Sas Institute’s “Best Employer Award” Essay Example for Free

Sas Institute’s â€Å"Best Employer Award† Essay SAS Institute’s â€Å"Best Employer Award† is based largely on its financial success and the overwhelming job satisfaction its employees report. From free health care to copious amounts of MMs, SAS spares no cost to keep their â€Å"chief assets† happy, for, as their CEO / majority owner says Contented cows give more milk. Still, today’s talented workers are not apt to spend the majority of their careers at one company because of luxurious perks. The truth is that what seems like random and excessive, is actually a well-crafted and impeccably executed strategy to create an unparalleled work and life environment. SAS is successful in applying the principles of Cognitive Evaluation Theory that emphasize keeping employees’ cognitive attention on intrinsic rewards rather than extrinsic ones. SAS steers clear of Insufficient Justification or Insufficient Punishment by deemphasizing such extrinsic rewards as pay and promotion, and instead emphasizing intrinsic controllable rewards as membership within a community and a way of life. For example, SAS’s unique sick-day policy which, in contrast to industry standards, does not have a set number of allowable sick-days. David Russo states, â€Å"If youre out sick for six months, youll get cards and flowers†, and â€Å"We expect adult behavior. The result is that SAS employees average only two sick days annually. The focus on â€Å"Adult behavior† makes employees feel responsible for their obligation to the company as part of their overall reciprocity for all that the company has done for them. The lack of any real explicit punishment actually creates intrinsic pressure on the individual employee to not to take advantage of the policy in order to keep his self-perception in line with beliefs about being a good and accountable employee. By downplaying pay as an extrinsic reward and gauge of performance, SAS successfully uses Insufficient Justification to help in sidestepping the usual salary comparisons issues. The informational aspect of Cognitive Evaluation Theory is crucial to the understanding of SAS’s unique structure and policies. SAS avoids assigning tasks that have high probability of failure. Also it allows its employees freedom in choosing what to work on. As Goodnight states, â€Å"If theyve grown bored with their job, they have great freedom to move horizontally instead of having to hunt for another employer.† Jenn Mann echoes Goodnight when she states, â€Å"nobody much cares whether you show up at 9 or 11.† Taking the focus off such trivial extrinsic matters frees up employees to focus their attention on intrinsic motivations such as having fun. Self-concordance suggests that these intrinsic motivations are stronger, more internally justifiable and therefore much more likely to make the individual work harder to achieve his goal. SAS uses Needs Theory to focus its recruiting on people who exhibit a high need for affiliation and achievement, while paying close attention to those with an overtly high need for power. To cater to high achievers’ needs managers make sure to assign tasks that are realistically achievable within the prescribed timeframe and the individual’s competencies. Managers provide subordinates with rapid feedback through everyday walking and talking techniques. Praise and recognition are also provided through increasing responsibilities and tasking employees with full ownership of their products including placing their names on the finished product. Knowing that high achievers generally do not possess the gamblers mentality, SAS tailors its incentive package around security and predictability. Bonuses are not emphasized and stock options are not granted. Instead, employees are offered a competitive salary, full 401K contribution and a myriad of non-merit based benefits for thems elves and their families. For those with a high need for power, SAS provides autonomy, a collaborative environment and control over the life-cycle of a product. For example, each employee gets to plan his own schedule. SAS’s thinly staffed management ranks are designed to boost reliance on an honor code that emphasizes, above all else, adult behavior. This produces ample opportunities for employees to take on additional responsibilities. As a result, employees feel a sense of power and control over their work. SAS does differentiate those individuals whose need for control extends to control over others, or whose need for recognition extends to being treated like superstars. David Russo states, â€Å"SAS is not a good place for someone who wants to feel like a star or feel particularly important†. Recruiters reject these want-to-be star applicants because they believe SAS’s structure and environment cannot accommodate their needs. The need for affiliation is nurtured through a work-life balance that stresses community over personal economic gain. As stated in the article, â€Å"The perks are the most obvious manifestation of corporate munificence, but at their core they are only part of a workplace ethos thats based on a degree of trust.