Dynamic analysis of an inventory and order based production control system

PurposeThe purpose of this study is to propose a new dynamic model of a production-inventory control system. The objective of the new model is to maximise the flexibility of the system so that it can be used by decision makers to design inventory systems that adopt various strategies that provide a balance between reducing the bullwhip effect and improving the responsiveness of inventory performance.Design/methodology/approachThe proposed production-inventory control system is modelled and analysed via control theory and simulations. The production-inventory feedback control system is modelled through continuous time differential equations. The simulation experiments design is conducted by using the state-space model of the system. The Automatic Pipeline Inventory and Order-Based Production Control System (APIOBPCS) model is used as a benchmark production-inventory control system.FindingsThe results showed that the Two Automatic Pipelines, Inventory and Order-Based Production Control System (2APIOBPCS) model outperforms APIOBPCS in terms of reducing the bullwhip effect. However, the 2APIOBPCS model has a negative impact on Customer Service Level. Therefore, with careful parameter setting, it is possible to design control decisions to be suitably responsive while generating smooth order patterns and obtain the best trade-off of the two objectives.Research limitations/implicationsThis research is limited to the dynamics of single-echelon production-inventory control systems with zero desired inventory level.Originality/valueThis present model is an extension and improvement to Towill’s (1982) and John et al.’s (1994) work, since it presents a new dynamic model of a production-inventory control system which utilises an additional flow of information to improve the efficiency of order rate decisions.

An Automatic Pipeline, Inventory and Order Based Production Control System (APIOBPCS), which is firstly proposed by Towill in 1982, lies at the heart of many commercial and bespoke ordering systems based on periodic review of stock and production targets. This simple and elegant control system works well, even when dealing with scenarios in which there are many competing value streams. However, when the demand is with time trend (such as ramp demand) rather than step changes, we show via linear s-transform analysis that there will be inventory drift in the APIOBPCS model. An innovative solution named PID-APIOBPCS model is proposed in this paper. In the new model, there are a PI controller in the inventory feedback loop which can eliminate the inventory drift and a PD controller in the order rate policy which can smooth the inventory level. At last, a simulation example is given to illustrate the benefit of PID-APIOBOBPCS model.

The aim of this paper is to investigate how different smoothing parameter levels of the Automatic Pipeline Inventory and Order Based Production Control System smoothing replenishment rule impact on the bullwhip dampening efficacy, under progressive information sharing strategies. The main results of this work are: (1) The smoothing parameter variations significantly impact on performance of the supply chains characterised by low information sharing level. (2) As smoothing parameters increase, the supply chain process performance improves and the customer service level worsens. This opposite trend noticeably decreases as information sharing level increases. (3) Amongst the bullwhip dampening techniques, deeper information sharing weights more than the value of smoothing parameters. The analysis is performed through continuous time differential equation modelling.

This paper considers a well-established production and distribution scheduling algorithm, called the Automatic Pipeline, Inventory and Order Based Production Control System (APIOBPCS) within a Vendor Managed Inventory (VMI) supply chain. It develops a transfer function model of the system using causal loop diagrams, block diagrams, difference equations and z -transforms. Important insights into the VMI supply chain are derived from the mathematical model pertaining to the stability and robustness of the VMI system. Analysis confirmed by dynamic simulation clearly demonstrates instability arising from poor design. We also demonstrate its avoidance via our recommended parameter settings for tuning the two feedback loops within the supply chain for a specific production delay. The procedure is readily extended for other production delays and distributions.

This paper studies the well-established automatic pipeline feedback compensated inventory and order-based production control system (APIOBPCS) for a single echelon supply chain, in which the uncertain demand is modelled using the fuzzy numbers. The bullwhip effect is therefore measured as the possibility variance amplification in replenishment orders. It has been found that the bullwhip effect measured using fuzzy approach has similar features as the one measured using probability theories, and the sharper the fuzzy demand forecast, the smaller the bullwhip effect.

