Ultra 3000 Sercos ControlLogix System

[Patriot 0]

I am pretty new to the ControlLogix platform, and I am working on a project where I am responsible for software development, and the customer is configuring/wiring hardware. I was a little puzzled by the customer's insistance on connecting overtravel limit switches to digital inputs on the ControlLogix PLC, rather than directly to the Ultra 3000 drive, which is a SERCOS model 2098-DSD-HV150-SE. My thinking is that if the hardware overtravel switches are connected to the drive, I then simply ready their status back to the PLC via SERCOS (for example via tag BIG_SERVO.PosOvertravelInputStatus). If they are wired to the PLC, I think I lose all of the benefit of connecting the overtravel switches to the drive, such as configuring the overtravel properties and fault actions within the servo configuration. I also am not sure how I would send the positive and negative overtravel switch information back to the drive over SERCOS so that the overtravels performed as if wired directly to the drive. The customer also wants to wire the homing switch to the PLC rather than the drive. I know that it would be possible to connect PLC discrete outputs back to the drive for the overtravel and home switches, but it seems silly to do that sort of hardwiring, when the overtravels could be hardwired to the drive, and the PLC could get the switch status over SERCOS. They claim it is for troubleshooting. I say that I can have indicators on a PanelView that show the overtravel status whether the data is hardwired or through SERCOS. The customer has also NOT provided wiring from PLC outputs back to the drive to allow this "chaining" of the switch info. Is there a way to send switch status back to the drive from the PLC over SERCOS? I don't see that type of functionality. Like I said, I am pretty new to this platform, but would appreciate any comments from the more experienced.

[gmferg 1]

You are absolutely correct. The proper way is to wire the overtravel and home inputs to the drive. These can be read directly in the PLC over SERCOS just as you described and be displayed on an HMI. Trying to wire to the PLC and then sending the info to the drive is not as clean and you lose the benefits of programming drive to do what you want when these inputs are triggered. Plus, there is a bit of added time since the PLC has to read the input and then perform some motion instruction to the drive.

[Patriot 0]

Thank you. When I looked at the controller tags defined for the drive (under the type AXIS_SERVO_DRIVE), I just did not see anything that would allow me to write data from the PLC to the drive. I saw lots of status data that I could read. I am trying to form an intelligent response to the customer, and wanted to be sure I was on the right track. The drawings also show an upper home and lower home switch wired to the PLC that are to be used as "home" switches for the servo. The ability to define home at the top or bottom is desired. From what I see, there is only one home sensor input on a SERCOS Ultra 3000, so these switches would have to be wired in one at a time, and the drive would have to be setup for whichever home is defined. Edited 22 Apr 2008 by Patriot

[hbamos 0]

I have alot of experiance with the ab kinetix system and this is really no big deal and have seen this done both ways. You cannot write to the status bits in the drive. How you go about this is by issuing a MAS or an instintaious home once a prox or limit is tripped. I Have some logic to show how this works if I can find it. I personnaly have mixed oppinions wither way but prefer to use the internal I/O in the drive over PLC I/O. However If you are planning on using soft limits or if their is a posibility of the cust shutting the enable off the the dive in an overtravel situation using the drive I/O you are in for a real treat. The drive once re-enabled if locked up as if in a pysical axis fault no matter what direction you want to go in. The solution is to use some logic to detect the overtravel and direction. Then turn off the hard or soft limit, rest the drive, make a short move and then turn the soft and/ or hard overtravel dectection back on, In AB;s knowledge base keyword "soft-overtravel" described how to do this. They over did thier logic but basically both types of overtravels work the same way and are corrected the same way. And just so their is no confusion this "lock-up" actually it a Phsical Axis fault only stops the drive cold if enable is removed while in a O/T condiction, the drive can be moved and rest normally as long a enable is not lost. hope this helps.

[Patriot 0]

I would love to see an example of how to recover from the soft overtravel. I could not reset the fault code on my Ultra 3000 SERCOS. I had to go in to RSLogix5000 and disable the software overtravels so I could reset the drive and jog it away. Then I could go back to RSLogix and re-enable soft limits. Looking for an alternative to that.