Run-to-run control of PECVD systems: Application to a multiscale three-dimensional CFD model of silicon thin film deposition

Deposition of amorphous silicon thin films via plasma-enhanced chemical vapor deposition (PECVD) and batch-to-batch operation under run-to-run control of the associated chambered reactor are presented in this work using a recently developed multiscale, three-dimensional in space, computational fluid dynamics model. Macroscopic reactor scale behaviors are linked to the microscopic growth of amorphous silicon thin films using a dynamic boundary which is updated at each time step of the transient in-batch simulations. This novel workflow is distributed across 64 parallel computation nodes in order to reduce the significant computational demands of batch-to-batch operation and to allow for the application and evaluation in both radial and azimuthal directions across the wafer of a benchmark, run-to-run based control strategy. Using 10 successive batch deposition cycles, the exponentially weighted moving average algorithm, an industrial standard, is demonstrated to drive all wafer regions to within 1% of the desired thickness set-point in both radial and azimuthal directions across the wafer surface. This is the first demonstration of run-to-run control in reducing azimuthal film nonuniformity. Additionally, thin film uniformity is shown to be improved for poorly optimized PECVD geometries by manipulating the substrate temperature alone, without the need for re-tooling of the equipment. © 2018 American Institute of Chemical Engineers AIChE J, 65: e16400 2019     

Smart manufacturing: Handling preventive actuator maintenance and economics using model predictive control

Integrating components and systems of the manufacturing process is an important area of research to enable the future development and deployment of the Smart Manufacturing paradigm. An economic model predictive control (EMPC) scheme is proposed that effectively integrates scheduled preventive control actuator maintenance, process economics, and process control into a unified methodology. To accomplish this goal, a Lyapunov‐based EMPC (LEMPC) scheme is formulated for handling changing number of online actuators (i.e., changing number of manipulated inputs). Closed‐loop stability under the proposed LEMPC is proven. Subsequently, the LEMPC is applied to a chemical process network used for benzene alkylation to demonstrate that the LEMPC can maintain stability and improve dynamic economic performance of the process network in the presence of changing number of available control actuators resulting from scheduled preventive maintenance tasks. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2179–2196, 2014     

Monitoring and retuning of low-level PID control loops

In this work, we focus on the problem of monitoring and retuning of low-level proportional-integral-derivative (PID) control loops used to regulate control actuators to the values computed by advanced model-based control systems like model predictive control (MPC). We consider the case where the real-time measurement of the actuation level is unavailable, and thus PID controller monitoring has to be achieved on the basis of process state measurements. A fault detection and isolation (FDI) method involving process models and real-time process measurements is used to monitor the PID control loops and compute appropriate residuals. Once poor tuning is detected and isolated, a PID tuning method based on the estimated transfer function of the control actuator is applied to the isolated, poorly functioning PID controller. An example of a non-linear reactor–separator process operating under MPC with low-level PID controllers regulating the control actuators is used to demonstrate the approach.     

Physical evaluation of a maize-based extruded snack with curry powder

Response surface methodology was used to analyze the effect of screw speed (200-280 rpm), feed moisture (13.0-17.0%, wet basis), and curry powder (6.0-9.0%) on the bulk density, lateral expansion, and firmness of maize-based extruded snack with curry powder. Regression equations describing the effect of each variable on the responses were obtained. Responses were most affected by changes in feed moisture followed by screw speed and curry powder (p < 0.05). Lateral expansion increased linearly as the amount of curry powder added was increased whereas a quadratic increase was obtained in lateral expansion with decreasing feed moisture. The firmness of samples was increased with an increase in feed moisture. The bulk density of samples was increased with increasing feed moisture and screw speeds. Radial expansion was found to be a better index to measure the physical properties of the extruded product indicated by a higher correlation coefficient.     

