Tesi sul tema "Steering-gear"

Det här examensarbetet består av en livscykelanalys av en styrsystem. Genom den studien har man försökt att fokusera och ta reda på hur en styrsystem kan påverka miljön genom sin livs längd. Alla faktorer som koldioxid utsläpp, energi-och material använding samt hur mycket detta påverkar miljön har studerats. Eftersom Livscykelanalysen brukar vara tidskrävande och detaljrat, har en enklare metod för snabbare result och analys av styrsystem valts. Den här metoden kallas för fast track LCA, det är en mindre komplicerad metod. Motivationen bakom denna studie är resurshushållning och energieffektivitet. Resultatet från denna analys skall användas för vidareutveckling av hydrualiska styrsystem, vilket skulle kunna ge möjlighet till en förbättring i de nya modellen av styrsystemet. Denna utveckling är tänkt att ske i miljövänlighets syfte. I det avslutande kapitlet tolkas och presenteras resultaten i tabeller och figurer. Baserat på dessa tolkningar kommer resultaten och utvecklingsmöjligheter att diskuterass ytterligare.Utifrån dem dras slutsatsen samt förbättringar från mijösynpunkten föreslås.
This thesis work mainly contains a fast track Life Cycle Assessment (LCA) study of a hydraulic steering gear. The study gives a picture of the hydraulic steering gear through its complete Lifecycle from an environmental point of view. The main motivations behind this study are natural resources conservation and energy efficiency. According to ISO 14040 and 14044 LCA is a complex and time consuming method, the chosen approach for LCA in this study is the Fast Track LCA. The Fast Track LCA gives results which are equally accurate and still could be achieved by taking a shorter way and applying an easier and less complicated method. The intended application of this study is to use the results for further development of the new hydraulic steering gear design, in comparison to the current one. These developments are supposed to be more environmentally friendly. In the final chapter, the findings are interpreted in tables and figures, based on these interpretations the findings are discussed further and the environmentally improvements are suggested and the conclusions are drawn.

This thesis covers the development of a component specification for the steering system of vehicles engineered by CEVT. This includes the components steering column, intermediate shaft, steering gear and tie rods. Due to the reuse of requirements on the component specification from previous projects it now lacks connection to customer needs. A verification of the component specification is necessary to ensure that no redundant or unnecessary requirements are present. The verification was performed through a comparison between a newly established specification and the current one. Identified customer needs were gathered on complete vehicle level and classified according to customer satisfaction with respect to implementation according to the Kano model. The subjective customer needs were translated into objective, quantifiable metrics on complete vehicle level that was then decomposed onto component level. Customer needs and metrics were then correlated against each other and visualized through the House of Quality matrix. Numeric targets for the metrics were based on its impact on customer satisfaction. This resulted in 50 identified metrics connected to the steering column and 58 metrics connected to the steering gear. The comparison resulted in 22 deviations between the new and current specification where 8 metrics was identified for further investigation. Further development would include investigation of these 8 identified metrics and relate targets to competitors’ performance.

Future heavy duty vehicles will be designed and manufactured with improved Advanced Driver Assistance Systems, ADAS. When developing ADAS, an accurate model of the vehicle dynamics greatly simplifies the development process. One element integral to the vehicle lateral dynamics and development of ADAS is the steering system. This thesis aims to develop an accurate model of a heavy duty vehicle steering system suitable for simulations. The input to the system is an input torque at the steering wheel and the output is the wheel angle. Physical models of the system components are developed using bond graphs and known relations. Some components are modelled with non-linear inefficiencies and friction of different complexity. Unknown parameters and functions are identified from measurement data using system identification tools such as, for example, linear regression and non-linear grid search. The different subsystems are identified separately to the extent deemed possible. Different model designs are considered, validated, and compared. The advantages and disadvantages of different model choices are discussed. Finally, a non-linear state space model is selected for its high accuracy and efficiency. As this final model can be used to simulate a heavy duty vehicle steering system on a desktop computer faster than real time, it fulfills its purpose.

A microestrutura de uma peça temperada determina suas características mecânicas. Dessa forma, torna-se fundamental conhecer os parâmetros que influenciam na formação da estrutura do componente tratado com função dos tratamentos térmicos aplicados, permitindo obter melhorias de qualidade de uma peça frente a sua aplicação. Métodos distintos podem ser empregados para obtenção da camada de têmpera. Entretanto, esses métodos devem ser parametrizados adequadamente para garantir a qualidade do produto final. No trabalho em questão, aplicaram-se dois metódos distintos de têmpera: por indução e por condução para obtenção da camada martensítica, dureza e durabilidade requerida em cremalheiras de aço SAE 1045, utilizadas em mecanismo de direção automotiva. Fabricou-se um lote de peças, do qual metade das peças foram tratadas por indução e a outra por condução. Após a têmpera e após o revenido, foi avaliado o nível de empenamento, a dureza superficial, a microdureza, a microestrutura formada. A peças após o término do processo de fabricação, foram montadas no sistema caixa de direção, sendo realizados ensaios de durabilidade e impacto dos mesmos. Os tratamentos realizados demonstraram resultados de empenamento, dureza, microestrutura e ensaios de durabilidade e impacto no produto final, dentro das especificações. O processo de têmpera por condução levou a melhor micrestrutura, mais alta dureza e menores níveisde empenamento comparado com o processo de têmpera por indução. Mas, também constatou-se que é possível desenvolver melhorias no processo de indução para atingir-se resultados melhores.
The microstructure of a hardened part is determining its mechanical characteristiscs. Thus, the knowledge of pararameters influencing the heat treated part’s microstructure is of fundamental importance. This allows to obtain quality improvements for specific applications. Diferent methods can be used for the obtation of a hardened layer. However, in these methods the parameters have to be correctly set to reach the final product quality. In this work, two diferente techniques were applied, induction and conduction surface hardening to obtain a required martensitic layer depth, hardness and durability of SAE 1045 steel racks used in automotive driving systems. A batche of parts were manufactured, being half of the parts surface hardened by Induction and half by conduction. After hardening and after tempering, the warpage level, surface hardness, microhardness and microstructure were investigated. The parts were mounted in a steering gear system and then endurance tests and impact tests were carried out. The results of warpage levels, hardness, microstructure and endurance tests, as well as the impact tests were in the range of the specifications. The conduction hardening process leads to better microstructure, higher hardness and lower warpage levels compared to induction hardening. But it was found that the Induction hardening can be optimized to reach better results.

