Travis Reese
01-17-2016, 9:17 PM
I've been slowly figuring out the laser machine. I was having a heck of a time calibrating the distance the head actually moves vs what it should move. I have some artwork printed on an 8.5"x11" piece of veneer that I needed to very precisely cut around. Even though I'd align the registration marks in the upper left corner very carefully it was cutting a larger pattern than it should have. I searched and searched both here and around the Internet and determined the setting I needed to change was the Move setting in the Pulse Unit Calculation dialog. See screen shots below. The question was what value to use to achieve a given result? Most of what I found on this was related to the rotary attachments and how to set it for a rotary.
Forgive me if this information is indeed somewhere else in these forums but I've not been able to find it. Below is what I think I figured out. If I'm incorrect on any of this, someone please correct me.
The Need Pulse value is the number of pulses/micropulses the driver must output in order to turn the stepper one full revolution. Everything I read said that the Pulse Unit value is the distance, in mm, that the head would move for a given pulse. There was someone who wrote an alternate manual for LaserCut 5.3 that gave a formula for determining the values to use. Basically everything I've found written says to have the laser cut a square that is 100mmx100mm. Next, measure the square. For each axis measure the respective side of the square. The formula is very basic math which is...
Current Pulse Unit Value/Measured Length = Needed Pulse Unit Value/Input Length. Solve for Needed Pulse Unit Value. Simplified for a 100mm square, a Measured Length of 105mm, and my Current Pulse Unit Value of .00718091 the math would be Needed Pulse Unit Value=100*.00718091/105. That would give me a value of .06666667. Makes sense, correct? If I'm getting a 105mm square and I should be getting a 100mm square and everyone says this Pulse Unit value is the distance that the head moves per step of the motor, then I should get a Needed Pulse Unit Value less than my Current Pulse Unit Value because I want the head to move a shorter distance for each pulse. What was killing me was that this doesn't work. If I decrease the pulse unit value to .06666667 the square actually measures BIGGER than 105mm, not the expected 100mm. This put me back to square one. Am I the only one that's tried this and come up with this result when using this formula? The question I still couldn't answer was what the heck do these numbers actually represent? You can also rejigger the math for the formula above and simply divide 100/105 which is .95238095. That gives you the correction factor to multiply the current pulse unit by resulting in the .06666667 that I came up with.
I believe the Need Pulse value represents the number of pulses needed to rotate the stepper one revolution.
The Pulse Unit value is nothing more than the Move value divided by the Need Pulse value. You can change the Pulse Unit or the Move value and the other will update accordingly. So in my forula above you could have used the Pulse Unit or the Move value interchangably for a given Need Pulse value. So, what does the Move/Pulse Unit actually represent?
On a whim, knowing that increasing the Pulse Unit/Move value actually gave me a smaller measured length I tried using 1/.95238095 as the correction value, in other words, 105. That worked. WHY? Why does increasing the Pulse Unit/Move actually give me a smaller measured length? The big revelation here is that I believe the Move value represents the dimension of some pulley. Makes total sense. If you tell the software you have a bigger pulley then it knows it needs to turn it fewer steps to drive the head a given distance.
Sorry if this is all common knowledge to those who have been here a while but I just couldn't seem to find this information anywhere. Everyone kept saying that the Pulse Unit was the distance the head moved for a given pulse which clearly isn't the case.
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Forgive me if this information is indeed somewhere else in these forums but I've not been able to find it. Below is what I think I figured out. If I'm incorrect on any of this, someone please correct me.
The Need Pulse value is the number of pulses/micropulses the driver must output in order to turn the stepper one full revolution. Everything I read said that the Pulse Unit value is the distance, in mm, that the head would move for a given pulse. There was someone who wrote an alternate manual for LaserCut 5.3 that gave a formula for determining the values to use. Basically everything I've found written says to have the laser cut a square that is 100mmx100mm. Next, measure the square. For each axis measure the respective side of the square. The formula is very basic math which is...
Current Pulse Unit Value/Measured Length = Needed Pulse Unit Value/Input Length. Solve for Needed Pulse Unit Value. Simplified for a 100mm square, a Measured Length of 105mm, and my Current Pulse Unit Value of .00718091 the math would be Needed Pulse Unit Value=100*.00718091/105. That would give me a value of .06666667. Makes sense, correct? If I'm getting a 105mm square and I should be getting a 100mm square and everyone says this Pulse Unit value is the distance that the head moves per step of the motor, then I should get a Needed Pulse Unit Value less than my Current Pulse Unit Value because I want the head to move a shorter distance for each pulse. What was killing me was that this doesn't work. If I decrease the pulse unit value to .06666667 the square actually measures BIGGER than 105mm, not the expected 100mm. This put me back to square one. Am I the only one that's tried this and come up with this result when using this formula? The question I still couldn't answer was what the heck do these numbers actually represent? You can also rejigger the math for the formula above and simply divide 100/105 which is .95238095. That gives you the correction factor to multiply the current pulse unit by resulting in the .06666667 that I came up with.
I believe the Need Pulse value represents the number of pulses needed to rotate the stepper one revolution.
The Pulse Unit value is nothing more than the Move value divided by the Need Pulse value. You can change the Pulse Unit or the Move value and the other will update accordingly. So in my forula above you could have used the Pulse Unit or the Move value interchangably for a given Need Pulse value. So, what does the Move/Pulse Unit actually represent?
On a whim, knowing that increasing the Pulse Unit/Move value actually gave me a smaller measured length I tried using 1/.95238095 as the correction value, in other words, 105. That worked. WHY? Why does increasing the Pulse Unit/Move actually give me a smaller measured length? The big revelation here is that I believe the Move value represents the dimension of some pulley. Makes total sense. If you tell the software you have a bigger pulley then it knows it needs to turn it fewer steps to drive the head a given distance.
Sorry if this is all common knowledge to those who have been here a while but I just couldn't seem to find this information anywhere. Everyone kept saying that the Pulse Unit was the distance the head moved for a given pulse which clearly isn't the case.
329595
329596