Errors Of Machine Tools Research Articles

An improved machine tool volumetric error compensation method based on linear and squareness error correction method

Error compensation is one of effective and economical means to improve the machining accuracy of machine tools. The measurement accuracy of kinematic errors has great impact on the accuracy of machine tool error modeling. Some measurement errors are inevitably generated due to the distortion of the slide table and the limit of local measuring stroke. To solve these problems, an improved machine tool volumetric error compensation method is proposed in this paper, based on linear and squareness error correction method. The linear errors, including position errors and straightness errors, are corrected by considering the distance effect between optical mirror groups and the surface of worktable. The squareness errors are corrected through modifying local squareness errors measured with double ball bar to global squareness errors, with the aid of straightness errors measured with multi-laser calibrator. Then volumetric errors are obtained based on multi-body system theory, and volumetric diagonal errors are measured with laser interferometer. It is illustrated that the bidirectional systematic deviation of positioning of four volumetric diagonals reduced about 81.3%, 35.2%, 29.2%, and 4.5% respectively by using this improved machine tool volumetric error compensation method, and it is of obvious advantages in contrast with traditional compensation method with direct measurement data. The improved error compensation method proposed in this paper has universal applicability and has great significance on machine tool accuracy improvement.

Mapping and compensation of geometric errors of a machine tool at different constant ambient temperatures

Thermo-mechanical effects due to changes in the ambient temperature on the shop floor and internal heat sources caused by the manufacturing process significantly contribute to the geometric deviations of a machine tool and therefore, the geometric deviations of the manufactured workpiece. Minimizing these thermally induced geometric deviations is worthwhile since the requested tolerances of machined workpieces become continually smaller nowadays. To investigate the overall deformations of a machine tool structure due to variations in ambient temperature the geometric errors of a five-axis machine tool at different ambient temperatures by means of a portable climate simulation chamber are systematically mapped. While positioning and squareness errors of the linear axes are significantly influenced by the ambient temperature, straightness as well as rotational errors were less sensitive to temperature effects. For the investigated machine tool errors of the two rotational axes are negligible due to an active cooling of these axes. Through numerical error compensation of the linear axes, the geometric errors of the investigated machine tool can be reduced up to 80%. Finally, an outlook how a temperature-dependent compensation could be derived from previously measured compensation fields at discrete temperatures and afterwards applied on-the-fly during manufacturing is given.

Thermal behaviour in CNC machine-tools

This article describes errors in machine-tools focusing on thermal errors. The internal and external heat sources in machine tools. The basic concepts of heat transfer and an introduction to Finite Element Method FEM applied to heat transfer.

Measurement and compensation method of gantry CNC machine tool based on single laser synchronisation method

The gantry CNC machine tool has unique structure and characteristic. It does not always form a symmetrical structure and symmetrical force during the machining process. The inconsistency will cause a non-synchronised error in the biaxial synchronous system. The no-synchronised error will affect the machining accuracy, cause the beam to be pulled and the gantry frame or drive element to be damaged. Therefore, the biaxial synchronisation error of the CNC machine tool is one of its most important specifications, and it should be solved firstly when compensating. This paper presents a new method called single laser synchronisation method, and puts forward the measurement method and compensation method of positioning error. This new method includes a special optical path layout, a characteristic way of measurement and compensation. This method has some advantages such as high precision, low-cost, efficiency, etc.

Thermal error and energy-saving performance evaluation of the energy-saving machine tool using new structural materials

Thermal error and energy-saving performance evaluation of the energy-saving machine tool using new structural materials

A multi-sensor system and its error compensation for on-machine measurement

In order to enhance the accuracy and efficiency of the measurement of on-machine test, a multi-sensor system is developed in this paper. This multi-sensor system consists of a touch trigger probe and a laser displacement sensor, so this measurement system has both the characteristics of high efficiency of laser displacement sensor and high precision of trigger probe. To enhance the accuracy of this measurement system, the main errors including sensor errors and motion errors of machine tools are tested and compensated respectively. Finally, experiments are conducted to validate that this multi-sensor system is suitable for on-machine measurement of workpiece.

