Digital Type Synthesis Theory Of Spatial Multi-loop Coupling Mechanisms

Structural creation of mechanisms is crucial to original design of machine equipment important and can be effectively realized by means of synthesis. Spatial muti-loop coupled mechanisms can be classfied into spatial parallel mechanisms with three or more limbs and spatial mechanisms with coupled chains. Such mechanisms have advantages of high rigidity, high load capacity, high accuracy and low inertia so that they can be applied to industry extensively. The existing methods for synthesizing spatial muti-loop coupled mechanisms are mainly dependent of manual numeration, which has low efficience so that those mechanisms along with great quantities and varieties are hard to synthesize sysemmatically, and the synthesized results are not convininet for store and selection. Digital structural synthesis can overcome those disadvantages. This thesis concentrates on spatial muti-loop coupled mechanisms and aims to study the theory of digital structural synthesis of them.A new structural representation is proposed for spatial parallel mechanisms. Combining parametric expression of screws and representation string, automatic solution of twist system of a limb can be performed. Based on elementary row transformation, automatic solution of the number of overconstraints can be realized. By checking the relative degree-of-freedom(DOF) between nonadjacent joint axes with “undeterminate geometrical relations”, the instantanexity of analyzed mobility can be identified automatically.Based on screw theory, the geometrical contitions providing constraint forces or constraint couples is found for 3-DOF, 4-DOF and 5-DOF limbs. Further, those limbs are synthesized through generating the combinations of geometrical relations between joint axes and adding the symbols of joints. Finally, the structure databases of 3-DOF, 4-DOF and 5-DOF limbs are established, respectively.A method for digital structural synthesis of spatial parallel mechanisms is proposed. Constrtaint modes of nine kinds of lower-mobility parallel mechanisms are derived systemmatically, repectively. Digital structural synthesis of parallel mechanisms under a given constraint mode is studied. Finally, structure databases of nine kinds of lower-mobility parallel mechanisms are established, respectively. The relevant human-computer interfaces are developed for showing structures of parallel mechanisms.An important class of spatial mechanisms with coupled chains(called two-layer and two-loop spatial mechanisms) is concerned. Based on twist equation, mathematical model of coupled relations brought by the coupled chains is set up. Based on the model, a method for identifying rigid substructures of two-layer and two-loop spatial mechanisms is proposed, and the principle of mobility analysis of the class of mechanisms is established. Last, the programmable process of mobility analysis is studied.Based on the proposed principle of mobility analysis, a general structural synthesis method for two-layer and two-loop spatial mechanisms is proposed. Further, the class of mechanisms with forteen kinds of mobility properties is synthesized systemmatially. Many novel two-layer and two-loop spatial mechanisms are invented. Last, the programmable process of structural ysnthesis is studied.