Encoder-free control

[Johny5]

I have a production line with 14 AC motors (7.5 kW - 75kW). They are coupled with Siemens VC Masterdrives and overlooked by Siemens CPU400 through Profibus. I want to switch from encoder to encoder-free control. Is it enough to change some drive parameters, or there is more? Will I need to change the PLC program? Where should I start?

 

[rdrast]

First question, is WHY?
If you have sections running in Torque mode, or Torque Limit, you absolutely must have the encoders on at least those sections.

If you need precise coordination between machine sections, you must have the encoders.

If you are just running a 14 section conveyor, no, you don't need the encoders, but you will have to retune in sensorless vector mode.

 

[Johny5]

We are experiencing many encoder's failures (A043, F053). Often the connector is loosed. I applied Loctite, but doesn't always help. Motors are in speed control mode (P100=4). Yes, the speed has to be coordinated between motors. I just think, encoder-free control will be more reliable.

 

[rdrast]

I'd suggest first just fixing the problem with the encoders.
Use proper, low-capacitance cable. Use full differential encoders and connections (A/ANOT, B/BNOT), install connectors properly.

We have several hundred encoders around here, and except for SSD MicroTachs, they very rarely fail.

 

[Tharon]

Don't be afraid to buy premade cables designed specifically for your motor/encoder type either. Your Siemens supplier for your drives can provide them. They cost more but are guaranteed and come with the correct type of connectors.

Also, aren't masterdrive and simodrive encoder connections 9, 15, 25, etc D-Sub connections? Those are usually very tight. We have about 100 of them connected that have never came loose.

Not trying to sound rude, I just want to help you save money and not have to convert your working system.

 

[DickDV]

The previous posters all make excellent points but here are a couple of more issues to ponder. First, sensorless vector is never as accurate as flux vector. You will have to know precisely how much speed error your process can tolerate before making any change.

Second, speed error with encoders is non-cumulative whereas speed error no matter how small is alway negative with sensorless vector. If cumulative error cannot be tolerated, encoders are a must.

Hope this helps motivate you to make an informed decision.

 

[Johny5]

Thanx for your advices.

I want to see if I can run the line without encoders and how good (bad). I can still go back, can't I.