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Due to the advantages of low cost, high flexibility, and large workspace, industrial robot has been considered to be the most promising plan to replace traditional CNC machine tool. However, the low absolute positioning accuracy of robot is a key factor that restricts further application in high-precision metal-cutting scenarios. In order to improve the absolute positioning accuracy of robot, a positioning error compensation method based on the stacked ensemble learning is proposed. Firstly, the sources of positioning errors and compensation strategies are clarified by analyzing the kinematic model and structural composition of industrial robot. Then, based on the stacked ensemble learning algorithm, robot positioning error prediction model containing multi-layer learners is constructed. And a discrete grid optimization method is presented for model hyper-parameters optimization calculation. Next, predicted positioning errors are adopted to realize the positioning compensation by offline compensation method. Finally, by setting up a robotic milling platform based on MOTOMAN ES165D robot, a series of error compensation experiments have been implemented to verify the proposed method. After compensation, the maximum absolute position error and average position error have decreased by 83% and 89%, respectively, in the compensation experiments of a single point. Moreover, the error compensation of the end milling experiments has also brought significant accuracy improvement, which proved the effectiveness of the proposed method in robotic machining. [ABSTRACT FROM AUTHOR]

In order to solve the problem of nonlinear error for a dual rotary table five-axis CNC machine tool due to the linkage of rotary and translational axes, the simulation of motion nonlinear error compensation for a multi-axis linkage CNC machine tool is proposed. The adjacent points in the tool position file are selected as the tool position points for building the model, and then the nonlinear error model resolved by the harmonic function is established according to the error distribution in the classical post-processing. The nonlinear error between the two tool position points is quickly predicted by the analytical expression of this model, and the real-time error compensation of the intermediate interpolation points is realized. Finally, MALTLAB simulation analysis is performed on the tool position file of an impeller part machining to verify the effectiveness of the proposed algorithm. The experimental results show that it can be seen from the distribution curve of the nonlinear error that it is about 10% after compensation as before compensation, thus verifying the effectiveness of the nonlinear error compensation mechanism. The correctness of the nonlinear error analysis and compensation method and the effectiveness of post-processing are verified. [ABSTRACT FROM AUTHOR]

Considering the detrimental impact of thermal phenomena on the geometric precision of machine tools, a machine tool ball screw's omni-directional error model is created using the LSTM neural network algorithm. Subsequently, the machine tool ball screw's omni-directional error compensation module is devised by combining the core functions of the Huazhong numerical control system with the visual programming environment of QT and the numerical computation capability of Matlab. To enhance the practicality and accuracy of the compensation model, this study has employed the Whale Optimization Algorithm (WOA) to optimize the parameters of the LSTM model. This has resulted in an improvement in the model's generalization ability and prediction performance, making it more effective. During the experimental validation phase, the Z-axis error of the machine tool was practically operated and analyzed using the compensation method. Results manifestly show that, after employing the compensation method, the peak amplitude of the Z-axis error fluctuations have been notably curtailed to ±0.006 mm -- a considerable reduction compared to the initial error bandwidth of ±0.0145 mm. These empirical findings substantiate the efficacy of the proposed compensation strategy in substantially boosting the machining precision of products, thus furnishing a substantial and instructive benchmark for future inquiries into CNC machine tool error compensation technologies. [ABSTRACT FROM AUTHOR]

Machining efficiency and accuracy are subjected to higher requirements due to the increasingly widespread application of sculptured surface parts in the fields of aerospace, transportation, and energy. However, the influence of geometric error, tool deflection, and other factors decreases the quality and reliability of CNC machined workpiece. Error compensation is a popular and effective way to improve the machining accuracy of the workpiece. A novel multi-stage error compensation methodology that combines model-based and data-driven approaches is proposed, which realizes the closed-loop quality control process of the sculptured surface by five-axis flank milling. The global process consists of two special stages. First, the compensated machining of stage I is completed by a flexible mirror compensation method after establishing the tool deflection prediction model, which is the major factor causing the geometric error of the machined part. Subsequently, based on the on-machine measurement (OMM) data, the surface is automatically reconstructed by mirror points in 3D software and the toolpath for stage II compensated machining is generated. Finally, the verification experiment on the five-axis machine tool demonstrates that the methodology introduced in this research can effectively enhance the machining accuracy of the workpiece. [ABSTRACT FROM AUTHOR]

Thin-walled parts processed by five-axis CNC machine tools are widely used in aerospace and other fields due to their excellent performance. However, due to the weak rigidity of thin-walled parts, they are prone to deformation during milling, which poses great difficulties for efficient and precise machining of thin-walled parts. This paper introduces the classification and corresponding machining methods of thin-walled parts. By analyzing the causes and evolution mechanisms of errors in the machining process of thin-walled parts, and combining modeling methods with factors such as milling force, residual stress, and cutting chatter, the current research status of domestic and foreign scholars on deformation factors is summarized. At the same time, two deformation control methods, adaptive machining and error compensation, were introduced. Finally, the overall research status of thin-walled parts machining was summarized, and prospects for efficient and precise machining of thin-walled parts were proposed based on actual machining conditions. [ABSTRACT FROM AUTHOR]

