Exoskeletons – wearable robotic structures that can increase human strength – are familiar to fans of sci-fi and superhero films. Sigourney Weaver encased in a cargo handling frame walloping an extra-terrestrial was a standout moment in the film Aliens. But on a smaller scale such devices could soon be put to more plausible use in the fight against work-related musculoskeletal disorders (MSDs).
Most of the development of exoskeletons for "real world" applications in the past 20 years has focused on medical rehabilitation and the military.
"The wearable industrial exoskeleton is a bit newer," says Michiel de Looze, professor in production ergonomics at Vrije Universiteit Amsterdam and senior project manager at TNO, a Netherlands-based research organisation. "The idea is to give support – to take away the risks of too much load on the human body – which is in contrast to many military exoskeletons where the idea is to produce some kind of superhuman who can do more than is natural."
An industrial exoskeleton takes over muscle functions, so the muscles do not have to work as hard as they otherwise would. In reducing the internal loading on the body's structures, the exoskeleton cuts the risk of injury. Like personal protective equipment, exoskeletons are low in the hierarchy of controls, behind redesigning working environments and processes to eliminate or mitigate risk. But where residual risks remain, evidence suggests exoskeletons could reduce the risk of MSDs on some tasks.
Early work on industrial exoskeletons centred on the kind of large, full-body frames that protected Sigourney Weaver from all those rows of alien teeth.
"It soon became clear that those types of exoskeleton would never be acceptable or usable at work," says de Looze. "So in the past two to three years, a lot has been happening – in the US, Europe, Japan and [South] Korea – and, in particular, there have been more efforts to make exoskeletons that are specific to areas of the body."
Ask the right questions
In 2016, a US National Institute for Occupational Safety and Health blog post calling for stakeholder input on exoskeletons noted that some of the devices being developed appear to have "benefits in some specific industry applications for reducing injury risk factors".
However, the post cautioned that "their occupational use should be evaluated for their potential benefits and potential competing risks before widespread workplace adoption".
It went on to identify a set of key questions to address:
Do devices create load transference between musculoskeletal regions that still put workers at risk?
Does the added weight of some devices increase energy expenditure/metabolic workload?
Do devices affect user comfort?
Do devices affect the wearers' balance by changing their centre of mass or increasing the rate of fatigue in the lower extremity muscles?
Do some devices affect patterns of muscle use or change normal joint mechanics, putting workers at risk while using the devices or when not wearing them in their non-work activities?
Do devices create a potential "false sense of security" for handling heavy loads?
If exoskeletons prove to be effective, how do we establish workplace practices that appropriately increase acceptable lifting or handling weight limits while maintaining safe physical loads for the worker's augmented capacity?
Herman van der Kooij, professor of biomechatronics and rehabilitation technology at the University of Twente in the Netherlands, adds: "Whole-body exoskeletons can support any body motion and different joints but in general they are bulky and heavy." The body-part specific exoskeletons are lighter and more user-friendly, so they are more likely to fit well into the workplace and be accepted by workers and employers.
"Exoskeletons for the back, arms and legs are the most interesting for OSH professionals," says de Looze. "Economies are generally doing well and people are looking at new technologies and robots, so quite a lot of companies where workers are exposed to heavy loads and where it's not feasible to automate or find alternative solutions are interested."
The ageing workforce and skills shortages in traditional sectors such as engineering and construction are other driving factors.
Exoskeletons divide into two main types: active and passive. Active models include one or more actuators (such as electrical motors) to augment the body's power.
"These are the real wearable robots," de Looze says. "You measure the muscle function or kinetics of a person -- the movement -- and, based on that, the motors in the exoskeleton are driven and controlled to give exactly the right power at the right time."
Passive systems, by contrast, have no external power source; instead, they use materials, springs or dampers that store energy from human movements and release it when needed.
Most of the exoskeletons in commercial production are body-part specific and passive. In Europe, examples include SkelEx, which focuses on the upper body and arms, and Laevo, which targets the back, allowing the wearer to work in a bent-forward posture longer than they would manage unaided or to carry out repetitive lifting or bending.