† SAS takes advantage of its relative isolation to reinforce its middle class utopian environment. By design, almost all essential services are provided on campus and by SAS employees. This includes healthcare, education, food services, entertainment, recreation and even subsidized housing (near the campus). The company organizes a plethora of extracurricular group activities that encourage collaboration, provide needed support and connects people on a personal level. Its success in satisfying employees Need for Affiliation manifests itself in SAS’s historical low turnover rate. An unfortunate byproduct of SAS’s homogenous environment is its relative lack o f innovation. Innovation, the better use of a novel idea or method, is a crucial element to the growth of a corporation. SAS has indubitably been successful in reshaping its own software and selling it to additional markets, but has not had the same success in branching out and innovating in other areas. Perhaps SAS, a monopoly in the data software industry, has consciously elected to steer clear of this more risky innovation because of financial and social concerns. Attraction-Selection-Attrition (ASA) model helps explains why today’s SAS, while still being remarkably efficient at providing new or improved software, is not truly a leading innovator. SAS’s pay structure and overall emphasis on a family friendly, low stress environment is a conscious effort to attract the more risk adverse individual. The selection process takes care to repel mavericks who seek power and fame. The problem is that these competitive, challenging personalities are willing to take more chances. SAS is a g reat example of ASA’s chief assertion that â€Å"The People Make the Place†. But while preaching autonomy and individuality, SAS employees are quietly advocating for conformity, cloaked as corporate citizenship. The resulting atmosphere works, through attrition, to weed out any nonconformist. Pushing out dissident voices makes the remaining collective even more homogenous and less likely to innovate. The fact that SAS’s retention at this point is so low is another indication of the high level of homogeneity. The company’s reliance on a small number of working managers makes self-regulation or as they call it â€Å"adult behavior† an essential part of the overall strategy of an employee-regulated firm. Thus, SAS’s focus on attracting and selecting a particular type of risk adverse individual, while allowing attrition to remove dissidence is an effective use of ASA, all be it a rather insensitive one. These polices have essentially forced SAS to outsources the task of innovating to its client base through constant solicitation of fee dback and ideas. Another theory that could explain SAS’s relative weakness in innovation is Equity Theory which focuses on perceptions of fairness. SAS does a good job of shaping their employees perceptions of its overall Organizational Justice through such techniques as the allocation of offices for all, having no executive cafeterias and providing identical health plans for all. The two core principles for SAS are â€Å"†¦that all people at SAS are treated fairly and equally† and â€Å"†¦that the workplace should be fun and people treated with dignity and respect†. The problem is that the two principles are different. The first advocates equality and the latter respect. Treating people with respect and dignity is universally accepted and supports employees’ feelings of Interactional Justice. Equal treatment for all is not universally accepted, and conflicts with the reality of varying levels of individual contributions to a company’s success. Universal equality skews the individual’s perception of Procedural and Distributive Justice. Talented, hardworking employees find it hard to stand out because both the evaluation process and the resulting recognition are purposefully watered down. This lack of strong correlation between risk and reward, input and output makes it less likely that unique innovation will occur b ecause the risk–taking innovator will perceive an inequitable Distributive Justice. The inequitable feeling is compounded by SAS casually defined performance review process which could leave successful innovators feeling a lack of Procedural Justice. Equity theory states that there are four referent comparisons that an employee can use to gauge equitability of his situation. Even if SAS is successful, through isolationist polices, in sheltering its employees from other-outside comparison, it still needs to contend with employees’ past experiences and internal company comparisons. Admittedly, general perception of equality is a major factor in SAS’s tremendous retention rate, but for those few want-to-be superstars it’s a major deterrent to joining the firm. This is evident in the interviewee who stated â€Å"I want to have performance that permits me to do whatever I want. When I walk down the hall, I want to feel like ‘I’m the man.† Who wouldn’t want their stellar performance to lead to more money, autonomy, recognition and better future opportunities? At SAS this potential innovator was quickly ushered out the door. For good or bad, SAS is built around a sense of equality and homogeneity, even if these terms are relative and somewhat reminiscent of an Orwellian Society, where all are equal, but some are just more equal than others. To protect its successful egalitarian culture, SAS would do better to create (like many other have) a separate off-campus RD offshoot. With a distinct culture and a more equitable compensation structure, this entity can compete for innovative talent.

