考虑非线性补偿的棉秆生物质制粒机模辊间隙模糊PID控制

Fuzzy PID Control of Die‑roller Gap for Cotton Straw Biomass Pellet Mill Considering Nonlinear Compensation

摘要:

针对棉秆生物质颗粒环模制粒机模辊间隙调节过程存在的非线性耦合干扰、气动系统时滞及高温工况下润滑黏度下降、热膨胀间隙增大、部件刚度衰减等问题，本文建立了气动驱动传动系统的传递函数，并设计了模糊PID控制系统。传动系统由气动马达、蜗轮蜗杆和丝杠3个子系统串联组成，结合高温工况物理特性，分别推导含0.358 s时滞的气动马达一阶模型、85℃下效率降至0.82的蜗轮蜗杆一阶模型，以及引入热刚度衰减系数的丝杠二阶模型，最终构建反映实际工况的整体传递函数。所设计的模糊PID控制系统以成型力偏差E和偏差变化率EC为输入，动态调整ΔKp、ΔKi、ΔKd参数，实现超调抑制;并采用机械限位器确保间隙不小于0.6 mm，防止模辊碰撞。为验证系统性能，搭建原型机试验平台并开展动态响应测试。结果表明，系统上升时间均值为4.8 s、调节时间均值为10.5 s、超调量仅2.5%、稳态成型力误差不大于5.8%，模辊间隙稳态变异系数为2.05%，生产的颗粒燃料成型率达96%、密度为1 290 kg/m3，各项指标均满足工业生产要求，证明系统精度高、可靠性强。

Abstract:

Aiming at the problems existing in the die?roller clearance adjustment process of the cotton straw biomass pellet ring die mill, such as nonlinear coupling interference, time delay of the pneumatic system, decrease in lubricating viscosity, increase in thermal expansion clearance and attenuation of component stiffness under high?temperature working conditions, a transfer function model of the pneumatic drive transmission system was established and a fuzzy PID control system was designed. The transmission system was composed of three subsystems in series, namely the pneumatic motor, worm gear and worm, and ball screw. Combined with the physical characteristics of high?temperature working conditions, the first?order model of the pneumatic motor with a time delay of 0.358 s, the first?order model of the worm gear and worm with efficiency reduced to 0.82 at 85℃, and the second?order model of the ball screw with the thermal stiffness attenuation coefficient introduced were derived respectively. Finally, the overall transfer function model reflecting the actual working conditions was constructed. The designed fuzzy PID control system took the forming force deviation E and deviation change rate EC as inputs, and dynamically adjusted the ΔKp, ΔKi and ΔKd parameters to realize overshoot suppression. In addition, a mechanical limiter was adopted to ensure that the clearance was not less than 0.6 mm, so as to prevent die?roller collision. To verify the system performance, a prototype test platform was built and dynamic response tests were carried out. The results showed that the average rise time of the system was 4.8 s, the average adjustment time was 10.5 s, the overshoot was only 2.5%, the steady?forming force error was not more than 5.8%, and the steady?state coefficient of variation of die?roller clearance was 2.05%. The forming rate of the produced pellet fuel reached 96% with a density of 1 290 kg/m3. All indicators met the requirements of industrial production, which proved that the system had high precision and strong reliability.