Pure Feedback Research Articles

Composite iterative learning controller design for gradually varying references with applications in an AFM system

Learning control for gradually varying references in iteration domain was considered in this research, and a composite iterative learning control strategy was proposed to enable a plant to track unknown iteration-dependent trajectories. Specifically, by decoupling the current reference into the desired trajectory of the last trial and a disturbance signal with small magnitude, the learning and feedback parts were designed respectively to ensure fine tracking performance. After some theoretical analysis, the judging condition on whether the composite iterative learning control approach achieves better control results than pure feedback control was obtained for varying references. The convergence property of the closed-loop system was rigorously studied and the saturation problem was also addressed in the controller. The designed composite iterative learning control strategy is successfully employed in an atomic force microscope system, with both simulation and experimental results clearly demonstrating its superior performance.

Design Artificial Intelligent Parallel Feedback Linearization of PID Control with Application to Continuum Robot

Refer to this research, an intelligent robust fuzzy parallel feedback linearization estimator for ProportionalIntegral-Derivative (PID) controller is proposed for highly nonlinear continuum robot manipulator. In the absence of robot knowledge, PID may be the best controller, because it is model-free, and its parameters can be adjusted easily and separately. And it is the most used in robot manipulators. In order to remove steadystate error caused by uncertainties and noise, the integrator gain has to be increased. This leads to worse transient performance, even destroys the stability. The integrator in a PID controller also reduces the bandwidth of the closed-loop system. Model-based compensation for PD control is an alternative method to substitute PID control. Feedback linearization compensation is one of the nonlinear compensator. The first problem o f the pure feedback linearization co mpensator (FLC) was equivalent problem in certain and uncertain systems. The nonlinear equivalent dynamic problem in uncertain system is solved by using parallel fuzzy logic theory. To eliminate the continuum robot man ipulator system’s dynamic; Mamdani fuzzy inference system is design and applied to FLC. Th is methodology is based on design parallel fu zzy inference system and applied to equivalent nonlinear dynamic part of FLC. The results demonstrate that the model free fuzzy FLC estimator works well to co mpensate linear PID controller in presence of part ly uncertainty system (e.g., continuum robot).

Inverse-feedforward and robust-feedback control for high-speed operation on piezo-stages

This article demonstrates an approach to compensate for tracking errors resulting from hysteresis and vibration when operating piezo-stages and to achieve precision motion control on them. In order to achieve this goal, inverse-feedforward control and H ∞-feedback control were utilised to augment each other. Experimental results showed that pure feedforward control would suffer from modelling uncertainty and pure feedback control would be limited on its bandwidth; therefore, both of these could compensate for partial tracking errors. In contrast, the proposed approach integrated the merits of feedforward and feedback controls to improve the tracking performance when operating piezo-stages in long-stroke and high-speed.

In Silico Evaluation of an Artificial Pancreas Combining Exogenous Ultrafast-Acting Technosphere Insulin with Zone Model Predictive Control

Because of the slow pharmacokinetics of subcutaneous (SC) insulin, avoiding postprandial hyperglycemia has been a major challenge for an artificial pancreas (AP) using SC insulin without a meal announcement. A semiautomated AP with Technosphere® Insulin (TI; MannKind Corporation, Valencia, CA) was designed to combine pulmonary and SC insulin. Manual inhalation of 10 U ultrafast-absorbing TI at mealtime delivers the first, or cephalic, phase of insulin, and an SC insulin pump controlled by zone model predictive controller delivers second-phase and basal insulin. This AP design was evaluated on 100 in silico subjects from the University of Virginia/Padova metabolic simulator using a protocol of two 50 g carbohydrate (CHO) meals and two 15 g CHO snacks. Simulation analysis shows that the semiautomated AP with TI provides 32% and 16% more time in the controller target zone (80-140 mg/dl) during the 4 h postprandial period, with 39 and 20 mg/dl lower postprandial blood glucose peak on average than the pure feedback AP and the AP with manual feed-forward SC bolus, respectively. No severe hypoglycemia (<50 mg/dl) was observed in any cases. The semiautomated AP with TI provides maximum time in the clinically accepted region when compared with pure feedback AP and AP with manual feed-forward SC bolus. Furthermore, the semiautomated AP with TI provides a flexible operation (optional TI inhalation) with minimal user interaction, where the controller design can be tailored to specific user needs and abilities to interact with the device.

