Abstract: Large gears are the indispensable parts of large-scale equipments, but it is a tough task to inspect large gears owing to their increasing technical specifications, large size and heavy weight. Many factors affecting large gears measurement are analyzed. The measuring principals, methods and typical instruments of two kinds of large gears measurement: off-machine measurement and on-machine measurement, are reviewed in detail, as well as their specific advantages and disadvantages are discussed. Based on the analysis of manufacture characters and application requirements for large gears, the general requirements and development direction are summarized, that are holistic model description and fast measurement. The new ideas, principles, solutions and artifact are introduced as well, especially, to inspect large gears with small instruments effectively will become a trend. As a solution, a new on-machine measuring method combining the virtues of laser tracking with coordinate metrology can figure out the problem of establishing relationship between the measuring instrument and large gear, this method also can be applied to the inspection of others complex and large parts, so it shows a favorable application prospect.

Key words: Gear standard, Gears, Laser tracking measuring technique, Off-machine measurement, On-machine measurement