The theme of dissertation is "Inheritance and steering gear of inheritance in Czech Republic" because I widen the original theme of procedural law to material law - inheritance, according to New Civil Code (NOZ) which brought to Czech legal order many changes, also in the area of inheritance in Czech legislation. The thesis also analyses the changes which brought Zákon o zvláštních řízeních soudních. Dissertation then compares the new and the old legislation, highlights its pluses and minuses and also resolves if the new legislation is better the the old legislation and where are these changes obvious. This thesis should be general knowledge of changes in area of inheritance and steering gear according to NOZ, not at all detailed processing of institutes of inheritance law. Practical part of the thesis analyses judicature and three concrete testaments.

This thesis deals with the design of steering holder for a race car in the category Formula Student using topology optimisation and analysis of this design. The objective of this thesis is gaining knowledge about topology optimisation and application of this knowledge to the design of a replacement of the steering gearbox and its holder.

The diploma thesis is focused on design of electrohydraulic system for nose gear control on small civil airliners. First part consists of brief review of small civil airliners, nose gears and CS 23 restrictions relevant for the design. In practical part a typical small civil airliner is defined and kinematic of landing gear mechanisms is designed. Then the electrohydraulic system itself is designed and parameters of some components are suggested. The wheel steering mechanism is simulated and, in conclusion, the whole system is evaluated.

This thesis presents a new nonlinear automobile dynamical model and investigates the possibility of automobile dynamic control with wheel torque utilizing this model. The model has been developed from first principles by applying classical mechanics. Inputs to the model are the four independent wheel torques, while the steer angles at each wheel are specified as independent time-varying signals. In this way, consideration of a variety of steering system architectures, including rear-wheel steer, is possible, and steering introduces time-varying structure into the vehicle model. The frictional contact at the wheel-road interface is modeled by use of the LuGre dynamic friction model. Extensions to the existing two-dimensional LuGre friction model are derived and the steady-state of the friction model is compared to existing static friction models. Simulation results are presented to validate the model mathematics and to explore automobile behavior in a variety of scenarios. Vehicle control with wheel torque is explored using the theory of input-output linearization for multi-input multi-output systems. System relative degree is analyzed and use of steady-state LuGre friction in a control design model is shown to give rise to relative degree singularities when no wheel slip occurs. Dynamic LuGre friction does not cause such singularities, but instead has an ill-defined nature under the same no-slip condition. A method for treating this ill-defined condition is developed, leading to the potential for the system to have relative degree. Longitudinal velocity control and combined longitudinal and angular vehicle velocity control are demonstrated in simulation using input-output linearization, and are shown to produce improved vehicle response as compared to the open-loop behavior of the automobile. Robustness of the longitudinal velocity control to friction model parameter variation is explored and little impact to the controller's ability to track the desired trajectory is observed.

This research studied the tractive performance of integrated steering-drive systems by investigating a two-wheel-drive vehicle having two independent rear drive wheels and non-driven steerable front wheels. The feasibility of integrating the steering and drive systems and the performance advantages that may be obtained was investigated. In order to demonstrate the feasibility of the concept, the steering system and the drive system of a test vehicle were integrated using a computer with a specially-developed program. The software algorithm developed for the program used the mathematical relationship between the rear drive wheel speeds and the steer angles of the non-driven front wheels to set the steer angles. A test-bed vehicle was fitted with instrumentation to implement the computer-integrated system. The circuitry of the hydraulic lines of the hydraulically-driven test vehicle was modified to allow changes in drive configuration. These changes are not possible with conventional vehicles. The test vehicle could be configured for the following steering-drive configurations: open differential rear drive with steerable front wheels, independent rear drive wheels with front castors, locked differential rear drive with steerable front wheels and the computer-integrated steering-drive system developed. The sensors on the vehicle allowed data collection for characterising the vehicle and wheels. omputer models were developed for the various steering-drive configurations from the force relationships, longitudinal slip relationships, vehicle geometry and turning geometry. Characteristics of the test vehicle's wheels for use in the models were measured experimentally. he models were used to simulate the behaviour, and calculate the tractive performance, of the four steering-drive configurations in various situations but actual tests were not able to be conducted with the available resources. Unlike previous models, the models of this research used force and longitudinal slip information rather than power input and power output to produce values for drawbar efficiency. theoretical analysis was conducted into the optimal slip conditions for maximum tractive efficiency. The analysis was conducted using a more rigorous mathematical analysis than previous researchers and used a thorough graphical analysis to substantiate the mathematical analysis. Previous studies concluded that under all traction conditions the efficiency of slip will be a maximum when the slip of each wheel is equal. This research revealed that, contrary to the previous literature, efficiency of slip will not be a maximum when the slip of each wheel is equal under non-uniform traction conditions. The simulations were focussed on turning situations, non-uniform traction conditions and traversing slopes. The optimal slip conditions and steer angles for turning situations were also investigated and analysed. The computer-integrated steering-drive system achieved a drawbar pull 50% higher than that for a conventional open differential when undertaking a 10 m radius turn with non-uniform traction conditions. Under these conditions, the drawbar efficiency of the computer-integrated steering-drive system was 5% greater than that for the open differential at the lower drawbar pull. It was concluded that it is feasible and beneficial to use a computer-integrated steering system. Vehicles using such a system would operate more effectively and efficiently when turning under load, moving across slopes and in non-uniform traction conditions. More effectiveness was provided through greater drawbar pull and higher drawbar efficiency.
thesis (PhD)--University of South Australia, 2005.

