Ramp Disturbances Research Articles

Integrating run-to-run control with feedback control for a spatial atomic layer etching reactor

Semiconductor manufacturing employs an intricate framework of processes that require accurate design specifications at the nanoscale level. Thermal atomic layer etching fulfills these stringent criteria in an exemplary manner by conducting top-down removal of transistor films to further downsize thicknesses and facilitate transistor densification on wafers. However, it has low productivity. Thus, a spatial sheet-to-sheet reactor is appropriate for achieving high throughput while maintaining substrate quality. In order to continuously regulate the process, a run-to-run (R2R) controller coupled with a continuous feedback proportional–integral (PI) controller is proposed to mitigate a kinetic shift disturbance and a continuous pressure ramp disturbance through a multivariate input correction procedure. A tuning methodology is employed to determine the optimal tuning parameters to enhance the performance of the R2R and PI controller response to their respective disturbances. Results indicate that the combined R2R and PI controller outperforms the sole R2R controller by minimizing the amount of input correction needed to minimize the etching per cycle offset from the setpoint.

Traffic behavior analysis of the urban expressway ramp based on continuous cellular automata

Urban expressway is an essential part of the urban transportation network, and its role is to speed up traffic operation and relieve traffic congestion. To investigate the complex traffic flow phenomena at urban expressway ramps, we use the Continuous Cellular Automata (CCA) model to model and analyze the urban expressway with entrance and exit ramps in a unified manner. Considering the vehicle's merging, diverging and following behaviors on urban expressway with an entrance and exit ramp, we design the vehicle's main road merging rules, ramp inflow and outflow rules, Cooperative Car-Following for Lane Change process analysis (LC-CCF) model, and improved Nagatani lane change rules to control the overall road vehicle operation. Based on this, we propose a CCA model for urban expressway ramp traffic flow. To clarify the model, The Chengdu Second Ring Elevated Road with entrance and exit ramps as a scenario is used for experiments. The results show that: (1) The spatio-temporal diagrams show a significant metastable congestion phenomenon and distinct congestion boundaries primarily located near the merge and divergence area. Congestion tends to start at the merge and divergence area and then spread outward. (2) The ramp disturbance has an increasingly pronounced effect on average speed and density as Pin−main and Pin−ramp increases. (3) The density-lane change frequency relationship tends to increase and then decrease, with an increase in the frequency of lane changes increasing the interference between vehicles in different lanes and affecting the average traffic speed. The lane change frequency is the main reason for the differences in traffic flow between lanes. (4) The CCA model can effectively characterize congested traffic flows on urban expressway ramps.

Control strategy study and cascade control system design for space thermionic nuclear reactor

Nuclear reactors are gaining increasing attention for use in spacecraft owing to their long life and high power-density. Because the dynamic characteristics and operation strategy of a space nuclear reactor (SNR) are different from those of a traditional reactor, its control strategy must be investigated to design an appropriate control system. In this study, the dynamic characteristics of the time and frequency domains are analyzed. Based on this analysis, a control strategy is proposed. The cascade control method is applied to the design of control systems, including electric power and coolant temperature control systems. The controller parameters are tuned using the frequency-domain analysis method. To verify the control performance, step and ramp disturbances of the electric power and coolant temperature setpoints are introduced, and comprehensive comparisons are made. Additionally, the startup process is simulated; it reveals that the cascade control systems perform better compared with the traditional proportional-integral-derivative (PID) control. Moreover, the control performance of the wide-range power regulation is smooth and steady. Thus, the control strategy and cascade control system designed in this study can be applied to the thermionic nuclear reactors in space.

Stability Analysis of 3D UAV Gimbal using Flexible Body

Unmanned aerial vehicle (UAV) application in visual object tracking requires a gimbal to stabilize the camera in following the object’s movement. External disturbance and gimbal stability are the issues in this application. This study aims to analyze disturbance effects and study the stress and modal analysis on UAV gimbal using flexible body concepts. The three-dimensional (3D) gimbal is modeled using the RecurDyn software consisting of 3 arms and a camera. Each of the arms is connected using a revolute joint and a rotational force to represent a motor. The considered disturbances are step, pulse, ramp, and sine wave input. The PID controller is used to stabilize the gimbal arm from the gravity of the camera and external disturbance. The result shows that the PID controller is robust to step, pulse, and ramp disturbance, but not to the sin wave disturbance. In addition, the second arm of the gimbal is the most stressed component and is prone to vibration.

