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extruder: Determine start step offset using last commanded position 

The existing code calculates the number of steps in a move and then
spreads them out evenly throughout that move.  Change the code so that
step timing is based on where the head is commanded to be relative to
the stepper step locations.  This makes the timing more accurate - in
particular the stepper velocities will be more accurate during
cornering introduced by the lookahead code.  It also results in
slightly smoother stepper motion which results in better step
compression.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2016-10-25 21:06:20 -04:00
parent f0cefebff7
commit 8f331f08d2
1 changed files with 16 additions and 10 deletions
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26
klippy/extruder.py
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@ -73,20 +73,23 @@ class PrinterExtruder:
# Determine regular steps
extrude_r = move.axes_d[3] / move_d
forward_d = accel_d + cruise_d + decel_d
self.extrude_pos += forward_d * extrude_r
new_step_pos = int(self.extrude_pos*self.stepper.inv_step_dist + 0.5)
steps = new_step_pos - self.stepper_pos
if steps:
start_pos = self.extrude_pos
end_pos = start_pos + forward_d * extrude_r
inv_step_dist = self.stepper.inv_step_dist
new_step_pos = int(end_pos*inv_step_dist + 0.5)
if new_step_pos != self.stepper_pos:
steps = forward_d * extrude_r * inv_step_dist
step_offset = self.stepper_pos - start_pos * inv_step_dist + 0.5
self.stepper_pos = new_step_pos
sdir = 0
if steps < 0:
sdir = 1
steps = -steps
step_offset = 1. - step_offset
mcu_time, so = self.stepper.prep_move(move_time, sdir)
move_step_d = forward_d / steps
inv_move_step_d = 1. / move_step_d
step_offset = 0.5
# Acceleration steps
#t = sqrt(2*pos/accel + (start_v/accel)**2) - start_v/accel
@ -115,10 +118,12 @@ class PrinterExtruder:
, decel_sqrt_offset, -accel_multiplier)
# Determine retract steps
self.extrude_pos -= retract_d * extrude_r
new_step_pos = int(self.extrude_pos*self.stepper.inv_step_dist + 0.5)
steps = self.stepper_pos - new_step_pos
if steps:
start_pos = end_pos
end_pos -= retract_d * extrude_r
new_step_pos = int(end_pos*inv_step_dist + 0.5)
if new_step_pos != self.stepper_pos:
steps = retract_d * extrude_r * inv_step_dist
step_offset = start_pos * inv_step_dist - self.stepper_pos + 0.5
self.stepper_pos = new_step_pos
mcu_time, so = self.stepper.prep_move(
move_time+accel_t+cruise_t+decel_t, 1)
@ -130,5 +135,6 @@ class PrinterExtruder:
accel_time_offset = retract_v * inv_accel
accel_sqrt_offset = accel_time_offset**2
accel_multiplier = 2.0 * move_step_d * inv_accel
so.step_sqrt(mcu_time - accel_time_offset, steps, 0.5
so.step_sqrt(mcu_time - accel_time_offset, steps, step_offset
, accel_sqrt_offset, accel_multiplier)
self.extrude_pos = end_pos