30,947 research outputs found
Predictive feedback control and Fitts' law
Fittsâ law is a well established empirical formula, known for encapsulating the âspeed-accuracy trade-offâ. For discrete, manual movements from a starting location to a target, Fittsâ law relates movement duration to the distance moved and target size. The widespread empirical success of the formula is suggestive of underlying principles of human movement control. There have been previous attempts to relate Fittsâ law to engineering-type control hypotheses and it has been shown that the law is exactly consistent with the closed-loop step-response of a time-delayed, first-order system. Assuming only the operation of closed-loop feedback, either continuous or intermittent, this paper asks whether such feedback should be predictive or not predictive to be consistent with Fitts law. Since Fittsâ law is equivalent to a time delay separated from a first-order system, known control theory implies that the controller must be predictive. A predictive controller moves the time-delay outside the feedback loop such that the closed-loop response can be separated into a time delay and rational function whereas a non- predictive controller retains a state delay within feedback loop which is not consistent with Fittsâ law. Using sufficient parameters, a high-order non-predictive controller could approximately reproduce Fittsâ law. However, such high-order, ânon-parametricâ controllers are essentially empirical in nature, without physical meaning, and therefore are conceptually inferior to the predictive controller. It is a new insight that using closed-loop feedback, prediction is required to physically explain Fittsâ law. The implication is that prediction is an inherent part of the âspeed-accuracy trade-offâ
Disturbance Observer-based Robust Control and Its Applications: 35th Anniversary Overview
Disturbance Observer has been one of the most widely used robust control
tools since it was proposed in 1983. This paper introduces the origins of
Disturbance Observer and presents a survey of the major results on Disturbance
Observer-based robust control in the last thirty-five years. Furthermore, it
explains the analysis and synthesis techniques of Disturbance Observer-based
robust control for linear and nonlinear systems by using a unified framework.
In the last section, this paper presents concluding remarks on Disturbance
Observer-based robust control and its engineering applications.Comment: 12 pages, 4 figure
Nonlinear Receding-Horizon Control of Rigid Link Robot Manipulators
The approximate nonlinear receding-horizon control law is used to treat the
trajectory tracking control problem of rigid link robot manipulators. The
derived nonlinear predictive law uses a quadratic performance index of the
predicted tracking error and the predicted control effort. A key feature of
this control law is that, for their implementation, there is no need to perform
an online optimization, and asymptotic tracking of smooth reference
trajectories is guaranteed. It is shown that this controller achieves the
positions tracking objectives via link position measurements. The stability
convergence of the output tracking error to the origin is proved. To enhance
the robustness of the closed loop system with respect to payload uncertainties
and viscous friction, an integral action is introduced in the loop. A nonlinear
observer is used to estimate velocity. Simulation results for a two-link rigid
robot are performed to validate the performance of the proposed controller.
Keywords: receding-horizon control, nonlinear observer, robot manipulators,
integral action, robustness
Model following control with discrete time SMC for time-delayed bilateral control systems
This paper proposes a new algorithm based on model following control to recover the uncompensated slave disturbance on time delayed motion control systems having contact with environment. In the previous works, a modified Communication Disturbance Observer (CDOB) was shown to be successful in ensuring position tracking in free motion under varying time delay. However, experiments show that due to the imperfections in slave plant Disturbance Observer (DOB) when there is rapid change of external force on the slave side, as in the case of environment contact, position tracking is degraded. This paper first analyzes the effect of environment contact for motion control systems with disturbance observers. Following this analysis, a model following controller scheme is proposed to restore the ideal motion on the slave system. A virtual plant is introduced which accepts the current from the master side and determines what the position output would be if there was no environment. Based on the error bet ween actual system and model system, a discrete time sliding mode controller is designed which enforces the real slave system to track the virtual slave output. In other words, convergence of slave position to the master position is achieved even though there is contact with environment. Experimental verification of the proposed control scheme also shows the improvement in slave position tracking under contact forces
A survey on fractional order control techniques for unmanned aerial and ground vehicles
In recent years, numerous applications of science and engineering for modeling and control of unmanned aerial vehicles (UAVs) and unmanned ground vehicles (UGVs) systems based on fractional calculus have been realized. The extra fractional order derivative terms allow to optimizing the performance of the systems. The review presented in this paper focuses on the control problems of the UAVs and UGVs that have been addressed by the fractional order techniques over the last decade
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