## 4 Results
### Tip Position  
The results (experimental and simulated data) for both actuators tested without load are shown in Figure 7. Of all the data points (shown as unfilled circles), we consider particularly important extreme positions (shown as filled circles) at which (i) the pressure of one chamber is maximum and of the others is zero (Positions 1, 3, 5), (ii) the pressure of two chambers is maximum and of the third is zero (Positions 2, 4, 6), and (iii) the pressure of all chambers is maximum (Position 7). For these extreme positions, a comparison of the coordinates and the error are additionally shown in Figure 7.  
Figure 7: _Cont._  
Throughout all measurements (also with load), the deflection of Position 2 is remarkably larger than for the other extreme positions, which also applies for the other data points in this \"direction\". However, a structural error in the setup could not be identified. In addition, hand manufacturing has a significant influence, as can be seen from Position 7 since the \(x\)-coordinates and \(y\)-coordinates in the experiments are not zero. Comparison of the experimental data of the two actuators results in deviations of 2.1% (mean deviation of the extreme positions relative to the actuator length).  
In general, the simulation results and the experimental results without load in Figure 7 agree well. This is also depicted by the mean error of the extreme positions relative to the actuator length (3.3%/3.4%), which is in a range similar to comparable approaches [3, 8, 10, 23, 24]. Position 6 of Actuator 2 in Figure 7B is an outlier (the only one of all data points measured) and therefore not considered in the mean error. Note that restricting on the extreme positions increases rather than decreases the mean error compared to considering all data points.  
The results with a load of 1 N applied to the free end of the actuator are shown Figure 8. Again, the mean error of the extreme positions (2.9 %/3.1 %) is still in a range typical for comparable approaches without load and with load [25]. However, it is significantly lower than the error of [PERSON] et al. [7], where also a load is applied to the tip of the actuator.  
Figure 8: _Cont._  
Figure 7: Actuator 1 (**A**) and Actuator 2 (**B**) without load: tip position in \(x\)–\(y\) plane with extreme positions highlighted (top), coordinates of seven extreme positions (middle) and error at these positions (bottom).  
The extensional stiffness \(E\) has an important impact in our approach, since it also determines the bending stiffness. For the simulations, we used \(E=200\,\mathrm{N}\) that was identified as a mean value in a simple experiment without any fitting methods. In order to verify the sensitivity of the error on \(E\), we performed additional simulations with varied \(E=180\,\mathrm{N}\) and \(E=220\,\mathrm{N}\), and with a pressure-dependent extensional stiffness \(E(F)\) being known from the experimental parameter identification. The results are shown in Table 3. As expected from Figures 7 and 8, where the simulation predicts too large deflections of the tip, increasing the extensional stiffness to \(E=220\,\mathrm{N}\) lowers the error compared to \(E=200\,\mathrm{N}\). Using a pressure-dependent extensional stiffness \(E(F)\) lowers the error to a range close to the deviation between the prototypes due to manufacturing errors.