基于双前馈-改进串级PID的设施蔬菜表型信息采集稳衡云台设计与试验

Design and Experiment of Stabilized Platform for Vegetable Phenotype Acquisition Based on Double Feedforward-Improved Cascade PID in Greenhouse

摘要:

针对设施蔬菜表型信息采集过程中，由于地形不平整产生3~6Hz振动造成采集装置出现高频小角度倾斜、动态响应滞后，进而导致采集图像分辨率下降等问题，设计了基于重力补偿角加速度双前馈-改进串级PID复合控制系统的适用设施表型采集装置的稳衡云台。硬件上，针对30cm窄行距与多源传感器搭载需求，设计300mm×280mm×250mm单臂稳衡云台，整机仅5kg，最大负载能力达15kg。集成X-Y-Z轴重心滑轨，将负载重心偏差控制在±5mm，由此引起的重力矩波动小于0.5N·m。控制策略上，通过线性拟合构建重力补偿前馈模型（R2=0.9912），以抵消重力矩干扰。提出内环速度环叠加外环位置环的改进串级PID，引入积分分离、积分限幅及误差过零复位机制，解决传统PID小角度调整积分饱和问题，稳态误差控制在0.1°以内。融合载体与云台双IMU角加速度前馈，抵消采集车2~3m/s2启停/转向带来的惯性扰动。运行效果验证试验表明，复合控制使系统阶跃响应时间缩短80%且全程无超调。采集车以0.5m/s行驶时，云台三轴角度围绕目标值小幅度振荡，其中横滚轴角度±0.5°、俯仰轴角度±0.3°、航向轴角度±0.2°，满足设施蔬菜表型采集对姿态稳定性的要求。

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.