Leonardo Acho

Fast autofocus algorithm for automated microscopes

We present a new algorithm to determine, quickly and accu- rately, the best-in-focus image of biological particles. The algorithm is based on a one-dimensional Fourier transform and on the Pearson cor- relation for automated microscopes along the Z axis. We captured a set of several images at different Z distances from a biological sample. The algorithm uses the Fourier transform to obtain and extract the image frequency content of a vector pattern previously specified to be sought in each captured image; comparing these frequency vectors with the fre- quency vector of a reference image (usually the first image that we cap- ture or the most out-of-focus image), we find the best-in-focus image via the Pearson correlation. Numerical experimental results show the algo- rithm has a fast response for finding the best-in-focus image among the captured images, compared with related autofocus techniques pre- sented in the past. The algorithm can be implemented in real-time sys- tems with fast response, accuracy, and robustness; it can be used to get focused images in bright and dark fields; and it offers the prospect of being extended to include fusion techniques to construct multifocus final images.

Global position regulation of friction manipulators via switched chattering control

Switched position control algorithms are developed to globally stabilize friction mechanical manipulators around a desired position. Both static and dynamic position feedback designs are presented. The controllers constructed, referred to as chattering controllers, do not rely on the generation of sliding motions while providing robustness features similar to those possessed by their sliding mode counterparts. Stability analysis is given within the Lyapunov vector functions framework extended to discontinuous dynamic systems. Performance issues of the chattering controllers are evaluated in an experimental study of a three degrees-of-freedom robot manipulator.

A modified Chua chaotic oscillator and its application to secure communications

A new modification to the Chua oscillator is proposed.Bifurcation diagrams, Poincare map and the Lyapunov exponents are presented.An application to secure communications is presented.A synchronization scheme based on the modified oscillator is proposed.System simulations are performed for analysis. In this paper, a new modified Chua oscillator is introduced. The original Chua oscillator is well known for its simple implementation and mathematical modeling. A modification of the oscillator is proposed in order to facilitate the synchronization and the encryption and decryption scheme. The modification consists in changing the nonlinear term of the original oscillator to a smooth and bounded nonlinear function. A bifurcation diagram, a Poincare map and the Lyapunov exponents are presented as proofs of chaoticity of the newly modified oscillator. An application to secure communications is proposed in which two channels are used. Numerical simulations are performed in order to analyze the communication system.

Force‐derivative feedback semi‐active control of base‐isolated buildings using large‐scale MR fluid dampers

The combination of passive and active schemes has been increasingly considered in the structural control com munity as a promising way to design efficient smart hybrid base isola tion systems for seismic protection. This paper considers a hybrid system in which an active feedback control law is derived to b e applied in parallel with a passive isolation device. The ac tive control uses the restoring force supplied by the passive isolator as the main feedback signal. This paper can be divided in two mai n p rts: in the first one, the paper presents the theoretical formulat ion nd stability analysis in the active control strategy; i n the second part, a set of numerical simulations is performed when the force is supplied in a semi-active way to validate and discuss the effi ci ncy of the approach in a more realistic scenario. Moreover, the p erformance of the proposed semi-active control algorithm i s compared with passive-off, passive-on and clipped-optimal control lers. The proposed control scheme reduces the base displace ment without increasing the floor accelerations.

Model Orbit Robust Stabilization (MORS) of Pendubot with Application to Swing up Control

Orbital stabilization of a simple underactuted manipulator, namely, two-link pendulum robot (Pendubot) is under study. Since underactuated systems cannot be stabilized by means of smooth feedback, the solution to the stabilization problem is sought within switched control methods. The quasi-homogeneous control synthesis is utilized to design a switched controller that drives the Pendubot to its zero dynamics in finite time and maintains it there in sliding mode. The constructed controller is such that the Pendubot zero dynamics is generated by a modified Van der Pol oscillator, being viewed as a reference model. The closed-loop system is thus capable of moving from one orbit to another by simply changing the parameters of the proposed modification of the Van der Pol oscillator. Performance issues of the controller constructed are illustrated in a simulation study of the swing up control problem of moving the Pendubot from its stable downward position to the unstable inverted position and stabilizing it about the vertical.

