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1、semi-automatic control system for hydraulic shovelhirokazu araya, masayuki kagoshimamechanical engineering research laboratory, kobe steel, ltd., nishi-ku, kobe hyogo 6512271, japanaccepted 27 june 2000abstracta semi-automatic control system for a hydraulic shovel has been developed. using this syst

2、em, unskilled operators can operate a hydraulic shovel easily and accurately. a mathematical control model of a hydraulic shovel with a controller was constructed and a control algorithm was developed by simulation. this algorithm was applied to a hydraulic shovel and its effectiveness was evaluated

3、. high control accuracy and high-stability performanee were achieved by feedback plus feedforward control, nonlinear compensation, state feedback and gain scheduling according to the attitude. q2001 elsevier science b.v. all rights reserved.keywords: construction machinery; hydraulic shovel; feedfor

4、ward; state feedback; operati onntroductiona hydraulic shovel is a construction machinery that can be regarded as a large articulated robot.digging and loading operations using this machine require a high level of skill, and cause considerable fatigue even in skilled operators on the other hand, ope

5、rators grow older; and the number of skilled operators has thus decreased the situation calls for hydraulic shovels, which can be operated easily by any personwl-5x.the reasons why hydraulic shovel requires a high level of skill are as follows.more than two levers must be operated simultaneously and

6、 adjusted well in such operations.the di recti on of lever operatio ns is d iff ere nt from that of a shovel's attachment moveme nt.for example, in level crowding by a hydraulic shovel, we must operate three levers z arm, boom, bucket, simultaneously to move the top of a bucket along a level sur

7、facezfig1. 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 automatically, the operation becomes very easily. we call this system a semi-automatic control

8、 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 of a hydraulic shovel to improve the precision of control.we have developed a control alg

9、orithm to solve these technical problems and confirm the effect of this control algorithm by experiments with actual hydraulic shovels. using this control algorithm, we have completed a semi-automatic control system for hydraulic shovels. we then report these items.2. hydraulic shovel modelto study

10、control algorithms, we have to analyze numerical models of a hydraulic shovel. the hydraulic shovel, whose boom, arm, and bucket joints are hydraulically driven, is modeled as shown in fig.2. the details of the model are described in the following.2.1. dynamic model 6supposing that each attachment i

11、s a solid body, from lagrange's equations of motion, the following expressions are obtained:j 讣 & + 丿（妬01 一 0 j叫"| 0,）0$ + ./j jmii（ | 趴）",一a |$tn01 = 7|心- +厶（： - - ”： wf +./：lmn（«: - j"； -=门jhcos（秒l _ 叭）叫 + 厶、cos（ ": _ “1 + fyyoy 一”| 0.（k 一_ 人小“"、=（i）where, = ,

12、wi+ （/2 + 必）；* 人；片2 ""屮&2 +刃jq； 厶=dg3；如=加2】；2+ "d + 厶；丿22 =加+ "hf +厶、厶3=心1：3+厶，a'| =（加|+叫打+伽1）尺；心=（处】卫+加.丿&心=川山3&；g is the joint angle, 0i is the supply torque, ri is the attachment length, li is the distance between igi the fulcrum and the center of gravity, mi i

13、s the mass of the attachment, li is the moment of inertia around the center of gravity （subscripts i=l-3, mean boom, arm, and bucket, respectively）2.2. hydraulic modeleach joint is driven by a hydraulic cylinder whose flow is controlled by a spool valve, as shown in fig.3. we can assume the followin

14、g:1. the open area of a valve is proportional to the spool displacement.2. there is no oil leak.3. no pressure drop occurs when oil flows through piping.4. the effective sectional area of the cylinder is the same on both the head and the rod sides.in this problem, for each joint, we have the followi

15、ng equation from the pressure flow characteristics of the cylinder:when,where, ai=seffective cross-sectional area of cylinder; hi=cylinder length; xi= spool displacement; psi= supply pressure; pli=cylinder head-side pressure; p2icylinder rod-side pressure; vi=oil volume in the cylinder and piping; b