Analysis of a Hybrid Wind/Photovoltaic Energy System Controlled by Brain Emotional Learning-Based Intelligent Controller

Recently, hybrid wind/PV microgrids have gained great attention all over the world. It has the merits of being environmentally friendly, reliable, sustainable, and efficient compared to its counterparts. Though there has been great development in this issue, the control and energy management of these systems still face challenges. The source of those challenges is the intermittent nature of both wind and PV energy. On the other hand, a new intelligent control technique called Brain Emotional Learning-Based Intelligent Controller (BELBIC) has garnered more interest. This paper proposes the control and energy management of hybrid wind/PV microgrids using a BELBIC controller. To design the system, simple power and energy analyses were proposed. The proposed microgrid was modeled and simulated using MATLAB. The responses of the energy system were tested under two different types of disturbances, namely step and ramp disturbances. These disturbances are applied to the wind speed, the irradiation level of the PV, and the load power. The results indicate that the AC load voltage and frequency are steady with negligible transients against the previous disturbance. In addition, the performance is better than that of the classical PI controller. Also, energy management acts perfectly to compensate for the intermittence and disturbances of the wind and PV energies. On the other hand, the system robustness against model parameters uncertainties in the microgrid parameters are studied.

Control of Very Lightweight 2-DOF Single-Link Flexible Robots Robust to Strain Gauge Sensor Disturbances: A Fractional-Order Approach

This article deals with the control of two degrees of freedom manipulators that have a flexible and very lightweight link. These robots have a single low-frequency and high-amplitude vibration mode. Their actuators have high friction, and their vibration sensors are often strain gauges that have offset and high-frequency noise. These problems reduce the robot precision and produce noisy control signals that saturate actuators. An efficient control system is proposed to overcome these drawbacks. Actuator friction effect is nearly removed by closing a high gain position control loop around the actuator. It causes the separation of the robot dynamics into the controlled actuator fast subsystem and the link dynamics slow subsystem. Based on that, an innovative control system is designed to remove vibrations using the singular perturbation theory combined with the input-state linearization technique. This control system includes fractional-order controllers that nearly remove unknown sensor offset and sensor ramp disturbances while reducing the high-frequency component of the control signal caused by sensor noise. Simulated and experimental results show the superior performance of these controllers over other standard integer-order controllers of similar complexity and nominal behavior.

Pressure Gradient Control Strategies Based on Disturbance Rejection for Typical Pharmaceutical Cleanrooms

Keeping pressure gradient is an excellent approach to prevent the reveal of airflow direction and cross infection in manufacturing circumstances of pharmaceutical cleanrooms, thus how to keep cleanroom’s pressure is critical. In the paper, we study a positive pressure pharmaceutical cleanroom system which is composed by a cleanroom and an airlock. We divide the system’s disturbances into step disturbance, ramp disturbance and sine wave disturbance. We design its pressure gradient control strategies, including CAV control, PID control and active-disturbance-rejection-control. We build the system’s model and make simulations based on Matlab/Simulink software platform. Results show that active-disturbance-rejection-control algorithm has good capabilities for shorter responding time and lower overshot of the pressure gradient. The results reveal that active-disturbance-rejection-control method has good control performances in responding time, accuracy and disturbance rejection.

A Pore-Scale Investigation of the Transient Response of Forced Convection in Porous Media to Inlet Ramp Inputs

Abstract This paper investigates the transient response of forced convection of heat in a reticulated porous medium through taking a pore-scale approach. The thermal system is subject to a ramp disturbance superimposed on the entrance flow temperature/velocity. The developed model consisted of ten cylindrical obstacles aligned in a staggered arrangement with set isothermal boundary conditions. A few types of fluids, along with different values of porosity and Reynolds number, are considered. Assuming a laminar flow, the unsteady Navier Stokes and energy equations are solved numerically. The temporally developing flow and temperature fields as well as the surface-averaged Nusselt numbers are used to explore the transient response of the system. Also, a response lag ratio (RLR) is defined to further characterize the transient response of the system. The results reveal that an increase in amplitude increases the RLR. Nonetheless, an increase in ramp duration decreases the RLR, particularly for high-density fluids. Interestingly, it is found that the Reynolds number has almost negligible effects upon RLR. This study clearly reflects the importance of conducting pore-scale analyses for understanding the transient response of heat convection in porous media.

On monitoring industrial processes under feedback control

AbstractThe concurrent use of statistical process control and engineering process control involves monitoring manipulated and controlled variables. One multivariate control chart may handle the statistical monitoring of all variables, but observing the manipulated and controlled variables in separate control charts may improve understanding of how disturbances and the controller performance affect the process. In this article, we illustrate how step and ramp disturbances manifest themselves in a single‐input–single‐output system by studying their resulting signatures in the controlled and manipulated variables. The system is controlled by variations of the widely used proportional‐integral‐derivative(PID) control scheme. Implications for applying control charts for these scenarios are discussed.

