3D-Printed ANGELEGS Give the Miracle of Mobility

Sogang University Professor Kyoungchul Kong has used SOLIDWORKS to create a new exoskeleton technology called ANGELEGS.

Watching a wheel chair-bound person get up and walk has become the paragon of a miraculous event. Yet, thanks to modern advances in engineering, it’s becoming increasingly possible for this miracle to actually be realized as researchers develop new devices for assisting those with disabilities.

In fact, there’s an entire event dedicated to such devices, the Cybathlon, a world championship for athletes with disabilities using robotic devices. Among the groups competing at this year’s event in Switzerland was Team SG Mechatronics, which took home a medal in the Powered Exoskeleton Race for its WalkON device.

The mobility technology was developed by Sogang University Professor Kyoungchul Kong and his firm SG Robotics (formerly SG Mechatronics). Thanks to the researchers’ work on SOLIDWORKS, the WalkON is designed to give complete paraplegics the ability to walk without additional human assistance. Kong has since expanded his technology portfolio to include a device called ANGELEGS, which he aims to commercialize for those with limited mobility. ENGINEERING.com spoke with Kong to better understand the design process, as well as the impact he hopes to make with his devices.

Varying Degrees of Mobility

Complete paraplegics, such as those who have endured spinal cord injury, may be the greatest beneficiaries of exoskeleton devices such as the WalkON. With the WalkON, SG  aimed to provide paraplegics the ability to walk without assistance.

Cybathlon athlete Byeongwook Kim in his WalkON device. (Image courtesy of SG Robotics.)

Cybathlon athlete Byeongwook Kim in his WalkON device. (Image courtesy of SG Robotics.)

While promising, the WalkON and other exoskeleton robots fail to address some issues faced by paraplegic patients. For instance, involuntary oscillatory muscular contractions and joint contracture can make it difficult for complete paraplegics to wear an exoskeleton.

“Although quite a lot of wearable robots are being commercialized, most of them have been developed from the viewpoint of engineers,” Kong explained. “[T]he exoskeletons are definitely helpful for people with walking disabilities, but the problem is that the target user group is too narrow and specific. For instance, about 80 percentof the complete paraplegics due to spinal cord injury (SCI) suffer from osteoporosis, but therapists must be extremely careful to let such people wear the exoskeletons.”

Kong, then, began to tackle the mobility issues suffered by another population, those with partial impairments. Roughly one-fifth of the global population suffers from some sort of muscular weakness, while 1 percent rely on physical assistance due to neuromuscular diseases, injuries or old age. To help those with partial mobility regain independence and the ability to walk, Kong developed ANGELEGS.


Existing devices for those with partial mobility are still limited, according to Kong. Such issues as the direct application of electric sensors to the skin or excessive friction and resistance from the device as the patient walks prevent some commercially available products from being truly viable.

The ANGELEGS device was designed entirely in SOLIDWORKS. (Image courtesy of SOLIDWORKS.)

The ANGELEGS device was designed entirely in SOLIDWORKS. (Image courtesy of SOLIDWORKS.)

Kong has tried to eliminate these problems and more with ANGELEGS, a wearable robot designed to help the partially impaired to walk again. Made up of a robotic frame, four serieselastic actuators for the hips and knees, two flexible ankle joints, and a backpack with a computer and battery stowed inside, the ANGELEGS device is meant to be extremely light, ergonomic and easy on the eyes. You can see a patient with Guillian-Barret Syndrome walking with the system in the video below.

ANGELEGS relies on an “assistance as needed” philosophy, in which the robot generates assistive torque to the joints only when necessary. Otherwise, this “transparent actuation,” as Kong refers to it, provides little friction, allowing for minimal strain on the wearer.Additionally, ANGELEGS has a great many degrees of freedom, allowing for as natural and fluid motion as possible.

Transparent Actuation

Kong was able to achieve this concept of transparent actuation through the use of an adjustable pseudoresistance setting in the device. While there is no actual resistance from the various joint modules of the ANGELEGS, a spring deflection within a series elastic actuator in each module provides the feeling of increased or decreased weight for the wearer.

Specifications for the ANGELEGS robot. (Image courtesy of SG Robotics.)

Specifications for the ANGELEGS robot. (Image courtesy of SG Robotics.)

Kong explained, “As it does not generate resistive force by its Series Elastic Actuators, the provided assistive forces are very natural and precise. In addition, the Series Elastic Actuators enable ‘assistance as needed,’ which implies that the robot does not disturb the voluntary human motion when assistance is not needed, but that it powerfully assists when the human needs it.”

