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1. Introduction:

The main intention of the assignment is to carry out the programming and document the automation of a Bytronic associated with Industrial Control Trainer using an Allen-Bradley Micrologix 1000 PLC. It includes

  • Analysing the mechanical system, sensors and actuators.
  • Establishing the control requirements.
  • High-level design of the PLC program using the Sequential Function Chart (Grafcet) notation.
  • Implementation of the program in ladder logic form using RSLogix 500 software.
  • Program testing.
  • Critical assessment of the completed program adjacent to the stated requirements.

Programmable Logic Controller (PLC):

Programmable Logic Controller (PLC) is a programmable electronic device that is used in the industrial automation systems in order to examine the system inputs and responses the behaviour of program to manage the output devices based upon the sequence and logic provided to the system.

Approximately in all manufacturing line, electronics and electrical shops and as well as in some type of the mechanicals; this process is greatly enhanced. PLC is mainly used in industries and machineries. For general purpose, the PLC is mainly designed for the multiple inputs and responses the arrangements of output. But in real-time PLC, the output must be produced within a restricted time for the given input conditions.

The main benefits of the PLC are:

  • Communication possibilities.
  • Flexibilities.
  • Reliability
  • Realization of complex control algorithms.
  • System is very simple.
  • Special devices are available.

The main functionality of the PLC is to include sequential relay control, statistical discipline that deals with the algorithms and mechanism for controlling the output of a process and distributed control systems.

History Of PLCs:

In the need of the American automotive manufacturing industry, the PLC was invented. Initially the programmable controllers were adopted by the automated industry. When production models changed, the software revision has been replaced by re-wiring hard-wired control panel. The first programmable logic controllers were designed and developed by Modicon as a relay re-placer for GM and Landis.

Later the PLCs were designed to replace the relay logic systems after that the PLC were programmed in ladder logic which strongly resembles in relay logic. Modern PLC, in Variety ways the programmed can be altered from ladder logic to more traditional languages like C and BASIC. While reducing the cabinet space that housed the logic, the new system severely increased the functionality of the controls. The first PLC, model 084, was invented by Dick Morley in 1969. The first commercial successful PLC, the 184, was introduced in 1973 and was designed by Michael Greenberg.

Interior Structure Of PLC:

Programmable Logic Controller is a microprocessor based device that mainly consists of CPU, I/O devices and memory. Additionally it is also connected to the program reader, memory unit and programming and printer.

  • Perform housekeeping activities like communications through RS-232, internal diagnostics etc.
  • Perform the control instructions contained in the user's programs. This program is stored in ‘ROM/EPROM' which is non-volatile memory (data/program cannot be lost when the power has lost).
  • Communicate with other devices like I/O devices, network, programming devices.

The main difference between the PLCs and other microprocessor based devices are;

  • PLCs are designed rough for the industrial settings and secured for improving the electric noise immunity and they are modular.

2. System Description:

Programmable Logic Controller (PLC) is a programmable device that hub too many manufacturing industries processes. The internal structure of the PLC is similar to many parts of the systems and embedded controllers. The PLC depends upon the types of systems i.e. small, medium and large and depending on that the component of the system is built in the distributed unit. The microprocessor based unit is equipment used for controlling and tracking the manufacturing processes. The main advantage of the PLC is easy to design and modify the control process and also the programming languages were adopted.

Microprocessor is the main part of the PLC which acts as a vice-versa in the systems. The commands and the instructions from the user's program depend on the microprocessor to results system. PLC consists of microprocessor, memory integrated unit and it also consists of storage and reclaim the data from the memory unit. The PLC also includes the communication ports, so that it can transfer the data from system to the PLC and to other terminal devices. In real-time world, it has a capability to control the processes. The main position of the processor is to examine the number of inputs and results the responses from the system.

RAM is a Random Access Memory which is a volatile memory (i.e. when the power has lost the data will be lost). This type of RAM is not used in the system and it may causes some battery back up in slot. The CMOSRAM (Complementary Metal Oxide Semiconductor RAM) is used for storage memory and ladder logic diagram.

EEPROM (Electrically Erasable Programmable Read Only Memory) is also a non-volatile memory and this type of memory is used for the storage of large amount of data. The other electric devices are used for the storage of small amount of data. It is used to back up the major program in the CMOSRAM processor.

ROM (Read Only Memory) is also a non- volatile memory. It can only read the program and the program cannot be modified. It is mainly used to distribute firmware and it does not require an external power supply.

