Tarik Uzunovic

Adaptive control of piezoelectric walker actuator

This work focuses on the design of adaptive controller for high precision positioning purposes using PiezoLegs actuator. Actuator is driven with the set of periodical sine shaped voltages with known frequency, amplitude and phase shift between the phases. Clear relationships between the amplitude and phase shifts between the phases and actuator step size have been established. Based on these relationships adaptive controller has been designed. Controller is a linear, cascaded type of feedback controller that uses position feedback from an encoder. Based on the information of the absolute error controller performs the adaptive step size modulation by changing amplitude or phase shift of the driving voltages. Proposed algorithm is validated experimentally. Experimental results show satisfactory level performance, controller achieves fast settling time, no overshoot response and high accuracy of positioning with small steady state errors.

Configuration space control of a parallel Delta robot with a neural network based inverse kinematics

This paper describes configuration space control of a Delta robot with a neural network based kinematics. Mathematical model of the kinematics for parallel Delta robot used for manipulation purposes in microfactory was validated, and experiments showed that this model is not describing “real” kinematics properly. Therefore a new solution for kinematics mapping had to be investigated. Solution was found in neural network utilization, and it was used to model robots inverse kinematics. It showed significantly better mapping between task space coordinates and configuration (joint) space coordinates than the mathematical model, for the workspace of interest. Consequently positioning accuracy improvement is expected. Neural network is then used as a part of the control system. Applied control strategy was configuration space acceleration control with disturbance observer.

Piezo LEGS Driving Principle Based on Coordinate Transformation

This paper offers a new approach for specifying the waveforms of driving voltages for a Piezo LEGS motor. A novel idea of coordinate transformation to define the waveforms of driving voltages, based on the motor static model, is presented. This transformation defines driving voltages according to the desired motion of the motor legs in the x- and y-directions. The approach allows a user to first define force acting on the motor rod in the y-direction and define the rods x-direction trajectory profile. Waveforms of the driving voltages are subsequently defined to meet these requirements. The proposed approach also enables the possibility of defining the desired step shape for the motor and, according to that definition, producing driving voltages. Based on the given coordinate transformation, a simple method for Piezo LEGS motor control, identified as virtual time control, is presented. This method results in overshoot-free high precision positioning.

Neural networks for helicopter azimuth and elevation angles control obtained by cloning processes

Neural networks have been applied very successfully in the identification and control of nonlinear dynamic systems. The paper presents a design of neural network based control system for 2DOF nonlinear laboratory helicopter model (Humusoft CE 150). The main objective of this paper is to develop artificial neural networks to control helicopters motors, or consequently elevation and azimuth angles. Neural networks are obtained by cloning various type of controllers designed in our previous papers. Those procedures included a cloning linear PID controller, gain scheduling controller and fuzzy controller.

FPGA based control of a walking piezo motor

This paper describes FPGA based control system for a piezoelectric motor, commercially available Piezo LEGS motor. Driving voltages waveforms are defined as a combination of linear functions. This definition provides possibility for easy implementation on very simple hardware. Linear functions parameters allow forming of the driving voltages according to desired trajectory of motors legs. Considering that FPGA technology offers many advantages over the classical microprocessor based systems, it is used as control system implementation hardware. Realized control system can be very easily expanded to control multiple motors, if hardware resources are big enough. Also modularity is provided, making the future application very simple. In the paper control system structure is described in detail along with a very simple control algorithm for Piezo LEGS motor positioning control. Experimental results are given to validate designed control system. They showed satisfying control performance, responses with no overshoot and expected steady state error.

Three-dimensional contour tracking control of a parallel manipulator: Comparison of two control techniques

In this paper a novel design for three-dimensional (3-D) contour controller is proposed. This design relies on dynamics projection to the moving Frenet-Serret frame defined for each point on reference trajectory. Contour controller consists of independent joint controller and additional sliding mode controller, added as corrective term. Control task is defined as contour tracking with constant tangential velocity. Contour controller was compared with independent joint controller designed as acceleration controller with first order disturbance observer. Reference trajectory is generated using time based spline approximation to provide smooth reference trajectory. Experimental results showed significant improvement that contour controller provides over independent joint control with relatively high velocity references.

Control system for high precision positioning applications based on Piezo motors

In this paper implementation of a control system for high precision applications is presented. The control system is developed for a Piezo LEGS motor, which is a walking piezo motor that can be employed in nanometric precision applications. In the control system structure, two main components are digital signal controller which executes control algorithm and power driver that is generating driving voltages for the motor. The waveforms of the driving voltages are designed using a recently presented coordinate transformation. This transformation enables synthesis of driving waveforms according to design requirements regarding force imposed to the motors rod and rods x-direction trajectory profile. In this work, the waveforms are selected to ensure no relative motion between the motors legs and rod, and constant velocity of the rod within one step. Control algorithm is named as virtual time control. Despite its simplicity, the algorithm allows high precision positioning which is very close to theoretically achievable one.

Desktop microfactory for high precision assembly and machining

This work presents a modular and reconfigurable desktop microfactory for high precision machining and assembly of micro mechanical parts. Miniature factory is inspired by the downsizing trend of the production tools. The system is constructed based on primary functional and performance requirements such as miniature size, operation with sub-millimeter precision, modular and reconfigurable structure, parallel processing capability, ease of transportation and integration. Proposed miniature factory consists of several functional modules such as two parallel kinematic robots for manipulation and assembly, galvanometric laser beam scanning system for micromachining, camera system for inspection, and a rotational conveyor system for sample part delivery. The overall mechanical structure of the proposed microfactory facilitates modularity and reconfigurability, parallel processing, flexible rearrangement of the layout, and ease of assembly and disassembly of the whole structure. Experiments involve various tasks within a single process such as pick-place of the 3 mm diameter metallic ball, marking a 2D sub-millimeter image on the ball surface with high power laser, and inspection along with verification of the image by means of microscopic camera. Results have shown the possibility of implementation of the desktop microfactory concept for machining and assembly of tiny mechanical parts with microprecision.

Averaged Control for Fractional ODEs and Fractional Diffusion Equations

We generalize results concerning averaged controllability on fractional type equations: system of fractional ODEs and the fractional diffusion equation. The proofs are accomplished by introducing appropriate Banach space in which we prove observability inequalities.

System for Distributed Measurement of Ambient Conditions in Homes

Measurement of ambient conditions in homes is one of the main preconditions for their control what represents one of the steps toward the complete implementation of smart homes. The objective of this study is to implement a system for distributed measurement of temperature, illuminance and humidity. In this work, all parameters to be measured will be analyzed, and applied sensors will be described. In order to have better insight in the measured parameters, measurements on different locations are made and all data are sent to one place. One of the main purposes of the project is to accomplish low price of the implemented system. In addition, a simple software application is made, and it allows visualization of the measurement results and their statistical analysis.