delta: Better delta build volume constraint check

Existing code uses very restrictive build volume constraint checking
with just narrow cone on top of fully cylinder for delta printers.

Code here implements more permissive and still safe build volume
constraint checks.

Signed-off-by: Jan Herich <jan.herich@gmail.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/klippy/kinematics/delta.py b/klippy/kinematics/delta.py
index 2278dbca..bb81ab18 100644
--- a/klippy/kinematics/delta.py
+++ b/klippy/kinematics/delta.py
@@ -65,6 +65,8 @@ class DeltaKinematics:
         self.min_z = config.getfloat('minimum_z_position', 0, maxval=self.max_z)
         self.limit_z = min([ep - arm
                             for ep, arm in zip(self.abs_endstops, arm_lengths)])
+        self.min_arm_length = min_arm_length = min(arm_lengths)
+        self.min_arm2 = min_arm_length**2
         logging.info(
             "Delta max build height %.2fmm (radius tapered above %.2fmm)"
             % (self.max_z, self.limit_z))
@@ -123,7 +125,11 @@ class DeltaKinematics:
         end_z = end_pos[2]
         limit_xy2 = self.max_xy2
         if end_z > self.limit_z:
-            limit_xy2 = min(limit_xy2, (self.max_z - end_z)**2)
+            above_z_limit = end_z - self.limit_z
+            allowed_radius = self.radius - math.sqrt(
+                self.min_arm2 - (self.min_arm_length - above_z_limit)**2
+            )
+            limit_xy2 = min(limit_xy2, allowed_radius**2)
         if end_xy2 > limit_xy2 or end_z > self.max_z or end_z < self.min_z:
             # Move out of range - verify not a homing move
             if (end_pos[:2] != self.home_position[:2]