碩士
國立臺北科技大學
車輛工程系所
98
Most of steering systems use the rack and pinion to transform the rotation of motor into straight-line motion currently. The rack and pinion have good performance in mechanical efficiency, but the overall size will increase when the motor and gear box are used .Not only the manufacturing cost raise ,but the spatial arrangement becomes complicated. Therefore, this study plans to substitute the lower cost and smaller size of the planetary gear set for the existing mechanism to meet the required straight-line motion. In this research, the new straight-line motion mechanism use a basic five planetary gear set with the ring gear fixed and sun gear input. In this study, the three-DOF gear steering mechanism is based on the basic planetary gear straight line , the mechanism refer steering angle and speed to adjust the motors to achieve the appropriate steering condition.

碩士
國立臺北科技大學
自動化科技研究所
90
This thesis deals with the research and development of a new variable-gear-ratio steering system (VGS). The main purposes of the variable-gear-ratio steering system are to connect the steering wheel and the front-wheel steering mechanism and to coordinate the turning angle of the front wheels, according to the steering-wheel angle and the speed of the vehicle, in order to maintain a constant “desired yaw rate gain” at a constant speed of vehicle. However, the value of the desired yaw rate gain should be varied at different vehicle speed to give better maneuverability, stability, and mobility. The definition of the above-mentioned “desired yaw rate gain” is the ration between the yaw rate and the steering wheel angle. This research collects all kinds of vehicle variable-gear-ratio (VGS) steering systems from academic journals and patent publications to conduct a thorough classification and kinematic analysis. This research mainly studies the vehicle steering behaviors from the viewpoint of kinematics to develop a new variable-gear-ratio steering system with more ideal performances. This research wants to achieve two goals: first, keep the desired yaw rate gain constant at a constant speed; second, vary the value of the desired yaw rate gain when the vehicle speed is changed. According to the dimensions of the production vehicles and the ideal vehicle cornering properties, this research derived the ideal relationship between the front wheels and the steering wheel when cornering and accomplished the mechanism design of the new variable-gear-ratio steering system. Finally, Pro/ENGINEER software was employed to construct the solid models of the new design and to conduct dynamic simulations and interference check, in order to verify the performance of the new design.

碩士
國立臺北科技大學
車輛工程系所
100
Most current electric parking brake systems use thread and worm gear sets or self-locking screws to transfer the rotational motion of the electric motor into the linear motion, required by a braking actuator and to maintain braking effort, because of the system’s irreversible nature, i.e. the friction angle between the contact surfaces is larger than the lead angle of the worm or the screw; however, worm gear sets and self-locking screws have low transmission efficiency, resulting from the friction force, which consumes more power from the motor. This study proposes a novel parking brake mechanism, which uses a special planetary gear train without a sun gear to improve upon the performance of existing electric parking brake systems. The dimensions of the gear sets are determined through a systematic design process. Kinematic and force analysis demonstrate that an approximately square locus, generated from a specific point on the planet gear, allows transfer of motion and a level of self-locking. Furthermore, in this research, the new straight-line motion mechanism, based on the basic planetary gear mentioned in the last design of electric parking brake, refers to the steering wheel angle to achieve variable-gear ratio in different condition of vehicle, so that the vehicle will steering with smaller steering wheel angle compared with conventional vehicle. With this advantage, the vehicle can reach the ideal of turning radius to minimize the wear of tire.

