Accuracy Of CNC Machine Tools Research Articles

An Improvement Geometric Error Identification Method of CNC Machine Tool Based on Double Ball Bar

The double ball bar is widely used because it can quickly, easily and cost-effectively detect and evaluate the accuracy of CNC machine tools. But since the error recognition algorithm based on the double ball bar ignores the quadratic item, its recognition accuracy would be reduced. In this paper, an improved CNC verticality error and position error identification formula, combined with the machine tool error model to deduce a new error recognition model of double ball bar measurement is proposed. It can be drawn that the accuracy of the model are better than the existing methods because it keeps the second item in the derivation process of the model.

Error Source Identification of Machining Accuracy of Five-Axis Linkage CNC Machine Tools

The error sources of machining accuracy of CNC machine tools including geometric error, thermal error, system error and error of load control etc. The error source affect the relative position of the cutting tool and the workpiece by the dynamic motion, and then affect the machining accuracy of the workpiece. By trial cutting method, "S" test part is a new test part for detecting machining accuracy of five-axis linkage machine tools. Through experiment and simulation, identification of the error source of the machining accuracy and the regular of "S" test part surface errors, surface quality, results show that "S" test part can reflect the machining accuracy of CNC machine tool.

Research of On-Line Monitoring Technology of Machining Accuracy of CNC Machine Tools

This paper analyzes CNC machine tools machining error sources, put forward a kind of on-line monitoring technology of CNC machine tools machining accuracy based on online neural network. Through the establishment of CNC machine tools condition monitoring platform, collection sensor signal of the key components of CNC machine tools, using time domain and frequency domain method of the original signal processing, extract the characteristic related to machining accuracy change, input to the neural network, identification the changes of machining accuracy. The experimental results show that, the on-line monitoring technology based on neural network, can identify the changes of machining accuracy.

Investigate the spindle errors motions from thermal change for high-precision CNC machining capability

As the demand for high speed and highly accurate machines has significantly increased, error motions from thermal change, which is up to 70 % of the total machining error, is found to be the main hurdles to overcome in improving the accuracy of CNC machine tools. In this research work, the authors installed four eddy current displacement sensors in the spindle structure near to the front bearing to monitor the spindle offset in the bearing level, which is mainly attributable to the thermal error motions of the spindle. In addition, another three capacitance sensors are mounted on the machine table level and aligned with the x-, y-, and z-axis of the machine to monitor the spindle shift in the table level to find out the correlation between temperature change and the thermal error motions of the spindle. To measure the temperature changes, we attached thermal sensors in the machine and cooling system. The estimation of the spindle thermal displacement based on temperature data from these thermal sensors can provide more information for the monitoring of thermal error motions of the spindle.

Improving the HSC Linear Motor Milling Machine Contouring Accuracy

In recent years, instrumentation circular profile tests have been specified to assess the contouring accuracy of CNC machine tools. Such an instrumentation type test is the HEIDENHAIN grid encoder system, which is particularly appropriate for dynamic measurements, especially at high feed rates. In this paper influence of the position loop gain and sampling period on the contouring accuracy are effectively studied.

A Review of Geometric Error Modeling and Error Detection for CNC Machine Tool

Error compensation can improve the accuracy of machine tools effectively. Among the error sources affecting the accuracy of CNC machine tool, geometric error is always set as a key performance criterion. This paper summarizes several methods of geometric error modeling and reviews the characteristics of different methods. Furthermore, available methods for measuring geometric errors have been reviewed also based on the advanced instruments. This work aims at enhancing the efficiency of error detection and give a perspective for the application of error compensation in the future.

A Multisensor Approach for Error Compensation in CNC Machine Tools

This paper presents a comprehensive ANN based multisensor fusion approach designed to support the implementation of an adaptive error compensation of geometric, thermal and dynamic errors for enhancing the accuracy of CNC machine tools. Accurate and efficient model to perform on-line error prediction is an essential part of the compensation process. The proposed approach consists of the following major steps: (i) design of an integrated spatial-variant model describing the machine topology, (ii) measurement of path-dependent rigid-body errors according to the model, (iii) design of time-variant models for error components through sensors fusion, (iv) continuous monitoring of the machine conditions using position, force, speed and temperature sensors for one-line error components prediction and integration to produce a correction vector, (v) total positioning error synthesis and software compensation. Implemented on a turning center, the proposed approach led to a consistent model able to accurately and reliably provide an appropriate error identification and compensation under variable machine tool conditions. 

