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stepper: Fix set_min_stop_interval() calculation 

The previous calculation was only valid if the stepper is always
commanded to a position that is an exact multiple of the
step_distance.  The safety check was programmed with a value too large
for other commanded positions, which could result in "No next step"
errors.  Fix by changing the calculation to use the worst case
scenario.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2017-03-15 23:08:29 -04:00
parent cbdc54843d
commit df6d3107f2
1 changed files with 10 additions and 4 deletions
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14
klippy/stepper.py
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@ -50,11 +50,17 @@ class PrinterStepper:
self.position_endstop = config.getfloat('position_endstop') self.position_endstop = config.getfloat('position_endstop')
self.position_max = config.getfloat('position_max', 0.) self.position_max = config.getfloat('position_max', 0.)
self.need_motor_enable = True self.need_motor_enable = True
def _dist_to_time(self, dist, start_velocity, accel):
# Calculate the time it takes to travel a distance with constant accel
time_offset = start_velocity / accel
return math.sqrt(2. * dist / accel + time_offset**2) - time_offset
def set_max_jerk(self, max_halt_velocity, max_accel): def set_max_jerk(self, max_halt_velocity, max_accel):
jc = max_halt_velocity / max_accel # Calculate the firmware's maximum halt interval time
inv_max_step_accel = self.step_dist / max_accel last_step_time = self._dist_to_time(
min_stop_interval = (math.sqrt(3.*inv_max_step_accel + jc**2) self.step_dist, max_halt_velocity, max_accel)
- math.sqrt(inv_max_step_accel + jc**2)) second_last_step_time = self._dist_to_time(
2. * self.step_dist, max_halt_velocity, max_accel)
min_stop_interval = second_last_step_time - last_step_time
self.mcu_stepper.set_min_stop_interval(min_stop_interval) self.mcu_stepper.set_min_stop_interval(min_stop_interval)
def motor_enable(self, move_time, enable=0): def motor_enable(self, move_time, enable=0):
if enable and self.need_motor_enable: if enable and self.need_motor_enable: