Hi, I'm new to S7 1200 motion control.  In my program which I could partially attach herewith in pdf due to the upload size limit, I'm controlling an analog servo motor via S7 1200 PLC analog output.  The encoder is external and connected to HSC inputs at I33.0 and I33.1.  I'm facing the problems below.

(1) The switching between jog/velocity and absolute positioning modes.  For instance, after it executed the jog mode successfully and the homing function was called, the error code always indicated that it is at the wrong mode.  I monitored online the mode inside the multiple instance and noticed that it's still at the jog mode.  I'm pretty sure that the jog mode was already disabled with interlock to the jog function block.

(2) In fact the whole system worked fine for the first piece of the product cut to length after the CPU was powered up.  The 2nd piece failed due to the machine was trying to reverse to the position 0 (reference position).  I noticed it was due to the failure in the MC_Home to set the reference position to new 0 after cutting the first piece.  The MC_Home at mode=0 was enabled by every cutting.

I'm using multiple instances for all the MC instructions.  Shall it be single instance instead if there is only one axis control involved?

To ease your reading, the homing+absolute FB call is at NW14 and the jog FB call is at NW15 of OB1.

Appreciate very much if anyone could help.

Hello.

Best not to use the ".backup" folder. Archive the project from the software to a ZAPxx file (xx will be a number). Thereafter ZIP the archive before attaching here.

Good luck.

LKY2020

Hi, after archive and zipped, the file size is about 6.8MB which exceeds the size limit.

Think if there is not a way to make a smaller project.
Only the piece that is needed for the question.
Hopefully tested.

-OR-

Have the archive software (like 7zip) make multiple pieces of the project.

-OR-

Make a PDF print of the project. 

-OR- 

Make screenshots of the affected program with something like ShareX.

-OR-

{give up} 

What do you think?

Hello.

Throughout the program you have the style to switching the EN (enable) of the code block. From the PDF you shared, one such sample:

Disabling the EN pin of the code block has the effect that all processes inside is frozen in their state. In this specific case: The MC_JOG instruction does not have the opportunity to "let go" of the control of the technology block. The instruction needs to see at least one scan of being off, before it can give control over.

Right through your code you will see this type of problem making things difficult for you. Some blocks needs to be scanned to release cleanly.

My suggestion is to have 1 control block where all the motion control blocks are. Do not remove the EN from any of the blocks. Let the control signals do their job.

In my own designs I have a general block for which I give signals like Jog / Absolute Move / Relative Move / Homing. There is only one MC_POWER per axis that is always scanned. If MC_POWER is shutdown for just an instance, the homing reference is lost which causes problems for me.

Now I stop myself to not go deeper into detail that you do not need. Consider lastly that the problem you face is not a motion control problem. It has to do with structuring of code blocks: the use / miss-use of the block enable.

Think about the situation. If you have question then return with them. 

Good luck.

Hi Qwazee,

Appreciative, your advise totally makes sense!  I was wrong to think that disabling the code block would release all the MC states inside the code block.  I’ll rewrite my code block with all the required MC instructions inside as suggested.  Another question is on the MODE of the MC_Power, does it work on both jog and absolute positioning if I just set it at 1?

LKY2020

Hi Qwazee,

Appreciative, your advise totally makes sense!  I was wrong to think that disabling the code block would release all the MC states inside the code block.  I’ll rewrite my code block with all the required MC instructions inside as suggested.  Another question is on the MODE of the MC_Power, does it work on both jog and absolute positioning if I just set it at 1?

And thanks to you for the star rating. /s

I am happy to hear that you are making progress with my suggestions.

I am not sure what MODE you are asking about on MC_Power instruction. Please show me a screenshot picture to make it clear.

Greetings.

Hello.

The StartMode and StopMode only applies to the situation where Enable is switched on (start) and off (stop). It is not specifically related to any other motion control function. This is stated in the documentation of MC_Power.

The state of StartMode and StopMode is consulted at the transitions of Enable. Putting constant values in those inputs is acceptable. Carefully consider the value for StopMode: Stopping without decelerating may cause mechanical problems.

I confess:  I have no clear idea what StartMode does exactly. The description in the documentation does not help me understand it.

I recommend you have this manual with you:
SIMATIC STEP 7 S7-1200 Motion Control V6.0 to V7.0 in TIA Portal V16

This topic pulls attention now that it is star rated. It is my hope that your topic will get contributions from others while I am absent. May you get the answers you need.

Best health