UNIT V ACTUATORS AND MECHATRONICS SYSTEM DESIGN 9

Types of Stepper and Servo motors – Construction – Working Principle –

Characteristics, Stages of Mechatronics Design Process – Comparison of Traditional
and Mechatronics Design Concepts with Examples – Case studies of Mechatronics
Systems – Pick and Place Robot – Engine Management system – Automatic Car Park
Barrier.

INTRODUCTION:
Actuators:

 In a control system, the element which transforms the output of a controller into a controlling
action / motion is called as actuators.
 Actuators produce physical changes such as linear and angular displacements.
 Examples of actuators are solenoids, electric motors, hydraulic cylinders, pneumatic cylinders and
motors.
 Actuators can handle the static or dynamic loads placed on it by control valve.
 The important aspects of actuators are proper selection and sizing.

Functions of actuator

An actuator has two major functions.

i) To respond an external signal directed to it causing inner value to move accordingly hence to control
flow rate of fluid by positioning the control valve.
ii) To provide support for valve accessories e.g. limit switches, solenoid valves.

Classification of Actuators

 Actuators are available in various forms to suit the particular requirement of process control.
 It can be classified into 3 main categories.
1. Pneumatic actuators
2. Hydraulic
3. Electrical actuators

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5.1 STEPPER MOTOR:
 A stepper motor is an electromechanical device which converts electrical pulses into discrete
mechanical movements.
 The stepper motor is a device that produces rotation through equal angles when digital pulses are
supplied as input.
 In other words, the stepper motor transforms the electrical pulses in to equal increments of rotary
shaft motion.
 Example : If 1 pulse produces a rotation of 60, then for complete rotation of 3600, there will be 60
pulses needed.
 These motors rotate a specific number of degrees as a respond to each input electric pulse.
 Typical types of stepper motors can rotate 2°, 2.5°, 5°, 7.5° and 15° per input electrical pulse.
 The speed of the motor shafts rotation is directly related to the frequency of the input pulses and
the length of rotation is directly related to the number of input pulses applied.

Stepper motors offers many attractive features such as:

i) Available resolutions ranging from several steps up to 400 steps (or higher) per revolution.
ii) Several horse power ratings.
iii) Ability to track signals as fast as 1200 pulses per second.

Stepper Motor Types:

1. Variable Reluctance Stepper Motor :

Construction :
 This type of motors have three to five windings and a common terminal connection creating several
phases on the stator.
 The rotor is made up of soft steel and it is cylindrical in shape with four poles.
 Usually the number of poles on the rotor is less than number of poles on the stator.
 The stator poles have windings and it is switched by means of electronic switching device.
 The function of the switching device is to switch the control windings in the stator of stepper
motor.

Page.No. 2
 Fig.5.1.1 Variable Reluctance Stepper Motor

Working:
 When current is switched to a pair of windings in stator, a magnetic field is produce. The line of
force passes from stator poles to nearest set of poles on the rotor.
 The rotor will move until the rotor and stator lineup. This is termed as position of minimum
reluctance. This motor generally gives step angels of 7.50 or 150.

2. Permanent Magnet Stepper Motor

Construction:

 Permanent magnet stepper motors are similar in construction to that of variable reluctance stepper
motors except that the rotor is made of permanent magnet.
 The Stator has four poles. Each pole is wound with a field winding, the coils on opposite pair of
poles being in series.
 The rotor is a permanent magnet and when current is switched to a pair of stator poles, the rotor
will move to lineup with it.

Fig.5.1.2 Permanent Magnet Stepper Motor

Working :
 Thus for the currents given in the situation shown in Figure, the rotor moves to 450 position.
 If the current is switched so that the polarities are reversed, the rotor will move a further 450 in
order to line up again.

Page.No. 3
 Thus by switching currents through the coils, the rotor rotates by 450 steps.
 With this type of motor, step angle of 1.80, 7.50, 150, 300, 340 or 900 can be achieved.

3. Hybrid Stepper Motor

 It combines the features of both the variable reluctance and permanent magnet motors.
Construction :
 This motor provide better performance with respect to step resolution, torque and speed.
 The rotor of a hybrid stepper is multi toothed like the variable reluctance steppers and it contains
an axially magnetized concentric magnet around its shaft.
 The Permanent magnet is encased in iron caps which are cut to have teeth.

