Adaptive cutting force control for a machining center by using indirect cutting force measurements

This paper presents an adaptive cutting force controller for the milling process, which can be attached to most commercial CNC machining centers in a practical way. The cutting forces of x, y and z axes are measured indirectly from the use of currents drawn by a.c. feed-drive servo motors. A typical model for the feed-drive control system of a horizontal machining center is developed to analyze cutting force measurement from the drive motor. The pulsating milling forces can be measured indirectly within the bandwidth of the current feedback control loop of the feed-drive system. It is shown that indirectly measured cutting force signals can be used in the adaptive controller for cutting force regulation. The robust controller structure is adopted in the whole adaptive control scheme. The conditions under which the whole scheme is globally convergent and stable are presented. The suggested control scheme has been implemented into a commercial machining center, and a cutting experiment on face milling process is performed.     

Direct adaptive control of end milling process

A direct adaptive control algorithm, which is spindle speed and drive dynamics independent, has been developed for machining operations. The combined dynamics of feed motion and cutting process are modelled as a third order system whose parameters may vary with spindle speed and part geometry changes during machining. The algorithm does not use any specific time interval, thus sampling time dependent discrete transfer functions and pole assignments are avoided. The adaptive controller is designed to have a closed loop characteristic function which behaves like an open loop regular and stable machining operation. The proposed direct adaptive controller is practical, can be used in any multi-axes machining, and can be combined with chatter suppression techniques which require spindle speed regulation. The algorithm is applied to the adaptive control of milling. Satisfactory results are obtained in constraining the maximum cutting forces and dimensional surface errors in milling experiments.     

Modelling and adaptive pole assignment control in turning

A mathematical model relating feed rate to feed force is formulated in a turning process with the compliance of the machine tool taken into consideration. The model is used for the control of the feed force by a fixed gain PI and an adaptive pole assignment control algorithm.Effects of consideration of the structural compliance for the control model are investigated through stability analysis of the controlled system and a comparison study of the predicted and measured feed forces.It is shown that inclusion of the machine tool compliance into the control model enables predictions closer to the measurements of the stability and is hence desirable. The adaptive pole assignment controller is found to be stable with good performance characteristics over a wide range of operating conditions.     

A pole/zero cancellation approach to reducing forced vibration in end milling

An analytical model for the forced vibration in an end milling process is derived and a criterion in selecting cutting parameters to reduce the forced vibration is presented in this paper. The analytic expression for the forced vibration due to the periodic milling force is obtained as the product of the Fourier transform of the milling force and the frequency response function of the structure dynamics. The pole/zero cancellation technique is then employed for reducing the forced vibration. Analysis shows that the suppression of forced vibration can be achieved by choosing cutting parameters so that one of the zeroes of the Fourier transform of the milling process function is near the pole of the structure dynamics. A design equation in terms of cutter geometry, axial depth of cut, spindle speed and structure resonant frequency is derived for the conditions when the forced vibration can be minimized. The presented analysis is illustrated through numerical simulation and verified by experimental results.     

Active vibration control in palletised workholding system for milling

This paper presents the development implementation and testing of an active controlled palletised workholding system for milling operations. The traditional approach to controlling vibration in a machining system is to develop control systems for cutting tools or machine spindles as in the case of milling machines. This work is a deviation from the traditional approach and targets a workholding system for the control of unwanted vibration. Palletised workholding systems, due to their compact design, offer an opportunity to design active control systems that are economical and easier to implement in the case of milling machines. The active control system developed here is based on an adaptive filtering algorithm, the filtered X-LMS, and employs piezo-actuators for dynamic control force. The system has been tested experimentally to demonstrate the reduction in dynamic force due to vibration. Extensive testing has been carried out to validate the performance of the system in terms of parameters of practical importance such as improvement in surface finish and increase in tool life.     

基于模糊自抗扰的镜像加工稳定支撑控制北大核心

针对大型薄壁零件镜像加工过程中的稳定支撑问题,提出了基于模糊自抗扰的力/位混合控制策略。通过支撑-工件系统模态锤击实验,分析了磁流变集成支撑装置线圈中电流变化对系统模态参数的影响。设计了支撑侧基于模糊线性自抗扰控制(FLADRC)的力/位混合柔顺控制策略,通过MATLAB/Simulink仿真实验平台建立了系统控制模型并进行了仿真分析。仿真结果表明,相较于传统PID控制,FLADRC对目标函数跟踪速度快、误差小,鲁棒性与自适应能力强。通过薄壁件镜像铣削实验验证所设计控制策略的有效性。研究结果表明,该控制策略可有效维持工件加工时支撑侧的稳定支撑。     

Fuzzy control of spindle torque for industrial CNC machining

Developing a dedicated control system for each and every machining process or machine is costly and time-consuming. Such a practice has obviously undermined the usefulness of many current systems. This paper presents a fuzzy control system that can be used for different machining processes. This system consists of a basic fuzzy logic controller, a fuzzy rule base, and a tuning mechanism used to enhance the adaptability of the system. Industrial tests have been carried out for both end milling and turning processes. The control signal is spindle torque, readily available on many CNC machines. The test results show that the system performs well on both end milling and turning operations and can easily adapt to tool changes as well as workpiece material changes.     

