fix(api): temporarily increase Z_L hold current to prevent 96-channel…

… from falling when motor is re-engaged (#14377)

* temporarily increase Z_L hold current to prevent stage from falling RQA-2251

api/src/opentrons/hardware_control/backends/flex_protocol.py

@@ -267,6 +267,14 @@ def restore_z_r_run_current(self) -> AsyncIterator[None]:
  """
  ...
 
+ @asynccontextmanager
+ def increase_z_l_hold_current(self) -> AsyncIterator[None]:
+ """
+ Temporarily increase the hold current when engaging the Z_L axis
+ while the 96-channel is attached
+ """
+ ...
+
  async def watch(self, loop: asyncio.AbstractEventLoop) -> None:
  ...
 

api/src/opentrons/hardware_control/backends/ot3controller.py

@@ -1091,6 +1091,24 @@ async def restore_z_r_run_current(self) -> AsyncIterator[None]:
  {Axis.Z_R: high_throughput_settings[Axis.Z_R].run_current}
  )
 
+ @asynccontextmanager
+ async def increase_z_l_hold_current(self) -> AsyncIterator[None]:
+ """
+ Temporarily increase the hold current when engaging the Z_L axis
+ while the 96-channel is attached
+ """
+ assert self._current_settings
+ high_throughput_settings = deepcopy(self._current_settings)
+ await self.set_hold_current(
+ {Axis.Z_L: high_throughput_settings[Axis.Z_L].run_current}
+ )
+ try:
+ yield
+ finally:
+ await self.set_hold_current(
+ {Axis.Z_L: high_throughput_settings[Axis.Z_L].hold_current}
+ )
+
  @staticmethod
  def _build_event_watcher() -> aionotify.Watcher:
  watcher = aionotify.Watcher()

api/src/opentrons/hardware_control/backends/ot3simulator.py

@@ -578,6 +578,14 @@ async def restore_z_r_run_current(self) -> AsyncIterator[None]:
  """
  yield
 
+ @asynccontextmanager
+ async def increase_z_l_hold_current(self) -> AsyncIterator[None]:
+ """
+ Temporarily increase the hold current when engaging the Z_L axis
+ while the 96-channel is attached
+ """
+ yield
+
  @ensure_yield
  async def watch(self, loop: asyncio.AbstractEventLoop) -> None:
  new_mods_at_ports = [

api/src/opentrons/hardware_control/ot3api.py

@@ -1455,7 +1455,14 @@ async def _home_axis(self, axis: Axis) -> None:
 
  if encoder_ok:
  # ensure stepper position can be updated after boot
- await self.engage_axes([axis])
+ if axis == Axis.Z_L and self.gantry_load == GantryLoad.HIGH_THROUGHPUT:
+ # we're here if the left mount has been idle and the brake is engaged
+ # we want to temporarily increase its hold current to prevent the z
+ # stage from dropping when switching off the ebrake
+ async with self._backend.increase_z_l_hold_current():
+ await self.engage_axes([axis])
+ else:
+ await self.engage_axes([axis])
  await self._update_position_estimation([axis])
  # refresh motor and encoder statuses after position estimation update
  motor_ok = self._backend.check_motor_status([axis])