Intelligent Control Strategy of Electro-hydraulic Drive System for Raising Boring Power Head

: The power head is the key part of the rock breaking work of the raise boring machine. Because the power head cannot adjust speed in time with the change of complex rock stratum, it leads to high failure rate, low work efficiency and even accidents, so it is urgent to improve the controllability of the power head. In this paper, the electro-hydraulic coupling mathematical model of the power head is established by using the characteristic equations of dynamics and hydraulic components, and the control strategy of the fractional electro-hydraulic drive system of the power head is proposed; Genetic algorithm (GA), particle swarm optimization (PSO) and whale algorithm (WOA) are used to adjust the parameters of FOPID, so as to improve the control effect of electro-hydraulic system; The results show that the step response of WOA-FOPID control strategy is also better than that of genetic algorithm (GA) and particle swarm optimization (PSO). It can reach a stable state in 0.02 seconds, and the overshoot is only 0.12137%; The test verifies the correctness of the adaptive control and simulation results of the power head, which can effectively improve the adaptability of the power head to complex coal seams.

Due to the advantages of the high safety, relatively low cost and ensuring the safety of operators to the greatest extent, the reverse well drilling rig is widely used in underground roadway space, mine development, subway tunnel and other projects, and the drilling technology is also a fundamental change technology for well hole drilling. In recent years, with the improvement of intelligent control technology of the drive system of the reverse well drilling rig, it has not only accelerated the speed of excavation, but also greatly alleviated the labor intensity.
The power head is the key component of the reverse well drilling rig, and its control method and effect directly affect the safety and stability of the reverse well drilling rig in construction. At the same time, the intelligent control of the power head also has a positive role in promoting the intelligent construction of coal mines nationwide. Therefore, the intelligent control strategy of the electro-hydraulic drive system of the power head has attracted the attention of the majority of scientific researchers at home and abroad. For example, Xiu-kunHu, Zhi-qiangLiu [1] and others studied the relationship between the four parameters of drill pipe tension, torque, rotational speed and drilling speed in the power head control system. Shen Wei [2] et al. formulated the mathematical modeling and robust integral adaptive controller of the power head valvecontrolled hydraulic motor based on The Padde's theorem and the reverse step derivation method, which improved the accuracy and tracking speed of the system control. Yang Yanlin [3] et al. proposed a fuzzy PID control algorithm based on the problem of synchronization of four hydraulic motors in the power head device, which improved the synchronization accuracy of the motor. Cheng Lilin [4] Using AMESim and Matlab-Simulink to construct a joint simulation model of the test bench drilling simulation system, Cheng Lilin designed a fuzzy adaptive PID controller to analyze the control performance of the power head system. Zhang Yang [5] Using the method of cosimulation between AMESim and Matlab-Simulink, the adaptability of different control algorithms of traditional PID fuzzy and feedback linear synovial membrane structure to the position tracking control of valve-controlled asymmetrical hydraulic cylinders is analyzed, and the problems of nonlinearity and low control accuracy of the electro-hydraulic control system of the power head are solved. Foreign hydraulically driven reverse well drilling rig, power head drive using electro-hydraulic proportional PID control technology, control unit using PLC or engineering controller [6][7][8][9] , due to the introduction of computer control technology, a variety of more complex control logic and PID control algorithms can be realized. The above literature research has made certain contributions to the intelligent control of the electro-hydraulic drive system of the power head of the reverse well drilling rig, and laid a certain foundation for the intelligent control algorithm of the power head. However, the research in the above article is based on the traditional PID control algorithm, especially in the downhole operation, the surrounding rock parameters, the drilling rig underground force complex these uncertain factors will make the driving head of the drilling rig can not adjust the control parameters in time, and eventually lead to low drilling efficiency, short life of the rock breaking hob, and even cause drill damage, jam drilling, etc. Under special working conditions, the traditional PID control effect is not ideal, even if the PID is re-parameter tuned, it still cannot achieve a good control effect, and it is essentially impossible to overcome the shortcomings of traditional PID control technology. Therefore, the complex system has a low control accuracy, reflecting the poor sensitivity and other issues, it is difficult to explore the intelligent control principle of the electro-hydraulic drive system of the power head from a deep level, and the parameter selection of the PID controller has a great impact on the control effect, the traditional parameter tuning method is still based on experience, it is difficult to find a set of parameters with good control effect in a short period of time.
Fractional order FOPID controller has 5-bit adjustable parameters. Compared with other control laws, it has better dynamic performance, parameter adjustment flexibility and control accuracy [10][11][12] ,There is a great vacancy in the research and application of fractional order fopid in the research of electrohydraulic system control method of raising boring. Based on the internal control principle of the reaming operation of the power head of the reverse well drilling rig, if the control effect is required to have good timeliness and reliability, the parameter adjustment research of the intelligent control algorithm is also indispensable, such as the particle swarm algorithm [13][14][15] , the genetic algorithm [16] , the gravity search algorithm [17] , the neural network algorithm [18] , the ILMI algorithm [19] and the whale algorithm [20] , which are all applied in the PID controller, improving the control effect of the traditional PID controller. Got rid of the method of parameter tuning that relies on experience.
Based on this, this paper establishes the electrohydraulic coupling model of the power head of raise boring machine from the dynamic principle, electrohydraulic coupling properties and the characteristic equation of hydraulic components, and puts forward the control method of the power head electro-hydraulic drive system based on fractional FOPID. In order to further improve the control effect of the system, the genetic algorithm (GA), particle swarm algorithm (PSO), whale algorithm (WOA) three groups of intelligent optimization algorithms are used to adjust the FOPID and PID controller parameters, and the influence of the above different combination algorithms on the control system is evaluated, so as to provide theoretical guidance for the reliability of the reaming operation of the reverse well drilling rig [21][22][23][24] . Finally, field experiments were conducted in Liuqiao Town, Suixi County, Anhui Province, to prove the effectiveness of WOA-FOPID control strategy in electro-hydraulic drive control system. It further provides new theoretical guidance for the intelligent control strategy of the electro-hydraulic drive system of the power head.

