Feedforward control using the higher-harmonic, time-averaged gradient descent algorithm

This thesis investigates how insects control movement using adaptive feedforward control and efference copies, and how these principles can be applied to robotic systems. A phenomenological control architecture—the fully-separable-degrees-of-freedom (FSDoF) controller—is developed to formalise efference copies in a control-theoretic context. The FSDoF architecture is used in simulation to examine control advantages of efference copy-based systems. Specifically, it enables sensors to remain within their operating range, thereby optimising sensitivity to external disturbances, and is particularly effective in systems with time delays and significant sensor noise. When combined with high-pass-filter-like sensors, the FSDoF controller also exhibits a unique robustness to changes in sensor gain and bandwidth. Furthermore, a method is introduced to design FSDoF controllers for multi-input multi-output (MIMO) systems with multiple, distinct time delays. This work formalises the efference copy hypothesis in insects from an engineering perspective, offering a functional explanation for their evolutionary advantages, and enabling the generation of experimentally testable hypotheses. One such hypothesis is that insect feedforward controllers adapt to changes in system dynamics. A series of free-flight experiments in Drosophila melanogaster supports this idea. Following unilateral wing damage, flies exhibited increased flight speeds in darkness compared to intact controls. When flying in light, with visual feedback, their speed was reduced to near-control levels. Altogether, the results indicate that the adaptation was not solely due to changes in mechanosensory feedback, but suggest adaptive feedforward control. Building on these insights, an implicit adaptive feedforward (IAFF) control strategy is proposed and implemented on a quadrotor platform. This controller uses adaptive sensitivity derivatives, so that it could, in theory, cope with an inversion of the system dynamics. IAFF control improved the reference tracking in a Parrot Mambo mini-drone within minutes of operation, starting from a randomised feedforward controller.

The structure and performance requirements for active vibration isolation control systems motivate the use of adaptive control. This is especially true for spacecraft platforms subject to uncertainties inherent in on-orbit operation. This paper is an initial investigation into adaptive control strategies and algorithms that may have application to isolation on spacecraft platforms. Analysis of the algorithms, numerical simulation, and laboratory test data are used to evaluate adaptive feedforward control. Of particular interest are the performance characteristics and limitations of the filtered-x LMS (FXLMS) algorithm. The augmented error algorithm and combination feedback/feedforward control are two means investigated to extend the capabilities of FXLMS by desensitizing the algorithm to the specific dynamics of the plant. Several experiments were conducted on a laboratory testbed which serves as the prototype for a planned active vibration isolation flight demonstration.

In this paper, high speed synchronization of multiple motion control axes under adaptive feedforward control is considered. The adaptive feedforward control system for one axis system consists of a proportional feedback controller and an adaptive feedforward controller. To synchronize the multiple motion control axes, the synchronizing controller, which responds to the tracking errors, is introduced. The structure of the synchronizing controller is investigated. The parameters of the adaptive feedforward controller are adjusted by the adaptation algorithm so that the tracking errors and the synchronization errors are removed. This results in the significant improvement of the tracking responses and the quick removal of the synchronization errors during transient as well as steady state. The synchronization for a four axes motion control system, of which parameters are significantly different, is investigated. Stability of the proposed synchronizing system is analyzed. Experimental results demonstrate the effectiveness of the proposed control scheme for synchronization.

In this paper we focus on the adaptive control of structural acoustics using intelligent structures with embedded piezoelectric (PZT) patches and low cost digital signal processor systems. After a discussion on the adaptive feedforward control scheme, a hybrid adaptive control scheme is proposed, which takes advantage of both feedback control and adaptive feedforward control. The two schemes are realized on a low-cost, small volume, convenient and universal digital signal processing (DSP) board. A carbon fiber reinforced polymer plate with two embedded PZT patches is developed and used in two experiments. The first experiment is adaptive interior noise control using the intelligent plate, in which the adaptive feedforward control scheme is employed. Obvious noise reduction is obtained for constant frequency, swept frequency and varying amplitude harmonic disturbances. The second experiment is adaptive control of sound-induced vibration of the plate, where two embedded PZT patches are used as an actuator and a sensor, respectively, and the hybrid adaptive controller is applied. The full vibration reduction for various harmonic excitations is obtained, verifying the advantage of the hybrid adaptive control. It is demonstrated that active control of structural acoustics can be efficiently achieved by employing intelligent structures, advanced adaptive control schemes and the low-cost DSP board.

