Powerflex Trim PLC or Dancer

irondesk40

Member
Join Date
Jan 2008
Location
nc
Posts
630
Have some equipment we built a few years ago that we utilized the micrologixs 1400 plc and allen bradley powerflex 525 drives in.
Will refer to them as lamination machines. Currently running in production and working great.
What i did was have the line speed set from the HMI and run a master motor used to feed fabric. There are a total of two other motors on the machine and i am sending a analog signal from the plc to the master that corresponds to the correct value to run the master motor from 0-10 yards per minute based on the size of the rollers etc. All the motors are driving identical size rollers but on the two other motors running with the master motor i installed prox switches on a swing arm that we use as a dancer. If one prox gets made then i slowy increase the speed of that motor until it comes off the prox, if the other prox gets made i slowly decrease. All of this is done in the PLC and at 0-10 yards per minute works very well.
Now that we are looking at making the machine capable of running 0-100 yards per minute i am wondering if it may work better if used a inclination sensor that is programmable to give a 0-10v signal out and connect that directly to the powerflex drive and trim the powerflex speed directly in the drive. Is it possible to connect a sensor up to a powerflex 525 and use it to trim a analog master speed reference. If so, hopefully someone on here has already went through it and share which way you think would be best.
Thanks
 
I am afraid you will need to use the Architecture Class PF750 VFD family (at least for the 'Master') if intending to implement a Dancer/Follower application at drives' level without a PLC being directly involved.

The PF52x Component Class series cannot 'link' the value of its on-board Analog Output channel but to "drive conditions" (e.g. Output Frequency, Output Current, Output Power) and not to the value of an on-board Analog Input which could would constitute the 'classic' Master-Follower implementation.

You will need to 'read' the dancer sensor with a PLC Analog Input channel (or from the VFD as a Data Link if the sensor is connected to the Master's on-board Analog Input) and then Logix application compute and write to the 'Slave' VFDs the 'Follower' Speed Reference.
 
Last edited:
I'm not being critical, but I'm very curious... I don't understand this implementation of a very recent drive with a very old PLC. Why use a ML1400? Put a Compactlogix on this thing, use the 525's, and implement the whole architecture with Ethernet/IP. The very idea of using a 1400 and analog circuits makes me shudder. I lived through when that was "how you did it". I don't want to go back, why are you still doing it?
 
Do all the speed speed references to the drives come from the PLC? If so, i would take your analog input into the PLC and use a PID instruction from there. You can then scale the PID output to a range, such as -500 to 500 and add that count to metering/base speed reference to trim the speed. The other option is the scale the PID value to like .9 to 1.1 and multiply that with your base speed for your downstream motor. We do this process with load cells for feedback to control to precise tensions at 2500+ FPM.
 
You technically could pull this off with 525’s, but I’m unsure if the performance would be acceptable. Your tensioning drives would need to operate with the PID loops as it’s speed reference. The analog input from the dancer would provide the process value to the loop and you set point would be whatever the scaled value that equals the correct tension. When you give a start command to the drives everything must be at 0 speed command and you will ramp the speed command to the main drive slowly enough that the slave drives can respond. This will not give and feed forward to speed changes and will most likely not handle process disturbances well.

If this is a simple machine a 750 series architecture drive is probably overkill. But they will certainly work. I’ve used them and I’m definitely a fan

I would look I tothe 527 which is controlled similar to a servo using CIP motion. It’s the identical form factor to the 525/523. You will need to swap the PLC for a compact logix with motion control capability. This will probably get you the best performance for a moderate cost.

As far as your feedback device, an inclinometer can certainly work. If you’re already using a prox I would suggest investigating swapping it for an analog output model and attaching a cam in place of the flag. This is a static solution that you don’t have to worry about cable flexing.
 
Califflash
That’s not the way it works
The pid output adds typically +-10% to the slave drive speed reference
So if the dancer is in the center when starting, the master and the slave are going the same speed because both reference values are the same
If the dancer is at the bottom then the slave is receiving the masters speed reference plus 10 %
This is typical on a system like he has
 
JRW

I was referring to ‘exclusive’ control mode whereas I believe you are referencing trim control. Yhe exclusive control mode provides an internal speed reference to achieve a set point without an outside speed reference. The trim control takes two analog inputs and behaves the way you are describing. I forgot about this and couldn’t quickly find the spot in the manual.

That being said, my recommendation would be to use CIP motion with a motion axis gear (MAG) command to slave the axis to the master. This would be the easiest to troubleshoot, in my opinion, when there is an issue. Tying in HMI’s and tuning process response is a little easier also.
 
