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Juil 29, 2019

Project MARCH – MARCH IV and the use of 3D printing

Guest

written by Guest

For a number of years, Innofil3D has provided Project MARCH with a choice of filaments to design, produce and iterate their exoskeleton. This year it is the turn of the MARCH IV team, and this is their blog.

Project MARCH - MARCH IV and the use of 3D printing

3D printing is an important technique of creating three-dimensional objects and this technique is therefore frequently used in Project MARCH. Project MARCH is a student team from the Delft University of Technology that designs, builds and tests a new prototype of exoskeleton every year. The use of this exoskeleton is meant for paraplegics: people with a spinal cord injury who have lost all functionalities of their legs and the corresponding senses. The exoskeleton gives the user the ability to stand up and walk again. There are already existing three prototype MARCH exoskeletons. And this academic year the team has been working on the latest version, the MARCH IV.

Before we will tell you about the use of 3D printing in the team MARCH IV, you need to have a global view of how the exoskeleton functions. First of all, the exoskeleton consists of different sets of joints placed on the hips, knees and ankles. With these joints, which include motors, the exoskeleton is able to take steps forward and to the side. The joints are connected with each other by metal parts, called the bones of the exoskeleton. Electronics are placed on the bones for data communication and power distribution. Covers are placed on the bones and electronics for protection. The joints are controlled by the so called input device, which is located in the crutch and consists of a screen with buttons. With this input device the user can command which action to perform. These actions are for example walking forward, sitting down or ascending a stair.

March IV - Team members with 3D printed parts of the MARCH IV exoskeleton

Team members with 3D printed parts of the MARCH IV exoskeleton

 

In this Project MARCH year, 3D printing is something that is very valuable for the team. We use 3D printing for different purposes and for these different purposes we use different types of filament. With the support of Innofil3D, we were able to test the different types of filament and use them for prototyping and producing our final designs.

Prototyping

In the beginning of the year, we started with a long brainstorm about what the new exoskeleton should consist of and should be capable of doing. After we had set up a list of requirements, we began designing the different parts of the exoskeleton. Step by step, the designs were getting more detailed. During this process we used the 3D printers to test and iterate the designs. Because 3D printing goes fast, it is very easy to quickly view and check your 3D model in real size. For 3D modelling, we use the three-dimensional CAD program CATIA.

The 3D models from CATIA can easily be transported to the programs needed for the 3D printers. That is the reason why it is faster for us to test our designs with 3D printing compared to actually manufacturing our own 3D model. For example, the design of the input device is also subject to a long iterative process. The input device must be easy-to-use. This means that both the shape of the handle and placement of the buttons have to be well adjusted with the user. In figure 3 and 4 you see a few of the many different prototypes for the handle and the buttons.

 Project MARCH Input Devices
Project MARCH Input Devices

Project MARCH Input Devices

During this design iteration process for all the different parts of the exoskeleton, it is essential to keep in mind that eventually all these parts must fit together. To test this, we 3D print all the different parts and we try to connect them. In figure 5 and 6 these fittings are shown for the hip structure and the bone structure of the MARCH IV exoskeleton.

After we are sure that all the parts fit together, we send our 3D models to the manufacturers of the metal parts of the joints and bones. For prototyping we use normal PLA filament, because this is a low-cost filament, it is easy to print and it prints with high speed. That way, it meets all requirements for prototyping.

Different designs of buttons for the input device

Different designs of buttons for the input device

 

Final parts

This year we decided to research if we could print some of the parts of the exoskeleton with our own 3D printers. We choose to investigate this, because printing our own final parts is easier and cheaper than have it printed professionally. If the final part turns out to be wrong after all, it is possible to adjust the part immediately. After testing the 3D printers and the different types of filament, we were happy to conclude that the quality of the parts matched our specifications. Two examples are the covers and the foot sole.

For the final covers of our exoskeleton, we need a material that is strong enough to protect the electronics and bones. The cover will consist of two parts that are attached to each other by click connections. Therefore, the material must be able to make this click connection possible as well. The click connection can be seen in figure 7. We tested different types of filament for the cover: normal PLA, PET, PLA PRO1 and ABS Fusion. First we compared normal PLA and PET. PET seemed to have better properties with respect to durability of the material, strength and heat resistance. When we found out that Innofil3D offered a professional line of filament as well, we started to compare PET with ABS Fusion and PLA PRO1. The properties of ABS Fusion and PLA PRO1 are better than those of PET. Looking at the level of flexibility, ABS Fusion appeared to be more flexible than PLA PRO1. After testing both materials for the click connections, we noticed that ABS Fusion was too flexible for the functioning of the click connections. That is why we choose to print our final covers with PLA PRO1 from Innofil3D. After printing, we will post-process the covers with epoxy, sanding and varnishing.

Another important final 3D printed part of the exoskeleton is the foot sole. The foot sole, shown in figure 8, is connected to the ankle joint of the exoskeleton and is meant for the support of the exoskeleton. For this foot sole, it is needed to have the possibility to slightly bend the feet during walking. Because of the need for more flexibility, we choose for ABS Fusion instead of normal PLA filament or PLA PRO1. We choose for ABS Fusion instead of normal ABS, because ABS Fusion turned out to be easier to print and was less prone to wrapping.

When printing with these different types of filament, we found out that the settings of the 3D printers needed to be adjusted for the different types of materials. The difference was mainly in the temperature settings of the nozzle and the printbed, the distance between the nozzle and printbed and the working of the fan. We learned that for every printer and every material it is needed to be aware of the right distance between the nozzle and the printbed. If we put the nozzle too close to the printbed, the filament will not have enough space to extrude the material. When putting the nozzle too far away from the printbed, the filament will not find the right place on the printbed because it is floating in the air for too long.

The Foot Sole connected to the ankle

The Foot Sole connected to the ankle

The click connections for the covers

The click connections for the covers

 

With the support of Innofil3D, we are able to test our designs and produce our own parts of the exoskeleton. Therefore, Project MARCH is very grateful!

 

More about project MARCH can be found on the Project MARCH website

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