Yannis Koveos

UAV State Estimation Using Adaptive Complementary Filters

We address the complete state estimation problem of unmanned aerial vehicles, even under high-dynamic 3-D aerobatic maneuvers, while using low-cost sensors with bias variations and higher levels of noise. In such conditions, the control demand, for a robust real-time data fusion filter with minimal lag and noise, is addressed with the efficiency of a complementary filter scheme. First, the attitude is directly estimated in Special Orthogonal Group (SO(3)) by complementing the noisy accelerometer/magnetometer vector basis with a gyro propagated vector basis. Data fusion follows a least square minimization in SO(3) (Wahbas problem) solved in an analytic nonrecursive manner. Stability of the proposed filter is shown and performance metrics are extracted, whereas the computational complexity has been minimized with an appropriate reference frame and a custom singular value decomposition algorithm. An adaptation scheme is proposed to allow unhindered operation of the filter to erroneous inputs introduced by the high dynamics of a 3-D flight. Finally, the velocity/position estimation is mainly constructed by complementary filters combining multiple sensors. In addition to the low complexity and the filtering of the noise, the proposed observer is aided through a developed vision algorithm, enabling the use of the filter in Global-Positioning-System-denied environments. Extensive experimental results and comparative studies with state-of-the-art filters, either in the laboratory or in the field using high-performance autonomous helicopters, demonstrate the efficacy of the proposed scheme in demanding conditions.

Design and experimental evaluation of an innovative SMA-based tendon-driven redundant endoscopic robotic surgical tool

The development and experimental evaluation of a prototype endoscopic robotic surgical tool is presented in this article. Smart memory alloys (SMA) are used as wires in a tendon-driven actuation mechanism. The 2N-DOF redundant manipulator is a cascade configuration of N-universal joint modules. The kinematics of the tool is analyzed and simple yet effective controllers relying on a constrained non-linear optimization problem are offered. The surgical tools shape can be deformed according to a predefined profile leading to more versatile configurations than the existing designs. The efficiency of the overall system is investigated in experimental studies where its performance is evaluated by a customized 3D-video system.

Experimental Study of a Shape Memory Alloy Actuation System for a Novel Prosthetic Hand

Recently, the development of compact, light-weight and powerful actuation systems has been in the centre of investigation at many scientific institutions and research groups all over the world. These systems can be used in devices of almost every aspect of modern life and based on their inherent technology they come with certain benefits and costs. One of the most demanding applications field in terms of actuator selection and design is the field of upper-extremity prosthetics. Modern commercial advanced hand and arm prostheses are conventionally actuated by electric servomotors. Although these motors achieve reasonable kinematic performance, they have been proven insufficient in meeting amputees’ demands, mainly due to their noisy operation and limited energy density which leads to the use of bulky and heavy driving systems (Herr, 2003). Therefore, an alternative nonconventional actuation technology is requisite in order to overcome these limitations which make a substantial proportion of upper-limb amputees avoiding the use of their prostheses. One of the most promising actuation technologies is based on Shape Memory Alloys (SMA) and phenomena related to change of their atomic structure. SMA are metallic alloys that can exhibit an actuation mechanism resembling the biological muscle they contract producing actuation forces. These muscle-like actuators present high power to weight ratio enabling the development of compact, lightweight prosthetic devices without too much compromising power capabilities and eliminating the forced-tradeoff between dexterity and anthropomorphic size, weight and appearance (Bundhoo, 2009). Additional benefits include an inherent position feedback method (given a near linear relationship between ohmic resistance and contraction), silent, smooth and life-like operation, and the lack of requirement for force or motion transmission devices (Kyberd et al., 2001). During the last two decades SMA have been studied and reviewed as possible actuation technology in prosthetics by many researchers but efficiency and response time are claimed as the most limiting factors (Del Cura et al., 2003). So, in order to render this material appropriate for application in upper-limb prostheses, these impediments must be overcome. Towards this scope, an innovative SMA actuation system for a newly developed prosthetic hand is constructed and studied. The technology applied in this hand offers a series of improvements when compared to current commercial prosthetic devices. Its design 5

Mobile robot odometry relying on data fusion from RF and ultrasound measurements in a wireless sensor framework

This article focuses on the development of an integrated system for mobile robot odometry relying on an existing wireless transceiver infrastructure. The robot concurrently emits RF and ultrasound signals which are captured by the wireless sensor nodes. These nodes compute their distance from the robot and transmit back to the robot this information. The robot computes its location based on these measurements by rejecting the inaccurate ones using cluster-theory (k-means). The remaining measurements along with wheel distance (shaft encoders), orientation (magnetic compass) are used in a recursive kinematics-framework to compute in a more precise manner the robotpsilas location. Experimental studies are presented to investigate the efficiency of the localization scheme as the robot moves in curvature-controlled trajectories defined by Bezier-curves.

