One Very Smart Chair
Category: Furniture, Material Tech
Tags: architecture, carbon fiber, carbon fibre, CFRP, composite, composites, digital fabrication, fiber reinforced polymer, FRP, furniture, furniture design, Greg Lynn, Nike
← 5 Chairs
How to Make a Building Sexy →
We recently had the opportunity to visit Greg Lynn's studio and talk about his work with composites. Lynn, the architect and designer sometimes described as the originator of "blobitecture," is one of the foremost practitioners and explorers in the use of composites in architecture and related design projects. He is a forward thinker with hands-on experience, and is so widely renowned in these efforts that fascinating projects come to him.
His company, Greg Lynn Form, just had a very unusual chair on display at the Milan furniture fair. Created for Nike, the sports equipment powerhouse, this "intelligent microclimate chair" is designed to help an athlete maintain a peak body state during the time he or she is off the court or the field during a game.
The technology that was built into the chair to accomplish this goal is cutting edge. However, the chair itself is perhaps an even more significant development in the use of composites, because it is both rigid and flexible. It is made of an extremely thin form of carbon fiber, with two different resins that transition from one to the other in different areas of the chair, in a single composite sheet.
"About five years ago," recalled Lynn, "we made hanging chair, kind of like a hammock. It would have like a shell shape instead of looking like a hanging piece of fabric, it actually had a shape, but when you would sit in it, it would go into tension. So it was a compressive structure that turned into a tension structure when you loaded it."
It was made of an unusual epoxy resin that remains flexible after it is cured, unlike the conventional epoxy resins used for many rigid composite structures. The difference between "rigid" and "flexible" is not really a different nature of material, just a matter of degree. Rigid epoxy is not completely rigid: when bent, it might have a maximum elongation of 15% before it snaps. The flexible epoxy has very high elongation, orders of magnitude higher. It can be molded into a shape and it will hold when at rest, but will stretch when loaded. "They use it for sails," said Lynn, who has also worked in designing high-performance racing sailboats. "You can form it into a sail, but the resin is so flexible you can roll it up it doesn't crack."
The carbon fiber used for that hanging chair is made by North Sails. Lynn described it as carbon fiber tow that has been spread and flattened into an ultra-thin tape. (Carbon fiber is often produced as tow, a 'thread' that is a bundle of miniscule carbon fiber filaments. 3K tow, for example, is a bundle of approximately 3000 filaments, and in its usual 'gathered' state, it measures about 6/1000 inch.) The North Sails material is even thinner than usual carbon fiber tow, making it extremely flexible, but still very high in tensile strength.
"The hanging chair was great," exclaimed Lynn. "It weighed less than a pound. Those are at the Art Institute of Chicago. We had one sitting here [in Los Angeles] at Joel Chen's gallery. The Nike design leadership came through and saw it, and we started talking about what we could do with that material."
"John Hoke at Nike asked, can we take this flexible carbon fiber and come up with a lightweight piece of furniture that could have a lot of the intel? He gave us the example of LeBron James. I think it was three playoffs ago, San Antonio knew that if they got him overheated, he would go out in the third and fourth quarter. So they allegedly heated up the arena… I don't know if that's true or not. But three games out of four, LeBron went out in the 3rd or 4th quarter because he overheated."
"So we came up with this carbon fiber shell that would measure your body temperature and moisture loss. Then, with these little Peltier chips that we put into the shell, you could heat and cool the athlete selectively."
The chair is a kind of recliner, a diagonally-angled carbon fiber sheet with a human form scooped out of it. The shell is rigid around the perimeter, supporting the weight of a sample 260 lb. athlete. (It was molded based on a body-scan of an actual, unnamed, athlete.) The center area, where the sitter is supported, is the flexible composite.
"The idea was to get as much of an athlete's body in contact with the carbon as possible," explains Lynn, "because it's all about surface contact." The flexible composite, when loaded, conforms closely to the sitter's back, butt, and legs.
