Definition And Process Modelling Engineering Essay

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The overall aim of the project is to design a flawless system that could replace the space consuming and costly industrial control trainer with some extra functionality enhancement and fault detection features which makes it reliable and gives it edge over the real system. Moreover the aim is to provide a combined model of process, controller, sensors and actuators. This allows the future studies to go further look at the problems caused by the faulty sensor and actuator and develop methods for fault diagnosis and reconfiguration. The figure 4.1 shows the enhancement of plant and controller model with all the actuator and sensor fault diagnosis stages and methods designed to rule out errors.

SENSORS FAULT MODEL

ACTUATOR FAULT MODEL

Figure 4.1 Fault proof model of the system

The above figure shows the actuator and sensor fault model which can be designed to diagnose and rule out the sensors and actuator faults in future. All the above discussion was related to future studies.

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This dissertation is focused only to design an ideal controller and plant model which means that all the sensors and actuator are working in perfect condition without any fault. Figure 4.2 clearly shows the ideal plant model and the controller model designed in this dissertation.

Figure 4.2 Ideal plant and controller model

The plant variables and the controller variables shown in figure 4.2 are basically equal in this dissertation because they are ideally performing but just for the understanding of the future study and in real they can't be same. But In here for the plant they are like:

ps1 = s1

ps2 = s2

ps3 = s3

ps6 = s6

ps7 = s7

ps8 = s8

And, for the controller:

ac1 = pac1

ac3 = pac3

ac4 = pac4

4.2 Process description

The process is basically performed by Bytronic industrial control trainer which is an assembly plant for of rings over pegs. The view of the system is shown in figure 4.1 which will be helpful in order to visualize the process.

3

6

8

7

Collection tray

Lower motor

Reject solenoid

Ring place

Lower conveyor

Solenoid

Upper motor

Peg chute

Ring chute

Sensor 1

Solenoid   Reject tray

Surplus rings tray

Peg Ring

Component belt

Figure 4.3 View of Bytronic Industrial control trainer

The Trainer consists of number of I/O devices attached to it which are controlled by a PLC which in this case is AB Micrologix 1000. The PLC I/O addresses assigned to the devices are given in Table 4.1 and 4.2.

Table 4.1 Input Components

Sensor No.

Description

PLC input address

1

Downward looking reflective IR sensor at the upper sort area which detects the presence of a peg near to and in front of the solenoid at the top of the ring chute.

I:0/4

2

Sideways looking IR sensor at upper sort area which detects a component in front of a solenoid at the top of the ring chute.

I:0/1

3

Reflective IR sensor at the assembly area which detects the presence of component at the very bottom of the ring chute beyond the rotary solenoid.

I:0/0

4

Black pushbutton used to commence the assembling.

I:0/18

5

Red pushbutton used to terminate the assembling.

I:0/19

6

Capacitive sensor, near the lower sort area which detects the presence of passing complete assemblies near the reject solenoid at the motor end of the lower conveyor.

I:0/6

7

IR reflective sensor which detects the complete assembly or incomplete peg after sensor 6

I:0/7

8

Reflective IR sensor at the lower sort area which detects the presence of components and assemblies in front of the reject solenoid at the motor end of the lower conveyor.

I:0/2

Table 4.2 Output Components

Actuator No.

Description

PLC output address

1

Upper conveyor motor that drives the upper toothed chain conveyor.

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O:0/3

2

Lower conveyor motor that drives the lower plain belt conveyor.

O:0/4

3

Solenoid at upper sort area that knocks the rings into ring chute.

O:0/0

4

Rotary solenoid at the bottom of the ring chute before the assembly area that release the rings into the assembly area.

O:0/1

5

Solenoid at the reject area that rejects unassembled components before the complete assembly collection tray.

O:0/2

4.2.1 Start/Stop

Initially the two START (black) and STOP (red) buttons are available in the system. If START button is pressed, the motors of both the conveyors start to move. Now if STOP button is pressed, the both conveyors will stop immediately. The controls of both the buttons are arranged in such a way that if both the buttons are pressed at the same time, no action will be taken by the PLC.

4.2.2 Upper sort area

The two sensors in the sorting area wait for the item to come. The combination of two sensors differentiates between the rings and the pegs. If we get low from sensor1 and high from sensor2, ring is detected and now it will check for the number of rings in the chute. At this stage the ring counter is read by the PLC which checks for the space in the chute as it can accommodate only five rings at a time. If number is less than five the ring is knocked into the chute and counter is incremented by one, otherwise it is allowed to pass to the surplus ring tray.

4.2.3 Chute area

The sensor3 detects the ring in the assembly area located at the end of chute. If the ring is not in the area, we get low signal from the sensor3 and then the PLC checks for the ring count greater than zero. If there is a ring in the chute then actuator4 actuates another ring to go in the assembly area. The counter is decremented by one at this stage.

4.2.4 Assembly area

As no action associated if the complete assembly is detected by the sensor6, the sensor8 detects the complete assembly in front of the reject solenoid and solenoid is not activated allowing assembly to pass to the assembly tray and the process goes on when assembly is detected and no action is performed in this process.

If we get low from Sensor6 and high from sensor7 that means there is an object but it's an incomplete assembly or unassembled peg. The PLC then waits for the signal from the sensor8. As this condition goes true the actuator5 is activated, pushing the unassembled item into the rejection tray.

