## 5 Experimental Results
### Experimental Results  
After filming, we used image analysis software (Dipp-Motion V, DITECT Corp., Toronto, ON, Canada) to track the markers on the wiper blade in advance. From the  
Figure 10: Enlarged view of the wiper blade.  
Figure 9: Experimental apparatus (**a**) without attack angle and (**b**) with an 18-degree attack angle.  
tracking results, we obtained the angular changes of the two links and the change in displacement of the tip of the wiper blade in the direction perpendicular to the wiping surface.  
Figure 11 shows the experimental results obtained during the wiping process; Figure 12 shows an enlarged view of Figure 11c,f near the occurrence of the jump phenomenon. Figure 11d,e confirm that attack angles of 0 and 10 degrees do not produce the jump phenomenon. When the attack angle is 18 degrees, however, the jump phenomenon occurs, as shown in Figures 11f and 12b. We can also confirm from Figures 11c and 12a that the angles \(\theta\) and \(\varphi\) converge to 0 at the same time when the jump phenomenon occurs. In turn, these two angles do not converge to 0 at the same time when no jump phenomenon occurs, as shown in Figure 11a,b.  
The experiments also suggested that the stick-slip motion does not occur around the reversal point. Thus, even if the angles become 0 at the same time, there is no jump phenomenon. Figure 13 shows the experimental results obtained around the reversal point  
Figure 11: Experimental results during wiping process with zero and nonzero attack angles. (**a**) Angular displacements of two links with zero attack angle. (**b**) Angular displacements of two links with 10-degree attack angle. (**c**) Angular displacements of two links with 18-degree attack angle. (**d**) Variation of \(y\)-coordinate of the tip with zero attack angle. (**e**) Variation of \(y\)-coordinate of the tip with 10-degree attack angle. (**f**) Variation of \(y\)-coordinate of the tip with 18-degree attack angle.  
Figure 12: Enlarged view of Figure 11c,f from 0.09–0.1 s. Panels (**a**) and (**b**) correspond to Figure 11c,f, respectively.  
with different attack angles. Figure 13d-f confirm that the wiper blade does not jump away from the wiping surface around the reversal point at the different attack angles. This is despite the two angles becoming 0 at the same time in this process, as shown in Figure 13a-c.  
There are quantitative discrepancies between the theoretical and experimental results. For example, in the theoretical results, the angles of the two links vary periodically also in the state where the jump phenomenon does not occur, as in Figure 7a,b. However, the angles of the two links do not change significantly in the experiments in such a state, as in Figure 11a,b. Besides, although it was theoretically and experimentally shown that the jump phenomenon becomes more likely as the attack angle increases, the theoretical and experimental values of the attack angle where the jump phenomenon starts to occur are different quantitatively. In the theoretical result, a 10-degree attack angle produces the jump-up phenomenon, as shown in Figure 7c,f. However, there is no jump phenomenon with a 10-degree attack angle in the experimental result, as shown in Figure 11b,e. In addition, in the theoretical results where the jump phenomenon occurs, the angles of the two links are very close to 0 at about 1.66 s and 1.68 s before they become 0 at the same time, as in Figure 8a. However, the angles of the two links are not so close to 0 at about 0.05 s, 0.06 s and 0.07 s before they become 0 at the same time in the experimental results shown in Figure 11c. The actual wiper blade is an infinite-degree-of-freedom elastomer rather than the low-degree-of-freedom two-link model used in the theoretical analysis. This is the reason for the quantitative discrepancies between the theoretical and experimental results.