基于自适应降阶滑模算法的受约束多机械臂力/位混合控制

针对多机械臂系统末端受环境约束而产生的力/位混合控制问题,提出一种基于自适应降阶滑模算法的受约束多机械臂力/位混合控制方法。通过运用多个坐标系建立受约束多机械臂系统动力学模型,并将位置控制、约束力控制以及内力控制引入同一控制器中。将自适应滑模算法与降阶方法相结合,对动力学模型中的未知扰动进行了补偿。基于李雅普诺夫方法,证明系统的稳定性。经仿真验证,该方法不仅提高了控制器的控制精度和系统的响应速度,同时还能保证约束力误差及内力误差均稳定在极小的范围内。     

通用立铣刀真实切削轨迹下五轴铣削力计算

针对五轴铣削中刀具位姿变化和刀具类型差异所导致的铣削力预测难的问题，提出通用立铣刀五轴铣削力计算方法。基于通用立铣刀结构形式，建立通用立铣刀几何模型；综合考虑刀齿真实运动轨迹和刀具姿态变化，构建刀具瞬时切屑厚度模型；将刀具沿轴线方向等分成若干切削刃微元，并根据线性切削力假设建立刀具微元铣削力；将微元铣削力从刀具坐标系转换至工件坐标系下，并沿刀具轴向铣削深度进行积分，获得通用立铣刀的五轴铣削力模型；最后，在混联五轴数控加工实验平台上开展了铣削力测试。实测结果表明:所提铣削力计算方法正确有效，可作为后续五轴铣削工艺参数优选的理论依据。     

Parameter adaptive control in peripheral milling

Various parameter adaptive control strategies are applied to the problem of regulating the cutting force in peripheral milling under varying cutting conditions. The dynamics of the relationship between feed rate and cutting force are represented by a first order linear model which includes the effect of spindle stiffness on the mechanics of chip formation.The relationship is further expressed in the form of the Hammerstein model to include the nonlinearities in the force behaviour, particularly at low feed rates. The performance of the corresponding nonlinear controller is analyzed.The main contribution of this work is the application of theoretically based strategies and structures for parameter adaptive control in peripheral milling which can be readily implemented using available microprocessor technology. These strategies are shown to be stable with good performance characteristics over the full range of operating conditions.     

阀控对称液压缸先进控制策略对比研究

针对阀控缸系统先进控制算法理论和应用研究不足的问题,仿真研究多种控制算法在阀控对称缸液压系统控制中的应用。推导阀控对称缸的非线性微分方程,将伺服阀的动态性能考虑为一阶系统问题;进行PID、极点配置和基于反步法的自适应控制器算法的理论推导;建立阀控对称缸的功率键合图理论模型,应用上述控制算法对它进行控制效果仿真。结果表明：基于反步法的自适应控制器具有规范的设计方法和广泛的适应性,其控制效果和应用价值都优于传统控制方案。     

Application of MRAC theory for adaptive control of a constrained robot manipulator

This study presents the compliance control of a robot manipulator under a constrained environment. Considering the impact of frictional force allows us to more accurately simulate the relationship between the manipulator and environmental contact forces. The controller design proposed herein is based on the adaptive control scheme. In this design, the feed forward and feedback controllers control the position and the contact force of end-effector. Applying these controllers allows us to adapt the manipulator to the unknown surface of the surrounding environment and to have close contact with the curved surface. A Lyapunov function ensures the stability of the system. For an unknown contour, most controllers fail since the desired trajectory can not be obtained, and the parameters of the manipulator are unknown and may varied with the contact force and position. However, in this study, when performing compliant motion, the desired trajectory is generated from the controller based on the tangential direction of the measured contact force. This tangential direction changes according to the operating point. We approach the original nonlinear system with a second order linear system at each instantaneous operating point. Correspondingly, the contour of workpieces can be measured. Experimental results conform the feasibility of the proposed adaptive control scheme. Without knowledge of the contour of workpiece and gains of the controller in advance, the adaptive controller performs well for various unknown contours.     

Application of self-tuning feed-forward and cross-coupling control in a retrofitted milling machine

In this work, a traditional manually operated milling machine with a lead screw transmission system is retrofitted to AC servo motor control. This obsolescent milling machine has nonlinear time-varying behaviors due to obvious backlash and irregular Coulomb friction of the sliding surfaces. Classical digital control cannot assure the required stability and accuracy of a closed loop system. Hence, a pole placement self-tuning control strategy is proposed for this nonlinear time-varying system by introducing an on-line estimator of system parameters to adjust the feedback gains. Concepts of feed-forward and cross-coupling control are employed to improve the accuracy of trajectory tracking control. The experimental results show that this control method achieves satisfactory performance of stability, transient response, tracking and robustness under the influence of about 0.4 mm backlash on each axis and large stick-slip friction. This performance verifies the applicability of this economical approach to automation of traditional milling machines.     

