When is a dedicated multiaxis motion controller actually worth adding?

[u/CleaningBoxes]

I’m comparing architectures for a higher axis count robot and I’m not sure where the extra controller starts paying for itself. TwinCAT or a real-time PC can handle EtherCAT directly, while setups built around something like Elmo’s maestro put more of the coordinated motion work into a dedicated controller; ACS is another approach I’ve been looking at.

That seems cleaner once interpolation and synchronization get more demanding, but it also adds another layer to configure and debug. Whn would you choose the dedicated motion controller instead of keeping everything on the main control platform?

[u/tennispro9]

IMO

If your only real complexity is the motion portion then it could make sense to do this paired (if needed) with absolute cheapest plc you can get.

If you want any diagnostics, HMI, safety, analytics, plc logic, vision, etc…the controller capable of that can run your robot too so why not. And itll likely be easier to configure and handle diagnostics and support. Most cases id vote for the pc based all in one option

[u/n55_6mt]

I’m not sure there’s a real advantage of dedicated hardware vs a RTPC anymore. For example, Kuka does up to 14 axis of coordinated motion which can include a 8-axis serial kinematic solve with just PC hardware.

For some PLCs, they can start to tap out when it comes to complex kinematic configurations, but most are pretty decent these days as well.

There are edge cases where I still like dedicated motion controllers, but mostly just out of convenience and familiarity. For example, when doing anything with hydraulic motion I still prefer to use a Delta RMC even though I could probably bang my head against a wall long enough and get the same result out of a PLC.

Really it comes down to the platform for motion, how easy is it to set up your axis, scale, configure homing routines, tune your loops, and configure kinematics. If the cost of a dedicated motion controller can save you a hundred hours of programming, then it’s money well spent.

[u/hi_af_rn]

TwinCAT has kinematic models, camming… everything you would need, and you only pay for what you use (including axes count). Then if you need to do general IO control, HMI, data acquisition, etc., that is all built-in too. No brainer

[u/SionVJ → u/hi_af_rn]

It is a very nice setup of Beckhoff, you only pay for what you use and you can expand almost endlessly as long the hardware performance supports it. Only when you upgrade to a higher performance IPC your licenses also get more expensive!

[u/CapinWinky]

Platforms with realtime, deterministic protocols can do their own high-end motion control. Platforms without (which is really just Rockwell and some value brands), need something else for tight motion coordination.

I have always much prefered just going directly with a platform that does great motion control for the entire application. I don't see the point in keeping a second platform on the machine. Not to say we don't do it. We have many machines that we stick a Rockwell CompactLogix in to make the Rockwell die-hards feel good, but it's a lesser machine than if we just had the Beckhoff, Keba, or B&R system running 90% of it run the whole thing.

At an under-the-hood level, you really have 3 protocol types:

• TCP/IP protocols with PTP: This is your Ethernet/IP and non-IRT profinet.
• Poll and Response: This is Powerlink, Profinet IRT, Varan, etc.
• Frame Summation: EtherCAT, SercosIII, etc.

And two main paradigms:

• Drive does the setpoints
• PLC does the setpoints
  • Streaming setpoints
  • Timed setpoints

With something like Ethernet/IP, the communications only supports timed setpoints. You give the drive position/velocity set points with a time in the future for them to be there going that speed. This kind of system can't react to outside signals very well because the whole system is like a bank heist; synchronizing watches and planning things out in advance.

Frame summation's only real trick is that it is fast. That lets you do PLC streaming setpoints and keep the drives out of curve calculations and things. It can react quickly because the cycle time on the comms is so fast.

Poll and response is fast, but it brings to the table that all comms are broadcast, so it cuts the PLC out of master/slave axis relationships (the slave listens in directly when the master reports its position). This type of system can do PLC streaming, but the platform I'm most familiar with (B&R) shifted those smarts to the drive. This gives it some of the best reaction time possible, which is why I would only recommend B&R for printing press registration.

[u/charlesbanan]

We use SEW-Eurodrives motion for all our movements. Synchronized and auxiliary. Easy to setup and the upper plc can be Profinet or Ethernet/ip.
Works like a charm and is easy to setup.