Copyright of Machine Tool & Hydraulics is the property of Guangzhou Mechanical Engineering Research Institute (GMERI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The thermal error is a significant factor that influences the machining accuracy of machine tools, and error compensation is an economical and effective method for enhancing the accuracy of machine tools. However, establishing a precise thermal error prediction model is crucial for thermal error compensation. In this paper, the subtraction-average-based optimizer-based CNN-GRU neural network (SABO-CNN-GRU) is applied to integrated thermal error modeling. Through conducting a thermal characteristic experiment, temperature rise data and thermal error data were collected from the linear feed system of LXK300X helical groove CNC machine tool. The fuzzy c-means clustering and grey correlation analysis are employed to identify temperature-sensitive points in the linear feed system. By utilizing the temperature rise data from these sensitive points along with feed shaft thermal errors as data samples, and using the SABO algorithm to optimize the CNN-GRU prediction model, the thermal error prediction model of SABO-CNN-GRU is established. To validate its superiority and practicality, a comparative analysis is conducted with traditional thermal error prediction models based on CNN-GRU and SO-ELM. The results demonstrate that SABO-CNN-GRU model outperforms both models in terms of mean absolute error (MAE), root mean square error (RMSE), remaining prediction deviation (RPD), mean square error (MSE), and determination coefficient (R2) in accurately predicting results. Building upon this achievement, this paper develops a real-time thermal error compensation system which effectively reduces maximum thermal errors from 80.5 to 17.6 μm after implementing compensation measures. Effectively reducing the influence of thermal errors and improving the machining accuracy of machine tools. [ABSTRACT FROM AUTHOR]

For the problem of geometric error prediction of CNC machine tools, an improved hybrid grey wolf optimization (IHGWO) algorithm is proposed to optimize the geometric error modeling scheme of the support vector regression machine (SVR). The predicted and measured values of the geometric error are combined to construct the fitness function. In IHGWO, principles of particle swarm optimization (PSO) algorithm and dimension learning-based hunting (DLH) search strategies are introduced while retaining the excellent grey wolf position of the basic grey wolf optimization (GWO) algorithm. IHGWO algorithm uses Euclidean distance to construct the neighborhood of individual grey wolves, which enhances the ability to communicate between individual grey wolves and improves the convergence speed and accuracy of the algorithm. Predictive performance of SVR models using sum squared residual to quantify geometric error. Based on the screw theory, space models of geometric errors of CNC machine tools are established and combined with SVR models of geometric errors for compensation. Empirical evidence proves that the proposed method surpasses current error modeling methods in terms of precision and efficiency, as evidenced by a minimum reduction of 9% in circular trajectory error and a reduction to two overruns in S-shaped test pieces after error compensation. This research contributes to the field of CNC machine tool error modeling and has practical implications for manufacturing industries. [ABSTRACT FROM AUTHOR]

Higher-order error terms (HOET) occur inevitably during the geometric error modelling and compensation of a machine tool using both screw theory and multi-body system (MBS) theory. Though the HOET has little influence on machining accuracy, it will make analysis and compensation of geometric errors complicated and tedious. Especially, it is necessary to eliminate the higher-order error terms artificially when deriving the analytical expressions for geometric error compensation. Hence, a novel geometric error modelling and compensation algorithm without the interference of HOET is proposed in this paper. Taking a three-axis CNC machine tool as an example. A new summation operation rule for geometric error modelling was defined according to the homogeneous transformation matrix (HTM) method, which has no multiplication between error matrices. And the analytical expressions of motion-axis commands for error compensation could be calculated directly according to the new modelling algorithm without manual deletion of HOET. Active elimination of HOET can simplify the process of geometric error modelling and compensation and can significantly improve efficiency. The results show that the acquisition efficiency of symbolic compensation expressions can be improved by at least 70% compared to the traditional actual inverse kinematics. Moreover, the HOET are automatically eliminated and has a small influence on the compensation accuracy. Finally, a cutting experiment was conducted and analyzed to verify the high efficiency and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Due to their greater workspace and lower cost, industrial robots can provide an alternative solution to CNC machine tools for milling of aerospace parts. However, current machining robots fail to meet the required finishing tolerances (0.1 mm) of the aerospace industry. To improve the accuracy of industrial robots during milling, this paper proposes a new feedback method using an off-the-shelf passive CMM-arm. Unlike laser trackers and optical CMMs, CMM-arms are not susceptible to occlusion or line of sight issues, which may arise due to machining debris or robot movements. In this work, the performance and robustness of a CMM-arm used to guide a robotized machining process in optically challenging conditions are studied. First, the kinematic model of the CMM-arm is developed and the shared workspace between the CMM-arm and a KUKA KR300 Ultra industrial robot is analyzed. This ensures adequate reach of the robot's tool center point (TCP) while the CMM-arm is attached to the machining spindle. The CMM-estimated tool center point is then calculated in real time on an external PC based on the combined kinematic chain of the robot and the CMM-arm. The positioning error of the TCP is determined in real time at a rate of 80 Hz, and the corresponding correction signals are sent to the robot via the Robot Sensor Interface (RSI). Experimental results show over 80% reduction in maximum error during 5-axis milling of aluminum. [ABSTRACT FROM AUTHOR]

Ultra-precision machining technology was a key technology in high-end manufacturing fields. At present, ultra-precision machining has entered the nano scale. Mastering the key technology of ultra-precision machining error control, ensuring and improving the machining accuracy of CNC machine tools, become a hot research point to improve the machining and manufacturing levels. This paper systematically summarized the research status and development trend of ultra-precision machining error compensation technology, and focused on the geometric errors, force induced errors, thermal induced errors and their compensation methods, which had the greatest impact on ultra-precision machining. Then, a series of problems of ultra-precision machining in geometric error separation, cutting force, thermal induced error measurement and compensation were deeply discussed, and it is further pointed out that the ultra-precision machining error compensation technology should also pay attention to the development direction of high efficiency, high precision, generalization, modularization, intelligence and flexibility. [ABSTRACT FROM AUTHOR]

