Allen Bradley Servo programming tips and examples

[jtashaffer]

My company is about to adventure in to servo motion. I have never programmed them and I am just looking in to it. I am just looking for any tips or program examples. Which types of Allen Bradley compactlogix controller to use etc. I am under the understanding that you have to use a special processor but what about the input and output cards? Any info you can throw at me.

 

[jtashaffer]

I mentioned above about the motion processor. With that you also have to have a servo drive to go along with the setup? Motion able processor, motion servo drive and a servo motor right?

 

[jstolaruk]

A few of the CompactLogix processors don't support motion; for instance the 1769-L33ER doesn't but the 1769-L33ERM does. Just something to be aware of.

I/O cards are not an issue.

 

[lostcontrol]

All depends on what type of motion you want to do, indexed or interpolated?
You may not need a high end CPU (even though it gives you so many more options...)

 

[seth350]

I will give you my take on AB servo drives...

Kinetix 300
-"Dumber" PLC can control it (Micrologix over ethernet using MSG insctructions)
-The drive is the motion planner
-Control using a Compactlogix is much like controlling a Powerflex over ethernet
-Capable of using discrete inputs to control the drive, while having all your motion indexes saved inside in the drive. This is setup via the drives built-in webpage. This means you dont need a PLC to control it, if you dont need it.
-Very reliable drive and cheap for small projects.

Kinetix 350
-Must have a Motion PLC, noted by "1769-(E)Ethernet(R)Ring(M)Motion"
-The PLC is the motion planner and you program using Motion instructions.
-No webpage setup, still has discrete I/O but mainly used for homing sensors, positive/negative overtravel sensors.

As far as which one to use for a beginner...
I would say go with the Kinetix 300, they are easy to setup and like I said if you have controlled a Powerflex over ethernet, then you will be comfortable with controlling the Kinetix 300.
The Kinetix 300 will do just about anything the Kinetix 350 will, except with a lot more effort on your end.

 

[jtashaffer]

What is indexed and interpolated? Indexed I am sure is move forward

 

[seth350]

What is indexed and interpolated? Indexed I am sure is move forward

The term "index" in the motion world is a type of move where the servo motor takes a position command, velocity command, max accel, and max decel and moves using that profile one time. It also applies to "Absolute positioning" and "Incremental positioning".
Absolute = A position command referenced from a homed position (usually zero).
Incremental = A position command referenced from its current position.

So if your servo was looking at a tape measure and it was sitting at "zero", and the servo was in absolute mode.
If you told the servo to go to 24", the servo would go directly to 24" and stop. If you told it to go to 13", it would reverse and go directly to 13". The motion planner knows that 24" is greater than its current position, so it knows to go forward. The planner knows 13 is less that 24, so it reverses to go to that position.

So now say your servo is in incremental mode.
Starting with your servo at zero, you tell it to go to 24". The servo will move 24" then stop. So far so good right? Then you give the same command of 13", the servo will then move another 13" in the same direction. Now the servo is at 37".

In this mode, the planner does not care what position command you give it. All it cares about is in what direction it should make the move and how far it should go. You do this by giving it a positive command (forward) or a negative command (reverse).
So, your servo is sitting at 37". You give it a command of -13, the servo will then subtract 13 from its current position of 37 and return back to 24". If you gave the same -13 command again, the servo would be at 11".

All of these moves are considered "indexes".


Interpolated is a mixture of moves or indexes being done by two or more servo drives. One of the servos being a master and the others being slaves.

Think of two trucks, truck #1 is traveling down an interstate at 70MPH and truck #2 is approaching an on ramp at 40MPH. The trucks need to meet at the merging lane at the exact same time. Their speed needs to be interpolated or communicated in order for truck #2 to meet with truck #1 at the merge lane. Where truck #1 will not change speed, truck #2 will speed up on the on-ramp to catch up to truck #1.


If you want more tailored info and can share, let us know what kind of servo motion you are looking at. Will it need to just index back and forth? Or, will one servo need to know what the other is doing so they dont crash?

 

[jtashaffer]

It will be on a stacking machine for ingots. It will have a main head that picks the ingots up and then travels to the stacking table. Before that it will rotate every other one.

 

[Archie]

The Kinetix 300 will do just about anything the Kinetix 350 will, except with a lot more effort on your end.

I would say this really isn't true if using simple point to point (indexed) on independent axes and using CompactLogix controllers. Once configured with the web interface and setup on Ethernet/IP, there is no need for MSG instructions and moving is very simple. Simply write the accel, decel, velocity, and position with move instructions, then set the bit to start the move.

 

[Donnchadh]

Hi

I not a big fan of the 300 or the 350 drives. It has a look a feel that they are not Allen Bradley servo drives. I have been using motion with ab since ver 6 and I have always found the motion very good until I used these. The new 5500 and a compact logix I think would be easier as I found the tuning on both the 300 and 350 to be a bit poor.
As you are doing a lifting motion about what weight are you lifting and what is the over distance you will be travelling and then what is the cycle time you would like as maybe some camming might work
Donnchadh

 

[seth350]

I would say this really isn't true if using simple point to point (indexed) on independent axes and using CompactLogix controllers. Once configured with the web interface and setup on Ethernet/IP, there is no need for MSG instructions and moving is very simple. Simply write the accel, decel, velocity, and position with move instructions, then set the bit to start the move.

You are correct sir, what I intended was that if you needed it to do any more than point to point, then it would take some more programming effort than the 350.

The 5500 would be a very good choice if you are also going to have to control the speed of induction motors as they can pull double duty as either run a servo or an induction motor.

So you have three servos and probably a fourth in order to move side to side. I would imagine that you wont be stacking them in one tier but on some sort of "pallet".

Of those three and the possible fourth,
X- Fourth servo
Y- Traversal
Z- Up & Down
R- Rotational

You can program this as either coordinated or simple point to point.
The differences will be that coordinated will give a shorter "time of flight" and generally be smoother. Point to point motion will give a little longer "time of flight" and less fluid motion. That is, if you only move one axis at a time.
Your real efficiency comes from moving more than one axis at a time, so that goes back to how long your cycle times should be.

 

[jtashaffer]

The input will be around 20 to 25 a min

 

[seth350]

Ok, so the unit has anywhere from 2.5 to 3 seconds to complete each ingot.
What is the distance needed to travel and weight?

 

[jtashaffer]

About 2 ft. It will move 7 ingots per layer.

 

[seth350]

Running those numbers didn't give good results from atleast what I put in.
Running motion analyzer and creating a profile to move 100lbs:
Clamp -> Lift -> Travel -> Lower -> Unclamp -> Lift -> Travel -> Lower

A servo to just do the lifting motions could be realized if your input wasn't so high. You are ultimately giving the servo 0.4secs to complete each move. Trying to use a VPL motor with 5500 drive would put the power level at 100%, Peak Torque: 92%, Peak Speed 80%, and Inertia ratio at 2.25. The inertia would be best below 1.00, but you would be maxed out on all other aspects. Which is fine as long as you don't want to ever
move more than 23-25 ingots a min.

This was calculated with a 1" lead ball screw with a 3" drive sprocket on servo motor and 2" driven sprocket on screw.