Person:
UĞURLU, Regaip Barkan

First Name

Regaip Barkan

Last Name

UĞURLU

Organizational Unit

Mechanical Engineering

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Now showing 1 - 10 of 45

Open Access
Variable ankle stiffness improves balance control: experiments on a bipedal exoskeleton
(IEEE, 2016-02) Uğurlu, Regaip Barkan; Doppmann, C.; Hamaya, M.; Forni, P.; Teramae, T.; Noda, T.; Morimoto, J.; Mechanical Engineering; UĞURLU, Regaip Barkan
This paper proposes a real-time balance control technique that can be implemented to bipedal robots (exoskeletons, humanoids) whose ankle joints are powered via variable physical stiffness actuators. To achieve active balancing, an abstracted biped model, torsional spring-loaded flywheel, is utilized to capture approximated angular momentum and physical stiffness, which are of importance in postural balancing. In particular, this model enables us to describe the mathematical relation between zero moment point (ZMP) and physical stiffness. The exploitation of variable physical stiffness leads to the following contributions: 1) Variable physical stiffness property is embodied in a legged robot control task, for the first time in the literature to the authors' knowledge. 2) Through experimental studies conducted with our bipedal exoskeleton, the advantages of variable physical stiffness strategy are demonstrated with respect to the optimal constant stiffness strategy. The results indicate that the variable stiffness strategy provides more favorable results in terms of external disturbance dissipation, mechanical power reduction, and ZMP/center of mass position regulation.
Open Access
ZMP-based online jumping pattern generation for a one-legged robot
(IEEE, 2010-05-01) Uğurlu, Regaip Barkan; Kawamura, A.; Mechanical Engineering; UĞURLU, Regaip Barkan
This paper is aimed at presenting a method to generate online jumping patterns, which can be applied to one legged jumping robots and optionally to humanoid robots. Our proposed method is based on ensuring the overall dynamic balance through the complete jumping cycle. To be able to reach this goal, we discretized the ZMP equation in polar coordinates so that we are able to include angular momentum information in a natural way. Thus, undesired torso angle fluctuation is expected to be more restrainable comparing to other methods in which angular momentum information is ignored or zero-referenced. Moreover, we unified support and flight phases in terms of motion generation. Having obtained successful simulation results and vertical jumping experiments in our previous work, we conducted forward jumping experiments. As the result, we obtained successful and repetitive jumping cycles, which satisfactorily verify the proposed method.
Open Access
Tepki kuvveti gözetleyici tabanlı tork kontrolü
(Gazi Üniversitesi, 2021-12) Özçınar, Erim Can; Uğurlu, Regaip Barkan; Mechanical Engineering; UĞURLU, Regaip Barkan; Özçınar, Erim Can
In this article, a reaction force observer-based torque controller was designed and experimentally implemented to a non-backdrivable actuator unit. Torque control is of importance when considering physical human-robot interaction and researchers usually use torque sensors or custom-built torsional springs. These elements lead to relatively more complicated systems and increase the total weight. In contrast, reaction force observers can estimate external forces acting on the system and thus enable torque control with no need of torque sensing. The estimation process performs better for backdrivable systems, therefore, its implementation to non-backdrivable systems, e.g., systems with a gear ratio of 1:100, is limited. To remedy this issue, a reaction force observer-based torque controller was designed and implemented. As a result, experimental data showed that reaction force observer leads to favorable torque control performance when supported with friction compensation.
Open Access
Torque and variable stiffness control for antagonistically driven pneumatic muscle actuators via a stable force feedback controller
(IEEE, 2015) Uğurlu, Regaip Barkan; Forni, P.; Doppmann, C.; Morimoto, J.; Mechanical Engineering; UĞURLU, Regaip Barkan
This paper describes a novel controller that is capable of simultaneously controlling torque and variable stiffness in real-time, for actuators with antagonistically driven pneumatic artificial muscles (PAMs). To this end, two contributions are presented: i) A stable force feedback controller that can cope with inherent PAM nonlinearities is synthesized using the dissipativity theory, for each PAM unit. ii) On top of this force feedback controller, a mathematical formulation is developed to compute reference force inputs that correspond to desired joint torque and joint stiffness inputs, concerning both agonist and antagonist PAMs. This strategy enables us to introduce real-time sensory feedback; torque and stiffness control is addressed by means of PAM force feedback control with guaranteed stability. To validate the proposed control scheme, a series of experiments were conducted on an experimental setup. As the result, the controller exhibited favorable torque and stiffness tracking in real-time, demonstrating that it could meet the performance criteria to power exoskeleton systems.
Open Access
