Open-loop Tests Research Articles

An investigation on the application of predictive control for controlling screw position and velocity on an injection molding machine

AbstractInjection velocity is one of the key parameters in the injection molding process that has significant effect on part quality, influencing common problems, such as flashing and short shots. Different products require specific molding conditions, including mold and melt temperatures, velocity profiles, and polymers, making the injection velocity dynamics vary significantly and difficult for high precision velocity control. Two predictive controllers were developed to control the screw injection velocity. The first approach uses a position sensor as feedback and a simplified predictive controller to track an injection velocity setpoint profile. The controller was developed and implemented utilizing single‐step change and multistep change open loop tests. The second strategy uses a multimodel dynamic matrix predictive controller to overcome the nonlinear characteristics of the injection velocity dynamics as the mold is being filled. Velocity feedback is provided by high speed processing of the position analog signal. This approach utilizes several open loop injection velocity profiles to generate corresponding dynamic matrices for the controller. As a result, this controller is modified or retuned automatically when setpoint changes in injection velocity occur, as well as when using different polymers and molds. The close loop results for both simulations and real time control have demonstrated that the two predictive controllers provided good setpoint tracking performance for wide ranging position and velocity profiles. POLYM. ENG. SCI., 47:390–399, 2007. © 2007 Society of Plastics Engineers.

Linear analysis of the viscoelastic response of polymer micro-pillars using the open-loop flat punch indentation test

A method for testing the viscoelastic property of polymer micro-pillars, based on open-loop flat punch indentation, is presented. The difficulties in performing a conventional creep or stress relaxation test using a nanoindentation apparatus with a leaf-spring structure are described and the advantages of our method explained. An analytic model for the test was devised and a simple formula for measuring creep compliance provided. As an example, polymer micro-pillars were fabricated on a glass substrate using nano-stereolithography (NSL) and their creep compliance measured. Experimental details are presented, including testing procedure, processing of raw data and analysis of test results, plus some issues, related to measurement uncertainty, are discussed, such as sensor resolution, parallelism, thermal drift and damping force.

Simple control-relevant identification test methods for a class of ill-conditioned processes

The identification of a class of ill-conditioned processes is considered. The goal of identification is model predictive control (MPC). For this class of processes, it is essential to have good estimation of the very small difference between certain transfer functions, or, low gain direction. Two simple and practical test methods will be proposed that can enhance the model quality of low gain direction. The main idea is to use the high amplitude and high correlation test signals that excite the low gain direction more and that will not disturb process operation. The test signals can be used in both open-loop and closed-loop tests. A high purity distillation column model is used to show the effectiveness of the methods.

Pole-Placement Vibration Control of a Flexible Composite I-beam using Piezoceramic Sensors and Actuators

This article concerns active vibration control of a flexible 3.35-m long composite I-beam that is used in civil structures in a cantilevered configuration by using piezoceramic materials, in particular the PZT (lead zirconate titanate), in the form of patches. These PZT patches are surface-bonded on the I-beam and function as actuators and sensors. A real time data acquisition and control system is used to record the experimental data and to implement controllers. To assist the control system design, open loop testing and system identification are conducted. A pole-placement controller is designed and is simulated using the identified model. Simulations show a dramatic increase in damping of the beam. Experimental results verify the simulated results and demonstrate the effectiveness of active control of a civil structure using smart materials.

Active Control of a hybrid actuation system for aircraft vertical fin buffet load alleviation

AbstractTwin-tail fighter aircraft may experience intense buffet loads when flying at high angles of attack. One such aircraft is the F/A-18 where the broadband buffet loads primarily excite the first bending and torsional modes of the vertical fin, resulting in significant vibration and dynamic stresses on the vertical tail structure. This buffet phenomenon reduces the fatigue life of the aircraft structure while decreasing mission availability.An international technical co-operation program was initiated to develop a novel hybrid actuation system to actively alleviate the buffet response of a full-scale F/A-18 vertical fin. A hydraulic rudder actuator was used to control the bending mode of the vertical fin using rudder inertia forces. Multiple macro fiber composite actuators were distributed optimally to provide maximum induced strain control authority for the torsional mode. In order to develop an effective control law, a system identification approach was conducted to obtain a state-space model of the vertical fin using open-loop test data. An LQG control law was selected to minimise the dynamic response of the vertical fin at critical locations. The effectiveness of the control law was verified through extensive simulation prior to closed-loop experiments. The LQG control law demonstrated high robustness in all excitation load conditions; both bending and torsional vibration modes of the vertical tail were suppressed effectively and simultaneously. The dynamic stress and acceleration response at critical locations were also reduced significantly. A closed-loop experiment was conducted on a full-scale F/A-18 empennage using the IFOSTP test rig, and the experimental results verified the effectiveness of the control law development methodology used for the full-scale hybrid buffet load system for the F/A-18 aircraft. In addition, the ground vibration test demonstrated that the hybrid actuation system is a feasible solution to alleviate the vertical tail buffet loads in high performance fighter aircraft.

