Improvement of Torque Estimation for Series Viscoelastic Actuator Based on Dual Extended Kalman Filter

Abstract

Adding damping such as viscoelastic element in series elastic actuators (SEA) can improve the force control bandwidth of the system and suppression of high frequency oscillations induced by the environment. Thanks to such advantages, series viscoelastic actuators (SVA) have recently gained increasing research interests from the community of robotic device design. Due to the inconvenience of mounting torque sensors, employing the viscoelastic elements to directly estimate the output torque is of great significance regarding the real-world applications of SVA. However, the nonlinearity and time-varying properties of viscoelastic materials would degrade the torque estimation accuracy. In such a case, it is paramount to simultaneously estimate the output torque state and viscoelastic model coefficients in order to enhance the torque estimation accuracy. To this end, this paper first completed the design of a rubber-based SVA device and used the Zenner linear viscoelastic model to model the viscoelastic element of the rubber. Subsequently, this paper proposed a dual extended Kalman filter- (DEFK) based torque estimation method to estimate the output torque and viscoelastic model coefficients simultaneously. The noisy observations of two Kalman filters were provided by motor current-based estimated torque. Moreover, the dynamic friction of harmonic drive of the designed SVA was modeled and compensated to enhance the reliability of current-based torque estimation. Finally, a number of experiments were carried out on SVA, and the experimental results confirmed the DEFK effectiveness of improving torque estimation accuracy compared to only-used rubber and only-used motor current torque estimation methods. Thus, the proposed method could be considered as an effective alternative approach of torque estimation for SVA.

Desenvolvimento E Controle De Um Acoplador Elástico Baseado Em Elastômeros Para Sea

“…O método proposto para a modelagem do elemento elástico apresentou uma significativa melhora em comparação a estimativa do modelo Zener que é usado em [61,62,105] por exemplo. A função de Chirp apresenta uma característica importante para a identificação em relação as outras entradas utilizadas.…”

“…No primeiro momento foi avaliado o modelo de Zener que é o modelo padrão para um material viscoelástico assim como foi feito por Austin et.al., (2015) e Wei et.al., (2021) [104,105]. Em seguida, o elemento elástico foi estimado no modelo de Burgers que possui um parâmetro a mais que o de Zener.…”