The current situation and development trend of coordinate measuring machine
Industrial production has developed dramatically since the 1960s. This growth accelerated, especially with the rise of industries such as machine tools, machinery, automobiles, aerospace, and electronics.
As these industries evolved, developing and producing various complex parts required more advanced detection technologies and precision instruments. This need led to the emergence of three-dimensional measurement technology.
As a result, the three-coordinate measuring machine (CMM) was developed. Since its introduction, this technology has experienced rapid development and has become increasingly refined and sophisticated.
As a new high-efficiency precision measuring instrument developed in the past 30 years, CMM has been widely used in machinery manufacturing, electronics, automotive and aerospace industries.
It can inspect the size, shape, and mutual position of parts and components, such as the measurement of boxes, guide rails, turbines and blades, cylinders, cams, gears, forms, and other space profiles.
In addition, it can also be used for scribing, centering holes, photolithography of integrated circuits, etc., scanning continuous surfaces, and preparing machining programs for CNC machine tools.
Because of its versatility, measuring range, high precision, high efficiency, and good performance, it can be connected to a flexible manufacturing system. It has become a class of large precision instruments, so there is a “measurement center” name.
Three-coordinate measuring machine in the role of three-dimensional measurement
The emergence of the three coordinate measuring machine is a milestone marking the transition of measuring instruments from the classical manual way to modern automatic testing technology. Coordinate measuring machine in the following aspects of three-dimensional measurement technology has an important role:
1 Solve the complex shape surface contour size measurement, such as box parts of the hole diameter and hole position, blades and gears, automobiles and airplanes, etc., the outer contour size inspection;
2 improve the accuracy of three-dimensional measurement, the current high-precision CMM single-axis accuracy, up to 1 μm per meter of length, three-dimensional spatial accuracy of up to 1 μm ~ 2 μm-. For the workshop inspection with the CMM, per meter measurement accuracy of the single axis can be up to 3μm ~ 4μm.
3 As the three coordinate measuring machine and CNC machine tools and machining centers supporting the composition of the production line or flexible manufacturing system, thus promoting the development of automated production lines;
4 With the continuous improvement of the accuracy of the CMM, the degree of automation continues to develop, promoting the progress of three-dimensional measurement technology, greatly improving the measurement efficiency.
The introduction of electronic computers, not only to facilitate data processing but also to complete the CNC control function, can shorten the measurement time up to 95% or more.
The attached table compares the efficiency of CMM and traditional methods of measurement.
Coordinate measuring machine research status
The first CMM in the world was manufactured in 1959 in England. Nowadays, its application is quite common. According to the statistics of international professional consulting companies, the sales growth rate of CMM is about 7% 25%.
Developed countries have higher ownership, but the growth rate is decreasing yearly, about 7%~10 %; developing countries have lower ownership, but the growth rate is increasing, about 15%25 %.
There are more than 50 manufacturers of measuring machines worldwide, and there are more than 300 kinds of specifications.
General
Coordinate measuring machines are manufactured in many varieties, most of which have the function of scribing. Famous foreign manufacturers are Germany’s Zeiss Zeiss and Letiz Letiz, Italy’s DEA, the U.S. Brown—Sharp Brown & Sharp, Japan’s Mitutoyo Mitutoyo, and others.
In general, it has the following characteristics:
1 Most of the machines are cantilevered in overall layout, with good space openness, which is convenient for installing large parts or complete vehicles.
2 Adopting AutoCAD and limited element method to optimize the design, the structure is more reasonable and the shape is beautiful;
3 Strong specialized development force, more special software and accessories, can meet the special needs of more users;
4 Most of the moving parts are made of alloy aluminum, and the mass of moving parts is as small as possible to achieve high rigidity and low inertia;
5 Equipped with 21 items of error compensation software, which can cheaply improve the accuracy of the machine;
6 Equipped with 32-bit DSP continuous trajectory control system, which is a kind of data signal processor with better performance than CPU and is an ultra-large-scale integrated circuit. In addition to its high computing and control functions, it has internal storage of many high-level language programs that can be developed;
7 The vast majority of machines use Renishaw (UK) electric probes, which are fully functional and reliable;
8 Equipped with full-featured control measurement software, specialized and error correction software;
9 The performance of the machine is highly stable and reliable with long service life;
10 CMMs are networked with computer workstations and CNC machine tools;
11 CMM technology has developed rapidly over the past decade, especially the CNC system and measurement software are updated every two or three years;
12 Series of complete varieties, “three” (i.e. standardization, generalization, serialization) degree is high.
Coordinate Measuring Machine Future Development Trend
Advanced manufacturing technology, a variety of engineering projects, and the need for scientific experiments on the three-coordinate measuring machine constantly create new and higher requirements.
From the three coordinate measuring machine development and science and technology, production of three coordinate measuring machine requirements, in the next period of time, its main development trend can be summarized in the following aspects.
(1) Popularize high-speed measurement
Quality and efficiency have always been measures of the performance of various machines, the two main indicators of the production process. The traditional concept is to ensure measurement accuracy; measurement speed should not be too high.
As the pace of production continues to accelerate, users are demanding higher and higher measurement speeds from CMMs while ensuring measurement accuracy. Increasing the measuring speed of the CMM will bring innovations to the CMM in the following aspects.
Structural design improvements and material changes in CMMs, structural optimization to improve rigidity and reduce the mass of moving parts;
Optimizing geometry and material selection can improve measuring machines’ structural design. One key approach is to enhance rigidity while simultaneously reducing the mass of moving parts.
This can be achieved through structural optimization techniques that focus on reducing unnecessary weight without compromising performance. Using lightweight materials helps to lower motion inertia, leading to more responsive and efficient machine movement.
