Adequate Tracking Performance Research Articles

A Robust Impedance Controller for Improved Safety in Human–Robot Interaction

Abstract This paper presents a novel impedance controller modified with a switching strategy for the purpose of improving safety in human–robot interactions. Under normal operating conditions, an impedance controller is enabled when adequate tracking performance is maintained in the presence of bounded disturbances. However, if disturbances are greater than anticipated such that tracking performance is degraded, the proposed controller temporarily switches modes to a control strategy better apt to limit control inputs. With disturbances returning to the prescribed bounds, tracking performance will be restored and the impedance controller will resume for nominal operation. The control parameters are constrained by a few conditions necessary for smooth operation. First, a pair of equality constraints is required for the control signal to be continuous when switching control modes. Second, a Lyapunov analysis is performed to formulate an equality constraint on the control parameters to ensure only a single switch occurs when changing control modes to avert control chatter. Third, a matrix inequality constraint is necessary to ensure a robust positive invariant set is formed for when impedance control is active. Numerical simulations are provided to illustrate the controller and conditions. The simulation results successfully validate the presented theory, demonstrating how the constraints yield a continuous control signal, eliminate switching chatter, and permit robustness to disturbances.

Positioning and Trajectory Tracking for Caterpillar Vehicles in Unknown Environment

This paper proposes positioning and trajectory tracking for Caterpillar Vehicles (CVs) in unknown environments. To do these tasks, the following are performed. Firstly, a system modeling of the Caterpillar Vehicle is presented. Secondly, solving the complicated tracking control problem in unknown environments is a challenging mission. Therefore, to guarantee the Caterpillar Vehicle system to be strong robustness against external disturbances in the unknown environments, a MIMO robust servo controller for tracking the desired trajectory is designed by using a Linear Shift Invariant Differential (LSID) operator. The CVs are able to accomplish various tasks in dangerous places where workers cannot enter. Thirdly, the positioning of the CV can be obtained using a Simultaneous Localization and Mapping (SLAM) method. This paper develops perfectly the SLAM algorithm for positioning of the CV based on laser sensor Lidar. The main advantage of this method is that it does not need to use more landmarks. Landmarks can be obtained from the unknown environment. Thus, the CV can work even in unknown environments and unsafe places. Finally, to verify the effectiveness of the proposed MIMO robust servo controller and the SLAM positioning algorithm, the experimental results are presented. The experimental results demonstrate the adequate tracking performance of the proposed MIMO robust servo controller in the unknown environment.

선형 이동불변 미분 연산자를 이용한 전방향 무인운반차량용 MIMO 강인 서보제어기 설계

This paper proposes a multi-input multi-output (MIMO) robust servo controller design for three-wheeled Omnidirectional Automated Guided Vehicles (OAGVs) with a disturbance to track desired references using a linear shift invariant differential (LSID) operator. To design the proposed MIMO robust servo controller, the followings are performed. Firstly, a MIMO model of a threewheeled OAGV is presented. Secondly, by operating the LSID operator according to a state-space model and an output error vector, a new extended system and a new control law are obtained. Thirdly, the proposed MIMO robust servo controller for the given threewheeled OAGV is designed by using the pole assignment approach. Fourthly, by applying the inverse LSID operator, a servo compensator and a control law for the MIMO system are obtained. Finally, to verify the effectiveness of the proposed MIMO robust servo controller, the numerical simulation and experimental results are presented. The simulation and experimental results demonstrate that the proposed MIMO robust servo controller has adequate tracking performance under an external disturbance and complicated higher-order reference signals such as step, ramp, and parabola. These results are compared with those of the sliding mode control method proposed by N. Hung in 2010. The proposed MIMO robust servo controller demonstrates faster tracking performance than the sliding mode control method.

