Redundant Actuation Research Articles

Substructure Modeling and Loading-Control Techniques for the Test of a Full-Scale Spatial RC Frame with Buckling-Restrained Braces Subjected to Bidirectional Loading

To investigate the performance of reinforced-concrete frames with buckling restrained braces (RCF-BRB) subjected to bidirectional earthquakes, a full-scale two-story RCF-BRB was tested using substructured pseudodynamic (PsD), quasistatic, and pushover techniques. This paper focuses on the structural modeling for the substructured PsD tests, and the control and measurement issues of the bidirectional loading system. To make a credible reproduction of the structural response using substructured PsD technique, an overlap modeling technique together with tuning the mass of the lamped-mass model and stiffness of the numerical substructure was employed to reduce errors caused by the incomplete boundary condition. The outer-loop control method based on Newton’s iteration method was introduced for the loading system, with the data from external displacement sensors as the feedback to avoid errors caused by possible gaps in the connection parts of the loading system. The redundancy issue, caused by the actuators outnumbering the degrees of freedom of the floor to be controlled, is addressed with a force-displacement mixed control technique. The three of four actuators were controlled in displacement mode, whereas the redundant one was in force mode. The force command to the redundant actuator was determined with the optimization criteria to minimize the loads relative to the capacities of the actuators. The working range of the displacement sensors is investigated using numerical and geometric approaches. Failure examples from numerical simulation and experiment were shown to emphasize the importance of proper arrangement of displacement sensors. A rearrangement of the displacement sensors was proposed for the pushover test to enlarge the working range. Time-history results of the prototype structure using the calibrated finite-element model show that the PsD substructure test results could represent seismic responses of the prototype structure. The measured mass-center displacements accurately tracked the target displacements throughout the test, indicating the effectiveness of the loading control and measuring system.

Kinematics, dynamics, and load distribution analysis of a 4-PPPS redundantly actuated parallel manipulator

In this paper, the kinematics, dynamics, and load distribution algorithm of a 4-PPPS redundantly actuated parallel manipulator are investigated with the screw theory. For the forward kinematic analysis, we propose the major joint set, a minimum set for determining the kinematic and dynamic state of the mobile platform with six specially selected prismatic joints. The reciprocity of screws is applied for simplifying the derivation of the Jacobian matrix. The driving forces of the active joints are solved with the principle of virtual work for the non-redundant and the fully redundant actuation mode with the major joint set. For the fully redundant actuation mode, to avoid joint overload resulted from the conventional least-norm load distribution solution, to smooth the force transition, and to increase the positioning accuracy of the manipulator, a load distribution algorithm based on Lagrange optimization is proposed. These effects are achieved by means including reducing the deformations of the z-axis links and considering the sensitivity and elasticity of major joints. At last, the effectiveness of the modeling method and the proposed algorithm is verified with a case study.

A Redundantly Actuated Chewing Robot Based on Human Musculoskeletal Biomechanics: Differential Kinematics, Stiffness Analysis, Driving Force Optimization and Experiment

Human masticatory system exhibits optimal stiffness, energy efficiency and chewing forces needed for the food breakdown due to its unique musculoskeletal actuation redundancy. We have proposed a 6PUS-2HKP (6 prismatic-universal-spherical chains, 2 higher kinematic pairs) redundantly actuated parallel robot (RAPR) based on its musculoskeletal biomechanics. This paper studies the stiffness and optimization of driving force of the bio-inspired redundantly actuated chewing robot. To understand the effect of the point-contact HKP acting on the RAPR performance, the stiffness of the RAPR is estimated based on the derived dimensionally homogeneous Jacobian matrix. In analyzing the influence of the HKP on robot dynamics, the driving forces of six prismatic joints are optimized by adopting the pseudo-inverse optimization method. Numerical results show that the 6PUS-2HKP RAPR has better stiffness performance and more homogenous driving power than its non-redundant 6-PUS counterpart, verifying the benefits that the point-contact HKP brings to the RAPR. Experiments are carried out to measure the temporomandibular joint (TMJ) force and the occlusal force that the robot can generate. The relationship between these two forces in a typical chewing movement is studied. The simulation and experimental results reveal that the existence of TMJs in human masticatory system can provide more homogenous and more efficient chewing force transmission.

