## 5 Experimental Verification
### Experimental Results  
The flow inter-conversion of the accumulator and piston chamber in group 1 is shown in Figure 14. The positive values indicate that the oil flows from the piston chamber to the accumulator, while negative values represent the opposite direction. It is can be seen that, as the piston movement changes from extension to retraction, the accumulator undergoes a process of storing and releasing oil during each swing phase. In the swing phase, the extension of the piston accompanies the flow released, while the retraction of the piston accompanies the flow absorbed by the accumulator. In the supporting phase, all of the actuators are in the contraction stage. The reversing of the piston causes the pressure in the piston chamber to increase, and then part of the oil that should be expelled from of the actuators flows into the accumulator, so the values are negative. Due to errors of the sensor and calculation mode, there are little differences between the simulation and the experiment.  
The energy consumption curves of the leg prototype in group 1 are shown in Figure 15. The energy consumption values of different conditions at time of two seconds are shown in Table 8. It can be seen from the data that the energy consumption of the leg prototype driven by HPCAs is reduced by more than 50 J compared to the original actuator.  
Figure 14: Flow of accumulator in group 1.  
Figure 15: Energy consumption of leg prototype in group 1.  
Figure 16 shows the flow curves of group 2. It can be seen that the experimental results of group 2 are similar to those of group 1. The piston movement changes from extension to retraction, the accumulator undergoes a process of storing oil, and it undergoes a process of releasing oil when the reverse change takes place. According to the test results of the hip actuator, the changes in the initial inflation pressure and working volume of the accumulator have no obvious effect on the energy consumption of the HPCA, but for the HPCA that drives the knee F/E, the results are reverse. The main reason is that the knee actuator is subjected to a greater load than the hip joint due to the topology of the leg, and to a certain extent.  
The energy curves of the leg prototype in group 2 is shown in Figure 17. The energy consumption values of different conditions at time of two seconds are shown in Table 9. It can be seen from the data that the energy consumption of the leg prototype driven by HPCAs is reduced by more than 80 J compared to the original actuator.  
From the above experiment results, it can be summarized that, although the initial inflation pressure or working volume of the accumulator does not have significant influence on the energy efficiency of the HPCA in the experiment, it is undeniable that the energy efficiency characteristics of the HPCA are also related to the load.  
Figure 16: Flow of the accumulator in group 2.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Description** & **Energy** \\ \hline original actuator & 1997 J \\
2 Mpa & 1945 J \\
4 Mpa & 1915 J \\ \(1.3\times 10^{-5}\) m\({}^{3}\) & 1893 J \\ \(4\times 10^{-5}\) m\({}^{3}\) & 1921 J \\ \hline \hline \end{tabular}
\end{table}
Table 8: Energy consumption of two gait cycle in group 1.