LightBurn Demo 20 – Backlash Simulation

The Lightburn Software Series

The Lightburn Software is probably the best generic laser cutting software available (I use it for almost all of my laser work). This series has LightBurn tutorials, hints and tips as well as the occasional speed comparisons between it and RDWorks. My thanks to the team at Lightburn for allowing me to embed their videos.

LightBurn Backlash Simulation Feature - Not Available on Standard Wersion of Software
LightBurn Backlash Simulation Feature – Not Available on Standard Version of Software

Contents

A demo of one of the internal tools built in to LightBurn for testing and development. The preview window in LightBurn has a backlash simulator built in to our development version so we can test the effectiveness of the ‘Hide Backlash’ option.

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https://lightburnsoftware.com/pages/trial-version-try-before-you-buy

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Video Transcript for LightBurn Backlash Simulation

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0:00 i thought it might be interesting for

0:01 you guys to see how i’m

0:03 checking for backlash and uh

0:06 analyzing the results so that we’re

0:08 getting um so i have

0:10 in our internal version of lightburn

0:12 this is the debug build

0:13 um we have a switch here in the preview

0:15 that turns on the backlash simulation

0:18 and so if i rewind all the way back to

0:19 the beginning and we zoom in on the box

0:23 so this is showing my it’s i think it’s

0:25 set to two millimeters of backlash it

0:27 might only be one i can’t remember

0:29 but it’s huge it’s way larger than you

0:31 would ever have in a real machine

0:33 and then the little red dot is the

0:34 crosshair that you normally see that is

0:36 the position of the laser

0:38 and so if i start going forward

0:41 you can see and if i turn on travel

0:43 moves so you can see that’s where the

0:44 laser started and this is where it’s

0:46 moving

0:46 and as soon as it hits the end of this

0:49 box

0:50 or the edge of the box it’s going to

0:52 start pulling the box with it

0:54 and the middle of the box is what’s

0:57 actually

0:58 being output by the laser so

1:02 we’ll scan forward a little bit and so

1:04 right there

1:05 this is the first point at which

1:06 backlash actually is

1:08 a visible problem if i scan forward

1:11 here we’re getting to the edge of the

1:13 shape that we’re starting to draw

1:15 and now it’s drawing the shape

1:18 and you can see the very very first

1:22 thing that it does

1:22 is change direction in the x-axis

1:26 so it’s now going in the opposite

1:27 direction and still going down

1:30 so at first because it’s still going

1:32 down

1:33 it’s pulling this center of the box down

1:36 with it

1:36 but it’s not moving in the same

1:38 direction in y or sorry in x

1:40 so we aren’t actually moving

1:44 the laser output yet because we haven’t

1:47 gotten to the other side of this box

1:49 so if your laser is a little bit loose

1:52 or you’ve got a little bit of play

1:54 in the gears every time you change

1:56 direction

1:57 you have to take up that slack

2:00 until uh it’s tight again

Video Transcript for LightBurn Backlash Simulation (Cont…)

2:03 and then the the actual laser beam

2:06 starts moving and so that’s what’s

2:07 happening

2:08 here and so this is the path being

2:11 sent by the controller to your motors

2:13 it’s the path that the motors believe

2:15 they are taking

2:17 this is the path that the laser head is

2:19 actually drawing

2:20 and as you get to the next direction

2:23 change which happens right here on the

2:24 x-axis

2:26 um you’ll see again now we’re starting

2:29 to move

2:30 this way through the backlash box

2:33 but the laser head itself is just

2:35 continuing to draw a vertical line

2:36 because we haven’t

2:37 eaten up that slop in the other

2:39 direction and so once we get to the

2:41 other side of this box

2:43 now it starts pulling the laser head

2:46 and so that’s why when you see files

2:50 that have been output by

2:52 machines that are loose they look like

2:54 these weird

2:55 ovals with flat sides

2:58 on top bottom and sides and they’ll have

3:00 strange gaps in them and so on

3:02 and if i run this simulation all the way

3:04 to the end and you look at

3:06 individual shapes in here you can see

3:09 there’s gaps between where it starts and

3:11 ends

3:12 gaps between where it starts and ends

3:15 this one same deal this one same

3:17 you may actually get shapes that are

3:20 quote unquote correct um but it’s just a

3:24 matter of chance

3:25 based on which direction the laser

3:27 starts and ends and which way that it

3:29 enters the shape and exits the shape and

3:31 so on

3:32 so the hide backlash optimization

3:35 if i turn that on and rerun the preview

3:39 you’ll notice that all of these shapes

3:42 now even though they still look like

3:43 hell

3:44 are actually sealed meaning the start

3:47 point and end point actually lines up

3:49 on every one of these shapes if you look

3:51 at it

3:52 um and it does this by deciding

3:56 how to enter the shape and where to

3:58 change directions

4:00 so that the backlash is

Video Transcript for LightBurn Backlash Simulation (Cont…)

4:03 minimized at the start and end points or

4:06 the start and end points have

4:07 the same backlash and that’s probably

4:10 the better way to think of it

4:11 so in this case the laser was moving

4:14 downward and to the right when it

4:17 started this shape

4:19 and so it continues moving downward

4:23 and changes direction because we have to

4:27 um but it ends the shape moving

4:30 downward and to the right so the start

4:33 point and the end point

4:35 actually match they meet up because

4:38 we started the shape moving down into

4:40 the right and if we end

4:41 the shape going in that same direction

4:43 the backlash will match

4:45 and then we head over to the next shape

4:48 and the next shape we arrive

4:50 at however it is that we get there

4:53 and we’re moving slightly upward you can

4:56 see

4:56 we’re going upward and to the right

4:58 again

5:00 so when this shape is finished we want

5:02 to be moving

5:03 upward and to the right in order for the

5:05 backlash to be minimized

5:07 and so again you can see here when we

5:09 get to the end of this shape we’re going

5:10 upward and to the right

5:12 and so the start point matches the end

5:15 point

5:16 we head over to the next shape and the

5:18 process repeats and so in this case we

5:20 were going down into the right

5:22 and so at the end of this shape we’re

5:23 going to go down into the right again

5:25 and so on and so on and so on and

5:29 this just works as long as your entry

5:33 and exit directions

5:34 for a shape are the same you should be

5:37 able to

5:38 not or you should not be able to see

5:41 the misalignment where the start points

5:44 and endpoints meet

5:45 um from everything that i’ve read and

5:48 researched this is correct

5:49 now that’s not to say that i’m perfect

5:52 and

5:52 that this is actually right i could be

5:55 wrong i’m

5:56 willing to accept that i’m wrong but

6:00 this is a reasonable simulation of

Video Transcript for LightBurn Backlash Simulation (Cont…)

6:02 backlash

6:03 and according to my simulation the

6:06 output is correct

6:07 so um until i find a way to prove myself

6:11 wrong i’m going to believe that this is

6:12 working

6:13 and the people that i’ve sent it to so

6:15 far aside from one user who’s been

6:17 having trouble

6:18 um i have all given back very positive

6:21 results and said that the output is

6:29 great

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