Order release planning with clearing functions: A queueing-theoretical analysis of the clearing function concept

We consider the problem of planning future order releases in hierarchical production planning and control systems. An established research direction is the clearing function concept: the planned material flow through a production unit is modelled by inventory balance equations for WIP and final products, and the consequences of the stochastic properties of the material flow are modelled by clearing functions, which is the functional relationship between the level of WIP and the maximum output of a work centre in a period.Using a transient M/M/1 model, our paper shows that the usual definition of a nonlinear clearing function suffers from substantial shortcomings concerning both the definition of the function and empirical estimation of its parameters. We propose an alternative transient clearing function and derive a procedure for its parameterization.     

Variance amplification and the golden ratio in production and inventory control

A discrete linear control theory model of a generic model of a replenishment rule is presented. The replenishment rule, which we term a “Deziel Eilon—automatic pipeline, inventory and order-based production control system”, is guaranteed to be stable. From a z-transform model of the policy, an analytical expression for bullwhip is derived that is directly equivalent to the common statistical measure often used in simulation, statistical and empirical studies to quantify the bullwhip effect. This analytical expression clearly shows that we can reduce bullwhip by taking a fraction of the error between the target and actual inventory and pipeline (or work in progress (WIP) or “orders placed but not yet received”) positions. This is in contrast to the common situation where ordering policies account for all of the error every time an order is placed. Furthermore, increasing the average age of the forecast reduces bullwhip, as does reducing the production/distribution lead-time. We then derive an analytical expression for inventory variance using the same procedure to identify the closed form bullwhip expression.We assume that a suitable objective function is linearly related to the bullwhip and inventory variance amplification ratios and then optimise the PIC system for different weightings of order rate and inventory level variance. We highlight two forms of the objective function, one where “the golden ratio” can be used to determine the optimal gain in the inventory and WIP feedback loop and another that allows the complete range of possible solutions to be visualised. It is interesting that the golden ratio, which commonly describes the optimum behaviour in the natural world, also describes the optimal feedback gain in a production and inventory control system.     

Integrated product specifications and productivity decision making in unreliable manufacturing systems

This paper considers joint production control and product specifications decision making in a failure prone manufacturing system. This is with the knowledge that tight process specifications, while leading to a product of more reliable quality and higher market value, are at the same time associated with higher levels of non-conforming parts, a higher rate of parts rejection and thus a lowering of overall plant productivity. The decision making is further complicated by the lack of reliability of the production process, which imposes that an adequate, also to be designed, level of inventory of finished parts be maintained. The overall optimal decision policy is defined here as one that maximizes the long term average per unit time profit of a combined measure of quality and quantity dependent sales revenue, minus inventory and backlog costs, in the presence of random plant failures and random repair durations. Policy optimization is achieved via a revisited model of the Bielecki–Kumar theory for Markovian machines and a simulation and experimental design based methodology for the more general cases.     

锅炉汽包水位模糊RBF自适应控制

针对汽包水位常规的PID控制方式,采用了一种模糊神经网络智能控制器,该控制器结合了模糊控制与神经网络学习能力强的特点,将2种智能控制相结合,在线调整控制器参数,整定出一组优化的控制器参数。仿真结果表明此控制器显著地改善了汽包水位的动态性能和稳定性能。     

基于线性二次型的永磁同步电机最优滑模控制

永磁同步电机的伺服控制系统是一个典型的非线性、强耦合、多输入多输出的系统,负载扰动和参数摄动都会使系统不稳定。针对这一问题,提出了一种基于线性二次型最优的滑模控制设计方法。将滑模控制与最优控制二者的优点相结合,设计了最优滑模控制律,并分别搭建基于传统滑模控制的永磁同步电机速度控制器和基于线性二次型最优的滑模速度控制器的仿真模型,在相同的条件下进行仿真,观察系统在两种控制器下的抗干扰能力。结果表明,不论系统受到突加负载信号还是突减负载信号的干扰,最优滑模控制器都具有很好的抗干扰能力,有效地增强了系统的鲁棒性。所提出的方法提高了永磁同步电机控制系统的动静态性能,对深入研究永磁同步电机控制系统具有一定的参考价值。     

