High-Precision Piezoelectric Sensor Positioning with SMC Control for Robotic NDT in Pipelines

Non-destructive testing of confined pipelines requires high-precision sensor positioning under nonlinear and dynamically constrained operating conditions. This work presents the design, modeling, and closed-loop control of a compact piezoelectric-driven positioning mechanism for ultrasonic pipeline inspection in internal diameters of 50–100 mm. The system employs a multilayer PZT-5H stack actuator integrated with a rack-and-pinion transmission and radial flexure guidance to convert micrometer-scale axial displacement into precise radial deployment. A corrected displacement-source actuator model based on the Generalized Bouc–Wen formulation is developed to capture electromechanical coupling, preload interaction, and rate-dependent hysteresis dynamics. To compensate for hysteresis nonlinearities and parameter uncertainty, an improved Sliding Mode Controller incorporating derivative damping, integral action, feedforward compensation, filtered switching dynamics, actuator saturation, and anti-windup compensation is developed and validated through high-fidelity Simulink simulations. The filtered unsaturated controller achieved a rise time of 23.20 ms, settling time of 153.00 ms, overshoot of 0.14%, and near-perfect steady-state tracking accuracy. Under practical actuator voltage constraints (0–100 V), the final filtered saturated controller maintained stable near-aperiodic operation with bounded control effort, achieving a rise time of 86.58 ms, settling time of 236.35 ms, and overshoot of only 0.23%. Hysteresis suppression analysis demonstrated substantial reduction in loop distortion and improved tracking consistency across multiple excitation frequencies. The results establish a physically realizable nonlinear control framework for robust high-precision piezoelectric positioning in autonomous pipeline inspection systems.