Levent Çetin

Modelling of an Under-Hip Prosthesis with Ankle and Knee Trajectory Control by Using Human Gait Analysis

Abstract In this paper, depending on bipedal human walking analysis, knee and ankle joint control of special under-hip prosthesis is investigated. After the designing of the prosthesis and its parts by using SolidWorks, strength analyses under various pedestal loads are given, to ensure an optimal and convenient model. Depending on measurements of hip, knee and ankle motions by using vision techniques, bipedal human gait analysis is investigated. After these measurements using the hip motion as reference, knee and ankle joint angles are derived and calculated.The calculated values are then used to control the motions of knee and ankle joints via DC-motors so that the investigated trajectories for optimal bipedal walking could be realized. A mathematical model for bipedal walking is then executed as a combination of two serial manipulators, each having two revolute joints, in other words, having two degrees of freedom. Inverse kinematics analysis and recursive Newton-Euler computation methods are given to obtain the dynamic equations, which describe the motion of the walking system. For desired walking characteristics, knee and ankle trajectories are derived. With this novel method both ankle and knee joint positions in case of upper knee amputees can be determined and controlled for various gait instants.

Electromechanical characterization of multilayer graphene-reinforced cellulose composite containing 1-ethyl-3-methylimidazolium diethylphosphonate ionic liquid

Abstract In this study, multilayer graphene (Gr)-reinforced cellulose composites were synthesized by using 1-ethyl-3-methylimidazolium diethylphosphonate ionic liquid. The composites were fabricated via dissolving the cellulose in 1-ethyl-3-methylimidazolium diethylphosphonate and Gr loading at different ratios (0.2, 0.4, and 0.6 wt.%). Both sides of the composites were coated with gold leaf to generate electrodes. The effect of Gr loading on chemical functional groups, crystallographic properties, thermal stability, and morphological and mechanical properties of cellulose film was investigated by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and tensile test, respectively. Electromechanical behavior of the cellulose composite films reinforced with Gr (0.2, 0.4, and 0.6 wt.%) was investigated under DC excitation voltages of 1, 3, 5 and 7 V. Gr loading of 0.2 wt.% increased maximum tip displacement by 400% when the actuator is excited with 3 V.

Investigation of the effects of PWM parameters on ionic polymer metal composite actuators

The effects of the PWM excitation signal parameters, such as frequency and magnitude, on the Nafion-based ionic polymer metal composite (IPMC) actuator response were found out. The first set of experiments was designed to observe the actuator response when the actuators were biased with constant DC voltages. These experimental results were exploited to build an experimental data based dynamic model. The model and these results were also used as references to evaluate the experimental results in the proceeding experiments. The second set of experiments was designed to observe the actuator response when the DC square wave signals at different frequencies (0 to 1000 Hz) were applied. The third set of experiments was designed to observe the actuator response when the PWM signals at different magnitudes (6, 8 and 10 V) were applied. It is observed that back relaxation reduces with increasing frequency, but after a certain frequency value, it remains approximately constant. It is seen that the input output relationship of the actuators are linear only for a range of PWM signal magnitudes. The observations in both the PWM frequency and the magnitude experiments indicated that the performance of the Nafion-based IPMC actuator could be improved by selecting a magnitude of PWM signals between 6–8 Volts and by selecting a frequency between 400–1000 Hz.

Design and control of a mobile manipulator with stereo vision guidance

Using vision based control, two different control types for mobile platform and manipulator is applied. Mobile platform is controlled with a hybrid visual servo controller. Its instantaneous linear velocity is controlled via position based visual servoing and its angular velocity is controlled via image based visual servoing. Manipulator motion is controlled through dynamic look and move control strategy. Control of the mobile manipulator is done by task sequencing. A task is separated into two parts: Mobile platform moves till target is placed in manipulator workspace afterwards manipulator moves to hold target. Experimental results demonstrates success of control system in autonomus positioning tasks.

