How to choose the right coordinate measuring machine?

How to choose the right coordinate measuring machine?

　　 There are many brands and models of coordinate measuring machines on the market, and many friends do not know how to choose. Miaoji Precision reminds that under normal circumstances, the following aspects should be paid attention to when choosing a coordinate measuring machine.

　　1, CMM measurement range. This is the primary factor in choosing CMM. When we plan to purchase a three-coordinate measuring machine, we must first clearly grasp the outer dimensions of the measured product, and determine the corresponding specifications of the three-coordinate equipment according to the size. For example, when selecting a bridge structure CMM, the equipment price is proportional to the span of the beam, and the lengthwise dimension has little effect on the price. Therefore, we only need to meet the measurement range and do not need to pursue an unnecessary large range. If the workpiece to be measured is only a part of the entire product, the CMM selected at this time must also place the entire workpiece on the work surface, and at the same time, consider the weight of the product and cannot exceed the load-bearing range of the CMM. The measurement range selected by CMM is also affected by the selected probe system, because the probe will occupy a certain measurement space, so when selecting the measurement range, the influence of the selected probe must be considered.

　　2, measurement accuracy. The coordinate measuring machine is a measuring instrument that detects the geometric size and form and position error of the workpiece, and meeting the accuracy requirements is the first choice. When CMM is selected, it is generally possible to compare the required detection accuracy of the measured workpiece with the measurement uncertainty given by the measuring machine to see whether the accuracy of the measuring machine meets the requirements. The user should choose a coordinate measuring machine with a slightly higher accuracy (including repeatability). This is not only because when measuring complex workpieces, the error that the measuring point may bring is larger than expected (due to the change or lengthening of the probe rod will introduce greater measurement errors), but the accuracy of the measuring machine will increase with the number of uses. Generally, when the uncertainty value of the coordinate measuring machine is less than or equal to 1/2 of the required uncertainty of the measured size, it can be selected.

　　3. Probe form. From the perspective of the influence of the working form of the probe on the accuracy of the measurement results, the commonly used probes include contact trigger probes, contact scanning probes and non-contact optical probes. When selecting the probe of a coordinate measuring machine, select the probe form according to the measurement requirements, measurement speed and measurement frequency.

　　4, grating ruler. The grating ruler is the reading standard of the coordinate measuring machine, so the coefficient of thermal expansion is required to be as low as possible to ensure the accuracy of the reading. The current research and development of materials for grating scales is also centered on reducing the coefficient of thermal expansion. According to the degree of automation, the coordinate measuring machine is divided into two categories: manual (or motorized) and CNC (automatic control). When selecting, it should be weighed according to the batch size of the test object, the degree of automation, the technical level of the operator and the size of capital investment. Of course, the three-coordinate measuring machine has a high level of accuracy and fast measurement speed, but the preparation time before measurement is relatively long, the technical requirements are relatively high, and the capital investment is relatively large.