When engineer Mark Doyle started to put together plans for an exoskeleton to support surgeons in 2012, he wanted to develop a lightweight product that they could wear comfortably for extended periods of time. Doyle and his team at Levitate Technologies (San Diego, CA) had to carefully choose the products that would be included in the device because any additional ounces could have made the device uncomfortable and unwieldy, thus ending development before it entered production.

Levitate Technologies manufactures The Airframe, a lightweight exoskeleton that supports the upper extremities of those exposed to repetitive arm motions and/or stationary arm elevation.

“Asking human beings to wear a metallic frame and do their jobs is not an easy task,’' said Joseph Zawaideh, Vice President of Marketing and Business Development for Levitate. “We needed something that was lightweight, low-profile, and could adjust to the user's movement comfortably and without interference into the workspace. It required attention to detail on every screw and every bolt. Our mindset was ‘if you don't need it, don't add it.’"

The Airframe™ was introduced to the commercial market in 2016. While it worked for surgeons, other industries quickly learned of its availability, and Levitate, seeing an opportunity for significant business growth, switched its marketing focus to manufacturing clients. Designed similarly to a backpack, The Airframe can be adjusted to almost any body size with an adjustable frame and straps. The exoskeleton supports the upper extremities of professionals and skilled trade workers who are exposed to repetitive arm motions and/or stationary arm elevation.

Doyle and his team of engineers could have used steel bushings in the application. Instead, they chose engineered plastic bearings manufactured by Germany-based igus. The company, which has a facility in Rhode Island, manufactures an assortment of engineered plastic products that are self-lubricating, lightweight, and maintenance-free. All of those properties, and more, appealed to Doyle in the design of The Airframe. One unit contains 32 igus plastic bushings. “There are a lot of exoskeletons on the market,” Zawaideh said. “This is the lightest one out there. It's light enough that workers can wear it all day.”

Reduced Weight

The key to the light weight of The Airframe is the bushings. Steel bearings are always much heavier than plastic — as much as six times the weight. In an application such as the exoskeleton, the engineered plastic bushings proved essential in keeping weight to a minimum.

The bushing used most extensively in The Airframe is the iglide® G300, which has a density of 1.46 g/cm3, a PV value of 12,000, and a tensile strength of 30,460 at 68°. Typical applications include medium to high loads, medium sliding speeds, and medium temperatures. “It's a general-purpose bearing and has a good mix of wear, low friction, and reasonable cost,’' Doyle said.

Doyle chose the iglide® T500 and Z bushings to stand up to higher temperatures in the exoskeleton. The T500 bushing, with a density of 1.44 g/cm3, is temperature-resistant to 482° and has a tensile strength of 24,660 at 68 °F. The bushing has very low moisture absorption and universal resistance to chemicals. The Z bushing (density 1.40 g/cm3) is used in applications that require high dynamic loads and wear resistance. The bearings are suitable to temperatures up to 482°, and have compressive strength of 9,425 psi. The Z series also offers a 348,1000 modulus of elasticity.

Doyle also selected the iglide® M250 bushing for the exoskeleton — it has several important qualities, especially relating to manufacturing. Each unit weighs just 1.14/g/cm3, but can absorb dirt and dampen vibration, which reduces noise and results in an extended life for The Airframe.

The Lightweight Plastics Trend

The use of plastic components in the design of The Airframe is consistent with growing trends in production of plastics. In 2016, the global production of plastics reached 335 million metric tons. The global plastics market is expected to reach about $654 billion by 2020, according to a 2015 study by Grand View Research, Inc.

The key to the light weight of The Airframe is self-lubricating, maintenance-free, engineered plastic bushings manufactured by igus.

Weight reduction is a primary driver in the trend toward plastic components rather than steel and other metals. The automobile industry embraced the plastics trend for years to reduce the weight of vehicles. Now, many engineers and designers are seeking ways to use plastics in their projects, primarily to reduce weight and improve durability. Many construction projects are also now using plastic building components to replace wood, steel, and concrete. Companies are also using plastics to create structural components for buildings, bridges, and railroads.

Plastics have been particularly widespread in automobile manufacturing. In 2014, plastic/polymer composites totaling an average of $430 per vehicle were used in light vehicles in North America.

The Airframe is used in many manufacturing plants, including automobile assembly, aerospace and airplane assembly, and shipbuilding.

Making the Core Secure

The Airframe transfers the weight of the arms from the shoulders, neck, and upper back to the core through pads that rest on the outside of the hips, thus relieving muscle and joint strain. By transferring upper extremity load, the device helps sustain high-quality performance, protects health, and improves overall work conditions.

The unit is flexible and scalable to individuals of any size, slips on and off easily, and moves seamlessly with the wearer without limiting dexterity or intruding upon the workspace. The mechanical support system progressively activates as the arm is raised, and gradually releases as the arm is lowered to provide the right level of support at each point in the movement. The Airframe lowers exertion levels up to 80 percent.

The Airframe was initially designed for surgeons who suffered from fatigue and pain after long surgeries.

“The difference between The Airframe and other exoskeletons now on the market is that it's very lightweight and extremely comfortable,” Doyle said. “It makes motion very natural.” The Airframe is now being used in manufacturing plants in aerospace and airplane assembly, heavy machinery, shipbuilding, agriculture, paper, and chemical industries. Even the U.S. Navy is using The Airframe for maintenance work.

Tests have confirmed the exoskeleton's effectiveness. Over a five-day period at a manufacturing facility in which welders and painters wore The Airframe, productivity and quality spiked. In dynamic tasks where painters wore The Airframe, the amount they were able to paint increased 53 percent before their muscles became fatigued. Quality improved as well, as the exoskeleton helped subjects maintain a steady hand while performing tasks. Tests in static tasks in evaluating welders saw an 86 percent increase in productivity and an increase in quality. Welders were able to complete successful welds over a much longer period while wearing The Airframe, according to statistics provided by Levitate.

The Airframe might also help workers stay healthy. A safety and ergonomic risk assessment at one auto manufacturer found that The Airframe reduced physical work stress by 20 percent. “The benefits of this device have been incredible,” said Terry Butler, former Director of Environmental Health & Safety at the Vermeer Corporation, a manufacturer of industrial and agricultural equipment in Iowa. “The team members that have used this tool are more than happy to use it, and have seen more prolonged work activities without feeling fatigued by the end of their shift.”

This article was written by Thomas Renner for igus, East Providence, RI. For more information, visit here.