Scheduling Strategy of Multiple Semi-Active Controllers With Information on the Disturbance and the Structural Response

We propose an adaptive gain scheduled semiactive control method using an artificial neural network for structural systems subject to earthquake disturbance. In order to design a semiactive control system with high control performance against earthquakes with different time and/or frequency properties, multiple semiactive control laws with high performance for each of multiple earthquake disturbances are scheduled with an adaptive manner. Each semiactive control law to be scheduled is designed based on the output emulation approach that has been proposed by the authors. As the adaptive gain scheduling mechanism, we introduce an artificial neural network (ANN). Input signals of the ANN are the measured earthquake disturbance itself, for example, the acceleration, velocity, and displacement. The output of the ANN is the parameter for the scheduling of multiple semiactive control laws each of which has been optimized for a single disturbance. Parameters such as weight and bias in the ANN are optimized by the genetic algorithm (GA). The proposed design method is applied to semiactive control design of a base‐isolated building with a semiactive damper. With simulation study, the proposed adaptive gain scheduling method realizes control performance exceeding single semiactive control optimizing the average of the control performance subject to various earthquake disturbances.

The optimal control problem of a quarter-car semi-active suspension has been studied in the past. Considering that a quarter-car semi-active suspension can either be modelled as a linear system with state dependent constraint on control (of actuator force) input, or a bi-linear system with a control (of variable damping coefficient) saturation, the seemingly simple problem poses several interesting questions and challenges. Does the saturated version of the optimal control law derived from the corresponding un-constrained system, i.e. “clipped-optimal”, remain optimal for the constrained case as suggested in some previous publications? Or should the optimal deviate from the “clipped-optimal” as suggested in other publications? If the optimal control law of the constrained system does deviate from its unconstrained counter-part, how different are they? What is the structure of the optimal control law? Does it retain the linear state feedback form (as the unconstrained case)? In this paper, we attempt to answer some of the above questions by utilizing the recent development in model predictive control (MPC) of hybrid dynamical systems. The constrained quarter-car semi-active suspension is modelled as a switching affine system, where the switching is determined by the activation of passivity constraints, force saturation, and maximum power dissipation limits. Theoretically, over an infinite prediction horizon the MPC controller corresponds to the exact optimal controller. The performance of different finite-horizon hybrid MPC controllers is tested in simulation using mixed-integer quadratic programming. Then, for short-horizon MPC controllers, we derive the explicit optimal control law and show that the optimal control is piecewise affine in state. In the process, we show that for horizon equal to one the explicit MPC control law corresponds to clipped LQR as expected. We also compare the derived optimal control law to various semi-active control laws in the literature including the well-known “clipped-optimal”. We evaluate their corresponding performances for both a deterministic shock input case and a stochastic random disturbances case through simulations.

The increased prevalence of semi-active control systems is largely due to the emergence of cost effective commercially available controllable damper technology such as Magneto-Rheological (MR) devices. Unfortunately, MR dampers are highly nonlinear, which presents an often over-looked complexity to the control system designer. The well-known Skyhook Damping control algorithm has enjoyed great success for both fully active and semi-active control problems. The Skyhook design strategy is to create a control force that emulates what a passive linear damper would create when connected to an inertial reference frame. Skyhook control is device independent since it generates a desired control force command output that must be produced by the control system. For simplicity, MR dampers are often assumed to have a linear relationship between the current input and the force output at a given relative velocity. Often this assumption is made implicitly and without knowledge of the underlying nonlinearity. In this paper, we show that the overall performance of a semi-active Skyhook control system can be improved by explicitly inverting the nonlinear relationship between input current and output force. The proposed modification will work with any semi-active control algorithm, such as Skyhook, to insure that the controller performance is at least as good as the performance without the proposed modification. This technique is demonstrated through simulation on a quarter-vehicle system.

The seismic response reduction of the semi-active fuzzy control system including a newtype of piezoelectric variable-friction damper and fuzzy controller was investigated on theshaking table under various earthquake records for a building model. The performance ofthe piezoelectric actuator under different preloads was tested in advance to identify itsforce generation. The feature test of the damper under either constant or linear increasedvoltage was carried out to study its motion characteristics. Based on the experimental testsof the damper, a semi-active fuzzy control algorithm was presented for the real-timemanipulation of the damper according to the structural response. The seismicperformance of the building structural model was tested for the uncontrolled,passive-controlled and semi-active controlled cases. The semi-active control effectiveness ofthe damper was compared with other cases. Experimental results have indicatedthat the proposed semi-active control system based on the fuzzy controller andpiezoelectric variable-friction damper can be more efficient in reducing the inter-storeydrifts and accelerations of the building under various earthquake excitations.