Observer Based Dynamic Surface Control of A Hypersonic Flight Vehicle

Abstract This paper describes the design and analysis of a proportional integral air speed controller and a nonlinear adaptive dynamic surface altitude controller for the longitudinal dynamics of a generic hypersonic flight vehicle. The uncertain nonlinear functions in the pure feedback flight vehicle model are approximated by using radial basis function neural networks. For the controller design, the complete states are assumed to be available for measurement, then a sliding mode observer is incorporated to estimate the states which are difficult to measure in practice. A detailed stability analysis of the designed altitude controller shows that all the signals of the closed loop system are uniformly ultimately bounded. The robustness and performance of the designed controllers, with and without the observer are verified through numerical simulations of the flight vehicle model for trimmed cruise conditions of 110,000 ft and Mach 15.

Design and Control of an Elevated-Pressure Air Separations Unit for IGCC Power Plants in a Process Simulator Environment

A rigorous pressure-driven dynamic model for a heat-integrated double-column air separation unit (ASU) has been developed in a process simulator environment to investigate feasibility and applicability of high ramp-rate demands posed by gasification island within the integrated gasification combined cycle (IGCC) power plant, while maintaining the oxygen purity constraints. Some of the operability and controllability issues, including the “snowball effect” observed due to ASU’s condenser–reboiler and feed-product heat integration, which may be extended to many heat-integrated processes, have been identified and addressed. Initial model based PID control structures were proposed and implemented in pure feedback, pure feedforward/ratio, and feedforward–feedback modes and corresponding responses were assayed and compared. In addition, the importance of oxygen storage and degradation of controllability when fast-refrigeration is actively enabled during large ramp-changes has been discussed in detail, in view o...

Pseudohaptic interaction with knot diagrams

To make progress in understanding knot theory, we need to interact with the projected representations of mathematical knots, which are continuous in three dimensions (3-D) but significantly interrupted in the projective images. One way to achieve such a goal is to design an interactive system that allows us to sketch two-dimensional (2-D) knot diagrams by taking advantage of a collision-sensing controller and explore their underlying smooth structures through a continuous motion. Recent advances of interaction techniques have been made that allow progress in this direction. Pseudohaptics that simulate haptic effects using pure visual feedback can be used to develop such an interactive system. We outline one such pseudohaptic knot diagram interface. Our interface derives from the familiar pencil-and-paper process of drawing 2-D knot diagrams and provides haptic-like sensations to facilitate the creation and exploration of knot diagrams. A centerpiece of the interaction model simulates a physically reactive mouse cursor, which is exploited to resolve the apparent conflict between the continuous structure of the actual smooth knot and the visual discontinuities in the knot diagram representation. Another value in exploiting pseudohaptics is that an acceleration (or deceleration) of the mouse cursor (or surface locator) can be used to indicate the slope of the curve (or surface) of which the projective image is being explored. By exploiting these additional visual cues, we proceed to a full-featured extension to a pseudohaptic four-dimensional (4-D) visualization system that simulates the continuous navigation on 4-D objects and allows us to sense the bumps and holes in the fourth dimension. Preliminary tests of the software show that main features of the interface overcome some expected perceptual limitations in our interaction with 2-D knot diagrams of 3-D knots and 3-D projective images of 4-D mathematical objects.

