Mert Ankarali - Academia.edu (original) (raw)

Papers by Mert Ankarali

2022 9th IEEE RAS/EMBS International Conference for Biomedical Robotics and Biomechatronics (BioRob)

Underactuated legged robots depict highly nonlinear and complex dynamical behaviors that create s... more Underactuated legged robots depict highly nonlinear and complex dynamical behaviors that create significant challenges in accurately modeling system dynamics using both first principles and system identification approaches. Hence, it makes a more substantial challenge to design stabilizing controllers. If physical parameters on mathematical models have miscalibrations due to uncertainty in identifying and modeling processes, designed controllers could perform poorly or even result in unstable responses. Moreover, these parameters can certainly changeover time due to operation and environmental conditions. In that respect, analogous to a living organism modifying its behavior in response to novel conditions, adapting/updating system parameters, such as spring constant, to compensate for modeling errors could provide the advantage of constructing a stable gait level controller without needing "exact" dynamical parameter values. This paper presents an online, model-based adaptive control approach for an underactuated planar hexapod robot's pronking behavior adopted from antelope species. We show through systematic simulation studies that the adaptive control policy is robust to high levels of parameter uncertainties compared to a non-adaptive model-based dead-beat controller.

European Journal of Science and Technology

Bu çalışmada, sensörsüz elastik seri tekniği ile kablo sürümlü bir düzlemsel mekanizmanın kontrol... more Bu çalışmada, sensörsüz elastik seri tekniği ile kablo sürümlü bir düzlemsel mekanizmanın kontrolü incelenmektedir. Kablo sürümlü robotlar, gösteri alanlarında örümcek kamera olarak yatay düzlemde çalışan şekilde hali hazırda kullanılmaktadırlar. Bu çalışmada ise düşey düzlemde çalışan bir kablo sürümlü robot üzerinde çalışılmaktadır. Mekanizmanın düşey düzlemde çalışması sebebiyle de örümcek kameralardaki gibi her motora eşit kuvvet uygulanmamaktadır. Kablo sürümlü robotların kontrolü için kullanılan, sensörlerden alınan bilgilerin işlenmesine dayalı yöntemleri kullanmak yerine, sensörlerden elde edilen bilgilerde oluşabilecek herhangi bir gecikmeden veya hatadan etkilenmemek için bu çalışmada sensörsüz bir kontrol tekniği kullanılmaktadır. Sırasıyla, mekanizmanın mekanik, donanım ve yazılım kısımlarının açıklanmasının ardından, kontrol stratejimizin matematiksel olarak derinlemesine çalışılacağı modelleme ve varsayımlar sunulmaktadır. Çalışmanın sonuç bölümünde simülasyon ve gerçe...

2020 IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM)

The Spring-Loaded Inverted Pendulum (SLIP) template and its extensions have long been used as ben... more The Spring-Loaded Inverted Pendulum (SLIP) template and its extensions have long been used as benchmark models for analyzing the dynamics of legged systems in biology and robotics. The fundamental SLIP model is composed of single point mass attached to the ground (during stance phase) via an ideal lossless spring. Many researchers introduced various extensions to this fundamental model, such as damping & torque actuation, to handle critical physical phenomena that are unavoidable in real systems. Another crucial missing concept in SLIP template is the effect of the upper body in humans and humanoid robotic systems on the closed-loop system dynamics. Even though the SLIP template can effectively capture COM behavior, it cannot provide a framework for describing fullbody stabilization and control. In this paper, we present a new control policy called the Central Pivot Point (CPP) for the body attached spring-mass runners. In the stance phase, CPP directs ground reaction forces through the center of mass and cancels the torque created by these forces on the body. In this way, the CPP model makes it possible to develop different controllers for both the body’s rotational and euclidean dynamics. Firstly, we analyze the characteristics and stability of the periodic solutions of the CPP model. Then, we develop a PD controller for pitch dynamics and an LQR (Linear Quadratic Regulator) for gait level apex to apex discrete dynamics to stabilize the system’s periodic solutions. We compute the basin of attraction of the proposed control scheme and show examples of how the model behaves under disturbances. The results show that the purposed model and associated control policy could be beneficial in the design and control of humanoid robotic systems.

2018 26th Signal Processing and Communications Applications Conference (SIU), 2018

In this paper, we present the comparison of different optimization algorithms that are used to op... more In this paper, we present the comparison of different optimization algorithms that are used to optimize the parameters of a simulated legged robotic platform. We compare the results obtained by applying different algorithms on the same model and show the relative advantages and disadvantages of these algorithms. The tested algorithms are Particle Swarm Optimization, Binary Coded Genetic Algorithm, Broyden-Fletcher-Goldfrab-Shannon Algorithm and Method of Zoutendijk. We showed that the globally optimal parameter set reduces the total dissipated energy approximately 50% with respect to the reference paremeter set in the literature. The implemented optimization methods can also be applied to other legged platforms to obtain efficient systems without affecting the performance and the stability.

2020 28th Signal Processing and Communications Applications Conference (SIU)

The advantages of autonomous agriculture over traditional agriculture have been reported both in ... more The advantages of autonomous agriculture over traditional agriculture have been reported both in national and international literature. Motion and trajectory planning is one of the fundamental problems an agricultural robot has to solve. Several trajectory guidance patterns have been developed in the literature. In this work, a visual trajectory planning interface based on Google maps is designed, and A+ pattern is implemented on it. The position of the vehicle obtained via GPS is shown on the interface in real time.