The economy of a developing nation like India depends on various sectors such as: Agriculture, Commerce and Industries, Finance, Communication and Information Technology, etc. The manufacturing industries play a key role in contributing to the economy of a nation. They mainly consist of industries like steel casting, automobiles and other heavy manufacturing. This research study is related to automobile industry and particularly the gear manufacturers. The automobile industry is an important industry from the manufacturing point of view. This is due to the fact that it has deep forward and backward linkages with several key segments of the economy and it has a strong multiplier effect. Hence, it is capable of being the driver of economic growth. The recent trend among the automobile manufacturing organizations is to outsource individual components to sub-contractors and conduct the sub-assemblies and assemblies in-house. Some components like gears are important in terms of quality. So in case of these components the automobile manufacturing organizations normally partially outsource the components. They carry out the important finishing operations in-house. Due to this practice, many micro to medium scale gear manufacturers have emerged as sub-contractors to different automobile manufacturing organizations. There is a high amount of competition among different gear manufacturers. To survive the competition any gear manufacturer must focus on the three major aspects: cost, quality and delivery. The focus in this study is on the delivery aspect. Precisely, this thesis attempts to address the scheduling problems in automobile gear manufacturing by proposing efficient solution methodologies in order to aid the gear manufacturers in the delivery of orders in the form of semi-finished gears, to the customers (i.e. automobile manufacturing organizations). The automobile gear manufacturing process can be broadly divided into three distinct stages, starting from the machining of the gear blanks. These three stages in automobile gear manufacturing are: pre heat treatment (pre-HT), heat treatment (HT) and post heat treatment (post-HT). Out of these three stages, the gear manufacturers carry out the first two stages namely pre-HT and HT, and deliver the semi-finished gears to the automobile manufacturing organizations. As most of the operations are carried out by the gear manufacturers, the real research problem lies in identifying bottleneck operations in both pre-HT and HT stages. By addressing the bottleneck operations, one can expect to have a competitive advantage among the gear manufacturers and in turn among the automobile manufacturing organizations. Since every gear manufacturer is involved in both: the pre-HT stage and the HT stage of gear manufacturing, they will always try to achieve both: throughput (from their own company’s perspective) and due date compliance (from the customer’s i.e. automobile manufacturing organizations’ perspective). In order to meet these two objectives for the gear manufacturer, there are two research problems identified in this thesis based on the bottleneck operations: one at the pre-HT stage and the other at the HT stage. The Research Problem 1, identified in the pre HT stage consists of a variety of machining operations. In all the pre-HT operations, one single gear is processed on a machine at a time. The machines used in these operations are essentially the discrete processors as known in the scheduling literature. Among the different operations carried out in the pre-HT stage, the gear shaving operation is the final operation which takes a relatively longer processing time compared to other operations in this stage. Hence this operation becomes the bottleneck operation and the Research Problem 1 is related to this operation. Normally, there are more than one machines available for carrying out the gear shaving operations. The processing time of a job is independent of the type of machine used (identical parallel machines). However, since automobile gears vary widely in terms of size, all the available machines may not be able to process a given job (machine eligibility restrictions). The jobs are made available for processing as and when the job orders are received from the automobile manufacturing organizations. Thus all the jobs may not be available for processing at the same time (unequal release times or dynamic job arrivals). After a job is completed on a machine, a setup is incurred before processing the next job. The setup operations involve cleaning of the machine, changing of cutting tools and toolings, setting of the machining parameters and fine tuning of the machining parameters. The amount of time required for the setup depends on both, the job that has been completed and the job that is to be processed (sequence dependent setup time). Different jobs will have different priorities depending on the nature of the job order, monetary value of the job and urgency for the next stage (job weights). Since the pre-HT stage is an upstream stage in gear manufacturing, particularly to the heat treatment (HT) stage, the aim of this stage will be to feed the downstream stage as quickly as possible. Hence, a completion time based scheduling objective is considered. Since the release times of jobs are unequal, the flowtime of a job is of interest in determining the throughput. Also, since the jobs have different weights, the weighted flowtime is of significance. Therefore, the scheduling objective for Research Problem 1 is taken as minimizing the total weighted flowtime of the jobs in a scheduling window. A vast amount of literature is available on scheduling of parallel machines. However, to the best of our knowledge, no study has simultaneously addressed the job characteristics: unequal release times, sequence dependent setup times and machine eligibility restrictions for identical parallel machines to minimize the total weighted flowtime. The Research Problem 2 was identified at the HT stage of gear manufacturing. The aim of the HT stage in the metallurgical terms is to achieve case hardening of gears. The types of machines used in the HT stage are essentially the batch processing machines (BPM) or simply batch processors (BP). A BP unlike the discrete processor, can process several different jobs at a time. The constituent jobs that are processed together form a batch in the BP. The different operations of this stage are: hardening and soaking, quenching, tempering and shot blasting. The hardening and soaking operation typically takes a longer processing time (6-18 hours) as compared to the other operations (15 minutes to 90 minutes). Also, being the first operation of the HT stage, once the hardening and soaking operation is completed, the other operations can be streamlined. Hence the scheduling of this bottleneck operation is of managerial importance. The jobs arrive at the hardening and soaking operation as and when they are completed at the pre-HT stage (unequal release times). Different jobs may have different processing requirements corresponding to time and temperature setting. Therefore, although a BP can process multiple jobs at a time, jobs with different processing requirements cannot be processed together. Jobs that can be processed together are grouped in job families. Since jobs of different families cannot be processed together we get the situation of incompatible job families. The BP has a fixed and finite capacity (expressed in terms of mass). Jobs will have different masses – which represents the size of jobs (non-identical job sizes). While constructing a batch, a job can be split in case there is a capacity violation for the BP (job splitting). The same priorities of the jobs (job weights) as in the pre-HT stage, will continue in this stage as well. As the Research Problem 2 deals with downstream stage of the gear manufacturing the objective of scheduling will be efficient delivery of the job to the automobile manufacturing organizations. The non-conformance to the due date will result in tardiness of the job. Also, since the jobs have different weights, the weighted tardiness of a job is of significance. Therefore, the scheduling objective for Research Problem 2 is taken as minimizing the total weighted tardiness (TWT) of the jobs in a scheduling window. Compared to the discrete processors, the scheduling of batch processors is a relatively new field (about two decades old). However, a review of literature reveals that no study has simultaneously addressed in any problem domain, the characteristics: unequal release times, incompatible job families, non-identical job sizes and job splitting for scheduling batch processors to minimize the total weighted tardiness. For Research Problem 1, an integer linear programming (ILP) model is developed. A suitable numerical example is developed and the workability of the proposed ILP model is validated for a small sized