Error compensation is an effective method to guarantee the machining accuracy of machine tools. This paper proposes a method for geometric error identification and compensation of CNC machine tools based on volumetric diagonal error measurements. A geometric error model for CNC machine tools was established. Thereafter, the error measurement principle of the laser tracker was established. Based on this characteristic, error identification equations used to describe the position-dependent geometric errors were derived based on polynomials. A regularisation method was then selected to identify geometric error parameters. The identified geometric errors could be substituted in the space compensation module for error compensation. This paper takes a horizontal three-axis machining centre as an example to illustrate the proposed method. Results of the experiment reveal that the error identification and compensation method is convenient and effective in reducing volumetric diagonal errors. Moreover, the final volumetric diagonal positioning error with compensation was controlled at approximately 20 μm. [ABSTRACT FROM AUTHOR]

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The contour error of the machined parts is an important index to evaluate the accuracy of CNC machining. Considering a multi-axis servo control system, a predictive compensation strategy for contour error is presented in this paper. First, the offline identification method is adopted to establish the transfer function of each motion system. In this case, the relationship between the interpolation command and the feedback position of the grating is determined for the selected machine tool. Thus, before machining, the trajectory information of each motion axis can be predicted according to the interpolation instruction and the transfer relationship. It can be converted into the contour trajectory of the part through kinematic analysis, so as to predict the contour error. Finally, the predicted contour error is compensated into the command trajectory to ensure the contour accuracy of the part to be machined. Compared to existing methods, our method can effectively reduce the trial-produced cycle of parts and avoid unnecessary waste of processing materials. Moreover, without increasing the complexity of the control system and greatly reducing the machining efficiency, the dynamic error caused by the dynamic characteristics of the shaft is reduced. Taking the starfish pattern and the contour line of the impeller as the milling processing experiment case, the contour error after compensation is greatly reduced compared with the contour error processed by the original command. Therefore, the predictive compensation method proposed in this paper can significantly improve the machining accuracy. In addition, it also has application value for trial production of complex curved parts. [ABSTRACT FROM AUTHOR]

The key temperature points are the input variables of the thermal error model for prediction and compensation of thermal errors for precision CNC machine tools. However, the revealed time-varying characteristics of the key temperature points may jeopardize the robust prediction. To this end, the segment fusion least squares support vector machine (SF-LSSVM) thermal error modeling method is proposed. Firstly, the temperature data and thermal error data are divided into different segments according to time. Then, using the LSSVM with excellent nonlinear mapping capabilities as the basic model, the sub LSSVM thermal error model building and the corresponding key temperature points selection in each segment are fulfilled with genetic algorithm (GA) in a wrapper manner to preserve the corresponding local prediction characteristics. Finally, pick some of or all the sub LSSVM thermal error models to fuse together as the final thermal error model which may incorporate both the local and global prediction characteristics. The modeling and prediction experiment results on the spindle thermal error of a horizontal machining center demonstrate that the mean root-mean-square error (RMSE) on 5 spindle speeds after compensation is only 3.1 μm. Comparing with two traditional thermal error models, the prediction performance of the present model is improved by up to 51%. This research casts new light on both the mechanism of key temperature points and the prediction method of thermal errors. [ABSTRACT FROM AUTHOR]

Free-form surfaces are widely used in many applications in today’s industry. This paper presents a new approach to identify and compensate process-related errors in machining of free-form surfaces. The process-related errors are identified online by a newly developed in-process inspection technique. In this technique, the surface is first machined through an intermediate semi-finishing process that is specifically designed to machine different geometric shapes on the surface with different process parameters. An inspection method is developed to identify the process-related errors in the selected regions on the semi-finished surface. The relationship between the machining/surface parameters and process-related error is then achieved using a neural network. This relationship is used to predict the process-related errors in the finishing process. The process-related errors, together with the machine tool geometric errors identified using a method developed in our previous work, are compensated in the finishing tool paths through tool path re-planning. Experiment has been conducted to machine a part with a free-form surface to show the improvements in the machining accuracy. [ABSTRACT FROM PUBLISHER]

Fixture errors are one of the error sources in machining operations. The fixture errors consist of positioning inaccuracies and errors due to workpiece and fixture deformations. Fixture locators’ height error causes incorrect positioning of the workpiece in the fixture and inaccuracy in machined surfaces which can be much more than the locators’ height error. For machining precise workpieces, it is necessary to eliminate these errors. This paper presents a method for modelling and compensating the fixture locators’ height error effect on workpiece machined surfaces. In this method, the planes of workpiece actual coordinate system (ACS) are mathematically modelled in the workpiece theoretical coordinate system (TCS). Using the model, required homogenous transformation matrix for coinciding ACS with TCS and modifying machining toolpath for compensating the errors is generated. The presented model is used to develop a post-processing fixture locator error compensation module, which can modify CNC machining codes to eliminate the effect of fixture locators’ height error on the workpiece machined surfaces. For verifying the presented method, machining simulations and cutting experiments have been performed in this work. The results show that the method can eliminate the effect of fixture locators’ height error on the workpiece machined surfaces considerably. [ABSTRACT FROM PUBLISHER]

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The selection of the measurement point is one of the key steps in modelling. The traditional closed-loop control method can enhance the machine tool precision to a certain extent; however, there are some limitations in this technique. This paper presents a method that simplifies modelling a geometric error by integrating the Abbe and Bryan principles. It is found that the modelling accuracy directly affects the machining accuracy, and that the manufacturing process and effect can be simulated using VERICUT. The machining simulation of a hemispherical workpiece provides a theoretical basis for error compensation. A compensation module is integrated into a CNC system, and the effectiveness of error compensation is verified by applying the double ball bar method. The measuring results before and after error compensation are compared, demonstrating that the errors are reduced and compensated successfully. [ABSTRACT FROM AUTHOR]