Input Module:

There are several types of input devices to be taken such as pushbuttons, thumb switches and some other devices etc. And some other DC inputs devices like electronic card access, thumbprint, etc are used for the application to access the input module. But in most of the industrial sector system are provided with the essential noisy and electric isolation between the processor and the module.

In majority of industrial systems, the processor for the input module takes from 8 to 32 input bits. For each and every input bit the address will be allocated according to the processor instructions.

Output Module:

The output module can be used for both the device (AC or DC) such as solenoids, relays, contractors and LED readouts. The result depends upon the input module to which the connection has been made through the ports or terminals. The connection towards the input and output devices may vary according to the power supply as well as load. For an analog device, the special type of output device is used to convert from a digital to analog. Whereas for the digital, the special type of output device is used to convert from analog to digital. For analog output device, the results are stored in 12 bit file and convert it to analog signal. The signal may vary from 0 to -10v for DC.

Communications:

The most commonly used for communication port is RS-232 9-pin connector. In PLC, RS-232 is an in built communication protocol to communicate within the peripheral interfaces and other terminal devices. In today's world, the wide range of communication link in some of the PLC is RS-485 which can access more speed.

For peer to peer communication, the larger I/O devices are used in PLC program. There are different methods to communicate between a PLC and a programmer or even with two different PLC. In PLC, the application programs are written in personal computer and downloaded to the system (PC) using the plug in cable to the programming port of the PLC. This communication can be forwarded through the RS-232 or RS-485. The communication between two PLC can be conceded by the keen links supplied through the RS-232.

Operation Of PLC:

The operation of the all PLCs is followed in four steps continuously takes place in rotationally. The four basic steps followed by the PLC are

  • Input Scan
  • Program Scan
  • Output scan
  • Housekeeping.

The below figure shows the operation of the PLC:

1) Input Scan: It detects all the state of inputs that are connected to the PLC.

2) Program Scan: Examine the program logic created by the user to execute.

3) Output Scan: All the output devices that are connected to the PLC can be energizes or de-energizes.

4) Housekeeping: This step is used to communicate with the peripherals, programming terminals and other devices etc.

PLC Diagram Description:

In PLC the programs are fabricated based upon the ‘gates' simultaneously with the inputs, timers, counters, outputs, internal memory bits, analog inputs, comparators, analog output etc.

Inputs: The physical connections that are connected to the PLC are switches, pushbuttons, sensors and anything which acts like a switch or signal to the state of ON and OFF position. The voltages that accept to some of the devices are 24V DC and some may not; it may vary.

The switch when it is in ON state, then status of the device bit is ‘1' and when it goes to OFF state the status of the device bit is ‘0'.

Output: The result that appears from the input devices is the communication between the PLC and other terminals. They are used to control the solenoids, sensors, and connectors etc to on and off position.

In the PLC, there are 8 sensors and 5 actuators were used. The result from each sensor response the actuators and other sensors to perform the task. These eight sensors has different task they are

1) Sensor1: It detects the presence of peg in the upper sort area.

2) Sensor2: It detects the components in front of the solenoid at the upper sort area of the ring chute.

3) Sensor3: It detects the presence of ring in assembly area.

4) Sensor4: It is used to commence assembling.

5) Sensor5: It is used to terminate the assembling.

6) Sensor6: It is used to detect the complete assemblies.

7) Sensor7: It is used to detect the components at the lower sort area.

8) Sensor8: It is used to detect the components and assemblies near the reject area solenoid.

The purpose of 5 actuator which are used in PLC area are

1) Actuator1: It drives the upper chain conveyor motor.

2) Actuator2: It drives the lower chain conveyor motor.

3) Actuator3: It knocks the ring in the ring chute.

4) Actuator4: It releases the ring into the assembly area.

5) Actuator5: It rejects the unassembled components.

Relay: A relay is a switch which is operated on the electromagnetic.

Counters: when a pre-assigned count value is reached, the digital counters are in the form of relay contact.

Timers: Timer consists of internal clock, a count value register and an accumulator which is used to count the time.

3. Requirements:

The requirements for the PLC diagram are

  • Ladder diagram
  • Structure text programming
  • Instruction list
  • Functional block programming
  • Sequential functional chart.

