文献翻译--用于施工服务的最小自由度混合爬杆操纵机器人 英文版

Research articleA hybrid pole climbing and manipulating robotwith minimum DOFs for construction andservice applicationsM. Tavakoli, M.R. Zakerzadeh, G.R. Vossoughi and S. BagheriSharif University of Technology, Tehran, IranAbstractPurpose Aims to describe design, prototyping and characteristics of a pole climbing/manipulating robot with ability of passing bends and branchesof the pole.Design/methodology/approach Introducing a hybrid (parallel/serial) four degree of freedom (DOF) mechanism as the main part of the robot andalso introduces a unique gripper design for pole climbing robots.Findings Finds that a robot, with the ability of climbing and manipulating on poles with bends and branches, needs at least 4 DOFs. Also an electricalcylinder is a good option for climbing robots and has some advantages over pneumatic or hydraulic cylinders.Research limitations/implications The robot is semi-industrial size. Design and manufacturing of an industrial size robot are a good suggestion forfuture works.Practical implications With some changes on the gripper module and the last tool module, the robot is able to do some service works like pipetesting, pipe/pole cleaning, light bulb changing in highways etc.Originality/value Design and manufacturing of a pole-climbing and manipulating robot with minimum DOFs for construction and service works.Keywords Design, Parallel programming, Kinematics, Poles, RoboticsPaper type Research paperIntroductionClimbing robots have received much attention in recent yearsdue to their potential applications in construction and tallbuilding maintenance, agricultural harvesting, highways andbridge maintenance, shipyard production facilities, etc.Use of serial multi-legged robots for climbing purposesrequires greater degrees of freedom (DOFs), withoutnecessarily improving the ability of robots to progress in acomplex workspace. It is also well known that serialconfigurations demand a greater amount of torque at thejoints, thus calling for larger and heavier actuators andresulting in smaller payload to weight ratio, which is critical inclimbing robots. In contrast using parallel platforms can resultin the decrease of the weight/power ratio, thus allowing forlarger payloads.Earlier research in this area has focused on six-DOFuniversal prismatic spherical (UPS) mechanisms (Merlet,2000； Tonshoff, 1998).Saltaren et al. has modeled and simulated a parallel six-DOF parallel robot with pneumatic actuators. The modeledrobot has a large payload capacity which is an important issuefor industrial pole climbing robots (Salataren et al., 1999).Later Aracil et al. fabricated a parallel robot for autonomousclimbing along tubular structures. This robot uses the Gough-Stewart platform as a climbing robot. The platform actuatorsare six pneumatic cylinders with servo control. Theirmechanism also used six cylinders as the grippers (threecylinders for each gripper) using a total of 12 actuators notcounting the actuators needed for the manipulator arm(Aracil et al., 2003). The mechanism is rather complicatedand has the ability of passing bends in any direction, making itsuitable for traveling along trees and complex structures. Sothere is a need for a less complicated robot, which has theability of traveling along human made and less complicatedstructures with minimum DOFs and minimum number ofThe Emerald Research Register for this journal is available /researchregisterThe current issue and full text archive of this journal is available /0143-991X.htmIndustrial Robot: An International Journal32/2 (2005) 171178q Emerald Group Publishing Limited ISSN 0143-991XDOI 10.1108/01439910510582309This paper was first published at CLAWAR 2004, 7th InternationalConference on Climbing and Walking Robots and the SupportTechnologies for Mobile Machines, 22-24 September 2004, Madrid,Spain.This work has been made possible by a grant from the Tavanir Electricresearch Center. The authors would like to thank Tavanir for supportingthis research.171actuators. Furthermore, using pneumatic cylinders in themechanism has the problem of transferring compressed airfrom the compressor to the cylinders.But in recent years some industrial applications such asmachine tools have resulted in more attention to parallelmechanisms with less than six DOFs. Most of the research inrecent years have focused on three-DOF mechanisms (Pierrotet al., 2001； Gosselin et al., 1992b； Tsai, 1996).Traveling along a pole or tubular structures with bends andbranches requires four DOFs (two translations and tworotations along and perpendicular to the tubular axis). Thesesame DOFs are also essential for most manipulation andrepair tasks required in the pole climbing applications. Moredetails on modeling of the mechanism and selection process ofthe planar parallel mechanism as the parallel part of the robothas been discussed in Vossoughi et al. (2004).To the best knowledge of the authors, there is no four-DOFmechanism providing two translational and two rotationalDOFs suitable for such operations. The mechanism proposedin this paper takes advantage of a parallel/serial mechanismproviding two degrees of translation and two degrees ofrotation along the