Aeronautical Engineers Essay example -- Papers

Aeronautical Engineers Description Aeronautical engineers apply the principle of science and technology in work with highly sophisticated products such as aircrafts, missiles and space satellites. They usually specialise in research, design manufacture and production, or the management of maintenance programs Qualifications required The usual qualifications for entry into this career is a degree. However, it may be possible to enter with an HND or HNC. Entry to a relevant engineering degree with: * 2/3 A-levels with GCSEs (A-C) 2/3 in other subjects * A relevant GCSE in a vocational subject or Intermediate GNVQ may be acceptable as an alternative to academic GCSEs * At A level, Maths and Physics are often preferred and may be essential. Equivalent qualifications such as an Edexcel (BTEC) or National Certificate or National Diploma or a Vocational A level (Advanced GNVQ) may be acceptable, it may also b advisable to check the prospectus. 1 A-level with 4 GCSEs (A-C). At A level, maths or physics is preferred. Again, equivalent qualifications are usually acceptable. Skills and Qualities necessary * You must be able to combine an analytical, logical approach with creativity and imaginations to solve problems * Engineers must be able to work as part of a team. The ability to encourage other peoples ideas is important, and you must aslope be flexible and able to compromise. You will need strong communication skills to write reports and to explain complex engineering information to people from non-technical backgrounds. * You will need organisationa... ...rlines, the Armed Forces and the Ministry of Defence. Some Aeronautical Engineers apply their knowledge of Aeronautical in other areas, for example, in companies that make vehicles such as cares, trains and hovercrafts. You can also work in the communication industry, dealing with satellites, or in construction, dealing with high, winds blown structures. Contacts EMTA, Engineering Careers Information Service (ECIS), Emta House, 14 Upton Road, Watford, Hertfordshire WD18 0JT. (Freephone: 0800 282167)] Telephone :01923 238441 Email: ecis@emta.org.uk Website: www. Enginuity.org.uk Employer Engineering and Physicals Sciences Research Council (EPSRC), Polaris House, North Star Avenue, Swindon SN2 1ET (Award) Telephone :01793 444100 Email: infoline@epsrc.ac.uk Website: www. epsrc.ac.uk

Electromechanical Energy Conversion

Introduction Chapter 3 Electromechanical Energy Conversion Topics to cover: 1. Introduction 3. Force and Torque 5. Friction 2. Electro-Motive Force (EMF) 4. Doubly-Excited Actuators 6. Mechanical Components Introduction (Cont. ) For energy conversion between electrical and mechanical forms, electromechanical devices are developed. In general, electromechanical energy conversion devices can be divided into three categories: – Transducers (for measurement and control), which transform signals of different forms. Examples are microphones, pickups, and speakers Force producing devices (linear motion devices), which produce forces mostly for linear motion drives, such as relays, solenoids (linear actuators), and electromagnets. – Continuous energy conversion equipment, which operate in rotating mode. A device would be known as a generator if it convert mechanical energy into electrical energy, or as a motor if it does the other way around (from electrical to mechanical). Lor entz Force & EMF Lorentz force is the force on a point charge due to electromagnetic fields. It is given by the following equation in terms of the electric and magnetic fieldsF ? q(E? v? B) The induced emf in a conductor of length l moving with a speed v in a uniform magnetic field of flux density B can be determined by a e ? ?v? B? ? dl ? b In a coil of N turns, the induced emf can be calculated by e ? ? Concept map of electromechanical system modeling d? dt where ? is the flux linkage of the coil and the minus sign indicates that the induced current opposes the variation of the field. It makes no difference whether the variation of the flux linkage is a result of the field variation or coil movement. EMF EMF – Example: EMF in a Linear Actuator – Example SolutionSketch L(x) and calculate the induced emf in the excitation coil for a linear actuator shown below. Assuming infinite permeability for the magnetic core and ignore the fringing effect, we can express the self inductance of the coil as L? x ? ? where Rg ? x? ? N2 ?o N 2 l ?d ? x? ? Rg ? x ? 