This thesis studies in detail the dynamics of ball screw feed drives and expands understanding of the factors that impose limitations on their performance. This knowledge is then used for developing control strategies that provide adequate command following and disturbance rejection. High performance control strategies proposed in this thesis are designed for, and implemented on, a custom-made ball screw drive. A hybrid Finite Element (FE) model for the ball screw drive is developed and coded in Matlab programming language. This FE model is employed for prediction of natural frequencies, mode shapes, and Frequency Response Functions (FRFs) of the ball screw setup. The accuracy of FRFs predicted for the ball screw mechanism alone is validated against the experimental measurements obtained through impact hammer testing. Next, the FE model for the entire test setup is validated. The dynamic characteristics of the actuator current controller are also modeled. In addition, the modal parameters of the mechanical structure are extracted from measured FRFs, which include the effects of current loop dynamics. To ensure adequate command following and disturbance rejection, three motion controllers with active vibration damping capability are developed. The first is based on the sensor averaging concept which facilitates position control of the rigid body dynamics. Active damping is added to suppress vibrations. To achieve satisfactory steady state response, integral action over the tracking error is included. The stability analysis and tuning procedure for this controller is presented together with experimental results that prove the effectiveness of this method in high-speed tracking and cutting applications. The second design uses the pole placement technique to move the real component of two of the oscillatory poles further to the left along the real axis. This yields a faster rigid body response with less vibration. However, the time delay from the current loop dynamics imposes a limitation on how much the poles can be shifted to the left without jeopardizing the system???s stability. To overcome this issue, a lead filter is designed to recover the system phase at the crossover frequency. When designing the Pole Placement Controller (PPC) and the lead filter concurrently, the objective is to minimize the load side disturbance response against the disturbances. This controller is also tested in high-speed tracking and cutting experiments. The third control method is developed around the idea of using the pole placement technique for active damping of not only the first mode of vibration, but also the second and third modes as well. A Kalman filter is designed to estimate a state vector for the system, from the control input and the position measurements obtained from the rotary and linear encoders. The state estimates are then fed back to the PPC controller. Although for this control design, promising results in terms of disturbance rejection are obtained in simulations, the Nyquist stability analysis shows that the closed loop system has poor stability margins. To improve the stability margins, the McFarlane-Glover robustness optimization method is attempted, and as a result, the stability margins are improved, but at the cost of degraded performance. The practical implementation of the third controller, was, unfortunately, not successful. This thesis concludes by addressing the problem of harmonic disturbance rejection in ball screw drives. It is shown that for cases where a ball screw drive is subject to high-frequency disturbances, the dynamic positioning accuracy of the ball screw drive can be improved significantly by adopting an additional control scheme known as Adaptive Feedforward Cancellation (AFC). Details of parameter tuning and stability analysis for AFC are presented. At the end, successful implementation and effectiveness of AFC is demonstrated in applications involving time periodic or space periodic disturbances. The conclusions drawn about the effectiveness of the AFC are based on results obtained from the high-speed tracking and end-milling experiments.

This thesis aims to develop a comprehensive usable engineering design approach to the fatigue analysis of threaded connections. Although primarily concerned with the fatigue-fracture mechanics behaviour of screw threads, a broad review of stress analysis investigations in such connections is reported. Connection types, their functions and standardisation authorities are presented with the purpose of familiarising the reader with the subject and the options available to the design of threaded fasteners. Fatigue crack initiation is discussed with reference to the specific setting of a critical thread root. A crack initiation model is adapted for employment in thread root design. A novel weight function approach is developed for use in the determination of stress intensity factors for threaded connections. A generic solution is proposed valid for the fatigue crack growth from any thread root under any symmetrical stress system. Its development and discussion is examined in detail, remaining close to its proposed application. Two engineering situations where the chief structural components are comprised of threaded members are taken as case studies. The background to each situation is elaborated in detail and full-scale fatigue tests were conducted on the critical components. In all, fourteen full-scale tests under constant and variable amplitude loading are reported. The results of these are analysed and used to validate the fatigue crack initiation and propagation models. Useful observations which are helpful to understanding the fracture mechanisms operating during the fatigue of threaded connections are reported. Material and environmental considerations are examined and a survey of relevant materials and their behaviour in environments associated with threaded fasteners is presented. The merits or otherwise of some common engineering practices are discussed with regard to fatigue. A method has been developed for predicting fatigue life in large threaded connections under random loading. Experimental results have been gathered on two types of components used on certain oil rigs, tether joints and drill strings. The agreement found between prediction and experiment is appreciably better than by previous methods of analysis and also points to aspects open to further improvement.

Diploma thesis is focused on desing of the screw press, which is used for laboratory testing of materials by ECAP. Thesis included design of individual scructural groups and their destcription, including the creating of 3D model.

