I wonder how are you dealing with an issue that Im dealing with from time to time. Currently, Im working on a NGS library prep and need to put a plate on magnet like this:
Of course, the issue here is that, on the magnet, the deepwell plate im using doesnt stand on the rim as usual, but on the wells, which lowers it approximately 2mm from where the VWorks expect it to be based on labware definition and a teachpoint.
Easiest way to handle this is just to fork the profile, teach the magnet lower and associate with new device file, specific for this protocol.
While this works just fine, it gets cumbersome over time managing many profiles and device files, especially on multiple Bravos. I think the intent of creators of Bravo was to have one profile for one Bravo configuration, and handle the rest in protocols.
I already tried task.distancefromwellbottom, but VWorks wont let me make it less than 0. I am also considering using plate.labware, and changing the labware on the magnet to account for the offsets - here I think I will have problem with gripper offsets when moving the plate to and from the magnet.
I feel like there should be some more elegant solution, but cant figure it out. Wondering how others are dealing with this, Im sure this is a common thing.
Are you concerned with the place plate step to loc 7 or with pipetting?
As you surely know we typically use the Twin Tech PCR and the Deep Well with the same Z teachpoint at loc 7. What changes is only the default DFWB which is 0.15 for the PCR and 0.85 for the deep well plate. If you can survive with just one Z teachpoint for all your labware, then changing the task.Distancefromwell bottom will not be an issue. No negative values, you are right, but if you teach a little lower then you can always have positive values for this parameters.
In the protocol you could easily create a function (say, getDFWB) that gets the labware and returns the DFWB so that all your ASP and DISP on the magnet can be set with
task.Distancefromwellbottom = getDFWB(myLabware)
where myLabware contains the labware type.
To me this is better than changing the labware entry, which potentially is used in other protocols, too.
For the pipetting, this is surely a good way to do it. Just the teachpoint has to be low enough. You are right that the teachpoint is likely improperly set on this machine.
And how do you work with gripper? If I would like to have one profile, used by different protocols where in one I use Twintech PCR on the magnet and in second I use deepwell, it seems to me with one teachpoint there will be an error (0.7mm in this case) for at least one of the plates, no? Either dropping it or pushing into the platepad.
The gripper can handle a small discrepancy probably, but I like to fine tune things when possible.
Try with Z-teachpoint (magnet) = Z-teachpoint (center of the plate pad cross) - 29.6 (for Agilent magnet). This usually works well for both deep well and PCR. No probs when placing both plates on the magnet with the gripper. The different in the DFWB depends on the different way the plates sit on the magnet.
