Introduction_to_Mechatronics_Chapter67.pdf

Chapter VII
Chapter VI Microcontroller and microprocessors
Intr. to Mechatronics Prepare by: Bereket 1

5. Micro-processors and Micro-controllers
Introduction
Programmable Logic Devices (PLD) are programmable systems and are
generally used in manufacturing.
There are following three types of PLDs are being employed in mechatronics
systems
1. Microprocessor
It is a digital integrated circuit which carries out necessary digital functions to process the
information obtained from measurement system.
2. Microcomputer
It uses microprocessor as its central processing unit and contains all functions of a
computer.
3. Programmable Logic Controller (PLC)
It is used to control the operations of electro-mechanical devices especially in tough and
hazardous industrial environments.

6. Micro…
A typical programmable machine has basic three components
1. Processor, which processes the information collected from measurement system and
takes logical decisions based on the information.
2. Memory, it stores the input data collected from sensors and the programs to process the
information and to take necessary decisions . A group of programs is called software.
3. Input/output devices: these are used to communicate with the outside world/operator.

6. Micro…
A. Microprocessor
It is a multi-purpose programmable device
• It reads binary instructions from a storage device called memory
• It processes the data according to the instructions, and then provides results as
output.
• known as CPU (central processing unit).
• CPU can be referred as complete computational engine on a single chip.

6. Micro…
A. Microprocessor
• Applications of microprocessors are classified in two categories:
i. Reprogrammable Systems
supports CPUs for the personal computer and workstation industry, where the
main constraints are high speed and large word size (32 and 64 bits).
ii. Embedded Systems
Used for development of the microcontroller, which is a single IC
containing specialized circuits and functions that are applicable to
mechatronic system design.
Eg. photocopying machine, Digital camera
• First Microcontroller, Intel 4004 was launched in 1971.
• It was able to process just 4 bits. It started a new era in electronics engineering

6. Micro…
• Microprocessor works or operates in binary digits i.e. 0 and 1, bits.
• These bits are nothing but electrical voltages in the machine,
• Generally 0 - low voltage level, and 1 - high voltage level.
• A group of bits form a ‘word’. In general, the word length is about 8 bits. This is
called as a ‘byte’.
• A word with a length of 4 bits is called as a ‘Nibble’

6. Micro…
Basic blocks of a microprocessor functions
• ALU: ALU stands for Arithmetical Logical Unit. As name indicates it
has two parts:
a. Arithmetical unit which is responsible for mathematical
operations like
addition, subtraction, multiplication and division,
b. Logical unit which is dedicated to take logical decisions like
greater than, less than, equal to, not equal to etc. (Basically
AND/OR/NOT Operations)
• Register Array: Registers are small storage devices that are available to
CPU or processors. They act as temporary storage for processing of
intermediate data by mathematical or logical operations.

6. Micro…
• Control: This part of CPU is dedicated to coordinate data flow and signal
flow through various types of buses i.e. Data Bus, Control Bus, and Address
Bus etc. It directs data flow between CPU and storage and I/O devices.
• Memory: There are two different types of memory segments being used by
the CPU. First is the ROM which stands for Read Only Memory while other
is R/W which stands for Read and Write Memory or Random Access
Memory (RAM).
• Input Devices: Input devices are used to enter input data to microprocessor
from Keyboard or from ADC which receives data from sensors/signal
conditioning systems.
• Output Devices: These devices display the results/conclusions coming out
from ALUs either in soft copy (Monitor) or in Hard Copy (Printer).

End of Chapter VI

Chapter VII
Programable logic Controller (PLC)

7. PLC…
• Introduction:
• PLC was introduced in late 1960’s.
• First commercial & successful Programmable Logic
Controllers was designed and developed by Modicon as a
relay replacer for General Motors.
• Earlier, it was a machine with thousands of electronic parts.
Later ,in late 1970’s,the microprocessor became reality &
greatly enhanced the role of PLC permitting it to evolve form
simply relay to the sophisticated system as it is today.

7. PLC…
• PLC is actually an industrial microcontroller system where you
have hardware and software specifically adapted to industrial
environment.
• PLC is a digital computer designed for multiple inputs and output
arrangements, extended temperature ranges, immunity to electrical
noise, and resistance to vibration and impact.
• A PLC is an example of a real time system.
• Program unit is usually a computer used for writing a program
(often in ladder diagram).

7. PLC…
Key Terminologies:
1. Control task definition
• Control task is determining what needs to be done.
• This information provides the foundation for the control program.
• Proper definition of the task is directly related to the success of the control
program.
2. Control strategy
• After the control task has been defined, the planning of its solution can begin.
• It is determining the sequence of steps that must occur within the program to
produce the desired output control.
• This part of the program development is known as the development of an
algorithm.

