Browsing by Author "Uyanik, I."

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Open Access
Efficient bipedal locomotion on rough terrain via compliant ankle actuation with energy regulation
(Institute of Physics Publishing Ltd., 2021-08-12) Kerimoğlu, Deniz; Karkoub, M.; Uyanik, I.; Morgül, Ömer; Saranli, U.
Legged locomotion enables robotic platforms to traverse on rough terrain, which is quite challenging for other locomotion types, such as in wheeled and tracked systems. However, this benefit—moving robustly on rough terrain—comes with an inherent drawback due to the higher cost of transport in legged robots. The ultimate need for energy efficiency motivated the utilization of passive dynamics in legged locomotion. Nevertheless, a handicap in passive dynamic walking is the fragile basin of attraction that limits the locomotion capabilities of such systems. There have been various extensions to overcome such limitations by incorporating additional actuators and active control approaches at the expense of compromising the benefits of passivity. Here, we present a novel actuation and control framework, enabling efficient and sustained bipedal locomotion on significantly rough terrain. The proposed approach reinforces the passive dynamics by intermittent active feedback control within a bio-inspired compliant ankle actuation framework. Specifically, we use once-per-step energy regulation to adjust the spring precompression of the compliant ankle based on the liftoff instants—when the toe liftoffs from the ground—of the locomotion. Our results show that the proposed approach achieves highly efficient (with a cost of transport of 0.086) sustained locomotion on rough terrain, withstanding height variations up to 15% of the leg length. We provide theoretical and numerical analysis to demonstrate the performance of our approach, including systematic comparisons with the recent and state-of-the-art techniques in the literature.
Open Access
Enhancing 3D range image measurement density via dynamic Papoulis-Gerchberg algorithm
(SAGE Publications, 2018) Kuzucu, E.; Öztürk, D.; Gül, M.; Özbay, B.; Arisoy, A. M.; Sirin, H. O.; Uyanik, I.
As one of the most popular range detection methods, lidar is commonly used in various robotic applications. Although most robotic platforms easily adopt 2D lidar for range sensing, 3D lidar is rarely used in mobile robots, owing to its high cost. Some methods reported in the literature obtain 3D range information by rotating a single 2D lidar device. However, for most of these methods, there is a trade-off between 3D scan frequency and measurement density. Existing methods discussed in the literature for increasing the measurement density in high-frequency lidar have high time complexity and require certain conditions on data distribution. In a previous work, we showed the usability of an image super-resolution method, the Papoulis-Gerchberg (P-G) algorithm, on range data represented in the form of a greyscale image. However, the low convergence rate of the original P-G algorithm impedes its use for online applications. In this study, we advanced the P-G algorithm to drastically reduce the convergence time and improve performance by utilizing previous range images. The proposed algorithm now supports application on a mobile robot with online measurement density enhancement for 3D range images collected by rotating a 2D lidar device around its pitch axis with a high 3D scan frequency. We show illustrative examples for different scenarios to present the effectiveness of the proposed method on a 3D range sensor mounted on a mobile robot.
Open Access
Experimental validation of a feed-forward predictor for the spring-loaded inverted pendulum template
(IEEE, 2015-02) Uyanik, I.; Morgül, O.; Saranli, U.
Widely accepted utility of simple spring-mass models for running behaviors as descriptive tools, as well as literal control targets, motivates accurate analytical approximations to their dynamics. Despite the availability of a number of such analytical predictors in the literature, their validation has mostly been done in simulation, and it is yet unclear how well they perform when applied to physical platforms. In this paper, we extend on one of the most recent approximations in the literature to ensure its accuracy and applicability to a physical monopedal platform. To this end, we present systematic experiments on a well-instrumented planar monopod robot, first to perform careful identification of system parameters and subsequently to assess predictor performance. Our results show that the approximate solutions to the spring-loaded inverted pendulum dynamics are capable of predicting physical robot position and velocity trajectories with average prediction errors of 2% and 7%, respectively. This predictive performance together with the simple analytic nature of the approximations shows their suitability as a basis for both state estimators and locomotion controllers. © 2004-2012 IEEE.
Open Access
Frequency-domain subspace ıdentification of linear time periodic (LTP) systems
(Institute of Electrical and Electronics Engineers, 2019) Uyanik, I.; Saranli, U.; Ankaralı, M.; Cowan, N. J.; Morgül, Ömer
This note proposes a new methodology for subspace-based state-space identification for linear time-periodic (LTP) systems. Since LTP systems can be lifted to equivalent linear time-invariant (LTI) systems, we first lift input-output data from the unknown LTP system as if it was collected from an equivalent LTI system. Then, we use frequency-domain subspace identification methods to find an LTI system estimate. Subsequently, we propose a novel method to obtain a time-periodic realization for the estimated lifted LTI system by exploiting the specific parametric structure of Fourier series coefficients of the frequency-domain lifting method. Our method can be used to both obtain state-space estimates for unknown LTP systems as well as to obtain Floquet transforms for known LTP systems. IEEE
Open Access
A low-cost feedback control systems laboratory setup via Arduino-Simulink interface
(John Wiley and Sons, 2018) Uyanik, I.; Catalbas B.
Control theory education, when supported by practice, becomes more comprehendible for students and useful for their professional career. This paper presents low-cost experiments for laboratory sessions of a feedback control systems course, which introduces them modeling feedback control systems, proportional-integral-derivative (PID) controller design, root locus and Bode plots. The experiments are organized around the Arduino-based identification and control of a DC motor via Matlab/Simulink. The objective of this laboratory session is to support teaching feedback control systems via experimental investigations on a low-cost laboratory kit. The built in-house setups support Arduino-Simulink interface, so that students can download their control diagrams in Simulink to the Arduino board directly. This interface allows students to utilize high level control design tools, such as Matlab/Simulink while working on a low-cost hardware laboratory setup. Students’ performance in the written exams before and after the laboratory setup were reported to evaluate the instructional effectiveness. Besides, student feedback for four semesters are also presented to evaluate the effectiveness of the laboratory experiments.