Hi Mike:I looked through the Door Simulation exercises to determine which one you referred to in your email. The closest one I could find is Exercise #1. Thus, this is the problem I have solved and explained below. First, note a few things about the limit switches as well as the problem itself:The limit switches use Normally Open switches. When the garage door is fully open, the contacts of both limit switches are OPEN. As soon as the door starts moving down, the top limit switch (LS1) closes. When the door is fully closed, both limit switches are closed. The OPEN_D and CLOSE_D push buttons are used to control the movement of the door. Movement will not be maintained when either switch is released. Therefore the STOP switch is not required and is not used in solving the problem. However, it is assumed that all other Inputs and Outputs in the LogixPro Door Simulator are available and are therefore used in solving the problem. Because door movement is not maintained when either switch is released, there is no need to use seal-in contacts.It is assumed that that the motor direction can be changed by changing voltage polarity through suitable wiring using contactors.
Solution of Exercise #1:
I am reproducing below the criteria provided in the LogixPro Exercise #1 in the Door Simulation exercises: Pressing the Open Switch will cause the door to move upwards (open) if not already fully open. The opening operation will continue as long as the switch is held down. If the switch is released, or if limit switch LS1 opens, the door movement will halt immediately. Pressing the Close Switch will cause the door to move down (close) if not already fully closed. The closing operation will continue as long as the switch is held down. If the switch is released, or if limit switch LS2 closes, the door movement will halt immediately. If the Door is already fully opened, Pressing the Open Switch will Not energize the motor. If the Door is already fully closed, Pressing the Close Switch will Not energize the motor. Under no circumstance will both motor windings be energized at the same time. The Open Lamp will be illuminated if the door is in the Fully Open position. The Shut Lamp will be illuminated if the door is in the Fully Closed position.
Logic Used in Solving the Problem:
IF [OPEN_D is pressed AND LS1 is closed] THEN energize UP Motor Contactor.IF [CLOSE_D is pressed AND LS2 is open] THEN energize DN Motor Contactor.IF [LS1 is open] THEN turn green light ON (Door is fully open).IF [LS1 is closed AND LS2 is closed] THEN turn RED light ON (Door is fully closed)IF [OPEN_D is released AND CLOSE_D is released] AND [LS1 is closed AND LS2 is open] THEN turn Yellow light ON (Door is ajar).The ladder logic is as shown in the figure.