Production planning of a hybrid manufacturing-remanufacturing system under uncertainty within a closed-loop supply chain

This paper deals with the production planning and control of a single product involving combined manufacturing and remanufacturing operations within a closed-loop reverse logistics network with machines subject to random failures and repairs. While consumers traditionally dispose of products at the end of their life cycle, recovery of the used products may be economically more attractive than disposal, while remanufacturing of the products also pursues sustainable development goals. Three types of inventories are involved in this network. The manufactured and remanufactured items are stored in the first and second inventories. The returned products are collected in the third inventory and then remanufactured or disposed of. The objective of this research is to propose a manufacturing/remanufacturing policy that would minimize the sum of the holding and backlog costs for manufacturing and remanufacturing products. The decision variables are the production rates of the manufacturing and the remanufacturing machines. The optimality conditions are developed using the optimal control theory based on stochastic dynamic programming. A computational algorithm, based on numerical methods, is used for solving the optimal control problem. Finally, a numerical example and a sensitivity analysis are presented to illustrate the usefulness of the proposed approach. The structure of the optimal control policy is discussed depending on the value of costs and parameters and extensions to more complex reverse logistics networks are discussed.     

Simultaneous control of production, repair/replacement and preventive maintenance of deteriorating manufacturing systems

This paper presents a method to find the optimal production, repair/replacement and preventive maintenance policies for a degraded manufacturing system. The system is subject to random machine failures and repairs. The status of the system is deemed to degrade with repair activities. When a failure occurs, the machine is either repaired or replaced, and a replacement action renews the machine, while a repair action brings it to a degraded operational state, with the next repair time increasing as the number of repairs increases as well. A preventive maintenance action is considered in order to improve the reliability of the machine, thereby reducing the amount of disruptions caused by machine failures. The decision variables are the production rate, the preventive maintenance rate and the repair/replacement switching policy upon machine failure. The objective of the study is to find the decision variables that minimize the overall cost, including repair, replacement, preventive maintenance, inventory holding and backlog costs over an infinite planning horizon. The proposed model is based on a semi-Markov decision process, and the stochastic dynamic programming method is used to obtain the optimality conditions. A numerical example is given to illustrate the proposed model, and a sensitivity analysis is considered in order to confirm the structure of the control policy and to illustrate the usefulness of the proposed approach.     

电网谐波下并网逆变器功率脉动抑制策略

电网电压中常含有一定的5次、7次谐波,导致并网逆变器输出功率产生6倍频脉动。为提高并网逆变器的运行性能,采用了一种基于谐振调节器的直接功率脉动控制策略,以实现并网逆变器输出有功功率和无功功率无波动的目的。基于瞬时功率理论,通过改变注入系统的有功和无功电流分量,结合谐振控制器抑制功率振荡。改进后的系统工作时无需获取谐波电流与电压的正负序分量,简单实用。基于1kW光伏并网逆变器实验平台对控制策略进行验证,实验结果表明,此控制策略能有效提高光伏并网逆变器的系统动态和稳态性能。     

基于T-S模型的一类时滞非线性系统模型预测控制

针对具有状态时滞特性的非线性离散系统,利用线性矩阵不等式的方法和Lyapunov稳定性理论,研究了基于状态反馈的非线性系统模型预测控制问题。基于T-S模糊模型对非线性离散系统进行描述并给出一种"min-max"预测控制算法,采用模型预测控制与模糊理论相结合的方法,利用平行分布补偿的原理,通过在每一个采样时刻优化无穷时域的性能指标,来求解在范数有界条件下相应的状态反馈控制律,讨论了预测控制器的设计问题,分析了此设计问题的可解性,给出了状态反馈控制器基于线性矩阵不等式的设计算法,保证了系统的稳定性,通过仿真实例证明了所提控制算法的有效性及系统的稳定性。该方法能够在化工、冶金、机械等具有时滞特性的工业生产过程中得到很好的应用。     