System identification and active vibration control of a composite I-beam using smart materials

This research concerns active vibration control of a 3.35-m-long composite I-beam in a cantilevered configuration by using peizoceramics smart materials, in particular the PZT (lead zirconate titanate), in the form of patches. These PZT patches are surface-bonded on the I-beam and function as actuators and sensors. A real-time data acquisition and control system is used to record the experimental data and to implement designed controllers. To assist control system design, open-loop testing and system identification are conducted. To excite the 3.35-m composite I-beam, a sweep sinusoidal input is used and then a state space model is derived for the system. This state space model is used for simulation and development of control algorithms. A positive position feedback (PPF) controller is designed and is simulated using the identified model. Simulations show the dramatic increase in damping of the beams which, when implemented experimentally, shows an increase in the damping up to 1100%. Experimental results verify the simulated results and demonstrate the effectiveness of active control of a civil structure using smart materials. Copyright © 2005 John Wiley & Sons, Ltd.

QUANTIFYING CLOSED LOOP PERFORMANCE BASED ON ON-LINE PERFORMANCE INDICES

This article aims to construct an “inference model” (IM) that assesses the closed loop performance and robustness for SISO controllers, with no need of intrusive tests (i.e. set-point changes or open-loop step tests). The IM is generated for a large set of plants, disturbances, and tuning parameters. The possible inputs for the IM are 9 standard assessment measurements (e.g., FCOR, standard deviation, etc) on-line available, commonly present in commercial tools. Three IMs were developed for the following targets: the closed loop and open loop rise time ratio (RtR), Gain Margin (GM), and normalized integral of square error (ISE). These values are obtained by intrusive tests. Four different classes of inferential models (i.e., Neural Networks, Neuro Fuzzy, PLS, and QPLS) are compared. The best results are obtained by Neural Network IM. The results obtained show that the methodology is very promising.

Aerodynamic Active Control For Fin-Buffet Load Alleviation

The efficiency of an active auxiliary rudder system in alleviating fin buffeting of modern fighter aircraft is investigated. Low-speed wind-tunnel tests are performed on a detailed 1/15-scale model of canard-delta-wing type. A digitally controlled auxiliary rudder is installed on a specific fin model providing harmonic oscillations at varying frequency and deflection angle. The vertical tail is instrumented to measure unsteady surface pressures, fin-tip accelerations, and auxiliary rudder moments. At open-loop tests the fin unsteady pressure field is fed with energy at the frequencies of the auxiliary rudder motions. The corresponding rms values increase with increasing frequency and deflection angle at all angles of attack tested. The motion-induced rms pressures reach values well above the levels of the nonoscillating case. Thus, a potential to reduce rms buffet loads by approximately 18% for closed-loop operations exists. There is no decrease in the rudder moment with increasing angle of attack substantiating the effectiveness of the auxiliary rudder concept also for high angles of attack. The active control system uses single-input single-output control laws to alleviate buffeting in the fin first bending and torsion mode, respectively. With active control the spectral density peaks of fin-tip accelerations at the frequencies of the considered eigenmodes can be reduced by as much as 60% at angles of attack up to 31 deg.

Design and Implementation of Feedback Control for Counterflow Thrust Vectoring

Aircraft thrust vector control is currently implemented using movable control surfaces such as vanes and flaps. Counterflow thrust vectoring (CFTV) is a fluidic approach to thrust vectoring that has the potential to improve on the conventional approaches by reducing weight and increasing the reaction speed. Open-loop implementation of CFTV has been demonstrated in laboratory settings. However, ultimately this technology must be implemented using feedback control. The primary control objective is to achieve fast slew rates by compensating for the transportation delay and parameter uncertainties. The paper describes an experimental test bed for investigating feedback control of CFTV. System estimation results based on open-loop test data are presented. This paper then develops a PID control law, which is sometimes implemented with a Smith predictor to compensate for the transportation delay and/or an antiwindup scheme to compensate for actuator saturation. The control laws are experimentally demonstrated, and their performance is compared using different types of reference signals.

