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基于分段式积分分离PID的兔用颗粒饲料精准称重控制方法

Precise weighing control method for rabbit pellet feed based on segmented integral-separation PID

  • 摘要: 针对兔用颗粒饲料单搅龙定量称重中排料不可回收、给料速度与终点精度难以兼顾的问题,该研究提出一种分段式积分分离比例-积分-微分(proportional-integral-derivative,PID)控制方法,按目标喂料量与实时称重值的控制偏差切换PID参数组,并在偏差小于积分分离阈值时启用积分。通过设置2个积分分离阈值系数(0.10、0.05)水平以及不采用积分分离(以0.00标识)的对照水平,配合单段式和分段式2种参数模式,得到6种控制方案,在80 、90 和100 mm螺距搅龙下开展试验,选出各螺距下评分最高的方案;再将这3种方案分别与5档分频系数组合,得到15组系统配置,二次评分,选出评分最高的配置。结果表明,3种螺距下评分最高的方案依次为分段式积分分离PID、单段式积分分离PID和分段式积分分离PID,与同螺距传统PID相比,平均绝对误差、变异系数和最大偏差分别降低60.3%~87.4%、44.5%~72.0%和53.2%~77.8%;100 mm螺距搅龙、分段式积分分离PID(阈值系数0.05)和分频系数为1.00组成的配置评分最高,在3种兔用颗粒饲料、180~390 g目标喂料量下,平均相对误差、平均变异系数和平均称重时间分别为0.94%、1.09%和9.08 s。该方法在3种螺距搅龙下均能获得优于同螺距传统PID的称重性能,兼顾了称重精度与给料速度,可为颗粒饲料定量称重的控制参数配置提供参考。

     

    Abstract: This study addressed the trade-off between feeding speed and endpoint accuracy in screw-fed batch weighing of rabbit pellet feed. Discharged pellets cannot be retrieved, making endpoint overshoot difficult to correct. A segmented proportional-integral-derivative (PID) controller with integral separation was developed to regulate feeding throughout the weighing cycle. The controller switched parameter sets according to the difference between the target feed mass and the real-time weighing value, and enabled integral action only when the error entered a prescribed small-error range. The study evaluated both the control scheme and the conversion from controller output to pulse frequency, because their combined effects determined the feeding response. Two selection stages were conducted at a target feed mass of 200 g. First, six schemes representing conventional PID, segmented PID, integral-separation PID, and segmented integral-separation PID were compared using auger pitches of 80, 90, and 100 mm. Mean absolute error, coefficient of variation, maximum deviation, and mean weighing time were included in entropy-weighted scoring to identify a preferred scheme for each pitch. The three selected pitch–scheme combinations were then tested with five frequency division coefficients, producing 15 system configurations. These configurations were evaluated using mean absolute error, coefficient of variation, and mean weighing time. The highest-scoring configuration was subsequently tested with three rabbit pellet feeds at five target feed masses from 180 to 390 g. A separate static test assessed the weighing subsystem at tilt angles from 0° to 5°. The preferred scheme varied with auger pitch. Segmented integral-separation PID with a threshold coefficient of 0.10 ranked first for the 80 mm auger, whereas integral-separation PID with the same coefficient ranked first for the 90 mm auger. Segmented integral-separation PID with a coefficient of 0.05 ranked first for the 100 mm auger. Compared with conventional PID at the same pitch, the three selected schemes reduced mean absolute error by 60.3%-87.4%, coefficient of variation by 44.5%-72.0%, and maximum deviation by 53.2%-77.8%. Mean weighing time increased by 44.7%-76.5%, indicating an accuracy–time trade-off rather than an improvement in all performance indices. All three selected schemes used integral separation, while two also used parameter segmentation. In the second stage, the 100 mm auger with segmented integral-separation PID at a threshold coefficient of 0.05 and a frequency division coefficient of 1 received the highest score. Its mean absolute error, coefficient of variation, and mean weighing time at 200 g were 0.92 g, 0.49%, and 8.59 s, respectively. The preferred frequency division coefficient was 1 for the 80 mm combination and 0.75 for the 90 mm combination. Reducing the coefficient from 1 to 0.75 for the selected 100 mm combination shortened mean weighing time from 8.59 to 6.18 s but increased mean absolute error from 0.92 to 8.05 g. With controller parameters and the coefficient fixed, validation across the three feeds and five target masses yielded an overall mean relative error of 0.94%, a mean coefficient of variation of 1.09%, and a mean weighing time of 9.08 s. Mean relative errors across individual conditions ranged from 0.38% to 1.87%. The maximum relative deviation from the horizontal baseline in the static tilt test was 3.10%, below the prescribed 5% engineering limit. These results supported joint selection of the control scheme and frequency division coefficient for a given auger pitch. The selected configuration provided a practical balance between weighing error and cycle time within the tested feeds and target masses. Further work could combine discharge-dynamics measurements with threshold-decoupling tests and extend validation to additional feeds and target masses.

     

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