Fig.5.1.3 Hybrid Stepper Motor

Working :
 The rotor sets itself in minimum reluctance position if a pair of stator coils is energized. In this
stepper motor, step angles of 0.90 and 1.80 are achieved.
 The most commonly used types of stepper motors are the hybrid and permanent magnet.

Figure shows the General characteristics of Stepper Motor:

Stepper motor characteristics

Page.No. 4
Applications of stepper motor:
 Floppy disc head drives
 Printer carriage drives
 Positioning of printer heads and pens in X-Y plotters
 NC and CNC machine tool slide drives
 Automatic teller machines(ATM)
 Camera iris control mechanisms
 Recording heads in computer disc drives
 Paper feed motors in typewriters and printers.

Advantages of stepper motor:

 The rotation angle of the motor is proportional to the input pulse.
 The motor has full torque at standstill.
 Excellent response to starting, stopping and reversing.
 Very reliable since there are no contact brushes in the motor.
 The motors response to digital input pulses provides open loop control, making the motor
simpler and less costly to control.

Disadvantages :
 They have low torque capacity compared to DC motors.
 They have limited speed.

5.2 SERVO MOTORS:

 A servo motor is a simple electrical motor, controlled with the help of servo mechanism.
 Servo motor is a special type of motor which is automatically operated up to certain limit for a
given command with the help of error sensing feedback to correct the performance.

 If the motor as controlled device, associated with servo mechanism, then it is known as DC
servo motor.

 If the motor is operated by AC, then it is known as AC servo motor.

Types of Servo motors:

 It is classified depending upon the nature of the electricity supply to be used for its
operation.

Page.No. 5
1. AC Servomotors.

Features of A.C. Servomotor

The various features of A.C. servomotor are,

1. Light in weight for quick response.

2. Robust in construction.
3. It is reliable and its operation is stable in nature.
4. Smooth and noise free operation.
5. Large torque to weight ratio.
6. Large resistance to reactance ratio.
Construction

 The A.C servomotor is basically consists of a stator and a rotor.

 The stator carries two windings, uniformly distributed and displaced by 90° in space, from each
other.
 One winding is called as main winding or fixed winding or reference winding. The reference
winding is excited by a constant voltage a.c. supply.
 The other winding is called as control winding.
 It is excited by variable control voltage, which is obtained from a servo amplifier.
 The winding are 90° away from each other and control voltage is 90° out of phase with respect
to the voltage applied to the reference winding.
 This is necessary to obtain rotating magnetic field.
 The schematic stator shown in the Fig. 5.2.1.

Page.No. 6
 Fig. 5.2.1.Stator of A.C. Servomotor.

 To reduce the loading on the amplifier, the input impedance i.e. the impedance of the control
winding in increased by using a tuning capacitor in parallel with the control winding.
 The rotor is generally of two types:
1. Squirrel cage rotor 2. Drag cup type rotor

Working Principle of AC Servo Motor

 The schematic diagram of servo system for AC two-phase induction motor is shown in the
figure below.
 In this, the reference input at which the motor shaft has to maintain at a certain position is
given to the rotor of synchro generator mechanical input theta.
 This rotor is connected to the electrical input at rated voltage at a fixed frequency.
 The three stator terminals of a synchro generator are connected correspondingly to the
terminals of control transformer.
 The angular position of the two-phase motor is transmitted to the rotor of control transformer
through gear train arrangement and it represents the control condition alpha.
 Initially, there exist a difference between the synchro generator shaft position and control
transformer shaft position.

Page.No. 7
 Fig. 5.2.2 Schematic diagram of AC servo system

 This error is reflected as the voltage across the control transformer.

 This error voltage is applied to the servo amplifier and then to the control phase of the motor.
 With the control voltage, the rotor of the motor rotates in required direction till the error becomes
zero.
 This is how the desired shaft position is ensured in AC servo motors.
 Alternatively, modern AC servo drives are embedded controllers like PLCs, microprocessors and
microcontrollers to achieve variable frequency and variable voltage in order to drive the motor.
 Mostly, pulse width modulation and Proportional-Integral-Derivative (PID) techniques are used to
control the desired frequency and voltage.
 The block diagram of AC servo motor system using programmable logic controllers, position and
servo controllers is given below.

