An exoskeleton must be lightweight, compact, powerful, reliable, and easy to use – what could be easier? Many developers around the world dabble in this discipline with different degrees of success.

How to Design an Exoskeleton
How to Design an Exoskeleton

Article from | maxon group

Mechanics

“Emulating the human gait with mechatronic systems is a huge engineering challenge. The structure that supports the person must be as light as possible yet also robust, as every additional kilogram has an impact on the drive systems. For this reason, lightweight materials such as carbon are often used. It is also important that the exoskeleton is not too broad, as the pilot must be able to pass through any door without difficulty.”

 

Drives

“The drive systems, consisting of a motor and gearhead, must deliver high torque. Enormous forces are at work, especially when walking up and down stairs. At the same time, a high level of dynamics is required, as the motors must constantly change the direction of rotation due to the walking movement. The final item on the wish list is a compact design that takes up as little space as possible.”

 

User interface

“The pilots need to have complete control over their locomotion, so the movement controls must be easily accessible and intuitively designed. Furthermore, to ensure that the nterface reliably transmits the large forces at play while also protecting the sensitive skin of the pilot, it must be individually adjusted to the pilot’s legs and torso.”

 

Pilot and experience

“This is arguably the most important point. How well an exoskeleton works in practice depends primarily on the pilot, who must get used to the robotic assistance and learn how to use it to best effect. Some people rely more on strength, others more on technique. Either way, it requires a huge amount of training.”

 

Degrees of freedom

“How many degrees of freedom should there be? That’s a tricky question. Exoskeleton designers often opt for two degrees of freedom per leg, so only the hip and the knee move. The benefits of this are: less weight, a simpler control system, and therefore fewer sources of error. However, it is possible to have three or four degrees of freedom. This means that you can have lateral movement, for example, or additionally actuate the ankle. This gives the pilot extra freedom of movement and increased stability on uneven ground. On the other hand, this makes the entire system heavier and more complex, and also decreases the battery life.”

 

Software

“At first glance, controlling fewer degrees of freedom seems simple. However, when you get down to the detail, the implementation is rather more complex. This is because many different movements must be controlled and accidents prevented by safety features. In addition, the entire exoskeleton should be developed further in cooperation with the pilot. This can only be achieved with a viable software architecture.”

Christian Bermes is Team Leader at VariLeg enhanced and Professor for Automation and Mechatronics at HSR University of Applied Sciences, Rapperswil.

 

New VariLeg exoskeleton with motors twice the power

The VariLeg enhanced team is developing and building an exoskeleton for the Cybathlon 2020. However, the ongoing project has little to do with the VariLeg team from ETH Zurich that took part in 2016. The current exoskeleton was developed as a student project. A mixed team from ETH Zurich and the HSR University of Applied Sciences Rapperswil is now working on the completion of the robotic system. The system has two degrees of freedom. There are two brushless flat motors from maxon on each side to move the hips and knees. These deliver up to 600 W of power.

Otto Ineichen, Business Development Medical at maxon: “Above all else, drives for exoskeletons must be lightweight. And a low overall height is also important. At the same time, however, high power density and dynamics are required, as the motors must change the direction of rotation frequently and very quickly. At maxon, we are currently developing a new product platform of motors specially designed to meet the needs of the robotics market. These new drives are based on the EC-i frameless concept. They can then be combined with suitable gearheads, depending on the application and requirements.”
 
The content & opinions in this article are the author’s and do not necessarily represent the views of RoboticsTomorrow
maxon group

maxon group

maxon is a leading supplier of high-precision DC brush and brushless servo motors and drives. These motors range in size from 4 - 90 mm and are available up to 500 watts. We combine electric motors, gears and DC motor controls into high-precision, intelligent drive systems that can be custom-made to fit the specific needs of customer applications.

Other Articles

5 Challenges a Motor Has to Overcome on Mars Home
Outer space is unforgiving. This is why precision drives embarking on a trip to other planets need to meet extremely high quality standards.
Smart ArM: Pushing the limits of the human body
The result of several years of research, the design of this prosthesis represented a real challenge as it involved creating a prosthetic elbow. This article looks back at this technological feat and human adventure.
IP65, IP67, IP68…What Do Protection Ratings Mean?
If you are working on a project that calls for an electric motor unit, you will certainly have come across the terms IP65, IP67 and IP68. What do these protection ratings cover? Which protection should be chosen based on your project? Here's a brief answer to these questions.
More about maxon group

Comments (0)

This post does not have any comments. Be the first to leave a comment below.


Post A Comment

You must be logged in before you can post a comment. Login now.

Featured Product

Real Time Systems - ALL APPLICATIONS ON ONE HARDWARE PLATFORM

Real Time Systems - ALL APPLICATIONS ON ONE HARDWARE PLATFORM

The RTS Hypervisor enables work-load consolidation of both real-time and non-real-time operating systems on a single x86 based platform. Unlike traditional virtualization, we partition and allocate the hardware for each work-load and provide a "privileged" mode for real-time operating systems that guarantee zero impact to determinism while adding zero jitter. This is instrumental for work-loads such as robotic controllers managing motion control where minimum jitter is required. And, our hypervisor is designed for easy setup and configuration for any work-load consolidation scenario. This equates to deterministic real-time applications taking advantage of all the benefits of virtualization immediately, without costly implementation projects.