2g L(x) L(0) 2g ?o ? d ? x? l O is the air gap reluctance. ? e? ? N 2l d? d ? Li ? di dL dx di ? ? L ? i =L? x ? ? i o v 2g dt dt dt dx dt dt EMF – A Single Conductor in a Uniform Field e ? ? I dc If i=Imsin? t , e? Force and Torque – Example Solution (Cont. ) If i=Idc , ?o N 2 l 2g ? Im ? Im ?o N 2l 2gFor a single conductor in a uniform magnetic field, we have v ? d ? x I m cos ? t ? vI m sin ? t ?o N l 2 2g ?o N 2 l 2g d Fm ? Il ? B ?o N 2 l In a rotating system, the torque about an axis can be calculated by 2g d ? x cos? t ? v sin ? t ? ? T? r ? Fm v ? ? ? ? d ? x ? ? ? ? d ? x ? 2 ? 2 ? v 2 cos t ? arctan? ? where r is the radius vector from the axis towards the conductor. B Fm l I X Force and Torque – A Singly Excited Actuator Consider a singly excited linear actuator. After a time interval dt, we notice that the plunger has moved for a distance dx under the action of the force F.The mechanical work done by the force acting on the plunger during this time interval is thus dWm ? Fdx Force and Torque – A Singly Excited Actuator The amount of electrical energy that has been transferred into the magnetic field and converted into the mechanical work during dt is dWe ? dWf ? dWm ; dWe ? eidt ? vidt? Ri2dt e ? d? dt ? v ? Ri Because dWf ? dW ? dW ? eidt ? Fdx ? id? ? Fdx e m we obtain From the total differential dW f ? ? , x ? ? ? W f , x ? i? Therefore, ? W f , x ? d? ? and ? W f , x ? ?x F dx ?W f ? ? , x ? ?x Force and Torque Force and Torque – A Singly Excited Actuator (Cont. ) A Singly Excited Actuator (Cont. ) From the knowledge of electromagnetics, the energy stored in a magnetic field can be expressed as ? Wf ? ? , x? ? ? i? ? , x? d? In the diagram below, it is shown that the magnetic energy is equivalent to the area above the magnetization or ? -i curve. Mathematically, if we define the area underneath the magnetization curve a s the coenergy (which does not exist physically), i. e. 0 For a magnetically linear (with a constant permeability or a straight line magnetization curve such that the inductance of the coil is independent of the excitation current) system, the above expression becomes 1 ? Wf ? ?, x? ? 2 L? x? and the force acting on the plunger is then F ?Wf ? ?, x? ?x 1 ? ? ? dL? x? 1 2 dL? x? ?i 2 ? L? x? ? dx 2 dx ? 2 we can obtain Wf ‘ ? i, x? ? i? ?Wf , x? ? Wf (? , x ) dW f ‘ ? i , x ? ? ? di ? id? ? dW f ? ? , x ? ? ? di ? Fdx Therefore, ? ?W f ‘ ? i , x ? ?i ? W f ‘ ? i , x ? ?i di ? and ?W f ‘ ? i , x ? ?x F? dx ? W f ‘ ? i , x ? ?x (? , i ) Wf ‘ ( i, x ) O i Force and Torque Force and Torque – A Singly Excited Actuator (Cont. ) – Example 1 Calculate the force acting on the plunger of a linear actuator as shown below. From the definition, the coenergy can be calculated by iWf ‘ ? i , x? ? ? ? ? i , x? di ? 0 Wf ‘ ? i, x? ? ? (? , i ) Wf (? , x ) For a magnetically linear system, the above expression becomes Rg 1 L? x? i 2 2 Ni Wf ‘ ( i, x ) Rg and the force acting on the plunger is then F? ?Wf ‘ ? i , x ? ?x 1 dL? x ? ? i2 dx 2 O i (c) Force and Torque Force and Torque – Singly Excited Rotating Actuator – Solution to Example 1 Assume infinite permeability for the actuator core. The self inductance of the excitation winding can be readily obtained as L? x? ? N 2 ? o N 2l? d ? x? ? 2Rg 2g Therefore, the force acting on the plunger is F? ? Rg Ni ?l 1 2 dL ? x ? 2 i ? ? o ? Ni ? 