The application of newer three-dimensional space error compensation technology for CNC machine tools Newmaker has long used space precision compensation technology in three-coordinate measuring machines to ensure its high accuracy as a measuring instrument, and its mechanical manufacturing and electrical debugging The accuracy is difficult to meet the relevant requirements. The general coordinate measuring machine is compensated so that it can meet the needs of high-precision measurement. With the continuous development of CNC machine tool technology, the requirements for the accuracy of machine tools are also increasing. The accuracy of existing machine tools is only taken into consideration in mechanical design and hardware manufacturing, and has become a widely used Renishaw company that has been a leader in measurement technology in the industry of the CMM industry, and it is also implementing its coordinate measuring machine UCC controller. More than 10 years after the successful application of “Spatial Error Compensation Technology”, the “Space Error Compensation Technology” has recently been introduced for CNC systems such as Fanuc and Siemens. Based on Renishaw's mature XL-80 laser interferometer (shown in Fig. 1) and QC-20 ballbar meter as the testing basis, two RVC-Fanuc and RVC-Siemens spatial error correction software were introduced to the market. Three-dimensional space compensation options use machining centers, CNC boring and milling machines and gantry machines from Fanuc or Siemens CNC systems to improve their spatial accuracy. The actual feedback from the current users indicates that the RVC software is flexible and easy to use on the relevant CNC machine tools. The bottleneck encountered. The space precision compensation technology of the coordinate measuring machine is introduced into the numerical control machine tool, and the key problem of the accuracy improvement of the numerical control machine tool can be successfully solved.
Compensation principle 1 The 21 common errors in the geometric accuracy of CNC machine tools are in the three-axis movement space of the machine tool. There are 9 translation error parameters, 9 angular error parameters and 3 vertical error parameters, and a total of 21 errors. To completely eliminate the effect of 21 errors on the spatial position of the machine, it is necessary to accurately detect each error and research and develop related software to convert the detected error data into parameters that can be accepted by the CNC system with corresponding functions. Provides system compensation results to improve machine tool space accuracy. In the actual situation, the error cause of a machine tool is the result of the superposition of multiple errors. Obviously, a single error measurement cannot completely improve the geometric accuracy of the machine tool, especially the precision in all directions within the working area of the entire machine. 2 The new function of the numerical control system uses the space precision compensation method to revise the error produced when the numerical control machine tool works. As mentioned before, the early 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 internationally renowned CNC system manufacturers, such as Siemens and Fanuc, support this spatial accuracy compensation method (three-dimensional error compensation or VCS) in their high-end numerical control systems. Using this method can generate the entire working space of the machine tool. The error parameters to fully compensate for deviations in the geometric accuracy of the machine tool during operation, thus real-time correction of the existing space positioning error of the machine tool. 3 Development Trends at Home and Abroad Several years ago, after the high-end numerical control systems Siemens 840Dsl (called VCS) and Fanuc 31i (called three-dimensional error compensation) with space precision compensation functions were introduced to the market, foreign manufacturers of high-end CNC machine tools began to study Spatial accuracy measurement and error compensation parameter calculation method, and a small amount of research results were published. From the available published data, there are laser tracking and measurement methods used to measure the error of each spatial positioning point of the machine tool in different parts of the machine tool, and use a certain mathematical model to separate error sources; there are also other measuring tools such as laser interferometer and ball bar instrument. , according to the 21 item error detection method. The use of laser interferometers to test various error sources is a common practice at home and abroad. Its test results are all traceable to the accuracy, and it is possible to measure and calibrate the accuracy of the machine tools by one item, whether the measurements are correct, stable and reliable, and convenient. Check the effect of space compensation at any time. The most widely used British XL-80 laser interferometer on the market also has an open software interface that allows users to research and develop their own software. Application examples are shown in Figure 2.
The software XL-80 laser interferometer for space error compensation required for Fanuc 31i and Siemens 840D 1 Measurement equipment XL-80 laser interferometer: Measure linear displacement, straightness, pitch angle, torsion angle, etc., respectively, to provide necessary calculation compensation parameters for RVC software Required error data file. QC20-W ball bar: Measure the verticality between axes; and provide directional error diagnosis of machine tool electrical equipment and mechanical error. RX10 turntable (optional): Measure and provide rotation angle accuracy measurement and compensation for the rotary table. Electronic level meter, etc.: Measuring machine roll and other parameters. 2 The correction software for spatial error correction software Fanuc 3D space compensation is RVC-Fanuc, and the correction software for Siemens is RVC-Siemens. RVC software has the following three functions, each of which can perform compensation for different items for the machine under test: normal linear error compensation, three-dimensional spatial error compensation (linear displacement, straightness, angle), and three-axis perpendicularity error compensation. 