When Switches Can Act Proportionally

switchesFor new power wheelchair users, switch systems can be a wonderfully accessible introduction to independent mobility. The simplicity of a switch — which is either on or off — makes cause and effect easy to understand, and for that reason, switch systems are often the first driving systems deployed, especially for children who have never been independently mobile before.

But the switch’s simplicity can also be frustrating, because humans typically expect a greater result when we put in more effort. Don’t we keep pressing the down button over and over, and harder, if an elevator doesn’t materialize promptly?

So for switch-driving power chair users, if pushing a forward switch lightly makes the chair go, shouldn’t pressing the switch harder make the chair go faster? If power chair users are unable to finesse a joystick, are they stuck with the black-and-white simplicity of switches?

Sunrise Medical’s new Cool Cube with Pro Spot proportional switches offers a newly nuanced option.

Introducing Proportional Switches

Mark Greig, VP of Research & Development for Sunrise Medical, calls Pro Spot switches the first proportional ones on the market. “They look a lot like a switch,” Greig said. “They behave like a switch in some regards. But they’ve got technology that makes them proportional. The more you push down, the response is proportional to that input. So if I want to go faster in a forward direction, I get my forward switch and push down harder, and that means that my chair will now go faster in a forward direction. Likewise with left, right and reverse. Although they look like switches, they behave more like a forward joystick, a right joystick, a left joystick or a reverse joystick.”

Angie Kiger, M.Ed., CTRS, ATP, SMS, is Sunrise’s Clinical Strategy & Education Manager. “Historically when you teach proportional versus non-proportional, you use a gas pedal versus a light switch analogy,” Kiger said. “Now I feel like we’ve got a bit of a dimmer switch when it comes to switches, as opposed to you’re either completely off or you’re wide open with the speed. You can grade up to it with acceleration programming, but once you get to top speed, no matter how hard or soft you’re pushing it, that’s all you get. What I like about having a dimmer switch is that I can slowly ramp up that speed.”

Kiger used a hypothetical example of a user with cerebral palsy who understands the nuances of a joystick, but lacks the motor skills to consistently maneuver one. “You’ve got somebody with a number of contractures, and it’s not unusual to use multiple switch sites, whether it’s down by their knees or up at their head,” she said. “But for some of the switch sites, they may be able to control how hard or how soft they actually push.”

While Pro Spot is proportional, the Cool Cube adapter — which Pro Spot plugs into — also accepts traditional switches. So Cool Cube could accept a Pro Spot proportional switch for one switch site, and a traditional switch at a different site.

“I think it’s really going to open a door,” Kiger said. “Potentially, it could decrease the learned helplessness that some kids get where they [are tired of] going one speed and want another challenge, but physically, they just can’t use a proportional joystick. Now, you don’t have to have the ability to do proportional in all four directions. You can have one switch at the back of the head, one at the right hand, one at the right knee — two of them can be proportional, and one of them is not. It just depends on what movement they have.”

Two-Phase Activation for a Proportional Response

The Pro Spot proportional switch also functions with varying amounts of force applied to it.

“The Pro Spot is designed as a two-phase activation,” Greig said. “For the first part, all you have to do is come close to the switch, and it will activate because there’s a proximity sensor in there. All it has to do is sense that you’re close to the switch, and the switch will activate. That accounts for about the first 40 percent of the switch activation. From there, as you start to touch the switch, it becomes proportional. Its maximum force, when you want to go full speed and fully activate the proportionality of that switch, takes about 250 grams. But you get proportionality right from the point that you’re touching the switch circuits, right up to the point that you achieve that full 250 grams.

“Even if the user couldn’t put a full 250 grams on the switch — they could, say, put only half — you still get a level of proportionality to it. You would customize the wheelchair settings to achieve the speed that the person wants at, say, 125 grams.”

Kiger expects the Pro Spot and Cool Cube to bridge the sizable gap that currently exists between traditional switches and fully proportional driving systems.

“Some folks stay on switches for a long time, and maybe they could have gotten over to a joystick sooner,” she said. “But it’s such a drastic gap. With switches, it’s a light switch on and off; with a joystick, it’s a gas pedal. There’s a pretty big learning curve there. If you’re able to add in just one direction that goes proportional, that will help you bridge that gap to hopefully get to a higher level faster.”

“The biggest difference in using the Pro Spot and the Cool Cube is in turns,” Greig said. “Kids [driving] forward, especially when they’re starting out, are not going too fast. But turns are very difficult with just a switch because you’re either doing a full, fast turn or not. With the Pro Spot and the Cool Cube, you can grade the amount of turn. If you were driving a car, with a switch I’ve either got the steering wheel fully turned or I have it going exactly straight. With the Pro Spot, I can grade that steering wheel, turn it slightly, do minor turns and be able to navigate that chair much more easily than I can with a switch.”

To make teaching and learning easier for clients of any age, Pro Spots are available in five different colors, and Cool Cube can produce (or mute) a different audible tone for each switch as it’s engaged.

Kiger even suggested that Pro Spot and Cool Cube could help a chair user maintain proportional driving longer, citing kids with Duchenne muscular dystrophy as an example.

“They don’t want to change to switches because they lose that ability to drive fast,” she said of Duchenne clients. “Teenage boys want to drive fast, but with switches, it’s either on or off. [Cool Cube and Pro Spot] could take them in the opposite direction. For somebody who has a degenerative condition, this has the ability to have proportionality longer than if they were using a standard joystick.”

This article originally appeared in the August 2019 issue of Mobility Management.

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