French fries a la Doosan

DHR Engineering was created as a company for developing new tools and solutions, and the spirit of innovation still thrives in our team. It sounds entirely realistic for us to dedicate a whole weekend, outside of working hours, to have fun with something related to the company’s daily tasks. On that account, we decided to organise a homemade hackathon and make some french fries with the help of the DOOSAN six-axis robot.

Introduction

Project Goals

• Program a six-axis robot to fry potatoes in a standard deep fryer and serve them.
• Record a video of the robot in action.

Why We Did It

• To demonstrate the capabilities of DOOSAN and its applications in various fields.
• For fun! The opportunity to solve a new, interesting problem with a 24-hour dealine tested the team’s creativity and the capabilities of the machines we have at our disposal.

Action Plan

• Brainstorm and outline the different actions the robot will need to perform for successful cooking (e.g., opening the refrigerator, transporting the fries, frying, etc.).
• Purchase and modify various materials and tools to be used (e.g. a box for transporting raw fries, a deep fryer, etc.); for each item, design interface parts to facilitate the connection between the robot’s gripper and the respective object.
• Set up the “kitchen” – positioning of the robot, deep fryer, refrigerator; prepare for video recording.
• Program the robot – determine the sequence of movements, find the right settings and speeds.
• Test, debug, and record the video.

Ready! Set! Go!

With great enthusiasm, we began discussing exactly what we wanted to achieve and how to do it. Some steps were suitable for the robot, while others were left for ourselves to save time. Here is the final result of our brainstorming:

Preparation (human tasks)

1. Arrange and anchor all objects included in the process (the robot, the fryers, various containers).
2. Pour the oil in the fryers and heat it up.
3. Prepare the boxes with raw french fries in the refrigerator.
4. Place a bowl for the finished products.

Frying the French fries (robot movements)

1. Open the refrigerator.
2. Grab the first box with raw fries.
3. Close the door.
4. Remove the lid from the box.
5. Drop the fries into the deep fryer net.
6. Leave the box aside.
7. Grab the fryer net and immerse it in the hot oil.
8. After a certain time, repeat steps 1-7 for the next box of raw fries.
9. After a certain time, grab the fryer nets with the cooked fries and empty it into the bowl.
10. Take the salt shaker and season the potatoes.
11. Serve the potatoes in a special basket.

From the list, it is evident that a special interface was needed for each of the following items: box, lid, deep fryer, salt, serving basket, refrigerator. We started designing and printing the parts.

Design and Fabrication of 3D Parts

Interface

In order to perform all the necessary operations for frying the potatoes, we first needed to determine how the robot would manipulate each item in the process. To ensure repeatability and a secure grip, we decided to use a dovetail clamp assembly wherever possible – it allowed for fixed positioning in two planes and provided a secure grip during the robot’s movements. To each item that the robot needed to grasp, we attached (bolted or glued) a 3D-printed complementary dovetail component – this way, the robot was able to grasp most of the items with the same interface.

Jaw Design

As we mentioned in the first article from our 3D printing series, the jaws of the gripper can combine multiple operations in one. In our case, we used the front of the jaws to grasp the dovetail clamps, while the middle cylindrical part was designed for the salt. By chance, the refrigerator door had a very convenient geometry and a simple bolt, sticking out of the jaws, was enough for the robot to open the fridge. Not the prettiest solution in the world, but hey, we needed it to work ASAP!

Since the gripper had only two positions for the jaws – open and closed – we needed to model a slight overlap when the jaws were fully closed to ensure that the robot wouldn’t drop the item it carried.

Manufacturing of 3D Printed Parts

We had limited time and several printers at our disposal. To accelerate the process, each part was printed separately, as soon as its design was complete. This, of course, led to a few unsuccessful designs that needed to be adjusted and reprinted – an iterative process that is common in the engineering field. The most complex parts were ready in less than 90 minutes.

Kitchen setup and programming the robot

Once we started the 3D printers, we went on to set up the “kitchen”- half of our workshop was rearranged, we moved the robot and brought a few tables. Various parameters were taken into account, such as the robot’s reach, order of movements and framing and light for the video.

The programming of the robot was a tricky task as well. Like most six-axis robots, the Doosan has two movement modes – “linear” and “joint”. The linear movement allows for better control over the trajectory and was used for accurate positioning and gripping the objects we manipulated. The joint movement, on the other hand, is designed for shortest and fastest operation between two predefined locations. That mode was used for transition between the different steps in the process. We started with a few steps, outlining the workflow and added or adjusted the list with each test iteration. Speed of movements (directly related to inertia of the carried objects) was also something we had to figure out by trial and error.

Testing, debugging and video

The most intensive part of the whole adventure was when we started testing the kitchen setup. As expected, various problems popped up – some of the printed parts didn’t fit the containers, some weren’t strong enough and we had to enhance and reprint them.

The most important lesson we learned though, was that it is crucial to fix everything very well to the ground. There were several occasions where somebody would accidently displace a table by a few centimetres and all the robot positions would run off. That was a hard lesson to learn but a valuable one.

Finally, after a long and intensive day, we were ready for the real test: recording a one-shot video of the robot, going through all the steps and delivering freshly made French fries … After three long minutes it was done and we sat down to enjoy some delicious, effortlessly-made French fries!

Conclusion

To sum it all up, it was a great weekend! Three ingredients were necessary for it to happen: a dedicated team, the powerful Doosan robot and the incredible 3D printing technology!

As always, we will be more than happy to help you with anything related to automation, robots or 3D printing (or cooking)! Let us know in the comments!