Programming S-curve motion profiles

Ramp Generator from converting library

TurkSaleh

Did you look at this one from the Siemens Converting Library?

its similar to the G120's RFG

its similar to the G120's RFG- but plc based

jhenson29 said:

Do you actually have to run a motion profile or do you just need to generate a speed reference as an s-ramp from the PLC? Can you provide more information about the actual application?

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I think I miss-used the terms here. Indeed the speed reference with smooth acceleration at the start/stop will be enough.

JRW said:

its similar to the G120's RFG- but plc based

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This is exactly what I need.
Still it is great to know the math and physics behind the block

If TurkSaleh is using a Siemens PLC I recommend he takes JRW's advice and use the library. We have played with it for comparison. It will work. It is better to use a library that has been debugged than to try to re-invent the wheel.


drbitboy, break out your python and sympy and solve the 17 equations for 17 unknowns. Assuming all 7 segments are used the 17 unknowns are
t01, x1, v1, t12, x2, v2, t23, x3, t34, x4, t45, x5, v5, t56, x6, v6, t67
This assume point 0 is the starting point and x7 is the ending point.
The initial and final PVA are known and and commanded P, V, A are given.

you do not need everything Peter is referencing.

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Probably not but we don't know for sure.
In my case the motion controller must be able generate any motion profile the customer wants. Whether the equipment can actually follow it is up to the designers.

The OP mentions 7-segment profiles, which implies the former.

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I mentioned before the commanded acceleration and velocity may not be reached when making short moves. In this case there are only 3 segments and the motion is jerk limited.

Peter Nachtwey said:

I mentioned before the commanded acceleration and velocity may not be reached when making short moves. In this case there are only 3 segments and the motion is jerk limited.

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What I meant was, is it acceleration or jerk that has a Heaviside Function-like profile i.e. is discontinuous.

The Siemens library image from JRW looks like acceleration is discontinuous.

drbitboy said:

What I meant was, is it acceleration or jerk that has a Heaviside Function-like profile i.e. is discontinuous.

The Siemens library image from JRW looks like acceleration is discontinuous.

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The motion profiles I saw on a S7-1500T were true 7 segment motion profiles. They just weren't optimal. They were not easy to use either but the accelerations were either constant or ramp up or down depending on the jerk rate. The segments were continuous. Only the jerk changed in steps.


Where is the solutions for the 17 unknowns?

Peter Nachtwey said:

Where is the solutions for the 17 unknowns?

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Where are the equations? The delta link is broken, or maybe I missed it.

Thomas_v2 said:

It's not too difficult.

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So where is your solution? If you don't know the equations then programming them or how much time it takes to execute them doesn't make much difference. Turbine controls are easy.

drbitboy, you are supposed to derive them using sympy.

Siemens has a library somewhere. What JRW presented was not it.


An old thread on s-curves
http://www.plctalk.net/qanda/showthread.php?t=35902&page=2

Peter Nachtwey said:

drbitboy, you are supposed to derive them using sympy.

Siemens has a library somewhere. What JRW presented was not it.

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It’s not supported with g120 , DSC is not supported and telegram 105 is needed

Peter Nachtwey said:

Delta is going to add Ethercat capability sometime this year. It will be used mostly to control output devices like valves and drives.
The problem I have with Ethercat is that the packets are essentially CAN Open packets on Ethernet. The CAN Open packets have 8 bytes of data. 8 bytes permit sending a 32 bit float and some command bits that tell what the float is. Usually the float is a position. While it is possible to move from position to position every 50 microseconds there is no feed forward data or target velocity and acceleration, just a target position. This is why I think Ethercat is great for sending output values to valves and drives but not so good for sending motion profiles to multiple controllers.

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Very good. I've reached out to Delta with inquiries about the availability of EtherCAT in their controllers and I've not gotten much back in terms of a timeline. Our next machine build is scheduled for end of this year but we're about to start ordering our grocery list of components now, to include the RMC-200 controller.

There were a couple of new standards of EtherCAT released last year, broadband EtherCAT-G and G10. It's intended for transmitting high volumes of data for such things as motion and vision applications. I'm not real familiar with them and only have explored them briefly.

EtherCAT G and G10

More EtherCAT G and G10

I used the library LCon_RFGJ and it gave exactly what im looking for.

everyone, thanks a lot, I learned many things from the discussion.

Good
And Peter thought only an RMC could do it

JRW said:

Good
And Peter thought only an RMC could do it

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I didn't say that.
I did say Siemens has a library that would do an OK job but...

Why are the discontinuities in the output acceleration ( dark blue line )? This is not good.
The red line looks like it is the integral of the blue line or velocity.
The green line looks like velocity without s-curves.
The RMC can do it better.


I am still waiting for someone to find the equations for the 17 variables I listed above. If you don't know the formulas for this variable then how can you say that writing the code in a PLC is easy? It is obvious that Siemens hasn't got it right yet in even a simple case above.


JRW, I still remember you called me arrogant. You do know that Siemens used RMC100s for their plastics solution in the late 1990s and early 2000 until Siemens came out with their own solution. I don't think either Siemens or Delta do much in plastics now because too many OEMs want a package they made themselves where as Delta and Siemens sell components and some assembly is required. We do sell a few RMC75s for plastic applications on retrofits.

JRW said:

Good
And Peter thought only an RMC could do it

Click to expand...

I didn't say that.
I did say Siemens has a library that would do an OK job but...

Why are the discontinuities in the output acceleration ( dark blue line )? This is not good.
The red line looks like it is the integral of the blue line or velocity.
The green line looks like velocity without s-curves.
The RMC can do it better.


I am still waiting for someone to find the equations for the 17 variables I listed above. If you don't know the formulas for this variable then how can you say that writing the code in a PLC is easy? It is obvious that Siemens hasn't got it right yet in even a simple case above.


JRW, I still remember you called me arrogant. You do know that Siemens used RMC100s for their plastics solution in the late 1990s and early 2000 until Siemens came out with their own solution. I don't think either Siemens or Delta do much in plastics now because too many OEMs want a package they made themselves where as Delta and Siemens sell components and some assembly is required. We do sell a few RMC75s for plastic applications on retrofits.