Fuzzy estimation of feed-cutting force from current measurement-a case study on intelligent tool wear condition monitoring

It is very important to use a reliable and inexpensive sensor to obtain useful information about manufacturing processing, such as cutting force for monitoring automated machining. In this paper, the feed-cutting force is estimated using inexpensive current sensors installed on the ac servomotor of a computerized numerical control (CNC) turning center, with the results applied to the intelligent tool wear monitoring system. The mathematical model is used to disclose the implicit dependency of feed-cutting force on feed-motor current and feed speed. Afterwards, a neuro-fuzzy network is used to identify the cutting force with current measurement only. This hybrid math-fuzzy approach will reduce the modeling uncertainty and measurement cost. Finally, the estimated cutting force is applied in the tool-wear monitoring process. Successful experiments demonstrate robustness and effectiveness of the suggested method in the wide range of tool-wear monitoring applications.     

Fuzzy logic for constant force control of end milling

The machining condition usually has significant variation resulting from the change of cutting depth and the intrinsic property of the workpiece. In order to maintain the performance of a classical proportional integral derivative control system, the tool life and machining quality, conservative feedrate, and cutting depth change are prespecified as the limitations of computer numerically controlled operators. Therefore, constant cutting force control is proposed as a useful approach for increasing the metal removal rate and the tool life. However, the model-based controller cannot handle the nonlinearity of a force control system due to cutting condition variations. Here, a fuzzy controller with learning ability was employed to improve both the system performance and the adaptability. This control approach vias implemented on a retrofit old-fashioned milling machine for the end milling process. The experimental results show that this control strategy has smooth feedrate and good cutting force dynamic responses     

Cross-coupled fuzzy logic control for multiaxis machine tools

This paper presents a design and implementation case study that focuses on contour control of a biaxial CNC machine tools. Since, it is difficult to obtain an accurate nonlinear mathematical model of cross-coupled multiaxis machine tools, here we investigate an alternative to conventional approaches where we employ crosscoupled fuzzy logic controllers for improving the contouring accuracy of multiaxis CNC machine tools. A new fuzzy rule-generated method which is based on a performance index of the contour error obtained from an on-line estimation algorithm is proposed. An adapted output scale factor is adopted to improve the system performance. Experimental results have shown that the desired contouring accuracy can be achieved, and the proposed approach outperforms over uncoupled approaches. In conventional control, increasing contour feedrate for productivity may result in larger contour errors. However, the experimental results have shown that the performance of the proposed approach is still quite good with increasing contour feedrate.     

数控机床主轴系统衰变监测技术

主轴系统是数控机床的重要组成部分,为金属切削提供切削力矩和切削速度,其性能直接影响机床的加工精度和效率。文中对数控机床主轴系统主要部件进行故障机理分析,基于故障机理设计了一种监测方案,通过外置传感器采集主轴系统主要部件的运行信息,并采用小波分析技术分析其运行信息,从而达到对主轴系统实时监测的目的。实验结果表明,文中案可以有效地检测出主轴系统主要部件的故障情况。     

数控机床多故障诊断专家系统设计

系统以数控机床的数控系统为分析对象,结合某数控公司提供的故障分析手册和积累的案例以及参照该公司故障诊断专家给出的诊断方法,学习其他的专家系统的成功经验,设计了一套数控机床图形化多故障诊断系统.文中介绍了数控机床故障诊断专家系统中的一个故障诊断的方法,它具有多故障诊断的能力,可以图形化辅助诊断过程.开发了一种新的匹配算法,它是由最近相邻算法根据本系统的实际情况而开发的一种新算法.对于多故障诊断,系统采用化多故障为单故障处理的方法.开发了图形化辅助诊断功能,提高了诊断系统的实用性.开发了针对数控机床故障诊断的自学习功能,实现了故障诊断的经验积累.     

A new health estimation model for CNC machine tool based on infinite irrelevance and belief rule base

To guarantee the normal workflow and determine scheme of optimal maintenance, it is important to accurately estimate the health condition of computerized numerical control (CNC) machine tool. In current studies, the health condition of CNC machine tool is modeled by using one feature. Due to the complexity of CNC machine tool, the estimating accuracy of the current models is poor and real-time performance cannot be satisfied when multiple features are chosen. Moreover, it is difficult to obtain more effective monitoring data when the CNC machine tool is from normal to failure. To solve the problems, based on infinite irrelevance and belief rule base (BRB), a health estimation model which is named as the infinite irrelevance BRB model is proposed in this paper. In particular, the infinite irrelevance method is used to select key features to optimize the model structure, and BRB is applied to estimate the health condition according to the monitoring data and expert knowledge. Thus, the quantitative monitoring data and expert knowledge can be used effectively to improve accuracy and real-time performance of health estimation. Furthermore, because the initial values of the parameters in the proposed infinite irrelevance BRB model given by experts may not be accurate, the constraint covariance matrix adaptation evolution strategy (CMA-ES) algorithm is employed to train the parameters. A case study for the servo system of the CNC milling machine is used to verify the effective and accuracy of the proposed model. The results show that the infinite irrelevance BRB model can accurately estimate the health condition of the servo system.     