Design and optimization of three-degree-of-freedom planar adaptive cable-driven parallel robots using the cable wrapping phenomenon

Cable-driven parallel robots (CDPRs) are gaining increasing attention due to their low weight, cost, and power consumption characteristics. Adaptive CDPRs are special cable-driven systems in which the locations of the pulley blocks can be modified. In this paper, we propose a new type of adaptive CDPR that can passively modify the attachment points on the end-effector (moving platform) without augmented kinematic redundancy, but this depends on the cable wrapping over these adaptive attachment points. We demonstrate the proposed approach on some practical cases of planar adaptive CDPRs to expand the workspace and dexterity of the robot especially for the large rotation capability. The proposed robot can be passively reconfigured to several configurations. The kinematics modeling and static equilibrium of the adaptive CDPRs are established. Scale optimization of the adaptive attachment point is performed. The results show that this design can effectively increase the workspace, especially the rotation workspace, without increasing the actuation redundancy and kinematic redundancy.

Robust adaptive neural network event-triggered compensation control for continuous stirred tank reactors with prescribed performance and actuator failures

This paper studies the event-triggered compensation tracking control problem of the Continuous Stirred Tank Reactor (CSTR) with actuator failures. By actuator redundancies, a novel adaptive neural network (NN) event-triggered controller (ETC) design scheme is proposed based on the switching threshold event-triggering mechanism (SWT-ETM). To constrain the maximum overshoot and the convergence rate within given specifications, a prescribed performance function (PPF) error transformation is employed. It is shown that the tracking error will exponentially converge to an adjustable neighborhood of zero with prescribed transient performance, despite the presence of failures, system nonlinearities, parametric uncertainties and external disturbances. Besides, the system’s burden is significantly alleviated requiring less system resources for signal transmission and actuator execution to decrease the occurrence rate of the actuator failures; and the minimum inter-event interval is guaranteed to be positive to avoid the Zeno phenomenon. Simulation results illustrate the effectiveness of the proposed adaptive NN ETC scheme.

Reconfigurable Slip Vectoring Control in Four In-Wheel Drive Electric Vehicles

Controllability, maneuverability, fault-tolerance/isolation and safety are significantly enhanced in electric vehicles (EV) equipped with the redundant actuator configuration of four-in-wheel electric motors (4IWM). A highly reconfigurable architecture is proposed and illustrated for the adaptive, nonmodel-based control of 4IWM-EVs. Given the longitudinal force, yaw-moment requests and the reconfiguration matrix, each IWM is given a slip reference according to a Slip Vectoring (SV) allocation strategy, which minimizes the overall slip vector norm. The distributed electric propulsion and the slip vector reference allow for a decentralized online estimation of the four-wheel torque-loads, which are uncertain depending on loading and road conditions. This allows for the allocation of four different torques depending on individual wheel conditions and to determine in which region (linear/nonsaturated or nonlinear/saturated) of the torque/slip characteristics each wheel is operating. Consequently, the 4IWMs can be equalized or reconfigured, including actuator fault-isolation as a special case, so that they are enforced to operate within the linear tire region. The initial driving-mode selection can be automatically adjusted and restored among eighteen configurations to meet the safety requirements of linear torque/slip behavior. Three CarSim realistic simulations illustrate the equalization algorithm, the quick fault-isolation capabilities and the importance of a continuous differential action in a critical double-lane-change maneuver.

Adaptive Fuzzy Actuator Failure Compensation Control for a Class of MIMO Nonlinear Systems

In this paper, an adaptive fuzzy control scheme is developed for a class of uncertain multi-input multi-output (MIMO) nonlinear systems with uncertain actuator failures. Within this scheme, a fixed grouping of redundant actuators and a proportional actuation scheme for each group are considered. Afterward, a fuzzy system is used for the online approximation of a nominal control vector. The parameter adaptation laws for the nominal controller are driven by the prediction error, which is defined as the difference between the unknown nominal controller and the fuzzy controller. The proposed controller can compensate for both total and partial loss of effectiveness failure types. Closed-loop system stability and convergence properties of the tracking errors are proved based on Lyapunov theory. A piecewise analysis is carried out to prove that these properties hold despite the presence of parameter jumps caused by abrupt failures. A simulation study is carried out on a redundant joint two-link robot manipulator with joint failures at each link. Simulation results show the effectiveness of the proposed control scheme.

Unified Chassis Control of Electric Vehicles Considering Wheel Vertical Vibrations.