US examples include Lockheed Martin's FORTIS, which assists operators using heavy tools, and EksoVest (trialled in partnership with Ford), another upper body exoskeleton that elevates and supports a worker's arms to help them with tasks at chest height and above.
"We mainly sell into the automotive sector: Audi, Daimler, FCA (Fiat Chrysler Automobiles) and many others," says Boudewijn Wisse, CEO of Laevo. "The other main sector group is logistics and warehousing where order picking is done. We also get enquiries from construction, healthcare and agriculture, which can all be very demanding on the back."
De Looze emphasises the importance of considering the individual, the task and work environment. "Then, based on that information, you can select, or design, the right exoskeleton." Tailoring is crucial for effectiveness and acceptability. "There are benefits but there can also be disadvantages," he adds. "It might limit the range or speed of motion, or the user might experience discomfort. What is right will vary according to the work environment, so clearly the process must start in the workplace with a good analysis of the task and risks."
Where's the evidence?
A 2015 literature review by de Looze and colleagues concluded that exoskeletons (both passive and active) "have the potential to considerably reduce the underlying factors associated with work-related musculoskeletal injury". The papers reviewed covered information on 26 exoskeletons, of which 19 were active and seven passive. For 13 models, the effect on physical loading had been evaluated.
These analyses showed that the passive exoskeletons, all of which aimed to support the lower back, resulted in reductions of between 10% and 40% in back muscle activity during dynamic lifting and static holding. The active exoskeletons targeted the lower body, trunk and upper body regions and reported muscle activity reductions up to 80%.
According to de Looze, the evidence so far suggests that the passive exoskeletons now coming to market could be effective in supporting workers in tasks where the posture is relatively static -- working with arms above the head or bending forward. "But if the movement becomes more dynamic so that larger movements are made it becomes more questionable," he warns.
Actuated exoskeletons have the potential to be more effective because they are more adaptive to job tasks and to the user. They can also work with dynamic movements. "We can build in motors and the right control mechanisms that provide extra power exactly at the time you need it," says de Looze. But though the long-term potential of active exoskeletons may be higher, they are further away from widespread adoption in industrial settings because of problems with worker acceptability and usability.
Comfort and weight
"The benefits of exoskeletons must outweigh the costs or effort asked from the user or purchaser," says Wisse. "The end user is of course wearing something, so they can feel that and they have to get used to that; that is a cost for them."
For van der Kooij, wearer comfort is crucial: "It's very important that the exoskeleton fits well and applies forces at the right points. Of course people are only going to wear it if it is comfortable or it doesn't slow them down or impede the task, and that can be quite a challenge."
The size of the structure remains a significant barrier for some workplaces and tasks. Aerospace manufacturer Airbus, for example, is currently testing exoskeletons. In this context, it is critical not to damage the aircraft or parts during the production process. "If you touch something, you can't risk any damage, so size is a big issue, as is weight," says van der Kooij.
Laevo end users are mainly operators, and include automotive workers who have to bend into cars for assembly work or to lay carpet.
"These are the kinds of applications where you have many repetitive back loadings," says Wisse. "It's the same in warehouses, where bending can't be solved in any other way. There must be a frequent load otherwise such a solution is not sensible or useful."
He adds: "When a customer first approaches us, we always look at whether it is sensible to use the exoskeleton in that context or workplace. For example, we ask whether they could do simple workplace adjustments to remove the risk. But in reality there are many situations where there is no option to change the environment so the work gets lighter."
The EU-funded Robo-Mate project ran from 2013 to 2016 and involved 12 partners from seven countries, including end users, industrial robotics technology developers and ergonomics research groups. The project aimed to develop a user-friendly, intelligent and lightweight wearable exoskeleton to assist manual handling.
The resulting Robo-Mate involves three different modules that can be combined or used as a standalone support technology. This allows users to select one module or combination of modules best suited to a task. The modules include one trunk and two upper body exoskeletons (passive arms and active arms). The trunk module provides a torque at the hip using motors to support the upper body during bending and lifting.
