- Detail

Using laser vector technology to measure and compensate three-dimensional spatial positioning errors

Abstract

in response to the competition in today's global manufacturing market, we need to rely on machine tools with higher accuracy and better quality. Therefore, it is not enough to only verify and compensate the three displacement errors (pitch errors). If the spatial positioning accuracy can be measured, all three displacement errors Six straightness errors and three verticality errors can be measured and compensated

in recent years, Optronics has developed a laser vector measurement technology for spatial errors including three displacement errors, six straightness errors and three perpendicularity errors. The whole measurement takes only a few hours, replacing the traditional measurement that takes several days. Using laser vector measurement technology, the spatial positioning error has been measured on the vertical machining center equipped with FANUC 18m controller model fv-1000 in Yawei. Without any compensation, the space error is 110mm, under the condition of pitch error compensation, the space error is 95mm, and under the condition of space compensation, the space error is 12.5mm, which is an improvement of 900%. The operation principle, hardware architecture, data acquisition and processing and some test results of this technology will be discussed in this article

i. introduction

cnc machine tools can measure the performance or accuracy of CNC machine tools from the spatial positioning accuracy including linear displacement error, straightness error, angle error and elastic error. However, the measurement of these errors is quite complex and time-consuming. At present, ceramic matrix composites have exceeded metal heat-resistant materials in withstanding high temperatures. For these reasons, some international standards such as ISO and ASME b5.54[1] recommend using body Diagonal displacement measurement for rapid inspection of spatial performance. This is because the body diagonal is quite sensitive to all error components, so when the error exceeds the specification, There is not enough data to identify the error source and make compensation

in recent years, a new laser vector technology [2,3] developed by photodynamic company can be used to measure these spatial errors including three displacement errors, six straightness errors and three perpendicularity errors with laser displacement gauge (LDDM). Using this laser vector measurement technology, relevant data have been measured in the vertical cutting center of Yawei model fv-1000

II. Body Diagonal displacement measurement

the body Diagonal displacement measurement method is suggested to be used for machine positioning and rapid verification of geometric accuracy. In short, it is similar to laser linear displacement measurement, which replaces the direction of the laser beam in the axial direction, but points in the diagonal direction of the body. Fix the reflector on the main shaft, and move the main shaft along the diagonal direction of the body, starting from the zero point position, and make the three axes move to the new position in increments along the diagonal direction, then the displacement error can be measured. The accuracy of any position along the diagonal is determined by the positioning accuracy of the three axes, which includes straightness error, angle error and Perpendicularity Error. Therefore, volume Diagonal displacement measurement is a good method for machine verification, but there is not enough information to identify the error source

iii. vector or segmented diagonal measurement

the new vector measurement method or segmented diagonal measurement method is different from the traditional method, because each axis moves separately, and the positioning error is to do cold and hot shock tests on x-axis, Y-axis and z-axis each time. The original microcomputer large liquid crystal LCD (320*240dots) Chinese and English display control system is adopted to collect after moving. For this reason, more than three times of data can be collected, At the same time, the positioning error can be separated because each axis moves separately. These collected data can be treated as the projection of the displacement of each axis along the diagonal

in general body Diagonal displacement measurement, the target track is a straight line, and the angular square mirror is used as the target, so only small lateral displacement can be allowed. In the vector method, move along the X axis, Y axis and Z axis respectively, and repeat these actions until the opposite endpoint of the diagonal. The laser interferometer is a single beam laser with a plane mirror as the target. It is noted that when the plane mirror is used as the target and the parallel plane mirror is moved, the laser beam will not be blocked and the distance from the light source will not be changed, so the measurement will not be affected. Therefore, the movement of the laser direction can be measured and a large target lateral movement can be allowed

iv. measurement on Yawei machine

measurement is carried out on the vertical cutting center of Yawei model fv-1000. Fv-1000 is a thick steel structure with reinforcing ribs designed for high-speed mold processing, which provides better rigidity of the machine and prevents any bending or torsion that may affect the accuracy of cutting. The door post is integrally formed and cast, which can meet the greater cutting performance and absorb vibration. The door post is locked on the top of the bed to ensure the adjustment and perpendicularity of the best accuracy, and can meet the maximum rigidity. The working space of the machine is 1050mm multiplied by 600mm multiplied by 540mm. The controller sets the test coefficient for F, such as time and speed. Start the experiment anuc 18m

