Question about motion controllers

Hi,

This may be a kind of a newbie question: Could somebody let me know what motion controllers have that makes them special?

I've done many projects involving servos and I have always used plc + servodrives cofigurations.

Where or when should I utilize a motion controller like deltamotion, kollmorgen, yaskawa, etc?

Another question: Can a ControlLogix processor with some SERCO modules be considered a motion controller?

Thank you

I wouldn't be surprised if it is just a name given to commercialize the product.

Hi,

Peter Nachtwey gives an answer to the same question in a recent thread.

The difference between PLCs and motion controllers is blurred. The main difference software and what is given priority. Our controllers and have been used as PLCs or as the only controlling device in the machine. However, a motion controller must largely stick to motion control. PLCs do not need to be deterministic and must support a wider range of I/O devices and much larger amount of I/O.


http://www.plctalk.net/qanda/showthread.php?t=119883&highlight=trajectory+generator

chantecler said:

Hi,
Where or when should I utilize a motion controller like deltamotion, kollmorgen, yaskawa, etc?

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Where the application becomes more demanding. There are some things you just don't want to do in a PLC because it isn't deterministic or if it is then it isn't very fast. Also, the target generators in a motion controller should be much better than what is available on a PLC.

Another question: Can a ControlLogix processor with some SERCO modules be considered a motion controller?

Click to expand...

I wouldn't call anybody that said this was a motion controller but it is really a collection of components that make up a motion controller.


A motion controller has 3 main parts. A command processor, a target generator, and the control with PID and feed forwards.
A motion controller has all that in one package. A control logix can do the command processing and the target generation but the the closed loop control is done out at the drive.


The advantage that a motion controller has is that the motion between multiple axes is more tightly coupled whereas a distributed system requires an axis send data back to the PLC, the PLC figures out what to do then sends and corrections to the other drives. A motion controller does not have the communication delays.


I can run a six degree of freedom stewart platform from a RMC150 or RMC200. Writing the code for this in any PLC would be a pain. This goes for flying shears. Our RMC75 has replaced the HYD02 and M02AS in flying shear applications. Note we make the HYD02 and M02AS for Rockwell. Both of those are limited by the PLC. The RMCs do not even need a cam table or cubic splines for flying shears because everything can be computed on-the-fly.



A RMC has some special commands that a PLC does not have. I could give examples if necessary. I don't keep track of what all the other motion controllers can do.


Our RMC200 controller has special filters you do not find in PLCs.


The list goes on and on. However, if you are just controlling a conveyor then a PLC and drives are fine.

chantecler said:

Hi,

This may be a kind of a newbie question: Could somebody let me know what motion controllers have that makes them special?

I've done many projects involving servos and I have always used plc + servodrives cofigurations.

Where or when should I utilize a motion controller like deltamotion, kollmorgen, yaskawa, etc?

Another question: Can a ControlLogix processor with some SERCO modules be considered a motion controller?

Thank you

I wouldn't be surprised if it is just a name given to commercialize the product.

Click to expand...

There is no standards body that defines "this is what a device must do to be a motion controller", as far as I know. It's more than just a buzz word, but it is mostly marketing. Rockwell calls the compact/controlLogix a PAC vs the older ones being PLCs. Are there real feature differences under discussion? Absolutely. Is it a completely arbitrary naming division? Also absolutely.


A Motion Controller is a Controller that can do Motion. "Motion" means different things to different people. Is it "Motion" if you're just turning on a VFD to move a conveyor at a fixed speed? Something is moving, but I don't think most people would consider it "Motion". Is a robot or a 6 axis CNC motion? Most certainly, although you typically have dedicated controllers for those applicaitons. Where does motion fit in the middle? I have no idea, and I think everyone has a different opinion.

Thank you three for your answers,


Peter, I just read that you get asked this all the time. Funny!

The difference is clearer for me now. I haven't done anything like a stewart platform yet (I didn't even know they existed) but I have done flying shears using drives and meeting the tolerances required so far.

If I got it right one of the differences is who does the control loops.

Do motion controllers still need a drive between the controller and the actuator for the power part?

