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Discussion on the robotization of concrete pump truck pouring process

Abstract: the optimal control is adopted for the movement attitude adjustment of concrete pump truck distribution mechanism, which solves the movement analysis and arm solution of key and difficult problems of pump truck roboticization, discusses the problems that should be solved and paid attention to in the dynamic analysis of pump truck, and gives the program flow chart and control system diagram of pump truck control automation, Thus, a new idea is put forward to improve the automation of pump truck construction process and the roboticization of pump truck

key words: concrete pump truck; Roboticization; Automatic control

roboticization and control automation have become the development direction of high-performance construction machinery. The distributing mechanism of concrete pump truck is composed of multi section boom. For multi section boom pump truck with large-scale operation, manual control requires not only high technical level of operators, but also high labor intensity. Especially in the construction of high-rise buildings, the pump truck operator can't see the construction site and can only rely on the command and control of whistles or flags. However, if the automatic control technology is used, the construction operation will be much more convenient. Therefore, the automation of the construction process of the pump truck and the roboticization of the pump truck have attracted people's attention. The problems to be solved in the roboticization of pump truck: (1) kinematic analysis of distribution mechanism; (2) Dynamic characteristic analysis of the distributing mechanism or pump truck system; (3) The control automation of the distributing mechanism

1 kinematic analysis and Simulation of the distribution system

the roboticization of pump truck requires the computer to control the flow of hydraulic oil in the oil cylinder to control the expansion and contraction of the oil cylinder and the rotation angle of the rotary mechanism, so as to complete the movement of the pouring point along the predetermined track. In order to realize the automation of pouring process control, firstly, the expansion and contraction of each arm drive cylinder and the rotation angle of the slewing mechanism should be calculated from the coordinate position of the pouring point, and then the computer controls the distribution mechanism to reach the predetermined pouring area

Figure 1 the included angle relationship between the boom and the middle arm

the calculation process of the forward problem of the kinematic analysis of the distributing mechanism is to calculate the relative rotation angle of each arm through the trigonometric function relationship on the premise of knowing the expansion amount of the oil cylinder and the rotation mechanism, and then calculate the geometric coordinate position of the pouring point through the matrix transformation principle. From the rotary table corner β Relative angle with each arm θ i. Some researchers have done a lot of research on calculating the geometric position of the pouring point through matrix transformation. Here we only briefly explain the relationship between the relative rotation angles of each arm derived from the expansion amount of the oil cylinder. Figure 1 shows the local relationship of the rotating part between any two arms, where Bi is the length of the drive cylinder; Xi and xi+1 are the axis directions of arm I and i+1 respectively; θ I is the relative included angle between arm I and arm i+1: α I is the included angle corresponding to the length Bi of the side cylinder. because α I and θ I is a one-to-one correspondence, so a given Bi can be uniquely determined θ The value of I, so that Bi and θ Correspondence of I:

θ I=f (BI) (1)

in Figure 2, the reference coordinate system o0x0y0z0 is fixed on the vehicle body, the other coordinate system oixiyizi (i=1, 2, 3, 4) is the attached coordinate system (taking the three arm pump truck as an example), and Li (i=1, 2, 3, 4) is the structural parameters of the turret and arm

Figure 2 Schematic diagram of distribution mechanism parameters and coordinate system

according to the coordinate relationship in Figure 2, the solution of the inverse problem of pump truck kinematics analysis is to obtain the pouring point (x, y, z) and the rotation angle parameters of the actuator through matrix transformation when the pouring point coordinates (x, y, z) are known（ β，θ 1， θ 2， θ 3) By substituting equation (1) into equation (2), the parameters of pouring point (x, y, z) and oil cylinder and rotary table can be obtained（ β， The relationship between B1, B2, B3) (3)

because equation (3) is a multiple solution, when the pouring point is close to the origin of the basic coordinate system, especially when the number of arm nodes of the distribution mechanism is large (the number of arms is 4 ~ 6), when the pouring point is automatically controlled to move along the discrete points of the set track, even if it is the pouring point close to each other, after the iterative solution of equation (3), the value of the change of each arm cylinder may be larger, resulting in problems such as long attitude change time and large vibration, It is necessary to control the change process, such as taking the principle of minimum energy or the maximum change time of each executive component as the optimal control objective function. In this paper, the largest change of the oil cylinder rod of each arm is the smallest, that is

Δ bmax=min｛max(│ Δ b1│，│ Δ b2│，│ Δ B3 │) 、 (4)

the control realized by using the largest or smallest telescopic change of each arm cylinder can maintain the relatively stable attitude change of the whole mechanism to a certain extent when pouring in a certain area. The optimal objective function adopts penalty function method and weighted processing

minF( β， b1，b2，b3)=min｛max(│ Δ b1│，│ Δ b2│，│ Δ b3│)+A(│fx│+│fy│)+B│fz│｝+C ξ (B1, B2, B3) (5)

where: A, B, C are penalty coefficients

Δ b1=bnext1-blate1；

Δ b2=bnext2-blate2；

Δ b3=bnext3-blate3；

fx=( β， b1，b2，b3)-x；

fy= ω ( β， b1，b2，b3)-y；

fz= ψ ( β， b1，b2，b3)-z；

where bnexti and blatei (i=1, 2, 3) are the cylinder lengths corresponding to the two adjacent pouring points respectively; ξ (B1, B2, B3) is the control function of the cylinder length boundary condition. When the cylinder length exceeds the range defined by the boundary condition, the formula (5) is punished, that is, there is ξ (B1, B2, B3) =1, otherwise equal to 0

