Abdullah Özer

Analytical, numerical and experimental investigation of a giant magnetostrictive (GM) force sensor

Purpose – This paper aims to investigate a novel giant magnetostrictive (GM) force sensor using Terfenol-D rod. Design/methodology/approach – First of all, principle of GM force sensor based on positive magnetostriction of Terfenol-D is presented. Then, design procedure of the GM force sensor is stated. Magnetic properties such as B-H curve and permeability of Terfenol-D are measured by a novel experimental setup and the results are used in analytical model, sensitivity estimation and numerical simulations. Then, an analytical model is presented and a numerical simulation using CST Studio Suite 2011 software is done. So as a result of numerical simulations, optimum geometry of the GM force sensor is obtained related to the condition in which the GM force sensor has highest sensitivity. After that, the sensor is fabricated using the simulation results and is tested by means of an experimental setup. Characteristic curve of the GM force sensor in several conditions is measured and the optimum operational co...

A novel design for lower extremity gait rehabilitation exoskeleton inspired by biomechanics

The use of robotic assistive devices and exoskeletons to supply movement therapy for the rehabilitation of patients following variety of diseases is noticeably growing presently. In order to provide consistent therapy as well as walking assistance, we are developing a wearable lower-limb exoskeleton robot with an adaptive foot device for better walking ability and enhanced stability. In this paper, we focus on the mechanical design of an active knee orthosis. The proposed kinematic design is inspired by the knee biomechanics. Therefore, it is expected that the proposed configuration will help to provide more natural gait during theraphy sessions of patients or in daily use as a sophisticated system. It is based on efficiently controlling the knee motions with hybrid actuations. The two actuators will be implemented with the proposed design; one as hamstring and the other as quadriceps. It is anticipated that the new system will offer an enhanced walking capacity for the patients.

Effective vibration suppression of a maneuvering two-link flexible arm via an event-based stiffness controller

Vibration control of a maneuvering flexible robotic arm is a challenging task in the presence of changing structural dynamics which has to deal with measurement inaccuracies and complex modeling efforts. This paper presents an effective and versatile controller for a maneuvering flexible arm. Proposed Variable Stiffness Control (VSC) is stable, due to its being dissipative in nature. The technique is suitable to be implemented as an add-on controller to existing robots, and it requires no additional hardware. Control is based on the detection of a kinematic event, peak relative displacement, rather than an accurate knowledge of structural dynamics. Hence, although there may not be a claim for the suggested control to be the most effective, it certainly represents significant practical advantages for cases where there may be structural uncertainties.

A novel dynamic walker with heel, ankle, and toe rocker motions

This paper proposes a novel dynamic walker capable of walking with heel, ankle, and toe rocker motions. The heel and toe rocker motions are obtained by using inelastic stoppers between leg and foot, which limit the range of rotation of the foot about the ankle joint. A generalized set of equations of motion and associated transition equations applicable for multiple foot segments is derived. Passive dynamic walking is studied with equal heel and toe strike angles for the case of symmetric foot walking. It is shown that by including the ankle joint, low-speed walking is made possible. The energy efficiency of the proposed walker is studied theoretically and through numerical simulations. Finally, three different underactuated modes of active walking that do not require toe and heel actuation are presented. In order to implement these modes of walking, the proposed walker can be constructed with little modification from an existing flat-foot walker that uses ankle rocker motion alone. Results show that substantial benefits can be obtained in efficiency and stability compared to point/flat-foot walker of the same leg length and mass distribution.

Design and Experimental Implementation of a Beam-Type Twin Dynamic Vibration Absorber for a Cantilevered Flexible Structure Carrying an Unbalanced Rotor: Numerical and Experimental Observations

This paper presents experimental and numerical results about the effectiveness of a beam-type twin dynamic vibration absorber for a cantilevered flexible structure carrying an unbalanced rotor. An experimental laboratory prototype setup has been built and implemented in our laboratory and numerical investigations have been performed through finite element analysis. The proposed system design consists of a primary cantilevered flexible structure with an attached dual-mass cantilevered secondary dynamic vibration absorber arrangement. In addition, an unbalanced rotor system is attached to the tip of the flexible cantilevered structure to inspect the system response under harmonic excitations. Numerical findings and experimental observations have revealed that significant vibration reductions are possible with the proposed dual-mass, cantilevered dynamic vibration absorber on a flexible cantilevered platform carrying an unbalanced rotor system at its tip. The proposed system is efficient and it can be practically tuned for variety of design and operating conditions. The designed setup and the results in this paper can serve for practicing engineers, researchers and can be used for educational purposes.

