Mühendislik Fakültesi

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Citation Count: Özdemir, M., İder, S.K. (2016). A switching inverse dynamics controller for parallel manipulators around drive singular configurations. Turkish Journal Of Electrical Engineering And Computer Sciences, 24(5), 4267-4283. http://dx.doi.org/10.3906/elk-1502-50
A switching inverse dynamics controller for parallel manipulators around drive singular configurations
(TUBİTAK Scientific&Technical Research Council Turkey, 2016) Özdemir, Mustafa; İder, Sıtkı Kemal; 108608
Despite many advantages, parallel manipulators are known to possess drive singularities where the control of one or more degrees of freedom is lost. Around these singular configurations, the required actuator forces grow unbounded. Previous efforts in the literature put forward singularity-consistent trajectory planning and singularity robust modification of the dynamic equations as a solution to this problem. However, this previous method is applicable only for the open-loop operation of the manipulator, whereas initial configuration errors, external disturbances, and modeling errors should necessarily be taken into account in a closed-loop sense in real-life applications. With this aim, a switching inverse dynamics controller is proposed in this study for the trajectory tracking control of parallel manipulators as they pass through drive singular configurations. Simulations of the application of the developed controller result in good tracking performance, even in the presence of modeling errors, while the actuator efforts remain bounded and continuous in the neighborhood of the singularity
Citation Count: Özdemir, Mustafa; İder, Sıtkı Kemal (2021). "Desingularization of Flexible-Joint Parallel Robots", Acta Polytechnica Hungarica, Vol. 18, No.6, pp. 85-106.
Desingularization of Flexible-Joint Parallel Robots
(2021) Özdemir, Mustafa; İder, Sıtkı Kemal; 108608
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 Count: Çiçek, Burak Can; Acar, Bülent; İder, Sıtkı Kemal (2021). "Dynamic analysis and design optimisation of a heavy military vehicle", International Journal of Heavy Vehicle Systems, Vol. 28, No. 3, pp. 309-328.
Dynamic analysis and design optimisation of a heavy military vehicle
(2021) Çiçek, Burak Can; Acar, Bülent; İder, Sıtkı Kemal; 108608
This paper investigates the dynamic response of a heavy military vehicle which is subjected to a dynamic firing load while it is settled on its outriggers. Dynamic behaviour of a settled heavy military vehicle under a dynamic firing load is one of the major design factors of a launching vehicle. Two different finite element (FE) models are created in ANSYS software to obtain the dynamic behaviour of the launching vehicle. The first model is a detailed finite element model (DFEM) and the second model is a simple and less degree of freedom (DOF) parametric FE model which is created with the ANSYS Parametric Design Language (APDL) in order to perform the design optimisation by swiftly varying the parameters such as clamp attachment positions on the chassis, outrigger deployment and outrigger case cross section.
Citation Count: Özdemir, M., İder, S.K., Gökler, M.İ. (2016). Experimental and numerical investigation of comparability of whiplash sled test results. Journal Of The Brazilian Society Of Mechanical Sciences And Engineering, 38(2), 395-402. http://dx.doi.org/10.1007/s40430-015-0407-4
Experimental and numerical investigation of comparability of whiplash sled test results
(Springer Heidelberg, 2016) Özdemir, Mustafa; İder, Sıtkı Kemal; Gökler, Mustafa İlhan; 108608; 182869
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 Count: Kilicaslan, Sinan; Özgören, Mustafa Kemal; Ider, Sıtkı Kemal. (2022). Hybrid Force and Motion Control of a Three-Dimensional Flexible Robot Considering Measurement Noises", Machines, Vol.10, No.7.
Hybrid Force and Motion Control of a Three-Dimensional Flexible Robot Considering Measurement Noises
(2022) Kilicaslan, Sinan; Özgören, Mustafa Kemal; Ider, Sıtkı 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 Count: Korkmaz, O., İder, S.K. (2014). Hybrid force and motion control of flexible joint parallel manipulators using inverse dynamics approach. Advanced Robotics, 28(18), 1221-1230. http://dx.doi.org/10.1080/01691864.2014.920719
Hybrid force and motion control of flexible joint parallel manipulators using inverse dynamics approach
(Taylor&Francis Ltd, 2014) Korkmaz, Ozan; İder, Sıtkı Kemal; 108608
An inverse dynamics control algorithm is developed for hybrid motion and contact force trajectory tracking control of flexible joint parallel manipulators. First, an open-tree structure is considered by the disconnection of adequate number of unactuated joints. The loop closure constraint equations are then included. Elimination of the joint reaction forces and the other intermediate variables yield a fourth-order relation between the actuator torques and the end-effector position and contact force variables, showing that the control torques do not have an instantaneous effect on the end-effector contact forces and accelerations because of the flexibility. The proposed control law provides simultaneous and asymptotically stable control of the end-effector contact forces and the motion along the constraint surfaces by utilizing the feedback of positions and velocities of the actuated joints and rotors. A two degree of freedom planar parallel manipulator is considered as an example to illustrate the effectiveness of the method
Citation Count: Özdemir, M.; İder, S.K. (2023). "Integrated Force/Motion Trajectory Design of Parallel Robots for Singularity Robustness during Contact Tasks", Acta Polytechnica Hungarica, Vol.20, No.2, pp.41-61.
