Programming spindle speed variation for machine tool chatter suppression

This paper presents a novel method for programming spindle speed variation for machine tool chatter suppression. This method is based on varying the spindle speed for minimum energy input by the cutting process. The work done by the cutting force during sinusoidal spindle speed variation S³V is solved numerically over a wide range of spindle speeds to study the effect of S³V on stable and unstable systems and to generate charts by which the optimum S³V amplitude ratio can be selected. For on-line application, a simple criterion for computing the optimal S³V amplitude ratio is presented. Also, a heuristic criterion for selecting the frequency of the forcing speed signal is developed so that the resulting signal ensures fast stabilization of the machining process. The proposed criteria are suitable for on-line chatter suppression, since they only require knowledge of the chatter frequency and spindle speed. The effectiveness of the developed S³V programming method is verified experimentally.     

二次转速调节静态神经网络非线性控制策略研究

本文针对二次转速调节系统的阻尼小、精度低和开环不稳定等实际情况，介绍了一种静态神经网络非线性控制策略，并对所组成的控制系统进行了数字仿真研究，给出了有价值的结论。     

调速阀的新结构

本文简要介绍了一种调速阀的新结构及其应用。     

数控车床主轴变频调速传动控制的优化设计

文章介绍了数控车床主轴变频调速传动控制的设计方法,通过对传动控制的负载特性与容量适配选型、变频调速控制原理及系统的接口设计、干扰的抑制、变频器参数合理设置的分析研究,从而达到优化设计的目的,掌握其运用方法,是确保数控车床主轴传动系统能够稳定、可靠运行的保证。     

Stability-based spindle speed control during flexible workpiece high-speed milling

High-speed machining (HSM) is a technology used to increase productivity and reduce production costs. The prediction of stable cutting regions represents an important issue for the machining process, which may otherwise give rise to spindle, cutter and part damage. In this paper, the dynamic interaction of a spindle-tool set and a thin-walled workpiece is analysed by a finite element approach for the purpose of stability prediction.The gyroscopic moment of the spindle rotor and the speed-dependent bearing stiffness are taken into account in the spindle-tool set finite element model and induce speed-dependent dynamic behaviour. A dedicated thin-walled workpiece is designed whose dynamic behaviour interacts with the spindle-tool set. During the machining of this flexible workpiece, chatter vibration occurs at some stages of machining, depending on the cutting conditions and also on the tool position along the machined thin wall.By coupling the dynamic behaviour of the machine and the workpiece, respectively, dependent on the spindle speed and the relative position of both the systems, an accurate stability lobes diagram is elaborated.Finally, the proposed approach indicates that spindle speed regulation is a necessary constraint to guarantee optimum stability during machining of thin-walled structures.     

Spindle speed ramp-up test: A novel experimental approach for chatter stability detection

Chatter is one of the most limiting factors in improving machining performances. Stability Lobe Diagram (SLD) is the most used tool to select optimal stable cutting parameters in order to avoid chatter occurrence. Its prediction is affected by reliability of input data such as machine tool dynamics or cutting coefficients that are difficult to be evaluated accurately, especially at high speed.This paper presents a novel approach to experimentally evaluate SLD without requiring specific knowledge of the process; this approach is called here Spindle Speed Ramp-up (SSR) test. During this test spindle speed is ramped up, and chatter occurrence is detected by the Order Analysis technique. As result one single test ensures optimal spindle speed identification at one cutting condition, while if few tests are performed the entire SLD could be obtained. Results of the method applied to slotting operation on aluminum are provided and a comparison between different measurements devices is presented. This quick, easy-to-use and efficient test is suitable for industrial application: no knowledge of the process is required, different sensors can be used such as accelerometer, dynamometer or microphone.     

一种异步电动机SPWM变频调速的新方案

本文介绍了一种切线采样方法以产生三相SPWMM波，与规则采样法相比，提高了采样精度，而计算的复杂度稍有增加。最后给出了实现对异步电动机的SPWM凋速控制的梯形图。     

A new perspective and analysis for regenerative machine tool chatter

The paper contains a practical perspective on regenerative machine tool chatter. Chatter is a well known phenomenon, occurrence of which is undesired in manufacturing. Aggressive machining conditions, in the sense of removing more metal rapidly, usually cause chatter. In most cases, these conditions can be determined a priori to the operation. A chatter stability study and its reasoning based on root locus plot analysis of time delayed systems is presented as a new and practical perspective in the field. At the junction of root locus and chatter concepts an area of particular interest to the authors arises: a new method for active vibration suppression, the Delayed Resonator. It is an active vibration absorber tuning of which is achieved utilizing a simple time delayed feedback. The cross linking between the Delayed Resonator study and the subject matter, machine tool chatter, is exciting to share. This is the primary motivation in pursuing this study. One of the highlights of the work appears at the phenomenon called Dual Frequency Delayed Resonator. This feature has been conjectured in the literature using the well known “stability lobes”, but never discussed with detail.     

