关于混凝土泵车的主动控制研究：数值模型和实验分析 毕业论文外文翻译.doc

外文翻译ON THE ACTIVE CONTROL OF A TRUCK MOUNTED CONCRETE PUMP: NUMERICAL MODEL AND EXPERIMENTAL ANALYSISC.Ghielmetti, H.Giberti, F.RestaPolytechnic of Milan, Mechanical Department, Via La Masa, 34 - 20156 Milan, ItalyABSTRACTIn this paper the study on the behaviour of a "pumping group" used in industry to pump a big amount of concrete will be presented. The characteristics of the pumping group, its working and its mathematical model will be explained. Moreover numerical model results will be compare with the experimental ones. The purpose of this work is to show, through the mathematical model, the improvement of the pumping group system after the introduction of control. In detail, the aim its, on one hand, to optimize the mechanical lay out in order to support some requirements about concrete flux and pressure and, at the other hand, to develop and complete the control system application of a bigger work in which the pumping group is a part.1. INTRODUCTIONThe study of this pumping group is inserted to a bigger research in which, in addition to the pump, are studied the vibration problems of an associated boom. Both pumping group and boom form the complete system called “truck mounted concrete boom pump”.In Fig 1 the 3D image of the system including the concrete vessel and the couple of cylinders and the real (test rig) pumping group are shown. In Fig 2 theres an image of a truck on which the pumping group is linked and there's an example of mechanical boom movements. About the booms can be said that their main feature is the extent and this distance can be changed, assuming various positions, in function of the situation. There are different kinds of booms and their length is variable from a minimum of 28m to a maximum of 58m.Actually, the study of boom behaviour and booms vibration problems are doing by others bevies and some results about this problems are related in others works (A.N.Arbel, 1981; H.B.Kuntze, U.Hirsch, A.Jacubasch, F.Eberle, B.Goller, 1995).At the other hand the study about concrete and pumping group system for concrete will be described. Retracing the story of the pumped concrete can be said that this is a technique for the transport of freshly mixed concrete, allowing the supply of fresh material in the formwork without the use of any bucket nor conveying belt. It has been known in the world for almost 70 years. Concrete pumps in witch the concrete circulates in metal pipes were used in the U.S. as early as 1933. The technique of pumping is widely spread, and has profited from many improvements, particularly on the pumps (for example, high span pumps and pumps with high pressure). It's very widely used in the field of industrial construction. There are several advantages compared with the other techniques. The importance of rheological properties of concrete can be attested to by the large body of literature (C.F.Ferraris, F.de Larrard, 1998; H.Mori, Y.Tanigawa, 1992; P.Bartos, 1992; P.F.G. Banfill, 2003) while few are the study about the way to pump the concrete (ACI Committee 304, 1995; Kaplan,Francois de Larrard, Thierry Sedran, 2005).In this sense this paper presents the compare between the numerical model and theexperimental tests of a pumping group system for concrete, underlining the good results obtained and with the aim to integrate the control system of the pumping group in order to improve the complete control system.The pumping group is a system installed on a truck and its aim is to pump a big amount of concrete to a large distance from the cockpit. This is possible because the concrete moves along a pipeline rigidly connected with a mechanical long boom. The pump develops a variable flow and pressure in function of a type of work requirement.Usually the pumping group is used in dirty field and its in contact with extremely aggressive materials so that, the selected design solution, has to be strong and easily to clean and repair. Fig 1. pumping group system, CAD 3D and real test rig.The pumping group is an alternative volumetric pump with two pistons. One of those sucks up the concrete from the concrete vessel and, at the same time, the other pushes the inert along the pipeline. This motion of the concrete is discontinuous and, because of this, induces many forces on pipeline due to the friction between concrete and metal pipe and depending upon to the position of the boom. These forces induce dangerous mechanical oscillations on the boom so that its work is compromised. Moreover, the simple layout and the easy employment of the pumping system makes difficult to adjust the provided flow. Fig 2. K41L truck - mounted concrete boom pump.It's clear that the adjustment of the flow in terms of continuity and regularity of the concrete flux inside the metal pipe is fundamental to decrease the oscillations on the entire system and especially of the boom. There isnt in