Electromagnetic induction , Transformer , Stepper motor , Actuator , Mechatronics , UPSC ESE

 Basics of electromagnetic induction 

• Whenever there is a change in the magnetic flux linked with the coil, an EMF is induced.
  
  
  
• If magnet is stationary then flux remain constant in the coil, there will not be any induction. 
• If magnet is moving left side then flux will changes in the coil there will be induction. 

Basics of transformer 

Linear variable differential transformer 

• It is a displacement sensor which is used to measure linear displacement, angular displacement.
• It works on the principle of electromagnetic induction (mutual inductance variation). 
• It consists of single primary coil and two secondary coils which are connected in series opposition. 
• It has movable magnetic core which couples the magnetic flux generated by primary coil to secondary coil. 
  
  
  
  
  
  

Working of LVDT

Resolver 

• Let us analyse the below diagram 
  
  
  
• It is a position sensor which is able to measure linear displacement ,angular displacement. 
• It works on electromagnetic induction. 
• It has single primary coil which acts like rotor and two secondary coil which acts like stator. 
• At each position of the primary winding the component of magnetic field is coupled with secondary windings. As a result we will get voltage at both the secondary windings. 
• The ratio between the amplitude of output voltage across secondary winding provides the information shafts position. 

Inductosyn

 Construction and working 

• Inductosyn is a position sensor which is used to measure linear displacement ,angular displacement .
• It works on the principle of electromagnetic induction. 
• It consists of two parts scale which is static and slider which is movable element .
• Scale :it has trace of conductive material which is regular rectangular shape as shown in figure. 
• Slider box: it has two sliders and each slider is in regular rectangular shape as shown in figure.
• When the slider box displaces laterally on the scale then voltage will be generated across the slider because of induction .
• When the conductor of slider lies exactly above the conductor of scale then voltage generated across slider will be maximum. 
  
  
  
• 23 conductor of scale are behaving like electromagnet. 

Tachometer 

Construction

• It consists of a rotor which rotates with rotating shaft and a coil which is winded on magnet. 
• The rotor has teeth made up of magnetic material so it is called a toothed rotor. 
• A transformer is used to collect the voltage from the coil. 
• Electronic counter count number of pulses in second. 
• Pulse frequency is used to calculate to the speed of shaft. 
  
  
  

Working 

• The magnetic flux generated by magnetic links to the coil .
• When the rotor rotates inside the magnetic flux then the magnetic flux linked to the coil changes.
•  When the teeth comes close to the coil then magnetic flux linked to the coil will be maximum as a result generated voltage is also maximum. 
• Voltage generated by a coil is connected to transformer so that it can be processed further. 
• Each rotor teeth when it comes close to the magnet and coil the voltage generated across the coil will be maximum and it will be considered as one pulse. 
• Electronic counter counts the number of pulses in one second this information is used to measure the shaft speed. 

Proximity sensor 

• They are used to detect the presence of nearby objects without any physical contact. 
• These sensors are capable of measuring linear displacement, angular displacement. 
• These sensors find the application .
• Proximity sensors of three types :capacitive type sensor, inductive type sensor and photoelectric type sensor .
  
  
  

Capacitive proximity sensor 

• The capacitance is increased .
• If object is not moving then capacitance is equal to Co. 
• If object comes close to the fixed plate then capacitance increases. 
• If object moves away from the fixed plate then capacitance decreases. 

Real-time capacitive type proximity sensor 

Inductive type proximity sensor 

• Inductance :amount of magnetic flux linked to the coil per 1 ampere current ,if more amount of magnetic flux is linked per one ampere current then we can say that the inductance of coil is high. 
• Reluctance :it is the opposition offered by medium to magnetic flux .

Note: air has more reluctance compared to magnetic material example soft iron .

• If air gap increases reluctance faced by magnetic flux increases and total flux decreases therefore inductance decreases. 

Real-time inductive type proximity sensor 

Photoelectric proximity sensor

• It used a beam of light to detect the presence of objects that block or reflect the light beam. 
• A beam of light passes from the light source and a photo detector detects the presence or absence of light from source. 
• Incandescent lamps or infrared led is may be used as light source. 
• Photodiode, phototransistor are used as light detectors.
  
  
  

 Types of stepper motor 

1. Variable reluctance type stepper motor 
2. Permanent magnet type stepper motor 
3. Hybrid stepper motor

Variable reluctance type stepper motor 

• The rotor is having low mass. 
• It is more responsive. 
• The torque provided is low. 

Permanent magnet stepper motor 

• It requires very low current this means it requires very low electrical power. 
• It provides high torque compared to variable reluctance type stepper motor. 

Hybrid type stepper motor

Application of stepper motor

• Stepper motor is used where resize positioning is required in combination with the microprocessor controller. 
• It can accelerate its load easily on maximum torque occurs at low pulse rate. 
• It is used in computer printers ,robotics, machine tools ,etc. 

Mechanical actuators

• They convert liquid air pressure into mechanical power. 
• Hydraulic actuator use liquid pressure.
• Pneumatic actuator use air pressure. 

Hydraulic actuator 

• It is a device convert liquid press pressure into linear displacement or angular displacement.
• The output mechanical power depends on flow rate applied and pressure applied on piston .
• There are two types of hydraulic actuato: 

1.  Linear actuator (hydraulic cylinder)
2.  Hydraulic motor (rotary actuator)

 Types of hydraulic cylinder:

1.  Single acting type cylinder 
2. Double acting type cylinder
3.  Telescopic type cylinder
4.  Tandem type cylinder

 Single acting cylinder

•  It can provide only one side stroke with the help of liquid pressure energy. 
• Energy stored in the spring can be used to get return stroke. 
  
  
  

Double acting cylinder 

• It provides two sides stroke with the help of liquid pressure energy .
  
  
  

Telescopic type cylinder

• Both extension and retraction will be done stage by stage. 
• When we require large stroke length we use telescopic type cylinder. 
  
  
  

Tandem cylinder

• More than one cylinder connected in cascade configuration forms tandem type cylinder .
• It transmit heavy force without changing the dia of cylinder. 
  
  
  

Rotary actuators

•  They are the hydraulic or pneumatic equivalent of electric motors which are used when a twisting or turning motion is required. 

Rack and pinion type rotary actuator

 Gear motor

 

 Electrical actuator vs mechanical actuator

•  They are portable and low power devices.
• These can be programmable hence they can be used in digital control applications. 
• They provide very low output, hence cannot be used to drive heavy loads .
• Maintenance of these actuator is quite easy compared to mechanical actuator. 

Mechanical actuator

• These are little bit complicated to built. 
• It is comparatively difficult to program. 
• These provide very high mechanical output ,hence they can be used to drive heavy load also.
•  Maintenance of these actuator is quite difficult.