A stability analysis for the acceleration-based robust position control of robot manipulators via disturbance observer
(IEEE, 2018-10) Sarıyıldız, E.; Sekiguchi, H.; Nozaki, T.; Uğurlu, Regaip Barkan; Ohnishi, K.; Mechanical Engineering; UĞURLU, Regaip Barkan
This paper proposes a new nonlinear stability analysis for the acceleration-based robust position control of robot manipulators by using disturbance observer (DOb). It is shown that if the nominal inertia matrix is properly tuned in the design of a DOb, then the position error asymptotically goes to zero in regulation control and is uniformly ultimately bounded in trajectory-tracking control. As the bandwidth of a DOb and the nominal inertia matrix are increased, the bound of error shrinks, i.e., the robust stability and performance of the position control system are improved. However, neither the bandwidth of the DOb nor the nominal inertia matrix can be freely increased due to practical design constraints, e.g., the robust position controller becomes more noise-sensitive when they are increased. The proposed stability analysis provides insights into the dynamic behavior of DOb-based robust motion control systems. It is theoretically and experimentally proved that non-diagonal elements of the nominal inertia matrix are useful in improving the stability and in adjusting the tradeoff between robustness and noise sensitivity. The validity of the proposal is verified by simulation and experimental results.
Metadata only
Topology optimization-based design and development of a compact actuator with a high torque-to-weight ratio for quadrupeds
(IEEE, 2022) Akın, Barış; Özçınar, Erim Can; Balcı, Barış; Emre, Sinan; Şendur, Polat; Bebek, Özkan; Ünal, Ramazan; Uğurlu, Regaip Barkan; Mechanical Engineering; ŞENDUR, Polat; BEBEK, Özkan; ÜNAL, Ramazan; UĞURLU, Regaip Barkan
This paper presents the design, development, and testing procedures for a compact actuator with a high torque-to-weight ratio, generally aimed to actuate legged robots, e.g., quadrupeds. The main goal of designing the actuator was to keep its total weight minimum while ensuring a high torque output. Therefore, the following design steps were implemented: i) the actuator was designed in accordance with the torque output requirement and the stress distribution that was mapped on actuator frames, ii) topology optimization was conducted on the initial design and it is modified in accordance with optimization results, and iii) the optima actuator design was built and tested on in a realistic scenario in which it powered an actual quadruped robot for validation. As the result, the proposed actuators could track the desired walking trajectory with a relatively low error. In conclusion, continuous torque output of 48 Nm was obtained via a lightweight (1.6-1.7 kg) actuator design.
Metadata only
Robust locomotion control of a self-balancing and underactuated bipedal exoskeleton: Task prioritization and feedback control
(IEEE, 2021-07) Soliman, Ahmed Fahmy; Uğurlu, Regaip Barkan; Mechanical Engineering; UĞURLU, Regaip Barkan; Soliman, Ahmed Fahmy
This letter presents a study to understand how an underactuated bipedal exoskeleton with an arbitrary human user can exhibit robust dynamic walking behavior despite severe parameter uncertainty and external disturbances. Unlike in the case of classical bipedal robots where each leg possesses 6 or more active joints, it is very challenging to satisfy multiple constraints simultaneously to ensure robust dynamic walking. To overcome this problem, we first propose an optimization algorithm that makes use of a prioritized stack of tasks to satisfy the constraints hierarchically. Furthermore, we synthesized a locomotion controller named ZMP impedance feedback and identified two other state-of-the-art locomotion controllers (admittance control, centroidal momentum control) all of which were built on top of the proposed task prioritization algorithm. In order to verify the validity and robustness of these controllers for a thorough benchmarking, a series of simulation experiments were conducted via MSC ADAMS in which a human-robot coupled model with a 40 kg underactuated exoskeleton and 12 distinct anthropomorphic subjects (66 similar to 102 kg) was considered. As the result, all 3 controllers showed adequate performances to address balanced locomotion behavior when used with the proposed task priority-based optimization algorithm. In addition, the proposed ZMP impedance controller showed statistically significant results, indicating its comparatively more robust feature.
Open Access
Discussing modernizing engineering education through the Erasmus + Project Titled "Open Educational Resources on Enabling Technologies in Wearable and Collaborative Robotics (WeCoRD)
(Ege University) Kılıç-Bebek, Ebru; Nizamis, K.; Karapars, Gülhis Zeynep; Gökkurt, Muharrem Ali; Ünal, Ramazan; Bebek, Özkan; Vlutters, M.; Vander Poorten, E.; Borghesan, G.; Decré, W.; Aertbelien, E.; Borisova, O.; Borisov, I.; Kolyubin, S.; Kodal, M. I.; Uğurlu, Regaip Barkan; Industrial Design; Sectoral Education and Professional Development; Mechanical Engineering; BEBEK, Ebru Kılıç; KARAPARS, Gülhis Zeynep; GÖKKURT, Muharrem Ali; ÜNAL, Ramazan; BEBEK, Özkan; UĞURLU, Regaip Barkan
