PowerFlex 525 Positioning

Hi all,

Just looking for some advice and feedback from anyone who has used a PowerFlex 525 for simple positioning control.

We have an application where we have a flighted conveyor which we are placing empty containers onto. We need to index this conveyor a set distance or flight every move sequence (lets say exactly 300mm for simplicities sake), to put these containers underneath a filling head.

I've been told a PF525 with encoder is suitable for this task, as it can be put into position mode and told to increment this distance, however I'm concerned with the accuracy or accumulative error that may occur as I can't find any information in the manuals or on the knowledgebase about what type of accuracy can be achieved.

I've been told verbally by one of our distributors that accuracy to within half a motor revolution can be achieved, which if coupled to a high ratio gearbox may not equate to much on the drive end. I am not completely sold on the idea.

This is a retrofit to an existing system and trying to avoid going to a servo drive/motor at this stage.

Interested to hear peoples opinions.

Cheers.

We have this exact set up running in our plant, two applications. Both applications are built the same, SEW motor/gearbox with an incremental encoder mounted to the motor shaft, there is also an auxiliary fan that is a must if we don't want to fry the encoder and motor. The encoder is connected to the drive via an add on encoder module.

One application is a conveyor belt that we are very capable of stopping at a desired point. In Inches! I can adjust it to at least 1/2" accuracy very easily, I should mention though there is very little load on the belt. This is a 1HP motor and moves relatively easy at low torque.

The other application is a gantry that moves on rollers. Its a moving carriage with a belt drive system and the belt drive system is ran by the very same SEW motor and gearbox as on the conveyor application. This one also incorporates a motor brake as the motor needs a little more speed to keep moving the gantry until the stop location is reached, then quickly apply the brake, its a little more of a sudden stop than desired but if you slow the motor down just a little early than it might stop just shy of its mark and cause a position error in the drive. It works well for us but I think the motor is just a wee tiny for the application.

In either case it seems to work out well. We did have some fiddling with the gantry application as any brake troubles can seem as though you are having encoder troubles at first. There was some learning necessary but overall its a pretty simple setup that I will likely recreate again.

It's all in the gearbox....you'll need a high precision gearbox to eliminate accumulative error. I've done this application many times with various powerflex series, usually the 7 series, but see no reason a 5 series won't work if it has positioning control.

With that said, if your application is as simple as moving a fixed distance every time, or putting a box in place, why aren't you just using a prox or photoeye? Move the conveyor with multiple pickups to a prox, or move the box off a photoeye.

Instead of dealing with an encoder, just detect the flights on the belt with a sensor.

The reason for using encoders on a belt is because a flat belt has no frame of reference.
Your application is ideal because your reference point for positioning are the flights and they are easy to detect.
In addition belt stretch, tension, sag, windup, may affect encoder based positioning (if its a long belt). Detecting flights will be spot on every time... and is not affected by any wear or physical characteristics of the belt or drive train.

The reason why you will not see anything on the positioning accuracy of a PF525 is because even with the encoder input, it is a VELOCITY vector control drive, not a positioning drive. The mP does not have the processing power to do motion control level positioning, it does not even do full on Torque control. You need a 7 series for either of those functions. That's why the 520s are cheaper...

That said, the 525 has an "Indexing" function that uses the encoder pulses in what it calls "Step Logic Positioning". it is described in detail in Appendix E of the manual. It is actually very accurate and there is a way to do a "homing" reset, which you could do with each "step" to maintain accuracy, but would require that sensor input. The caveat to this is however that it cannot do high torque starts and braking for the kind of accuracy you would get with a true positioning control capable drive, for the reasons I stated above.

Here is how it is worded in the manual:

The PowerFlex 525 drive includes a simple position regulator which can be used in a variety of position applications without the need for multiple limit switches or photo-eyes. This can be used as a stand-alone controller for simple applications (up to 8 positions) or in conjunction with a controller for more flexibility.
Please note that this is not intended to replace high end servo controllers or any application that needs high bandwidth or very high torque at low speeds.

Click to expand...

Thanks for the replies and information so far.

I suppose I should have added some more context to the original post.

This machine is actually an existing machine that is being refurbished/repurposed. It currently has a B&R controller and servo drives/motor doing the exact function I described. Our client is making significant modifications to this line and the machine is being pulled apart, and we are only keeping this indexing conveyor as part of the new process.

So I guess what prompted my original post was that currently there is a servo doing this indexing function (going by position, not by detecting the flights), and as the new process has an AB controller we were having the discussion with our distributor whether we should go with servo control or whether a PF525 with encoder would be adequate for the task.

In saying that, I've just found out that this indexing conveyor could be required to do up to 90 cycles per minute (which is the theoretical max speed of the filling head) which now makes me think with this type of cycle time I should be disqualifying the PF525 idea altogether.

There just doesn't seem to be much information or application notes / real world examples on the position capabilities of the PF525, and our distributor can't give me a definite 'yes this will work' answer, hence my queries here.

I think we will now be going with a Kinetix 300/350 for this application, but am still keen to hear peoples stories or opinions on the PF525's capabilities.

Cheers.

Yeah, 90 / min., I would use a servo.

Hi,

I try to use PF525 in positioning mode for almost the same application like Brendan has described. My application requires to move the belt for 350mm in about 1.2-2.5 sec. The encoder has been placed on the drive shaft (not on the motor) and connected to PF525 exactly like in the manual. The drive was configured for the positioning mode, but I could not find any information how to implement it in control program ( CompactLogix controller v28). Has anyone can share some sample code? When I switch the drive to standard mode and run it, I can read the velocity from the encoder but in positioning mode it doesn't work, the drive is running with 0 Hz.

I will be pleased for getting any advice.

Cheers

Similar application/question

Hi all,

I was about to post a new topic but decided that replying to this "old" one could be a good option and involve some experienced members.

I a looking for a simple and cost-effective solution (OEM application, need to lower cost) for driving 3 motors :

1st motor needs to precisely run at x speed (encoder feedback)
2nd motor need to follow precisely 1st motor with a ratio (dynamic, from a variable) (y:1 ratio)
3rd motor need to follow precisely 2nd motor, stop for let's say 20degrees rotation (dynamic, from a variable) and resume following 3rd motor speed.

So far I though about doing speed following for 1st and 2nd motors with encoders and PM motors as per Rockwell KB QA20549. The only problem is I am not sure how to achieve the dynamic radio. This example is for a 1:1 following between the 2 motors.

Then on the 3rd motor I thought about either a PM motor again with a PF525 or a servo motor Kinetix 3.

I am planning to use a Micro850 PLC. Again, I would like to find a cheap solution while having a certain amount of precision.

Any guys have this kind of experience on an application ?