As far as the gear in place measurement is concerned, the common problem is how to accurately determine the position of the measuring instrument and the measured gear, whether it is the on-board measurement system or the on-board measurement system. This kind of position relation includes two basic problems: one is to determine the attitude of the measuring instrument according to the position of the gear; the other is to determine the real space distance between the gear axis (or datum plane) and the measuring instrument. In order to establish the position relationship between the measuring device and the measured gear, a “third party” with high measuring accuracy and large measuring range is needed to complete this work. High precision laser tracking measurement technology provides a means for this.
Based on the advantages of laser tracking interferometry, a laser tracking in place measurement system for super large gears has been developed [26]. The measurement system consists of laser tracking interferometer, three-dimensional measurement platform and measurement and control software (Figure 18). During the measurement, the coordinate system of gear and three-dimensional measurement platform is established by using laser tracking interferometer. The coordinate system of gear and instrument is transformed into the measurement coordinate system of laser tracker, and the position relationship between the coordinate system of gear and the coordinate system of three-dimensional measurement platform is determined. The measurement of super large gear can be converted into the conventional measurement of gear, That is to say, the super large gear is moved to the three-dimensional measuring platform for measurement.
Laser tracking in-situ measurement technology integrates the advantages of laser tracking and coordinate measurement technology, and has better flexibility. Through the idea of “large-scale small” or “measuring large with small”, it realizes the high-precision measurement of super large gears, which is essentially different from the traditional way of “measuring large with large”. This scheme can also be used in the measurement of other large and complex parts, with high precision, strong generality and development prospect.
(1) Due to the characteristics of the big gear, the measurement of the big gear is mainly based on the analytical measurement, but rarely uses the functional comprehensive measurement; the measurement of the big gear displacement and in place measurement oriented to the analytical measurement have been developed to some extent. The large gear measuring center and the large precise CMM are two kinds of instruments for measuring the large gear out of position. Restricted by the precise mechanical technology, the maximum diameter of the measured gear is less than 5000 mm. There are many problems in the measurement of large gears. The main problems are the lack of large-scale samples and the non traceability of measurement values.
(2) With the increase of the size of large gear and the change of its processing technology, the measurement technology of large gear changes from quantity to quality. Based on the 3D representation of gear accuracy with full information, it is the general requirement and development direction of the measurement technology of large gear to realize the global representation and rapid measurement of the quality of large gear. At present, the measurement technology of large gear presents a new development trend, mainly as follows: (1) multi site integrated parallel measurement technology of large gear; (2) large gear template; (3) new measurement method to overcome the difficulties of traditional measurement mode; (4) in place measurement technology of large gear based on the principle of laser tracking measurement.
(3) “Measuring large with small” is a new way to solve the problem of high precision measurement of super large gears. Laser tracking in place measurement technology integrates the advantages of laser tracking and coordinate measurement technology, has better flexibility, and is a better way to achieve “small measurement large”. This scheme can also be applied to the measurement of other large and complex parts, with high precision, strong generality, and development prospect.