Since its inception in the early 1960s, the Coordinate Measuring Machine (CMM) has been widely used in the manufacturing industry worldwide and has become the industry standard equipment for 3D inspection. The three-coordinate measurement technology has been rapidly developed, and the development of supporting detection software is advancing by leaps and bounds. The earliest CMM can only display XYZ coordinates, and the current various detection software can solve most of the user's problems. Software is increasingly becoming the key to affecting user use.
CMM measurement software development trend
For the traditional CMM inspection, the design department usually provides 2D drawings, and the inspection department checks the dimensions and shape tolerances of the workpiece according to the drawings. With the application of 3D CAD software, more and more technical departments use 3D CAD modeling technology to design. Therefore, each coordinate machine manufacturer has launched measurement software based on 3D CAD technology, and directly introduces the customer-designed 3D CAD model into the measurement software for testing. The advantages of this are very obvious, no additional drawings are needed, the theoretical values ​​can be directly captured, and the measurement simulation, the probe interference check, etc. can be performed, so that the user is highly praised. CAD-based measurement has become a hot spot in the development of current three-coordinate measurement software.
In CAD design, the general rule workpiece can complete the 3D solid design through basic feature commands, such as stretching and punching. It is relatively simple to detect such workpieces. With the development of industrial styling and the application of machining centers, more and more workpieces are designed into complex shaped surfaces, such as covers, interiors and the like. The construction technology of curves and surfaces belongs to the advanced design category in CAD modeling. Many high-end 3D CAD softwares have special curve and surface processing modules, which allows users to design B-level or even A-level surfaces. The detection of surface-like workpieces puts forward higher requirements for the three-coordinate measurement software.
CMM surface inspection
3.1 Traditional measurement methods
In the case of not using CAD digital model, the CMM is used to detect the curved part. Usually, the coordinates of the section line and the point are generated on the surface digital model by using the relevant commands in the CAD software. The measuring machine goes to the corresponding position, performs detection, and compares the deviation of the coordinate values. This method requires the designer to provide additional theoretical data, and the compensation of the probe tip diameter is not easy to accurately realize. For single-point measurement, the compensation of the probe cannot be realized because the vector direction cannot be determined. Therefore, this approach has certain limitations.
3.2 Based on 3D digital-to-analog measurement
The use of surface digital models to detect surfaces is a requirement for the development of CMM measurement technology. Due to the complexity of the surface construction technology, it is also a high-end technology in the CAD application category, which is generally completed by a professional CAD/CAM system. In the measurement software, it is a problem that is utilized by importing a design digital model. In order to achieve this goal, it is necessary to solve four technical problems: digital-to-analog interface, alignment, tip compensation, and theoretical value capture.
Digital analog import interface
The first thing to do with digital mode detection is, of course, to ensure that the digital model is correctly imported into the measurement software. In fact, due to well-known reasons such as technology and interests, major CAD manufacturers around the world have developed different software and formats. For example, UG, PROE, CATIA, etc., which have relatively large domestic influences, cannot directly read each other.
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