v. laser vector method, measurement and compensation

1 Laser measurement system

the laser calibration system is laser Doppler displacement gauge (LDDM), which is manufactured by American optodynamics company and the model is mcv-500. It is a new generation of single beam laser interferometer using Doppler effect. This system has an adjusting mirror, which is easy to control the laser beam to the diagonal direction

the target at the moving part of the machine is a 75 × 100mm flat mirror, air temperature and pressure can be measured and can compensate for the heat of the machine. The fatigue test of parts should be carried out in the force control mode, including expansion, automatic data collection, error analysis and automatic generation of compensation table, which are all implemented on the window software of LDDM version 2.50 of optical dynamics company

2. Erection and adjustment

using the laser vector method, the machine can measure along the diagonal of four bodies. The laser head is fixed on the machine table, and the adjusting mirror is used to adjust the laser beam to make it parallel to the diagonal. The plane mirror is fixed on the spindle, and its surface is perpendicular to the laser beam. As shown in Figure 1, the machine can design a workpiece program to make the spindle move from the starting endpoint to the relative endpoint

the appearance of Yawei vertical cutting center and the sectional diagonal measurement and erection photos of laser on the bed and plane mirror on the spindle

3 Collection and analysis of spatial error data

the measurement data will be automatically collected by LDDM window software after each machine stop or each single axis move. The error data will be analyzed by LDDM software, and the error of each axis will be automatically calculated. The application of these errors can also automatically generate an error compensation table. In this test, the machine does not have any error compensation, has pitch error compensation These measurements with spatial error compensation will be collected

4. Measurement result

the body Diagonal displacement error of the machine without any compensation is shown in Figure 2, in which the direction of the diagonal is represented by the positive or negative increment of the diagonal

the total error of four body Diagonal displacement errors without any compensation is 110mm

the maximum Diagonal displacement error measured by the machine without any compensation is 110mm. Similarly, the body Diagonal displacement error of the machine with pitch error compensation is shown in Figure 3. Here, the maximum displacement error is 95mm, and the improvement rate is 15%. While the body Diagonal displacement error of the machine with spatial error compensation is shown in Figure 4, The maximum displacement error is 12.5mm, and the improvement rate is 900%

the total Diagonal displacement error of four bodies with pitch error compensation is 95mm, with only a small improvement

the total Diagonal displacement error of four bodies with spatial error compensation is 12.5mm, with an improvement of 900%

vi. discussion and summary

summary as mentioned above, we have completed vector measurement and spatial compensation on the vertical cutting center of Yawei, and the spatial positioning accuracy of the vertical cutting center of Yawei can be improved by more than 900%. It can be noted here that if only pitch error compensation is performed, it will only be improved by 15%. Therefore, only pitch error compensation is not enough, and it is relatively important to be able to compensate pitch error and straightness error at the same time

in addition, the laser vector measurement takes only 2 to 4 hours, which greatly replaces the time that the general laser interferometer takes 20 to 40 hours to measure. The laser erection is quite simple, and the data can be collected automatically. The data processing and compensation file generation are automatic, eliminating manual operation and reducing errors. Therefore, there is no need for experienced engineers, and the machine operator can operate the laser calibration and verification after receiving training

references

[1] "methods for performance evaluation of computer numerically controlled machining centers" an American national standard, ASME b5 by the American Society of Mechanical Engineers, p69, 1992.

[2] C. Wang, “ Laser Vector measurement Technique for the determination and compensation of volumetric positioning errors. Part I: Basic theory”, Review of Scientific Instruments, Vol. 71, No 10, pp , October 2000.

[3] J. Jenecko, B. Griffin and C. Wang, “Laser Vector Measurement Technique for the determination and compensation of volumetric positioning errors. Part II: Experimental verification”, Review of Scientific Instruments, Vol. 71, No. 10, pp., October 2000. (end)

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