【作者】 王海峰；

【导师】 胡德金；

【作者基本信息】 上海交通大学 ， 机械制造及其自动化， 2006， 博士

【摘要】 非圆回转类零件在工业中的应用日益广泛,在其形状日趋复杂化的同时,对加工精度的要求也随之提高,而相应的精密高效加工技术逐渐成为当今加工领域的研究热点。活塞是发动机的心脏,为了满足发动机性能不断提高的要求,目前活塞型面通常被设计成具有中凸变椭圆特征的复杂三维立体曲面,而其数控车削加工的关键在于硬件上配置一套高频响、大行程和高精度的快速刀具进给机构(Fast Tool Servo,简称FTS),软件上拥有相应的高效伺服控制算法。本文以基于压电堆致动器(PZT Stack Actuator,简称PSA)的FTS机构为研究对象,探索了该机构在非圆回转类零件车削加工中的若干控制问题,并进行了相关的试验分析与验证。本文首先根据中凸变椭圆活塞的精密数控车削加工要求,确定了快速刀具进给机构的主要设计参数,如位移精度、频响、行程范围、刚度、驱动力和动态性能等。鉴于PSA的行程较小这一事实,目前基于PSA的FTS机构中普遍采用了柔性铰链微位移放大机构。由于被控对象模型的精确度对系统的控制精度有很大的影响,所以本文还介绍了借助频率扫描获取FTS机构的频率响应,然后利用受控自回归(AutoRegressive with eXogenous input,简称ARX)模型对其进行系统辨识的方法。频率响应和阶跃响应结果表明,所用的FTS机构具有较宽的频带和良好的随动性能。在开环、变频、变负载情况下,压电堆致动器具有非常强烈的迟滞非线性特性,最大迟滞可高达满行程的43%。因此,建立迟滞模型进行前馈补偿是十分必要的。在对传统迟滞建模方法进行回顾的基础上,提出了一种基于Preisach原理和支持向量机(Support Vector Machine,简称SVM)算法的动态混合泛化模型,一方面利用SVM代替了传统Preisach建模过程中的双线性插值算法和查找表的功能,另一方面能够在宽频变负载工况下,更精确地描述压电陶瓷的迟滞特性,从而显著提高了迟滞模型的泛化能力和预测精度。对比试验的结果表明,所提出的SVM动态混合泛化模型是十分有效的。中凸变椭圆活塞裙部的外型曲面在数控车削加工时,刀具进给运动的目标轨迹是精确预知的,而且刀具进给运动具有较强的周期性和重复性。针对这些特点,提出了一种改进的嵌入式重复控制系统结构,并在稳定性分析的基础上,给出了控制器参数的选择方法。试验结果表明,变负载情况下,重复控制器的跟踪误差有所增大,但仍具有较高的跟踪控制精度。采用数控车床加工中凸变椭圆活塞时,完成活塞中凸型线加工的纵向进给运动和实现裙部椭圆加工的高频径向往复运动可以采用不同的运动轴来实现,因此,在普通车床上利用FTS机构建立非圆车削加工试验系统是可行的。本文最后以铝合金棒料为加工对象,在不同椭圆度和不同转速下进行了非圆车削试验,初步验证了所提出的控制策略在基于压电堆致动器的快速刀具进给机构应用中的有效性。更多还原

【Abstract】 The noncircular parts have been widely used in industry. As their shapes are be-coming more and more complicated, the requirements for machining accuracy are im-proved too, and the corresponding accurate high-efficient process technology evolvesas the research focus of the field gradually. Piston is the heart of an engine. To meetthe challenge of constant improvement in the engine performance, pistons are oftendesigned to be of middle convex and variable ellipse at present. The key point ofnumerically controlled turning process lies in two sides: one is the fast tool servo(FTS), which is of high frequency, long travel and high precision; the other is thecorresponding servo control algorithm of high performance. The subject investigatedin this paper is the PZT stack actuator (PSA) based FTS mechanism. Using thismechanism, several control problems are explored to make the noncircular turningprocess possible. Some experiments were carried out to validate the proposed controlalgorithm.According to the machining requirements of middle convex and variable ellipsepistons used in sedan cars, the main design parameters of FTS are determined, suchas position accuracy, frequency response, travel range, stiffness, driving force andseveral dynamic performance. Since the stroke of PSA is not long enough, the ?ex-ible hinge amplifier is popular in the PSA based FTS mechanism. For the controllerdesign, a more accurate model is needed. So, the swept sine method is used to ob-tain the frequency response of this FTS, and an autoregressive with exogenous input(ARX) model is utilized to identify the model parameters of FTS. The test results offrequency response and step response indicate that the used FTS has broader bandwidth and better follow-up performance. In the case of open-loop control, high-frequency and heavy-load applications, thenonlinear hysteresis of PSA is so serious that it can be up to 43% of the full stroke.Therefore, it is necessary to model the hysteresis to compensate feedforwardly. Toimprove the control precision of PSA, a dynamic generalized hybrid model is putforth, which is based on the Preisach principle and the support vector machine (SVM)algorithm. The linear spline kernel based SVM hybrid model can substitute the look-up table and complete the bilinear interpolation used in the classical Preisach model,but also can describe the nonlinear hysteresis characteristic of PSA when load andfrequency change in a large range. As a result, both the generalization ability and theprediction precision are improved obviously. Comparison test results show that theproposed SVM hybrid model is valid.In the turning process of middle convex and variable ellipse pistons, the referencetarget is known, and the feed movement of the lathe tool is of periodic and repetitive.Based on these characteristics, a modified plug-in repetitive controller is put forward.In accordance to the stability analysis, the design method of controller parameter isrecommended. Although the tracking error is enlarged when the load is varied, ahigher tracking control accuracy is obtained.Since the longitudinal feed motion to machine the middle convex shaped con-ductor, and the high-frequency reciprocating motion to shape the oval piston skirt canbe separated in the realization of numerically controlled turning process, it is possibleto build up a noncircular cutting pilot system on a centre lathe. In the end, a group ofaluminum alloy bar stocks are machined with different ovalities and distinct speeds,to validate the proposed control methods used for the PSA based FTS mechanismprimarily.更多还原