Browsing by Author "Ider, Sitki Kemal"

Now showing 1 - 7 of 7

Citation - WoS: 1
Citation - Scopus: 2
Desingularization of Flexible-Joint Parallel Robots
(Budapest Tech, 2021) Ozdemir, Mustafa; İder, Sıtkı Kemal; Ider, Sitki Kemal; 108608; Makine Mühendisliği
Parallel robots possess a characteristic type of singularities, called type II or drive singularities, inside their workspace. In the neighborhood of these singularities, the inverse dynamics solution grows unboundedly and the robot becomes uncontrollable. There is growing literature on methods that enable parallel robots to pass through drive singularities. Most of this literature relies on dynamic models that presume rigid joints. However, the flexibility of the drive train elements should also be taken into account for high accuracy. In this paper, we propose a systematic trajectory planning method for enabling flexible-joint parallel robots to pass through drive singular configurations. Our method generates admissible polynomial trajectories of degree eleven. Four conditions are derived and incorporated into the method to prevent undesired back-and-forth motion of the endpoint. This ensures not only an efficient operation of the robot but also the avoidance of unintended multiple occurrences of the same singularity. The boundedness of the inverse dynamics solution is also guaranteed.
Citation - WoS: 1
Citation - Scopus: 2
Experimental and numerical investigation of comparability of whiplash sled test results
(Springer Heidelberg, 2016) Ozdemir, Mustafa; İder, Sıtkı Kemal; Ider, Sitki Kemal; Gokler, Mustafa Ilhan; 108608; 182869; Makine Mühendisliği
Whiplash-associated neck injuries represent an important health and socioeconomic problem attracting more and more attention of the vehicle safety community. Sled tests are conducted for the dynamic whiplash assessment of seats. However, reproducibility of the initial backset distances and of the sled pulses in every test plays an important role on the comparability of these results. In this study, in order to investigate these aspects, three different driver seat types are considered with three identical and unused samples for each of them, and by strictly following the European New Car Assessment Program (Euro NCAP) whiplash protocol and using the BioRID II dummy, totally nine sled tests are performed. The sled pulses are in general reproduced quite well for different vehicle seats in these tests. However, it is seen that there are differences of up to 5 mm in the initial backset distances recorded for the identical seats of the same type, while this difference increases up to 7 mm among the different seat types considered. Moreover, taking into account the associated tolerances allowed in this protocol, this uncertainty in the backset can even increase up to 10 mm. Based on the previous simulation results obtained by using the finite element model of the BioRID II dummy, linear regression models are constructed, and it is shown that a 10-mm increase in the backset will yield an increase of 2.25, 2.89 and 3.11 m(2)/s(2) in the NICmax values for the low, medium and high severity Euro NCAP pulses, respectively. Being 38, 22 and 31 % of the differences between the associated Euro NCAP higher and lower performance limits, and 68, 96 and 124 % of the differences between the associated Euro NCAP lower performance and capping limits, such increases in the NICmax values are found to bring an unacceptably high uncertainty in the test results, and they can even easily lead to the application of capping, which means giving a zero score for the entire test. In light of these findings, several suggestions are recommended for a more solid whiplash dynamic assessment procedure.
Citation - WoS: 2
Citation - Scopus: 2
Hybrid Force and Motion Control of a Three-Dimensional Flexible Robot Considering Measurement Noises
(Mdpi, 2022) Kilicaslan, Sinan; Ozgoren, Mustafa Kemal; Ider, Sitki Kemal; 108608
This work addresses the end-effector trajectory-tracking force and motion control of a three-dimensional three-link robot considering measurement noises. The last two links of the manipulator are considered as structurally flexible. An absolute coordinate approach is used while obtaining the dynamic equations to avoid complex dynamic equations. In this approach, each link is modeled as if there is no connection between the links. Then, joint connections are expressed as constraint equations. After that, these constraint equations are used in dynamic equations to decrease the number of equations. Then, the resulting dynamic equations are transformed into a form which is suitable for controller design. Furthermore, the dynamic equations are divided as pseudostatic equilibrium and deviation equations. The control torques resulting from the pseudostatic equilibrium and the elastic deflections are obtained easily as the solution of algebraic equations. On the other hand, the control torques corresponding to the deviations are obtained without any linearization. Encoders, strain gauges, position sensors and force and moment sensors are required for measurements. Low pass filters are considered for the sensors. For the crossover frequencies of the sensors, low and high values are chosen to observe the filtering effect on the robot output.
