Linear Encoder Motion Control Allen Bradley

[konableurocks]

Hi, I have an application that currently utilizes SEW drives and programming that we are attempting to convert to Allen Bradley CompactLogix and PF drives. The application makes use of an incremental linear encoder to perform accurate cuts within 2-3 mm. This is the first time I am working with CIP motion control on Allen Bradley, my idea was to connect the linear encoder to the HSC on the CompactLogix and utilize CIP motion capabilities of the PF755 to send instructions on where to travel to from the HMI. However, when attempting to configure CIP motion I do not see any way to set up a 3rd party linear encoder. Am I missing something? What would be the best way to do this?

 

[JTCat]

Look on the manufacturer website for an AOI. Or contact them. That’s the first step. 3rd parties usually have EDS files and AOI’s if they expressly support AB hardware.

 

[konableurocks]

The current linear encoder on the machine is an AMO encoder. Part of the reason were are wanting to convert to Allen Bradley is because we are having hard time reaching manufacturers of both the machine and the encoder. I can understand how to get the encoder into the PLC using the the HSC inputs, but I cannot seem to get it to act as the motor reference for CIP motion.

 

[JTCat]

I understand now. First, please do the checks with the manufacturer. What version of studio are you using? How are you trying to use the encoder feedback? If this is brand new to you then it will help you a ton to walk through this from step 1. We are here to assist.

 

[konableurocks]

I am using Studio 5000 version 32.03.00 - Professional Edition. I have used it to create an HMI screen where the operator can enter measurements in inches to cut a cardboard tube to. I was planning on taking this measured setpoint, converting this to encoder counts and sending this count information to the positioning drive. Effectively what I want to do is PID control using encoder counts, however, I was asking if this was possible using CIP motion in the Allen Bradley system or if I just needed to utilize and write separate PID logic.

 

[JTCat]

Are you using position as a feedback or as a starting point? Sorry I’m native Armenian speaker so English isn’t my best. Are you going to tell the motor to run until x+y has been satisfied or start at X and run a known duration that will arrive at x+y? Or are you going to use the encoder all the time? What triggers the input that says run for y distance? The encoder or a sensor?

 

[Ken Roach]

It sounds like your architecture is a little hinky. A-B High Speed Counters are rate and count accumulating devices, not CIP Motion axis feedback devices.

Let's talk about the motors and encoders and drives a little bit.

Is your motor a servomotor with an integrated encoder feedback built into it ? Or are you using a more ordinary induction motor ?

Is there an encoder built into or attached close to the motor shaft itself, or is the linear encoder on the mechanism your only form of position feedback ?

Is your AMO linear encoder an incremental or absolute device ? What kind of signal does it put out ?

Are you using a ControlLogix, or a CompactLogix with an "M" in its part number ?

"I want to use a VFD and a counter card and write my own PID motion" is not a great way to approach a motion control system. I won't say you will never get satisfactory results, but there's a reason that motion controllers aren't just PLCs with discrete and analog I/O.

 

[konableurocks]

Is your motor a servomotor with an integrated encoder feedback built into it ? Or are you using a more ordinary induction motor ?
Current motors are SEW gearmotors

Is there an encoder built into or attached close to the motor shaft itself, or is the linear encoder on the mechanism your only form of position feedback ?
The gearmotors are fitted with an encoder placed close to the shaft, however, the carriage that it travels on is on a belt and pulley, we attempted to run it with only this encoder but the cuts were far outside of our desired tolerance ranges. The linear encoder appears to be the most accurate.

Is your AMO linear encoder an incremental or absolute device ? What kind of signal does it put out ?
It is an incremental TTL encoder device. The old tape became damaged and we had to replace it, issue was that our storeroom didn't stock the correct part and got an encoder tape without zero points. This led us to try and adapt the SEW code to refence off of our overtravel cam, however, we were unable to do so and could not reach proper support from the manufacturer.

Are you using a ControlLogix, or a CompactLogix with an "M" in its part number ?
Current plan was to buy a 1769-L27ERM-QBFC1B as this would have the sufficient amount of I/O and the ethernet capabilities to communicate with the drive and HMI.

The old system just took the linear encoder feedback and sent it to the SEW drives which then instructed the gearmotors to arrive at a certain point. Issue is the programming is in French and I had great difficulty translating and understanding it English. Hope this helps.

 

[Ken Roach]

Thanks for that information and detail !

You might be able to connect that linear encoder to your PowerFlex 755 as an outer position control loop.

https://rockwellautomation.custhelp...7814/~/powerflex-755-dual-loop-position-setup

How many pulses per revolution are the encoders fitted to the gearmotor tailshaft ? A higher resolution encoder might help your positioning accuracy.

 

[konableurocks]

We believe that this inaccuracy is due to belt slippage, unsure if a higher resolution encoder would help. We were also discussing the possibility of utilizing a SICK laser instead of the encoder. We aren't really concerned with the speed of the positioning, more with the accuracy, if it takes a longer time but it repeatable within 1-3mm then we have no issues. Possibly we could just send digital inputs to the drive with jog and crawl commands in the respective directions.