Master of Science

thesisManual Material Handing (MMH) is a common activity for many workers in the workplace. Back compressive force has been described as a leading factor causing back injuries and musculoskeletal disorders (MSD) associated with lifting. To prevent such injuries, mechanical Lift Assist Devices (LAD) have been developed. To improve device usability and allow more interaction with human body movements, a significant step has been taken towards developing an automatic feedback control system for a hybrid lift assist device. The control system is highly responsive which would likely result in a reduction of required erector spine muscle force during lifting tasks. The control system is based on multiple input and multiple output (MIMO).This design was chosen to control the outputs of Torque (τ) and Speed (ω) generated from a DC motor from the inputs: hip angle, torso angle and HD (Horizontal Distance from L5/S1 to center of load derived from the Force and Center of Pressure (COP) using Flexi Force Sensors in the shoe insole). All the inputs were derived and compared with parameters of human body movement recorded using Vicon Nexus and 8 Bonita cameras. The Utah Back Compressive model was used to estimate the desired torque required by the LAD. The motor is controlled to generate the amount of torque to lift the load and to assist the body to a specified percent assist (0-100%). The design of the control system was achieved using a proper controller and DC motor with a closed loop feedback system. The control system produces reliable and robust performance for a variety of sagittal plane lifting techniques. This was accomplished by deriving the system input parameters from measurable device features and fine tuning the controller and selected DC motor model. These results indicate that a hybrid lifting assist device is feasible and can be programmed to provide variable assistance during lifting tasks