Nonlinear H ∞ -control of time-varying systems

Nonlinear H/sub /spl infin//-controller synthesis is developed for time-varying systems via measurement feedback. Both global and local solutions of the problem are derived. The global solution is based on a solution to appropriate strict Hamilton-Jacobi-Isaacs inequalities, whereas the local solution is derived by means of a certain perturbation of the Riccati equations used in solving the linear H/sub /spl infin//-control problem for the linearized system.

An Experimental Realization of a Chaos-Based Secure Communication Using Arduino Microcontrollers

Security and secrecy are some of the important concerns in the communications world. In the last years, several encryption techniques have been proposed in order to improve the secrecy of the information transmitted. Chaos-based encryption techniques are being widely studied as part of the problem because of the highly unpredictable and random-look nature of the chaotic signals. In this paper we propose a digital-based communication system that uses the logistic map which is a mathematically simple model that is chaotic under certain conditions. The input message signal is modulated using a simple Delta modulator and encrypted using a logistic map. The key signal is also encrypted using the same logistic map with different initial conditions. In the receiver side, the binary-coded message is decrypted using the encrypted key signal that is sent through one of the communication channels. The proposed scheme is experimentally tested using Arduino shields which are simple yet powerful development kits that allows for the implementation of the communication system for testing purposes.

Swing up and Balancing Control of Pendubot via Model Orbit Stabilization: Algorithm Synthesis and Experimental Verification

A model orbit stabilization approach to swing up control of a two-link pendulum robot (Pendubot) is under study. The quasihomogeneous control synthesis is utilized to design a variable structure controller that drives the actuated link of the Pendubot to a periodic reference orbit in finite time. A modified Van der Pol oscillator is involved into the synthesis as an asymptotical generator of the periodic motion. Performance issues of the proposed synthesis are illustrated in an experimental study of the swing up/balancing control problem of moving the Pendubot from its stable downward position to the unstable inverted position and stabilizing it about the vertical

Asymptotic harmonic generator and its application to finite time orbital stabilization of a friction pendulum with experimental verification

A second order sliding mode approach to orbital stabilization is presented and tested on a friction pendulum, operating under uncertain conditions. The quasihomogeneous control synthesis is utilized to design a variable structure controller that drives the pendulum to a model orbit in finite time in spite of the presence of external disturbances with an a priori known magnitude bound. A well-known Van der Pol oscillator is modified to be introduced into the synthesis as a reference model. This modification is made to shape the oscillator limit cycle to a harmonic one, thereby yielding an asymptotic harmonic generator of the periodic motion. The parameters of the asymptotic harmonic generator are shown to specify amplitude and frequency of the limit cycle production and damping of non-linear oscillations of the generator. The resulting closed-loop system is capable of moving from one orbit to another by changing these parameters dynamically. Performance issues of the controller constructed are illustrated in an experimental study.

Quasihomogeneity Approach to the Pendubot Stabilization around Periodic Orbits

Abstract Orbital stabilization of a simple underactuted manipulator, namely, two-link PENDUlum roBOT is under study. Since underactuated systems can not be locally stabilized by means of smooth feedback, the solution to the stabilization problem is sought within switched control methods. The quasihomogeneity-based synthesis is applied to design a switched controller that drives the PENDUBOT to its zero dynamics in finite time and maintains it there in sliding mode. The constructed controller is such that the pendubot zero dynamics is generated by a modified Van der Pol oscillator, being viewed as the reference model. The proposed Van der Pol modification aims to enlarge the region of attraction of the zero dynamics while also exhibiting a desired stable periodic behavior. Performance issues of the controller constructed are illustrated in a simulation study.