Modal Analysis of CK52125 a New Type CNC Lathe of Ball Screw Based on ANSYS Software

The ball screw is a main driving component in the CNC machine tools. The ball screw’s structural performances and working conditions will have an important impact on the machining accuracy of CNC machine tools. However, the previous research method can not suffice the precise results’ requirements. So it is very necessary to do an in-depth analysis of the ball screw, which use dynamic research and be combined with the FEA software ANSYS. This article uses the above methods to do the modal analysis, and then gets the intrinsic frequency and the vibration model. It will make an important significance for guiding the practice.

The Application of System Parameters in Eliminating Oscillation and Improving Machining Accuracy of CNC Machine Tool

The measures of eliminating system oscillation by using parameters were put forward in semi-closed loop and closed loop control. The setup procedures of parameters were introduced, which included position loop gain, bi-position feedback, mechanical speed feedback. The setting of the parameters such as acceleration of backlash, compensation for static friction, feed forward and look-ahead feed forward of servo were also proposed, for purpose of improving the position accuracy and interpolation accuracy. The application of the system parameters is significant for improving the machining accuracy and ability of CNC machine tools.

A New Test Part for Detecting Processing Accuracy of Five Axis CNC Machine Tools

Five axis linkage CNC machine tools, with its high speed, high precision characteristics, are widely used in large aircraft structure part machining. By trial cutting method, "S" test part is a new test part for detecting processing accuracy of five-axis linkage machine tools. Through analysis and simulation, exploring the influencing factors to CNC machine tools processing accuracy and the regular of "S" test part surface errors, surface quality, results show that "S" test part can reflect the processing accuracy of CNC machine tools.

Synthetical Analysis and Experimental Study of the Geometric Accuracy of CNC Machine Tools

As the main error source of machine tools,the geometric accuracy is studied theoretically and experimentally.A modeling method of synthesis error is established in the coordinate system of machine tools based on the multi-body system theory,which is applied to a 3-axis CNC machine tool considering the interaction of error terms such as positioning errors,straightness errors and angular errors.By using the laser interferometer system,the positioning errors,straightness errors and angular errors are illustrated by a large number of experiments,which indicates that the positioning errors value is much higher than others.And the distribution and evolution of the synthesis error subjected to the coupling effect of all axes errors are studied in the workspace further.It is found that the synthesis error in the direction of a certain axis is close to its positioning error,which proves that the positioning error is the decisive factor contributing to the synthesis error.The analysis of geometric accuracy is of theoretical and practical significance to error compensation.

Model of relative position deviations of the executive bodies of a multiaxis machine tool

Precision five-axis machines are the basis for modern engineering. One of the main ways of increasing the accuracy of CNC machine tools is a correction of initial abnormalities of its mechanisms.

A universal modeling method for enhancement the volumetric accuracy of CNC machine tools

The volumetric error modeling method is an important technique for enhancement of the accuracy of CNC machine tools by error compensation. Based on an multi-body system (MBS), a universal kinematics error modeling method and the error analysis method for NC machine tools is presented in this paper. The essential condition for precision machining is derived through mathematical equations. The numerical solution method for the precise NC instruction value is also presented in this paper. A series of simulation and experiment results shows that the machining accuracy of CNC machine tools can be improved by more than 60% by using the method presented in this paper.

Accuracy test of five-axis CNC machine tool with 3D probe-ball. Part II: errors estimation

To improve the accuracy of CNC machine tools, error sources and its effects on the overall position and orientation errors must be known. Most motional errors in the error model of five-axis machine tool can be measured with modern laser interferometer devices, but there are still some not measurable geometric errors. These not measurable errors include constant, inaccurate link errors of components such as rotary axes block, main spindle block and tool holder. After setting all measured errors in the error model, a reduced error model is defined, which describes the influence of each unknown and not measurable link error on the overall position errors of the five-axis machine tool. On the other hand, the newly developed probe-ball device can measure the overall position errors of five-axis machine tools directly. Based on the reduced model and the overall position errors, the link errors can be estimated very accurately with the least square estimation method. The error model is then fully known and can be used for advanced purposes such as error prediction and compensation.

