Kinematic Analysis of Lifting Booms System for Aerial Work Platform Based on Differential Forward Incremental PID controller Tianhong Luo* Haiyan He** Xinxian Yin*** Sunke Zhu**** Jiayuan Luo***** *Professor, Department of Mechanical-electrical and Automotive Engineering, Chongqing Jiaotong University, Chongqing, 400074, China; **Graduate Student, Department of Mechanical-electrical and Automotive Engineering, Chongqing Jiaotong University, Chongqing, 400074, China; ***Graduate Student, Department of Mechanical-electrical and Automotive Engineering, Chongqing Jiaotong University, Chongqing, 400074, China; ****Associate Professor, Department of Mechanical-electrical and Automotive Engineering, Chongqing Jiaotong University, Chongqing, 400074, China; *****Doctor, Department of Mechanical-electrical and Automotive Engineering, Chongqing Jiaotong University, Chongqing, 400074, China; Abstract: By analyzing the kinematic characteristics of lifting booms system (LBS) of aerial work platform (AWP) about its working process, this paper provided a differential forward incremental PID (DFI-PID) controller to improve its control accuracy. Based on operating principles and structural parameters of LBS, three mathematical models were established: the mechanical motion system of each lifting booms, the mechanical-hydraulic coupling system and the electro-hydraulic proportional system. Meanwhile, a model of LBS was built up based on the electro-hydraulic proportion of AMES. A joint simulation was conducted by integrating the differential forward incremental PID (DFI-PID) controller into AMES (working as a major simulation environment) through certain software interface. Then, a DFI-PID closed-loop controller was designed to analyze the effect of the PID controller on LBS. The result showed that compared with the conventional PID controller, the DFI-PID closed-loop controller had better steady and higher robustness towards command changes and load disturbance. Besides, the validity of joint simulations was also proved. Keywords: Aerial work platform (AWP); Lifting booms system (LBS); Kinematic analysis; Closed-loop control system; Differential forward incremental PID (DFI-PID) controller obstacles and reach the predetermined position, this 0 Introduction As an emerging technological industry, AWP is an important branch in the engineering machinery field and is widely applied in shipbuilding, construction, municipal construction, fire control and port cargo etc [1,2]. Stability of LBS is an important factor to evaluate the success of AWP products and to ensure the safe operation of AWP as well. What’s more, the flexible structure of the folding-arm AWP makes it possible to surmount can be applied to lower operating height AWP [3,4]. With the development of digital control technology, problems that could not be solved by analog PID controller before [5,6] are now easily done on a digital computer. Thus, based on current digital control technology, a series of control algorithm has been promoted to improve system quality and meet the needs of different control systems [7]. Therefore, in this paper, an algorithm of the DFI-PID controller was established, in which two advantages of incremental PID and differential forward PID was highlighted, respectively. Firstly, this algorithm is only related to the change of the most recent K power instead of accumulating, so that the faulty operations influence is minored and a better control effect can also be obtained by weighted processing [8]. Secondly, this method only has differential influence on the output rather than a 1-lower arm;2- the middle arm;3-upper arm;4- job hopper; given instruction [9]. Overall, the improved PID 5-arm mechanical;6-arm mechanical; algorithm can be applied to situations where the 7-lower arm cylinder;8-in arm cylinder;9-leveling cylinder; instructions of lifting arms are frequently given in 10-rotary table the process of adjusting the lifting positions. At this Fig 1: The structure of folding-arm AWP point, it is useful to avoid the excessive overshoot from instruction changes. Additionally, it also can avoid some tiny faulty operations that affect the control accuracy. Thus, the improved algorithm contents the needs of being continuous, stable, and fast dynamic responded in lifting and lowering process. Based on current lifting booms control system (LBCS) technology, this paper employed the MATLAB/Simulink software to establish an integrated system model with the closed-loop controller. Meanwhile an integrated environment of the LBCS was built, with this integrated environment conducting combination to analyze of this system. 