Solvent-free extrusion emulsification (SFEE) is new top-down technique specially suited to high viscosity polymers (100-1000 Pa.s) for producing sub-micron (100-500 nm) particles inside a twin screw extruder (TSE) without the use of hazardous solvents. SFEE has been difficult to implement in industry due to process sensitivities and a lack of mechanistic knowledge on how the polymer-water morphology must develop prior to inversion. To devise a mechanistic explanation of the critical stages of the process, an inline orifice-plate type viscometer was developed to monitor rheological changes previously witnessed in early batch studies. The general variables of study throughout the thesis included the manner by which sodium hydroxide (NaOH) can be added as well as the NaOH content necessary, resin-to-water (R/W) ratio, and surfactant content. The last study in the thesis explores the influence of matrix viscosity, which was accomplished by crosslinking the polyester. The striated lamellae morphology of the polyester-water system, critically controlling the final particle size, depended on two factors, specifically surface energy (determined by endgroup conversion and added surfactant) and matrix viscosity. Analysis of the rheological response indicated that a higher polar surface energy contribution had the greatest influence on the morphological state, demonstrating a steeper viscosity transition due to more favourable and more rapid incorporation of water within the polyester matrix. A strong correlation was repeatedly found between particle size and this viscosity transition, which has been related to the thickness of striated lamellae through a theory of lamellae coarsening (or thinning as is more relevant to the current process). The reported lamellae coarsening model in the literature, which shows the predominant effects of interfacial energy and viscosity on lamellae thickness in a mixed phase system showed excellent correspondence to the results in this thesis. Among the variables of study in this thesis, the dissolution of the sodium hydroxide species (when added as a solid particle) and the kinetics of end-groups conversion proved to be rate-limiting phenomena to generating thinner striated lamellae. The ionic strength of the system was notably important to the viscosity change occurring in the process as water was added for the first time and subsequently influenced the particle size produced, particularly when additional surfactant was not added and the system relied exclusively on the carboxylate endgroups present. Finally, with mounting evidence that SFEE showed significant sensitivity to the matrix viscosity, a final study examined the effectiveness of SFEE in the face of ever increasing viscous force by blending a crosslinked polyester into the neat resin at different weight fractions. With higher viscosity there was a corresponding decrease in interfacial area growth between the polyester and water, resulting in increased particle size but even with a viscosity near 800 Pa.s, far above a traditional oil-in-water system, it was still found possible in this study to create nano-sized particles by SFEE. / Thesis / Doctor of Philosophy (PhD)

Fracture to the neck of femur is frequently stabilised with a hip screw system, however the host bone is often weak or osteoporotic. This causes premature failure of the system, commonly by cut-out of the lag screw through the head of the femur. While augmentation of the fixation with bone cement improves the holding power and decreases failure rate, current methods of administering the cement are messy and inaccurate. This project proposes a lag screw design which allows for direct injection of the cement, via the lag screw itself, after the screw has been inserted and correctly positioned in the femur. A method is also suggested to reduce the risk of cement leakage into the joint space when the guide wire has punctured the head of the femur. The design uses a system of holes in the threaded section of a cannulated screw to allow delivery of cement to the desired area; the modified screw was also tested with and without the tip of the screw closed. These design and implantation techniques were compared to the standard design lag screw both with and without bone cement augmentation by traditional methods. Initial testing in a synthetic bone analogue looked promising. The modified screw with closed end performed better in push out tests than the standard screw alone and comparably with the standard screw with cement augmentation. A second phase of testing with the synthetic material was then conducted to more closely represent physiological loading conditions. In this case again the closed ended modified screw with cement augmentation outperformed the original screw and was comparable with the augmented original screw. However, during this phase of testing problems were observed with the synthetic testing material and it was decided to conduct further testing in paired porcine cadaveric femurs. Several further problems occurred in this phase of testing, including the bending of the test screws. It was concluded that the modified screw showed potential in being a more accurate and consistent method of cement augmentation, however neither the synthetic bone analogue or the porcine material was an adequate model of an osteoporotic human femur. If a suitable testing material could be found, continued study of this prototype may prove beneficial.

This Master‘s thesis deals with the construction design of the ball screw shaft supports. Designed supports will serve to increase stability of rotating ball screws. In the introduction detailed description of the ball screws is presented including description of the individual parameters of the ball screw. Next part includes parameters of different ball screw properties and design of individual supports with description and design calculations of individual parts of the supports. Concepts of the supports will be designed in compliance with the ball screw product series of the KSK Precise Motion a.s. company.

Call number: LD2668 .T4 1978 W91 / Master of Science

No description available.