I am interested in learning more about motion controllers and their uses, could you recommend some readings, please?


mk42, I know there is much of what you wrote too. As far as I know the first to call their processors "pac" was Opto22, now they call their last product "Edge Programmable Industrial Controller" to differentiate it from the rest.

I also know there are many "motion controllers" but the ones I am interested in are the ones Peter refers to.


Thanks again

chantecler said:

<snip> Do motion controllers still need a drive between the controller and the actuator for the power part?

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Yes, at a minimum, you need a 'Servo Amplifier' or drive.

There are a few motion controllers out there that have small drives included, such as the hobby-grade CNC machines.

There are also some Servo Drives with (limited) Motion Controllers built-in. These are typically 1.5 axis, but some offer full-blown co-processors for motion and machine control, with 'real-time' communications and sync'd clocks, etc.

The distinction can get fuzzy!

chantecler said:

Do motion controllers still need a drive between the controller and the actuator for the power part?

Click to expand...

Ours does because it would be difficult to draw that much power from the back plane.

I am interested in learning more about motion controllers and their uses, could you recommend some readings, please?

Click to expand...

I don't know of any books. The people that know the most work for motion control companies. There is no money or incentive to write a book. We learn this on our own or it is intuitively obvious to us.

I also know there are many "motion controllers" but the ones I am interested in are the ones Peter refers to.

Click to expand...

We specialize in hydraulic servo control but we also control servo motors. This may seem more like advertising but Delta has been making french fry defect removal systems for years. There is no way this can be done in a PLC although we do use a Compact Logix for some of the I/O. We make the scanners that scan potato strips moving at 400 to 500 fpm. We can see many types of defects and cut them out. The motion profile cut the potato strip without moving the rest of the fry. One of these machines may have up to 96 servo motors that are specially made to our specifications. The knives move so fast you can not see them. The go down and up in 16 ms. We must use high speed cameras to view the motion. The controllers that control the cutting are basically stripped down RMC75s
https://deltamotion.com/peter/Videos/Delta Fry Cutting Machine Demo.mp4
We don't make the conveyor part or the cabinet but we make the rest or farm it out to have it made to our specifications.

Hi,

Peter Nachtwey said:

We specialize in hydraulic servo control but we also control servo motors. This may seem more like advertising but Delta has been making french fry defect removal systems for years. There is no way this can be done in a PLC although we do use a Compact Logix for some of the I/O. We make the scanners that scan potato strips moving at 400 to 500 fpm. We can see many types of defects and cut them out. The motion profile cut the potato strip without moving the rest of the fry. One of these machines may have up to 96 servo motors that are specially made to our specifications. The knives move so fast you can not see them. The go down and up in 16 ms. We must use high speed cameras to view the motion. The controllers that control the cutting are basically stripped down RMC75s

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Very impressing!!!

I watched the video too

Thank you


I am very interested in this subject and I am going to investigate more about it.

Thanks again, bye

Peter Nachtwey said:

Where the application becomes more demanding. There are some things you just don't want to do in a PLC because it isn't deterministic or if it is then it isn't very fast. Also, the target generators in a motion controller should be much better than what is available on a PLC.

Click to expand...

Can you elaborate on what determines if a PLC is deterministic? I understand about the limitations of speed, but what determines deterministic?

Maxkling said:

Can you elaborate on what determines if a PLC is deterministic? I understand about the limitations of speed, but what determines deterministic?

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No PLC I know of is deterministic, at least not deterministic enough for motion control. Deterministic means things happen a regular intervals. For instance a PLC can be said to be deterministic enough if it samples at 10 ms intervals using interrupts. The question I would ask the PLC guys is how do you know the interrupt is happening every 10 ms. It could be 9.9 ms or 10.1 ms. That is only change of 1% but that can make a big difference in calculating speeds and accelerations. If the encoder is a 1000 pulse encoder you would expect to get 10 counts every 10 millisecond but if the sample time is varies from 9.9 milliseconds to 10.1 millisecond then the number of counts PLC see can vary from 9 to 11 counts or a 10% variation in velocity. That is a not acceptable because the derivative gain is multiplied by the error between the target velocity and the measured velocity. The problem is even worse when trying to calculate the acceleration.


A motion controller can not use the normal formula you see posted here for filtering velocity because it adds phase lag.