Kinetix 5500 Homing - Unconventional

Sensorless

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Feb 2021
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Ontario
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Hi all, this is my first post here so please bear with me.

I am retrofitting a ballscrew and slide with a Kinetix 5500 system. The system will have one home sensor, should of been no issues.

The problem I have is that the home sensor was wired to a PLC input and not the input on the Kinetix drive and unfortunately the PLC and the drive are in separate areas.

I am wondering how I would go about homing the drive, I have come up with two options:

1. Issue a MAH and once the home sensor is triggered use an SSV to write to Axis1.DigitalInputs.1

2. MAJ to home sensor, MAS once home sensor is reached, MRP to set the home position

I have been combing through several of the motion/kinetix manuals to try and come up with a solution so any imput is greatly appreciated.
 
Steve Bailey said:
Why not just rewire the home sensor to the Kinetix drive?
Click to expand...

One problem with the K5500 is that you only get 2 inputs, so if you have positive and negative over-travels, those chew up the inputs. We use the negative over travel as the home as well. There is a hack where you MSG the drive to change the selection of the input. So when our machine is running, we MSG it to a overtravel and during homing, we MSG it to a home input.

That being said, OP, if you are rolling your own home, you probably wouldn't use a MAH, you would use motion instructions (MAM/MAJ) to position you system onto the home input, then use a position redefine instruction to zero out your position, or whatever position value you want.
 
dmroeder said:
One problem with the K5500 is that you only get 2 inputs, so if you have positive and negative over-travels, those chew up the inputs. We use the negative over travel as the home as well. There is a hack where you MSG the drive to change the selection of the input. So when our machine is running, we MSG it to a overtravel and during homing, we MSG it to a home input.

That being said, OP, if you are rolling your own home, you probably wouldn't use a MAH, you would use motion instructions (MAM/MAJ) to position you system onto the home input, then use a position redefine instruction to zero out your position, or whatever position value you want.
Click to expand...

OK that's what I thought originally, use a position redefine. However, do you see any reason why I couldn't issue a MAH and use a ssv to write to the drives digital input? Little bit of trickery...lol
 
Sensorless said:
OK that's what I thought originally, use a position redefine. However, do you see any reason why I couldn't issue a MAH and use a ssv to write to the drives digital input? Little bit of trickery...lol
Click to expand...

If you can successfully trigger the input via SSV (never tried that), then sure, you could home it using a MAH. If you have homing setup to reach the home input, then move off of it, you will have to set the input, then "unset" it. Not sure what precision you are looking for, I'm sure there is some time difference using your method vs having the input directly wired to the drive, just keep that in mind...
 
Sensorless said:
OK that's what I thought originally, use a position redefine. However, do you see any reason why I couldn't issue a MAH and use a ssv to write to the drives digital input? Little bit of trickery...lol
Click to expand...
I've not used that device specifically, and have no understanding of what process the SSV uses to set the digital input status, but I'd be wary...

Let's say you're talking a scenario where you want to pretend a PLC's digital input has turned on. You can just use an OTE to write to that input tag, and the PLC will happily do it. The input will be on, as far as the PLC and its subsequent logic is concerned. Until, that is, the PLC updates its input image from the physical input card, at which point it will note that the physical input is off, and turn that input tag off to match. Since I/O is updated asynchronously to the program scan, this could happen at any time. So, let's say that when this input is on, I want to increment 10 counters. I do some trickery and tell the PLC that it's input is on (even though it's not), and then the logic starts incrementing those counters. Halfway through, however, the input image is updated and the input is turned off. So now half my counters will increment, and half won't. They'll be out of sync.

I don't know for sure, but I'd be concerned that the same thing could likely happen with your drive. You issue an SSV, but then at some point the Kinetix will read the status of the physical input and turn it back off. Did your homing operation complete before that happens? Maybe it will, maybe it won't. You might end up with a solution that works most of the time, but occasionally does not.

Again, purely speculation because I've not worked with that specific drive before, but I'd have some reservations about doing it that way. I'd be more leaning toward the other posted solutions.
 
ASF said:
I've not used that device specifically, and have no understanding of what process the SSV uses to set the digital input status, but I'd be wary...

Let's say you're talking a scenario where you want to pretend a PLC's digital input has turned on. You can just use an OTE to write to that input tag, and the PLC will happily do it. The input will be on, as far as the PLC and its subsequent logic is concerned. Until, that is, the PLC updates its input image from the physical input card, at which point it will note that the physical input is off, and turn that input tag off to match. Since I/O is updated asynchronously to the program scan, this could happen at any time. So, let's say that when this input is on, I want to increment 10 counters. I do some trickery and tell the PLC that it's input is on (even though it's not), and then the logic starts incrementing those counters. Halfway through, however, the input image is updated and the input is turned off. So now half my counters will increment, and half won't. They'll be out of sync.

I don't know for sure, but I'd be concerned that the same thing could likely happen with your drive. You issue an SSV, but then at some point the Kinetix will read the status of the physical input and turn it back off. Did your homing operation complete before that happens? Maybe it will, maybe it won't. You might end up with a solution that works most of the time, but occasionally does not.

Again, purely speculation because I've not worked with that specific drive before, but I'd have some reservations about doing it that way. I'd be more leaning toward the other posted solutions.
Click to expand...

Thanks ASF, that is a good point to consider and does make sense.
 
Drive and PLC are in different areas, running a new cable cost $$ when I know there is a way to perform the homing with the current wiring.
Click to expand...
The function of homing is to move the mechanism to a fixed,repeatable position and establish that position in the axis controller. You have to balance the cost of rewiring against the cost of the inaccuracy introduced by your alternate homing procedure.
 
Rockwells Knowledgebase article QA28637, called 'Overtravels as Home Inputs on Kinetix 5500 Drive', describes how to use an overtravel as a home sensor. Messaging is used to change the input configuration. Change it to an home input just prior to the MAH and then change it to an overtravel after homing is complete. I have used it a couple times now and I am currently working on a system with many K5500 drives.

It was a cheap move of AB to provide only two inputs to the drive.

Some tricks:
- Configure the one input as a 'Home' in the drive setup. I have not been able to change it to a 'Home' input if it is configured as an overtravel input. This also means logic is required to verify that the input is set as an overtravel when used with an multiturn absolute encoder.
- Adjust the homing value and homing offset as needed to make the system behave properly especially if softlimits are used.
 
Maybe I missunderstand the issue, but if your Home input sensor is wired to your PLC, you can use the MAH instruction triggered by the Home sensor.
When you configure your Kinetix 5500 in the Home Tab to Immidiately, it will define the actualy position to be the home position.
If you want your axis to search the home sensor, just jog (MAJ instruction ) to the sensor with a low speed. When the sensor is hit stop the Axis ( MAS instruction ) followed by a MAH instruction.

Regards, Jack
 
nightline said:
Maybe I missunderstand the issue, but if your Home input sensor is wired to your PLC, you can use the MAH instruction triggered by the Home sensor.
When you configure your Kinetix 5500 in the Home Tab to Immidiately, it will define the actualy position to be the home position.
If you want your axis to search the home sensor, just jog (MAJ instruction ) to the sensor with a low speed. When the sensor is hit stop the Axis ( MAS instruction ) followed by a MAH instruction.

Regards, Jack
Click to expand...

Thanks Jack, I also was wondering about this and was going to try it. I am assuming I would also use passive instead of active homing as I would initiate the move with logic instead of the drive initiating the move?
 

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