This paper introduces a control system for Doubly Fed Induction Generator (DFIG) based on a Disturbance Observer (DOB) for island mode operation. The proposed control system is validated through experiments, confirming its effectiveness in maintaining stable operation during island mode. The system responded efficiently to variations in wind speed and load conditions, demonstrating the efficacy of the implemented control scheme. The proposed control system unifies the design approach for both the inner and outer loops of the cascaded control system structure, simplifying implementation and parameter tuning.

In shared human-robot environments, control systems operate based on the information about both human and robot activities to facilitate the successful collaboration between the two. This paper contributes to the emerging field of human-robot collaboration (HRC) by unifying human action recognition (HAR) and high-level robot control technique into single control system. Approach in this paper includes artificial neural network based classifier for recognition of human activity and task-based control as an example of high-level control technique. Classifier is developed based on the data from wearable sensors attached on the human arms. Recognized human activity is used as the input for the selection of functions that describe robot's activity (task). This papers combines both the theoretical approach to the task-based control and it's synergy with HAR while the developed artificial neural network classifier is experimentally validated.

This paper is concerned with the force control of a walking piezoelectric motor, a commercially available Piezo LEGS motor. The motor is capable of providing high precision positioning control on nanometer scale, but also relatively high forces up to 6 N. The proposed force control algorithm is very simple, but effective, and it is based on a recently presented coordinate transformation. The transformation allows definition of the driving waveforms for the motor according to a desired motion of the motor legs in the plane of motion. Such a possibility opens a path for creating the y-direction interaction force between the motor legs and the rod which is enough to ensure no relative motion between the legs and the rod. Once that is achieved, one can control the x-direction force imposed by the motor rod on its environment. The presented force control scheme has been successfully validated through a series of experiments.

In this study, a novel compression and decompression algorithm, namely the selected discrete cosine transform (DCT), is presented for implementation in networked motion control systems. The proposed method relies on the utilization of a selection algorithm based on bubble sorting to choose the highest power coefficients of the signal obtained by using DCT. In order to better illustrate the effectiveness of the proposed method, comparisons are made with the methods existing in the literature. To this aim, the basics of the compression schemes used in the comparison, namely, the DCT, discrete Fourier transform, and wavelet packet transform, are also briefly discussed followed by the derivation of the proposed method. The algorithmic bases of all four schemes are given to provide further reference for practical applications. The proposed method is tested on an experimental platform consisting of a single-single-degree-of-freedom master and slave systems, and the results are comparatively analyzed based on relevant performance evaluation metrics. The obtained results demonstrate the improvement achieved by the proposed compression scheme over the existing compression methods used in network-based motion control applications, hence proving the feasibility of the approach in teleoperation systems.

This paper presents a compact and low cost digital signal controller (DSC) based implementation for power control of a doubly fed induction generator (DFIG) based wind energy setup for micro-grid applications. The experimental setup consists of a back to back converter, a 1.1 kW DFIG and two low cost, industry standard DSCs. Stator active power and reactive power are controlled by means of the rotor currents. Decoupled components of the rotor current in a rotating frame are controlled by a robust, disturbance observer based control structure. The proposed controller was validated through experiments.

A novel approach for formation control of differential-drive mobile robots is presented in this paper. The control design is done in the framework of functionally related systems. Functionally related systems are the systems that are `virtually' interconnected. The term `virtually' denotes the situation in which the states or outputs of otherwise separated systems are functionally related to each other. If a formation of mobile robots is analyzed, it can be considered as a group of functionally related systems. Therefore, formation control of the robots can be synthesized in the mentioned framework.

This paper presents the development and implementation of a new, computer controlled microscope setup targeted to be used as the inspection unit of a microfactory system. The presented design has two degrees of freedom responsible for changing the magnification and focus level over the image respectively. Following the discussion on mechanical design and production, the couplings observed in experiments between magnification and focus levels are analyzed. Originating from the infeasibility of modeling the maximum sharpness point (i.e. maximum focus point) for any arbitrary object, a self optimizing controller structure is proposed that can work for any magnification level set by the user. The proposed controller structure is validated by experiments to restore the maximum focus point while the magnification level is arbitrarily set by the user.

In the past decade wind energy systems were developed for efficient energy conversion. Most of the variable speed wind turbine systems include doubly fed induction generator (DFIG). DFIGs are used in electrical grid connected and standalone systems. This paper presents a novel, robust, rotor current controller structure for both grid connected and stand-alone DFIG applications. Controller is designed for the robustness against change in machine parameters, generator speed changes and load changes in stand alone systems. In the heart of controller design lays low pass filter based disturbance observer. Experimental results are provided that verify controller performance in grid connected scenario and stand alone generator scenario (local grid). Experiments are done using 1.1KW DFIG experimental test bed and custom developed switching inverter.

