| In the huge equipment manufacture fields, such as ship building, there are lots oflong-distance welding works in the manufacture process. The cost and the property ofthese products are mainly depending on the efficiency and the quality of the weldingworks. In the traditional heavy industry, the tasks of welding, maintaining and detecting onthe vertical wall are finished by human workers. The working environment is hazardousand the efficiency of welding works is hard to guarantee. With the development ofeconomics, the demand of large unstructured equipments grows rapidly. Being with abright future, it is meaningful to design a wall-climbing welding robot(WCWR) which iscapable of on-wall locomotion, obstacle crossing and completing long-distance weldingworks in hazardous environments. The WCWR can be the substitution of traditionalworkers, and it will improve the huge equipment manufacture level of our country.Under the support of the863program N0.(2009AA04Z21), the novel structure ofWCWR and the non-contact magnetic-changeable adsorption mechanism are designed.The parameters of the suction cup are optimized. The control method of on-walllocomotion and the coordination strategy of the mobile platform and5-DOF manipulatorare researched. And the prototype of a wheel leg all-position WCWR with adjustablemagnetic adhesion mechanism is introduced. The main research contents are as follows:1) Obstacle-crossing ability and load capacity in the WCWR structure design. Inorder to realize all-position autonomous welding in the huge equipment manufacture, theproperty of general WCWRs are deeply researched. Our WCWR has a non-contactmagnetic-changeable adsorption mechanism, can cross obstacles by wheel-leg locomotionmechanism. The welding torch is handled by the5-DOF manipulator and the welding traceis monitored by the visual camera. The suction force can be changed by theobstacle-crossing and adsorption mechanisms automatically. It can be found from theexperiment results that the obstacle-crossing ability and load capacity of our WCWR arebetter than the traditional WCWR. The WCWR is capable of finishing long-distancewelding works. 2) WCWR system modeling under the screw theory and the control method for themanipulator. Considering the mobile platform as a two-wheel differential system, thekinematic equation of the mobile platform is built by constructing virtual links. And thekinematic models of5-DOF manipulator and the integrative robot system are proposedrespectively. Using Jacobi matrix J, the operability function of the manipulator is definedand the operability is researched in work space.3) The static and dynamic models for the WCWR and the research on WCWR’son-wall locomotion property. Firstly, the static model of the WCWR is built, and theminimum adsorption force for reliable on-wall locomotion is calculated. Then undergeneralized coordinates, the dynamic model of the WCWR is built. Based on simulationresults, the relationships between adsorption force, inclination angle of the wall, thegesture of the WCWR and mobile resistance, driving torque are found. A formula tomeasure the steering flexibility is deduced. And the effect of turning radius and adhesionforce on steering flexibility is also researched. It can be found that decreasing theadsorption force and increasing the turning radius can improve the steering flexibility. Inorder to ensure that the robot can maintain continuous movement when crossing obstacles,the moving gait and the obstacle crossing process have been studied. When crossingobstacles on wall, by changing and justly distributing the adhesion force for each magneticsuction cup to keep each wheel’s load in equal, the WCWR’s total adhesion force can beenreduced. Moving and turning round resistance can been decreased and the movingflexibility can been improved.4) The optimized design of the magnetic adhesion mechanism. Thepermanent-magnetic suction cup is a magnet array, consisting of permanent-magnetic units.Its property is determined by the arrangement mode permanent-magnetic units and thestructure parameters of the suction cup. The ratio which is between magnetic energydensity and the magnetic adhesion mechanism weight is considered as the propertymeasurement of magnetic adhesion mechanism. The property of the suction cup isimproved by increasing the magnetic energy density and decreasing the leakage magneticflux. The adhesion force is modeling under the electromagnetic field algorithm, and theparameters of the suction cup are optimized by the simulations, using the finite elementmethod. Based on these optimal parameters, a novel suction cup is designed. Theexperiment shows the suction cup can satisfy the requirement that ensure safety when therobot is climbing and crossing obstacles on the vertical wall.5) The mobile manipulator path planning, based on modified ant colony optimization（MACO）and the trajectory tracking research. Our WCWR consists of a mobile platform and a5-DOF manipulator. In order to achieve the target that the mobile manipulator cantrack the targets’ trajectory, coordination control algorithm, path planning and trajectorytracking for the mobile manipulator are researched. In order to improve the trajectorytracking property, we consider the path planning for the mobile vehicle and trajectorytracking for the manipulator as an integration issue. Base on the ant colony optimization（ACO）and the general control method of trajectory tracking, a coordination controlstrategy for the mobile manipulator is proposed. Firstly, the steering resistance is made asan important factor to effect the probability of path selection. Under this condition, aMACO is used to make the WCWR choose the shortest path which has the fewest turns.Secondly, a integration controller is designed to solve the coordination controlling andtrajectory tracking problems. From the simulations and experiments, it can be found thatthe WCWR has an accurate trajectory tracking ability. The coordination control methodand path planning algorithm are reliable.Based on the results of the previous researches, the contributes and the innovations ofthis work can be concluded as follows:(1) A novel wheel-leg WCWR’s obstacle-crossinglocomotion mechanism is introduced. As a combination of wheel type and leg typelocomotion mechanisms, the WCWR has a good on-wall mobility and a reliableobstacle-crossing ability. And it can be widely used in other mobile robots.(2) Anon-contact magnetic-changeable adsorption mechanism is designed. The optimizationmethod of the suction cup design is also researched. The suction cup is not contacting thewalls. The height of the gap can be continuously changed. This adsorption mechanismincreases the wall-climbing security and adaptability of changeable wall conditions.(3)Based on MACO, the WCWR’s path planning strategy is introduced. And the coordinationcontrol algorithm for trajectory tracking is also researched. The steering resistance is madeas an important factor to effect the probability of path selection. And a integrationcontroller is designed to solve the coordination controlling and trajectory trackingproblems. |
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