The application of three-dimensional space error compensation technology for CNC machine tools has been used for a long time since the space precision compensation technology has been applied to the coordinate measuring machine to ensure the high precision of the coordinate measuring machine as a measuring instrument, and its mechanical manufacturing and electrical debugging The accuracy is difficult to meet the relevant requirements. Generally, the CMM is compensated to meet the needs of high-precision measurement. With the continuous development of CNC machine tools, the requirements for machine tool accuracy are getting higher and higher. The existing machine tool precision is considered from the mechanical design and hardware manufacturing, and it has become a common leader in the industry. It is the pioneer of measurement technology in the CMM industry. Renishaw is in the UCC controller of its coordinate measuring machine. After more than ten years of successful application of "space error compensation technology", the "space error compensation technology" has been newly introduced for numerical control systems such as Fanuc and Siemens. Based on Renishaw's mature XL-80 laser interferometer (shown in Figure 1) and QC-20 ballbar as the basis for testing, RVC-Fanuc and RVC-Siemens two sets of spatial error correction software were introduced to the market to match The 3D space compensation option uses the machining center of the Fanuc or Siemens CNC system, CNC boring and milling and gantry machines to improve its spatial accuracy. The feedback from the actual user use shows that the RVC software is flexible, simple and effective on the relevant CNC machine tools. The bottleneck encountered. The introduction of the space precision compensation technology of the CMM into the CNC machine tool can successfully solve the key problems of improving the accuracy of the CNC machine tool.

Compensation principle 1 The common 21 error of CNC machine geometry accuracy In the three-axis moving space of the machine tool, there are 9 translation error parameters, 9 angle error parameters and 3 verticality error parameters, totaling 21 errors. To completely eliminate the influence of 21 errors on the position of the machine space, it is necessary to accurately detect the errors and research and develop the software to convert the detected error data into parameters acceptable to the CNC system with corresponding functions. Provides system compensation results to improve machine space accuracy. In the actual situation, the error of one machine tool will be the result of the superposition of multiple errors. The single error measurement obviously cannot completely improve the geometric accuracy of the machine tool, especially the accuracy of each direction in the working area of ​​the whole machine. 2 The new function of the numerical control system uses the space precision compensation method to correct the error caused by the operation of the CNC machine. As mentioned above, the previous stage has been proved to be one of the effective methods to reduce the positioning error of the machine tool in the 3D measuring machine industry. At present, many well-known CNC system manufacturers in the world, such as Siemens and Fanuc, support this method of spatial precision compensation (3D error compensation or VCS) in their high-end CNC systems. This method can be used to generate the entire workspace of the machine tool. The error parameters are used to fully compensate for the deviation of the geometrical accuracy of the machine tool during operation, so as to correct the existing spatial positioning error of the machine tool in real time. 3 Development trends at home and abroad A few years ago, when the high-end CNC systems with space accuracy compensation function, Siemens 840Dsl (called VCS) and Fanuc 31i (called 3D error compensation), were introduced to the market, foreign manufacturers of high-end CNC machine tools began to research related. Spatial accuracy measurement and error compensation parameter calculation methods, and a small number of research results are published. From the existing published data, there are laser tracking measurement methods, which measure the spatial positioning point error of the machine tool in different parts of the machine tool, and separate the error source with a certain mathematical model; also use other measuring tools such as laser interferometer and ball bar instrument. , according to the 21-item error-by-item detection method. The use of laser interferometer to test various error sources is a common method at home and abroad. The test results are accurate and traceable. It can measure and check whether the accuracy of the machine tool is accurate, stable and reliable. Check the space compensation effect at any time. The UK's most popular British XL-80 laser interferometer also has an open software interface that allows users to research and develop their own software. An application example is shown in Figure 2.

