kiteman2011-08-30

I programmed it to only keep the plunger pulled back for 2 seconds. I didn't test it yet, but if there are no leaks in the balloon or hose, you should be able to hold the object indefinitely (as long as the plunger is pulled back). When I was first getting the servo to work it definitely held the bolt for a minute or two while I was trying to get all of the connections right.

author
Kiteman (author)techiebot2011-08-31

Cool - so when it's on the arm, you'll need to programme separate "pick up" and "put down" commands.

author
techiebot (author)Kiteman2011-08-31

Yes, that would be necessary. What I like is that an arm could be programmed to descend until the pressure of the balloon against the funnel is at a certain level. That way the robot would know that it was in contact with the object even if the object was on an irregular surface.

author
AJMansfield (author)techiebot2013-03-24

Or be fancy and do capacitive profiling instead.

author
tswaroop (author)Kiteman2011-08-31

sir,im trying to build a wall climbing robot, i got problem about the suction to be held between the robot and the wall.in my search i found that gecko adhesive is the efficient one,but im using air pushres to held the vacuume pressure ,but im unable to design the body,ofcourse im trying but i need ur help

author
Kiteman (author)tswaroop2011-08-31

That's probably better as a forum topic, then you get more help.

author
propellerheadgeek (author)2011-08-31

Hi - nice instructable. I made something similar awhile back, but used a different approach to the suction device; should be perfect for your gripper and will let you get rid of the servo AND the syringe...  a miniature pump

author

The pump looks cool. And so cheap! Depending upon how the pump is constructed, it might have to remain on in order to keep a vacuum. What I liked about the syringe is that once the plunger is pulled back, it takes no power to keep the grip on the object. And for most robots, power consumption is a major concern.

Thanks for the pump source.

author
AJMansfield (author)techiebot2013-03-24

Put a normally-shut solenoid valve between the pump and the gripper.

author
rj44319 (author)2011-09-01

This would be great for a quad rotor to pick up items and move them around!!!

author
AJMansfield (author)rj443192013-03-24

Having to lug around that balloon full coffee grounds or sand or cement or whatever, might be too heavy, though.

author
rj44319 (author)AJMansfield2013-03-24

coffee grounds are not heavy

author
formellini (author)2011-08-31

Hi, whi don't you put a spring in the siringe to keep always active the gripper?
I think is more easy press a siringe with one hand than pulling. with the spring inside the gripper is autolocking and you can hold an object without using your Hand, you need it only for grabbing and releasing.

author
techiebot (author)formellini2011-08-31

That is a good idea. I was just experimenting with the syringe in the video to see if it would work. Then I had to see if the servo was strong enough to pull the plunger back. My real goal was to have it totally automated and hands-free.

author
survivorwolf (author)techiebot2013-02-07

I like the spring idea or i saw a neat instructable recently about how to turn an aquarium pump into a mini vacuum pump
It could be possible to combine both this and your project....
https://www.instructables.com/id/Electric-Vacuum-Pen-From-Aquarium-Air-Pump/

author
techiebot (author)survivorwolf2013-02-08

Thanks for the link. My idea was that every robot struggles with having enough power to operate. I thought that a servo holding position would consume less power than any pump I could think of. Plus, it's silent. But the aquarium pump is something I want to look into. Thanks again!

author
Sketch98 (author)2012-11-10

Can you pick up round or smooth things like a ping pong ball?

author
techiebot (author)Sketch982012-11-19

It actually does pretty well with smooth objects. The rubber membrane of the balloon has a certain amount of friction to it. If you read the article by the university researchers, there's also some vacuum created between the object and the membrane. So it works better than you think it would.

author
vigilantice (author)2012-02-12

Ha a buddy of mine is doing the science olympiad robot arm competition. I had seen the cornell version a while back and told him he should try to do something like it but he told me it could never be done cheap enough and without a vacuum pump. Showed him, didn't you? Excellent job on the gripper.

author
ElectroFrank (author)2012-01-09

Perhaps this could be useful to the elderly and disabled, if the whole system was installed in something like one of those "litter picker" grab sticks.

author
techiebot (author)ElectroFrank2012-01-12

I agree. It seems to me that there could be many uses for this concept. It could help a lot of people. I imagine that it must be extremely frustrating to not be able ot pick up a medication or some other small object successfully.
Thanks for the comment.

author
ramicaza (author)2011-11-01

Thats supper cool!!!!! i must use this in a robot! thanks for the instructable

author
Kaptain Kool (author)2011-10-02

Wow, great idea!

