extruder: Do sanity checks on extrusion rates

Add a run-time check to ensure the incoming g-code doesn't have a
ridiculously large e move.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

3 files changed, 23 insertions, 5 deletions

diff --git a/config/example.cfg b/config/example.cfg
index 75684d16..98d1c0d1 100644
--- a/config/example.cfg
+++ b/config/example.cfg
@@ -115,6 +115,16 @@ nozzle_diameter: 0.500
 filament_diameter: 3.500
 #   Diameter of the raw filament (in mm) as it enters the
 #   extruder. This parameter must be provided.
+#max_extrude_cross_section:
+#   Maximum area of the cross section of an extrusion line (in
+#   mm^2). If a move requests an extrusion rate that would exceed this
+#   value it will cause an error to be returned. The default is: 4.0 *
+#   nozzle_diameter^2
+#max_extrude_only_distance: 50.0
+#   Maximum length (in mm of raw filament) that an extrude only move
+#   may be. If an extrude only move requests a distance greater than
+#   this value it will cause an error to be returned. The default is
+#   50mm.
 max_velocity: 200000
 #   Maximum velocity (in mm/s) of the extruder motor for extrude only
 #   moves. This parameter must be provided.
diff --git a/docs/Todo.md b/docs/Todo.md
index 71c68c3f..e16196e1 100644
--- a/docs/Todo.md
+++ b/docs/Todo.md
@@ -58,10 +58,6 @@ Safety features
   can be useful to detect a sensor failure (eg, thermistor short) that
   could otherwise cause the PID to command excessive heating.
 
-* Possibly implement host based checking on the ratio between extrude
-  amount and head movement.
- * Enforce acceleration and speed limits on extruder stepper motor.
-
 Testing features
 ================
 
diff --git a/klippy/extruder.py b/klippy/extruder.py
index 23ed7f54..9e3d8143 100644
--- a/klippy/extruder.py
+++ b/klippy/extruder.py
@@ -3,7 +3,7 @@
 # Copyright (C) 2016  Kevin O'Connor <kevin@koconnor.net>
 #
 # This file may be distributed under the terms of the GNU GPLv3 license.
-import logging
+import math, logging
 import stepper, heater, homing
 
 class PrinterExtruder:
@@ -12,6 +12,11 @@ class PrinterExtruder:
         self.stepper = stepper.PrinterStepper(printer, config, 'extruder')
         nozzle_diameter = config.getfloat('nozzle_diameter')
         filament_diameter = config.getfloat('filament_diameter')
+        filament_area = math.pi * (filament_diameter * .5)**2
+        max_cross_section = config.getfloat(
+            'max_extrude_cross_section', 4. * nozzle_diameter**2)
+        self.max_extrude_ratio = max_cross_section / filament_area
+        self.max_e_dist = config.getfloat('max_extrude_only_distance', 50.)
         self.max_e_velocity = config.getfloat('max_velocity')
         self.max_e_accel = config.getfloat('max_accel')
         self.pressure_advance = config.getfloat('pressure_advance', 0.)
@@ -30,7 +35,14 @@ class PrinterExtruder:
                 move.end_pos, "Extrude below minimum temp")
         if not move.is_kinematic_move:
             # Extrude only move - limit accel and velocity
+            if move.axes_d[3] > self.max_e_dist:
+                raise homing.EndstopMoveError(
+                    move.end_pos, "Extrude only move too long")
             move.limit_speed(self.max_e_velocity, self.max_e_accel)
+        elif move.extrude_r > self.max_extrude_ratio:
+            logging.debug("%s vs %s" % (move.extrude_r, self.max_extrude_ratio))
+            raise homing.EndstopMoveError(
+                move.end_pos, "Move exceeds maximum extrusion cross section")
     def move(self, move_time, move):
         if self.need_motor_enable:
             self.stepper.motor_enable(move_time, 1)