A multi-input multi-output adaptive feed-forward controller for vibration alleviation on a large blended wing body airliner

When prior knowledge of the plant controlled is available, feedforward control is preferred over feedback control for disturbance rejection.The stability characteristics of the system using feedforward control are the same as the original plant.Adaptive feedforward control design for gust loads alleviation of both a two degrees of freedom aerofoil with polynomial structural nonlinearity and a free flying flexible aircraft with large geometric wing deformations is investigated.Two dimensional thin aerofoil theory based on Theodorsen theory is used to perform aerodynamic analysis in the aerofoil aeroelastic model.The same aerodynamic model coupled with geometrically exact nonlinear beam is used to formulate the multi-disciplinary fluid-structure-flight framework for highly flexible aircraft.Gust loads analysis in terms of both discrete and continuous turbulence gusts are performed based on the aerofoil model and the free flying trim configuration of the highly flexible aircraft.Finite impulse response model is used to design an adaptive feedforward controller to alleviate the gust loads.Adaptive feedforward control shows good gust loads alleviation performance for both discrete and continuous gusts.Compared with adaptive feedback control, it exhibits a greater potential to reduce gust loads from the initial transient of the encounter.

Sinusoidal reference strategy for adaptive feedforward vibration control: numerical simulation and experimental study

This paper focuses on a frequency-weighted hybrid adaptive control with application tosimultaneous precision positioning and vibration suppression of smart composite structures.Following the introduction of the structure and materials system of an active compositepanel (ACP) with a surface-mounted and two embedded piezoelectric ceramic patches, thesensor selection for the purpose of precision positioning or vibration control is discussed,and the function assignment of a laser displacement sensor as well as the embeddedpiezoelectric sensor is determined for the ACP. The frequency-weighted hybrid adaptivecontrol approach is then developed. The approach consists of an adaptive feedforwardposition controller for precision positioning, an adaptive feedforward vibrationcontroller for vibration suppression as well as an adaptive feedback controller for bothprecision positioning and vibration suppression. The frequency-weighted filtersintroduced in the approach realize the signal fusion of the two sensors. Finally,experiments are also performed for harmonic disturbances at the first two naturalfrequencies of the ACP and a random disturbance for both cases of with/without theadaptive feedforward vibration controller, demonstrating that the frequency-weightedhybrid adaptive control approach can provide satisfactory precision positioningand vibration suppression in both cases, and that better position accuracy canbe achieved if the adaptive feedforward vibration controller is also employed.

An Adaptive Feedforward Control Algorithm for Computer Control of Wastewater Neutralization

An adaptive feed-forward control method combining with feedback control was proposed to improve the command tracking performance of control circuit in an inertial stabilized platform. On the basis of subspace system identification, the input-output data were used to identify a state space of the stabilized platform model and the frequency-domain loop shaping technique was used to design the feedback loop controller to reject the external disturbance. Furthermore, a Recursive Least Square (RLS) adaptive filter was taken to build the inverse model of the feedback control loop and to construct the all-pass transfer function for increasing tracking performance. Several tracking experiments were conducted on different command inputs to verify the validity of the adaptive feed-forward controller. Experimental results show that this method responses quickly to step commands and the overshoot has decreased from 30% to 4.5% as compared with that of the feedback control. For a sinusoidal signal at the frequency of 30 Hz, the adaptive feed-forward controller can obtain an amplitude response without attenuation and the phase lag is reduced to 54 from 90 as compared with that of the feedback control. This method significantly improves the transient performance and is superior to the feedback control alone. , 2015, Chinese Academy of Sciences. All right reserved.

