LinuxCNC S-Curve Accelerations

The new PR with comp kinematics support for TP2 will have artifact debs at the end of this link

github.com/LinuxCNC/linuxcnc/actions/runs/23100211514?pr=3807

Thanks for the comp file kinematics update.

I am trying that out.In the meantime, I have been experimenting with current update.
I find that the planner type 2 also cannot accelerate across multiple segments. For a file with very small lines, it is not taking up adequate speed and the file execution is very slow. I am going to try to increase the jerk and try it on a real machine too...  
 

The ngc/tap file is also attached.  

I was thinking this could be solved with defining zones for acceleration. Where segments with similar kinematic parameters and some tolerance of direction can be accelerated over simultaneously. 
I have tried to capture my "Zones" based acceleration idea (using Claude.ai to elaborate on the details).A zone is a group of consecutive path segments that are treated as a single kinematic unit for acceleration planning. Segments are grouped into a zone when they are nearly collinear — i.e., the direction change between them is below a threshold (angle_threshold, default ~0.57°). A zone boundary is created when:

• The direction change exceeds the threshold  or 
• The kinematic limits (v_max, a_max, j_max) differ between adjacent segments 

This collapses thousands of micro-segments (e.g. from a linearized arc) into just a handful of zones

Corner Velocity Constraint: At each zone boundary (a "corner"), the maximum speed the machine can carry through the junction is computed geometricallyradius = path_tolerance / (1 - cos(θ/2))  
v_corner = sqrt(a_max × radius)

• path_tolerance = max allowable deviation from the sharp corner (e.g. 0.01 mm)  
• θ = junction angle between the two direction vectors
• A 90° corner at 0.01 mm tolerance and a_max=500 gives v_corner ≈ 4.1 mm/s — forces a near-stop
• A collinear junction (θ→0) gives v_corner → ∞ — no speed reduction needed

Zone-Level Bidirectional Velocity Planning: This is where acceleration is actually resolved:
Forward pass — starting from v_start, for each zone compute how fast the machine can exit given the distance and limits:          
           v_fwd[k 1] = min(max_reachable_from(v_fwd[k]), zone_Vmax, v_corner[k 1])
Backward pass — starting from v_end, do the same in reverse:          
           v_bwd[k] = min(max_reachable_from(v_bwd[k 1]), zone_Vmax, v_corner[k])
Merge pass — take the minimum at every zone boundary:          
           v_zone[k] = min(v_fwd[k], v_bwd[k], v_corner[k])

VelocityPlanner.max_reachable_velocity computes how fast you can reach the end of a segment given jerk/accel limits. Zones are then classified as accel, cruise, or decel based on whether the entry/exit velocities rise, stay flat, or fall. Consecutive same-type zones are merged into runs, and one S-curve (7-phase jerk-limited profile from SCurveSolver) is planned per run.This means for a linearized arc with 1000 micro-segments, only ~3–4 S-curve phases are generated (ramp-up, cruise, ramp-down), instead of 1000 independent profiles.

Regards,

-automata

There already is some basic merging, I'm sure it can be improved upon

@automata
Did you run it with bigger jerk limits? Can you share your sim configs?

grandixximo wrote:

The new PR with comp kinematics support for TP2 will have artifact debs at the end of this link

github.com/LinuxCNC/linuxcnc/actions/runs/23100211514?pr=3807
 

thanks a lot and 9d branch is now avaible for rip testing with TP2 without spindle sync movement? 

Yes, test in sim for now, I have not run on a machine yet, but sim doesn't look too bad

Ive allready tested the last update ...

TP2 and it is working only with simple shapes really well, I did not notice infinity spikes of anything..

no more difficult shaping avaible.. it just froze at cloud of points as G2\G3 transfered to cloud of points .. time spiking increased from last testing

testing only in simulation level ... no real hardware avaible for now

thanks Luca for your job!
 

You are welcome, still lots to be done, can you share your configuration, does it always freeze on the point cloud? I'd like to replicate. Time spiking meaning the servo thread? Can you share that as well?

Hello,

notice > well tuned RT machine with less then 2us latency

I every time start with the LinuxCNC logo startup file ... create the scope of acc + velocity preview and analyze step by step movement ... jerk 10k m\s3 then I move to the 3d chips and 3d test ... if this works well i am shifting to the my code 1d movement, 2.5 d movement and finally 3d movement .. I start with 0 type then I move to other one for right comparation.. it is freezing TP2 with 3dchips.ngc from default local folder after last update ... no diagnoze possible from my side right now

all step by step analyzing the scopes

Configuration starting basically from axis_mm.ini with custom tool table which is missing from default

Spiking was mainly during start of the scope at servothread and then periodicaly, looks like at each end of segment - but no exact proofing 

I am staying tune for more testing or cooperation ... 

thanks E.
 

I will try to replicate, thank you!