Improved control structure for extractive divided-wall column with vapor recompression

A novel process for ethanol dehydration using extractive distillation in a modified divided-wall column has been proposed and its control studied. A single vessel is used to perform the tasks of pre-concentrating the dilute feed, producing high-purity water and ethanol products and recovering the ethylene glycol solvent. Feed is introduced on one side of the wall that receives no liquid from the rectifying section. Water is removed from bottom of this side that has an intermediate reboiler, which is heated by compressed overhead vapor. Ethanol is the distillate product and solvent comes out the bottom of the column to be fed near the top of the column.A complex control structure has been proposed that appears to lack robustness since it can only handle slow ramp disturbances. This paper demonstrates that a more simple control structure can provide effective regulatory control for large step changes in throughput and feed composition.

Improved plantwide control structure for extractive divided-wall columns with vapor recompression

The conventional extractive distillation flowsheet for dehydration of low-concentration bioethanol uses three-columns: a pre-concentrator, an extractive column and a solvent-recovery column. A recent paper studied the control of a process using a single divided-wall column. The complex flowsheet uses both main and intermediate reboilers. Ethanol goes overhead, water is removed as a liquid sidestream and solvent is recovered from the base.The control challenges of such a complex multivariable interacting process are obvious. The published control structure is complex and dynamically very sensitive. Only slow ramp disturbances can be handled. The purpose of this paper is to develop a more simple control scheme that is robust and is capable of handling large step disturbances. The key feature of the modified process is to only compress what is needed in the side reboiler.

Effect of ambient heat-in-leak on transient behaviour of three-fluid heat exchanger with two thermal communications using finite element method

In the current paper the effect of ambient heat in leak on transient behaviour of three-fluid heat exchangers is described using the finite element method. The solution is obtained for parallel flow three-fluid heat exchanger with two thermal communications; it is obtained for step change in the inlet temperature of hot fluid. Comparison with the previously published steady results shows excellent agreement. The effect of heat in leak is studied on the time to reach steady state, temperature profiles and outlet temperatures. As the cold fluid is exposed to ambient the effects are more significant on it than intermediate and hot fluids. This method is so versatile that it could be applied to calculate the step, exponential, sinusoidal, ramp disturbances in inlet temperatures of any of the fluids.

Transient behavior of three-fluid heat exchanger with three thermal communications under step change in inlet temperature of fluids using finite element method

In the present paper the transient temperature response of a counter-flow three-fluid heat exchanger with three thermal communications is investigated numerically using finite element method. Comparison with the previously published steady state results shows excellent agreement. The effects of step change in inlet temperature of fluids on time to reach steady state, outlet temperature of fluids, effectiveness are studied. Variation of design parameters like H1, H2 R1, R2 and NTU is also studied. The time to reach the steady state is independent of the amplitude of step change in the inlet temperature of fluids. For a step-change in the inlet temperature of the any fluid, the outlet temperature of other two fluids reach steady state faster than the fluid whose inlet temperature is changed. This method is so versatile that it could be applied to calculate the exponential, sinusoidal, ramp disturbances in inlet temperatures of any of the fluids.

Predictive functional control using state estimator-based internal model for ramp disturbance rejection

We propose a state estimator-based disturbance suppression technique for predictive functional control (PFC), which puts emphasis on attenuation of ramp disturbances. Augmenting the plant model with a disturbance model, we build a prediction-type estimator for the augmented model, which estimates ramp disturbances as well as the plant states. The state estimator enables us to predict the future output in the presence of ramp disturbances. We also analyse the structure of the proposed PFC system and controller poles and prove that the estimator-based PFC system actually has two integral actions. Finally, several numerical simulation tests are conducted to validate the effectiveness of the proposed method.

Design of an Estimator-Based Predictive Functional Control for Ramp Disturbance Suppression

We propose a state estimator-based ramp disturbance suppression technique for the predictive functional control (PFC). On the basis of the augmented system including both the plant and disturbance states, we build a predictiontype estimator for the augmented model which estimates the ramp disturbance as well as the plant states. The state estimator enables us to compute the optimal control input sequence in the presence of ramp disturbances. Also, analyzing the structure of the proposed PFC system and controller poles, we prove that the estimator-based PFC system has actually two integral actions. Finally, numerical simulation tests are conducted to check the effectiveness of the proposed method.