In the process of vehicle chassis electrification, different active actuators and systems have been developed and commercialized for improved vehicle dynamic performances. For a vehicle system with actuation redundancy, the integration of individual chassis control systems can provide additional benefits compared to a single ABS/ESC system. This paper describes a Unified Chassis Control (UCC) strategy for enhancing vehicle stability and ride comfort by the coordination of four In-Wheel Drive (IWD), 4-Wheel Independent Steering (4WIS), and Active Suspension Systems (ASS). Desired chassis motion is determined by generalized forces/moment calculated through a high-level sliding mode controller. Based on tire force constraints subject to allocated normal forces, the generalized forces/moment are distributed to the slip and slip angle of each tire by a fixed-point control allocation algorithm. Regarding the uneven road, H∞ robust controllers are proposed based on a modified quarter-car model. Evaluation of the overall system was accomplished by simulation testing with a full-vehicle CarSim model under different scenarios. The conclusion shows that the vertical vibration of the four wheels plays a detrimental role in vehicle stability, and the proposed method can effectively realize the tire force distribution to control the vehicle body attitude and driving stability even in high-demanding scenarios.

Development of a hardware-in-the-loop demonstrator for the validation of fault-tolerant control methods for a hybrid UAV

Many aircraft are inherently over-actuated with regard to their input variables. This can be particularly advantageous in the context of unmanned aerial vehicles (UAV), where actuator functions can fail in critical situations. In such cases, the redundant actuators can be used to further fulfil the control strategies used and thus increase the operational safety. Within such an active fault-tolerant control system, a fault detection and isolation (FDI) module is required. To evaluate such safety–critical systems, hardware-in-the-loop simulations (HIL) are a necessary step prior to real flight tests. These simulations can verify the correct implementation of the flight controller on the target hardware as well as the real-time capability of the algorithms used. Particularly in the context of active fault-tolerant control, investigations concerning the robustness of the used FDI module with regard to real, noisy sensor signals, which can be generated by a HIL demonstrator, are of utter importance. This paper presents the development of a HIL demonstrator for the validation of fault-tolerant control methods for a hybrid UAV. This includes a detailed description of the demonstrator’s design, control and interfacing between the integrated subsystems. As an application example, a hybrid UAV model will be shortly presented, which, in addition to the primary aerodynamic control surfaces, can also use four lift rotors to control the aircraft during cruise and is therefore inherently over-actuated. Finally, a closed-loop real-time simulation of the UAV model on the HIL demonstrator is presented on the basis of the exemplary simulation of an actuator failure and subsequent reconfiguration by the fault-tolerant flight control law.

Fractional adaptive SMC fault tolerant control against actuator failures for wing rock supervision

This article presents a new fractional order adaptive control scheme design based on sliding mode configuration for actuator failure compensation applied to a wing rock system with redundant actuators. The main objective of this work is to establish an adaptive control law that compensates faulty actuators by taking into account actuator redundancy and introducing fractional calculus. First, a non-integer sliding mode surface is defined. Next, an adaptive scheme is derived from the ideal control law to accommodate for the occurring failures during operation. Then, the stability analysis of the closed loop system is performed using the Lyapunov theory under certain assumptions on the system and the failures. Finally, simulations were carried out on a wing rock system subjected to various actuator failures scenarios in order to illustrate the effectiveness of the proposed control law.

Adaptive Fault Tolerant Flight Control for Input Redundant Systems Using a Nonlinear Reference Model

In this article, an adaptive fault-tolerant control scheme is proposed for nonlinear systems with actuator redundancy. To simultaneously consider multiple types of actuator faults and enable the use of an ideal system with nonlinear dynamics, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathcal {L}_1$</tex-math></inline-formula> adaptive control scheme for nonlinear time-varying reference systems is extended to systems with redundant inputs and an input gain uncertainty. The time-varying state-dependent additive uncertainty and the effectiveness of each input are selected as the adaptive parameters. A fixed, predictable control allocation is achieved through a feedback loop within the control block. The conditions for the performance bounds on the system relative to the ideal system are derived. It is shown that the performance bounds can be arbitrarily improved by increasing the adaptation rate and the feedback gain. The proposed adaptive control scheme is applied to the fault-tolerant control of an aircraft using a backstepping controller as a baseline controller, and numerical simulations are conducted to demonstrate the performance of the proposed controller for various fault scenarios. Monte Carlo simulations are conducted to verify the robustness property of the proposed controller.

