OT Flex: Gripper Force

hkjawn · September 24, 2025, 5:33pm

Hello everyone!
Does anyone know how to adjust the gripper force on the Opentrons Flex?

in the API docs I see that there’s close_gripper_jaw(self, force: Optional[float] = None)

Does this mean I would have to control the gripper step by step instead of using move_labware()?

Another thing I tried was adding the gripForce parameter to my labware’s definition, based on this page

However, when I make that change the Opentrons app says that my labware definition is invalid. (I checked my JSON using JSONLint and it said that the file itself was valid!)

I do notice though, that the labware definitions on github don’t have gripForce in their JSON files despite it being mentioned as a parameter on the website.

PS. I also tried adding gripForce as an argument in move_labware but it didn’t work haha.

MeghanFerzoco · September 24, 2025, 6:43pm

Hey, RobotContext.close_gripper_jaw gives this control

Here’s the documentation. Let me know if this helps or if you need more clarity here!

Shinedalgarno · September 29, 2025, 11:16am

Hello there @hkjawn

I think you’re correct in your assumption that you would need to control the gripper step by step here instead of using move_labware (which personally I think is kind of silly, it should be included in the move_labware function)

I can get

protocol.robot.close_gripper_jaw()

to at least simulate, but when trying to use build_axis_map (which seems necessary to move your gripper around like this) I cannot seem to figure out what goes into the “location” parameter.
eg.

protocol.robot.axis_coordinates_for(“gripper”,plate)

One would assume it would be a labware object or a deck location, but it appears to be neither

I may be missing something obvious though, maybe opentrons could respond @MeghanFerzoco? It would be nice to have a code example of this functionality

MeghanFerzoco · September 29, 2025, 12:34pm

Happy to help. Here’s a code example using custom labware:
{
“ordering”: [
[“A1”, “B1”, “C1”, “D1”, “E1”, “F1”, “G1”, “H1”],
[“A2”, “B2”, “C2”, “D2”, “E2”, “F2”, “G2”, “H2”],
[“A3”, “B3”, “C3”, “D3”, “E3”, “F3”, “G3”, “H3”],
[“A4”, “B4”, “C4”, “D4”, “E4”, “F4”, “G4”, “H4”],
[“A5”, “B5”, “C5”, “D5”, “E5”, “F5”, “G5”, “H5”],
[“A6”, “B6”, “C6”, “D6”, “E6”, “F6”, “G6”, “H6”],
[“A7”, “B7”, “C7”, “D7”, “E7”, “F7”, “G7”, “H7”],
[“A8”, “B8”, “C8”, “D8”, “E8”, “F8”, “G8”, “H8”],
[“A9”, “B9”, “C9”, “D9”, “E9”, “F9”, “G9”, “H9”],
[“A10”, “B10”, “C10”, “D10”, “E10”, “F10”, “G10”, “H10”],
[“A11”, “B11”, “C11”, “D11”, “E11”, “F11”, “G11”, “H11”],
[“A12”, “B12”, “C12”, “D12”, “E12”, “F12”, “G12”, “H12”]
],
“brand”: {
“brand”: “NEST”,
“brandId”: [“402501”],
“links”: [“96-Well 0.1ml Full skirt PCR Plates China Manufacturers Suppliers Factory Exporter”]
},
“metadata”: {
“displayName”: “NEST 96 Well 100 µL Vacuum Collection Plate”,
“displayCategory”: “wellPlate”,
“displayVolumeUnits”: “µL”,
“tags”:
},
“dimensions”: {
“xDimension”: 127.76,
“yDimension”: 85.48,
“zDimension”: 15.7
},
“gripForce”: 15,
“gripHeightFromLabwareBottom”: 10.65,
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“diameter”: 5.34,
“totalLiquidVolume”: 100,
“x”: 113.38,
“y”: 29.24,
“z”: 0.92
},
“G12”: {
“depth”: 14.78,
“shape”: “circular”,
“diameter”: 5.34,
“totalLiquidVolume”: 100,
“x”: 113.38,
“y”: 20.24,
“z”: 0.92
},
“H12”: {
“depth”: 14.78,
“shape”: “circular”,
“diameter”: 5.34,
“totalLiquidVolume”: 100,
“x”: 113.38,
“y”: 11.24,
“z”: 0.92
}
},
“groups”: [
{
“metadata”: {
“wellBottomShape”: “v”
},
“wells”: [
“A1”,
“B1”,
“C1”,
“D1”,
“E1”,
“F1”,
“G1”,
“H1”,
“A2”,
“B2”,
“C2”,
“D2”,
“E2”,
“F2”,
“G2”,
“H2”,
“A3”,
“B3”,
“C3”,
“D3”,
“E3”,
“F3”,
“G3”,
“H3”,
“A4”,
“B4”,
“C4”,
“D4”,
“E4”,
“F4”,
“G4”,
“H4”,
“A5”,
“B5”,
“C5”,
“D5”,
“E5”,
“F5”,
“G5”,
“H5”,
“A6”,
“B6”,
“C6”,
“D6”,
“E6”,
“F6”,
“G6”,
“H6”,
“A7”,
“B7”,
“C7”,
“D7”,
“E7”,
“F7”,
“G7”,
“H7”,
“A8”,
“B8”,
“C8”,
“D8”,
“E8”,
“F8”,
“G8”,
“H8”,
“A9”,
“B9”,
“C9”,
“D9”,
“E9”,
“F9”,
“G9”,
“H9”,
“A10”,
“B10”,
“C10”,
“D10”,
“E10”,
“F10”,
“G10”,
“H10”,
“A11”,
“B11”,
“C11”,
“D11”,
“E11”,
“F11”,
“G11”,
“H11”,
“A12”,
“B12”,
“C12”,
“D12”,
“E12”,
“F12”,
“G12”,
“H12”
]
}
],
“parameters”: {
“format”: “96Standard”,
“isTiprack”: false,
“isMagneticModuleCompatible”: true,
“magneticModuleEngageHeight”: 20,
“loadName”: “nest_96_pcr_vacuum_collection_plate”
},
“namespace”: “custom_beta”,
“version”: 2,
“schemaVersion”: 2,
“cornerOffsetFromSlot”: {
“x”: 0,
“y”: 0,
“z”: 0
},
“stackLimit”: 5,
“stackingOffsetWithLabware”: {
“opentrons_96_pcr_adapter”: {
“x”: 0,
“y”: 0,
“z”: 10.2
},
“opentrons_96_well_aluminum_block”: {
“x”: 0,
“y”: 0,
“z”: 12.66
},
“millipore_vacuum_manifold_base”: {
“x”: 0,
“y”: 0,
“z”: 5
}
},
“stackingOffsetWithModule”: {
“thermocyclerModuleV2”: {
“x”: 0,
“y”: 0,
“z”: 10.8
}
}
}