Software and hardware equipment for space error compensation for Fanuc 31i and Siemens 840D 1 Detecting equipment XL-80 laser interferometer: measuring linear displacement, straightness, pitch angle, torsion angle, etc., respectively, to provide the required calculation compensation parameters for RVC software Required error data file. QC20-W ball bar meter: measure the verticality between each axis; and provide directional diagnosis of machine tool electrical error and mechanical error. RX10 turntable (optional): Measure and provide measurement and compensation of the corner accuracy of the rotary table. Electronic level, etc.: Measure parameters such as machine roll. 2 The spatial error correction software Fanuc 3D space compensation corresponding correction software is RVC-Fanuc, and the corresponding correction software for Siemens is RVC-Siemens. The RVC software has the following three functions, each of which can compensate for different items of the machine under test: common linear error compensation, three-dimensional spatial error compensation (linear displacement, straightness, angle) and triaxial vertical error compensation. 3 The CNC system and the corresponding space compensation function select the accessory Fanuc 3D Compensation function and the Siemens VCS function. Among them 840D sl1.3 or newer, you need to load the correct ELF file; RVC-Siemens developed by Renishaw is suitable for "VCSplus", "VCS A3" and "VCS A5". The following steps are taken to perform the compensation function: • Collect measurement data in the machine workspace, evaluate the deviation parameters and save them as data files; • Copy the files into the CNC system subdirectory “Manufact.Cycles” (CMA) ; Use GUD-variable to activate compensation; • The system calculates the compensation result in real time and offsets it to the position according to the actual MCS position of the three geometric axes. 4 Requirements for the basic condition of the machine before the space compensation Before the spatial error compensation, it is best to use the ball bar to evaluate the comprehensive precision of the machine. If the machine has large electrical errors such as reverse jump and servo mismatch, then Even if the spatial error compensation is performed, the machining accuracy of the machine tool is not improved much. It is especially necessary to adjust the machine tool electrical error to the secondary accuracy before the spatial error compensation (see the QC20-W ballbar instruction manual for the evaluation of the machine's comprehensive accuracy). Even if the machine with poor repeatability is compensated for spatial error, the compensation effect is not obvious. For CNC machine tools with an accuracy requirement of up to 5μm, it is recommended that the environment in which they are used should be in accordance with the environment in which the CMM is used. Otherwise, the accuracy of the machine itself due to environmental changes will be to some extent in the long run. Reduce the effect of spatial error compensation. Application case of RVC spatial error correction software 1 RVC-Fanuc software application On the Fanuc Robodrill machine equipped with Fanuc 31i used by a British company in daily production, the machine is subjected to three-dimensional error using Renishaw RVC spatial error correction software. Compensation, and according to ISO230-4 "CNC machine circle inspection" standard, the ballbar instrument is used to verify and compare the roundness in the XY plane before compensation and the compensation is effective. The roundness error is reduced from 9.1μm to 5.7μm. . The machine was subjected to a comprehensive precision test on the Fanuc 31i CNC coordinate boring machine recently produced by a machine tool research institute in Beijing. Before the 3D spatial error compensation, the verticality XWY of the XY plane was 24.9 μm/m. The overall roundness is 11.5 μm. When the 3D spatial error compensation parameter and the verticality compensation parameter are added and the compensation is validated, the verticality error XWY is 2 μm/m; the comprehensive roundness error is 5.2 μm to 6.6 μm (including the repeatability error of multiple measurements). In order to explain the details of the machine's spatial error compensation, the Y-axis is taken as an example. The accuracy test and compensation effect of the machine tool are described in detail as follows: The Y-axis of the machine's Y-axis motion in the X direction is up to 12 〃; the Y-axis pitch error YRZ of the Y-axis is up to 9〃; the Y-axis positioning accuracy YTY is measured at the X-500 Z-791.235 position (ie, the spindle end) with an error of approximately 14μm. The positional accuracy of the Y-axis is measured at a position of 450 mm from the spindle. The error YTY is about 12 μm. Obviously, due to the influence of the angular error of the Y-axis of the machine tool in the X direction, the Y-axis positioning accuracy is also measured at different positions from the end face of the spindle. The accuracy curves vary widely. After three-dimensional compensation of the straightness YTZ in the Z-direction of the Y-axis, the compensation effect is verified immediately, as shown in Fig. 3. Blue is the pre-compensation trend curve (error bandwidth is about 7 μm), and the green curve is the compensated curve (error bandwidth). For about ±1μm), the compensation effect is obvious.

