| Description |
The goal of this project was to study a control system and prototype for a wearable lift assist device. The purpose of this device is to support the upper body during torso flexion and extension to reduce the erector spinae muscle activity and decrease back compressive force. It could also be used in rehabilitation or return to work scenarios after back injury or surgery. The proposed device is actively controlled and able to provide support based on the wearer's position, anthropometry, and desired level of assist. The upper body is supported by direct current (DC) motors and bilateral torsion springs. The assist level is a function of the percentage of torque needed to statically support the torso for a given angle and can range from 0 to 100%. To develop and test the control system, an electromechanical system was developed to simulate the human torso during lifting. The torso and support mechanism were driven by separate DC motors and drive trains. The torso and support of the mechanism were operated independently, as would be required of an actual assist device. The support control used a position sensor to approximate torso angle and a load cell to determine if the correct amount of torque was applied. The load cell also served to measure the amount of actual assistance provided and gave feedback to the control system. The support control system and mechanism were evaluated using three angular trajectories, derived from actual lifting data. The measured trajectory of the torso with no assist was compared at each level (20 - 100%, in increments of 10%). Ten percent was not analyzed because the support system was unstable at such a low assist level. The torso's trajectory, load cell measurements, and torque produced by the motor driving the torso were analyzed to determine performance. There was a statistical difference when comparing the torso's trajectory with no assist to each level of assist (t < 0.0001) but may not be practically different. No statistical difference was found when comparing the load cell measurement to the target value for each trial (t > 0.05). The torque produced by the torso motor was reduced for all trials and were statistically different (t < 0.0001). This study demonstrates that a mechanism can be actively controlled to provide assistance during lifting. A feasible control system was developed and tested. System stability and mechanical losses in the apparatus were the primary sources of error. Further work on active lifting assist devices and studies to determine actual benefits to users is warranted. The next step is to develop a wearable prototype and explore the benefits of using it in rehabilitation, and low back pain relief. |
