For large-scale CNC machine tools, during the machining process, due to the wear of the machine guide rails, the deformation of the force, the temperature field changes, and the influence of the interpolation error, the ideal motion curve of the tool holder will change, which will inevitably affect the contour of the contour shape of the part. error. The error separation technique EST (Error Separation Technique) facilitates the online measurement of the contour error of such parts. This paper discusses the application of error separation technology to real-time online measurement in large-scale CNC machine tools, which separates the tool holder motion curve error and the part contour curve error from the measurement results, and provides the basis for dynamic error compensation processing in CNC powerful cutting. 2 On-line measurement line profile error principle 2. 1 Error separation mathematical model When machining a workpiece with contour shape on a CNC machine tool, the tool holder motion path must follow the ideal contour curve. The workpiece is mounted, and the coordinate system shown in the figure is established. xoy is the measurement reference coordinate system, and x'oy is the measurement coordinate system. Let U(x) be the ideal motion curve function of the tool holder, V(x) is the ideal contour curve function of the part, R(x) is the actual motion curve function of the tool holder, and S(x) is the actual line contour curve function of the part, then the part The line profile error H(x) can be expressed as H(x)= S(x)- V(x)(1) The tool holder motion curve error h(x) can be expressed as h(x)= R(x) - U(x)(2) In the measurement, we are concerned with measuring the H(x), h(x) error, and mounting the three probes A, B, C on the head. The distance between the probes is l. 1, l 2, the measuring seat is installed on the CNC machine tool holder, the tool holder is driven by the CNC servo system and the two coordinates are linked, and the ideal contour motion curve is taken to measure the contour error of the part line. When the tool holder moves the distance x, the three probes A, B, and C have a set of output signals, which are set to A(x), B(x), C(x). Obviously, this set of output signals is a set of mixed signals. It contains the part line profile error H(x) and the tool holder motion curve error h(x). Preprocessing the sampled signal while considering the effect of removing the ideal line contour gradient value in the adjacent probe sample signal (this is considered in software), the following relationship can be used to find the line profile error H in the frequency domain ( n) A series of discrete values. Perform an inverse Fourier transform on H(n) to obtain the line profile error H(k)h(k)= A(k)- H(k)(16)r(k)≈ of the part in the time domain≈ < B(k)- H(k + m 1)- h(k)>/(m 1Δl)(17)2. 2 Simulation part line profile error curve set three sets of error signals H(k), h(k ), r(k), determine the relevant parameters according to the parameter selection conditions, and generate the probe analog output signals A(k), B(k), C(k) according to equations (9), (10), and (11). Then, according to the error separation formulas of (15), (16), and (17), the three sets of separated signals H'(k), h' are obtained by separating A(k), B(k), and C(k). k), r'(k), and compared with the set of three sets of error signals H(k), h(k), r(k). We performed error separation simulation on the 586 PC. The simulation results show that the three-point error separation technique is reliable for line profile error measurement. The contour line error curve of the part line shows that when the sampling length (l) is certain, the number of sampling points (N) and the sampling interval (Δl) are different, when the different parameters m 1 and m 2 are selected according to the parameter selection conditions, the error is separated. The part line contour error curve H(k), (the tool holder motion curve h(k) is slightly), the curve a is the ideal curve, the curve b is the set array H(k) error curve, and the curve c is the error separation The following array H'(k) error curve. It can be seen from the figure that the curve b and the curve c are different by one translation amount, but the error curve has the same shape and does not affect the line profile error evaluation result. The line profile error can be estimated by drawing method or analytical method (programming calculation), and the maximum difference Δy max and minimum difference Δy min of the corresponding point of the ideal ideal contour curve in each discrete point in the Y direction, the line profile error f = Δy max - Δy min, if necessary, the measured value can be converted to a numerical value perpendicular to the direction of the ideal profile (normal). 3 Measured results We used the measuring system as shown to measure a test piece on the CJ K630 economical CNC lathe. The tested piece is 1 300 mm long and the line profile is an arc with a radius of 4 120 mm. The convexity is 50 mm, the three probes are adjusted to the axial section of the test piece, and every 10 mm is sampled at a sampling length of 1 270 mm. The number of sampling points is 128, and the sampled discrete point error value is evaluated by the line profile error of 0. 095 mm. The measured results greatly improve the measurement accuracy and measurement efficiency compared with the sample detection. 4 Conclusion We have conducted in-depth research on the error separation technique applied to the measurement of straightness error. On this basis, the error separation technique is extended to the line profile error measurement. After the simulation study, we give the following tips: 1 The three-point error separation technique is reliable for line profile measurement and is suitable for online or offline measurements. However, line profile error measurement is different from straightness error measurement. It is more suitable for online measurement on CNC machine tools. 2 Measurement system parameter selection should meet the parameter selection conditions, otherwise harmonic loss will occur, affecting the accuracy of error separation, and even lead to errors. When the sampling length is constant, the more sampling points, the higher the measurement accuracy. In this paper, the error separation technique is applied to the measurement of line profile error, which is easy to be applied to the surface profile error measurement, and then the on-line measurement and compensation processing of the space surface on the three-axis NC machine tool. Provide the basis. (Finish) Anvil Cylinder,High Precise Anvil Cylinder,Hardened Anvil Cylinder,Durable Anvil Cylinder Jetfly High Precision Manufacturing Co.,Ltd , https://www.jetflytech.com
November 04, 2023