Comparison and analysis of the control modes of th

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Comparison and Discussion on the control mode of hydrostatic system of underground electric LHD

underground electric LHD is developed on the basis of diesel LHD. Because it has the advantages of no exhaust gas pollution, low noise, low working temperature, small maintenance, low production cost and high operation efficiency, it is adopted by more and more underground mining enterprises, and has achieved obvious economic and social benefits. The basic technical level of domestic electric LHD is close to the international advanced level, but there is still a certain gap in the research on the operation and control of the transmission system

according to the application of LHD and the analysis of relevant literature, the drive system of small LHD below 1m3 mostly adopts the stepless speed regulation scheme of electric hydrostatic mechanical drive. Choosing a reasonable operation and control mode of hydrostatic drive has become an important link for Jinan testing machine factory to improve the handling, safety and reliability of LHD. At present, there are two main ways to operate and control the hydrostatic drive of small underground electric LHD in China:

(1) mechanical servo control: this way is to select the variable displacement pump and motor of manual servo as the basis to form the hydrostatic drive system, and use the multi link (or push-pull flexible shaft) and the operating rod mechanism to form the multi link mechanism to transmit the operating motion. Manual servo hydraulic pump (motor) is easy to select, so it is most widely used in domestic electric LHD. However, this method is affected by many factors, such as the space and the position of the console, the layout of multiple connecting rods is complex, and it is easy to have motion dead points; The volume sealed due to emergency is changing, but the braking and hydrostatic control system is difficult to realize linkage and other shortcomings. In case of emergency braking, the hydrostatic drive system continues to work, resulting in unsafe factors such as excessive braking torque and motor overload operation

(2) electric servo control: it is a hydrostatic drive system based on the electronically controlled variable displacement pump and motor, which controls the hydrostatic drive system to achieve stepless speed change by changing the current of the two proportional electromagnets on the electromagnetic directional valve of the variable displacement pump (motor) through the electrical system. Its advantage is that when the braking system is controlled by the electromagnetic directional valve, it can realize the linkage between the emergency braking and the hydrostatic driving system without too much force through reasonable electrical and hydraulic design. However, due to safety requirements, its operating voltage must be controlled below 36V, and the current domestic low-voltage electrical components, especially the sliding wire rheostat, generally can not adapt to the underground humid environment and the vibration and impact of the machine, so the electrical control method can not achieve satisfactory results on the underground electric LHD

2 working principle of hydraulic servo control system

in order to overcome the shortcomings of the above two methods, Shandong Jinling iron mine has designed a set of hydraulic servo control system integrating mechanical, electrical and hydraulic while widely collecting and studying foreign advanced technology and combining the domestic hydraulic technology level. It is based on the hydraulic variable pump and motor to form the hydrostatic drive system. The stepless speed change of the hydrostatic drive system is realized by controlling the pilot valve to change the pressure difference between the two hydraulic control oil ports on the hydraulic control reversing valve of the hydraulic pump (motor). This method uses hydraulic oil as the working medium, and the working oil circuit is completely closed, so it has the characteristics of not afraid of humidity, impact resistance, vibration resistance, etc. At the same time, the use of spring braking, hydraulic release, fully enclosed oil-cooled wet multi disc brake can make most of the hydraulic servo control and braking oil circuit almost blank; On the other hand, China's industry has developed rapidly in recent years. The same hydraulic circuit (as shown in the figure) is designed to realize the linkage between hydrostatic drive system and braking system

2.1 servo control circuit of hydrostatic drive system

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