## 3 Proposed Intelligent Control System
### Mathematical Model  
The cut-tobacco dryer is in the first stage before the cut tobacco reaches the outlet moisture meter. The actual outlet moisture content of cut tobacco cannot be measured because there is no cut tobacco at the outlet; thus, the actual moisture feedback cannot be formed. The temperature control of the dryer was achieved using the feed-forward mathematical model. Thus, the accuracy of the feed-forward mathematical model is key for determining the accuracy of the cut-tobacco drying control. Indeed, the operator can intervene and adjust the temperature during the entire process. We set \(F_{1}\) as the tobacco mass flow at the inlet [kg/h], and \(M_{1}\) as the inlet moisture content of cut tobacco (lsb%). The mass flow of dry-cut tobacco is the flow of water changes, the mass flow of dry-cut tobacco \(F_{2}\) (moisture content of 0%) is given as:  
\[F_{2}=F_{1}(1-M_{1}) \tag{1}\]  
We set the value of moisture increase at the Sirox as \(C_{1}\). Therefore, the mass flow after Sirox [kg/h], \(F_{3}\), is given as:  
\[F_{3}=\frac{F_{2}}{1-M_{1}-C_{1}} \tag{2}\]  
We set \(M_{2 sp}\) as the outlet moisture content of cut tobacco (lrb%) because there is no tobacco at the outlet at this time. The theoretical value of mass flow after the winnower [kg/h] is given by \(F_{4}\) as:  
\[F_{4}=\frac{F_{2}}{1-M_{2 sp}} \tag{3}\]  
Equations (4) and (5) are used to obtain the dryer moisture reduction (kg/h) \(F_{5}\) as:  
\[F_{5}=F_{3}-F_{4} \tag{4}\]  
We set the target moisture reduction (kg/h) in the process recipe as \(D_{1}\). The variation in the dryer moisture reduction (kg/h) is denoted by \(\Delta F_{5}\) and is given as:  
\[\Delta F_{5}=F_{5}-D_{1} \tag{5}\]  
Figure 3: Schematics of the proposed control system. We can define the dry factor as \(CK\) [\({}^{\circ}\)C /(kg/h)]; then, the variation of the dryer temperature according to the feedforward control \(\Delta T\) [\({}^{\circ}\)C] is given as:  
\[\Delta T=\Delta F_{5}\times CK \tag{6}\]  
The feedforward control data flow diagram is shown in Figure 4:  
When the moisture detected by the detector deviates from the target value after passing through the winnower, there is a deviation between the actual outlet value of the cut tobacco flow and the expected value. That is, the deviation is equivalent to that between the actual value of the dryer moisture reduction flow and the expected value. However, the flow deviation can be converted into temperature, and the formula is calculated and applied to the control system immediately. The variation in the dryer temperature based on feedback control is \(\Delta T_{b}\), where \(M_{2}\) represents the outlet moisture content of the cut tobacco. \[\Delta T_{b}=\left(\frac{F_{2}}{1-M_{2}}-\frac{F_{2}}{1-M_{2 sp}}\right)\times CK \tag{7}\]  
The dryer calculates the actual temperature value based on steam pressure. The saturated steam pressure used by the dryer is 0-1 MPa (approximately 99-183 \({}^{\circ}\)C). The program can be realized using look-up tables or empirical formulas. Although the amount of calculation required when using look-up tables is small, the control accuracy is directly affected by the amount of data in the table. The amount of data must be increased to improve accuracy. To this end, an optimized empirical formula is adopted for determining the relationship between steam pressure and temperature [29]. \[T_{pv}=101.55\times\sqrt[4]{P+0.9529} \tag{8}\]  
As shown in Figure 5, the set point of temperature T consists of four values: the manual setting value \(T_{NoP}\), the feedback control temperature variation \(\Delta T_{b}\), the actual dryer temperature \(T_{pv}\) and the feed forward control variation \(\Delta T\). The temperature is then converted into steam pressure and sent to dryer which is achieved by the steam valve. \(T\) is given as:  
\[F_{3}=\frac{F_{2}}{1-M_{1}-C_{1}} \tag{2}\]0  
During the different stages, IIoTs collected the data and the mathematical model was validated. Experimental results of the proposed model are summarized in Tables 1 and 2.