Need more Servo Drive/Motor Input from Experts

[busarider29]

We are still not yet fully decided on the brand of motors and drives that we want to go with and standardize to. We are now looking at Rexroth drives and motors. How are they comparable to Kollmorgen or Emerson?? Also, any expert opinions on the reliability and ease of use with the Rexroth line of motors and drives? It will be integrated into a Beckhoff controlled machine using EtherCAT for the fieldbus. Any input is appreciated.

 

[Christoff84]

The only thing I would look at is the EtherCAT spec. I know recently I tried to integrate a set of Rexroth servos to an Omron NJ and Omron found that their EtherCAT was not compatible with Rexroths. Something to watch out for.

 

[Peter Nachtwey]

The only thing I would look at is the EtherCAT spec. I know recently I tried to integrate a set of Rexroth servos to an Omron NJ and Omron found that their EtherCAT was not compatible with Rexroths. Something to watch out for.

I find this hard to believe. Usually a product must pass some sort of certification before they can say they are compatible with a field bus or Ethernet specification. For instance we had to be certified by ODVA before we would claim to support Ethernet/IP.

I wouldn't bother to look at the whole specification but rather if the Bosch products are EtherCat certified.

 

[Gene Bond]

One of the Emerson App Engineers recently told me about the loops he had to jump through for EtherCat w/ Omron... He had never seen such a strange implementation...

 

[mjoubert]

In answer of the original question. Regardless of which drive manufacturer you choose, the most important thing is service.... Do they have service exchange units in the event that yours should fail? Will they be able to supply a replacement unit to you at 2am on an idle Wednesday, and assist with programming if required? What is the lead time when ordering? How steep is the learning curve?

 

[jdbrandt]

We are still not yet fully decided on the brand of motors and drives that we want to go with and standardize to. We are now looking at Rexroth drives and motors. How are they comparable to Kollmorgen or Emerson?? Also, any expert opinions on the reliability and ease of use with the Rexroth line of motors and drives? It will be integrated into a Beckhoff controlled machine using EtherCAT for the fieldbus. Any input is appreciated.

Is there are reason why you would NOT consider Beckhoff's motion stuff?

 

[josepholka]

I would be careful with EtherCAT. I support several Manufacturers who have EtherCAT devices. What I have run into when Integrating systems is some devices communicate COE "Can over EtherCat" while others are using EOE "Ethernet over EtherCat" I would Suggest sticking with one manufacturer. If you are already using Beckhoff stick to there motors also.
My 2 Cents

 

[Peter Nachtwey]

What I have run into when Integrating systems is some devices communicate COE "Can over EtherCat" while others are using EOE "Ethernet over EtherCat".

Yes!!!
The Can Open Packets over EtherCat only allow downloading one data item per packet. I find this to be a limitation because it is harder or impossible to due very smooth interpolation between the points. Download position, velocity and acceleration in each back is what I would prefer but then I would need to use bigger non standard packets.
If the application isn't too demanding the Can Open Packets should be OK but doing a simple second order ( quadratic ) interpolation between the points is not very good.

Here is my evaluation of second order interpolation.
http://deltamotion.com/peter/Mathcad/Mathcad - Quadratic Interpolation.pdf

Third order interpolation is much better but I would prefer 5th order, but both require packets bigger than Can Open packets.

It is possible if one is tricky to download accelerations instead of positions and then the accelerations are integrated to get smooth velocities and positions but I think both the drive and the master would need to be from the same manufacturer to do this.

 

[Onstege]

I switched to SEW a few years ago and they haven't disappointed me yet... Thumbs up!

 

[CapinWinky]

Why wouldn't you just use Beckhoff's drives? That would no doubt be the easiest and most integrated solution. If you don't like their drives, it would be easier to just change to a whole different platform than screwing around getting 3rd party servo control to work.

As far as servo motors, Lafert out of Italy are some of the best, but AKM are good too, as are the DDR cartridge motors from Kollemorgan. The only thing to make sure is that you can get an encoder and cable set that will work for your drive. Also, some motors can be purchased with a temperature sensor instead of a thermistor, which is nice if your drive supports it. You also should keep in mind that most drives expect the temperature and brake lines to be in the motor cable while some put them in the encoder cable, so check that or be prepared to have flying leads Y-ing off of your encoder plug at the drive.

Beckhoff invented EtherCAT, any other supplier that supports EtherCAT does so to be inter-operable with Beckhoff, so there should be zero chance of an EtherCAT product not working with a Beckhoff PLC.

Same story with Powerlink and B&R, Sercos III and Rockwell, and Profinet is more or less Siemens's baby. All of them are high speed, deterministic Ethernet protocols. As a PSA, Ethernet/IP is neither Real-Time nor Deterministic and is not appropriate for mid to high end motion control.