The accuracy of swing angle directly bears on the machining performance of computer numerical control (CNC) machine tools. Any error in the swing angle will greatly affect the machining quality. In actual engineering, it is very important to compensate for the angle error in the machine tool. This paper attempts to design an effective method to compensate for the swing angle error in special-shaped rock turning-milling machining center HTM50200. Firstly, the commonly used swing angles of the tool axle were measured, and fitted into curves through polynomial regression. Based on the fitted curves, the error between the theoretical and actual swing angles was obtained and corrected, and the change law of the angle error was derived. After error compensation, the actual swing angle was measured again for verification. According to the measured results, our error compensation technique greatly enhanced the rotation accuracy of the swing axle, and mitigated the effects of swing angle error on machining accuracy. This research breaks new ground for the development of high-end high-precision rock machining equipment. [ABSTRACT FROM AUTHOR]

Contouring error has a significant effect on machining accuracy. In this paper, a model predictive contouring error precompensation method is presented that performs model-based error precompensation with feedback and constraints. The proposed method uses the predicted contouring error without compensation obtained by simulation, as the reference trajectory of the model predictive compensator. It then calculates the compensation signal using a constrained model predictive control algorithm and adds it to the original reference position as the new system input. Experiments were conducted on an X–Y table to compare the proposed method with a traditional cascaded proportional-integral (PI) controller and two existing contouring error precompensation methods. The experimental results show that higher contouring accuracy can be achieved with the proposed method for both sharp corners and free-form curves. [ABSTRACT FROM AUTHOR]

The workpiece accuracy has always been a top priority for manufacturers. In mass production, variations in the workpiece accuracy are mainly affected by thermal errors, which cause unacceptable process capability index (Cpk) and often require frequent manual adjustment of cutting tool location when machining errors exceed tolerances. In this work, a novel comprehensive thermal error model is proposed by utilizing the workpiece inspection data and Cpk from production line. The Cpk is employed in the modeling, and Cpk influence analysis is conducted to select the thermal key points (TKPs). Thermal errors predicted using the proposed model are then compensated in real time during machining. The proposed method is proved to be feasible and effective; the produced workpiece in both the verification test and mass production all meet the specification. The workpiece Cpk is improved from 0.56 to 1.35. Manual adjustment of the cutting tool is no longer necessary as a result of thermal error compensation and 100% workpiece inspection can be replaced by sampling inspection. This work contributes to the workpiece quality improvement and the cost savings for the factory. [ABSTRACT FROM AUTHOR]

On a five-axis CNC machine tool, the pretravel errors of touch-trigger probes are severely affected by gravity and must be compensated to ensure the required measurement accuracy. The situation is more complex than that of the three-axis on-machine inspection system. This paper proposes a simple and accurate modeling and compensation method for the probe pretravel error of a five-axis on-machine inspection system. First, the pretravel error for the 5-axis CNC tool is decoupled into three parts, which are analyzed based on the probe's mechanical structure. Then, a new calibration point selection strategy is proposed to obtain the accurate reference sphere center. Finally, we carry out calibration tests to validate the proposed method. The compensation results show that the proposed compensation method for the probe pretravel error under the influence of gravity (PPEUG) can improve the accuracy considerably. • The pre-travel error for 5-axis CNC is decoupled into three parts which are analyzed based on probe's mechanical structure. • A new calibration point selection strategy is proposed to obtain the accurate reference sphere centre. • The compensation results show that the proposed PPEUG compensation method can improve the accuracy considerably. [ABSTRACT FROM AUTHOR]

This paper proposes a new geometric error model and compensation algorithm for the three-axis machine tools. First, the relative motion matrix to the coordinate system is constructed by the homogenous transformation matrix (HTM). Next, the geometric error model is deduced based on homogenous transformations. Then, an error compensation algorithm is developed by means of the computer numerical control (CNC) program reconstruction by using the geometric error model. Finally, the simulation is implemented on a virtual machine tool established in the VERICUT software to validate the efficiency of the model and the compensation algorithm. An autocollimator is used to measure the yaw errors and an experiment is implemented on a real machine tool. The results simulation and experiment indicate that the error modele and compensation algorithm can significantly improve the machining precision. [ABSTRACT FROM AUTHOR]

Complex surface parts are widely used in aerospace, automotive, and precision molds. Modern manufacturing aims to improve the machining accuracy and efficiency of these parts. The machining accuracy of surface parts can be significantly improved using a series of error compensation technologies to compensate for machining errors. Based on the analysis of the measurement data of the parts, empirical mode decomposition (EMD) method is used to decompose the machining errors into systematic and random errors, which are used to modify the numerical control (NC) codes to compensate for the systematic errors of the surface parts. An example of a complicated surface part proves that the method proposed in the current study can effectively improve the machining accuracy of surface parts. [ABSTRACT FROM AUTHOR]

