| Metamorphic mechanism can not only adapt to different task requirements by changing its topology and degree of freedom,but also has low cost and simple structure,and It is a new field of robot development.One of the main ways to realize metamorphic-cell is to design the metamorphic hinge and its change mode.The commonly used technology of metamorphic hinge is to set several motors at the metamorphic hinge to realize the metamorphic hinge through the transformation of motor rotation and braking.However,the problem brought by this technology is that it increases the cost of machinery and occupies a large space.Therefore,the study of new metamorphic technology is of great significance for the study of metamorphic mechanism.In this paper,a reconfigurable sphere hinge(rS)is installed in a three legged parallel mechanism(3-(?) S),forming a parallel metamorphic mechanism(3-(?) S/(rS)PS),where(rS)PS represents the middle branch chain connecting the upper and lower platforms by the reconfigurable sphere hinge(rS),prismatic pair(P)and spherical pair(S).The core idea of the new imagine of metamorphic hinge proposed in this paper is: using the motion of the platform on the parallel mechanism,move the metamorphic hinge from a certain state to near a phase of the reconfigurable spherical hinge(rS);Then,the phase of the metamorphic hinge is stabilized;In the process of stabilization,the corresponding components are locked by magnetic force or other means,so as to realize metamorphic-cell.The main research work of this paper is as follows:1.Using the screw theory,it is explained that when the reconfigurable sphere hinge(rS)in the 3-(?) S/(rS)PS parallel metamorphic mechanism is in two special different phases,the reconfigurable sphere hinge(rS)can be equivalent to the revolute pair(R)and universal hinge(U)respectively,and the upper platform of the corresponding mechanism can realize the motion modes of five degrees of motion(3R2T)and six degrees of motion(3R3T)respectively.2.In order to establish the kinematic relationship between the platform on the mechanism and the reconfigurable sphere hinge(rS),the middle branch chain(rS)PS is analyzed.The research shows that the branch chain is an underactuated system,and the kinematic relationship between the upper platform and the reconfigurable spherical hinge(rS)can not be completely determined only by using the geometric constraints of the mechanism.Dynamics and control technology must be used.According to the characteristics of two specific different phases of reconfigurable sphere hinge(rS),that is,when the reconfigurable sphere hinge(rS)is equivalent to revolute pair(R)and universal hinge(U),this paper puts forward different control strategies and algorithms respectively.When the reconfigurable spherical hinge(rS)is equivalent to the universal hinge(U),according to the characteristics of the system mass matrix,the branch chain dynamic equation is divided into two subsystems,and a control algorithm combining obstacle function and energy control is designed.The stability of the control algorithm is proved by Lyapunov function,and the effectiveness of the algorithm is verified by numerical simulation;When the reconfigurable spherical hinge(rS)is equivalent to the revolute pair(R),a control algorithm based on coordinate transformation and obstacle function is proposed as the generation algorithm of platform trajectory.The effectiveness of the algorithm is also verified by numerical simulation.3.In order to stabilize the trajectory determined by the two specific phases of the metamorphic hinge on the platform of the 3-(?) S/(rS)PS parallel mechanism,firstly,the velocity distribution of the branch chain of the parallel mechanism is analyzed by using the correlation of the screw system,and the velocity composition of the branch chain is described by using the generalized coordinates of the task space;Then,according to the kinematic equations of the middle branch chain and the upper platform,the dynamic equations of the whole configuration of the parallel mechanism are established;Finally,the extended disturbance observer of the Improved Super-Twisting algorithm and the Modified Fast Adaptive Super-Twisting algorithm(MFAST)are combined to form a controller for the trajectory tracking of the upper platform of the 3-(?) S/(rS)PS parallel metamorphic mechanism,and the stabilization control of the U-phase and R-phase of the metamorphic hinge is successfully realized. |
