Different Classification of Measurement Methods
Measurement method is to get the measuring results based on a given measurement principle, the measuring method is divided into different categories, here are several common measurement methods.
The direct measurement method is the method that can directly obtain the measured value, such as measuring the length of the part by using the vernier caliper and measuring the diameter of the shaft by micrometer.
Indirect measurement method is a method to obtain the measured value by measuring other quantities which have function relationship. For example, coordinate measuring machine, optical measuring machine and laser measuring machine are all indirect measurement methods.
Contact measurement method is a measurement method that the measuring equipment sensor contact the surface of the part. Common contact measurement methods include: vernier caliper, micrometer, measuring styli and joint arm measuring machine, etc. Contact measurement is very common in current industrial applications. It is characterized by high reliability, high accuracy and good repeatability. However, the disadvantage of contact measurement is that the measuring contact force may cause deformation to the measuring instrument and the surface of the part (such as soft surface), which can affect the uncertainty of measurement.
Non-contact measurement is a measurement method that the measuring equipment sensor do not contact the surface of the part. Common non-contact measurement methods include optical measurement, laser measurement, tool microscopy, etc. The advantages of non-contact measurement is measurement sensor is not in contact with the surface being measured, the parts to be measured surface will not pose any damage, more suitable for complex curved surface parts and soft surface measurement. Its disadvantage is the accuracy not as high as the contact measurement accuracy.
The vision measuring machine is a typical non-contact measurement and indirect measurement. Two dimensional video measuring instrument using hardware itself (CCD, the eyepiece, objective data line, video acquisition card) will can capture the image through the cable to the computer data acquisition card, after imaging by software on a computer screen, and rapid measurement. The optical measuring instrument can read the displacement value of the optical ruler quickly and obtain the desired result through the software module operation based on the spatial geometry. The graph is generated on the screen to be used by the operator to control the image, so as to visually distinguish the possible deviation of the measurement result.
CMM is a typical example of contact measurement and indirect measurement. The three-coordinate measurement is a method of obtaining the coordinate information of the part surface in a given measurement space, and digitizing the shape information of the object is also called "sampling". These sampling values are discrete spatial point coordinate information, rather than specific geometric features of size, location and other information. The measuring procedure is processed by a series of measuring points, and the corresponding geometric eigenvalues are extracted to obtain the required measurement results.
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