液压挖掘机设计(外文).pdf

A REAL- TIME SIMULATION SYSTEM FOR EXCAVATOR CONTROLLER GONG WEN The State Key Laboratory of Fluid Power Transmission and Control, Zhejiang University, Hangzhou, China WANG QING- FENG The State Key Laboratory of Fluid Power Transmission and Control, Zhejiang University, Hangzhou China ABSTRACT In order to supply a reliable and low- cost method for testing excavators controllers and evaluating the performance of strategies, an excavator real- time simulation system has been developed. The hardware- in- the- loop system, including dynamic model of the arms, dynamic model of the main hydraulic system and an 3D real- time display subsystem, is presented in this paper. The simulation results are also described at the end of the paper. KEY WORDS Real- time simulation, Hydraulic excavator, Three dimensional 1. INTRODUCTION Heavy duty machines are widely used all over the world. Excavators are one of the most important parts in the heavy duty machines field. They play a vital role in construction, mining industries and so on. As the development of the technology and the requirement of the consumer and environment, controllers become more and more important for the solution of all the problems, such as energy saving, low- noise and environmental protection. However, traditional method for controller testing is time- consuming and resouce- wasting. Furthermore, controller testing on a real excavator sometimes is a dangerous work. Therefore, a hardware- in- the- loop simulator, which is developed under real- time environment, can take place of the real system for the testing work 1,2. The real- time system can improve security and reduce the period of test cycle as well as cost. 2. SYSTEM ARCHITECTURE As arranged in Fig.1, the systems hardware comprises a real- time system(dSPACE) for running the dynamic models and processing the signals in Fig.1 Architecture of real- time system 489 Downloaded 08 Apr 2012 to 52. Redistribution subject to ASME license or copyright; see /terms/Terms_Use.cfm real- time, two vector joysticks for manipulating the digital excavator and a graphic display server for monitoring the simulation process. During the simulation, the real- time system receives the signals from the vector joysticks and controller, computes the models and sends the required signals to the controller as well as the graphic display server. 3. DYNAMIC MODEL FOR THE EXCAVATORS ARMS Before building the dynamic model, some assumptions have to be given. Considering the real- time performance of the system, the arms are regarded as rigid body. The joint friction and deformation are neglected in the following analysis, because they are both small. As show in Fig.2, the arms are assigned variables,andfor the boom, arm and bucket joint angles respectively. 1 c, 2 cand 3 care the centers of gravity for arms. The 1 L, 2 Land 3 Lare length of the arms. 11 L, 21 Land 31 Lare length from the center of gravity to joint. 1 , 1 and 1 are angles from joint- joint to center of gravity- joint. As the dynamic system is of holonomic constraints, a set of second- order coupled differrntial equation is obtained using the Lagrange formulation 3. The conservative dynamic system is writen in matrix form as following: ( )()( )qGq ,qhqqD+= where joint torque vector; q joint- variable vector; q angular acceleration; ( )qD inertia matrix; ()q ,qh vector of Coriolis and centrifugal terms; ( )qG gravity torque vector. Each arm is driven by the cylinder repectively. When the joint angle changes, so does the joint torque. Suppose the force supplied by each cylinder is i F. So the joint torque vector gets the form as: ()()() TT F,F,F, 332211321 = Using the Pascal principle and Newtons law, the leakage of the cylinders is neglected, so i Fis described as iiBiiAi BPAPF=, where iAPand iB Pare rod cavity and non- rod cavity pressure; i Aand i Bare area of cylinder raw chamber and rod chamber respectively. Comparing to others, the friction inside the cylinders has more effects. Therefore, it should be considered in the model. The friction is comprised of Fig.2 Schematics of excavator and arms 490 Downloaded 08 Apr 2012 to 52. Redistribution subject to ASME license or copyright; see /terms/Terms_Use.cfm Coulomb friction and viscous friction. A common linear model is used to describe the friction effects on the force. The classical model can be expressed to describe friction as: ( ) + = s vc f vfvsgnf f 0 0 = v v Where v velocity of cylinder; c f Coulomb friction; v f viscous friction coefficient; s f static friction. So the force i Fis modified and an expression is finally described as: iiiBiiAi fBPAPF+=. 