To me, the message “Force the laser power to be constant regardless of current movement speed” could mean:
If you enable this option I will adjust the laser output dynamically so that a constant energy hits different bits of the target, in other words when I speed up I will increase the laser power to compensate for moving faster, and when I slow down I will lower the laser power to prevent over-burning.
If you enable this option I will supply the laser with a constant amount of power, regardless of my speed, so when I slow down, the target will receive more energy per unit length, and when I speed up it will receive less.
Which is it, please?
And, whichever mode it is that adjusts the laser power, does it do it according to the SET speed, or the ACTUAL speed of the laser head?
Which do people use? In theory there shouldn’t ever need to be a reason to use the mode that doesn’t change dynamically, no? It makes the most logical sense, although maybe only if it uses the actual speed, and not the set speed.
With constant power mode on the laser power remains the same regardless of the speed the head is traveling. This is the power setting you chose in Cuts/Layers panel. Because the laser MUST slow down to make direction changes, I.e. corners, this causes excessive burning in those locations.
With constant power mode off the laser reduces the power when changing direction helping to prevent over burn in corners. This is the preferred mode of operation in my opinion.
There may be specific reasons why you would want constant power mode enabled, but I haven’t found any in my laser use.
So if you set a speed that is much higher than your laser is capable of, the engraving will be lighter, since it never reaches the desired speed and therefore the power also stays below the desired power.
It will run at the set speed if possible. Some shapes / areas are too small for the laser to reach the desired speed. Physics dictates that the laser head cannot change direction without slowing down and it takes time to get back to the set speed. Just like driving your car, you cannot make a sharp turn at 100 MPH. You have to slow down to a navigable speed, make the turn then accelerate again. If there is only 200 feet of road after the turn before the next turn, you won’t be able to get back to 100 MPH. The same holds true with your laser, only at a much smaller scale.
In fill mode this is where overscan comes into play. It allows the laser to go past the edge of the engraving, reverse direction and get back to speed before firing the laser for the next pass.
He means if you set the speed to 100,000 mm/min, but your machine is only capable of 100 mm/min, it will run at 100 mm/min regardless of what you “told” it to do.
No, I think he was asking if the power is the same in both cases you described. So if you set it at 100,000 mm/min, but the machine is only capable of 100 mm/min, his question is, if the power level will be the same, once it reached a certain speed. So whether the dynamic power is set based on the “actual” / real speed or the value you commanded it (whether possible or not).
Thank you for the replies, you’re basically both/all right.
I understand about acceleration, inertia, and momentum.
By “actual speed” I meant the speed that the laser is actually moving at any point.
If the software is modulating the laser output using the speed value you have set (which, as explained above, it’ll never reach if it’s too high), that would explain the lighter patches in the middle of long passes which I’ve been seeing in my first real forays into engraving (text).
It would make a lot more sense (to me) for it to modulate the power using the actual speed the laser is moving at every point.
It would be good if the software could work out the overscan values, given the mass of the moving head, torque of the motors, length of each pass, etc etc, and just do it.
And deliver power based on the laser’s actual speed rather than the user’s speed setting.
I’m a bit surprised it doesn’t, and I kinda hope I’m wrong and it actually does, though it doesn’t look that way.
Which is exactly what Ruida controllers on CO₂ machines do. They work from the configuration values for the maximum speed & acceleration for the X axis , figure the overscan distance required to get up to the layer speed, set the power according to the layer power, and away they go.
Presumably, the axis configuration takes into account all the physical factors, but from what we see around here that is … sometimes not the case.
G-Code controllers don’t have that function built in, so making it happen requires some trickery.
Yes, that’s true, but those mechanics don’t have a closed loop motor control. You never know how fast the steppers are turning in reality. That’s also why the laser never knows its real position until you do homing, loses its position very often etc.
Yes, but the firmware is very, very basic. It’s been written for tiny Arduino microcontrollers with 8bit and 16MHz computing speed. So it’s a real simple design. I think the developer would never have imagined that this piece of software will get a standard in millions of DIY devices We now have newer and faster controllers, but the basic firmware has not changed (there are new firmwares out there that might support this someday, like FluidNC).
As mentioned above, that would require a closed loop system, which is not available in all of these consumer type devices. I have never seen one yet.
We now have newer and faster controllers, but the basic firmware has not changed (there are new firmwares out there that might support this someday, like FluidNC).