Laser head is slowing down during rastering

[drom89]

Hi,

another "problem" when engraving/rastering with higher speeds the laser head is slowing down considerably, is this normal ?
I thought that laser head should be running with consistent speed and only change the power of the laser.

See video below
https://photos.app.goo.gl/U3dMczxaXWyc69ma8

[terjeio]

Yes, it is normal because lots of short movements causes the planner buffer to limit the feed rate. Try with a larger planner buffer. Each entry requires around 40 bytes of RAM.

FYI the iMXRT1062 driver, which has a 600MHz processor with FPU and plenty of RAM, can be tuned to feedrates > 50.000 mm/min for laser engraving.

Some info here and here.

[drom89]

So i boosted the planner buffer from 36 to 180.
Im using lightburn and with synchronous transfer mode its still almost same.
With buffered mode its ok but only like 10 sec and after that laser head stop moving and just fire in place.

I think USB communication is too slow...
Is there any way to boost USB baud rate from default 115200 to higher ?

[terjeio]

zip and attach a file that shows the symptom to acomment so I can check here.

Is there any way to boost USB baud rate from default 115200 to higher ?

Which board map are you using?

[drom89]

SKR 1.4 Turbo board.
Tomorrow i will record video.

[drom89]

When trying to go with 200 buffer size i run our of memory.

[terjeio]

Tomorrow i will record video.

I do not need one, I would rather have a file showing the symptoms so I have something to test with.

When trying to go with 200 buffer size i run our of memory.

Not much I can do about that, it is an old processor with limited RAM. I do not know if the AHB region can be made accessible by tweaking the linker script, you can look into that? And perhaps it is not something that will gain you any speed - there is no FPU (floating point unit) in this processor so too many entries in the buffer may start to slow it down instead.

Can you run a program in Check mode and time that? That will give you the raw transfer speed. With a native USB connection (IIRC the SKR 1.4 uses that) the configured speed does not matter, AFAIK the max speed available will be used anyway. At least it is for the iMXRT1062 driver.

[drom89]

Tomorrow i will record video.

I do not need one, I would rather have a file showing the symptoms so I have something to test with.

Do you want G code file ?

When trying to go with 200 buffer size i run our of memory.

Not much I can do about that, it is an old processor with limited RAM. I do not know if the AHB region can be made accessible by tweaking the linker script, you can look into that? And perhaps it is not something that will gain you any speed - there is no FPU (floating point unit) in this processor so too many entries in the buffer may start to slow it down instead.

What boards do you recommend performance/cost wise ? For lasers, cnc mills etc.

Can you run a program in Check mode and time that? That will give you the raw transfer speed. With a native USB connection (IIRC the SKR 1.4 uses that) the configured speed does not matter, AFAIK the max speed available will be used anyway. At least it is for the iMXRT1062 driver.

How can i run it in Check mode ?

[terjeio]

Do you want G code file ?

Yes please.

What boards do you recommend performance/cost wise ? For lasers, cnc mills etc.

That is a hard one to answer - the iMXRT1062 (Teensy 4) driver and board is the fastest and most expandable you can get but needs external drivers as there is currently no boards available for Polulu style drivers. A processor with FPU is IMO preferable, but the Pi Pico is interesting due to its PIO peripherals. I have not checked what its limits are though. More info here. BTT SKR Pro 1.1/1.2 boards will hopefully soon be programmable via SD card - I had a breaktrough yesterday with a dev board that brings that closer.

How can i run it in Check mode ?

By sending $C before starting. Some senders has a button or a checkbox for enabling Check mode.

[drom89]

Ok thanks, i will test it tomorrow and send the files.

[drom89]

files are here: gcode foto.zip

[terjeio]

I have tested the largest file (grey scale engraving) with ioSender, aggressive buffering enabled.

150 steps/mm, max speed 25000mm/min, acceleration 1000 mm/sec2

iMXRT1062 (Teensy 4) controller, planner buffer set to 1000:

• Check mode streaming: 1:53, from SD card 0:11 (uses DMA).
• Run: 11:02, I've seen momentary feed rates above 17000mm/min.

LPC176x with BTT SKR 1.3 controller, planner buffer set to 150:

• Check mode streaming: 1:54, SD card not checked.
• Run: I've seen a few momentary feed rates above 10000mm/min, I canceled the job at 40:00 due to the pauses (see below).

There was several pauses during the run, the job restarted by itself after a little while (a little less than 3 minutes). This is likely due to missed stepper interrupts causing the 32 bit timer used to not firing a new until the next wrap around. The timer runs at 24MHz so that matches well with 3 minutes. Most of these were at the end of the job.

After increasing the stepper interrupt priority, lowering the USB priority and fixing a bug in the SD card driver code I get these results:

• Check mode streaming: 1:58, from SD 2:45 (no DMA, single byte reads).
• Run: 13:42, I've seen a few momentary feed rates above 10000mm/min at the start of the job, many peaking at 18000 at the last 3rd of it. No pauses.
• SD card run: 13:52, I've seen a few momentary feed rates above 15000mm/min.

Not bad compared with the iMXRT1062 results.

Note that I have performed these tests without motors connected!

[drom89]

There was several pauses during the run, the job restarted by itself after a little while (a little less than 3 minutes).

I didnt wait for the resume, so i dont know if it will resume or not. Some times it stops and laser is still firing.

After increasing the stepper interrupt priority, lowering the USB priority and fixing a bug in the SD card driver code I get these results:

How can i do that ?

[terjeio]

How can i do that ?

Change priority in this line from 2 to 0.

LPC176x/src/driver.c

Line 1306 in 929596c

NVIC_SetPriority(STEPPER_TIMER_INT0, 2);

Add this line before line 330:
NVIC_SetPriority(USB_IRQn, 1);

LPC176x/src/usb_serial.c

Lines 329 to 330 in 929596c

	/* enable USB interrupts */
	NVIC_EnableIRQ(USB_IRQn);

What is your steps/mm setting for X? Number of microsteps per step? More is not necessarily better as it increases processor load.

[drom89]

I have 80 steps per mm

[readeral]

Reading through this thread, with the changes, are raster engravings now viable on the SKR 1.4T?