problem. The computational intractability of the proposed ILP model is verified empirically. Due to the computational intractability, real life large-size problems cannot be solved using the proposed ILP model. This has motivated us to propose simple heuristic algorithms. Accordingly, ten heuristic algorithms are proposed. Out of these ten proposed heuristic algorithms, five heuristic algorithms allow the use of unforced idleness and the remaining five heuristic algorithms do not allow the use of unforced idleness. In scheduling, unforced idleness is a situation when a machine is kept idle even if there are jobs available for processing. In order to understand the performance of the proposed heuristic algorithms, various factors that can affect the performance of the heuristic algorithms are identified based on the literature as well as based on the knowledge gained from the industry. An experimental design is developed based on the identified factors with different levels. A series of computational experiments has been conducted for absolute evaluation of the heuristic algorithms: (a) in comparison with optimal solution for small size problem instances (there are 96 problem instances) and (b) in comparison with the estimated optimal solution for large size problem instances (there are 2880 problem instances). The evaluation is based on computational time and the quality of the solution. With respect to the computational time, it is observed that the time required for obtaining results from the heuristic algorithms is meager. For evaluating the quality of the solution, the two standard performance measures – Average Relative Percentage Deviation (ARPD) which indicates the average performance of the proposed heuristic algorithms and Maximum Relative Percentage Deviation (MRPD) which indicates the worst case performance of the proposed heuristic algorithms have been used. From the results of the experimental evaluation it is observed that the heuristic algorithms incorporating the information on machine eligibility restrictions along with other job characteristics worked relatively better compared to other proposed heuristic algorithms. It is also observed that system congestion plays an important role in determining the performance of the heuristic algorithms. Hence, a further study based on the effect of system congestion on different heuristic algorithms is carried out. The system congestion effect was controlled using the two problem factors: number of jobs and release time of jobs. The computational experiments were based on a total of 48 problem instances. Based on the results it was inferred that for congested systems, the proposed heuristic algorithms allowing unforced idleness perform better than the corresponding heuristic algorithms not allowing unforced idleness. For Research Problem 2, two situations are examined. The first situation pertains to the micro and small scale gear manufacturers. In this case, the gear manufacturers can have a single batch processor (BP) for the operation: hardening and soaking. The other situation pertains to small and medium scale gear manufacturers, and in this case, there are more than one batch processors with possibly different capacities (multiple non-identical batch processors). For the Research Problem 2 with single BP, an ILP model is developed. A suitable numerical example is developed and the workability of the proposed ILP model is validated for a small sized problem. The computational intractability of the proposed ILP model is verified empirically. Due to the computational intractability it is proposed to develop simple heuristic algorithms. Based on the pilot experimental analysis and based on the fact that allowing unforced idleness gave superior results in case of Research Problem 1, it is decided to incorporate unforced idleness while developing heuristic algorithms for the Research Problem 2 with single BP. Accordingly, three groups of heuristic algorithms are proposed for Research Problem 2 with single BP by allowing unforced idleness – (i) Seven variants of the heuristic algorithms are based on the computation of the weighted tardiness, (ii) Three variants of the heuristic algorithms based on computation of the composite job scores and (iii) Three variants of the heuristic algorithms based on the computation of composite family scores followed by the composite job scores. For evaluating the performance of the thirteen proposed heuristic algorithms various factors that can affect the workability of the heuristic algorithms are identified based on the literature as well as based on the knowledge gained from the industry. An experimental design is developed based on these factors with levels. A series of computational experiments has been conducted for absolute evaluation of the heuristic algorithms: (a) in comparison with optimal solution for small size problem instances (192 problem instances) and (b) in comparison with the estimated optimal solution for large size problem instances (7680 problem instances). The evaluation is based on computational time and the quality of the solution. With respect to the computational time, it is observed that the time required for obtaining results from the heuristic algorithms is meager. For evaluating the quality of the solution, the two standard performance measures – ARPD and MRPD, used in Research Problem 1, could not be used here due to the nature of the scheduling objective: minimizing the TWT (as the TWT tends to zero). Therefore, a suitable performance measure was identified in the literature and suitably modified for the Research Problem 2 with single BP under study. This performance measure gives stable results even when the TWT value approaches zero. From the results of the experimental evaluation it is observed that variants of heuristic algorithms based on accommodation of non-consecutive jobs while batch construction, perform better than the other variants of the heuristic algorithms. Following the research study on single BP sitaution, the multiple non-identical BPs situation of Research Problem 2 is studied. The ILP model proposed for the Research Problem 2 with single BP problem is suitably extended to account for multiple non-identical BPs and the workability of the model is demonstrated. Additionally, the proposed heuristic algorithms for the Research Problem 2 with single BP problem have been suitably modified for the multiple non-identical BP situation. After developing a suitable experimental design for Research Problem 2 with multiple non-identical BPs, a series of computational experiments has been conducted for absolute evaluation of the heuristic algorithms in comparison with the estimated optimal solution for large size problem instances, based on the 7680 problem instances. Similar performance measure as that used in the Research Problem 2 with single BP problem is used. The observations made from the experimental evaluation for the Research Problem 2 with multiple non-identical BPs are similar to and therefore consistent with those made for the Research Problem 2 with single BP problem. Finally, a sensitivity analysis to determine the effect of capacity of batch processor sets (BP sets) in terms of: number of batch processors and capacities of each batch processor, for Research Problem 2, is carried out. That is, considering different combinations of the two factors: number of batch processors and capacities of each batch processor, seven different BP sets are considered for the proposed sensitivity analysis. The effect on the scheduling objective: Total Weighted Tardiness for different problem configurations is studied by conducting computational experiments. It is observed that higher net capacities of the BP sets give a proportionately better advantage as compared to lower net capacities of the BP sets. Proportionately better advantage means that the percentage of improvement observed in the scheduling objective is higher than the percentage increase in the net capacity of the BP set. Another observation made is that for a given net capacity, it is better to have multiple BPs with smaller capacities than a single BP with high capacity. Although the problems pertaining to the gear manufacturing process simultaneously considering many real life situations have been addressed in this study, there are some limitations to it such as addressing of identical parallel machines instead of a general case of unrelated parallel machines (for Research Problem 1) and consideration of only deterministic situations for both the research problems. There are many immediate future research directions for the problem studied in this thesis such as overcoming the limitations mentioned in this study, proposing good lower bounds and additional heuristic algorithms, and coming up with integrating both, Research Problem 1 and Research Problem 2 and proposing solution methodologies for the integrated problem.

