NC Machine Tools Research Articles

永久磁石同期電動機の高精度駆動のための電圧飽和を回避し磁気飽和を考慮した電流制御パラメータ決定法

For use as a drive motor in a high precision NC machine tool feed axis, a permanent magnetic synchronous motor (PMSM) requires a highly responsive current control loop. Without consideration of the PMSM electromagnetic characteristics such as voltage saturation and magnetic saturation, the current control loop may be unstable. This paper proposes a method for determination of the PMSM current control parameters providing such high response, while avoiding voltage saturation by inverter output voltage constraint or declination of inductance by magnetic saturation. Experiments were done using two representative PMSMs alone and also using a machine tool. Testing confirmed that the proposed method is effective for achieving a highly responsive current control loop and making the cutting surface smoother.

Reliability Parameter Interval Estimation of NC Machine Tools considering Working Conditions

Aiming at the problem that the parameter interval estimation of NC machine tool’s reliability model considering working conditions established by Hongzhou is difficult to implement, given that it has several independent variables, an improved interval estimation method based on Bootstrap is proposed. Firstly, the two-step estimation method was used to calculate the point estimation of NC machine tool’s reliability parameter in test field, based on which B resamplings are generated based on the point estimation. The reliability parameter’s point estimation of the resamplings was obtained by maximum likelihood estimation. Permutation of B point estimations was made in ascending order and the interval estimations were obtained by the α quantile of the permutation. Case study indicated that the location and length of the interval estimation of NC machine tools’ reliability parameter, under different levels of working condition covariates, vary obviously.

NC工作機械の運動誤差を考慮した加工面シミュレーション技術

NC工作機械の運動誤差を考慮した加工面シミュレーション技術

An accuracy design approach for a multi-axis NC machine tool based on reliability theory

Accuracy design constitutes an important role in machine tool designing. It is used to determine the permissible level of each error parameter of a machine tool, so that any criterion can be optimized. Geometric, thermal-induced, and cutting force-induced errors are responsible for a large number of comprehensive errors of a machine tool. These errors not only influence the machining accuracy but are also of great importance for accuracy design to be performed. The aim of this paper is the proposal of a general approach that simultaneously considered geometric, thermal-induced, and cutting force-induced errors, in order for machine tool errors to be allocated. By homogeneous transformation matrix (HTM) application, a comprehensive error model was developed for the machining accuracy of a machine tool to be acquired. In addition, a generalized radial basis function (RBF) neural network modeling method was used in order for a thermal and cutting force-induced error model to be established. Based on the comprehensive error model, the importance sampling method was applied for the reliability and sensitivity analysis of the machine tool to be conducted, and two mathematical models were presented. The first model predicted the reliability of the machine tool, whereas the second was used to identify and optimize the error parameters with larger effect on the reliability. The permissible level of each geometric error parameter can therefore be determined, whereas the reliability met the design requirement and the cost of this machining was optimized. An experiment was conducted on a five-axis machine tool, and the results confirmed the proposed approach being able to display the accuracy design of the machine tool.

Key geometric error extraction of machine tool based on extended Fourier amplitude sensitivity test method

Machining accuracy is a very important index to measure the performance of NC machine tools, and how to improve the machining accuracy grabs the attention of both manufacturers and users. Since the geometric errors are intercoupling and are one of the main factors affecting machining accuracy of machine tools, in this paper, a new method for extracting key geometric errors based on the screw theory and extended Fourier amplitude sensitivity test (EFAST) method was proposed. First, screw theory was introduced, and the machining accuracy modeling of a three-axis vertical machining center (VMC) was established. Then, in order to analyze the coupling effects between geometric errors by high-dimensional nonlinear model, EFAST global sensitivity analysis method was adopted to help in extracting the main geometric errors. An illustration example on a three-axis VMC shows that the proposed method is effective and can be helpful to improve the geometric accuracy of machine tool.

Kinematic Structures for Processing of Surfaces with a Circle Directrix and a Straight Line Generatrix (Part IV)

A body with a given geometry can be obtained by various manufacturing procedures, entailing, however, different surface quality, dimensional precision and (most importantly) productivity. Each body is characterised by one or more surfaces, simple or complex, as the case may be. It is known that a surface is characterised by a directrix and a generatrix, as well as by the modality of its physical achievement by means of the machines and tools uses for manufacturing. The directrix is obtained as a result of a primary motion and possibly one or more secondary motions. The generatrix is obtained as a result of one secondary motion, rarely more. If the generatrix is materialized on a tool, then a secondary motion is not necessary. In addition one or more auxiliary motions are needed. Other generation modalities not excluded, from the theory of surface generation on machine-tools it is known that the directrix, as well as the generatrix can be: materialized; generated by copying; kinematically generated as the trajectory of a point; kinematically generated as the envelope of a family of curves; generated by rolling; or programmed. Typically in literature generation “by copying” and “programmed generation” of the directrix and generatrix are not addressed distinctively, both being assumed as of the same nature. The recent evolution of industrial electronics and implicitly of machine-tools has determined a clear differentiation between the kinematics and construction of machine-tools (still) using generation by copying from a master and the kinematics of NC machine-tools. The paper is one of kinematic synthesis, oriented towards innovation-invention, and presents by means of examples, not necessarily known or typical, all six cases of generation of surfaces characterised by a straight line generatrix and a circle directrix obtained kinematically as the envelope of a family of curves.

