Authors: Mercedes Sanchis Almenara, Sofía Iranzo Egea, Juanma Belda Lois, Alicia Piedrabuena Cuesta, Alberto Ferreras Remesal, Sandra Alemany Mut, Enric Medina Ripoll, Raquel Ruiz Folgado

Instituto de Biomecánica de Valencia
Universitat Politècnica de València
Edificio 9C. Camino de Vera s/n
(46022) Valencia. Spain

While new technologies have undoubtedly led to a significant increase in process automation in the industrial sector, certain jobs still involve a high physical workload.

Together with the ageing of the working population, this means that solutions such as exoskeletons are becoming more and more common in organizations.

Selecting and properly fitting exoskeletons to suit the characteristics of the task and the person in question is key to ensuring that it has a positive effect, both in terms of muscle load and worker acceptance.

INTRODUCTION

The efforts required to perform certain work tasks, even in those cases where the ergonomic risk is tolerable according to current assessment methodologies, can lead to discomfort and soreness in some body segments. Particularly in cases where workers adopt inappropriate postures or have to handle loads.

Passive exoskeletons have been introduced in recent years, mainly in the industrial sector, as a possible aid to improve comfort and reduce muscular discomfort, the aim being to reduce the muscular load on the body segments involved in certain tasks. There is a wide range of commercial models for different joints, such as devices for lumbar load reduction, lower limb support (the chairless chair) or upper limb devices that relieve stress on shoulders and arms.

In addition to passive exoskeletons, currently the most widely known devices in the workplace, we should also mention another development: semi-active exoskeletons equipped with actuators that exert a force that helps workers to perform certain movements.

This text aims to offer some insight into how to approach the integration of a passive exoskeleton into a company or what aspects should be taken into account when designing a semi-active exoskeleton.

Image 1: Example of how an exoskeleton can be used in a work environment.

DEVELOPMENT

The Instituto de Biomecánica (IBV) has amassed a great deal of knowledge in relation to human beings and their behavior, knowledge that has allowed it to approach the study of exoskeletons from different perspectives.

On the one hand, we have carried out studies with companies interested in implementing devices of this type in their production processes, identifying their impact on muscular activity and the performance of the work task; and, on the other hand, we have worked with exoskeleton manufacturing companies on different approaches in response to the specific problems encountered with their products.

The following is a description of how these studies have been carried out and the results obtained.

INCORPORATION OF EXOSKELETONS INTO A WORK TASK

The incorporation of exoskeletons into an organization’s processes, no matter what the sector may be, involves the following phases:

PHASE 1. Identifying the most appropriate exoskeleton according to the characteristics of the task    

As mentioned above, the most appropriate type of exoskeleton for each task will depend on the specific activity that the workers have to undertake and the muscle groups involved.

In this sense, before a company begins working on the introduction of an exoskeleton, it needs to know what specific task or tasks it will be used for, what movements are performed during those tasks, what muscle groups are involved and what other tasks - albeit less frequent ones - are performed in the job (for example, if the worker has to drive a vehicle, walk up or down stairs, etc.).

All this information will help identify the most suitable exoskeleton(s) available on the market.

PHASE 2. Field study: Assessing the features of the exoskeleton

Once the most suitable exoskeleton has been identified, a series of tests will have to be carried out in the workplace to analyze, on the one hand, the impact of the exoskeleton on the muscular activity of the persons carrying out the tasks and the movements involved in such activity; and, on the other hand, whether or not the workers are happy to use the exoskeleton during their working day.

- In order to analyze the muscle load, surface electromyography (EMG) is usually used and muscle activation is analyzed during the performance of the task with and without an exoskeleton, to see whether this activation decreases during the performance of the same task when the person is wearing the exoskeleton. A decrease in muscle activation will mean less fatigue.

- Inertial sensors are used to capture the worker’s movements in order to compare these movements during the performance of the same task with and without an exoskeleton, thus making it possible to make sure that using an exoskeleton does not imply a risk of inadequate postures being adopted.

- Finally, a survey was carried out among the people who took part in the study in order to obtain their opinion on the use of the device, whether they perceive it as an aid and whether they would use it during their working day, etc.

