1. 11. Actuation

2. 전자학 프로젝트 예비발표 : 4분 발표, 2분 논의
11월 18일 1시 ~ 2시 50분, 전자학 실험실(24-114)
전자학 학기말 시험 : 12월 9일 금요일 1시 ~ 2시 50분, 강의실(28-301)
1) 회로 분석/설계만
2) 강의 7(Digital Circuits)까지의 회로에 대한 원리 이해가 중요
전자학 프로젝트 발표 : 12월 16일 금요일 1시 ~ 6시, 전자학 실험실(24-114)

3. Electric motors
An electric motor uses electrical energy to produce mechanical energy. The reverse process, that of using mechanical energy to produce electrical energy, is accomplished by a generator or dynamo. Electric motors are found in household appliances such as fans, refrigerators, washing machines, pool pumps, floor vacuums, and fan-forced ovens. They are also found in many other devices such as computer equipment, in its disk drives, printers, and fans; and in some sound and video playing and recording equipment as DVD/CD players and recorders, tape players and recorders, and record players. Electric motors are also found in several kinds of toys such as some kinds of vehicles and robotic toys.

4. AC Motor
In 1888 Nikola Tesla invented the first practicable AC motor and with it the polyphase power transmission system. Tesla continued his work on the AC motor in the years to follow at the Westinghouse company.
Tesla's patents and theoretical work formed the basis of modern alternating current electric power (AC) systems, including the polyphase power distribution systems and the AC motor, with which he helped usher in the Second Industrial Revolution. The SI unit measuring magnetic flux density or magnetic induction (commonly known as the magnetic field B), the tesla, was named in his honour
Statue of Nikola Tesla in Niagara Falls State Park on Goat Island, New York.

5. Synchronous AC Motor
An AC motor is an electric motor that is driven by an alternating current. It consists of two basic parts, an outside stationary stator having coils supplied with AC current to produce a rotating magnetic field, and an inside rotor attached to the output shaft that is given a torque by the rotating field.
There are two types of AC motors, depending on the type of rotor used. The first is the synchronous motor, which rotates exactly at the supply frequency or a submultiple of the supply frequency. The magnetic field on the rotor is either generated by current delivered through slip rings or by a permanent magnet.
The second type is the induction motor, which turns slightly slower than the supply frequency. The magnetic field on the rotor of this motor is created by an induced current.
Induction motors are now the preferred choice for industrial motors due to their rugged construction, absence of brushes (which are required in most DC motors) and — thanks to modern power electronics — the ability to control the speed of the motor.
The basic difference between an induction motor and a synchronous AC motor is that in the latter a current is supplied onto the rotor. This then creates a magnetic field which, through magnetic interaction, links to the rotating magnetic field in the stator which in turn causes the rotor to turn. It is called synchronous because at steady state the speed of the rotor is the same as the speed of the rotating magnetic field in the stator.
By way of contrast, the induction motor does not have any direct supply onto the rotor; instead, a secondary current is induced in the rotor. To achieve this, stator windings are arranged around the rotor so that when energised with a polyphase supply they create a rotating magnetic field pattern which sweeps past the rotor. This changing magnetic field pattern can induce currents in the rotor conductors. These currents interact with the rotating magnetic field created by the stator and the rotor will turn.

6. Induction Motor 원리 단상 3상

7. DC Motor

8. Figure 1. The central rotating magnet will turn until it is aligned with the two fixed magnets, north pole to south pole.
Figure 2. Once aligned, it will resist being turned further
Figure 3. If we magically reverse the poles of the central magnet just before it comes to rest, it will keep turning.
Figure 4. Eventually, it will get back into the position it started from in Figure 1.
Figure 8. Replacing the central magnet in Figure 1 with an electromagnet gives us the beginnings of a motor.
Figure 9. By adding a commutator (the semi-circular arcs) and brushes (the wide arrows), we can change the polarity of the electromagnet as it turns.
Figure 10. The magnets are almost aligned, but soon, the polarity will reverse, sending the rotating electromagnet on its way around once again.

9. Figure 11. In many motors, the two fixed magnets are really one the two poles of what is effectively one magnet (although it may be made up of two separate magnets connected by the motor housing). Click to enlarge.
Photo 1. This is a three-slot armature from an inexpensive 540-sized ferrite "can" motor.
Photo 2. The brushes in a "can" motor are held in place by alloy leaf springs that also serve to carry current. The commutator has been simulated with a piece of dowel with some markings on it to better show how it mates with the brushes.
Figure 11. In many motors, the two fixed magnets are really one the two poles of what is effectively one magnet (although it may be made up of two separate magnets connected by the motor housing). Click to enlarge.