Integrated Force/Motion Trajectory Design of Parallel Robots for Singularity Robustness during Contact Tasks
(2023) Özdemir, Mustafa; İder, Sıtkı Kemal; 108608
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 Count: Kılıçaslan, Sinan; İder, S. Kemal; Özgören, M. Kemal (2021). "Motion Control of a Spatial Elastic Manipulator in the Presence of Measurement Noises", ARABIAN JOURNAL FOR SCIENCE AND ENGINEERING, Vol. 46, No. 12, pp. 12331-12354.
Motion Control of a Spatial Elastic Manipulator in the Presence of Measurement Noises
(2021) Kılıçaslan, Sinan; İder, S. Kemal; Özgören, M. Kemal; 108608
This paper presents a method for the end effector motion control of a spatial three-link robot having elastic second and third links including measurement noises. In the derivation of equations of motion, not to face with complex equations of motion, each link is modeled as though the links are not connected and the restrictions on the links due to connecting them by joints are written as constraint equations. After that the Lagrange multipliers are eliminated and the constraint equations at the acceleration level are substituted into the equations of motion to reduce the number of equations. To handle the non-minimum phase property, the equations of motion of the elastic manipulator are divided as the equations corresponding to a pseudostatic equilibrium and the equations of the deviations from them. Definition of the pseudostatic equilibrium used in this study can be given as a hypothetical state in which the end effector velocity and the end effector acceleration possess their reference values while the elastic deflections are instantly constant. The advantages of this control method are that the elastic deflections and the control inputs required for the pseudostatic equilibrium are obtained by an algebraic method and the feedback stabilization control inputs for the deviation equations are determined without linearizing the dynamic equations. The required measurements are obtained from the strain gauges on the links, the encoders placed on the joints and the position sensors attached to the end effector. For each sensor, a low pass filter is used. Simulations are made with low and high values of crossover frequencies to show the positive and negative effects of filtering on the responses of the system.
Citation Count: Ider, Sitki Kemal; Korkmaz, Ozan; Denizli, Mustafa Semih, "On the stability of inverse dynamics control of flexible-joint parallel manipulators in the presence of modeling error and disturbances", Turkish Journal of Electrical Engineering and Computer Sciences, Vol. 27, No. 1, pp. 649-662, (2019).
On the stability of inverse dynamics control of flexible-joint parallel manipulators in the presence of modeling error and disturbances
(Tubitak Scientific & Technical Research Council Turkey, 2019) İder, Sıtkı Kemal; Korkmaz, Ozan; Denizli, Mustafa Semih; 108608
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 Count: Özdemir, M., İder, S.K., Gökler, M.İ. (2015). Parametric analysis of an anti-whiplash system composed of a seat suspension arrangement. Journal Of The Brazilian Society Of Mechanical Sciences And Engineering, 37(2), 777-784. http://dx.doi.org/10.1007/s40430-014-0192-5
Parametric analysis of an anti-whiplash system composed of a seat suspension arrangement
(Springer Heidelberg, 2015) Özdemir, Mustafa; İder, Sıtkı Kemal; Gökler, Mustafa İlhan; 108608; 182869
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.
Citation Count: Korkmaz, O., İder, S.K., Özgçren, M.K. (2016). Trajectory tracking control of an underactuated underwater vehicle redundant manipulator system. Asian Journal Of Control, 18(5), 1593-1607. http://dx.doi.org/10.1002/asjc.1291
Trajectory tracking control of an underactuated underwater vehicle redundant manipulator system
(Wiley-Blackwell, 2016) Korkmaz, Ozan; İder, Sıtkı Kemal; Özgören, M. Kemal; 108608; 7866
The purpose of this study is to control the position of an underactuated underwater vehicle manipulator system (U-UVMS). It is possible to control the end-effector using a regular 6-DOF manipulator despite the undesired displacements of the underactuated vehicle within a certain range. However, in this study an 8-DOF redundant manipulator is used in order to increase the positioning accuracy of the end-effector. The redundancy is resolved according to the criterion of minimal vehicle and joint motions. The underactuated underwater vehicle redundant manipulator system is modeled including the hydrodynamic forces for the manipulator in addition to those for the autonomous underwater vehicle (AUV). The shadowing effects of the bodies on each other are also taken into account when computing the hydrodynamic forces. The Newton-Euler formulation is used to derive the system equations of motion including the thruster dynamics. In order to establish the endeffector trajectory tracking control of the system, an inverse dynamics control law is formulated. The effectiveness of the control law even in the presence of parameter uncertainties and disturbing ocean currents is illustrated by simulations.

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