Wearers are able to adjust this so that they feel the need to exert more or less effort in order to push forward. Those with greater muscle control can work with less support and vice versa. Interestingly, each joint module, whether it’s the knee or the hip, can be adjusted in case the user is stronger or weaker in one area or another.

Different movements are programmed and an “Assistance Gain” panel allows for further refinement of the amount of assistance needed for a wearer. (Image courtesy of SG Robotics.)

Different movements are programmed and an “Assistance Gain” panel allows for further refinement of the amount of assistance needed for a wearer. (Image courtesy of SG Robotics.)

The device offers a variety of modes for helping the wearer to perform such tasks as sitting, standing, climbing stairs and ramps, and walking, all of which rely on predefined algorithms associated with the torque needed for each position. In the automatic assistance mode, however, this torque is generated in real time, detecting the angle at which the wearer wishes to move and then providing the necessary assistance.

This approach differs from existing exoskeletons that rely on electrical feedback from the wearer, predicting how much force the wearer is using and adjusting appropriately. By giving the user the power to determine how much assistance is needed, there’s no need for uncomfortable electrical sensors attached directly to the wearer’s skin.

It’s hard to believe, but ANGELEGS weighs only 10 kg altogether. The sensors for the robot are embedded within the frame and, because the actuators provide very little friction, the wearers can feel as though they’re wearing no device at all.

What’s It Take to Make an Exoskeleton

The original prototype for ANGELEGS was developed in 2011 and, as development has continued, Kong and his team have been able to make significant improvements. For instance, rather than use a CNC machine to cut metal parts from scratch, Kong 3D printed many of the structural components, allowing him to reduce the device’s total weight to less than 8 kg before the high-capacity lithium-ion battery is added. To further reduce the weight associated with wiring, ANGELEGS features a local communication network.

Throughout the process, Kong iterated the design of the robot with SOLIDWORKS software. Kong explained, “Both WalkON and ANGELEGS have been developed by SOLIDWORKS. Without any exaggeration, every single part was designed with the software. It not only is a simple and powerful 3D mechanical drawing tool, but also provides complete design diagnosis tools, such as finite element method (FEM), electromagnetic analysis, rendering tools, and so on.”

Kong pointed out that the safety analysis necessary for the devices were also performed with SOLDIWORKS. “All the rendering images have been directly generated from the software, and the safety factors of all the mechanical parts were checked by the software before manufacturing,” Kong said.

Because these devices are in intimate contact with their wearers, safety is essential. Such mechanical characteristics as the amount of torque a module would be capable of applying were limited, while mechanical angle limiters prevent a module’s range of motion from extending too far beyond natural human limits.

The Future for ANGELEGS

ANGELEGS is not exactly cheap, but it is less than half the price of the other exoskeletons on the market, which can cost upward of $70,000. Moreover, Kong aims to make the device accessible through a rental or lease program.

The process by which he envisions patients obtaining an ANGELEGS robot would involve the patient first undergoing a compatibility test at a designated rehabilitation center. Once they are diagnosed as compatible for the exoskeleton, an orthotics specialist can 3D print custom components tailored to the wearer, such as the braces. In addition to the ergonomic benefits of patient-tailored devices, these parts may be further personalized in terms of color and engravings.

The patient will then be trained to use the exoskeleton at the rehab center, just as a new driver must practice driving before getting behind the wheel alone. Once they are prepared, they can go about daily life with the assistance of the ANGELEGS robot.

ANGELEGS is not just intended to aid in the physical movement of its wearer; Kong has also created a service dubbed Connected Healthcare (ConHeal) that is aimed at providing regular health updates for both the patient’s doctor and for the rehab center. ConHeal can feed data such as a patient’s muscular strength to their doctor, who can, in turn, remotely provide further physical therapy prescriptions or adjustments to the device.

A concept diagram of the ConHeal service, which would allow users to connect with a medical professional for further treatment plans. (Image courtesy of SG Robotics.)

A concept diagram of the ConHeal service, which would allow users to connect with a medical professional for further treatment plans. (Image courtesy of SG Robotics.)

“It is not just a mobile robot that a person can wear; it diagnoses the abnormality from the gait pattern and the ground reaction forces, and it is connected to the doctors remotely.” Kong added, “Another important point of ANGELEGS is that it is a service platform. Not only for medical or rehabilitation purposes, ANGELEGS can be utilized for sport training, health monitoring, telelearning and so on. In the near future, the control software of ANGELEGS will be opened such that a number of programmers in the world can utilize the ANGELEGS hardware for their own purposes.”

While WalkON may have been a star at the Cybathlon event this year, ANGELEGS stands to make a big impression next year. Four hospitals in Korea have signed on to begin testing ANGELEGS starting January 2017. After clinical testing, the product will then be ready for the public market.

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