Type Synthesis And Design Method Of Truss-Type Deployable Morphing Mechanisms

With the rapid development of manned spacecraft,space stations,earth observation and other aviation fields,a large number of spacecrafts have been launched.For example,China has completed Beidou networking,Mars exploration,and Chang’e lunar exploration missions in 2020.However,with the increasing number of spacecraft launches,space junk,mainly spacecraft debris generated by explosions and other factors,has rapidly increased.Although all over the world have begun to develop space junk recycling technologies,there are currently more than5,000 tons and millions of space junk hovering over the earth,posing a serious threat to the orbiting spacecrafts.Compared with the existing space flying nets,space harpoons,micro-satellites with capturing performance and other devices that can be used in space junk recycling,the space truss-type deployable morphing manipulators have high grasping rigidity,wide application range,and easy control,which indicates that such manipulators have extremely high application value.However,the current design of such mechanisms is not yet mature and urgently needs to be studied in depth.Therefore,the modules of the space truss expandable grasping manipulator,the deployable morphing mechanisms,are the research object in this thesis,and will focus on the design of ori-blocks,the comprehensive type synthesis method and performance evaluation index of the deployable morphing mechanism.The deployable morphing mechanisms designed in this thesis are divided into single Do F(degree of freedom)deployable morphing mechanisms and two Do Fs deployable morphing mechanisms.The single Do F deployable morphing mechanism belongs to a metamorphic mechanism,which is composed of a deployable submechanism,two supporting sub-mechanisms,a leaf-like sub-mechanism and two couples of connecting pairs.In this thesis,a scissor mechanism with bifurcated mobility is designed first,and this mechanism is used as the deployable submechanism of the overall mechanism.Then the deployable sub-mechanism and the supporting sub-mechanism are connected by two couples of connecting pairs.At the same time,a leaf-like sub-mechanism is introduced to connect the two symmetrically arranged support sub-mechanisms.The motion-screw system of the deployment/grasping motion sub-chain consisting of the deployable sub-mechanism and the connecting pairs is analyzed based on screw theory,and the restraining screw motion system is obtained according to the reciprocal screw theory.Combining the geometrical relationship between the constraint-screw system and three planes,constraint conditions that the support sub-mechanism need to meet are derived by applying the constraint force decomposition theorem.Supporting sub-mechanisms can be type synthesized using screw theory,which is used to assemble with the deployment/grasping motion sub-chain to obtain a space truss-type single Do F deployable morphing mechanism that is capable of performing deployment tasks and grasping tasks.The two Do Fs deployable morphing mechanisms are also type synthesized in this thesis.The two Do Fs deployable morphing mechanism belongs to a parallel mechanism that is composed of a deployable sub-mechanism,two supporting submechanisms,a platform,and a base.The deployable sub-mechanism,a platform and a base construct a deployment / grasping sub chain,which is used to connect the deployable sub-mechanism and the supporting sub-mechanisms.Four types of oriblocks based on three-dimensional solid geometries such as quadrangular pyramids,triangular prisms,cylinders,and cones are designed in this thesis.Kinematic analysis of these ori-blocks is also provided based on D-H parameters,draws kinematic curves,and reveals that ori-blocks have kinematic equivalence with classic over-constraint linkages.Taking the cylindrical ori-block as an example,the mobility of such mechanism is analyzed based on the decomposition theorem of the constraint screw system,and the relative motion-screw of the specified block structure is calculated.After cutting some materials of this cylindrical ori-block,the obtained mechanism is taken as the deployable sub-mechanism.Then,the deployment/grasping motion sub-chain is constructed,which is composed of the deployable sub-mechanism,a platform and a base.According to mobility analysis of such deployable sub-mechanism,the motion-screw system of this deployment/grasping sub-mechanism is calculated,after which its constraint-screw system is obtained based on the reciprocal screw theory.Subsequently,a series of two Do Fs deployable morphing mechanisms with folded,deployed,and grasping configurations are constructed by applying the proposed type synthesis method based on the constraint force decomposition theorem.Compared with the single Do F deployable morphing mechanism,the two Do Fs deployable morphing mechanism has a wider working space.Therefore,such a morphing mechanism is selected as the research object,and its performance evaluation index is proposed: the deploy/fold ratio and stiffness/mass ratio.The configuration of the deployable sub-mechanism is determined by the calculation result of the fully deploy/fold ratio,maximum deploy/fold ratio is also calculated using three types of deployable sub-mechanism.The model of two Do Fs deployable morphing mechanism is constructed using the deployable sub-mechanism with bigger deploy/fold ratio.Then,the overall Jacobian matrix of this model is derived using semi-analytical method based on screw sub-space,which is used to obtain the stiffness matrix.Considering the mass of the model,its stiffness/mass ratio is calculated and is verified by applying finite element method.The model of the two Do Fs deployable morphing mechanism is prototyped and processed,and the motor driving mode is studied,and the deployment motion and grasping motion tests are carried out to verify its various configurations and maximum deploy/fold ratio.A class of block-shaped ori-blocks is designed in this thesis,which is kinematic equivalent to classic over-constraint links,proposes a comprehensive type synthesis method for both metamorphic mechanisms and parallel mechanisms,analyze performances of a deployable morphing mechanism,and completes the prototype processing that is used to verify the feasibility of the proposed type synthesis method.The obtained deployable morphing mechanism can be used to construct a large-size space truss-type deployable grasping robotic finger using a mobile assembly method.Such a manipulator can be used to grasp space non-cooperative targets such as space junk.Therefore,the results in this thesis lay the theoretical foundation and technical support for the design of space truss-type deployable grasping robotic finger that is capable of recycling space junk.