Design And Performance Research On Ground Mobile Ditetrahedron Mechanism

As a new auxiliary tool to assist humans in production and life,mobile robots are widely used in advanced manufacturing,sea and air exploration,medical service,military reconnaissance and other sophisticated,heavy,dangerous or unknown tasks.It requires mobile robots to have stronger complex-terrain adaptability.As an important executive part of mobile robots,a variety of wheeled,tracked,legged,hybrid and other new ground mobile mechanisms have been explored and developed to improve the mobility of robots.From the spatial relations of polyhedrons in geometry,use the design principle of linkages in mechanics,the geometrical and mechanical polyhedron are constructed,and the design method of ground mobile polyhedron mechanism with new configurations and locomotion mechanisms is explored,thus to obtain ground mobile polyhedron mechanisms with both moving and folding functions.Specific for tetrahedron units,ditetrahedrons are constructed,and a class of ground mobile ditetrahedron mechanisms with full attitude moving and folding functions is proposed.Firstly,the geometrical and mechanical ditetrahedrons are constructed,and a design method of ground mobile ditetrahedron mechanism is proposed.Further,the Bennett-based single-motor coplanar ditetrahedron mobile mechanism,the PPP-based multi-mode opposite ditetrahedron mobile mechanism and the Sarrus-based deployable dual ditetrahedron mobile mechanism are designed,and moving and folding functions of the three mechanisms are deeply analyzed.Meanwhile,the motion planning strategy of rolling ditetrahedron mechanisms is explored.The specific research content is as follows:(1)Based on geometrical and mechanical characteristics of tetrahedrons,reasons for using tetrahedrons as units and necessities and requirements of constructing ditetrahedron mechanisms are clarified.Then a design method of ground mobile ditetrahedron mechanism based on gemetrical and mechanical construction is proposed.By structural compound and geometric evolution of two tetrahedrons,three typical ditetrahedrons are constructed.By mechanism design,a family of ditetrahedron mechanisms is obtained,in which three are selected based on the degree of freedom(DOF)and mobile ability.Then they each is coupled by deployable single-loop overconstrained linkages,three ground mobile ditetrahedron mechanisms with limited DOFs and folding function are obtained.(2)Based on the single coupling loop coplanar ditetrahedron mechanism with the Bennett linkage from the design method,the Bennett-based single-motor coplanar ditetrahedron mobile mechanism is proposed by specific design of structural parameters.By shape design of links,it has cylinder-shape folding function.Based on kinematic and mobility analyses,the basic principle and the implementation strategy of the continuous moving,turning and folding functions of the mechanism with a single motor are acquired.(3)Based on the three coupling loops opposite ditetrahedron mechanism with PPP linkages from the design method,the PPP-based multi-mode opposite ditetrahedron mobile mechanism is proposed by analogy with segmented worms.Combining the locomotion mechanisms of segmented worms and polyhedron mechanisms,using center of mass control method,the integrated design of multi-mode gaits including rectilinear mode start gait and straight-going gait,lateral undulation mode turning gait and vertical undulation mode stair-climbing gait is realized.Further,its locomotion performance on typical terrains of slopes,stairs,gaps and narrow passages is analyzed quantitatively,and a matrix-based path generation algorithm for multi-mode locomotion and obstacle crossing tasks is proposed to provide it a motion planning strategy.(4)Based on the multiple coupling loops dual ditetrahedron mechanism with Sarrus linkages from the design method,the Sarrus-based deployable dual ditetrahedron mobile mechanism is proposed by a specific shape design of its nodes.It is composed of only R joints,and each node and two chains connected to it is a Sarrus linkage.Take advantage of the kinematic characteristic of the Sarrus linkage that can convert rotary motion to exact straight-line motion,two non-impact rolling gaits are designed to make the mechanism possess full attitude non-impact rolling capability.Besides,two folding modes of folding as an umbrella shape and deploying in radially reciprocating motion are proposed,which increase the portability and functional diversity of the mechanism.(5)Since both the coplanar and the dual dithetrahedral mobile mechanisms have irregular triangle moving trajectory,a general rolling ditetrahedral mechanism model is built,and a layered motion planning strategy including upper-layer path planning and lower-layer gait planning is designed to get the input parameter sequence and locomotion path of the mechanism from its initial pose to the target.Then taking moving,turning and operation tasks respectively as examples to be planned,and planning results are verified by motion simulations.Finally,comparison on motion performance of four ditetrahedron mobile mechanisms including the general rolling ditetrahedron mechensim is carried out.