Zdeněk Hurák

Image-Based Pointing and Tracking for Inertially Stabilized Airborne Camera Platform

This paper describes a novel image-based pointing-tracking feedback control scheme for an inertially stabilized double-gimbal airborne camera platform combined with a computer vision system. The key idea is to enhance the intuitive decoupled controller structure with measurements of the camera inertial angular rate around its optical axis. The resulting controller can also compensate for the apparent translation between the camera and the observed object, but then the velocity of this mutual translation must be measured or estimated. Even though the proposed controller is more robust against longer sampling periods of the computer-vision system then the decoupled controller, a sketch of a simple compensation of this delay is also given. Numerical simulations are accompanied by laboratory experiments with a real benchmark system.

Nonzero Bound on Fiedler Eigenvalue Causes Exponential Growth of H-Infinity Norm of Vehicular Platoon

We consider platoons composed of identical vehicles and controlled in a distributed way, that is, each vehicle has its own onboard controller. The regulation errors in spacing to the immediately preceeding and following vehicles are weighted differently by the onboard controller, which thus implements an asymmetric bidirectional control scheme. The weights can vary along the platoon. We prove that such platoons have a nonzero uniform bound on the second smallest eigenvalue of the graph Laplacian matrix-the Fiedler eigenvalue. Furthermore, it is shown that existence of this bound always signals undesirable scaling properties of the platoon. Namely, the H-infinity norm of the transfer function of the platoon grows exponentially with the number of vehicles regardless of the controllers used. Hence the benefits of a uniform gap in the spectrum of a Laplacian with an asymetric distributed controller are paid for by poor scaling as the number of vehicles grows.

Wave-absorbing vehicular platoon controller

Abstract The paper tailors the so-called wave-based control, popular in the field of flexible mechanical structures, to the field of distributed control of vehicular platoons. The proposed solution augments the symmetric bidirectional control algorithm with a wave-absorbing controller implemented on the leader, and/or on the rear-end vehicle. The wave-absorbing controller actively absorbs an incoming wave of positional changes in the platoon and thus prevents oscillations of inter-vehicle distances. The proposed controller significantly improves the performance of platoon manoeuvrers such as acceleration/deceleration or changing the distances between vehicles without making the platoon string unstable. Numerical simulations show that the wave-absorbing controller performs efficiently even for platoons with a large number of vehicles, for which other platooning algorithms are inefficient or require wireless communication between vehicles.

2-D polynomial approach to control of leader following vehicular platoons

Abstract This paper formulates the problems of stabilization and asymptotic following in infinite platoons of vehicles within the 2-D polynomial framework, that is, the dynamics of the problem are described using a fraction of two bivariate polynomials. In contrast to some previous works, the platoon here assumes a leader (and an infinite number of followers), therefore the often used bilateral z -transform should not be used here since it assumes a doubly infinite vehicular strings. The unilateral z -transform seems better suited. However, it brings about the need to take the boundary conditions into consideration; among other, the leader vehicle comes into the scene. The necessary formalism is introduced in the paper and used to provide elegant alternative proofs of some well-known facts about the platooning problem.

Tremor analysis by decomposition of acceleration into gravity and inertial acceleration using inertial measurement unit

Decomposition of acceleration was investigated as an alternative to commonly used direct spectral analysis of measured acceleration or angular velocity for tremor quantification. Orientation estimation algorithm was devised to decompose the measured acceleration into inertial acceleration caused by sensor movement in inertial reference frame and gravitational artifact. Resulting signals, beside measured acceleration and angular velocity, were used to assess tremor amplitude and frequency by spectral peak detection. The algorithm was tested on experimental data from a clinical study including patients with essential tremor. Influence of sensor calibration and connections of results to analytic approach are analyzed briefly.

Scaling in Bidirectional Platoons With Dynamic Controllers and Proportional Asymmetry

We consider platoons composed of identical vehicles with an asymmetric nearest-neighbor interaction. We restrict ourselves to intervehicular coupling realized with dynamic arbitrary-order onboard controllers such that the coupling to the immediately preceding vehicle is proportional to the coupling to the immediately following vehicle. Each vehicle is modeled using a transfer function and we impose no restriction on the order of the vehicle. The only requirement on the controller and vehicle model is that the platoon is stable for any number of vehicles. The platoon is described by a transfer function in a convenient product form. We investigate how the H-infinity norm and the steady-state gain of the platoon scale with the number of vehicles. We conclude that if the open-loop transfer function of the vehicle contains two or more integrators and the second smallest eigenvalue of the graph Laplacian is uniformly bounded from below, the norm scales exponentially with the growing distance in the graph. If there is just one integrator in the open loop, we give a condition under which the norm of the transfer function is bounded by its steady-state gain—the platoon is string-stable. Moreover, we argue that in this case it is always possible to design a controller for the extreme asymmetry—the predecessor following strategy.

Feedback control for noise-aided parallel micromanipulation of several particles using dielectrophoresis

The paper describes a novel control strategy for simultaneous manipulation of several microscale particles over a planar microelectrode array using dielectrophoresis. The approach is based on a combination of numerical nonlinear optimization, which gives a systematic computational procedure for finding the voltages applied to the individual electrodes, and exploitation of the intrinsic noise, which compensates for the loss of controllability when two identical particles are exposed to identical forces. Although interesting on its own, the proposed functionality can also be seen as a preliminary achievement in a quest for a technique for separation of two particles. The approach is tested experimentally with polystyrene beads (50 microns in diameter) immersed in deionized water on a flat microelectrode array with parallel electrodes. A digital camera and computer vision algorithm are used to measure the positions. Two distinguishing features of the proposed control strategy are that the range of motion is not limited to interelectrode gaps and that independent manipulation of several particles simultaneously is feasible even on a simple microelectrode array.

2D polynomial approach to stability of platoons of vehicles

Abstract This paper formulates the problems of stability testing and stabilization of an infinite platoon of vehicles within the 2D polynomial framework, that is, the dynamics of the problem is described using a fraction of two bivariate polynomials. Recent computational tools for testing positivity of polynomial matrices are suggested for stability testing and stabilization.

Dielectrophoretic actuation strategy for micromanipulation along complex trajectories

The paper presents application of dielectrophoresis for manipulation of a microparticle in a liquid medium above a planar surface. The force on the microparticle is exerted by a non-uniform AC electric field. The field is generated by a set of micro-electrodes patterned on the planar surface and connected to a multi-channel voltage waveform generator. An novel yet simple control approach based on changing the phase delays among voltages on the electrodes is introduced together with a description of an efficient hardware implementation. Laboratory experiments with a 250-micron polystyrene bead are documented. This work was partly motivated by the series of international competitions called Mobile Microrobotics Challenge and organized by NIST and taken over by IEEE RAS recently.

On computing the l/sub 1/ norm of a polynomial matrix fraction

This paper proposes a new algorithm for computing the l/sub 1/ norm of a linear MIMO system described by a polynomial matrix fraction. The algorithm follows the one proposed by Balakrishnan and Boyd (1992) with the only difference that there is no need to obtain a state space realization first. Instead, the coefficients of the polynomial matrices are used directly. The algorithm is based on two computational steps: an FFT-based long division of polynomial matrices and the polynomial computation of Hankel singular values presented by Kwakernaak (1992).