A Soft Pneumatic Exosuit for Lifting Assistance

Highlighted Skills

Prototyping
Medical Robotics
Pneumatic Artificial Muscle (PAM)
EMG sensors
Arduino

For the final group project in Medical Robotics, we designed and fabricated a soft pneumatic exosuit with EMG sensors to activate Arduino controlled Pneumatic Artificial Muscle (PAM) actuators to support users with an assistive torque around the hip joint.

Creating a soft pneumatic exosuit to assist with the lifting task has the potential to reduce the risk of lower back pain in people who often repeatedly lift heavy objects, such as healthcare workers who often are injured by repetitive motion, overuse, and strain from manual lifting required for transferring or repositioning patients.

Current exosuits available on the market are expensive, bulky, and rigid. Many exoskeletons designed for lifting tasks are tailored for industrial workers and fail to fit the needs required by healthcare workers working closely with patients. Soft pneumatic systems do not limit movement with rigid structure, and has the potential to be beneficial for this specific application.

We had two specific goals in mind:

1. To create a pneumatic actuator to apply an assistive torque to the user.

2. To integrate EMG sensors to control the timing of the actuation.

PAMs trade off extension for lateral expansion to allow significant force production upon pressurization. Furthermore, they are low in weight and hold a high power-weight ratio, which is useful when it comes to building mobile robots.

The PAM actuators were manufactured by cutting 30 cm of 0.5” nylon mesh to create the base structure. A heat gun was used to apply 740 °F of heat to bond the mesh to the textile end-effectors on either side of the mesh. One end of the mesh we inserted a balloon to create an inflatable cavity. Tubing was zip-tied
to each balloon in order to create a seal for inflation.

To test the strength of a PAM, we attached various weights to the bottom of an individual PAM and inflated the cavity with air controlled by a solenoid and Arduino Uno; this test aimed to see if the inflated PAM was able to lift the weight without tearing. We tested up to 1000 grams; despite the PAM appearing to be capable of supporting more weight, we didn't test heavier weights due to the concerns that the PAM would reach its failure point.

To determine the effectiveness of a soft pneumatic exosuit for reducing the strain on the user’s lower back, one participant underwent two conditions: 1) without assistance; 2) with assistance. During each condition, the participant lifted a 4.5 kg weight from an angled position to a position where their back was
fully extended. An EMG sensor was placed on the participant’s erector spinae muscle on the lower back which would open the active solenoid valves and trigger the pump to inflate the actuators. The design of the soft exosuit used pneumatic actuators. For the purposes of this preliminary study, a prototype of a soft pneumatic exosuit was created to test this proof-of-concept.

The final exosuit was designed with 4 PAMs attached to a posture corrector. Two PAMS were strategically placed on each side of both erector spinae. The EMG recorded a baseline value when the user starts at the bottom position of a back extension. When the user start utilizing the erector muscles when lifting their torso up, the EMG senses an increase in muscle activation, triggering the solenoid release; this starts the PAM inflation. This contraction creates a pulling force on both ends of the effector, causing an assistive torque about the hip joint.

In future iterations, weight effective pumps must be chosen to continue to emphasize portability and comfortability as important factors in the design. As the user wore the suit, the PAMs had a tendency to rotate along the user's body due to the lack of mechanical constraints guiding the actuators to be in line with the erector spinae muscles. To tackle these shortcomings, a more complete vest could be used to fit the PAMs into a channel the runs directly along the target muscles for a more controlled system.