2 dx 4gThe minus sign of the force indicates that the direction of the force is to reduce the displacement so as to reduce the reluctance of the air gaps. Since this force is caused by the variation of magnetic reluctance of the magnetic circuit, it is known as the reluctance force. Rg The singly excited linear actuator becomes a singly excited rotating actuator if the linearly movable plunger is repla ced by a rotor. Through a derivation similar to that for a singly excited linear actuator, one can readily obtain that the torque acting on the rotor can be expressed as the negative partial derivative of the energy stored in the agnetic field against the angular displacement or as the positive partial derivative of the coenergy against the angular displacement. Force and Torque Solution b) Voltage induced – Example †¢ The magnetically-linear electro-mechanical circuit breaker as shown is singly-excited via a N-turn coil. Its magnetic reluctance varies with the angle ? as R ? Rm? ? R0 , where Rm and R0 are constant. †¢ Derive the torque developed by the field from the system co-energy. †¢ When the device is excited with a direct current i=I, the angular displacement increases quadratically as ? ?t ? ? 1 ? t 2 ? ?t ? ? 0 , 2 where ? ? and ? 0 are constant. Find the voltage induced in the coil . Singly Excited Rotating Actuator Total turns, N = N1 + N2 Frame relu ctance Rf ? rf 2 Gap reluctance Rg ? 2rg ? ? lf 2? 0 ? r wd 2lg ?0rd (2? ? ? ) , 2? ? 760 ? 1. 33 rad Rg(? ) Rcore ?g Rarmature Fm=Ni e(t ) ? ? N 2 IRm (? t ? ? ) [ R0 ? Rm 1 ? t 2 ? ?t ? ? 0 ]2 2 ? Singly Excited Rotating Actuator ? Singly Excited Rotating Actuator airgap length, lg = 0. 001 m airgap radius, r = 0. 0745 m airgap depth, d = 0. 0255 m frame length lf = 0. 496 m limb width w = 0. 024 m Singly Excited Rotating Actuator ? (? ) ? T? ? NI R f ? Rg (? ) lf Rf ? 2 ? ? r wd Magnetic flux at equilibrium : ? NI ?0 ? ? ? R (? ) ? R f ?g ? ? ?0 NI lf 2 ? 0 ? r wd ? lg ?0rd? ? , Rg ? 2l g ?W f? ? ? ? N2 ? ?, ? R (? ) ? R ? f? ?g dRg dRg 2l g sign(? ) , where ? d? d? ?0 rd (2? ? ? )2 1 2 ? L(? ) 1 2 ? I ?I 2 2 122 ?1 IN 2 ?Rg (? ) ? R f ? 2 2l Rr sign(? ) 1 ? ? I 2N 2 , where Rr ? g 2 2 ?0 rd 4 ?Rg (? ) ? R f ? (2? ? ? ) ?0 rd (2? ? ? ) Restoring Torque ?1, x ? 0 sign ( x ) ? ? 1, x ? 0 NI? 0d lf l ?g 2 ? r w r? Force and Torque Singly Excited Rotating Actuator – Sing ly Excited Rotating Actuator (Cont. ) Torque Nm Flux mWb Flux, Torque for 2-pole motorEnergy In g eneral, 1. 5 Coenergy dW f ? id? ? Td ? dW f ‘ ? ? di ? Td ? ? i W f ? ? , ? ? ? ? i ? ? , ? ?d ? W f ‘ ? i , ? ? ? ? ? ?i , ? ?di ?W f ? ? , ? ? i? ?W f ? ? , ? ? T ?W f ‘ ? i , ? ? ?i ?W f ‘ ? i , ? ? T? 0 1. 0 mWb, Nm 0. 5 0 If the permeability is a constant, W f , ? ? ? 0. 0 0 5 10 15 20 25 30 35 40 45 rotor angle 50 55 60 65 70 75 80 1 ? 2 2 L ? 1 ? ? ? dL ? 1 2 dL ? ?i 2 ? L ? ? d ? 2 d? ? ? W f ‘ ? i , ? ? ? 2 T? T? 12 i L ? 2 1 2 dL ? i 2 d? Force and Torque Force and Torque – Doubly Excited Rotating Actuator – Doubly Excited Rotating Actuator (Cont. If a second winding is placed on the rotor, the singly excited actuator becomes a doubly excited actuator. The general principle for force and torque calculation discussed here is equally applicable to multi-excited systems. The differential energy and coenergy functions can be derived as dW f ? dWe ? dWm where dWe ? e1i1dt ? e2 i2 dt , e1 ? d? 1 dt , e2 ? d ? 2 dt , and dWm ? Td ? Hence, dW f 1 , ? 2 , ? ? ? i1d ? 1 ? i2 d ? 2 ? Td ? ? and ? W f 1 , ? 2 , ? ? ? W f 1 , ? 2 , ? ? ? W f 1 , ? 2 , ? ? d ? 1 ? d ? 2 ? d? 1 2 ? ? dW f ‘ ? i1 , i 2 , ? ? ? d i1 ? 1 ? i 2 ? 2 ? W f ? 1 , ? 2 , ? ? ? ?1 di1 ? ?2 di 2 ? T d ? ? ? W f ‘ ? i1 , i 2 , ? ? Therefore, T ? i1 di1 ? ? W f ‘ ? i1 , i 2 , ? ? ?Wf 1 , ? 2 , ? ? ? i2 or di 2 ? T? ? W f ‘ ? i1 , i 2 , ? ? Force and Torque – Doubly Excited Rotating Actuator (Cont. ) – Example 3 ? ? L? 1 For magnetically linear systems, ? ? 1 ? ? L11 ? ? ? L ? 2? ? 21 L 1 2 ? ? i1 ? L 22 ? ?i2 ? ? ? i1 ? ? ? 11 ?i ? ? ? ? ? 2? ? 21 or ? 1 2 ? ? ? 1 ? ? 22 ? ? ? 