Vergence eye movements are essential to daily life. When driving down a highway a person typically looks between the speedometer and the road signs. This form of eye movement initiates a vergence response. Vergence is composed of convergence (inward) and divergence (outward) eye movements. Convergence movements are a combination of dual controllers, described as feedforward and feedback components. The feedforward component is a pulse of energy released by burst cells in the initial stage of the eye movement. Feedback is a series of steady periodic pulses released by tonic cells to fixate the eyes onto the target. However, divergence eye movements have not been studied extensively in the past This study will examine the neuro-control strategy used to mediate divergence eye movements (looking from near to far), when given different initial positions for the eyes to begin moving from. Preliminary data using independent component analysis (ICA) shows the divergence system contains an initial pulse, similar to the burst cells found to initiate convergence movements, when the movement began with a large initial bias (target very close to the subject). In responses beginning at a target located further away from the subject and continuing to move farther away, there is no noticeable pulse based on ICA. Demonstrated in this study is the dynamics of divergence movements at different initial conditions.

Adaptation and coaching of periodic motion primitives through physical and visual interaction

In this paper, we propose a method for repeatedly updating the coefficients of the feedback control filter used for canceling a feedback path from a loudspeaker to a noise detection microphone. The coefficients are usually estimated by feeding a sequence of extra noise to the loudspeaker. However, feeding such extra noise under active noise control is undesirable. The proposed method estimates the coefficients without feeding the extra noise. Concretely the proposed method provides two independent equations using the estimation errors involved in the coefficients of the noise control filter and then estimates the coefficients by solving those equations. One problem is that the feedback component is extremely small in comparison with the primary noise incident on the noise detection microphone. In this case, estimation of the coefficients is difficult. In this paper, we solves this problem by estimating first the primary noise and then the feedback path.

Mobility impairments in older adults have been well documented, and much information is gleaned from comparison with gait of younger adults. However, many impairments likely begin in middle age and progress gradually till they become acute issues in older adults. If such changes can be spotted early, then one can intervene early. Physical therapy and movement sciences, unlike cardiac science, have always intervened after the inception of gait impairments rather than promoting prevention in younger adults.Gait research and clinical tests use indoor walking even though much ecological locomotion also happens outdoors. Clinical tests, in particular, are designed for identifying acute gait issues in older adults. These tests are unlikely to identify subtle gait changes in middle age because these adults will neither reach their physiological limits nor exhaust their compensatory mechanisms during indoor walking. Therefore, this thesis investigated whether changes in the gait of middle-aged men and women will be apparent while walking outdoors on various terrains. Gait quality was quantified using kinematic variability measures, and sex differences were also assessed given the asymmetric impacts of falls for men vs women.Portable inertial measurement units (IMUs) were used to measure ankle kinematics when healthy young and middle-aged men and women walked outdoors on various concrete and grass surfaces of different slopes at their self-selected comfortable speed. Statistical models tested for surface, age and sex differences in gait variability. Study 1 focused on task and sex effects in young adults. Study 2 investigated task and age effects in young and middle-aged adults. To quantify performance, novel metrics were introduced to measure gait variability. This dissertation applies the spatio-temporal index (STI) – a metric commonly used in the speech sciences – to the analysis of gait. This thesis introduces two new derivatives, STIref and <b>Δ</b>STI, that partitioned the variability into a feedforward and a feedback plus noise component, respectively. STIref quantified one feature – the average local roughness – of the ankle acceleration, which is a peripheral consequence of the feedforward motor command. <b>Δ</b>STI quantified the residual, including the magnitude of the feedback-driven step-to-step corrections and neuromotor and external noise evident in the ankle accelerations.In healthy young adults, the feedback-driven corrections and noise component (<b>Δ</b>STI) increased substantially on slopes and on more irregular grassy surfaces. The feedforward component (STIref) was slightly higher in men, likely due to morphological differences. Despite reported differences in fall rates, the variability measures used in this study did not identify differences in the gait of young men and women. The same patterns were evident in middle-aged individuals, and there was no change in these metrics with age. Therefore, a key finding was that a feature of the feedforward component of gait control is relatively invariant, whereas young and middle-aged individuals navigate different terrains mainly through feedback-driven step-to-step corrections. Another key finding was that variability was inversely related to the self-selected walking speed on different surfaces. Individuals may have slowed down on harder terrains so that they have time to implement the step-to-step corrections. Therefore, a plausible explanation of the null age effect in the data is that middle aged adults adapted to the terrains by modulating speed. As motor capacities start to decline in middle-age, individuals adapt to maintain key functions.In conclusion, differences in gait were evident on different surfaces, but the tasks used in this work did not tax the middle-aged adults to reveal gait deficits, especially because individuals were free to select their walking speed. The novel metrics were highly sensitive to terrain but not sensitive to sex differences and early aging. However, the results indicate the path forward: controlling walking speed or increasing task difficulty will be essential to identify gait differences in middle age. The STI-based metrics dissociate the feedforward contributions to gait from the feedback and noise components and provide testable predictions that can be validated with future work.

