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One axis control movement


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  • MVP 2023


i try to post some tips about standard  VFD, Encoder and PLC:

1) It is not possible to build closed loop control (servo control) on standard VFD+encoder + standard PLC;

2) Standard PLC with HSC connected to encoder can offer positioning machine driven via VFD.

3) For positioning two speed - FAST and SLOW setpoint  must be proggrammed  on VFD (or provided by PLC). Then user must program ladder net with FAST to SLOW changeover based on distance to setpoint.

4) If positioning used for CUT to LENGTH application - simple encoder register reset is used for -0- setting.

5) If you need to set position of standard linear axis - home position evaluation is the main problem.

6) It is hard to build (or not possible )positioning based on Modbus RTU command (to slow for send stop command). VFD logic input and analog setpoint input must be used.


Then please post your machine setup and application type.

Some type of VFD+encoder+PLC based application posted in forum topics.

You must define what you need to do with this VFD+Encoder+PLC.


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  • 2 weeks later...
On 5/28/2021 at 6:11 PM, Eliran said:

Is there any example/tutorial that learn how to control an AC motor with VFD and encoder, using PLC?

Basiclly you are right, but...
Unitronics is now in the process of imlementing a new VFD product line (UMI-B7)
That VFD support Encoder extention cards and support Close-loop. (Position and Velocity ) including "Standstill" capability. 

If you need more information please contact
Support@unitronics.com  and provide more information about the application. 


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