7. PLC…
3. Creating flowcharts
• Flowcharting is a method of pictorially representing the operation of a
process in a sequential manner.
• It is a technique often used when planning a program after a written
description has been developed.
• A flowchart is a pictorial representation that records, analyzes, and
communicates information, as well as describes the operational process in a
sequential manner.
• Each step in the chart performs an operation, whether it is an input/output,
decision, or data process.

7. PLC…

7. PLC…
Figure Simple flowchart

7. PLC…
• Program coding—the process of translating a logic or relay diagram into PLC ladder
program form.
• Once the flowchart is completed, the user can employ either logic gates or contact
symbology to implement the logic sequences.
• Logic gates implement a logical output sequence given specific real and/or internal input
conditions, while PLC contact symbology directly implements the logic necessary to
program an output rung.

7. PLC…
Major Components of a Common PLC

7. PLC…
1. POWER SUPPLY; Provides the voltage needed to run the primary PLC components
2. I/O MODULES; Provides signal conversion and isolation between the internal logic
level signals inside the PLC and the field’s high level signal.
Input Signals can be AC or DC, Analog or Digital
1. PROCESSOR; Provides intelligence to command and govern the activities of the entire
PLC systems.
2. PROGRAMMING DEVICE; Used to enter the desired program that will determine the
sequence of operation and control of process equipment or driven machine.
3. Output Modules: Outputs are either AC or DC Analog Signals (Although it is possible to
‘Construct’ Digital Outputs)
• Modern PLC’s have Expansion Ports to Increase the Number of Available Inputs and
Outputs.

7. PLC…
PLC operation sequence
1. Self test: Testing of its own hardware and software for faults.
2. Input scan: If there are no problems, PLC will copy all the
inputs and copy their values into memory.
3. Logic solve/scan: Using inputs, the ladder logic program is
solved once and outputs are updated.
4. Output scan: While solving logic the output values are updated
only in memory when ladder scan is done, the outputs will be
updated using temporary values in memory.

7. PLC…
Programming Languages of PLC
 There are four most common PLC programming languages;
1. Ladder Logic
 The ladder logic is the oldest programming language for PLC.
 It is well suited to express Combinational logic.
 The main ladder logic symbols represent the elements:
 Ladder Logic Diagrams Provide a Method to Symbolically Show
How Relay Control Schemes are Implemented
 Relay Contacts and Coils, Inputs and Outputs lie on “Rungs”
Between the Positive and Ground Rails

7. PLC…
Basic Ladder Logic Symbol

7. PLC…
Simple Ladder Logic

7. PLC…

7. PLC…
• Ladder Logic Program for Start/Stop of Motor :

7. PLC…

7. PLC…
Starting of Motor:

7. PLC…
Ladder Logic Diagram
Example 1
Draw a ladder diagram that will cause the output, pilot light PL2, to be on when selector
switch SS2 is closed, push button PB4 is closed and limit switch LS3 is open.
Example 2
Draw a ladder diagram that is
equivalent to the following
digital logic diagram

7. PLC…
Y is on when (A is on, B is on and C is off ) or D is on, or E is off
 What happens if the D
contact refers to Y?

7. PLC…
 Output Y is set (latched) indefinitely

7. PLC…
Repeated Output
• Do not repeat normal output coils that refer to the same address
• The coils for first and second rung refer to Out1
 Second rung overrides the logic in first rung

7. PLC…
Repeated Output Correction
First consider the output
Next, consider ALL the conditions that drive the output (Out1)
(Implement the conditions in parallel)

7. PLC…
Reverse Power Flow
• This is not allowed:
• If the reverse power flow path is truly needed, then put it as a
separate path, where the power flows from left to right:

7. PLC…
Reverse Power Flow

7. PLC…
Ladder Logic Evaluation

Push Button (PB) Scan Timing Diagram

7. PLC…
Advantage of PLCs;
• Reliability.
• Flexibility in programming and reprogramming.
• Cost effective for controlling complex systems.
• Small physical size, shorter project time.
• High speed of operation.
• Ability to communicate with computer systems in the
plant.
• Ease of maintenance /troubleshooting.
• Reduced space.
• Energy saving.

7. PLC…
Disadvantage of PLCs;
• PLC devices are proprietary it means that part or software of one manufacturer
can’t be used in combination with parts of another manufacturer.
• Limited design and cost option
• Fixed Circuit Operations.

7. PLC…
Applications
• Wherever automation is desired the PLCs are best suited to meet the task.
• Few examples of industries where PLCs are used :
1. Robots manufacturing and control
2. Car park control
3. Train control station system
4. Food processing
5. Materials handling
6. Machine tools
7. Conveyer system etc.

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