Research On The Configuration Design Method Of Hybrid Mechanisms Based On Fractal Theory

Hybrid mechanisms(HMs)have combined the advantages of serial mechanisms and parallel mechanisms,and at the same time the HMs also avoid the weakness of both.To be in detail,serial mechanism features large workspaces and easy to control,while the parallel mechanism is distinguished by good stability,rigidity,dynamic performance,accuracy and declined accumulative error.Due to the excellent performance,HMs are becoming an important research field and attracting more and more attentions from both academia and industry.However,the research on the design and type syntheses methods of hybrid mechanisms of HMs is still in development at present,especially the multipath atypical HMs with horizontal branches.Hence,a novel and systematic structural design and type synthesis methodology are proposed based on the fractal theory and topological graph.Firstly,the theoretical foundation of spatial multi-loop topological structure is introduced which is divided into open-loop and closed-loop according to the work condition.On the one hand,the amount of moving platform in the open-loop topology mostly is more than one,which makes it behave better in the coordinated multi-point work environment.On another hand,the amount of moving platform in the closed-loop topology is only one and is spread in industry.Meanwhile,through branch fractal,platform fractal and branch-platform fractal,the fractal theory is applied to the spatial multi-loop topological structure,which leads to an efficient and quick pattern to create new topological graph.Secondly,the kinematic features are analyzed as route,branch and kinematic pair.The HMs is comprised of routes in parallel;the route is constituted of branches in serial,while the branch is composed of kinematic pairs by different combination modes.And the kinematic pair is represented by an eight-bit binary string.In the meantime,the route rule is proposed to fix up the calculating problems caused by route which is a novel concept.According to the topological relationship,the calculation rule of union-intersection-preserving is established to obtain the output of motional features.Then,the detailed HMs design methodology based on fractal theory is proposed according to the theoretical knowledge above.And the layout of HMs is judged after choosing suitable kinematic pairs based on the topological graph.And the type synthesis method is proposed,while the method is applied to low-mobility HMs.As a result,the type synthesis of 3-,4-,5-DoFs HMs are achieved,meanwhile,the terminal output analyzing method is utilized to verify the HMs.Finally,a 5-DoFs hybrid ankle rehabilitation mechanism is proposed for dealing with the treatment of ankle injury facility which is composed of a 2R1 T mechanism and a 2T mechanism.The rehabilitation mechanism as a three-rotational and two-translational HMs is designed to achieve dorsiflexion,plantar flexion,over-pronating,supinating and three-dimensional translation.Meanwhile,the 2R1 T mechanism has two options.The kinematic analysis is led by the modeling and simulation in ADAMS,which also demonstrates the output motion and choose the configuration of rehabilitation mechanism.The mechanism is verified to achieve the stable output which convinces the application in the future.