Modeling and Control of a Partial Body Weight Support System

This paper reports on the modeling, control design and implementation as well as experimental results of a partial body weight support (PBWS) system, which facilitates walking and the relearning process for people suffering from gait impairment as a result of a neurological injury such as strokes. This apparatus is equipped with a load cell which constantly monitors the provided support force, and a linear motor, capable of taking immediate action to keep this support force very close to a predefined profile. To design a feedback control law that governs the action of the linear motor, a dynamic model of the PBWS system with a patient has been developed along with a procedure to identify the model parameters. Based on this model, the design of the feedback law is formulated and solved as an output regulation problem. The implementation of the resulting feedback law is described in detail and practical limitations of output regulation in this application are discussed. Simulation results as well as preliminary data from a clinical study with a stroke patient demonstrate the ability of this novel PBWS system to provide the desired support force patterns.