This work focuses on the design of driver for PiezoLegs actuator used for high precision positioning purposes. Motor is driven with the set of periodical voltages with known frequency, amplitude and phase shift between the phases. Motor's operation has been investigated in detail and clear relationships between the amplitude and phase shifts between the phases and motor step size have been established. According to the motor analysis, set of design requirements for the design of driver is given. Particular solution meeting these requirements and satisfying the given design constraints is presented. Driver is experimentally evaluated for power consumption and analyzed in frequency domain, it's performance is compared to the performance of a commercially available driver for the same motor. Designed driver shows improved performance.

This paper analyzes two recently proposed compression decompression algorithms used in networked motion control systems. The algorithms contain discrete cosine transform (DCT) based and discrete fourier transform (DFT) based codecs for the realization of signal transmission over network. The backgrounds of the algorithms are presented along with a discussion on the advantages and disadvantages. Comparison of the performances of both algorithms are presented based on three different evaluation criteria including compression ratio, buffer size and power error. The differences between the algorithms are validated with results obtained from a series of experiments. Theoretical details regarding the differences between the results obtained from experiments are provided to present a complete analysis between two approaches.

This paper introduces a codec scheme for compressing control and feedback signals especially for bilateral control systems. The method uses a low pass filter and Wavelet Packet Transform (WPT) for coding and Inverse Wavelet Packet Transform (IWPT) for decoding. Data compression is handled in low pass filter output by reducing sampling rate; and in high pass filter output by reducing wavelet outputs. Codec works on both data paths, which flows between a master system and a slave system over a networked control architecture. With the proposed scheme, a greater percent of the compressed data can be recovered using the same compression rate. It is confirmed that the controller using compressors and decompressors performs similarly as the uncompressed one while enabling transmission of much less data over network. The viability of the proposed scheme is proven by experiments on a single-DOF motion control system controlled over network. Proposed method is also compared with a benchmark method which uses DFT for compression.

This article presents a kinematic model and control of a galvanometric laser beam steering system for high precision marking, welding or soldering applications as a microfactory module. Galvo systems are capable of scanning laser beam with relatively high frequencies that makes them suitable for fast processing applications. For the sake of flexibility and ease of use 2D reference shapes to be processed are provided as CAD drawings. Drawings are parsed and interpolated to x - y reference data points on MATLAB then stored as arrays in C code. C header file is further included as reference data points to be used by the system. Theoretical kinematic model of the system is derived and model parameters are tuned for practical implementation and validated with respect to measured positions on rotation space with optical position sensor and image field with position sensitive device. Machining with material removal requires high power laser to be employed that makes position measurement on image field unfeasible. Therefore for closed loop applications optical position sensor embedded in galvo motors is used for position feedback. Since the model approved to be approximately linear in the range of interest by simulations, a PI controller is used for precise positioning of the galvo motors. Experimental results for tracking circular and rectangular shape references are proved to be precise with errors of less than 2%.

This work presents functional description of a walking piezoelectric motor and its control in nanometer precision. For this purpose a dynamical model of the actuator is derived based on simple mass spring damper system. Model parameters are estimated from step response plot and the system is expressed with second order transfer function. Additional identification experiments verified the theoretical kinematics of the bimorph legs. These experiments demonstrate approximately linear relation between the legs displacement in x and y directions to the applied voltages. Based on derived system model and identification results a PI controller followed by Hadamard transformation is proposed as a controller scheme. Experimental results for staircase and sinusoidal references reveal precise positioning capabilities of the system with the proposed control scheme down to few nanometers.

This work presents an energy-based state estimation formalism for a class of dynamical systems with inaccessible/unknown outputs, and systems at which sensor utilization is impractical, or when measurements can not be taken. The power-conserving physical interconnections among most of the dynamical subsystems allow for power exchange through their power ports. Power exchange is conceptually considered as information exchange among the dynamical subsystems and further utilized to develop a natural feedback-like information from a class of dynamical systems with inaccessible/unknown outputs. This information is used in the design of an energy-based state observer. Convergence stability of the estimation error for the proposed state observer is proved for systems with linear dynamics. Furthermore, robustness of the convergence stability is analyzed over a range of parameter deviation and model uncertainties. Experiments are conducted on a dynamical system with a single input and multiple inaccessible outputs (Fig. 1) to demonstrate the validity of the proposed energy-based state estimation formalism.

This paper presents a comprehensive overview of the application of Variable Structure Systems (VSSs) with Sliding Mode (SM) methods in motion control systems. Our aim is to give implementable sliding mode design solutions for complex motion systems, actuators and supply converters. This paper provides a frame for further study of sliding mode applications in motion control systems.

This paper presents an algorithm for parameters and positions estimation of lumped flexible systems. As soon as the parameters and the positions are estimated they can be used to design virtual sensors that can be moved along the system to estimate the position of any lumped mass keeping the system free from any attached sensors. The virtual sensors are nothing but a chain of estimators that are connected at the end of each other, starting with two actuator's measurements and ending up with system parameters and all the system lumped positions. An estimation based PID controller is presented based on the feedback of the virtual sensor's estimates instead of the actual measurement.

