Progress and key technologies in thread machining for planetary roller screw mechanism

As a high-precision transmission mechanism, the planetary roller screw mechanism (PRSM) has been extensively utilized in applications such as robotics, precision manufacturing, and aerospace systems, owing to its exceptional reliability, superior load-bearing capacity, and remarkable environmental adaptability. Nevertheless, the emergence of humanoid robot research has presented substantial challenges for the practical implementation of the inversed planetary roller screw mechanism (IPRSM). The inherent structural characteristic of IPRSM, which typically features a large length-to-diameter ratio in its nut component, poses significant difficulties in internal thread machining. These manufacturing limitations adversely affect part quality, operational performance, and production efficiency, consequently restricting the broader adoption of IPRSM. This paper conducts a comprehensive analysis of four distinct threading methodologies: turning, cyclone milling, rolling, and grinding. Based on this assessment, key technologies in tool design, process optimization, and evaluation methods for large length-to-diameter ratio internal thread are summarized. Furthermore, the study explores potential research directions and technological advancements in the machining of internal threads with large length-to-diameter ratios, providing insights into future developments in this specialized field.