End-Effector Compliant Control System for Tunnel Surrounding-Rock Detection Manipulator During Construction

During tunnel construction, ground-penetrating radar detection requires stable contact between the antenna and the tunnel wall, whereas manual operation is labor-intensive, risky, and difficult to maintain with consistent coupling. To improve automated tunnel surrounding-rock quality detection, this study develops an end-effector compliant control system for a tunnel inspection manipulator. A three-degree-of-freedom manipulator equipped with a passive compliant end-effector mechanism was designed, and an admittance controller was established to regulate the contact force between the radar antenna and the tunnel surface. To improve adaptability under irregular wall conditions, a fuzzy variable-damping strategy was introduced, in which the equivalent end-effector velocity and acceleration were used to adjust the damping coefficient online. The proposed controller was evaluated through MATLAB/Simulink simulations, indoor experiments with wall and ground irregularities, and field tests in an actual tunnel. Compared with fixed-damping admittance control, the proposed method reduced contact-establishment overshoot by 69.3% and inspection-stage force fluctuation by 36.49% in simulation. Indoor experiments further verified lower peak contact force and shorter settling time under different wall and ground conditions. Field tests at the tunnel crown and sidewall demonstrated that the radar antenna maintained effective wall contact. The results indicate that fuzzy variable-damping admittance control improves contact stability and practical applicability for robotic tunnel inspection.