Sometime in early 2013, a few of the engineers at Fiskars—maker of the world’s most ubiquitous orange scissors in addition to gardening and pruning gear—noticed a discrepancy. “We always do our testing [for heavy hand tools] based on a machine cutting a branch,” says Dan Cunningham, a senior engineer at the company. Yet, “we humans are not machines. So we thought, well, how far away are we?”
The industrial machines at Fiskars test loppers, shears, and pruners, by applying a fixed, steady amount of pressure on saplings until they snap. The human arm maneuvers differently than a couple pieces of metal. We have joints, bones, and varying levels of strength. Cunningham and the engineers at Fiskars wanted to figure out how to design their tools for the latter, which is how they ended up launching the PowerGear2 line of tools.
Old Tools, New Data
The answer to Cunningham’s question—how different is the human arm from a machine’s—lies in data, all of which is pretty new. Tools like loppers are practically primitive (“In the 1700s you can find pictures of people using them,” Cunningham says, but earlier versions surely existed in some form.) but it wasn’t until recently that the makers of said tools gained nuanced insight into what happens when people use them.
There’s a team at Georgia Tech Institute that studies this specific brand of ergonomics. The Arthritis Foundation has a stamp of approval they issue to products that meet standards decided upon by research conducted by that Georgia Tech team, so that’s where Fiskars took its human-versus-machine problem. All of Fiskars’ products have earned the approval stamp in the past, but Cunningham says with this line they “wanted to go even further, and really tweak it.”
The team at Georgia Tech started taking measurements, by asking over 100 test subjects to squeeze shearing tool handles outfitted with sensors that measure force. Subjects squeeze for five seconds, stop then squeeze again with arms held in a new positions. With all that, the researchers compiled what Cunningham calls “some complicated math and models of people over 50, under 50, male, female. It’s given us a model of how strong a person is as they’re moving.” In essence, the Fiskars team was doing what user-centric designers have been doing for years. This time, they have the benefit of sensor-powered, ultra-precise measurements.
Armed with those models, the Fiskars team reengineered the gear at the crux of all the heavy hand tools. “Typically a gear is two circles that spin around,” Cunningham says. “With circular gears, that’s saying the mechanical advantage is constant.” But what the Georgia Tech models showed—and what the Fiskars engineered knew through practice—is that when a person cuts a branch it’s easy at first, then much more difficult, and then easier again right before it snaps.
To deliver a mechanical boost in the middle, the engineers created a non-circular gear that adjusts the ratio of force applied during a snip. Cunningham compares it to the change that clicks in when you change bike gears, only it happens automatically here. The subtle design decision “allows us to tune the power that the lopper is providing,” Cunningham says. “That tuned curve feels very smooth all the way through.”
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