Why should I use SERCOS?


Thread Starter


Everything is changing, some systems getting easier, some getting more complex, 1-Axis today, 40-Axes tomorrow, PCs getting faster (Still waiting for PC Control train to leave the station), PLCs being a commodity, sensors being boring, Software integration, Motion Controllers handling I/O and PLCs doing Motion Control, and the everyday heard words: connectivity, connectivity, connectivity and WHERE IS MY ETHERNET.... where is Motion Control going? Where is the future?

I strongly feel that SERCOS will be the path all motion controllers will or should be going. Faster, less wiring, no more analog, ease of connectivity, torque control across multi-axis, drive status back to controller, centralized control, Soft Motion, SoftPLC...these are just some of the advantages SERCOS can offer. With PCs being faster and faster, what will be the future of PLCs and Motion Controllers? Maybe SoftPLC and SoftMotion? I see EtherNet (Modbus/IP, EtherNet/IP, maybe others) being the PC to PLC, PLC to Motion, OIT to PLC, I/O to PC/PLC type use but not used for motion "control." I feel that SERCOS will be the choice for servo to controller (PC, PLC, SA-Box). Why use SERCOS and not Fire Wire or some other weird network? SERCOS has been around for a long time and is proven its reliability. So now you’re asking, "If it has been around for so long, why has it never taken off?" My answer to that is lack of education and the failure of the general motion control market to "change." Another huge influence is that it typically has not been cost effective on smaller 1-4 axis machines.

SERCOS is digital, open, proven, expandable, fast, "plug & play", cross-vendor compatible, supported worldwide!

I currently don't use SERCOS (never had), but looking into it heavily. I am trying to convience others in my company that we need to use this technology and prepare ourselves for the future.

Are you using SERCOS?

Do you agree with my thoughts above (If you don't, tell my why)?

Are all SERCOS systems compatible? I keep hearing that AB has SERCOS but is not cross vendor compatible? Is that true? If so, how can they call it SERCOS then? Does the standard just have minor requirements and then you can modify your system to do more?

If you use SERCOS, please tell me why you use it and how you use it if you can?

Thank you.
> If you use SERCOS, please tell me why you use it and how you use it if you can?<

We (Staubli) just released a new robot control cabinet, the CS8. It is PC based (running VxWorks, not windows) and uses SERCOS to connect the PC to the Amplifiers (Servotronic amps from Kollomorgen). Why did we chose SERCOS? It works and does what we need. Using Fiber Optics allowed us to increase our speed, reduced wire count (and therefore costs), and the digital control gave us better control of the robot's motion.

James Ingraham

Sort of. We're using the Allen-Bradley flavor of SERCOS, which isn't really SERCOS at all. This brings up one of the problems with SERCOS (and all digital networks); incompatibility. Not all SERCOS drives act the same way, and some SERCOS controllers can't understand some drives. This is also true of FireWire; proprietary "drive" information going over the standard FireWire network.

Incidentally, Motion Engineering ( "www.motioneng.com":http://www.motioneng.com ) has a wonderful white paper on why their motion bus, SynqNet, is superior to FireWire. "http://www.synqnet.org/pdf/SynqNet_Overview.pdf":http://www.synqnet.org/pdf/SynqNet_Overview.pdf
They also seem to think it's better than SERCOS, but they convinced me SERCOS was pretty good.

The biggest advantage of a digital network over the traditional analog signals is wiring. You cut out ten wires per axis and gain the ability to locate the drives virtually any distance from the controller. My favorite thing is that if you get two SERCOS cables backwards the network just won't work. If you get two analog wires backwards you get a runaway.

Why SERCOS over anything else? Well, you're into fieldbus wars, and I wouldn't make a prediction on fieldbuses if you paid me.

-James Ingraham
Sage Automation, Inc.


You seem to refer SERCOS as a field bus, but is it? When I think of fieldbus, I think, DeviceNet, MODBUS, Profibus...(this bus, that bus)...etc. SERCOS is like you said, a replacement for the 8 or 10 wires used for command and feedback. So wouldn't SERCOS just be a different form of command/feedback? A Digital command/feedback cable with some added features (like maybe with an imbedded fieldbus).

SERCOS Seeker,

James Ingraham

From the SERCOS N.A FAQ availabe at "www.sercos.com/faq.htm:"http://www.sercos.com/faq.htm

"Q: Is SERCOS a fieldbus?"

"A: Yes, and no ...
Fieldbus protocols are intended for low-level devices -- such as sensors, motor starters and inverters -- which are mainly turned on and off, or which require an asynchronous analog command value.
Although SERCOS was not designed primarily to be a fieldbus, it has the ability to decentraize I/O via multiple I/O nodes that connect to the field devices.

The decision of whether to use a fieldbus, SERCOS, or both, depends on the application. If only loose coupling between axes is required, a series of single-axis position drives connected via a fieldbus may be adequate. In a synchronized motion application, however, SERCOS is required.

The I/O requirements may even be satisfied via SERCOS, negating the need for a fieldbus. In high power applications, such as flexible machine systems, both a fieldbus and SERCOS exist in the same control."

This, I think, is pretty much what you said: "A Digital command/feedback cable with some added features (like maybe with an imbedded fieldbus)." However, not "just a different form of command/feedback." The key reason I say that is that this is a network. Information can be passed from slave to slave in a synchronized manner. Intelligent slaves can make decisions based on information circling the ring. With analog, if the command is "Go", the drive goes no matter what. With SERCOS, the drive can decide whether or not to go based on configuration plus information on the network. This is fundamentally different. That's why I call it a fieldbus. A highly specialized fieldbus, yes, but a fieldbus nonetheless.