Research on the Effect Law of Machine Tool Errors on Tooth Surface Errors of Curvilinear Gear

Research on the Effect Law of Machine Tool Errors on Tooth Surface Errors of Curvilinear Gear

Research on the application of multiplication dimension reduction method in global sensitivity analysis of CNC machine tools

Three-axis computer numerical control (CNC) milling machines have a wide range of application in practical processing. The error transfer principle of machine tools is an important factor to improve the precision of machine tools. Based on multibody system theory and homogeneous transformation matrix theory, a geometrical error model of three-axis CNC milling machines is proposed in this paper. In addition, the global sensitivity analysis of machine tool errors was carried out to identify important errors. The analysis model has two layers of higher dimensional integration; hence, in the aim of solving this issue, a multiplication dimension reduction method was used in this paper. By this means, a one-dimensional integration model was obtained, and sensitivity analysis of machine tool geometric errors was realized. The present work provides a good theoretical basis for the optimization design and error compensation of machine tools.

The Errors Recognition and Compensation for the Numerical Control Machine Tools Based on Laser Testing Technology

Abstract To improve the accuracy of numerical control machine tools error, this paper studies the application of laser testing technology in numerical control machine tool, and put forward a laser interferometer automatic aiming system which can conduct space error measurement. The system, in the process of the NC machine tool operating, can measure the machine tool space curve through changing the direction of the laser. The principle of laser interferometer and matlab analysis are adopted, through the experiment of laser interference technology in the numerical control machine tool, the law curve of error in NC machine tools is obtained, getting the method of error of NC machine tools. When conducting laser testing error experiment in NC machine tool, the results show that the laser testing can measure aggregated error and thermal error of NC machine tool better, with small control of environment and high accuracy of measurement.

Cnc machine tool error compensation system implementation strategies and their constraints

This paper deals with the constraints imposed on error compensation systems by their implementation strategies. Constraints stemming from the structure of the control system with an NCK architecture of the ADCBI type are presented. Practical realizations of compensation and potential solutions offered by contemporary commercial CNC controllers are discussed.

Dynamic error of CNC machine tools: a state-of-the-art review

The dynamic error of CNC machine tools, which often exceeds the quasi-static error at high-speed machining, becomes the main reason affecting the machining error of the sculptured surface parts. Although much research efforts have been dedicated to dynamic error, there is a lack of systematical summaries. In this review, firstly, the dynamic error is defined as the deviation of actual displacement of effector end of axis relative to reference displacement during feed motion. Secondly, according to the mechanical and control structure of the servo feed system, the dynamic error is divided into two components: dynamic error inside the servo loop (component 1) and dynamic error outside the servo loop (component 2). Based on the two components, the causes resulting in the dynamic error are analyzed from the points of view of the servo feed system itself and its input (setpoints). Thirdly, the basic strategies for reducing the dynamic error of individual axis, as well as for reducing the trajectory dynamic error by coordinating the dynamic error of individual axis, are summarized. Finally, the problems and future research directions on dynamic error are analyzed. It is concluded that resolving the contradiction between the setpoints and the servo feed system is still a great challenge for dynamic error in high-speed machining. To achieve high dynamic accuracy at high-speed machining, the control strategies on the dynamic error outside the servo loop should be further developed and integrated into dynamic error inside the servo loop-oriented control strategies. Meanwhile, the servo feed system itself and its input need to be investigated as a whole, so that the servo feed system of each axis can adapt to the differences and changes of the setpoints, and the differences in the servo dynamics of each axis can be considered in the setpoints.

Data-driven thermally-induced error compensation method of high-speed and precision five-axis machine tools

The data-driven thermal error compensation method of high-speed and precision five-axis machine tools was proposed based on the homogeneous transformation. The compensation component was obtained by analyzing the error transmission chain of machine tools and was expressed as the transmission matrix consisting of thermal error terms of linear axes and spindle system according to the differential movement of the compensation axis. From the view of thermal error generation mechanism, the thermal error of the linear axis was formulated as the product of the polynomial function with time as its independent variable and the polynomial function with position as its independent variable. Then the thermal errors of the linear axes were decomposed and identified from the measured positioning error. The thermal error of the spindle system was identified by the thermal characteristic experiments. The compensation component in each direction is calculated by substituting the identified thermal error terms of the linear axes and spindle system into the data-driven thermal error model. Finally, to demonstrate the effectiveness of the proposed method, the thermal error at a new working condition was predicted, and then the error compensation and actual machining were carried out. The results show that the machining error is reduced by more than 85% and 37% with the present error compensation compared with that without compensation and that without traditional error compensation, respectively. This research sheds new light on both the generation mechanism and the compensation method of the thermally-induced error of five-axis machine tools.

