Browsing by Author "Sariyildiz, E."

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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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Agile and stable running locomotion control for an untethered and one-legged hopping robot
(Springer, 2021-09) Uğurlu, Regaip Barkan; Sariyildiz, E.; Kawasaki, T.; Narikiyo, T.; Mechanical Engineering; UĞURLU, Regaip Barkan
This paper is aimed at presenting a locomotion control framework to realize agile and robust locomotion behaviors on conventional stiff-by-nature legged robots. First, a trajectory generator that is capable of characterizing angular momentum is utilized to synthesize reference CoM trajectories and associated force inputs, in accordance with the target locomotion profile. Second, the controller evaluates both force and position errors in the joint level, using a servo controller and an admittance control block. The trade-off between the position and force errors is naturally adjusted via admittance control coefficients. Implementing the controller on a 4-link, 3-jointed one-legged robot, we conducted several balancing and running experiments under challenging conditions; e.g., balancing on a moving cart, balancing on a surface with varying orientation, running on a flat surface, running on an inclined surface. The experimental study results indicated that the locomotion controller enabled the robot to perform untethered one-legged running and to maintain its balance when subject to disturbances.
Open Access
A comparison study on observer-based force control of series elastic actuators
(IEEE, 2018) Kansızoğlu, Ahmet Talha; Sariyildiz, E.; Uğurlu, Regaip Barkan; Mechanical Engineering; UĞURLU, Regaip Barkan; Kansızoğlu, Ahmet Talha
This paper presents a comparison study for the robust force control of series elastic actuators (SEAs). In most robotics systems, SEAs are used as an essential actuation method due to the benefits such as lower reflected inertia and safety. However, the robustness to the modeling uncertainties and external disturbances is still a study material for researchers. It is known that when model-based control methods are used with disturbance observers, high precision tracking results can be obtained. Therefore, in this study, model predictive control and model-based feedforward control methods are investigated in different scenarios and simulation results are provided for comparison.
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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.
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A high-torque density compliant actuator design for physical robot environment interaction
(IEEE, 2020) Dunwoodie, E.; Mutlu, R.; Uğurlu, Regaip Barkan; Yıldırım, Mehmet Can; Uzunovic, T.; Sariyildiz, E.; Mechanical Engineering; UĞURLU, Regaip Barkan; Yıldırım, Mehmet Can
Compared to the traditional industrial robots that use rigid actuators, the advanced robotic systems are mobile and physically interact with unknown and dynamic environments. Therefore, they need intrinsically safe and compact actuators. In the last two decades, Series Elastic Actuators (SEAs) have been one of the most popular compliant actuators in advanced robotic applications due to their intrinsically safe and compact mechanical structures. The mobility and functionality of the advanced robotic systems are highly related to the torque-density of their actuators. For example, the amount of assistance an exoskeleton robot can provide is determined by the trade-off between the weight and output-torque, i.e., torque-density, of its actuators. As the torque outputs of the actuators are increased, the exoskeleton can expand its capacity yet it generally becomes heavier and bulkier. This has significant impact on the mobility of the advanced robotic systems. Therefore, it is essential to design light-weight actuators which can provide high-output torque. However, this still remains a big challenge in engineering. To this end, this paper proposes a high-torque density SEA for physical robot environment interaction (pREI) applications. The continuous (peak) output-torque of the proposed compliant actuator is 147Nm (467 Nm) and its weight is less than 2.5kg. It is shown that the weight can be lessened to 1.74, but it comes at cost. The performance of the proposed compliant actuator is experimentally verified.