3 The numerical control system and the corresponding space compensation function select the accessory Fanuc 3D Compensation function and Siemens VCS function. Among them, 840D sl1.3 or later requires the correct ELF file to be loaded; RVC-Siemens developed by Renishaw is suitable for "VCSplus", "VCS A3" and "VCS A5". To perform the compensation function, take the following steps: • Collect measurement data in the workspace of the machine, evaluate the deviation parameters and save them as data files; • Copy the files into the CNC system subdirectory "Manufact.Cycles" (\CMA) Medium; • Use GUD-variables to activate compensation; • The system calculates the compensation result in real time and offsets its write position according to the actual MCS position of the three geometry axes. 4 Before the space compensation, the basic condition of the machine tool is required to evaluate the comprehensive accuracy of the machine before using the space error compensation. If the machine tool has large electrical errors such as reverse leaping and servo mismatch, then Even if spatial error compensation is performed, the machining accuracy of the machine tool is not improved much. It is particularly necessary to adjust the error of the machine tool to a secondary accuracy before performing spatial error compensation (see the QC20-W ballbar instruction for the evaluation of the machine's overall accuracy). Even if the machine tool with poor repeatability performs spatial error compensation, the compensation effect is not obvious. For numerically-controlled machine tools with an accuracy requirement of up to about 5 μm, it is recommended that the environment for use of the CNC machine should be determined in accordance with the environment in which the coordinate measuring machine is used. Otherwise, in the long-term, the accuracy of the machine tool itself due to environmental changes will be changed to some extent. Reduce the effect of spatial error compensation. Application Case of RVC Spatial Error Correction Software 1 RVC-Fanuc software uses three-dimensional spatial error of Renishaw RVC spatial error correction software on a Fanuc Robodrill machine equipped with Fanuc 31i used by a company in the UK for daily production. Compensation, and according to the ISO230-4 "CNC Machine Tool Circle Test" standard, using a ball bar to verify and compare the roundness in the XY plane before and after the compensation of the machine tool, the roundness error is reduced from 9.1μm to 5.7μm . In the newly-built Fanuc 31i CNC coordinate boring machine of a machine tool research institute in Beijing, the QL20-W ball bar instrument was used to test the accuracy of the machine tool. Before the 3D space error compensation, the verticality XWY of the XY plane was 24.9 μm/m. The overall roundness is 11.5 μm. With 3D spatial error compensation parameters and verticality compensation parameters added to make the compensation effective, the verticality error XWY is 2μm/m; the overall roundness error is 5.2μm to 6.6μm (including repeatability errors with multiple measurements). In order to explain the details of the space error compensation of the machine tool, the Y axis is taken as an example. The accuracy test and the compensation effect of the machine are described in detail as follows: The Y-axis motion of the machine tool has a maximum Y 〃;Y-axis Y-axis pitch error YRZ up to 9〃; X-500 Z-791.235 position (that is, spindle end) Y-axis positioning accuracy YTY is measured, the error is about 14μm. The Y-axis positioning accuracy is measured at a distance of 450 mm from the spindle. The error YTY is approximately 12 μm. However, apparently due to the influence of the Y-axis of the machine tool on the angular error in the X-axis, the Y-axis positioning accuracy is also measured at different positions from the spindle end face. The accuracy curve is very different. After three-dimensional space compensation of the Y-axis straightness YTZ in the Y-axis direction, the compensation effect is immediately verified. 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). About ±1μm), the compensation effect is obvious.
2 The RVC-Siemens software was applied to the Flymill 1000 gantry machine equipped with Siemens 840D in Breton, Italy. XL-80 laser interferometer and ball bar were used to measure various geometrical accuracy and complete VCS spatial error compensation. The comparison of the results before and after the compensation is shown in Fig. 4: The most obvious improvement in the top three positions is that X-axis positioning accuracy XTX is reduced from 68μm to 2μm; Z-axis straightness error in Y direction is reduced from 18μm to 3.7 Μm; the X-axis straightness error in the Z direction decreases from 15 μm to 1.1 μm. For the above measurements and VCS compensation, the spatial accuracy is improved by using spatially-adjusted linear positioning accuracy. For example, in the absence of space compensation, the position errors at high, medium, and low positions in a space are 5.8 μm, 3.9 μm, and 8.0 μm, respectively; and after VCS spatial error is measured with an XL-80 laser interferometer and a ballbar. The position errors at the high, middle, and low positions were 2.7 μm, 1.9 μm, and 2.1 μm, respectively. The overall positional accuracy of the visible space has improved after the entry into force of the VCS and has been consistent. The roundness of the ISO230-4 ballbar test has also been improved by 25%. A Siemens 840D equipped Huron machine was tested in 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. The XY verticality XWY is increased from -9.8 到 to -0.1 〃. At the same time, the linearity and angle compensation results are also good. The personnel involved in the test commented that the use of Renishaw ballbars and XL-80 laser interferometers is much faster than other similar products because Renishaw's products are more convenient to use. According to the comparison before and after the compensation of the linear positioning accuracy of the Y-axis according to ISO 230-2, the blue curve is the post-compensation error (as shown in Fig. 5). The roundness accuracy of the ballbar test according to ISO 230-4 increased by nearly 40% (see Figure 6).
Conclusion In view of the difference between the three-axis geometric accuracy compensation technology of numerical control machine tools and the rotary axis compensation technology of five-axis machine tools (rotary axis compensation requires additional options and additional testing methods of the numerical control system), according to the needs of most users, the current RVC software is mainly aimed at It is the spatial error compensation of the three-axis machine tool. Current users' opinions in the test application: (1) Based on the test feedback of multiple customers, the XL-80 laser interferometer and QC20-W ballbar meter are used for spatial error compensation testing, as they can be conveniently Each error of the machine tool is tested and the compensation effect is quickly verified. It is also possible to selectively select only some of the key error items to compensate. Therefore, under the premise of ensuring accuracy, a selective compensation method can also be used to save time. (2) Using the ML10/XL80 laser interferometer to test the linear displacement, straightness, and angle error item by item, it is easy to trace the source of error and to easily determine the direction of error. (3) The QC20-W wireless ball bar instrument is used to test the three planes of the machine XY, YZ and ZX in one installation, and the verticality can be measured and compensated quickly. (4) Test results prove that Renishaw's RVC software performs three-dimensional error compensation on the machine tools of Fanuc 31i and Siemens 840D sl, laser interferometers are used according to ISO 230-2, and/or clubs are used according to ISO 230-4 Instrument validation, the effect is obvious before and after compensation.
