Crossed Roller Bearings Give Physical Therapy Exoskeletal Robot a Helping Hand

Updated: May 13, 2020

Each year, approximately 700,000 people survive a stroke. As deaths caused by stroke decrease and our population ages, an ever-increasing number of stroke survivors will require rehabilitation in order to regain independence and quality of life. However, the rapidly increasing demand for post-stroke rehabilitation cannot be addressed through traditional physical therapy means alone.

An Exoskeletal Robot Improves Physical Therapy Outcomes for Stroke Survivors

Harmonic Bionics — a company that creates innovative rehabilitation robotics platforms for the clinical market — developed an upper-limb exoskeletal robot platform to enable the patient to relearn how to use limbs that are often left paralyzed by the stroke. Their Harmony exoskeleton platform is based on the principles of neuromuscular physiology and is designed to take advantage of known neurological coupling between human joints, using coordinated movements and forces to boost true functional therapy. It wraps around the patient’s shoulders, arms and wrists and can power their joints to assist patients as they perform the various dynamic movement tasks they must relearn. The highly sensitive and repeatable platform creates an assist-as-needed paradigm that encourages active patient participation and can greatly improve the effectiveness of shoulder therapy for stroke survivors. It also frees up the therapist to massage a patient’s arm or even monitor multiple patients at once.

For it to work properly, the designers needed a crossed roller bearing that could carry large moment loads so the exoskeleton can move coaxially with the patients’ skeletal structure as they move their arms. The bearing also needed to be small, lightweight and offer a low coefficient of friction (CoF). According to Rohit Varghese, the Head of Product Development, “An exoskeleton like ours has very unique challenges. Few bearings can satisfy them.”

Crossed Roller Bearings Carry High Moment Loads to Assist Patients

That’s why Harmonic Bionics chose IKO’s CRBH and CRBF Series crossed roller bearings. With rollers alternately crossed at right angles between the inner and outer rings, the compact units can handle radial, thrust and moment loads at the same time with high rotational accuracy and rigidity, making them well-suited for robotics and medical equipment. Harmonic Bionics’ chosen model provided more than enough moment load carrying ability to meet their requirement of 100 newton-meters, and they had no problem incorporating the unit within limited space. And the CRBH's CoF after modifications allows the system to feed sensor data into algorithms that customize the levels of resistance and support that the patient receives relative to gravitational forces. High friction could compromise these measurements.

In addition, IKO’s CRBF bearing was perfect for prototyping. With mounting holes on both the inner and outer rings, the engineers were able to install the bearing without machining, special housings or fixing plates to the micrometer-level bearing tolerances.

Transforming Post-Stroke Physical Therapy and Survivors’ Lives

The rehabilitation robot has undergone extensive clinical trials, and Harmonic Bionics reports that the CRBH is meeting expectations: “We’re happy with its performance,” said Varghese. “It is holding up.” He also notes that renowned hospitals have flown their therapists to Harmonic Bionics’ Texas facility to explore the technology. Thanks to IKO International’s CRBH and CRBF crossed roller bearings’ combination of high moment load handling capabilities, rigidity and small size, Harmonic Bionics is poised to revolutionize physical therapy and improve the lives of many stroke survivors.

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