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Magnetic encoders for ‘life-changing’ exoskeletons

Posted on 05 Dec 2020 and read 1178 times
Magnetic encoders for ‘life-changing’ exoskeletonsWhile millions of people suffer from debilitating neurophysical conditions such as paraplegia, cerebral palsy and spinal muscular atrophy (SMA), recent advances in robotics mean that neurological rehabilitation can move away from passive aids such as canes and walkers to more advanced technologies.

Marsi Bionics SL is a leading technology start-up based in Madrid, Spain, that designs and builds custom robot exoskeletons that give physically disabled people the freedom to stand, move and ‘interact with their environment’; and because data collected from encoders fitted to the exoskeletons is fundamental for generating position references, Marsi Bionics approached Renishaw associate company RLS to provide the best encoder feedback solutions for its applications.

This approach resulted in the supply of the latest in magnetic encoder technology for the development of two new products: the ATLAS 2030 exoskeleton for children and the MB-Active Knee (MAK) single-joint exoskeleton for adults.

The ATLAS 2030 exoskeleton has up to six degrees of freedom per limb, allowing the user to perform actions such as walking and sitting.

However, to allow patients to complete these actions, the designer must find a compromise between a lightweight and compact structure that facilitates handling by a user and a robotic system that implements a ‘physiologically complete biomechanical model’.

Alberto Plaza, R&D engineer and manager of the MAK project at Marsi Bionics, said: “Obtaining reliable and accurate angular position references is the most difficult challenge when developing exoskeletons.

“Previously we used our own custom-made PCB encoders but the joint motors regularly generated stray magnetic fields that can interfere with magnetic encoders and cause faulty readings.

When designing the ATLAS and MAK devices we needed encoders that were as compact as possible without compromising on performance and gave accurate and reliable angular positions of each axis.”

Marsi Bionics selected the RLS Orbis encoder for its ATLAS exoskeleton and the RLS RM08 encoder for its MAK knee-joint exoskeleton.

The Orbis encoder is a component-level absolute rotary encoder designed for ‘space constrained’ applications and has a through-hole design that enables direct mounting on the joint motor shaft. The RM08 encoder is a miniature high-speed rotary magnetic encoder that is just 8mm in diameter and is IP68-rated for use in harsh environments.

Both encoders feature low weight and volume to minimise inertias, a non-contact and frictionless design to eliminate mechanical wear, and high angular resolution and accuracy to ensure ‘excellent servo performance’.

Mr Plaza said RLS magnetic encoders have enabled Marsi Bionics to design and build exoskeletons that could improve the quality of life for people suffering from neurophysical conditions, adding that active exoskeletons will particularly impact the lives of young children, aged six and above, who are unable to move around by themselves.