The economy of a developing nation like India depends on various sectors such as: Agriculture, Commerce and Industries, Finance, Communication and Information Technology, etc. The manufacturing industries play a key role in contributing to the economy of a nation. They mainly consist of industries like steel casting, automobiles and other heavy manufacturing. This research study is related to automobile industry and particularly the gear manufacturers. The automobile industry is an important industry from the manufacturing point of view. This is due to the fact that it has deep forward and backward linkages with several key segments of the economy and it has a strong multiplier effect. Hence, it is capable of being the driver of economic growth. The recent trend among the automobile manufacturing organizations is to outsource individual components to sub-contractors and conduct the sub-assemblies and assemblies in-house. Some components like gears are important in terms of quality. So in case of these components the automobile manufacturing organizations normally partially outsource the components. They carry out the important finishing operations in-house. Due to this practice, many micro to medium scale gear manufacturers have emerged as sub-contractors to different automobile manufacturing organizations. There is a high amount of competition among different gear manufacturers. To survive the competition any gear manufacturer must focus on the three major aspects: cost, quality and delivery. The focus in this study is on the delivery aspect. Precisely, this thesis attempts to address the scheduling problems in automobile gear manufacturing by proposing efficient solution methodologies in order to aid the gear manufacturers in the delivery of orders in the form of semi-finished gears, to the customers (i.e. automobile manufacturing organizations). The automobile gear manufacturing process can be broadly divided into three distinct stages, starting from the machining of the gear blanks. These three stages in automobile gear manufacturing are: pre heat treatment (pre-HT), heat treatment (HT) and post heat treatment (post-HT). Out of these three stages, the gear manufacturers carry out the first two stages namely pre-HT and HT, and deliver the semi-finished gears to the automobile manufacturing organizations. As most of the operations are carried out by the gear manufacturers, the real research problem lies in identifying bottleneck operations in both pre-HT and HT stages. By addressing the bottleneck operations, one can expect to have a competitive advantage among the gear manufacturers and in turn among the automobile manufacturing organizations. Since every gear manufacturer is involved in both: the pre-HT stage and the HT stage of gear manufacturing, they will always try to achieve both: throughput (from their own company’s perspective) and due date compliance (from the customer’s i.e. automobile manufacturing organizations’ perspective). In order to meet these two objectives for the gear manufacturer, there are two research problems identified in this thesis based on the bottleneck operations: one at the pre-HT stage and the other at the HT stage. The Research Problem 1, identified in the pre HT stage consists of a variety of machining operations. In all the pre-HT operations, one single gear is processed on a machine at a time. The machines used in these operations are essentially the discrete processors as known in the scheduling literature. Among the different operations carried out in the pre-HT stage, the gear shaving operation is the final operation which takes a relatively longer processing time compared to other operations in this stage. Hence this operation becomes the bottleneck operation and the Research Problem 1 is related to this operation. Normally, there are more than one machines available for carrying out the gear shaving operations. The processing time of a job is independent of the type of machine used (identical parallel machines). However, since automobile gears vary widely in terms of size, all the available machines may not be able to process a given job (machine eligibility restrictions). The jobs are made available for processing as and when the job orders are received from the automobile manufacturing organizations. Thus all the jobs may not be available for processing at the same time (unequal release times or dynamic job arrivals). After a job is completed on a machine, a setup is incurred before processing the next job. The setup operations involve cleaning of the machine, changing of cutting tools and toolings, setting of the machining parameters and fine tuning of the machining parameters. The amount of time required for the setup depends on both, the job that has been completed and the job that is to be processed (sequence dependent setup time). Different jobs will have different priorities depending on the nature of the job order, monetary value of the job and urgency for the next stage (job weights). Since the pre-HT stage is an upstream stage in gear manufacturing, particularly to the heat treatment (HT) stage, the aim of this stage will be to feed the downstream stage as quickly as possible. Hence, a completion time based scheduling objective is considered. Since the release times of jobs are unequal, the flowtime of a job is of interest in determining the throughput. Also, since the jobs have different weights, the weighted flowtime is of significance. Therefore, the scheduling objective for Research Problem 1 is taken as minimizing the total weighted flowtime of the jobs in a scheduling window. A vast amount of literature is available on scheduling of parallel machines. However, to the best of our knowledge, no study has simultaneously addressed the job characteristics: unequal release times, sequence dependent setup times and machine eligibility restrictions for identical parallel machines to minimize the total weighted flowtime. The Research Problem 2 was identified at the HT stage of gear manufacturing. The aim of the HT stage in the metallurgical terms is to achieve case hardening of gears. The types of machines used in the HT stage are essentially the batch processing machines (BPM) or simply batch processors (BP). A BP unlike the discrete processor, can process several different jobs at