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

Abstract

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.

Error motion analysis and design of a synthetic probe of thread functional diameter based on the compliant mechanism

“…Our method is not to measure the contour of the tooth directly, but to measure the effect of the thread profile to the standard profile on the whole circumference. It is more in line with the definition of the functional diameter [34,35]. The thread probe is advanced in the measurement principle, but still has the potential for improvement in the measurement accuracy.…”

A novel measuring tip for thread functional diameter: error compensation of the effect of lead angle and curvature radius

“…The parameters of the tooth profile between A and B do not work, such as tooth 2 and tooth 3. The calculated functional diameter does not represent the actual effect [37]. The measurement of the functional diameter has not achieved metrological traceability [40,41].…”

“…According to the Guide to the Expression of Uncertainty in Measurement (GUM), in choosing a coverage factor k = 2 [36,37], the expanded uncertainty with level of confidence p = 95% is…”