Dimensional Analysis of Bilinear Oscillators under Pulse-Type Excitations

In this paper the response of a bilinear oscillator subjected to pulse-type motions is revisited with dimensional analysis. Using Buckingham’s Π theorem the number of variables in the response analysis is reduced from six (6) to four (4). When the response is presented in terms of dimensionless Π terms remarkable order emerges. It is shown that for a given value of dimensionless strength and dimensionless yield displacement, the response (relative dimensionless displacements and dimensionless base shears) is self-similar regardless of the intensity and duration of the pulse excitation. These self-similar solutions scale better with the peak pulse acceleration rather than with the peak pulse velocity, indicating that peak pulse acceleration is a superior intensity measure of the induced shaking. Most importantly, the paper demonstrates that for relatively small values of strength (larger values of ductility) the value of the normalized yield displacement is immaterial in the response, a finding that shows that the response of the bilinear single-degree-of-freedom oscillator exhibits a complete similarity (similarity of the first kind) in the normalized yield displacement. This finding implies that under a strong earthquake an isolated bridge will exhibit the same maximum displacement regardless if it is supported on lead-rubber bearings or friction pendulum bearings that exhibit the same strength and offer the same isolation period.     

Fault-tolerant control of fluid dynamic systems via coordinated feedback and switching

This work addresses the problem of designing a fault-tolerant control system for fluid dynamic systems modeled by highly-dissipative partial differential equations (PDEs) with constrained control actuators. The proposed approach is predicated upon the idea of coordinating feedback controller synthesis and switching between multiple, spatially-distributed control actuator configurations. Using appropriate finite-dimensional approximations of the PDE system, a stabilizing feedback controller is designed for a given actuator configuration, and an explicit characterization of the constrained stability region is obtained. Switching laws are then derived, on the basis of these stability regions, to orchestrate the switching between the control actuator configurations, in a way that guarantees constraint satisfaction and preserves closed-loop stability of the infinite-dimensional system in the event of actuator failures. The results are demonstrated through an application of the proposed methodology to the suppression of wave formation in falling liquid films via the stabilization of the zero solution of the one-dimensional Kuramoto–Sivashinsky equation (KSE), with periodic boundary conditions, subject to actuator constraints and failures.     

Viscous Heating of Fluid Dampers under Small and Large Amplitude Motions: Experimental Studies and Parametric Modeling

This paper summarizes the results from a comprehensive experimental program in an effort to better understand the phenomenon of viscous heating of fluid dampers under small-stroke (wind loading) and large-stroke (earthquake loading) motions. Two dampers, one with 15-kip and one with 250-kip force output at peak design velocity, have been instrumented and tested under various amplitudes and frequencies. Temperature histories at different locations along the damper casing and within the silicon fluid that undergoes the shearing action have been recorded. Experimental data under small-stroke motions of the 250-kip damper showed that a single closed-form expression derived from first principles is capable of predicting the temperature rise at different locations of the damper with fidelity. The recorded data under long-stroke motions suggest a two-parameter law of cooling that allows the estimation of the internal temperature of the silicon oil once the external temperature on the damper casing is known. The presented cooling law is an extension of Newton’s law of cooling. The study concludes that for both dampers, the same values of the model parameters provide a good approximation of the cooling behavior. The study presents a valuable formula that can be used in practice to estimate the internal fluid temperature of the damper given the external shell temperature.     

Selection of control configurations for economic model predictive control systems

Economic model predictive control (EMPC) is a feedback control method that dictates a potentially dynamic (time‐varying) operating policy to optimize the process economics. The objective function used in the EMPC system may be a general nonlinear function that describes the process/system economics. As this function is not derived on the sole basis of classical control considerations (stabilization, tracking, and optimal control action calculation) but rather on the basis of economics, selecting the appropriate control configuration, and quantifying the influence of a given input on an economic cost is an important task for the proper design and computational efficiency of an EMPC scheme. Owing to these considerations, an input selection methodology for EMPC is proposed which utilizes the relative degree and the sensitivity of the economic cost with respect to an input to identify and select stabilizing manipulated inputs with the most dynamic and steady‐state influence on the economic cost function to be assigned to EMPC. Other considerations for input selection for EMPC are also discussed and integrated into a proposed input selection methodology for EMPC. The control configuration selection method for EMPC is demonstrated using a chemical process example. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3230–3242, 2014