基于滑模控制的无刷直流电动机直接转矩控制

为了降低无刷直流电动机的转矩脉动,增强运行稳定性和控制精准度,提出了一种基于滑模控制的无刷直流电动机直接转矩控制方法。基于无刷直流电动机的数学模型,采用超扭曲算法(super-twisting)的滑模控制器代替原有的转矩、磁链滞环比较器,分析了滑模控制器的稳定性,设计了磁链、转矩观测模型;利用空间矢量调制技术代替原有的开关表,实现了对控制系统开关频率的优化;仿真分析了改进前后两种方法的电动机输出特性。结果表明:采用滑模变结构控制提高了控制精准度,有效地抑制了无刷直流电动机的转矩脉动,滑模控制器的稳定性良好,开关频率恒定,逆变器的通断可控性得到改善。改进后的控制方法可以提高无刷直流电动机的系统性能,使电动机运行具有更好的鲁棒性和稳定性。     

基于电磁直线作动器的主动悬架控制方法研究

为了实现电磁直线作动器主动悬架中电磁阻力的有效跟踪输出,进一步提高悬架的性能,利用1/4主动悬架系统的动力学模型和作动器驱动电路模型,设计了LQG控制器和Fuzzy-PID控制器相结合的主动悬架分层控制系统。给出了电磁直线作动器主动悬架控制系统的设计方案,利用MATLAB/Simulink搭建模型进行仿真,并通过具体的台架试验验证。结果表明,主动悬架的减振性能得到了明显改善,其车身加速度和悬架动行程得到了大幅降低。研究结果对电磁悬架的主动控制方法研究具有一定的参考价值。     

基于模型预测轮廓控制的自动驾驶车辆路径跟踪控制

为了实现无人驾驶汽车的路径跟踪和避障功能,基于模型预测轮廓控制提出一种路径跟踪控制策略。首先将二自由度单轨车辆模型和Pacejka轮胎模型结合在一起搭建整车模型,遵循模型预测的思路将路径规划和跟踪问题结合为一个非线性优化问题,利用线性化得到线性时变模型,在每个采样时间内以凸二次规划的形式建立非线性优化问题的局部逼近。其次,为了使车辆在跟踪路径的时候维持稳定,结合车辆稳定包络线,施加横向稳定性约束,并通过施加车道线边界约束,实现自动驾驶车辆的避障功能。最后将Matlab/Simulink和Carsim结合进行联合仿真。仿真结果表明,所设计的控制器在较宽路面能自主规划出一条最短路径,实现了跟踪和避障功能,同时维持了车辆在行驶中的稳定性和安全性,在赛道竞速下具有较明显的优势。研究结果可为结构化道路下的汽车自动驾驶提供技术参考,具有一定的应用价值。     

基于AMESim的防抱死制动系统控制研究

为了提高ABS制动模型的准确性,提出液压数值模拟的方法,并结合Simulink软件环境,建立车辆单车轮ABS动力学模型。采用PID控制和有限状态机相结合的控制方法,实现对ABS液压系统的制动控制。应用AMESim与Simulink对系统进行联合仿真,分析不同动力黏度的液压油对ABS的影响。结果表明,所采用的控制策略能使车轮滑移率稳定在最佳滑移率0.2附近,实现了对ABS的有效控制;随着液压油动力黏度由0.725 Pa·s增加到1.425 Pa·s,制动距离由24.28 m增加到25.51 m,说明油液黏度增加会使制动距离加长。因此,所建立的车辆单车轮ABS动力学模型比线性化制动模型更能体现参数的特性变化,研究方法可应用于ABS液压系统设计中的参数选择与匹配。     

The multidivisional firm and control over the work process

This paper investigates the role of M-form organisation in enabling management in large UK companies to regain control over the work process subsequent to the growth of strong shopfloor trade union organisation in the 1950s and 1960s. A dynamic model is proposed in which the degree of control over the work process shifts between managers and workers. Logit analysis is employed to test two specific propositions: (i) that management in M-forms will seek to relocate bargaining at a level where unions are organisationally weak — the division, (ii) that unions will subsequently respond by creating inter-plant organisations. Both propositions receive empirical support.     