desired axes (which will be described later).The parallel/serial robots also have the advantages of highrigidity of fully parallel manipulators and extended workspaceof serial manipulators (Romdhane, 1999). Full kinematicanalysis of the four-DOF mechanism has been presentedcompletely in Zakerzadeh et al. (2004).The mechanism also takes advantage of a novel gripperdesign, making it suitable for safe pole climbing operations.ConceptAs mentioned earlier, locomotion along tubular structures,with bends and branches, requires a minimum of four DOFs.These include Tz: a translational DOF for motion along thepole axis (Figure 1), Rz: a rotational DOF for rotation aroundthe pole (Figure 2), Rx: a secondary rotational DOF forrotation around a radial direction of the pole (Figure 3).Combination of the above three DOF with Tx a translationalDOF for motion along the pole radial direction provides thenecessary manipulability to perform the many necessaryoperations after reaching the target point on the pole (i.e.repair, maintenance or even manufacturing operations such aswelding) (Figure 4).The robot designThe proposed pole climbing robot consists of three main parts(Figure 5), the three-DOF planar parallel mechanism, theserial z-axis rotating mechanism and the grippers.Combining the three-DOF planar parallel mechanism witha rotating mechanism around the pole axis provides tworotations and two translations, which is necessary to achievethe design objectives as explained in the last section.Figure 1 Climbing along the poleFigure 2 Rotation around the pole axisFigure 3 Overtaking the bent sectionFigure 4 Robot performing a welding operationFigure 5 The pole climbing robot modelA hybrid pole climbing and manipulating robotM. Tavakoli, M.R. Zakerzadeh, G.R. Vossoughi and S. BagheriIndustrial Robot: An International JournalVolume 32 Number 2 2005 171178172Furthermore, the linear cylinders used in the parallelmanipulator are arranged to encircle the pole and thusreduce the grasp moments on the gripper.One of the grippers is attached to a manipulator, and theother one is attached to the base of the rotating platform. As aresult, the grippers have four DOF with respect to each other,allowing for movements along the poles with different cross-sections and geometric configurations.The three-DOF planar three-RPR parallelthree-RPR manipulatorA general planar three-legged platform with three DOFsconsistsofamovingplatformconnectedtoafixedbasebythreesimple kinematics chains. Each chain consists of threeindependent one DOF joints, one of which is active (Gosselinet al., 1992a). Hayes et al. (1999) showed that there are 1,653distinctgeneralplanarthree-leggedplatformswiththreeDOFs.For the proposed mechanism, the three-RPR mechanism hasbeen selected as the planar parallel part of the robot.The rotating mechanismThe rotating mechanism consists of a guide, a sliding unit, agear set and a motor. Plate 1 shows the guide and sliding unit.The guide is a T-shape circular guide, which encircles thepole. The slider unit consists of a particular bearingsarrangement, which can withstand the forces and torquesgenerated during various maneuvers and maintains the robotstability in all its possible configurations. The slider holds thelower gripper and is driven by a motor with a simple gearingarrangement. By rotating the motor while keeping one of thegrippers fixed (to the pole), the other gripper can rotatearound the pole axis.The grippersThe proposed gripper has a unique multi-fingered design,which is able to adapt to various pole cross sections anddimensions with only a single actuator. Each gripper consistsof two v-shaped multi-fingered bodies, a double shaft motor,two right and left handed screws and two linear guides. Use ofthe particular multiple finger arrangement not only increasesthe torque handling capability of the gripper but alsoimproves the adaptability of the gripper to different poledimensions without having fingers interfere/collide with eachother. Using ballscrews with a friction coefficient of 0.1, andtwo linear bearing which stand the load of the robot duringthe climbing process, the selected double shaft electric motoris rather small with respect to the weight of the robot. Plate 2shows the fabricated gripper.The combined actions of the various components in a typicalpole climbing application are shown in Plates 3-5.Table I shows the specifications of the prototype versionand the estimated specifications of the industrial version ofrobot.The robot prototypeFollowing the kinematic analysis of the proposed mechanism(Vossoughi et al., 2004； Zakerzadeh et al., 2004), a prototypeunit was designed and built for a hypothetical municipal lightbulb change operation.The prototype of the robot weighs 16kg. The body of robotis fabricated from aluminum. The robot is driven by three dcmotors and three electrical cylinders. Use of electricalcylinder rather than pneumatic or hydraulic cylinderssimplifies the control of cylinders and increases theprecision. Also there is no need for a compressor or pump.This also eliminates hydraulic or pneumatic tubes, which arenot safe in pole climbing applications.The electrical cylinders weigh 1.1kg each. Each cylinder isable