Framework and case study of cognitive maintenance in Industry 4.0

We present a new framework for cognitive maintenance (CM) based on cyber-physical systems and advanced artificial intelligence techniques. These CM systems integrate intelligent deep learning approaches and intelligent decision-making techniques, which can be used by maintenance professionals who are working with cutting-edge equipment. The systems will provide technical solutions to real-time online maintenance tasks, avoid outages due to equipment failures, and ensure the continuous and healthy operation of equipment and manufacturing assets. The implementation framework of CM consists of four modules, i.e., cyber-physical system, Internet of Things, data mining, and Internet of Services. In the data mining module, fault diagnosis and prediction are realized by deep learning methods. In the case study, the backlash error of cutting-edge machine tools is taken as an example. We use a deep belief network to predict the backlash of the machine tool, so as to predict the possible failure of the machine tool, and realize the strategy of CM. Through the case study, we discuss the significance of implementing CM for cutting-edge equipment, and the framework of CM implementation has been verified. Some CM system applications in manufacturing enterprises are summarized.

Research on Reliability of Positioning Error Measurement for NC Milling Machine

Laser interferometer is the common tool to measure the positioning error of CNC machine, and its measurement process will be affected by external factors. Therefore, it is very important to ensure the error accuracy which measured by laser interferometer for compensating the error of CNC machine tools. The positioning error of MVC850B CNC milling machine was measured by Renishaw laser interferometer. Firstly, the positioning error of it was measured in standard and actual environmental parameters, and measured results were comparatively shown in factors of temperature, air pressure and humidity. Secondly, the influence degree that in three conditions of feeding speed, interval distance and processing time was analyzed by the errors of reverse clearance and screw pitch cumulative. Finally, with the statistics of positioning errors measured in a certain period of time, this paper analyzed the reliability of positioning errors measured by laser interferometer and analyzed the variation of milling machine motion axis errors. Meantime, the possible location of machine errors can be predicted, and the positioning accuracy of CNC milling machine would be promoted.

Machine-Tool Error Observer Design With Application to Thermal Error Tracking

Abstract A parameter identification procedure for identifying the parameters of a volumetric error model of a large machine tool requires hundreds of random volumetric error components in its workspace and thus takes hours of measurement time. It causes thermal errors of a large machine difficult to be tracked and compensated periodically. This paper demonstrates the application of the optimal observation design theories to volumetric error model parameter identification of a large five-axis machine. Optimal designs maximize the amount of information carried in the observations. In this paper, K-optimal designs are applied for the construction of machine-tool error observers by determining locations in the workspace at which 80 components of volumetric errors to be measured so that the model parameters can be identified in 5% of an 8-h shift. Many of optimal designs tend to localize observations at the boundary of the workspace. This leaves large volumes of the workspace inadequately represented, making the identified model inadequate. Therefore, the constrained optimization algorithms that force the distribution of observation points in the machine’s workspace are developed. Optimal designs reduce the number of observations in the identification procedure. This opens up the possibility of tracking thermal variations of the volumetric error model with periodic measurements. The design, implementation, and performance of a constrained K-optimal in tracking the thermal variations of the volumetric error over a 400-min period of operation are also reported. About 70–80% of machine-tool error can be explained using the proposed thermal error modeling methodology.

The formation of a variation method for calculating the accuracy of metal cutting systems

The paper is devoted to the topical issue of the formation of a variation method for calculating the accuracy of metal cutting systems. The current state of the basic variation method for calculating the geometric accuracy of metal cutting machines is determined. A transition from considering the geometric accuracy of only the metal cutting machine to considering the accuracy of the metal cutting system is made, which includes the metal cutting tool. The proposed directions for the development of the method are recommended to be divided into groups according to the criterion of linearized and non-linear formulation when building accuracy balances. The solution of the problem posed in the paper serves as a methodological basis for work on normalization and compensation of geometrical errors of machine tools, including the creation of the foundations of standards for the accuracy of metal-cutting machines and tools. This work is useful for scientists engaged in the study of the geometric accuracy of processing on metal-cutting machines, as well as the normalization and compensation of the geometric errors of machines.