2 ? ? The magnetic energy and coenergy can then be expressed as W f ? ?1 , ? 2 , ? ? ? Therefore, d? ? W f ‘ ? i1 , i2 , ? ? Force and Torque and 1 1 2 ? 1 1 ? 12 ? 2 2 ? 2 ? ? 1 2 ? 1 ? 2 2 2 W f ‘ ? i 1 , i 2 , ? 1 1 L 1 1 i 12 ? L i 2 ? L 1 2 i1i 2 2 2 22 2 ? W f ‘ ? i 1 , i 2 , ? ? 1 2 d L 1 1 ? 1 2 d L 2 2 ? d L 1 2 ? ? i1 ? i2 ? i1i 2 2 2 T ?W f 1 , ? 2 , ? ? ? A magnetically-linear doubly-fed electromechanical actuator has two windings and a mechanical output with spatial rotary displacement ?. The self and mutual inductances of the windings are respectively L11 ? ? 5 ? cos(2? ) mH, L22 ? ? 50 ? 10 cos(2? ) mH, and L12 ? ? L21 ? ? 100 cos? mH. Brushless doubly-fed machine The first winding is supplied with i1 = 1. A while the second winding draws i2 = 20 mA. Determine: a) The general electromagnetic torque of the actuator as a function of ? . b) The maximum torque that the actuator can develop. Solution to Example 3 (a) Solution to Example 3 (cont. ) The  energy  stored  at  the  doubly? fed  actuator  is, 1 1 2 2 W f ? L11i1 ? L12 i1i2 ? L22 i2 2 2 1 1 ?3 2 ?3 2 ? (5 ? cos 2? ) ? 10 i1 ? (0. 1cos? )i1i2 ? (50 ? 10 cos 2? ) ? 10 i2 2 2 The  ex pression  of  electromagnetic  torque  is  obtained  as  follows:   ? ?W f (i1 , i2 ,? ) T ? i1 ? 1. 5, i2 ? 0. 02 ? 2 2 1 ? (i1 L11 ) ? (i1i2 L12 ) 1 ? (i2 L22 ) ? ? ? 2 2 1 1 (1. 5) 2 ( ? 2 sin 2? ) ? 10 ? 3 ? (1. 5)(0. 02)(? 0. 1sin ? ) ? (0. 02) 2 ( ? 20 sin 2? ) ? 10 ? 3 2 2 ?3 ? ? ( 2. 25 sin 2? ? 3 sin ? ) ? 10 Why Magnetic Field? Ratio of Electric and Magnetic Energy Densities in the air gap we ? 0 ? 0 E 2 1 ? ? wm B2 3. 6 ? 10 5 †¢ Saturation Flux Density Bs = 2T in commonlyused magnetic materials †¢ Air breakdown voltage Ebd=1,000,000 V/m b) At  maximum  torque, dT ?0 d? Differentiating  T  from  part  (a), 4. 5 cos 2? ? 3 cos ? ? 0 ? 1. 5 cos 2? ? cos ? ? 0 or               1. 5( 2 cos 2 ? ? 1) ? cos? ? 0 Solving  for  ? by  the  quadratic  formula, ?  =  55. 94 °Ã‚  and  153. 25 °Ã‚  (extraneous)Substituting  the  value  of  ? into  the  torque  expression  yields, T(max) ? ?(2. 25 s in 2(55. 94) ? 3 sin(55. 94)) ? 10 ? 3 ? ?4. 57 ? 10 ? 3 Nm Electric Machines †¢ Electric motor converts electrical energy into mechanical motion. †¢ The reverse task, that of converting mechanical motion into electrical energy, is accomplished by a generator or dynamo. †¢ In many cases the two devices differ only in their application and minor construction details, and some applications use a single device to fill both roles. For example, traction motors used on locomotive often perform both tasks if the locomotive is equipped with ynamic brakes. Introduction Electric Motors Electric Machine Insulation Class DC Motors Universal (DC/AC) AC Motors †¢ Induction †¢ Synchronous Stepping Motors Brushless DC Motors Coreless DC Motors Linear Motors MEMS Nano Motors †¢ A critical factor in the reduced life of electrical equipment is heat. The type of insulation used in a motor depends on the operating temperature that the motor will experience. †¢ Average insulation life decreases rapidly with increases in motor internal operating temperatures. †¢ Electric motor converts electrical energy into mechanical motion: Lorentz force on any wire when it is onducting electricity while contained within a magnetic field †¢ Rotor: rotating part †¢ Stator: stationary part †¢ Armature: part of the motor across which the voltage is supplied MaglevMagnetic Levitation Three phase AC induction motors rated 1 Hp (750 W) and 25 W with small motors from CD player, toy and CD/DVD drive reader head traverse DC Generators / Dynamos AC Generators / Alternators As the first electrical generator capable of delivering power for industry, the dynamo uses electromagnetic principles to convert mechanical rotation into a pulsing direct electric current through the use of a commutator.Without a commutator, the dynamo is an example of an alternator, which is a synchronous singly-fed generator. With an electromechanical commutator, the dynamo