SURALP is a new walking humanoid robot platform designed at Sabanci University - Turkey. The kinematic arrangement of the robot consists of 29 independently driven axes, including legs, arms, waist and a neck. This paper presents the highlights of the design of this robot and experimental walking results. Mechanical design, actuation mechanisms, sensors, the control hardware and algorithms are introduced. The actuation is based on DC motors, belt and pulley systems and Harmonic Drive reduction gears. The sensory equipment consists of joint encoders, force/torque sensors, inertial measurement systems and cameras. The control hardware is based on a dSpace digital signal processor. A smooth walking trajectory is generated. A variety of controllers for landing impact reduction, body inclination and Zero Moment Point (ZMP) regulation, early landing trajectory modification, and foot-ground orientation compliance and independent joint position controllers are employed. A posture zeroing procedure is followed after manual zeroing of the robot joints. The experimental results indicate that the control algorithms presented are successful in improving the stability of the walk.

In 2D microassembly applications, it is inevitable to position and orient polygonal micro-objects lying on a flat surface. Point contact pushing of micro-objects provides a feasible way to achieve the task and it is more flexible and less complex compared to pick and place operation. Due to the fact that in micro-world surface forces are much more dominant than inertial forces, and tend to be unevenly distributed, these dominant forces obstruct the desired motion of the micro-object when using point contact pushing alone. Thus by adopting an hybrid vision/force feedback scheme, it is possible to attain a translation motion of the object as the uncertainties due to varying surface forces and disorientation of the micro-object is compensated by force and vision feedback respectively. In this paper, a hybrid vision/force feedback scheme is proposed to push micro-objects with human assistance using a custom built tele-micromanipulation setup to achieve translational motion. The pushing operation is divided into two concurrent processes: In one human operator acts as an impedance controller alters the velocity of the pusher while in contact with the micro-object through scaled bilateral teleoperation to compensate for varying surface forces. In the other process, the desired line of pushing for the micro-object is determined continuously using visual feedback procedures so that it always compensate for the disorientation. Experimental results are demonstrated to prove nano-Newton range force sensing, scaled bilateral teleoperation with force feedback and pushing micro-objects.

This paper presents an experimental comparison of conventional (calibrated and uncalibrated) image based visual servoing methods in various microsystem applications. Both visual servoing techniques were tested on a microassembly workstation, and their regulation and tracking performances are evaluated. Calibrated visual servoing demands the optical system calibration for the image Jacobian estimation and if a precise optical system calibration is done, it ensures a better accuracy, precision and settling time compared with the uncalibrated approach. On the other hand, in the uncalibrated approach, optical system calibration is not required and since the Jacobian is estimated dynamically, it is more flexible.

This article provides in-depth knowledge about our undergoing effort to develop an open architecture micromanipulation system with force sensing capabilities. The major requirement to perform any micromanipulation task effectively is to ensure the controlled motion of actuators within nanometer accuracy with low overshoot even under the influence of disturbances. Moreover, to achieve high dexterity in manipulation, control of the interaction forces is required. In micromanipulation, control of interaction forces necessitates force sensing in milli-Newton range with nano-Newton resolution . In this paper, we present a position controller based on a discrete time sliding mode control architecture along with a disturbance observer. Experimental verifications for this controller are demonstrated for 100, 50 and 10 nanometer step inputs applied to PZT stages. Our results indicate that position tracking accuracies up to 10 nanometers, without any overshoot and low steady state error are achievable. Furthermore, the paper includes experimental verification of force sensing within nano-Newton resolution using a piezoresistive cantilever end- effector. Experimental results are compared to the theoretical estimates of the change in attractive forces as a function of decreasing distance and of the pull off force between a silicon tip and a glass surface, respectively. Good agreement among the experimental data and the theoretical estimates has been demonstrated.

A number of approaches based on sliding mode control methodology are proposed in the literature for the position control of robotic manipulators. An important problem in this context is chattering, that is high frequency oscillations in the velocity. In this paper, a novel approach is considered which eliminates chattering if the controller parameters are set suitably. A fuzzy adaptation scheme is devised for the online adaptation of the parameters of this method. Simulation results show that the fuzzy rule based adaptation scheme ensures good controller performance without chattering.

A vision-controlled robot conveyor tracking system is presented here. The vision system utilizes a constant in-time sensing field. In its normal mode of operation, this system takes a picture, analyses the image, recognises the object, extracts position information from it. Utilising this information along with the velocity information from the conveyor belt, the robot maneuvers to track and grasp the recognised object.>

Sliding mode control (SMC) of a system which is linear with respect to control and its application to robotic manipulator control system design is presented. The controller is designed to provide sliding mode motion on selected manifolds in the state space. These manifolds are selected as a linear combination of the state coordinates. This selection allows the formulation of the path tracking control, force control, and impedance control problems to be very similar. The control is selected to satisfy selected Lyapunov function and stability criteria.