Adaptive Fault-Tolerant Boundary Control of an Autonomous Aerial Refueling Hose System With Prescribed Constraints

In this article, we propose a redundant fault-tolerant and boundary constraint control in the framework of adaptive method, the neural network approximation, and the barrier Lyapunov function (BLF) with a relaxed initial condition. The actuator failures are compensated by a combination of adaptive methods and redundant actuators when some actuators suffer from partial or even total loss of effectiveness. The radial basis function’s neural network structure is introduced to strengthen the adaptivity in various orientations of the hose and other additionally unmodeled dynamics. To maintain the boundary deflection within a predefined open set after a constraint time, a novel asymmetrical and time-varying BLF is constructed by applying a shifting function to transform the original state into a new state with zero value initially. The performance of the developed adaptive control is demonstrated by numerical simulations. Note to Practitioners—This article is motivated by the limited performances in the existing control designs for flexible unmanned aerial refueling hose systems with failed actuators and boundary constraints. This article considers a redundant actuator case to solve time-varying and partially and totally failed actuator failures that are not settled by adaptive and Nussbaum-based single control. Unlike conventional barrier Lyapunov functions (BLFs), in this article, we resort to a shifting function and propose a novelly asymmetric and time-varying BLF, which is well defined initially and capable to address a deferred constraint control problem. The control design and stability analysis of the actuated system is a Lyapunov-based method rather than relying on semigroup theory or functional analysis, which makes the developed method more engineering orientated. The proposed control strategy is tested to illustrate performances in numerical simulations with the finite difference method.

Modeling and Adaptive Fault Compensation for Two Physically Linked 2WD Mobile Robots

This article addresses the fault-tolerant control problem of two-wheel-drive (2WD) mobile robots under actuator faults. To improve the actuation redundancy, a physical link is employed to connect two 2WD mobile robots. The kinematics and dynamics of such a two-robot system are modeled. An adaptive fault-tolerant control scheme is developed to make the two-robot system asymptotic track a desired reference. To deal with the uncertainty of the control gain matrix caused by actuator faults, a new positive definite control gain matrix is constructed, and its minimum eigenvalue is utilized for the adaptive compensation design. Simulation results verify the effectiveness of the proposed fault-tolerant control scheme.

Prescribed performance incremental adaptive optimal fault-tolerant control for nonlinear systems with actuator faults

In this paper, a model-free incremental adaptive optimal fault-tolerant controller with prescribed performance is proposed for nonlinear systems subject to actuator faults. Considering the system actuator redundancy, an actuator grouping scheme is introduced according to the actuator functions. An incremental adaptive fault observer is designed to estimate the faults. The recursive least squares (RLS) identification is utilized to identify the incremental system parameters. Both dynamic process requirements and optimal performance index of the closed loop system are taken into consideration by combining prescribed performance bound (PPB) and incremental adaptive dynamic programming (IADP). Simulations are given to verify the effectiveness of the proposed IADP reconfigurable fault-tolerant control scheme.

Fault-tolerant control allocation of a flexible satellite with an infinite-dimensional model

Fault-tolerant control allocation (FTCA) strategy is proposed for attitude stabilization of a flexible satellite with actuator redundancy. The control scheme is based on the infinite-dimensional model of a flexible satellite with no discretization, so the spillover instability is eliminated. This is one of the important benefits of the proposed control scheme over the previous FTCA schemes that have been used for the flexible satellite. The proposed scheme contains two modules. The first module provides a virtual control law to meet stabilization and vibration control objectives in the presence of uncertainties and external disturbances. There is no need to implement in-domain actuators on panels to stabilize their vibration. In this module, the virtual control is designed using adaptive integral sliding mode approach where the sliding surface includes angular velocities, internal reaction torques, and nominal control for healthy system. The second module, based on fault/failure information and using a control allocation scheme, provides redistribution of the virtual control law among the available actuators. Due to simultaneous actuator faults and control constraints, there is an error between the actual virtual control and the designed control that affects the overall system stability. To eliminate this error, gain of the virtual control signal is adjusted by an adaptive updating law. The closed-loop system stability is guaranteed for small changes in a neighborhood of the sliding surface with simultaneous vibration damping. A numerical example illustrates the effectiveness of the proposed control strategy.

Robust Adaptive Control Allocation for a Class of Cascade ODE-String Systems With Actuator Failures

A robust adaptive control allocation algorithm with actuator failure compensation is presented in this article for a class of cascade ODE-string systems depicted by ordinary differential equations (ODEs) and partial differential equations. The proposed control scheme including actuator fault compensation and allocation algorithm uniformly stabilizes the cascade ODE-string system in the presence of actuator faults, parameter uncertainties and environmental perturbations, and effectively reduces the controller complexity by adaptively grouping redundant actuators. Since this control method needs full-state measurement of the ODE system, it can be regarded as a state-feedback control instead of an output-feedback control. Control design and proof of the closed-loop system stability are implemented by Lyapunov’s direct method. Numerical simulations are finally analyzed to illustrate the feasibility of the proposed control scheme.

