We propose a generalizable strategy for planning the sit to stand movement of a powered lower limb orthosis and its user. Modeling the system as a three rigid link planar robot, we rely on its kinematic equations to obtain a set of transformations that allows us to compute reference trajectories for the angular positions of the links, starting from a desired kinematic behavior for the center of mass of the robot and the angular position of link 2 relative to link 1; as we consider them more suitable to define for achieving a safe sit to stand transition. We then proceed to design a tracking controller via feedback linearization and solve a constrained least-squares program to address the control allocation problem from including the loads applied by the arms of the user as inputs. We simulate two relevant STS movements to illustrate the system tracking the reference trajectories generated with our strategy, in the presence of parameter uncertainty.

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