Development and evaluation of a three-component micro-cutting force wireless measurement apparatus and method in turning-milling compound machining

As a supplement to silicon micromachining technology, micro-turning-milling compound machining technology is perceived as a core requirement for non-silicon complex three-dimensional microstructures. In the micro-turning-milling compound machining process, three-component cutting force is the key factor that affects machining accuracy, surface roughness, machining efficiency and processing stability of the component; it is also a prerequisite in determining reasonable cutting parameters and in the machining process. In this study, a new design scheme of ‘direct measurement, wireless transmission’ was proposed to measure the three-component micro-cutting force in a turning-milling-compound machining process. On one hand, the three-component micro-cutting force was measured directly by four sensors installed on the turning spindle. On the other hand, the measured cutting force was sent to a computer indirectly through a Zigbee wireless communication system. Furthermore, a three-component micro-force sensor and wireless measurement apparatus were proposed for the measurement of the three-component micro-cutting force. A series of simulations were conducted to verify the performance of the designed sensor and the wireless measurement apparatus. A calculation method was proposed to extract the three-component cutting force from the 12 channels of signals from four force sensors during static and dynamic measurement. Calibration experiments for the designed sensor, as well as for the whole measuring apparatus, were conducted both statically and dynamically. A series of actual turning-milling compound machining experiments on a turning-milling-lapping compound five-axis NC machine tool was also presented. The results of calibration, and actual machining, experiments indicate that the proposed apparatus and method work well and could measure a three-component cutting force to an uncertainty of ±2‰.

An approach of comprehensive error modeling and accuracy allocation for the improvement of reliability and optimization of cost of a multi-axis NC machine tool

Machining accuracy is critical for the quality and performance of a mechanical product, and the reliability of a multi-axis NC machine tool reflects the ability to reach and maintain the required machining accuracy. The objective of this study is to propose a general methodology that will simultaneously consider geometric errors and thermal-induced errors to allocate the geometric accuracy of components, for improving machining accuracy reliability under certain design requirements. The multi-body system (MBS) theory was applied to develop a comprehensive volumetric error model, showing the coupling relationship between the individual errors of the components of this machine tool and their volumetric accuracy. Additionally, a thermal error model was established based on the neural fuzzy control theory and was compared to the common thermal error modeling method called BP neural network. Based on the traditional cost model and the reliability analysis model, a geometric error-cost model and a geometric error-reliability model were established, taking the weighted function principle into consideration. Then, an allocation approach of the geometric errors, for optimizing total cost (manufacture and QLF) and reliability, subject to the geometrical and operational constraints of the machine tool, was proposed and formulated into a mathematical model, in order to perform the optimization process of accuracy allocation by using the advanced NSGA-II algorithm. A case study was also performed in a five-axis machine tool, and the traditional NSGA algorithm was used for comparison. The optimization results for the five-axis machining center showed that the proposed approach is effective and able to perform the optimization of geometric accuracy and improve the machining accuracy and the reliability of the machine tool.

Development of an Information Management System for NC Machine Tools Based on B/S Architecture

With the development of computer and Internet technology, enterprises need scientific and effective management of the available information resources to make full use of them. Traditionally, paper is used as the medium. However, information on paper is hard to edit, store, and check. Moreover, this way has a higher requirement for employees. This study adopts B/S architecture to build an information management system, which contains complete NC machine tools as well as components. The system uses a framework as the development platform, and uses SQL Server 2005 as the database. This application can fit most browsers.

Research on Online Collision Detection Algorithm of CNC Machine Tools

Collision detection is the core of the numerical control system of intelligent manufacturing in the manufacturing process of rapid feeding, positioning and cutting. We need to avoid collision between the cutting tools, machine tools and workpiece. Based on the characteristic of five-axis CNC system, we analyze the advantages and disadvantages of Hierarchical Mesh Segmentation and Octree. At last, we use the collision detection algorithm of cuboid and separation axis to optimize the algorithm of traditional NC machine tool collision detection, which improve the detection efficiency and accuracy.

Assessment method of heavy NC machine reliability based on Bayes theory

It is difficult to collect the prior information for small-sample machinery products when their reliability is assessed by using Bayes method. In this study, an improved Bayes method with gradient reliability (GR) results as prior information was proposed to solve the problem. A certain type of heavy NC boring and milling machine was considered as the research subject, and its reliability model was established on the basis of its functional and structural characteristics and working principle. According to the stress-intensity interference theory and the reliability model theory, the GR results of the host machine and its key components were obtained. Then the GR results were deemed as prior information to estimate the probabilistic reliability (PR) of the spindle box, the column and the host machine in the present method. The comparative studies demonstrated that the improved Bayes method was applicable in the reliability assessment of heavy NC machine tools.