Rapid advances in information processing, communication and sensing technologies have enabled more and more devices to be provided with embedded processors, networking capabilities and sensors. For the field of estimation and control, it is now possible to consider an architecture in which many simple components communicate and cooperate to achieve a joint team goal. This distributed (or networked) architecture promises much in terms of performance, reliability and simplicity of design; however, at the same time, it requires extending the traditional theories of control, communication and computation and, in fact, looking at a unified picture of the three fields. A systematic theory of how to design distributed systems is currently lacking. This dissertation takes the first steps towards understanding the effects of imperfect information flow in distributed systems from an estimation and control perspective and coming up with new design principles to counter these effects. Designing networked systems is difficult because such systems challenge two basic assumptions of traditional control theory - presence of a central node with access to all the information about the system and perfect transmission of information among components. We formulate and solve many problems that deal with the removal of one, or both, of these assumptions. The chief idea explored in this dissertation is the joint design of information flow and the control law. While traditional control design has concentrated on calculating the optimal control input by assuming a particular information flow between the components, our approach seeks to synthesize the optimal information flow along with the optimal control law that satisfies the constraints of the information flow. Thus besides the question of 'What should an agent do?', the questions of 'Whom should an agent talk to?', 'What should an agent communicate?', 'When should an agent communicate?' and so on also have to be answered. The design of the information flow represents an important degree of freedom available to the system designer that has hitherto largely been ignored. As we demonstrate in the dissertation, the joint design of information flow and the optimal control input satisfying the constraints of that information flow yields large improvements in performance over simply trying to fit traditional design theories on distributed systems. We begin by formulating a distributed control problem in which many agents in a formation need to cooperate to minimize a joint cost function. We provide numerical algorithms to synthesize the optimal constrained control law that involve solving linear equations only and hence are free from numerical issues plaguing the other approaches proposed in the literature. We then provide and analyze a model to understand the issue of designing the topology according to which the agents interact. The results are very surprising since there are cases when allowing communication to happen between two agents may, in fact, be detrimental to the performance. We then move on to consider the effects of communication channels on control performance. To counter such effects, we propose the idea of encoding information for the purpose of estimation and control prior to transmission. Although information theoretic techniques are not possible in our problem, we are able to solve for a recursive yet optimal encoder / decoder structure in many cases. This information flow design oriented approach has unique advantages such as being optimal for any packet drop pattern, being able to include the effect of known but random delays easily, letting us escape the limits set by reliability for transmission of data across a network by using intermediate nodes as 'repeaters' similar to a digital communication network and so on. We finally take a look at combining the effects of multiple sources of information and communication channels on estimation and control. We look at a distributed estimation problem in which, at every time step, only a subset out of many sensors can transmit information to the estimator. This is also a representative resource allocation problem. We propose the idea of stochastic communication patterns that allows us to include the effects of communication channels explicitly during system design. Thus, instead of tree-search based algorithms proposed in the literature, we provide stochastic scheduling algorithms that can take into account the random packet drop effect of the channels. We also consider a distributed control problem with switching topologies and solve for the optimal controller. The tools that we develop are applicable to many other scenarios and we demonstrate some of them in the dissertation. Along the way, we look at many other related problems in the dissertation. As an example, we provide initial results about the issue of robustness of a distributed system design to a malfunctioning agent. This notion is currently lacking in the control and estimation community, but has to be a part of any effective theory for designing networked or distributed systems.

In this paper, the characteristics of forces in active control systems connected to adjacent levels of a building are analyzed. The following characteristics are observed: (1) active control can provide significantly superior supplemental damping to a building, but causes a small frequency shift; (2) the linear quadratic regulator (LQR)-based control force is composed of an elastic restoring force component and a damping force component, where the damping force is almost identical to the total control force, however, the elastic restoring force is very small; and (3) the active control forces prevent motion most of the time during the entire control process. These three characteristics imply that active control systems connected to adjacent levels of a building behave like passive damping devices with adjustable parameters, namely damping characteristics in an active control, which is the mechanism used by semi-active control devices to reach similar performance as active control systems. Two indices are defined to quantify the damping characteristics of control forces in active control systems. These two indices can also be used to quantify the capacity of semi-active control to achieve the performance of active control. Based on the above observations, two principles are founded for optimization of parameters of semi-active control devices and passive dampers. The first is that the maximum output force of a semi-active or passive device to be designed is identical to an active device, called “design principle”. The other is the response equivalent principle, which states that the response of a building with semi-active or passive devices is the same as with active devices when the same maximum output force is applied. The design procedure for semi-active control devices and passive dampers is described in detail. Finally, numerical simulations of two benchmark problems is conducted to demonstrate the damping characteristics of active control and investigate the capacity of semi-active control to achieve the same performance as active control.

