Nizami Aktürk

An Investigation of Rolling Element Vibrations Caused by Local Defects

In this paper, a shaft-bearing model is developed in order to investigate the rolling element vibrations for an angular contact ball bearing with and without defects. The shaft-bearing assembly is considered as a mass-spring system. The system shows a nonlinear characteristic under dynamic conditions. The equations of motion in radial and axial directions were obtained for shaft and rolling elements, and they were solved simultaneously with a computer simulation program. Additionally, the effect of localized defects on running surfaces (i.e., inner ring, outer ring, and ball) on the vibration of the balls is investigated. Vibration of rolling elements in the radial direction is analyzed in time and freguency domains. Characteristic defect frequencies and their components can be seen in the frequency spectra of rolling element vibrations. Comparison of the obtained results with similar studies available in literature showed reasonable qualitative agreement.

Three-finger SMA robot hand and its practical analysis

Gripping of different types of objects with a multi-finger robot hand is a vital task for robot arms. Grippers, which are end effector elements in robot applications, are employed in various industrial operations such as transferring, assembling, welding and painting. However, if a gripper is considered for handling different jobs or to carry different types of parts in an assembly line, a general-purpose robot hand is going to be required. There are various technological actuators of robot hands such as electrical, hydraulic and pneumatic motors, etc. Besides these conventional actuators, it is possible to include Shape Memory Alloys (SMA) in the category of technological actuators. The SMA can give materials motion by moving to a predetermined position, at a specific temperature. The conversion of this motion to a gripping action of the robot hand is the heart of the matter. In this study, a robot hand is developed using Ni-Ti SMA and a set of experiments were performed in order to check the compatibility of the system in an industrial environment.

Vibrations of a grinding spindle supported by angular contact ball bearings

In the current paper, the radial, axial, rocking, and yawing vibrations of a rigid grinding spindle supported by a pair of angular contact ball bearings are studied. A computer program was developed to simulate the dynamic behaviour of the spindle and results are presented in the time, frequency, and waterfall diagrams. Results from the simulations for different spindle speeds show the characteristic ball passage frequency (BPF) (varying compliance) and its harmonics due to non-linear Hertzian contact between the balls and the races for even a defect free bearing. This behaviour is, of course, predicted theoretically, but most of the previous simulations only give the effect of BPF when it coincides with the natural frequencies of the system or under specific conditions. This paper will be a guide for researchers studying vibrations of a spindle supported by ball bearings as it describes the details of the theoretical background of the modelling and simulation.

Damping the Vibrations of a Rigid Shaft Supported by Ball Bearings by Means of External Elastomeric O-ring Dampers

In this paper the radial and axial vibration behaviour of a rigid shaft supported by a pair of back-to-back angular contact ball bearings, mounted on elastomeric O-ring dampers, is studied. The use of elastomeric dampers for reducing the untoward effects of vibrations, due to unbalance of the shaft centre, is investigated. A computer program was developed to simulate such situations with the results presented in the form of frequency response curves and shaft centre orbits. All results showed that elastomeric O-ring dampers can successfully be used for shaft-ball bearing systems as long as the dynamic characteristics of both the system and the elastomeric O-rings are known very well.

Effect of powder metallurgy Cu-B4C electrodes on workpiece surface characteristics and machining performance of electric discharge machining

The main aim of this study is to produce new powder metallurgy (PM) Cu-B4C composite electrode (PM/(Cu-B4C)) capable of alloying the recast workpiece surface layer during electric discharge machining process with boron and other hard intermetallic phases, which eventually yield high hardness and abrasive wear resistance. The surface characteristics of the workpiece machined with a PM/(Cu-B4C) electrode consisted of 20 wt% B4C powders were compared with those of solid electrolytic copper (E/Cu) and powder metallurgy pure copper (PM/Cu) electrodes. The workpiece surface hardness, surface abrasive wear resistance, depth of the alloyed surface layer and composition of alloyed layers were used as key parameters in the comparison. The workpiece materials, which were machined with PM/(Cu-B4C) electrodes, exhibited significantly higher hardness and abrasive wear resistance than those of machined with the E/Cu and PM/Cu. The main reason was the presence of hard intermetallic phases, such as FeB, B4C (formed due to the boron in the electrode) and Fe3C in the surface layer. The improvement of the surface hardness achieved for steel workpiece when using PM/(Cu-B4C) electrodes was significantly higher than that reported in the literature. Moreover, the machining performance outputs (workpiece material removal rate, electrode wear rate and workpiece average surface roughness (Ra)) of the electrodes were also considered in this study.