Value creation by knowledge‐based ecosystems: evidence from a field study

A growing number of research and development‐driven companies are located in knowledge‐based ecosystems. Value creation by these ecosystems draws on the dynamics of single firms (interacting and partnering) as well as the ecosystem at large. Drawing on a field study of a Dutch high‐tech campus, two key sources of value creation are identified: (1) facilitation of the innovation process for individual companies and (2) creation of an innovation community. Furthermore, the coevolution of the ecosystem's business model with firm‐level business models explains why technology‐based firms join, stay in, or leave the ecosystem at a certain point in time. A remarkable finding is that ecosystem managers have to deliberately facilitate exit routes for companies that no longer fit the ecosystem in order to enhance and reinforce its business model. As such, this study suggests a dynamic capability perspective on knowledge‐based ecosystems that need to develop a business model at the ecosystem level to create sufficient innovative capacity and entrepreneurial fitness.     

基于动态解耦的卷筒纸印刷机速度-张力控制研究

卷筒纸印刷机的速度-张力耦合,是实现印刷机速度-张力精确控制的一个难题。为了精确控制印刷机的速度-张力,首先建立卷筒纸印刷机机电系统状态方程模型,依据状态反馈动态解耦控制理论,进行解耦控制。仿真结果表明,动态解耦控制在速度-张力控制中具有一定作用,为卷筒纸印刷机速度-张力的精确控制提供了一种有效方法。     

Platform capitalism and neo-normative control: “Autonomy” as a digital platform control strategy in neoliberal Chile

A key element of the platform business model is concentrating great organisational power over the work process while simultaneously allowing workers certain degrees of autonomy and encouraging them to see themselves as self-employed. This study applied the neo-normative control concept to analyse the mechanisms platforms use to promote freedom of choice and self-regulation values, which are formed extra-organisationally in deeply neoliberal societies such as Chile. The Uber ride-hailing and Pedidos Ya home delivery platforms in Chile were examined using a labour process theory framework based on an ethnographic design. The results show the specific ways in which these platforms deploy forms of neo-normative control, how this deployment is anchored in the labour context of neoliberal Chilean society, and how workers re-signify, stress, or seek to subvert this control strategy. The findings' theoretical and empirical implications are discussed.     

一类神经网络自校正控制器的设计与研究

提出一种新的神经网络自校正控制器的设计方法 ,采用神经网络 BP算法作为控制器来控制实际对象 ,动态地修改神经网络的权值作为自校正方法 ,使系统较好地适应负荷和外扰的变化 ,获得满意的控制质量。     

基于单片机的遥控自动送药小车及门禁系统

介绍了基于单片机的自动送药小车控制系统的软硬件设计。本设计的最大特点是小车能够自动充电,保证了工作的连续性。并设计了与小车协调的门禁系统,在小车进出防爆室时,可以及时准确地控制门的开关,保证了防爆室的密封性,提高了工作的安全性。该成果经实际使用取得了良好的应用效果。     

Production planning: An improved hybrid approach

This paper proposes an extended linear programming model for the hybrid approach proposed by Byrne and Bakir (International Journal of Production Economics 59 (1999) 305) and Kim and Kim (International Journal of Production Economics 73 (2001) 165). In this new model the workload of jobs is sub-divided to introduce the unit load concept of JIT. While an optimum plan is sought, due to this unit load concept, the model takes account of the requirement of small lot sizes which is one factor of the JIT approach. The effective loading ratio (ratio of the output quantity to the input quantity) is modified by omitting the slack time for each job. This helps to ensure that correct quantity of product is produced in each period, thus minimising any excess inventory or backlogging. Omission of slack time will also improve equipment utilisation and throughput. A flexible capacity constraint is also introduced which takes into account the availability of resources based on their previous histories.The incorporation of the unit load concept and modification of resource requirements and constraints in the proposed LP formulation are expected to help to improve the planning model by reducing the level of WIP and total flow time.