Citation - WoS: 0
Citation - Scopus: 3
Integrated Force/Motion Trajectory Design of Parallel Robots for Singularity Robustness during Contact Tasks
(Budapest Tech, 2023) Ozdemir, Mustafa; İder, Sıtkı Kemal; Ider, Sitki Kemal; 108608; Makine Mühendisliği
Parallel robots have an increasing use in industrial and medical applications. Many of these applications require the execution of contact tasks. However, parallel robots possess drive singularities, which act as invisible barriers inside their workspace. In this paper, we develop an integrated force and motion trajectory planning method for removing drive singularities of parallel robots which perform contact tasks. The method is based on satisfaction of a consistency condition at the singularity, which is stated in terms of the generalized velocities, accelerations and contact forces, provided that the derivative of the associated determinant with respect to time does not simultaneously vanish. It is shown that, in the presence of singularity crossing, either the motion or the force trajectory can be arbitrarily chosen while the other is planned to satisfy the necessary conditions.
Citation - WoS: 0
Citation - Scopus: 0
Kinematic Design and Analysis of a Novel Overconstraint Walking Mechanism
(Cambridge Univ Press, 2025) Selvi, Ozgun; Cindioglu, Cagri; Ider, Sitki Kemal; Ceccarelli, Marco
Walking mechanisms offer advantages over wheels or tracks for locomotion but often require complex designs. This paper presents the kinematic design and analysis of a novel overconstrained spatial a single degree-of-freedom leg mechanism for walking robots. The mechanism is generated by combining spherical four-bar linkages into two interconnecting loops, resulting in an overconstrained design with compact scalability. Kinematic analysis is applied using recurrent unit vector methods. Dimensional synthesis is performed using the Firefly optimization algorithm to achieve a near-straight trajectory during the stance phase for efficient walking. Constraints for mobility, singularity avoidance, and transmission angle are also implemented. The optimized design solution is manufactured using 3D printing and experimentally tested. Results verify the kinematic properties including near-straight-line motion during stance. The velocity profile shows low perpendicular vibrations. Advantages of the mechanism include compact scalability allowing variable stride lengths, smooth motion from overconstraint, and simplicity of a single actuator. The proposed overconstrained topology provides an effective option for the leg design of walking robots and mechanisms.
Citation - WoS: 2
Citation - Scopus: 3
On the stability of inverse dynamics control of flexible-joint parallel manipulators in the presence of modeling error and disturbances
(Tubitak Scientific & Technological Research Council Turkey, 2019) Ider, Sitki Kemal; İder, Sıtkı Kemal; Korkmaz, Ozan; Denizli, Mustafa Semih; 108608; Makine Mühendisliği
Inverse dynamics control is considered for flexible-joint parallel manipulators in order to obtain a good trajectory tracking performance in the case of modeling error and disturbances. It is known that, in the absence of modeling error and disturbance, inverse dynamics control leads to linear fourth-order error dynamics, which is asymptotically stable if the feedback gains are chosen to make the real part of the eigenvalues of the system negative. However, when there are modeling errors and disturbances, a linear time-varying error dynamics is obtained whose stability is not assured only by keeping the real parts of the frozen-time eigenvalues of the system negative. In this paper, the stability of such systems is investigated and it is proved that the linear time-varying system can be rendered stable by selecting the feedback gains such that the variation of the system becomes sufficiently slow. To illustrate the performance of the control method, deployment motion of a 3-(R) under bar PR planar parallel manipulator subject to impact is simulated. For the impact model, the impulse-momentum and the coefficient of restitution equations for the system are derived.
Citation - WoS: 2
Citation - Scopus: 2
Parametric analysis of an anti-whiplash system composed of a seat suspension arrangement
(Springer Heidelberg, 2015) Ozdemir, Mustafa; İder, Sıtkı Kemal; Ider, Sitki Kemal; Gokler, Mustafa Ilhan; 108608; 182869; Makine Mühendisliği
Neck injuries frequently seen in low-speed rear-end collisions are referred to as whiplash injuries. Most of the proposed anti-whiplash systems in the literature rely on reducing the backset. A relatively new and promising alternative concept is a slideable seat. This study aimed to parametrically analyze an anti-whiplash vehicle seat that can slide backward against a horizontal suspension arrangement composed of a spring and a damper in response to a rear-end collision, and to investigate the effects of the suspension parameters on the injury risk. A simplified model of a slideable vehicle seat is developed, and simulations are conducted in LS-DYNA (R) environment using this slideable seat model and the commercially available finite element model of the BioRID II dummy. The maximum value of the Neck Injury Criterion (NICmax) is used as the measure of the injury risk. As a result, a strong linear inverse correlation is observed between NICmax and the maximum seat sliding distance, while the stiffness and damping coefficients of the suspension are varied. This result is also verified by obtaining the same NICmax value for the same maximum seat sliding distance (although the stiffness and damping coefficients are different). It is also shown that, for a given backset value as large as 60 mm, a slideable seat with the suspension parameters selected to yield a reasonable maximum seat sliding distance such as 100 mm significantly improves NICmax compared to a standard seat. As the maximum seat sliding distance is increased, the injury risk becomes smaller.