Need help for Test

Sorry if this is the wrong place to ask but I was hoping to get some help/advise before my handwritten ladder logic test in the morning. I'm desperate. Here is the practice scenario given by my instructor:

Create the logic to control a drilling machine dual acting air cylinder, one that extends and retracts the cylinder in the given cycle. This is a closed loop system so there will be sensors in place to ensure the cylinder completely extends and completely retracts, thus ensuring that the tool completes the cycle. There is a drill motor at the end of the cylinder that drills a hole in a part. In order to start the cycle there must be a part correctly loaded in the machine verified with a sensor. The operator needs to press two momentary start buttons, one with each hand that starts the drill motor and extends the cylinder. The machine must stay running after the operator lets go of the start buttons. The extend cylinder feed rate is controlled using a preset flow control valve (that you have no control over) that should take 10 seconds to drill through the part allowing the cylinder to contact the extended sensor if the cylinder is completely extended and the drill bit is sharp. If the drill bit gets dull it can affect the cycle time and slow the extension cycle down. If it takes longer than 15 seconds to run the cylinder/drill extension cycle and contact the extend limit switch, stop the cycle and turn on an alarm light to notify the operator to change the drill bit. Once the extended sensor is set, the cylinder will automatically retract. The machine cycle turns off after the cylinder is completely retracted, verified when the retracted sensor is set. For safety purposes include an e-stop button to stop the machine cycle. Safety guards and sequences are already in place to prevent the operator from getting injured during a cycle. Include an operator maintenance alarm light in your program to lubricate the drill motor every 50 parts and a button to reset the maintenance alarm.

I understand the simple parts of this program but have a hard time figuring out how to add the "If it takes longer than 15 seconds to run the cylinder/drill extension cycle and contact the extend limit switch, stop the cycle and turn on an alarm light to notify the operator to change the drill bit." part. We never learned any type of "if / than" instructions. Am I missing something? I'll try to post what I have so far. Thanks in advance.

Use a timer that is cancelled if the drill time does not exceed the 15s.
If it does then turn on your alarm bit and turn off the outputs.

Alan

You can think of most relay ladder logic "rungs" as IF/THEN statements.

Rung 1 in your program, for example, can be thought of as


So let's look at the part you specifically cited:

"If it takes longer than 15 seconds to run the cylinder/drill extension cycle and contact the extend limit switch, stop the cycle and turn on an alarm light to notify the operator to change the drill bit."

Talk it out as IF/THEN statements related to the I/O:

IF Drill_Motor is on AND Extend_Cylinder_Valve is on, THEN run Jam_Timer.
IF Jam_Timer is done, THEN latch on Alarm_Lamp

In addition, you will put an XIC ("contact") instruction addressed to the Jam_Timer.DN bit in series with the logic that extends the cylinder and turns on the motor.

I'm intentionally leaving out how to un-latch Alarm_Lamp and how to interrupt the Cylinder_Extend and Drill_Motor rungs; this is a learning exercise after all.

RLL is mostly "IF / AND / OR ... THEN" logic, with various interesting functions other than output coils on the right side of the rung.

When doing automation programming, even seasoned experts talk to themselves while writing out conditions: "if, then, else, or.... OK, that ought to do it."

Since the output instruction is OTE I would modify Ken's interpretation of rung 0001 of the OP's logic.

IF Drill_Motor is on
THEN turn on Extend_Cylinder_Valve
ELSE turn off Extend_Cylinder_Valve

If the output instruction is OTL, Ken's original interpretation is accurate.

Welcome to the forum.

Since you have typed everything out, may I suggest the following.
Your assignment is the customers specifications.
break the specifications into segments.
1. drill machine with dual action cylinder that extends and retracts.
2. this is a closed loop system with sensors on the extend and retract side.
and so on.
this is how I do my programming and design the plc I/o at the same time
write the specs and get a good understanding, then add the I/O

regards,
james