fix rounding error

Author: ryanthecoder

api/src/opentrons/hardware_control/ot3api.py

@@ -5,6 +5,7 @@
 from dataclasses import replace
 import logging
 from collections import OrderedDict
+from math import isclose
 from typing import (
     AsyncIterator,
     cast,
@@ -2709,7 +2710,11 @@ async def liquid_probe(
         error: Optional[PipetteLiquidNotFoundError] = None
         pos = await self.gantry_position(checked_mount, refresh=True)
         #  probe_start_pos.z + z_distance of pass - pos.z should be < max_z_dist
-        while (probe_start_pos.z - pos.z) < max_z_dist:
+        # due to rounding errors this can get caught in an infinite loop when the distance is almost equal
+        # so we check to see if they're within 0.01 which is 1/5th the minimum movement distance from move_utils.py
+        while (probe_start_pos.z - pos.z) < max_z_dist and not isclose(
+            (probe_start_pos.z - pos.z), max_z_dist, rel_tol=0.01
+        ):
             # safe distance so we don't accidentally aspirate liquid if we're already close to liquid
             safe_plunger_pos = top_types.Point(
                 pos.x, pos.y, pos.z + probe_safe_reset_mm
@@ -2749,9 +2754,9 @@ async def liquid_probe(
             except PipetteLiquidNotFoundError as lnfe:
                 error = lnfe
             pos = await self.gantry_position(checked_mount, refresh=True)
-        #await self.move_to(checked_mount, probe_start_pos + top_types.Point(z=2))
-        #await self.prepare_for_aspirate(checked_mount)
-        #await self.move_to(checked_mount, probe_start_pos)
+        # await self.move_to(checked_mount, probe_start_pos + top_types.Point(z=2))
+        # await self.prepare_for_aspirate(checked_mount)
+        # await self.move_to(checked_mount, probe_start_pos)
         if error is not None:
             # if we never found liquid raise an error
             raise error