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docs: Reword smoothed look-ahead description in Kinematics 

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2017-05-01 11:27:14 -04:00
parent 631b0e6c37
commit e177d4f70d
2 changed files with 15 additions and 12 deletions
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2
docs/Features.md
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@ -44,7 +44,7 @@ Klipper has several compelling features:
that can dramatically improve the accuracy of typical endstop
switches. When properly tuned it can improve a print's first layer
bed adhesion.
* Support for limiting the top speed of short "zig-zag" moves to
* Support for limiting the top speed of short "zigzag" moves to
reduce printer vibration and noise. See the
[kinematics](Kinematics.md) document for more information.

25
docs/Kinematics.md
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@ -101,7 +101,7 @@ Smoothed look-ahead
-------------------
Klipper also implements a mechanism for smoothing out the motions of
short "zig-zag" moves. Consider the following moves:
short "zigzag" moves. Consider the following moves:
![zigzag](img/zigzag.svg.png)
@ -109,20 +109,23 @@ 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 "zig zag" moves
rate. Using this system, the top speed of these short "zigzag" moves
are limited to smooth out the printer motion:
![smoothed](img/smoothed.svg.png)
In the above, note the dashed gray lines - this is a graphical
representation of the "pseudo acceleration". Where the two dashed
lines meet enforces a limit on the move's top speed. For most moves
the limit will be at or above the move's existing limits and no change
in behavior is induced. However, for short "zig-zag" moves the limit
comes into play and it reduces the top speed. Note that the grey lines
represent a pseudo-acceleration to limit top speed only - the move
continues to use it's normal acceleration scheme up to its adjusted
top-speed.
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
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
use the normal acceleration scheme up to its adjusted top-speed.
Generating steps
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