液压挖掘机的半自动控制系统 外文翻译

1、Semi-automatic control system for hydraulic shovelAbstractA semi-automatic control system for a hydraulic shovel has been developed. Using this system, unskilled operators canoperate a hydraulic shovel easily and accurately. A mathematical control model of a hydraulic shovel with a controller wascon

2、structed and a control algorithm was developed by simulation. This algorithm was applied to a hydraulic shovel and itseffectiveness was evaluated. High control accuracy and high-stability performance were achieved by feedback plusfeedforward control, nonlinear compensation, state feedback and gain s

3、cheduling according to the attitude. Keywords: Construction machinery; Hydraulic shovel; Feedforward; State feedback; Operation1. IntroductionA hydraulic shovel is a construction machinery that can be regarded as a large articulated robot.Digging and loading operations using this machine require a h

4、igh level of skill, and cause considerablefatigue even in skilled operators. On the other hand, operators grow older, and the number of skilledoperators has thus decreased. The situation calls forhydraulic shovels, which can be operated easily byany person w15x.The reasons why hydraulic shovel requi

5、res a high level of skill are as follows.1. More than two levers must be operated simultaneously and adjusted well in such operations.2. The direction of lever operations is different from that of a shovels attachment movement.For example, in level crowding by a hydraulicshovel, we must operate thre

6、e levers arm, boom,bucket. simultaneously to move the top of a bucketalong a level surface Fig. 1. In this case, the lever operation indicates the direction of the actuator, but this direction differs from the working direction. If an operator use only one lever and other freedoms are operated autom

7、atically, the operation becomes very easily. We call this system a semi-automatic control system.When we develop this semi-automatic control system, these two technical problems must be solved.1. We must use ordinary control valves for automatic control.2. We must compensate dynamic characteristics

8、of a hydraulic shovel to improve the precision of control.Fig. 1. Level crowding of an excavator and frame model of anexcavator.We have developed a control algorithm to solve these technical problems and confirm the effect of this control algorithm by experiments with actual hydraulic shovels. Using

9、 this control algorithm, we have completed a semi-automatic control system for hydraulic shovels. We then report these items.2. Hydraulic shovel modelTo study control algorithms, we have to analyzenumerical models of a hydraulic shovel. The hydraulicshovel, whose boom, arm, and bucket jointsare hydr

10、aulically driven, is modeled as shown in Fig.2. The details of the model are described in thefollowing.Fig. 2. Model of hydraulic shovel.2.1. Dynamic model 6Supposing that each attachment is a solid body,from Lagranges equations of motion, the followingexpressions are obtained:其中 K sm 1 g; and gsgra

11、vitational acceleration. 3 3 g 3iis the joint angle, i is the supply torque, li isthe attachment length, lgi is the distance between g ithe fulcrum and the center of gravity, miis the mass of the attachment, Iiis the moment of inertia around (the center of gravity subscripts is13; mean boomarm, and

12、bucket, respectively.)2.2. Hydraulic modelEach joint is driven by a hydraulic cylinder whoseflow is controlled by a spool valve, as shown in Fig.3. We can assume the following:1. The open area of a valve is proportional to thespool displacement.2. There is no oil leak.3. No pressure drop occurs when

13、 oil flows throughpiping.4. The effective sectional area of the cylinder isthe same on both the head and the rod sides.In this problem, for each joint, we have thefollowing equation from the pressure flow characteristicsof the cylinder:when,where, Aiseffective cross-sectional area of cylinder; hiscy

14、linder length; Xisspool displacement;Psissupply pressure; Piscylinder head-side pressure; Piscylinder rod-side pressure; Visoil volume in the cylinder and piping; Bisspool width; soil density; Ksbulk modulus of oil; and csflow coefficient.2.3. Link relationsIn the model shown in Fig. 1, the relation

15、 betweenthe cylinder length change rate and the attachmentrotational angular velocity is given asfollows:(1)leg(2). arm(3). bucket当 时，Fig. 3. Model of hydraulic cylinder and valve.2.4. Torque relationsFrom the link relations of Section 2.3, the supplytorque t is given as follows, taking cylinder fri

16、ction Iinto consideration:Where, Cci is the viscous friction coefficient andFi is kinetic frictional force of a cylinder.2.5. Response characteristics of the spoolSpool action has a great effect on control characteristics.Thus, we are assuming that the spool hasthe following first-order lag against