A Bio-Robotic Toe & Foot & Heel Models of a Biped Robot for More Natural Walking: Foot Mechanism & Gait Pattern

Humans possess a complex physical structure and can perform difficult movement tasks. Over the past few decades, many researchers around the world have concentrated on achieving human-like artificial mobility or dexterity either on humanoid robots or during the implementation of robotic assistive devices. In particular, humanoid-type robots mainly focused on hands to understand the mechanical and dynamical functions of ourselves. On the other hand, there have been few researches to achieve human like foot. Until now, human-like skillful mobility has not been achieved on humanoid robots, since the robotic feet are far from adaptation to keep stable contact on the ground and the current kinematic structures of a humanoid foot is different from that of a real human foot. Stability related issues have been the main goal for humanoid robots in relevant researches. Initially, humanoid robots were built so that they can walk stably with flat foot (Sakagani et al., 2002; Okada et al., 2004 ). These initial walking patterns were optimized for the highest stability, and the resulting walking pattern had knee bending and flat-feet walking. A more advanced strategy was developed for generating biped walking pattern involving heel strike and toe off motion in (Huang et al., 2001). However, because of the mechanism’s limitation the knee bending walking patterns were always chosen for the benefit of stability, thus making it less natural. Today, more advanced control approaches, faster and more powerful actuators, and more sophisticated walking pattern generation strategies have helped the research goal to be shifted to pursue more natural walking patterns for biped robots, with the expectation that someday humanoid robot can coexist with human. To improve walking capacity of humanoid-type robots, toe mechanisms with 1-dof was suggested earlier, (Ahn et al., 2003; Takahashi et al., 2004). For walking in a straight direction, 1-dof toe mechanism can supply faster walking for a robot. In addition, relative toe motion can increase the naturalness of robot walking and help to reduce the load on the knee joints, where high force and speed are required to achieve robot locomotion (Nishiwaki & Kagami, 2002). However, the foot device with 1-dof toe mechanism cannot

Elimination of thermal instability in precise positioning of Galfenol actuators

This paper presents a new method to eliminate deviation in positioning caused by coil’s heat generation in magnetostrictive actuators. The advantages of the proposed system are compactness, high controllability and high reliability. The actuator package consists of Galfenol as active element and a magnification mechanism combined with a Peltier element or thermoelectric cooler (TEC). By using the temperature sensor, a thermoelectric cooler (TEC) is activated to reduce the temperature of the coil. However, the reduction of temperature by TEC alone is not enough to eliminate the error and controlling of applied voltage is also required. A simple PI controller for coil’s current is combined with TEC and by reducing the temperature and current simultaneously, the positioning error is vanished completely.

Model identification of terfenol-D magnetostrictive actuator for precise positioning control

Feedback control strategies are desirable for disturbance rejection of human-induced vibrations in civil engineering structures as human walking forces cannot easily be measured. In relation to human-induced vibration control studies, most past researches have focused on floors and footbridges and the widely used linear controller implemented in the trials has been the direct velocity feedback (DVF) scheme. With appropriate compensation to enhance its robustness, it has been shown to be effective at damping out the problematic modes of vibration of the structures in which the active vibration control systems have been implemented. The work presented here introduces a disturbance observer (DOB) that is used with an outer-loop DVF controller. Results of analytical studies presented in this work based on the dynamic properties of a walkway bridge structure demonstrate the potential of this approach for enhancing the vibration mitigation performance offered by a purely DVF controller. For example, estimates of controlled frequency response functions indicate improved attenuation of vibration around the dominant frequency of the walkway bridge structure as well as at higher resonant frequencies. Controlled responses from three synthesized walking excitation forces on a walkway bridge structure model show that the inclusion of the disturbance observer with an outer loop DVF has potential to improve on the vibration mitigation performance by about 3.5% at resonance and 6-10% off-resonance. These are realised with hard constraints being imposed on the low frequency actuator displacements.

Design, sensitivity analysis and fabrication of DC Linear Direct-Drive Motor (LDDM)

This paper presents a new analytical model for both magnetic flux density and thrust force in a DC tubular Linear Direct-Drive Motor (LDDM). Two-dimensional finite element method (FEM) is used for numerical analysis. Magnetic flux density and thrust force computed numerically shows a good agreement with the values resulted from proposed analytical model. This research, investigates the effect of some geometrical dimensions of LDDM. The sensitivity analysis of parameters highlights the influence of air gap, permanent magnet radius, coils length of phases and thickness of back-iron. It is found that lower air gap and thinner back-iron cause higher ratio of maximum thrust force to movers mass. Furthermore, the optimum value for coils length is also presented. The general shape of thrust force is also confirmed by experimental results.