Browsing by Author "Ulu, Erva"

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Open Access
Adaptive correction and look-up table based interpolation of quadrature encoder signals
(ASME, 2012-10) Ulu, Erva; Geçer-Ulu, Nurcan; Çakmakçı, Melih
This paper presents a new method to increase the available measurement resolution of quadrature encoder signals. The proposed method features an adaptive signal correction phase and an interpolation phase. Typical imperfections in the encoder signals including amplitude difference, mean offsets and quadrature phase shift errors are corrected using recursive least squares with exponential forgetting and resetting. Interpolation of the corrected signals are accomplished by a quick access look-up table formed offline to satisfy a linear mapping from available sinusoidal signals to higher order sinusoids. The position information can be derived from the conversion of the high-order sinusoids to binary pulses. With the presented method, 10nm resolution is achieved with an encoder having 1μm of original resolution. Further increase in resolution can also be satisfied with minimizing electrical noises. Experiment results demonstrating the effectiveness of the proposed method for a single axis and two axis slider systems are given. Copyright © 2012 by ASME.
Open Access
Development of a modular single-axis slider for high precision positioning applications
(2012-06) Geçer-Ulu, Nurcan; Ulu, Erva; Çakmakçı, Melih
In this paper, design and implementation of a modular single-axis micro/nano-positioning system which is driven by a permanent magnet linear motor is presented. The system is represented by modest amount of effort for mathematical modeling which is improved by series of experiments on open loop characteristics. Moreover, the system is proposed to be controlled by a PID controller. Conventional point to point position control, velocity control with trajectory planning and position control with trajectory planning approaches are accomplished and compared in terms of their suitability to the proposed system. The comparisons are supported by experimental results obtained with the single-axis slider mechanism. Using the position control with trajectory planning, better performance characteristics are observed. Moreover, experimental results have shown that trajectory planning approaches are more suitable for precision positioning applications due to their smooth motion characteristics.
Open Access
Learning based cross-coupled control for multi-axis high precision positioning systems
(ASME, 2012-10) Geçer-Ulu, Nurcan; Ulu, Erva; Çakmakçı, Melih
In this paper, a controller featuring cross-coupled control and iterative learning control schemes is designed and implemented on a modular two-axis positioning system in order to improve both contour and tracking accuracy. Instead of using the standard contour estimation technique proposed with the variable gain cross-coupled control, a computationally efficient contour estimation technique is incorporated with the presented control design. Moreover, implemented contour estimation technique makes the presented control scheme more suitable for arbitrary nonlinear contours. Effectiveness of the control design is verified with simulations and experiments on a two-axis positioning system. Also, simulations demonstrating the performance of the control method on a three-axis positioning system are provided. The resulting controller is shown to achieve nanometer level contouring and tracking performance. Simulation results also show its applicability to three-axis nano-positioning systems. Copyright © 2012 by ASME.
Open Access
Mechatronic design of a modular three-axis slider system for high-precision positioning applications
(2012) Ulu, Erva
Following the recent improvements in precision engineering related technology, interest for micro/nano-engineering applications are increased and various micro/nano-scale operations and products are developed. For micro/nano-scale applications, high-precision equipment including micro/nano-positioning devices with high accuracy and precision are required. In this thesis, mechatronic design of a three axes micro/nano-positioning device is discussed in detail. In order to satisfy nanometer level precision, an adaptive method to increase the available measurement resolution of quadrature encoders is presented. Performance characteristics of micro/nano-positioning devices usually include positioning accuracy of their each individual axis, operation range, maximum velocity and maximum acceleration. For this reason, permanent magnet linear motors (PMLM) are chosen as actuators in the presented design due to their outstanding characteristics. Moreover, in order to provide high-flexibility in terms of applications and simplify the control of the system, modularity is one of the main concerns while designing the micro/nano-positioning system presented here. Building the modular single axis slider system, three axes positioning device is constructed by assembling three of them perpendicularly. In this design, linear optical encoders are used as feedback sensors. Movement range of the designed system is 120mm in each direction. Since the available linear optical encoders have measurement resolution of 1µm, resolution of them is to be improved in software for sub-micron level positioning applications. For this purpose, a new method to increase the available measurement resolution of quadrature encoders is presented in this thesis. This method features an adaptive signal correction phase and an interpolation phase. Imperfections in the encoder signals including amplitude differences, mean offsets and quadrature phase shift errors are corrected by using recursive least squares (RLS) with exponential forgetting and resetting. Interpolation of the corrected signals is accomplished by a quick access look-up table calculated offline to satisfy linear mapping from available sinusoidal signals to higher order ones. With the conversion of the high-order sinusoids to binary pulses, position information is derived. By using the presented method, 10nm measurement resolution is achieved with an encoder with 1µm off-the-shelf resolution. Experiment results demonstrating the effectiveness of the proposed method are presented. Validation of the method is accomplished for several cases including the best resolution obtained. Practical constraints limiting the maximum interpolation number are also discussed in detail.