Mathematical modeling
This article takes a deep well lane full-section test drilling rig (raising boring) as an example to study, which is the most widely used [25] and belongs to the lower lead upward expansion type. In order to make the intelligent drilling technology be applied in the reverse well drilling rig, with the power head as the research object, the PLC combined with the HMI design rock breaking control system, four variable piston pump A11VLO130LRDS are connected in series into two groups, driven by 132kw motors, driving four MCR15A1500W80Z32A0M2L4 2S The 506U twospeed radial piston motor, hydraulic motor also controls the rotation of the power head [26][27] . The overall idea of the structure composition, construction process and control scheme of the reverse well drilling rig and the power head is shown in Fig. 1. In order to facilitate the theoretical modeling and analysis, the basic assumptions of hydraulic motor modeling are made. On this basis, the proportional amplifier, electro-hydraulic proportional control valve, power head electro-hydraulic coupling model and the transfer function of power head hydraulic motor speed are established respectively.
The signal output by the controller is a voltage signal or a current signal, which is a component that amplifies its input signal, and simplifies this model to a proportional link because of its input and output characteristics, and its transfer function is: K is the gain of the proportional amplifier.
The current signal output by the proportional link is based on dynamics and electromagnetic induction to drive the proportional solenoid movement, and then the valve spool generates motion, thereby controlling the size of the valve opening and the direction of the liquid in and out. The working principle of the electrohydraulic proportional control valve is established, and the following expressions are established for the relationship between the coil current in the electromagnet, the driving force of the electromagnet, and the displacement of the valve core: The transfer function obtained by pulling the change of equation (2) is: In the formula, is the natural frequency of the spool,  is the damping ratio of the spool, and is the gain of the electro-hydraulic proportional valve. The electro-hydraulic coupling model of the power head is composed of the hydraulic motor connected to the power head through the deceleration device, so the following relationship is established according to the flow continuity of the hydraulic motor valve, the static characteristic equation, the dynamic balance equation of the shaft and ( ) ( ) mm s s s   As can be seen from the Fig., the hydraulic motor and the power head are connected through the deceleration device, and the angular velocity exists: .Perform a pull transform on equation (4) to get the following equation: From equation (5) amplifier, electro-hydraulic proportional valve, hydraulic motor related parts of the parameters are as follows: the inertia of the motor shaft J is 67kg•m 2 , e J is 0.4755kg•m 2 , the total volume t V of the connecting pipe is 3×10 -4 m 3 , the elastic modulus of the system is 6.9×10 8 N/m 2 , the flow gain q K is 2.42m 2 /s, the motor displacement is 2.39×10 -4 m 3 /rad, the gear ratio of the reducer is i of 6.817, and the open-loop transmission function of the power displacement signal by calculating the angular velocity of the power head is: By formula (7) to obtain the system without interference and control Bode diagram as shown in Fig. 2. From Fig. 2, it can be seen that when the amplitude-frequency characteristics reach zero decibels, the phase frequency characteristics are below -180 ° line, and the phase lag point has a negative stability margin at the 180 ° point, so there is a stability problem in the system, but due to the stability of the system itself and the dynamic characteristics, to make the system have a stable margin, it is necessary to add a controller to adjust to meet the stability requirements. As a branch of the control field, fractional order (FOPID) control has many advantages such as flexible and precise parameter adjustment, large system stability margin, and strong system robustness, and has been widely used in different types of controller design [28][29][30] . Fractional-order   D PI control was first proposed by Igor Podlubny, and its superiority over traditional PID control was demonstrated through response analysis [31][32][33][34][35][36][37][38][39][40][41] .Fractional order   D PI controller of the order of parameters  ,  , can take any real number, in the D I P --plane, according to the different controller parameters to take the value, FOPID control system structure as shown in Fig. 3. Compared with traditional PID control, fractional   D PI control can more subtly reflect the transition process from proportional control to integral control and differential control, so as to achieve a control effect with higher accuracy, better stability and stronger antiinterference ability. The mathematical expression for the FOPID controller is : Where p K is the proportional gain, i K is the integral gain, d K is the differential gain, and  ,  is the fractional and integral order, respectively.