Effectiveness of passive and semi‐active seismic response control on a cable‐stayed bridge was studied by numerical analyses. An existing cable‐stayed bridge which has fixed‐hinge connections between deck and towers is modeled and its connections were replaced by isolation bearings and dampers. The isolation bearings are of elastic and hysteretic type. The dampers are of linear and variable type. The variable damper uses semi‐active control that incorporates a pseudo‐negative stiffness algorithm. A pseudo‐negative stiffness hysteretic loop produced by the variable damper, combined with a positive stiffness curve of the deck‐tower connections, creates nearly rigid–perfectly plastic force–deformation characteristics with a large damping ratio. The damping ratio for the main mode of the bridge for both passive and semi‐active control was also calculated. Soil‐structure interaction and three‐dimensional effects on structural responses were studied. Copyright © 2002 John Wiley & Sons, Ltd.

The concept of applying semi-active control systems to vibration isolation and shock attenuation is proposed. In this paper, a semi-active isolator for enhancing the pointing performance of optical equipment on-board satellites and its characteristics are first introduced and then a generally applicable semi-active control law is proposed for vibration isolation. The isolation performance of the semi-active control law proposed in this study is evaluated through numerical simulations. The performance of the system with the semi-active control law proposed in this study is compared with those of a passive system and a semi-active system with a previously proposed semiactive control law. Next, to investigate whether or not the isolator is also effective for attenuating shock that is induced by rocket lift-off and pyrodevice ignition for inter-stage separation, we also performed numerical simulations and evaluated its effectiveness.

Controlling the damage process, avoiding the global collapse, and increasing the seismic safety of the super high-rise building structures are of great significance to the casualties’ reduction and seismic losses mitigation. In this paper, a semiactive control platform based on magnetorheological (MR) dampers comprising the Bouc-Wen model, the semi-active control law, and the shear wall damage criteria and steel damage material model is developed in LS-DYNA program, based on the data transferring between the main program and the control platform; it can realize the purpose of integrated modeling, analysis, and design of the nonlinear semi-active control system. The nonlinear seismic control effectiveness is verified by the numerical example of a 15-story steel-concrete hybrid structure; the results indicate that the control platform and the numerical method are stable and fast, the relative displacement, shear force, and damage of the steel-concrete structure are largely reduced using the optimal designed MR dampers, and the deformations and shear forces of the concrete tube and frame are better consorted by the control devices.

This paper presents a new control approach for piezoelectric switching shunt damping. Recently, semi-active controllers have been used to switch piezoelectric materials in order to damp vibration. These switching shunt circuits allow a small implementation and require only little power supply. However, the control laws to switch these shunts are derived heuristically and therefore it remains unclear, if a better control law for a given shunt topology exists. We present a new control approach based on the Hybrid System Framework. This allows the modelling of the switched composite system as a hybrid system. Once the hybrid system description is obtained, a receding horizon optimal control problem can be solved in order to get the optimal switching sequence. As the computation time to solve this optimisation problem is too long for real-time applications, we will show that the problem can be solved off-line and the solution stored in a look-up table. This allows a real-time implementation of the switch controller. Moreover, control rules can be derived from this look-up table, and we will demonstrate that in some situations the controllers proposed in previous papers generate near optimal switching. In this paper, we will investigate several shunt topologies with switches and compare the performance between the heuristically derived control laws and the optimal new control laws. Simulations and experiments show the improvement with the new controllers. This is very promising, since this new control approach can be applied for more complex shunt circuits with many switches, where the derivation of a switching law would be very difficult.

The minimum-time thrust-vector control law in the Apollo lunar-module autopilot

Semi-active modal control for seismic structures with variable friction dampers

The main purpose of this paper is to develop a new and innovative hybrid force/position control method able to adapt in real time to any kind of situation and event that the robot may encounter in the workspace. For this, in hybrid control development phase, multiple control laws are chosen, and to them is associated their way of use, followed by the definition of a real time control laws’ set that the robot will use according to the situation met in the workspace, by states and uncertainty areas for which will be defined control laws and methods with wide spectrum applicability.

The Minimum-Time Thrust-Vector Control Law in the Apollo Lunar-Module Autopilot

A pose-estimation-based approach to perform visual control for differential-drive robots is presented in this paper. Our scheme recovers the camera location (position and orientation) using an extended kalman filter (EKF) algorithm with the 1D trifocal tensor (TT) as measurement model. This new visual servoing scheme allows knowing the real world path performed by the robot without the computational load introduced by position-based approaches. A state-estimated feedback control law is designed to solve a tracking problem for the lateral and longitudinal robot coordinates. The desired trajectories to be tracked ensure total correction of both position and orientation using a single control law, even though the orientation is a DOF in the control system. The effectiveness of our approach is tested via simulations.