Research On The Type Synthesis Of Decoupled Hybrid/Parallel Mechanisms Based On Screw Theory

Hybrid mechanism is the mixture of serial and parallel mechanism which combines the advantages of both and avoids the shortness at the same time. Especially in the high-end equipment manufactory and robot industry, hybrid mechanism has a better application prospect. As for the type synthesis of hybrid mechanism, on the one hand, an efficient and systematic type synthesis theory is still lack at present. On the other hand, coupling problems impedes the application owing to parallel mechanism existed in the hybrid mechanism. Dealing with the type synthesis of decoupled hybrid mechanism, a simple and effective method based on screw theory is proposed. The main content of this paper is shown as followed:(1) According to analysis on the structural characteristic of hybrid mechanism, a type synthesis method of decoupled hybrid mechanism is proposed. For dealing with the problem in synthesis of parallel unit existed in decoupled hybrid mechanism, a type synthesis method of fully-decoupled parallel mechanism is presented based on screw theory. Moreover, the detailed process of two synthesis theories is given, respectively.(2) The detailed process of decoupled hybrid mechanism is finished. Firstly, according to the number of degree-of-freedom(Do F), the hybrid mechanism is classified into 3, 4, 5 and 6 Do F. Secondly, in accordance with type of output Do F, the above hybrid mechanism is classified again. Finally, the whole configuration of hybrid mechanism is obtained according to the number and type of Do F.(3) According to the type synthesis of fully-decoupled parallel mechanism, the type synthesis of 2T, 3T, 1T1 R, 2T1 R and 3T1 R fully-decoupled parallel mechanism can be achieved. Meanwhile, the 3T and 2T1 R fully-decoupled parallel mechanism is synthesized as examples. From the point of analysis of input and output for fully-decoupled parallel mechanism, the type synthesis of 2R, 2R1 T, 2R2 T and 2R3 T fully-decoupled parallel mechanism can be achieved. Finally, the comprehensive current situation and problems of structural synthesis of 3R fully-decoupled parallel mechanism is analyzed.(4) Based on the synthesis theory of decoupled hybrid mechanism, the 3, 4, 5, 6-Do F decoupled hybrid mechanisms are obtained with the aid of synthesized decoupled hybrid mechanism and low-mobility parallel units. According to the synthesized decoupled hybrid mechanism, the instantaneous characteristic of the hybrid mechanism is analyzed and the singularity of degree-of-freedom of the hybrid mechanism is summarized. Finally, in terms of certain synthesized hybrid mechanism, the kinematics analysis of the mechanism is carried out, the Jacobian matrix of the mechanism is obtained, and the decoupling characteristics of the mechanism are verified. Meanwhile, simulationby software Adams is applied to verify relationship between the input and output of the mechanism which is linear and one-to-one correlation. In addition, the mechanism can be used in assembly and flexible inspection and other fields.