1 The structure of the Lifting Booms System 2 Mathematical models of the LBS This section mathematical researched model three parts of for the LBS, such as mechanical motion for each lifting arm, the hydraulic coupling mechanical of the LBS and the electro-hydraulic system for the mechanical of the LBS. 2.1 Mathematical model of mechanical motion for each lifting arm There provided three motion mathematical models, the lower arm, the middle arm and the upper arm as objects. 2.1.1 Motion mathematical model of the lower arm and the upper arm. The structure of the opening chain of series arm forms applied in the LBS was commonly used in industry, including the lower arm, the middle arm, upper arm, and a work platform. Each lifting arm and the link of the lower arm with the rotary table were hinged with the horizontal hinge pin. The Fig 2: Vector diagram of arms barycenter hinge joint was provided with a special sliding bearing to reduce the resistance while the working arm rotating. The concrete structure is shown in Fig. 1: From the simplified mechanical model of the arms, the mechanical movement was coincided with the cosine theorem formula and the equation was defined: y 2 a 2 b 2 2ab cos (1) Where y is total length of the lower arm (the upper arm)cylinder; For the lower arm, a is the distance of the two hinge joints, one hinge joint is intersection for the oil cylinder of the lower arm and for the lower arm and the middle arm, another hinge point is intersection for the middle arm lower connecting rod and the lower arm; l 2 , l3 the rotary table, another hinge joint is intersection for the rotary table and the lower arm; b is the middle arm connecting rods of isometric; distance of the two hinge joints, one hinge joint is total length of middle oil cylinder. are the l5 is the intersection for the rotary table and the lower arm, With the method of the reverse theory, namely another hinge joint is intersection for the oil that the middle arm and the lower arm were cylinder of the lower arm and the lower arm; is assumed to be frame and the driving link , the angle of the lower arm and rotary table. While, for the upper arm, a respectively. Then the change of is the distance l5 ( y ) was of the two hinge points, one hinge point is confirmed through the variation of angle of the intersection for the upper arm cylinder and the driver and the frame. middle arm, another hinge point is intersection for the middle arm and the upper arm; b is the distance of the two hinge points, one hinge point is This equation can be defined via the complex vector method: A sin B cos C 0 (3) intersection for the upper arm and the middle arm, another hinge point is intersection for the upper arm and the upper arm cylinder; is the angle of the middle arm and the upper arm. y and with respect Took the derivative of to time t, then the equation is given as y ' f t ' , where t represents the lower ab sin Furthermore, the following relations can be tan( / 2) ( A A2 B 2 C 2 ) /( B C ) (4) (2) a b 2ab cos 2 And C l 22 l12 l32 l 42 2l 1 l 4 cos 1 achieved based on above equation formulas. arm or the upper arm. ft With A 2l1l3 sin 1 , B 2l3 l1 cos 1 l 4 , 2 2.1.2 Motion mathematical model of the middle arm 2.2 Mathematical model of the hydraulic coupling and mechanical of the LBS Suppose that a scheme that considered the lifting arm was rotating at a speed of equiangular and the electro-hydraulic proportion servo valve was matching and symmetry. This application x1 required , x2 y , x3 dy , x4 p1 , x5 p 2 , hence, dt Fig 3: Vector diagram of middle arm barycenter state space formula of nonlinear model was defined via flow continuity equation and force balance l4 , l 6 are the simplified connecting rods of the middle arm(In order to facilitate the analysis, the arm is divided into two sections), namely the rack; l1 is the driver parts which is the distance of the two hinge points, one hinge point is intersection equation. x1 x 3 / f t proportion of link, resulting from the dynamic x 2 x3 x 3 K / m x 2 B / m x 3 A1 / m x 4 A2 / m x 5 (5) performance of the amplifier was very high. x 4 A1 / V1 x 3 C i / V1 ( x 4 x 5 ) C e / V1 x 4 Transfer function is defined as: (C d wxv / V1 ) 2 / p s x 4 Wi s I s / U s K a (C d wxv / V2 ) 2 / x 5 2) Transfer function of the electro-hydraulic x 5 A2 / V2 x 3 C i / V2 ( x 3 x 4 ) C e / V2 x 5 (6) proportional valve. Where, t represents