SEAs导纳控制的μ综合方法

Series elastic actuators (SEAs) are an effective technique to balance robot safety and performance. Therefore, SEAs are widely used in rehabilitation robots. For the application of robots in rehabilitation training to be effective, specific requirements such as admittance-controlling are necessary. In this paper, the μ synthesis technique is used to design an admittance controller for the SEAs. Firstly, the unpredictable nature of factors like parameter perturbation, sensor noise, input disturbance and control input restriction is an essential consideration in the modeling of the SEAs. Second, the concept of mixed stability is adopted to analyze interaction stability. Since passive environments must have small-gain property in high-frequency range in reality, interaction stability is maintained as long as the port admittance displays passivity in low-frequency range and small gain in high-frequency where the small-gain theorem is satisfied. Third, the admittance control synthesis converts into the admittance matching μ synthesis problem. By selecting the appropriate weight functions, the actual port admittance is forced to approach the desired admittance while the mixed stability conditions are satisfied. Consequently, an admittance controller can be devised independently of the interacted environment. Simulation results show that the controller based on μ synthesis can not only force the SEAs system to achieve the desired admittance, but can also guarantee the interaction stability. Furthermore, the reduced controllers based on Hankel approximation displayed satisfactory control performance.