| Hydraulic system has the characteristics of large ratio between power and weight, compact conformation, flexible configuration, large torque in low-velocity and easy to implement. So it has been applied in drill design widely. At present, the fully hydraulic drill rig with the top drive head is the leading type for the foreign drill, which was extensively applied to exploration of mineral resources, groundwater resources, and geothermal energy, engineering geological investigation and foundation engineering etc. The results and analyses have shown that the drilling load is complex and variable, the main affecting factors are drilling technology, drilling parameters, stratum, equipment conditions, and drilling conditions etc.During the drilling process, these affecting factors are non-linear, time-varying and indeterminate. Moreover, there are complicated interactions among them, difficult to estimate and control accurately. Therefore, drilling load change not only has the characteristics of randomicity, fuzziness, and relevance, but also the discreteness, dynamic development etc.The functions and characteristics of hydraulic system are the key factors to decide whether the fully hydraulic drilling's performance is excellent. For the hydraulic system of drill rig, the key question is how to satisfy the objective request of the drilling load characteristics with the driving characteristics of hydraulic systems. However, at present, majority of entire hydraulic drill used the simple switch control hydraulic system consist of manual control valve and pump in domestic and foreign , which not only result in the bad drilling control ability and load adaptability, but also the low drilling efficiency and energy efficiency.In order to overcome the performance deficiencies of the hydraulic system applied in old drilling machine, and satisfy the requirements of high power drilling and the complex drilling control, this paper introduces a new scheme of drilling hydraulic system for improving the load adaptability, and a lot of analyses and the researches have been done such as the system structure, the control principle and the function characteristic etc. The researches establish the foundation of the automation and the intellectualization of drilling equipment for further improving the ablility of drilling control and load adaptability of the entire hydraulic drill and achieving the higher drilling efficiency.First, this paper fully introduces the analyses and researches of the function and load characteristic of the drill rig . At present, the drill hydraulic system was instability which is easy to be influenced by load and has large energy loss and low drilling efficiency. For meeting the requirement of adapting to characteristic of load, this paper put forward the general scheme of new drill hydraulic system with load adaptability, which has the ability to monitoring and identifying variety of load in real-time, and can adjust states of control system automatically according to condition of load, for keeping optimum drilling efficiency.Then, on the base of establishing the control model, by theoretical analysis and computer simulation, the further analyses and researches were carried out fully in this paper, which include the dynamic or static characteristic of load sensing system, key influential factor and load adaptability of drilling. The result was as follows:①In normal operating condition, the flow rate of load sensing system is proportional to the opening of throttle valve, which is not affected by load change, and has a good rigid mechanical characteristic;②As the load pressure and pressure difference set up by LS valve are both low, the load sensing system may be in the unstable state;③The larger opening of throttle valve will result in supersaturation of system, in which the flow rate can not be adjusted;④Increasing the length of oil pipe and damping of LS pipe will cause response lag, but enhance the stability of system;⑤When the pressure difference is set up to 2MPa by LS valve, the response speed of system is vary fast, further increasing value of pressure difference is not effective;⑥Increasing damping of load properly will be help for improving the stability of system, and reducing the overshoot and adjustment time;⑦The large moment of inertia of load will lead to low response speed of the system , large overshoot and adjustment time.Based on research above, the new type hydraulic control system of core drill rig was developed, which adopt the load sensing system and constant pressure control system. The load sensing system was applied to control the rotation operation and hoisting operation, and the constant pressure system was applied to control the feed operation. The system can supply flow required by feed force, according to load change, and satisfy the requirement of persistent and stable feed, so it has excellent load adaptability. The new hydraulic system enhanced the load adaptabiliy and drilling control ability, reduced the energy loss, and improved the overall performance of core drill. Compared to mechanical-hydraulic load sensing system, the electro-hydraulic control system further adapts to the demands of developing the intelligent drilling control system, because it can adopt the flexible control algorithm. Aiming at the operating characteristics of MWD system, which demand small vibration, much stability, and low rake, the electro-hydraulic control circuits for feed pressure and rotary speed were devised, which consisted of the pilot proportional pressure regulating pump and electro-hydraulic proportional displacement pump. By using computer simulation, the operating characteristics of control circuits were analyzed, which laid the foundation for optimizing structure and parameter of system. For the feeding control system, ti demanded that the output pressure of system is not affected by load change nor rotary speed of power machine, which has a upstanding load adaptability. It also demanded that the length of the pipe connecting proportional pressure must be short in order to assuring stability and precision of control system. For rotary control system, the rotary speed is not influenced by load change and has rigid mechanical features. The ramp control singal can assure the stability and not influence the response rate. Based on analyses above, combining the technical advantages of load sensing system and electro-hydraulic proportional control system, the scheme of electro-hydraulic closed-loop control system was brought forward, which was applied to design of MWD drill rig. It will further improve the control ability and load self-adaptability of hydraulic system, and supply the stable technical support for developing intelligent MWD drill rig.At last, by making use of electro-hydraulic proportional technology, the test-bed with automatic drilling control system was built up, which has the ability of monitoring, recording and controlling the drilling parameters in real-time. The results of dynamic testing of control system showed that both response rate of pressure and rotary speed were fast, and the response time of pressure was about 0.2s, and the that of rotary speed was about 0.5s, which can meet the requirement of the real-time control. But, because there were much disturbing factors, both accuracy and stability of the open-loop control system were not so well.For enhancing the anti-jamming ability of system, the ameliorate PID algorithm which structure and parameter were optimized by theoretical analysis and experimental investigation, was applied to realizing the feedback control of feed force and rotary speed. The testing results show that when proportional coefficient KP is 0.5, integral time coefficient TI is 10, and differential time coefficient TD is zero, the performance of closed-loop control system is outstanding. The pressure error is less than 50N, and rotary speed error is less than 7.5r/min. So the PID algorithm improved the accuracy and stability of control system.For improving the stability and adaptability to the complex environmental change of control algorithm, combining the advantages of fuzzy algorithm and PID algorithm, compound fuzzy-PID control algorithm was devised. By testing, after optimizing combination of control parameter, the more excellent performance of closed-loop control for rotary speed and penetration rate was achieved. The actual result showed that rotary speed became more stable, and the penetration rate was limited in a small setting range and the error was only about 10%. So Fuzzy-PID algorithm has outstanding control features such as stronger adaptability and higher precision. Both the stability and reliability of electro-hydraulic control system are enhanced. It will be a favorable basis for developing the more advanced control algorithm and strategy.
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