With the rapid development of aerospace, energy, and power technologies, the demand for high-performance parts with complex curved surface is increasingly large, and the multi-axis Computer-Numerical-Control (CNC) precision machining technique for such parts becomes a popular and difficult issue in the industrial field. In order to ensure the high-performance of complex curved surface parts, the requirement of the contour accuracy is higher and higher for such parts due to the important role they play in these fields. However, the limitation of dynamic properties for the CNC machine tools, which leads to the contouring-error, becomes a vital issue that affects the machining accuracy of the high-performance parts with complex curved surface. The contouring-error, defined as the orthotropic distance from the actual motion position of machine tool to the desired contour of curved surface in multi-axis contour-following tasks, is caused by the facts such as servo lag, dynamics mismatch, external disturbances, and so forth. The reduction of the contouring-error becomes of great significance for promoting the performance of CNC motion systems thus realizing the high-speed and high-precision machining, and the research on the contouring-error reduction in multi-axis CNC machining is therefore a hotspot issue in the machining engineering. This paper provides a comprehensive review to the state of the art of the contouring-error reduction methods. The massive and complicated studies on constraining the contouring-errors are classified and summarized, and accordingly, the advantages and the disadvantages of different kinds of methods are discussed and compared, which has a guiding significance for selection of the interested contouring-error reduction method. Furthermore, this paper systematically suggests the probable future studies that remain vacant and meaningful based on the discussion of the state of the art. Significantly, it is possible for active promoting and developing to further improve the contouring-error reduction of the complex curved surface parts in multi-axis CNC machining. [ABSTRACT FROM AUTHOR]

Absolute optical encoders have emerged as a preferable choice of accurate positioning measurement for high-end manufacturing. To further improve the measurement accuracy of the absolute optical encoder, a novel error compensation method is proposed based on the empirical mode decomposition (EMD) method. This method is operated as follows: First, the measurement error achieved by an absolute optical encoder is decomposed into a number of intrinsic mode functions (IMFs) and the residue based on EMD. Then, a novel Hilbert marginal spectrum (HMS) based scheme is proposed to extract the underlying trend of the measurement error. Finally, the underlying trend is eliminated from the measurement error to improve the measurement accuracy. Experimental results indicate that the proposed compensation method extracts the underlying trend of the measurement error very well and improves the measurement accuracy of the absolute optical encoder. [ABSTRACT FROM AUTHOR]

Parts with rapidly varied geometric features are often key components in high-end equipment and are difficult to process because of the special structures and the strict requirements. Due to the existence of rapidly varied geometric features and the moving characteristic of continuous-path running, the trajectory error will be formed during machining process, which seriously restricts the machining accuracy of such parts. Additionally, the formative trajectory error is more non-ignorable in high-feed-speed machining. Existing studies can hardly reduce this error for arbitrary free-form trajectories without sacrificing of the machining efficiency. Consequently, aiming at reducing this error thus improving the processing efficiency and precision, the estimation and compensation methods for the trajectory error in high-feed-speed continuous-path machining are proposed. The actual reachable feed speed is recognized based on geometry and drive constraints of the numerical control (NC) machine tool. The continuous-path running trajectory error is estimated by approximating the desired toolpath with spline curves. The error compensation approach by combining the mirror compensation and the Taylor's expansion compensation is provided. The advantage of the proposed approach is that the continuous-path running trajectory error can be easily estimated and compensated only by analyzing and modifying the NC codes, which means an extensive feasibility for free-form toolpaths. Experimental results demonstrate the favorable performance of the proposed methods. This study provides an effective approach for reducing the multi-axis high-speed machining trajectory error and is significant for improving the machining precision and efficiency of the parts with rapidly varied geometric features in engineering. [ABSTRACT FROM AUTHOR]

Thermal error significantly influences the accuracy of CNC machine tool. A high-performance compensation system depends upon the accuracy and robustness of the model and appropriate model inputs of temperatures. In this paper, fuzzy clustering is conducted in temperature classification. Based upon an evaluation model, an optimal temperature classification can be found. The representative temperatures from each group construct temperature candidates. Then, a sliced inverse regression (SIR) model is introduced in thermal error modeling, which can change the problem of high-dimensional forward regression into several one-dimensional regression and meanwhile further eliminate the coupling among temperatures candidates. To evaluate the performance of SIR model, measuring experiment was carried out on a horizontal machining center for temperature and thermal error information under two experimental conditions. The proposed classification method was used to classify 29 temperature variables into five groups. A SIR model was built upon the five temperature candidates. Meanwhile, stepwise regression (SR) theory is also conducted for temperature variable selection and thermal error modeling. Comparison shows that both of the two models have high fitting accuracy, while the SIR model is more excellent in robustness than the SR model. Finally, a compensation system was developed. Compensation experiment shows that the SIR model is practical and effective, which can reduce the axial thermal error from 43 to 7 μm. [ABSTRACT FROM AUTHOR]

In the sawing process, because of the changes of the material properties and the section shapes, the cutting load has a fluctuation, which affects the cutting precision and the surface quality. At the same time, in different conditions, the characteristic parameters of the cutting load are very different, which makes the dynamic characteristics of the drive system of the CNC sawing machine be not satisfactory, so that the driving system will decrease the efficiency and increase the energy consumption. In this paper, a method of adaptive frequency conversion control with load characteristic identification is proposed, and the corresponding control system is designed. The simulation and experiment show that the speed fluctuation, the load change, and the adjustment time of the control system are very short. The adaptive capability of the driving system of the CNC sawing machine for the load and other parameters is strong. On this basis, the numerical control system based on the real-time detection, the error compensation and the auxiliary machinery intelligent control is developed, which improves the cutting accuracy and production efficiency of the CNC sawing machine. [ABSTRACT FROM AUTHOR]

