Objective: To determine how to design a program to operate an automated process using sequencer instructions with an Allen-Bradley Micrologix1200C microcontroller with RSLogix500 programming software. To receive credit the solution must use a sequencer instruction to control the operations & timing of the outputs. Other solutions will not be accepted for credit, even if they accomplish the task.

ASSIGNMENT: The Washing Machine

In the textbook a classic example of a mechanical sequencer application is a washing machine. The assignment uses such a scenario for an automation control program design. A hardwood furniture manufacturing facility hand rubs stains into its pieces to provide the highest quality finish. To do this employees use large numbers of soft rags which are cleaned after each use and reused repeatedly. The stained rags are washed using solvent additives, and detergents, and then tumble dried in large batches in an industrial cleaner.

The washer has two settings; Heavy & Normal. The wash cycles are similar but the heavy has additional steps and cycle times. The settings are determined by the operator based on the state of the rags to be washed using the 3-way selector switches (I:6 & I:7). The Operator must load the washer, close the lid (I:5=TRUE), enter a setting (heavy or Normal), and press Cycle Start (I:0) for the operation to begin. If no setting has been entered, or the lid is left open, the washer will not attempt to start the cycle. Once the cycle is complete the washer will stop and indicate to the operator that it has finished. There are indicator lights to show the status of the washer, one indicator shows the washer is cycling, and one indicator shows when the cycle is complete. If the lid is opened (I:5=FALSE) once the cycle has started then an indicator will display that. We will use the PLC LEDs for these. For safety reasons, once the washer is cycling, if the operator opens the lid to check on the progress of the cycle then all of the actuators will stop operating. When the lid is lowered the Actuators will return to operation still in their original sequence (the washer remembers where you stopped it in the timing cycle).

For purposes of testing we will use the I/O addresses and sequences shown on the second page tables.

At startup ALL the actuators are off for both settings (position 0). A sample operational sequence would be: The operator loads the washer with stain soiled rags. The Lid (I:5) is closed and the selector is set to normal. When the Cycle Start PB is pressed the cycle starts. The Cycle in Progress light is turned on and remains on till the cycle is done. The First step lasts 2 seconds and actuators A, C, & E are active. That means that Outputs 4, 6 & 8 light up for two seconds. Then the second step is loaded. Actuators A & B (Outputs 4 & 5) are lit for three seconds. This continues until the full cycle is complete. When the last command in the sequence is done the Cycle Done indicator lights. The Washer can then have another load inserted and start a new cycle.

After the completion of three wash cycles (normal or heavy) the filters need to be cleaned, or replaced, by the operator. For this there is a maintenance indicator (O:3) which comes on after the completion of three wash cycles and blinks in 0.5 second intervals to alert the operator to clean the filters before another wash cycle can be started. Once the cleaning is done the operator can use a reset switch (I:9) to reset the cycle count to zero, after which a new wash cycle can be started.

In case of errors (started a normal wash but actually meant to run as heavy) or an emergency, I:1 (the second green pushbutton) acts as a Stop cycle input, when pressed the Cycle is interrupted (all actuators are turned off),

and the sequence is reset back to the starting position in the cycle. An interrupted cycle does not count towards the 3 wash cycle limit for filter cleaning. So when I:1 is pressed the current wash cycle stops, resets to its starting point (the sequencers are not stopped in a mid cycle point), and the operator must start a new cycle (set the selector switch and press cycle start).

Remember that the assignment must be accomplished using sequencer instructions (NOT Comparison) to control the operation & timing of outputs 4 9. All sequencer data files should have their own data folder. Note: Sequencers can use Binary or Integer words as data, so you can sequence a bit pattern and a number.

Input Description

Address

Output Description

Address

Start Cycle

I:0

Cycle in Progress (PLC)

O:0

Stop/Reset Cycle

I:1

Cycle Done (PLC)

O:1

Washer Lid

I:5

Washer Lid Open (PLC)

O:2

Heavy Wash Cycle

I:6

Clean or Replace Filters (PLC)

O:3

Normal Wash Cycle

I:7

Actuator A

O:4

Reset Filter Cleaning

I:9

Actuator B

O:5

Actuator C

O:6

Actuator D

O:7

Actuator E

O:8

Actuator F

O:9

Normal Wash: Actuator Control Sequence & Timing

Step

Step Title

A

B

C

D

E

F

Time Interval

1

Prewash 1

X

X

X

2s

2

Prewash 2

X

X

3s

3

Prewash 3

X

X

3.5s

4

Wash 1

X

X

2.5s

5

Wash 2

X

X

X

3.25s

6

Wash 3

X

X

X

X

4s

7

Wash 4

X

X

2.75s

8

Rinse1

X

X

3s

9

Spin 1

X

X

4s

10

Dry 1

X

X

2.5s

Heavy Wash: Actuator Control Sequence & Timing

Step

Step Title

A

B

C

D

E

F

Time Interval

1

Treatment 1

X

X

X

3.5s

2

Soak 1

X

X

1.25s

3

Prewash 1

X

X

2s

4

Prewash 2

X

X

4s

5

Wash 1

X

X

3s

6

Wash 2

X

X

X

X

2.75s

7

Wash 3

X

X

1.5s

8

Treatment 2

X

X

X

2.25s

9

Wash 4

X

X

X

1.5s

10

1st Rinse 1

X

X

3.25s

11

2nd Rinse 1

X

X

2s

12

Spin 1

X

X

1.75s

13

Dry 1

X

X

X

X

3s