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toolhead: Replace max_accel_to_decel with minimum_cruise_ratio

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The user facing max_accel_to_decel setting is complicated and
confusing.  Replace it with a new minimum_cruise_ratio parameter.
Internally this user-facing parameter will calculate the existing
low-level "accel_to_decel" mechanism.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor
2023-12-03 18:50:44 -05:00
parent 18de421c4a
commit 0105aa330f
10 changed files with 85 additions and 50 deletions
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28
docs/Kinematics.md
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@@ -96,7 +96,7 @@ Key formula for look-ahead:
end_velocity^2 = start_velocity^2 + 2*accel*move_distance
```
### Smoothed look-ahead
### Minimum cruise ratio
Klipper also implements a mechanism for smoothing out the motions of
short "zigzag" moves. Consider the following moves:
@@ -105,21 +105,27 @@ short "zigzag" moves. Consider the following moves:
In the above, the frequent changes from acceleration to deceleration
can cause the machine to vibrate which causes stress on the machine
and increases the noise. To reduce this, Klipper tracks both regular
move acceleration as well as a virtual "acceleration to deceleration"
rate. Using this system, the top speed of these short "zigzag" moves
are limited to smooth out the printer motion:
and increases the noise. Klipper implements a mechanism to ensure
there is always some movement at a cruising speed between acceleration
and deceleration. This is done by reducing the top speed of some moves
(or sequence of moves) to ensure there is a minimum distance traveled
at cruising speed relative to the distance traveled during
acceleration and deceleration.
Klipper implements this feature by tracking both a regular move
acceleration as well as a virtual "acceleration to deceleration" rate:
![smoothed](img/smoothed.svg.png)
Specifically, the code calculates what the velocity of each move would
be if it were limited to this virtual "acceleration to deceleration"
rate (half the normal acceleration rate by default). In the above
picture the dashed gray lines represent this virtual acceleration rate
for the first move. If a move can not reach its full cruising speed
using this virtual acceleration rate then its top speed is reduced to
the maximum speed it could obtain at this virtual acceleration
rate. For most moves the limit will be at or above the move's existing
rate. In the above picture the dashed gray lines represent this
virtual acceleration rate for the first move. If a move can not reach
its full cruising speed using this virtual acceleration rate then its
top speed is reduced to the maximum speed it could obtain at this
virtual acceleration rate.
For most moves the limit will be at or above the move's existing
limits and no change in behavior is induced. For short zigzag moves,
however, this limit reduces the top speed. Note that it does not
change the actual acceleration within the move - the move continues to