PHASE 3. Analysis of results

Once the field study ended, the results obtained from both the objective measurements and the surveys were analyzed, the aim being to reach conclusions on the suitability of incorporating the tested exoskeleton in the performance of the specific work task.

In this regard, the IBV has developed a biomechanical model by means of which, by introducing the movement data and anthropometric measurements of the participants in the study, it is possible to carry out simulations from which to extract information that cannot be measured directly during the course of the study, such as joint loads, for example.

The analysis of all this information allows a decision to be made on whether or not the exoskeleton under study is suitable for the specific task under analysis.

EXAMPLE 1. Incorporation of an upper limb exoskeleton in the industrial sector

Together with Ford, the IBV developed a project aimed at incorporating an exoskeleton into a production line. The company wanted to assess the suitability of using exoskeletons for a specific work task involving over-the-shoulder work, hence the most suitable device was identified as an upper limb exoskeleton (to be more specific, we studied Levitate’s AIRFRAMETM model). This device consists of a spring system with two arm supports that gradually activates when the arms are raised (assisting in the overhead position), and progressively reduces resistance when the arms are lowered (Figure 1).

Figure 1. The AIRFRAMETM exoskeleton used during the study at Ford.

Taking into account the muscles that are activated during the performance of the work task, it was decided to attach instruments to the following muscle groups (Figure 2 (a)): the anterior deltoid, trapezius, latissimus dorsi and erector spinae. The first two were the ones whose activity could potentially be reduced with the use of the exoskeleton, and the last two, because of the possibility of detecting adverse effects due to an increase in their activity when using the device.

To capture motion, inertial sensors were placed on the head, torso and arms, thereby making it possible to monitor the joints of interest: the neck and back (axial rotation, lateral flexion and flexion-extension), the shoulder (internal-external rotation, abduction-adduction and flexion-extension) and the elbow (pronation-supination and flexion-extension) (Figure 2 (b)).

Figure 2. Instrumentation: a) muscle activation sensors (EMG (electromyography)); b) motion sensors (inertial).

Fed with the measurements obtained, the biomechanical model we developed allows simulations to be carried out from which information not directly measured during the study (such as joint loading) can be obtained (Figure 3).

Figure 3. The biomechanical shoulder-lumbar model that we developed

The study subjects were monitored while performing the specific task with and without the exoskeleton and, once they had completed these tests, they filled in a questionnaire in which they were asked about their experience with the device and their perception of reduced muscle fatigue in the neck, back, shoulders and legs. The results of this study have been published in the scientific journal Applied Ergonomics under the title "Ergonomics Assessment of passive upper-limb exoskeletons in an automotive assembly plan" and are available free of charge.

Following this study, the company continued with the implementation phase of the exoskeletons, finding that the main obstacle to the use of these devices was the high temperatures at the Valencia plant.

EXAMPLE 2. Use of a lumbar exoskeleton in logistics tasks

Lumbar exoskeletons are primarily designed to reduce the load on the back muscle groups when handling loads. In this sense, the logistics sector is one of the main target areas for this type of exoskeleton.

The IBV has studied this type of exoskeleton both in the laboratory, in palletizing and depalletizing tasks under controlled conditions (a study financed by the Prevent Foundation) (Figure 3a), and in a real-life situation during the course of activities inherent to a workplace in which orders are prepared, in collaboration with Umivale Activa, a Mutual Insurance Company (No. 3) that collaborates with the Social Security (Figure 3b).

Figure 3. Studies assessing the impact of using a lumbar exoskeleton: a) in the laboratory; b) in a real-life situation.

The main objective of both studies was to systematically analyze the effect that lumbar exoskeletons have on the main risk factors for musculoskeletal injuries in jobs requiring manual handling of loads. The complete assessment therefore involved the measurement of the participants’ muscle activity, motion ranges and joint moments during the performance of the two series of tasks (with and without an exoskeleton).

The main conclusions of these studies were::

- The use of an exoskeleton proved to be beneficial as it reduced both the muscle activity in the erector spinae and the moments of force in the joints most involved in the task: the hips and the lumbar joint.

