## 2 Materials and Methods
### Design of Blade
#### 2.3.2 Determination of the Number and Inclination Angle of the Blade  
The number and inclination angle of the blades are the key structural parameters of the film removal device. The former design mainly considers two aspects: first, the effect of film removal. When the speed of the vane-type film removal roller is fixed, the greater the number of blades is, the greater the contact frequency between the blades and arc-shaped teeth is. It is necessary to ensure that the same arc-shaped teeth are acted by blades at least twice when the film picking device rotates one full circle. Second, dynamic balance. The blades are arranged at equal angles along the tangential direction of the surface of the roller, and the axial direction is symmetrical, which is conducive to the dynamic balance of the vane-type film removal roller [32]. Considering the above factors and combined with the structure of the whole machine, the number of blades was determined to be 6. There are three ways to install the blade: forward tilt, radial and backward tilt [33]. As shown in Figure 4, \(F_{1}\) is the force of the blade on the residual film when blades interact with arc-shaped teeth. Decompose \(F_{1}\) along the tip of the arc-shaped tooth and its normal direction to obtain \(F_{2}\) and \(F_{3}\). The main function of \(F_{3}\) is to make the residual film move along the direction of the tip of the arc-shaped tooth. At the same time, it exerts the effective force of the blade on the residual film, and \(F_{3}=F_{1}\cos\beta\). When \(F_{1}\) is fixed, for different blade installation methods, the size of \(F_{3}\) is as follows: forward tilt > radial > backward tilt. When a blade is installed with a forward inclination and an inclination of \(15^{\circ}\) (the blade is at the dotted line position in Figure 4), the blade is perpendicular to the tip of the arc-shaped tooth. At this moment, the effective force of the blade on the residual film reaches the maximum value, which is conducive to the removal of the residual film. Therefore, to better explore the effect of the blade inclination on the film removal effect, blades are evenly distributed on the surface of the roller by forward tilt, and the range of tilting angles is \(5^{\circ}\) to \(25^{\circ}\). Figure 4: Schematic diagram of the force of the blade on the residual film. Figure 3: Schematic diagram of the working of blade and arc-shaped tooth. 1. Spoke plate. 2. Arc-shaped tooth. 3. Blade. Note: \(a\) is the maximum distance between the teeth of adjacent blades, mm; \(b\) is the tooth height of the blade, mm; \(c\) is the distance between adjacent teeth, mm. 2.3.3. Analysis of the Conditions of Film Removal  
To separate the residual film from the blade, it is necessary to ensure that the centrifugal force of the residual film at the end of the blade is greater than the adsorption and winding force between them [34]. Due to the easy adsorption and floating of the residual film, the resistance effect of airflow should be considered in the motion analysis of the residual film [35]. Figure 5 shows the instantaneous force analysis of residual film separation. In the separation process of the residual film, according to the force balance relationship, the following results can be obtained:  
\[\left\{ \begin{array}{l}F_{\omega}\cos\theta+G\sin\theta_{1}=F_{f}\\ G\cos\theta_{1}+F_{N}=F_{a}+F_{\omega}\sin\theta\\ F_{a}=0.5c1 psv_{1}^{2}\end{array} \right. \tag{1}\]  
Note: \(c1\) is the resistance coefficient, and the value 0.4 is used in the calculation [36]; \(p\) is the air density, 1.29 kg/m\({}^{3}\); \(s\) is the windward area of the residual film, m\({}^{2}\); and \(v_{1}\) is the linear velocity of the blade, m/s. According to Equation (1), the conditions of film removal are as follows:  
\[F_{\omega}\cos\theta+G\sin\theta_{1}>F_{f} \tag{2}\]  
Namely:  
\[v_{1}<\sqrt{\frac{mgr\sin\theta_{1}(1+\mu)}{\left[\mu\left(\frac{1}{2}cpsr+m \cos\theta\right)-m\cos\theta\right]}} \tag{3}\]  
Figure 5: Schematic diagram of the force analysis of the separation of the residual film and blade.