17、the referenceinput.Where, XX is the reference input of spool displacement and T is a time constant.3. Angle control systemAs shown in Fig. 4, the angle u is basicallycontrolled to follow the reference angle u by position feedback. In order to obtain more accuratecontrol, nonlinear compensation and s

18、tate feedbackare added to the position feedback. We will discussdetails of these algorithms as follows.Fig. 4. Block diagram of control system3.1. Nonlinear compensationIn the ordinary automatic control systems, newcontrol devices such as servo valves are used. In oursemi-automatic system, in order

19、to realize the coexistenceof manual and automatic operations, we mustuse the main control valves, which are used inmanual operation. In these valves, the relation betweenspool displacement and open area is nonlinear.Then, in automatic operation, using thisrelation, thespool displacement is inversely

20、 calculated from therequired open area, and the nonlinearity is compensatedFig. 5. Nonlinear compensation.3.2. State feedbackBased on the model discussed in Section 2, if thedynamic characteristics for boom angle control arelinearized in the vicinity of a certain standard conditionspool displacement

21、 X , cylinder differential 10pressure P , and boom angle u ., the closed-loop transfer function can be expressed bywhere, K is position feedback gain; This system has a comparatively small coefficient , so the response is oscillatory. For instance, if in our large SK-16 hydraulic shovel, X10 is 0, t

22、he coefficients are given as a s2.7=10y2 , ,a1=6.010,a2=1.210. Addingthe acceleration feedback of gain Ka , to this the upper loop in Fig. a4., the closed loop transfer function is given asAdding this factor, the coefficient of s2 becomeslarger, thus, the system becomes stable. In this way,accelerat

23、ion feedback is effective in improving theresponse characteristics.However, it is generally difficult to detect accelerationaccurately. To overcome this difficulty, cylinderforce feedback was applied instead of accelerationfeedback the lower loop in Fig. 4. In this case,cylinder force is calculated

24、from detected cylinderpressure and filtered in its lower-frequency portion7.8. This is called pressure feedback.4. Servo control systemWhen one joint is manually operated and anotherjoint is controlled automatically to follow the manualoperation, a servo control system must be required.For example,

25、as shown in Fig. 6, in the level crowdingcontrol, the boom is controlled to keep the arm and height Z (calculated from 81and 82)tor. In order to obtain more accurate control, thefollowing control actions are introduced.4.1. Feedforward controlCalculating Z from Fig. 1, we obtainDifferentiating both

26、sides of Eq.(8). with respectto time, we have the following relation,The first term of the right-hand side can be takenas the expression (feedback portion)to convert Z to, and the second term of the right-hand side is the expression (feedforward portion)to calculate howmuch u should be changed when

27、u is changed manually.Actually, u is determined using the difference value of Du . To optimize the feedforward rate, feedforward gain K is tunned. ffThere may be a method to detect and use the armoperating-lever condition iangle. instead of armangular velocity, since the arm is driven at an angularv

28、elocity nearly proportional to this lever condition.4.2. AdaptiÕe gain scheduling according to the attitudeIn articulated machines like hydraulic shovels,dynamic characteristics are greatly susceptible to theattitude. Therefore, it is difficult to control the machinestably at all attitudes with

29、 constant gain. Tosolve this problem, the adaptive gain schedulingaccording to the attitude is multiplied in the feedbackloop Fig. 6. As shown in Fig. 7, the adaptive gain (KZ or Ku). is characterized as a function of twovariables, and Z. means how the arm is extended, and Z means the height of the

30、bucket.5. Simulation resultsThe level crowding control was simulated byapplying the control algorithm described in Section 4to the hydraulic shovel model discussed in Section 2.In the simulation, our large SK-16 hydraulic shovelwas employed. Fig. 8 shows one of the results. Fiveseconds after the con

31、trol started, load disturbanceFig. 6. Block diagram of control system (Z).Fig. 7. Gain scheduling according to the attitude.was applied stepwise. Fig. 9 shows the use of feedforwardcontrol can reduce control error.6. Semi-automatic control systemBased on the simulation, a semi-automatic controlsyste

