Long-term relative stability of thermistors: Part 2

The relative stability of four glass–bead thermistors has been analyzed for 66 months to determine if thermistors have sufficient relative stability to be used as feedback sensors for milliKelvin levels of temperature control. This paper provides additional drift data and new correlations beyond those described in a previous paper [Prec Eng, J Int Soc Prec Eng Nanotechnol 2001;25:24–8]. The thermistors were measured at 20±0.1 °C using commercial two-wire instrumentation. The thermistors have a nominal resistance of 12.5 kΩ and sensitivity of −4.5%/°C at 20 °C. They are nested together inside several layers of thermal resistance and capacitance which are held at nominal 20 °C with a heater controller that maintains the thermistor nest above the 19 °C ambient air temperature. After correction for instrumentation drift with two high-stability reference resistors, the average relative RMS drift of the thermistors is 48±16 μK, with an RMS fitted drift rate of 0.19±0.08 μK per week.     

A high-stability air temperature control system

A multiloop control system has been implemented in a relatively large recirculating air chamber that maintains one-sigma air temperature stability of 3 mK at the outer loop control point. The control system is a modification to a chamber that formerly held air temperature stability of approximately 0.1°C. A continuously running refrigeration system removes the nominal heat load from the air through a cross-flow heat exchanger. The control system maintains temperature stability in the chamber by modulating the power input to a coil heater. Four thermistors in DC bridges are used to generate the feedback signals.     

Optimization and temperature mapping of an ultra-high thermal stability environmental enclosure

Precision metrology, lithography and machining systems will soon require sub-nanometer tolerances in order to meet the evolving needs of industry. This, in turn, requires thermal control of large environmental enclosures with sub-millidegree single-point stability and control of temperature gradients to several millidegrees. In order to optimize the system's thermal controls, it is essential to measure the open-loop transfer function. We report a technique that obtains the open-loop transfer function by utilizing a dynamic signal analyzer to perform a closed-loop frequency response measurement of the thermal system. Based on the transfer function, we designed a PI-lead compensation controller and achieved one-sigma air temperature stability of less than 1 m°C at a single point over 2 h. In order to rapidly map temperature gradients over large regions inside the 7 m³-volume enclosure, we have developed a measurement scheme that involves mechanically scanning a network of thermistors. Accurate cross calibration of the thermistors and a study of self-heating effects on temperature measurement in moving air have also been performed, which assures the relative accuracy of the thermistors is less than 1 m°C. Comparing temperature gradient maps taken before and after control improvements shows improved temperature stability over the mapped volumes.     

Discrete-time setpoint-triggered reset integrator design with guaranteed performance and stability

According to Bode's gain-phase relationship, in linear time-invariant controllers, introducing an integral action to eliminate the steady-state error has an adverse effect of increased phase delay and overshoot, leading to performance deterioration. Moreover, increasing the bandwidth of the closed-loop system to enhance the low-frequency disturbance rejection invariably amplifies the sensitivity to high-frequency disturbances. Hence, the performance of the linear controllers is always limited due to these fundamental frequency- and time-domain limitations. Motivated by the desire to address the fundamental limitations of linear controllers and improve the time-varying closed-loop performance, we put forward a novel setpoint-triggered reset integrator strategy that varies the integrator cut-off frequency based on the setpoint information. Particularly, to tackle the time-varying disturbances and setpoint profiles, the proposed controller consists of a nominal linear controller and a variable-gain reset integrator. We show the global asymptotic stability of the proposed methodology using positive-real lemma along with the LaSalle's invariance principle and experimentally validate using measured frequency response function. Moreover, the efficacy of the proposed technique compared to that of the linear controller is experimentally demonstrated on a benchmark rotary servo system. Experimental results assessed using the tracking error and cumulative power spectral density substantiate that the proposed control strategy can not only improve the low-frequency disturbance rejection but also augment the high-frequency trajectory tracking performance.     

Robust stability of some oscillatory systems including time-varying delay with applications in congestion control

This paper focuses on the stability of some second-order linear systems with multiple constant and time-varying delays, under the assumption that the corresponding system without delays is an oscillator. Sufficient conditions for delay-dependent stability will be derived using the integral quadratic constraint approach combined with the generalized eigenvalue distribution of some appropriate finite-dimensional matrix pencils. As applications, we shall discuss some fluid approximation models used in congestion control of high-speed networks, under the natural assumptions that the control-time intervals are constant, but the round-trip times are time-varying.     

