1. CONTINUOUS-DRIVE ACTUATORS**
By:
Bharath reddy manyam
Naresh reddy guntaka
Prabhu sampathkumar
** An actuator is a mechanical device for moving or controlling a mechanism or system. The actuator is usually a physical mechanism but also refers to an artificial intelligent agent.

2. What's Inside DC Motors Control of DC motors Motor Selection Criteria
Induction motors
Induction motor control
Synchronous/Hydraulic motors
Hydraulic Actuators
Hydraulic Control Systems

3. DC MOTORS:
WHAT IT DOES : Converts electrical energy (DC) into rotational mechanical energy.
HOW?
Fig 2: Operating principle of DC motor
Fig 1: cross-section of a DC motor

4. Force F = B i l (B- flux density of the field
DC MOTORS…
Force F = B i l (B- flux density of the field
i- current thru the conductor
l- length of the conductor )
Back e.m.f vb =B l v (v- velocity)
BACK EMF : If the conductor is free to move, the force will move it at some velocity ‘v’ in the direction of the force. As a result of this motion in the magnetic field B, a Voltage is induced. This is the ‘back’ electromagnetic force.
Fig 3 : Physical Configuration of rotor

5. Brushless DC Motors: DC motors: Rapid wear-out Mechanical loading
Heating due to brush friction
Contact bounce
Excessive noise
Voltage ripples
Mostly permanent magnets
Better stator winding segments
Polarity of stator is switched by electronic means
Remedies :
Improved brush designs
Modified brush positions
Fig 4: brushless DC motor system.

6. Fig 5a : switching seq. for max.avg. torque
Fig 5b: static torque without switching

7. DC Motor Equations: Where va =supply voltage to armature
Ra =resistance of winding
La =leakage inductance in winding
K and k’ =motor constants
Comparison of DC motor winding types & equations:

8. Control of DC Motors :
Armature control : Here armature voltage is used as the control input, while keeping the conditions in the field circuit constant
Field control : here armature current is kept constant and the filed voltage is used as the control input.
Phase- locked control: This is a modern approach using a controlled signal generator and phase is locked.
Thyristor control: Here a variable resistor is connected in series with the supply source to the circuit.
Fig6: Steady-state speed-torque curves for armature controlled DC motor.

9. MOTOR SELECTION CONSIDERATIONS :
MECHANICAL CONSIDERATIONS:
Mechanical time constant
No-Load speed
Speed at rated load
No-Load acceleration
Rated Torque
Rated output power
Frictional torque
Damping Constant
Dimensions and weight
Armature moment of inertia

10. GENERAL APECIFICATIONS:
ELECTRICAL SPECIFICATIONS:
Electrical time constant
Input power
Armature resistance & inductance
Field resistance & inductance
Compatible drive specifications
GENERAL APECIFICATIONS:
Brush life and motor life
Efficiency
Operating temperature & environmental conditions
Heat transfer characteristics
Mounting configuration
Coupling methods

11. INDUCTION MOTORS : Advantages of AC motors: Cost effectiveness
Convenient power source (AC supply)
No commutator/ brush mechanism needed
Lower power dissipation, rotor inertia and light weight designs
Virtually no electric arcing
Less hazardous
Constant speed operation without servo control
No drift problems
High reliability

12. DISADVANTAGES ARE: Lower starting torque
AC MOTORS Contd…
DISADVANTAGES ARE:
Lower starting torque
Auxiliary starting device need for some motors
Difficulty of variable-speed control

13. INDUCTION MOTOR Principle Torque speed characteristics
Speed control of Induction motors

14. An induction motor operates on principle of induction.
Rotor receives power from stator due to induction rather than direct conduction of electric power.

15. Concept of Rotating magnetic field
As per Rotating Magnetic Field Theory
When windings are physically displaced by120 degree spatially and excited by currents which are displaced by 120 degrees with respect to time, it produces a magnetic field which is rotating.

16. In Induction motor, stator consists of windings which are physically displaced by 120 degree and excited by AC supply
Fig 7

17. SPEED CONTROL OF INDUCTION MOTORS
Excitation frequency control
Supply voltage control
Rotor resistance control
Pole Changing

18. The torque developed by induction motor is given by
Td = nV12R2 / S
αs[(R1+R2/S)2+(X1+X2)2
Where V1 is supply voltage
S is slip
R1 and R2 stator and rotor resistance respectively
X1 and X2 stator and rotor inductance respectively
αs synchronous speed

19. Torque-speed characteristic curve:
The induced voltage changes linearly with slip ‘S’ because it is proportional to the relative velocity of the rotating field with respect to the rotor
Fig 8

20. Rotor Resistance Control
It is a old technique prior to development of thyristor circuits and Digital signal processing chips.
As torque of induction motor depends on rotor resistance, by changing rotor resistance speed of induction motor can be controlled.
Fig 9

21. Supply voltage control
As we know Torque is proportional to square of supply voltage.
Induction motor can be controlled by varying supply voltage.
Most common method used is
Amplitude modulation of AC supply using ramp generator
Appropriate for small induction motors
Poor efficiency for wide speed range

22. Pole changing method
The number of pole pairs per phase in stator windings (n) is the parameter in speed torque equation.
It can be obtained by switching the supply connections in the stator winding.
Fig 10

23. Excitation frequency control
Frequency control can be accomplished using thyristor circuit.
The frequency of voltage is equal to inverse of firing interval of the two thyristors.
Fig 11

24. Fig 12

25. Three phase supply is rectified using Rectifier circuit.
Firing of thyristors is controlled by microprocessor.
Controller uses external command and feedback signals to generate required firing logic.

26. INDUCTION MOTOR CONTROL :
Excitation frequency control Wp
Supply voltage control (Vf)
Rotor resistance control (Rr)
Pole Changing (n)
Field Feedback control

27. Synchronous Motors :
Phase-locked servos and stepper motors can be considered synchronous motors because they run in synchronism with an external command signal under normal operating conditions.
Fig 13
The rotor of the synchronous AC motor rotates in synchronism with a rotating field generated by the stator windings.
These motors are widely used for constant speed applications
ADVANTAGE: It can operate with larger air-gap between rotor and stator in comparison with induction motor
DRAWBACK : A major drawback is that an auxiliary started is required is used to bring the rotor speed close to the synchronous speed
Schematic diagram of stator-rotor configuration of synchronous motor.

28. HYDRAULIC CONTROL SYSTEM:
Components of hydraulic control system
Fig 14
A SERVOVALVE
A HYDRAULIC ACTUATOR
A LOAD

29. EQUATIONS
VALVE: q = kqu-kcp
HYDRAULIC ACTUATOR: q = A (dy/dt) + (V/2B)(dp/dt)
LOAD : m(d2y/dt2) + b(dy/dt) = Ap - fl
FEEDBACK CONTROL:
A pressure feedback path and an associated hydraulic time constant Th
A velocity feedback path and an associated mechanical time constant Tm
Methods of feedback control
Proportional control (P)
Derivative control (D)
Integral control (i)

30. References:
Control sensors and actuators by Clarence W. De Silva

31. Thank you
Any Questions

32. QUESTIONS FOR ASSIGNMENT
DEFINE BACK EMF, BRING OUT THE DIFFERENCES BETWEEN DC MOTOR AND BRUDHLESS DC MOTOR
DISCUSS VARIOUS SPPED CONTROL METHOS OF INDUCTION MOTR
DRAW THE SCHEMATIC DIAGRAM OF HRDRAULIC CONTROL SYSTEM ALSO BRIEFLY EXPLAIN ABOUT FEEDBACK CONTROL OF IT