Purpose As manufacturing technology has developed, digital models from advanced measuring devices have been widely used in manufacturing sectors. To speed up the production cycle and reduce extra errors introduced in surface reconstruction processes, directly machining digital models in the polygonal stereolithographyformat has been considered as an effective approach in rapid digital manufacturing. In machining processes, Cutter Location (CL) data for numerical control (NC) machining is generated usually from an offset model. This model is created by offsetting each vertex of the original model along its vertex vector. However, this method has the drawback of overcut to the offset model. The purpose of this paper is to solve the overcut problem through an error compensation algorithm to the vertex offset model.Design/methodology/approach Based on the analysis of the vertex offset method and the offset model generated, the authors developed and implemented an error compensation method to correct the offset models and generated the accurate CL data for the subsequent machining process. This error compensation method is verified through three polygonal models and the tool paths generated were used for a real part machining.Findings Based on the analysis of the vertex offset method and the offset model generated, the authors developed an error compensation method to correct the offset models and generated the accurate CL data for the subsequent machining process. The developed error compensation algorithm can effectively solve the overcut drawback of the vertex offset method.Research limitations/implications The error compensation method to the vertex offset model is used for generating the CL data with the using of a ball-end cutter.Practical implications On the study of CL data generation for a STL model, most of the current studies are focused on the determination of the offset vectors of the vertexes. The offset distance is usually fixed to the radius of the cutter used. Thus, the overcut problem to the offset model is inevitable and has not been much studied. The authors propose an effective approach to compensate the insufficient distance of the offset vertex and solve the overcut problem.Social implications The directly tool paths generation from a STL model can reduce the error of surface reconstruction and speed up the machining progress.Originality/value The authors investigate the overcut problem occurred in vertex offset for CL data generation and present a new error compensation algorithm for generating the CL data that can effectively solve the overcut problem. [ABSTRACT FROM AUTHOR]

This study proposes a high-precision compensation system using an on-machine noncontact measuring system to improve the manufacturing accuracy and efficiency of large-diameter aspheric mirrors by reducing profile errors arising from tool setting errors and machine positioning errors. By measuring a standard hemisphere, the assembly tilt angle of the measurement sensor can be calibrated. The grinding wheel setting offset can be calculated by comparing the measured profile and the ideal profile, and the profile error caused by wheel offset can be reduced by adjusting the grinding origin coordinate. According to the normal unit vector and residual error in the Z direction of the measuring points, the normal residual errors corresponding to the grinding points could be generated as well as the compensation grinding numerical control (NC) program. An 800-mm-diameter K9 mirror was ground to verify the proposed compensation grinding method. The profile error was reduced from 65 to 35 μm during the semi-finish grinding stage. By using the compensation grinding path, the profile accuracy was improved from 35 to 8 μm in the fine grinding stage. The proposed compensation method effectively improves the profile accuracy and manufacturing efficiency for grinding large-diameter aspheric mirrors. [ABSTRACT FROM AUTHOR]

It has been proven that error compensation is a key technique to improve machining accuracy. However, existing iteration and recursive compensation algorithm is difficult to realize. Hence, a simple and rapid compensation method is considerably necessary for engineering application. In this paper, a novel compensation strategy just by algebraic operation was first proposed for machining accuracy improvement. Error motion transformation was introduced to build the position-independent geometric error (PIGE) model according to homogeneous transformation matrix (HTM). Then, the analytical numerical control (NC) code expression with error compensation was derived and used for NC code generation. In addition, the presented method is appropriate for post-processing of non-orthogonal machine tool. At last, simulation and cutting experiment were demonstrated to verify the feasibility and effectiveness of the proposed method. Taking hemisphere surface as the test object, the simulation results showed that the effects of PIGEs could be eliminated by the proposed method. The experiment results with compensation indicated that the machining accuracy improved to about 14 % compared with those without compensation. [ABSTRACT FROM AUTHOR]

This article proposes a method to measure, model and compensate both geometrically dependent and independent volumetric errors of five-axis, serial CNC machine tools. The forward and inverse kinematics of the machine tool are modeled using the screw theory, and the 41 errors of all 5 axes are represented by error motion twists. The component errors of translational drives have been measured with a laser interferometer, and the errors of two rotary drives have been identified with ballbar measurements. The complete volumetric error model of a five-axis machine has been modeled in the machine's coordinate system and proven experimentally. The volumetric errors are mapped to the part coordinates along the tool path, and compensated using the kinematic model of the machine. The compensation strategy has been demonstrated on a five-axis machine tool controlled by an industrial CNC with a limited freedom, as well as by a Virtual CNC which allows the incorporation of compensating all 41 errors. [ABSTRACT FROM AUTHOR]

This paper presents an experimental methodology of Design for Manufacturing (DFM) used for survey and analysis of geometric deviations of CNC Machine-Tools, through their final product. These deviations generate direct costs that can be avoided through the use of Intelligent Manufacturing Systems (IMS), by the application of Artificial Neural Networks (ANNs) to predict the fabrication parameters. Finally, after the experiments, it was possible to evaluate the experimental methodology used, the equations, the variables of data adjustment and thus enable the validation of the methodology used as a tool for DFM with high potential return on product quality, development time and reliability of the process with wide application in various CNC Machines. [ABSTRACT FROM AUTHOR]

Guideway-induced errors are the main factors affecting the machining accuracy in computer numerical control (CNC) machine tools. In this paper, the guideway-induced errors of a large CNC gantry guideway grinder are analyzed and measured to realize the traceability analysis and coupling compensation. To establish the error model, an automatic error modeling application is developed based on the least-square fitting of orthogonal polynomial method and visual basic. The comprehensive error model of the grinder is established using the homogenous transformation matrix to realize the error distribution analysis in a three-dimensional workspace. The error separation method is used to achieve the traceability analysis of the guideway-induced errors. To realize the coupling compensation for guideway-induced errors, an external mechanical origin offset (EMOO) and Ethernet-based error compensation method are proposed in this research. Experimental results showed that the maximum error was compensated by 91.2 % compared with no compensation. [ABSTRACT FROM AUTHOR]