无温漂滤光片的制备方法

随着光学薄膜技术的不断发展,光学薄膜器件应用的日益广泛,光学薄膜器件的温度稳定性研究也被提到了极重要的地位。针对这一问题进行了研究,并给出了相应的解决办法。     

汽车稳定性控制虚拟样机和试验研究

首先,采用自制的简易三坐标测量仪对样车的各铰点(硬点)进行实测,并通过实测或辨识方法确定减振器、转向系统等部分的特征参数;然后,在多体动力学软件中建立该样车整车虚拟样机模型,并建立基于横摆和侧偏的车身稳定性控制系统模糊控制器,其仿真结果表明所建控制器控制效果良好。最后,为了探析样车原装稳定性控制系统控制算法等,对样车进行了冬季试验,并得出了一些有益的启示,这为下阶段自主开发汽车稳定控制系统提供了参考。     

Partial eigenvalue assignment and its stability in a time delayed system

Active vibration control strategy is an effective way to control dangerous vibrations in a structure, caused by resonance and to manipulate the dynamics of vibrational response. Implementation of this strategy requires real-time computations of two feedback control matrices such that a small amount of eigenvalues of the associated quadratic matrix pencil are replaced by suitably chosen ones while the remaining large number of eigenvalues and eigenvectors remain unchanged ensuring the no spill-over. This mathematical problem is referred to as the Quadratic Partial Eigenvalue Assignment problem. The greatest challenge there is to solve the problems using the knowledge of only a small number of eigenvalues and eigenvectors that are computable using state-of-the-art techniques. This paper generalizes the earlier work on partial assignment to constant time-delay systems. Furthermore, a posterior stability analysis is carried out to identify the ranges of the time-delay that maintains the closed-loop assignment while keeping the stability of the infinite number of eigenvalues for the time-delayed systems. The practical features of the proposed methods are that it is implemented in the second-order setting itself using only those small number of eigenvalues and the eigenvectors that are to be assigned and the no spill-over is established by means of mathematical results. The results of our numerical experiments support the validity of our proposed methods.     

虎钳夹紧下工件定位稳定性的快速算法

提出一种简单的方法快速构造摩擦力和摩擦力矩形成的圆锥。利用该圆锥分析工件是否滑动并确定工件的最小夹紧力 ,以判断虎钳夹紧下工件定位稳定性。     

High precision and stability temperature control system for the immersion liquid in immersion lithography

The temperature stability of immersion liquid is one of the main factors that affect the performance of the immersion lithography tool. Since the temperature control system of immersion liquid has the characteristics of time delays, full of disturbance and non-linear, the system and control algorithm should be carefully designed to control the temperature of the immersion liquid within the specification. In this paper, a control system of cascade structure with feed forward and lag compensation is proposed to reduce the time delays and the disturbance caused by the temperature fluctuation of ambient environment. Then, the mathematical model of the temperature control system is built, and the parameters of the model are obtained by ‘gray’ identification method. Based on the model, an algorithm which combines hierarchical control algorithm, integral separation PI algorithm, feed forward algorithm and lag compensation algorithm is designed. Last, experiments are conducted to evaluate the algorithm. The results show that the algorithm improves the robustness, compensates the time delays and reduces the overshoot. The system achieves a temperature stability of the immersion liquid within 22±0.01 °C/30 mins, and it also has a good characteristic of anti-interference.     

Control design for the SISO system with the unknown order and the unknown relative degree

For the uncertain system whose order, relative degree and parameters are unknown in the control design, new research is still in need on the parameter tuning and close-loop stability. During the last 10 years, much progress is made in the application and theory research of the active disturbance rejection control (ADRC) for the uncertain system. In this study, the necessary and sufficient conditions are established for building the ADRC for the minimum-phase system and the open-loop stable system when the plant parameters, orders and relative degrees are unknown, the corresponding ideal dynamics are analyzed, and the theoretical results are verified by the simulations. Considering the wide application and the long history of the PID/PI controller, a method is given to design ADRC quickly based on the existing (generalized or conventional) PID/PI controller. A plenty of simulations are made to illustrate this PID/PI-based design method and the corresponding close-loop performances. The simulation examples include the minimum/nonminimum-phase plants, the stable/integrating plants, the high/low-order plant, and the plants with time delays. Such plants are from a wider scope than the theoretical result, and representative of many kinds of the industrial processes. That leads to a new way to simplify the ADRC design via absorbing the engineering experience in designing the PID/PI controller.     

The stability of active balancing control using influence coefficients for a variable rotor system

High-speed rotating machines can be very sensitive to rotating mass unbalance that is a major source of harmful vibration for many types of rotating machinery. A balancing procedure is therefore needed for all high-speed rotating systems. To save the time and cost of off-line balancing, many researchers have developed on-line balancing devices and methods. In this paper, an active balancing device, which is of an electro-magnetic type, has been developed and an active balancing method using the influence coefficient method is proposed. The stability of active balancing control is studied in this paper. A stable condition for active balancing control is derived by estimating the errors of influencing coefficients. A gain scheduling control using influence coefficients of the standard model is proposed when the dynamic characteristics of a rotor system are changed. The stability of the balancing method is verified by experiments.     

