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Top1. Introduction
Bomb/mine clearance and explosive ordnance disposal are urgent tasks of war-damaged countries worldwide. Many technologies have been developed for both semi-automation and full automation systems for decades. The first designing concept of a remote-controlled explosive ordnance disposal machine (EODM) was presented in the 1990s (Burks, 1992; Terwelp, 2003). Based on the draft concepts, many commercial products of EODMs have been introduced by manufacturers such as UBIM (Russia), Wisent (Germany), Kodiak (UK), etc. (Terwelp, 2003). In recent years, due to the high demand for cleaning bombs/mines after the Vietnam war, preliminary studies of EODMs have been investigated and applied to manufacture. EODMs have been equipped with integrated operational devices such as radar detectors, digging devices, bomb pickers, high-pressure water jets and hydraulic hammers. These machines can replace single functional machines which are currently used for clearing bombs and explosive ordnance disposals such as single-bucket excavators, high-pressure water jetting devices and bomb picking devices. Moreover, EODMs have been developed with more intelligent, multi-functional and multi-purpose operations, with fully controlled systems, high-resolution cameras and smart sensors. Not only is this application user-friendly, highly accurate and time-and-effort saving, but it also ensures almost perfect safety for operators following EODM standards (Manz, 2001; Fleming, 2004; Lee, 2019). These standards are also the current trend in applying autonomous systems to both civil and military industries when considering human factors and political risks in the near future of the automation technology (Pratt Rogers, 2019).
Through the continuous development and maturation of the current technology, numerous challenges have been faced by researchers in the practical use of EODMs and autonomous vehicles. These challenges have motivated business models, national ethics, legality, etc. to improve (Chai, 2020). Despite certain similarities in the use and functions of EODMs across manufacturers worldwide, significant differences in the control system design can be found. Especially, the design of hydraulic systems that drive working equipment (1. Base machine; 2. Boom; 3. Arm; 4. Excavation – gripper bomb mechanism in Fig. 1a) to carry out soil excavation (David, 1998; Chang 2002; Casoli, 2013; Wang, 2014; Ge, 2017), bomb picking and transportation (Sulaiman, 2016; Manz, 2001; Terwelp, 2003; Wang, 2014; Fleming, 2004) onto specialized vehicles and other tasks is unique to individual manufacturers. Comparing to electric and pneumatic drive systems, the hydraulic drive system has higher specific power, lower hysteresis and higher precision control (Casoli, 2013; He, 2018).