is a classical direct current (DC) generator. The DC generator can operate at any speed within mechanical limits but always outputs a direct current waveform. Mechanical energy is used to rotate the coil (N turns, area A) at uniform angular velocity ? in the magnetic field B, it will produce a sinusoidal emf in the coil: Permanent Magnet DC Generators d? d ? ? ( NBA cos ? ) dt dt ? NBA? sin ? t e(t ) ? ? http://micro. magnet. fsu. edu/electromag/java/generator/dc. tml Automotive alternator Rotor emf and current are induced by rotating magnetic field http://micro. magnet. fsu. edu/electromag/java/generator/ac. html Mechanical Components Mechanical Components – Mass and Inertia The mechanical component which stores kinetic energy is a mass in a translational system, and a moment of inertia in a rotational system. – Mass and Inertia (Cont. ) The kinetic energy stored by a mass moving at a velocity v, or a moment of inertia rotating at an angular speed ?. can be calculated by ? x M T F J Wk ? 1 Mv2 2 d? d 2? T? J 2 ? J dt dt dv d 2x F? M ?M dt 2 dt 1 J? 2 2 (translational system) rotational system) Comparing with the relationships of voltage, current, and magnetic energy in an inductor: V? L By the Newton’s second law, we have Wk ? or di dt and WL ? 1 Li2 2 we may regard a mass or a moment of inertia as an inductor which stores magnetic energy, if we let J? L M? L or Mechanical Components Mechanical Components – Springs An ideal spring is a device with negligible mass and mechanical losses, whose deformation is a single-valued function of the applied force or torque. A linear ideal spring has deformation proportional to force or ? 1 torque. – Springs (Cont. ) For a given distortion of x and ? the potential energy stored in a spring is 1 1 W p ? ? Td ? ? K ? 2 W p ? ? Fdx ? Kx 2 T x1 F ? K ? x 1 ? x o ? ? Kx (linear spring) (torsional spring) Comparing with the relationships of electric charge, voltage and electric energy in a capacito r: Q V? C F 2 2 WC ? and 1 1 Q2 VQ ? 2 2C we may regard a spring as an electric capacitor which stores electric potential energy, if we let T ? K 1 ? ?o ? ? K ? K? 1 C Friction Friction Modelling Friction: force that opposes the relative motion or tendency of such motion of two surfaces in contact. Friction between the two objects converts kinetic energy into heat.Coefficient of friction (Frictional coefficient): dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together, needs not be less than 1 – under good conditions, a tire on concrete may have a coefficient of friction of 1. 7. Static friction (stiction) occurs when the two objects are not moving relative to each other: Rolling friction occuring when one object â€Å"rolls† on another (like a car's wheels on the ground), is stiction as the patch of the tire in contact with the ground, at any point while the tire spins, is stationary relati ve to the ground.Kinetic (or dynamic) friction occurs when two objects are moving relative to each other and rub together: – Sliding friction is when two objects are rubbing against each other. – Fluid friction is the friction between a solid object as it moves through a liquid or a gas. The drag of air on an airplane or of water on a swimmer are two examples of fluid friction. Lu-Gre Model (1995): ? 0 , ? 1 bristles’ stiffness and damping coefficient ?2 viscous friction FC , F S Coulomb and Stribeck friction ? F f ? ? 0 z ? ? 1z ? ? 