Abstract:In greenhouse vegetable phenotyping, uneven terrain induces high-frequency vibrations in the 3~6Hz range, leading to small-angle vibration and hysteresis in the acquisition device, which degraded the resolution of collected images. A stabilized platform was developed based on a composite control system incorporating gravity-compensated dual angular acceleration feedforward and an improved cascade PID controller. A single-arm stabilized platform with dimensions of 300mm×280mm×250mm was constructed to accommodate a narrow line spacing of 30cm and support the integration of multi-source sensors. The stabilized platform had a self-weight of 5kg and can carry a payload of 15kg. It was equipped with X-Y-Z axis sliding rails for center-of-gravity adjustment, limiting the center-of-gravity deviation to within ±5mm and maintaining gravitational torque variation below 0.5N·m. A gravity compensation feedforward model was established by linear fitting, achieving a determination coefficient R2 of 0.9912. An improved cascade PID structure was implemented, combining an inner velocity loop with an outer position loop. Key enhancements included integral separation activated when the error exceeded 1°, integral limiting, and a resetting mechanism triggered by error zero-crossing. These measures effectively suppressed integral saturation during fine adjustments, achieved a steady-state error of 0.1°. In addition, angular acceleration feedforward from dual IMUs mounted on both the vehicle and the stabilized platform compensated for inertial disturbances caused by vehicle start-stop and turning accelerations of 2~3m/s2. The verification test results showed that the composite control strategy reduced the system step response time by 80% without overshoot. When the vehicle operated at 0.5m/s, the stabilized platform’s triaxial angular oscillation was constrained to ±0.5° in roll, ±0.3° in pitch, and ±0.2° in yaw. These outcomes confirmed that the system satisfied the requirements for high-accuracy phenotyping acquisition.