Discrete-time robust adaptive multi-axis control for feed drive systems

This paper presents a robust adaptive controller design for multi-axis feed drives systems. The proposed method is designed to compensate for the coupling effects among multiple axes that are neglected in most feed drive controllers. Because inertial force from one axial motion affects the contact force between mechanical parts in other axes, the magnitude of friction at the contact surface varies. Considering this coupling effect in controller designs can improve control performance. Because the coupling effect cannot be known in advance, and it varies with respect to environmental conditions such as temperature, this paper first presents an adaptive controller design. Next, the design is extended to have robust stability for unanticipated plant modelling errors disturbances, because the robustness of adaptive controllers is known to be low due to the complex mechanism of controllers and estimators of plant model parameters. The design problem of the robust controller is formulated as a minimization problem under the linear matrix inequality constraints. The effectiveness of the adaptive multi-axis controller is demonstrated by comparative experiments with an adaptive controller that neglects the coupling effect. In addition, the robust adaptive controller is confirmed to be effective by comparison with a non-robust adaptive controller.     

超声振动辅助微塑性成形系统设计与开发

针对微塑性成形工艺过程对位移、力等参数精确控制的要求,分析了超声振动辅助成形系统的设计要点,提出了关键设计参数。超声振动辅助微塑性成形系统由机床本体系统、超声振动系统和伺服控制系统等主要单元组成。机床本体设计参考四柱液压机结构形式,采用两端固支梁和压杆的简化模型,计算得到主要结构尺寸,并用ABAQUS验证其刚度。通过选用匹配的超声发生器和换能器,满足成形过程中的超声振动要求,利用理想变截面杆纵振波动方程设计变幅杆结构,并用ABAQUS进行变幅杆模态分析,确保设计振幅满足要求。伺服控制系统采用可编程多轴控制器PMAC卡控制伺服电机,通过光栅尺和力传感器反馈实现高精度的位置及成形压力控制。通过测试证明在纯铜压缩试验中叠加超声振动,成形压力显著降低,成形精度达到4μm。     

The application of neural networks in self-tuning constant force control

The constant force control gradually becomes an important technique of modern manufacturing processes. For example, the constant turning or cutting force is a useful approach for increasing the metal removal rate and increasing the tool life. The variation of machining condition may cause the robustness of a classical control theory (PID) to become ineffective, even make a control system unstable. The pole placement self-tuning control (PSTC) theory with a recursive least square parameters estimator is proposed to adapt the environmental variety. Unfortunately, the adaptability and the robustness of a self-tuning control system cannot be maintained in good condition simultaneously all the time. In this paper, a self-tuning controller equips with a neural network parameter classifier in conjunction with a least square estimator is developed to improve the adaptability and the robustness in suffering the obvious environmental variation. In order to verify the applicability of this control method, a prototype system is designed and constructed to resemble the feed rate mechanism of lathe. The dynamic responses of this force control system with different estimators are compared based upon the experimental data. The contact force is measured from a load cell and adjusted by regulating the feed rate.     

螺旋铣孔末端执行器控制系统研究

根据螺旋铣孔末端执行器的运动特性,提出了一种基于PC+DMC5480运动控制卡的末端执行器开放式运动控制系统的设计方案。以PC作为运动控制的核心处理器,DMC5480运动控制卡为运动控制器搭建了运动控制系统的硬件平台;并以VB为工具,开发了具有开放性、通用性和灵活性的运动控制系统软件平台。结合运动控制系统的软硬件平台搭建了开放式控制系统试验装置,验证了开发的螺旋铣孔末端执行器控制系统的可靠性。     

An adaptive fuzzy control system for turning operations

In the paper, an adaptive fuzzy control system is developed and then applied to control turning processes with highly non-linear and time-varying cutting characteristics. The control system employs linguistic rules to obtain a constant turning force under varying cutting conditions. In order to improve the performance of the non-adaptive fuzzy logic controler, and adaptive algorithm using a turning process identifier to adapt the output scaling factor of the fuzzy logic controller is included. It is shown, by experimentation, that the adaptive fuzzy control system is capable of providing an effective solution to the control of the constant turning force under varying cutting conditions.     

浅谈CAN总线控制器RC6-9在铣刨机上的应用

介绍了CAN总线控制器在铣刨机系统中的应用,同时介绍了其行走控制系统的硬件、软件设计.使用结果表明:铣刨机控制系统采用CAN总线控制器RC6-9性能可靠,控制系统稳定;采用加速度控制算法的行走控制系统调速方便、灵活,加减速平稳.     

基于自适应控制技术的铣削参数优化

采用BP神经网络算法应用于铣齿功率建模能较准确地预测铣齿功率大小,进而运用STATISTICA的正交设计优化试验数据对滚齿机进行再制造,通过在主轴箱加设传感器实现了机床振动稳定性的的在线监控,分析各个切削状态下主轴箱振动同铣削功率的关系,进行优化切削参数,实现了数控系统与在线监控技术的自适应闭环监控.完成了4m大型滚齿机向高速铣齿机床SKX-4000的智能化再制造.结果表明,采用的控制策略能适应强力铣削的工况变化,稳定地控制加工过程,达到保护机床、刀具和提高加工效率的目的.