Hi 

In what circumstances does the Homed Status of a drive reset?

Power Cycle of DRIVE or PLC?

Error on Drive? 

Is it possible to retain the homed position, so it will never be necessary to Home the drive after commissioning? 

Hello.

Possible workarounds will depend on the detail of what you have and what type of control you are doing. It sounds as if you are wanting to use an absolute encoder.

The homing state is cleared when the enable is switches off. That can because of the PLC or the feedback from the drive (error or enable-is-active). For a case like this the position can still be read. Direct homing can resolve most of the issues, provided that synchrony between PLC and drive is still in place.

Power off at the PLC will have the internal position register to zero and the homing state is lost. Recovery from that will again depend on what type of motion control you are using.

Another common problem is loss of homing state when a download is made that changes the code where the MC_POWER instruction is called. This happens when a shared datablock is used.. the DB is shared with the calling FB. Using an 'external' global DB to the MC_POWER instruction solves that problem.

Unfortunately my notes in itself will not solve your problem. I would encourage you to follow up with your thoughts and more detail of what you are doing.

~

Thanks for the explanation qwazee. 

I have two vibration hammers with servo motors, with absolute encoders. 
When the vibration hammers stop, they to retract to a absolute position. 

The only way to home the drive is manually. Jog the motor to retracted position, and home. 

I am looking for at solution where this manual homing is not necessary every time the system is turned off. 

jthyge1

Thanks for the explanation qwazee. 

I have two vibration hammers with servo motors, with absolute encoders. 
When the vibration hammers stop, they to retract to a absolute position. 

The only way to home the drive is manually. Jog the motor to retracted position, and home. 

I am looking for at solution where this manual homing is not necessary every time the system is turned off. 

Yo make no mention on how the PLC and drive is connected to each other. You also do not state which PLC you are using or what version motion control.

Shortly: Does the PLC know what the absolute position of the encoders are? Knowing the absolute position would mean that you can use relative motion and not even be worried about homing. Or use direct homing: setting the reference position without needing to move. 

Did you check this FAQ: https://support.industry.siemens.com/cs/de/en/view/84133347  ?

There it is described under which cicumstances the adjustment is withdrawn, and also what to check for in case the TO position with absolute encoder is not correct anymore after PLC or TO restart.

The FAQ basically covers all possibilities.

Regards,

daviso