Theoretical And Experimental Study On Holding Of Multi-stage Metamorphic Mechanism Driven By Single Motor

Continuous robots have strong self-adaptability and obstacle avoidance ability.Compared with traditional discrete rigid robots,continuous robots have obvious advantages in operating objects with different shapes and sizes.They can not only grasp objects through their mechanical claws like traditional robots,but also can be regarded as a holding claw.Envelope grasping of objects can be realized through the whole robot’s own structure.Elephant-nosed robot is a typical continuous robot.Existing elephant-nosed robots basically have distributed multi-drive sources and soft materials,which lead to complex drive systems and limit the application of elephant-nosed robots in dangerous extreme environments.In this paper,a further theoretical and experimental study is carried out on the basis of an elephant trunk robot configuration with few driving constraints proposed by our research group.The elephant trunk robot is formed by connecting a plurality of underactuated link mechanism units in series,each underactuated link mechanism unit is a single metamorphic mechanism,and can stably hold objects with different shapes and sizes under the driving of a motor.Therefore,it is of great significance to study the mechanical characteristics of the multi-stage metamorphic mechanism,the mechanical relationship and stiffness distribution between each unit segment,and the theory of stable envelope holding.In this paper,the kinematic model and mechanical model of the multi-stage metamorphic mechanism are established,the kinematic characteristics of the multi-stage metamorphic mechanism are analyzed,the mechanical characteristics between the whole and each unit section are analyzed,and on the basis of the mechanical characteristics analysis,the spring stiffness and spring installation angle of each unit section are studied,in addition,the envelope holding stability of the whole multi-stage metamorphic mechanism is also studied in depth.The main contents are as follows:(1)Establishment of kinematic model of multi-stage metamorphic mechanism.The multistage metamorphic mechanism is simplified and some structures are treated equivalently.The kinematic model of the multi-stage metamorphic mechanism is established.On this basis,the errors of the unit section and the whole of the multi-stage metamorphic mechanism are analyzed,including position error,velocity error and acceleration error.Finally,the correctness of theoretical calculation is verified through experiments and simulations.(2)Research on mechanical characteristics and spring related parameters.Firstly,the mechanical characteristics of the unit joints are analyzed,and then the force transmission law between each unit joint and the relationship between the force transmission law and the force transmission law are found.Then,starting from the extreme stress,the friction force between the contact point and each hinge point is taken into account,and the mechanical parameters of each position are solved,so that the parameters such as the stiffness of the spring,the installation angle,the installation position and the like can be optimally determined.(3)Study on the envelope holding range and holding stability.The overall structure of the multi-stage metamorphic mechanism is a series structure.The object to be held needs to be held and captured by enveloping holding.The holding state and holding stability of the multi-stage metamorphic mechanism holding an object with any shape are studied.At the same time,the optimal holding point is determined,thus making enveloping holding and grasping more stable.The criterion of stable enveloping holding of the multi-stage metamorphic mechanism is proposed,which can realize the determination of stable enveloping holding of an object with any shape.(4)Experimental research.On the basis of theoretical analysis and model design,a prototype of multi-stage metamorphic mechanism was developed,and the bending and stretching function was experimentally studied,which verified the correctness of the theoretical derivation of kinematics.At the same time,the bearing capacity of the multi-stage metamorphic mechanism and the relationship between the spring parameters and the mechanical properties are also experimentally investigated and verified.In addition,the relationship between the envelope angle,the extreme contact position and the size of the held object is also experimentally verified.The correctness of some theoretical contents has been verified.