A bending moment and a tension/compression force are two types of commonly used load patterns in loading test for mechanical components. A great number of simulator types available for the two loads have been reported widely. However, current types mainly focus on the single load pattern and only one-dimensional bending moment can be achieved. With the increasing demand of the mechanical part performance, it is urgent to build a more complex testing environment. In this situation, a novel compound load simulator capable of outputting single multi-dimensional load and compound load patterns gradually catches the attention of the researchers. The development of parallel mechanism (PM) supplies a new direction to the field of simulators, whereas there is still shortage of effective types and design principles. In this paper, type synthesis of the compound load simulators outputting the bending moment and tension/compression force is introduced. First of all, the relationship between load patterns and degree-of-freedom (DOF) of parallel mechanism is derived. Based on the derivation, the DOF correspondence with a two-dimensional pure bending moment is two-dimensional rotation and that with a tension/compression force is one-dimensional translation. Furthermore, a typical 3-PRS PM as a representative of the PM with 2R1T DOF is studied and the analysis reveals that there is parasitic motion during its two-dimensional rotation. The undesired parasitic motion will bring additional load to the part, such as shear force. Then the special characteristics of PM meeting the requirement of outputting pure bending moment are proposed. Finally, a graphical approach is utilized to synthesize the effective types of the compound simulator.

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