The Erasmus + project titled “Open Educational Resources on Enabling Technologies in Wearable and Collaborative Robotics (WeCoRD)", can serve as a model to establish strategic international and multidisciplinary partnerships to modernize engineering education. WeCoRD project is a collaboration among internationally renowned institutions from Turkey, Belgium, Russia, and the Netherlands to create an innovative course on wearable and collaborative robotics with Open Educational Resources (OERs) and an online Virtual Lab aimed at accessibility across Europe. This collaboration involves many fields from engineering, health, and design disciplines as well as an industry partner from the automotive manufacturing sector. The main objectives of the project are to: (1) prepare a graduate-level course in wearable and collaborative robotics, (2) enhance EU higher education capacity in the field with clear use-case scenarios from the industry and medical applications, (3) provide open-source materials including a virtual lab, and (4) fill the skill gap between the industry and the academia while also aiming a continued professional development. With these goals which aim to modernize engineering education and make it more relevant to the industry, the WeCoRD project brings both multidisciplinary and interdisciplinary aspects of robotics education to a new level. Each intellectual output (IO) of the project is allocated to a project partner based on their expertise. The course module design and development is planned as follows: The IO1 (the first course module) on “Components for wearable and collaborative robots” is led by Ozyegin University, Turkey; the IO2 (the second course module) on “Modeling, design and control or wearable and collaborative robots as systems” is led by ITMO, Russia; the IO3 (the third course module) on “Human-robot interaction for wearable and collaborative robots” is led by KU Leuven, Belgium; the IO4 (the fourth course module) on “Medical applications” is led by U.Twente; the IO5 (integration of the first three course modules into one course) on the graduate-level course to be integrated into graduate degree programs and to be adopted for continued professional development (CPD) training programs, as well as the translation of the course materials into Turkish is led by KU Leuven, Belgium; the IO6 on the “Virtual Lab” is led by ITMO, Russia; and finally IO7 on the “Video Collection” is led by Ozyegin University, Turkey. FORD-Otosan, which is one of the industry partners from Turkey will host students, provide site visits and offer workshops. Each project partner and their contributions will be addressing the fundamental need for modernizing engineering education through students’ active participation and boosting students’ skill development. In addition to multidisciplinary and interdisciplinary exposure, students will get a chance to work with industry partners and learn through authentic problem solving and relevant feedback. Providing a deeper and more effective learning experience will be among the core design principles of the course modules, labs, videos, and industry collaborations.
Metadata only
Preview control-based jumping and spot-jogging trajectory generation for quadruped robots
(IEEE, 2023) Özkaynak, İbrahim Burak; Uğurlu, Regaip Barkan; Mechanical Engineering; UĞURLU, Regaip Barkan; Özkaynak, İbrahim Burak
This work presents a vertical center of mass (CoM) trajectory generation approach based on preview control for quadruped robots to accomplish agile locomotion tasks such as jumping and jogging. Conventionally, preview control is implemented to walking planning with constant CoM height, since this condition renders the pendulum equation linear. In this matter, we show that the same implementation can be done for varying CoM height, while the pendulum frequency is constant. To this end, we compactly derived the infinite horizon and finite horizon time-invariant linear quadratic regulator solutions for potential real-time applicability. The proposed trajectory generation approach was tested and compared with conventional approaches via a set of simulation experiments, where we used a realistic model of our quadruped robot Kara. As a result, we obtained dynamically-balanced, coherent, and continuous jumping and spot-jogging behavior, adequately confirming our approach.
Metadata only
Assessments on the improved modelling for pneumatic artificial muscle actuators
(IEEE, 2015) Peternel, L.; Uğurlu, Regaip Barkan; Babic, J.; Morimoto, J.; Mechanical Engineering; UĞURLU, Regaip Barkan
In this paper, we present an analysis regarding the pneumatic air muscle modelling, with a particular emphasis on the exoskeleton robot control. We propose two calibration approaches for obtaining the model identification data. We used the measurement data acquired from the proposed approaches to identify different mathematical models of pneumatic muscles. These models specified the necessary muscle control pressure for the desired muscle force at a given muscle length value. We compared the performance between the different types of models identified by either of the calibration method. The identified model with the lowest validation error was implemented in pneumatic muscle control for an elbow exoskeleton system. As a result, the system exhibited satisfactory torque and position control tasks, adequately validating the proposed approach.