Intelligent cross-coupled fuzzy feedrate controller design for CNC machine tools based on genetic algorithms

In this paper, an intelligent contour control strategy has been investigated to improve the contour error of CNC machine tools. An uncoupled contour control system is first analyzed and then a cross-coupled controller is added in the control loop to form a cross-coupled contour control system. An algorithm for an on-line estimation of the contour error in arbitrary curved contouring is also proposed. To further reduce the contour error, a cross-coupled fuzzy feedrate control scheme is presented. The controller parameters are all optimized by a genetic based learning algorithm. Experimental results show that the proposed control scheme is effective to improve the contouring accuracy of CNC machine tools.

Enhancement of geometric accuracy via an intermediate geometrical feedback scheme

To enhance the geometric accuracy of a machined part, both the static and dynamic errors present in the NC machining procedure should be handled in some manner. This paper presents systematic compensation methods for these errors based on an intermediate geometrical feedback scheme. In the new scheme, the machined part is: (1) measured (on the machine), (2) compared with the CAD model, and (3) the toolpath is corrected repeatedly until the predefined geometric accuracy is obtained. The “execution-and-correction” method can be viewed as an interative part programming procedure, and it can be directly applied for the repetitive machining environment. This paper presents theories and algorithms for the scheme, including: (1) a method for enhancing the accuracy of CNC machine tools by the analytic volumetric error model, (2) a method for utilizing the machine tools for on-machine inspection, and (3) a machining error compensation method by path modification. The validity and effectiveness of the developed method was tested via contour cutting experiments with a vertical three-axis CNC milling machine.

Positioning Accuracy of CNC Machine Tools. Thermal Effect Prediction Using Neural Network.

Methods and results are presented for applying neural networks to the prediction of positioning error due mainly to thermal effects. Experiments on a machining center show that the positioning error is affected by the running conditions, such as the temperature variation of the nut of the ballscrew and the feedrate. In this study, we have tried to identify the relationships between the thermal-induced positioning error and running conditions. Both recurrent and feedforward neural networks have been used in the identification and their learning effectiveness has been compared. The results have shown that the recurrent network performs better than the feedforward network in this case. To further improve the error prediction accuracy of the network, a training technique that uses additional input has been proposed and its effectiveness has also been proved.

An Adaptive Error Correction Method Using Feature-Based Analysis Techniques for Machine Performance Improvement, Part 1: Theory Derivation

An adaptive error correction method using a feature-based analysis technique for improving the accuracy of CNC machine tools is presented. The method described in this paper emphasizes the integration of the process-intermittent gauging and analysis techniques with information from pre-process characterization and post-process inspection. The proposed method utilizes the information from pre-process characterization, process-intermittent gauging, and post-process inspection to improve machine performance automatically. Algorithms are derived for analyzing the post-process and process-intermittent inspection data to decouple process-related errors from machine errors and for identifying the residual systematic errors. A feature-based analysis technique is developed to relate the dimensional and form errors of manufactured features to the systematic machine tool errors. Inverse kinematics and statistical methods are used to identify and characterize the contribution of each residual error component on imperfect features. Also a recursive tuning algorithm is developed for fine tuning the geometric-thermal model.

An investigation of stick-slip friction on the contouring accuracy of cnc machine tools

Stick-slip friction has a great influence on the contouring accuracy of CNC machine tools. In this paper, a nonlinear model is used to simulate and analyze dynamic behaviors of stick-slip friction on the contouring accuracy of CNC machine tools. A simple control strategy is then developed to tune the control loop gain for reducing the contouring error due to stick-slip friction. Computational simulations and experimental tests are performed to illustrate the proposed method.

Stabilization for Feed Drive Accuracy of CNC Machine Tools with Autonomous Control System. Application of Neural Network.

CNC machine tools which use conventional feedback controllers usually result in significant tracking error when machining a contour, especially at high feed speed. This paper presents for the first time a new methodology for compensating general contour error. The new method uses contour error which is measured in advance to improve the feed drive accuracy of CNC machine tools. The eventual purpose of this study is to develop an autonomous control system for CNC machine tools, which should be able to perform precisely under a certain range of machining parameters. The contour error is considered to be related to several kinds of machining parameters and a neural network is used here, as the intelligent part of the autonomous control system, to learn the relation-ship between the contour error and machining parameters. This paper gives results of both simulation and experiments.