A significant change involves shifting from conventional materials, such as granite—which are commonly used—to alternative materials that offer a lower density ratio to Young’s modulus. This ensures better stiffness-to-weight performance.
Aluminum, ceramics, and synthetic materials are gaining more and more applications in measuring machines;
Dynamic compensation capability
High-speed dynamic performance requires improved dynamic compensation capability, and dynamic errors are related to the measuring machine’s structural parameters and motion protocols.
Based on the study of these characteristics, both the structural design of the measuring machine can be improved to improve the performance of the control system, and dynamic error compensation can be carried out to ensure high accuracy while realizing high-speed measurement;
Adoption of the non-contact probe measurement method
In the case of touch measurement, the contact speed between the workpiece and the probe can not be too large, which limits the measurement speed. The scanning measurement method is much more efficient than the point measurement method, but it is still limited by touch measurement.
The use of non-contact probe can avoid frequent acceleration, deceleration, collision, etc., greatly improving the measurement speed. Especially from the reliability and safety protection to put forward higher requirements, non-contact probe also has great superiority;
Offline programming technology becomes a trend
The so-called offline programming technology, that is, with the assistance of CAD technology, completes the preparation of the measurement program in cases where the measurement is not performed on a measuring machine, in a three-dimensional graphics environment.
This not only effectively improves the actual use of the measuring machine, but also improves the efficiency of the measurement program. Offline programming allows us to synchronize the measurement preparation with the production preparation and the production process, thus saving valuable CMM time.
(2) Application of New Materials and Technologies
To ensure reliable and high-speed measurement function, manufacturers attach great importance to the selection of raw materials for the machine body and have recently added new materials such as alloys, stone, and ceramics to traditional cast iron and cast steel.
Zeiss, Sheffield, Letiz, Ferranti (UK), DEA and other major CMM manufacturers in the world, most of the light weight, good rigidity, thermal conductivity of the alloy materials, to manufacture the measuring machine on the moving mechanism components.
Aluminum alloys, ceramic materials and various synthetic materials have been more and more widely used in CMMs.
Because of the good thermal conductivity of the new materials, when uneven temperature distribution occurs, thermal smoothness can be achieved quickly in a very short period, and thermal deformation caused by temperature changes can be minimized. For this reason, in recent years has given rise to the manufacturer’s reformulation of the climax, new varieties are emerging.
The progress of technical indicators in two aspects: A: the maximum operating speed of 15m / s or more; B: the ambient temperature requirements can be reduced to 20 ± 4 ℃.
Other new technologies, such as magnetic levitation, will also be used in measuring machines and other probes.
(3) Improvement of the control system
In modern manufacturing systems, the purpose of measurement is increasingly not limited to finished product acceptance inspection but to the entire manufacturing system. Measurement provides information about the manufacturing process and provides a basis for control.
The measuring machine must have an open control system with greater flexibility from this requirement. To this end, to take advantage of the rapid development of new electronic industrial technology, especially computers, the design of new high-performance / price ratio system.
In recent years, the price of computers has been decreasing, while their performance has improved. Suppose you use mass-produced, inexpensive, high-performance computer templates to design a special digital control system measuring machine. In that case, you can introduce a new, inexpensive, and high-performance measuring machine control system.
In addition, complex control systems can be compactly designed to reduce costs.
(4) Development of Measuring Machine Probes
In addition to the CMM’s mechanical body, the probe is the key to achieving high accuracy of the measuring machine and the CMM’s core. Compared with other technical indicators, improving the probe’s performance indicators is the most difficult task.
The ideal probe is the main performance indicator of the probe close to the parameters of the ability of the part: in the same accuracy indicators, the probe end of the probe body diameter D and the length of the probe rod L/D. The larger the value, the better its performance.
The solution to the ideal probe (L / D, accuracy higher than 0.1μm, trigger movement speed from 0.5mm / s to 80mm / s range) of the way will inevitably lead to the development of “solid sensor” technology, and the detection mode should be changed from “passive” perception to “active” detection. “Active” detection, otherwise, can not be resolved similarly to the piezoelectric probe, which has high sensitivity and low resistance to interference between the contradictions.
In addition, another important trend in measuring machine probes is that non-contact probes will be widely used. In the microelectronics industry, there are many two-dimensional patterns, such as large-scale integrated circuit masks, they are contact probe can not be measured.
In recent years, the development of optical coordinate measuring machines has been very rapid. Their core is non-contact measurement.
At the same time, a non-contact probe with high precision and a large range will be developed. It can be used for scanning measurement of the analog probe and can also reach into small holes. A specialized probe will also be developed to measure micro-parts.
Different types of probes used at the same time or alternatively, is also an important development direction.
(5) Innovation in software technology
The software mainly determines the function of the measuring machine. Coordinating measuring machine operation and ease of use also depends on the software. With every new technology development, there must be corresponding supporting software technology to keep up.
In order to incorporate the CMM into the production line, it is necessary to develop software with network communication, modeling, CAD, and reverse engineering;
According to the spline function, 12345 and other fitting, modeling and various simulation software is also developing.
In addition, we are accelerating the popularization of DMIS, a general-purpose measurement software, to facilitate data exchange with CAD/AM;
At the same time, improving the application of different types of workpieces in the development and use of specialized measurement software, and ultimately forming a software family based on the same platform for the development of measurement software has become an inevitable trend of software innovation.
It can be said that measuring machine software is one of the most rapidly developing technologies in CMM. The development of software will move the three-coordinate measuring machine in the direction of intelligent development. It will at least include the ability to carry out automatic programming according to the measurement task to optimize the measuring machine, automatic diagnosis of faults, and so on.