32、m was manufactured for trial, and applied to theSK-16 shovel. Performance was then ascertained byfield tests. This section will discuss the configurationand functions of the control system.6.1. ConfigurationAs illustrated in Fig. 10, the control system consistsof a controller, sensors, manmachine in

33、terface,and hydraulic control system.The controller is based on a 16-bit microcomputerwhich receives angle input signals of the boom, arm,and bucket from the sensor; determines the conditionof each control lever; selects control modes andcalculates actuating variables; and outputs the resultsfrom th

34、e amplifier as electrical signals. The hy-draulic control system generates hydraulic pressureproportional Fig. 8. Simulation result of level crowding.to the electrical signals from the electromagneticproportional-reducing valve, positions thespool of the main control valve, and controls theflow rate

35、 to the hydraulic cylinder.In order to realize high-speed, high-accuracy control,a numeric data processor is employed for theFig. 9. Effect of feedforward control on control error of Z.Fig. 10. Schema of control system.controller, and a high-resolution magnetic encoder isused for the sensor. In addi

36、tion to these, a pressuretransducer is installed in each cylinder to achievepressure feedback.The measured data are stored up to the memory,and can be taken out from the communication port.6.2. Control functionsThis control system has three control modes,which are automatically switched in accordanc

37、e withlever operation and selector switches. These functionsare the following(1). Level crowding mode: during the manual armpushing operation with the level crowding switch,the system automatically controls the boom and holdsthe arm end movement level. In this case, the referenceposition is the heig

38、ht of the arm end from theground when the arm lever began to be operated.Operation of the boom lever can interrupt automaticcontrol temporarily, because priority is given to manualoperation.(2)Horizontal bucket lifting mode: during themanual boom raising operation with the horizontalbucket lifting s

39、witch, the system automatically controlsthe bucket. Keeping the bucket angle equal tothat at the beginning of operation prevents materialspillage from the bucket.(3)Manual operation mode: when neither thelevel crowding switch nor the horizontal bucket liftingswitch are selected, the boom, arm, and b

40、ucketare controlled by manual operation only.The program realizing these functions is primarilywritten in C language, and has well-structured moduleto improve maintainability.7. Results and analysis of field testWe put the field test with the system. We confirmedthat the system worked correctly and

41、theeffects of the control algorithm described in Chaps. 3and 4 were ascertained as follows.7.1. Automatic control tests of indiÕidual attachmentsFor each attachment of the boom, arm, and bucket,the reference angle was changed "58 stepwise fromthe initial value, and the responses were measu

42、red;thus, the effects of the control algorithm described inChap. 3 were ascertained.7.1.1. Effect of nonlinear compensationFig. 11. Effect of nonlinear compensation on boom angle.Because dead zones exist in the electro-hydraulicsystems, steady-state error remains when simple positionfeedback without

43、 compensation is applied in the figure. Addition of nonlinear compensationin the figure. can reduce this error.7.1.2. Effect of state feedback controlFor the arm and bucket, stable response can beobtained by position feedback only, but adding accelerationor pressure feedback can improve fast-respons

44、ecapability. As regards the boom, with onlythe position feedback, the response becomes oscillatory.Adding acceleration or pressure feedback madethe response stable without impairing fast-responsecapability. As an example, Fig. 12 shows the testresults when pressure feedback compensation wasapplied d

45、uring boom lowering.7.2. LeÕel crowding control testControl tests were conducted under various controland operating conditions to observe the controlFig. 12. Effect of pressure feedback control on boom angle.Fig. 13. Effect of feedforward control on control error of Z.characteristics, and at th

46、e same time to determine theoptimal control parameters such as the control gainsshown in Fig. 6.7.2.1. Effects of feedforward controlIn the case of position feedback only, increasinggain K to decrease error DZ causes oscillation due pto the time delay in the system, as shown by AOFFBin Fig. 13. That

47、 is, K cannot be increased. Applying the feedforward of the arm lever value describedin Section 4.1 can decrease error without increasingK as shown by AONB in the figure. p7.2.2. Effects of compensation in attitudeLevel crowding is apt to become oscillatory at theraised position or when crowding is

48、almost completed.This oscillation can be prevented by changinggain K according to the attitude, as has been pdiscussed in Section 4.2. The effect is shown in Fig.14. This shows the result when the level crowdingwas done at around 2 m above ground. Compared tothe case without the compensation, denote