 

[busarider29]

Why wouldn't you just use Beckhoff's drives? That would no doubt be the easiest and most integrated solution. If you don't like their drives, it would be easier to just change to a whole different platform than screwing around getting 3rd party servo control to work.

As far as servo motors, Lafert out of Italy are some of the best, but AKM are good too, as are the DDR cartridge motors from Kollemorgan. The only thing to make sure is that you can get an encoder and cable set that will work for your drive. Also, some motors can be purchased with a temperature sensor instead of a thermistor, which is nice if your drive supports it. You also should keep in mind that most drives expect the temperature and brake lines to be in the motor cable while some put them in the encoder cable, so check that or be prepared to have flying leads Y-ing off of your encoder plug at the drive.

Beckhoff invented EtherCAT, any other supplier that supports EtherCAT does so to be inter-operable with Beckhoff, so there should be zero chance of an EtherCAT product not working with a Beckhoff PLC.

Same story with Powerlink and B&R, Sercos III and Rockwell, and Profinet is more or less Siemens's baby. All of them are high speed, deterministic Ethernet protocols. As a PSA, Ethernet/IP is neither Real-Time nor Deterministic and is not appropriate for mid to high end motion control.

Originally, I wanted to go with Beckhoff drives and motors but Beckhoff doesn't have a motor that meets our performance requirements and although I could use a Kollmorgen motor with a Beckhoff drive, I don't want to do that. For simplicity's sake, I want to keep motors and drives married together from the same manufacturer. No mixing and matching. So unfortunately, that eliminated Beckhoff from the deliberations.

 

[CapinWinky]

For simplicity's sake, I want to keep motors and drives married together from the same manufacturer. No mixing and matching. So unfortunately, that eliminated Beckhoff from the deliberations.

You have things bass ackwards, a motor is just a motor. All you need is a few parameters from a motor data sheet and the right cable and you can run it on any drive you want. Keeping the drives and motors matched is so much less important than keeping the drives and PLC match... I'm sure Beckhoff even supports a variety of encoder and resolver types, but for ease of use, you can order your motor with a Beckhoff friendly encoder on it.

If you're just doing VFDs, sure, use 3rd party drives, but servo motion of even mild complexity with a 3rd party drive is a nightmare.

EDIT: I feel like I should throw in that I did high end servo motion as an Integrator for 8 years, including dicking around trying to run Rexroth drives from a B&R PLC a few times. The PLC and servo drives are proprietary electronics/firmware, the motor is just some magnets and coils with an encoder on it.

 

[wolverine1981]

Hello

Here's my .02, What I have seen is that certain industries seem to lean towards certain types of drives, I think you also need to consider the industry you may be gearing towards. Rexroth has been a very reliable drive IMO, but when there's a problem at times they are a little more complicated then what your average electrician can handle. And finding documentation is at times difficult. Tech support, not as good as others.

Tom

 

[busarider29]

You have things bass ackwards, a motor is just a motor. All you need is a few parameters from a motor data sheet and the right cable and you can run it on any drive you want. Keeping the drives and motors matched is so much less important than keeping the drives and PLC match... I'm sure Beckhoff even supports a variety of encoder and resolver types, but for ease of use, you can order your motor with a Beckhoff friendly encoder on it.

If you're just doing VFDs, sure, use 3rd party drives, but servo motion of even mild complexity with a 3rd party drive is a nightmare.

EDIT: I feel like I should throw in that I did high end servo motion as an Integrator for 8 years, including dicking around trying to run Rexroth drives from a B&R PLC a few times. The PLC and servo drives are proprietary electronics/firmware, the motor is just some magnets and coils with an encoder on it.

It's not as simple as that if I have to replace cables and the cable pinouts are different, which they are from one motor and drive to the next. If I have to use custom cables or make my own due to using a different brand motor with a different brand drive, then I've just introduced unneeded complications into the system. Keeping motors, drives, and cables all from the same manufacturer is keeping things standardized, which we want to do as much as possible, and keeping it simple. Yes, I understand about the headaches that might be involved with getting a drive to play nice with the PLC, which is why I want to be sure that whatever drive we choose, plays nice with Beckhoff PLC hardware and is EtherCAT ready. I feel like with a PC based PLC platform like Beckhoff, it will be easier to integrate an unlike brand of drive, so I'm not as concerned with that part of it. If my Beckhoff tech support tells me "NO" on this drive or that one based on complications of integration, then yes, I will steer clear due to that problem. However, with all of the brand drives that I have mentioned thus far (Emerson, Rexroth, Kollmorgen), they have said "No problems" with integration to the Beckhoff PLC.

 

[Elijah58]

I'll have to bet on the SEW motors and drives as we have used these for years with very little issues.