Requirements & Constraints:

  • During the operation, Conveyor belts should be kept moving.
  • When sensor 1 senses it, the actuator 3 should knock only the ring.
  • Overloading of rings should be collected in the surplus rings box.
  • The ring should not enter the peg chute or vice versa.
  • The peg chute and the ring chute should be kept clean for the peg and the ring to slide in to that.
  • By the actuator 5, Unassembled components should be knocked down

Constraints

  • Actuator should not knock the ring when there are more than 5 rings in the chute if there are more rings 5 rings then the progress will be blocked.
  • The area between the actuator 4 and the sensor 3 should be clear for the next peg to occupy the space.
  • Only if the peg moves past the ring the assembly will be over.
  • If there are more than 5 rings in the ring chute, the actuator 3 cannot knock.

4. Program Design:

The graphical representation of the logic essential in relay logic is a ladder diagram. The ladder diagram instruction consists of relays, timers and counters, program control, data transfer, arithmetic operation and data manipulations.

In order to create programmable controller program, the ladder diagram language is used. The control logic can be obtained by reducing the ladder instructions symbols. The main objective of the ladder diagram is to control the outputs based on the input circumstances.

Based on the simple logic, the ladder rungs can be reduced and also the controlling rungs are based on the logic. The ladder instructions consist of some symbols to perform the program. The symbols to be used in the programming and instruction set are basic relay type contacts and coil symbols. The representation of the coil symbol is used at the output and whereas the representation of the contact symbol is used at the conditions in orders to control the output. For each and every contact and coil, an address number will be referred.

Function Block Programming:

In this function block, the instruction for the programming is very complex for the user's program such as data transfer, shift register instruction and so on. And these are also basic building blocks for the control systems.

Sequential Function Chart:

There are some steps to follow the sequential function chart program symbols, they are

  • Start block
  • Initial block
  • Step block
  • Transition
  • OR path
  • AND path

There are three basic standard rules to be followed by the chart

1) The first step is to active the program at the start block and the programming have an option of restarting the device.

2) After the completion of the steps one by one, the transition state will be tested and the action will be continued until the transition is in true state.

3) Once the transition is in true state, the processor scans the steps once again to rearrange all timer instructions and executes the next step.

The processor scans starts the sequential function chart from left to right side and if chart is encountered then it examines the ladder logic from left side to right side.

Grafcet is a graphical function chart programming language. This language was adopted by telemechanique into the programmable control language and this language is used for the sequence behaviour of the program. Each step represents the state of system to be controlled and the horizontal bar represents the conditions to perform the accomplishment.

6. Explanation Of Program:

Stage1:

0000

If flag1 (B3:1/1) is set to ON state and input sensor 4 is ON (I:0/18) but the input sensor 5 (I:0/19) is set to OFF state then LATCH (Enable) the flag2 and UNLATCH the flag1.

0001

If flag 2 (B3:1/2) is set to ON state then ENABLE both the output actuator 1 which is a lower conveyor motor (o:0/3) and the output actuator 2 which is a upper conveyor motor (o:0/4).

0002

If flag 2 is ENABLE and the input sensor 5 (I:0/19) is set to ON state then LATCH the flag1 and UNLATCH the flag 2.

Stage 2:

0003

If flag 3 (B3:2/1) is set to ON state and the input sensor 2 (I:0/1) is ON state and input sensor 1 (I:0/4) is set to OFF state and the counter C5 is less than five then LATCH the flag 4 (B3:2/2) and UNLATCH the flag 3 (B3:2/1).

0004

If the flag 4 (B3:2/2) is set to ON state then enables the timer 1 to 0.01 and preset value to 50 and ENABLES the output actuator 3 (o:0/0).

0005

If the flag 4 is set to ON state and the timer 1 is decrementing then UNLATCH the flag 4 and LATCH the flag 5 (B3:2/3).

0006

If the flag 5 (B3:2/3) is set to ON state and then set the timer 2 (T4:1) to 0.01 second and preset value to 20 seconds.

0007

If the flag 5 is set to ON state and the timer 2 (T4:1) is enable and then LATCH the flag 6 and UNLATCH the flag 5.

0008

If the flag 6 (B3:2/4) is set to ON state and then set the counter to up C5:0 and preset value to 5.

0009

If the flag 6 is set to ON state and counter up is enabled then LATCH flag 3 and UNLATCH flag 6.

Stage 3:

0010

If the flag 7 (B3:3/1) is set to ON state and the input sensor 3 (I:0/0) is set to OFF state and then C5:0.ACC source A< source 1 then LATCH flag 8 and UNLATCH flag 7.

0011

If the flag 8 (B3:3/2) is set to ON state and timer 3 (T4:2) is set to base as 0.01 and preset value to 50 and ENABLES the output actuator 4 (o:0/1).

0012

If the flag 8 is set to ON state and the timer 3 (T4:2) is decreasing and then LATCH the flag 9 and UNLATCH the flag8.