Non-Stationary response of a vehicle obtained from a series of stationary responses

Ride characteristics of a vehicle moving on a rough ground with changing travel velocity are analyzed in this paper. The solution is difficult due to the non-stationary characteristics of the problem. Hence a new technique has been proposed to overcome this difficulty. This new technique is employed in the analysis of ride characteristics of a vehicle with changing velocity in the time/frequency domain. It is found that the proposed technique gives successful results in modelling non-stationary responses in terms of a series of stationary responses.

BİLYALI RULMAN HASARLARININ TİTREŞİM ANALİZİ YÖNTEMİYLE İNCELENMESİ

Bu calismada, titresim yontemi kullanilarak radyal bilyali rulmanlardaki bolgesel yuzey kusurlari deneysel olarak incelenmistir. Bu amacla bilyali rulman elemanlari (ic bilezik ve dis bilezik) calisma yuzeylerinde yapay bolgesel kusurlar olusturulmus ve radyal yondeki mil titresimleri kaydedilmistir. Sistem icin teorik bir model olusturulmus ve bu modele gore saglam ve kusurlu rulmanlari analiz edebilen bir simulasyon programi gelistirilmistir. Bu simulasyon programi, deney setinde kullanilan mil ve rulman boyutlari girilerek calistirilmis ve farkli mil hizlari icin milin titresim spektrumlari elde edilmistir. Simulasyon programindan elde edilen teorik sonuclarla deneysel sonuclar karsilastirildiginda goreceli olarak bir uyum gozlemlenmistir.

AKTARMA ORGANI DİŞLİLERİNDE OLUŞAN FİZİKSEL HATALARIN TİTREŞİM ANALİZİ İLE BELİRLENMESİ

Disliler hareket veya guc iletimini saglayan onemli makina elemanlarindandir. Bir makinada bir elemandan digerine hareket iletiminin kesintisiz ve saglikli olmasi yapilan isin hassasiyet ve kalitesine etki etmektedir. Bu yuzden ozellikle surekli uretim sistemlerinde kullanilan dislilerde olusan hatalarin belirlenmesi ve tamiratinin uretimi etkilemeyecek sekilde yapilmasi onem kazanmaktadir. Bu calismada dislilerde olusan hatalarin neden oldugu titresimlerin analizi ile uygulanan erken uyarici bakim konusunda ozet bilgi verilmis ve bir kompresor disli kutusunda yapilan uygulama calismasinin sonuclari sunulmustur. Titresimlerin disli kutusu hatalarini belirlemede etkili bir arac oldugu belirlenmistir.

GERÇEK YOL GİRDİSİNE MARUZ İKİ SERBESTLİK DERECELİ ÇEYREK TAŞIT MODELİNİN SÜRÜŞ KARAKTERİSTİĞİNİN İNCELENMESİ

Bu makalede duzgun olmayan bir yolda hizi degiserek seyahat eden bir tasitin surus karakteristigi analiz edilmistir. Problemin duragan olmayan yapisindan kaynaklanan cozum zorlugunu asmak icin yeni bir yontem gelistirilmis ve bu yontemle hizi degisen bir tasitin surus karakteristigi zaman/frekans bolgesinde analiz edilmistir. Kullanilan bu yeni teknigin duragan olmayan sureclerin bir seri duragan cevaptan elde edilmesinde basarili bir sekilde uygulanabilecegi iki serbestlik dereceli bir ceyrek tasit modeli kullanilarak gosterilmistir.