# Grain Sieve Loss Fuzzy Control System in Rice Combine Harvesters
## 3 Results and Discussion
### Fuzzy Controller for Cleaning System  
There is no commercial grain impurity ratio monitoring system available at present; thus, it is currently impossible to obtain the grain impurity signals in a grain tank in real time. From the experiment shown in Table 5, it can be learned that when the sieve opening is 25 mm, the cleaning system has the lowest grain impurity ratio in a grain tank. Therefore, fixing the sieve opening at 25 mm, and selecting the fan speed and guide plate II as variables can establish the control strategy and thus ensure the grain impurity ratio \(\leq\)2% in the grain tank. As the control target is to keep the grain sieve loss ratio \(\leq\)0.5% under the condition of a grain impurity ratio \(\leq\)2% in the grain tank, according to the feeding rate of 2.5 kg/s, the optimal set point of the grain sieve loss ratio is 0.5%, the corresponding grain sieve loss is 12.5 g/s, and the grain sieve loss is about 420 gains/s, according to a 1000 grain mass of rice of 30 g. Based on the proportion of grain mass in the monitoring area, the control threshold is set to six gains/100 ms.  
The control variables of the fuzzy controller are the fan speed and the guide plate II angle. The adjusting range of the fan speed is 1100-1500 rpm, while the guide plate II angle is distributed within 13-45\({}^{\circ}\). As shown in Figure 8, the experimental results indicated that the grain sieve loss ratio increases at a rate of 0.75 g/r as the fan speed increases, and the decrease rate of the grain sieve loss is about 2.2 g/\({}^{\circ}\) with the increase of the guide plate II angle. The cleaning system has a good performance with the fan speed at 1300 rpm and a guide plate II angle of 29\({}^{\circ}\), as the corresponding grain sieve loss and grain impurity ratio are relative low. Combined with the cleaning performance under different conditions, the grain sieve loss ratio is larger when the fan speed is 1500 rpm, which is not conducive to getting a better cleaning performance. Therefore, the fan speed can be adjusted in the range of 1100-1400 rpm, and the guide plate II angle can be changed within 23-41\({}^{\circ}\).  
Figure 8: Effects of working parameters on grain loss with a confidence interval of 95%.  
Figure 7: Prediction profiler for grain impurity ratio.  
Experiments have shown that the fan speed has a major effect on grain sieve loss. Thus, a faster loop (cycle time of five seconds), which regulates the fan speed, and a slower loop, which regulates the guide plate II angle (cycle time of 10 s), were designed to control the working process. During the working process, the cleaning controller checks whether the current grain sieve loss is approximate to the optimal set point. If the monitored grain loss number is much higher than the optimal set point, the faster loop is activated, and the fan speed is changed. Once the monitored grain sieve loss approaches the optimal set point, the slower control loop will manage the fine-tuning of the guide plate II angle to keep the grain sieve loss below the set point and without impairing the cleaning efficiency. If the monitored grain sieve loss number falls below the optimal grain sieve loss set point, the fan speed can be increased to some extent to ensure cleaning efficiency. The basic domain of the grain sieve loss is obtained as shown in Table 6. The membership functions are all triangular, as shown in Figure 9; its fuzzy domains were E and EC, and U represents their fuzzy domains. The fuzzy subsets of the input and output linguistic variables are expressed as negative big (NB), negative middle (NM), negative small (NS), zero (ZO), positive small (PS), positive middle (PM), and positive big (PB). The fuzzy system includes 49 strips of rules for the fan speed and guide plate II angle, as shown in Tables 7 and 8.