2 The RVC-Siemens software is used on the Flymill 1000 gantry machine equipped with the Siemens 840D from Breton, Italy. The XL-80 laser interferometer and ballbar are used to measure the geometric accuracy and complete the VCS spatial error compensation. The comparison of the results before and after compensation is shown in Figure 4: the most significant improvement in the top three is the X-axis positioning accuracy error XTX reduced from 68μm to 2μm; the Z-axis straightness error ZTY in the Y direction is reduced from 18μm to 3.7 Μm ; the straightness error XTZ of the X-axis in the Z direction is reduced from 15 μm to 1.1 μm. For the above measurement and VCS compensation, the method of measuring linear positioning accuracy in multiple places is used to verify the conclusion that the spatial precision is improved overall. For example, before the spatial compensation is performed, the position errors of the high, medium, and low positions in a space are 5.8 μm, 3.9 μm, and 8.0 μm, respectively, and after the VCS spatial error is performed with the XL-80 laser interferometer and the ball bar. The positional errors at the high, middle, and low positions are 2.7 μm, 1.9 μm, and 2.1 μm, respectively. The overall positional accuracy of the visible space has improved and become consistent after the VCS takes effect, and the ISO230-4 ballbar test roundness has also increased by 25%. A Huron machine equipped with the Siemens 840D was tested at the Siemens Technology Center in Erlangen, Germany. Tests have shown that the RVCSiemens software and the VCS function of the Siemens system are fully effective on the machine. The verticality compensation effect is particularly noticeable, and the XY perpendicularity XWY is increased from -9.8〃 to -0.1〃; the linear and angle compensation results are also good. The people involved in the test commented that the Renishaw ballbar and the XL-80 laser interferometer are much faster than other similar products, because it is more convenient to see Renishaw's products from the installation and use of the instrument. Before and after the compensation of the linear positioning accuracy of the Y axis according to ISO230-2, the blue curve is the error after compensation (as shown in Figure 5). The roundness accuracy of the ballbar test according to ISO230-4 is increased by nearly 40% (see Figure 6).

Conclusion In view of the difference between the three-axis geometric precision compensation technology of CNC machine tools and the rotary axis compensation technology in five-axis machine tools (rotary axis compensation requires additional options and additional test methods for the CNC system), according to the needs of most users, the current RVC software is mainly targeted at It is the spatial error compensation of the three-axis machine tool. At present, the user has several views in the test application: (1) According to the test feedback of multiple customers, the spatial error compensation test is performed by using XL-80 laser interferometer and QC20-W ballbar instrument, because it can be conveniently and separately The various errors of the machine tool are tested and the compensation effect is quickly verified. It is also possible to selectively select only some of the key error terms to compensate, so that the method of selective compensation can also be used to save time under the premise of ensuring accuracy. (2) Linear displacement, straightness, and angular error are tested item by item with ML10/XL80 laser interferometer. It is easy to trace the error and facilitate the judgment of error direction. (3) Using the QC20-W wireless ballbar tester, the machine can be tested on the XY, YZ and ZX planes in one installation, and the verticality can be measured and compensated quickly. (4) The test results prove that the machine tools of Fanuc 31i and Siemens 840D sl are compensated by three-dimensional error with Renishaw's RVC software, by using laser interferometer according to ISO230-2 or / and by ISO230-4 The instrument verification, the effect before and after compensation is obvious.

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