Hemiplegia, the paralysis of one side of the body, is a common effect of stroke and provides unique challenges for afflicted individuals, including asymmetric body strength and limited mobility, especially in the sit-to-stand (STS) motion. Reducing weight-bearing asymmetry during STS is important for improving mobility outcomes of hemiplegic patients. To address this concern, a semi-wearable STS assistive robot is proposed to provide assistive force and motion guidance during the STS motion. It is a planar 2-DoF assistive robot attached near the hip, designed to reduce weight-bearing asymmetry and facilitate correct execution of the STS motion by guiding the user along a target STS path and constraining pelvic motion in the frontal plane, controlled using a single worn IMU. The method for generating unique target STS paths and assistive robot design is presented. Experiments on healthy test subjects with the motion of one leg constrained were conducted to determine the changes and correlations in force and motion parameters when using the assistive robot during STS. The assistive robot improved rising STS asymmetry in some test subjects and reduced stabilization weight-bearing asymmetry in all test subjects. Motion data showed that the assistive robot facilitated hip translation and tilt toward the test subjects’ constrained side, while a counter trunk tilt toward the unconstrained side was observed. The results of the experiments suggest that more active control of the hip position and tilt and providing real-time feedback during the STS motion could further improve the function of the robot.