the lower arm, the middle arm or the upper arm; Ws s xv s I s s 2 is the rotation angle of the lifting arm; m is the equivalent quality of piston and (7) s s 1 Here: Ksc is the proportional gain; load; s is B is the viscous damping coefficient of piston and load; s2 K SC 2 the inherent frequency of proportional valve; is the damping ratio. K is the spring stiffness of load; A1 and A2 are effective area of non-rod cavity and rod cavity for the hydraulic cylinder, 3) Transfer function of the power element. respectively; The hydraulic power units of each lifting arm ps is the pressure of oil supply; were valve controlled asymmetrical cylinder. The p0 is the return oil pressure, follow approximately pressure of 0; type took consideration of piston displacement variation, which cased by asymmetric Xv is the displacement of spool; cylinder area. Specifically, inertia load and external W is the area gradient of throttle window load were mainly taken into account, the transfer for slide valve; function is as shown: Kq Cd is the flow coefficient; X P Ci and Ce are the inside and outside Ap Xv leakage coefficient of the hydraulic cylinder, K ce Vt 1 s FL A2 p s 1 A p2 C T e K ce 1 2 s 2 2 s 2 s 1 h h respectively; p1 and p2 are the two cavity pressures of Here: Kq is the flow gain; (8) h is the inherent frequency of hydraulic; ξ is the hydraulic damping the hydraulic cylinder, respectively; V1 =V10 /β,V2 =V20 /β,V10 and V20 are the initial volume of the non-rod cavity and rod ratio; C is the variation coefficient of equivalent area for the load flow; T is the variation coefficient cavity for the hydraulic cylinder, respectively; β is the modulus elasticity of oil bulk. of elastic modulus for the effective bulk; is the oil tanks area; Kce is the flow-pressure coefficient; Ap is the equivalent area of the load flow; Ps is the 2.3 Mathematical model of electro-hydraulic system for mechanical of the LBS the the 1) Transfer function of amplifier. oil pressure; e is the modulus of elasticity for oil. 4) The principle of the DFI-PID controller algorithm. In order to discuss the formula accurately, the Compared with conventional PID controller, electrical links were regarded as general electric the DFI-PID algorithm combined advantages of the amplifier, namely the input and the output were differential forward PID and the incremental PID. voltage and current. Also, it could be seen as a The essence of the differential forward PID was early operation; this method was only to conduct the output in differential while not for a given k u k K p e(k ) K 1 e(i ) K D e(k ) - e(k 1) u 0 (11) i 0 instruction [10]. However, the incremental PID Here, u 0 is the based value of control control relevant to the change of the nearest K quantity,is the same as output value of controller when K=0; uk is the output value of controller power rather than accumulating, so that the missing movements have minor influence and it was easy to get a good control effect through weighted for k th sampling time; K1 coefficient; processing [11,12]. The input signals of r are present as lifting adjusting position of LBS. coefficient, a. Principle of the differential forward PID coefficient, K1 KD K PTS T1 Kp is KD ; K PTD T1 ; TS is proportion amplifying integral amplifying is differential amplifying is sampling period. control When The characteristic of this method only had the actuator was employed the incremental accumulation of control quantity differential influence on the output instead of a instead of actual value of control quantity, the PID given instruction [13]. The structure of differential control required incremental algorithm, according to forward PID controller is shown in Fig.4. the type (11) the output value of (k-1)th sampling r e time can be obtained: u Kp(1+1/Tis) k -1 u k - 1 K p e(k - 1) K1 e(i ) K D e(k - 1) - e(k 2) u 0 - (12) i 0 c (13) T e0 ek k T uk K p ek ei d ek ek 1 Ti 2 i 0 T (1+Tds)/(1+0.1Tds) Fig.4: The structure of differential forward PID controller The control formula of differential incremental is obtained: u(k ) u(k 1) K P [e(k ) e(k 1)] K P Ts e(k ) u d (k ) Ti u d (k ) T1u d (k 1) T2 y(k ) T3 y(k 1) T1 (9) (10) Where, Ts is the sampling time ; Td is Kp is scale coefficient; Ki is integral coefficient; =0.1; T1, T2 ,T3 are present as coefficients of differential parts;All of algorithm of the control quantity can be obtained: u(k ) uk uk 1 u(k ) q0 ek q1ek 1 q2 ek 2 Td T TS Td T d T Td TS ; 2 Td TS ; 3 Td TS differential time of constant ; With type (11) and type (12), incremental Kp、Ki、T1、T2、T3 are justified online. (14) uk uk 1 q 0 ek q1ek 1 q 2 ek 2 (15) Here, 3T Td q 0 K p 1 2 Ti T T T q1 K p 1 2 d T 2Ti q2 K p Td T Therefore, if analog parameters(Kp,Ti and Td) of the PID controller were available, then in a shortly sampling time, the parameters of q 0,q1 and q2 could be calculated out with Kp,Ti and Td. b.Basic principle of the incremental PID controller algorithm The AWP is only performing the differential for output y (t) of hydraulic cylinder piston rod for The discretization of the PID algorithm as each lifting arm; the differential output signal shown below, the differential equation of the contains controlled parameters and the change of continuous time PID algorithm turn into describes the rate. The output is worked as a measured value the difference equation of discrete time, and then putting into the proportional integral controller, as a PID algorithm for the discrete is obtained: result to strengthen the system to overcome the overshoot effect, thus, compensating the process lag 3.1 Models and setting parameters to improve the control quality. This method is only Under the environment of AMEsim with the related to the change of the nearest K power rather principle of the lifting arm electro-hydraulic system than accumulating, so the missing movements have and MATLAB / Simulink modeling, various kinds minor influence, moreover, it is easy to have a good of modules of AMEsim model could be got from control effect through weighted processing [14]. the Planar mechanical module library and the Although, piston rod displacement for a desired Mechanical module library. Finally, either with value changes, there has little error actions and the MATLAB /Simulink interface technology, AMESim output won't change substantially. In addition, played a major role in simulation environment and because of the controlled quantity has few built up the whole simulation model of the lifting mutations, even if the given value is to alter, the arm system [15, 16]. For the limits of the software charged quantity is slowly to change, thereby it is model library, some sections couldn’t be completely no longer result in mutant differential. copied from the prototype element, so that some of them were replaced, but all of them observed the 3. Dynamic characteristics analysis of the LBS principle of the system characteristic unchanged. The model is as shown in Fig.5. Fig 5: Simulation model of lifting system In Fig. 5, Body1 is the lower arm, Body2 is lower on lower connecting rod, Body8 is working bucket. connecting rod of the middle arm, Body3 is upper Denote the formula parameters by actual connecting rod of the middle arm, Body4 is the length and the function of (2) can be simplified, as middle arm, Body5 is the upper arm, Body6 is given below: leveling on upper connecting rod, Body7 is leveling 350250 sin ft Where (16) 1401000 cos 2212801 t (1) was negative. With the aid of the triangle cosine formula and actual structure parameters, a formula represents the lower arm. According to the initial installation of the for y and 1 can be defined: middle arm, determined the sign in the formula of y 16 sin 1 362 50 cos 21 312 cos 1 1 18761 10480 cos(2 arctan( )) 1.326 125 6 cos 1 6 That is the relation formula of the piston rod y (17) displacement(y) with angle : 1 16 sin 362 50 cos 2 312 cos 18761 10480 cos( 2 arctan( )) 1.326 125 6 cos 6 Took the derivative of y and with (18) y ' f t ' , where t represents the middle arm. respect to time t, then the equation is given as 128 sin 16a sin 2arctg 13 8 sin a 393 cos 1 ft 50 8 sin a 1 5 cos a 12.5 sin 2 11a 103 sin 18761 10480 cos 2arctg ( 3 cos 1 a 78 25 sin 2 78 cos (19) Pressure of relief valve e 21 MPa The diameter of piston 100 mm The diameter of piston rod 50 mm The length of the piston rod 0.52 m Kp 1.2 — Ki 0.01 — Kd 0.01 — The diameter of piston 113 mm The diameter of piston rod 56 mm The length of the piston rod 0.906 m Kp 1.25 — according to the actual type of each element, Ki 0.01 — submodel of corresponding element could be Kd 0.05 — selected in the drop-down list. Besides, simulation The diameter of piston 63 mm The diameter of piston rod 35 mm The length of the piston rod 0.33 m Kp 1.4 — Ki 0.01 — Kd 0.03 — Here, Denoted the formula parameters by actual length of the upper arm and the function of (2) can The lower arm be simplified, as given below: ft 102542 sin (20) 410168 cos 810857 Selecting submodel system is very important for obtaining the correct simulation results. In the actual situation and udder the mode of submodel, The middle arm parameters were set up, as shown in Table. 