Safe and robust GC (II) safety mode, if activated, maintains the spacecraft near a safety reference for all time. The algorithm utilizes separate feedforward and feedback components. In standard mode, the feedforward guidance solutions come from a way-point generation algorithm that uses a discrete linear-time-varying dynamics model. This approach provides a convex formulation of the problem (solvable onboard as a second-order cone program) that includes control and state constraints; the safety-mode availability adds a constraint in this standard-mode formulation as well. The feedback guarantees standard-mode resolvability to update the guidance prole in a robust, model-predictive manner. In safety mode, an oine-designed feedforward policy with the added feedback maintains the spacecraft in a hovering state in the proximity of its position at safety-mode activation time; this provides robustness to unexpected stateconstraint changes such as unexpected ground proximity during landing operations. A simulation demonstrating both the standard and safety modes is provided for a spacecraft autonomous-descent scenario toward a small asteroid with an uncertain gravity model and errors in the surface altitude constraint.

SUMMARY Neural static and dynamic training algorithms have been extensively applied to the control and identication of non-linear dynamic plants. In the present paper an extension of the static Marquardt learning algorithm, termed Dynamic Marquardt algorithm (DMA) is derived for the on-line training of neural networks with feedforward and feedback components. The performance of the method has been demonstrated by the neural control of a highly non-linear experimental #uid level. A stability analysis of the overall control scheme has been carried out using the conicity stability criterion. It has been found that the Dynamic Marquardt algorithm is much more e$cient than Dynamic backpropagation, when the relative size of the net is bounded. Copyright ( 1999 John Wiley & Sons, Ltd.

This paper presents a general formulation of the model predictive control (MPC) scheme for controlling in real time the response of structures under earthquakes. The MPC scheme is based on an explicit use of a prediction model of the system response to obtain the control actions by minimizing an objective function. Optimization objectives in MPC include minimization of the difference between the predicted and desired response trajectories, and the control effort subjected to certain constraints. In this study, the prediction model is formulated using both feedforward (FF) and feedback (FB) components to increase the effectiveness of the MPC scheme. The FF loop in the prediction model is formulated using two types of input. First, it is designed using the established Kanai–Tajimi‐type model to represent the earthquake input. Second, a real‐time FF loop is introduced using an auto‐regressive (AR) model for earthquake ground motion which is constantly updated using real‐time on‐line observations. The real‐time FF loop certainly promises to add predictive and adaptive features to the control actions to account for any unusual features in the ground motion. The structural response with and without the FF and FB loops are compared. Examples are used to demonstrate the efficacy of the proposed methodology. These examples show that the MPC‐based controller is effective in reducing the structural response under different earthquakes which contain distinct features in their spectral and non‐stationary descriptions. The performance of the MPC scheme is then compared to H2 control strategies for different time horizons. The effectiveness of MPC is shown to be equivalent to the optimal control. This paper lays a foundation for capturing the main strengths of MPC, i.e. computational expediency, real‐time application, intrinsic compensation for time delays, treatment of constraints and potential for future extensions in structural control. Copyright © 2001 John Wiley &amp; Sons, Ltd.