This thesis presents a thermodynamic model for a screw chiller and cooling tower system for the purpose of developing an optimized control algorithm for the chiller plant. The thermodynamic chiller model is drawn from the thermodynamic models developed by Gordon and Ng (1996). However, the entropy production in the compressor is empirically related to the pressure difference measured across the compressor. The thermodynamic cooling tower model is the Baker & Shryock cooling tower model that is presented in ASHRAE Handbook - HVAC Systems and Equipment (1992). The models are coupled to form a chiller plant model which can be used to determine the optimal performance. Two correlations are then required to optimize the system: a wet-bulb/setpoint correlation and a fan speed/pump speed correlation. Using these correlations, a "quasi-optimal" operation can be achieved which will save 17% of the energy consumed by the chiller plant.

In this work, the peroxide-initiated degradation of polypropylene (PP) in co-rotating intermeshing twin-screw extruders (COITSEs) is analyzed by means of numerical simulations. This reactive extrusion (REX) operation is simulated by implementing (i) a one-dimensional and (ii) a three-dimensional (3D) modeling approach. In the case of the 1D modeling, a REX mathematical model previously developed and implemented as a computer code is used for the evaluation of two scale-up rules for COITSEs of various sizes. The first scale-up rule which is proposed in this work is based on the concept of thermal time introduced by Nauman (1977), and the second one is based on specific energy consumption (SEC) requirements. The processing parameters used in testing the previously referred to scale-up approaches are the mass throughput, the screw rotating speed, and the peroxide concentration, whereas the extruder screw configuration and the barrel temperature profiles are kept constant. The results for the simulated operating conditions show that when the REX operation is scaled-up under constant thermal time, very good agreement is obtained between the weight-average molecular weight (Mw) and poly-dispersity index (PDI) from the larger extruders and the values of these parameters corresponding to the reference extruder. For the constant SEC approach, on the other hand, more significant variations are observed for both of the aforementioned parameters. In the case of the implemented constant thermal time procedure, a further analysis of the effect of the mass throughput and screw speed of the reference device on the scaled-up operation is performed. It is observed that when the lower mass throughput is implemented for the smaller extruder keeping a constant screw speed, the predicted residence times of extrusion for the larger extruders are lower, in general terms, than those corresponding to the reference device, and a converse situation occurs for the higher implemented value of the mass throughput. Also, in general terms, the higher increase of the reaction temperature on the scaled-up operation corresponds to the lower mass throughputs and higher screw speeds specified for the reference extruder. For the 3D modeling approach, two different case studies are analyzed by means of a commercial FEM software package. The REX simulations are performed under the assumption of steady-state conditions using the concept of a moving relative system (MRS). To complement the information obtained from the MRS calculations, simulations for selected conditions (for non-reactive cases) are performed considering the more realistic transient-state (TS) flow conditions. The TS flow conditions are associated to the time periodicity of the flow field inside the conveying elements of COITSEs. In the first case study, the peroxide-initiated degradation of PP is simulated in fully-filled screw elements of two different size COITSEs in order to evaluate scale-up implications of the REX operation. In the second case, the reacting flow is simulated for a conventional conveying screw element and a conveying screw element having a special design and corresponding to the same extruder size. For both of the analyzed cases, the effects of the initial peroxide concentration and mass throughput on the final Mw and PDI of the degraded resin are studied. The effect of the processing conditions is discussed in terms of the residence time distribution (RTD), the temperature of reaction, and the distributive mixing capabilities of the REX system. When analyzing the scale-up case, it is found that for the implemented processing conditions, the final Mws and PDIs are very close to each other in both of the analyzed flow geometries when the specified flow is close to that corresponding to the maximum conveying capabilities of the screw elements. For more restrictive flow conditions, the final Mws and PDIs are lower in the case of the screw element of the larger extruder. It is found that the distributive mixing ability of the reactive flow is mainly related to the specified mass throughput and almost independent of the specified peroxide concentration for a particular extruder size. For the analyzed screw elements, the conveying element corresponding to the small size extruder shows a slightly better distributive mixing performance. For this same case study, a further evaluation of the proposed scale-up criterion under constant thermal time confirms the trend of the results observed for the 1D simulations. In the second case study, the special type of screw element consists of screws rotating at different speeds which have different cross sections. In this case, the outer and inner diameters of both the special and the conventional type of screw elements are specified to be the same. As in the previous case study, the distributive mixing capabilities appear to be independent of the specified peroxide concentrations but dependent on the mass flow rate. It is speculated from the simulation results, from both the transient- as well as the steady-state flow conditions, that the screw element with the special design would yield lower final values of the PDI and Mw. Also, this screw element appears to have improved distributive mixing capabilities as well as a wider RTD.