Thermal error compensation in CNC machine tools using measurement technologies

The required machining accuracy can be realized by compensating the thermal error of the machine tool. The paper presents a method of constructing a system of compensation for the thermal error of the machine tool. The method is based on the part measurement system installed on the machine. A review of studies in the field of precision machining was conducted. The review showed that the methods of correction of machining errors caused by dynamic and static factors using OMM-technology (On Machine Measurement) is presented in the literature. At the same time, the methods of compensation of the thermal error of machine tool built on the use of OMM-technology are poorly represented. Therefore, the practical implementation of control algorithms of the working bodies of the machine allowing one to compensate for its thermal error using OMM-technology is in demand. The methodology contains seven main stages, methodologically covering four areas of research. In addition to the experimental, mathematical and measurement areas of research, they also distinguish the area of software development (preparation of NC programs for CNC machines). It is proved that the presented methodology allows one to develop own automated system of compensation of a thermal error for any machine tool. It is shown that the most important directions of the framework for the improvement of the effectiveness of such system are to ensure the completeness of the experimental base and the accuracy of the adjustment of the thermal error compensation algorithms of the machine tool.

Research on Error Modeling and Identification Technology of CNC Camshaft Grinder

Taking certain type of CNC camshaft grinders as the research object, through the analysis of its structure and movement to determine a total of 21 error parameters, a model describing the motion relations between adjacent body coordinate systems containing the error parameters was established. The machine movements were classified into two kinematic chains: the “bed-workpiece” and “bed-tool”. The topological structure of the machine tool was built and then the multi-body system theory was applied to model the errors of the machine tool. Body coordinate systems and motion reference coordinate systems were set up on each moving body and the corresponding transformation matrix was derived by joining the motion relation models between adjacent body coordinate systems. In order to achieve precision machining in the case of the existence of influential errors, a constraint equation Pw = Pt was put forward and solved. A mathematical model of the X-C axis linkage during camshaft grinding was proposed to work out the grinding point coordinates in the workpiece coordinate system and tool coordinate system. Three kinds of measurement methods were provided to identify 15 error parameters affecting the camshaft machining by using a cue instrument, which provides necessary conditions to research the machine tool error compensation.

Binocular vision-based 3D method for detecting high dynamic and wide-range contouring errors of CNC machine tools

Periodic checking for contouring error in unloading conditions can effectively evaluate the dynamic performance of machining centers. Existing measurement devices have limitations in the high accuracy three-dimensional (3D) measurement of arbitrary contouring errors (e.g. ballbar and cross-grid encoder). Thus, in this paper, a cost-effective binocular vision-based 3D method for detecting high dynamic and wide-range contouring error of computer numerical control machine tools is proposed. With this method, the strobe lighting method is first presented to suppress the blurring effect of the newly designed 1024 coded targets that were embedded in the measurement fixture. Thereafter, an encoding and decoding method based on finding the optimal initial non-encoding region is proposed to automatically identify, match, and reconstruct the time-varying targets. Then, to enhance the performance of the vision system, a calculated method based on three visible non-collinear coded targets is presented to deduce the dynamic and large-scale contouring error. Finally, contouring error detection experiments are carried out in a self-built five-axis machine tool to validate the advantages of the method. Both the proposed vision method and cross-grid encoder are used to measure contouring errors of three types of trajectories under different feed rates. By comparing the difference between the two trajectories measured by the two devices, the experimental results illustrate that the mean vision detection error at 7 m min−1 is about 4.3 µm, which verifies the accuracy and effectiveness of the proposed vision measurement method.

Measurement method for volumetric error of five-axis machine tool considering measurement point distribution and adaptive identification process

To improve the machine tool accuracy, geometric error identification is required for volumetric error compensation. This paper presents a method for the geometric error identification of a five-axis machine tool that considers the optimised distribution of measurement points and accurate description of geometric errors. The measurement is performed using a laser tracker that permits rapid error data collection over a large measurement range. In the volumetric error modelling, the geometric errors are described as position-dependent Chebyshev polynomials. Hence, the identification of geometric errors is converted into the identification of polynomial coefficients. In the identification process, a distribution method for measurement points is proposed to improve the identification accuracy by minimising the influence of measurement error on the identification result. At the same time, an adaptive approach is introduced to accurately define the polynomial orders of geometric errors to improve the identification accuracy. Simulations and experiments are conducted to verify the geometric error identification method. In addition, the proposed method is compared with other methods. Based on the identification result of geometric errors and the volumetric error model, the volumetric error of any position in a workspace can be predicted and further compensated.