Geared motor control using polarity reversal and end switches

[Dimitri Krut]

I am sure this topic has been addresses before, but I was not able to find references by searching and there were no similar examples/tutorials.

Perhaps someone can point me to a prior discussion or an example.

I need to control a geared AC motor for up and down motion of a small lift to two end point switches (top & bottom). 

If I use polarity reversing relays, I need to make sure that both up and down (HMI) buttons are not pressed at the same time.

Questions:

What's the best way to implement a tri state switch -- up, down and neutral or do a lockout of the unused button?

Should I do polarity reversal in the PLC or wire up two double pole relays (the old fashioned way)?

 

Thanks!

 

 

[Joe Tauser]

Is this AC motor a three phase unit?  For safety you should use a reversing contactor that is mechanically unable to have both on at the same time.  Otherwise you have thoroughly confused me mentioning polarity reversal on an AC motor.

The PLC scans the inputs before it solves the logic.  It's not like real electricity.  You can lock the directions out by unlatching the opposite action when one is called.

Is there is stop button?

Joe T.

[kratmel]

19 hours ago, Dimitri Krut said:

I need to make sure that both up and down (HMI) buttons are not pressed at the same time.

In Vision OPLC panel single touch sensor used. It is not possible to switch on both HMI button at the same time.

But logic needed (see Joe T. ladder) for prevent to fast (pseudo simultaneously) output switching.

By the way

11 hours ago, Joe Tauser said:

reversing contactor that is mechanically unable to have both on at the same time. 

  is the best solution.

In fast AC motors reversing by PLC   (like old CNC turret) is used 3 power contactor.

Two for reversing phase on AC motor and one for turn power on when one of reversing contactor is energised.

  

[Dimitri Krut]

Thanks for the code. This exactly what is needed.

We are modernizing a large optical illumination tool that contains the elevator mechanism. This tool was originally designed in 1962 and went only through minor changes in late 1970s. Currently this elevator mechanism runs with triple pole relays setup for polarity reversal, limit switches and also with complex push buttons (up/down). It uses a single phase geared motor used for very slow up/down movements. Only uses 3A 115AC.

One option is to maintain the basic relay arrangement and just use PLC to replace up/down buttons. The other approach is to feed the limit switches and everything else into the PLC and use it to energize relays in a proper order.

You are right about polarity reversing contactors. This is probably the cleanest way approaching it.

Thanks again for the PLC code!

 

 

[Dimitri Krut]

23 hours ago, kratmel said:

In Vision OPLC panel single touch sensor used. It is not possible to switch on both HMI button at the same time.

But logic needed (see Joe T. ladder) for prevent to fast (pseudo simultaneously) output switching.

By the way

  is the best solution.

In fast AC motors reversing by PLC   (like old CNC turret) is used 3 power contactor.

Two for reversing phase on AC motor and one for turn power on when one of reversing contractor is energized.

  

We are trying to replicate our current capability.  Users hold UP or DOWN buttons to move and no movement when neither button is pushed.  This would be a tri-state switch. I can see that it can be implemented using "Image by Range" button capability. I would rather just draw two buttons with the relay logic to make sure that two of them are not pressed simultaneously.

Your description of the motor phase reversal is exactly how this one operates. I need to use relays (contractors) anyway... so I will use a three line reversing contractor.

Thanks for your help!