Page.No. 8
 Fig. 5.2.3 Block diagram of AC servo motor

Advantages of AC servomotors are:

1. Low cost.

2. Higher efficiency and less maintenance (because no commutator and brushes).

Disadvantages of AC servomotors are:

1. Non-linear Characteristics.

2. More difficult to control in positioning applications.

Application of Servo Motors

 Servomotors are used in applications requiring rapid variations in speed without the motor getting
overheated.
 In Industries they are used in machine tools, packaging, factory automation, material handling,
printing converting, assembly lines, and many other demanding applications robotics, CNC
machinery or automated manufacturing.
 They are also used in radio controlled airplanes to control the positioning and movement of
elevators.
 They are used in robots because of their smooth switching on and off and accurate positioning.
 They are also used by aerospace industry to maintain hydraulic fluid in their hydraulic systems.
 They are used in many radio controlled toys.
 They are used in electronic devices such as DVDs or Blue ray Disc players to extend or replay the disc
trays.
 They are also being used in automobiles to maintain the speed of vehicles.

Page.No. 9
DC Servo motor:
Servo motor features:

1. Linear relationship between the speed and electric control signal.

2. Steady state stability.

3. Wide range of speed control.

4. Linearity of mechanical characteristics throughout the entire speed range.

5. Low mechanical and electrical inertia.

6. Fast response.

Construction:

 A DC servo motor consists of a small DC motor, feedback potentiometer, gearbox, motor drive
electronic circuit and electronic feedback control loop.
 It is more or less similar to the normal DC motor.
 The stator of the motor consists of a cylindrical frame and the magnet is attached to the inside of the
frame.
 The rotor consists of brush and shaft.
 A commutator and a rotor metal supporting frame are attached to the outside of the shaft and the
armature winding is coiled in the rotor metal supporting frame.
 A brush is built with an armature coil that supplies the current to the commutator.
 At the back of the shaft, a detector is built into the rotor in order to detect the rotation speed.
 With this construction, it is simple to design a controller using simple circuitry because the torque is
proportional to the amount of current flow through the armature,

Working Principle of DC Servo Motor

 A DC reference voltage is set to the value corresponding to the desired output.

 This voltage can be applied by using another potentiometer, control pulse width to voltage
converter, or through timers depending on the control circuitry. APP
 The dial on the potentiometer produces a corresponding voltage which is then applied as one of the
inputs to error amplifier.
 In some circuits, a control pulse is used to produce DC reference voltage corresponding to desired

Page.No. 10
 position or speed of the motor and it is applied to a pulse width to voltage converter.
 In digital control, microprocessor or microcontroller are used for generating the PWM pluses in
terms of duty cycles to produce more accurate control signals.

Fig. 5.2.4 Block diagram of Servo motor

 The feedback signal corresponding to the present position of the load is obtained by using a
position sensor.
 This sensor is normally a potentiometer that produces the voltage corresponding to the absolute
angle of the motor shaft through gear mechanism.
 Then the feedback voltage value is applied at the input of error amplifier (comparator).
 The error amplifier is a negative feedback amplifier and it reduces the difference between its
inputs.
 It compares the voltage related current position of the motor (obtained by potentiometer) with
desired voltage related to desired position of the motor (obtained by pulse width to voltage
converter), and produces the error either a positive or negative voltage.
 This error voltage is applied to the armature of the motor.
 If the error is more, the more output is applied to the motor armature.
 As long as error exists, the amplifier amplifies the error voltage and correspondingly powers the
armature.
 The motor rotates till the error becomes zero.
 If the error is negative, the armature voltage reverses and hence the armature rotates in the
opposite direction.
DC Servo motor Advantages
1. High output power relative to motor size and weight.

2. Encoder determines accuracy and resolution.

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3. High efficiency. It can approach 90% at light loads.

4. High torque to inertia ratio. It can rapidly accelerate loads

5. Has "reserve" power. 2-3 times continuous power for short periods.

6. Has "reserve" torque. 5-10 times rated torque for short periods.

7. Motor stays cool. Current draw proportional to load.

8. Usable high speed torque. Maintains rated torque to 90% of NL RPM

DC Servo motor Disadvantages

1. Requires "tuning" to stabilize feedback loop.

2. Motor "runs away" when something breaks. Safety circuits are required.

3.Complex. Requires encoder.