16、i=pool width; y=oil density; k=bulk modulus of oil; and c=flow coefficient.2.3. link relationsin the model shown in fig. 1, the relation between the cylinder length change rate and the attachment rotational angular velocity is given as follows:（l）. boom恥）_thqusin（伏+伙）+77t: + 2a7,7f.c（1 +armft:讪（1111

17、vttt: 4777 4 573777恥“人-仇 4 b“ njl bucketwhen 。3上人=冰；=(1 ”324 torque relationsfrom the link relations of section 2.3, the supply torque xi is given as follows, taking cylinder friction into consideration:+ 即wjfj办 w）（4）门=一厶（地）心一 «:/（%、血）他一务）+娜他-材"以佝血） 门二一厶«'/（02 如 16-血）+即他一对&厶（如

18、）where, cci the viscous friction coefficient and fikineticfrictional 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 has the following first-order lag against the ref ere nee input.（5）a tim

19、e constant.where, £ is the reference in put of spool displacement and t®3. angle control systemas show n in fig. 4, the angle 0 is basically con trolled to follow the ref ere nee angle 6y by position feedback. in order to obtain more accurate control, nonlinear compensation and state feedb

20、ack are added to the position feedback. we will discuss details of these algorithms as follows.3.1. nonlinear compensationin the ordinary automatic control systems, new control devices such as servo valves are used. in our semi-automatic system, in order to realize the coexistenee of manual and auto

21、matic operations, we must use the main control valves, which are used in manual operation. in these valves, the relation between spool displacement and open area is nonlinear. then, in automatic operation, using this relation, the spool displacement is inversely calculated from the required ope n ar

22、ea, and the nonlin earity is comp en sated(fig.5.)3.2. state feedbackbased on the model discussed in section 2, if the dynamic characteristics for boom angle control are linearized in the vicinity of a certain standard condition (spool displacement x 10, cylinder differential pressure p 110 , and bo

23、om angle 010)., the closed-loop ransfer function can be expressed by(6)where, kpposition feedback gain; and坳一 k忌一几汕+ 2期宀一_4-./12cos2 +./|3cos( 8； + ；)|仃m =2/(九)(儿-he)a'kkqn你一 pg+ j12cos2 + ./ucos( 02 + &；)2趴q) kk屈pj - pgthis system has a comparatively small coefficient al, so the response is

24、 oscillatory. for instance, if in our large sk-16 hydraulic shovel, xi0 is 0, the 10 coefficients are given263as , ao=2.7 x10,ai=6.0 x10,a2=1.2 x10 addingthe acceleration feedbackof gain ka , to this (the upper loop in fig. 4.), the closed loop transfer function is given as2adding this factor, the c

25、oefficient of s becomes larger, thus, the system becomes stable. in this way, acceleration feedback is effective in improving the response characteristics however, it is gen erally difficult to detect acceleratio n accuratel y to overcome this difficulty, cyli nder force feedback was applied in stea

26、d of accelerati on feedback(the lower loop in fig. 40. in this case, cylinder force is calculated from detected cylinder pressure and filtered in its lower-frequency portion 7,8. this is called pressure feedback.4. servo control systemwhen one joint is manu ally operated and another joi nt is con tr

27、olled automatically to follow the manual operation, a servo control system must be required. for example, as shown in fig. 6, in the level crowding control, the boom is controlled to keep the arm end height z(calculated from 0x and 02).to ref ere nee zr. in order to obtai n more accurate control, th

28、e following control actions are introduced4.1. feedforward controlcalculating z from fig 1, we obtainz = 1 j cos/? i + 12 cos 2 .(8)differentiating both sides of eq.(8). with respect to time, we have the followingrelation,the first term of the right-hand side can be taken as the expression (feedback

29、porti on).to con vertto1 , and the second term of the right-hand side is the 1expression(feedforward portion).to calculate how much 01 should be changed when 02 is changed 1 2= manually actually, 01is determined using the differenee value of a 02 . to optimize the feedforward rate, feedforward gain

30、kff tunned.there may be a method to detect and use the arm operating-lever condition(ie angle).instead of arm angular velocity, since the arm is driven at an angular velocity nearlyproportional to this lever condition.4.2. adapti6e gain scheduling according to the attitudein articulated machines lik