The article presents a methodology for compensating for systematic influences of computer numerical control (CNC) machining processes on free-form surfaces. The proposed procedure is performed off-line by introducing corrections compensating for these influences to machining programs. The effect of systematic influences of machining are deterministic deviations of surfaces. CAD models of these deviations, averaged for a number of surfaces machined under repeatable conditions, represent a machining pattern model (MPM) which serves as the basis for performing compensation. The basis for developing such models is surface deviations determined during coordinate measurements carried out along a regular grid of points. For estimating surface MPMs, a methodology is proposed in which regression analysis, spatial statistics methods, an iterative procedure, and NURBS modeling are applied. An MPM with the opposite sign was used for compensating systematic influences of the ball-end milling process by modifying the nominal geometry data and correcting the machining program. The results of machining error compensation carried out on the basis of a previously developed MPM were compared to the results of compensation performed on the basis of raw measurement data as well as to the results these after compensation on the basis of a model of deterministic deviations for the surface under study. [ABSTRACT FROM AUTHOR]

To improve the precision of CNC machine tools, a motorized spindle thermal error model based on least square support vector machine (LS-SVM) was proposed. A thermal error compensation method was implemented, which takes the length of cutting tools and thermal tilt angles into account. A five-point method was applied to measure radial thermal declinations and axial expansion of the spindle with eddy-current sensors. This resolves a problem arising out of the three-point thermal error measurement, where the radial thermal-induced angle errors cannot be obtained. Variables sensitive to thermal error were selected by grouping and optimizing temperature variables using a combined fuzzy cluster and correlation analysis. LS-SVM models were established for axial elongation and radial thermal yaw and pitch angle errors. Moreover, a method to test the goodness of prediction for the results based on the model is discussed. The results indicated that the LS-SVM has high predictive ability based on fuzzy cluster grouping, and prediction accuracy reached up to 90 %. In addition, the axial accuracy was improved by 82.6 % after error compensation, and the axial maximum error decreased from 39 to 8 μm. Moreover, the X/ Y direction accuracy can reach up to 77.4 and 86 %, respectively, which demonstrated that the proposed methodology of measurement, modeling, and compensation was effective. [ABSTRACT FROM AUTHOR]

This paper focuses on the problem of intelligent compensation of nonlinearly appeared dimensional error in the computer numerical control grinding process. An intelligent error pre-compensation scheme is proposed with intelligent controller, automatic dimensional error measurement, and feedback information. Iterative learning approach is applied to infer the error compensation of the next workpiece machining by using the historical data. The simulation results and the real system input and output responses show that the proposed intelligent error compensation scheme and the iterative learning approach have significant superiority. [ABSTRACT FROM AUTHOR]

The spindle error and geometric error are the main sources of inaccuracy in CNC machining. With the rising of the machine tool parts' temperature, the spindle error and geometric error increase continually, and the error curves have a nonlinear distribution. To analyze the thermal effects on spindle error and geometric error, an experiment is carried out. To improve the machining accuracy of a CNC machine, an error model is proposed based on orthogonal polynomials. With the application of the orthogonal polynomials, the polynomial regression can be transformed into multiple linear regressions which are easier to calculate. In order to implement the real-time error compensation for the thermally induced spindle error and geometric error, an error compensation method is proposed based on the external coordinate offset. The thermally induced spindle and geometric error are compensated by 90 % compared with no compensation. [ABSTRACT FROM AUTHOR]

Abstract: In order to obtain high machining accuracy for free-form surface components, an on-line inspection system with error compensation is proposed in this paper. Once the component is machined, it can be measured by the probe inspection system. Based on these measurement data, a deterministic surface can be established based on a bicubic B-spline surface. Through the spatial statistical analysis of the residual errors of a regression model, the machining errors are decomposed into systematic errors and random errors. For the systematic errors, the numeric control program is modified and the compensation for the machining errors calculated can be conducted without altering the machining benchmarks. Therefore, the combination of the on-line inspection and the compensation of the machining errors is achieved successfully. Experiments were conducted to verify the effectiveness of the proposed methodology. [Copyright &y& Elsevier]

Computer numerical control (CNC) machines are now widely used in the manufacturing industry. There is an increasing need for lower-costing machines capable of high precision machining. To achieve high precision machining, the motions of the axes of these machine tools need to be controlled precisely so that they follow a desired path, or contour, accurately. This paper discusses some of the factors that can affect the accuracy of the contour generated. Also discussed are some compensation approaches to compensating the geometrical errors of these machines so as to achieve precision results even with not-so-accurately build machines. Also presented and discussed are the results of approaches taken in improving contouring accuracy through the design and tuning of the machine axis controllers as well as some contour path compensation approaches. [ABSTRACT FROM AUTHOR]

To improve the machining accuracy of machine tool, the geometric error compensation for three-axis vertical machining center was studied through error compensation. Based on the idea of hierarchical compensation, analyzing the feature of the structure of machine tool and using geometric error compensation module in a commercial CNC system (SIEMENS 840D), the geometric errors of the machine center were divided into compensable errors and uncompensable errors and an error model for compensation was established according to the compensable errors. An experiment was carried out in 0540D three-axis vertical machining center. The results show that the kinematic accuracy after compensation is improved. [ABSTRACT FROM AUTHOR]

