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Objective Techniques to Measure the Effect of an Exoskeleton

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Abstract

Know in advance the effects of an exoskeleton on the worker’s body, before its implementation in the workplace, will give us valuable information to make decisions and optimize company resources. Three objective techniques (surface electromyography, 3D motion capture and dynamometry for the biomechanical analysis with the MH-Forces ergonomics assessment method) are used for this aim. Measurements results will show how the use of an exoskeleton while performing a task can modify the efforts, the muscular activity, the postures, the movements and the forces on the worker’s joints. These objective techniques can provide quantitative and reliable data to prevent potential exoskeleton users from suffering musculoskeletal disorders.
AbstractKnow in advance the effects of an exoskeleton on
the worker´s body, before its implementation in the workplace,
will give us valuable information to make decisions and optimize
company resources. Three objective techniques (surface
electromyography, 3D motion capture and dynamometry for the
biomechanical analysis with the MH-Forces ergonomics
assessment method) are used for this aim. Measurements results
will show how the use of an exoskeleton while performing a task
can modify the efforts, the muscular activity, the postures, the
movements and the forces on the worker´s joints. These
objective techniques can provide quantitative and reliable data
to prevent potential exoskeleton users from suffering
musculoskeletal disorders.
I. INTRODUCTION
Exoskeletons can be a satisfactory option to tackle
musculoskeletal disorders (CTD) [1]. However, the
implementation of an exoskeleton means changes [2] in the
workplace that will affect the user, their workmates and their
environment [3].
Mutua Universal has developed a methodology to assess
the effectiveness and the acceptance of the use of
exoskeletons in a company [4]. One of the axes of this
methodology is the objective analysis of the effect of the
exoskeleton on the worker´s body. This analysis tries to verify
whether the exoskeleton generates neither overload nor
unnecessary effort on the worker.
The aim of the objective techniques is to confirm that the
exoskeleton does not involve overexertion or unnecessary
strain on the worker´s body. Accordingly, we need to register
biophysical parameters such as the muscular activity
performed, postures, body segments motion or internal forces
on the joints caused by the weight, the loads handled and other
external forces the worker does.
The purpose of this work is not to present a specific data
analysis from a given trial, but to offer the instrumental
techniques on which a researcher can rely on to perform an
objective analysis of the impact of the exoskeleton on the user
in real working conditions.
II. MEASURING TECHNIQUES
This document presents three measuring techniques to
register biophysical parameters that can be applied to the
ergonomic study of exoskeletons. These techniques are
surface electromyography, 3D motion capture and
A.E, Planas-Lara, M. Ducun-Lecumberri and J.A. Tomás-Royo are with
Ergonomics Laboratory at Mutua Universal, Av. Tibidabo 17-19, 08022,
Barcelona, Spain (email: aplanasl@mutuauniversal.net)
Javier Marín and José J. Marín are with the IDERGO (Research and
Development in Ergonomics) Research Group, I3A (Aragon Institute of
dynamometry for biomechanical analysis.
A. Surface Electromyography
Surface electromyography (SEMG) is a non-invasive
measuring technique that, when applied in ergonomics,
allows, among other applications, to identify the muscular
groups having the principal role in the tasks performed,
analyse muscular activity in each muscular group of interest
or compare the muscular behaviour when the same tasks are
executed throughout different processes [5].
When applied to exoskeleton analysis, it permits us to
compare the muscular activity developed by the worker when
performing the task with and without the exoskeleton.
The protocol to perform the measurements consists of: (1)
identifying the muscles involved in the actions the worker
carries out, (2) placing the electrodes on their skin, (3)
recording the Maximum Voluntary Contraction (MVC) for
every muscle to use them as a reference and finally (4)
recording the electromyographic signals while the worker is
developing the working tasks. A significant number of
workers will be established for the analysis depending on the
resources available and the scope of the study.
The results obtained through SEMG show if the activity
required by a particular muscular group is higher or lower
with the use of the exoskeleton.
The percentage of difference in the muscular activity
between with and without exoskeleton considered significant
is established according to the muscular group and the type of
exoskeleton. For example, a 9% of the difference in the trunk
extensor activity is considered significant in the case of using
a passive exoskeleton for assistance for the back [6].
Based on these results, and depending on the quantity each
muscle contributes to the task, a study is carried out whose
conclusions guide the decision-making in terms of
implementation or not of the exoskeleton in the workplace.
B. 3D Motion Capture
The ranges of motion for the different joints constitute
another one fundamental parameter of analysis. They allow
us to verify how postures and movements are altered with the
use of the exoskeleton and if comfort areas are surpassed.
One of the most practical techniques to register the motion
of all body segments is through inertial sensors.
In this sense, it is possible to apply the MH-Sensors
motion-capture system based on inertial sensors [7]. This
Engineering Research), Department of Design and Manufacturing
Engineering, University of Zaragoza, C/Mariano Esquillor s/n, 50018
Zaragoza, Spain. (J.M.: 647473@unizar.es; J.J.M.: jjmarin@unizar.es)
Objective Techniques to Measure the Effect of an Exoskeleton
A.E. Planas-Lara, M. Ducun-Lecumberri, J.A. Tomás-Royo, Javier Marín, José J. Marín
system has significant advantages for application in the
workplace: (1) portability, which allows real-time capturing
in the workplace, (2) a straightforward process of anatomical
calibration or sensor-to-segment alignment, which adjusts the
human model to the anthropometric measurements of the
analysed subject in-situ, (3) non-influence of magnetic
disturbances, which could negatively affect this type of
technology, especially in production environments.