SummaryAt the present time, there is a great deal of interest in the adaptive control of systems with rapidly varying parameters. Such problems arise in different forms and in many disciplines including finance, sociology, biology, and engineering. In general, these problems are intractable mathematically and the time variations have to be classified in some form to obtain rigorous results. In this paper, we consider the adaptive identification and control of linear systems with periodically varying parameters (referred to as linear time‐varying periodic (LTP) systems). The class of systems with known periodic parameters has been investigated widely since the pioneering work of Floquet and lends itself to rigorous mathematical analysis. However, very little was known until the early years of the last decade concerning the adaptive control of such systems. The problem was introduced by Xu and explored in detail by Narendra and Zhiling in 2006 and 2009, respectively. In 2012, a new method was introduced in adaptive control by Han and Narendra and is referred to as second‐level adaptation. In this paper, the adaptive identification and control of LTP systems using second‐level adaptation is discussed.

Presents an approach to the design and real-time implementation of an adaptive controller for a robotic manipulator based on digital signal processors. The Texas Instruments DSP (TMS320C31) chips are used in implementing real-time adaptive control algorithms to provide enhanced motion control performance for robotic manipulators. In the proposed scheme, adaptation laws are derived from the direct model reference adaptive control principle based on the improved Lyapunov second method. The proposed adaptive controller consists of an adaptive feedforward and feedback controller and PI-type time-varying auxiliary control elements. The proposed control scheme is simple in structure, fast in computation, and suitable for real-time control. Moreover, this scheme does not require any accurate dynamic modeling nor values of manipulator parameters and payload. Performance of the proposed adaptive controller is illustrated by simulation and experimental results for an industrial robot with four joints in the joint space and Cartesian space.

Usage of frequency based error correction methods for repetitive disturbances becomes popular in data storage devices that use a rotating mechanical power plant. Two distinct disturbance cancellation methods, disturbance observer (DOB) and adaptive feed forward control (AFC) are the most popular approaches used for current drive servo integration. DOB reduces error using a predetermined function that is calculated thorough a complicated process. Generally the response to disturbance and initiation of control action of DOB is relatively fast even if the amount of error reduction is limited. Meanwhile the error elimination capability of AFC for the repetitive disturbance is normally better than DOB as it utilizes a Fourier coefficients updating feature that supports an enhanced fine adaptation of a certain frequency disturbance. Of course, AFC suffers for disturbances that have neighboring close frequencies due to the inherent fundamental frequency dependencies of AFC formulation. In the present work, an attempt for combining benefits of AFC and DOB is made. This might enables control action not only to generate fast response to disturbance but also perform an accurate error rejection. This feature also provides to the closed loop system a frequency selection for enabling a strategic selective error rejection. The proposed method named Hybrid Disturbance Observer (HDOB) is compared to the traditional AFC and DOB.

This work is focused on the active vibration control of piezoelectric cantilever beam, where an adaptive feedforward controller (AFC) is utilized to reject the vibration with unknown multiple frequencies. First, the experiment setup and its mathematical model are introduced. Due to that the channel between the disturbance and the vibration output is unknown in practice, a concept of equivalent input disturbance (EID) is employed to put an equivalent disturbance into the input channel. In this situation, the vibration control can be achieved by setting the control input be the identified EID. Then, for the EID with known multiple frequencies, the AFC is introduced to perfectly reject the vibration but is sensitive to the frequencies. In order to accurately identify the unknown frequencies of EID in presence of the random disturbances and un-modeled nonlinear dynamics, the time–frequency-analysis (TFA) method is employed to precisely identify the unknown frequencies. Consequently, a TFA-based AFC algorithm is proposed to the active vibration control with unknown frequencies. Finally, four cases are given to illustrate the efficiency of the proposed TFA-based AFC algorithm by experiment.

Adaptive traffic control systems continuously monitor traffic conditions on an arterial and adjust traffic signal timings to accommodate variation in traffic volume and minimize stops and delays. This paper describes currently practical adaptive control systems which have been used in the United States and worldwide, which include Adaptive Control System-Lite (ACS-Lite), Optimization Policies for Adaptive Control (OPAC), Real-Time Hierarchical Optimized Distributed and Effective System (RHODES), Sydney Coordinated Adaptive Traffic System (SCATS) and Split Cycle Offset Optimization (SCOOT). The comparisons of the benefits from past experiences, cost and hardware requirements will help the traffic engineers and decision makers a guideline to select the optimized adaptive control system based on research objectives.