I'm not being critical, but I'm very curious... I don't understand this implementation of a very recent drive with a very old PLC. Why use a ML1400? Put a Compactlogix on this thing, use the 525's, and implement the whole architecture with Ethernet/IP. The very idea of using a 1400 and analog circuits makes me shudder. I lived through when that was "how you did it". I don't want to go back, why are you still doing it?

What he said.

You have a 525. Is it being used for safety safe-off?

We usually solve process control problems in a PLC vs. The VFD. I guess it would depend if your machine is merely a feed unit with no need for a PLC, then you could use vfd based closed loop.

But if this drive is a small part of a larger system then I too vote the ML1400 "Off the island"

My $0.02
 
thanks for the response. we built inhouse about 5 years ago around 140 production machines we are using in our plants and due to the budget the 1400 plc and a small maples hmi was chosen.
sometimes we make a modification to one of the units for testing and the option to replace the whole control system is not a option at the moment.

what i have done on a couple of machines that we added another drive and set of rollers to feed another piece of fabric into what i will refer to as the bunch to be laminated together was i used a inclination sensor and connected it back into the plc and used that analog input to trim the speed the fabric was being fed if it needed to be trimmed and it works great.

Now looking at doing something similiar to another one of the machines and was wondering if it would be best to do it the same with the inclination sensor connecting back to the 1400 analog input or connecting it directly to the drive since the speed of the whole system is now around 80-100 yards a minute instead of 10-25 yards per minute.

Since this is a current production machine was looking at maybe doing something different such as connecting directly to the drive since when we actually go to make the modifications it involves getting all the parts together, fly to central america, take the machine out of production and make the modifications in a weeks time and put it back into production.

Thanks
 
Last edited:
Do all the speed speed references to the drives come from the PLC? If so, i would take your analog input into the PLC and use a PID instruction from there. You can then scale the PID output to a range, such as -500 to 500 and add that count to metering/base speed reference to trim the speed. The other option is the scale the PID value to like .9 to 1.1 and multiply that with your base speed for your downstream motor. We do this process with load cells for feedback to control to precise tensions at 2500+ FPM.
.

Thanks for the reply Helliana. all of the motors, which is a total of 3 at the moment get the speed reference from the PLC. The master speed is set through the hmi which is small 7 inch maples hmi and output to the master drive after it is scaled in the 1400 based on the diameters of the rollers etc. what the master raw speed needs to be in order to run the master speed selected. The other 2 motors that are being fed fabric are then sent the raw analog value value that is required based on the diameters of the rollers they are turning in order to run the same speed as the master. This has worked very well for about 5 years on these machines. Have made some modifications to a few of the machines and had to add another drive and rollers etc. to feed another piece of fabric into the machine and put a dancer arm with a flag and a couple of prox switches to detect if that fabric was needing to be run faster or slower. I did it quick and simple and used the two inputs from the switches to determine if i needed to increase or decrease the speed that motor was running +_10 percent. Since it is only running about 10 yards per minute it works very well, but since this machine we are looking at making a modification to now will need to run at about 100 yards per minute i thought maybe connecting a inclination type sensor directly into the drive as a trim feedback might work better, but at the moment since it is the lowly 1400 plc i think i will just do the trim in the plc. At least that way i can modify the values i need to trim it by through a set up screen in the HMI if needed.
Thanks
 
I am a firm believer in doing as much of the control in the PLC as possible. We usually always have a newest copy of the PLC program, but usually don't have any drive parameters modifications saved when a drive fails. Also, its easier for maintenance technicians to see what is going on in the PLC than dealing with some of the more obscure drive parameters.
 

Similar Topics

I have a PowerFlex 40 with a 0-10VDC analog in for the main speed reference. I also have a 4-20 mA signal set up for Setpnt Trm (A312=5)and...
Replies
3
Views
5,523
New to vfds. I put in parameters. IP, but I get ethernet flashing and link solid. What did I do wrong?
Replies
0
Views
10
Are the N files in the 525 the same as the 40p for ethernet? (E-Comm card) I have used 40P with Micrologix 1400 Messaging but don't see the N...
Replies
1
Views
63
How to remove faceplate from power flex 753 and not shutting the system down. What parameters should i change?
Replies
1
Views
77
Hey all, I am currently working on a depalletizer for a customer and we are doing a hoist upgrade. This is a SLC500 processor and the drives are...
Replies
6
Views
188
Back
Top Bottom