# Development, Experimental Assessment, and Application of a Vacuum-Driven Soft Bending Actuator
## 3 Experimental Results and Discussion
### Experimental Assessment of Angular Velocity-Bending Angle Characteristic  
Compared to the previous experimental assessment, this chapter analyzes the actuator's performance in actual working conditions. This means that the movement of the actuator's lower part is no longer constrained by the rope, allowing it to move freely to its final position. Therefore, the actuator was mounted on the profile structure as before, with a camera added to the same structure to capture its bending motion. The camera was used due to the complexity of using a sensor that could reliably measure the VSBA bending angle. The bending angles over time were determined using software the Microsoft Clipchamp 4.0 for video analysis ([[https://clipchamp.com/en/](https://clipchamp.com/en/)]([https://clipchamp.com/en/](https://clipchamp.com/en/)), accessed on 17 January 2025). The experimental measurements of bending angles over time were conducted at vacuum pressure values ranging from \(-0.2\) to \(-0.8\) bar. At a vacuum pressure of \(p=-0.1\) bar, all versions of the VSBA achieved only a small bending angle after a long time, so this measurement was excluded. Although the velocity of pneumatic actuators is a function of the airflow, according to the orifice equation, airflow depends on the pressure drop at the orifice. Therefore, the actuator's velocity was analyzed as a function of pressure, as proportional pressure control valve dynamics used in the experimental setup can described by the orifice equation. Additionally, the experimental assessments were first conducted without an external load and then with an external load. The results of the experimental measurements for the VSBA-1 without load are shown in Figure 6a. The results determined that for all vacuum pressure values, the VSBA-1 achieves a maximum bending angle of \(\theta=140^{\circ}\). However, it is evident that the VSBA-1 achieves 97% of the maximum bending angle in 1.6 s at \(p=-0.8\) bar, demonstrating the actuator's very fast response. As the vacuum pressure decreases, the time increases: at \(p=-0.2\) bar, the time is 3.7 s. Also, it is notable that a nearly linear relationship between bending angle and time was observed up to an angle of \(\theta=120^{\circ}\) for vacuum pressures ranging from \(-0.3\) bar to \(-0.8\) bar. Further experiments were conducted on the VSBA-1 with a 0.5 kg load to investigate the actuator's behavior under real load conditions. The results showed the same operating dynamics, but with a reduced maximum bending angle of \(\theta=135^{\circ}\) at \(p=-0.8\) bar and a longer time of 3.1 s (Figure S1a is provided in the Supplementary Materials), approximately 50% longer than without a load. The results of the maximum bending angle for different values of vacuum are provided in Table 2 for cases with and without external load. Figure 6: Bending angles over time for actuators without load: (**a**) VSBA-1; (**b**) VSBA-2; (**c**) VSBA-3; (**d**) VSBA-4. The following laboratory measurements were conducted for the VSBA-2 without load, and the results are shown in Figure 6b and Table 2. The results indicate that the actuator achieves a maximum bending angle of \(\theta=120^{\circ}\) at \(p=-0.8\) bar, requiring 3.5 s--about 57% more time compared to the VSBA-1. Also, when comparing the time required to reach 97% of the maximum bending angle, the VSBA-2 takes about 60% more time than the VSBA-1, demonstrating that the VSBA-2 has a slower response. Additionally, it is noticeable that the actuator reaches \(\theta=90^{\circ}\) (approximately 75% of the maximum bending angle) in 1.2 s, after which it requires 2 s to reach the final position. This operating dynamic results from the increased stiffness of the heat-shrinkable material and for bending angles greater than \(90^{\circ}\); the resisting force increases significantly, requiring more time to reach the final position.