Design of a 3D-printed end effector in collaboration with Penn State University

In 2021 we supported a Summer School project for students of the Additive Manufacturing and Design Masters program at Penn State World Campus. The students were asked to design a 3D printed end effector capable of moving four ping-pong balls (at different heights) between two locations using AM appropriate design. The project was supported by us, the Robotics Department at the University of Bath and also 3D Systems. We provided the students with free access to Sulis Flow and some training too. Sulis Flow is ideal for the design of hydraulic and pneumatic components for additive manufacturing and so was a great tool for these students. We want to showcase this project because it’s a great way to demonstrate that custom robotic end effectors produced using AM processes have great potential. 

What is an end effector?

An end effector is a part of a robot arm (a mechanical arm that looks like a human arm) that can be easily programmed and directed to carry out various tasks very efficiently. The arm has segments that resemble a wrist, elbow, shoulder and depending on the application, various attachments are attached to the wrist to perform different tasks. These attachments to the wrist are known as end-effectors. Sometimes referred to as end-of-arm-tooling (EOAT), end effectors traditionally include things like grippers, cutting tools and welding torches. With the advancement of additive manufacturing, highly customised end-effectors can now be designed for highly specialised applications. This is what this project at Penn State University demonstrated very well.

Why is additive manufacturing of end effectors so effective?

Additive manufacturing (AM) gives you the ability to customise the tool to a particular product easily and without expensive tooling. AM also gives you the ability to create freeform air channels that can be formed into practically any shape. This means that end effectors can be designed with dramatically reduced weight, and reduced energy use for the robot. Also, the improved fluid characteristics through the channels mean that smaller vacuum pumps can be used.

The Penn State World Campus Project

The Penn State students worked in small groups to design a robot end effector that would be used with a ‘UR3 Universal Robotics’ robotic arm and printed on a 3D Systems metal AM machine. Unlike a real-world situation, the students were provided with the final CAD model of the holder to locate the ping-pong balls. However, apart from this, a real-world design problem was mimicked as much as possible.

The video below demonstrates a full cycle of one of the end-effectors picking and placing the four ping-pong balls according to the design specification.

The students had to design the end effector and also had to select the rest of the components from a part catalogue. They could either consolidate certain components, such as the suction cups or vacuum generator into the 3D print or leave them as separate components to be assembled after printing. A method to secure the end effector to the robotic arm also had to be implemented by the students. Quite a challenge!

Designing the end effector

Using Sulis Flow, the students rapidly created the necessary 3D geometry. The design software allowed the students to easily design and iterate the fluid channel designs and also assess the manufacturability of the geometry. It also allowed them to automatically modify the geometry of the fluid channels to be self-supporting if required.

The students had many things to consider including the design constraints of the process and the printer that would be used. These constraints included the maximum overhang angle that can be printed. In some cases, the groups decided to modify the geometry to be self-supporting and in other cases, the groups designed their channels to be within the maximum circular channel size that could be printed using the 3D Systems printer (L-PBF).

Post-processing also had to be considered by the students during the design process. Since an EDM machine was used to cut the parts from the build plate, additional material needed to be added to the underside of the parts to enable easy removal from the build plate. Additional stock also needed to be left in the channels to ensure that the end-effectors could be machined to the correct tolerance.

Once the fluid channel designs were complete in Sulis they were then exported as STEP files. These were then imported into CAD/CAE software for simulation of the fluid channels using CFD or FEA. Additional features such as threads were also added to the CAD model. These were machined onto the component after it was printed.

3D printing of the metal end effectors

The image below shows one of the student designs after it has been 3D printed and machined. The end effector has an input for the vacuum generator and this is then split into four fluid channels. Four screw fixturing points are included to connect the part to the robot. The Penn State students in this group decided to purchase suction rather cups rather than consolidate them into the printed assembly.

Testing of the student’s end effectors

After printing, post-processing and finishing the end-effectors were then tested by the Robotics Department at the University of Bath. Each end-effector was attached to the UR3 robotic arm which was programmed to pick up the ping pong balls from the designated holder and transfer them to a second holding device.

All of the student groups designed effective, lightweight end-effectors that were capable of transporting the balls between the designated locations. Each of the designs demonstrated a clear knowledge and understanding of the principles of DfAM. The group that created the lightest end-effector completed a design weighing just 68g. The smooth fluid channels combined with the compact nature of the designs fulfilled the design requirement for an energy-efficient, lightweight design.

“This project truly demonstrates the World Campus aspect of Additive Manufacturing and Design program where students worked with researchers and industry to create unique solutions that are possible only through AM”   

Guha Manogharan, Assistant Professor – Mechanical Engineering, Penn State University

Acknowledgements

Thank you to Dr Guha Manogharan for inviting us to take part in the Summer School and Ankit Saxena of Penn State too.  Thank you to Ryan Overdorff and Samuel Kelly from 3D Systems who also collaborated on the project. Thank you also to Dr Ioannis Georgilas and Dr Uriel Hernandez for their help in testing the end effectors at the University of Bath. Thank you also Penn State University, College of Engineering, the students of the “Additive Manufacturing and Design Masters Program”