| Autonomous robots have received much attention in recent years due to their broadapplications in space exploration, military reconnaissance, farming, defense, demining,etc. in unstructured environments. These high-performance autonomous robots can beclassified into walking, wheeled, crawling and hybrid locomotion. Where, wheel-leggedrobots are considered to be the most promising hybrid mobility system, which inheritboth advantages of wheeled and walking systems, i.e. the high-speed and efficientrolling performance for the first one and the obstacle overcoming performance to roughterrains for the second. However, for most of the existing wheel-legged robots, theirdriving motors were added to the joints directly, caused a large load concentration atjoints, many of them have deficiencies in load distribution, structure stability andcarrying capacity.In view of the above deficiencies, this paper presents a new type of wheel leggedrobot: Rolling-Wolf, which with a simple wheel-leg structure, strong carrying capacityand excellent performance of overcoming obstacles. The knee and hip joint of this robotare driven by ball screws that fixed on the thigh and body, respectively, instead of usingmotors and reducers at joints generally. Through this way, the stress condition ofRolling-Wolf is improved, the carrying capacity of the system and the stability of thewheel-leg mechanism are enhanced.Focused on the designed Rolling-Wolf Robot, a series of researches are carried outas follows:The structure principles, kinematics and mechanical properties of the designedwheel-legged robot were analyzed in detail. Firstly, this paper presented a new kind ofwheel-leg mechanism which is designed according to the mobile robots designrequirements and the deficiencies of the existing wheel-legged robots. Second, thedifferent mechanical properties between Rolling-Wolf and the ordinary articulatedwheel-leg-robots were analyzed. Mechanical analysis results showed that Rolling-Wolfhas better load distribution, structure stability and carrying capacity. Then, three typesof Rolling-Wolfs with different structures were introduced, as well as the kinematicsmodel of Rolling-Wolf was built. Based on the kinematics model, the envelope diagramof leg motion of these three different Rolling-Wolfs were solved and plotted in Matlab. And finally, a wheel-legged structure which has the best motion characteristics isselected, and Rolling-Wolf’s3D model was built in detail.The motion performance and structure optimization of Rolling-Wolf wereanalyzed and calculated. In the third chapter, the positional posture model ofRolling-Wolf was analyzed first, and then it’s static model was built based on thekinematic theory and the principle of virtual works. Thirdly, several kinematic andmechanic evaluation indexes of Rolling-Wolf were defined according to these twomodels. Finally, the multi-objective optimization problem of this new locomotion wassolved numerically by the method of AMGA (Archive based Micro Genetic Algorithm)based on Isight and Matlab, the optimization targets were to minimize the maximumstatic equilibrium forces of the driving sliders under certain load conditions and toimprove the motion characteristics described by the evaluation indexes concurrently.Optimization results indicates that the mechanical properties and motion performance ofRolling-Wolf were significantly improved. The maximum obstacle clearance of theoptimized value is about500mm, improved65.53%, and the optimized maximum staticforce compared to the previous value is decreased by25.5%and12.58%, respectively,under the work load conditions of self-weight40kg and30kg.The dynamic model of Rolling-Wolf was deduced and built based on Lagrangemethod, and the dynamic performance of Rolling-Wolf was simulated by ADAMSsoftware. From the simulation results of the posture configuration of Rolling-Wolfimplemented under certain load conditions, the value of the driving forces and power ofthe drive systems were obtained. The dynamic simulation results of the damping systemof Rolling-Wolf, rolling on unstructured terrains, showed that the design of the dampingsystem can effectively reduce the impacts of the drive system and the vibrations of thebody. This simulation results provided valuable references for the design of dampingsystems of Rolling-Wolf and other wheel-legged robots.For the requirements of high stability and fast response of the control system ofwheel-legged robots, this paper designed a distributed multi-level control system basedon the MCU of STM32F103series. This system uses a multi-threaded task scheduler todecentralize the complicated control tasks of multi-DOF robot, successfully simplifiedthe complexity of the control system and improved its reliability and maintainability.Test results showed that: the control system designed is stable and fast, satisfied to thedesign specifications. In order to improve the adaptability of Rolling-Wolf in unstructuredenvironments, this paper designed a posture adjustment algorithm for its auto-adaptiveposture mode. The main method of this adjustment algorithm is to calculate the discreteangle data with respect to the height of the center of the wheel and stored it in thedatabase, once the leg need a specific height to maintain the body level, the controlsystem do not need to calculate the specific values of the angular data of the thigh andcalf which have infinite solutions. This method effectively reduced the computationalcomplexity and improved the speed of the posture configuration. Test results showedthat: the posture adjustment algorithm designed works very well when the body ofRolling-Wolf tilted, it successfully modified the posture of the wheel-leg according tothe parameters of sensors. |
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