Closed-Loop Neural Network-Based NMES Control for Human Limb Tracking

Closed-loop control of skeletal muscle is complicated by the nonlinear muscle force to length and velocity relationships and the inherent unstructured and time-varying uncertainties in available models. Some pure feedback methods have been developed with some success, but the most promising and popular control methods for neuromuscular electrical stimulation (NMES) are neural network (NN)-based methods. Efforts in this paper focus on the use of a NN feedforward controller that is augmented with a continuous robust feedback term to yield an asymptotic result (in lieu of typical uniformly ultimately bounded stability). Specifically, an NN-based controller and Lyapunov-based stability analysis are provided to enable semi-global asymptotic tracking of a desired limb time-varying trajectory (i.e., non-isometric contractions). The developed controller is applied as an amplitude modulated voltage to external electrodes attached to the distal-medial and proximal-lateral portion of the quadriceps femoris muscle group in non-impaired volunteers. The added value of incorporating a NN feedforward term is illustrated through experiments that compare the developed controller with and without the NN feedforward component.

Controller Design for Ascent Phase of Reusable Launch Vehicle Using Backstepping

Backstepping is a systematic method for nonlinear control design, which can be applied to a broad class of systems. The name “backstepping” refers to the recursive nature of the design procedure. First, only a small subsystem is considered, for which a “virtual” control law is constructed based on a Lyapunov function (Krstic et al., Nonlinear and Adaptive Control Design, Wiley Interscience, New York, 1995; Slotine and Li, Applied Nonlinear Control, Prentice-Hall, Englewood Cliffs, 1991) for the subsystem. Then, the design is extended in several steps until a control law for the full system has been constructed. Along with the control law, a Lyapunov function is successively constructed. An important feature of backstepping is that useful nonlinearities, which act stabilizing, can be retained. This is in contrast to feedback linearization control where nonlinearities are cancelled using nonlinear feedback. Retaining nonlinearities instead of cancelling them requires less precise models and may also require less control effort. Backstepping can be applied to nonlinear systems which are in strict feedback form or pure feedback form. In this paper controller design for ascent phase of reusable launch vehicle in pitch plane using backstepping is presented.

Permanence in general non-autonomous single-species Kolmo- gorov systems with pure delays and feedback control

Permanence in general non-autonomous single-species Kolmo- gorov systems with pure delays and feedback control

Disturbance rejection in space applications: Problems and solutions

Navigation, control and guidance of the propulsive phase of planetary landing, e.g. on Mars (or the Moon), with a soft landing being the only target, are driven by Inertial Measurement Units and a radar altimeter/velocimeter. Their measurements are affected by bias and scale errors. The latter ones are aggravated by the attitude navigation error as it accumulates during the ballistic (and aerodynamic) flight after orbiter separation and couples for most of the descent trajectory with the vehicle axis inclination from the local vertical direction. By complementing the center-of-mass dynamics with appropriate disturbance state equations driven by noise vectors and estimating the noise from the model error (plant measurements minus model output), scale errors and bias can be retrieved in real time in the form of disturbance state variables. Although a similar complement is adopted in the standard navigation algorithms, it takes the form of an output disturbance, which may lead to unobservability. In this paper instead, the disturbance complement is designed to be fully observable, which may require that the derivatives of smooth systematic errors be pushed up to the command channel (a form of back-stepping). It is then viable, unlike standard navigation, to eliminate them from position and velocity tracking errors through disturbance rejection, under appropriate convergence conditions and sensor layout. It will, however, be demonstrated in this paper that the same result cannot be achieved under pure feedback control. Since constant errors (bias) become zero through back-stepping, a well known fact derives: bias can only be eliminated by disposing of supplementary sensors. To further enlighten and solve the question of bias rejection, a further case study is treated. The attitude control of drag-free satellites is considered, where fine accelerometers allow for the rejection of wide-band aerodynamic torques (think of low-Earth orbit spacecrafts) at the price of attitude divergence because of accelerometer bias and drift. The spacecraft attitude can be made bounded and accurate, if bias and drift are modeled as angular accelerations, affecting the attitude. They are estimated by attitude sensors like star trackers and then are rejected by the attitude control. The results in the soft landing and drag free case studies are illustrated by simulated runs and Monte Carlo trials.