It has been proved that error compensation is an effective approach to improve machining accuracy of a machine tool cost efficiently. In this paper, the framework of an error compensation software system, which can realize software error compensation via numerical control (NC) programs reconstructing, is investigated. And the algorithms relating to error prediction are discussed in detail, such as positioning movement error compensation, linear interpolation movement, and circular interpolation movement error compensation. To realize the error compensation, NC program is reconstructed according to the predicted errors during virtual machining before it is fed to the actual machining. Two controlled machining experiments were carried out. The results show that error compensation methods via reconstructing NC programs can improve the movement accuracy of a computer numerical control CNC machine tool obviously. [ABSTRACT FROM AUTHOR]

To solve the problem of thermal error of heavy-duty CNC machine tools, a thermal error separating and modeling approach based on linear regression theory is proposed. Firstly, the thermal errors are separated from geometric error to get thermal error parameters. Secondly, based on temperature sensors optimizing distribution strategies, like main factor strategy and irrelevance strategy, the key points of thermal errors are selected. Finally, a multiple linear regression model is constructed for thermal errors, and an experiment is carried out on a TK6920 heavy-duty CNC floor-type boring and milling machine tool, and the results indicate that the thermal error of column is reduced from 0.45 mm and 0.25 mm to 0. 13 mm and 0.09 mm in X and W directions, that is 71% and 64% of thermal error can be compensated with this model. Error compensation technology can reduce the thermal error of heavy-duty CNC machine tools, therefore the manufacturing precision can be improved. [ABSTRACT FROM AUTHOR]

Error compensation implementing strategy of CNC machine tools is a key technique. Basing on handwheel offset function of CNC system, a novel error compensation implementing strategy were proposed, and an error compensator is developed to realize the error compensation implementing on machine tools with Siemens 840D CNC systems, which communicates with CNC system by the DRF offset function and substitutes for electronic handwheel of CNC system. The error compensator's hardware and software systems, in which multithread technique was used to parallel run to avoid CPU's long-playing employment by one task, were developed. Finally, to test the feasibility of the implementing strategy, an experiment was carried out to compensate geometric error of a heavy-duty CNC floor-typed boring and milling machine tool. Experimental results show that error synthetic compensation equipment developed in this paper can perfectly implement error compensation function. [ABSTRACT FROM AUTHOR]

The positioning accuracy of computer numerical control (CNC) machine tools is mainly limited by the manufacturing accuracy of their linear and circular motion axes and by the long-term dimensional stability of their structures. Maximizing this accuracy can prove to be a particularly challenging task, especially for large-sized systems. In fact, heat-induced deformations, long-period deformation of foundations and the manufacturing process itself, these all cause time-dependent structural deformations of the machine body, which are difficult to model and to predict. The usual approach is a model-based prediction of structural deformations, which is followed by a compensation of positioning errors at CNC level. This approach is often limited by the complexity of the problem from both geometrical (system geometry can be very complex and it can vary in time) and physical (it is difficult to model and consider any possible load type and loading condition) point of view. As a consequence, only limited success has been achieved in active error compensation based on the modelling of the relationship between the generalized dynamic loads and the structural deformation field. This paper illustrates a different approach in active error compensation, which exploits a new measurement system able to provide real-time measurement of the displacement field of a given structural component, without any model about its dynamic/thermal structural behavior. [ABSTRACT FROM AUTHOR]

Thermal errors are the major contributor to the dimensional errors of a workpiece in precision machining. Error compensation technique is a cost-effective way to reduce thermal errors. Accurate modeling of errors is a prerequisite of error compensation. In this paper, a thermal error model was proposed by using projection pursuit regression (PPR). The PPR method improves the prediction accuracy of thermal errors in the computer numerical control (CNC) turning center. A thermal error compensation system was developed based on the PPR model, and which has been applied to the CNC turning center in daily production. The results show that the thermal drift in workpiece diameter has been reduced from 34 to 5 μm. [ABSTRACT FROM AUTHOR]

Friction error in reverse motion is one of the principal factors influencing the contour accuracy of high-speed and high-precision computer numerical control (CNC) machine tools, on which closed-loop control is used. On the basis of transient response analysis of servo systems which a conventional proportion—integration—differentiation control strategy are used, the reason for quadrant protrusions occurring in circular motion for worktables is discovered, and the characteristics of the friction error during the feed process such as emergence time, duration, and magnitude of the error due to friction can be predicted correctly. A new approach of compensating for friction error using double compensation pulses is proposed in this article. The first compensation pulse made the worktable escape from the dead zone at the best times, and the second one made the worktable approach to the ideal feed path along the guide as fast as possible. Parameters of compensation pulses such as magnitudes, widths, and starting time are determined by simple mathematic calculation. Results of simulations and experiments show that the method using double pulses proposed in this article can effectively compensate for the friction error in circular motions for a high-speed and high-precision table. [ABSTRACT FROM AUTHOR]

In this paper, a new model-based Taylor series expansion error compensation (TSEEC) strategy is proposed to improve the contouring accuracy for computer numerically controlled (CNC) machines. In TSEEC, the contour error compensation problem is formulated as a Taylor series expansion problem, in which the value of the contour error is expanded around the reference points and the compensation components are calculated as the deviations from the reference points. Simulations show that, with perfect knowledge of the axial dynamics, zero contour errors can be achieved with TSEEC for both linear and circular contours. Due to modeling errors, external disturbances, and measurement noise, some modifications and experimentation need to be made to determine suitable parameters for implementation of the TSEEC scheme on a real machine. These measurements include a low-pass filter, a choice of a compensation target, and a compensation gain. Experimental results show the effectiveness of TSEEC in reducing contour errors and demonstrate the superiority of TSEEC over inverse feedforward compensation and cross-coupled control in improving the contouring accuracy. [ABSTRACT FROM AUTHOR]