Exoskeletons that enhance a human’s capabilities or enable a human to more readily perform normal tasks are being pursued by several organizations. The former design requirements are the military’s goals, but backpackers and other healthy individuals can take advantage of these designs as well. The latter are desired by individuals with disabilities or physical limitations.
For individuals with mobility issues, researchers at North Carolina State University and the University of North Carolina at Chapel Hill designed an artificial intelligence (AI) powered exoskeleton.
Developed for hip flexion and extension assistance, the portable, lightweight, and compliant exoskeleton consists of a waist belt, two thigh braces, and two inertial measurement unit (IMU) straps. For the user, the process involves attaching a fanny pack around their waist, a sensor on the front of each thigh, and securing a few buckles. After 10 to 20 seconds worth of AI learning, the new user is in control.
The wearable exoskeleton technology provides energy savings during human movement, so users feel as if they are carrying 26 pounds less. With less weight, they experience improvements in athletic performance as well as daily life activities.
Sensors in the system
The two IMUs in the exoskeleton have an orientation range of roll: ±180°, pitch: ±90°, and yaw: ±180°. The Resolution <is less than 0.01° with accuracy < 0. 5°(static) and < 2° RMS (dynamic).
The 3-axis 16-bit accelerometer’s accuracy was ±2 / ±4 / ±8 / ±16 g. Similarly, the 3-axis 16-bit gyroscope had ±125 / ±245 / ±500 / ±1000 / ±2000 °/s with noise density of 0.007 dps/√Hz and static orientation stability of 9 °/hour. The 3-axis 16-bit magnetometer had ± 4 / ± 8 / ± 12 / ± 16 gauss.
With real-time joint angles and joint angular velocities measurements from the wireless IMU sensors, the system implements continuous torque control of the joints in the exoskeleton.
Sensors in the verification process
To verify the capabilities of the exoskeleton, a few different measurements were made: including Center of Pressure (COP) and Torque tracking performance. COP involves the ground reaction force (GRF) on the foot or the contact area between a person and a support surface.
Typically, researchers use force platforms and pressure sensors to measure the COP during different activities such as standing, walking, jumping, and other dynamic movements. These measurements include displacement (the distance and direction that the COP moves from a reference point or position), velocity (the speed and direction of COP displacement over time), and acceleration (the rate of change of COP velocity over time).
The hip exoskeleton was evaluated for walking, running, and stair climbing at different speeds. Testing revealed that the trained controlled reduced energy expended by 24.3%, 13.1%, and 15.4% during walking, running, and stair climbing compared to no exoskeleton conditions.
Other exoskeletons
Several proof-of-concept demonstration efforts for exoskeletons have been reported. For example, engineers at another university created a boot-type robotic exoskeleton that allows users to walk 9% faster and consume 17% less energy per distance traveled.
Another group of researchers developed a robotic boot (lower limb exoskeleton) to help users prevent falls, a leading health concern for the elderly. To analyze the stability control, the team used motion capture technology and ultrasound sensors to track how the ankle and exo-boot work together.
References
Experiment-free exoskeleton assistance via learning in simulation
Center of Pressure (COP)
LPMS-B2 Series: 9-Axis Inertial Measurement Unit / AHRS with Bluetooth Classic and BLE Connectivity
Stanford researchers create robotic boot that helps people walk
Faster-than-reflexes robo-boots boost balance
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