Using robotic exoskeletons to reduce muscle activity of workers

This paper presents an experimental study demonstrating the advantages of different exoskeletons while performing workers’ tasks. The study illustrates that how the use of certain upper and lower body exoskeletons can reduce the muscle effort around the shoulder, hip, and knee joints. Therefore, overhead, shoulder level, virtual chair position, and deep squatting position drilling tasks were performed, and muscle activity was recorded using EMG sensors. The muscle activity of the participants was compared with and without wearing exoskeletons while performing the same tasks. It was found that up to 60% reduction in the human effort can be achieved while performing the same tasks using exoskeletons. Many of the large-scale automobile manufacturers have already adopted exoskeletons in their assembly lines, however, the use of exoskeletons in small and medium enterprises (SMEs) is still not recognized. Therefore, this study aims to create awareness and accelerate adoption of exoskeletons among SMEs and construction workers.


INTRODUCTION
Since the last century, technologists and scientists have actively sought the development of exoskeletons designed to support or assist workers in heavy work.While many challenges associated with exoskeleton designs still exist, the advancements in the field over the course of the past decades have been impressive.Construction and manufacturing workers perform physically strenuous activities which put them at risk of developing serious musculoskeletal disorders (MSDs) [1][2].Work Foundation Alliance reported that in the EU up to 44 million workers were affected annually by workplacerelated MSDs, inflicting more than € 240 billion to the European economy.Furthermore, bigger health issues and economic losses due to severe shortages of trained labor also arise.Owing to these reasons, several active and passive exoskeletons have been developed and tested to explore the possibility of aiding the workers and the elderly [3-8.].
This study has used two exoskeletons namely (1) EksoVest manufactured by Eksobionics to perform tasks involving the upper body and (2) LegX was used to perform tasks involving virtual chair position and deep squatting positions as shown in

LegX:
The LegX is suitable for virtual chair and deep knee positions.It has lock and unlock modes.Lock mode has two mechanical functions that can help to sit on chair and knee position.The lock mode provides extra security to the user and the exoskeleton is locked to the desired position.At unlock mode, the user can move around freely while wearing the exoskeleton.
The tasks performed in this study are shown in Figure 2, and a brief descriptions of the positions and postures is presented below, • stand and hold the drill machine, with and without wearing Eksovest, and perform drilling in the roof position using different drill machines having weights 2kg, 3kg and 4kg.Different weights of drill machines were used to assess the relation between changes in muscle activity and level of assistance provided by the exoskeleton.• sit in chair position, with and without wearing LegX, and drill a wooden board using three different drill machines (of weight 2kg, 3kg and 4kg).In virtual chair position, the angle between the thigh and shank is 107.5 degrees.

TEST SETUP
Shimmer EMG sensors were used to record the muscle activity.The data acquisition software, ConsensysPro (available by the Shimmer EMG sensors) was installed on the laptop which facilitated the data transfer from the sensors to the laptop wirelessly through Bluetooth.
There are five ports on the Shimmer3 EMG sensor kit.The four ports are used to measure the muscle activity, whereas the fifth port is used to record the signal from the reference point.The reference point can be chosen as the place of minimum muscle activity, such as nearby bone or joint.All of the five ports are connected through surface electrodes to obtain the EMG signals.
Shimmer sensor kit is connected through surface electrodes, which were placed on the surface of the skin, just above the muscles of significance.These surface electrodes composed of Silver-Silver Chloride (Ag/AgCl).The electrodes were surrounded by an electrolyte or body electrode gel with a resistance of 100 Ohm.This gel is known as a non-irritating gel with such a rear surround made of pre-gelled sticky components.The diameter of the surface electrode is 25 mm.In this study, the EMG sensors were attached around the shoulder and leg at biceps brachialis and biceps femoris, respectively, to observe the muscle activation while performing different tasks of workers at different positions such as Roof drilling, Wall drilling, lifting/shifting of loads, virtual chair position and knee position.The surface electrodes of EMG Sensors measured the EMG signal associated with muscle contractions, muscle response, and activation level.

RESULTS AND DISCUSSIONS
The results of the study are presented in Fig 3 and  4 showed that muscle activity was maximum (magenta line) when no exoskeleton was used.Muscle activity reduced gradually from level 1 to level 4 as the level of support from the exoskeleton is increased.Therefore, the green line shows minimum muscle activity as exoskeleton contributed more support in that case, hence, the result clearly verifies that the use of the proposed exoskeleton reduces the muscle activity up to 66%.This reduction in muscle activity has vast advantages as it reduces work-related injuries, workers' fatigue and, hence, improves productivity in the long term .Furthermore, the use of exoskeletons can also assist in rehabilitation of workers to put them back to work after sickness and injuries.Similarly, Fig. -4 shows the results of wall drilling in a virtual chair posture, as shown in Fig- 2. The purple line shows the highest muscle activity as it corresponds to the drilling without exoskeleton (in virtual chair position), whereas, the other color lines corresponds to the muscle activities while wearing LegX exoskeleton and carrying powered drill (PD) machines of different weights (2kg, 3kg and 4kg).It is important to note that the muscle activity is plotted for 15 seconds for all the cases as the drilling task was intended to complete in 15 seconds.It can be observed that muscle activity without wearing the exoskeletons is notably higher than the muscle activity with the exoskeletons.However, as shown in Fig- 4, the reduction in muscle activity without exoskeleton, near the end of the task, might occurred as the task was nearly completed which resulted in gradual muscle relaxation.Following mathematical relation was used to calculate the percentage reduction in human muscle activity, with and without wearing Where, "WOE" represents measured values without wearing exoskeleton and "WE" are measured values while wearing exoskeleton.