Whale optimization algorithm
Based on the advantages of Fractional Order PID control algorithm, this paper proposes a control strategy based on WOA-FOPID algorithm. There are many kinds of parameter tuning methods for FOPID. According to the regulation characteristics of the algorithm itself, it is mainly divided into traditional method tuning and intelligent optimization algorithm tuning, and intelligent optimization algorithm is widely used because of its self adaptability. In this paper, genetic algorithm (GA), particle swarm optimization (PSO) and whale algorithm (WOA) are combined with FOPID control theory respectively, and the above three intelligent optimization algorithms are used to set FOPID control parameters. The structure of intelligent control algorithm FOPID control system is shown in Fig. 4. Fig. 4 Structure diagram of intelligent control algorithm FOPID control system In order to fully explore the advantages of genetic algorithm (GA), particle swarm optimization (PSO) and whale algorithm (WOA), three intelligent optimization algorithms are combined with PID and FOPID respectively, and the speed control effect of power motor is further analyzed through different control strategies. The flow chart of setting FOPID parameters by the developed intelligent optimization algorithm is shown in Fig. 5. There are many kinds of parameter tuning methods for FOPID. With the development of intelligent and control technology, according to the regulation characteristics of the algorithm itself, it is mainly divided into traditional method and intelligent optimization algorithm. Intelligent optimization algorithm is widely used because of its self adaptability. Whale optimization algorithm (WOA) has been widely used because of its simple optimization mechanism and fast solution speed. The algorithm searches for the optimal solution by simulating the predation behavior of humpback whales [42][43] ,and solves the D-dimensional optimization problem in which f(x) is the optimization objective function: (9) In servo control, the ITAE performance index weights the error so that the error signal converges to zero as soon as possible. Therefore, the optimization objective function generates the objective function of control parameter optimization under the ITAE index, which is defined as: Since the position of the optimal design in the search speed is not known a priori, it is assumed that the current optimal solution is the target prey or close to the optimal solution. After the best search agent is defined, the remaining search individuals will update their locations based on the best search agent. The position update expression is as follows: Where, D represents the distance between the search individual and the optimal solution, X * (T) is the position of the current optimal solution, and the calculation method of coefficient vectors a and C is as follows: In the whole iterative process, a changes linearly from 2 to 0; r1 and r2 are random numbers of [0,1], and Tmax is the set value of the maximum number of iterations.

4) The parameter optimization process is as follows
Using WOA to optimize the control parameters, the optimization variables are expressed as x = [x (1), X (2), X (3), X (4), X (5),] and the optimization variables are mapped to the spatial dimension of whales, dim = 5. The optimization process of fopid control parameters based on WOA is as follows: Step 1: algorithm initialization. Set the population size n of the control parameter objective function, determine the spatial dimension dim of the optimization variable, and the maximum number of iterations of the search max_ ITER and the number of search targets and other related parameters; Step 2: analyze and compare the value of the objective function corresponding to the optimization variable obtained in each search, and then determine the location of the optimal individual, which is defined as X *; Step 3: when p < 0.5 and | a | 1, update the position according to formula (1); When p < 0.5 and | a | < 1, update the position according to equation (12); When p > 0.5 and | a | < 1, update the position according to equation (16); Step4: judge whether the error accuracy and termination conditions of the algorithm are met. If so, the algorithm ends and outputs the optimal variable and the corresponding objective function value; Otherwise, go to and continue the iteration of the optimal solution.

