# Development, Experimental Assessment, and Application of a Vacuum-Driven Soft Bending Actuator
## 3 Experimental Results and Discussion
### Experimental Assessment of a Maximum Blocking Force  
Experimental measurements were conducted for VSBA bending angles ranging from 15\({}^{\circ}\) to 90\({}^{\circ}\), in 15\({}^{\circ}\) increments. The polypropylene rope was used due to its resistance to stretching, and its length was precisely measured and adjusted to match the actuator's bending angle during the blocking force measurements. Vacuum pressure values varied from \(-0.1\) to \(-0.8\) bar in increments of \(-0.1\) bar. The maximum blocking force results for the VSBA-1 are presented in Figure 5a. These results indicate that the maximum blocking force occurs at an angle of \(\theta\) = 15\({}^{\circ}\), and as the bending angle increases, the force decreases for all vacuum values. This occurrence is due to two effects: first, the effect of vacuum pressure on the ribbed surface, producing both horizontal and vertical force components. The triangle ribs have the maximum angle in the actuator's initial position; as the bending angle increases, the rib angle decreases,which directly reduces the vertical force component and, consequently, the total force. The second effect is result of an increasing resisting force within the actuator as the bending angle increases, which is caused by the material's increased stiffness during deformation. Also, the ribs on the actuator bending side move closer, (see Figure 1c), which further contributes to the increase in resisting force, evident from the pronounced decrease in maximum blocking force observed between bending angles of \(30^{\circ}\) and \(45^{\circ}\). The maximum force was achieved at a vacuum pressure of \(p=-0.8\) bar, reaching \(F=108\) N at an angle of \(\theta=15^{\circ}\). As the bending angle increased to \(\theta=90^{\circ}\), the force decreased to \(F=20\) N. The results show that at an angle of \(\theta=90^{\circ}\), the force is approximately 20% of the maximum value, leading to the conclusion that further force measurements would not be conducted. Also, for blocking force measurement above \(90^{\circ}\), repositioning the load cell is needed to ensure the correct angle between the rope and the screw on the lower lid. The following experimental assessments of maximum blocking force were performed for VSBAs made from heat-shrinkable material. The measurements were conducted using  
Figure 5: Results of maximum blocking force: (**a**) VSBA-1; (**b**) VSBA-2; (**c**) VSBA-3; (**d**) VSBA-4. the same procedure, with identical bending angles and vacuum pressures as in the previous experiment. The maximum blocking force results for the VSBA-2 are shown in Figure 5b. The results again indicate that the maximum blocking force is reached at a smaller bending angle across all vacuum values. Similar to the VSBA-1, a decrease in force with increasing angle was observed. However, for the VSBA-2, the force reduction is more significant between angles of 15\({}^{\circ}\) and 30\({}^{\circ}\). Compared to the VSBA-1, the maximum blocking force is reduced, primarily due to slightly smaller dimensions and increased stiffness of the heat-shrinkable material. The maximum blocking force, achieved at \(p=-0.8\) bar, is \(F=50\) N at an angle of \(\theta=15^{\circ}\), while at an angle of \(\theta=90^{\circ}\), the force is \(F=6.6\) N.  
The maximum blocking force results for the VSBA-3, which has the same outer diameter as the VSBA-2 but features increased rib spacing, are shown in Figure 5c. A comparison of the measurement results shows that the VSBA-2 achieves a slightly higher maximum blocking force at \(\theta=15^{\circ}\) angle, while the VSBA-3 generates higher blocking forces at all other bending angles. This performance of the VSBA-3 is attributed to the increased rib spacing, which reduces ribs contact and consequently decreases the resisting force.