49、d by OFFin the figure, the ON case with the compensationprovides stable response.Fig. 14. Effect of adaptive gain control on control error of Z.7.2.3. Effects of control interÕalThe effects of control interval on control performancewere investigated. The results are:1. when the control interval

50、 is set to more than100 ms, oscillation becomes greater at attitudeswith large moments of inertia; and2. when the control interval is less than 50 ms,control performance cannot be improved somuch.Consequently, taking calculation accuracy into account,the control interval of 50 ms was selected forthi

51、s control system.7.2.4. Effects of loadA shovel with this control system carried outactual digging to investigate the effects of loading.No significant difference was found in control accuracyfrom that at no load.8. ConclusionsThis paper has shown that combining state feedbackand feedforward control

52、s makes it possible toaccurately control the hydraulic shovel, and alsoshowed that nonlinear compensation makes it possibleto use ordinary control valves for automaticcontrols. The use of these control techniques allowseven unskilled operators to operate hydraulic shovelseasily and accurately.We wil

53、l apply these control techniques to otherconstruction machinery such as crawler cranes, andimprove the conventional construction machinery tothe machines which can be operated easily by anyone.References1 J. Chiba, T. Takeda, Automatic control in construction machines, Journal of SICE 21 8 1982 4046

54、.2 H. Nakamura, A. Matsuzaki, Automation in construction machinery, Hitachi Review 57 3 1975 5562.3 T. Nakano et al., Development of large hydraulic excavator,. Mitsubishi Heavy Industries Technical Review 22 2 1985 4251.4 T. Morita, Y. Sakawa, Modeling and control of power shovel, Transactions of S

55、ICE 22 1 1986 6975.5 H. Araya et al., Automatic control system for hydraulic excavator, R&D Kobe Steel Engineering Reports 37 2 1987 7478.6 P.K. Vaha, M.J. Skibniewski, Dynamic model of excavator, Journal of Aerospace Engineering 6 2 1990 April.7 H. Hanafusa, Design of electro-hydraulic servo sy

56、stem for articulated robot, Journal of the Japan Hydraulics and Pneumatics Society 13 7 1982 18.8 H.B. Kuntze et al., On the model-based control of a hydraulic large range robot, IFAC Robot Control 1991 207212.液压挖掘机的半自动控制系统 摘要:开发出了一种应用于液压挖掘机的半自动控制系统。采用该系统，即使是不熟练的操作者也能容易和精确地操控液压挖掘机。构造出了具有控制器的液压挖掘机的精确

57、数学控制模型，同时通过模拟实验研发出了其控制算法，并将其应用在液压挖掘机上，由此可以估算出它的工作效率。依照此法，可通过正反馈及前馈控制、非线性补偿、状态反馈和增益调度等各种手段获得较高的控制精度和稳定性能。关键词：施工机械；液压挖掘机；前馈；状态反馈；操作1引言液压挖掘机，被称为大型铰接式机器人，是一种施工机械。采用这种机器进行挖掘和装载操作，要求司机要具备高水平的操作技能，即便是熟练的司机也会产生相当大的疲劳。另一方面，随着操作者年龄增大，熟练司机的数量因而也将会减少。开发出一种让任何人都能容易操控的液压挖掘机就非常必要了1-5。液压挖掘机之所以要求较高的操作技能，其理由如下。1.液压挖掘

58、机的操作，至少有两个操作手柄必须同时操作并且要协调好。2.操作手柄的动作方向与其所控的臂杆组件的运动方向不同。例如，液压挖掘机的反铲水平动作，必须同时操控三个操作手柄（动臂，斗柄，铲斗）使铲斗的顶部沿着水平面（图1）运动。在这种情况下，操作手柄的操作表明了执行元件的动作方向，但是这种方向与工作方向不同。如果司机只要操控一个操作杆，而其它自由杆臂自动的随动动作，操作就变得非常简单。这就是所谓的半自动控制系统。开发这种半自动控制系统，必须解决以下两个技术难题。1. 自动控制系统必须采用普通的控制阀。2. 液压挖掘机必须补偿其动态特性以提高其控制精度。现已经研发一种控制算法系统来解决这些技术问题，通过在实际的液压挖掘机上试验证实了该控制算法的作用。而且我们已采