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Old March 2nd, 2019, 06:15 PM   #16
ndzied1
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Quote:
Originally Posted by SD_Scott View Post
I like the idea of having a dedicated Hydraulic controller. I've used the Bosch Rexroth HACD controllers over the years but my issue is always integration and connectivity. If someone has a product that you can connect to and get data in and out of Then all the better.
We sell and have used both the HACD and Delta RMC controllers. I would say the HACD is configurable while the RMCs are programmable. They are definitely not apples to apples.
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Old March 2nd, 2019, 09:17 PM   #17
Peter Nachtwey
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Quote:
Originally Posted by ndzied1 View Post
We sell and have used both the HACD and Delta RMC controllers. I would say the HACD is configurable while the RMCs are programmable. They are definitely not apples to apples.
That is a start in explaining the differences.
The HACD was designed to compete with the RMC100, our second generation controller. I attended a presentation made by Bosch-Rexroth when the HACD was released. They had a slide with a picture of the RMC100 directly comparing the HACD with the RMC100. That same show we released the RMC75. The RMC75 had algorithms that go beyond PID with velocity and acceleration feed forward. We have test and training system at Delta that are very difficult to control.
Norm and other have seen this one
https://deltamotion.com/peter/Videos...Lab_Medium.mp4
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Old March 3rd, 2019, 09:55 PM   #18
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disclaimer:I have great respect for you for being the only person in this industry I've met (well, not MET, actually, "interacted with anonymously in the internet", maybe?) who actually tries to use math to design a control system. I've mostly given up trying to advocate for that. I do not do motion control on a daily basis, and definitely not hydraulics.


Quote:
Originally Posted by Peter Nachtwey View Post
We have what we call our basic hydraulic system. It is easy to control. Disconnected our controller. We changed out the SSI MDT rod for an analog MDT rod so we could use analog inputs and output from the PLC.

I/we are not done yet. That article will not come out for another two months or so.

It is not my intention to bash PLCs.
Why not use the SSI encoder with the PLC, as well? Might as well set up an apples to apples comparison. It feels like you're setting up a straw man, where a PLC is limited to slow things with old tech, and motion controllers are fast with new features. The lines are a lot more blurred than they used to be.

I'm willing to bet there are people on this forum that would be willing to help you maximize the capabilities of your various attempted PLC solutions. Some things could be use Y hardware instead of Z hardware, which may be too late to change, but there may be software best practices you're missing. I know from my experience that there can be many ways to use a system, but usually there is one way the system WANTS to be used, and it often isn't obvious.

Post a project; I'm curious what the response would be.

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Originally Posted by Peter Nachtwey View Post

I don't know for sure. I can find out on Monday. Assume it is the S7-1511.
I can make allowances for the speed but the motion blocks are a joke.
One thing I want to do is test the Siemens target generator. This is the most difficult part of a motion controller to write that actually does motion. The Ethernet code is a killer too.
Note that a 1518 is literally 60x faster (by bit processing speed) than a 1511, so picking the right CPU has a huge effect on what motion is possible. It can also handle 25x the axes at that 4ms time. Faster times become available in faster processors, but I'd be surprised if 4ms were the fastest even at the 1511.

Note also that there is a T variant (t for technology) for some of the processors that allows for added motion capability in an otherwise identical unit. I've never bumped into something called a target generator, but I'd be surprised if it were impossible. The motion instructions in the regular processors exist mostly to allow users to do position control with VFDs. The Ts are relatively new, and gaining functionality with every release, but it might be true that it really require Simotion to do it right.

That said, the precanned instructions are mostly puzzle pieces you use to make your own solution. I saw a hydraulics library mentioned on the support site, but it looks like it isn't freely available.

Maybe that's the difference between PLC and motion controller in your definition I'm missing? How much of the application is precanned?

Last edited by mk42; March 3rd, 2019 at 10:32 PM.
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Old March 3rd, 2019, 11:16 PM   #19
Peter Nachtwey
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Quote:
Why not use the SSI encoder with the PLC, as well?
This is a very good question. SSI MDT rods are far superior to analog rods. There is no noise but then there is the problem with sample jitter. A motion controller uses and FPGA to ask for the new position every millisecond on the nanosecond. There are no "house keeping" delays or times when interrupts are off. The point is that even if the feedback is SSI it makes little difference if the time between readings is not know. I/we had many arguments about this with Tempsonics in last half the the 1990s about this.

Most people that try to do hydraulic servo control do not know this so they use analog feedback MDT rods.

Quote:
I'm willing to bet there are people on this forum that would be willing to help you maximize the capabilities of your various attempted PLC solution
I bet there are. I am going to wait for JRW's suggestions when I post more data.

However, there real problem is the control algorithm. The PID function block in in PLCs is not good enough. The hardware can help but it will not get close to a solution.

Quote:
Note that a 1518 is literally 60x faster (by bit processing speed) than a 1511, so picking the right CPU has a huge effect on what motion is possible.
What it means that a S7-1518 can control more hydraulic cylinders incorrectly.
Th S7-1518 does not have the right algorithms for hydraulic motion control. I can make allowances for the difference in speed. Where I will crucify the competition is when I find things there control algorithm can not do or any flaws in the target generator.

Quote:

That said, the precanned instructions are mostly puzzle pieces you use to make your own solution. I saw a hydraulics library mentioned on the support site, but it looks like it isn't freely available.
How much do they charge for that? How good is it?

Quote:
Maybe that's the difference between PLC and motion controller in your definition I'm missing? How much of the application is precanned?
The difference it the attention to detail and control algorithms. I can go into detail but I would lose everybody unless they had a PhD in control theory. This is the honest truth.

There is no way a PLC can compete with a dedicated motion controller. I don't think that is the issue. However, if the application is extremely simple and the tolerance aren't too demanding the a PLC may have a chance but I from our experience the PLC has no chance. For instance the controller for a garbage truck will usually be an embedded micro controller. The control doesn't need to be exact or versatile. I just needs to get the job done.
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Old March 4th, 2019, 04:09 AM   #20
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My little contribution

Dear Peter,

I haven't used any S7-1500T but i can provide some extra information:

Quote:
Originally Posted by Peter Nachtwey View Post
How much do they charge for that? How good is it?
The 1511T-1 price 66% more than a regular 1511-1.

Some extra information on the path generator with S7-1500T can be found in:
https://support.industry.siemens.com...view/109757198

In PROFINET You could set a Isocronous cycle so every input or signal is read exactly every 250 us with jitter less than 1 us.

Best regards,
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Old March 15th, 2019, 10:52 PM   #21
Peter Nachtwey
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Finally, H&P got the formulas and the pictures right

https://www.hydraulicspneumatics.com...on-controllers

The next article will explore the difficulties of adding integrator, derivative and feed forward gains. It will have even more graphics to show the results of each case. I hope the H&P people will get this write. I think the magazine article is printed if you subscribe to H&P

There are two related thread to my H&P articles. On the eng-tips I am covering different types of control and evaluating Matlab tutorial.
https://www.eng-tips.com/viewthread.cfm?qid=450398

Cheeco just happened to start this topic.
http://www.plctalk.net/qanda/showthread.php?t=119883
It shows the complexity of generating the motion profiles.

I will get around to testing the motion blocks in the Siemens and Rockwell PLC. I sincerely doubt any will pass my tests.
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