The protocol followed to measure motion consists of: (1)
identifying the body joints involved in the actions carried out
by the worker, (2) placing the inertial sensors on the relevant
body segments under study, (3) recording the initial posture
as a reference to calibrate the system, (4) recording the motion
signal during the performance of the tasks and (5) creating a
biomechanical model to reproduce worker´s movements to
obtain the ranges of motion for each joint.
The outcomes obtained through this instrumental technique
allow us to conclude whether the movements executed by the
worker are less or more demanding with the use of the
exoskeleton. The percentage of difference in the range of
motion between with and without exoskeleton that is
considered significant is established according to the body
area and the type of exoskeleton.
C. Dynamometry for the biomechanical analysis
Another remarkable aspect to analyse is how the weight
and the stiffness of the exoskeleton can influence the worker´s
joints and if this impact might cause damage in the medium
and the long term.
In this sense, to assess the ergonomics of the workplace, the
MH-Forces [8] method uses motion capture to calculate joint
forces and moments and, with this information, estimates a
joint risk index (0 minimum risk to 5 maximum risk). For its
application, the forces and moments that the worker performs
during the work cycle must be introduced. Similarly, this
method would allow the consideration of the forces and
moments caused by the exoskeleton acting on the body. In this
way, the expected effect of the exoskeleton on the
biomechanics (kinematics and kinetics) of the worker during
the execution of the task can be objectified by simulation.
III. CHALLENGES
Despite the fact that the objective measuring techniques
provide valuable results that help the decision-making in
terms of the convenience or not to implement an exoskeleton,
they involve some difficulties in practice.
Wearing an unfamiliar element on the body, such as an
exoskeleton, is a challenge for the worker because of the
addition of weight, the extra volume and the resistance to
movement that it supposes. It causes physical interferences in
the environment and hinders worker mobility.
Furthermore, sensors and elements attached to the worker´s
body that are required to monitor the performance increase
this feeling of uncomfortability.
We require small, light and flexible devices that can be
placed between the worker´s body and the exoskeleton and be
as unnoticeable as possible to achieve the least invasive
possible measurement for the worker performing the activity.
Long-term studies entail time and resources, thus, they are
difficult to carry out. The development of versatile and
practical software will let the researchers achieve objective
and reliable results with the minimal time investment.
IV. CONCLUSION
The implementation of an exoskeleton in a company is
costly in terms of time, staff and other resources involved.
The use of measuring objective techniques to analyse the
effects of an exoskeleton on a user allows us to achieve
reliable results and establish a precise diagnosis of the
situation. It is possible to objectify the potential percentage in
muscular activity reduction, the force reaction magnitude on
the different joints and the periods during which the worker is
adopting awkward postures.
In addition to this, it avoids false expectations about the
convenience of the exoskeleton and confirms that it does not
physically harm in the short term. The use of these
instrumental techniques let us know in advance these effects
will allow the decision-making and optimise the company
resources before a potential implementation.
ACKNOWLEDGMENT
Mutua Universal wishes to thank its associated companies
for the collaboration provided in the studies with exoskeletons
that have served as the basis for this work.
REFERENCES
[1] The impact of using exoskeletons on occupational safety and
health, OSHA-EU, 2019.
https://osha.europa.eu/en/publications/impact-using-
exoskeletons-occupational-safety-and-health/view
[2] S. Kim et al. Assessing the potential for “undesired” effects of
passive back-support exoskeleton use during a simulated
manual assembly task: Muscle activity, posture, balance,
discomfort, and usability. Applied Ergonomics 89 (2020)
103194
[3] A.E. Planas-Lara, J.A Tomás-Royo, M. Ducun-Lecumberri,
Ergonomics 4.0 and Exoskeletons: Myths, legends and truths.
Ed. Mutua Universal, 2020
[4] J.A Tomás-Royo, M. Ducun-Lecumberri, A.E. Planas-Lara,
M.M. Arias-Matilla. A Methodology to Assess the
Effectiveness and the Acceptance of the Use of an Exoskeleton
in a Company. WeRob 2020.
[5] S. Kumar, A. Mital. Electromyography in Ergonomics. Ed.
Taylor & Francis, 1996
[6] S. Madinei, Biomechanical assessment of two back-support
exoskeletons in symmetric and asymmetric repetitive lifting
with moderate postural demands. Applied Ergonomics 88
(2020) 103156
[7] Marín, J., Blanco, T., de la Torre, J., & Marín, J. J. Gait Analysis
in a Box: A System Based on Magnetometer-Free IMUs or
Clusters of Optical Markers with Automatic Event Detection.
Sensors 2020, 20, 3338.
[8] Boné, M. (2016). Método de evaluación ergonómica de tareas
repetitivas, basado en simulación dinámica de esfuerzos con
modelos humanos. Phd Thesis. University of Zaragoza, Spain.
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Método de evaluación ergonómica de tareas repetitivas, basado en simulación dinámica de esfuerzos con modelos humanos
  • M Boné
Boné, M. (2016). Método de evaluación ergonómica de tareas repetitivas, basado en simulación dinámica de esfuerzos con modelos humanos. Phd Thesis. University of Zaragoza, Spain.
The impact of using exoskeletons on occupational safety and health
  • Osha-Eu
Electromyography in Ergonomics
  • S Kumar
S. Kumar, A. Mital. Electromyography in Ergonomics. Ed. Taylor & Francis, 1996