Aurelio Tergolina Salton

Improved Control Design Methods for Proximate Time-Optimal Servomechanisms

It is well known that minimum time-optimal control for servomechanisms can generate chattering in the presence of measurement noises, feedback delays, or model uncertainties; thus, it is not practical in applications. Maybe, the most popular alternative approach is the so-called proximate time-optimal servomechanism (PTOS). This approach starts with a near-time-optimal controller and, then, switches to a linear controller when the system output is close to a given target. However, the chattering problem is avoided at the expense of a slower time response. In this paper, two methods for eliminating the conservatism present in the PTOS are proposed. The first method applies a dynamically damped controller that allows the so-called acceleration discount factor to be pushed arbitrarily close to 1. The second method applies a continuous nonlinear control law that makes use of no switching. Experimental results show that the proposed designs practically eliminate the conservatism in the traditional PTOS.

Preview Control of Dual-Stage Actuator Systems for Superfast Transition Time

This paper introduces a preview control design method to reduce the settling time of dual-stage actuators (DSAs). A DSA system is comprised of two actuators connected in series, a primary (coarse) actuator, and a secondary (fine) actuator. The objective of the proposed design is to account for the redundancy of actuators and use the information of future reference levels in order to compute a pair of inputs to be applied before the output transition time. Experimental results show that the proposed design method significantly reduces the output transition time when compared to conventional forms of DSA control design.

Constrained Optimal Preview Control of Dual-Stage Actuators

This paper proposes constrained optimal trajectories for the preview control of dual-stage actuators (DSA). Relying on the redundancy of actuators preview control allows the primary stage to move before the transition instant, and uses the secondary stage to compensate its movements. Contrasting existing strategies that consider the secondary stage infinitely fast during preview control, this study takes into account its dynamic limitations when designing the trajectories to be followed during preactuation. It will be shown that the problem may be cast in terms of quadratic programming providing an optimal solution with respect to a quadratic criterion. Experimental results validated the proposed strategy, which is able to achieve a 30% improvement over state-of-the-art high-performance DSA controllers, while respecting the limitations of both actuators.

A novel rotary dual-stage actuator positioner

This paper presents the design and control of a rotary dual-stage actuator (DSA) system, which consists of a voice coil motor (VCM) and a piezoelectric (PZT) microactuator. The performance of the mechanical design is analyzed using a finite element method (FEM) software, whose simulation results are validated experimentally. A nonlinear tracking control is applied to the developed DSA platform for reduced settling time and improved disturbance rejection. Experimental results demonstrate that the applied control design reduces the settling time by up to 50% when compared to a conventional design. Moreover, it is shown that the DSA system can achieve an improvement of 80% regarding disturbance rejection when compared to a single-stage actuator.

A Comparative Analysis of Repetitive and Resonant Controllers to a Servo-Vision Ball and Plate System

Abstract This paper presents a comparative analysis of two alternative control strategies based on the Internal Model Principle: the Repetitive Controller and the Multiple Resonant Controller. The proposed implementations are evaluated experimentally in a servo-vision ball and plate balancing system. The plant is composed by an orientable platform with a free rolling sphere on top, where the controlled variable is the ball position. The methodology considered to synthesize the associated state gains parameters is the Linear Quadratic Regulator approach. The experimental results compare characteristics such as steady-state error, transient response and input signal for each implemented control strategy.

Optimal trajectories for the Preview Control of Dual-Stage Actuators

Preview Control for Dual-Stage Actuators (DSA) consists in allowing movement of the slow actuator while maintaining the system output at the reference point. This strategy is possible only if the fast actuator is able to compensate the movement of the slow one. The advantages of this control scheme are related to an improvement on the settling time of the output, a consequence of the fact that the slow actuator is allowed to move ahead of the reference transition time. This paper will discuss fundamental limitations that constrain the trajectories of the primary actuator to a feasible set, i.e., a set whose trajectories the secondary actuator is able to effectively compensate. From this initial discussion optimal trajectories will be devised via quadratic programming. Experimental results show the effectiveness of the proposed design.

Improved servomechanism control design - Dynamically damped case

Time optimal control (TOC) for servomechanism is not a practical controller due to the chattering phenomenon that occurs on the presence of noise and model uncertainty. Maybe the most popular attempt to transform this controller in a practical one comes from the so called Proximate Time Optimal Servomechanism (PTOS). This approach starts with a near time optimal controller and then switches to a linear controller when the system output approaches the target. While the chattering phenomenon is avoided, this comes at an expense in performance generated by the so called “acceleration discount factor”. This paper will present a controller that makes use of dynamic damping in order to push the acceleration discount factor arbitrarily close to one, thus practically eliminating the conservatism present in the PTOS. Experimental results support the proposed design.

A class of preview control for dual-stage actuator systems

This paper proposes a novel ¿preview control¿ approach to dual-stage actuator (DSA) systems based on the redundancy of actuators. While conventional tracking controllers are designed such that the primary actuator asymptotically approaches the set point, the proposed methodology allows it to move freely within the range of the secondary actuator. Then, the secondary actuator controller is designed such that the error between the primary actuator and the set point can be compensated. The main advantage of the proposed controller is exhibited in the successive set point control scenario, and its effectiveness is demonstrated by numerical simulation.

Disturbance observer and nonlinear damping control for fast tracking quadrotor vehicles

This paper considers the design and implementation of a discrete-time fast tracking controller for quadrotor vehicles subject to perturbations. The proposed controller consists of a model-based disturbance observer and a Composite Nonlinear Feedback (CNF) controller. The CNF control law introduces nonlinear damping to the system so that it possesses a fast rise time without overshoot. The least square identification method is applied to develop a model based disturbance observer, thus decoupling the problems of track following and disturbance rejection. Experimental results are provided in order to validate the proposed approach.

Repetitive controller with low-pass filter compensation applied to Uninterruptible Power Supplies (UPS)

In this paper is proposed a method to improve the tracking performance of repetitive controllers in Uninterruptible Power Supplies (UPS). The main idea is to simultaneously compensate the gain reduction and frequency shift caused by the introduction of a low-pass filter in series with the delay element. Also, an optimization problem based on LMI constraints is presented to determine controller gains that guarantee stability and performance of the closed loop system. Simulation results based on the output stage of 3.5kVA UPS demonstrate the effectiveness of the proposed method.