CONTINOUSDRIVE ACTUATORS - PowerPoint PPT Presentation

Title: CONTINOUSDRIVE ACTUATORS


1
CONTINOUS-DRIVE ACTUATORS

• EEEN 5324
• System Synthesis
• Dr. Rajab Challoo
• Mid Term- Paper
  Presentation
• Group 1
• Date April 03, 2006
• 
  
• 
  BY
• 
  Falguni Gandhi
• Feroza Salam
• Deepa Deshmukh
• Preethi Krishnan

2
INTRODUCTION

• Digital actuators causes the actuators to move by
  a predetermined, fixed increment of displacement.
• Direct current servomotors and servovalve driven
  hydraulic and pneumatic actuators were the most
  widely used .
• Presently AC motors are widely used as
  servomotors.

3

Contd..

• Pulse Width modulated signals (PWM)
• signals are increasingly being used to drive
  continuous (analog) actuators.
• Proper design and selection of actuator have a
  significant economical impact in many
  applications of industrial control.

4
DC MOTORS

• DC motor converts direct current into rotational
  mechanical energy.
• Magnetic force,
• F bil
• Electromotive Force or EMF,
• Vb blv

5
Principle of DC Motors
6
Brushless DC motors

• The main disadvantages of slip ring and brush
  mechanism were rapid wear out, mechanical
  loading, excessive noise, contact bounce and
  electrical arcing.
• Brushless DC motors were used to overcome the
  shortcomings of slip ring and brush mechanism.

7

Contd..

• In brushless DC motor , the polarity of the rotor
  (permanent magnet )is fixed relative to the rotor
  itself, and the polarity of the stator is
  switched by electronics means.

8
Brushless DC Motors
9
Static Torque Curve With No Switching
10
Switching Sequence For Maximum Average Torque
11
Control of DC motors

• DC motors are operated over a wide range of
  speeds and torques.
• Control of a DC motor is achieved by either
  controlling the stator field flux or the armature
  flux.
• There are two methods of control
• Armature Control
• Field Control

12

Contd..

• In armature control the field current in the
  stator circuit is kept constant and the input
  voltage is varied to achieve the desired
  performance.
• In field control the armature voltage is kept
  constant and the input voltage to the field
  current is varied.

13
DC Servomotors
14
Phase-Locked Control

• Phase locked loop is a modern approach to
  controlling DC motors.
• The position command is generated to the desired
  motion of the motor using a control signal
  generator.

15
Block Diagram
16
Thyristor Control

• A solid state switch frequently used in motor
  control circuits is the thyristor.
• The thyristor is also known as semi conductor
  controlled rectifier (SCR).
• It is made of four layers of semiconductor
  material and has three terminals-anode, cathode,
  and the gate.

17
Basic Thyristor Circuit
18
Servo Amplifiers

• It is used to drive DC motors in servo control
  applications.
• Servo amplifiers use PWM to drive servomotors
  efficiently under variable speed conditions, with
  less power losses.
• A typical servo amplifier card consists of a
  differential amplifier, servo preamplifier, and
  PWM amplifier.

19
Torque Motors

• Torque motors are high torque DC motors.
• These actuators posses a linear torque speed
  relationship.
• The output torque can be increased by using a
  gear system with high gear reduction.
• Torque motors are suitable for high precision
  applications.

20
Motor Selection Considerations

• To select a particular motor the two primary
  considerations are torque and speed.
• The specifications that are considered are the
  Mechanical, electrical and general
  specifications.

21
Contd

• The operating conditions of a motor can be
  determined by using its torque-speed curve.

22
INDUCTION MOTORS
23
TORQUE SPEED CHARCTERISTICS
24
INDUCTION MOTOR CONTROL

• 1.EXCITATION FREQUENCY CONTROL
• 2.SUPPLY VOLTAGE CONTROL.
• 3.ROTOR RESISTANCE CONTROL.
• 4.POLE CHANGING.

25
EXCITATION FREQUENCY CONTROL
26
ROTOR RESISTANCE CONTROL
27
SUPPLY VOLTAGE CONTROL
28
POLE CHANGING METHOD
29
SYNCHRONOUS MOTORS

• The rotor of the synchronous AC motor rotates in
  synchronism of the rotating field generated by
  stator windings.
• These motors are particularly suited for constant
  speed applications under variable load
  conditions.
• The drawback of this motor is that an auxiliary
  starter is required to bring the rotor speed
  close to synchronous speed.
• The staring torque is always zero.

30
RECTILINEAR MOTORS.

• Flat stators and rectilinearity elements are
  employed.
• These motors employ auxiliary kinematic
  transducer,such as cam follower mechanism ,a
  rack-pinion mechanism .
• Solenoid is a common rectilinear actuator that
  consists of a coil and a plunger.These are
  push-pull actuators and can be classified as
  digital actuators
• Common Applications include valve
  actuators,switches ,relays and other two position
  systems.

31
Hydraulic System

• Components of Hydraulic system
• Hydraulic actuator
• Hydraulic pumps and motors
• Hydraulic servovalves
• Hydraulic accumulators

32
Hydraulic control system

Power supply
(T, w)
Fluid return
Reference i/p
Pressurized fluid supply
Torque motor
Feedback signals
33
Hydraulic Actuators

• Hydraulic Actuators uses the hydraulic power of a
  pressurized liquid
• They are capable of providing large forces at
  very high power levels
• Control gains required in a high power hydraulic
  control system is less than the comparable
  electromagnetic control system

34
Hydraulic pumps

• Hydraulic pump is used to provide pressurized
  liquid to actuators
• The Vane pump
• The gear pump
• The axial piston pump

35
Contd
Vane Pump
Hydraulic pump efficiency ?p PQ/?T
where P pressure increase in the fluid
Q fluid flow rate
? rotating speed of the pump T
drive torque of the pump
Gear Pump
36
Hydraulic servovalves

• Valves can be categorized as
• Flow control valves
• Pressure control valves
• Functions of valves are as follows
• Change flow direction
• Change flow rate
• Change fluid pressure

37
Valve control systems

• Constant pressure systems
• The supply pressure to servovalve is maintained
  constant
• Constant flow systems
• The supply flow is kept constant at varying
  pressure levels

38
Hydraulic control system

• Block diagram

39
Hydraulic accumulators

• An accumulator is a tank to hold excessive fluid
  during pressure surges so that pressure
  fluctuations can be filtered

40
Conclusion

• DC motors
• AC motors
• Hydraulic systems