CFD-based predictive control of melt temperature in plastic injection molding

A unique method of coupling computational fluid dynamics (CFD) to model predictive control (MPC) for controlling melt temperature in plastic injection molding is presented. The methodology is based on using CFD to generate, via open-loop testing, a temperature and input dependent system model for multi-variable control of a three-heater barrel on an injection molding machine. Results clearly show the benefit of temperature and input dependent system models for MPC control, and that CFD can be used to dramatically reduce the time associated with open-loop testing through physical experiments.

In Situ Adaptive Tabulation for Real-Time Control

This paper outlines a method to reduce the computational requirements of nonlinear model predictive control (NMPC) in real-time control applications. Nonlinear model identification is generally seen as a major obstacle to implementing NMPC. However, after an accurate nonlinear model is identified, the computational effort is often too great to implement the model in a real-time application. The approach in this paper is a two-step process: model reduction, followed by computational reduction. Model reduction is accomplished by computing balanced empirical gramians for the dynamic system. Computational reduction is accomplished using the method of in situ adaptive tabulation (ISAT). ISAT was previously developed for computational reduction of turbulent flame direct numerical simulations and is extended to the sequential NMPC framework in this work. A case study is performed with a binary distillation column model with 32 states. By computing balanced empirical gramians and using ISAT, the computational speed is 85 times faster than the original NMPC, while maintaining the accuracy of the nonlinear model. Because ISAT is a storage and retrieval method, it is compared to artificial neural networks in another case study: a dual continuously stirred tank reactor (CSTR) model with six states. Open-loop and closed-loop step tests are performed to demonstrate the superior quality of ISAT in extrapolating outside of the training domain.

Modeling and Control of Steering System of Heavy Vehicles for Automated Highway Systems

This work presents modeling, analysis, and controller design of the steering subsystem of heavy vehicles as a subsystem of vehicle lateral control system for the automated highway systems. A physical model of the steering subsystem is derived where the hydraulic power assist unit is modeled as a family of static nonlinear boost curves. Based on open-loop frequency tests and analysis of the physical model structure and its dynamical characteristics, a nominal second order linear model of the steering subsystem is obtained. Then, a linear robust loop-shaping controller is designed to provide a good tracking performance of the closed-loop dynamics of the steering subsystem for varying gain cross over frequencies which is a result of the nonlinear characteristics of the hydraulic power assist. The controller has been successfully incorporated as an inner-loop controller into the nested lateral control architecture for autonomous driving and its efficacy has been demonstrated experimentally.

Control of shape memory alloy actuator using pulse width modulation

Shape memory alloys (SMA), in particular nickel–titanium alloy (or nitinol), have been usedas actuators in some astronautic, aeronautic and industrial applications. The future will seemore SMA application if less energy is required for actuation. This paper presents thedesign and experimental results of control of an SMA actuator using pulse widthmodulation (PWM) to reduce the energy consumption by the SMA actuator.A SMA wire test stand is used in this research. Open-loop testing of the SMAwire actuator is conducted to study the effect of the PWM parameters. Based ontest results and parameter analysis of the pulse width (PW) modulator, a PWmodulator is designed to modulate a proportional plus derivative (PD) controller.Experiments demonstrate that control of the SMA actuator using PWM effectively savesactuation energy while maintaining the same control accuracy as compared tocontinuous PD control. PWM also demonstrates robustness to external disturbances.A comparison with a pulse width pulse frequency modulator is also presented.

Design and performance of a rule-based controller in a naturally ventilated room

The objective of this work is to design and implement a fuzzy controller for naturally ventilated buildings. The controller is implemented in a test room using MATLAB™. Initially the controller was validated using simulated data. Simulations were carefully designed to allow simultaneous comparison of different controllers performances. Validation of the controller is performed in the test room by measuring the temperature distribution inside the room with no control action. The data are then compared to the open loop test results of the controller. The results illustrate that the fuzzy controller is capable of providing thermal comfort inside the room.

