Thermal error measurement and modelling in machine tools.: Part I. Influence of varying operating conditions

Thermal error in machine tools has been observed to be closely linked to the temperature of critical elements of the machine. It was found, in the experiments conducted herein, that there was a significant increase in the axis positioning error on account of an increase in the temperature of the machine elements due to continuous operation. However, it was also observed that the specific operating parameters of the test cycles carried out also significantly affected the positioning error. Different sets of operating parameters generated significantly different error values even though the temperature of the machine elements generated by those operating conditions was similar. As such, this observation forms a very important consideration in the development of a generic thermal error compensation system. It appears to indicate that such a system needs to be capable of evaluating the compensation depending upon the temperature values of the machine elements as well as account for the effect that different operating parameters induce upon the positioning error under the same thermal condition of the machine. This paper attempts to analyse the thermal behaviour of a three-axis vertical machining centre under the influence of various operating parameters and, through the experimental results obtained, point out and explain the effect of these parameters on the axis positioning error. This behaviour forms the basis of an improved modelling methodology that is presented separately in Part II of this paper.     

High-temperature oxidation of SiC in a glow-discharge oxygen plasma

The oxidation kinetics and structure of the oxide scales formed on high-density SiC were studied in molecular oxygen at 740 Torr and in a glow-discharge oxygen plasma at 0.1 Torr at temperatures of 1000, 1100, and 1200°C. The monatomic oxygen formed by the glow discharge markedly increased the reaction rate and the vaporization of some of the oxidation products. The marked differences in kinetics suggest that the rate-controlling step during oxidation in molecular oxygen is the dissociation of adsorbed diatomic oxygen to the monatomic species. Films formed in molecular oxygen were mostly amorphous SiO₂ with small inclusions of SiC and graphite, whereas films formed in dissociated oxygen were primarily amorphous SiO₂ containing SiO, S₂O₃, and the coesite form of SiO₂.     

初探混联法生产氧化铝的工艺优化

在目前的生产条件下。通过大量的混联法物料衡算，定量地研究了供矿铝硅比、熟料铝硅比和拜年法赤泥铝硅比对混联法的制造成本、能耗和拜年法与烧结法的生产比例的影响规律，提出我国混联法生产进一步优化的方向和途径。并开发了研究和评价的计算软件。为混联法的生产和设计的进一步优化奠定基础。     

Evaluation of the coupled multielectrode array sensor as a real-time corrosion monitor

Coupled multielectrode array sensors made of carbon steel and stainless steels were evaluated and compared with electrochemical noise (EN) sensors. Good correlations between sensor signals and solution corrosivity were observed for all multielectrode array sensors. Some correlation between the average pit index and solution corrosivity was observed for the carbon steel EN sensors, but not for the stainless steel EN sensors. The time-average noise resistances from the stainless steel EN sensors correlate well with solution corrosivity. There were, however, large random fluctuations and drifting for all EN signals, which make the EN sensors unreliable as real-time monitors.     

基于无线网络的森林防火系统的研究与改进

论文针对现行的无线传感器技术方式的森林防火系统中的弊端,提出了一种改进的系统设计方案.改进后的方案主要采用二级Ad-Hoc模式的网络,对传统的无线传感器进行有效的改造的同时,也增加了稳定可靠的中心网络节点,无线通信网络采用改进后的AODV作为多跳路由协议,中心节点的数据处理采用卡尔曼滤波预处理,数据发送采用ALOHA机制进行随机延迟发送.系统经过反复实验,最终验证并总结出一套可以有效应用于实际工程中的系统部署方案.     

高压切割喷嘴冲击磨损的数值分析

以复用矿井含煤颗粒的水对高压切割喷嘴的磨损物理问题为研究对象,采用计算流体力学理论进行数值计算,分析讨论了质量浓度为10、15、20、25、30、40 mg/L条件下速度、剪应力、磨损的分布以及变化关系。计算、分析结果表明:磨损主要发生在出口部位和锥体的后半部份,入口部份和锥体前半部份磨损较小;入口部位、锥体部位磨损量、剪应力随质量浓度增加变化较小;出口部位磨损量在质量浓度为10～20 mg/L减小较快,超过20 mg/L后变化不大;出口部位流体速度、磨损量、剪应力与质量浓度间存在对应关系。煤粒入口速度与混合物速度相同、锥体部位煤粒流体速度低于锥体部位混合物速度(平均值)约79.4%;煤粒出口部位速度随质量浓度的增大而呈现先增加后减小的趋势,速度最大值发生在浓度20 mg/L。     

供水管网中压力真实值的批次平差算法

分析了测压点优化布置的意义及原则,并根据供水周期性,依靠数量有限的测压点压力数据,结合管网的水力计算,利用传统的平差原理,将测压点以外的其它节点压力进行真实性校正,推算出了管网各节点的真实压力值,实现了通过有限测压点数据对管网所有节点压力的全面了解。     

故障自动防护微机械角速度传感器

微机械角速度传感器是目前市场上能够进行批量生产的最复杂的传感器之一。它由在真空中做复杂运动的惯性质量块和驱动该设备、分析其响应的多种复杂电路组成,并集中于一个在极狭小的空间内。本文介绍了由奥地利SensorDynamics公司成功研制的一种MEMS角速率传感器,可以满足现代应用的全部要求,尤其是汽车工业所要求的小尺寸、坚固的机械结构、长期稳定性、不受限制的故障自动防护性和AEC-Q100认证。