- There are some minor negative effects resulting from the use of the exoskeleton, such as a slight restriction in movements and a slight increase in the activity of the rectus femoris muscle.

The results of the laboratory study have been published in the scientific journal Sensors and are available free of charge (https://www.mdpi.com/1424-8220/22/11/4060/htm).

EXAMPLE 3. The importance of the user in the development of exoskeletons

In addition to the study of the selection and introduction of exoskeletons according to the demands of the tasks and their impact on the physical load exerted by workers, the IBV has also advised exoskeleton manufacturing companies in two main areas: sizing (based on the anthropometry of different population groups) and the definition of the requirements to be met by the device.

DEFINING THE SIZING OF EXOSKELETONS

Ensuring the optimal effect of an exoskeleton means ensuring a proper fit. This is even more important in the case of semi-active exoskeletons that have actuators that must be perfectly positioned if they are to apply the required force at the exact point in order to assist in the performance of the specific movement.

The IBV’s anthropometric databases and its knowledge in this field have allowed it to advise Japet on how it can identify the appropriate size for different population groups (specifically Japanese, Dutch, American and Spanish) for both men and women (Figure 4).

Figure 4. Semi-active lumbar exoskeleton used by Japet (https://www.japet.eu/)

DEFINING PRODUCT REQUIREMENTS

Proper design of an exoskeleton involves ensuring that it helps its wearer to perform specific tasks and does not interfere in the performance of complementary tasks. In this respect, it is essential to identify exactly what tasks are involved, what movements are entailed, whether other types of equipment must be worn (e.g. PPE), the climatic or environmental conditions in which it may be used, etc., and to design the exoskeleton taking all this information into account.

Along these lines, the IBV is working with GOGOA MOBILITY ROBOTS within the Eurostars program’s EXO-RESCUE project (Smart and modular semi-active full-body exoskeleton for rescue services) the objective of which is to develop a semi-active exoskeleton for rescue activities carried out by firefighters and/or mountain rescues carried out by the security forces.

Thanks to the Instituto de Biomecánica’s experience in projects related to exoskeletons and within the INNOWORK project (financed by the 2022 IVACE grants program for technology centers in the Valencian Community for the development of non-economic R&D projects carried out in collaboration with companies, co-financed by the European Union (IMDEEA/2022/34)), a guide has been prepared to help companies select and implement exoskeletons in the workplace. This guide contains information on criteria for the selection, adaptation and use of exoskeletons for physical load reduction. The guide, which companies can use to identify and implement the most suitable exoskeleton according to the specific characteristics of the task, contains a protocol broken down into phases to help them implement exoskeletons in the workplace or task. The guide also includes an interactive database that allows companies to select the most suitable type of exoskeleton according to the characteristics and needs of the job for which the company is interested in implementing an exoskeleton.

Likewise, within the framework of this project, the IBV is researching the development of a procedure to correlate the reduction of the physical load with the reduction of the ergonomic risk index obtained in the assessment carried out by means of classical ergonomic assessment methodologies.

CONCLUSIONS

The studies that the IBV has carried out to assess the effect of exoskeletons in specific workplaces reveal that these devices are an aid for the performance of certain tasks and that they help to reduce the load on certain muscle groups.

However, it must be taken into account that:

- The use of this equipment can represent a possible means of improvement in cases where other technical or organizational measures for the improvement of the ergonomic conditions of the workplace are not feasible or do not effectively reduce the physical load.

- The ergonomic assessment and redesign of the workstation - taking the results of the assessment into account - should always be the first priority for workstation improvement, and the incorporation of exoskeletons should be considered when this option has been exhausted and the necessary improvement has not been achieved.

Finally, it would be of great interest to carry out longitudinal studies to assess the long-term implications of their use, as well as to continue working on their design in such a way that some of the negative effects identified, mainly at a subjective level, can be minimized.

ACKNOWLEDGMENTS

Ford Motor Company

Prevent Foundation

Umivale Activa (a Mutual Insurance Company (No. 3) that collaborates with the Social Security)

Japet Medical Devices

GOGOA MOBILITY ROBOTS, S.L.

The Valencia Institute for Corporate Competitiveness (IVACE)