a time. The constituent jobs that are processed together form a batch in the BP. The different operations of this stage are: hardening and soaking, quenching, tempering and shot blasting. The hardening and soaking operation typically takes a longer processing time (6-18 hours) as compared to the other operations (15 minutes to 90 minutes). Also, being the first operation of the HT stage, once the hardening and soaking operation is completed, the other operations can be streamlined. Hence the scheduling of this bottleneck operation is of managerial importance. The jobs arrive at the hardening and soaking operation as and when they are completed at the pre-HT stage (unequal release times). Different jobs may have different processing requirements corresponding to time and temperature setting. Therefore, although a BP can process multiple jobs at a time, jobs with different processing requirements cannot be processed together. Jobs that can be processed together are grouped in job families. Since jobs of different families cannot be processed together we get the situation of incompatible job families. The BP has a fixed and finite capacity (expressed in terms of mass). Jobs will have different masses – which represents the size of jobs (non-identical job sizes). While constructing a batch, a job can be split in case there is a capacity violation for the BP (job splitting). The same priorities of the jobs (job weights) as in the pre-HT stage, will continue in this stage as well. As the Research Problem 2 deals with downstream stage of the gear manufacturing the objective of scheduling will be efficient delivery of the job to the automobile manufacturing organizations. The non-conformance to the due date will result in tardiness of the job. Also, since the jobs have different weights, the weighted tardiness of a job is of significance. Therefore, the scheduling objective for Research Problem 2 is taken as minimizing the total weighted tardiness (TWT) of the jobs in a scheduling window. Compared to the discrete processors, the scheduling of batch processors is a relatively new field (about two decades old). However, a review of literature reveals that no study has simultaneously addressed in any problem domain, the characteristics: unequal release times, incompatible job families, non-identical job sizes and job splitting for scheduling batch processors to minimize the total weighted tardiness. For Research Problem 1, an integer linear programming (ILP) model is developed. A suitable numerical example is developed and the workability of the proposed ILP model is validated for a small sized problem. The computational intractability of the proposed ILP model is verified empirically. Due to the computational intractability, real life large-size problems cannot be solved using the proposed ILP model. This has motivated us to propose simple heuristic algorithms. Accordingly, ten heuristic algorithms are proposed. Out of these ten proposed heuristic algorithms, five heuristic algorithms allow the use of unforced idleness and the remaining five heuristic algorithms do not allow the use of unforced idleness. In scheduling, unforced idleness is a situation when a machine is kept idle even if there are jobs available for processing. In order to understand the performance of the proposed heuristic algorithms, various factors that can affect the performance of the heuristic algorithms are identified based on the literature as well as based on the knowledge gained from the industry. An experimental design is developed based on the identified factors with different levels. A series of computational experiments has been conducted for absolute evaluation of the heuristic algorithms: (a) in comparison with optimal solution for small size problem instances (there are 96 problem instances) and (b) in comparison with the estimated optimal solution for large size problem instances (there are 2880 problem instances). The evaluation is based on computational time and the quality of the solution. With respect to the computational time, it is observed that the time required for obtaining results from the heuristic algorithms is meager. For evaluating the quality of the solution, the two standard performance measures – Average Relative Percentage Deviation (ARPD) which indicates the average performance of the proposed heuristic algorithms and Maximum Relative Percentage Deviation (MRPD) which indicates the worst case performance of the proposed heuristic algorithms have been used. From the results of the experimental evaluation it is observed that the heuristic algorithms incorporating the information on machine eligibility restrictions along with other job characteristics worked relatively better compared to other proposed heuristic algorithms. It is also observed that system congestion plays an important role in determining the performance of the heuristic algorithms. Hence, a further study based on the effect of system congestion on different heuristic algorithms is carried out. The system congestion effect was controlled using the two problem factors: number of jobs and release time of jobs. The computational experiments were based on a total of 48 problem instances. Based on the results it was inferred that for congested systems, the proposed heuristic algorithms allowing unforced idleness perform better than the corresponding heuristic algorithms not allowing unforced idleness. For Research Problem 2, two situations are examined. The first situation pertains to the micro and small scale gear manufacturers. In this case, the gear manufacturers can have a single batch processor (BP) for the operation: hardening and soaking. The other situation pertains to small and medium scale gear manufacturers, and in this case, there are more than one batch processors with possibly different capacities (multiple non-identical batch processors). For the Research Problem 2 with single BP, an ILP model is developed. A suitable numerical example is developed and the workability of the proposed ILP model is validated for a small sized problem. The computational intractability of the proposed ILP model is verified empirically. Due to the computational intractability it is proposed to develop simple heuristic algorithms. Based on the pilot experimental analysis and based on the