Hybrid active disturbance rejection sliding mode-admittance control for cervical rehabilitation robot

Cervical spondylosis is exerting an increasingly severe impact on people’s daily lives. Owing to the proven effectiveness of mechanical traction therapy in cervical rehabilitation, considerable research efforts have been devoted to the development of cervical rehabilitation robots (CRR). This paper presents the design and implementation of a CRR driven by pneumatic artificial muscle (PAM). In contrast to conventional motor-driven mechanisms, PAM provides superior compliance and continuous deformation capability, thereby offering cushioning protection for the cervical spine during traction. To guarantee both stability and safety during rehabilitation, an active disturbance rejection sliding mode–admittance control (ADRSM-AC) strategy is proposed for achieving force–displacement coupled compliant control of the PAM. Specifically, an inner-loop active disturbance rejection sliding mode control (ADRSMC) is designed to suppress the inherent nonlinearities of PAM and external disturbances, enabling high-precision displacement regulation. On this basis, an outer-loop admittance control scheme is implemented to evaluate deviations between actual and desired traction forces. By inferring the patient’s cervical muscle strength and movement intention, the system adaptively adjusts the target trajectory, thereby ensuring compliant interaction. Comprehensive experimental validation on a robotic prototype confirms the effectiveness of the proposed framework. The results demonstrate that the control scheme achieves accurate position tracking while adaptively regulating the trajectory in accordance with patient intention, ultimately safeguarding cervical spine safety throughout the rehabilitation process.