0013

If the flag 9 (B3:3/3) is set to ON state and then set the counter down by 1.

0014

If the flag 9 is set to ON state and the input sensor 3 (I:0/0) is set to OFF state then LATCH the flag 10 and UNLATCH the flag 9.

0015

If the flag 10 (B3:3/4) is set to ON state and the input sensor 9 (I:0/5) is set to ON state then LATCH the flag 7 and UNLATCH the flag 10.

Stage 4:

0016

If the flag 11 (B3:4/1) is set to ON state and the input sensor 6 (I:0/6) is set to ON state and then LATCH flag 12 and UNLATCH flag 11.

0017

If the flag 12 (B3:4/2) is set to ON state and the input sensor 8 (I:0/2) is set to ON state then UNLATCH the flag 12 and LATCH the flag 13.

0018

If the flag 13 (B3:4/3) is set to ON state and the input sensor 8 (I:0/2) is set to OFF state then LATCH the flag 11 and UNLATCH the flag 13.

0019

If the flag 11 (B3:4/1) is set to ON state and the input sensor 8 (I:0/2) is set to ON state then UNLATCH the flag 11 and LATCH the flag 14.

0020

If the flag 14 (B3:4/4) is set to ON state and then ENABLE the output actuator 5 (o:0/2).

0021

If the flag 14 is set to ON state and the input sensor 8 (I:0/2) is set to OFF state and then LATCH the flag 11 and UNLATCH the flag 14.

0022

END

7. The Rejection Component:

In PLC, the unassembled components are rejected by the sensor 8 (I:0/2). The problem in which the unassembled components are rejected due to the delay in the actuator 4 or the peg which comes from the peg chute initially but not the ring or the assembled components which comes from the sensor 3 moves a bit distance at which the sensor 6 cannot detects the component then the rejection of the component could be taken by the sensor 8. And also there must be delay in the actuator 3 in order to push the rings in to the chute. These are the reasons for the rejection of the assembled and unassembled components.

8. Testing:

There are four tests to check whether the PLC is working under conditions or not. The first test is to check whether the sensor one is detecting the peg or not and the actuator 3 is knocking the ring into the chute through the detection of sensor 2. The second test is whether the actuator 4 is holding the ring in the ring chute for some delay of time and allowing only the rings through detection of sensor 2. The third test is to check the whether the sensor 6 is detecting the assembled components at the lower sort area. The fourth test is to check the actuator 5 at the solenoid in order to reject the unassembled components.

9. Discussion:

In modern control systems, the mechanical and electrical parts are used to design the machinery. In most of the control systems, there is a relay in the circuits, programming controllers and some other special devices are used. There are several ways to select the PLC. The most important in selecting the PLC is the processor. The cost of the system is very cheap and it is reliable and flexible. In PLC the user program cannot be analyzed.

The main benefit of the Programmable controllers is the flexibility. The effectiveness of the use of the PLC is the software controller in which the PC software solution that relates devices via communications protocols. The main focus is based on the programming languages. These languages are built with the logic of the various instruction set.

The following are the methods for selecting the PLC are

1) Maximum number of inputs and outputs is allowed. (Digital, analogue, inputs, outputs).

2) Layout of sensors and actuators. ( peripherals)

3) Nature of solution.( New or existing)

4) Special signals and modules. (high speed digital outputs)

5) Processor properties. (program and data memory)

6) Working conditions. (temperature, humidity, dust)

7) Communications. (ASCII)

8) Specialities of program. (special functions)

The limitations of the PLC are

1) To store a large amount of data, the program controllers are not capable with sufficient memory.

2) The temporal network which is traceable by hardly overloads can cause the issue in automation system communication.

Conclusion:

The solution that set the industrial standard is the Allen-Bradley Micrologic 1000PLC. For the digital I/O, the micrologic 1000PLC are available in 10-points,16-points and 32-points and whereas fort the analogue I/O, the micrologic 1000PLC are available in 20-points digital I/O, with 4 analog inputs and 1 analog output. The successfully method for the Allen-Bradley manufactures-lower costs, flexibility, high quality and fast start ups. This control method has been successfully invented by the PLC program. The major parts of the PLC are sensors, solenoids and actuators. These sensors and actuators will acts as a vital role in the PLC. The pegs and the rings that come on the upper sort and lower sort area can be detected through the sensors. Thus, by placing the sensors and actuators in the suitable place, the rings and pegs can reach the destination successfully. The program is tested and thus the results is achieved successfully without any errors.

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