Abstract: The propulsion system is one of the key subsystems of a shield machine (SM). It is of great use for propulsion working, and bears heavy payload and interrupt dynamical payload which come from outside environment. At the same time, it transforms great propulsion forces, and can act high accuracy forces and motions transformation. On the one hand, if the thrust mechanism (TM) on a propulsion system is of lower rigidity, it will result in the lower capacity for bearing the heavy payload. On the other hand, if the TM is of lower flexibility, it will result in the lower capacity for accommodating the interrupt dynamical payload. To dissolve the rigidity-flexibility conflict and let it work under high efficiency, accuracy and safety conditions, a new approach of the payload compliance design (PCD) theory for the TM is introduced. To do this, several research works are investigated and are described as follow: The physical terms of movement coupling, deformation coupling and performance of energy stored for a shield machine are discussed, and their definitions are given, respectively. The inherent relationships between the performance of the remote compliance center (RCC) and the precision of position control, the performance of movement coupling and the heavy payload, the performance of deformation coupling and the interrupt dynamical payload, and the elastic energy and the intense impact come from the interrupt dynamical payload are also studied. Based on which an integration index, i.e. the payload compliance index (PCI), for the PCD is defined either. The comparisons of PCIs and joint forces of type Π mechanisms are done through different design parameters, and different products coming from different manufacturers. The results that payload compliances are inversely proportional to the joint forces would verify theoretically the rationality of the proposed PCI and the validity of the proposed PCD theory. Follow all the PCD criterions, a fine designed TM would ensure that it not only is of high rigidities to bear heavy payloads and reduce joint forces, but also is of high flexibilities to accommodate interrupt dynamical payloads, and reduce dynamic joint forces.

Key words: mechanical deformation coupling index, mechanical movement coupling index, payload compliance design, remote center of compliance, thrust mechanism