Shinedalgarno · September 29, 2025, 1:52pm

Thanks Meghan! Seems to work for me when I just put that into my .json file. I don’t have a machine in front of me to verify though using the move_labware command

Did it function as you expected @hkjawn ?

hkjawn · October 2, 2025, 2:43pm

Thank y’all for the replies and discussion! I tried adding gripForce at the location of the custom labware example from @MeghanFerzoco, but unfortunately I get an error message when trying to add the modified JSON as custom labware in the Opentrons app.

Error importing Software\Opentrons Custom Labware\cellvis_96_wellplate_350ul_gripforce5N.json. Invalid labware definition

(I was hoping that the gripforce parameter would allow me to use move_labware normally and have it automatically grip less forcefully)

My goal in controlling the grip force has been during lid removals of my 96 well plates (using @Shinedalgarno 's code from another thread ), where the gripper was only grabbing the lid but still pulling up both the plate and lid!

I thought that adjusting the offset such that gripping only the very top of the lid might prevent this issue since the lid would be less deformable there, so it might not end up grabbing the plate underneath.

But paradoxically, having the gripper grip lower on the lid (& not the plate!) seems to have worked better. Now most of the time it works! (Going to try lowering the grip position even more)

MeghanFerzoco · October 3, 2025, 12:59pm

Hey @hkjawn - I had our team take a look at this, and we think you may be using a different file than the one above. Do you mind emailing me the file you’re using at meghan.ferzoco@opentrons.com? I’ll loop in our relevant experts and hopefully we can figure out a go forward path!

hkjawn · October 6, 2025, 3:19pm

Sent!

hkjawn · October 31, 2025, 9:47pm

Just wanted to update - 5N grip force appears to be too weak to grab the lid or the plate. I’ve tried 7-10N and those forces are strong enough to lift the lid/plate. Haven’t tried 6N yet! The lower grip force seems to help somewhat with the plate being lifted up with the lid.

I seem to still be having an issue though. During lid removal, the gripper ends up slightly pulling the plate up, just at the back-left corner of the well plate.

I notice that the deck slots are designed to push the plate into this corner (the blue colored corner), so this could be the reason. (i.e, the plate is slightly out of alignment in this direction, so when the gripper comes by and lifts the lid, the lid drags against the back-left corner of the plate, which ends up lifting this part of the plate upwards)

I wonder if labware position check also adjusts where the gripper grips. If so, then making sure to perform labware position check (maybe once per day?) and placing the plate in the slots in a consistent manner could fix things. If LPC doesn’t adjust the gripper position, perhaps I need to add something in the top left corner to stop the plate from being pushed too far into that corner.

hkjawn · November 3, 2025, 4:41pm

Update 2:

I performed a precise Labware Position Check on my plates before my most recent attempt (8N grip force), and this time it seemed to work without issue! (Will continue over the coming weeks to see if it continues to work fine when labware position is well calibrated)

But yeah, perhaps keep labware position check in mind if you’re trying to do lid handling

hkjawn · November 11, 2025, 4:35pm

Update 3: Over several runs with Labware Position Check, it still seems to partially lift the plate corner in addition to the lid

Current workaround: Manually monitor lid removals

hkjawn · November 18, 2025, 6:52pm

Update 4:
I think that it may be my plates’ fault! I currently use Cellvis 96 well plates because they are comparatively low cost while having a really good coverslip-like bottom for great imaging.

I just tried the lid removal on some regular Corning 96 well plates and realized that the lids on these are a lot more sturdy/rigid. The lid handling seems much better with these, exhibiting no plate lifting (so far, again I’ll report back after further trials).