1. The upper Table 1: Simulation parameters of the system arm Numerical Parameter Company value -2 Viscosity of hydraulic oil 5.1×10 Pa.s Medium density of hydraulic oil 850 kg/m3 Model Bulk modulus of hydraulic oil 1700 MPa parameter Temperature reference of hydraulic oil 40 ℃ Maximum displace of main hydraulic pump 70 ml/r Rated engine speed 1500 r/min 3.2 Testing and analyzing the LBS 3.2.1 Steady state analysis of the lifting arm system When simulation model of the system was established and the corresponding initial parameters In this section, the results of the steady state were set, steady-state simulation of the lifting arm analysis of the electro-hydraulic system for each electro-hydraulic system could be in progress. Bode arm were achieved from the graph of Fig.6, 7 and 8, diagram of the LBS is as shown in Fig. 6, 7 and 8. as shown in Table 2. The tests reported above According to the control theory, quite stable showed that each LBS has better stability. conditions of the system are as shown: Table 2: The results of steady-state analysis Amplitude margin Kg ≥6dB Amplitude Phase margin γ =30 °~ 60 °. margin(db) Phase margin(°) The lower arm system 7.9 42.9 The middle arm system 7.13 55.6 The upper arm system 12.1 35.6 3.2.2 Dynamics analysis of the LBS When the LBS is working, lifting sequence and displacement of each lifting arms are different. In order to research it conveniently, this research took an example of the highest position and the operator used the most commonly operation Fig 6: Bode diagram of lower arm barycenter system sequence to analysis the result. What’s more, setting up simulation running time of 120s, step 0.01s. The analysis results of the simulation are shown as follows. 1) The lower arm In order to improve stability and reliability of the system, the DFI-PID controller algorithm was employed. The AMESim system with the aid of the batch processing, optimal parameters of the PID system was obtained. Furthermore, compared with the traditional hydraulic model (conventional PID controller) and draw the comparison chart of the entrance flow for the hydraulic cylinder, as shown Fig 7: Bode diagram of middle arm barycenter system in Fig. 9. 0.020 DFI—PID controller Y:Velocity[m/s] 0.015 Conventional PID 0.010 0.005 0.000 -0.005 0 20 40 60 80 100 120 X:Times [s] Fig 9: The velocity of lower arm barycenter Fig 8: Bode diagram of upper arm barycenter system In Fig. 9, barycentric velocity of the lower arm in the vertical direction can be quickly reached at a 0.020 the 0.015 using of the DFI-PID. The dynamic characteristic of the system was improved greatly. 2) The middle arm As the same with the lower arm, in order to Y:Velocity[m/s] steady value without overshoot, this occurs due to 0.010 DFI—PID controller 0.005 0.000 improve the dynamic characteristics, the DFI-PID -0.005 controller was applied. The same method was used -0.010 Conventional PID 0 20 40 compared with the traditional hydraulic model (conventional PID controller) and 60 80 100 120 X:Times [s] to get the optimal parameters of the PID system, Fig 11: The velocity of upper arm barycenter draw the comparison diagram of the entrance flow for hydraulic cylinder, as shown in Fig. 10. Fig. 11 shows that barycentric velocity of the upper arm in the vertical direction can be quickly reached at a steady value without an overstrike. This 0.020 DFI—PID controller was achieved by DFI-PID controller, the dynamic Y:Velocity[m/s] 0.015 characteristic of the system was improved greatly. 0.010 4) Working platform 0.005 In harmony with the method of the lifting booms 0.000 analysis, with the algorithm of DFI-PID controller, Conventional PID -0.005 0 20 60 40 80 100 120 X:Times [s] Fig 10: The velocity of middle arm barycenter then compared with the traditional hydraulic model (the conventional PID controller) and finished the contrast diagram of barycentric velocity in the vertical direction for the operating platform, as From the graph of Fig.10, velocity in the shown in Fig. 12. vertical direction of the middle arm can reach at a Conventional PID steady condition rapidly with no overshoot. This of the stability and reliability for the system were improved. 