Hadron beam test of a scintillating fibre tracker system for elastic scattering and luminosity measurement in ATLAS

A scintillating fibre tracker is proposed to measure elastic proton scattering at very small angles in the ATLAS experiment at CERN. The tracker will be located in so-called Roman Pot units at a distance of 240 m on each side of the ATLAS interaction point. An initial validation of the design choices was achieved in a beam test at DESY in a relatively low energy electron beam and using slow off-the-shelf electronics.Here we report on the results from a second beam test experiment carried out at CERN, where new detector prototypes were tested in a high energy hadron beam, using the first version of the custom designed front-end electronics. With a spatial resolution of 25 μm an adequate tracking performance was obtained, under conditions which are similar to the situation at the LHC.In addition, the alignment method using so-called overlap detectors was studied and shown to have the expected precision.

Fault-Tolerant Structured Adaptive Model Inversion Control

An adaptive dynamic inversion control formulation is presented that takes advantage of the inherent dynamic structure of the state-space description of a large class of systems. The formulations impose the exact kinematic differential equations, thereby restricting the adaptation process that compensates for model errors to the acceleration level. The utility of this formulation is demonstrated for the problem of fault tolerance to actuator failures on redundantly actuated systems. The approach incorporates an actuator failure model in the controller formulation, so that actuator failure can be identified as a change in the parameters of the failure model. Tracking of reference trajectories is imposed, and initial error conditions and structured parametric uncertainties are incorporated explicitly in both the plant parameters and the control influence matrix. A numerical example consisting of a nonlinear model of an F-16 type aircraft with thrust vectoring is presented. Simulation results show that the fault-tolerant adaptive controller is capable of simultaneously handling parametric uncertainties, large initial condition errors, and actuator failures while maintaining adequate tracking performance. N recent years, there has been much interest in the development of reconfigurable control systems that can accommodate actuator failures without compromising mission integrity. There has been substantial progress in the development of real-time failure detection and isolation algorithms, system identification after failure, and control reconfiguration techniques in aerospace applications. In Ref. 1, a survey of various reconfigurable flight control methodologies is presented and it is shown that most traditional reconfiguration flight control approaches rely on failure detection and isolation. The complexity of such a system with this feature grows with the increase in the number of failures, and there tends to be a significant possibility of false alarms. 1,2 A different approach to reconfigurable flight control is based on adaptive control theory, in which the adaptive control structure implicitly reconfigures the control law using adaptive estimates of the altered dynamics after failure. 3 In Ref. 3, an adaptive control scheme is presented that uses a linear approximation of the plant model to compute the control, and a neural network based adaptive control law for flight reconfiguration has been developed and successfully flight tested. 4−6 A robust fault-tolerant controller has also been developed to reject state-dependent disturbances. 7 The approach presented in this paper uses a structured nonlinear adaptive dynamic inversion control methodology. Instead of using an explicit failure detection and isolation algorithm, this methodology is based on the adaptive control theory where the controller is constantly updating itself. This methodology is applicable to a general class of nonlinear systems that are affine in the control with uncertain parameters appearing linearly. Fault-tolerance capability is introduced by incorporating a failure model in the controller so that a failure can be identified and compensated for by a change in the parameters of the failure model. First, model reference adaptive control, structured model reference adaptive control, and structured adaptive model inversion

Attitude Control of a Reentry Vehicle with Internal Dynamics

A control design for the X-38 reentry vehicle is presented. During a certain phase of reentry e ight, attitude control has to be accomplished using only two control effectors. This limits the number of controlled variables for which decoupled tracking can be realized. It is shown that an inappropriate selection of the output gives rise to unacceptable internal dynamics when applying inversion-based control. Therefore, the zero dynamics are locally stabilized by means of an output-redee nition technique. An optimal pole placement enhances the robustness of the zero dynamics with regard to parametric model uncertainty. Further, a direct adaptive controller using a cerebellar model articulation controller neural network ensures tracking performance in the redee ned outputs in the presence of model uncertainty. Simulation results are presented to cone rm that stabilization of the zero dynamics, and adequate tracking performance are achieved. Because only a minimal set of control effectors is used, such a control scheme could represent a contribution toward a less costly return from space.