This folder includes the preprocessed data at each frequency for all fish.

This folder includes the preprocessed data files for the response of each fish.

This folder includes the raw data collected from three fish including the digitized positions of ... more This folder includes the raw data collected from three fish including the digitized positions of fish, refuge and the nodal point.

IEEE Transactions on Automatic Control, 2018

This paper proposes a new methodology for subspace-based state-space identification for linear ti... more This paper 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.

This project includes data from experiments conducted with weakly electric fish Eigenmannia vires... more This project includes data from experiments conducted with weakly electric fish Eigenmannia virescens while tracking a moving a refuge. In this project, we studied the effect of sensory feedback on the variability of task performance. To examine this, we used data-driven system identification techniques to estimate transfer function models for the input—output behavioral response and the plant dynamics of the fish. We then, back-calculated associated sensorimotor controllers both in feedforward and feedback control topologies. Swapping controllers and plants across individuals in different control topologies allowed us to analyze the effect of sensory feedback on the variability of task performance. The project includes the data files for each experiment conducted with the fish.

2020 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2020

Robust and safe feedback motion planning and navigation is a critical task for autonomous mobile ... more Robust and safe feedback motion planning and navigation is a critical task for autonomous mobile robotic systems considering the highly dynamic and uncertain nature scenarios of modern applications. For these reasons motion planning and navigation algorithms that have deep roots in feedback control theory has been at the center stage of this domain recently. However, the vast majority of such policies still rely on the idea that a motion planner first generates a set of open-loop possibly time-dependent trajectories, and then a set of feedback control policies track these trajectories in closed-loop while providing some error bounds and guarantees around these trajectories. In contrast to trajectory-based approaches, some researchers developed feedback motion planning strategies based on connected obstacle-free regions, where the task of the local control policies is to drive the robot(s) in between these particular connected regions. In this paper, we propose a feedback motion plan...

Integrative and comparative biology, Jan 4, 2018

Unlike most manmade machines, animals move through their world using flexible bodies and appendag... more Unlike most manmade machines, animals move through their world using flexible bodies and appendages, which bend due to internal muscle and body forces, but also due to forces from the environment. Fishes in particular must cope with fluid dynamic forces that not only resist their overall swimming movements but also may have unsteady flow patterns, vortices, and turbulence, many of which occur more rapidly than what the nervous system can process. Has natural selection led to mechanical properties of fish bodies and their component tissues that can respond very quickly to environmental perturbations? Here, we focus on the mechanical properties of isolated muscle tissue and of the entire intact body in the silver lamprey, Ichthyomyzon unicuspis. We developed two modified work loop protocols to determine the effect of small perturbations on the whole body and on isolated segments of muscle as a function of muscle activation and phase within the swimming cycle. First, we examined how th...

Transactions of the Institute of Measurement and Control, 2015

A common approach to understanding and controlling robotic legged locomotion is the construction ... more A common approach to understanding and controlling robotic legged locomotion is the construction and analysis of simplified mathematical models that capture essential features of locomotor behaviours. However, the representational power of such simple mathematical models is inevitably limited due to the non-linear and complex nature of biological locomotor systems. Attempting to identify and explicitly incorporate key non-linearities into the model is challenging, increases complexity, and decreases the analytic utility of the resulting models. In this paper, we adopt a data-driven approach, with the goal of furnishing an input-output representation of a locomotor system. Our method is based on approximating the hybrid dynamics of a legged locomotion model around its limit cycle as a Linear Time Periodic (LTP) system. Perturbing inputs to the locomotor system with small chirp signals yield the input-output data necessary for the application of LTP system identification techniques, allowing us to estimate harmonic transfer functions (HTFs) associated with the local LTP approximation to the system dynamics around the limit cycle. We compare actual system responses with responses predicted by the HTF, providing evidence that data-driven system identification methods can be used to construct models for locomotor behaviours.

Adaptive Mobile Robotics, 2012

53rd IEEE Conference on Decision and Control, 2014

Nonlinear Dynamics, 2010

This paper introduces an accurate yet analytically simple approximation to the stance dynamics of... more This paper introduces an accurate yet analytically simple approximation to the stance dynamics of the Spring-Loaded Inverted Pendulum (SLIP) model in the presence of non-negligible damping and non-symmetric stance trajectories. Since the SLIP model has long been established as an accurate descriptive model for running behaviors, its careful analysis is instrumental in the design of successful locomotion controllers. Unfortunately, none of the existing analytic methods in the literature explicitly take damping into account, resulting in degraded predictive accuracy when they are used for dissipative runners. We show that the methods we propose not only yield average predictive errors below 2% in the presence of significant damping, but also outperform existing alternatives to approximate the trajectories of a lossless model. Finally, we exploit both the predictive performance and analytic simplicity of our approximations in the design of a gait-level running controller, demonstrating their practical utility and performance benefits.

2015 International Conference on Advanced Robotics (ICAR), 2015

Simple spring-mass systems, such as the Spring-Loaded Inverted Pendulum (SLIP) model, are widely ... more Simple spring-mass systems, such as the Spring-Loaded Inverted Pendulum (SLIP) model, are widely accepted in the literature both as accurate descriptive dynamical models for animal locomotion [3, 5] as well as the basis for numerous robots capable of dynamic locomotion [7, 11]. Most existing literature, however, focuses almost exclusively on telescoping leg models with only radial actuation, overlooking possible uses of hip torque actuation for running behaviors.