Development of a pneumatic power assist system for an upper limb with working posture assessment and conflict mitigation

The objective of this study is to develop an assist control system for a wearable power-assist device that aids joint motion by controlling the actuators installed in the device. In this system, actuator control is based on the real-time posture assessment of the device user. In particular, we utilized comfort scores for joint postures as an ergonomic approach to assess the working posture load. These scores enable continuous quantification of the load levels of human body posture. Furthermore, we created a cost function that includes both the comfort scores and joint torque of the device user. The proposed assist control system computes the control inputs from a predicted joint-angle trajectory to minimize the cost function. This control system reduces physical workload, which mainly depends on the body posture of the device user. In addition, we defined the interference between the power-assist device and its user as a conflict and proposed a conflict-detection technique based on the physical power of the user. The proposed assist control system incorporated an assist coefficient that was automatically tuned according to the detected conflict. Finally, we built a prototype of a two-degree-of-freedom power-assist device driven by rotary pneumatic actuators to simultaneously aid the user’s shoulder and elbow joints. The proposed assistive control system was embedded in the device and its assistive performance was experimentally verified based on the measurement of electromyogram signals obtained from participants wearing the device.