31、e hydraulic shovels, dynamic characteristics are greatlysusceptible to the attitude. therefore, it is difficult to control the machine stably at allattitudes with constant gain. to solve this problem, the adaptive gain scheduling accordingto the attitude is multiplied in the feedback loop(fig. 6). a

32、s shown in fig. 7, the adaptive gain (kz or k0 ).is characterized as a function of two variables 日 2, and z. 62means how the arm is extended, and z means the height of the bucket.5- simulation resultsthe level crowding control was simulated by applying the control algorithm described in section 4 to

33、 the hydraulic shovel model discussed in section 2. (in the simulation, our large sk-16 hydraulic shovel was employed.). fig. 8 shows one of the results. five seconds after the control started, load disturbance was applied stepwise. fig 9 shows the use of feedforward control can reduce control error

34、.6. semi-automatic control systemas illustrated in fig. 10, the control system consists of a controller, sensors, man-machi ne in terface, and hydraulic con trol system.the controller is based on a 16-bit microcomputer which receives angle input signals of the boom, arm, and bucket from the sensor;

35、determines the condition of each control lever; selects control modes and calculates actuating variables; and outputs the results from the amplifier as electrical signals. the hydraulic control system generates hydraulic pressure proporti onal to the electrical signals from the electromag netic prop

36、ortional-reducing valve, positions the spool of the main control valve, and controls the flow rate to the hydraulic cylinder.in order to realize high-speed, high-accuracy control, a numeric data processor is employed for the controller, and a high-resolution magnetic encoder is used for the sensor.

37、in addition to these, a pressure transducer is in stalled in each cyli nder to achieve pressure feedback.the measured data are stored up to the memory, and can be taken out from the communication port.62 control functionsthis control system has three control modes, which are automatically switched i

38、n accordanee with lever operation and selector switches. these functions are the following(1) .level crowding mode: during the manual arm pushing operation with the level crowding switch, the system automatically controls the boom and holds the arm end moveme nt level. i n this case, the ref ere nee

39、 positi on is the height of the arm end from the ground when the arm lever began to be operated. operation of the boom lever can interrupt automatic control temporarily, because priority is given to manual operation.(2) horizontal bucket lifting mode: during the manual boom raising operation with th

40、e horiz on tai bucket lifting switch, the system automatically con trols the bucket. keeping the bucket angle equal to that at the beginning of operation prevents material spillage from the bucket.(3) manual operation mode: when neither the level crowding switch nor the horizontal bucket lifting swi

41、tch are selected, the boom, arm, and bucket are con trolled by manual operation only.the program realizing these functions is primarily written in c language, and has well-structured module to improve maintainability7. results and analysis of field testwe put the field test with the system. we con f

42、irmed that the system worked correctly and theeffects of the control algorithm described in chaps 3 and 4 were ascertained as follows.7.1. automatic control tests of indi8idual attachmentsfor each attachme nt of the boom, arm, and bucket, the ref ere nee angle was cha nged "58 stepwise from the

43、 initial value, and the responses were measured; thus, the effects of the control algorithm described in chap. 3 were ascertaineck7.1. :l effect of nonlinear compensationfig. 11 shows the test results of boom lowering. because dead zones exist in the electro-hydraulic systems, steady-state error rem

44、ains when simple position feedback without compensation is applied (off in the figure). addition of nonlinear compensation (on in the figure).can reduce this error.7.1.2. effect of state feedback controlfor the arm and bucket, stable response can be obtained by position feedback only but adding acce

45、leration or pressure feedback can improve fast-response capability as regards the boom, with only the position feedback, the response becomes oscillatory. adding acceleration or pressure feedback made the response stable without impairing fast-response capability. as an example, fig. 12 shows the te

46、st results when pressure feedback compensation was applied during boom lowering.7.2. le9el crowding control testcon trol tests were con ducted under various con trol and operati ng conditions to observe the control characteristics, and at the same time to determine theoptimal control parameters (suc