Navigation and GPS based path control of an autonomous vehicle

In this work the navigation and GPS based trajectory control of an unmanned autonomous vehicle is introduced. The caterpillar tread like mobile vehicle with duo cycle drive is equipped with a mobile GPS and micro controller. To get accurate position data, a DGPS (Differential GPS) with a local base station is used. In order to let the vehicle to follow a desired trajectory, a reference path is given by using Way Points as GPS datas to micro controller, which provide the position and orientation control of the vehicle. The instant position and orientation of the vehicle in accordance to an assigned plane coordinate frame are calculated by micro controller from detected latitude and longitude values (land coordinates) of mobile GPS, which receive corrected on line datas from base station.The duo cycle vehicle is driven with geared DC motors, which are equipped with chained caterpillar tread drives, so that it can have better motion, clambering and tracking performances. Successful navigation and path following results are obtained with several experiments by various control applications.

Relative Localization of Wireless Sensor Nodes by Using the RSSI Data

Wireless sensor network is an emerging research field and a crucial infrastructure for Internet of Things (IoT) applications. Sensor nodes of a wireless network may connect via different wireless technologies like Wi-Fi, Bluetooth, ZigBee or WiMAX. In many applications, like field monitoring or smart buildings, the location of the nodes with respect to a global or relative coordinate system is essential information. The main focus of this work is the localization of wireless sensor nodes, using the Received Signal Strength Indicator (RSSI) metric of the wireless telecommunication infrastructure. We present both simulation and measurement results of the proposed method and compare the results with similar work.

Characterization and analysis of motion mechanism of electroactive chitosan-based actuator

In order to analyze the bending mechanism of the electroactive​ chitosan-based actuator, different amounts of poly(diallyldimethylammonium chloride) (PDAD) were incorporated in chitosan solution. The effects of PDAD concentration on electromechanical performance of chitosan actuator were investigated under various excitation voltages. With the incorporation of PDAD into chitosan solution, crosslinked chitosan film acts as an actuator showing a considerable displacement behavior. However it can be noted that higher incorporation of PDAD into chitosan solution decreased the performance of the actuators. Thermal, viscoelastic, and crystallographic properties of the chitosan films were examined by thermogravimetric analysis, dynamic mechanical analysis, and X-ray diffraction analysis, respectively. The effect of incorporation of PDAD in chitosan-based film on morphological properties of chitosan film was determined by scanning electron microscopy. It was observed that the films involving PDAD have larger pore size than the PDAD free film.

Indoor Localization for Swarm Robotics with Communication Metrics Without Initial Position Information

Swarm robotics is an emerging research field with many scientific and commercial application areas. Swarm robotic systems are composed of simple robots cooperatively accomplishing the given task. The cooperation and the organization of the robots require the location information of the robots; so that each robot will be able to achieve the task it is responsible. The main of this work is an indoor positioning for swarm robotic applications using standard metrics for Bluetooth or Wi Fi communication infrastructures. The main work includes fusion of several position estimation methods by setting a proper weight to each method; this paper presents the work on estimating the location by using TDoA and RSSI parameters.

Ferrofluid Plug Actuation for Micro Pumping Systems

Ferrofluids are colloidal mixtures which consist of nanosized magnetic particles suspended in a base fluid. The typical magnetic particles could be maghemite, magnetite or cobalt ferrite etc. To keep a ferrofluid suspension in a stable state is possible by an electrical double layer or by adding surfactant. They have many applications on electrical, mechanical and optical systems. Recently, the ability of being manipulated by an external magnetic field made them considerable for microfluidic systems such as micro operations, pumping and mixing. Among them, micro scaled pumping systems have appeared as a critical research area due to its notable potential to be applied on many biological and electronic systems. Moreover, the development of lab on a chip and the micro total analysis systems for biological issues has revealed the necessity of liquid transport for micro quantities. Micropumps with ferrofluid plug actuation mechanisms are considered to have the ability to fulfill this requirement. Therefore, driving the working fluids with ferrofluid plugs in a micro-sized tube or channel has attracted researchers’ interest. In this study, ferrofluid plug actuated micro pumping systems have been reviewed from the available literature based on their design and their maximum generated flow rate.

Effect of the Coil Shape on Magnetic Field of an Electromagnet for Contactless Power Transmission to Microrobots

This paper proposes a comparative study in order to investigate the effect of the coil geometry on the intensity and homogeneity of the magnetic field. For this purpose, a solenoid with rectangular prism core and two different coil shapes, cylindrical and cuboid, was modeled. Several finite element numerical studies at different structural design parameters combinations for two different distances between the coils were carried out. The obtained results were evaluated according to the flux intensity and the homogeneity at the center region between the coils. Consequently, it was found that cylindrical coils generate higher flux intensity with more homogeneous magnetic field.