Buğra Çetinkaya 030070094 Week 11 Part1

1) Advanced Composites (Group: Materials)

There is no old answer.

Advanced composite materials are defined as resin, metal, or ceramic matrix composite materials systems in which the reinforcement is com-posed of high-strength, high-modulus materials in continuous fiber or filament form. The reinforcement may also be discontinuous in form such as chopped fibers, whiskers, and in situ dispersions in metal, ceramic, and resin matrix materials. Principal attention is directed to the continuous fiber reinforced type of composite material in this discussion, although a brief review is provided for some composite systems that are reinforced with discontinuous forms.

Primary reinforcement materials are high-strength, high-modulus graphite, boron, glass, and aramid fibers. Although not truly an advanced reinforcement, fiberglass is included because of the broad, extensive use of this material in both military and commercial systems and products. Many other potential reinforcement materials are in more advanced stages of development than the primary materials and include reinforcements such as silicon carbide, alumina, and other oxide ceramics, and metallic wire or filaments including beryllium and tungsten. A brief consideration of some of these systems is included in this report.

(Admiral A. Watts, Commercial Opportunities for Advanced Composites, p. 1)

2) AC motor (Group: Mechanical Actuator)

Previous Answer
Electric motors designed to operate with alternating current (AC) supplies are themselves broadly categorized into two classes: induction and synchronous. There are many variations of synchronous machines. AC motors work by setting up a magnetic field pattern that rotates with respect to the stator and then employing electromagnetic forces to entrain the rotor in the rotating magnetic field pattern. Synchronous machines typically have a magnetic field which is stationary with respect
to the rotor and which therefore rotate at the same speed as the stator magnetic field. In induction motors, the magnetic field is, as the name implies, induced by motion of the rotor through the stator magnetic field.
(J.Kirtley, Electric Motor Handbook, pg.3)

New/Better Answer

AC motors consume alternating electrical power to produce mechanical actuation in terms of angular movement. The principle of operation for all AC motors relies on the interaction of a revolving magnetic field created in the stator by AC current, with an opposing magnetic field at the rotor. The opposing magnetic field is originated by virtue of induction or by supplying an armature current by a separate DC current source. The principle of operation of AC motor in relation to the origin of opposing field differs. Accordingly, AC motors are of two types. These are:

• Induction motor

• Synchronous motor

AC motors are either single phase or multiphase, depending upon the input signal requirement and internal construction.

1. Induction Motors:

The interaction of magnetic fields of the rotor and the stator makes the induction motor to rotate. The stator windings arc connected to the power supply, which could be one or multi-phase type. For example, a single-phase induction motors is connected to the single-phase power line and 3-phase induction motors to the 3-phase power line, respectively.

When an alternating voltage across the stator windings is applied, a radial rotating magnetic field is produced. The rotor has conductive loop (conductor coil) along its periphery. The rotating magnetic fields produced by the stator induce a current into the conductive loops of the rotor. Once that occurs, the magnetic field causes forces to act on the current carrying conductors, which results in a torque on the rotor.

2. Synchronous Motors:

The synchronous motor is a 3-phase system in which the magnets are mounted on the rotor and are excited by DC current. The stator winding is divided into three pans, which are fed with 3-phase AC current respectively. Because of the nature of connection, the magnetic field rotates at a constant speed that is determined by the frequency of the current in the AC signal. The variation of the three waves of current input to the stator winding causes a varying magnetic interaction with the poles of the magnets of the rotor. This, in turn, causes the rotor to rotate. Typical characteristics of synchronous motors can be attributable to as follows. They:

• Run at constant speed fixed by frequency of the input power signal

• Require DC current for excitation

• Have low starting torque
(Nitaigour Premchand Mahalik, Mechatronics, pp. 244-245)

3) DC motor (Group: Mechanical Actuator)

 
Previous Answer
DC motors, as the name implies, operate with terminal voltage and current that is “direct”, or substantially constant. While it is possible to produce a “true DC” machine in a form usually called “acyclic”, with homopolar geometry, such machines have very low terminal voltage and consequently high terminal current relative to their power rating. Thus all application of DC motors have employed a mechanical switch or commutator to turn the terminal current, which is constant or DC, into alternating current in the armature of the machine.DC motors have usually been applied in two broad types of application. One of these categories is when the power source is itself DC. This is why motors in automobiles are all DC, from the motors that drive fans for engine cooling and passenger compartment ventilation to the engine starter motor. A second reason for using DC motors is that their torque-speed characteristic has, historically, been easier to tailor than that of all AC motor categories. This is why most traction and servo motors have been DC machines. For example, motors for driving rail vehicles were, until recently, exclusively DC machines.
(J.Kirtley, Electric Motor Handbook, pg.2-3)

New/Better Answer

DC motor is the most versatile actuator and sometimes called rotating machine. The DC motor has two parts, stator and rotor. The stator is the outer part of the motor which contains evenly spaced magnetic poles as shown in the Fig. 7.2.

Depending upon the rotor's physical characteristics and other load related design parameters, such as rotational inertia, torque, speed, etc. the number of magnets to be put into place varies. Moreover, the design parameters entail whether to design a permanent magnet type or electromagnet type stator. DC motors are classified according to the way the magnetic field is established. The stator field is established by either permanent magnets or by an electromagnet. Taking into account of this, two types of DC motors are seen. They are:

• Permanent magnet type DC motors

• Electromagnet type DC motor or wound-field DC motor

Permanent magnet type motors have permanent magnet (s) in the stator. While small motors require low amount of torque, large motors employed in many heavy-duty applications such as traction, electric trolleys, locomotives, mills etc., require large torque. In the latter case, the electric field is established by electromagnets.

Practically two windings are there within the electromagnetic type motor system, namely, suitor winding (s) and rotor winding (s). In some literature the stator winding (s) is called field coil or field winding. The current through the field coil is called field current. Stator winding (s) develop electromagnet (s) which in turn establish the magnetic field. Rotor winding (s) develop electromagnet (s) which in turn rotates itself. The field winding (s) and armature winding (s) are connected in a number of ways, leading to different types of electromagnet type DC motors.

(Nitaigour Premchand Mahalik, Mechatronics, pp. 238-240)