Several commonly used flatness measurement methods and defects

Flatness (planeness) is one of the geometric tolerances, which refers to the deviation of the macroscopic concave and convex height on the surface of the object from the ideal plane. In the traditional detection method, flatness measurement usually includes: plug gauge / feeler measurement method, liquid level method, laser plane interferometer measurement method (planar interferometry method), level/digital level measurement method, and meter measurement law.

With the feeler gauge measurement, you can perform a rough measurement of flatness anytime, anywhere with a set of feeler gauges that you can carry with you. Many factories still use this method for testing. Due to its low precision, the conventional thinner feeler gauge is 10um, the detection efficiency is low, and the result is not comprehensive enough to detect the edge of the part.

The liquid level method, based on the working principle of the connected device, is suitable for measuring the flatness of a continuous or discontinuous large plane, but the measurement time is long and sensitive to temperature, and is only suitable for a plane with low measurement accuracy.

The most typical use of laser plane interferometer measurement is the flat crystal interferometry. However, it is mainly used to measure the measurement of smooth facets, such as the measuring surface of the gauge, the working surface of the gauge, and the optical lens.

Level measurement, widely used for straightness and flatness measurement of workpiece surfaces. High measurement accuracy, good stability, small size and easy to carry. However, when measuring by this method, it is necessary to repeatedly move the position of the instrument and record the data of each measuring point, which is time consuming, laborious, and has a long adjustment time, and the data processing program is cumbersome.

Table measurement method, the typical application is flat micrometer and three coordinate instrument, of which the three coordinate system is the most widely used. During the measurement, the indicator moves on the sample to be tested, the data of each measurement point relative to the measurement reference is measured according to the selected distribution point, and the flatness error is evaluated through data processing. But its efficiency is low, usually a sample takes a few minutes, far from the 15ppm expectation.