In 2016, tests in industrial settings and the laboratory found that, although the modules were effective and efficient, usability needed improving. For the trunk module, during dynamic lifting tasks, laboratory test subjects reported reduced physical exertion for the trunk and the legs. But for both dynamic lifting and static bending, test subjects did not reach an acceptable usability score.
Passive arms were effective at reducing perceived exertion for arms, but slightly increased exertion for legs and trunk. Usability scores for the passive arms were significantly higher than for the trunk module.
In company tests, workers preferred the trunk module because it reduced physical effort and decreased task duration. It also provided the best support for bending and lifting tasks and did not restrict movements.
To address the various comfort, size and weight issues associated with exoskeletons, many are bespoke for the individual wearer. "It needs to be very close to the body and if you make it very adjustable – which would be most convenient – it tends to get bigger," says Wisse. But custom-made exoskeletons can present scalability challenges for the customer. "We have now developed another device that is modular," Wisse says. "The customer can adjust the sizing itself by changing the size-sensitive parts, while still keeping the size down."
One of the most common questions de Looze is asked is whether people might lose muscle strength if they work with an exoskeleton over long periods. "They worry that if you wear a device at work, you can become less fit because the exoskeleton does the work and you lose muscle strength. My answer is that the exoskeleton never takes over all the work; it might be that 20% of the power you might have to generate is now provided by the exoskeleton, but 80% of it is still generated yourself, so there is really no need to worry."
The issue of muscle strength loss is also regularly raised in enquiries to Laevo. Wisse believes this is mainly due to problems with back belts or braces. "It's known that if you brace the back in that way you don't use your own muscles to some extent." But exoskeletons only reduce the amount of load, which is already too high. "It brings the load back from too high to acceptable. But you still need to do work yourself."
A more important consideration, according to de Looze, is the risk of shifting stress from one part of the body to another. "That is really something to bear in mind," he says. "With a back-support exoskeleton, it can become more difficult to remain in a balanced position, which may result in extra leg activity. If you wear an arm support exoskeleton, it might result in a shift from shoulder to back. So whether you are evaluating effects in the lab or in the field, it's very important to take into account potential negative effects of shifts in biomechanical loads."
Another obvious question is whether widespread adoption of exoskeletons could lead to employers putting pressure on workers to lift and bend more, deal with heavier loads or work longer at a given task. This is something unions and regulators will have to watch, and which might eventually prompt new or updated guidance or industry standards.
Van der Kooij does not see it as a significant risk, however. "In fact, I think it's the opposite," he says. "Exoskeletons will be used to prevent injuries and sickness. We have an ageing workforce and people are doing physical tasks into their seventies. These are additional aids that people can use throughout their career, meaning they have less ill health when they are working and after they retire."
Further into the future, the next generation of exoskeletons is likely to take the form of flexible exosuits rather than rigid-framed skeletons. "With new materials and technologies, including 3D printing techniques, you can make a suit that perfectly covers the body," says de Looze. These suits can integrate sensors as well as actuators, with everything kept close to the body. "Technologies are moving forward, and sensors and actuators are becoming smaller all the time," he adds.
Exosuits could incorporate passive systems -- the fibres may stretch to give support -- but whenever further support is needed the device could contain actuators, making it active as well. "A sensor could identify the need and then the actuators could give extra power to the fibres in the right position to support the body," says de Looze.
Another interesting prospect in the long term is improvement in the interface between the exoskeleton and the wearer. "Just as you don't think about which muscle you activate, you might not in future have to think about how the exoskeleton is being powered," says van der Kooij. "There could be some kind of symbiotic relationship between your brain and muscles and the exoskeleton, producing an intuitive and subconscious control of the exoskeleton. Instead of activating your muscles, you effectively activate the exoskeleton directly."
In the right context, exoskeletons seem to have the potential to tackle the underlying factors associated with work-related MSDs. But the research so far has largely been laboratory based and the effects of long-term use are yet to be assessed. In the US, the National Institute for Occupational Safety and Health (see box opposite) has called for more information on exoskeletons in practice. The feedback from large companies already trialling these devices, together with ongoing technological efforts to tackle the key comfort and weight issues, will be critical to whether the exoskeleton moves out of the realms of science fiction to become an everyday workplace tool.