4. Brush wear out limits life to 2,000 hrs. Service is then required.

5. Peak torque is limited to a 1% duty cycle.

6. Motor can be damaged by sustained overload.

7. Bewildering choice of motors, encoders, and servodrives.

8. Power supply current 10 times average to use peak torque.

9. Motor develops peak power at higher speeds. Gearing often required.

10. Poor motor cooling. Ventilated motors are easily contaminated.

Two different modes in DC Servo motor:

1. Armature control mode

2. Field control mode

1. Armature control of DC servomotor:

 In armature controlled dc servomotor, the controlling is provided at the armature. This means,
here the signal from the servo amplifier is provided at the armature and constant current is
provided at the field winding.

Page.No. 12
  The voltage from the servo amplifier, Va(t) with resistance Ra and inductance La is provided at
the armature. And this input voltage at the armature controls the shaft.
 The figure below represents the arrangement of armature coupled dc servomotor
 Here the constant field is provided using the permanent magnets and hence no field coils are
required.

Ra - Armature resistance ()
La - armature winding inductance (H)
Ia - Armature current (A)
If - Field current (A)
Ea - Applied voltage (V)
Eb - Back emf (V)
θ - Angular displacement
Tm - Motor torque (N-m)
F0 - Viscous friction coefficient (N-m rad-1/sec)
J - Moment of inertia (kg-m2)
The flux Φ is proportional to the field current If.
Φ ∞ If
= Kf If (Kf = constant)
Then, Tm Ia Φ
Tm = K1 Ia Φ
Substitute Φ= KF IF in the above equation.
Tm = K1 Ia KF IF.
The field current is constant, hence the flux is constant.
Tm = KT Ia.
[KT = K1 Ia IF. Where K1 - motor torque constant)
When the armature is rotating, a voltage proportional to product of the flux and the angular
velocity.

Page.No. 13
2. Field control of DC servomotor:

 In the field controlled dc servomotor, the torque is in direct proportion to the field flux and the
armature current. Thus, its operating principle is such that if the field flux is quite large then even
with the small change in the armature current there will be a large change in torque. Thereby
making the servomotor sensitive to armature current.
 It is to be noted here that in armature controlled dc servomotor, the sensitivity towards the field
current should be low. As the armature controlled motor must not respond to the field current.
 It offers a small value of the time constant so there is a rapid change in the armature current of the
motor with the change in the voltage applied at the armature. Thus, it provides a faster dynamic
response where the direction of rotation changes with the change in polarity of the error signal.

In which the armature current is maintained constant and speed of the DCservomotor is
controlled by field voltage.

Rf - Resistance of field winding ()

La - armature winding inductance (H)
Ia - Armature current (A)
If - Field current (A)
Ea - Applied voltage (V)
Eb - Back emf (V)
θ - Angular displacement
Tm - Motor torque (N-m)
F0 - Viscous friction coefficient (N-m rad-1/sec)
J - Moment of inertia (kg-m2)

Page.No. 14
5.3 STAGES OF MECHATRONICS DESIGN PROCESS
The design process consists of the following stages .

Stages in designing mechatronics systems

Stage 1: Need for design

 The design process begins with a need. Needs are usually arise from dissatisfaction with
an existing situation. Needs may come from inputs of operating or service personal or
from a customer through sales or marketing representatives.

 They may be to reduce cost, increase reliability or performance or just change because
of public has become bored with the product.
Stage 2 : Analysis of problem

 Probably the most critical step in a design process is the analysis of the problem i.e., to
find out the true nature of the problem.

 The true problem is not always what is seems to be at the first glance.

 Its importance is often overlooked because this stage requires such a small part of the
total time to create the final design.

Page.No. 15
  It is advantageous to define the problem as broadly as possible.

 If the problem is not accurately defined, it will lead to a waste of time on designs and
will not fulfill the need.
Stage 3 : Preparation of specification

 The design must meet the required performance specifications.

 Therefore, specification of the requirements needs to be prepared first.

 This will state the problem definition of special technical terms. Any constraints placed
statement includes all the functions required of the design, together with any desirable
features.

