Owing to the requirements for high performance and long life, the friction and wear problems of rolling piston type rotary compressors have drawn much attention. Various theoretical models have been developed and improved to reveal the inner state of the compressor and obtain the optimization schemes. However, there remain some disadvantages and research gaps in the corresponding modeling and mixed lubrication analyses, and a comprehensive summary is lacking. To have a better understanding of the research status, this paper reviews the theoretical model development and mixed lubrication analyses of the compressor in the past decades. The determination of compression pressure, the modeling process of moving components, and the key findings are presented in detail. On this basis, some important influencing factors and the problems remaining to be solved are also discussed. This paper provides multifaceted guidance for manufacturers and researchers to conduct further theoretical analysis and optimal design.

Although extensive research has been conducted on peristaltic robots, early designs are often constrained by mechanical configurations and material constraints, which restrict kinematic capability, particularly steering control. In contrast, snails steer by modulating mucus secretion to redistribute ventral friction along the foot. Inspired by this strategy, we propose a friction-differential steering mechanism and develop a novel crawler that implements it. The crawler is integrated with a peristaltic robot, and three experiments are conducted to evaluate steering performance. We further establish a physical model of friction-differential steering, including cases identified from the experiments. The proposed model captures the experimentally observed trend that the steering response increases with the friction differential and provides a qualitative physical interpretation of the steering mechanism. Finally, the method is generalized by analyzing its limiting behavior, thereby clarifying the operating bounds of the proposed approach. This work provides a principled framework for steering control in peristaltic robots and offers a promising direction for improving their motion controllability.