Research On Key Technologies Of Weave Compensation With Six DOFs Based On Cable Driven Parallel Mechanism

The marine replenishment can be divided into four ways: horizontal replenishment,longitudinal replenishment,vertical replenishment and face-to-face replenishment.the face-to-face replenishment can realize all types of cargo transport such as missile replenishment,torpedo loading at sea.When the crane is used during operations,the relative motion of six degrees of freedom(including swaying,surging,heaving,pitching,rolling,yawing)will be produced between the ships due to the influence of wind,wave and current.This may lead to the collision between the lifting cargo and its adjacent objects,which will lead to the loss of goods,and lead to safety accidents.Therefore,the crane used in replenishment task should have the function of wave compensation with six degrees of freedom,so as to eliminate the impact of wave on the hoisting operation,and ensure the safety,accuracy and efficiency of the operation.The existing ship-borne wave compensation cranes in China can only compensate the vertical motions,which is not suitable for the offshore face-to-face replenishment tasks such as container stacking and torpedo loading at sea.This paper introduces a new type of parallel mechanism driven by 8 cables with large workspace,low inertia and high anti-pendulation capability.This cable-driven parallel mechanism with the wave compensation device can precisely real-time control the 6-DOF of the lifting cargo and ensure the safety and efficiency of offshore face-to-face replenishment operations.It is very significant for promoting Chinas' s off-shore exploitation and the support capability of military operations.This paper focuses on the design of cable-driven parallel mechanism applied to the wave compensation operation,solution of the forward kinematics for redundant cable-driven parallel mechanism in real-time,parameter identification of end-effector dynamic for cable-driven parallel mechanism,tension distribution optimization of cable-driven parallel mechanism and the sliding mode control of cable-driven parallel mechanism.The main contents of this paper include:1)The cable-driven parallel mechanism applied to the wave compensation is designed.The principle of relative motion compensation of six degrees of freedom in wave compensation operation is introduced,and the inverse kinematics of cable-driven parallel mechanism is introduced.The workspace size of the kinematic determination and uncertain was studied by simulation,and the relationship between the working space and the size of the base,the position of the suspension point of the ropes was studied.2)A real-time forward kinematics method of redundancy cable-driven parallel mechanism was proposed.The problem of the forward kinematics of a suspended cable-driven parallel mechanism was transformed into the tetrahedron approach and optimum theory.In this study,the high-dimensional nonlinear equations of mutual coupling were transformed into independent low-dimensional nonlinear equations using the tetrahedron approach.The combination method does not require algebraic manipulation of orientation matrix elements and does not involve the high-dimensional polynomial equation.In addition,the initial value of Levenberg-Marquardt method is calculated by using the approximate tetrahedron approach to eliminate the influence of the initial value selection of the Levenberg-Marquardt method.The law between the initial value and the constraint equations is revealed:3)A method of dynamic parameter identification of end-effector of the cable-driven parallel mechanism is proposed.The dynamic model of the end-effector under the condition of no eccentricity and eccentricity is established,and the dynamics model is linearized.An identification strategy is proposed to identify the dynamic parameters of the end-effector only by measuring the rope length and the rope tension.The advantages and disadvantages of the multi variable least squares identification algorithm and particle swarm optimization(PSO)algorithm in the process of model identification are studied and discussed.On this basis,a particle swarm optimization algorithm based on least squares is proposed.4)The method of tension distribution optimization of cable-driven parallel mechanism is studied.At present,in solving optimization problem of the tension distribution algorithm,most of the tension distribution optimization problem is transformed into solving nonlinear optimization problems,this method can get the optimal solution of the tension distribution,but the computation time is longer every time and the number of iterations is more.In this paper,the tension distribution optimization problem is transformed into a linear programming problem,which can not only meet the requirements of control accuracy,but also improve the real-time performance compared with the nonlinear algorithm.5)A method of sliding mode control for cable-driven parallel mechanism is proposed.In this paper,under the control strategy of the task space coordinate system,the sliding mode control algorithm based on exponential reaching law is used to control the end-effector.The control strategy of cable-driven parallel mechanism is analyzed,and the linear sliding mode control and sliding mode control based on reaching law are introduced.Each of the two algorithms is simulated.Finally,the position tracking experiment with six degree of freedom is carried on the principle prototype of cable-driven parallel mechanism.