 The following are some of the statements about the problem.

 Mass and dimensions of design.

 Type and range of motion required.

 Accuracy of the element.

 Input and output requirements of elements. Interfaces.

 Relevant standards and code of practice, etc.,

Stage 4 : Generation of possible solution

 This stage is often known as conceptualization stage.

 The conceptualization step is to determine the elements, mechanisms, materials,

process of configuration that in some combination or other result in a design that
satisfies the need. This is the key step for employing inventiveness and creativity.

 A vital aspect of this step is synthesis.

 Synthesis is the process of taking elements of the concept and arranging them in the
proper order, sized and dimensioned in the proper way.

 Outline solutions are prepared for various models which are worked out in sufficient
details to indicate the means of obtaining each of the required functions.

Page.No. 16
State 5 : Selection of suitable or Evaluation :

 This stage involves a through analysis of the design.

 The evaluation stage involves detailed calculation. Often computer calculation of the
performance of the design by using an analytical model.

 The various solutions obtained in stage 4 are analysed and the most suitable is selected.

Stage : 6 : Production of detailed design

 The detail of selected design has to be worked out.

 It might have required the extensive simulated service testing of an experimental model or
a full size prototype in order to determine the optimum details of design.
Stage : 7 : Production of working drawing

 The finalized drawing must be properly communicated to the person who is going to
manufacture.

 The communication may be oral presentation or a design report.

 Detailed engineering drawings of each components and the assembly of the machine
with complete specification for the manufacturing process are written in the design
report.
Stage 8 : Implementation of design

 The components as per the drawings are manufactured and assembled as a whole
system.

Page.No. 17
5.4 COMPARISON OF TRADITIONAL AND MECHATRONICS DESIGN
CONCEPTS WITH EXAMPLES:

 Engineering design is a complex process which involves interaction between many skills
and discipline.

 In traditional design, the components are designed through mechanical, hydraulic or

pneumatic components and principles.

 But in mechatronics approach, mechanical, electronics, computer technology and

control engineering principles are included to design a system.

 For example design of weighing scale might be considered only in terms of the
compression of springs and a mechanism used to convert the motion of spring into
rotation of shaft and hence movements of a pointer across a scale.

 In this design measurement of weight is depended on the position of weight on the

scale.

 If we want to overcome foresaid problem, other possibilities can be considered.

 In mechatronics design, the spring might be replaced by load cells with strain gauges
and output from them used with a microprocessor to provide a digital readout of the
weight on an LED display.

 This scale might be mechanically simpler, involving fewer components and moving
parts. But the software is somewhat complex.

 Similarly the traditional design of the temperature control for a central AC system
involves a bimetallic thermostat in a closed loop control system.

 The basic principle behind this system is that the bending of the bimetallic strip changes
as the temperature change and is used to operate an ON/OFF switch for the
temperature control of the AC system.

 The same system can be modified by mechatronics approach.

 This system uses a microprocessor controlled thermo couple as the sensor.

Page.No. 18
  Such a system has may advantages over traditional system.

 The bimetallic thermostat is less sensitive compared to the thermodiode.

 Therefore the temperature is not accurately controlled.

 Also it is not suitable for having different temperature at different time of the day
because it is very difficult to achieve.

 But the microprocessor controlled thermodiode system can difficulties and is giving
precision and programmed control.

 This system is much more flexible.

 This improvement in flexibility is a common characteristic of the mechatronics system

when compared with traditional system.

The difference between traditional and mechatronic approach are as follows:

S. No Traditional approach Mechatronics approach

1 The cam operated rocker arm The valve operation is controlled by the
mechanism controls the valve signal received from electronic control
operation unit.
2 The rotation of cam is based on the The timing of valve operation is pre
crank rotation programmed in the microcontroller

Comparison between Traditional and Mechatronics Design:

S. No Traditional Design Mechatronics Design

1 It is based on traditional system such It is based on mechanical, electronics,
as mechanical, hydraulic and computer technology and control
pneumatic. engineering.
2 Less flexible More flexible
3 Less Accurate More Accurate
4 More complicated mechanism in Less complicated mechanism in design
design
5 It involves more components and It involves fewer components and
moving parts moving parts

Page.No. 19
5.5 CASE STUDIES OF MECHATRONICS SYSTEMS:
 Mechatronics systems are widely used nowadays in many industries.
 Some of the examples are explained here.
Case Study 1: 5.6 PICK AND PLACE ROBOT:
The basic form of a pick and place robot is shown in Figure. The robot has three axes
about which motion can occur.
The following movements are required for this robot.
 Clock wise and anticlockwise rotation of the robot unit of its base.
 Linear movement of the arm horizontally i.e., extension or contraction of arm.
 Up and down movement of the arm and
 Open and close movement of the gripper.

