A novel method for measuring the virtual pitch diameter of a thread

摘要

A novel measuring method for virtual pitch diameter of a thread was proposed. A customized measuring tip with a perfect threaded geometry was used to represent the appropriate counter piece of a geometric-ideal thread. During the measurement process, the tip moves along a helical path relative to the work-piece and always maintains the engagement with the work-piece to be measured. According to the changes of the tip's position and orientation, a unique imaginary and perfect thread that can just contain the actual thread in 3D space is identified finally, whose pitch diameter can be considered as virtual pitch diameter of the work-piece. Compared with existing measurement methods, the measurement result obtained in the newly established measurement process can fulfill the requirements from the definition of virtual pitch diameter given by ISO 5408: 2009. The feasibility of the proposed method was validated on a developed prototype.