My colleagues and I used an economics tool to measure the costs and benefits of wearing an exoskeleton, and we found that it provided a modest average benefit of $3.40 per hour when the combined effects of support and device weight were considered. This modest value contrasts with the value of support alone, which was much higher at $19.80 per hour. These values were derived using our novel approach that subtracts the values of costs and benefits.
Exoskeletons are mechanical devices that people can wear to increase their performance or efficiency. They can be used to assist with manual labor or to support rehabilitation after injury. Our approach brings the user into the evaluation process, which allows the diverse experiences of people using exoskeletons to be taken into account.
Perceptions matter. Users must want exoskeletons in their lives if the technology is to realize its potential to support mobility, endurance, and safety. And that means users must perceive the benefits, and those benefits must outweigh the costs of wearing the exoskeleton, including additional discomfort, weight, or noise.
To measure user perceptions, we examined the economic value of wearing an exoskeleton, measured in U.S. dollars. To determine these dollar values, we asked people how much money it would take them to walk uphill on a treadmill for two minutes. The two-minute bouts were repeated in succession for about 30 minutes. We also repeated these trials with users who wore the exoskeleton while it was unpowered and did not wear the exoskeleton. By comparing the costs between conditions, our approach provides a basis for evaluating the economic value of the entire exoskeleton, its support, and the cost of the additional weight.
To ensure that participants provide a truthful estimate of their cost for a two-minute walk - and not to maximize their profit - we used a special type of auction that ensures honest valuations, called a Vickrey auction. In a seller's Vickrey auction, the winning bidder gets the lowest bid, but receives the second-lowest bid. It is often used to measure the value of abstract concepts because the Vickrey auction breaks the link between the auction winner and his bid and removes incentives to underbid or overbid.
Today, many ways to evaluate exoskeletons focus on hard-to-access data, such as the number of calories burned and complex motion analyses. More subjective metrics, such as user preferences for exoskeleton support, are difficult to standardize and are only recently gaining acceptance.Exoskeletons are used in construction and manufacturing.
Why this is important
Our study underscores the substantial potential benefit of exoskeletal support. This is despite the fact that most of the value is offset by the cost of the additional weight. By measuring this user experience, researchers and developers can refine exoskeletons for user perception. For example, these results highlight the need to develop lighter and more compact exoskeletons.
Our method for determining economic value is intuitive because the public is more likely to understand the value of dollars than energy-related biomechanical metrics such as watts or joules. This approach also does not require expensive specialized equipment like that needed to measure metabolic rate or how much energy a person would burn while wearing an exoskeleton.
This technique can be used to measure the value of not only different types of exoskeletal support, but also a wide range of technologies, activities, and experimental conditions, and provides a useful alternative to the standard approach to metabolic rate assessment.
What comes next
With this data and approach, we plan to develop exoskeletons that reduce the cost of carrying the extra weight of the device. We also plan to explore better control systems to increase the economic benefit.
In our study, we found that the benefits and costs varied widely from person to person. Some people reported a negative overall value. We want to explore these differences to find out why people have such different perceptions. This may help overcome major hurdles to adoption of this technology.
