The Research Of Tip-Over And Slip For A Wheeled Mobile Manipulator

The wheeled mobile manipulator has gained extensive attention in the past few years. Statistical results showed that more than two thirds of applications in factory or at home will be complished by mobile manipulator in the next few years. Mobile manipulator can effectively overcome the limited working range and lack of flexibility of the fixed manipulator, at the same time, it has the advantage of fixed manipulator and mobile robot. However, there are problems with such a system consisting of an industrial manipulator mounted on a mobile platform which have not been fully researched in either research field. The tip-over and slip resulting from the movement of manipulator is one of them. This problem will affect the safety and performance of the system. In this paper, the dynamics of the manipulator, the wrench from manipulator onto mobile platform, tip-over moment resulting from the wrench, the optimization of the mobile platform’s design parameters and the slip of the system are researched. Specific researches are as follows:The dynamics of the manipulator was modeled based on Newton-Eurler method after kinematics modelling. The wrench acting on Joint 1 can be obtained. Three cases of the wrench are considered:static case, static with wrench at the tip case and dynamic case. The verification of dynamicis model is carried out with ADAMS.The tip-over criterion is derived to judge the system stability. Tip-Over Moment (TOM) is given as criterion which can represent the root of the tip-over. The compassion between TOM and ZMP is then carried out to prove its correctness and superiority. Four cases are considered, first static that deals with payload to show the effect of the horizontal position of the system’s center of gravity. The second case is the effect resulting from wrench at the tip to show the effect of manipulator’s configuration. The third and fourth cases are the inertial forces resulting from joint speeds and accelerations, respectively, to show the additional effect of the vertical position of the system’s center of gravity. At last, path planning with tip-over criterion result which can make the system stable along the path with minmum time elapsed is carried on.A method for optimizing a mobile platform to form a wheeled mobile manipulator is presented. This optimization is formulated as a max-min problem, i.e. to maximize a stable region ratio (SRR) over the manipulator’s workspace while minimizing a tip-over moment (TOM). For a practical solution, this max-min problem is converted to two sub problems. The first one is the worst case analysis to determine the maximum positive value of TOM through searching over the manipulator’s workspace. The three parameters used for this search are pertaining to the mobile platform itself, i.e. the number of support wheels, the size and mass of the mobile platform. The second sub-problem is to optimize the placement of the manipulator and accessory on the mobile platform against the identified worst case so that the entire manipulator’s workspace is stable. The effectiveness of the proposed method is demonstrated by applying it to optimize a mobile drilling and riveting manipulator.The slip analyses are carried out for two cases. One is statics case while mobile manipulator is static with reaction force of riveting at the end of manipulator. The other is dynamics case while mobile manipulator is moving from one point to another. At last path planning which can make the system no-slip along the path with minmum time elapsed is carried on.One fundamental research on the wheeled mobile manipulator is carried on in this paper, and the results can be used in the design, control and optimization of the system. The safety and performance of the wheeled mobile manipulator can be improved with the result in this paper. This reseach is essential step in the process of the wheeled mobile manipulator.