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PPmac - Macro or EtherCat


kmonroe023
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We currently do a fair amount of work on the Power Pmac using Gate3 cards and PWM (DT GPL) drives. But we're considering also using either Macro or EtherCat drives. We are not familiar with either, so we're not sure which one to go with.

 

So I'd like to ask the DT folks, and probably the Power Pmac community in general: EtherCat or Macro; what are the advantages and disadvantages of each? If you were building a system, which would you pick? Have you designed a system using either and what did you like or dislike?

 

Thanks,

kmonroe

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On the MACRO side, there are several advantages:

 

First, the fiber version provides complete noise immunity for the transmission between stations. A lot of people really value this, particularly for very large systems, so they just do not have to worry about shielding, etc.

 

Second, the protocol is very simple, so there is less detail to learn during the implementation.

 

Third, it has been around much longer -- people were putting MACRO systems into play as far back as 1994.

 

 

On the EtherCAT side, there are more vendors providing components for this network.

 

More types of communication can be done over EtherCAT with many of the devices (the flip side of it being more complex).

 

 

For both networks, you are trading hardware complexity for software complexity. That is, your wiring will become simpler, but your algorithms will become more complex. You must be sure you can manage the software complexity in development, operation, and diagnostics for the trade-off to be a good one.

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Curt,

 

Thanks for the information.

 

We're currently very comfortable with PWM control, but looking in our crystal ball, we may have some applications where the noise immunity, and options for distributed control offered by a Macro setup, make sense.

 

We'll probably get a small setup, a couple of motors and drives, to experiment with before committing ourselves.

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Having tested several different drive systems recently I came to the conclusion that Yaskawa Sigma 5 motors over Macro utilizing the acc85M from Delta Tau provided the best control solution for my current project. I am using the Turbo PMAC Ethernet Ultralite controller. I haven’t actually used the Ethercat drives on the Power PMAC but I have looked at several completive products using Ethernet based drives this includes Ethercat and Powerlink. I have run several different controllers and drives on a 5 meter long belt driven rail beam system with a moving mass of approximately 200lbs. The testing performed included utilizing a laser informatory system to verify the velocity stability and positional repeatability.

 

The major difference I found is the servo update rate. A motor controlled over macro allows you to update the servo loop at 8kHz. Ethernet based amplifiers only allow you to update the servo loop at approximately 2kHz. The best I have been able to determine this is just a physical hardware limit of the Ethernet based amplifiers. The higher servo update rates over macro allow you to control the servo with a torque output resulting in improved velocity stability.

 

Most Ethernet based amplifiers address the issues of a slower network speed by closing the torque loop in the amplifier and controlling the servo in a velocity or position mode. This can result in having to run two turning loops or difficulty closing the servo loop on a secondary encoder. As I haven’t yet worked with the Power PMAC I can’t speak to how the speed of the servo loop is handled over Ethercat in this system.

 

I will add that I am able to completely configure the Yaskawa Sigma 5 amplifier and a Copley amplifier over the macro network. We produce several systems a month at our factory. This design allows us to set the hardware address switches, load the Delta Tau source code and the system will configure the amplifiers at power up. If an amplifier is replaced this will be detected at power up and it will be programmed with all the required settings. Coding of the auto setup over macro was time consuming but has resulted in greatly simplified system startup.

 

I have come to the conclusion that using the Macro network for the servo motors and utilizing the Ethercat network for remote I/O or motion which can accept slower update rates such as VFD motors is a good general design approach.

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Dan,

 

Thanks for the detailed response!

 

It is good to know about the limited servo rate available using Ethercat; the dynamic performance required by our application means we're closing our servo loops at 8khz. A no-go for Ethercat.

 

I also like your idea of setting the Macro network up to auto-configure the drives. We build our machines for internal use, but the last thing we need is for maintenance to replace a drive a two in the morning and then have the machine down until an engineer can come in and setup the drive.

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kmonroe023:

 

I think Dan was talking about Ethernet, not EtherCAT. I have never used EtherCAT personally, but I have heard of EtherCAT networks with many drives running at VERY high speeds (up to 20kHz).

 

I tested a few different EtherCat amplifier and I also looked at some PowerLink amplifiers. They can close the servo loop quickly inside the amplifier itself if you are able to wire the feedback to the amp. This allows for the much faster servo rates at the amplifier. But if you need to coordinate though the motion controller the rate is about 2kHz.

The closest i got to an answer as to why is that PowerLink can't process data faster then 2kHz. The recommendation I received was to wire an encoder input to the amplifier and allow the amplifier to close the servo loop internally to solve this issue. To sync two servos faster then 2kHz on PowerLink it is recommend that you use an encoder output from one amp wired to the encoder input of the other amp. This can lead to some tricky issues with a secondary encoder or high speed vector locking.

Both EtherCat and PowerLink run on standard Ethernet hardware. PowerLink have some hardware requirements but basically it is standard cat 6 Ethernet. I am speculating the underlaying issue is the current ethernet hardware as both EtherCat and PowerLink seem to have the same limitation.

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@Dan: This link says you can update 100 servo drives at about 10kHz using EtherCAT:

 

http://www.rtaautomation.com/ethercat/

 

I'm not sure where the 2kHz limitation was on the drives you were using, but it definitely isn't coming from EtherCAT. Maybe the drives you are talking about aren't really using EtherCAT, but only Ethernet? This is possible, because you can embed Ethernet frames within an EtherCAT message.

