5/6/2011

Control and PLCs: 5EJ057 | M.A

ID: 100119869 PLC AND CONTROL

SYSTEM AND ANALYSIS

UNIVERSITY OF DERBY Faculty of Art Design and Technology Electronics and Sound

2

Contents PART SUPPLY CONTROL SYSTEM (PART-A) .......................................................................................... 3

Requirements ................................................................................................................................... 3

Description of the system inputs and outputs................................................................................. 3

Opration pseudo code ..................................................................................................................... 4

Overall control ............................................................................................................................. 4

Control of oranges ....................................................................................................................... 4

Control method .................................................................................................................................... 4

PLC software ........................................................................................................................................ 5

Section One: ON and OFF function of conveyor .............................................................................. 7

Section Two: supply command function .......................................................................................... 7

Section Three: box on conveyor detection ...................................................................................... 7

Section Four: supply oranges ........................................................................................................... 8

Section Five: count oranges and delay timer ................................................................................... 8

Section Six: reset and supply ........................................................................................................... 9

Conclusion .......................................................................................................................................... 10

3

PLC and Control System Analysis

PART SUPPLY CONTROL SYSTEM (PART-A) This report is based on the requirements listed below, from these requirements a software needs

are analysed and necessary information is extracted for the software design. Simulation test will

be carried out using designed software. The software code is broken down to six sections, which

will be described future its function within the program.

Requirements

Control Objective Place a specified number of oranges into a box located on the conveyor

Control Specification Overall Control

1. When switch SW1 on the operation panel is turned ON the conveyor moves forward. When switch SW is turned OFF the conveyor stops

2. When pushbutton PB1 on the operator panel is pressed SUPPLY COMMAND (Y1) for the robot is turned ON. SUPPLY COMMAND is turned OFF when the robot moves away from the starting point. When SUPPLY COMMAND is turned ON the robot supplies a box.

3. When the BOX ON SLIDE (X5) is turned ON, the robot must automatically supply another box after 5 seconds onto the conveyor.

Control of Oranges 1. When the sensor for BOX ON CONVEYOR in the orange feeder is turned ON, the conveyor

stops. 2. Twenty (20) oranges must be placed in the box. Full boxes containing oranges are carried

to the tray on the right. 3. Oranges are supplied when SUPPLY ORANGE COMMAND is set ON and the number of

oranges supplied are counted by the ORANGE SUPPLIED sensor 4. A 10 second delay is required before the filled orange box moves on to the tray on the

right.

Description of the system inputs and outputs

INPUTS DESCRIPTION FUNCTION

X0 Robot starting position Sensor

X1 Box on conveyor belt Sensor

X2 Orange supply counter Sensor

X5 Object light sensor Sensor

X20 Momentary contact Push switch Opration Command

X24 Rotary switch (ON/OFF) Opration Command

OUTPUTS

Y0 Operate robot arm (supply box) Transport

Y1 Start conveyor belt Transport

Y2 Supply oranges Supply material Table 1: brief description of PLC simulator systems, 6 inputs and 3 outputs

4

Opration pseudo code

By analysing the give task taking in consideration all available inputs and outputs from above

Table.1, the following functions are obtained.

Overall control

1) When Switch (SW1) is ON

i) Conveyor belt STARTS

2) When Switch (SW1) is OFF

i) Conveyor belt STOPS

3) When Pushbutton (PB1) is ON

i) Robot grabs a box (Y0)

ii) Robot moves to new position

iii) Supply command halted

iv) Robot supplies box to (Y1) conveyor

v) Robot moves back to start position (X0)

vi) Supply command resumed

4) When Sensor (X5) is ON

i) Delay timer waits 5 seconds

ii) Robot supplies box (Y0)

Control of oranges

1) When Sensor (X1) is ON

i) Halt conveyor (Y1)

ii) Counter Sensor (X2) ON

iii) Orange supply (Y2) switches ON

iv) Sensor (X2) Counts to 20 oranges

v) Orange supply (Y2) switches OFF

vi) Delay Timer Wait 10 seconds

vii) Start conveyor

Control method This procedure is represented in flowchart in Fig.1 below. By producing flow chart it is clear what

steps should be taken to accomplish this task.

5

Figure 1: Flow chart of PLC software, blocks outlined in colour as follow, red (switches), blue (sensor inputs) and yellow (outputs)

PLC software After careful study of flow-chart in Fig.1, the following program in Fig.2 is constructed to meet the

required task. The program is divided into six sections, each task performs given opration as

describe below.