author
LifeWarrior (author)2011-09-02

sorry pic screwed up this was the idea

Bulb.png
author
techiebot (author)LifeWarrior2011-09-05

It seems like it could work. Again, you are depending upon the strength of the bulb walls to create a vacuum. I didn't do any scientific testing on how much vacuum is needed to "jam" the coffee into a rigid form. Let me know if it works.

author
LifeWarrior (author)techiebot2011-09-05

Cool, when I can I'll try it, I have several other projects in the works right now, haven't had too much time to try many but this one is definitely worth the work up. Now that think of it a silk screen of some kind might prevent the grounds from getting sucked up through the hose, and with that maybe a shop vac attachment would be a cool addition too. Just brainstorming for when I try this.

author
techiebot (author)LifeWarrior2011-09-05

My local hardware store sells a very fine mesh metal screen meant for use in water pumps. I don't know what it's called, but I bought a piece some time ago. Perhaps it would work and not restrict the flow of air.

author
LifeWarrior (author)techiebot2011-09-05

I'll check for something like that, thanks for all the info

author
techiebot (author)LifeWarrior2011-09-03

That looks good for a one-way valve. What would you do to get positive pressure back into the balloon?

author
LifeWarrior (author)techiebot2011-09-03

I'm not sure how it works, I just put together this picture on how I think that type of valve operates, but I think that it follows your line of thinking that the walls of the bulb are so thick that it pushes the upper bearing through force up letting air in, but I'm just guessing. They sell these on ebay and after seeing your 'ible I was just wondering if you've ever encountered those or tried one for something like this because of the pumping action I wonder if it would it create the same effect on the balloon. I was considering buying one for a manual operation to try this project, but being the building I was interested in your experience regarding a pumping action rather than a single drawing motion like the syringe.

author
LifeWarrior (author)2011-09-02

Very cool, I wonder if this could be done with one of those squeeze bulb valves instead if a syringe, and also what would you say is the max weight that it can pick up

author
tjesse (author)LifeWarrior2011-09-02

YES, I would like to know if it can be used with a turkey baster style bulb! Good thinking!

author
techiebot (author)tjesse2011-09-02

I have used the type of bulb you suck boogers out of kid's noses for positive air pressure. I made a March Hare mask with a balloon hidden in the hair. One ear was hinged with a fabric hinge and rested on the balloon. A length of aquarium tubing ran down the back of the mask, into the costume, down the arm and was hidden in the actor's hand. When the actor squeezed the bulb, the ear went up in a crazy March Hare way.

It certainly might be possible to use a fairly rigid bulb to create the vacuum. If the bulb is too soft it probably wouldn't be strong enough to create enough vacuum. Only a test will tell!

Great idea!

author
LifeWarrior (author)techiebot2011-09-02

I was thinking of one of those type that has the 2 bearing valves so every time you squeeze the bulb air is expelled and when you release it draws the air from the balloon creating a pumping action

Bulb.png
author
RWWestbrook (author)2011-09-01

I like the concept of using this to grab things, especially for grabbing non-magnetic objects or if you dropped something between the body panels of a car such as a nut or bolt and the magnet can't get to the object without sticking to the car first. I noticed that there was still the issue of coffee grounds entering the hose. Would it be possible to make a tiny sock out of cheesecloth or some similar material to protect the hosemouth inside the grounds? It might make the seal on the syringe hold less of a vacuum if the coffee grounds get between the rubber seal and syringe tube. However, this is great documentation of your design process, and I would like to make a grabber for myself.

author
techiebot (author)RWWestbrook2011-09-02

Yes, I thought of putting a bit of gauze over the end of the tube and hot gluing it in place. But I had a good seal on the end of the balloon, so I've left it so far. If the tubing goes straight up from the balloon, very few coffee granules leave the balloon.

Thanks for your comments. Making the grabber is really quick and easy. I hope you try it out.

author
blckbuster (author)2011-09-01

sourcing a durable balloon is probably the next step, as it might not take much to rupture your coffee gripper

PS in the future if you get inspired to invent daleks, don't do it

author
techiebot (author)blckbuster2011-09-02

DALEKS!!!!!! Great idea! I thought that the balloon would be fragile too, but since it's not inflated, the walls are pretty thick. I did get a higher quality one. I think if the walls were too thick, they would not form around irregular objects. So far I can not tell that I have any pinholes and the vacuum still seems good. It might be worth a try to put a balloon inside a second balloon so the wall is double thick.

Good idea!

author
12beav (author)2011-09-01

While watching the video an idea popped into my head. Instead of the syringe pumping air pumping air back in once you pick up the gripper, why not had a switch to release the pressure?

author
aessam1 (author)2011-09-01

Really amazing
hope to see a robot using it soon.

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