in order to obtain the global optimal solution of the optimal control objective function, this paper adopts the genetic algorithm based on multi peak value [5], which has the ability to find the global optimal and is suitable for solving complex functions. The above solution process is to adjust and control each executive part to complete the pouring at the same time. Of course, one or several executive members can also be fixed, and other parts can be automatically adjusted to complete the pouring process. This requires setting some rules to make the pouring point reach the scope of operation

here, take the three arm pump truck as an example to simulate the automatic pouring of a rectangular area. The three arm lengths are l1=0.2, l2=5.4, l3=6.8, l4=5.2 respectively. Taking equation (5) as the objective function of optimal control, the adjustment of the distribution mechanism is shown in Figure 3

Fig. 3 simulation results of placing process of distribution mechanism

2 dynamic characteristic analysis of pump truck system

due to the working characteristics of concrete pump and the structural characteristics of distribution mechanism, there are large problems such as vibration and fatigue damage when the distribution mechanism works. Literature [6, 7] used the finite element method and dynamic analysis method to carry out the modal analysis and dynamic response analysis of the pump truck system, and obtained the natural frequency and vibration mode diagram of the system after coupling, as well as the stress and displacement change curve of the dynamic response, which provided the basis for the fatigue design and control simulation of the distribution mechanism. The impact effect produced by the pumping pressure of concrete and the distribution mechanism system is a strong coupling nonlinear relationship. For the dynamic analysis of the robot of the pump truck, the Newton Euler method can be used to establish the experimental machine for the zigzag of reinforcement. Operation instructions: the dynamic equation of the feeding mechanism (6) and the recursive formulas of the acceleration, inertia force and driving torque of each rod (7), (8). (6)

where: m (q) is the generalized mass matrix; G (q) is the gravity matrix; V (Q, q) is the centripetal force and Coriolis force matrix; P is the driving force matrix

(7)

fj=jj+1Rfj+1+Fj+Sj

nj=Nj+jj+1Rnj+1+rj × Fj+Pj × (jj+1rfj+1+sj)

(j=4, 3, 2, 1) (8)

sj is the impact force of concrete flow on each distributing rod, and other symbols can be described in reference [8]. In the dynamic analysis of the pump truck, the proportion of Coriolis force and centripetal force in the dynamic equation should be considered to determine the simplified dynamic model of equations (6), (7) and (8). In addition, we should also consider the impact of sudden braking when the distribution mechanism is in large-scale rotary motion. The electrical test shows that the impact force caused by sudden braking is more dangerous than normal work

3 distribution system control automation

the early product of pump truck roboticization is to use the joystick to control the motion trajectory of the distribution pouring point, and the rotation angle parameters of the mechanism are controlled by the computer. At present, some imported pump trucks have realized the remote control of the pouring construction process with a remote controller, which is the result of the continuous efforts of the robot of pump trucks

the robot control method of the pump truck can choose pre programming, teaching system or intelligent control. The complete pre programming operation has high technical content. Because the working environment of the pump truck is complex and changeable, it is not suitable to completely adopt intelligent control. The most suitable control method is to give priority to the teaching system, supplemented by others. Due to the characteristics of the working environment of the pump truck, when inputting the working range, the control method can be a combination of programming and teaching system. The choice of the two is mainly based on the rule degree and convenience of the working range. After the operation range is determined, the automatic discretization algorithm is used to discretize the operation range into an array set of pouring points, and then the optimal control algorithm for solving the inverse problem in the kinematic analysis described above is called to calculate the parameters of each executive component such as oil cylinder and rotary table（ β， L1, L2, L3), and then drive the hydraulic system through the controller to complete the automatic pouring process

in order to make the pump truck more intelligent, some anti-collision devices, such as proximity sensors, can be arranged on the actuator of the distribution mechanism. When the actuator encounters obstacles, the obstacle avoidance control algorithm can be called out to realize automatic obstacle avoidance. The control process of obstacle avoidance subroutine basically includes the control of extending the boom cylinder and shortening the jib cylinder at the same time, or the control of each boom cylinder operating at the same time to reach the lifting mechanism and bypass the obstacle, that is, when the distribution hose and other components encounter obstacles, the control of each boom cylinder to stretch and cross the obstacle to reach the next pouring point. In order to adapt to the complexity of obstacles, the obstacle avoidance subroutine should be a dynamic real-time control program based on expert system technology, which continuously receives the feedback of obstacle information. Due to the inverse problem of kinematic analysis, calculation parameter setting and other problems, the control system of construction machinery mostly adopts angle sensors, which are easy to be damaged by collision. Therefore, this paper takes the feed rate of oil cylinder as the control parameter for independent operation after mastering it. In this way, displacement sensors can be used, which is characterized by convenient layout and not easy to be damaged. To sum up, this paper gives the program flow of pump truck automatic control algorithm (Figure 4) and pump truck automatic pouring control system (Figure 5)

Figure 4 automatic control program flow chart

Figure 5 automatic pouring control system diagram

4 conclusion

through motion analysis, the optimal control of pump truck actuator pouring based on genetic algorithm is obtained, the arm solution problem of pump truck robotic motion analysis is solved, the problems solved and should be paid attention to in pump truck dynamic analysis are discussed, and the method of determining the automatic operation range of pump truck control is proposed, The program flow chart and control system diagram are given. (end)

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