6

Figure 2: Ladder Logic program layout and it is divided into six sections containing different functions

1

2

3

4

5

6

7

Section One: ON and OFF function of conveyor

At the start of this program no opration is preformed until rotary switch (X024) is turned ON,

which normally open (N.O) contact position and virtual relay-1 (M0) must be ON which is normally

closed (N.C) contact position or virtual relay-3 (M2) must be ON which is (N.O) contact position.

Overall function of this part of the software is to switch ON and OFF the conveyor (Y001).

Figure 3: start and stop function of conveyor

Section Two: supply command function

When momentary push switch (X020) is pressed or virtual relay five (M4) is active and robot arm

initial position (X000) is set and virtual relay-1 (M0) is active then supply command (Y000) is

initiated to supply a box to the conveyor (Y001).

Figure 4: supply command function

Section Three: box on conveyor detection

At this stage when box is detected by sensor (X001) on conveyor, sensor is triggered only once, a

positive pulse which is detected and virtual relay-3 (M2) must be active (N.C) and rotary switch

(X024) must be active in order to latch relay-1 (M0) active state.

The virtual relay 3 (M2) and rotary switch (X024) are used here for two reasons:

Relay-3 (M2) in (N.C) state acts as latch for output relay-1 (M0), this also ensures when the

box passes through final stages this circuit is un-latched.

The rotary switch (X024) is fail-safe to over-ride the sensor (X001) function by unlatching

relay-1 (M0) which in turn switches OFF conveyor if ON.

Overall function of this part of the software is to halt the conveyor when a box is detected.

8

Figure 5: box on conveyor detection process

Section Four: supply oranges

At this point output of relay-1 (M0), one positive pulse is detected and relay-2 (M1) in (N.C) state

and rotary switch (X024) must be switched ON, this activates output (Y002) to orange supply and

latches the output (Y002).

The virtual relay-2 (M1) is activated when counter reaches its limit, in this case 20 oranges; this

trigger unlatches the orange supply (Y002) which stops any future oranges added to the box.

Overall function of this part of program is to supply oranges into the box when input sensor (X001)

detects a box on the conveyor.

Section Five: count oranges and delay timer

An orange supply counter (X002) is assigned to output counter-1 (C0) variable and count (K20) is

set to twenty. Every time orange supply sensor (X002) is triggered the cunter-1 (C0) is incremented

by one until count is reached.

When counter (C0) is reaches twenty and end of line object sensor (X005) is (N.C) state then

output is set to timer-1 (T0) and countdown (K100) is set to ten seconds. Relay-2 (M1) is activated

to stop orange supply. While counter (C0) is in (N.C) state, the timer (T0) counts to ten seconds

and then latches the timer (T0).

Overall function of this part of the program is to count the required oranges and then wait ten

seconds before moving the box to next stage of process.

20

Figure 6: orange supply process

9

Figure 7: counter and timer process

Section Six: reset and supply

Final part of this program waits until counter-1 (C0) and timer-1 (T0) are true then output relay-3

(M2) is activated, this relay over-rides relay-1 (M0) and resumes the conveyor (Y001), relay-3 (M2)

stays active until object sensor (X005) is triggered. When sensor (X005) is triggered, counter-1 (C0)

is reset to zero. The counter-1 (C0) and timer-1 (T0) are set to unlatched state.

At the time object sensor (X005) is triggered and relay-1 (M0) is in (N.C) state and rotary switch

(X024) is in (N.C) state then output relay-4 (M3) is latched and timer-2 is set to count (K50) to five

seconds.

When timer-2 (M1) reaches five seconds, output relay-5 (M4) is activated and robot arm supplies

(Y000) another box to the conveyor (Y001).

Overall function of this part of the program is to reset the counter-1 and wait five seconds and

then supply another box to conveyor.

Figure 8: reset and supply command process

10

Conclusion This system is designed in such way to allow user to be able to stop the conveyor through rotary

switch off position by turning the switch back on will allow any content on conveyor to move to

final stage without any future processing, this implication may overcome some issues i.e. if orange

supply is depleted/defective or problem with packaging occurs, in any of these cases current

content of the production line will be rejected. This can ensure quality end product and minimum

loss.

Final stage will trigger five seconds delay before supplying another box to conveyor. As

precautionary measure if the rotary switch was turned off again during five seconds delay, this will

over ride the five seconds delay timer and return opration to its initial state where the user will

need to press the push-button to initiate the supply command. By implementing this method into

this software it gives the user ability to be able to set/reset the production line from one control.