literature a complete study of the pumping group in terms of mechanical and hydraulic models so, for this reasons, it was necessary to develop a mathematical model and an experimental test rig. The mathematical model is helpful in order to adjust the pump flow, reduce the forces on the mechanical boom and optimize the pumping group design in terms of overpressure problems, noise problems, duration and pumping capacity.Moreover, in the paper, will be well describe the physical system, the experimental tests doing on the real model, the mathematical model and control system associated to the pump.2. DESCRIPTION OF THE ENTIRE SYSTEMIn Fig 3 the pumping group test rig and the block diagram are shown; the position of the group, its constrains with the ground, its lean and all the circuits simulate perfectly the real group on the truck.The pump was positioned on steel ground constrained structure which has the same connections of the truck - mounted concrete boom pump so that the simulation is the most possible near to reality. The test rig is composed by the pumping group (the physical model in which we are interested) and by a pair of auxiliary circuits; the hydraulic one and the similar concrete one (called CLS circuit). Both the hydraulic circuit, connected to a diesel engines, and the CLS one are similar to the real system.The work fluid (see CLS in Fig 3), flows in a dedicate circuit that is connect with a steel tank of almost three meters high. Moreover it goes out alternatively from the concrete side pipes and, through the CLS circuit, puts itself into the steel tank from which, at the same time, come back to the pumping group concrete vessel. On board of CLS circuit a series of valves are mounted in order to pilot and to adjust the pressure of fluid or, to put it better, the load to which the pistons are subjected from outside.Fig 3. real test rig and test rig block diagram.The Fig 4 shows a scheme of the pumps block connected with the pumping group and with its auxiliary parts. Its to say that with this complete test rig is possible to make many type of experimental tests and in particular, the variation of the pump rpm and the variation of the dimension of reducing valve, permit us to check, compare and control some important state variables like the flux of oil and concrete, the pressure in the chambers of cylinders and the overpressure on the cylinders due to the presence of concrete. Moreover is to say that the oil pumps are driven by diesel motors on which theres the possibility to vary the rpm characteristic and the flux quantity of enter oil. Fig 4. scheme of pumps block.3. EXPERIMENTAL TESTSIn order to better understand the behaviour of pumping group, many experimental tests were done. In these tests was varied the pump rpm and the area of the reducing valve. The tests was organize to understand the functionality in three different velocity of the pump, ten different values flux of enter oil and seven different values of the area of reducing valve. In this manner its known the behaviour of the pumping group for a big range of functionality values. The layout of acquisition system is shown in Fig 5; there are many sensors with which is possible to measure position, velocity and acceleration of the pistons, pressure in all the chambers of the pumping group and flux of oil and concrete, as well as others less important measuresFig 5. sensors on test rig pumping group.During the experimental tests some interested results from which to take out some main phenomenon to study was obtained (see Fig 6). Moreover the Fig 7, Fig 8 and Fig 9 shows other interesting and necessary measures with which complete the model and understand the relationship between the pumping group components. In particular, the phenomena in which we are mainly interested are the high pressure peaks and dynamics of the pressure in the oil chambers as well as pressure regime values during the work cycle ( Fig 6) and the flux of work fluid (Fig 8). We are particularly interested to these phenomenon because the ideal system should be pump a lot of concrete (m3 / h of concrete) in a few possible time and without to induce forces and produce noise.Fig 6. oil chambers pressure during the work. Fig 7. oil flux from the pump 1. Fig 8. work fluid flux. Fig 9. work fluid back pressure. So in order to comprehend and solve that problem was necessary to understand the functionality of the pumping group and how it executes one work cycle. The scheme in Fig 10 describes in easy manner the components of the pumping group and how they interact one each other to pump the concrete along the metal pipe. The Fig 10 shows also the detail of one piston.The pumping group is a volumetric pump composed by two pistons (E) that, alternatively, suck up the inert from the concrete vessel (H) and, at the same time, pump it out along the pipeline (I). The pistons are driven by two hydraulic