STAR iswap & channel 0 collision checks (#687)

Author: rickwierenga

pylabrobot/liquid_handling/backends/hamilton/STAR_backend.py

@@ -3112,10 +3112,15 @@ async def move_channel_y(self, channel: int, y: float):
           f"(channel {channel - 1} y-position is {round(y, 2)} mm)"
         )
     else:
-      # STAR machines appear to lose connection to a channel if y > 635 mm
-      max_y_pos = 635
+      if self.iswap_installed:
+        max_y_pos = await self.iswap_request_module_y()
+        limit = "iswap module y-position"
+      else:
+        # STAR machines do not allow channels y > 635 mm
+        max_y_pos = 635
+        limit = "machine limit"
       if y > max_y_pos:
-        raise ValueError(f"channel {channel} y-target must be <= {max_y_pos} mm (machine limit)")
+        raise ValueError(f"channel {channel} y-target must be <= {max_y_pos} mm ({limit})")
 
     if channel < (self.num_channels - 1):
       min_y_pos = await self.request_y_pos_channel_n(channel + 1)
@@ -3125,7 +3130,7 @@ async def move_channel_y(self, channel: int, y: float):
           f"(channel {channel + 1} y-position is {round(y, 2)} mm)"
         )
     else:
-      # STAR machines appear to lose connection to a channel if y < 6 mm
+      # STAR machines do not allow channels y < 6 mm
       min_y_pos = 6
       if y < min_y_pos:
         raise ValueError(f"channel {channel} y-target must be >= {min_y_pos} mm (machine limit)")
@@ -6476,6 +6481,17 @@ async def move_iswap_y_relative(self, step_size: float, allow_splitting: bool =
       allow_splitting: Allow splitting of the movement into multiple steps. Default False.
     """
 
+    # check if iswap will hit the first (backmost) channel
+    # we only need to check for positive step sizes because the iswap is always behind the first channel
+    if step_size < 0:
+      y_pos_channel_0 = await self.request_y_pos_channel_n(0)
+      current_y_pos_iswap = await self.iswap_request_module_y()
+      if current_y_pos_iswap + step_size < y_pos_channel_0:
+        raise ValueError(
+          f"iSWAP will hit the first (backmost) channel. Current iSWAP Y position: {current_y_pos_iswap} mm, "
+          f"first channel Y position: {y_pos_channel_0} mm, requested step size: {step_size} mm"
+        )
+
     direction = 0 if step_size >= 0 else 1
     max_step_size = 99.9
     if abs(step_size) > max_step_size:
@@ -7213,6 +7229,17 @@ async def request_iswap_position(self) -> Coordinate:
       z=(resp["zj"] / 10) * (1 if resp["zd"] == 0 else -1),
     )
 
+  @staticmethod
+  def _iswap_y_inc_to_mm(y_inc: int) -> float:
+    mm_per_increment = 0.046302083
+    return round(y_inc * mm_per_increment, 2)
+
+  async def iswap_request_module_y(self) -> float:
+    """Request iSWAP module (not gripper) Y position in mm"""
+    resp = await self.send_command(module="R0", command="RY", fmt="ry##### (n)")
+    iswap_y_pos = resp["ry"][1]  # 0 = FW counter, 1 = HW counter
+    return STARBackend._iswap_y_inc_to_mm(iswap_y_pos)
+
   async def request_iswap_initialization_status(self) -> bool:
     """Request iSWAP initialization status