Coordination dynamics and model-based neural network synchronous controls for redundantly full-actuated parallel manipulator

Redundantly full-actuated parallel manipulator takes number of actuations exceeding its degree of freedom, and actuation coordination makes its basis of stable operation. This paper studies the coordination dynamics of general redundantly full-actuated parallel manipulator and derives coordination dynamics models for driving force coordination and internal force regulation respectively. Associated with coordination dynamics models, two neural network synchronous control methods are proposed for each situation correspondingly. Self-learning synchronous algorithms for those methods are designed additionally. Manipulator 6PUS+UPU is taken as a prototype for co-simulations and experiments. Results reveal that the two methods proposed above could improve actuation coordination and internal force precision of redundantly full-actuated parallel manipulator respectively. This paper provides new dynamics-based control methods for the research and control application of parallel manipulator with redundant actuation.

Accurate physical modeling and synchronization control of dual-linear-motor-driven gantry with dynamic load

To achieve high-accuracy tracking of a dual-linear-motor-driven (DLMD) gantry, high-level synchronization between redundant actuators becomes a non-negligible factor and also a difficult issue to be solved priorly. Especially, when both X and Y axes are simultaneously operating to accomplish complex tasks efficiently, additional coupling effects will be generated by the dynamic load presented on the crossbeam, which makes the synchronization issue more complicated than the case with static load. However, due to the absence of an accurate model to fully reveal the complete coupling characteristics, existing approaches to this issue still have inherent limitations. Therefore, this paper focuses on the systematic physical modeling and synchronization control of a DLMD gantry with a dynamic load presented on the crossbeam. A complete coupling mathematical model is established first, by fully considering two linear motions (X-axis and Y-axis) and also including the additional rotational motion of the crossbeam. Built upon the effective model information, corresponding solutions by compensating the dynamic load effects and actively controlling the rotational dynamics to regulate the internal forces have been proposed, leading to a novel adaptive robust synchronization control method. The results of comparative experiments verify the effectiveness and superiority of the proposed method in dealing with the synchronization issue subjected to dynamic load effects.

Elastodynamics of a spatial redundantly actuated parallel mechanism constrained by two higher kinematic pairs

A spatial redundantly actuated parallel mechanism (RAPM) constrained by two point-contact higher kinematic pairs (HKPs) has been designed for food texture evaluation during the mastication process. To this end, the mechanism must be capable of reproducing complex mandibular behaviours of human subjects in a biomimetic manner with satisfied motion accuracy. In this paper, first, the mechanism is described in detail, then elastodynamic behaviours of this mechanism are investigated based on the kineto-elastodynamics (KED) method and are formulated as a system of stiff ordinary differential equations. Due to the constraints of two HKPs onto the mandible, the derived mass matrix contains unknown generalized coordinates. This matrix is significantly different from those of parallel mechanisms (PMs) via the KED method in the literature. Third, the distributed torque under five performance criteria is employed as a feedforward to investigate its elastodynamic performance in two case studies, namely, without and with bite force onto the molar, respectively, given that the mechanism is specified to track a real human mandibular movement. The role of the damping effect in influencing vibrations is also studied. Finally, to explore the role of redundant actuations in elastodynamics, a non-redundantly actuated counterpart is proposed, where the aforementioned procedure is implemented. Results illustrate that the RAPM owns the satisfied elastodynamic performance in small vibrations, large stiffness and high natural frequency. Meanwhile, the damping effect can change the vibration distribution among different optimal torque criteria. It also shows that the RAPM outperforms its counterpart in the elastodynamic performance.

Precise Locating Control for a Polar Crane Based on Sliding Mode Active Disturbance Rejection Control and Quadratic Programming Algorithm

A polar crane is a large-scale special lifting equipment operated in a nuclear power plant. To address the precise locating control problem of a polar crane with the center of gravity shifting, with cross-coupling, and with external disturbance, an effective control scheme is proposed in this paper. Firstly, a nonholonomic constraint dynamic model of the polar crane is established according to the Lagrange–Rouse equation. Then, an expansion state observer (ESO) of the active disturbance rejection control (ADRC) method is applied to estimate and compensate the cross-coupling disturbance in real-time. To improve the robustness and convergence speed of the control system, the nonsingular terminal sliding mode (NTSM) control method is incorporated with ADRC and the stability of the controller is proven by the Lyapunov function approach. Furthermore, to solve the problem of redundant actuation and to reduce trajectory deviation of the bridge truck, the contact forces of the horizontal guide device are introduced into the quadratic programming (QP) optimization algorithm. Finally, the effectiveness and superiority of the proposed control scheme are illustrated by simulation results.