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.
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.