10. Figure 12. This is a schematic representation of a typical three-slot two-pole brushed motor. The armature has three electromagnets, and three commutator segments. The brushes sometimes contact more than one segment. Click to enlarge.
Figure 13. The same motor as in Figure 12, one twelfth of a rotation (30 degrees) later. Click to enlarge.
Figure 14. The motor from Figure 12, one sixth of a rotation (60 degrees) later. Click to enlarge.

11. In a real two-pole motor, the two poles are often the two ends of the same magnet. Although the motor may appear to contain two separate magnets, the steel motor case ties them together to act as a single magnet. It's really as if our motor were built like in Figure 11, with the rotating electromagnet inside a hole in the permanent magnet.
Practical real motors usually have at least a three-slot armature, and a commutator with three segments. There are however still only two brushes. Higher voltage and higher efficiency motors have even more slots (an odd number) and more segments on the commutator (the same as the number of slots), and more brushes (always an even number). Photos 1 and 2 show the armature, commutator, and brushes from a typical low-cost three-slot motor.
Figure 12 illustrates a three-slot motor in conceptual form. Notice that the brush is now wider, contacting the commutator segments over a wider area, and actually spanning two segments sometimes.
Also notice that both ends of electromagnet number 2 are contacting the "-" brush at the particular point in time captured by Figure 12. This means that no current is flowing through electromagnet 2, and only number 1 and 3 are on.
Effectively, the armature is now a pair of electromagnets; number 3 is being attracted by the north pole of the right hand permanent magnet, and number 1 is being repelled.
One twelfth of a turn later, as in Figure 13, all three electromagnets have current flowing through them.
Now, electromagnet number 1 is being both repelled by the right hand permanent magnet, and attracted by the left hand one. Number 2 is being repelled by the left magnet, and number 3 is still being attracted by the right magnet.
Another twelfth of a turn later, in Figure 14, electromagnet 1 is being attracted to the left hand magnet, and number 2 is still being repelled.
Electromagnet 3 is turned off. This progression of electromagnets switching on and off continues as the motor turns, eventually returning to the state of Figure 12.

12. One drawback to the motor is the large amount of torque ripple that it has. The reason for this excessive ripple is because of the fact that the coil has a force pushing on it only at the 90 and 270 degree positions. The rest of the time the coil spins on its own and the torque drops to zero. The torque curve produced by this single coil, as more coils are added to the motor, the torque curve is smoothed out.
The brushed DC motor generates torque directly from DC power supplied to the motor by using internal commutation, stationary permanent magnets, and rotating electrical magnets. Advantages of a brushed DC motor include low initial cost, high reliability, and simple control of motor speed. Disadvantages are high maintenance and low life-span for high intensity uses. Maintenance involves regularly replacing the brushes and springs which carry the electric current, as well as cleaning or replacing the commutator. These components are necessary for transferring electrical power from outside the motor to the spinning wire windings of the rotor inside the motor.
Synchronous DC motors, such as the brushless DC motor and the stepper motor, require external commutation to generate torque.
Generally, the rotational speed of a DC motor is proportional to the voltage applied to it, and the torque is proportional to the current. Speed control can be achieved by variable battery tappings, variable supply voltage, resistors or electronic controls. The direction of a wound field DC motor can be changed by reversing either the field or armature connections but not both. This is commonly done with a special set of contactors

13. A brushless DC motor (BLDC) is a synchronous electric motor which is powered by direct-current electricity (DC) and which has an electronically controlled commutation system, instead of a mechanical commutation system based on brushes. In such motors, current and torque, voltage and rpm are linearly related. Two subtypes exist:
The stepper motor type may have more poles on the stator.
The reluctance motor.

14. Stepper Motor
A stepper motor (or step motor) is a brushless, synchronous electric motor that can divide a full rotation into a large number of steps. The motor's position can be controlled precisely, without any feedback mechanism (see open loop control).
Frame 1: The top electromagnet (1) is turned on, attracting the nearest teeth of the gear-shaped iron rotor. With the teeth aligned to electromagnet 1, they will be slightly offset from right electromagnet (2). Frame 2: The top electromagnet (1) is turned off, and the right electromagnet (2) is energized, pulling the teeth into alignment with it. This results in a rotation of 3.6° in this example. Frame 3: The bottom electromagnet (3) is energized; another 3.6° rotation occurs. Frame 4: The left electromagnet (4) is energized, rotating again by 3.6°. When the top electromagnet (1) is again enabled, the rotor will have rotated by one tooth position; since there are 25 teeth, it will take 100 steps to make a full rotation in this example.

15. Piezoelectric Film
A piezoelectric disk generates a voltage when deformed (change in shape is greatly exaggerated)

16. Atomic Force Microscope using Piezoelectric Film