Control system for the waterjet cutting Machine

This paper addresses the field of factory automation within the scope of machine control. It presents the control system for a waterjet cutting machine. It involves a PC based computer numerical control (CNC) controller that has been built on a QNX real-time (RT) operating system platform. Microsoft Windows, which is a commonly accepted graphical user interface environment, serves as a human machine interface (HMI) front-end. The CNC controller and the HMI are interconnected by the Ethernet TCP/IP link. The control system is flexible and modular. It supports CAD/CAM and a network link to the office-level of factory automation. The application is thoroughly presented with the highlight on RT features; the QNX RT operating system is analyzed in detail. Moreover, Ethernet TCP/IP technology for the use in a networked automated factory is also put in the foreground.     

FPGA based acceleration and deceleration circuit for industrial robots and CNC machine tools

In order to make industrial robots and computer numerical control (CNC) machine tools perform tasks efficiently, many techniques for the acceleration and deceleration of industrial robots and CNC machine tools have been proposed. Polynomial technique can generate velocity profiles of various acceleration and deceleration characteristics, but it requires a lot of computations. Digital convolution technique can generate efficiently velocity profiles, but it cannot generate velocity profiles with some kinds of acceleration and deceleration characteristics. This paper proposes an efficient approach for generating velocity profiles that cannot be generated by previous techniques as well as velocity profiles generated by them. Based on the proposed approach, an acceleration and deceleration circuit for industrial robots and CNC machine tools is designed by using the VHDL and it is implemented with a FPGA. A velocity profile generated by the acceleration and deceleration circuit will be applied to one single-axis control system.     

Special purpose processor for parameter identification of CNC second order servo systems on a low-cost FPGA platform

The parameter identification process has an important role in servo systems tuning on computer numerical control (CNC) machine tools. The parameter identification is mostly done off-line due to the high computational load carried by the identification algorithms. In this work, we present a novel hardware architecture for an application specific processor implementing the recursive least-squares algorithm for the on-line identification. The developed processor is simulated and tested with the necessary elements to perform the CNC machine servo system control. The system was implemented in a low-cost FPGA, getting a maximum sample frequency of 40 kSps.     

Discrete-time model predictive contouring control for biaxial feed drive systems and experimental verification

In this paper we present a novel algorithm to model predictive contouring control for biaxial feed drive systems. model predictive control (MPC) refers to a class of model-based controllers that uses an explicit process model and tracking error dynamics to predict the future behavior of a plant, making it effective for machine tool feed drive systems that must achieve high-precision motion and are severely affected by friction, cutting force and changes in the workpiece mass. To improve contouring performance, we propose a new performance index in which error components orthogonal to the desired contour curve are given more importance than tracking errors with respect to each feed drive axis. Controller parameters are calculated in real time by solving an optimization problem. The parameters depend on the instantaneous slope of the reference trajectory and thus vary with time for curved reference trajectories, resulting in a time-varying controller. Weighting factors for the error components in orthogonal and tangential directions are used to adjust the error importance in each direction. In addition, to consider the required feed drive energy, the control inputs in both directions are included in the performance index. The effectiveness of the proposed control approach is demonstrated with an experimental biaxial feed drive system for circular and non-circular trajectories. The proposed contouring controller allows the feed drive to follow smooth curves and reduces contouring error.     

Control of linear motor machine tool feed drives for end milling: Robust MIMO approach

Linear motors are getting promising for use as high speed, high accuracy machine tool feed drives. The cutting force in the machining process are directly reflected to the linear motor due to no gearing mechanism. To achieve high accuracy machining, the controller for the linear motor system should be designed to compensate for the cutting force.

In this work, a MIMO H_∞ controller for the linear motor machine tool feed drives has been designed to reduce tracking errors induced by cutting forces for end milling. The controller is designed using normalized coprime factorization method for the dynamic model of the linear motor system. The model includes constant in-line and cross coupling force gain, since the feedback cutting force can be considered as the product of the constant gain and the moving velocity of each axis.

Analysis of the structured singular value shows that the designed controller has good robust performance despite wide variations of the cutting force and physical parameters. It is directly implemented on a linear motor X–Y table which is mounted on a milling machine to have cutting experiments via a DSP board. Experimental results verified effectiveness of the proposed scheme to suppress the effects of the cutting force in the high feed rate.     