Resistance, Resilience and Restoration

SummaryDisturbances (pulse, press and ramp) constitute a major force influencing, even determining, the structure and functions of ecological components – populations, communities and ecosystems. The capacity to weather a disturbance without loss is defined as resistance, whereas resilience is the capacity to recover from a disturbance after incurring losses, which may be considerable. This article seeks to resolve differences in the ecological definition of resistance and of resilience and to examine the importance of resilience as applied to ecological restoration. In restoration, interventions are designed and implemented with the aim of strengthening the resilience, that is, the capacity to recover, of degraded systems. In response to restorative measures, degraded systems may have both resistance and negative resilience to remain in the degraded state. The key aim of restoration is to overcome the resistance and negative resilience of the degraded state by strengthening positive resilience, the capacity to recover to the intact undegraded state. Restoration may be hindered by a lack of knowledge of acting disturbances (both past and present), of the previous intact condition and of appropriate interventions to implement. Resilience to a disturbance is determined after the disturbance has ceased. Thus, for current ongoing press and ramp disturbances, resilience can be hard to determine.

Double EWMA controller using neural network-based tuning algorithm for MIMO non-squared systems

The double exponentially weighted moving average (dEWMA) control method is a popular algorithm for adjusting a process from run to run in semiconductor manufacturing. For MIMO non-squared statistic systems, the singular value decomposition (SVD) method is used for decoupling and the SVD-based dEWMA control scheme is treated as a MIMO extension of dEWMA control design. To enhance the performance and robustness of the linear system in the presence of ramp disturbances and white noises, the neural network-based adaptive algorithm is used to automatically tune the dEWMA controller parameters. Under the specified input patterns, the early stop criterion for the training-validation neural networks, and the stability constraints added in the tuning mechanism, the simulations show that the proposed control technique can effectively improve the means and standard deviations of the process outputs.

CDM-based closed-loop transfer function design for ramp input

This paper presents a method to determine the denominator and numerator polynomials of a closed-loop transfer function in order to obtain desired transient and steady-state responses in terms of the overshoot, speed (time needed for the relative error to become less than a specific amount) and the steady-state error when the desired output is a ramp signal. Meanwhile, a controller is designed with the same characteristic equation for the closed-loop system to eliminate step and ramp disturbances.

Disturbance Observer for Estimating Higher Order Disturbances in Time Series Expansion

In the note, a generalized disturbance observer capable of estimating higher order disturbances in the time series expansion is newly proposed. Initiated from a constant disturbance observer, we extend it systematically to cope with ramp disturbance and general order disturbances. The generalized form for disturbance observer exhibits the novel structure incorporating the system model and integrals. To be practical, the noisy measurement and the performance in the frequency domain are addressed. In addition, for a class of linear systems, an output-based disturbance observer of reduce order is newly derived from the proposed full state disturbance observer, and its potential applicability will be demonstrated by an example.

Torque control of friction stir welding for manufacturing and automation

Friction stir welding (FSW) is a solid-state welding process that utilizes a rotating tool to plastically deform and forge together the parent materials of a workpiece. The process involves plunging the rotating tool that consists of a shoulder and a pin into the workpiece and then traversing it along the intended weld seam. The welding process requires a large axial force to be maintained on the tool. Axial force control has been used in robotic FSW processes to compensate for the compliant nature of robots. Without force control, welding flaws would continuously emerge as the robot repositioned its linkages to traverse the tool along the intended weld seam. Insufficient plunge depth would result and cause the welding flaws as the robot’s linkages yielded from the resulting force in the welding environment. The research present in this paper investigates the use of torque instead of force to control the FSW process. To perform this research, a torque controller was implemented on a retrofitted Milwaukee Model K milling machine. The closed loop proportional, integral plus derivative control architecture was tuned using the Ziegler–Nichols method. Welding experiments were conducted by butt welding 0.25 in. (6.35 mm) × 1.5 in. (38.1 mm) × 8 in. (203.2 mm) samples of aluminum 6061 with a 0.25 in. (6.35 mm) threaded tool. The results indicate that controlling torque produces an acceptable weld process that adapts to the changing surface conditions of the workpiece. For this experiment, the torque was able to be controlled with standard deviation of 0.231 N-m. In addition, the torque controller was able to adjust the tool’s plunge depth in reaction to 1 mm step and ramp disturbances in the workpiece’s surface. It is shown that torque control is equivalent to weld power control and causes a uniform amount of energy per unit length to be deposited along the weld seam. It is concluded that the feedback signal of torque provides a better indicator of tool depth into the workpiece than axial force. Torque is more sensitive to tool depth than axial force. Thus, it is concluded that torque control is better suited for keeping a friction stir welding tool properly engaged with the workpiece for application to robotics, automation, and manufacturing.