Coordinate measuring machine (CMM) is a new high-efficiency precision measuring instrument developed in recent 50 years. On the one hand, its emergence is due to the high-efficiency processing of automatic machine tools and CNC machine tools and the processing of more and more complex shape parts, which need fast and reliable measuring equipment; On the other hand, the development of electronic technology, computer technology, digital control technology and precision machining technology provides a technical basis for the emergence of CMM. Today, we are going to show you the working principle, compositions, applications and advantages of CMM.
Modern CMM can not only complete various complex measurements under the control of computer, but also realize the control of machining by exchanging information with NC machine tools, and also realize reverse engineering according to the measured data. At present, CMM has been widely used in machinery manufacturing, automobile industry, electronic industry, aerospace industry and national defense industry. It has become an indispensable universal measuring equipment for modern industrial testing and quality control.
Because of its strong universality, large measurement range, high precision, high efficiency and good performance, and can be connected with flexible manufacturing system, it has become a kind of large-scale precision instrument, so it is called “measurement center”.
Because of its strong universality, large measurement range, high precision, high efficiency and good performance, and can be connected with flexible manufacturing system, it has become a kind of large-scale precision instrument, so it is called “measurement center”
Basic Working Principle of CMM
Geometric measurement is based on the coordinate position of points. It is divided into one-dimensional, two-dimensional and three-dimensional measurement. The basic principle of CMM is to put the measured part into its allowable measurement space, accurately measure the values of the measured part in the three coordinate positions of X, y and Z, and fit the measured elements such as circle, ball, cylinder, cone and curved surface according to the values of these points through computer data processing, so as to obtain the shape Position tolerance and other geometric data.
Compositions And Characteristics of CMM
1.Pribo system
The probe system includes probe, suction cup, probe, reading head and grating ruler.
2. Hardware control system:
C99 control cabinet has computer-aided error correction function, which can make real-time dynamic correction for CMM and sensors to ensure accurate results. Electric drive system, including motor, friction roller, steel belt, belt, air cushion (air bearing), air pipe, filter, barometer and pressure regulating valve.
3.Other mechanical parts
Including granite table, three-axis guide rail, damping pad, support base frame, z-axis balance cylinder, solenoid valve, etc. Data processing software system (Calypso measurement software), using this software, CAD data can be transformed into measurement program, so as to obtain accurate detection scheme.
Applications of CMM in Precision Measurement
At present, the geometric flatness measurement of the surface with multiple slits of the workpiece shown in the figure below is carried out by using the contura G2 RDS CMM.
The preparation of measurement program makes use of the powerful open off-line programming function of calypso measurement software. One of the advantages of this programming method is that it can be programmed as long as the CAD drawing file designed by the designer is directly input into the measurement software. It is not necessary to wait for the workpiece to be processed before program measurement, which can greatly improve the work efficiency. Second, after the programming is completed, you can directly call the program in the CAD environment for simulation measurement, verify the program, find out the wrong measurement path and sampling point in the operation process, and correct the program to minimize the possible problems in the actual measurement and ensure the safety in the measurement process to the greatest extent.
When programming offline, the measurement software shall be set to offline working mode. Firstly, the model established in the CAD environment is directly imported into the measurement software (as shown in the figure below). The measurement software adopts a graphical visual interface, which is simple and easy to use, including basic CAD functions, such as zoom in, zoom out, translation, rotation, coloring (shadow), etc. the direct CAD interface of the software is applicable to all important CAD formats and will not lead to tolerance problems and loss of accuracy.
The second step is to establish the workpiece coordinate system and start measurement. The coordinate system is established by using the common surface line point (3-2-1), then select the plane measurement element, double-click the plane element, and set the measurement strategy. Because the plane to be measured is special, there are many slits on it, which makes it possible to exceed the flatness. In order to obtain comprehensive, accurate and reliable measurement results, the measurement path is selected as polyline according to the principle of equal breadth, so that the collected points cover the whole plane as much as possible. Click the position of the point to be collected on the workpiece model with the mouse, and the position of the point and its vector direction will be displayed on the workpiece model. Multiple point acquisition can be carried out according to the needs of the measured geometric elements. When the required points are collected and then determined at the midpoint of the acquisition point window, the system will drive the virtual probe to collect points and fit the geometric elements and graphics to be measured. The polysemy measurement interface is shown in the figure below.
Next, the polysemy of the measurement path shall be set in detail, including setting the probe speed and the number of collected points respectively according to the actual situation. Then, the evaluation method of plane elements shall be modified, set to the least square method, and select to remove the gross error.
After the element measurement is completed, the measured geometric flatness shall be evaluated. Select flatness in the shape and position tolerance in the menu, then double-click the flatness icon, select the measured plane element, and enter the design tolerance value to confirm the completion. The flatness evaluation interface is shown in the figure above.
Before the automatic operation of the measurement program, in order to prevent accidental collision between the probe and the workpiece to be measured in the actual measurement, a safety plane shall be set.
Finally, the completed measurement program is saved, and the flatness measurement result report as shown in the figure below is obtained through online actual measurement. Relevant measurement elements, coordinate values and all measurement data can be obtained intuitively from the report. Users can provide detailed information such as actual dimension, tolerance value, deviation from theoretical value and out of tolerance as needed, define the report header by themselves, and can adjust it at any time after saving.
Through the use of CMM in the measurement and application of workpiece, a large number of accurate and detailed measurement data are collected efficiently, and the functions that could not be realized by other workpiece flatness measuring tools (such as knife edge ruler) are completed. CMM has high precision, high flexibility and excellent digitization ability. The use of precision CMM in the manufacturing of high-quality products can reduce the measurement error, ensure the accuracy and quality of products, meet the needs of design and manufacturing, deepen the understanding and better grasp its working principle and performance, and will play an important role in completing and expanding the quality inspection of precision parts in equipment development.