 The foresaid movements can be obtained by pneumatic cylinders which are operated by
solenoid valves with limit switches. Limit switches are used to indicate when a motion is
completed.

 The clockwise rotation of the robot unit on its base can be obtained from a piston and
cylinder arrangement during pistons forward movement. Similarly counter clockwise

Page.No. 20
 rotation can be obtained during backward movement of the piston in cylinder. Linear
movement of the arm can result during forward and backward movement of the piston
in a cylinder.

 The upward movement of the arm can result from forward movement of the piston in a
cylinder whereas downward movement from its retardation. The griper can also be
operated in a similar way as explained above i.e., gripper is opened during forward
movement of the piston and closed during backward movement of the piston in the
cylinder. Figure 5.5 shows a mechanism used for this purpose.

Page.No. 21
  A microcontroller used to control the solenoid valves of various cylinders is shown in
Figure. The micro controller used of this purpose is M68HC11 type. A software program
is used to control the robot.

 TRIAC optoisolator consists of LED and TRIAC. If the input of the LED is 1, it glows and
activates the TRIAC to conduct the current to the solenoid valve. Otherwise TRIAC will
not conduct the current to the solenoid valve.

Case Study 1: PICK AND PLACE ROBOT:

 Pick and place robot is the one which is used to pick up an object and place it in the
desired location

 It can be a cylindrical robot providing movement in horizontal, vertical and rotational

axes, a spherical robot providing two rotational and one linear movement, an articulate
robot or a SCARA robot (fixed robots with 3 vertical axes rotary arms).

 Pick and place robot actually consists of:

1. A Rover: It is the main body of the robot consisting of several rigid bodies like a
cylinder or a sphere, joints and links. It is also known as a manipulator.

2. End Effector: It is the body connected to the last joint of the rover which is used for the
purpose of gripping or handling objects. It can be an analogy to the arm of a human
being.

3. Actuators: They are the drivers of the robot. It actually actuates the robot. It can be any
motor like servo motor, stepper motor or pneumatic or hydraulic cylinders.

4. Sensors: They are used to sense the internal as well as the external state to make sure
the robot functions smoothly as a whole. Sensors involve touch sensors, IR sensor etc.

5. Controller: It is used to control the actuators based on the sensor feedback and thus
control the motion of each and every joint and eventually the movement of the end
effector.
Working of a Basic Pick N Place Robot:

 The basic function of a pick and place robot is done by its joints.

Page.No. 22
  Joints are analogous to human joints and are used to join the two consecutive rigid
bodies in the robot.

Fig. 5.5.1 Pick and Place Robot

 They can be rotary joint or linear joint.

 To add a joint to any link of a robot, we need to know about the degrees of freedom and
degrees of movement for that body part.

 Degrees of freedom implement the linear and rotational movement of the body and
Degrees of movement imply the number of axis the body can move.

Advantages

1. They are faster and can get the work done in seconds compared to their human
counterparts.
2. They are flexible and have the appropriate design.

3. They are accurate.

4. They increase the safety of the working environment and actually never get tired

Practical Applications of Pick and Place Robot:

1. Defence Applications: It can be used for surveillance and also to pick harmful objects like
bombs and diffuse them safely.

2. Industrial Applications: These robots are used in manufacturing, to pick up the required
parts and place it in correct position to complete the machinery fixture. It can be also used to
place objects on the conveyer belt as well as pick up defective products from the conveyer
belt.

Page.No. 23
 3. Medical Applications: These robots can be used in various surgical operations like in
joint replacement operations, orthopaedic and internal surgery operations. It performs
the operations with more precision and accuracy.