actuators (B and C). It's to say that the pistons pipes are dipped in the concrete vessel.To pump the work fluid into the metal pipeline it's necessary an element to orientate the pumping flow toward the outlet pipeline, this element takes the name of S Valve (G) and later its functionality will be explained.Now is possible to identify the pumping group system with two subsystems called “oil side” and “concrete side”. The oil side represents the driving part while the other one is the part directly in contact with the concrete.We can define some keywords which describe many important components and theirpeculiarity. The term “active” refers to the piston (C) that, in that work phase andsimultaneously with its movement, push out and compress the concrete previouslyaccumulated in the pipes.The second piston (B) is called “passive” because it's conducted by the active one through an hydraulic circuit (the Slave, mark with D) and because its busy to refill its cylinder.Moreover it's not a party to (at this step of the cycle) the direct pumping of concrete. The two pistons will be called active or passive according to the phase of the cycle in which they find themselves. In addition to these relevant components, there are a number of hydraulic, electrical and mechanical elements, which well characterize this machine. The oil side elements are the oil pump, the ducts (A), the proximity sensors (X) and the slave.The oil is driven into the oil chambers (C1 or C4 depends on the phase of the work cycle) and comes from the oil chambers (C4 or C1) by means of two pipes in which the oil pumps impose the flux. These pumps send the flux in one side and, at the same time, receive another flux in the other side. This type of functionality impose the alternative movement to the pistons with an auto induction low managing by a proximity sensors system.It can be seen in Fig 10 the presence of some pipes called ducts, with retaining valves, which form a close circuit on the oil side cylinder. The ducts operate at the same time as a brake, as an oil duct (because of oil losses) and as a piston interlock during the operation cycles. These components are very important because they permit the passage of oil from the chamber C1 to C2 (or from C4 to C3) creating an balanced distribution of oil inside the entire oil circuit.About the reverse command of the oil pump navigation signal, it can be said that its due to by the proximity sensors positioned at the end of chambers 1 and 4 (C1 and C4). These intercept by the passive piston, when it's almost at the end of his stroke, gives the electric signal to the oil pumps (P) and to the S valve (G) I order to invert their sense of work and position respectively.The concrete side elements, shown in Fig 10, are the S valve and the concrete vessel (H). The Svalve connects the end of the cylinder in concrete side subsystem to the beginning of the metal pipeline. The switching of this valve that is its rotation is due to a proximity sensors signal (how said before). The concrete vessel is continuously refilled of work fluid by a concrete mixer and it keeps the fluid used during the cycles. In our experimental tests water was used as a work fluid so that the term “work fluid” means “water”.The presence of work fluid in concrete vessel represents a force to win by the active piston and in function of the regulation of proportional choking valves area is define the load to which the piston is subjected.The load conditions, that in the reality are due to the pressure of concrete, are simulated like an adjustable choking on the circuit. In this way the desired back pressure is obtained.Considering only one piston, the single work cycle is composed from two phases: in the first one (passive phase) there is an undertow of work fluid from the concrete vessel while during the second phase (active phase) there is the ejection of the work fluid along the metal pipeline through the S valve. The passage from one phase of work and the other is defined by the passive piston position; this element sets the sense of work of the pump and the position of S Valve. By a diesel engine its possible to command the oil pumps of the circuit with the possibility to adjust the rpm of the engine and, at the same time, the oil flow.After analyzing the physical model and understanding the work cycle of the system, was necessary to study all the phenomena underling in Fig 6, 7, 8 and 9 by the implementation of a mathematical and numerical model because wasnt easy to obtain physically the answers about why these phenomena appear.4. MATHEMATICAL MODELThe system was modelled with differential equations that describe both the motion of pistons and the continuity of working fluids (oil and water). In general we can identify three sets of equations used to describe the system: the dynamics of the piston, the dynamic of pressures in the oil side and the dynamic of pr