Development of Crane Tele-operation System using Laser Pointer Interface

Transcription

1 23 IEEE/RSJ International Conerence on Intellient Robots and Systems (IROS) November 3-7, 23. Tokyo, Japan Development o Crane Tele-operation System usin Laser Pointer Interace Masaki Neishi, Hisasi Osumi 2, Keiichirou Saito, Hikaru Masuda, Yusuke Tamura 2 Abstract A teleoperation system or a crane is developed. The crane uses a small actuator and lare actuator in each direction ( and y). The lare actuator is controlled by input sinals rom a laser pointer interace, and the small actuator is used as a reulator and is eedback-controlled by a wire anle sensor. To avoid overshoots in the suspended object at the taret point and to eliminate the eect o the tremblin o the irradiated liht by the laser pointer, the velocity commands sent to the lare actuator are desined by accumulatin cubic unctions, each o which is based on the displacement o the irradiated liht in a samplin period. The eectiveness o the developed control system and its control alorithm were veriied throuh eperimental results. I. INTRODUCTION Wire suspension systems, includin overhead cranes, are requently used in actories because a crane can transport suspended objects in a three-dimensional space. However, because o the characteristics o cranes, pendulum vibration occurs durin the transportation o suspended objects. This pendulum vibration must be controlled because it can lead to load collapse. Moreover, the method used to stop objects with residual vibration not only derades the work eiciency but can also cause accidents, includin load shitin. Thereore, operators must have advanced operation skills. One o the solutions to this problem is to automate the vibration control and transportation by cranes. However, the eistin studies have only treated two issues: the trajectory eneration and suppression o pendulum vibration usin eedback control or eedorward control [][2]. To control pendulum vibration, a transportation method that considers jerk has been proposed. Yet, this method does not take the hoistin wire into account. Moreover, these studies [3][4][9] did not consider three-dimensional transportation. On the other hand, the studies on teleoperation systems have mainly proposed operation interaces. Thereore, no method has previously been proposed to control the pendulum vibration that results rom disturbance and overshootin at the taret point. To improve the readiness and positionin precision, the authors developed a two-stae servo system. This system consists o a small actuator and lare actuator or each direction ( and y). The lare actuator is controlled by operator commands, and the small actuator is controlled by K. Saito, M. Neishi, and H. Masuda are with the Course o Precision Enineerin, Graduate School o Science and Enineerin, Chuo University, Kasua, Bunkyo, Tokyo 2-855, Japan 2 H. Osumi and Y. Tamura are with the Department o Precision Mechanics, Faculty o Science an Enineerin Chuo University, Kasua, Bunkyo, Tokyo 2-855, Japan eedback sinals obtained by wire anle sensors. Moreover, we invented an operation interace and developed a system that acilitates control o pendulum vibration caused by disturbance and overshoots at the taret point. In this paper, we proposed an operational system that uses a laser pointer. The operator can ive an instruction directly to the crane in the system. Furthermore, its eectiveness was veriied throuh an eperiment. We epect that this system could be used, not only or lare cranes in actories, but also or a lit travelin alon the ceilin o a care acility. First, an overview o the developed crane teleoperation system is provided in section II. Then, a control alorithm or the macro-micro servo system is described in section III. In section IV, the operation interace that we developed is presented. Section V discusses how the eectiveness o the proposed system was veriied throuh an eperiment. II. OVERVIEW OF TELEOPERATION SYSTEM The structure o the developed crane and the system coniuration are shown in Fi. and Fi. 2, respectively. The crane moves reely in a two-dimensional plane ( and y). The crane comprises a two-stae servo system. There is a lare actuator and a small actuator or each ais. The system is introduced in series usin a movable table with a ball screw. The lare actuator is used to transport suspended objects, and the small actuator controls the pendulum vibration. Thereore, this crane can respond to hih-requency disturbance. In addition, the small actuator has a wire windin mechanism. This mechanism is used or obstacle avoidance. DC servomotors are used in these ive actuators and control the speed. Each motor includes an encoder that detects the position o the crane and the heiht o the suspended object with hih accuracy. In addition, a camera is attached to the crane. Thereore, we can obtain imaes around the suspended object rom directly above. The teleoperation o the crane is accomplished by clickin on points in an imae, as shown in a previous research [8]. In this study, the operator irradiates a oal point with a laser, and the amount o laser liht is measured by the camera to enerate a control input. III. CONTROL LAWS OF TWO-STAGE SERVO SYSTEM A. Control model o crane The - and y-aes are orthoonal to each other, and we assume that the swinin motion o the suspended mass is small enouh to nelect the couplin eect in the - and y-directions. Thereore, the lare actuator and small actuator can be modeled independently in the two-dimensional plane /3/$3. 23 IEEE 5457

