Hsiao-Wecksler and ISE colleagues improve crutch with flexible robotics

MechSE Professor Elizabeth Hsiao-Wecksler and Industrial and Enterprise Systems Engineering Professor Girish Krishnan, along with their graduate students, Chenzhang Xiao and Gaurav Singh, are using robotics to make crutches safer and more comfortable. They have created a new crutch that implements “flexible robotics” to reduce physical stress and improve mobility.

The new research improves upon the Lofstrand crutch, a model where each crutch attaches to the forearm with a plastic cuff and has a horizontal handle for the user to hold. However, using the traditional Loftstrand crutch can result in hyperextension from putting significant stress on the wrist, potentially leading to carpal tunnel syndrome and other wrist issues.

A soft robotic device has been developed by the team to prevent these painful problems. Instead of a rigid, plastic arm cuff to hold the crutch in place, they created a flexible sleeve made of soft pneumatic fiber-reinforced actuators that create a constricting motion using air pressure.

Singh explains that the sleeve, which is attached to the modified Lofstrand crutch, squeezes the user’s forearm with each step.

“It applies a constriction force around your forearm, and that transfers some of the load from the palm to the forearm, reducing the load on the wrist,” he said. By easing the stress put on the wrists, this new design could prevent hyperextension.

Soft and flexible robotics provide benefits over conventional “hard” robotics, according to Singh. The sleeve can conform to the shape of many forearms rather than needing specific designs for each individual, and users would have an easier time performing tasks involving wrist motion, such as turning a doorknob.

Krishnan cited inspiration from nature for the design of the sleeve. He provided examples such as a grapevine tendril or an octopus tentacle wrapping around a support. Similarly, the robotic sleeve features actuators that spiral around the forearm in a helical shape, providing a better grip.

To power the sleeve, Hsiao-Wecksler and Xiao designed a piston system implemented into the bottom of the crutch. The mechanism is activated when placed on the ground.

“When the piston pump is compressed during crutch loading, one-way valves inside the piston chamber will force the air into a Pneumatic Elastomeric Accumulator (PEA) inside the crutch shaft,” the team wrote for the Design of Medical Devices Conference in 2017. “That collected and stored pneumatic energy [is then] used to inflate the sleeve orthosis.”

Because the crutch captures the energy needed for the sleeve, Krishnan described the self-sufficient device as “energy-harvesting.”

The research is in its final stages, with human testing being done by a team at the University of Wisconsin-Milwaukee, but the project holds a greater meaning in the timeline of human-wearable technology, where little successful research has been conducted.

“About five to six years ago there was talk about soft flexible devices in augmenting human motion and giving additional support, but there were no functioning prototypes,” said Krishnan. “Today, the success of this project paves way for more clothing-like devices that can be worn and give support to different parts of the body. This is certainly a seminal work in showing that perhaps all these visions can come true.”