An automatic spindle speed selection strategy to obtain stability in high-speed milling

Chatter vibration problems arise during machining. This paper aims to produce a strategy that can detect the emergence of chatter so that subsequently, in accordance with the lobe on the stability diagram where the process is located, the proper strategy may be determined, either by taking the machine to a stable spindle speed or causing continuous variation in spindle speed. The effectiveness of this strategy is contrasted for a number of different cases, using both simulation and experimental testing. The context targeted by the strategy is a high-speed mill roughing operation for cases of vibration arising on the headstock/cutting tool unit, when high material removal rates (MRR) must be maintained. Industrial implementation of the strategy and the chatter detection and diagnosis algorithm is carried out using a portable digital assistant (PDA).     

新型无速度传感器直接转矩控制系统

无速度传感器技术中最常用的方法是自适应观测器,观测器的增益和速度自适应律决定了观测器的性能。传统采用极点配置方法的自适应观测器存在区域不稳定的问题,针对此缺陷提出了一种基于线性矩阵不等式的新型观测器。仿真结果表明:新型观测器克服了传统方法存在的区域不稳定的缺点,能够在全速范围内准确辨识转速。     

The feasibility of eigenstructure assignment for machining chatter control

The eigenstructure assignment algorithm is proposed for controlling machining chatter by changing the response of the machine tool structure to dynamic cutting forces through the change of its modal properties so that the interaction between the tool and workpiece can be altered. The determination of the desired modal shapes is derived from a concept similar to gain scheduling in adaptive control system theory. By using computer simulations, the desired eigenstructure of the machine tool structure for different cutting conditions is determined and used to form the scheduling table. The gain matrix is adjusted according to the scheduling table and cutting conditions. It was found from experimental results that by changing the principal direction of the machine tool structure, the machining system could be stabilized and that the use of the proper eigenstructure to suppress machine tool chatter could significantly increase the material removal rate. Simulations have shown that the responses of the controlled machining system have been altered from unstable to stable, proving the feasibility of the proposed chatter control concept.     

Application of active disturbance rejection control to variable spindle speed noncircular turning process

In application of variable spindle speed machining to noncircular turning process, the tracking control of the fast tool servo yields a periodic sampling rate in the real-time domain. However, in the view of the angle domain, the sampling rate is constant. Moreover, the reference acceleration signal is easily available. This implies that it is advantageous to design the control system from the angle domain perspective, but the plant for a linear time-invariant system will become a periodically time-varying system. In this paper, the active disturbance rejection control strategy is applied to actively estimate the time-varying dynamics and other disturbances and compensate for them in the control law. The acceleration feed-forward strategy is employed to achieve better tracking performance. The stability analysis based on the lifting technique is proposed. Experimental machining results demonstrate the tracking performance of the proposed design, as well as the ability to increase machining stability using variable spindle speed machining.     

A new strategy for synthesizing polymer-ceramic nanocomposites

New polymer-ceramic nanocomposites are being developed by exploiting the unique intercalation and self-assembling characteristics of layered ceramics. Although quite ubiquitous in nature, self-assembly has only been recently recognized as a viable approach to synthesize nanoscale materials. The observed physical and mechanical properties of the resulting nanocomposites are attributed to the molecular features and the synergism between the individual components.     

基于DSP的开关磁阻电机的控制策略研究

介绍了以TMS240LF2407为核心芯片的开关磁阻电机(SRM)控制系统的基本原理、硬件结构和软件流程，着重分析了SRM的PI算法的控制策略，并在试验基础上给出了转速、转矩波形和绕组电流、电压波形，验证了策略。     

Effectiveness of continuous workpiece speed variation (CWSV) for chatter avoidance in throughfeed centerless grinding

The continuous rotation speed variation is demonstrated to be an efficient method to avoid regenerative chatter in different machining processes. This paper presents a time-domain dynamic model for throughfeed centerless grinding process that can predict chatter by means of part roundness error evolution. Continuous workpiece speed variation (CWSV) has been implemented in this model to analyze the influence of this disturbing method on the dynamic instability. Experimental results have validated the model and verified the effectiveness of CWSV for chatter avoidance and surface finish and dimensional tolerances improvement. It has been demonstrated that the selection of the optimal variation parameters is an important factor not only for chatter avoidance, but also for the stability of surface finish and dimensional tolerances since workpiece speed variation has a direct influence on throughfeed rate and grinding forces.     