Adaptive neural network predictive control for nonlinear pure feedback systems with input delay

This paper presents an adaptive neural control design for nonlinear pure-feedback systems with an input time-delay. Novel state variables and the corresponding transform are introduced, such that the state-feedback control of a pure-feedback system can be viewed as the output-feedback control of a canonical system. An adaptive predictor incorporated with a high-order neural network (HONN) observer is proposed to obtain the future system states predictions, which are used in the control design to circumvent the input delay and nonlinearities. The proposed predictor, observer and controller are all online implemented without iterative predictive calculations, and the closed-loop system stability is guaranteed. The conventional backstepping design and analysis for pure-feedback systems are avoided, which renders the developed scheme simpler in its synthesis and application. Practical guidelines on the control implementation and the parameter design are provided. Simulation on a continuous stirred tank reactor (CSTR) and practical experiments on a three-tank liquid level process control system are included to verify the reliability and effectiveness.

Comments on "Partial channel feedback schemes maximizing overall efficiency in wireless networks" [Apr 08 1306-1314

The proof of Proposition 2 in the above-mentioned paper was incorrect due to some flaws in the prerequisite analysis of the proposed hybrid feedback scheme. We fix the flaws and correct the proof in this comment. From the corrected proof, we arrive at a new observation that the hybrid feedback scheme has exactly the same feedback overhead as the pure opportunistic feedback scheme if the threshold is adaptively set for a target utilization. Simulation results demonstrate the correctness of our analysis.

Protein Degradation Kinetics and Biochemical Oscillations

Protein ubiquitination and degradation are very important posttranscriptional regulatory processes which are required for biological systems. It is well known that for biochemical oscillations to occur, besides other posttranscriptional regulation, such as phosphorylation and dephosphorylation, the rates of protein synthesis and degradation have to be properly matched. However, the properties of protein degradation kinetics and how they affect biochemical oscillations are not well understood. In this study, we first developed a biochemical reaction model of protein ubiquitination and degradation based on the up-to-date experimental information and calculated the degradation rate against the concentration of the free substrate. The model was tuned to a recent experimental dataset of protein ubiquitination. We show that when the substrate concentration (or synthesis rate) is low the degradation rate linearly increases with the substrate concentration, but as the substrate concentration increases further it becomes nonlinear and eventually saturates. We then studied analytically how linear and nonlinear degradation kinetics affect the instabilities that leads to oscillations using three generic biochemical oscillation models: pure negative feedback induced oscillations (the Goodwin model); pure positive feedback induced oscillations; and combined positive and negative feedback induced oscillations. In all three cases, nonlinear degradation kinetics promotes oscillations and results in much larger oscillation amplitude than the linear kinetics does. On the other hand, the time delay due to protein ubiquitination and deubiquitination generally suppresses oscillations. We finally used computer simulations of cell cycle and circadian rhythm models combined with the detailed protein ubiquitination and degradation model to demonstrate our theoretical predictions from the simplified models.

Smooth time-varying pure feedback control for chained non-holonomic systems with exponential convergent rate

The feedback stabilisation problem of non-holonomic chained systems and a novel feedback design scheme is proposed, which renders a smooth, time-varying, aperiodic, pure feedback control with exponential convergence rates. There are three main advantages with the proposed design. (i) In general, time-varying designs are mostly periodic and render asymptotic stability, whereas the proposed approach is aperiodic and have exponential convergent rates. (ii) A novel state scaling transformation is proposed. It shows that even though u1 vanishes in regulation problems, intrinsic controllability of chained systems can be regained by judiciously designing the input u1 and by applying the state scaling transformations. (iii) A class of memory functions is introduced into the control design, the controller dependency on the system&apos;s initial conditions in our previous work is removed and the control is a pure feedback. Moreover, the design is shown to be inversely optimal. Simulations and comparisons are conducted to verify the effectiveness of the proposed approach.