-James Ingraham
Sage Automation, Inc.
Go to Control.com and click on the BULL! luminary.
The last 3 Motion Control Forum transcripts are there. The "gurus" discussed SERCOS all three years. The essence of their discussions is that it is the best alternative now available and most of them are taking steps to support it.

Thomas B. Bullock, President
Bull's Eye Marketing Incorporated
Industrial Controls Consulting Division
104 S. Main Street, Suite 320
Fond du Lac, WI 54935
PH: 920: 929-6544
FX: 920: 929-9344
E-mail: [email protected]


We have a prototype system that uses a SERCOS fiber optic loop to talk from an AB controllogix to an AB drive.

It is not compatible with any other sercos equipment.

As I understand, Sercos is like ethernet in that everyone can be sercos compatible, without being able to talk to eachother.

I would not use it in the future, given a choice. I don't see the benefit of Yet Another Incompatible Network.

--Joe Jansen

Martinicky, Brian

Hi List,

There seems to be a lack of information about what SERCOS is and what it offers. Check out the following link: "www.MotionOnline.com/seminar.htm":http://www.MotionOnline.com/seminar.htm

Automation Intelligence offers free seminars that will answer any SERCOS questions that attendees may have in a vendor-neutral-non-product-pushing
environment. Anybody that is interested in SERCOS should attend one of these. Hopefully you can find a date/location that works for you. If not,
call AI about scheduling a seminar in your area...


Brian Martinicky
Manager, Software Development
Automation Intelligence, Inc
Duluth, GA

Tommy Thompson

SERCOS is not "Another Incompatible Network". It should be worded that this particular vendor decided to become "An Incompatible Vendor". AB has stated that their SERCOS master controller will not be made compatible to work with any other vendor's equipment, and that their drive will not be compatible with any other vendor's master controller. All other vendors work towards their SERCOS equipment being compatible with other vendor's equipment. This is just another fine example of AB implementing their version of an "Open" controls system.
The operative word here is "AB". From what I understand, please someone correct me if I am wrong, AB has not implemented a true "SERCOS" (as defined in the standard) system but has deployed their version of it. We use SERCOS here with Automation Intelligence's AML programming language running on standard industrial PCs ( some with NT4 and others with IRMX as their OS)
that talk to Pacific Scientific drives with no issues what so ever. Works very slick.

Best Regards...

Rick Kelly
Chief Electrical Technician
Natural Cuts, Ingleside, Ont.
Kraft Canada Inc.

Cameron Anderson

Thank you all for your feedback. Since my org. post, I have read a lot more and have much more understanding on SERCOS. Below are some email exchanges I had with SERCOS NA.

Here was my question to SERCOS NA:
I always hear about SERCOS, especially AB's SERCOS. But what I always here is that an AB SERCOS system in not compatible with other SERCOS systems out there. We have many customers out there using AB systems and would like to get into SERCOS controls/drives, but if I am always being told that they will not work with AB, then how can they say they are meeting SERCOS conformance/standards?

Tell me it is truly plug & play, cross-vendor compatible with AB?

Reply was:
Because I don't personally have enough nformation on AB systems, I have requested information from AB, so that I can respond to this inquiry. I will advise you as soon as I can.

Next Reply:
I relayed your question to Chris Roche of Rockwell Automation, who is also Secretary of SERCOS N.A. Here is his reply.

"Of course our products, specifically the drives are SERCOS compliant and are undergoing that testing as we speak. We are working to have our controller and software tested for compliance this coming fiscal year. We are committed to provide a fully compliant SERCOS system now and for anyother product we create that uses SERCOS.

Secondly, we have an integrated architecture called Logix which incorporates embedded logix, currently this implementation does not support third party SERCOS drives...which means we have a product which we believe provides a superior implementation of machine control and uses SERCOS as an enabler for this. We provide advanced diagnostics, one programming environment, and ease of use for various RA drive and motor configurations.

We don't offer this on competitors drive and motors because we wanted to make sure our system offered the functionality and performance that was
nessecary in the integrated motion market. We will refine that product plan in time."

My conclusions:
To me, something like SERCOS should have more strict regulations/guidelines like DeviceNet if the mfg is going to sell the name. It sounds like I need to read a lot more on SERCOS. It seems to be a "BIG" name but little to it. Like the feedback I got from several others, it is not cross-vendor compatible, not plug and play. It is just a simple means of eliminating the 8 to 10 command/feedback wires but with some added features (like an imbedded field bus). The problem I see is the fact that a system can be SERCOS compliant, but not universal. I was thinking it is more field bus like.

Now I see how they get away with it (see below), but this doesn't really make the systems plug & play. Starting to make sense...(i'm reading more on SERCOS). I guess like Firewire and EtherNet, SERCOS will never have a true cross-vendor, plug & play compatibility standard like the fieldbusses. I was thinking because it is eliminating the 8 to 10 command/feedback wires, that are pretty much all cross vendor compatible and plug & play, that the digital SERCOS command/feedback cable would do the same.

"...In addition, the standard defines 32,000 vendor-defined IDNs that can be used by individual vendors to incorporate special features in their drives. One of the values of the vendor-defined IDNs has proven to be in their use in incorporating new features into the SERCOS interface. On many occasions, a vendor has utilized the vendor-defined IDNs to introduce and field-prove some new control/drive feature, then has brought that feature to the SERCOS Technical Working Group, where it has been incorporated into the standard IDN set for use in a standardized manner by all manufacturers."

Thank you all who posted. Please continue to post.

-Cameron Anderson
Motion Control Specialist
St. Paul, MN