4.3 Stateflow model of the process

The Process trainer has been modelled using the Stateflow charts present in the MATLAB Simulink tool box. The Stateflow model of the process shown in figure 4.2 is designed in such a way that it imitates the whole process scenario. There is a PLANT model which imitate the plant and send the sensor signal to the CONTROLLER acting as the programmable logic controller(PLC) which send actuator signal back to the PLANT.

Figure 4.4 Plant Stateflow model

Figure 4.5 Plant model for stateflow

The inputs and outputs used in the Plant model with their description and type are given in Table 4.3 and 4.4

Table 4.3 Plant Input Variables

Plant Input Variables

Type

Description

po1

Input from Simulink

Refers to the data coming from sensor1 at the entry of entity1 into the system.

po2

Input from Simulink

Refers to the data coming from sensor2 at the entry of entity2 into the system.

pac1

Input from Simulink

Refers to the ring actuator signal from the controller.

pac3

Input from Simulink

Refers to the rotary solenoid chute actuator signal from controller.

pac4

Input from Simulink

Refers to the reject solenoid signal from the controller.

pswitch

Input from Simulink

Refers to the switch signal from the controller.

Table 4.4 Plant Output Variables

Plant Output Variables

Type

Description

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ps1

Output to Simulink

Sensor1 data which ensures the presence of a peg is fed to the controller.

ps2

Output to Simulink

Sensor2 data which ensures the presence of ring is fed to the controller.

ps3

Output to Simulink

Sensor3 data which ensures the presence of ring ready to assemble in an assembly area is fed to controller.

ps6

Output to Simulink

Sensor6 data which sees the complete assembly is fed to controller.

ps7

Output to Simulink

Sensor7 data which sees the object either a complete or incomplete assemble just next to sensor6 is fed to controller.

ps8

Output to Simulink

Sensor8 data which sees the object in front of the reject solenoid present at the end of assembly area.

pcnt

local

Plant ring counter

The plant designed using the Stateflow charts is divided into four parts. All these four parts are represented by each of the states labelled as:

Ring State

Peg State

Chute State

Reject State

All the states defined have the composition property of AND logic represented with dotted lines which means that all the states can be active and can be operated at the same time.

4.3.1 Ring state

Entering the ring state using the default transition enables the ring wait state which waits for the ring to come into the system. As the ring enters the system the sensor1 and sensor2 placed in the upper area of the plant recognize the entity whether it's a ring or the peg. If the signal from po1 is low and po2 is high that means a ring is detected by sensor1 and sensor2, immediately the transition to the next state known as ring is made which send the sensor signals to the controller using outputs ps1 and ps2.

The transition from ring state has two transition conditions either if there is no space for the ring in the chute shown by plant ring counter 'pcnt', the transition is made back to wait state and no action is performed or if there is space in the chute the transition to actuate state is done by getting actuate signal from the controller. At this state there is one possible way that in case due to jamming or malfunction of the actuator the ring is missed by the actuator, after 2 sec, the possession will be given back to the wait state. Otherwise if the ring is pushed, after 0.5 sec next state is activated which represents the ring sliding into the chute which after 2 sec delay which allows the ring to settle in the chute, the transition is made to wait state again.

Figure 4.6 Ring state with transition conditions.

4.3.2 Peg state

As shown in figure 4.4, the default transition activates the peg wait state in order to wait for a peg to come. When the plant object signal po1 is high and po2 is also high, the transition to the next state called as peg become active to assure the presence of peg detected by plant sensor1 and sensor2, this signal is sent to the controller. There is no action associated with the peg as it makes the place itself. So the peg is allowed to pass through and slide to the assembly area for assembling. The next transition is to the wait state which waits for the ring to come for assembly from upper sort area. After 5 sec as the peg assembles the ring over it, the plant sensor ps3 which shows the presence of ring ready to assemble goes to zero and final transition is made again to the first wait state to wait for the next peg. There is one limitation in the process that in 6 seconds only one ring will go through the process which can be overcome in the future.

Figure 4.7 Peg States with Transition Conditions

4.3.3 Chute state

The chute state shown in figure activates the no ring state with a default transition as shown in figure 4.5. Initially as no ring will be present in the chute, the system passes the signal to the controller as plant sensor ps3 shows low. The controller waits for the ring detection signal as the ring is detected and pushed into the chute, the transition with actuate signal pac3 to next state called chute actuate is made. There are two transition conditions at this stage if due to malfunctioning of sensors, the actuator is actuated, and initially no ring present in the chute. The transition will be made back to no ring state. Otherwise after 0.5 sec, transition to next state called ring ready will be taken which shows that there is a ring ready to be assembled as plant sensor ps3 shows 1.

The final transition will not be made until and unless the ring is assembled on the peg which is marked with transition condition of plant sensor ps3 shows low.

Figure 4.8 Chute States with Transition Conditions

4.3.4 Reject state

In the reject state shown in figure 4.6, there initial wait state with a default transition is activated. As the plant sensors detect the peg and if there is no ring in the assembly area as ps3 shows 0, the transition to next state called in incomplete assembly is activated. There are two transition conditions to come out of this state which are either an incomplete peg passes through the plant sensors ps6 and ps7. These two signals are sent to the controller which gives the actuate signal to the actuator4 through pac4 which knocks the unassembled peg into the reject tray or if the peg is on its way to the assembly area and the ring is detected and allowed to move in the assembly area which is show by plant sensor ps3 signal shows 1. After 0.5 sec, the control is again transferred back to the initial wait state which waits for the same condition again.

Figure 4.9 Reject States with Transition Conditions