## 5 Experimental Discussion
### Experimental Verification and Analysis  
For the purpose of verifying the principle of ALS-EHA, comparative experiment analysis is now conducted on two FPVM and ALS EHA systems. the experimental conditions are as follows: the position command is a sinusoidal signal with a frequency of 0.1 Hz and an amplitude of 40 mm, and the stiffness of the loaded spring is \(3.5\times 10^{6}\)\(N/m\), for which the operating condition is low speed and heavy load.  
Figure 17a,b present the position response curve and position error curve of the system. Figure 17a shows that the displacement output of ALS-EHA can accurately track the input command like EHA-FPVM under the condition of low speed and heavy load. According to Figure 8, it can be found that ALS-EHA has the highest tracking error at its maximum velocity point (blue circle), up to about 1 mm, which is 33.3% higher than that of EHA-FPVM at 0.75 mm, while the tracking error is smaller than that of EHA-FPVM near the zero point of velocity (black circle).  
Figure 18 displays the variation in displacement ratio of ALS-EHA and EHA-FVPM. the displacement ratio of EHA-FVPM is 1. However for ALS-EHA, the maximum displacement is maintained at the top velocity point, that is, its ratio is 1. With the decrease of velocity, it drops. When the velocity is 0, the displacement is declined to the value corresponding to the highest load pressure, and its ratio is 0.4 for the load pressure 14 Mpa as illustrated in Figure 18. It can be seen that in actual working conditions, active control for the displacement ratio of ALS-EHA can be achieved.  
Combining Figures 17 and 18, we can further notice that the reason why the tracking error of proposed ALS-EHA is smaller near the zero velocity is that the displacement is smaller, so the hydraulic reduction ratio is lower, and the damping in the dynamic stiffness model is more mini. Due to the poorer damping, the stiffness of ALS-EHA is higher than that of EHA-FPVM, which is consistent with the analysis results in the third part, so it has a strong ability to resist load disturbance. In addition, the reason why the tracking error of ALS-EHA at the maximum velocity point is larger is that  
Figure 17: Position response and error curve.  
Figure 18: Displacement ratio change curve.  
the displacement ratio shown in Figure 8 is not the largest at this time, resulting in a weaker tracking capability than that of EHA-FPVM. Therefore, our next research work is to solve this problem by designing an appropriate active load controller, that is, we hope that the regulation law of pump displacement conforms to the velocity variation of ALS-EHA.  
Figure 19a-c present the copper loss heating, iron loss heating, and total heating of the two structures of EHA. Figure 19a presents the copper loss heating of EHA-FPVM reaches 21.69 kJ after 140s and that of ALS-EHA is only 13.46 kJ with 37.9 percent less than the former. Figure 19b displays that the copper loss of EHA-FPVM climbs to 3.197 kJ after 140 seconds and that of ALS-EHA rises to 3.566 kJ, 11.54 percent higher than the former. It is easy to observe that under low-speed and large-load conditions, copper loss is the main factor that affects the system's heating. the total motor loss heating is obtained based on the two configurations After 140 seconds in Figure 19c, with EHA-FPVM 24.89 kJ and 17.02 kJ for ALS-EHA. It is proved that the calorific capacity of proposed ALS-EHA has weakened 31.6% than that of traditional EHA-FPVM, which is beneficial to solve the heating problem of motor applied for EHA, and improve the system efficiency, as well as a smaller power motor can be selected in the EHA design. This shows that the ALS-EHA is correct in principle.