Test & measurement
Helping to build life-changing exoskeletons
RLS magnetic encoders are enabling Marsi Bionics to design and build exoskeleton orthopaedic devices that could improve the quality of life for people suffering from diseases such as spinal muscular atrophy, multiple sclerosis, and hemiplegia caused by stroke
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arsi Bionics is a leading technology start-up based in Madrid, Spain. It designs and builds custom exoskeletons
for medical applications with the aim of potentially replacing the wheelchair in everyday life for some patients. Millions of people suffer from debilitating neurophysical conditions such as paraplegia, cerebral palsy and spinal muscular atrophy (SMA). Neurological rehabilitation with passive aids such as canes, crutches and walkers is vital in the treatment of mobility issues caused by these conditions. Recent advances in robotics have allowed treatment with powered (active) robot exoskeletons that support the patient's body and enable greatly improved outcomes. The exoskeletons, created by Marsi Bionics, give
physically disabled people the freedom to stand, move and interact with their environment. Data collected from the encoders is fundamental for generating the position references. RLS and Renishaw provided Marsi Bionies with the best encoder feedback solutions for its applications. RLS, a Renishaw associate company, has been chosen by Marsi Bionics to supply the latest in magnetic encoder technology for the creation of two new products: the ATLAS 2030 exoskeleton for children and the MB-Active Knee (MAK) single-joint exoskeleton for adults.
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THE CHALLENGE The ATLAS 2030 exoskeleton has up to six degrees of freedom per limb. This device enables the user to perform both unaided and self- actuated actions such as walking and sitting. Full exoskeletons consist of motorised joints, limbs, electronic control and power systems. The designer must find a compromise between
a lightweight and compact structure that facilitates easy handling by the user, who might be physically weakened, and a robotic system that implements a physiologically complete biomechanical model. For stable walking, equilibrium control of the
exoskeleton-user assembly is achieved by tracking its zero-moment point (ZMP) references, which are based on the desired Normalised Dynamic Stability Margin (NDSM). The exoskeleton’s controller can subsequently adapt reference walking gait patterns, stored in memory, to maintain stability.
Successful dynamic walking requires precise control of the legs’ joint angles in terms of position, velocity and acceleration via rotary encoder feedback. This is difficult to achieve as each mechanical joint is compliant and includes elastic elements to help mimic and support the real joints and muscles of the human user. Alberto Plaza, R&D engineer and manager of the MAK project at Marsi Bionics, describes
the stringent encoder requirements of human exoskeletons: “The most difficult challenge when developing exoskeletons is the reliability of obtaining accurate angular position references, as they change from one structure to another, complicating standardisation and assembly of the devices.
September 2020 Instrumentation Monthly
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