1. Two groups of interneurons that are involved in the organization of the lateral geniculate nucleus (LGN) are described. The cell bodies of one group lie within the LGN; these units are referred to as intrageniculate. The cell bodies of the other group are found immediately above the LGN at its border with the perigeniculate nucleus; these units are referred to as perigeniculate. 2. Intrageniculate interneurons have center-surround receptive fields that resemble those of relay (principal) cells. They can be subdivided into brisk or sluggish and sustained or transient categories. They are stimulated transsynaptically from the visual cortex and have a characteristic variation in the latency of their spike response to such stimulation both at threshold and for suprathreshold stimuli. The pathway for this stimulation appears to be via cortical efferents to the LGN. Intrageniculate interneurons receive direct, monosynaptic retinal inputs, as determined by recording simultaneously from such interneurons and from the ganglion cells which provide excitatory input to them. Similar to relay cells, they are shown to have one or two major ganglion cell inputs. 3. Perigeniculate interneurons are generally binocularly innervated and give on-off responses to small spot stimuli throughout their receptive field. They respond well to rapid movement of large targets. They respond to electrical stimulation of the retina with a spike latency that falls between that of brisk transient and brisk sustained relay cells. This latency is one synaptic delay longer than that of brisk transient relay cell activation and suggests that they are excited by axon collaterals of these relay cells. Electrical stimulation of the visual cortex is also consistent with this model; the latency of the response of perigeniculate interneurons is approximately one synaptic delay longer than the latency of the response of brisk transient relay cells. 4. The interneuronal pathways described are consistent with proposed circuits that subserve the generation of IPSPs that arise in response to optic nerve and visual cortical stimulation. We now show that such inhibition has feed-forward (intrageniculate) and feed-back (perigeniculate) components that are mediated by two different classes of geniculate interneurons. It is suggested that the intrageniculate interneurons are involved in precise, spatially organized inhibition and that the perigeniculate interneurons are part of a more general, diffuse inhibitory system that modulates LGN excitability.

Multi-objective integrated robust H∞ control for attitude tracking of a flexible spacecraft

view Abstract Citations (84) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Elliptical Galaxies with Dark Matter. I. Self-consistent Models Bertin, G. ; Saglia, R. P. ; Stiavelli, M. Abstract A large survey of two-component, spherically symmetric, collisionless, self-consistent models is carried out with the aim of studying elliptical galaxies embedded in massive dark halos. Although many factors and options are explored in quantitative detail, the main focus is on a family of models where the luminous component is mostly isotropic inside the half-light radius and the dark component is slightly warmer (and normally more diffuse) than the luminous component, consistent with the picture that ellipticals were generically formed as a result of collisionless collapse (or merging) in the presence of cold/warm dark matter. The constraints imposed by self-consistency are found to be quite complex, but a few important features (such as limits on the amount of dark matter inside the half-light radius in terms of observed quantities and a characterization of the physical parameter space) are clarified by a proper use of the Jeans equations and of the virial theorem. In spite of the variety of kinematical profiles realized in our self-consistent models, we note a natural "conspiracy" to support realistic photometries, that is, luminosity profiles consistent with the ^1/4^ law. Within our main family of models, we develop the concept of "minimum-halo models" as a way to fit a given set of data by minimizing the request of dark matter. This paper, where many of the results are illustrated in terms of projected quantities for a direct application to observed objects, forms the theoretical basis for a systematic study of photometric and kinematical properties of elliptical galaxies that may give quantitative estimates on the amount of dark matter present in these systems. Publication: The Astrophysical Journal Pub Date: January 1992 DOI: 10.1086/170884 Bibcode: 1992ApJ...384..423B Keywords: Astronomical Models; Dark Matter; Elliptical Galaxies; Self Consistent Fields; Astronomical Photometry; Celestial Mechanics; Lenticular Bodies; Astrophysics; COSMOLOGY: DARK MATTER; GALAXIES: ELLIPTICAL AND LENTICULAR; CD; GALAXIES: FUNDAMENTAL PARAMETERS; GALAXIES: KINEMATICS AND DYNAMICS full text sources ADS | data products SIMBAD (1) Related Materials (1) Part 2: 1992ApJ...384..433S