fact that allowing unforced idleness gave superior results in case of Research Problem 1, it is decided to incorporate unforced idleness while developing heuristic algorithms for the Research Problem 2 with single BP. Accordingly, three groups of heuristic algorithms are proposed for Research Problem 2 with single BP by allowing unforced idleness – (i) Seven variants of the heuristic algorithms are based on the computation of the weighted tardiness, (ii) Three variants of the heuristic algorithms based on computation of the composite job scores and (iii) Three variants of the heuristic algorithms based on the computation of composite family scores followed by the composite job scores. For evaluating the performance of the thirteen proposed heuristic algorithms various factors that can affect the workability of the heuristic algorithms are identified based on the literature as well as based on the knowledge gained from the industry. An experimental design is developed based on these factors with levels. A series of computational experiments has been conducted for absolute evaluation of the heuristic algorithms: (a) in comparison with optimal solution for small size problem instances (192 problem instances) and (b) in comparison with the estimated optimal solution for large size problem instances (7680 problem instances). The evaluation is based on computational time and the quality of the solution. With respect to the computational time, it is observed that the time required for obtaining results from the heuristic algorithms is meager. For evaluating the quality of the solution, the two standard performance measures – ARPD and MRPD, used in Research Problem 1, could not be used here due to the nature of the scheduling objective: minimizing the TWT (as the TWT tends to zero). Therefore, a suitable performance measure was identified in the literature and suitably modified for the Research Problem 2 with single BP under study. This performance measure gives stable results even when the TWT value approaches zero. From the results of the experimental evaluation it is observed that variants of heuristic algorithms based on accommodation of non-consecutive jobs while batch construction, perform better than the other variants of the heuristic algorithms. Following the research study on single BP sitaution, the multiple non-identical BPs situation of Research Problem 2 is studied. The ILP model proposed for the Research Problem 2 with single BP problem is suitably extended to account for multiple non-identical BPs and the workability of the model is demonstrated. Additionally, the proposed heuristic algorithms for the Research Problem 2 with single BP problem have been suitably modified for the multiple non-identical BP situation. After developing a suitable experimental design for Research Problem 2 with multiple non-identical BPs, a series of computational experiments has been conducted for absolute evaluation of the heuristic algorithms in comparison with the estimated optimal solution for large size problem instances, based on the 7680 problem instances. Similar performance measure as that used in the Research Problem 2 with single BP problem is used. The observations made from the experimental evaluation for the Research Problem 2 with multiple non-identical BPs are similar to and therefore consistent with those made for the Research Problem 2 with single BP problem. Finally, a sensitivity analysis to determine the effect of capacity of batch processor sets (BP sets) in terms of: number of batch processors and capacities of each batch processor, for Research Problem 2, is carried out. That is, considering different combinations of the two factors: number of batch processors and capacities of each batch processor, seven different BP sets are considered for the proposed sensitivity analysis. The effect on the scheduling objective: Total Weighted Tardiness for different problem configurations is studied by conducting computational experiments. It is observed that higher net capacities of the BP sets give a proportionately better advantage as compared to lower net capacities of the BP sets. Proportionately better advantage means that the percentage of improvement observed in the scheduling objective is higher than the percentage increase in the net capacity of the BP set. Another observation made is that for a given net capacity, it is better to have multiple BPs with smaller capacities than a single BP with high capacity. Although the problems pertaining to the gear manufacturing process simultaneously considering many real life situations have been addressed in this study, there are some limitations to it such as addressing of identical parallel machines instead of a general case of unrelated parallel machines (for Research Problem 1) and consideration of only deterministic situations for both the research problems. There are many immediate future research directions for the problem studied in this thesis such as overcoming the limitations mentioned in this study, proposing good lower bounds and additional heuristic algorithms, and coming up with integrating both, Research Problem 1 and Research Problem 2 and proposing solution methodologies for the integrated problem.

Thesis with the title "Life stories and professional careers of women headmasters of vocational high schools" deals with professional life of women headmasters of vocational high schools and analyzes this professional life. Per this analysis is detected, what is the benefit of these headmasters for school and if they promote a development of the school. Narrative analysis was used on this research.Beside the research there are answered other questions, which are related to professional life and are associated with the primary research question. There are described the phases of professional life and there are stated the effects, which influence the decision making of the headmasters. In the conclusion of research the headmasters alone evaluate their actions in position of headmaster.The primary research question is answered, how it results from research, all headmasters are benefit for their school. Schools, which were guided by them, had evolved and it is them, who are the reason of its growth. Recommendations for futher research is analysis of professional men headmasters.