to exert a 800N force and has a stroke of 200mm andspeed of 0.6m/min.Revolute joints in the planar parallel mechanism should befabricatedwitharelativelyhightolerance.Otherwise,theplanarparallel mechanism will either be overconstrained or exhibitextra DOFs. In addition the assembly process precision is alsohighlyimportantfortheproperoperationofthemechanism.Toaccommodate the light bulb change operations two miniaturegrippers have been used. One to carry the new lamp, and theother to remove the old lamp. The grippers are two smallpneumatic grippers. Also a small reservoir with capacity of300cc has been used. A dome remote control camera has beenattached to the manipulator to assist in the bulb changingoperation using a joystick as the robot remote control teachpendentunit.ThecamerahastwoDOFsandcanrotatearoundtwo perpendicular axes and is enveloped by a dome. Plate 6shows the fabricated prototype.Plate 7 shows the fabricated prototype moving along thepole axis, Plate 8 shows the fabricated prototype passing thebent section of pole and Plate 9 shows the fabricatedprototype in the operation of light bulb changing.Control of the robotAs mentioned earlier, the prototype unit is actuated by threeelectrical cylinders and three dc motors. Each motor has acontrol driver board, which is attached to a central PC.Plate 1 The serial rotating mechanismPlate 2 The robot fabricated gripperA hybrid pole climbing and manipulating robotM. Tavakoli, M.R. Zakerzadeh, G.R. Vossoughi and S. BagheriIndustrial Robot: An International JournalVolume 32 Number 2 2005 171178173Plate 5 The robot is passing the bent sectionTable I Estimated characteristic of the prototype version and the industrial version of robotNumber of linear actuators Number of rotary actuators Weight (kg) Dimensions (cm)Prototype 3 3 16 18 25 60Industrial 3 3 30 50 50 100Plate 4 The robot rotation around pole axisPlate 3 The robot movement along pole axisA hybrid pole climbing and manipulating robotM. Tavakoli, M.R. Zakerzadeh, G.R. Vossoughi and S. BagheriIndustrial Robot: An International JournalVolume 32 Number 2 2005 171178174Plate 6 The fabricated prototypePlate 7 Moving of fabricated prototype along pole axisA hybrid pole climbing and manipulating robotM. Tavakoli, M.R. Zakerzadeh, G.R. Vossoughi and S. BagheriIndustrial Robot: An International JournalVolume 32 Number 2 2005 171178175The gripper motors are controlled using current feedback.Once the grippers touch the pole the current will increaseto reach to a certain value thus exerting a proportionalamount of force. Owing to the large gear ratio of thegrippers dc motor the motor is not back-drivable. As a resultin case of power failure, the gripper will continue to exertthe force continuously, making it fail-safe in case of powerfailure.The electrical cylinders comprise a dc motor, a gearingarrangement and an acme screw. Using a 500-pulse encoderon the shaft of the dc motor, the cylinders have a precision of0.1mm in linear movements. Also using a 100-pulse encoderon the shaft of the serial rotating mechanisms dc motor, theserial mechanism has a precision of 0.68 with the given gearingarrangement of the serial mechanism.An array of touch switches, which have been assembled onthe upper grippers, not only detect bend and other possiblebarriers on a pole, but also can detect the angle of a bentsection of the pole with respect to the present direction of therobot gripper. This will allow the serial mechanism to rotatePlate 8 The fabricated prototype is passing the bent sectionA hybrid pole climbing and manipulating robotM. Tavakoli, M.R. Zakerzadeh, G.R. Vossoughi and S. BagheriIndustrial Robot: An International JournalVolume 32 Number 2 2005 171178176in a way that the robot mechanism is positioned properly forpassing along the bent section.The control system architecture includes a higher levelinverse kinematic module and a lower lever PID-based jointlevel position control system.ConclusionIn this paper, a solution to the autonomous robot poleclimbing problem is presented. A unique multi-fingeredgripper with the ability to adapt to various poles cross sectionsand dimensions with only a single actuator is also presented.Then some of the issues concerning the prototyping andcontrol of the robot mechanism are discussed.ReferencesAracil, R., Saltaren, R. and Reinoso, O. (2003),“Parallel robots for autonomous climbing along tubularstructures”, Robotics and Autonomous Systems, Vol. 42,pp. 125-34.Gosselin, C.M., Sefrioui, J. and Richard, M.J. (1992a),“Polynominal solution to the direct kinematic problem ofplanar three degree of-freedom parallel manipulators”,Mechanism and Machines Theory, Vol. 27, pp. 107-19.Gosselin, C.M. et al. (1992b), “On the direct kinematics ofgeneralspherical3-degree-of-freedom parallelmanipulators”, ASME Biennial Mechanisms ConferenceProc., Scottsdale, AZ, pp. 7-11.Plate 9 The fabricated prototype in changing bulb operationA hybrid pole climbing and manipulating robotM. Tavakoli, M.R. Zakerzadeh, G.R. Vossoughi and S. BagheriIndustrial Robot: An International JournalVolume 32 Number 2 2005 171178177Hayes, M.J.D., Hysty, M.l. and Zsombor-Murray, P.J. (1999),“Solving the forward kinematics of a planar three-l