 

@kmonroe023: Either way you go, both MACRO and EtherCAT seem to be very good protocols in terms of speed.

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@Dan: This link says you can update 100 servo drives at about 10kHz using EtherCAT:

 

http://www.rtaautomation.com/ethercat/

 

I'm not sure where the 2kHz limitation was on the drives you were using, but it definitely isn't coming from EtherCAT. Maybe the drives you are talking about aren't really using EtherCAT, but only Ethernet? This is possible, because you can embed Ethernet frames within an EtherCAT message.

 

@kmonroe023: Either way you go, both MACRO and EtherCAT seem to be very good protocols in terms of speed.

 

Yes in theory the EtherCat network is very fast. In practice I have not seen an amplifier which is able implement that speed on EtherCat. Check out this document from Yaskawa about their Sigma 5 amplifier with the EtherCat option.

http://www.yaskawa.com/site/dmservo.nsf/536df907f9fe9d5586256c4e0056b851/86256ec30069fdef8625771a006b3d92/$FILE/FL.SGDV-EC.01.pdf

 

Sigma-5 with Real-Time

Ethernet Communication

Ethernet for Control Automation Technology

System Performance

• 1.6kHz velocity loop bandwidth delivers increased machine throughput

by slashing settling time

 

As I stated i don't understand why but every EtherCat amplifier I looked at ended up at this same sub 2kHz bandwidth. If you know of a 10kHz amplifier and motor combo on EtherCat please share I would enjoy working with it.

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Dan,

 

Here are some Beckhoff drives, which claim they can do 16kHz on the current loop and 8kHz on the speed loop:

 

http://www.beckhoff.com/english.asp?drive_technology/ax5000_ethercat.htm

 

My guess is that the reason Sigma 5 drives are so much slower is because they use CoE (CAN over EtherCAT). I would bet that Yaskawa took an existing design using CAN (very slow) and just packed their CAN messages into EtherCAT frames. This could explain why it's so slow.

 

Again, I have never used any drives over EtherCAT. Maybe it is all just big talk...theory is much easier than practice!

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kmonroe023:

 

I think Dan was talking about Ethernet, not EtherCAT. I have never used EtherCAT personally, but I have heard of EtherCAT networks with many drives running at VERY high speeds (up to 20kHz).

 

I tested a few different EtherCat amplifier and I also looked at some PowerLink amplifiers. They can close the servo loop quickly inside the amplifier itself if you are able to wire the feedback to the amp. This allows for the much faster servo rates at the amplifier. But if you need to coordinate though the motion controller the rate is about 2kHz.

The closest i got to an answer as to why is that PowerLink can't process data faster then 2kHz. The recommendation I received was to wire an encoder input to the amplifier and allow the amplifier to close the servo loop internally to solve this issue. To sync two servos faster then 2kHz on PowerLink it is recommend that you use an encoder output from one amp wired to the encoder input of the other amp. This can lead to some tricky issues with a secondary encoder or high speed vector locking.

Both EtherCat and PowerLink run on standard Ethernet hardware. PowerLink have some hardware requirements but basically it is standard cat 6 Ethernet. I am speculating the underlaying issue is the current ethernet hardware as both EtherCat and PowerLink seem to have the same limitation.

 

EtherCAT is not really standard ethernet hardware. It only uses standard hardware for the master. Slaves have a special ASIC or FPGA that extracts process data and inserts data on the fly so that the network is realtime and data doesn't stop at every slave. The Master which does use a standard ethernet adapter does have the responsibility of reading all the slaves and writing back to all of the slaves. This is the only time the ethercat packet slows down.

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@Dan: This link says you can update 100 servo drives at about 10kHz using EtherCAT:

 

http://www.rtaautomation.com/ethercat/

 

I'm not sure where the 2kHz limitation was on the drives you were using, but it definitely isn't coming from EtherCAT. Maybe the drives you are talking about aren't really using EtherCAT, but only Ethernet? This is possible, because you can embed Ethernet frames within an EtherCAT message.

 

@kmonroe023: Either way you go, both MACRO and EtherCAT seem to be very good protocols in terms of speed.

 

Yes in theory the EtherCat network is very fast. In practice I have not seen an amplifier which is able implement that speed on EtherCat. Check out this document from Yaskawa about their Sigma 5 amplifier with the EtherCat option.

http://www.yaskawa.com/site/dmservo.nsf/536df907f9fe9d5586256c4e0056b851/86256ec30069fdef8625771a006b3d92/$FILE/FL.SGDV-EC.01.pdf

 

Sigma-5 with Real-Time

Ethernet Communication

Ethernet for Control Automation Technology

System Performance

• 1.6kHz velocity loop bandwidth delivers increased machine throughput

by slashing settling time

 

As I stated i don't understand why but every EtherCat amplifier I looked at ended up at this same sub 2kHz bandwidth. If you know of a 10kHz amplifier and motor combo on EtherCat please share I would enjoy working with it.

 

 

The bandwidth limitations are determined by the slaves processing power.

For instance in the lab we used one amplifier in torque mode at 16kHz over EtherCAT. However, that amplifier can only operate at 16kHz with quadrature encoders. If other types of feedback are that require more processing by the slave the maximum rate decreases down to 4kHz.

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