(a) Force analysis during lifting (the simplified model is built in the sagittal plane under static or quasi-static conditions). (b) Working principle of the passive back support exoxksleton. (c) Working principle of the spring-cable-differential (torque generator, the weight of the spring is ignored). (d) The spring is compressed when both hip joints are flexed for lifting (the legs move forward relative to the trunk and the hip joint angle $\theta_{hl}$ and $\theta_{hr}$ are both positive). (e) The spring slides to one side when one hip joint is extended and the other hip joint is flexed during walking (legs are staggered). The reserved space between the cable fixator and the spring fixator can compensate for the difference in the magnitude of hip extension and flexion during walking.

We have designed a novel back support exoskeleton with a single actuator for industrial workers who perform lifting and lowering tasks. Rather than two actuators, our novel exoskeleton uses a single actuator and a differential mechanism with a cable drive to transmit force equally to the two hip joints. This novel design results in lighter weight, independent leg movement, wide range of motion, and balanced force to both sides of the body. The passive version uses a spring and and the active version a Series Elastic Actuator (SEA) to achieve compliant force control instead of position control. Sensor data collected from the use of the device to provide potentially useful information on productivity and worker wellbeing. Experimental results show that it reduces up to 50% of the peak muscle forces used when lifting a 25 kg load.