4. DYNAMIC MODEL FOR THE EXCAVATORS MAIN HYDRAULIC SYSTEM Fig.3 shows the main hydraulic system. The system mainly consists of two pumps, three proportional servo valves and proportional relief valves 4. The high- pressure fluid from the pump passes by the relief valve, flows through the proportional servo valve and executives the cylinder. Assuming no leakage in valves, the booms cylinder is taken for an example. The flow rate from pump to valve is rpi QQQ= Where p Q flow rate of pump; i Q flow rate through relief valve. The relationship between pressure and flow rate at the pumps exit port is given by Fig.3 Main hydraulic system 491 Downloaded 08 Apr 2012 to 52. Redistribution subject to ASME license or copyright; see /terms/Terms_Use.cfm () =tQQQ V E P irp p p d Where E bulk modulus of the fluid; p V total volume contained between pump and valve. The flow rate through relief r Qis a function of pressure p P. The flow rate from valve to cylinders is () () = 0 2 0 2 x PP AC x PP AC Q ta pad ap pad a () () = 0 2 0 2 x PP AC x PP AC Q bp pbd tb pbd b where x spool position of the valve relative to its center; d C flow coefficient; pa A, pb A flow area of valve; t P tank pressure; fluid density. The pressure of the valves exit ports are expressed as ()tvAQ V E P a A a d = ()tvBQ V E P b B b d += where A V, B V total volume contained between valve and cylinder; v velocity of cylinder; A,B area of raw and rod cylinder chambers. 5. 3D REAL- TIME DISPLAY PLATFORM BASED ON DIRECTX In order to improve the man- machine interaction environment, an 3D display platform has been developed. The platform using the Microsoft DirectX SDK and VC+ can run real- time along with the system. Firstly, an 3D excavator model should be built. Excavator is of complex body parts, and therefore this paper uses a professional three- dimensional modeling software to create the various parts of the excavator model. In this paper, 3ds Max is used to build the model of the excavator. 3ds Max provides users with a high- level command of three- dimensional modeling for a wide variety of modeling complex shapes 5. More importantly, it provides powerful rendering functionality and the ability to edit material to ensure that the model has enough realistic three- dimensional effect, which can meet the platforms requirements on the fine of the model. In the 3ds Max environment, the establishment of the three- dimensional solid model of the base, cab, boom, arm and bucket is taken respectively. In order to facilitate the following procedures for the reading of model data, model file is saved, a DirectX can be identified, as an X format. .X format document preserves the required information for DirectX Mesh model mesh object and a 492 Downloaded 08 Apr 2012 to 52. Redistribution subject to ASME license or copyright; see /terms/Terms_Use.cfm list of materials and other information, so that using 3ds Max software to obtain the model data. DirectX SDK is a set of APIs which provides a set of multimedia development tools for Windows system applications and hardware associated itself with a strong three- dimensional graphics display ability 6,7. The framework of three- dimensional rendering procedure is designed and the rendering process flow chart(Fig.4) is as follows. The result of the 3D real- time platform is shown in Fig.5. 6. CONCLUSIONS AND ACKNOWLEDGE The whole process provides a convenient and rapid method of developing the new car which acceleration domestic motor- dom development. The real- time system, using hardware- in- the- loop technology, is a reliable method for excavator controller testing. The method is time and cost saving. It can also make the controller development easier and more safe. The authors gratefully acknowledge the financial support of National Natural Science Foundation of China (Granted NO. 50875233) and “985 Project” of China. REFERENCES 1 S.E. Salcudean, P. Drexel, D. B