More efficient motion

The earliest accounts of the manual wheelchair exist in documents from the sixth century. Surprisingly, the model used back then doesn’t look too much different than the one that wheelchair-bound individuals use today. For Jim Maerzke, president of Kenosha-based Procubed LLC, that is a concern and one he hopes to correct with the company’s Linear to Rotary Motion (LRM) conversion mechanism.

Procubed LLC

Innovation: Linear to Rotary Motion conversion technology


“The wheelchair is in need of an update,” Maerzke said. “Because of the motion needed to propel a traditional manual wheelchair, users often end up hurting themselves or suffering from severe shoulder pain. Our technology can help them, and also has many other real-world implications.”

Maerzke, who has a background in engineering, says he took a look at the mechanical equation for a traditional “capstan” device, also known as a “belt-friction” equation, and modified it so that an input of linear motion produced an output of rotational motion in a single direction.

“We came up with the current version of the patented technology after years of refinement,” Maerzke said.

He started thinking about the problem in a college course that he took in 1983 at the University of Wisconsin-Parkside.

“I had a very intelligent engineering professor who challenged us in a group to come up with a more efficient capstan system,” Maerzke said. “I guess I’ve been thinking about it ever since.”

Procubed is in the process of producing a working wheelchair prototype using the LRM technology. The chair would look similar to a traditional manual wheelchair, but it would have two handles in front that the user would push and pull, in and out in a linear, back-and-forth fashion to make the wheelchair go.

The LRM mechanism would convert that linear motion of the handles into rotational motion used to power the wheels on the wheelchair, Maerzke said.

“Traditional ‘crank’ systems are terribly inefficient,” Maerzke said. “The LRM system converts linear motion into rotational motion, which is going to be a much more efficient process.”

The design is intended to eliminate the shoulder pain and injuries suffered by people who use manual wheelchairs, he said.

Users won’t need gears to change speeds with the LRM mechanism and will most likely be able to utilize levers to switch the direction of the rotational motion.

Maerzke and his engineering partner, Chris Baugher are working with students in the UW-Parkside graphic design program to come up with a prototype that not only changes the way people use a wheelchair but also looks, “industrial and cool,” Maerzke said.

The company hopes to have a tested, working prototype by June of next year, and has already had initial discussions with the Veterans Association about purchasing the new model, Maerzke said.

According to Maerzke, the new model would sell for approximately $2,000, about halfway between the cost of a traditional manual wheelchair ($500-$1000) and a motorized one ($3000-$5000).

“We knew that in order to really improve on the existing model we had to make sure the price point was affordable too,” Maerzke said.

Once the prototype for the wheelchair is completed, Maerzke hopes the company can apply the technology to other devices like high-speed bicycles, and engine and transmission combinations.

“If you take a look at a standard motor, or even a bicycle, the most torque is generated when the piston or crank is perpendicular. Half-way through the cycle the pressure has already diminished from the force originally applied,” Maerzke said. “The LRM would be much more efficient and allow for more constant torque. We’re excited to be able to test the technology in a variety of different arenas.”

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