2 A simple model in the -z plane is shown in Fi. 3. The equations o motion or the small actuator, lare actuator, and suspended object are epressed in equations (), (2), and (3), respectively. F M m 2l l cos l l 2 sin () Fc M c c F c (2) 2 ml 2mll ml c cos ml sin (3) The parameters o these equations are shown in Fi. 3. M c is the mass o the movin part o the lare actuator, M is the mass o the small actuator, and is the ravitational acceleration. The control input is the orce enerated by the lare actuator and small actuator. Settin the z-ais as the vertical direction, the suspended object has translational and rotational movement on the - and y-aes. F c and F are the orces enerated by the lare and small actuators, respectively. Equation (4) is the linear approimation result o equations (), (2), and (3). F (4) e e Equation (4) shows that F e, the orce applied to the suspended object is proportional to the delection anle. Because we cannot apply any orce directly to the suspended object, we apply a pseudo-orce to it by determinin the delection anle o the wire correspondin to the taret input. Fi. Structure o developed crane B. Desired trajectory o suspended object From equations (3) and (4), the relationship between the position o the carrier and the movin table is shown in equation (5). l (5) e e Thereore, the velocity unction o the crane must be physically continuous. In other words, a jerk in the position o the suspended object needs to be described as a continuous unction. Thus, the taret velocity is divided into three sections: an acceleration section, deceleration section, and constant velocity section. The acceleration section consists o two quadratic unctions. These two quadratic unctions enerate a velocity trajectory that satisies equation (5). As shown in Fi. 5, to simpliy the ormula o crane trajectory, motion commands or suspended object durin acceleration and deceleration start rom T acc. I the oal position iven by the operator is chaned durin a displacement, the trajectory between the previous taret point and the new one is calculated in the same manner, and the suspended object is transported toward the new taret position via the previous taret position. The duration o the acceleration and deceleration sections is 2T acc, where T acc is set to s. T c is the duration o the constant velocity section. V o is the constant velocity. The velocity is calculated usin the distance rom the initial point to the end point and the maimum velocity o the crane. In addition, is the value o the jerk and is determined by T acc and the initial and end velocities, as shown in equation (6). 4V 3 T acc (6) Fi. 2 Coniuration o crane control system Fi. 3 Simpliied dynamic model o crane system Fi. 4 Desired velocity o suspended object 5458

3 actuator is controlled by the velocity control system. The acceleration is reely controlled by chanin the taret velocity. Accordinly, an acceleration input iven to the movin table can be described as equation (2). c u (2) Here, the acceleration input is shown in equation (3). u K ) K ( ) (3) cd v ( cd c l cd c where K v and K l are proportional ains. Equation (4) is the state equation derived rom equations (2) and (3), i the error o the taret input and output is e = ( cd - c ), Fi.5 Motion commands or suspended object durin acceleration and deceleration C. Control law or small actuator and lare actuator The small actuators control the pendulum vibration caused by disturbances. The lare actuators transport the suspended object. Thereore, the rane o movement o each small actuator is narrow. Moreover, it is desirable to stay as close to the oriin as possible. On the other hand, the lare actuators must ollow a iven trajectory, as shown in equation (5), without delay or deviation. Each desired trajectory is determined by equations (7) and (8), where subscript d indicates the desired value. (7) d cd d (8) Reulators are used or the small actuators to achieve equations (7) and (8). Because the delection anle is needed to control the suspended object, based on equation (3), we adopt a reulator whose equilibrium point shits with the drive o the lare actuator. The taret delection anle obtained rom equation (3) is shown in equation (9). The state equation o the system is shown in equation (). I the wire lenth is chaned by hoistin, the pendulum period is chaned. Thereore, equation () considers the velocity component o the wire lenth to cope with a chane in the wire lenth. ed cd (9) d d l 2 i l u a d d l () u a is the state eedback, which shits its equilibrium point, as shown in equation (). 2 () ua d T d This eedback ain,, can be desined usin the pole placement method. The system sets the pole at j, j, and the eedback ain is calculated and controlled momentarily accordin to the wire lenth. Thereore, i the wire lenth chanes, the swin o the suspended object converes at the same pole. The lare e e e K l K v e (4) I we properly select the proportional ain, the system can convere arbitrarily. When the wire lenth chanes, the reaction orce aects the actuator. However, i the speed control o the motors is desined appropriately, the developed control system can be used directly. This is why a chane in the reaction orce is caused by a chane in the wire lenth. Even i the power is temporarily deraded, it immediately ollows the taret trajectory. IV. DEVELOPMENT OF OPERATION INTERFACE A. Overview o taret position input by laser pointer Fiure 6 shows how to operate the developed crane system. An operator who is close to the suspended object uses a laser pointer to taret the location where he wants to transport the object. Potential taret locations are speciic points or objects on the loor. The irradiated point is detected by the camera that is attached to the top o the crane and pointed in a downward direction. Feedback control is conducted as the crane ollows the irradiation point. At that time, the crane not only ollows the last irradiation point, but also transports the object alon the trajectory o the laser liht as ar as possible. Furthermore, when the laser liht passes a hih obstacle, the system can measure the heiht o the obstacle usin motion stereo. Thereore, the wire is automatically hoisted to a heiht that allows the suspended object to avoid the obstacle. Then, the stop position o the laser liht or the position where the laser liht inally disappears is determined to be the inal taret stop position. B. Generation o taret trajectory o suspended object There are two problems in realizin the above system, in which a laser pointer is used as an input device. The irst is how to enerate a taret trajectory without overshoot, and the other is how to avoid instability in the irradiation point rom hand movement. The ollowin method is adopted as a countermeasure to these problems. First, the irradiation position o a laser pointer and the taret point o the suspended object are measured at each samplin time T, as shown in Fi. 7(a). In this system, the samplin time is 3 ms. P i+ denotes a measure point at the (i+)-th control samplin point, and each increment in the - and y-directions or the i-th samplin is i and y i, respectively. Based on the calculated travel distance, the taret velocity trajectory is enerated, as shown in Fi. 4. However, the 5459