The NC Machine Tool Roundness Error Test Method Based on EIB741

The NC Machine Tool Roundness Error Test Method Based on EIB741

Research on geometric error measurement system of machining center BV75 based on laser interferometer

This paper measures the twenty one geometric errors of numerical control machining center with parameter identification through laser interferometer, the main contents illustrate the measurement system, measurement model and some testing results combined with specific experimental conditions, at the same time provide particular reference value on numerical control machine tool(NC machine tool) geometric precision detection.

NC工作機械の送り軸のための2慣性系モデルによる低周波振動抑制制御の研究

Large NC machine tools or NC machine tools with elastic parts such as reducers tend to have mechanical low frequency vibration. With high gain servo control, low frequency vibration appears as machining point vibration, and results in deterioration of machining surface. In this article, two anti-vibration control methods to suppress machining point vibration are proposed based on two-mass model; one is for semi-closed control and the other is for full-closed control. The basic idea of the proposed control laws is to regard the position reference from NC not as for motor but as for load of two-mass system. Experiments were done and it is shown that both proposed laws effectively suppress the load angular error by allowing motor angular error.

振動操作関数によるＮＣ工作機械送り系軌道の離散サンプル値制御（減衰を考慮しない場合について）

振動操作関数によるＮＣ工作機械送り系軌道の離散サンプル値制御（減衰を考慮しない場合について）

Controlling the Parameters of the Component Quality Using Program Means While Performing Mechanical Machining

In this article the methods of program control for forming of the quality parameters and operational properties of surfaces of machine components by the set law both using universal metal cutting machines and NC machine-tools are considered. The working principle of the programming system of surface plastic deformation having an elastic effect with the use of universal lathes is presented. Using the example of a technological system, featuring the preliminary cutting and finishing surface plastic deformation processing, a method of controlling quality parameters and operational properties of surfaces of machine components taking into account technological heredity is considered. Several dependencies received on the basis of physical-statistical models are shown which give an opportunity to envisage the results of controlling the machining processes or to determine the required machining regimes. The results of controlling the parameters of roughness of a flat surface following the trapezoidal law of changing the load during the diamond burnishing of the processed part are presented.

Reliability Evaluation of NC Machine Tools considering Working Conditions

Reliability evaluation is the basis for reliability design of NC machine tools. Since traditional reliability evaluation methods do not consider the working conditions’ effects on reliability, there is a great error of a result of a traditional method compared with an actual value. A new reliability evaluation model of NC machine tools is proposed based on the Cox proportional hazards model, which describes the mathematical relation between the working condition covariates and the reliability level of NC machine tools. Firstly, the coefficients of working condition covariates in the new reliability evaluation model are estimated by the partial likelihood estimation method; secondly, the working condition covariates which have no effects on the reliability of NC machine tools are eliminated by the likelihood ratio test; then parameters of the baseline failure rate function are estimated by the maximum likelihood estimation method. Thus, the reliability evaluation model of NC machine tool is obtained under different working conditions and the reliability level of NC machine tools is obtained. Case study shows that the proposed method could establish the relation between the working condition covariates and the reliability level of NC machine tools, and it would provide a new way for the reliability evaluation of NC machine tools.

Free Surface NC Machining Tool Path Optimization Algorithm Based on the Iso-Scallop Method

In order to solve the problem of free surface processing of tool redundancy,the tool lack problem, and the demerit of low machining efficiency, etc., based on the iso-scallop method, based on the iso-scallop method, we put forward a kind of free surface NC machining tool path optimization algorithm,make the surface boundary discrete point set, which is generated by point set ring machining path, diagonal connection and then use the path of the adjacent curve, forming cutting tool machining line.finally, the calculation of step size and line spacing in machining path based on the iso-scallop method and the process of feeding direction is optimized. Proved by the simulation process, the algorithm is feasible and can effectively avoid tool redundancy and tool lack problems,concesquently, processing efficiency improved significantly.

Makespan estimation of a production process affected by uncertainty: Application on MTO production of NC machine tools

In this paper we address the estimation of the duration of the production process of a complex product in a Make-To-Order (MTO) or Engineering-To-Order (ETO) environment, a common situation in the manufacturing sector, specifically when production operations are executed by human operators. The addressed products, due to their complexity and high degree of customization, are specifically designed for a customer, together with their production process. On the other hand, the uncertainty affecting the production problem must be considered due to the presence of operations executed by human operators, the high level of customization entailing the need to cope with new products and processes and the behavior of the production environment.The proposed approach deals with the estimation of the duration of a production process modeled through a project network whose activities have an uncertain duration. It can provide support to a manager in the estimation of the makespan of the production of a product to provide a realistic and competitive due date to the customer, as well as to manage the scheduling of production and supplying operations and the resources assignment within the plant.The proposed approach is described, validated and compared with existing approaches through an ideal case. Moreover, a real case application is provided, related to the assembly process of a NC machine, to demonstrate its industrial viability.

The Modeling Methods of Heavy NC Machine Tool Bolt Joint Based on Virtual Media

The Modeling Methods of Heavy NC Machine Tool Bolt Joint Based on Virtual Media