Hi everyone,

I  have a 1211 Cpu and tia portal V17 . I'm doing some testing with Motion Control and the stepper motor  is working well .

Now I would like to drive the motor with an encoder so that each revolution of the encoder corresponds one revolution of the motor . I tried with motion Control blocks (Jog , Absolute , Relative) but with poor results . I set the encoder with HSC but now I don't  know how to handle it .

Does anyone have any advice for me ?

@Technology Team:
Hello Team. The topic starter is asking how he can construct a closed loop control for his stepper motor using the S7-1200. His stepper motor drive accepts a pulse/direction signal pair as controls. He wants to add an external encoder to monitor the progress of the motion and use that as feedback.

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@Randalh:
The motion control available on the S7-1200 only offers open loop control when using pulse/direction signals. You can write your own code to monitor the movement of the motor and have the user code compensate for variations.

But it would be best to have a drive that is able to monitor a stepper motor and compensate the voltage and current according to the compensation needed. Drives like that is available on the market. Again the PLC can monitor progress and compensate roughly if some slippage occurs.

An untested / unproven method is perhaps available also. You could use analog controlled motion control instead as primary technology object. The trick there is to use the "analog" output (it can be a integer tag) from the motion control to manipulate the PTO.

A secondary technology object is the one that controls the PTO. You will have to use something like the JOG instruction to vary the PTO. That instruction would need to sit in OB_PostServo linked to the primary technology object.

Consider the workaround idea above and discuss with Siemens if you feel you want to experiment.