Case Study 2: 5.7 ENGINE MANAGEMENT SYSTEM:

 An electronic engine management system is made up of sensors, actuators, and related
wiring that is tied into a central processor called microprocessor or microcomputer (a
smaller version of a computer)

 Electronic management systems monitor and gather data from a number of sensors in the
engine and continuously adjust the fuel supply and injection timing.

 This minimizes emissions and maximizes fuel efficiency and engine output at any given
workload.

 The electronic engine management generally consists of the following basic components: An
electronic control unit (ECU), a fuel delivery system (typically fuel injection), an ignition
system and a number of sensors. Figure 5.21 shows the various components in the typical
engine management system.

Page.No. 24
Electronics control unit (ECU) :

 The sensors provide feedback to the ECU to indicate how the engine is running so that
the ECU can make the necessary adjustments to the operation of the fuel delivery and /
or ignition system.

Fuel delivery system :

 This system consist high pressure fuel pump which is mounted in or near the tank.

 The fuel line the pump passes through a filter before it runs forward to the engine bay.
The fuel line connects to a fuel rail that feeds each of the injectors.

 At the end of the rail is a fuel pressure regulator, with surplus fuel heading back to the
tank in the return line.

Ignition system :

 Ignition system consists of ignition coil, distributor and spark plug.

 These components are connected with the ECU to receive the signal for proper timed
operation.

Various sensors :

 Engine sensors fall into five broad categories.

 Throttle – Position Sensors, Exhaust Gas Oxygen Sensors, Manifold Absolute Pressure
Sensors, Temperature Sensors and Speed / Timing Sensors.

 All these sensor functions are centrally controlled by microcontroller as shown in

Figure.

Throttle – Position Sensors :

 A throttle – position sensor sends the signal to ECU about the throttle opening and the
force applied by the driver.

 Then the ECU controls the fuel delivery and spark timing based on the throttle position.
Two common throttle – position sensors are potentiometric and Hall – effect sensors.

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Exhaust Gas Oxygen (EGO) Sensors :

 Exhaust gas oxygen (EGO) sensors are places within the engine’s exhaust system.

 The amount of oxygen in the exhaust gas indicates whether or not the ECU has directed
the fuel delivery system to provide the proper air – to fuel ratio. If the relative amount of
air is too high or too low, engine power, smoothness, fuel efficiency and emissions will
all suffer.

Manifold Absolute Pressure (MAP) Sensors:

 Manifold Absolute Pressure (MAP) Sensors measure the degree of vacuum in the
engine’s intake manifold.

 The amount of vacuum depends on engine rpm and throttle opening. The most common
MAP sensors are piezoresistive and variable capacitor sensors.

Temperature Sensors:

 Temperature sensors are used to report engine temperature to the driver / operator via
dash panel mounted temperature gauge, report engine temperatures to the ECU to
activate / de – activate cooling fans in water – cooled engines, to richen fuel mixtures for
easier starting in cold weather and to lean out mixtures for maximum fuel economy.
Two common temperature sensors are thermistors or thermodiodes.

Engine Speed / Timing Sensors :

 Speed / Timing sensors provide information to the ECU regarding engine speed and the
crank position.

 This information is used by the ECU to control fuel and ignition, as well as to make sure
that engine speed does not exceed safe operating limits.

 It is also used to control the fuel injectors and spark plugs. Most common speed/timing
sensors are variable reluctance, optical crankshaft position and Hall Effect sensors.

Exhaust Gas regulation (EGR) Valve Position Sensor:

 The signal from EGR valve position sensor is used to adjust the air fuel mixture. The

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 exhaust gases introduced by the EGR valve into the intake manifold reduce the available
oxygen and thus less fuel is needed in order to maintain low hydro carbon level in the
exhaust.

Mass Air flow (MAF) sensor :

 MAF sensor is used to measure engine load to squirt in the right amount of petrol,
and fire the spark at just the right moment.

 The amount of power being developed depends on how much air the engine is
breathing.

 Most common air flow sensors are Hot Wire Airflow sensor and V and Airflow
Meter.

Knock Sensor :

 The knock sensor is used to identify the sounds of knocking and sends signal to ECU to
avoid knocking.

 It is screwed into the engine block and is designed to separate out the special noise
which means that knocking is occurring.

 Many Electronic Fuel Injection (EFI) engines run ignition timing very close to knocking.

