Several commonly used flatness measurement methods
Flatness is one of the geometric tolerances, which refers to the deviation of the macro-concave-convex height on the surface of the object from the ideal plane. In the traditional detection methods, the measurement of flatness usually includes: plug gauge/feeler gauge measurement method, liquid level method, laser plane interferometer measurement method (flat crystal interferometry method), level meter/digital level measurement method, and meter measurement Law.
The feeler gauge measurement method only needs a set of portable feeler gauges to perform a rough measurement of flatness anytime and anywhere. At present, many factories still use this method for detection. Due to its low precision, the thinnest conventional feeler gauge is 10um, the detection efficiency is low, the result is not comprehensive enough, and only the edge of the part can be detected.
The liquid level method, based on the working principle of the connector, is suitable for measuring the flatness of continuous or discontinuous large planes, but it takes a long time to measure and is sensitive to temperature, so it is only suitable for planes with low measurement accuracy.
Laser plane interferometer measurement method, the most typical usage is flat crystal interferometry. But it is mainly used for the measurement of smooth small planes, such as the measuring surface of the micrometer, the working surface of the gauge, and the optical lens.
The level measurement method is widely used in the straightness and flatness measurement of the workpiece surface. High measurement accuracy, good stability, small size, easy to carry. However, when using this method to measure, it is necessary to repeatedly move the position of the instrument and record the data of each measuring point, which is time-consuming, laborious, long adjustment time, and the data processing procedure is cumbersome.
The typical application of meter measurement method is flat micrometer and three-coordinate instrument, among which three-coordinate instrument is the most widely used. During the measurement, the indicator moves on the sample to be tested, and the data of each measurement point relative to the measurement reference is measured according to the selected layout points, and then the flatness error is evaluated through data processing. But its efficiency is low, usually a sample takes several minutes, far from the expectation of 15ppm.
