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How to Decide if Your Gripper Needs Custom Fingertips

Alex Owen-Hill
by Alex Owen-Hill on Jun 11, 2018 7:00:00 AM

What do you do if your gripper doesn't grasp your objects? Here are 10 types of object which may need custom fingertips.

You've done your research for the perfect robot gripper. You've searched the market, read up on all the pros and cons of each gripper type. You've found a gripper which looks like it suits your needs. You buy it. It arrives and you start the integration.

But then … disaster! The gripper doesn't grasp objects as well as you hoped it would!

Perhaps your objects are too flexible and the gripper can't get a good hold on them. Perhaps they're an awkward shape. Perhaps they're too fragile and the gripper applies too much force to them.

What should you do!? Should you just give up and forget about robots completely?

No. There's a solution: custom fingertips. Many of the experts in our community make custom fingertips to overcome the challenges presented by their applications.

 

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Sometimes custom fingertips can be the best solution!

 

Why would you want custom fingertips?

You have two options if your gripper doesn't grasp your objects properly:

  1. Get another gripper — This is expensive, wastes time and might not even work — the new gripper may have the same problem.
  2. Make custom fingertips — This is cheap, quick and very flexible. You can design new fingertips which work exactly as you want them to.

Members of our DoF community use custom fingertips all the time. Application Engineer Grady Turner from Cross Robotics told us that he prints 2-3 custom fingertip designs every week to test applications for their customers. This allows them to cater the robot to the specific needs of the application.

Custom fingertips are not always necessary. There are many advantages to using an adaptive gripper without customization. For example, the gripper will be able to grasp a wide range of objects with no need to change the fingertips. However, when your application has special requirements, custom fingertips are often the way to go.

 

10 types of objects which may need custom fingertips

How do you tell if an object requires custom fingertips? The easiest way to tell for sure is to test it out! Try to pick up your objects using the gripper. If there are problems, a new set of fingertips could get you out of trouble.

 

Some objects regularly require customization. Here are the ten most common:

1. Cylindrical objects

Ideally, the gripper should be able to grasp an object with more than two points of contact. This isn't possible with flat fingertips and a cylindrical object. You can either use the gripper's encompassing grip to solve this problem or use a V-shaped fingertip to add an extra two points of contact.

 

2. Large objects

Some objects are too big for most grippers. We created an extra wide gripper to overcome this problem. However, you might not need a new gripper. Custom fingertips can increase the gap between the fingers to more than the specified stroke of the gripper.

 

3. Small objects

If you've ever tried to pick up a ball bearing, sewing needle or grain of rice with your fingers, you'll know that small objects can be tricky to grasp. Even with a precision gripper, like our Hand-E, you might need custom fingertips to get a good hold on small objects.

 

4. Thin objects

Few objects are thinner than a playing card. As part of the Olympus Games back in 2016, Tyler Berryman and the rest of the Robotiq team decided to make a robot Blackjack dealer in 48 hours. They used custom 3D printed fingertips to pick up and deal the playing cards.

 

5. Fragile objects

If your gripper has a good force resolution, it should be able to hold an object without squeezing it too much. However, using a low gripping force can introduce extra problems, e.g. there's a risk of dropping the fragile object. The team's Blackjack robot also had to give a shot glass of drink to the winner of each game, which meant that it had to securely, but gently, hold a small glass.

 

6. Flexible objects

Bendy, squashable and otherwise flexible objects are not easy to pick up with a robot. Custom fingertips are often a good solution. Sebastien Blanchette from Revtech Systems was looking for a way to pick up magazines and flexible books with a gripper. He asked on DoF and fellow members of the community helped him to work out a feasible solution using wide custom fingertips.

 

7. Objects with strict force torque needs

If you need to control the force or torque applied by your robot, a sensor is usually a good option. However, sometimes a custom fingertip can improve your control or even remove the need to add an extra sensor. DoF member Vijay Chhapparghare from Ford Motor Company was looking for a way to screw in bolts with zero torque. Our integration coach David Gariepy suggested custom fingertips to allow the gripper to twist without applying torque. Grady Turner also told us that he has used fingertips with custom ridges to get a better grip on bottle caps and apply more turning torque. 

 

8. Low-friction objects

Objects with sheer, shiny surfaces can be a problem for gripping. In order to ensure that the robot doesn't drop the object, you have to apply a lot of force which could damage the object. We supply silicon fingertips to improve the friction between the gripper and the object, although some members of the DoF community have found their own ways to increase fingertip friction.

 

9. Hollow objects

Tubes and hollow objects can be picked up with a normal encompassing grip. However, there is also another gripping strategy which people sometimes forget about: the internal grip. This is when you pick up the object with the outside edge of the gripper fingers instead of the inside surface. For some hollow objects, it may be necessary to add custom coverings to the outside edge — for example, to increase the friction.

 

10. Objects with a combination of these

Sometimes you are faced with an object which has many of these problematic properties. For example, a small, flexible, hollow cylinder made of thin, low-friction, fragile material. In situations where you have so many restrictions, custom fingertips are often the best way to ensure that your gripper maintains a reliable hold on the objects.

Need some help? To benefit from the combined wisdom of the most knowledgeable robotics experts we know, post details of your application in the DoF community.

Choose the right gripper!

 
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Alex Owen-Hill
Written by Alex Owen-Hill
Alex Owen-Hill is a freelance writer and public speaker who blogs about a large range of topics, including science, presentation skills at CreateClarifyArticulate.com, storytelling and (of course) robotics. He completed a PhD in Telerobotics from Universidad Politecnica de Madrid as part of the PURESAFE project, in collaboration with CERN. As a recovering academic, he maintains a firm foot in the robotics world by blogging about industrial robotics.
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