Adaptive Fuzzy Control of Nonlinear Systems in Pure Feedback Form Based on Input-to-State Stability

Using mean value theorem and backstepping technique, a robust adaptive fuzzy control scheme is proposed for a class of pure-feedback nonlinear systems with unknown dead zone and disturbances via input-to-state stability. Takagi-Sugeno (T--S) type fuzzy logic systems are used to approximate the uncertain nonlinear functions and fewer learning parameters need to be adjusted online. Based on small gain theorem, the closed-loop control system is proven to be semiglobally uniformly ultimately bounded, and the tracking error converges to a neighborhood of zero by choosing appropriate parameters. Simulation results demonstrate the effectiveness of the control scheme.

Extinction in Nonautonomous Discrete Lotka-Volterra Competitive System with Pure Delays and Feedback Controls

The paper discusses a nonautonomous discrete time Lotka-Volterra competitive system with pure delays and feedback controls. New sufficient conditions for which a part of then-species is driven to extinction are established by using the method of multiple discrete Lyapunov functionals.

A Scan Controller Concept for Low Power Scan Tests

Test technology based on multiple parallel scan chains is widely used for production tests of integrated circuits. Beyond the problem of efficient test data compression, aspects of heat dissipation during testing have become a major matter of concern in recent years. In normal operation modes circuits may work close to their thermal limits. Therefore innovative test technologies and automatic test pattern generators (ATPG) algorithms need to generate test stimuli that utilize circuits more efficiently without causing excessive high thermal stress. For this reason a modified STUMPS architecture together with an optimization strategy is presented which aims at reduced power consumption (80 percent reduction over pure linear feedback shift register solutions) during scan test and high test compaction rates. Both aims could be weighted against each other as required.

Towards fused vision and force robust feedback control of nanorobotic-based manipulation and grasping

This paper presents the design and development of a fused vision force feedback robust controller for a nanomanipulator used in nanofiber grasping and nano-fabric production applications. The RRP (revolute revolute prismatic) nanomanipulator considered here utilizes two rotational motors with 0.1 μrad resolution and one linear Nanomotor ® with 0.25 nm resolution. The nanomanipulator is capable of achieving well-behaved kinematic and backlash-free characteristics in addition to atomic scale precision to guarantee accurate manipulation at the nanoscale. A mathematical model of the nanomanipulator is formulated, along with direct and inverse kinematics and dynamic equations of the system. Unlike typical macroscale manipulator models and controllers, the controller development is not trivial due to nanoscale movement and forces, coupled with unmodeled dynamics, nonlinear structural dynamics and mainly the lack of position and velocity feedbacks in this particular nanomanipulator. Utilizing pure vision feedback to acquire nanomanipulator’s tip position is shown to have limited capabilities in achieving the desired control accuracy. To remedy this, a controlled fusion of visual servoing and force feedbacks for nanomanipulator positioning is proposed and analyzed extensively. Following the development of the controller, numerical simulations with generic feedback using a realistic scenario with fused vision and force feedbacks are presented to demonstrate the positioning performance capability in the nanomanipulation applications considered here.

Unit Quaternion-Based Output Feedback for the Attitude Tracking Problem

In this note, we propose a quaternion-based dynamic output feedback for the attitude tracking problem of a rigid body without velocity measurement. Our approach consists of introducing an auxiliary dynamical system whose output (which is also a unit quaternion) is used in the control law together with the unit quaternion representing the attitude tracking error. Roughly speaking, the necessary damping that would have been achieved by the direct use of the angular velocity can be achieved, in our approach, by the vector part \mathtilde q of the error signal between the output of the auxiliary system and the unit quaternion tracking error. The resulting velocity-free control scheme guarantees almost global asymptotic stability which is as strong as the topology of the motion space can permit. In the regulation case, our control law is a pure quaternion feedback (i.e., consisting of two terms that are vector parts of unit-quaternion), and hence, the control torques are naturally bounded by the control gains. Simulation results are provided to show the effectiveness of the proposed control scheme.