47、h as the control gainsshown in fig. 6).7.2.1. effects of feedforward controlin the case of position feedback only, increasing gain kp to decrease error az causes oscillation due p to the time delay in the system, as shown by aoffb in fig. 13. that is, kp cannot be in creased apply- p ing the feedfor

48、ward of the arm lever value described in section 4.1 can decrease error without increasing k as shown by aonb in the figure7.2.2. effects of compensation in attitudelevel crowding is apt to become oscillatory at the raised position or when crowding is almost completed. this oscillation can be preven

49、ted by changing gain kp according to the attitude, as has been p iscussed in section 42 the effect is shown in fig.14. this shows the result when the level crowding was done at around 2 m above ground. compared to the case without the compensation, denoted by off in the figure, the on case with the

50、compensation provides stable response.7.2.3. effects of control inter9althe effects of control interval on control performance were investigated. the results are:1. when the control interval is set to more than 100 ms, oscillation becomes greater at attitudeswith large moments of inertia; and2. when

51、 the control in terval is less tha n 50 ms, con trol performs nee cannot be improved so much.consequently, taking calculation accuracy into account, the control interval of 50 ms was selected for this control system.7.2.4. effects of loada shovel with this control system carried out actual digging t

52、o investigate the effects of loading.no significant differenee was found in control accuracy from that at no load8. conclusionsthis paper has shown that combining state feedback and feedforward controls makes it possible to accurately control the hydraulic shovel, and also showed that nonlinear comp

53、ensation makes it possible to use ordinary control valves for automatic controls. the use of these control techniques allows even unskilled operators to operate hydraulic shovels easily and accurately.we will apply these con trol techniques to other con struct! on machi nery such as crawler cranes,

54、and improve the conventional construction machinery to the machines which can be operated easily by any one 液压挖掘机的半自动控制系统hirokazu araya ,masayuki kagoshima日木机械工程研究实验室 kobe steel, ltd., nishi-ku, kobe hyogo 6512271,2000年7月27日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

55、确数学控制模型，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，由此可以估算岀它的工作效率。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。自然杂志2001 版权所有关键词：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，被称为大型较接式机器人，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牛相当 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

56、求较高的操作技能，其理由如下。1. 液压挖掘机的操作，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

57、度。现己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。而且我们己采用这种控制算法，设计出了液压挖掘机 的半自动控制系统。具体阐述如下。2.液压挖掘机的模型为了研究液压挖掘机的控制算法,必须分析液压挖掘机的数学模型。液压挖掘机 的动臂、斗柄、铲斗都是由液压力驱动，其模型如图2所示。模型的具体描述如下。2.1动态模型6假定每一臂杆组件都是刚体，由拉格朗日运动方程可得以下表达式：丿19& + |jcos（ % 0）"）+ 丿i2、e（ "i °,）"$ + 片小八（% asino（ =juco!i（|

58、）"+厶20$（" -+厶*诃如外）。：a2sin£i2 = t2厶丸-）"| + ./;lcos（ 0：-攸）仇 +片8、./t）sin（0| 9）9 +.a*sm（ k小m". = rb（i）其 中 <al = w|l；r| +（叫 + 加3）l： 4- /|；./|2 = 川2屮&2 +加1 厲3；13厶 2 =加2】；2 + 丿“3 垃 + 厶；厶2=叫吒2 + 丿.占+厶，厶' 二川j汁；厶3 =血+厶, =（加j卍+叫11 +如i）g；心= （"卫+切jg； k严叫1品;g是重力加速度；61接点角度；ti是提供的扭矩；li组件的长度；lgi转 轴中心到重心z距；mi组件的质量；ii是重心处的转动惯量（下标i=l-3;依次表示 动臂，斗柄，铲斗）。2. 2挖掘机模型每一臂杆组件都是由液压缸驱动，液压缸的流量是滑阀控制的，如图3所示。可 作如下假设：1.液压阀的开度与阀芯的位移成比例。2 系统无液压油泄漏。3. 液压油流经液压管道时无压力损失。4. 液压缸的顶部与杆的两侧同样都是有效区域。在这个问题上，对于每一臂杆组件