A generalized approach for the acceleration and deceleration ofindustrial robots and CNC machine tools

Many techniques for the acceleration and deceleration of industrial robots and computer numerical control (CNC) machine tools have been proposed in order to make industrial robots and CNC machine tools perform given tasks efficiently. Although the techniques selecting polynomial functions can generate various acceleration and deceleration characteristics, the major problem is the computational load. The digital convolution techniques are more efficient than the techniques selecting polynomial functions. However, neither velocity profiles of which the deceleration characteristics is independent from the acceleration characteristics nor those of which the acceleration interval is different from the deceleration interval can be generated by the digital convolution techniques. This paper proposes a generalized approach for generating velocity profiles that cannot be generated by the digital convolution techniques. According to the desired characteristics of acceleration and deceleration, each set of coefficients is calculated and is stored. Given a moving distance, and acceleration and deceleration intervals, a velocity profile having the desired characteristics of acceleration and deceleration can be efficiently generated by using these coefficients. Several velocity profiles generated by the proposed technique are applied to one single-axis control system     

钛合金超精密切削过程的数值模拟与实验分析

以钛合金材料TC源的超精密切削加工机理为研究目的,采用有限元技术与实验验证相结合的方法,建立了钛合金材料超精密切削过程的正交切削有限元模型,深入介绍了有限元建模过程中有限元模型的建立、材料应力应变关系等关键技术。采用建立的有限元模型对钛合金的加工过程进行了正交切削有限元模拟。通过模拟获得了切屑形成过程、切削力曲线以及温度分布等结果。应用单点金刚石车床进行了钛合金TC4 的超精密车削实验, 研究结果显示数值模拟结果与实验结果比较吻合。数值模拟方法的有效性也得到了验证,可以进一步用来研究钛合金材料的切削过程。     

基于PLC的数控机床电气控制系统研究

为了提高数控机床的加工精度及安全可靠性,本文基于PLC对数控机床的电气控制系统进行设计,设计了上位机功能、PLC程序、伺服机构,并对系统的精度进行了验证,结果表明,数控机床的精度较高。     

CNC机床功率传感型记忆式监控技术

本文提出了ＣＮＣ机床功率传感器记忆式监控技术和机床加工功率信息窗参数记忆技术，同时给出了ＣＮＣ机床批量加工的起控技术方案，成功地解决了变负载加工过程的监控。     

Spatial hybrid/parallel force control of a hexapod machine tool using structure-integrated force sensors and a commercial numerical control

Structure-integrated force measurement in hexapod structures or kinematics offers great potential for spatial process force control in six degrees of freedom. Although force control has been studied for many years, research questions remain unanswered, especially when regarding parallel kinematic machine tools with numerical control and integrated sensors. This contribution summarizes the technology of structure-integrated force sensing in hexapod machine tools and develops two approaches to use the measured signals for direct hybrid/parallel force control. For different use-cases, such as teach-in or synchronous force/position control with variable task frame, different approaches of set-point specification and injection of manipulated values are studied from a practical point of view. As a result of the work, the feasibility of the force control with structure-integrated sensors on a commercial CNC can be confirmed through appropriate experiments. Furthermore, the realized G-Code integration represents a practical solution for programming force-controlled machine tools in an easy and concise way from the NC programme.     

汇川技术在数控高速立式月饼机上的系统解决方案

本文介绍了汇川技术触摸屏、PLC、伺服和变频器全系列产品在数控高速立式月饼机上的成功应用,通过优异的矢量控制变频器保证皮子和馅子准确定量地被挤出,通过完善的PLC控制程序,保证了切刀开合角度的准确控制,保证了月饼压制成型和进行多样化的图案排列,与原系统比较,在易用性上大为提升,并且降低了成本。     

Computationally efficient parametric analysis of discrete-time polynomial based acceleration–deceleration profile generation for industrial robotics and CNC machinery

Accurate position control and its related dynamics have been under research for industrial robotics and CNC machinery applications. Several works have developed techniques to fulfil the trajectory planning and profile generation from the CADCAM point of view, however, there is a lack in the mathematical foundations on computationally efficient profile generation for implementation in digital systems. This paper shows a novel approach for acceleration–deceleration profile generation based on polynomials at the discrete-time domain which is computationally efficient and easy to implement in most digital system available technologies. Results in the form of simulations and a servomotor driving the axis position on a CNC milling machine are presented to show the procedure efficiency and jerk reduction. It is shown that the proposed parameterisation of polynomial based profile generation requires half the operations to be computed, compared with the currently available methodologies for direct polynomial evaluation. Furthermore, the proposed procedure is multiplier free which means that almost every low-cost processor or embedded digital system can easily perform the generation task.     

汽车板激光拼焊系统的研制

针对汽车板激光拼焊工艺特点,研制了激光自动焊接系统, 此系统由激光器、焊接机床和控制系统组成, 采用 IPG5000光纤激光器作为光源, 机械人上、下料, 切割原焊接组合技术, 柔性电磁铁定位、夹紧, 西门子 840D数控系统。解决了汽车板装夹、定位, 曲线、折线焊缝拼接、自动控制系统等关键技术。结果表明:此焊接系统光束质量好,性能稳定、可靠;可以焊接板厚0.5-3 mm, 长度小于 2 000 mm的直线、曲线、折线汽车板, 汽车拼焊板的焊接精度高, 焊缝质量好, 达到 ISO18001标准。