************************

5.7 ENGINE MANAGEMENT SYSTEM:

 Engine management system is, now-a-days, used in many of the modern cars such as
Benz Mitsubishi, and Toyota etc.

 This system uses many electronic control system involving micro controllers.

 The generalised block diagram of this system is shown in Fig. 5.7.2

 The objective of the system being to ensure that the engine is operated at its optimum
settings.

 The system consists of many sensors for observing vehicle speed, engine temperature,
oil and fuel pressure, airflow etc.

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 These sensors are supplying input signals to the micro controller after suitable signal
conditioning and providing output signals via drivers to actuate corresponding
actuators.

 A single cylinder engine consists of some of these elements in relation to an engine is

shown in Fig. 5.7.2.

Fig. 5.7.1 Block diagram of Engine Management System

 The engine sensor is an inductive type.

 It consists of a coil and sensor wheel.

 The inductance of the coil changes as the teeth of the sensor wheel pass it and so
results in an oscillating voltage.

 The engine temperature sensor is generally thermocouple which is made of bimetallic

strip or a thermistor.

 The resistance of the thermistor changes with change in engine temperature. This
results in voltage variation.

 Hot wire anemometer is used as a sensor for measuring mass airflow rate.

 The basic principle is that the heated wire will be cooled as air passes over it.

 The amount of cooling is depending on the mass rate of flow.

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 The oil and pressure sensors are diaphragm type sensors.

Fig. 5.7.2 Engine Management system with sensors and actuators

 According to the pressure variation, the diaphragm may contract or expand and

activates strain gauges which produce voltage variation in the circuit.

 The oxygen sensor is usually a close end tube which is made of Zirconium oxide with
porous platinum electrode on the inner and outer Surfaces

 The sensor becomes permeable to oxygen ions at about 300°C.

 This results in generation of voltage between the electrodes.

 The various drivers such as fuel injector drivers, ignition coil drivers.

 Solenoid drivers and used to actuate actuation according to the signal by various
sensors.

 Analog signals given by sensors are converted into digital signal by using analog to
digital converters (ADC) and sent it to micro controllers.

 The various output digital signals are converted into analog signals by DAC(i.e.,
Digital to Analog Converter) and shown in various recorders or meters.

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The comparison of traditional and mechatronics approach in engine management is
given in Table.
Sl.No. Traditional approach Mechatronics approach

1. The cam operated rocker arm The valve operation is controlled by the
mechanism controls the valve signal received from electronic control
operation. The rotation of cam is unit. The timing of valve operation is pre
based on the crank rotation. programmed in themicro controller.
2. The engine speed regulation is based The engine speed regulation is based on
on the governor controlled throttle the input signal from and MAF sensor.
valve. The governor is actuated by the Based on the sensor information the
speed of the crank shaft. The speed throttling valve is controlled by
control has not effect on the engine microcontroller.
temperature and air flow rate.
3. Spark timing of the spark plug is Spark timing of the spark plug is controlled
controlled by the ignition coil and by the ignition coil that receives signal
distributor at constant pre set from the microcontroller through a
interval timing sequence program

Case Study 3: 5.8 AUTOMATIC CAR PARK BARRIER:

 Consider an automatic car park barriers operated by coin inserts.
 The system uses a PLC for its operation.
 There are two barriers used namely in barrier and out barrier.
 In barrier is used to open when the correct money is inserted while out barrier opens
when a car is detected in front of it.

Fig. 5.8.1 Automatic Car park barrier system

 It consists of a barrier which is pivoted at one end, two solenoid valves A and B and a
piston cylinder arrangement.
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 Solenoid valves are used to control the movement of the piston.
 Solenoid A is used to move the piston upward in turn barrier whereas solenoid B is
used to move the piston downward.
 Limit switches are used to detect the foremost position of the barrier.
 When current flows through solenoid A, the piston in the cylinder moves upward and
causes the barrier to rotate about its pivot and rises to let a car through.

Fig. 5.8.2 PLC arrangement for operating barrier

 When the barrier hits the limit switch, it will turns on the timer to give a required
time delay.
 After that time delay, the solenoid B is activated which brings the barrier downward
by an operating piston in the cylinder. This principle is used for both the barriers.
 Figure shows the ladder program for that PLC system.

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