Advantages and Affordability Limitations of Exoskeletons for SMEs
The adoption of exoskeletons can significantly improve the wellbeing of the labor force, attributed to the MSD-preventing capacity of exoskeleton technology.The impact of exoskeletons on MSDs will be most noticeable for the construction, manufacturing, logistics, human health, and agricultural sectors due to the high prevalence of work-related MSDs and the high number of SMEs in these sectors.However, in order to reap these economic benefits, occupational exoskeletons should be provided only to those that need it.Exoskeletons allocated to individuals with a low risk of suffering work-related MSDs may not contribute sufficiently to cost savings in terms of occupational injuries and illnesses for a positive return on investment.There is insufficient knowledge available on how to allocate exoskeletons effectively, targeting the individuals or groups of people within the working population exposed to substantial risks of incurring work-related MSDs.Manufacturers of exoskeletons have been focusing recently on the acceptance of their products as personal protective equipment (PPE), which even though more demanding and more costly, offers the additional status of a protective device that workers should really use, even if it adds acceptable levels of discomfort or reduction of productivity (similarly to how helmets or protective gloves for meat industry workers were perceived 50 years ago).Exoskeleton manufacturers will continuously upgrade and optimize their products, conducting clinical trials and expanding their sales and distribution network.Over time, orders will increase, in turn greatly decreasing manufacturing costs due to the economies of scale that will develop.In time, design refinements and agreements with insurers will also bring down the cost of ownership for exoskeletons.However, exoskeleton companies can't sell more units until they have more financial capital to refine their products, and so the cycle continues.Limited resources and the lack of cooperation amongst stakeholders reduce the rate at which upgraded and optimized products are developed and cost reductions are achieved.While exoskeleton technologies will have reached a reasonable level of sophistication; available in different sizes, improved practicality, final steps need to be made for widespread market adoption to occur.While revenues for manufacturers will increase, prices for exoskeletons remain too high for most SMEs and freelancers to start using exoskeletons.

CONCLUSION
In this experimental study, it was found that the passive exoskeletons significantly reduced muscle activity while performing workers' tasks for overhead, shoulder, prolonged virtual chair, knee bending positions, and lifting/shifting of loads.The results showed a remarkable reduction in human effort for upper body tasks, thereby demonstrating a potential solution of reducing work-related MSDs.
For the upper body tasks, as much as 66% reduction in muscle activity was observed as compared to performing the same tasks without using the exoskeleton.For the lower body task positions, the reduction in muscle activity was up to 54%.This is also quite significant, however, further reduction in muscle activity can be achieved by practice and balancing of LegX.It was observed that while performing the prolonged virtual chair position and kneeling position tasks, the users not only have to correctly position of the lower body but also have to properly balance the upper body as well.Due to these reasons, a relatively lower percentage reduction in human effort was achieved as compared to the upper body.
The focus of this work was to investigate and compare reduction in muscle activities while performing workers' tasks, with and without wearing exoskeletons.Further benefits of exoskeletons can be achieved by improving usability aspects such as adjustability to use the exoskeleton in different positions (other than the optimal positions).Also, more freedom of mobility during operation can be attained by reducing the exoskeleton mass and weight distribution.The results of this study successfully demonstrated a prominent solution to reduce human muscle activity and, thereby reduce the work-related injuries which are caused due to strenuous loading/unloading of workers' muscles.

Figure 1 :
Figure 1: Eksovest and LegX Fig 1, respectively.The results compared human efforts and muscle activities while undertaking different tasks with and without wearing these exoskeletons.The salient features of Eksovest and LegX exoskeletons are summarized below,

Figure 2 :
Figure 2: (a) drilling at overhead position and, (b) Wall drilling at virtual chair position Fig 4 show one case, each from the upper body (overhead drilling) and one from the lower body (virtual chair position), respectively.In below Figures, magenta line shows muscle activity without wearing exoskeleton and the green line represents muscle activity while wearing Eksovest at maximum support level (level 4).The black, blue and red color lines represents muscle activities at support Level 1, 2 and 3 of the Eksovest.Fig-3 and Fig-

Figure 3 :Figure 4 :
Figure 3: Overhead position drilling for three different drill machines, and for 4 different level of support of Eksovest