When developing a cobot application that needs to handle different items, an issue is how to grab and hold these items. Often there are no fitting standard solutions available on the market, so for most product/market combinations, robot grippers and end-effectors will have to be custom designed. For the production of these designs, 3D printing or Additive Manufacturing is becoming increasingly popular. This blog discusses how 3D printing can be used for gripper design in robotics, what the advantages are and how these grippers are manufactured.
When considering a cobot application palletizing closed boxes, one of the main challenges is how to pick the box. A common solution is for the cobot to pick a box from the top using a vacuum gripper; a gripper that uses vacuum power to hold onto the box when picking and placing it.
A vacuum gripper designed to handle closed boxes should meet requirements like:
- Low weight – cobots have a weight limit: this weight includes both products and gripper
- Safe to use
- Easy to maintain
- Easy to assemble
- Stiff – accurate placing
- High durability (1.000.000 picks)
- Double pick – the gripper should be able to pick and place one or two boxes separately to meet the required performance of the palletizer.
Traditional vs. new gripper production methods
Traditionally, many cobot grippers are made from aluminum profiles. They can pick a box, however none of the criteria above are met. These types of grippers are usually built to test a cobot system and software, and should not be used in a production environment.
If you want to build a gripper that meets all the requirements described above, using a new production method such as Additive Manufacturing, or 3D printing, is a good option. Implementing 3D printing requires a completely new design of cobot grippers, since design rules and the materials used are different from conventional production methods.
Advantages of 3D printed grippers
Using 3D printing for gripper design can have several advantages:
- It provides the opportunity to design a safe solution. With 3D printing, it is easier to implement rounded edges which enhances the safety of the design and helps
realize safe human-robot collaboration. As you can see in the image, this gripper design has no sharp edges. - The designs can be simplified using techniques like design for manufacturing/assembly. 3D printing allows you to integrate parts and
- components as much as possible. For example, the Smart Robotics Vacuum Gripper has integrated vacuum chambers and channels, which means there are less separate parts to be mounted. A few things should be taken into account:
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- When integrating parts, it is important to use proper channel dimensions and material thickness.
- In addition, wear parts should be easy to replace and exchange, without the need for any tooling.
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The result is an integrated gripper frame on which wear parts (such as suction cups) and control parts are mounted, which is safe to use and easy to maintain.
What about durability?
During the gripper design phase, some calculations (FEM, Finite Element Methods) are made to test the stiffness and strength of the newly designed gripper. Unfortunately, there are no (or no accurate) material parameters available that can be used as input for these calculations. Therefore, the results of these calculations are not always used to optimize the 3D design, as they may not be reliable. However, theoretical parameters are available, but these will be affected by how the 3D printing service providers produce the parts. For example, the location and orientation of the parts in the printing bed can possibly influence the parts.
Therefore, besides test calculations, it is even more important to determine whether the gripper meets the mechanical properties. Hence, a pilot version of the gripper should be produced and tested in a test bench. During these tests, the frame undergoes varying loads, after which it is assessed. How does the gripper perform? Can we see any cracks or other damage? Once the mechanical test is positive, the newly designed gripper can be manufactured.
3D manufacturing a gripper
The gripper design files are sent to a 3D printing service provider, where the gripper frame will be printed, often using a Selective Laser Sintering technique
After printing, the 3D printing service provider will manually remove the remaining powder from channels and vacuum chambers. Hence, the gripper design should be optimized to help the cleaning process. Afterwards, the complete product is processed (tumbling, grinding) to improve the surface. Next, the frame is primed and varnished to prevent dirt getting into the printed material. This makes the gripper easier to clean, and in addition it looks better too.
The 3D production of parts takes some time. In general, a printing schedule looks like this:
- Production must be planned by the 3D printing service provider
- Production starts. Printing takes about 12 hours, as printing is a batch process where the 3D printing machine can only process a certain amount of products at the same time (depending on the machine size)
- The printed batch needs to cool down to room temperature: this takes about 2-3 days.
- One day is needed for post-processing (cleaning, grinding, tumbling) the part.
After this process, the printed parts will have to be transported, painted, assembled and packed for the customer.
When implementing a new technique like 3D printing, there are usually some issues that arise. This happens mainly because the production method and materials are new; the long-term performance is yet unknown. Some designs (e.g. a long and thin design, 800 x 240 x 25mm) tends to deform in about a year, whereas the same item at a different production location does not. Causes for such issues are not yet known; there can be differences in the original production process or the material can be influenced by environmental conditions.
3D printing techniques requires new design rules. Try not to restrict yourself by creating a design using casting, molding or milling techniques. Many rules of thumb and best practices are available from your 3D printing service provider.
3D printing at Smart Robotics: what have we learned?
The use of 3D printing will become increasingly important in the development of robot parts, such as grippers. At Smart Robotics, having an ever growing experience in designing grippers using 3D manufacturing, we have learned a few things over the years:
- Operators want to work with a safe and easy to maintain gripper – 3D printing allows us to.
- 3D printing allows for flexibility: improving or upgrading grippers is easy. Features can be added between manufacturing series. For example, to handle different box sizes or types, design and production variations of a gripper are possible. It helps to build gripper designs in CAD, where a variation can be created by changing certain parameters.
- During gripper development, more and more functionalities will be integrated in the gripper design, resulting in updated or new grippers.
- However, no matter how easy it is to create or update a gripper design; we always advise to choose from the standard range designed by Smart Robotics, as these designs have already proven themselves.