The intelligence consists in the chair getting feedback about the state of the person sitting in it, and using that data to adjust the person's body temperature selectively. The chair has heat sensors embedded in the composite. The entire chair also sits on three load sensors that monitor weight. Changes in weight can be used to infer moisture loss, and that data can tell the athlete when and how much to rehydrate.
Adjusting the sitter's body temperature i accomplished with clusters of Peltier chips embedded at key locations to either heat or cool the sitter selectively. Peltier chips are small, flat squares with a metal plate on each side and two wires coming out of the edge. They have the unusual property that, when electrified, one side gets hot and the other side gets cold. There are 76 Peltier chips embedded in the chair. 12 are for heating, 64 are for cooling. There is also an air diffuser running around the perimeter of the shell. The diffuser was 3-D printed separately and then attached.
"We thought you wanted to just cool the whole thing down," recalls Lynn. Then they talked to Nike's biologist, and found out that cold and hot must be applied to the right places. "There's a lot of blood vessels and stuff on your spine, but not a lot of muscle groups that will cramp up. If you cool down the spine and have the shoulders be cool but not too cold, you can bring down somebody's core temperature in a minute, two minutes." There is a long cluster of Peltier chips that runs down the spine area of the chair, and all those chips are used for cooling.
"At the calves and thighs you want to actually give heat." Lynn continues. "While you're bringing somebody's body temperature down, you want to heat up their muscles, because even if you don't cool those muscles down, they'll involuntarily cramp."
The cooling aspect of the Peltier chips had a catch to it. The chips definitely get cold when the current is turned on but over time, if the hot side has no good way to dissipate its heat, it overcomes the cooling effect and the chip ceases to function. To overcome this, they added CNC-machined aluminum heat sinks to the underside of the chair to diffuse heat from the Peltier clusters. The Peltier cluster and heat sinks together added about 30 pounds to the chair, more technology than a person could comfortably wear, hence the need to create a chair for it.
The aluminum heat sinks were machined in Nike's extensive aluminum machine shop where they usually make molds for prototypes of shoe soles. Nike also 3-D printed the rigid perimeter air diffuser, and the flexible perimeters around the Peltier clusters that keep the sitter from feeling the hard edges of the chips.
While all the feedback and temperature control technology is very exciting, Lynn is more enthused about the composite chair itself. "The cool thing is the shell. It's a super thin shell that holds a 260 lb. athlete, and it just weighs a few pounds. In terms of a composite material, this is the coolest thing I ever been involved with, because it goes from hard to soft in one sheet."
"It's the first rigid-to-flexible carbon shell ever made," Lynn continues. "There was a material sample that Bill Pearson [of North Sails] had. He gave us a sample of a strip that had one resin system that was rigid at one end, and then ply-by-ply, it changed to a resin system that's flexible. But this is the first shell made this way."
Greg Lynn's associate, Sean Boyd, explained that the composite for the chair was done by laminating multiple layers of normal carbon fiber twill at the rigid perimeter areas, and then tapering down the laminate from eight layers to just two layers of the ultra-thin carbon fiber tape as it transitioned from one resin to the other towards the center of the shell. The two resins were compatible, and the entire piece was cured in one shot in the oven.
"Start to finish, four months at the most," recalls Lynn. "We spent two-and-a-half of those months just chatting. We played around with sensors and the heating and cooling and the air stuff. With the material, we didn't do a whole lot of R&D. We never really did a test. We just went straight to the final object with the material. We just assumed it would work and it worked, first shot."
The Nike chair is complete physically, but the intelligent aspects have not been fully implemented. For the Milan show, they just programmed a cycle of heating and cooling to demonstrate the technology. At the show, there's a thermal camera that's pointed at the chair, monitoring its temperature changes and displaying them on an iPad. The heat sensing and feedback aspects will be programmed into it soon, once it returns to the US.
Lynn envisions that in the long run, the composite rigid-and-flexible technology may evolve into built-in furniture that can be part of the walls, and in effect customize itself to the sitter.
As construction materials go, this composite that is both rigid and flexible is pretty much unprecedented. A while new kind of thinking will be needed to explore its full potential.
Images courtesy of Greg Lynn Form.