Improved stability and stabilization design for networked control systems using new quadruple-integral functionals

This paper investigates stability analysis and stabilization for networked control systems. By a refined delay decomposition approach, slightly different Lyapunov–Krasovskii functionals (LKFs) with quadruple-integral terms and augmented vectors containing triple-integral forms of state are constructed. New integral inequalities are proposed to estimate the cross terms from derivatives of the LKFs, which can be proved to offer tighter bounds than what the Jensen one produces theoretically. Moreover, the non-strictly proper rational functions in deriving process are fully handled via reciprocally convex approach. A state feedback controller design approach is also developed. Numerical examples and applications to practical power and oscillator systems demonstrate the superiority of the proposed criteria in conservatism reduction compared to some existing ones.     

塔式起重机载重滑轮组的稳定性研究

对塔式起重机载重滑轮组的稳定性进行了深入讨论并推出了各参数之间的关系式以及My对稳定性的影响。另外,还提供了具体的实验数据。     

Robust stability and performance of time-delay control systems

Most of the optimal and adaptive regulators assume an a priori known time delay. The time-delay mismatch can cause unwanted instability. Influence of this uncertainty is investigated in connection with the required performance and robustness.     

基于系统稳定性的可靠性分析研究

从控制理论的角度出发，认为“可靠性”本质上是产品功能的稳定性问题，同时给出了基于稳定性的产品可靠性分析的定量方法与定性方法。进一步结合机械可靠性设计理论作了具体分析。     

A Pressure Dam Bearing Analysis with Adiabatic Thermal Effects©

To improve the stability of fixed geometry journal bearings in high-speed rotating machinery, pressure dam or stepped bearings have often been used in place of plain or other bearings. Despite their long history and wide range of applications in industry, only isoviscous analyses have been reported in the literature. Since stability problems usually occur at relatively high speeds where considerable heating occurs, it is desirable to include the thermal effects in pressure dam bearing analysis. This study presents a full adiabatic thermohydrodynamic analysis for pressure dam bearings. The theoretical results show that the pressure and temperature distributions on a stepped pad are quite different from those on a smooth pad. The thermal effects have significant influence on the predicted bearing performance, such as journal eccentricity, dynamic coefficients, and rotor stability. The example of a flexible rotor indicates improved stability prediction with the thermal effects included.     

双向拉伸机保温腔的温度控制

温度是一种不确定性、非线性的控制对象,以双向拉伸机的保温腔为研究对象,采用模糊控制策略实现温度控制,给出输入-输出变量的隶属函数值,并对温度进行采集.实践表明,该系统切实可行,达到了所要求的控制精度.     

一种智能PID控制器在铍青铜热处理中的应用

针对常规PID控制参数多是离线人工整定，且一次性整定的PID参数难以保证其控制效果始终处于最佳状态等缺陷，依据专家经验，模仿人类思维，通过辨识系统响应的瞬态特征，提出了一种智能PID控制方法，确定PID控制时系统加速、“刹车”、还是保持，以修正不同阶段的控制作用，改善常规PID控制性能。仿真结果及该方法在铍青铜热处理炉温控制系统中的应用表明，专家经验和传统PID控制的结合既保持了PID控制简捷、可靠，又提高了控制器性能，有实际应用价值。     

An integer order approximation method based on stability boundary locus for fractional order derivative/integrator operators

This paper introduces an integer order approximation method for numerical implementation of fractional order derivative/integrator operators in control systems. The proposed method is based on fitting the stability boundary locus (SBL) of fractional order derivative/integrator operators and SBL of integer order transfer functions. SBL defines a boundary in the parametric design plane of controller, which separates stable and unstable regions of a feedback control system and SBL analysis is mainly employed to graphically indicate the choice of controller parameters which result in stable operation of the feedback systems. This study reveals that the SBL curves of fractional order operators can be matched with integer order models in a limited frequency range. SBL fitting method provides straightforward solutions to obtain an integer order model approximation of fractional order operators and systems according to matching points from SBL of fractional order systems in desired frequency ranges. Thus, the proposed method can effectively deal with stability preservation problems of approximate models. Illustrative examples are given to show performance of the proposed method and results are compared with the well-known approximation methods developed for fractional order systems. The integer-order approximate modeling of fractional order PID controllers is also illustrated for control applications.