2v ? z? v? v z g (v ) 2 1 g (v ) ? [ FC ? ( F S ? FC ) e ? v / v S ) ] ?0 Mechanical Components Mechanical Components – Damper The mechanical damper is analogous to electrical resistor in that it dissipates energy as heat. An ideal damper is a device that exhibits no mass or spring effect and exerts a force that is a function of the relative velocity between its two parts. A linear ideal damper has a force proportional to the relative velocity. In all cases a damper produces a force that opposes the relative motion of the two parts. Mechanical friction occurs in a variety of situations under many different physical conditions.Sometimes friction is unwanted but must be tolerated and accounted for analytically, as, for example, in bearings, sliding electrical contacts, and the aerodynamic drag on a moving body. In other cases friction is desired and is designed into equipment. Examples are vibration dampers and shock absorbers. d ? x2 ? x1 ? dt dx ?B dt F? B ? B? R d 2 ? ?1 ? dt d? ?B dt T? B – Damper (Cont. ) Mechanical Components Mechanical Components – Damper (Cont. ) The damping due to Coulomb friction, as shown by the characteristic, can be regarded as a nonlinear resistor, which can keep the voltage across it to be constant.The Coulomb friction force can be expressed as – Damper (Cont. ) There is another kind of damping caused by the drag of a viscous fluid in turbulent flow. 2 F ? ? Bs d x2 ? x1 dt F ? ?d Fn ? ? d Fn d ? x2 ? x1 ? dt ? ? ? Bs dx dt d ? x2 ? x1 ? dt ? 2 ? R ? B s dx dt dx dt ? dx dt or T ? ? Bs d 2 ? ?1 ? dt Comparing with V=RI, we may conclude that ?F R? d n dx dt ? ? ? Bs d? dt ? ? 2 2 ? R ? B s d ? dt MR Dampers as a semi-active device MR Damper New Models Non-symmetrical Model (2007) ? F ( x) ? c0 x ? ko ( x ? x0 ) ? ?z ? ? ? z ? (? ? ( ? ? ? sign( zx) z ) x n : hysteresis variable, ? , ? , ? , ? , n, c0 , k0 : model parameters Bouc-Wen Model: ? F ( x ) ? c0 x ? k o ( x ? x0 ) ? ? z ? ? ? ? z ? ? ? z | x || z | n ? 1 ? ? x | z | n ? ? x z: hysteresis variable , ? , ? , ? , ? , n , c 0 , k 0 : model parameters Static Hysteresis Model (2006) ? F ( x) ? cx ? kx ? ?z ? f 0 ? z ? tanh( ? x ? sign( x)) z : hysteresis variable, ? , ? , f 0 , c, k : model parameters Minimally-Parameterised Model (2007) ? F : G ( x ) ? D ( x ), F ( x) ? ? 1 ? F2 : G ( x ) ? D ( x ), b G ( x) ? a ? ? 1 ? exp ( cx ) ? D ( x ) ? rexp{? ( x / 2? ) 2 } ? 0 x ? 0, x

What Is The Pioneer Of An Atfolios - 1168 Words

Organization composing reveals that speculations have been refined and changed with segment of time and none of the theory is absolutely unnecessary. As indicated, congruity depends on upon the setting in that it is associated. The kind of organization associated in limits including abnormal state of precision, assurance level, affectability, mind and concentrated capacity may be not the same as in clear organization orchestrated portfolios, as one that does not fit all heads (Dess, and Picken, 2000). It infers that conditions, settings, culture, working condition, new laws and bearings, information over-weight, various leveled complexities and psycho-socio upgrades astoundingly influence the organization thought along these lines, making†¦show more content†¦Transformational pioneers animate others to finish more than they at first proposed and consistently a great deal more than they thought possible. They set all the more troublesome cravings and consistently finish highe r execution. Truthfully, transformational activity tends to have more devoted and satisfied followers. This is generally so in light of the fact that transformational pioneers connect with enthusiasts. Esteem based Leadership Style Esteem based expert style contains three sections; surprising prize, organization by-exception (dynamic) and organization by-extraordinary case An esteem based pioneer takes after the arrangement of unexpected prizes to reveal execution yearning to the fans and recognizes awesome execution. Esteem based place stock in legitimately restricting understandings as fundamental partners (Bass, 1985) and use outward rewards toward redesigning supporters motivation. The composition revealed that the esteem based style ruins creative ability and can inimically affect laborers work satisfaction. Organization by-exceptional case clears up pioneers direct with deference capable acknowledgment of deviations from expected supporters lead. The utilization of both styles changes from situation to condition and setting to setting. The conditions including abnormal state of