Precision tracking control of shape memory alloy actuators using neural networksand a sliding-mode based robust controller

This paper presents a new approach to controlling shape memory alloy (SMA)actuators with hysteresis compensation by using a neural network feedforwardcontroller and a sliding-mode based robust feedback controller. SMA actuatorsexhibit severe hysteresis, which is often responsible for position inaccuracy in aregulation or tracking system and may even cause instability in some cases. Asingle SMA wire actuator is used in this research. A testing system, whichincludes a wire stand, a linear bearing, a bias spring, a position sensor, aprogrammable current amplifier and a PC-based digital data acquisition andreal-time control system, is used to test the SMA wire actuator in both open-andclosed-loop fashions. The proposed control includes two major parts: afeedforward neural network controller, which is used to cancel or reduce thehysteresis, and a sliding-mode based robust feedback controller, which is employedto compensate uncertainties such as the error in hysteresis cancellation andensures the system’s stability. The feedforward neural network controller isdesigned based on the experimental results of open-loop testing of the wireactuator. With the proposed control, tests of the SMA actuator followingsinusoidal commands with different frequencies and magnitudes are conducted.The experiments show that the actual displacement of the SMA actuator with theproposed control closely followed that of the desired sinusoidal command.

Robust Tracking Control of a Piezoactuator Using a New Approximate Hysteresis Model

A new approximate model, which consists of a variable gain and a variable time-delay, is proposed to describe the hysteresis behavior of a piezoactuator. The variable gain is assumed to be a function of the magnitude of the input command, while the time-delay is assumed to be a function of the frequency of the input command. The ranges of these two variable parameters are determined through open loop tests. According to the proposed approximate model, a Smith predictor-based robust H∞ controller is developed to achieve high-precision tracking control of a piezoactuator. Analytical simulation and experimental results on tracking several types of reference inputs demonstrate that the maximum tracking error can be reduced to be less than 2% of the traveling path by utilizing the proposed controller design.

Closed-Loop Endoatmospheric Ascent Guidance

A comprehensive treatment to the optimal atmospheric ascent problem of launch vehicles subject to path constraints and final condition constraints is presented. The development is particularly tailored for the purpose of the eventual realization of closed-loop endoatmospheric ascent guidance. It is demonstrated that the classical finite difference method for two-point boundary-value problems is well suited for solving the optimal ascent problem onboard. The performance and execution of the guidance algorithm are assessed with a series of open-loop and closed-loop tests using the vehicle data of a reusable launch vehicle. The test results render strong supporting evidence to the belief that closed-loop optimal endoatmospheric ascent guidance is now feasible.

Design and Application of Model-on-Demand Predictive Controller to a Semibatch Copolymerization Reactor

This article considers the design of a multivariable model-on-demand predictive controller (MoD-PC) and its application to polymer quality control in a semibatch MMA/MA copolymerization reactor. The MoD-PC is designed by combining the model-on-demand (MoD) framework with the conventional model predictive controller. For this purpose, a local autoregressive exogenous input model is constructed with a small portion of data located in the region of interest at every sample time when a model equation is needed for output prediction. This model equation is then used to calculate the optimal control input sequence. Through the open-loop test, the reaction temperature and free volume are shown to be an adequate choice for the elements of the regressor state vector in the data searching step. The validity of the identified model is corroborated by the prediction method. The results of simulation studies for the regulation and disturbance rejection problems with and without noise demonstrate that, despite the nonlinearity of the system, the MoD-PC is an effective strategy with a low computational load for the production of copolymers with desired properties.

1541 電極壁を有する円管を流れる混合液晶の圧力降下

In the present experiments two arrangements of the electrodes fixed on the inner surface of the circular tube are developed. One is that the four pair of the electrodes is fixed to add the voltages in the peripheral direction. The other is that the electrodes are lined up along the inner surface to add the voltages in the axial direction. The pressure drops are measured when the liquid crystal mixture made of some kinds of the nematic liquid crystal flows in the circular tubes for the constant flow rates. When the voltages are applied on the liquid crystal mixture and removed, the pressure responses of the inlet of the circular tube are measured with the pressure transducer. The diameter of the circular tube is 1.0mm. The isotropic-nematic transition is 90.0℃ and smectic-nematic transition is -44.0℃ for the liquid crystal mixture. The open-loop test facility with the liquid crystal is set in a pyrostat to keep the temperature constant.

Control of Shape Memory Alloy Actuators Using Pulse-Width Pulse-Frequency (PWPF) Modulation

This paper presents the design and experimental results of control of a Shape Memory Alloy (SMA) actuator using Pulse-Width Pulse-Frequency (PWPF) modulation to reduce the energy consumption of the SMA actuator. An SMA wire test stand is used in this research. Based on results of open-loop testing of the SMA wire actuator and parameter analysis of the PWPF modulator, a PWPF modulator is designed to modulate a Proportional plus Derivative (PD) controller. Experiments demonstrate that control of the SMA actuator using PWPF modulation effectively save actuation energy while maintaining same control accuracy as compared to continuous PD control.