Institute for Systems Research

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Injection Molding Process Control - A Review.
(1986) Agrawal, Rakesh; Pandelidis, I.O.; Pecht, M.; ISR
This paper reviews control strategies employed in the injection molding process. For clarity, the controlled variables have been categorized into all phase control, phase-dependent control and cycle to cycle control. All phase control includes variables which must be monitored and controlled at all times i.e. in all the phases. Control of variables which are triggered during a specific phase are discussed under phase dependent control. In cycle to cycle control, use is made of the previous data in order to predict future trends and take corrective actions thereof. The cyclic, dynamic and unsteady state nature of the injection molding process has been discussed with respect to the conventional PI and PID controllers as well as the more advanced control schemes such as self-tuning control, optimal control, and statistical process control. Suggestions involving specific advanced control schemes and recommendations for-future research in injection molding process control have also been made.
Observers for Optimal Anticipatory Control of Ram Velocity in Injection Molding.
(1986) Agrawal, Rakesh; Pandelidis, I.O.; ISR
The application of optimal anticipatory control assumes that the entire state is available for feedback. However, in the case of injection molding this assumption is violated due to economic considerations. For that purpose, this paper discusses the effectiveness of optimal anticipatory control using estimates of the states obtained from a dynamic system, called observer. State estimation is essential to optimal control techniques since in general the states are used in some form of feedback and the number of measurable states is usually much less than the actual number of state variables, limited by the availability of cheap and rugged sensors and the ease of installation. Furthermore the measurements from the existing sensors may be corrupted by significant noise. In the present paper both the stochastic and the deterministic cases are investigated for application to optimal control of ram velocity in injection molding.
On a Reduced Load Equivalence under Heavy Tail Assumptions
(1998) Agrawal, Rakesh; Makowski, Armand M.; Nain, P.; ISR; CSHCN
We propose a general framework for obtaining asymptotic distributional bounds on the stationary backlog W^A₁+A₂,c in a buffer fed by a combined fluid process A₁+A₂ and drained at a constant rate c.
The fluid process A₁ is an (independent) on-off source with average and peak rates r₁ and r₁, respectively, and with distribution G for the activity periods. The fluid process A₂ of average rate r₂ is arbitrary but independent of A₁.
These bounds are used to identify subexponential distributions G and fairly general fluid processes A₂ such that the asymptotic equivalence P[W^A₁+A₂,c > x]~P[W^A₁,c-r₂ > x](xלּ/font>/font>) holds under the stability condition r₁+r₂ < c and under the non-triviality condition c-r₂ < r₁.
The stationary backlog W^A₁,c-r₂in these asymptotics results from feeding source A₁ into a buffer drained at reduced rate c-r₂. This reduced load asymptotic equivalence extends to a larger class of distributions G a result obtained by Jelenkovic and Lazar [18] in thecase when G belongs to the class of regular intermediatevarying distributions.
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On Maintaining Priorities in a Production Rule System
(1991) Agrawal, Rakesh; Cochrane, Roberta J.; Lindsay, Bruce G.; ISR
We present a priority system which is particularly suited for production rules coupled to databases. In this system, there are default priorities between all rules and overriding user-defined priorities between particular rules. Rule processing using this system is repeatable: for a given set of rules and priorities, the rules are considered for execution in the same order if the same set of transactions is executed twice on the same initial database state. The rule order adheres to the default order as closely as possible: rules are considered in the same order as the default order unless user-defined precedence constraints force an inversion.
We present data structures an efficient algorithms for implementing such a priority system. We show how the data structures can be incrementally maintained as user- defined priorities are altered. We also discuss how the proposed scheme can be extended to build a multi-level hierarchical priority system.
Optimal Anticipafory Control of Ram Velocity in Injection Molding.
(1986) Pandelidis, I.O.; Agrawal, Rakesh; ISR
This paper discusses a computer control system for ram velocity of an injection molding machine using optimal state feedback based on the linear quadratlc control theory. A new approach for the selection of appropriate weighting matrices is presented in this context. The simulation results reveal that the optimal controller has improved performance over the conventional PID controller presently used, having faster speed of response, significantly better and the core storage requirements would allow implementation even on a small online computer.