Dynamic Modeling and Robust Trajectory Tracking Control of a Heavy-Duty Manipulator for Shield Cutter Replacement Under Variable Payloads

Automatic cutter replacement in large-diameter shield tunneling requires a manipulator to track prescribed motions while carrying a heavy cutter, releasing or acquiring the payload, and operating under uncertain dynamics and external disturbances. This study develops a reduced-order three-revolute-joint model for the dominant cutter-transfer motion and compares gravity-compensated PID control, computed-torque control (CTC), and CTC with a first-order disturbance observer (CTC-DOB). The disturbance formulation is derived with an explicit sign convention that separates the physical disturbance, nominal-model mismatch, generalized disturbance, residual, and disturbance estimate. Five principal operating conditions are considered, including a known heavy payload, abrupt payload release, parameter mismatch, and impact disturbance. An implementation-oriented test further introduces encoder noise, filtered velocity and acceleration reconstruction, a one-sample command delay, and first-order actuator dynamics. Robustness is examined using multiple reference trajectories and randomized trials with simultaneous variations in the initial configuration, release time, payload level, link mass, inertia, geometry, friction, and disturbance characteristics. In the principal benchmark, CTC-DOB reduces the end-effector RMSE from 29.112 mm to 0.630 mm under abrupt payload release and from 44.588 mm to 5.776 mm under impact disturbance. The numerical results show that disturbance compensation is most beneficial when the nominal inverse-dynamics model becomes inaccurate, whereas the implementation-oriented evaluation quantifies the degradation caused by sensing and actuator nonidealities. The conclusions are limited to the proposed numerical model and do not constitute experimental positioning-accuracy claims for a physical cutter-changing robot.