Fig. 6 WOA algorithm steps and contents
Where, N is the number of search targets; L(t) is the time series; e(t) is the error signal between the response frequency and the reference frequency. The smaller Fy, the better the effect of dynamic response.
As shown in Fig.6, the contents and steps of WOA algorithm are summarized.
In this paper, genetic algorithm (GA), particle swarm optimization (PSO) and whale algorithm (WOA) are combined with PID and FOPID respectively. Through different combined control strategies, the control effect of raising boring power head is further analyzed and compared. The specific parameter settings of each algorithm are shown in Table 1 below.  Table 2 for comparison of different combination strategies and control indicators; The dynamic response curve comparison diagram of each combination strategy of the regulation system is shown in Fig.7. Fig.7 (a) is the step response diagram of each intelligent optimization algorithm and PID combination strategy, and Fig.7(b) is the step response diagram of each intelligent optimization algorithm and FOPID combination strategy; The comparison of PID and FOPID combined control strategies based on WOA algorithm is shown in Fig.8.  As can be seen in Fig.7, after adding PID and FOPID controllers, the system can quickly tend to a stable state. Comparing Fig.7 (a) with Fig.7 (b), in the control based on the same algorithm, the FOPID control is significantly better than the PID control in terms of response time and dynamic response; In Fig. 7(a), the step response of WOA-FOPID control strategy is obviously better than the control strategy based on GA and PSO algorithm, and the overshoot is 8 35%, only 0.5% Stable state is reached in 1s; In Fig. 7(b), the step response of WOA-FOPID control strategy is also better than the control strategy based on GA and PSO algorithm, at 0.5% It reaches a stable state within 02s, and the overshoot is only 0.5% 12137% 。 The simulation results in Fig. 7 (a) and Fig. 7(b) show that in the PID/FOPID combination strategy, the whale algorithm (WOA) has more advantages than the genetic algorithm (GA) and particle swarm optimization algorithm (PSO) in the process of intelligent parameter adjustment. The results show that WOA-FOPID is more dominant, which further verifies the superiority of FOPID controller. In these combination strategies, it is concluded that the optimal controller is the FOPID controller based on WOA algorithm, and the parameters of the controller is:

Experiment
In order to verify the correctness and effectiveness of WOA-FOPID control strategy in the electrohydraulic drive control system of the power head of raise boring machine, the performance test of the power head of raise boring machine was carried out in Liuqiao Town, Suixi County, Anhui Province. The on-site commissioning layout is shown in Fig. 9. Fig.9 Site layout In order to meet the normal operation of the rock breaking test rig, the rock breaking control system mainly adopts Siemens s7-1200 series PLC and its expansion module, combined with the control system designed by HMI to realize the start / stop action of the pump station motor, the forward / reverse action of the power head motor, the stepless speed regulation of the power head output shaft, the lifting/lowering action of the thrust cylinder, the pressure, displacement, stroke, constant pressure/constant torque drilling mode switching Precise control of temperature control and automatic operation of pump station. At the same time, the rock breaking control system is equipped with a remote control function to facilitate remote operation. S7-1200 series PLC and large screen display form the control core in the control cabinet, and each working condition monitoring and input/output drive unit cooperate with each other to ensure the stable operation of various control functions of the system. The general scheme of electric control system of raise boring machine is shown in Fig. 10.

Power head speed control scheme
Power head speed regulation control model in the process of power head speed adjustment potentiometer from minimum to maximum, adjust the displacement of variable pump from 0 ~ 145ml /R and variable motor from 215 ~ 65ml /R in turn. That is, in the first half of the speed regulation process, the displacement of the motor remains unchanged, and only the displacement of the variable pump is adjusted to meet the requirements of speed adjustment. In the second half, the maximum displacement output of the variable pump is maintained, and only the displacement of the variable motor is adjusted to meet the requirements of speed adjustment. In this way, no matter at any speed, the output torque is the maximum torque corresponding to the speed.
(1) Remote control and valve group control of hydraulic pump station. Before the remote control of hydraulic pump station operates the control system, the pump station motor must be started first to make the pump station in working state. In order to avoid starting the pump station in another place, the system adds the start and stop button of the pump station motor on the control cabinet, and the start signal sent by the button acts on the soft starter remotely to realize the start and stop function of remote control motor.
Control scheme: the main pump motor is started by soft starter, and the start / stop signal of soft starter is controlled through the console button to realize the start/stop control function of corresponding motor. Control process: as shown in Fig. 11 and Fig. 12   The valve group control system sends the control command to PLC through the knob on the operation panel or the virtual button on HMI, and the output signal drives the corresponding solenoid valve action through the relay to realize the corresponding functions.
(2) The power head is driven by 160ml/R variable pump and variable motor. In order to realize the adjustable steering and speed, the system designs a three position knob to control the action of the electromagnetic directional valve, so as to realize the steering control of the power head. At the same time, the potentiometer is designed to input 0 ~ 5V analog signal, and then through the calculation of PLC speed regulation model, output the first conductive signal of 0~10V driving proportional amplifier, control the proportional amplifier to output 200~600mA current, and then control the speed of power head.
Forward/reverse control scheme of power head: forward/reverse switching control is realized through three position four-way solenoid directional valve. That is, the control of the electromagnetic directional valve is realized through the console knob or the remote controller knob, so as to realize the control of the forward/reverse switching function. Control flow: as shown in Fig.13.

