Abstract utilized in measuring the motion chain analysis machine to enhance the accuracy of the measured heart header; wherein while the internal error analysis to deal with the probe. Comparing the experimental data before and after compensation with the coordinate measuring machine, the results show that the compensation effect is good.
Keywords NC machine tool error compensation line detection
Application of Error compensation Technique for NC Machine
ToolsCompensating Technique for Improving On-line Inspecting Accuracy
Zhang Qing, et al
Abstract :The manufacture proceeding is of high integration and flexibility. It is emphasized how to percerve high efficiency of manufacture system and reduce the waste products. The technique of on-line ispection is one of the most important meanings for monitoring the cutting procedure. The Kinematics chain of on-line inspection is discussed, so as to enhance the positioning accuracy of the ballcenter of a probe, day, the system error of a probe is considered by means of the method of feature analysis. Compared the testing data with and without Compensation with measured data on CMM, the result shows that the compensative effect is good.
Key Words : On-line Instection, Error Compensation, NC Machine Tools
1 Overview
The quality monitoring of the processing process has always been the focus of people. How the manufacturing industry meets the challenges of the 21st century with low-cost, high-precision, flexible and flexible processing technology is also a concern. Quality monitoring is an important part of modern processing technology. As a machining process monitoring method, the on-machine probe can effectively monitor the installation and positioning of the workpiece, wear and tear of the tool, tool, and the dimension of the workpiece. The current research on measurement accuracy focuses on how to improve the accuracy of the probe system [5]. When the probe is used as an on-machine measurement tool, the coordinate accuracy of the machine tool directly affects the measurement accuracy. This article measures on the machine
Process machine tool kinematic chain analysis, and the characteristics analysis method to deal with the probe internal error, using software compensation method to improve the measurement accuracy.
2 Analysis of the kinematic chain during online testing
The kinematic chain of the on-line inspection process is similar to the machining process. The difference is that the tool is replaced with a probe. According to the analysis of machine tool geometric error compensation technology, the on-machine measurement system including the machine tool is extracted abstractly, and the topological structure of the machine tool is described in the form of a low sequence array, and the basic transformation (including the position transformation matrix and displacement transformation matrix) is performed by the adjacent body. , in the form of (where: c = cos, s = sin; αk, βk, γk are relative azimuths between the coordinate systems)
The positioning error model for calculating the probe ball center is:
In the formula: 
Representation of multi-body systems with low sequence 
It is the coordinate value of the probe center with respect to the tool coordinate system.
The error parameters in the basic transformation are mainly the geometric errors of the machine tool and are obtained by the parameter identification method (which can also be directly measured by the dual-frequency laser distance meter) [6].
3 Based on feature probe error processing technology
The basic elements measured by the machine probe are points, lines, and surfaces, which form the measurement of the dimension of the shape. During the measurement process, the probe ball position reflected by the coordinates of the machine tool, when processing and compensating the probe error, is based on the normal direction of the measurement point, and the influencing factor for the probe accuracy is obtained—pre-travel error (dead zone) Error). Other error terms such as dynamic error, repeatability, etc., have their effects reduced by multiple measurements.
3.1 Measurement Types 1) Basic measurements: Mainly include points, lines, straight line distances and coordinate systems.
2) Simple combination measurement: mainly includes keyway, step, rectangular hole, center and diameter, ellipse, sector, and angle.
3) Basic spatial measurement:
Ball Centers and Ellipticity Cylinders with Different Heights Roundness, Center Coordinate Cone Height, Bus Measurement Curve Measurement Plane Curve Measurement Space Curve Measurements Measured on a Grid
3.2 characterization <br> geometric features: concave, convex.
Location features:
Direction X,Y,Z
Base planes XY, YZ, ZX, XYZ
3.3 Measurement and error processing techniques (1) Measurement process The following is a program segment for measuring a point in the Z direction:
G31 G91 Z-10.F30; (Measured at a speed of 30 mm/min, previously the tool was positioned above the probe)
G31 G91 Z10. F600; (Cutting up)
G28 G91 Z0; (Tool return reference point)
G01 P10; (pause)
#12=#4014;(Get current coordinate system number)
#100=#5063; (Z coordinate at read trigger)
#101=#[2700+#12]+#100;(convert trigger coordinates to machine coordinates)
#102=#101-#506;(calculate tool length measurement)
#2010=#102;(Send the length of the knife to the specified knife number: 10)
(Program tail)
(2) Processing It can be seen from Fig. 1 that for different geometrical features, the same coordinates and diameter of the circle center are measured, and the measurement path and the triggering direction of the probe are inconsistent.
For the measurement of regular shapes, the specific processing flow is shown in Figure 2. The measurement of the space surface can also be handled in a similar manner, but mechanically triggered measurement systems are less efficient and analog probes are recommended.
4 Online detection error compensation experiment
This experiment adopts the standard test piece for machine tools (Figure 3).
It was realized on the MAKINO FANUC86-A20 three-coordinate vertical machining center. Renishaw MP3 mechanical triggering heads are used, in which the pre-travel error of the probe is shown in Table 1. Through the RS232C port NC system and the computer connection, measurement data in
Post processing on the microcomputer. The test piece was verified on the MITUTOYO-BLN231 CMM with a PH6 touch probe. There are no compensation, coordinate and probe error compensation, and coordinate measurement results of the coordinate measuring machine are shown in Table 2. From the measurement results, through the error compensation, the measurement accuracy has been significantly improved, close to the three-coordinate measurement results.
Table 1 Pre-travel error with 50mm probe length
Angle (°) 0 30 60 90 120 150 180 210 240 270 300 330 Error value (μm) 17 25 29 19 21 22 16 8 5 15 23 21Table 2 Test results of basic dimensions of standard test pieces under different conditions
Dimensions (mm) A B H D Measurement results without compensation 213.901 123.808 14.934 245.220 Measured results after coordinate and probe error compensation 213.920 123.839 14.945 245.247 Measured results for CMM 213.922 123.841 14.946 245.2505 Conclusion
With the continuous deepening of the application of computer integration technology in the machinery manufacturing industry, mechanical manufacturing has evolved from labor-intensive to technology-intensive. On-line inspection technology has replaced manual measurement and has become an important monitoring tool in the processing process. The low cost and high reliability of the mechanical triggering probe are accepted by the majority of users and there are many suppliers in China. This article focuses on the on-machine measurement error processing method, the use of software compensation method to improve the measurement accuracy, through the comparison of the experimental data before and after compensation with the three coordinate measuring machine, indicating that the compensation effect is good. This method has certain universality and is suitable for other types of probe error processing.
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