Person:
UĞURLU, Regaip Barkan

First Name

Regaip Barkan

Last Name

UĞURLU

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Mechanical Engineering

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Now showing 1 - 10 of 45

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.
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.
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Transdisciplinarity as a learning challenge: Student experiences and outcomes in an innovative course on wearable and collaborative robotics
(IEEE, 2023-06) Kılıç-Bebek, Ebru; Nizamis, K.; Vlutters, M.; Bebek, Özkan; Karapars, Gülhis Zeynep; Ünal, Ramazan; Yılmaz, Deniz; Uğurlu, Regaip Barkan; Industrial Design; Sectoral Education and Professional Development; Mechanical Engineering; Mitchell, J.; BEBEK, Ebru Kılıç; KARAPARS, Gülhis Zeynep; BEBEK, Özkan; ÜNAL, Ramazan; UĞURLU, Regaip Barkan; Yılmaz, Deniz
Contribution: This study provides evidence for the benefit of short online courses for transdisciplinary competence development of graduate students. It shows the significant challenges students face while learning, and provides instructional recommendations to improve students’ learning quality and professionalism. Background: Developing wearable and collaborative robots requires industry collaboration and transdisciplinary competence. Industry’s involvement in long-term programs is becoming infeasible, and the nature of transdisciplinary learning has not been explored to inform instructional practices. Intended Outcomes: This study aimed to provide instructional recommendations based on an in-depth examination of a diverse group of graduate students’ learning and teamwork experiences as well as outcomes in a 5-day online transdisciplinary course. Application Design: 31 graduate students of engineering, industrial design, and health fields from 4 countries participated in online mixed-discipline instructional sessions and teams to address a real industry challenge. A mixed-methods approach was used to examine students’ experiences and learning outcomes based on a competence measure, session participation data, student journal entries, team progress reports, team elaboration visuals, and final team presentations. Findings: Students’ knowledge of industrial design, medical considerations, ethics and standards, effective teamwork, and self-regulated learning were increased. Students’ high motivation helped them deal with the challenges involved. Daily student journals, team reports, and visual elaboration tools were found to be beneficial for determining the challenges and learning quality. The observed student progress within 5 days is promising, making it worthwhile to further explore the benefits of short online courses for increasing graduates’ readiness and establishing university-industry collaborations in education.
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.
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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
Active compliance control reduces upper body effort in exoskeleton-supported walking
(IEEE, 2020-04) Uğurlu, Regaip Barkan; Oshima, H.; Sariyildiz, E.; Narildyo, T.; Babic, J.; Mechanical Engineering; UĞURLU, Regaip Barkan
This article presents a locomotion controller for lower limb exoskeletons so as to enable the combined robot and user system to exhibit compliant walking characteristics when interacting with the environment. This is of critical importance to reduce the excessive ground reaction forces during the walking task execution with the aim of improved environmental interaction capabilities. In robot-aided walking support for paraplegics, the user has to actively use his/her upper limbs via crutches to ensure overall balance. By virtue of this requisite, several issues may particularly arise during touchdown instants, e.g., upper body orientation fluctuates, shoulder joints are subject to excessive loading, and arms may need to exert extra forces to counterbalance these effects. In order to reduce the upper body effort via compliant locomotion, the controller is designed to manage the force/position tradeoff by using an admittance controller in each joint. For proof of concept, a series of exoskeleton-aided walking experiments were conducted with the participation of nine healthy volunteers, four of whom additionally walked on an irregular surface for further performance evaluation. The results suggest that the proposed locomotion controller is advantageous over conventional high-gain position tracking in decreasing undesired oscillatory torso motion and total arm force, adequately reducing the required upper body effort.
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Design and control of a novel variable stiffness series elastic actuator
(IEEE, 2023-06) Sariyildiz, E.; Mutlu, R.; Roberts, J.; Kuo, C. H.; Uğurlu, Regaip Barkan; Mechanical Engineering; UĞURLU, Regaip Barkan
This article expounds the design and control of a new variable stiffness series elastic actuator (VSSEA). It is established by employing a modular mechanical design approach that allows us to effectively optimize the stiffness modulation characteristics and power density of the actuator. The proposed VSSEA possesses the following features: no limitation in the work range of output link; a wide range of stiffness modulation (∼20 N·m/rad to ∼1 KN·m/rad); low-energy-cost stiffness modulation at equilibrium and nonequilibrium positions; compact design and high torque density (∼36 N·m/kg); and high-speed stiffness modulation (∼3000 N·m/rad/s). Such features can help boost the safety and performance of many advanced robotic systems, e.g., a cobot that physically interacts with unstructured environments and an exoskeleton that provides physical assistance to human users. These features can also enable us to utilize variable stiffness property to attain various regulation and trajectory tracking control tasks only by employing conventional controllers, eliminating the need for synthesizing complex motion control systems in compliant actuation. To this end, it is experimentally demonstrated that the proposed VSSEA is capable of precisely tracking the desired position and force control references through the use of the conventional proportional-integral-derivative controllers.
Open Access
Learning to exploit passive compliance for energy-efficient gait generation on a compliant humanoid
(Springer Nature, 2019-01) Kormushev, P.; Uğurlu, Regaip Barkan; Caldwell, D. G.; Tsagarakis, N. G.; Mechanical Engineering; UĞURLU, Regaip Barkan
Modern humanoid robots include not only active compliance but also passive compliance. Apart from improved safety and dependability, availability of passive elements, such as springs, opens up new possibilities for improving the energy efficiency. With this in mind, this paper addresses the challenging open problem of exploiting the passive compliance for the purpose of energy efficient humanoid walking. To this end, we develop a method comprising two parts: an optimization part that finds an optimal vertical center-of-mass trajectory, and a walking pattern generator part that uses this trajectory to produce a dynamically-balanced gait. For the optimization part, we propose a reinforcement learning approach that dynamically evolves the policy parametrization during the learning process. By gradually increasing the representational power of the policy parametrization, it manages to find better policies in a faster and computationally efficient way. For the walking generator part, we develop a variable-center-of-mass-height ZMP-based bipedal walking pattern generator. The method is tested in real-world experiments with the bipedal robot COMAN and achieves a significant 18% reduction in the electric energy consumption by learning to efficiently use the passive compliance of the robot.
Open Access
Proof of concept for robot-aided upper limb rehabilitation using disturbance observers
(IEEE, 2015-02) Uğurlu, Regaip Barkan; Nishimura, M.; Hyodo, K.; Kawanishi, M.; Narikiyo, T.; Mechanical Engineering; UĞURLU, Regaip Barkan
This paper presents a wearable upper body exoskeleton system with a model-based compensation control framework to support robot-aided shoulder-elbow rehabilitation and power assistance tasks. To eliminate the need for EMG and force sensors, we exploit off-the-shelf compensation techniques developed for robot manipulators. Thus, target rehabilitation tasks are addressed by using only encoder readings. A proof-of-concept evaluation was conducted with live able-bodied participants. The patient-active rehabilitation task was realized via observer-based user torque estimation, in which resistive forces were adjusted using virtual impedance. In the patient-passive rehabilitation task, the proposed controller enabled precise joint tracking with a maximum positioning error of 0.25°. In the power assistance task, the users' muscular activities were reduced up to 85% while exercising with a 5 kg dumbbell. Therefore, the exoskeleton system was regarded as being useful for the target tasks, indicating that it has a potential to promote robot-aided therapy protocols.