chippieboy
Member
I am having this issue trying to figure out how to do this. I have a Hydraulic ram that travels when a machine is running. The ram extends to the maximum travel then trips a limit switch and then retracts to the minimum travel then trips the other limit switch extends to the maximum travel .This cycle repeats indefinitely until power off.
The main issue I have, is the hydraulic directional valve starts out in a neutral position during the first power up. The valve does not know what way to go. If the ram is not at either travel limit (touching the limit switch) it does not matter what direction to start first. I was thinking of doing a one shot at first cycle then some sort of flip-flop or a Set-Reset or a Keep-Reset when the PLC is powered up to trigger the hydraulic directional valve and let the cycle begin. The problem is if the ram is touching either limit switch at power up, I have no idea how to factor that in the logic and what way to send the Ram. This machine is using an Omron PLC but the logic should be the same or I can alter it once I understand how to do this. I can do it with AB as well. I attached a primitive picture of what is happening.
The main issue I have, is the hydraulic directional valve starts out in a neutral position during the first power up. The valve does not know what way to go. If the ram is not at either travel limit (touching the limit switch) it does not matter what direction to start first. I was thinking of doing a one shot at first cycle then some sort of flip-flop or a Set-Reset or a Keep-Reset when the PLC is powered up to trigger the hydraulic directional valve and let the cycle begin. The problem is if the ram is touching either limit switch at power up, I have no idea how to factor that in the logic and what way to send the Ram. This machine is using an Omron PLC but the logic should be the same or I can alter it once I understand how to do this. I can do it with AB as well. I attached a primitive picture of what is happening.