Using the Function Block Model for Robotic Arm Motion Control

The IEC 61499 standard enhances the 1131 function block (FB) concept to support the development of open, interoperable, distributed control applications. The first prototype software tools that support the FB model have already appeared in the market. The industry shows a growing interest in the function block model but more research and reference implementations are required to investigate and demonstrate the applicability of the new paradigm in this domain. In this paper the applicability of the IEC 61499 model in a well known PID-based control application for robotic arms is examined. To prove the correctness of the FB-based design specs, a specific code generator was developed to automatically produce the executable model of the application for a prototype Linux-based FB execution environment. The system was demonstrated successfully, proving the effectiveness of the FB model as well as the usability of the proposed execution environment

Modeling and identification of a resonance fluid actuator

In this article, a novel piezo - hydraulic actuator exploiting resonance effects is presented. The proposed actuator relies its operation on the significant pressure built up in a fluid pipe during resonance. The actuators piston houses a valve which rectifies the waves motion into direct mechanical motion. Since pressure waves are to be examined, a model capable of capturing the wave dynamics and fluid motion is derived. A state space model derived from the compressible Navier - Stokes equations is formed by linearizing these equations followed by a discretization using the Chebyshev collocation method. The model parameters are identified using a simple adaptive algorithm based on experimental data. A feature extraction technique, incorporating the wavelet transform on the experimental and simulated data, is used to calculate the resonance frequency and damping factor of the system. Experimental studies are used to investigate the efficiency of the proposed modeling approach.

Resonant Fluid Actuator: Modeling, Identification, and Control

In this article a novel piezo-hydraulic actuator exploiting resonance effects is presented. The operation of the proposed resonant fluid actuator (RFA) relies on the significant pressure raised in a fluid pipe during wave resonance. The piston of the actuator houses a valve, which rectifies the waves motion into direct mechanical motion. A state-space model, derived from the compressible Navier-Stokes equations, is formed by linearizing these equations and then discretizing them using the Chebyshev collocation method. In order to track the deformable control space, the resulting equations are reformed in an Arbitrary Lagrangian Eulerian framework. The fluid model is augmented with the valve and piezo dynamics, and, therefore, the final model is capable of capturing the performance of the RFA. The overall model is formulated in a time-variant state-space form and an optimal controller is designed to maximize the differential pressure across the piston. Experimental studies are used to investigate the efficacy of the proposed modeling approach, via utilization of a wavelet transform and finite element analysis. Simulation studies and experimental data are offered for verification of the actuators principle of operation.

Robot-Assisted Target Localization using a Cooperative Scheme relying on Wireless Sensor Networks

In this article, a control/communication scheme for mobile robots operating in an uncertain environment in a target localization problem is considered. These robots need to exchange information with a base station via a mobile ad-hoc wireless network. This network is composed of both stationary and mobile nodes. Experimental results indicate a significant deterioration of the robot performance when the network is congested and the RF-signal strength is low resulting in loss of packets. Primitive, yet reliable cooperative schemes are evaluated in a target acquisition problem and experimental results are offered to validate the efficacy of the suggested scheme

Experimental design, development and visual-servoing of a shape memory alloy actuated finger

In this paper an experimental study on the design, development and visual-servoing of a shape memory alloy (SMA) actuated finger is presented. The SMA have been utilized as tendons for the production of a satisfactory, in terms of workspace and actuation times, human-like actuated finger. This manipulator has two rotational degrees of freedom and its main objective is to control the position of the end-tip. The special characteristics and properties of the SMA have been taken under consideration and all inherent non-linearities and saturations have been embedded in the development modelling and control application. Decoupled PD-controllers provide the command input, while the sensory information is provided through a monoscopic vision system. This visual-servoing scheme drives the manipulators tip at specified trajectory positions. The final construction is a lightweight, compact device, while the experimental results prove the efficacy and the usability of the overall design and implementation process.

On the interaction of temperature-sensing, Shape Memory Alloy dynamics, and control design for a bending actuator

Temperature based control of Shape Memory Alloys faces difficulties in the determination of the actual material temperature profiles due to the typically small geometrical characteristics and possible high rates of excitation. Under such operating conditions, the expected hysteretic response can be transformed into a temperature rate-dependent one, with peculiar response characteristics. The intricacies of temperature sensing on a thin-wire SMA-actuator are coupled with a control-relevant model to enable the application of a sliding-mode controller. Experimental studies are used to validate the controlled systems performance.