A new method to quantify radial error of a motorized end-milling cutter/spindle system at very high speed rotations

The radial error motion of a machine tool cutter/spindle system is critical to the dimensional accuracy of the parts to be machined. The spindle's radial error motions can be measured by mounting a sphere target onto the spindle as a reference. A set of sensors is used to measure displacements of the reference sphere in various directions to determine spindle error motions. This measurement technique can be reliably carried out when the spindle is at rest or at low rotational speeds. However, at very high speeds, the reference sphere must be carefully centered and balanced to avoid introducing additional error motions. In addition, the sensors must be held with very rigid mounts in order to avoid measurement errors caused by vibrations. For high-speed end milling spindles, the spindle is operated with a cutter. The cutter must be removed when mounting a reference sphere. Because the cutter itself can introduce errors due to centering and unbalancing effects, the error motions measured by the reference sphere method do not include the error caused by the cutter. This paper introduces a new and practical method to provide an indicator of the radial error of a motorized end-milling cutter/spindle system at very high speed rotations without the need of a reference sphere. This indicator of the radial error is based on the size of the cutting marks produced by the end mill, which is attached to the spindle. The cutting marks are circular, and their diameters are related to the radial error of the cutter/spindle system. Quantitative precision analysis was carried out to confirm the accuracy and repeatability of this new measurement technique. This technique has been implemented in order to determine the effects of the spindle speed, the level of unbalanced mass, and the spindle stiffness on the cutter/spindle's radial error. The results reveal that the centrifugal force generated by the unbalanced mass is the main factor causing the increase in radial error. One way to compensate for the effect of unbalanced mass is to increase the spindle stiffness. Experimental results confirm that a higher front bearing preload can render the spindle stiffer, thus reducing the radial error of the cutter/spindle system. Finally, it should be pointed out that the proposed cutting mark measurement cannot replace the sphere method because it cannot provide time-resolved or angle-resolved information as those obtained from polar charts. However, the proposed cutting mark measurement can provide the characterization of the spindle with the cutter attached. As a result, both methods can complement each other to provide a more complete picture of the behavior of the cutter/spindle system at high speeds.     

Characterizations and models for the thermal growth of a motorized high speed spindle

In this paper, the characterizing and modeling of the thermal growth of a motorized high speed spindle is reported. A motorized high speed spindle has more complicated dynamic, non-stationary and speed-dependent thermal characteristics than conventional spindles. The centrifugal force and thermal expansion occurring on the bearings and motor rotor change the thermal characteristics of the built-in motor, bearings and assembly joints. It was found that conventional static models using regression analysis and artificial neural network failed to give satisfactory model accuracy and robustness. An auto-regression dynamic thermal error model, that considers the temperature history and spindle-speed information, has been proposed and proved to improve the model accuracy. However, it was found that temperature-based thermal error models, that correlated thermal displacement of the rotating cutting tool to the temperature measurements on the spindle housing, were not robust. Many nonlinear and time-varying thermal sources, such as coolant jacket, motor air gap, motion joints and assembly interfaces influence thermal displacement. The relationship between temperature measurements and thermal displacements is highly nonlinear, time-varying and non-stationary. A new thermal model which correlates the spindle thermal growth to thermal displacements measured at some locations of the rotating spindle shaft has been proposed. It was found that the displacement-based thermal error model has much better accuracy and robustness than the temperature-based model.     

变速泵控闭式转向系统复控策略设计及动态特性北大核心CSCD

针对变速泵控闭式转向系统工作原理,开发了一种可以实现对压力-位置参数进行复合控制的方案,从而达到与液压缸相近的预压紧与运行控制过程。同时,构建实验平台,完成了上述原理的验证分析。测试结果表明:构建的系统与控制方案是可行的,能够实现类似阀控系统的控制功能,表现出了优异的运行性能,并获得了较高的能效利用率。通过压力-位置复控的方式完成了变速泵控闭式转向系统的控制过程,实现了对压力与位置回路的快速动态响应。总压力只发生了小幅波动,可以快速恢复到设定参数,从总体上看,液压缸表现出了良好的运行特性,能够满足电液控制系统的实际控制要求。     

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.     

A passive adaptor to enhance chatter stability for end mills

A design procedure is suggested in this paper to enhance the chatter stability of an end mill cutter. Tool chatter is a well recognized self-excited vibration problem where the excitation force is the cutting force required to machine a workpiece. The cutting force magnitude is proportional to the thickness of the chip removed from the workpiece. The thickness of the chip, on the other hand, is affected by two distinct sets of events, namely, the instantaneous oscillations of the tip of the cutter and the undulations left on the surface from the earlier passes of the cutter. Hence, the excitation force, which is the cause of the oscillations, feeds on the oscillations.In this investigation, an end mill is simplified to be a beam cantilevered from a relatively rigid spindle. A local structural modification technique of the authors is then applied to this beam to suppress its proneness to excessive resonance vibrations. An add-on passive adaptor is developed for this purpose. Numerical simulations with random tip excitation and experimental verification with a scaled model are discussed. Suggested designs promise to enhance the chatter stability of a cantilevered cutter. Cutting tests are being planned for the next stage of work.