Devicenet versus SSI encoder

Hi,

I have to chose some encoders and interface them with a ML1500.
If encoders are SSI I will use an SSI interface module
If they are devicenet I will use an devicenet scanner, in wich case I will use devicenet for some remote I/O, communicationg with the one AV drive and maybe with the Panelview.

What would you choose in terms of comunicating speed Devicenet or SSI ?
Any encoders as a preference?

As I see both are 1M networks, distance between encoders and plc approx 15feet(5 meters).
In Devicenet I will have other devices but they will not use bandwidth when encoders will be used.

Thanks,
Marian

what kind of application is this?

Hope you won't laugh.

I have 4 rolls and to adjust their height at .001" precision
the roll is moved through a wormgear by an hydraulic orbit motor.
I action the orbit motor with a hydraulic valve.

Up till now we had switches to action the valves and check the height on some counter.

Now I will ad an HMI , people will punch in numbers and rolls shoud move accordingly.

They want this to be able to store jobs and when they will change job rolls will be moved by just selecting a job number.

So application is encoder-interface-plc-hydraulic valve.
I am just playing around as reaction time from valve is so slow so I guess it won't matter my network.
However if I have opportunity to play with this I want to learn about both of them.

Thanks
Marian

NO, it makes shake my head in wonder.

I am just playing around as reaction time from valve is so slow so I guess it won't matter my network.
However if I have opportunity to play with this I want to learn about both of them.

Click to expand...

You know you have the wrong solution and using SSI will make only a small difference.

1 Get a motion controller that is made for hydraulic control and can interface to SSI feedback. Make sure the SSI feedback is also synchronous to the motion controller PID update.
To do otherwise is just wasting your time and money.

2. Use SSI Balluff or Tempsonic rods with 2 micron resolution and don't even consider DeviceNet. If using a rotary encoder consider a Stegmann/Sick absolute SSI encoder.

3. Make sure the valve is very close to the motor. One should keep the trapped volume of oil between the valve and the motor as small as possible for best response.

4. 0.001 inches requires that the machinery be built with very fine tolerances and there is no slop in the worm gear. Well?

I was helping a customer yester who just added a motion controller because he couldn't control 4 axes with an AD PLC alone. As it turns out he was fighting much more than just the PLC programming.
However, he is runnning now.

I am always amused at specifications such as 0.001 inches.
People always get out the dial indicators so we can prove we are getting back to the same place within 0.001 inches never thinking that the dial indicator moves on the steel frame as the frame expands and contracts.
It is almost like the customers think they can put a controller of any type on a system and it will fix all their problems. Metal expands and contracts more than 0.001 inches with any distance.

And with a good reason.

Today people like to put rocket engines on their lawnmower and show to the neighbours how smart they are.

This machine was made about 4 years ago, using resolvers (please do not ask why) - interface to plc- directional valve -orbit.

The wormgear have accuracy .005 from catalog. plus from other elements .002-.004 we go let's say .010. tear and wear??? who knows

I was asked to make it look better.
But not to change too much.
And not to go over budget.

So again, rolls go up-down max 2". if you change the material to be threaded you will go max .2" difference.

What I will do is to change the resolver (to much a overkill for a 200rpm shaft)to an encoder. incremental will do just fine here,
(we are using them with counters in manual application) nothing will go nowhere being mechanically designed to be ok, but I will use magnetic absolute multiturn for easier control and less headache.
Already I have an quote from Sick , Siko and others

Yep, using motion controller for hydraulic will be the best ideea, but if they will give me let's 200 more per valve as I would like some with faster response I will be happy.
Yep, waste of time and money, luckily they are not mine.

Valves are about 3 feet from orbit motors, and I will add flow control on manifold to be able to gain something on valve response time.

Thanks for your help
Marian

What is the difference between a motion controller for hydraulic aplications and a motion controller for for example servomotors?

Peter did a good job of explaining this to me here

http://forums.mrplc.com/index.php?showtopic=7679

Karsten said:

What is the difference between a motion controller for hydraulic aplications and a motion controller for for example servomotors?

Click to expand...