A Presentation on CONTINUOUSDRIVE ACTUATORS

1
A Presentation on 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
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

• 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
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
• as(R1R2/S)2(X1X2)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
• as 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
• WWW.Wikipedia.com
• www.google.com

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