# A Study on a New Independent Metering Valve for Hydraulic Boom Excavator
## 5 Conclusions  
In this paper, a new IMV configuration that could regenerate gravitational potential energy was developed for a boom system. The proposed structure included three EHPVs and one directional valve that could ensure similar working modes as the CIMV system. In addition, a control strategy was developed based on the velocity feed-forward and position feedback method to improve the stability and safety of the proposed system. A real test bench, based on laboratory conditions, was built to evaluate the effectiveness of the NIMV system in detail. Then, the NIMV system was compared with the CIMV system in terms of the working performance and energy-saving potential. The results showed that the NIMV system outperformed the CIMV system in terms of the following characteristics:  
* The energy savings of the NIMV system was higher than the CIMV system by approximately 4% in the PE mode, 22% in the PR mode and 6.5% in the HSRE mode. The proposed system removed the use of a check valve, which is the main factor that caused energy loss in the CIMV system. Moreover, the throttling loss was reduced by the valves, which were logically connected, and are shown in the HSRE mode. * In the proposed configuration, the cost of the system was significantly reduced by reducing one EHPV and a check valve, while ensuring the stability of the IMV system. * Both systems applied a simple controller and achieved a high tracking performance. However, by eliminating the factors that cause losses in the system, the NIMV system could work with a higher precision and stability. Especially, the displacement tracking error of the cylinder in the NIVM system was about 0.043 m in the HSRE mode and about 0.034 m in the LSRR mode, while in the CIMV system it was around 0.065 m and 0.04 m, respectively. However, the test bench still exhibits some limitations. First, these studies only focused on the boom system, so the LSRR mode was omitted in the experiments. Second, the PE and HSRE modes were differentiated based on two factors, the velocity and load force. However, the load force in this test bench was a fixed value. Thus, the switching mode must be designed based on the speed to determine the mode of operation. Generally, a NIMV, with its proper logic control, has a strong ability to be applied in practical applications. In future research, we will improve the proposed configuration, apply mode switching for the system, and integrate the NIMV system into a real excavator. With the energy-saving potential and a good working performance, the proposed NIMV will be a trending research direction in the future. [PERSON] was the supervisor providing funding and administrating the project, and he reviewed and edited the manuscript. [PERSON] carried out the investigation, methodology, analysis, and validation and wrote the original manuscript. [PERSON]-[PERSON] checked the manuscript and supported the model for research. All authors have read and agreed to the published version of the manuscript. This research was supported by Basic Science Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT, South Korea (NRF 2020R1A2B5B03001480) and this work was supported by \"Regional Innovation Strategy (RIS)\" through the National Research Foundation of Korea(NRF) funded by the Ministry of Education(MOE) (2021 RIS-003). Not applicable. **Data Availability Statement:** Thank you very much. We have understood and agreed to the policies of MDPI. The authors declare no conflict of interest. [PERSON]; [PERSON]; [PERSON] High Precision Energy Saving Motion Control of Hydraulic Cylinder Based on Integration of Valves and Pump. In Proceedings of the BATH/ASME 2018 Symposium on Fluid Power and Motion Control, Bath, UK, 12-14 September 2018; 2018; p. V001T01A019. * [PERSON] et al. (2020) [PERSON]; [PERSON]; [PERSON] Precision Motion Control of a Servomotor-Pump Direct-Drive Electrohydraulic System With a Nonlinear Pump Flow Mapping. _IEEE Trans. Ind. Electron._**2020**, _67_, 8638-8648. [CrossRef]
* [PERSON] et al.