4 displacement in T is small enouh to inore the constant velocity section shown in Fi. 4. The taret velocity trajectory in the -direction is shown in Fi. 7(b). The taret velocity trajectory in the y-direction is the same as that in the -direction. The travel time, 4T acc, is the sum o the acceleration and deceleration times. The velocities or the displacements in the - and y-directions are V o and V oy, respectively, as shown in equations (5) and (6). Vo i / 2Tacc (5) Voy yi / 2Tacc (6) The velocity command is modiied by superposin equations (5) and (6) on the current velocity command o the crane. As shown in Fi. 7(c), the superposed velocity trajectory ends at T ater the previous taret arrival time. Thereore, the crane ollows the taret point while passin near the inal taret. In addition, in a case where the irradiation point o the laser liht sways because o hand movement, the eect becomes neliibly small because the plus and minus eect is oset when the control order is summed up. The velocity o the crane helps achieve the superposition value shown in Fi. 7(c), which can eceed its maimum limitation. In this case, the system seeks the maimum value o the velocity by repeatedly displacin the inal taret arrival time backward by T, and the superposition is perormed only when the velocity is slower than the maimum velocity o the crane. This situation occurs when the velocity o the laser pointer is hiher than that o the crane. Thus, a method that makes the travel time o the crane loner than that o the laser pointer is reasonable. Moreover, i an operator uses a laser pointer around a crane that remains stationary, the velocity waveorm o the crane is shown in Fi. 7(d). In this case, the trajectory o the velocity, as shown in Fi. 7(b), is continuously enerated or each samplin time. This velocity trajectory is shown in Fi. 7(b). Moreover, in this case, when the maimum taret velocity eceeds the maimum velocity o the crane, the same control alorithm as shown in Fi. 7(c) can be applied. Fi. 6 Method or indicatin taret location usin laser pointer (a) Samplin point (b) Generated trajectory V. EXPERIMENT A. Parameters The parameters o the developed system are listed in Table. There is a ap between the samplin time o the control system and that o the camera. Until a new imae is obtained, the system calculates usin the previous imae. (c) Modiied command by latest samplin B. Eperimental procedure The proposed control law was applied to the developed system, and we conducted an eperiment to transport a suspended object usin the system. The eperiment was rouhly divided into the ollowin three phases. (d) Velocity command consistin o each samplin Fi. 7 Crane motion command based on taret position ) Veriication o the eect o the pole placement method The crane transported suspended objects in the -ais direction usin wire hoistin. At that time, the vibration suppression perormance o the proposed control law was compared with that o the case in which the eedback ain was 546