3) The upper arm Y:Velocity[m/s] great phenomenon was obtained by DFI-PID, much 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 DFI—PID controller -0.05 Simulation analysis of the upper arm was identical with the middle arm. The AMESim system -0.10 -0.15 0 20 40 60 80 100 120 X:Times [s] with the aid of the batch processing, optimal parameters of the PID system was obtained. The comparison chart of the entrance flow for the Fig 12: The velocity of working platform hydraulic cylinder (see Fig. 11) was achieved by comparing with DFI-PID controller and the conventional PID controller. From the graph of Fig.12, the speed of operation platform in the vertical direction is running smoothly without jitter. Stability and reliability of the proposed system had been improved obviously. 4. Conclusion This paper analyzed the operational mechanical of the AWP-LBS, based on which mathematical model of lifting system, electromechanical coupling model and transfer function of electro-hydraulic multi-body dynamics[J]. International Conference system were established. By taking advantages of on Intelligent Control and Information Processing, simulation analysis software in MATLAB and AMES 2010:798 - 802 and the interface technology, an integrated simulation [3] Xue Jinlong. Research on platform of the LBS was built to make united Electro-hydraulic Control System for Self-propelled simulation realized. The results show that the system and Folding-arm Type Aerial Working Platform’s simulation model is effective and the DFI-PID Working Device[D]. Xi'an: Chang'an University, controller can achieve better dynamic characteristics. 2013.07 The major aim of this paper is to research on the DFIPID controller, the results are as follows: [4] Li Huai, Shi Hui-chao, Dai Yu. Dynamics simulation and finite element analysis of aerial 1) Efficiency of the design can be improved by building a simulation model with AMES and platform folding arm[J].Construction Mechanization, 2010,(02):41-43. modifying the design parameters instead of the physical parameters debugging. truck [5] Masao NOZAWA. Development and Improvement of Mobile Work Platform for Use in 2) Steady-state analysis of lifting booms for the upper arm, the middle arm and the lower arm (with Apple Orchards[J]. Japanese Journal of Farm Work Research, 2010, (02): 41-42 Bode diagrams) shows that electro-hydraulic system of each arm is stable. [6] Shu-wang Du, Zhi-lin Feng, Zhi-ming Fang. Design of improved PID algorithm for position 3) DFI-PID controller can perform better in control of servo unit[J]. International conference on vertically changing the speed of each arm smoothly Computer and Communication Technologies in and stably than conventional PID controller. Thus, Agriculture Engineering, 2010,(3): 333 - 335 [7]M.Zhou,N.Pagaldipti,H.L.Thomas,Y.K.Shyy. good dynamic and static characteristics are obtained, without overshoot and oscillation. An integrated approach to topology,sizing,and shape 4) Practical function of the promoted DFI-PID in this paper has been proved through this research optimization[J]. Structure and Multi disciplinary Optimization,2004(26):208-317. and the MATLAB /Simulink and AMESim are tested [8] Liang Chunying, Wang Xi, Ji Jianwei, etc. to be valid and reliable, which puts lights on the future Research of PID Algorithm for Valve Controlled research and design on the AWP. Hydraulic Motor Variable Rate Fertilizer Control System[J].Computer and Computing Technologies in Acknowledgment Agriculture VII, 2014. The authors are thankful for the support of the [9] Zhang Jing. Differential forward PID Scientific and Technological Project of Chongqing City controller based on RBF network[J]. Ordnance (CSTC 2009AC6077) and also give their sincere thanks Industry Automation,2007,(09):60-62. to Chongqing Jiaotong University for [10] Yang Xiao-sheng, PENG Zhi-jian, XIAO offering experiment support. Yi-bo. Temperature control system based on differential ahead PID algorithm of poly-silicon ingot References [1] Wu Gang. Operating Arm of18m Aerial furnace[J]. Equipment for Electronic Products Manufacturing, 2009,38(7):42-45. Vehicles Structure Design and Optimization of [11] Shen Li-quan, Zhang Zhao-yang, Li Ying, Simulation Analysis[D]. Hefei: Hefei University of Liu Zhi. Improved H.264 GOP-level bit allocation by Technology, 2012. incremental PID algorithm[J]. IET Conference on [2] Hai-dong Hu, En Li, Xiao-guang Zhao, etc. Modeling and simulation of folding-boom aerial platform vehicle based on the flexible Wireless, Mobile and Sensor Networks, 2007:521 – 524 [12] M. Nithyasree, K.V. Kandasamy. A Generic PID Controller Based on ARM Processor[J]. Procedia Engineering. 2012.06. 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