Main control system
Judge whether there is alarm information? Stepless speed regulation control scheme of power head output shaft: adjust the flow by controlling the swing angle of variable pump, so as to realize the function of stepless speed regulation of power head output shaft. That is, the proportional electromagnet is controlled by the knob potentiometer, and then the swing angle of the variable pump is controlled to realize the function of stepless speed regulation of the output shaft of the power head. Control flow: as shown in Fig.14

implementation plan
Field commissioning stage: speed regulation of power head under shunt state. The experimental parameters are shown in Table 3、Table 4 and Table 5.

Empirical conclusion
Compared with 《the power head parameter table of enhanced TD2000 drilling rig under shunting state and turning into working condition》, there is an error in the maximum displacement control of hydraulic pump station, with an error of about r ml 5 .
there is still a little room for optimization, which can be optimized on site. Compared with 《the power head parameter ,so the optimization needs to be careful (during in plant commissioning, when the speed regulation exceeds a certain position, the speed of power head decreases instead) In the whole speed regulation process, the trend is basically consistent with the table of power head parameters under shunting condition of enhanced td2000 drilling rig, but there is a little error at the two end points. The error is as described in points and above. The position number described in the table is included in the whole speed regulation process and does not need to be corrected separately. Only the corresponding speed identification needs to be carried out on site, Mark the corresponding position.

Conclusion
Aiming at the problem of whether the power head of raise boring machine can be driven in complex environment during reaming operation, using the finetuning characteristics of FOPID control to apply to the nonlinear control object, a method of adjusting FOPID control parameters based on whale algorithm (WOA) is proposed. Through the establishment of the electrohydraulic coupling model of the power head of the raise boring machine and the simulation analysis in MATLAB software, the following conclusions are obtained: (1) From the simulation results of six different combined control strategies, it can be seen that the overall control effect of FOPID is much better than PID control in the overshoot and response time in the frequency response curve. In PID control, the overshoot is at least 8.35%, while the overshoot of FOPID control is at most 6.9309%, The results show that FOPID is more suitable for the electro-hydraulic control of raising boring than PID, and the overall response time is shorter. It can adjust the angular speed of the power head in time, and then control the fast and slow switching of the power head, which shows that FOPID control has a better application prospect in the electro-hydraulic drive control of raising boring.
(2) Among the six combined control strategies, the combined strategy based on WOA algorithm has obvious advantages in each control method. The overshoot of WOA-PID control strategy in PID control is at least 8.35% and takes 0.1s; The overshoot of WOA-FOPID control strategy in FOPID control is at least 0.12137%, with a time of 0.02s. From the numerical iteration process of WOA objective function, it can be found that WOA has good optimization ability and convergence performance, which verifies the excellent performance of WOA in control parameter tuning. The experimental data show that the WOA-FOPID combined control strategy studied in this paper can respond to the input in time, and the FOPID parameters are adjusted through WOA algorithm, which has a good effect on the optimization of control parameters and can effectively improve the control accuracy of FOPID.
(3) After the design of the control system is completed, it is debugged and applied on the raise boring rig. The control system realizes various functions including remote pump station start and stop control and single / double drive motor switching control, and meets the requirements of process operation. Experiments show that the WOA-FOPID control strategy is effective in the electro-hydraulic drive control system. The control strategy can make the electro-hydraulic drive control have good real-time, accuracy and rapidity, and can realize fast power head Slow switching and high-precision control can be used as the exclusive control system of raise boring rig.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal elation-ships that could have appeared to influence the work reported in this paper.