5 ied. The initial lenth o the wire was.37 [m], and the initial heiht o the suspended object rom the round was.3 [m]. 2) Veriication o the eectiveness o the laser pointer system An operator drew a circular trajectory, as shown in Fi. 8, and the crane ollowed this trajectory. It took us 3.9 [s] to transport it around the circular trajectory. At this time, the velocity o the crane corresponded to Fi. 7(d). 3) Veriication o the ability to ollow a three-dimensional taret trajectory As shown in Fi. 9, an obstacle was placed alon the travel direction. The start and oal points were connected by a straiht line usin a laser pointer, and laser liht was irradiated over the obstacle. Here, the windin operation was conducted usin the eperimenter s button operations. The heiht o the obstacle was.5 [m], and the transportation distance was.94 [m]. C Eperimental results ) The variation in the wire lenth is shown in Fi., and the variation in the eedback ain usin the pole placement method is shown in Fi.. The delection anle o the wire is shown in Fi. 2. As shown in Fi. 2, the pendulum vibration was controlled ater hoistin the wire. Thereore, we conirmed that the system could adapt to chanes in the pendulum vibration cycle. 2) The transportation location is shown in Fi. 9. The transportation results or each aial direction component are shown in Fi.. As shown in Fi. 9, the taret trajectory was enerated smoothly. Thereore, the hand movement o the laser pointer had little eect on the taret trajectory eneration, and we conirmed that a suspended object could ollow the taret trajectory. As shown in Fi., the suspended object ollowed the taret trajectory with no time la in either aial direction. We also conirmed that the suspended object could stop at the taret position with no overshoot or steady-state error. 3) A trajectory where the suspended object had to avoid an obstacle is shown in Fi.. The altitudinal resolution depended on the wire lenth and the velocity o the crane. In this system, the altitudinal resolution was about [mm]. As shown in Fi., the suspended object could avoid the obstacle by hoistin the wire. Even i the heiht o the irradiation point chaned erratically, the taret trajectory was measured correctly. At that time, we conirmed that the suspended object did not eperience pendulum vibration. In addition, the suspended object ollowed close to the critical point. Fi. 8 Overview o transportation area Fi. 9 Overview o transportation area containin obstacle Fi. Variation o wire lenth Fi. Feedback ain Table Parameters o crane system Fi. 2 Measured wire anle with hoistin 546

6 Fi. 3 Locus o suspended object when usin laser pointer VI. CONCLUSION In this study, we considered the windin operation or a suspended object and proposed a vibration control method usin the pole placement method. Moreover, we developed an operation that uses a laser pointer. The developed control system and operation interace were applied to an eperimental system. To conirm the eectiveness o the proposed methods, we conducted a transportation eperiment. The results o this eperiment demonstrated that the developed laser pointer interace systems were eective or transportation in an area with obstacles. We also demonstrated that an operator could intuitively control and transport an object to a taret point with hih accuracy. In uture work, windin automation will be conducted. The eect o illumination chane at the scene and the shape o the suspended object will also be considered. -direction y-direction Fi. 4 Observed position o suspended object when usin laser pointer Fi. 5 Locus o suspended object durin transportation REFERENCES [] H. Aschemann, O. Sawodny, S. Lahres, E.P. Hoer, Disturbance Estimation and Compensation or Trajectory Control o an Overhead Crane, Proceedins o the American Control Conerence, pp.27-3, 2. [2] W. Sridokbuap, S. Nundarkwan, T. Benjanarasuth, J. Namwiwit, N. Komine, I-PD and PD Controllers Desined by CRA or Overhead Crane System, Proceedins o the International Conerence on Control, Automation and Systems, pp , 27. [3] N. Sun, Y. Fan, X. Zhan, Y. Yuan, Phase Plane Analysis Based Motion Plannin or Underactuated Overhead Cranes, Proceedins o the 2 IEEE international Conerence on Robotics and Automation, pp , 2. [4] N. Sun, Y. Fan, X. Zhan, Y. Yuan, Transportation Task-Oriented Trajectory Plannin or Underactuated Overhead Cranes usin Geometric Analysis IET Control Theory and Applications, Vol.6, No., pp.4-423, 22. [5] M. Yoneda, F. Arai, T. Fukuda, K. Miyata, T. Naito, Operational Assistance System or Crane usin Interactive Adaptation Interace-Desin o 3D Virtual Crane Simulator or Operation Trainin, Proceedins o the 6 th IEEE International Workshop on Robot and Human Communication, pp , 997. [6] K.C.C. Pen, W.E. Shihose, S. Gessesse, D. H. Frakes, Crane Operation usin Hand-Motion and Radio Frequency Identiication Tas, Proceedins o the IEEE International Conerence on Control and Automation, pp.-5, 29. [7] H. Osumi, A. Miura, S. Eiraku, Positionin o Wire Suspension System usin CCD Cameras, Proceedins o the 25 IEEE/RSJ International Conerence on Intellient Robots and Systems, pp , 25. [8] H. Osumi, M. Kubo, S. Yano, K. Saito, Development o Tele-Operation System or a Crane without Overshoot in Positionin, Proceedins o the 2 IEEE/RSJ International Conerence on Intellient Robots and Systems, pp , 2. [9] N. Sun, Y. Fan, Y. Zhan, Bojun Ma, A Novel Kinematic Couplin-Based Trajectory Plannin Method or Overhead Crane, IEEE/ASME Transactions on Mechanics, vol. 7, no., pp ,Feb. 22. Fi. 6 Measured position o suspended object durin transportation 5462